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Presentation type:
TS – Tectonics & Structural Geology

EGU24-16741 | Orals | MAL34-TS | Stephan Mueller Medal Lecture

Fault segmentation, off-fault deformation, and fault maturity 

Yann Klinger

Large continental strike-slip earthquakes produce significant surface ruptures, tens to hundreds of kilometers long, with displacement that can reach several meters, depending on the magnitude of the earthquake. However, this information, and more specifically the detail of the surface ruptures has long been overlooked, as we missed efficient ways to document extensive ruptures. In the last decade, with the emergence of new remote sensing tools, our community came to realize that earthquake surface ruptures could bear significant information about fault structure and the way deformation is accommodated during earthquakes. Hence, through a systematic survey of surface ruptures, based on field observation and remote sensing data, we demonstrate that it is possible to define a fault segmentation that would not be arbitrary, but instead is related to some first-order characteristic of the brittle crust, the thickness of the brittle crust, also called the seismogenic thickness. This observation result has been tested and confirmed through a series of analogue and numerical experiments that allowed us to systematically study fault segmentation when varied the thickness of the brittle material. We also questioned the distribution of deformation along those fault segments during earthquakes, as the development of high-resolution image correlation technics gives us access to a more detailed picture of the ground deformation distribution around large strike-slip earthquake ruptures. More specifically, we have been able to show that in some places a significant part of the deformation is distributed off fault, up to 30%, accommodated by micro-cracks, or even in the bulk. This deformation is almost impossible to measure in the field and thus is not considered in classic models of earthquake source inversion. It might in fact be the reason why many models involve some shallow slip deficit, which is physically not understood, while it might only be an artefact of modeling. Eventually, the evolution through time of fault geometry and off-fault deformation is questioning the long-term evolution of fault geometry, a potential proxy for fault maturity. Here we show through analogue experiments that in fact, once a growing fault system has gone pass through a localization stage, where distributed deformation is drastically reduced, the fault system never simplifies further and keeps having some level of complexity associated with a steady amount of distributed deformation close to 20%, independently of the total amount of deformation accommodated by the fault system, suggesting that a fault system can probably be considered definitively mature almost immediately after its localization stage, for a small amount of total displacement.

How to cite: Klinger, Y.: Fault segmentation, off-fault deformation, and fault maturity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16741, https://doi.org/10.5194/egusphere-egu24-16741, 2024.

TS1 – Deformation mechanisms, rheology, and rock-fluid interactions

The metamorphic basement of the Southern Alps occurs in the Brixen unit (Meran – Brixen – Timau, “Brixner Quarzphyllite”), the Valsugana Unit (Trient – Borgo Valsugana – Agordo) and the Recoaro Unit (Recoaro Terme – Schio). The associated Variscan P-T conditions correspond to a greenschist-facies metamorphic overprint, which exhibits a metamorphic gradient that extends from the lower greenschist-facies in the South to the amphibolite-facies in the North. The aim of this study was to provide mineralogical and mineral-chemical constraints of major mineral phases as well as accessories such as apatite and tourmaline on this gradient and obtain P-T conditions along a North-South profile

Quartzphyllite samples were collected along a traverse from Reccoaro in the South to Brixen in the North. Petrographic investigations revealed that the metapelites contain quite a complex polyphase mineral assemblage. The mineral assemblage in the South is represented by chlorite + muscovite + albite + quartz. Towards the center of the traverse, biotite occurs in the mineral assemblage, which has subsequently been replaced by chlorite. Samples in the vicinity of the Permian Cima d’Asta intrusion show petrographic evidence for contact metamorphism. In the North the mineral assemblage is chlorite + muscovite + plagioclase + quartz + garnet. Therefore, the metapelite zones of chlorite, biotite and garnet were observed along the traverse from South to North.

Mineral chemical investigations of samples without the contact metamorphic overprint reveal additional hidden traces of the polymetamorphic nature of some of the samples. Although the chemical compositions of muscovite, chlorite and plagioclase vary continuously with increasing P-T conditions from South to North, the chemical data also reveal that the southernmost sample shows for instance chemical evidence for a later T-accentuated overprint texturally not visible.

The chemical composition of apatite changes continuously from South to North with slightly increasing F and FeO and Y2O3 contents. Tourmaline shows an increase in Ca(X) from the biotite to the garnet zone. Reliable multi-equilibrium geothermobarometry yielded P-T conditions of 554 ± 11°C and 6.49 ± 1.3 kbar in the northernmost sample. In contrast, muscovite-chlorite-quartz geothermobarometry shows considerable scatter in the data due to pervasive later retrogression.

Additionally, we applied low temperature thermochronology to the samples to reveal the post Variscan to Neoalpine thermal history of the rocks. Zircon U/Th-He (ZHe) data suggest cooling of the Valsugana Unit in the upper Carboniferous below 160°C whereas cooling in the Brixen Unit occurs only at the border of Middle to Upper Triassic. The latter can be interpreted as cooling after a thermal event related to the Ladinian Volcanism, which also reset the Apatite Fission Track (AFT) system in the Brixen Unit. This Ladinian AFT reset does not occur in the quarzphyllites of the Valsugana Unit. AFT data and time-Temperature models suggest Permian and Triassic cooling to 70 ± 10°C before 240 Ma in the Valsugana Unit, and post-Ladinian cooling of the Brixen Unit before 70 Ma.

This study shows that quartzphyllites are able to record complex metamorphic histories hidden in petrographic, geochronological and mineral chemical data.

How to cite: Tropper, P., Klotz, T., Pomella, H., and Dunkl, I.: Visible and invisible complexities in low-to medium grade metamorphic rocks: mineralogical and petrological constraints on the Variscan metamorphic gradient in the Southalpine metamorphic basement (Brixen quartzphyllites, Northern Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1731, https://doi.org/10.5194/egusphere-egu24-1731, 2024.

EGU24-2884 | Posters on site | TS1.1

Seismic induced anisotropy and kinking in quartz 

Michel Bestmann, Bernhard Grasemann, Giorgio Pennacchioni, Rüdiger Kilian, John Wheeler, Luiz F.G. Morales, and Andreas Bezold

Recognition of seismically induced microstructures is important to unravel the different deformation processes during seismic cycles, especially at the base of the upper crust where many earthquakes nucleate. Deformed quartz veins related to a strike-slip shear zone within the Schobergruppe (Austroalpine Crystalline Complex, Eastern Alps) contain intense kinking in elongated quartz grains. The kink band boundaries are inclined into the general dextral sense of shear. Cathodoluminescence (CL) images reveal that the entire thin section contains a very high density of intragranular, sub-planar microstructures developed as thin dark CL lamellae accompanied with nanometre-scale fluid inclusions. Based on the oscillating orientation variation across low angle boundaries (misorientation angle 1-9°) these lamellar microstructures are referred as short-wavelength undulatory extinction microstructures - SWUE (Trepmann & Stöckhert, 2013). Only grains with SWUE, orientated parallel to the foliation, are kinked. In general, kinked microstructures mainly develop in strongly anisotropic material or minerals with a strong cleavage, e.g. micas. Deformation at high differential stresses e.g. during coseismic loading can produce a strong anisotropic microstructure in quartz by the development of deformation lamellae. Trepmann & Stöckhert (2013) showed in deformation experiments of quartz that SWUE preserve evidence of an earlier coseismic stress peak, even when overprinted during subsequent crystal plastic creep deformation at lower stress. The SWUE in the deformed Schober quartz veins are interpreted in a similar way. These microstructures were primary deformation lamellae developed during coseismic loading. TEM images reveal a high degree of recovery (low dislocation density) across the SWUE. Subsequent overprint by ongoing creep at lower stresses is recorded by vein quartz samples with mylonitic microstructures. The densely spaced sub-planar microstructures cause a high anisotropy of the quartz grains, which finally were kinked. Electron backscatter diffraction data give evidence of different slip systems that were active during the development of the deformation lamellae followed by recovery (SWUE), and during the subsequent kink band formation. The opposite direction of the Burges vectors (based on Weighted Burges Vector analysis, Wheeler et al., 2009) at the corresponding kink band boundaries is geometrical consistent with sinistral shearing within the kink domain along the anisotropic deformation lamellae/SWUE related to the dextral sheared kink band. Intensively kinked micas (muscovite and biotite) in the mica-rich host rock (in direct contact to the kinked quartz vein sample) point to seismic induced kinking, which is supported by the vicinity (1-1.5m) of a fault zone with pseudotachylytes.

How to cite: Bestmann, M., Grasemann, B., Pennacchioni, G., Kilian, R., Wheeler, J., Morales, L. F. G., and Bezold, A.: Seismic induced anisotropy and kinking in quartz, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2884, https://doi.org/10.5194/egusphere-egu24-2884, 2024.

EGU24-3483 | ECS | Orals | TS1.1

Mechanisms for the nucleation and deformation of symplectites during omphacite breakdown      

Sascha Zertani, Luiz F. G. Morales, and Luca Menegon

The breakdown of omphacite is one of the first signs of eclogite retrogression, and typically results in the formation of vermicular intergrowths of sodic plagioclase and diopside (± quartz ± amphibole), termed clinopyroxene-plagioclase symplectites. Such symplectites occur in most, if not all, eclogite localities worldwide. The reaction is associated with a substantial grain size reduction, and may thus significantly impact bulk rock rheology during eclogite exhumation. We study a suite of natural clinopyroxene-plagioclase symplectites by electron backscatter diffraction (EBSD). The sample suite comprises symplectites in various stages of their evolution: the beginning stages of nucleation (vermicular symplectites), partially recrystallized symplectites, and completely recrystallized and strongly deformed symplectites. We determine crystallographic relationship between the parent omphacite and the reaction products and interphase misorientation relationships between the reaction products (plagioclase and diopside), to shed light on nucleation and deformation mechanism during eclogite retrogression. 
We find that the nucleation of diopside and plagioclase in the symplectites is strongly controlled by the crystallography of the parent omphacite, with the diopside copying the crystal lattice of the parent grain, and the plagioclase nucleating in special orientation relationships to the diopside, along planes with favorable interplanar spacing. Initially strong crystallographic relationships are weakened as deformation of the symplectites proceeds by fracturing transitioning into grain boundary sliding accommodated by diffusion creep, i.e., grain-size sensitive (GSS) creep.
The results indicate that the formation of clinopyroxene-plagioclase symplectites does not increase permeability in crustal rocks, initially, but that deformation by GSS creep leads to progressive hydration and weakening of eclogites during retrogression. The symplectites thus significantly impact bulk crustal rheology. 

How to cite: Zertani, S., Morales, L. F. G., and Menegon, L.: Mechanisms for the nucleation and deformation of symplectites during omphacite breakdown     , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3483, https://doi.org/10.5194/egusphere-egu24-3483, 2024.

EGU24-3884 | Orals | TS1.1

Metamorphism induced strength inversion at high-pressure conditions – Implications for strain localization in eclogite. 

Anna Rogowitz, Simon Schorn, Benjamin Huet, Bernhard Grasemann, and Luca Menegon

The geodynamic evolution of the Earth is highly governed by the mechanical behavior of rocks at plate boundaries. In convergent settings, continental and/or oceanic mafic rocks are subducted to great depths where they experience high pressures and temperatures and transform to eclogite. Accompanied mineral transformations subsequently result in mechanical changes and in density variations. In the last decades, many field, experimental and numerical studies targeted eclogite and aimed at quantifying its mechanical behavior as well as characterizing strain weakening processes. Especially, experimental investigations have shown that eclogite and its main constituents omphacite and garnet are strong phases which are not expected to creep at differential stresses below 1 GPa for tectonically relevant strain rates. Nevertheless, highly localized shear zones and mylonitic fabrics are frequently observed in eclogite, raising the question how and why strain localization occurred.
To characterize processes causing strain localization in eclogite, we investigate an eclogite facies shear zone located at the Hohl locality (Koralpe, Eastern Alps, Austria). The shear zone bears rocks with two distinct eclogite facies mineral assemblages of which one is dominated by clinozoisite, amphibole and garnet. This lithology occurs as foliated sigmoidal lenses hosted by typical eclogite containing omphacite, garnet, clinozoisite, amphibole, quartz, kyanite and rutile. Both lithologies derived from NMORB gabbro which intruded during Permian rifting. Protolith assemblage calculations suggest that lenses have originally been plagioclase-rich cumulates within a clinopyroxene-plagioclase gabbro matrix. Modal-composition based viscosity estimates indicate that previous to the high-pressure metamorphic overprint the cumulate was less competent than the gabbro. However, the sigmoidal shape of lenses surrounded by ultramylonitic eclogite suggests that the lenses were stronger during shear zone development. Microstructural investigations reveal an ultramylonitic fabric dominated by euhedral clinopyroxene (aspect ratio ~1.7) within the host eclogite. Triple- and quadruple-junctions, open grain boundaries and lack of intracrystalline strain suggest that eclogite dominantly deformed by grain boundary sliding. On the other hand, the microstructure of lenses is dominated by elongated clinozoisite (aspect ratio ~4) and elongated sigmoidal amphibole aggregates (aspect ratio ~3). Amphibole aggregates are characterized by coarse-grained highly strained clasts and strain free slightly elongated crystals in strain shadows. These observations indicate that lenses deformed by combined dislocation and dissolution-reprecipitation creep.
Our data show how mineral replacement resulted in strength inversion with lenses, initially weaker than their host, becoming stronger than the surrounding eclogite after metamorphism at eclogite-facies conditions (720 ± 20 °C, 21 ± 3 kbar). The switch in strength caused stress concentration at the lithological contacts and subsequent strain localization in the weaker eclogitic mineral assemblage.

How to cite: Rogowitz, A., Schorn, S., Huet, B., Grasemann, B., and Menegon, L.: Metamorphism induced strength inversion at high-pressure conditions – Implications for strain localization in eclogite., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3884, https://doi.org/10.5194/egusphere-egu24-3884, 2024.

EGU24-4410 | Orals | TS1.1

Formation of multistage garnet grains by fragmentation and overgrowth constrained by microstructural and microchemical mapping 

Paola Manzotti, Daniele Regis, Duane Petts, Riccardo Graziani, and Matthew Polivchuk

Garnet is an exceptionally useful mineral for reconstructing the evolution of metamorphic rocks that have experienced multiple tectonic or thermal events. Understanding how garnet crystallizes and its mechanical behaviour, is important for establishing a petrological and temporal record of metamorphism and deformation, and to recognize multiple geologic stages within the growth history of an individual crystal. In this study, we integrate fine-scale microstructural (EBSD) and microchemical (LA-ICP-MS mapping) data obtained on a polycyclic garnet-bearing micaschist from the Alpine belt. Results suggest that fragmentation of pre-Alpine garnet porphyroblasts occurred during the late pre-Alpine exhumation and/or the onset of the Alpine burial, such that the older pre-Alpine garnet fragments were transported/redistributed during Alpine deformation and acted as new nucleation sites for Alpine garnet growth. These processes produced a bimodal garnet size distribution (macro mm-sized and micro sub-mm-sized grains). Thermodynamic modelling indicate that Alpine garnet grew during the final stage of burial (from 1.9 GPa 480 °C to 2.0 GPa 520 °C) and early exhumation (down to 1.6 GPa 540 °C) forming continuous idioblastic rims on macro- and micro-grains, and sealing fractures preserved in pre-Alpine garnet porphyroblasts. We propose that fragmentation-overgrowth processes coupled with ductile deformation in polycyclic rocks may produce a bimodal garnet size distribution and form multistage crystals resembling neoblasts. This study highlights the importance of linking microstructural (EBSD) and microchemical (LA-ICP-MS mapping) data by providing valuable information about the dominant deformation mechanisms at a given site by identifying potential links between major/trace element mobility and crystal deformation.

How to cite: Manzotti, P., Regis, D., Petts, D., Graziani, R., and Polivchuk, M.: Formation of multistage garnet grains by fragmentation and overgrowth constrained by microstructural and microchemical mapping, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4410, https://doi.org/10.5194/egusphere-egu24-4410, 2024.

Mantle heterogeneity is closely related to the distribution and circulation of volatile components in the Earth’s interior, and the behavior of volatiles in the mantle strongly influences the rheological properties of silicate rocks. In mantle xenoliths, these physicochemical properties of the upper mantle can be recorded in the form of microstructures and fluid inclusions. In this paper, I summarized and reviewed the results of previous studies related to the characteristics of microstructures and fluid inclusions from peridotite xenoliths beneath the Rio Grande Rift (RGR) in order to understand the evolution and heterogeneity of upper mantle. In the RGR, the mantle peridotites are mainly reported in the rift axis (EB: Elephant Butte, KB: Kilbourne Hole) and rift flank (AD: Adam’s Diggings) regions. In the case of the former (EB and KB peridotites), the type-A lattice preferred orientation (LPO), formed under low-stress and low-water content, was reported. In the case of the latter (AD peridotites), the type-C LPO, formed under low-stress and high-water content, was reported. In particular, in the case of AD peridotites, at least two fluid infiltration events, such as early (type-1: CO2-N2) and late (type-2: CO2-H2O), have been recorded in orthopyroxene. The upper mantle heterogeneity recorded by these microstructures and fluid inclusions is considered to be due to the interaction between the North American plate and the Farallon plate.

How to cite: Park, M.: Upper Mantle Heterogeneity Recorded by Microstructures and Fluid Inclusions from Peridotite Xenoliths Beneath the Rio Grande Rift, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5017, https://doi.org/10.5194/egusphere-egu24-5017, 2024.

In the realm of modern solid Earth research, a profound understanding of rocks' intricate microstructures is essential for unraveling geological history and addressing critical challenges in the energy transition. These microstructures—grain boundaries, preferred orientation, twinning, and porosity—play a pivotal role, influencing the physical strength, chemical reactivity, and fluid flow properties of rocks. Their direct impact on subsurface reservoirs used in geothermal energy, nuclear waste disposal, and hydrogen/carbon dioxide storage underscores the importance of comprehending their distribution for the stability and efficacy of subsurface activities.

However, addressing the need for statistical representativeness requires imaging numerous samples at high magnification. In response, our research introduces an innovative image enhancement process for scanning electron microscopy datasets, showcasing a substantial potential for resolution improvement through Deep-Learning-Enhanced Electron Microscopy (DLE-EM).

Our proposed workflow involves capturing one or more high-resolution (HR) regions within a low-resolution (LR) area. Precise image registration is achieved in two steps: first, determining the HR region's location within the LR region using a Fast Fourier Transform algorithm (Lewis, 2005), and second, refining image registration through iterative calculation of a deformation matrix. This matrix, utilizing Newton's optimization method, aims to minimize differences between both images (Tudisco et al., 2017). Subsequently, paired HR and LR images undergo processing in a Generative Adversarial Network (GAN), comprising a generator and a discriminator. This GAN learns to generate HR images from LR counterparts through joint training in an adversarial process.

We benchmark our workflow using four distinct rock types and demonstrate that this approach accelerates imaging processes up to a factor of 16 with minimal impact on quality, offering possibilities for real-time super-resolution imaging of unknown microstructures. Additionally, we show that a model trained on a specific geological material is able to generalize its learned features to new domains, reducing the need for extensive training data.

[1] Lewis, J. P. "Fast normalized cross-correlation, Industrial Light and Magic." unpublished (2005).

[2] Tudisco, Erika, et al. "An extension of digital volume correlation for multimodality image registration." Measurement Science and Technology 28.9 (2017): 095401

How to cite: van Melick, H. and Plümper, O.: Breaking Boundaries: Deep-Learning-Enhanced Electron Microscopy for Accelerated Super-Resolution Imaging in Solid Earth Research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8470, https://doi.org/10.5194/egusphere-egu24-8470, 2024.

EGU24-8497 | Posters virtual | TS1.1

Phase-field modeling of texture evolution in magmatic rocks 

Julia Kundin and Sumit Chakraborty

Texture formation in rocks is modeled using a quantitative phase-field model of eutectic growth with three thermodynamic phases (e.g. Diopside - Anorthite - Melt) in a quasi-binary magmatic system with unlimited quantity of crystals of different orientation and anisotropy. In nature, specific layering microstructures have been observed for which many possible explanations have been provided. Moreover, textural irregularities initially induced during nucleation, by fluctuation in crystal size or by other mechanisms continue to develop and sharpen over time. By phase-field modeling, we verify two models of igneous layering. The first mechanism is that, due to the formation of a layer with crystals of larger size, these crystals will grow faster at the expense of smaller crystals. The second mechanism is that a layer with an increasing fraction of the second phase is formed on top of the initial layer of the first phase to have crystallized. We have found that, in this case, without anisotropy of surface energies, no layering is produced. The boundary conditions and parameters of the models necessary for the formation of layers will be discussed.

How to cite: Kundin, J. and Chakraborty, S.: Phase-field modeling of texture evolution in magmatic rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8497, https://doi.org/10.5194/egusphere-egu24-8497, 2024.

EGU24-8853 | Posters on site | TS1.1

Experimental study on high-temperature rheology of hot-pressed mafic granulite 

Qianqian zhang and Yongsheng Zhou

The earth's internal dynamic processes are closely related to the rheological behavior of its internal constituent minerals under high temperature and high pressure conditions. Feldspar and pyroxene are the main constituent minerals in granulite in the continental lower crust. High-temperature experimental research on them is one of the main ways to understand the rheology of the continental lower crust. This experiment uses the Paterson high temperature and high pressure rheology device, at a temperature of 1273K-1423K and a strain rate of 6×10-6 s -2×10-5s-1, to test the hot-pressed feldspar and pyroxene aggregates with and without water respectively. Creep experiments were carried out under added water conditions to determine the rheological parameters of the two-phase aggregate under different water conditions. By collecting infrared spectra and microscopic pictures of the two-phase aggregate of hot-pressed feldspar and pyroxene, the water content in the samples before and after deformation was calculated and its microstructural characteristics were analyzed. The Q value of the sample without adding water is 797.87±184.7 KJ/mol, and the n value is about 3. The Q value of the water-added sample is 472.57±96.29KJ/mol. From 1273K to 1373K, the n value is about 2. At 1373K, the n value is about 4. This shows that water has a significant weakening effect on rocks.

How to cite: zhang, Q. and Zhou, Y.: Experimental study on high-temperature rheology of hot-pressed mafic granulite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8853, https://doi.org/10.5194/egusphere-egu24-8853, 2024.

EGU24-9288 | ECS | Posters on site | TS1.1

Three-dimensional kinematic analysis of Northern Kapıdağ Pluton: Implications for a transtensional deformation in NW Anatolia  

Tunahan Arık, Alp Ünal, and Şafak Altunkaynak

The Kapıdağ Shear Zone (KSZ) is located in the Kapıdağ Peninsula (NW Anatolia) and syn-kinematically intruded by Northern Kapıdağ Pluton (NKP) along the northern coastline of the peninsula. The NKP displays a granodioritic composition with a discernible progressive deformation from south to north. The southern part is characterized by an isotropic granodiorite with no trace of deformation. Towards the north, it gradually passes into a deformed granodiorite in which the development of ductile and brittle structures is widely observed. To comprehend the nature and origin of deformation within the KSZ, a thorough analysis of micro- and mesostructural features was undertaken, accompanied by a three-dimensional kinematic analysis of the NKP. The NKP exhibits a well-defined mylonitic foliation and stretching lineation, characterized by the shape-preferred alignment of feldspar, quartz, and biotite crystals. Various shear sense indicators, including S-C fabrics and "σ"-type rotated porphyroclasts, are extensively distributed throughout the NKP, pointing to a dextral sense of shear. Microstructures such as chessboard extinction and Grain-Boundary Migrations (GBM) in quartz, myrmekitic textures, and flame pertites in feldspar, as well as sub-grain rotations and bulging recrystallization of quartz, along with the presence of micro-faults and cracks collectively suggest continuous deformation of the NKP from temperatures starting at 600°C to those below 250°C.

Three-dimensional strain analysis was conducted on the Northern Kapıdağ Pluton (NKP) using quartz crystals as shear sense indicators, and various parameters including kinematic vorticity (Wk) numbers, Flinn k values, Lode’s ratio, and octahedral shear strains were computed. The outcomes reveal a range of Flinn k values from 1.1 to 5.32. On Flinn’s diagram, the majority of samples plot above the k=1 line, indicative of a transtensional regime. Lode’s ratios exhibit a variation from -0.64 to +0.13, with the Hsu diagram showing that the majority of samples fall within the general constrictional field. To discern the strain component of the NKP, kinematic vorticity numbers (Wk) were determined, ranging from 0.73 to 0.99. This suggests a dominance of simple shear in the deformation rather than pure shear components. The U-Pb zircon and 40Ar/39Ar biotite dating results show that this deformation has developed between 48-36 Ma. 

In summary, both micro/mesostructural data and three-dimensional strain analyses of the NKP collectively suggest that the Kapıdağ Shear Zone (KSZ) is characterized by a dextral transtensional shear zone dominated by simple shear. We hypothesize that the KSZ was likely formed during the Eocene period as a consequence of strain localization along the break-off of the Tethyan oceanic slab.

How to cite: Arık, T., Ünal, A., and Altunkaynak, Ş.: Three-dimensional kinematic analysis of Northern Kapıdağ Pluton: Implications for a transtensional deformation in NW Anatolia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9288, https://doi.org/10.5194/egusphere-egu24-9288, 2024.

EGU24-9588 | Orals | TS1.1

Deformation of quartz aggregates : interplay between plasticity and grain boundary processes, and the role of water 

Hugues Raimbourg, Holger Stünitz, Petar Pongrac, Subhajit Ghosh, Giulia Palazzin, Lucille Nègre, Renée Heilbronner, Jacques Précigout, and Petr Jeřábek

The interplay between H2O and quartz deformation is a long-standing question since the discovery of the H2O-weakening effect by Griggs and others in the 60’s. Some of the early works focused on single crystal experiments and on intra-crystalline processes, but a complete understanding of the phenomenon requires to consider quartz aggregates, where both intra- and intercrystalline processes contribute to bulk strain and strength.

We have carried out a series of deformation experiments on quartz polycrystals at high pressure (0.6 to 2 GPa) and high temperature (800°C), at strain rates of ~1.10-6 to 2.10-5s-1, in a Griggs-type apparatus. The main set of experiments used a natural quartzite with a large starting grain size (~150-200µm) in coaxial geometry (~30% strain). A second series used synthetic mixtures of large (~100-200µm) and dry quartz clasts embedded in a matrix of fine-grained (~6-10µm) powder of natural quartz in a shear geometry, up to large strains (𝛄 ≈ 3-4). In both sets of experiments, 0.1 to 0.15 wt% H2O was added to the assemblage. The H2O content was measured by FTIR on thick (~100-200µm) plates after deformation, either as spot analyses on grain interiors or on regions containing grain boundaries.

Nearly all strain in the coarse grained quartzite was acquired by crystal-plastic deformation of quartz grains, determined by the shape change of original sand grains that constitute the quartzite (revealed by cathodoluminescence) before and after deformation. Crystal plastic deformation is accompanied by minor recrystallization along grain boundaries, where a mantle of small-sized (~3-5µm) grains developed around some porphyroclasts. While crystallographic fabrics remained weak because of the low strain, low-angle grain boundaries are abundant and indicate incipient recrystallization by subgrain rotation and dominant prism <a> slip. In addition to this classic pattern of intracrystalline plasticity and dynamic recrystallization, there is evidence for fracturing and dissolution-precipitation that have produced small grains around the original large grains.

In the starting material, H2O was mostly contained in fluid inclusions and aggregates, characterized in FTIR by broad-band molecular H2O, (typically ∼4500 H/106Si). The H2O content in quartz grains was strongly diminished by (i) the application of pressure and temperature and (ii) deformation, down to ∼1000 H/106Si. Irrespective of the conditions of deformation, the H2O content systematically remains higher in grain boundary regions  compared to grain interiors. The H2O expelled during deformation concentrated in domains of fine recrystallized grains of euhedral shapes with large intergranular porosity. These domains are interpreted as pockets of excess H2O (sometimes with partial melt) where the storage capacity of the grain boundary regions of the quartz aggregate is exceeded. The FTIR spectra show no significant variation with the pressure conditions of the experiments, except for the peak at 3585cm-1, which increased with pressure. As the strength of the aggregates decreased with pressure, we tentatively correlate this peak with point defects in quartz responsible for the pressure-dependent weakening. 

How to cite: Raimbourg, H., Stünitz, H., Pongrac, P., Ghosh, S., Palazzin, G., Nègre, L., Heilbronner, R., Précigout, J., and Jeřábek, P.: Deformation of quartz aggregates : interplay between plasticity and grain boundary processes, and the role of water, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9588, https://doi.org/10.5194/egusphere-egu24-9588, 2024.

EGU24-9750 | ECS | Posters on site | TS1.1

Micro-porosity found in quartz shear bands from Ikaria, Greece: insights from Hyperspectral Cathodoluminescence and High-Resolution Electron Backscatter Diffraction 

Gina McGill, Jacques Précigout, Cécile Prigent, Laurent Arbaret, Laura Airaghi, and David Wallis

Extensive micro-porosity can be found in numerous examples of quartz-rich mylonites deformed in crustal shear zones, but whether or not deformation is involved in the production of such pores remains a matter of active debate. The occurrence of syn-kinematic micro-scale porosity could result in overall changes in rock strength, as well as potentially generating a deep permeability. This would have major implications for fluid-rock interactions, earthquake nucleation and ore deposits. In this study, we focus on micro-pores occurring in quartz-rich shear bands from mylonitic granitoids which outcrop in Ikaria (Cyclades, Greece). Related to the back-arc geodynamics of the Aegean domain during the Miocene, this granitic body intruded the Cycladic basement during active detachment faulting, which has led to heterogeneous deformation of the pluton. While the granite exhibits large-scale levels of strain, increasing with proximity to the detachment fault, quartz-rich shear bands develop as a result of viscous strain localisation, giving rise to S-C structures. Micro- (to nano-) pores occur in pure quartz aggregates of these shear bands, where micro-structural features indicate dominant crystal plasticity, mostly recovering by subgrain rotation.

Based on five samples collected at different distances from the detachment fault, we performed microprobe-based hyperspectral cathodoluminescence and electron backscatter diffraction (EBSD) to characterise the micro-pores in pure quartz aggregates. In cathodoluminescence maps, parent and recrystallized quartz grains produce blue (420 nm wavelength) and yellow (650 nm wavelength) signals respectively. Furthermore, both parent and recrystallised grains exhibit a distinct increase in luminescence at 650 nm, which appear visually as very bright yellow rims/halos at their grain boundaries and, to a minor extent, at their subgrain boundaries. Using high-resolution and standard EBSD, we highlight high (to very high) geometrically necessary dislocation densities that partly coincide with such rims/halos, particularly where micro-pores are described. Most of the dislocations that may contribute to these high densities are related to the main dislocation slip system of quartz (prism <a>), as deduced from from lattice preferred orientation and subgrain analyses. Our findings, therefore, suggest that highly luminescent "yellow" boundaries of quartz grains result from dislocation accumulation, and hence, from crystal plasticity, which can be linked to the production of micro-porosity in these rocks. 

How to cite: McGill, G., Précigout, J., Prigent, C., Arbaret, L., Airaghi, L., and Wallis, D.: Micro-porosity found in quartz shear bands from Ikaria, Greece: insights from Hyperspectral Cathodoluminescence and High-Resolution Electron Backscatter Diffraction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9750, https://doi.org/10.5194/egusphere-egu24-9750, 2024.

EGU24-9882 | Posters on site | TS1.1

Quartz amorphization to produce porosity in crustal shear zones 

Jacques Précigout, Cécile Prigent, Gina McGill, Laurent Arbaret, Laura Airaghi, and David Wallis

Micropores are commonly observed in quartz-rich rocks that deformed at depths of the viscous, metamorphic continental crust. Although the presence of such porosity – often occurring with angular, pyramidal shapes – has major implications for fluid circulations and rock strength, whether or not they are produced by deformation remains unclear. Here we provide detailed documentations of pure quartz aggregates decorated by micropores in granitic shear bands from Naxos (Greece). Through estimations of geometrically necessary dislocation densities, we first document very high values (>> 1015 m-2) along intragranular boundaries, several of them containing micropores. We then performed focused ion beam (FIB) cross-sectioning and transmission electron microscopy to image pore shapes along all types of quartz boundaries. Pores do not necessarily arise with angular shapes, but they are systematically embedded within amorphous SiO2, i.e., silica glass, along both grain and intragranular boundaries. FIB volume reconstruction also revealed pyramid-like pits occurring with round-shape faceted pores, the shape of which challenges long-lasting hypotheses for pores to originate. Together with recent studies[1,2], our findings support deformation to produce porosity through (1) mechanical amorphization where dislocations accumulate and (2) fluid exsolution from the resulting glass because of a pressure/stress drop, here attributed to grain boundary sliding.

 

[1] Idrissi, H., Carrez, P. & Cordier, P. On amorphization as a deformation mechanism under high stresses. Current Opinion in Solid State and Materials Science 26: 100976 (2022)

[2]Li, B. Y., Li, A. C., Zhao, S. & Meyers, M. A. Amorphization by mechanical deformation. Materials Science & Engineering R 149: 100673 (2022)

How to cite: Précigout, J., Prigent, C., McGill, G., Arbaret, L., Airaghi, L., and Wallis, D.: Quartz amorphization to produce porosity in crustal shear zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9882, https://doi.org/10.5194/egusphere-egu24-9882, 2024.

Transient creep of olivine in the upper mantle plays an important role in large-scale Earth processes such as glacial isostatic adjustment and postseismic creep, as well as (exo-)planetary tidal heating and orbital dynamics. Yet, an experimentally confirmed microphysical understanding of transient creep across all timescales relevant to Earth processes remains elusive. An increasing body of laboratory and geodetic work suggests that nonlinear, dislocation-based dissipation mechanisms may play a more important role than previously thought. In response, several dislocation-based transient creep mechanisms have been proposed to explain transient creep in the upper mantle, including intergranular plastic anisotropy and the build-up of backstresses arising from long-range dislocation interactions. 

 

The time-dependent dissipation of strain energy during transient creep manifests as attenuation, Q-1, in the frequency domain. Therefore, the constitutive equations of the proposed mechanisms should be able to predict the attenuation in polycrystalline olivine subjected to forced oscillations, providing an independent test of their applicability. Here we present numerical investigation of the nonlinear constitutive equations of these models in the frequency domain and comparisons thereof to the mechanical results of a set of high-stress, forced-oscillation experiments on polycrystalline olivine performed in a deformation-DIA coupled with synchrotron analysis techniques. Key microstructural variables needed to inform these comparisons, such as grain size, plastic anisotropy, and dislocation density, were obtained from electron backscatter diffraction and dislocation decoration.

 

The experiments demonstrate amplitude-dependent attenuation, which is characteristic of dislocation-based dissipation. In addition, we find that Q-1 depends on the maximum stress amplitude experienced by the sample. Dislocation-density piezometry indicates that this history effect can be linked to dislocation density evolution as post-experiment dislocation densities reflect the highest stresses obtained in the experiment rather than the stresses obtained near the end of the experiment. Numerical analysis of the constitutive equations yields high Q-1 values, up to ~5, which is similar to the experimental observations. We find that the experimental observations are consistent with predictions from the backstress model for the grain sizes and dislocation densities of our samples. When extrapolated to lower stress amplitudes, the backstress mechanism produces approximately linear behavior and behaves as a Burgers model in frequency space, suggesting that dislocation interactions may contribute to seismic wave attenuation as well.

How to cite: Hein, D. and Hansen, L.: Experimental and numerical investigation of dislocation-based transient creep mechanisms in the upper mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10734, https://doi.org/10.5194/egusphere-egu24-10734, 2024.

EGU24-11323 | ECS | Posters on site | TS1.1

Microscale investigations of the evolution of deformation mechanisms in a low-temperature marble mylonite, NE Attica, Greece 

Christina Bakowsky, Renelle Dubosq, David Schneider, and Bernhard Grasemann

Carbonate rocks compose 15% of Earth’s ice-free continental surface and commonly consist of kilometer thick sequences that host complex crustal-scale fault zones, accommodating displacements on the order of tens of kilometers. These intricate fault networks significantly influence fluid migration, further controlling crustal mechanics. Understanding the deformation mechanisms of calcite and dolomite, two of the dominant carbonate forming minerals, is therefore essential for predicting the rheological properties of carbonate rocks. Herein, we conduct a microstructural analysis to investigate the interactions between brittle-ductile structures under greenschist facies conditions in a naturally occurring biphasic marble mylonite. The framework of the mylonite, which is exposed in a tectonic window north of the Greek Cyclades on the Attica peninsula, indicates deformation occurred at 300-350°C and 7-8 kbar during the late Oligocene. The mylonitization is overprinted by a weak, but pervasive axial plane cleavage. A second strong, and densely spaced axial plane cleavage, oriented perpendicular to and truncating the first set, creates a ‘pseudo-boudinage’ of the dolomite layers. Localized shear bands cross-cutt the second axial plane cleavage set, suggesting a fourth phase of deformation. Electron backscatter diffraction analysis of the mylonite reveals coarse (30-200 µm) calcite with evidence of crystal-plasticity in the form of low-angle (<15°) grain boundary development (LAGB) and linear to heterogeneous misorientation patterns. LAGB density and misorientation angles increase towards the clast rims, to maximum misorientations reaching 44° relative to the mean orientation of the grain. The coarse grains are surrounded by fine (<25 µm) calcite revealing little to no intracrystalline misorientation. Fine calcite is similar in size to subgrains defined by LAGBs within high misorientation domains of coarser grains, which is consistent with subgrain rotation recrystallization and lower greenschist facies conditions. Calcite in the mylonite record a grain-shape preferred orientation that is parallel to the main foliation and oblique to that of the cross-cutting ductile shear bands. These shear bands are characterized by fine grained (2-10 µm) inequigranular calcite with no internal misorientation and sparse, 20-30 µm anhedral calcite with weak heterogeneous misorientation patterns and a maximum misorientation of 8° in the panhandles of grains. Contrastingly, deformation in the dolomite bands is dominantly brittle as evinced from the brecciation of these layers. Clasts commonly display primary growth twinning characterized by a rotation of 180° around one of the [11̅2̅0] axes, 12-120 µm in diameter and show minor evidence for crystal-plasticity in the form of intragranular lattice distortions (maximum misorientation of 22° relative to the grain average orientation). Calcite infilling the space between dolomite fragments exhibits no grain-shape preferred orientation and consists of 5-25 µm diameter grains with minimal intracrystalline lattice distortion (0°-8°) and e-twins characterized by an 80° rotation about the [0̅2̅21] axes. The same twinning is observed in the coarse calcite with twin density increasing with proximity to dolomite ‘boudins’. Our study identifies the active deformation mechanisms in calcite and dolomite during four successive phases of deformation to clarify the feedback between brittle-ductile microstructures on strain localization, yielding insight into rheological evolution of carbonates.

How to cite: Bakowsky, C., Dubosq, R., Schneider, D., and Grasemann, B.: Microscale investigations of the evolution of deformation mechanisms in a low-temperature marble mylonite, NE Attica, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11323, https://doi.org/10.5194/egusphere-egu24-11323, 2024.

EGU24-12851 | ECS | Posters on site | TS1.1

The deformation mechanisms of Upper Cretaceous Neotethyan Orhaneli ophiolite, NW Turkey 

Yunus Can Paksoy, Nefise Paksoy, and Boris A. Natal'in

Orhaneli ophiolite is an Upper Cretaceous ophiolitic suite obducted over the Late Cretaceous high-pressure rocks. It covers approximately 43 km in length and 14 km in width. It is part of the Neotethyan ophiolite belt along the southern side of the Izmir-Ankara-Erzincan Suture. The lithological and structural mapping of the Orhaneli ophiolite revealed that the mantle rocks, the Moho Transition Zone (MTZ), and the ophiolitic lower crust are exposed along the region but the subvolcanic and volcanic sequences are missing. The study of the deformation mechanisms of available three units is our research.

The mantle rocks in the Orhaneli ophiolite comprise harzburgite (~50%), dunite (~40%), websterite, and clinopyroxenite (~10%). Harzburgite and dunite are coarse-grained and show well-developed L-S tectonic fabric. Websterite and clinopyroxenite are coarse/very coarse-grained with granular texture. The mantle tectonites (harzburgite and dunite) in the region are characterized by widespread high-temperature (1200-1250 °C) deformation partially overprinted by low-temperature (800-1000 °C) deformation. The grain boundary migration (GBM) and subgrain rotation (SGR) recrystallizations are the dominant mechanisms of the high-temperature deformation in this unit. The subsequent low-temperature deformation predominantly proceeded through subgrain rotation (SGR), and bulging (BLG) recrystallizations accompanied by kinking and twinning. Contrarily to the mantle tectonites, the pyroxenite (websterite and clinopyroxenite) predominantly shows low-temperature deformation structures. They are mainly deformed through the kinking of the pyroxene grains, however, high-temperature deformation structures also exist. A possible explanation is that the pyroxenite predominantly deformed through viscous flow under spreading center conditions.

The MTZ in the Orhaneli ophiolite is a ~1 km thick, strongly sheared zone between the mantle and lower crustal rocks. It mainly consists of serpentinite, layered gabbro, and mylonitic peridotite. The serpentinite, the most prevalent lithology in this zone, commonly shows anastomosing foliation. The layered gabbro mainly consists of orthopyroxene and plagioclase. It is characterized by thin and continuous layers of plagioclase and orthopyroxene. In some cases, these layers are transposed into isoclinal folds with detached limbs by continuous, layer-parallel, simple shearing. The stretching lineation is well-developed and defined by plagioclase and orthopyroxene. The mylonitic peridotite mainly consists of olivine and orthopyroxene. It is characterized by ribbons of orthopyroxene and elongated aggregates of olivine within a fine-grained olivine and pyroxene-rich matrix. The orthopyroxene ribbons indicate high-strain conditions within the MTZ. The aggregates of olivine suggest that the SGR recrystallization is an important mechanism of deformation within this zone.

The lower crust in the Orhaneli ophiolite comprises cumulates of gabbro, peridotite, pyroxenite, and anorthosite, in order of prevalence. Peridotite is more abundant in the stratigraphically lower sections of the crust and it diminishes stratigraphically upward. The serpentinization of peridotite is commonly over 90%. In general, the crustal section does not show evident plastic deformation. The gabbroic rocks commonly show magmatic foliation defined by the preferred orientation of undeformed plagioclase and pyroxene grains. This suggests that the crustal section is mainly deformed through viscous flow in the magmatic state.

How to cite: Paksoy, Y. C., Paksoy, N., and Natal'in, B. A.: The deformation mechanisms of Upper Cretaceous Neotethyan Orhaneli ophiolite, NW Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12851, https://doi.org/10.5194/egusphere-egu24-12851, 2024.

EGU24-13583 | ECS | Posters on site | TS1.1

On the microstructural evolution of Carrara marble during semi-brittle deformation 

Tongzhang Qu, Nicolas Brantut, David Wallis, and Christopher Harbord

Semi-brittle deformation, which is characterized by the simultaneous occurrence of fracturing and crystal plasticity, plays a critical role in determining the mechanical properties of the middle crust. Laboratory experiments have identified semi-brittle deformation as ductile flow involving distributed microfracturing, an absence of localized macroscopic failure, and widespread plasticity. However, a constitutive law of semi-brittle deformation remains elusive, and a lack of quantitative microstructural analyses has hindered the development of micromechanical models for semi-brittle deformation.

This study aims to address these limitations by providing quantitative characterization of twins, lattice distortion, and intragranular fractures in Carrara marble that has undergone semi-brittle deformation. Three sets of samples were uniaxially shortened to varying strains up to 8% under a confining pressure of 400 MPa and different temperatures at 20, 200, and 350ºC. The tested samples were examined by forescattered electron imaging and electron backscattered diffraction mapping. The results reveal that, in the early stages of deformation (strain < 2%), deformation is primarily accommodated by twins. Lattice distortion, linked to geometrically necessary dislocations, becomes prominent in the later stages (strain > 4%). Intragranular fracture intensity shows a linear correlation with strain. Despite some nuanced variations, the qualitative development of each microstructure type remains similar at different temperatures. At the onset of semi-brittle deformation, microstructural evidence has shown that the nucleation of microfractures or lattice distortion is induced by strain incompatibility at granular scale. The local stress concentrations associated with such strain incompatibility are enhanced by irregularities of grain boundaries. These observations provide a foundational microstructural understanding, facilitating the development of a robust microphysical model for semi-brittle deformation in the lithosphere.

How to cite: Qu, T., Brantut, N., Wallis, D., and Harbord, C.: On the microstructural evolution of Carrara marble during semi-brittle deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13583, https://doi.org/10.5194/egusphere-egu24-13583, 2024.

EGU24-15060 | ECS | Posters on site | TS1.1

Breccia Mechanisms and Hydrothermal Evolution from Both Colombian Emerald Belts 

Camilo Andrés Betancur Acevedo, Andreas Kammer, and Javier Garcia Toloza

This study presents the conditions of pressure, temperature, and breccia mechanisms that allow the migration of emerald-bearing hydrothermal fluids within the emerald belts of Colombia. Based on detailed petrographic analysis, three different hydrothermal events were determined, establishing a chronological framework that enhances our understanding of geological processes in these emerald belts. The first event is characterized by the high presence of albite, due to an albitization event that altered the rock. The other events are marked by an early stage of carbonatization (second) and a late carbonatization stage (third). After understanding the hydrothermal events, Fermi diad bands were obtained by Raman spectroscopy in fluid inclusions. This approach permits the calculation of the rock pressure using the vibrational modes of the CO2 and their relationship with its density. These analysis was performed in minerals associated with each hydrothermal event. The data obtained from these analyses provides the evolution of the pressure in the whole hydrothermal history. 

Finally, a fractal analysis applied to breccias from both (western and eastern) emerald belts was performed. This analytical approach aimed to understand the breccia mechanisms throughout the entire hydrothermal history, providing a view of the geological evolution of these emerald belts. Even though both belts present similar events, the western emerald belt reveals higher mechanical energy in comparison with the eastern emerald belt, in which the pressure is generally lower and breccia mechanisms show a higher-intensity corrosive event, the presence of fluidization breccias manifests that the migration of the fragments may be fluid assisted against Halokinesis

How to cite: Betancur Acevedo, C. A., Kammer, A., and Garcia Toloza, J.: Breccia Mechanisms and Hydrothermal Evolution from Both Colombian Emerald Belts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15060, https://doi.org/10.5194/egusphere-egu24-15060, 2024.

EGU24-16284 | ECS | Posters on site | TS1.1

Relicts of high-temperature fabric in the Strandja Massif, NW Turkey 

Nefise Paksoy, Yunus Can Paksoy, and Boris A. Natal'in

The Strandja Massif, exposed along northwestern Turkey is an NW striking polymetamorphic belt. The massif is mainly composed of a Neoproterozoic-Paleozoic metamorphic sedimentary complex intruded by plutons of various ages, all of which are covered by Mesozoic metasedimentary units. In previous studies Natal’in and co-authors have shown crosscutting relations between bedding or intrusive contacts were well documented all above-mentioned rocks reveal uniform penetrative foliation, which is observed in stratigraphic units of various ages. Isotopic dating shows that the massif has undergone at least two metamorphic events during the Mesozoic and Paleozoic. Greenschist to lower amphibolite facies metamorphism and intense deformation occurred in the Middle Jurassic to Early Cretaceous times as is evident from Ar-Ar and Rb-Sr studies. However, the formation of migmatites in some rocks assigned to the Paleozoic and the heterogeneous distribution of metamorphic rock types contrary to the more or less regular behavior of fabric require additional attention to the reconstruction of P-T conditions of deformations and their variations in time. The goal of this research is to improve our understanding of the P-T conditions during Paleozoic metamorphism and deformation. For this purpose, we studied the northwest part of the Strandja Massif which mainly consists of migmatitic biotite gneiss, metagranite, migmatitic biotite garnet gneiss, amphibolite, and quartzo-feldspathic schist.

The metamorphic conditions of the Paleozoic metamorphism are restricted by the following criteria: (1) The units that have undergone the Paleozoic metamorphism show evidence of migmatization. The temperature should exceed ~650 °C for the beginning of partial melting. (2) The occurrence of amphibolite indicates that the Paleozoic metamorphism was within the amphibolite facies conditions. (3) The founding of partially preserved kyanite restricts the pressure conditions of the Paleozoic metamorphism. By these criteria, the peak metamorphic conditions of the Paleozoic metamorphism are restricted to 650-720 °C and 6-12 kbar.

The Paleozoic metamorphism is accompanied by highly ductile deformation compatible with the metamorphic conditions. The Paleozoic deformation is characterized by mesoscale intrafolial folds, macroscale sheath folds, and migmatitic foliation. The intrafolial folds have foliation parallel axial planes and can only be recognized through their hinges since their limps are commonly detached. The presence of melt, due to migmatization, possibly has a crucial role on the rheological properties during this deformation.

The microstructural imprints of the Paleozoic metamorphism are investigated within the framework of this study. The chessboard subgrain pattern of quartz within the leucosomes of the migmatitic gneiss provides evidence that peak metamorphism occurred during one of the episodes of a prolog structural history of the Strandja Massif. The absence of this subgrain pattern out of leucosomes supports that the Paleozoic metamorphism did not advance into the granulite facies. The grain boundary migration (GBM) and subgrain rotation (SGR) recrystallizations and the growth of deformation myrmekites along the high-stress sites of feldspar also require higher temperature conditions than the compared with those that are seen in rocks that are assigned to the Mesozoic. These structures could be formed or represent relicts of Paleozoic metamorphism.

How to cite: Paksoy, N., Paksoy, Y. C., and Natal'in, B. A.: Relicts of high-temperature fabric in the Strandja Massif, NW Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16284, https://doi.org/10.5194/egusphere-egu24-16284, 2024.

The Koralpe Complex of the Eastern Alps hosts a major crustal-scale shear zone within which the exhumation of Eo-Alpine eclogites and the formation of highly-strained, high-P-T (680-700°C, 12-13 kbar) Plattengneis mylonites was localised. Although no convincing kinematic indicators have been published and macro- and microscopic fabrics record an orthorhombic symmetry in the N-S section parallel to the prominent stretching lineation, a top-north shear sense has been inferred from published quartz EBSD analyses. In this contribution, we present a clear monoclinic fabric perpendicular to the stretching lineation revealing a top-west shear sense. Vorticity axes preserved in the crystal lattice of deformed quartz grains (constrained by EBSD data) are used as a quantitative solution for deciphering the strain history and to establish a newly informed constraint on the Eo-Alpine kinematics of the Koralpe.

Observations of macro- and micro-scale monoclinic fabrics (e.g. feldspar sigma-clasts and tourmaline and garnet delta-clasts) revealed an unequivocal and consistent top-west shear sense, localised around a north-south (N-S) striking vorticity axis (VAFsp), perpendicular to previous estimations of kinematics. To resolve the conflict between reported and observed shear sense, our investigation probed for crystalline vorticity axes preserved in quartz grains that experienced crystal plasticity and rotational distortion of the crystal lattice during deformation. The vorticity analysis of quartz EBSD data revealed a bulk crystalline vorticity axis (CVAQ) striking east-west (E-W), inclined 60-70° to the west. The inclined orientation of CVAQ is geometrically incompatible with the kinematic configuration of pure-shear dominated general shear necessary to produce the defining structural fabric of the Plattengneis (N-S stretching lineation, LS; pervasive planar foliation, S1). This incompatibility, along with the implication of an additional vorticity axis (VAFsp), indicates that CVAQ resembles a compound vorticity axis re-orientated into an inclined position during a two-phase deformation history.

To resolve the two-phase transposition of vorticity axes, we modelled a theoretical solution: a horizontally inclined initial orientation of CVAQ with subsequent rotation around VAFsp using mechanically compatible quartz slip-systems. The initial orientation of CVAQ (E-W striking) is predicted to form during D1 by dominant prism<a> slip under nearly plain strain pure-shear conditions. During D2, CVAQ is subsequently rotated c. 60-70° around the N-S striking VAFsp with a top-W shear sense. Based on the quartz EBSD dataset (CPO and misorientation axes of low angle boundaries (LAB)) we presume a dominance of prism<a> slip during the initial pure-shear deformation in D1 (under upper amphibolite facies condition). In the second deformation, continuation of prism<a> slip is inhibited by sub-optimal orientation of quartz grains relative to the D2 stress field; based on the heterogeneous distribution of LAB misorientation axes, we propose that the D2 rotation of CVAQ was accommodated by the interaction of multiple, non-dominant and geometrically-necessary slip-systems.

The crystal-scale kinematic analysis revealed a previously unknown poly-phase deformation during the formation of the Plattengneis shear zone with a top-west component in accord with the overall Eo-Alpine kinematics and demonstrated the vast potential of the crystalline vorticity axis analysis method for accurately resolving complex kinematics.

How to cite: Hill, L., Grasemann, B., and Bestmann, M.: Using EBSD crystalline vorticity axes to deduce complex kinematics during the Eo-Alpine deformation of the Plattengneis Shear Zone (Koralpe, SE Austria)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16733, https://doi.org/10.5194/egusphere-egu24-16733, 2024.

EGU24-17253 | Posters on site | TS1.1

Phase mixtures in shear zones 

Rüdiger Kilian

Deformation of polymineralic rocks at elevated temperatures usually results in grain size refinement but also in a grain scale mixture of mineral phases. Phase mixtures may either be homogeneous or exhibit a compositional and microstructural layering. Depending on the host rock stability, mixtures may consist of combinations of redistributed or newly, synkinematically formed phases. In general either neighbour-switching or heterogeneous nucleation are envisaged as processes responsible for mixing during diffusion creep s.l. including grain boundary sliding and grain-scale transport processes. In order to quantify phase mixtures, neighbourhood relations can be analysed to differentiate random, clustered or anti-clustered distributions. Heterogeneous nucleation is usually considered to allow for anti-clustered distributions, while neighbour switching during grain boundary sliding potentially produces random distributions.

Here, phase mixing is explored based on contact densities as well as on centre-to-centre distances. In particular, the effect of directionality that is neighbour relations as a function of the relative position in a 2D section is considered. The direction of neighbours is considered by the normal of the boundary trace as well as alternatively, by the direction of the centre-to-centre join.

Given sufficiently large datasets and non-extreme mixtures (e.g. with 0.2 < phase proportion < 0.8) a confidence interval of the results can be defined. Large datasets of ultramylonites of different metamorphic grade, phase proportions, compositions (ultramafic, mafic, quartzo-feldspatic) and microstructures (layered, isotropic) are tested.

It is found that phase anti-clustering is generally more pronounced in a direction close to the stretching direction in either layered or homogeneous ultramylonites. In layered mylonites, layer-normal relations are frequently found to be random while intralayer relations are often anti-clustered.

In the different rock types, specific anti-clustered phases can be discriminated, e.g., orthopyroxene with respect to olivine, k-feldspar with respect to plagioclase and quartz, and hornblende with respect to plagioclase. Other phase assemblages e.g. quartz-plagioclase are frequently found to be distributed randomly, hinting at mineral specific roles during diffusion creep s.l. and generally at element mobilities in deforming metamorphic rocks.

How to cite: Kilian, R.: Phase mixtures in shear zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17253, https://doi.org/10.5194/egusphere-egu24-17253, 2024.

EGU24-20305 | Orals | TS1.1

Texture of quartzite pebbles in metaconglomerates: strain paths across an extensional detachment  

Juan Gómez-Barreiro, Hans Rudolf Wenk, Sven Vogel, Immaculada Palomeras, Puy Ayarza, and José Ramón Martínez Catalán

The shape of pebbles in metamorphosed conglomerates has been used as an indicator of strain during tectonic deformation. Here we analyze deformed quartzite pebbles from metaconglomerates across the Salamanca detachment shear zone (SDSZ),  with variations of strain and deformation temperature. This structure is related to the late Variscan gravitational collapse in the Iberian Massif, Central Spain and has significant control on mineral resources. Strong preferred orientation is documented with time-of-flight neutron diffraction measurements and EBSD. The c-axes are in an asymmetric maximum perpendicular to the pebble elongation direction and there is considerable variation between samples. The oblique c-axis maximum relative to the elongated shape axis can be explained as a result of extension, combined with simple shear and dominant basal and rhombohedral slip, based on polycrystal plasticity modeling. It may also be influenced by recrystallization resulting in orientation patterns that resemble single crystals. The role of inherited textures is discussed and seems to be dominant in lower temperature segments on the base of the SDSZ hanging-wall.

Funding: grant PID2020-117332GB-C21 funded by MCIN/ AEI /10.13039/501100011033; SA084P20 from the JCyL government, and TED2021-130440B-I00 funded by MCIN/AEI/10.13039/501100011033.

How to cite: Gómez-Barreiro, J., Wenk, H. R., Vogel, S., Palomeras, I., Ayarza, P., and Martínez Catalán, J. R.: Texture of quartzite pebbles in metaconglomerates: strain paths across an extensional detachment , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20305, https://doi.org/10.5194/egusphere-egu24-20305, 2024.

EGU24-20713 | Orals | TS1.1

Fluid-mediated reactivation of brittle faults in the Bristol Channel Basin, UK 

Mark Anderson, Joe Connolly, Catherine Mottram, Gregory Price, and David Sanderson

Faults act as sites for preferential failure in the continental crust when it is subjected to sequential tectonic events. To do so, they will typically have favourable orientation, geometry and/or be weaker than the adjacent crust and are therefore prone to slip. However, fluid flow that is focussed along faults has a role in modifying their mechanical strength, especially where different fluids, and resulting mineralisation, are partitioned along particular structures. The East-Quantoxhead Fault (EQHF) in the Bristol Channel Basin (BCB), SW England has been identified as a reactivated normal fault with multiple slip events, the cause and precise timing of which are unknown. Using U-Pb geochronology of calcite veins located in the fault core we show that the timing of mineralisation (as a proxy for fluid flow) along the EQHF spans from 151-35 Ma. Microstructural analysis of different vein generations within the fault core shows that the longevity of this structure is a result of progressive weakening of the fault core. Initially this is represented by crystal plastic deformation of early-stage calcite mineralisation in the fault core, compatible with protracted phases of normal-sense slip. This is most likely mediated by the flow of syn-kinematic fluids that are hotter than the ambient temperature of the wall-rocks. However, later weakening of the fault core results from the precipitation of relatively weak fibrous celestine (SrSO4) along the margins of older calcite veins. Celestine shows evidence of reverse-sense S-C fabrics and was therefore a site of strain localisation and fault reactivation during regional contraction. This later fluid is sourced from deeper formations within the BCB which are only accessed by larger faults like the EQHF. Smaller normal faults in the BCB containing no celestine do not show a protracted fluid history, however crystal plastic textures (GBM, SGR) can also be seen within these faults. Understanding the role different fluids play in altering fault core composition, and strength via the analysis of vein textures plays a key role in understanding the partitioning and significance of fluid flow along fractures. 

How to cite: Anderson, M., Connolly, J., Mottram, C., Price, G., and Sanderson, D.: Fluid-mediated reactivation of brittle faults in the Bristol Channel Basin, UK, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20713, https://doi.org/10.5194/egusphere-egu24-20713, 2024.

EGU24-277 | ECS | Posters on site | TS1.2

Fracture porosity and equivalent horizontal permeability computed for shallow-water carbonates of the southern Apennines fold-and-thrust belt, Italy 

Ian Bala Abdallah, Elisa Panza, Stefania Dastoli, Canio Manniello, Giacomo Prosser, and Fabrizio Agosta

Fracture and fault networks are characterised by complex spatial and dimensional properties that might affect the flow and accumulation of subsurface fluids. In geological applications, DFN models are commonly employed to compute the multiscale properties of fractured rock volumes in terms of porosity and equivalent permeability. In the present contribution, we focus on an outcrop-to-reservoir investigation of Mesozoic shallow-water carbonates exposed along the axial zone of the southern Apennines fold-and-thrust belt, FTB, Italy. The carbonates were originally deposited in lagoon-to-proximal ramp settings of the Paleo Apenninic Platform during Lower Jurassic–Upper Cretaceous times and include well-layered and massive associations of bed packages several m-thick. By integrating the results of both field and digital structural analyses, we build multiple DFNs to assess the hydraulic behaviour of geocellular volumes representative of the different scales of observation, and stochastically populated with high-angle fractures, small, and medium faults. Fractures are either strata-bound, SB, or non-strata-bound, NSB, and results compartmentalized within single-bed packages. Small faults crosscut multiple bed-packages and show a few cm-to-m throws, whereas medium faults displace multiple bed-package associations and have throws > 1m. Both small and medium faults exhibit high peaks of fracture density, P20, and intensity, P21, in correspondence with the releasing jogs disrupting mechanical interfaces such as bed package boundaries and pre-existing low-angle thrust faults. As data input for DFN modeling, the aperture values of the stochastic fractures are set as proportional to either fracture length (most favourable flow conditions) or to the square root of fracture length (least favourable conditions). At the outcrop scale, 5m-side DFN models show the highest values of fracture porosity among those considered in this work. These results are therefore consistent with both SB and NSB fractures forming the main repository for fluid accumulation. At larger scales, the 50m-side and 500m-side DFN models including small and medium faults, are characterized by higher values of equivalent permeability, which range between 10-2 and 10-1 mD. Considering the computed Kxx and Kyy values for the single geocellular volumes, near-isotropic horizontal conditions are assessed across all scales of investigation. Accordingly, altogether, high-angle SB and NSB fractures, small and medium faults form a system of well-connected network through the shallow-water carbonates. Interpreting these data in light of published values for platform carbonates in Italy, we interpret this multiscale horizontal permeability isotropy due to the severe exhumation (~ 4 to 5km) the studied carbonates went through during the Quaternary downfaulting of the southern Apennines FTB.

How to cite: Abdallah, I. B., Panza, E., Dastoli, S., Manniello, C., Prosser, G., and Agosta, F.: Fracture porosity and equivalent horizontal permeability computed for shallow-water carbonates of the southern Apennines fold-and-thrust belt, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-277, https://doi.org/10.5194/egusphere-egu24-277, 2024.

A wide range of deformation and diagenetic mechanisms have been observed within faulted carbonate lithofacies.  These processes are known to influence the permeability of a fault, and hence the flow properties.  The mechanisms active during faulting are influenced by a range of factors, including: lithofacies, host porosity, host permeability, juxtaposition type, depth of burial, depth at time of faulting and kinematics.  Although we can estimate the fundamental controls on resulting fault rock permeability, the ability to predict flow properties within and surrounding faults in carbonates remains highly uncertain.  This presentation will discuss conditions for when a fault may act as a conduit or a potential barrier to flow, along with the gaps in current data and knowledge.

Further, conditions for when a permeability anisotropy may be created within the fault core of carbonate lithofacies will be presented, along with the implications for fluid migration across or along the slip surface.  A permeability anisotropy is observed within carbonate fault cores, dependent on lithofacies and juxtaposition.  The significant heterogeneity created when different lithofacies are juxtaposed outweighs the resulting permeability anisotropy that is created, such that no systematic permeability anisotropy can be defined.  However, when self- or similar juxtapositions occur, a systematic permeability anisotropy is recorded, creating a permeability that can be as much as over 5 orders of magnitude lower normal to fault strike than parallel to fault strike.  The permeability anisotropy is formed from differing mechanisms dependent on lithofacies; the intersections of shears with fractures/veins in recrystallised lithofacies, and oriented pores in high porosity grainstones.  This is similar to previous crystalline and siliciclastic studies.  The permeability anisotropy can act to allow flow in one orientation but prevent it in another.

How to cite: Michie, E.: Can we ever predict how fluids may flow within and surrounding faults in carbonates?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-390, https://doi.org/10.5194/egusphere-egu24-390, 2024.

EGU24-536 | ECS | Posters on site | TS1.2

Pore space properties of solution surfaces in shallow-water carbonates 

Canio Manniello, Vincenzo La Bruna, Hilario Francisco Rego Bezerra, Renata Emily Brito Araùjo, Xavier Milton Morais, Emma Michie, Daniel Faulkner, Michael John Allen, Giacomo Prosser, and Fabrizio Agosta

Diagenetic and tectonic processes taking place in platform carbonates produce significant textural and mineralogical modifications through time, controlling the pore space in terms of dimension, geometry, shape, and connectivity of single pores, and influencing both total and effective porosity. Focusing on the different types of solution surfaces, this study is conducted on Lower Jurassic, Cretaceous, and Eocene, carbonates exposed at the Viggiano Mt. and Raparo Mt., southern Apennines, Italy. Microscale analyses show that the primary porosity of these rocks was occluded by pervasive blocky cements, which precipitated during burial diagenesis of the carbonates. We aim to assess the role exerted by the roughness of bed-parallel and low-angle to bedding solution surfaces, on the pore properties and permeability values of a variety of carbonate lithofacies such as mudstones, packstones, grainstones and rudstones. Specifically, we show the results of Nuclear Magnetic Resonance (NMR), gas-porosimetry and water-permeability tests conducted on plugs cored either orthogonal or parallel to bedding interfaces. All the study plugs show an amount of effective porosity lower than 5%, with mean values of ca. 3%. Excluding larger microfractures, and sporadic intrafossil and intercrystal molds, among the various types of solution surfaces we document that the rough, seismogram-type stylolites localize secondary porosity, while smooth, wave-type stylolites do not. The seimogram type stylolites, due to the non-selective carbonate’s dissolution, form a poorly connected vuggy porosity, and the NMR results the pores are subspherical to tubular (r<3 µm), with low aspect ratios (stiff pores), differently from the pores associated to open fractures (soft pores). Connectivity in the seismogram-type stylolites-related pores is due mainly to small microfractures forming capillary porosity (pore throat ca. r=1 µm). The results of permeability measurements at room pressure indicate that the amount of bed-perpendicular permeability is generally low (10-1 and 10-3 mD). The results of permeability measured at increasing confining pressure show that the in stylolite-dominated the bed-parallel samples have slightly higher values with respect to the bed-orthogonal ones and, at increasing confining pressure conditions, the permeability decreases of less than one order of magnitude. Differently, the fracture-dominated plugs show a permeability decrease of two orders of magnitude. These results are therefore consistent with a pore connectivity affected by open fractures only at shallow depths (<25 MPa) and influenced by both stylolites and primary pores at depths. Results of ongoing X-ray tomography analyses will better clarify the pore distribution along stylolites and at the fracture-stylolite intersections.

How to cite: Manniello, C., La Bruna, V., Bezerra, H. F. R., Araùjo, R. E. B., Morais, X. M., Michie, E., Faulkner, D., Allen, M. J., Prosser, G., and Agosta, F.: Pore space properties of solution surfaces in shallow-water carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-536, https://doi.org/10.5194/egusphere-egu24-536, 2024.

On a global scale, the South Caspian is a basin where mud volcanoes are
most densely distributed. Numerous active volcanoes are registered here, both on
land and in the adjacent sea basin (Caspian Sea), which, as a result of their daily
activity, discharge water fluids to the Earth's surface.
In this work, using samples taken from coastal and island mud volcanoes, a
comparative study of the chemical compositions of the fluids expelled from the
salse and gryphon-type emissions, as well as their origin, including the
contribution of various stratigraphic units to the water formation processes.
According to our results, the contribution of the condensed waters of the
Caspian Sea was greater in the formation of Na-Cl type waters of mud volcanoes
in the South Caspian Basin. In addition, the origin of volcanic waters also formed
as a result of the contribution of shallow ‘low-mineralized’ pore fluids and deep-
seated ‘high-mineralized’ brines correlates well with the depths (1-5.5 km) of the
Productive Series strata.

How to cite: Bayramova, A.: A Comparative study of water fluids of coastal and island mud volcanoes: Acase study of the South Caspian Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-569, https://doi.org/10.5194/egusphere-egu24-569, 2024.

EGU24-1240 | ECS | Posters on site | TS1.2

Understanding the Heterogeneity and Anisotropy of Permeability in Carbonate Rocks Within a Fault Network 

Mohammadreza Akbariforouz, Qi Zhao, and Chunmiao Zheng

The complexity of fault zone structure and faulting mechanisms significantly impact the permeability of fault zone rocks. Various factors, including the type and porosity of the host rock, the fault’s geometry, differential strain, the history of deformation, and the tectonic setting, can cause permeability to exhibit wide fluctuations. However, research into the permeability of complex fault zones is constrained by the scarcity of in situ measurements. Utilizing analytical relationships, laboratory tests, outcrop measurements, or numerical modeling often yields biased results, as they may not accurately represent real-world conditions. Moreover, the effects of fault branching and interconnections have not been thoroughly explored. This study compares the permeability of faulted carbonate rocks using a comprehensive database of in situ permeability tests. We investigate how a network of seven faults influenced permeability variations at different locations and depths by examining surface and subsurface data, including information from excavated tunnels. Our findings reveal that factors such as fault dips, length, fault structure, and rock characteristics can create diverse impacts on permeability. We observe permeability values in fault damage zones one to five orders of magnitude higher than those in the host rocks. The thickness and condition of damage zones shed light on the range of fault zone permeability. Furthermore, we find that faulted rocks with higher porosity and lower mechanical strength exhibit more substantial alterations in permeability. This study provides valuable insights into the behavior of faulted carbonate rocks.

How to cite: Akbariforouz, M., Zhao, Q., and Zheng, C.: Understanding the Heterogeneity and Anisotropy of Permeability in Carbonate Rocks Within a Fault Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1240, https://doi.org/10.5194/egusphere-egu24-1240, 2024.

Shallow-water carbonates include a variety of heterogeneities such as bed interfaces, laminations, stylolites, and pressure solution seams forming rock multilayers crosscut by high-angle strata-bound fractures. At a larger scale, bed package interfaces and other primary stratigraphic contacts exert a similar control compartmentalizing high-angle faults within discrete sedimentary units. The aforementioned heterogeneities commonly form within the depositional environments, and/or at specific diagenetic conditions under given burial depths. Mechanical compaction, dissolution, cement precipitation, and other physical/chemical processes hence alter the original framework of the carbonates, and contribute to the acquirement of their long lasting mechanical properties. To further investigate this topic, in other words to assess the time-dependent fracture stratigraphy of shallow-water carbonates, this presentation focuses on the influence exerted by tectonics on the mechanical layering of the Mesozoic platform carbonates of southern Italy. By analyzing outcrops lying along the axial zone of the southern Apennines fold-and-thrust belt, and within its forebulge area, published data are discussed altogether to decipher the control exerted by thrusting tectonics on the formation of mechanical interfaces within Lower Jurassic to Upper Cretaceous carbonates. Rocks exposed in the foreland domain include a number of high-angle fractures. These fractures are mainly bounded by bed interfaces, and their spacing values vary proportional to the bed thickness. Such a proportionality is exhibited by both mud- and grain-supported carbonate lithofacies, which show saturated to oversaturate conditions. Differently, carbonates lying in the axial zone of the southern Apennines belt are characterized by values of fracture density and intensity that do not vary proportionally with the bed thickness. In order to investigate the significance of the latter data, detailed microstructural analyses aimed at assessing the timing of pressure solution processes with respect to the diagenetic history and tectonic evolution of the carbonates are considered. Besides the effects of early embrittlement of the carbonate grainstone lithofacies, which occurred due to cement precipitation in phreatic marine environment that prevented the effects of localized dissolution at the grain-to-grain contacts, two main phases of pressure solution characterized the carbonates. The first one took place during Meso-Cenozoic sedimentary burial with formation of wave-like, bed-parallel surfaces. In cat, the continuous burial of the carbonates, down to depths of ca. 1.5 km, promoted the development of solution surfaces along the bed interfaces, and also within the single beds. Small, isolated, wave-like surfaces formed as isolated elements within the single carbonate beds. The second phase occurred during Upper Miocene thrusting tectonics, at depths of ca. 4 km, with formation of seismogram-like surfaces at low-angle to bedding. The latter surfaces consisted of both stylolites and slickolites with sub-vertical teeth, which cut across the pervasive blocky cements of the carbonates, dissolved the pre-existing veins, and formed laterally persistent surfaces throughout the carbonates. Accordingly, the combination of both pure shear (stylolites) and sub-simple shear (slickolites) strain caused formation of new mechanical interfaces in the carbonate beds, and therefore modified the thickness of single mechanical units throughout the Mesozoic carbonates.

How to cite: Agosta, F.: Evolving fracture stratigraphy properties of layered carbonates through time: examples from the southern Apennines fold-and-thrust belt, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2077, https://doi.org/10.5194/egusphere-egu24-2077, 2024.

EGU24-2471 | ECS | Posters on site | TS1.2

Petrographic Heterogeneity and Sandstone Evolution in the Groningen Gas Field: Implications for Reservoir Geomechanics 

Sebastian Mulder, Dmitry Bublik, and Johannes Miocic

Fluid extraction from geological formations for purposes of subsurface utilization leads to pore pressure drop in reservoirs and subsequent compaction and seismicity, especially in porous sandstones. Petrography controls the geomechanical properties of the reservoir, crucial for predicting a reservoir's response to fluid extraction and understanding its lateral variability. This study focuses on the Groningen gas field in the Netherlands, addressing its compaction-induced surface subsidence and seismic events resulting from gas depletion. Core samples were examined to delineate spatial petrographic trends and develop a microscale model of the Groningen gas field. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to determine mineralogical compositions, textural relationships and diagenetic processes. Predominantly constituted of sublitharenites, the sandstones exhibit dolomite and quartz cement as primary authigenic cements. Variations in clay types—kaolinite, illite, and chlorite—were observed, influencing localized pore-filling cementation processes.  Across the field, mineral relations revealed notable trends: depth-related feldspar decrease, correlation between kaolinite and feldspar abundance, and elevated chlorite content towards the northern sector together with the presence of an early quartz cementation phase, which is also observed within aquifer cores. The dissolution of feldspar potentially impacts the structural integrity of the sandstones, while authigenic mineralization appears intricately linked to depositional facies and localized fault-related fluid movements. The timing and extent of these diagenetic processes emerged as pivotal factors dictating sandstone stability within the reservoir. This comprehensive analysis enhances our understanding of Groningen's reservoir heterogeneity, offering critical insights to predict and manage subsurface responses to extraction-induced pressure changes. By providing predictive models, this study facilitates the evaluation of reservoir behavior and aids in mitigating risks associated with compaction-induced subsidence and seismicity.

How to cite: Mulder, S., Bublik, D., and Miocic, J.: Petrographic Heterogeneity and Sandstone Evolution in the Groningen Gas Field: Implications for Reservoir Geomechanics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2471, https://doi.org/10.5194/egusphere-egu24-2471, 2024.

Just how much do sorting, cementation and compaction control the porosity and permeability of rocks? In this work we start with making extremely accurate porosity and permeability measurements on binary grain mixtures, arriving at good agreement between them and theoretical results. These seemingly simple experiments are difficult to carry out with the degree of precision needed to test the models. We have developed a methodology allowing porosity and permeability to be measured to within ± 4.415% and ± 4.989% (at a flow rate of 5.13 cm3/s) of each value, respectively. The newly developed theoretical framework includes both the interstitiation mixing process and several replacement processes.

A major result of this work is that the theoretical models describing these two processes are independent of grain size and grain shape. The latter of these two findings infers that the models developed in this work are applicable to any shape of grain or type of packing, providing that a representative porosity of each size of grain pack is known independently, either experimentally or theoretically. Experimental validation has shown that the newly developed relationships for porosity described measurements of porosity for near-ideal binary mixtures extremely well, confirming that porosity is always reduced by binary mixing, and that the degree of reduction depends upon the size of the ratio between the two grain sizes.  

Calculation of permeability from the packing model has also been carried out. Six different permeability estimation methods have been used. It was found that the most accurate representations of the experimental permeability were obtained (1) when the exact RGPZ method was used with the porosity mixing models developed in this work, and (2) when the exact RGPZ method was used with the weighted geometric mean to calculate a representative grain size. For mixtures where there is a large difference in grain sizes, permeability (k) varies little for the ranges of mixtures from 28% to 100% of small grains (about 4*k), only increasing significantly as the fraction of small grains falls below 28% to zero (to 2 orders of magnitude in k) because the small grains then only partially occupy the space between the large grains. For mixtures of grains of similar sizes, the situation is remarkably different. The variation in permeability for small grain fractions between 100% and about 28% is much amplified (2 orders of magnitude in k), while the increase in permeability as the fraction of small grains falls from about 28% to zero is similar to the other case, and perhaps slightly less pronounced (about 1.5 orders of magnitude in k). This counterintuitive behaviour is important for the interpretation of how sorting affects permeability, implying a greater spread of permeabilities for rock composed of grains with a small difference in grain size.

How to cite: Luo, M., Glover, P., and Lorinczi, P.: Theory and modelling of the effects of grain sorting, compaction & cementation on porosity and permeability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3571, https://doi.org/10.5194/egusphere-egu24-3571, 2024.

EGU24-4381 | ECS | Posters on site | TS1.2

Tracing the origin of parental fluids and paleo-temperature distribution in fault zones: case studies from the Carboneras Fault (Spain) and Lemnos Island (Greece) 

Vincenzo Moretto, Leonardo Del Sole, Manuel Curzi, Luigi Dallai, Gianluca Vignaroli, Giulio Viola, Fabrizio Balsamo, Luigi Riccardo Berio, Georg Grathoff, Lurence Noel Warr, and Luca Aldega

Multiple episodes of brittle deformation tend to increase the structural complexity of fault zones. This commonly results in the development of juxtaposed and non-coeval distinct Brittle Structural Facies (BSF) formed at different times, depths, and temperature. Indeed, these BSFs are characterized by an irregular distribution of inherited, syn-kinematic, and post-kinematic minerals, whose study provides useful information about the temperature conditions of (de)formation, and the origin of fluids circulating within faults. We combined X-ray diffraction (XRD) analyses and polytype determinations of whole-rock and several grain-size fractions (6-10 μm, 2-6 μm, 0.4-2 μm, 0.1-0.4 μm, and <0.1 μm), with H-isotope data of 76 fault rocks and 6 protoliths from two structurally and well-characterized fault zones with different kinematics: the Carboneras strike-slip fault zone (Betic Cordilleras, SE Spain) and the Kornos-Aghios Ioannis extensional fault zone on the Lemnos Island (North Aegean Trough, Greece). Mineralogical and geochemical data allowed us to (1) reconstruct the distributions of syn/post-kinematic minerals in distinct BSFs, (2) constrain their formation temperature, and (3) unravel the origin of fluids involved during faulting. In the Carboneras fault rocks, we distinguished a protolithic mineralogical assemblage consisting of quartz, carbonates, K/Na-micas (2M1 polytype), chlorite, kaolinite, and Fe/Ti-oxides, a syn-kinematic assemblage composed of mixed layers chlorite-smectite and illite-smectite (1Md polytype), and a post-kinematic assemblage made up of smectite, chlorides, and sulphates. The coexistence of randomly (R0), short-range (R1), and long-range (R3) ordered illite-smectite in different BSFs indicates contrasting formation temperatures. Bulk samples generally display δ2H values (V-SMOW) between -15‰ and -60‰ (with a few exceptions at -90‰), while their respective <2μm fractions show δ2H values between -10‰ and -60‰. The combination of mineralogical and geochemical data from the Carboneras fault zone depicts a complex history of multiple brittle events occurring at different temperature conditions, wherein parental fluids of mostly meteoric origin infiltrated into the fault zone and interacted with the host rocks at various degrees and depths. In the fault rocks of Lemnos Island, we identified a host-rock mineralogical assemblage composed of quartz, feldspars, carbonates, K-mica (2M1 polytype), chlorite, R0 illite-smectite, anatase, and Fe-oxides and hydroxides, a syn-kinematic assemblage made up of R3 illite-smectite (1Md polytype), and kaolinite, and a post-kinematic assemblage characterized by halite and gypsum. Bulk samples display δ2H values (V-SMOW) between -70‰ and -140‰, while their respective <2μm fractions show δ2H values between -60‰ and -85‰. Such results indicate that Kornos-Aghios Ioannis fault rocks formed during a deformation event with predominantly hydrothermal fluids circulating into the fault zone (>160°C). This multidisciplinary approach represents an innovative point of view for studying fluid circulation, mineral crystallization, and temperature evolution in complex fault zones, and it can be applied to both orogen scale faults and smaller fault systems.

How to cite: Moretto, V., Del Sole, L., Curzi, M., Dallai, L., Vignaroli, G., Viola, G., Balsamo, F., Berio, L. R., Grathoff, G., Warr, L. N., and Aldega, L.: Tracing the origin of parental fluids and paleo-temperature distribution in fault zones: case studies from the Carboneras Fault (Spain) and Lemnos Island (Greece), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4381, https://doi.org/10.5194/egusphere-egu24-4381, 2024.

EGU24-5693 | ECS | Posters on site | TS1.2

Microstructural characterization of deformation bands in shallow porous carbonates of Apulian Platform, Southern Italy 

Giovanni Freda, Silvia Mittempergher, Fabrizio Balsamo, Mattia Pizzati, Raffaele Di Cuia, and Angelo Ricciato

Deformation may exert a positive or negative impact on rock strength, stiffness and porosity depending on the initial properties of the rock. In porous rocks, deformation bands (DBs) reduce both porosity and permeability, and potentially increase rock strength and stiffness. In low porosity (tight) rocks, deformation occurs via shear and opening-mode fractures, thus enhancing permeability and deteriorating strength and stiffness.

In this study we describe field observations and laboratory analyses to characterize sub-vertical deformation bands in the porous carbonates of the Calcarenite di Gravina Fm. exposed in Matera and Gravina in Puglia, Southern Italy. Matera and Gravina in Puglia are located at the boundary between the Apulian foreland and the foredeep of the Southern Apennines thrust belt. Both study areas consist of an asymmetrical horst structure involving the Cretaceous (Senonian) tight carbonates of the Apulian platform (Calcare di Altamura Fm.) unconformably overlain by Plio-Pleistocene shallow-marine coarse-grained lithic sandstone and grainstone (Calcarenite di Gravina Fm.). The Calcarenite di Gravina Fm. is dominated by pervasive DBs organized into 2 main sets dipping at high angle and striking N-S and NNE-SSW, except in some limited areas where the DBs form a complex network with the presence of a secondary set, striking NW-SE, showing mutual crosscutting relationships. The DBs have a positive relief, due to their relatively higher resistance to erosion, and appear whitish, tabular with some slight undulations, 10’s of meters long in map view, continuous and steeply inclined (from 75° to 90°). These structures have thicknesses from few mm up to a few cm depending on the facies of the calcarenite. At the outcrop scale the DBs don’t seem to accommodate significant shear offsets. A total of 53 oriented samples were collected for thin sectioning, petrophysical, and microstructural analysis. We acquired porosity measurements using a Hg-intrusion porosimeter, which showed that the DBs have an average porosity of 11%, while for the host rock is 38%. 29 Blue-impregnated thin sections of host rocks and DBs were analysed by standard microscopy, cathodoluminescence (CL), and a scanning electron microscope (SEM). The analysis of the CL images shows that the clast size distributions are similar in the DBs and host rock, and they are not crushed or fractured. Furthermore, while in the host rock the clasts are randomly oriented, in the DBs they are iso-oriented with the long axis describing low angles to the band.

Our work shows that these DBs are characterized by the absence of grain size reduction with a strong preferred orientation of long axes without significant fragmentation. These data may indicate that DBs formed in high porosity conditions, at very shallow depths. Moreover, given the strong difference between the petrophysical properties of the host rock and DBs and the apparent abundance and continuity of the DBs, they would provide a significant anisotropy in the flow pathways of the calcarenite.

How to cite: Freda, G., Mittempergher, S., Balsamo, F., Pizzati, M., Di Cuia, R., and Ricciato, A.: Microstructural characterization of deformation bands in shallow porous carbonates of Apulian Platform, Southern Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5693, https://doi.org/10.5194/egusphere-egu24-5693, 2024.

EGU24-9013 | Posters on site | TS1.2

A new geological model for the Lefka Ori Massif in the accretionary wedge of the Hellenic Subduction Zone.  

Daniel Moraetis, Aris Leontaritis, Andreas Scharf, Charalampos Fassoulas, Stylianos Zacharias, Kosmas Pavlopoulos, Frank Mattern, Asma Alnaqbi, Xuan Yu, Christos Pennos, Kostas Adamopoulos, Hamdan Hamdan, and Nikolaos P. Nikolaidis

Here we present the results of surface and subsurface (caves) geological mapping in the Lefka Ori Massif. The structural field data collection and the stratigraphy analysis were supported by the IGCP-715 project in collaboration of the Speleological Association of Crete (SPOK) and the Gourgouthakas 2023 exploration team. The overall structure of the Lefka Ori Massif consists of a roughly E-W trending open anticline. Regional uplift is related to compressional and extensional events during the Late Oligocene to present. The primary lithologies of the Lefka Ori Massif are comprised of the Plattenkalk Unit and the Trypali Unit. The Plattenkalk Unit contains (1) black brecciated karstified marbles/dolostones with interbedded stromatolites (Triassic), (2) white to gray marbles/dolostones (Triassic-Lias), and (3) thin bedded marbles (Dogger-Oligocene). Black dolostones and brecciated marbles (with stromatolite fragments) are building up the overlying Trypali Unit (Late Triassic-Lias).

The results from the structural analysis in the Lefka Ori Massif highlight 3 sets of faults, which are of (A) E-W striking thrust faults, (B) dextral NNW-SSE strike-slip faults and (C) E-W striking steep dip-slip faults. A regional thrust (hereafter "Pachnes Thrust") has a vertical displacement of 1000 m and duplicates the Plattenkalk Unit stratigraphy (sections 1 and 2) in the Lefka Ori Massif. The hanging wall consists of Plattenkalk units 1 and 2, while the footwall comprises the Plattenkalk unit 3. The Pachnes Thrust has an apparent horizontal displacement of approximately 12 km. The cross-cutting relationship of the thrust with the strike-slip faults indicate that the faults are coeval. The steep dip-slip faults are still of an unknown relative age but certainly most of them appear as normal, younger faults. The Pachnes Thrust is folded around a roughly E-W trending open fold axis. The Late Oligocene green and red, calcschist sediments in the footwall of the Pachnes Thrust indicates the maximum age of thrusting.

The third deepest cave in Lefka Ori Massif (Sternes Cave, depth -616 m) contains a system of galleries reaching a total length of 5.6 km. This karst system of subhorizontal galleries is well explained by the Pachnes Thrust as it parallels the thrust. Likewise, the Pachnes Thrust has been delineated in the deepest cave (Gourgouthakas) at a depth of -700 m. In addition, the accepted hydrology in the Lefka Ori Massif is defining an upper fast flowing reservoir and a lower slow flowing reservoir. The physical model for these two reservoirs is explained by the hanging wall 1 and 2 lithologies (fast flowing reservoir) and the footwall lithology 3 (slow flowing reservoir) of the Pachnes Thrust.

The Pachnes Thrust in Lefka Ori Massif probably correlates with the recorded southward thrusting and nappe stacking due to convergence between the African and Eurasian plates (Oligocene-Early Miocene). The deformed Pachnes Thrust plane is coeval with the southward thrusting, due to the uplift and exhumation phases during extension described in the literature. The present findings are offering new evidence of the tectonic evolution and the exhumation of the high pressure metamorphosed rocks in the Hellenic Subduction Channel.

How to cite: Moraetis, D., Leontaritis, A., Scharf, A., Fassoulas, C., Zacharias, S., Pavlopoulos, K., Mattern, F., Alnaqbi, A., Yu, X., Pennos, C., Adamopoulos, K., Hamdan, H., and Nikolaidis, N. P.: A new geological model for the Lefka Ori Massif in the accretionary wedge of the Hellenic Subduction Zone. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9013, https://doi.org/10.5194/egusphere-egu24-9013, 2024.

EGU24-10510 | ECS | Posters on site | TS1.2 | Highlight

Influence of pre-existing faults on damage distribution in carbonate fault zones: the case study of the Roccapreturo Fault, central Apennines 

Marco Mercuri, Fabrizio Agosta, Michele Fondriest, Luca Smeraglia, Andrea Billi, Stefano Tavani, and Eugenio Carminati

Understanding the origin and distribution of damage within carbonate-hosted fault zones is crucial, yet it remains a complex challenge, which hampers the overall assessment of their mechanical and hydraulic structure. In carbonate-hosted fault zones, shattered to intensely brecciated non-cohesive rocks have been reported. Although their origin has been related to the propagation of multiple seismic ruptures, great uncertainties persist regarding their interpretation and distribution.

The NW-SE striking, approximately 15 km long Roccapreturo Fault, in the central Apennines of Italy, is an intriguing case study where non-cohesive fault rock domains occur within its footwall damage zone. These domains elongate in a NE-SW direction for ~200 meters from the main slip surface.

We employed a multiscale approach to better understand the distribution and origin of the non-cohesive fault rocks. The fault geometry and throw distribution along the main fault segments were characterized through fault-perpendicular geological cross-sections. Virtual outcrop models of key exposures, located in and around an abandoned quarry, were constructed using Structure from Motion-Multiview Stereo photogrammetry. These models utilized photos taken with a Mavic Mini 2 drone. The interpretation of virtual outcrop models, combined with classical fieldwork, allowed us to map the damage and minor fault strands.

The Roccapreturo Fault displaces Cretaceous rocks originally deposited in various depositional environments. Along its strike, from NW to SE, the fault intersects rocks from internal or restricted carbonate platform, margin, and proximal slope to basin depositional environments. Notably, non-cohesive fault rocks are exposed between the margin and proximal slope rocks. This area coincides with the maximum throw of the fault, which is ca. 600 meters, and with the intersection with a system of pre-existing NE-SW-striking steeply dipping faults.

At the outcrop scale, faults exhibit two preferred orientations, parallel and perpendicular to the main slip surfaces of the Roccapreturo Fault, respectively. The former ones show predominant dip-slip kinematics, while the latter ones show both dip-slip and strike-slip kinematics.

We interpret the distribution of non-cohesive fault rocks along the Roccapreturo Fault as influenced by its intersection with the NE-SW fault system, where most of the slip accumulated. Accordingly, the pre-existing NE-SW faults accommodated transtensional slip during latest extensional deformation and coeval rock exhumation from depth. The transition of the Cretaceous depositional environments, which was accommodated by the NE-SW-striking faults, therefore highlights the pivotal role of pre-existing anisotropies in dictating the distribution of damage, particularly of non-cohesive fault rocks, in carbonate hosted faults.

How to cite: Mercuri, M., Agosta, F., Fondriest, M., Smeraglia, L., Billi, A., Tavani, S., and Carminati, E.: Influence of pre-existing faults on damage distribution in carbonate fault zones: the case study of the Roccapreturo Fault, central Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10510, https://doi.org/10.5194/egusphere-egu24-10510, 2024.

EGU24-16378 | Orals | TS1.2 | Highlight

Calcite veins as local fluid flow barriers in reservoir rock? The odd occurrence of veins in highly porous aeolian sandstone in Namibia 

Eric Salomon, Anna Nele Meckler, and Harald Stollhofen

In porous sandstone, fluids are guided by major features such as faults or lithologic discontinuities. At the local scale, deformation bands are common structures to baffle fluid flow in such rock. Potential flow-hindering structures less frequently reported of are veins in porous sandstone (Skurtveit et al., 2015, as a rare case), which may root in the circumstance that they do not appear very often and/or have simply been overlooked. 

We here present a case where calcite veins formed in the highly porous (up to 25 % porosity) and partially poorly lithified eaolian Lower Cretaceous Twyfelfontein Formation in NW Namibia. This sandstone was buried by the extrusion of voluminous Paraná-Etendeka flood basalts at around 130 Ma and was since then subject to exhumation. Calcite veins occur in roughly half of the visited outcrops of the Twyfelfontein Formation and their dominant parallel trend to the continental margin suggests a tectonic origin. As the host rock is void of carbonate framework material or cement, the veins must have formed through advective fluid circulation. An external source of the calcium may possibly be the alteration of overlying and intercalated basalt. The veins exhibit a remarkable multitude of textures ranging from blocky, colloform, to microcrystalline calcite generations, that have partially experienced brecciation. This argues for highly variable formation conditions, potentially spanning from normal fluid advection to boiling and injection (c.f., Moncada et al., 2012; Salomon et al., 2021). 

Preliminary clumped isotope data of the veins indicate a low temperature formation in the range of 19-61°C, which suggests overall shallow burial conditions. This is in agreement with the diagenetic paragenesis of the rock arguing for late stage vein formation, i.e. during exhumation of the rock. Upcoming U/Pb calcite dating is expected to bring greater clarity on this regard. A halo in the host rock surrounding the veins became calcite cemented due to the growth of calcite from the fractures into the sandstone body. This appearance demonstrates the following evolution: (1) fracturing of the sandstone, which enhances advective fluid flow in the rock body; (2) vein precipitation and near-vein host-rock cementation; and consequently (3) reduction of permeability in the fracture and adjacent wall rock. 

Due to their potential of forming effective barriers to fluid flow, we stress that their formation needs to be understood in greater detail. The variable vein textures indicate differing formation conditions, which sets the base for a more common occurrence of calcite veins in porous uncemented sandstone. 


References:

Moncada, D., et al. (2012). Journal of Geochemical Exploration 114, 20-35, doi:10.1016/j.gexplo.2011.12.001.

Salomon, E., et al. (2021). Journal of Structural Geology 153, 104463. doi:10.1016/j.jsg.2021.104463.

Skurtveit, E., et al., (2015). Petroleum Geoscience 21, 3-16, doi:10.1144/petgeo2014-031.

How to cite: Salomon, E., Meckler, A. N., and Stollhofen, H.: Calcite veins as local fluid flow barriers in reservoir rock? The odd occurrence of veins in highly porous aeolian sandstone in Namibia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16378, https://doi.org/10.5194/egusphere-egu24-16378, 2024.

The shortening of sediments in accretionary prisms is accomplished by localized faulting as well as non-localized deformation. While faulting is often easily recognized from seismic sections, accessing the amount and extent of non-localized deformation is rather challenging. In order to address this challenge, we explore samples from the active accretionary prism offshore Gisbourne, NZ at the Hikurangi margin which contains accreted sediments of Pliocene to recent age. Drilling at Site U1318F of IODP Expedition 375 recovered non- to semi-lithified sediments from a major accretionary fault, the Papaku Fault, including its hanging wall and footwall. The crystallographic preferred orientation (CPO) of the clay minerals is a measure for their alignment and was determined in 66 sediment samples from the drill core (250-500 mbsf) using high energy X-rays. The results show that the CPO strength of the clay mineral basal planes (00l) is in general weak and no depth-related trend can be observed. In the hanging wall of the Papaku Fault, (00l) pole figures have non-rotationally symmetric, unimodal density distributions displaying incomplete girdles. In the footwall, most (00l) pole figures exhibit unimodal, rotationally symmetric to weak girdle density distributions, with most maxima pointing parallel or subparallel to the drill core axis. Fault zone samples also exhibit rotationally symmetric, unimodal (00l) distributions, with maxima perpendicular to the fault plane.

We assume that pre-shortening and pre-faulting, sediments had a weak initial CPO related to sedimentation and compaction with a rotationally symmetric, unimodal (00l) distribution. The girdle shape of the distribution in the hangingwall and to a minor extent in the footwall is introduced by non-localized deformation which results in grain-scale folding. Accordingly, diffuse shortening was larger in the present-day hanging wall than in the present-day footwall. Furthermore, we interpret the CPO in the Papaku fault itself to be a result of sediment shearing, overprinting any pre-existing CPO. The position of the Papaku fault is compatible with fault initiation where diffuse shortening was unable to propagate sufficiently towards the foreland.

While our results also confirm existing tectonic models from this part of the Hikurangi margin, more importantly they demonstrate implications for strain distribution in fault and thrust systems as well as the usefulness of clay mineral CPO for unravelling deformation and tectonic processes in accretionary prism sediments.

How to cite: Kühn, R., Kilian, R., and Stipp, M.: Crystallographic preferred orientation of clay minerals in sediments from the Hikurangi accretionary prism offshore New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17144, https://doi.org/10.5194/egusphere-egu24-17144, 2024.

EGU24-17174 | ECS | Posters on site | TS1.2 | Highlight

Spatial variability in topology, connectivity and permeability within deformation band networks 

Hakan Heggernes, Atle Rotevatn, Matteo Demurtas, Casey W. Nixon, and Haakon Fossen

Networks of deformation bands in porous granular rocks represents potential low-permeable baffles to fluid flow in subsurface reservoirs. However, little work addresses the network properties of such networks, like spatial intensity, network connectivity and network geometry. Motivated by this, we here present an investigation of two-dimensional, horizontal exposures of deformation band networks within the Jurassic Entrada Sandstone in the San Rafael Desert (Utah). We analyse the geometry and topology (i.e. a network represented as nodes and branches) of the studied networks to: 1) characterise deformation band orientation, connectivity and areal intensity; 2) assess spatial topological variability; 3) elucidate large scale variation across the study area; 4) evaluate effective network permeabilities. Effective deformation band network permeability is calculated by incorporating a topological measure of network connectivity into the permeability calculations. Deformation band networks show distinct topological signatures, typically being dominated by Y-nodes, and IC- and CC-branches. Depending on the orientation of deformation bands and numbers of different sets of deformation bands within each studied network, both topology and areal intensity vary. Low proportion of isolated II-branches reflects the evolution of deformation bands through bifurcation and abutment, creating Y-nodes, to form interconnected networks. We document great spatial variability I network connectivity and topology within individual networks. Similarly, the effective permeability within well-connected (parts of) the studied deformation band networks (>1.5 connections per branch) significantly reduce effective permeabilities, whereas areas within the networks with low connectivity offer higher-permeable pathways for tortuous fluid flow.

How to cite: Heggernes, H., Rotevatn, A., Demurtas, M., Nixon, C. W., and Fossen, H.: Spatial variability in topology, connectivity and permeability within deformation band networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17174, https://doi.org/10.5194/egusphere-egu24-17174, 2024.

EGU24-20887 | Orals | TS1.2 | Highlight

Deformation, fluid flow and diagenesis in deformed granular rocks across scales 

Atle Rotevatn, Vilde Dimmen, Hakan Heggernes, Matteo Demurtas, Haakon Fossen, Edoseghe Osagiede, and Thibault Cavailhes

The study of deformation, fluid flow and diagenesis within porous granular rocks includes processes spanning from the sub-millimetric pore and grain scale, to 10s to 100s km-long fault systems that delineate entire sedimentary basins and rift systems. Based on outcrop examples globally, we here show how selective, structurally controlled diagenesis is manifested across scales, discuss some of the key aspects of the governing processes involved and how such understanding may be used in attempts to subsurface predictions. Grain scale observations are focused on deformation within siliciclastic, carbonates and volcaniclastic rocks, allowing us to investigate the role of material properties in controlling how deformation is localized and accommodated. We further discuss how grain-scale deformation affects permeability, fluid flow and structurally controlled fluid-rock interaction. At the opposite end of the spectrum, we discuss the relations between deformation, fluid flow and diagenesis at the scale of basin bounding fault systems in rift basins. Finally, we address the significance of understanding structures as elements of structural networks, and how network properties may hold the potential for a more quantitative understanding of structurally controlled fluid flow.

How to cite: Rotevatn, A., Dimmen, V., Heggernes, H., Demurtas, M., Fossen, H., Osagiede, E., and Cavailhes, T.: Deformation, fluid flow and diagenesis in deformed granular rocks across scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20887, https://doi.org/10.5194/egusphere-egu24-20887, 2024.

EGU24-639 | ECS | Orals | TS1.5

Fractures versus flow: How variations in carbonate composition control the rheology of altered subducting rocks  

Ritabrata Dobe, Francesco Giuntoli, and Alberto Vitale Brovarone

Carbon recycling in subduction zones involves metamorphism and fluid-rock interactions that are responsible for dissolution or destabilization of carbon-bearing minerals. Such large-scale devolatilization of carbonates should impose profound alterations in the rheology of subducted lithologies, but this is an aspect that has received relatively scant attention so far.  

This work focuses on the mechanical behaviour of carbonates in subducted carbonated serpentinites that constitute a substantial fraction of carbon input into subduction zones. These investigations have been conducted on carbonated serpentinites from the Negru Shear Zone in Corsica (France). Petrographic and fluid inclusion analyses indicate that these rocks recorded partial carbonate reduction by infiltrating H2-rich fluids, as indicated by the conversion of carbonate to graphite and CH4(Peng et al., 2021; Vitale Brovarone et al., 2017). The first generation of carbonate occurs as mm-sized equigranular, subhedral dolomite, with sutured grain boundaries (hereafter referred to as Carb1) along which graphite is distributed as discontinuous seams. Carb1 is fractured and brecciated, with limited evidence for crystal plasticity. A second generation of carbonate (calcite; Carb2), is observed in sheared carbonate + serpentinite domains, wherein the proportion of graphite is substantially higher. Carb2 grains are anhedral, elongate and form S-C structures within localized (~200 microns thick) shear zones.  

Electron Backscatter Diffraction (EBSD) analyses on the different carbonate domains provide greater insights into the deformation of Carb1&2. The microstructures within the dolomite-rich domains are dominated by twinning, with a strong crystallographic preferred orientation manifested by an M-index of 0.61. Dolomite grains display limited low angle boundaries and dislocations, which imply minimal strain accommodation by crystal plasticity and recrystallization during deformation. The occurrence of extensive twinning in dolomite coupled with antigorite being the dominant serpentine mineral, constrains the brecciation of dolomite grains to temperatures higher than 380 °C during the high-pressure evolution of Alpine Corsica. On the other hand, calcite grains within the shear zones have a weaker preferred orientation (M-index of 0.086), abundant low angle boundaries and dislocations, and lesser twin boundaries compared to the dolomite grains. Our observations are relevant for an improved understanding of the deformation of carbonated lithologies in faults associated with subduction zones. If these lithologies are dominated by dolomite, brecciation, likely associated with seismicity, may be the dominant mechanism of deformation, as crystal plastic mechanisms within dolomite are non-operative at the temperatures (<400°C) and pressures (~1GPa) prevalent till at least intermediate depths within subduction zones. On the other hand, if calcite is the dominant carbonate mineral undergoing subduction, crystal plasticity may be the dominant mechanism that accommodates strain. The presence of graphite in association with both dolomite and calcite rules out the possibility of it having influenced these rheological variations. Our results provide novel insights into the role of chemistry in controlling the rheology of carbonated lithologies undergoing subduction, with implications on our understanding of the localization of seismicity in subduction settings.   

How to cite: Dobe, R., Giuntoli, F., and Vitale Brovarone, A.: Fractures versus flow: How variations in carbonate composition control the rheology of altered subducting rocks , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-639, https://doi.org/10.5194/egusphere-egu24-639, 2024.

Frictional motion is mediated by rapidly propagating ruptures, akin to shear cracks, that detach the ensemble of contacts that form the interface between
contacting bodies. While fracture mechanics describe the rapid motion of these singular objects, the nucleation process that creates them is not currently understood. By extending fracture mechanics to explicitly incorporate finite interface widths, we fully describe the nucleation process. We show, experimentally and theoretically, that slow steady creep ensues at a stress threshold. Moreover, as creeping patches approach the interface width, a topological transition occurs where they smoothly transition to rapid fracture. This new picture of the nucleation dynamics of fracture (and friction) is directly relevant to earthquake nucleation dynamics and the transition from aseismic to seismic rupture in natural faults.

How to cite: Fineberg, J.: The nucleation of frictional ruptures, theory and experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3417, https://doi.org/10.5194/egusphere-egu24-3417, 2024.

EGU24-4370 | ECS | Orals | TS1.5

Fault weakening due to CO2-fluid-rock interaction – evidence from deformation experiments of carbonated serpentinites 

Lisa Eberhard, Manuel D. Menzel, André R. Niemeijer, and Oliver Plümper

To assess the seismogenic potential of fault zones it is crucial to understand fluid-rock interactions in these zones, because alteration affects the fault strength and stability, as well as the deformation mechanisms.

The San Andreas fault (SAF) system is known for infrequent large magnitude (M≥7) earthquakes, whereas some segments lack such strong seismic events [1]. Here, strain is largely accommodated by creep motion. Aseismic creep can be enhanced by the presence of fluids, which may additionally drive mineral reactions. For example, fluid composition and magnesite deposits in the SAF segment between San Juan Bautista and Parkfield suggests carbonation due to infiltration of CO2-bearing fluids into the fault [2]. Carbonation of ultramafic rocks leads to the formation of talc, which is known to be frictionally weak and promotes creep when wet [3]. However, our thermodynamic fluid-infiltration calculations show that carbonation will not produce pure talc but lizardite-talc-magnesite (LTM) and talc-magnesite rocks (soapstone) and, with increasing extent of reactive fluid flow, talc-magnesite-quartz (TMQ) and magnesite-quartz rocks (listvenite). The strength and seismogenic potential of serpentinite fault zones undergoing carbonation thus may change dynamically as the mineral proportions and assemblages change, but the respective frictional behaviour of these assemblages is unknown.

We performed rotary-shear experiments on gouge layers with compositions ranging from lizardite-serpentinite to LTM, soapstone, TMQ and listvenite at pressure, temperature and pore fluid pressures corresponding to a depth of about 10 km (300 °C, 250 MPa normal stress and 100 MPa pore pressure). We measured the frictional strength within the velocity range of 0.002 µm/s to 10 µm/s.

Our data show that lizardite gouges are relatively strong and slightly velocity-weakening. The friction coefficient dropped from 0.45 at 0.002 µm/s to 0.42 at 10 µm/s. A similar velocity-dependence is observed for soapstone gouges, although at lower absolute friction coefficients of 0.3 to 0.28. Interestingly, listvenite gouges show the opposite behavior, with friction coefficients increasing from 0.25 at 0.002 µm/s to 0.48 at 10 µm/s. Stick-slips were only observed in serpentinite and soapstone gouges at low velocities. Increasing velocities and progressing carbonation causes stable slip behavior. Microtextural observations indicate strong grain-size reduction and basal cleavage in serpentinite gouges. On the contrary, soapstone and listvenite gouges show a fine-grained magnesite matrix surrounding the silicates.

Our results suggest that serpentinized fault zones have the potential to nucleate unstable slip. The results further confirm the strong weakening effect of carbonation. CO2-fluid-rock interaction in ultramafic fault gouges may effectively suppress the nucleation of earthquakes. Since also listvenite gouges deformed aseismic and are found to be frictionally weak at low velocities, we suggest that besides talc also magnesite plays an important role in the deformation behavior of carbonated ultramafic fault zones.

 

[1] Jolivet et al. 2015. Geophys. Res. Lett. doi:10.1002/2014GL062222.

[2] Klein et al. 2022. Geophys. Res. Lett. doi:10.1029/2022GL099185.

[3] Moore et al. 2008. Tectonophysics. doi:10.1016/j.tecto.2007.11.039

 

Funding

LE: NWO (VI.Vidi.193.030)

M.D.M: Junta de Andalucía (Postdoc_21_00791) and MCIU, Spain (PID2022-136471N-B-C22)

How to cite: Eberhard, L., Menzel, M. D., Niemeijer, A. R., and Plümper, O.: Fault weakening due to CO2-fluid-rock interaction – evidence from deformation experiments of carbonated serpentinites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4370, https://doi.org/10.5194/egusphere-egu24-4370, 2024.

Variations in pore fluid pressure modulate effective normal stresses along fault zones and the subducting interface. Fluid availability is controlled by the decomposition of hydrous mineral phases and the subsequent rate of drainage. Geophysical observations suggest that the plate interface is a fluid-enriched region under near-lithostatic pore fluid pressure that may result in slow slip events (SSE) and non-volcanic tremor (NVT). The potential for fluid redistribution depends on dynamic changes of the porosity and permeability of the host rock as a function of solid-bound fluid volume change and the total system volume change during dehydration. Understanding the mechanisms involved with the evolution of porosity and permeability below the seismic zone is critical to gain insight into the formation of fluid networks and their rheological implications.

Here we present a petrological and mechanical analysis of the evolution of a suite of eclogite-facies veins from an archetypal HP-LT terrain: the Eclogite Zone, Eastern Alps. We define two dominant compositional types of mafic eclogite: banded and metagabbroic, respectively. Prograde metamorphic evolutions are similar for the two types of eclogites and comprise garnet core growth at 2.1 ± 0.25 GPa, 585 ± 15°C and rim equilibration at 2.6 ± 0.2 kbar, and 630 ± 10 °C. Contemporaneously to prograde garnet growth, the mafic eclogites underwent dehydration via the breakdown of several volumetrically significant hydrous phases: lawsonite, Na-amphibole (glaucophane), and epidote. The decomposition of lawsonite and glaucophane released up to 8 wt. % H2O, resulting in the formation of a transient fluid filled porosity of ∼ 15 vol. %.

Phase equilibria calculations serve as a framework to constrain a mechanical model explaining the formation of both tensile fractures (type I) and vein segregates (type II) within the brittle-ductile transition zone. We propose a petrological-mechanical model for the formation of Type I tensile veins associated with periods of rapid dehydration and Type II dilatant structures in which rock deformation is outpaced by the reduction in pore fluid pressure, leading to a decrease in silica solubility and the precipitation of high-pressure mineral phases. Finally, this suggests that the rate of dehydration during the blueschist-eclogite transition plays a significant role in determining the dominant mode of deformation possibly affecting the fluid storage capacity of the subducting interface.

How to cite: Strobl, L. and Smye, A.: Pore-fluid pressure evolution across the blueschist-to-eclogite-facies transition:  constraints from the Eclogite Zone (Eastern Alps), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4680, https://doi.org/10.5194/egusphere-egu24-4680, 2024.

EGU24-4702 | ECS | Posters on site | TS1.5

Feedbacks between metasomatism, rheological heterogeneities and strain localization in deep subduction interface shear zones 

Jesus Munoz, Whitney Behr, Dominic Hildebrant, and Leif Tokle

Characterizing deep subduction dynamics is crucial for understanding processes of high-pressure-rock exhumation, fluid flow, seismicity and transient slip events. Metamorphic phase transformations at the blueschist-to-eclogite transition induce important rheological changes, commonly transitioning from a more brittle to a mixed brittle-viscous plate interface rheology. This shift may promote slip transients such as slow slip and tremor (SST) observed in modern subduction zones. Geophysical and geologic data as well as numerical models suggest that slow slip is likely accommodated along weak, fluid-rich shear zones and that accompanying tremor may represent km-scale brittle asperities embedded within localized slip zones. Here we use the geologic record exposed on Syros Island (Greece) to investigate the relationships between strain localization and fluid-rock interactions along the deep megathrust, and explore their implications for SST.

We used high-resolution drone surveys, along with microstructural, geochemical, and petrologic data, to examine a blueschist-to-eclogite facies subduction shear zone in the Kampos Belt near Grizzas locality on northern Syros. The estimated P-T conditions are comparable to the SST zone along active warm subduction margins such as Cascadia and Central Chile. Our approach involved mapping strain and lithologies, constructing a 3D geological model, and performing detailed analyses of localized shear zones and metasomatic rocks.

At the hectometre-scale, the Grizzas locality exposes a stack of progressively underplated oceanic and metasedimentary rocks. Individual slices include brittlely deformed metagabbros up to 200 m-thick, weakly-strained to undeformed igneous breccias up to 30 m-thick, and foliated quartz-mica schists. These slices are repeated along five localized shear zones composed of chlorite-tremolite and glaucophane schists that are less than 10 m-thick. Fine-scale characterization of one of these shear zones reveal several discrete intercalations of blueschists/glaucophanites, tremolite-chlorite schists and metasediments. Microstructural and petrologic analyses suggest that blueschist/glaucophanite layers formed through the transformation of a gabbro/blueschist breccia precursor, likely induced by along-dip fluid influx. This metasomatic process extensively replaced the precursor gabbro fabric with nearly pure glaucophane and also enhanced the development of high-strain zones. Geochemical analyses indicate the formation of tremolite-chlorite (+/- talc) schists through chemical exchange between metamafic and metaultramafic rocks or by the interaction with serpentinite-derived fluids. This is supported by the presence of partially-digested metagabbro pods which contain garnet and chlorite with anomalously high Cr2O3 contents (up to 1.2 and 2.1 Wt%, respectively) as well as omphacitites associated with glaucophane-phengite veins and glaucophane-bearing veins crosscutting the chlorite schists.

We suggest that metasomatism triggered localized deformation around gabbro blocks and permitted repeated down-slicing and underplating of subducting oceanic material on the deep subduction interface. The metasomatism likely exploited precursory features such as lithological contacts, fractures, and/or fabric heterogeneity, to transiently increase permeability and allow further fluid ingress eventually resulting in the development of major shear zones. The degree of localization in these major shear zones and the concentration of foliated phyllosilicates within them mean they may have been capable of hosting slow slip (to be explored further), and the up-to-km-scale of brittlely deformed metagabbro blocks embedded between the shear zones are compatible with tremor sources.

How to cite: Munoz, J., Behr, W., Hildebrant, D., and Tokle, L.: Feedbacks between metasomatism, rheological heterogeneities and strain localization in deep subduction interface shear zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4702, https://doi.org/10.5194/egusphere-egu24-4702, 2024.

EGU24-5618 | ECS | Orals | TS1.5

Deformation and healing processes in the damage zone of a lower-crustal seismogenic fault 

Stephen Paul Michalchuk, Nils B Gies, Mona Lüder, Markus Ohl, Kristina Dunkel, Jörg Hermann, Oliver Plümper, and Luca Menegon

In anhydrous, strong, and metastable lower-crustal rocks, coseismic fracturing is an effective mechanism for creating pathways for fluids to infiltrate and interact with the host rock, ultimately resulting in metamorphism and rheological weakening. In this study, we have characterized the damage zone flanking a lower-crustal pseudotachylyte (solidified frictional melt produced during seismic slip) to understand the fracture generating and fluid-assisted healing processes operating during and immediately after a seismic event.

The Nusfjord East shear zone (Lofoten, Norway) is a network of coeval pseudotachylytes and mylonitized pseudotachylytes that formed at lower-crustal conditions within anhydrous anorthosites. We present a micro- and nanostructural analysis focusing on plagioclase in the damage zone of a pseudotachylyte using focused ion beam (FIB) prepared scanning transmission electron microscopy (STEM), Fourier Transform Infrared (FTIR) Spectroscopy, electron backscatter diffraction (EBSD) analysis, electron microprobe analysis (EMPA), and SEM-cathodoluminescence (CL) imaging.

The damage zone of the host anorthosite is characterized by a network of comminuted primary plagioclase (plagioclase1) grains with minimal offset. Very fine (<15 mm) plagioclase1 grains and secondary plagioclase neoblasts (plagioclase2), differentiated from each other by SEM-CL and EBSD observations, fill the fractures along with a minor amount of K-feldspar. Plagioclase1 and plagioclase2 have the same major element compositions (average: An52) and are not zoned aside from a small increase in anorthite along the grain boundaries. Away from the pseudotachylyte margin, plagioclase2 grains filling the fractures show a host-controlled crystallographic preferred orientation (CPO) governed by plagioclase1 grains. With decreasing distance toward the vein margin, the CPO is weakened as a result of minor amount of solid-state deformation by grain-boundary sliding after the coseismic event. Plagioclase1 grains often exhibit a diffuse CL intensity zonation from bright grain cores to a dark grey in healed cracks, while plagioclase2 have a uniform mid-tone grey CL intensity with dark grain boundaries. CL zonation in the plagioclase1 does not correlate with EMPA major element maps nor EBSD misorientation maps. TEM foils across the dark CL grain boundaries reveal microfractures filled with nanograins of plagioclase2 containing few dislocations. FTIR maps transecting the thin section do show the presence of molecular water trapped along fractured plagioclase1 grain boundary regions. At the thin section scale, there is no measurable gradient of molecular water with increasing or decreasing distance toward the pseudotachylyte margin.

In summary, these observations suggest that (1) fracturing was in accordance to a pulverization-style fragmentation process, (2) water is from a local source; presumably coseismic fracturing released fluid inclusions enclosed within plagioclase1 and the frictional heating caused the melting of primary biotite, and (3) the little amount of molecular water freely available did not diffuse within the plagioclase grains, and did not promote hydrolytic weakening in the damage zone. Strain localization is primarily determined by repeated occurrences of extreme grain-size reduction and phase mixing, in addition to some amount of fluid wetting the grain boundaries. Therefore the “wet and weak” structure, preferential for further ductile deformation, is often the pseudotachylyte vein when present and not the surrounding damage zone.

How to cite: Michalchuk, S. P., Gies, N. B., Lüder, M., Ohl, M., Dunkel, K., Hermann, J., Plümper, O., and Menegon, L.: Deformation and healing processes in the damage zone of a lower-crustal seismogenic fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5618, https://doi.org/10.5194/egusphere-egu24-5618, 2024.

EGU24-5807 | Orals | TS1.5 | Highlight

Transient deformation leading to earthquakes: bridging observations from the lab and the field  

Patricia Martínez-Garzón, Grzegorz Kwiatek, Piero Poli, Georg Dresen, and Marco Bohnhoff

A longstanding question in geoscience concerns whether earthquakes show a preparatory process and precursory seismic activity. Some models hold that in the intermediate-term (from months to years), seismicity and/or aseismic transients in fault slip and in other fault properties occur. During the last decades, improvements in earthquake monitoring, the integration of geodesy capturing slow deformation, and the incorporation of novel data analysis techniques including machine learning and artificial intelligence have improved our ability to better discern how earthquake sequences evolve before a mainshock. The few available observations of transient deformation preceding well-recorded earthquake sequences show a high variability, thus our potential for improving earthquake forecasting is still limited. The body of knowledge available from mechanical models, numerical simulations, experimental work and field observations highlighted a wealth of structural, tectonic and boundary conditions which may control the dynamics of earthquake sequences. These suggest that several processes can affect earthquake preparation on different temporal and spatial scales, ultimately yielding highly varying transient observations prior to mainshocks. These observations also highlight that existing theoretical and conceptual models of the preparation/nucleation process may not fully capture the governing physics.

We analyzed seismicity transients prior to the occurrence of the 2023, MW 7.8 Kahramanmaraş/Türkiye earthquake. We identified seismic precursory activity composed of a handful of isolated spatio-temporal clusters occurring in a complex fault network within 65 km of the future earthquake epicenter. Some of these clusters contributed to acceleration of seismicity rates in an area surrounding the future mainshock and starting ca. 8 months before the event. Within that area, we also observed a decrease in Gutenberg-Richter b-values. Comparable seismic transients were not observed in the region at least since 2014. The complex preparatory process differs significantly from the cascade of close (<200 m) foreshocks observed before the 1999 MW 7.6 Izmit/Türkiye earthquake rupturing a mature fault segment. This indicates that fault structure and heterogeneity expressed as roughness or segmentation exert a strong control on deformation transients before an earthquake. This bears strong similarities with laboratory studies on faults with varying roughness. Trends of seismic preparatory attributes observable in the field follow those documented in both laboratory stick-slip tests and numerical models of heterogeneous earthquake rupture affecting multiple fault segments. In the lab, rough faults before stick-slip tend to display prolonged phases of precursory slip including an interplay of (dominating) slow transients combined with high-frequency seismic deformation in stark contrast to smooth faults.

How to cite: Martínez-Garzón, P., Kwiatek, G., Poli, P., Dresen, G., and Bohnhoff, M.: Transient deformation leading to earthquakes: bridging observations from the lab and the field , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5807, https://doi.org/10.5194/egusphere-egu24-5807, 2024.

EGU24-6361 | ECS | Posters on site | TS1.5

Pleistocene near-surface earthquake events recorded in high-porosity fluvial sandstone sequence (Crotone forearc Basin, Italy) 

Mattia Pizzati, Anita Torabi, Luca Aldega, Cristian Cavozzi, Fabrizio Storti, and Fabrizio Balsamo

In scientific literature, the seismogenic zone is defined as the portion of the Earth's upper crust where most hypocenters are located. According to seismological data collected in different geodynamic settings and under different kinematics, the depth interval of the unstable seismogenic zone is typically comprised between 5 and 35 km. However, worldwide earthquake distribution shows extensive occurrence of shallow seismicity with hypocentral depths < 5 km, shallower than the unstable seismogenic zone’s upper boundary. Such shallow seismic sources represent potential additional threats and deserve to be thoroughly investigated and included in current seismic hazard evaluations.

To shed light on this subject, we studied a Pleistocene-age fault system which affects poorly consolidated deltaic, sandstone-dominated sequence composing the Late Pliocene-Pleistocene infilling of the Crotone forearc Basin, in South Italy. We focused on an extensional fault zone exposed along the walls of the Vitravo Creek Canyon, displaying a maximum displacement of ~50 m, with a sharp master fault surface separating the fault blocks. The footwall block is composed of an 8-10 m-wide damage zone with extensive occurrence of deformation bands and subsidiary faults. Towards the master fault, a 1-1.5 m-wide mixing zone is located, characterized by tectonic mixing of sandstone strata with different textural features due to the presence of high-displacement boundary faults. Eventually, the fault core is composed of ~1 m-wide, tightly cemented, cataclastic volume with subsidiary slip surfaces and deformation bands. The hanging wall damage zone shows a wealth of thin deformation bands with diminishing frequency moving away from the master fault. The master fault, where most of the displacement is accommodated, is decorated with a 1-2 cm-thick dark gouge layer. The dark gouge can be traced along the entire fault exposure and maintains a straight pattern parallel to the master fault. Locally it appears to have been injected into the fractures affecting the underneath calcite-cemented fault core. Microstructural analysis allows to document a severe and asymmetric cataclastic grain size reduction, with the footwall side of the dark gouge being more comminuted than the hanging wall side. Grain size analysis reveals a strong mechanical comminution of particles in the 70-500 µm size interval. XRD analysis conducted on the < 2 µm grain-size fraction of the gouge layer displays short-ordered illite-smectite mixed layers which support deformation temperatures of 100-120°C. Conversely, XRD analysis performed on clay fraction of the fault core, at few cm distance from the dark gouge layer, indicates temperatures < 50°C, consistent with the expected shallow burial conditions (< 800 m). We link the localized temperature increase within the dark gouge with frictional heating during coseismic deformation. Combining the microstructural, grain size and mineralogical data could facilitate the study of coseismic deformation affecting high-porosity granular materials at near surface conditions. Such multidisciplinary study could be useful to enhance the earthquake risk and hazard evaluation in seismically active geodynamic settings.

How to cite: Pizzati, M., Torabi, A., Aldega, L., Cavozzi, C., Storti, F., and Balsamo, F.: Pleistocene near-surface earthquake events recorded in high-porosity fluvial sandstone sequence (Crotone forearc Basin, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6361, https://doi.org/10.5194/egusphere-egu24-6361, 2024.

EGU24-6392 | ECS | Posters on site | TS1.5

Consolidation characteristics of offshore sediments in the Christiana, Santorini, and Kolumbo volcanic field, Greece (IODP Expedition 398) 

Takeru Yoshimoto, Michael Manga, Sarah Beethe, Iona McIntosh, Adam Woodhouse, Shun Chiyonobu, Olga Koukousioura, Timothy Druitt, Steffen Kutterolf, and Thomas Ronge and the IODP Exp. 398 Scientists

An abnormal rapid accumulation of volcaniclastics is expected in sedimentary basins around submarine volcanoes. This phenomenon makes the sedimentary basin unstable because the drastic increase in overburden leads to generation of excess pore fluid pressure which prevent consolidation of sediments. Therefore, consolidation state of the sediments would be a crucial information for assessing the slope instability around volcanos.

IODP Expedition 398 cored marine sediments in the Christiana, Santorini, and Kolumbo (CSK) volcanic field in the Aegean Sea of Greece. In this study, we performed consolidation tests on mudstones and calcareous oozes just below the thick volcaniclastics in three basins (Anafi, Anydros, and Christiana Basin) oriented roughly NE-SW including Santorini caldera. Consolidation trends (void ratio vs. applied stress) show clear yield stress which indicate maximum consolidation stress of sediments. Some of ooze-dominated mudstones show the effects of cementation in their consolidation trends.

In the IODP site U1590 (Anydros Basin) and U1592 (Anafi Basin), consolidation yield stress of sediments was ~2 MPa lower than the overburden. It implies that the excess pore fluid pressure generates in the sediments and prevents the normal consolidation. The Anydros and Anafi basins represented underconsolidation state at 300-400 mbsf and ~300 mbsf, respectively. Both underconsolidated intervals are covered by >200 m thick volcaniclastics derived from the Santorini and the Kolumbo volcanos. Therefore, rapid sediment-supply (0.8-1.0 m/ky) from the submarine volcanos apparently makes the surrounding sedimentary basins unstable.

On the other hand, IODP site U1591 (i.e., Christiana Basin) and U1599 (i.e., Anafi Basin) represents the normal-consolidation state and the consolidation yield stress balances the overburden. There is relatively thin cover of volcaniclastics (~100 m) above the non-volcanic sediments and the sedimentation rate is moderate (0.1-0.4 m/ky).

In this presentation, we are going to compare the consolidation characteristics of three basins and discuss their spatial-temporal variation in relation to the sedimentation rate and physical properties of sediments.

How to cite: Yoshimoto, T., Manga, M., Beethe, S., McIntosh, I., Woodhouse, A., Chiyonobu, S., Koukousioura, O., Druitt, T., Kutterolf, S., and Ronge, T. and the IODP Exp. 398 Scientists: Consolidation characteristics of offshore sediments in the Christiana, Santorini, and Kolumbo volcanic field, Greece (IODP Expedition 398), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6392, https://doi.org/10.5194/egusphere-egu24-6392, 2024.

EGU24-7188 | Posters on site | TS1.5

Deformation of carbonated serpentinite controlled by Al- and Si-partitioning in phyllosilicates: a record of deep episodic tremor and slip? 

Keishi Okazaki, Samuele Papeschi, Kenta Kawaguchi, and Takehiro Hirose

Fluids are generally thought to assume a key role in controlling fast and slow earthquakes, not only because they lower the effective stress, but also because they act as catalysers of mineral reactions, moving chemicals in the rock mass. Serpentinites are particularly prone to carbonation reactions, which cause bulk-rock and volume change. The feedback between CO2 ingress in serpentinites, H2O-release, and tectonic appears to be able to sustain cycles of fluid pressure build-up and stress release that may be compatible with slow slip and tremor. However, the carbonation of pure serpentine (Mg3Si2O5(OH)4) should run to completion over geologic time scales, bearing the question if carbonation can sustain slow earthquakes in the long term at the subduction interface. On the other hand, the presence of Al, which does not enter the structure of talc, should slow down carbonation reactions and the products of serpentinite carbonation, allowing the process to be sustainable over long time scales.

We, therefore, investigated natural samples of sheared carbonated serpentinite from a fossil shear zone in the Sanbagawa metamorphic belt exhumed from ~ 35–45 km and ~ 450–550 °C, corresponding to the present-day conditions of the source region of deep episodic tremor and slow slip in the nearby Nankai Trough. The shear zone preserves ‘intact’ antigorite-serpentinite, talc- and chlorite-bearing serpentinite breccia, and complex brittle/ductile shear zone consisting of quartz-bearing carbonate-chlorite-talc schists, talc - carbonate veins, and talc-rich mylonitic shear zones. We document that the presence of Al in antigorite and spinel causes the formation of abundant chlorite which inhibits carbonation reaction. We show that the formation of talc- and carbonate-rich domains is primarily related to the formation of veins crosscutting the carbonated rock fabric. Hence, the formation of talc mylonites is primarily associated with parts of the rock that became Si-rich, whereas Al-rich domains deform primarily by fracturing and veining. Finally, the presence of fractured sulphides in the rock documents multiple cycles of fracturing, sulphide precipitation, and healing, compatible with successive embrittlement, stress release, fluid infiltration, and fluid pressure drop events.

We suggest that the presence of Al in the protolith serpentinitic material, which is common for ultramafic rocks, (1) slowed-down carbonation reactions, (2) prevented the rapid formation of talc-rich domains, and (3) kept the fabric heterogeneous and the rheology mixed, overall preventing the formation of weak domains that should have localized aseismic creep and possibly hosting episodic tremor and slow slip.

How to cite: Okazaki, K., Papeschi, S., Kawaguchi, K., and Hirose, T.: Deformation of carbonated serpentinite controlled by Al- and Si-partitioning in phyllosilicates: a record of deep episodic tremor and slip?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7188, https://doi.org/10.5194/egusphere-egu24-7188, 2024.

EGU24-7980 | ECS | Orals | TS1.5

Evolution from a clean surface to a mature gouge interface in a seismic fault – asperity system through the lens of pin-on-disk experiments 

Adriane Clerc, Guilhem Mollon, Amandine Ferrieux, Lionel Lafarge, and Aurélien Saulot

Understanding earthquakes mechanisms still represents a challenge, motivated by the large consequences of the numerous earthquakes occurring each year. A number of uncertainties remain concerning the complexity of the fault structure, the constitutive properties of materials or the fault rheology. To address those points, we borrow from the tribological approach the pin-on-disk experiment so that the two rough surfaces in contact through a series of asperities fault concept is downscaled to a single asperity sliding on a rough surface. The single asperity response to shearing induced by sliding and the evolution of friction are studied closely to understand the different stages undergoing by the asperity and the consequences on the fault behaviour during co-seismic events.

The original experimental apparatus consists in a centimetric pin with a hemispherical extremity representing the fault asperity while a large flat rotating disk stands for the opposite surface of the experimental fault. Both pieces are made in the same carbonate rock (Carrara white marble) with controlled roughness. The experimental downscaled fault is submitted to co-seismic conditions: contact size of 0.1-5 mm, contact normal stress of 10-200 MPa, sliding velocity of 0.01-1 m/s, and sliding distance of 10 - 60 m. A number of high-sampling-rate sensors are used to constrain the observation of the asperity contact during the simulated seismic events. Complete post-mortem analyses of the wear tracks with optical microscopy, SEM and roughness images allow to quantify the regime features and to reconstruct friction scenarios in accordance with the time-series acquired during tests.

Independently of the velocity and the normal load applied, the friction coefficient exhibits a clear transition between an idealized lab conditions regime and a mature interface with the formation of granular gouge, as a function of the sliding distance. Within the same regime (clean surface, intermediate, mature gouge), velocity weakening and hardening due to higher loading are pointed out. We propose to focus on the clean surface to mature gouge transition and on the stability of the mature gouge interface regime to address the fault rheology and the role of asperities in seismic weakening.

How to cite: Clerc, A., Mollon, G., Ferrieux, A., Lafarge, L., and Saulot, A.: Evolution from a clean surface to a mature gouge interface in a seismic fault – asperity system through the lens of pin-on-disk experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7980, https://doi.org/10.5194/egusphere-egu24-7980, 2024.

EGU24-8060 | ECS | Posters on site | TS1.5

Exploring fault preparation and earthquake nucleation from the laboratory 

Patrick Bianchi, Paul Antony Selvadurai, Luca Dal Zilio, Antonio Salazar Vásquez, Claudio Madonna, Taras Gerya, and Stefan Wiemer

The initiation of unstable fault slip leading to earthquakes involves intricate physical processes and interactions. Understanding these mechanisms is crucial for advancing our knowledge in earthquake seismology. Investigations at both field and laboratory scales have highlighted the existence of spatio-temporal variations in seismic or aseismic observations near the epicenter of a major seismic event, such as a rise in frequency of precursory earthquakes (Kato and Ben-Zion, 2021)  or even strong fluctuations in seismic velocities (e.g., Campillo & Paul, 2003). These variations are often associated with the preparatory phase of major earthquakes believed to involve processes resulting from progressive localization of deformation around the eventual rupture zone that eventually accelerates leading up to failure. However, the time and spatial scales of this behavior are not well understood due to our lack of understanding into the physical mechanisms within the preparatory zones.

In this study, we combined innovative laboratory techniques and numerical modelling to investigate (a)seismic preparatory deformation during a triaxial failure test in the laboratory. Employing distributed strain sensing (DSS) with optical fibers, we closely monitored strain rates on the sample surface. This was supplemented by active ultrasonic surveys and passive acoustic emission (AE) monitoring to investigate changes in P-wave velocity and locate regions prone to AEs within the sample. Using a physics-based computational model, we investigated strain localization within the sample by monitoring rock regions exhibiting high dissipation of mechanical energy. Highly dissipative regions spatio-temporally correlated with the observed AE locations and with sample regions experiencing P-wave velocity reduction. By further tracking the dissipation field within the sample, we recognized a system of conjugate bands that first emerged and quickly merged into a single band growing from the center towards the sample surface. The latter was interpreted to be related to the preparation of a weak plane. Shortly prior to failure, the model showed an acceleration of deformation that was also observed during the laboratory test with the DSS measurements and correlated with an increase of the seismicity rate in a similar volume of the sample. The combination of increased deformation and seismic rates mimics observations of precursory seismicity in nature. By methodically segregating the laboratory experiments from the numerical modeling, this study provides a comprehensive analysis of the physical processes underlying earthquake nucleation. The integration of cutting-edge laboratory techniques with advanced numerical modeling offers a novel perspective on the (a)seismic preparatory deformation that sets the stage for major seismic events.

 

References:

Campillo M., Paul A. (2003) Science 299, 547-549.

Kato, A., Ben-Zion, Y. (2021) Nat Rev Earth Environ 2, 26–39.

How to cite: Bianchi, P., Selvadurai, P. A., Dal Zilio, L., Salazar Vásquez, A., Madonna, C., Gerya, T., and Wiemer, S.: Exploring fault preparation and earthquake nucleation from the laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8060, https://doi.org/10.5194/egusphere-egu24-8060, 2024.

EGU24-8130 | ECS | Orals | TS1.5

Tracing the extent of fluid circulation in subduction zone forearcs using lithium isotopes 

Kristijan Rajič, Antonin Richard, Hugues Raimbourg, Tomáš Magna, Clément Herviou, Catherine Lerouge, and Romain Millot

Despite the recognition that fluids play an important role in subduction zone processes, the extent of fluid circulation and fluid-rock interactions within subduction and accretionary complexes is still not fully understood. Here, we examined Li elemental and isotopic systematics in fluid inclusions trapped within hydrothermal quartz veins in metasedimentary rocks from three paleo-accretionary complexes (Kodiak complex, Alaska; Shimanto Belt, Japan; Western Alps), which are contemporaneous with the burial and metamorphism at temperatures ranging from 250 to 400°C. To provide a fuller understanding, we investigated (i) fluid inclusions, (ii) host quartz, and (iii) wall-rocks of syn-subduction veins.

The δ7Li of fluid inclusion leachates range from −1.5‰ to +17.1‰ and are variable among three localities. Two important processes control the 7Li/6Li ratios of fluids from inclusions: (i) Li release/uptake from the host rock, and (ii) the reactive volume of the rock. Higher δ7Li values of fluids in Kodiak (+8.1‰ to +17.07‰) are interpreted as a result of closed-system behavior, with a small reactive volume of metasediments. Lithium has not been lost to the fluid, where 6Li is dominantly preserved in metamorphic chlorite and illite. In closed-system samples from the Western Alps, the fluids are buffered by the host rock, causing a shift in δ7Li values of pore fluids (from −1.5‰ to +9.5‰) towards the values of the protolith. Conversely to the samples from Kodiak, the reactive volume of rock is significantly greater, resulting in a complete fluid–rock equilibration. Equally low δ7Li values of pore fluids in Shimanto (+2.53‰ to +10.39‰) is attributed to the large flow of externally derived fluids and interpreted to result by Li leaching from illite and chlorite.

The δ7Li values of quartz are globally higher than those of paired leachates (+10.93‰ and +22.61‰) without temperature-dependent isotopic fractionation between quartz and fluid. This is explained by either (i) a significant drop in pore fluid pressure which, in turn, facilitates rapid crystallization of quartz, or (ii) post-entrapment re-equilibration between fluid inclusions and the host quartz.

By comparing the metamorphic fluids in the present study with seawater or pore water from deep sea sediments, elevated Li concentrations in leachates (up to 24 ppm) combined with relatively low δ7Li values indicate that Li is progressively leached from sediments during burial, and that the δ7Li value of fluids is consequently shifted towards the signature of the protolith. Similarities in Li concentrations and δ7Li values between leachates and fluids expulsed through mud volcanoes in modern examples of subduction zone forearcs further confirms the origin of mud volcano fluids dominantly from subducted sediments. Such similarities imply that fluid circulation across permeable zones may reach at least a 20 km-scale in the forearc region. This study further demonstrates the relevance of Li elemental and isotope systematics to efficiently trace fluids across large distances within subduction zone forearcs. 

How to cite: Rajič, K., Richard, A., Raimbourg, H., Magna, T., Herviou, C., Lerouge, C., and Millot, R.: Tracing the extent of fluid circulation in subduction zone forearcs using lithium isotopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8130, https://doi.org/10.5194/egusphere-egu24-8130, 2024.

EGU24-8597 | Posters on site | TS1.5

Brittle/cataclastic deformation and dissolution-precipitation creep in the Goshikinohama fault (Shimanto Belt, SW-Japan): Indication of seismic cycling and possible slow slip? 

Yoshitaka Hashimoto, Jinpei Mitani, Rüdiger Kilian, Rebecca Kühn, and Michale Stipp

Microstructural evidence for slow earthquakes is a matter of debate as micromechanical processes are not fully understood and hence resulting deformation microstructures remain unclear. One of the best study areas to investigate the phenomena of seismic and aseismic deformation and also possible paleo-events of slow slip in an exhumed accretionary complex is the Shimanto Belt in SW-Japan, where lithologies, age, and pressure-temperature conditions are well-constrained. Our investigations focus therefore on the Yokonami mélange of the Cretaceous Shimanto Belt. The Goshikinohama fault is a fossil seismogenic fault at the northern margin of the Yokonami mélange. It contains several 20 cm thick cataclastic faults within which thin (less than 1 mm), discrete slip zones occur. Based on vitrinite reflectance the paleo-maximum temperature of the surrounding host rocks is about 250˚C. An exothermic event was identified in the cataclasite of up to 300-360˚C evidenced by paleomagnetic and rock-magnetic analyses [Uchida et al., 2024]. In order to access microstructures related to the seismic cycle as well as to explore whether this proposed thermal event resulted in characteristic changes in deformation mechanism, we conducted observations on the cataclastic shear zone using optical microscopy,electron microscopy,  electron backscatter diffraction (EBSD), energy dispersive X-ray spectroscopy (EDS) and cathodoluminescence (CL).

The studied cataclasite consists of mm- to cm-size fragmented quartz veins in a shale matrix with quartz and feldspar clasts. Quartz displays solution-seam contacts to the shale and various generations of subsequent fracturing and healing are recognized. Characteristic are (i) synkinematic fiber growth microstructures related to a crack-seal mechanism accommodating foliation-parallel stretching of quartz aggregates within the shale matrix as well as numerous generations of blocky veins and (ii) static shattering of quartz grains at the µm-scale and subsequent healing. The static nature of the shattering is interpreted from the lack of any offset or misorientation in the affected quartz grains. In addition, there is some undulous extinction and very minute and local indication of quartz dynamic recrystallization by grain boundary bulging. The shale matrix exhibits a compositional flow banding detected by EDS.

Veining, solution seams and the general clast-in-matrix structure are interpreted to relate to the interplay of brittle fracturing, cataclastic flow and dissolution-precipitation processes. Very few and local evidence for bulging recrystallization fits deformation conditions at the brittle to ductile to viscous transition in accordance with the temperature estimates given before. The origin of shattered quartz is hypothesized to relate to seismic wave-induced shock deformation.Mutual overprinting of brittle/cataclastic deformation and creep deformation as well as synkinematic and static vein growth might be an indication for the formation of these microstructures during the seismic cycle and possible transient creep or slow slip. However, if these processes produced heat to the extent of the proposed exothermic event is a matter of further investigations.

[Ref] Uchida,T., Hashimoto, Y., Yamamoto, Y. and Hatakeyama, T., 2024, Exothermic events in a fossil seismogenic fault acquiring thermoviscous remanent magnetization in an exhumed accretionary complex, Tectonophysics, V. 871,https://doi.org/10.1016/j.tecto.2023.230177. 

How to cite: Hashimoto, Y., Mitani, J., Kilian, R., Kühn, R., and Stipp, M.: Brittle/cataclastic deformation and dissolution-precipitation creep in the Goshikinohama fault (Shimanto Belt, SW-Japan): Indication of seismic cycling and possible slow slip?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8597, https://doi.org/10.5194/egusphere-egu24-8597, 2024.

EGU24-8751 | ECS | Posters on site | TS1.5

Water-induced superplastic deformation and its mechanism of quartz  

Lefan zhan, Shuyun Cao, Yanlong Dong, Wenyuan Li, Christoph von Hagke, and Franz Neubauer

The deformation behavior and mechanisms of mineral grains play a pivotal role in comprehending the solid-state rheological behavior of the lithospheric crust. However, the fluid present during the deformation processes of grains is often overlooked. The study presents a comprehensive analysis of water-induced superplastic deformation within deformed quartz veins exposed in the continental-scale exhumed Gaoligong shear zone by combining microstructure analysis with EBSD mapping and infrared spectroscopy. We observe fine-grained aggregates of quartz form micro-shear zones that are either localized at the rims or within the coarse clasts during deformation. The nucleation of these fine-grained zones is controlled by microcracks/fracturing, which are further associated with dynamic recrystallization. Numerous fluid inclusions are leaked and water is pumped into thicker fine-grained shear zones. The water migration plays a crucial role in accommodating boundary plasticity, with tiny water clusters being sealed within grain boundaries. The recycling of water is linked to a superplastic flow process, involving water influx, grain boundary sliding (GBS), accommodation of strain incompatibilities, and sealing of water. Our findings suggest that water migration into fine-grained aggregates within micro-shear zones not only restrict grain growth but also releases strain incompatibilities, enhancing grain boundary sliding. This process delays brittle fracturing of quartz, highlighting the significant role of water in influencing the deformation behavior of quartz.

 

How to cite: zhan, L., Cao, S., Dong, Y., Li, W., von Hagke, C., and Neubauer, F.: Water-induced superplastic deformation and its mechanism of quartz , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8751, https://doi.org/10.5194/egusphere-egu24-8751, 2024.

EGU24-9295 | ECS | Posters on site | TS1.5

Friction, Mineralogy, and Microstructures: How Complex is the Brittle Deformation of Faults? 

Giacomo Pozzi, Giuseppe Volpe, Roberta Ruggieri, Cristiano Collettini, Marco Scuderi, Telemaco Tesei, Chris Marone, and Massimo Cocco

Faults accommodate most of the brittle deformation that occurs in the lithosphere  through a spectrum of fault slip behaviours including, but not limited to, seismic and aseismic slip. The rocks deforming inside the core of the faults are the main actors that control the modality of slip and thus their mechanical properties are a key subject of study that is carried out through experimental investigation. The most relevant characterization is that of friction, a property that commensurates the resistance to shear motion of the rocks. Nevertheless, friction is not an intrinsic constant feature of the investigated materials. It is instead modulated by several attributes and external factors. For instance, the rate and state constitutive framework describes the sensitivity of friction to the sliding velocity, proving a successful theory to quantify the potential of the onset of dynamic instabilities and seismic slip in natural faults. Several works have also demonstrated that the frictional properties of the same material can dramatically change as function of the fabric (textural, geometrical attributes of the deforming rock). It is therefore evident that brittle deformation of rocks cannot be assessed in isolation of the conditions at which the phenomenon is measured. To fully understand the complex bulk behaviour of a deforming fault zone material we must investigate the interaction of several scale-dependent mechanisms that are active from the grain-scale up to the entire fault zone thickness.

In this work we present the results of several case-studies that cover relevant lithotypes: anhydrite-dolomite, quartz-calcite-mica, lizardite-magnetite mixtures. These studies collect more than 60 friction experiments performed on BRAVA biaxial apparatus (INGV, Italy), presented here by associating the analysis of mechanical data with the analysis of rock microstructures. This joined investigation highlights the mechanisms that control rock friction: cataclasis, crystal plasticity, pressure-solution, grain-boundary sliding, cementation, and indentation. We also show the emergence of complex slip behaviours (experimental fault stability) as function of the coexistence of processes with different timescales and explained by the spatial arrangement of the mineral phases in the fault core.

Our results shed light on the origin of the macroscopic frictional properties of fault rocks, stressing the fact that they are not a characterising property but rather the observable of a complex, dynamic, and highly non-linear system.

How to cite: Pozzi, G., Volpe, G., Ruggieri, R., Collettini, C., Scuderi, M., Tesei, T., Marone, C., and Cocco, M.: Friction, Mineralogy, and Microstructures: How Complex is the Brittle Deformation of Faults?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9295, https://doi.org/10.5194/egusphere-egu24-9295, 2024.

The Fen Carbonatite Complex in Norway contains the largest deposit of Rare Earths Elements (REE) in Europe, with estimated resources in the range of 30 – 50 Mt of total Rare Earth Oxides. If Fen will be targeted as an exploitable mineral resource, the geological processes that formed it must be understood, with specific emphasis on what controls the location and composition of the REE resources.

The Fen complex formed at 580 Ma through different stages of carbonatite melt intrusions followed by hydrothermal alteration. Fluid- and melt-assisted deformation accompanied the intrusive and hydrothermal evolution of the Fen Complex extensively and resulted in the formation of shear zones and breccias. However, the mechanism and significance of carbonatite deformation are poorly understood, and so are the effects of post-crystallization deformation processes on the remobilization of trace elements in carbonatites.

This study investigates deformation processes and REE remobilization in shear zones in dolomite-carbonatites from Fen. The shear zones display a compositional banding defined by alternating dolomite- and apatite-rich layers, where apatite grains are variably elongated with aspect ratio ranging from 2 to 11 and grain length from 50 to 500 µm. SEM images reveal the presence of carbonatitic melt pseudomorphs in the form of intergranular beads, cusps, films, and pools, which are particularly evident in the apatite layers, where individual grains are locally entirely rimmed by melt films. The apatite grains appear zoned in cathodoluminescence (CL) images, with dark cores and bright rims that are thicker parallel to the foliation. In the most elongated grains, the dark core forms less than 20% of the grain area, which is otherwise dominated by the bright rim. On the contrary, more equidimensional grains are dominated by the dark core. Hyperspectral analysis of CL images indicates that the elongated rims of apatite are enriched in REE (particularly in Nd) compared to their core. Electron backscatter diffraction (EBSD) analysis demonstrates that (1) the elongated apatite grains are internally strain free, and (2) grain elongation occurs parallel to apatite c-axis.

Our data show that deformation of apatite occurred by melt-assisted dissolution-precipitation creep, which was responsible for grain elongation and remobilization of REE. Thus, post-crystallization deformation and melt-rock interaction played an important role in redistributing REE within the Fen Complex.

How to cite: Menegon, L., Valter, O., and Dahlgren, S.: Deformation-induced Rare Earth Elements (REE) redistribution in apatite from the Fen Carbonatite Complex (Norway), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9352, https://doi.org/10.5194/egusphere-egu24-9352, 2024.

EGU24-9877 | ECS | Orals | TS1.5

From slow to fast earthquakes: laboratory insights on acoustic and mechanical fault slip behavior 

Federico Pignalberi, Carolina Giorgetti, Pierre Romanet, Elisa Tinti, Chris Marone, and Marco Scuderi

A critical aspect of studying earthquake mechanisms involves understanding why a single fault can exhibit various slip behaviors. Fault heterogeneity leads to different slip behaviors in different fault portions: some slip seismically, generating catastrophic earthquakes, while others slip a-seismically in a stable and silent manner. Additionally, some fault portions exhibit slow, intermittent slip that can persist for months. Unraveling the physical mechanism at the base of these different fault slip behaviors is crucial for understanding how fault portions that slip slowly interact with portions capable of producing earthquakes.

In a laboratory setting, we can replicate the entire spectrum of fault slip behaviors by changing the loading stiffness of our experimental apparatus. Tuning the loading stiffness, we are able to match the critical rheological stiffness of the fault (kc) and investigate conditions around the critical point where k/kc = 1. Moreover, monitoring acoustic emissions (AEs) during laboratory earthquakes allows us to capture the rupture processes throughout the seismic cycle.

To constrain the nucleation mechanisms and rupture processes of different slip behaviors, we conducted friction experiments using quartz powder (MinUSil, average grain size 10 µm) to simulate fault gouge. The experiments were carried out in a double direct shear configuration, using an array of calibrated piezoelectric sensors for continuous, high acquisition rate (6 MHz) AE recording. The experiments were conducted at a constant displacement rate of 10 µm/s. During each experiment we maintained a constant normal stress and changed three acrylic blocks of different areas to change the apparatus stiffness (k). This technique allows us to reproduce both fast (i.e., when the apparatus stiffness is lower than a critical stiffness, k<kc) and slow (i.e., k=kc) slip events under the same stress conditions and test if the same fault patch can host a variety of slip behaviors.

Continuous AE recording, that is a proxy for seismicity, allows us to relate mechanical and acoustic fault behaviors. Our results show that different slip behaviors produce distinct acoustic waveforms during slip, with impulsive (high amplitude, short duration) AEs for fast slip, and emergent (low amplitude, longer duration) and continuous acoustic signals for slow slip. The distribution of AEs throughout the seismic cycle is characterized by an accelerating phase with small emissions for slow slips. While, fast slips exhibit no clear pre-seismic activity, and only strong AE in the co-seismic phase produced by fault rupture. Analyzing the frequency content of the acoustic signals also provides insights into the size, duration and the evolution of the seismic source along the seismic cycle.

By changing the stiffness of the fault, and monitoring acoustic emissions, our experiments not only accurately show that the same fault patch can experience different slip behaviors under the same stress conditions but also gives important insights into the complex dynamics of fault slip and rupture processes.

How to cite: Pignalberi, F., Giorgetti, C., Romanet, P., Tinti, E., Marone, C., and Scuderi, M.: From slow to fast earthquakes: laboratory insights on acoustic and mechanical fault slip behavior, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9877, https://doi.org/10.5194/egusphere-egu24-9877, 2024.

EGU24-10106 | ECS | Posters on site | TS1.5

Probing the Micromechanics of Velocity Strengthening Laboratory Faults using Ultrasonic Waves  

Michele Mauro, Michele De Solda, Carolina Giorgetti, and Marco Scuderi

Geophysical and geological evidence highlighted that faults can slip in a wide spectrum of modes, ranging from stable aseismic creep to unstable dynamic slip. Rocks composition plays a key role among the multiple factors favoring a specific type of frictional sliding. 

In particular, phyllosilicates in fault zones can change the mechanical behavior of the rocks involved in deformation. A relevant example is the presence of smectites (hydrated phyllosilicates) in subduction zones that are thought to influence the updip limit of the seismogenic zone. This group of clay minerals exhibits remarkably low friction values due to their platy microstructure and the tendency to absorb water within their lattice, making faults particularly weak. Therefore, studying the mechanical properties of clay minerals, especially smectites, has become crucial to illuminate the dynamics leading to the generation/arrest of large earthquakes in subduction zones.

Frictional laboratory experiments make it possible to evaluate the stability of experimental faults using the Rate and State Friction (RSF) framework. However, upscaling these phenomena and laws formulated in the laboratory to natural cases is still challenging due to a fundamental lack of understanding of the microphysical processes governing friction, mainly due to the empirical nature of the laws.

Modern friction theories propose that the frictional forces holding the fault in place are controlled by small asperities defining the real contact area (RCA). In the laboratory, experimental faults can be probed with ultrasonic waves to investigate the mechanics and evolution of contacts under applied stress variations.

Here, we present preliminary results on the stability of experimental faults with varying percentages of montmorillonite gouge (a specific type of smectite). The experiments are conducted using the biaxial apparatus BRAVA2 in the Rock Mechanics and Earthquake Physics laboratory at Sapienza University of Rome. 

Velocity steps experiments are performed in Double Direct Shear (DDS) configuration to obtain RSF parameters under different normal stress conditions. The apparatus is equipped with a recently developed UW generation and acquisition system.

The system comprises longitudinal and transversal polarized piezoelectric transducers, where a well-characterized pulse and frequency response allow the exploitation of information contained in the entire waveforms. The variation of transmitted amplitude, compressional, and shear velocity is used to track the changes in elastic properties. 

The synchronization procedure between mechanical and ultrasonic measurements will allow inferring the physical processes leading to RCA evolution from the obtained data.

How to cite: Mauro, M., De Solda, M., Giorgetti, C., and Scuderi, M.: Probing the Micromechanics of Velocity Strengthening Laboratory Faults using Ultrasonic Waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10106, https://doi.org/10.5194/egusphere-egu24-10106, 2024.

EGU24-10158 | Orals | TS1.5

Seismic faulting and fluid interactions: a structural study from carbonated fault damage zones within ultramafic rocks 

Laura Federico, Michele Locatelli, Laura Crispini, Elisabetta Mariani, Giovanni Capponi, and Marco Scarsi

Faults and shear zones within the metamorphic ultramafic rocks of the Voltri Massif (Ligurian Alps, NW Italy) often exhibit significant or complete carbonation of the host rocks and are locally associated with gold mineralization hosted in quartz veins (e.g., in the Lavagnina Lakes area). Here, a specific fault zone part of a larger regional system (i.e., the Bisciarelle Fault Zone) displays distinct structural characteristics linked to a fluid-assisted multistage brittle deformation in serpentinized peridotites, possibly indicating paleoseismic activity. Within the fault rocks, cataclasite and breccias are present along with saponite-bearing gouge, featuring layers of coseismic spherulitic grains interspersed in silica/chalcedony veins and cement. Spherulites consistently crystallize as concentric bands of fibrous Fe-dolomite and display multiple layers of radial crystal growth regularly alternating with darker, oxides-rich concentric bands. The concentric growth of spherulites is evident from the microtextural relations between successive bands, which depart radially from the spherulite cores, made of a submillimetric nucleus of carbonates or single grain of the host rock (e.g., relicts of fragments of fault core).

In this study, we present a multiscale analysis of this fault zone, integrating field observations, microstructural examination, SEM-EDS investigation, and electron backscattered diffraction (EBSD). The primary focus is on the microstructures within the fault core and the significance of distinctive carbonate spherulite layers in conjunction with silica/chalcedony cement and veins.

Our findings reveal that these structures are indicative of the interaction between CO2-rich fluids released during both coseismic and interseismic phases of faulting. This interaction occurs during cycles involving fluid pressure build-ups, faulting events, fluid flushing, and the subsequent precipitation and sealing of minerals during seismic failure of the fault.

How to cite: Federico, L., Locatelli, M., Crispini, L., Mariani, E., Capponi, G., and Scarsi, M.: Seismic faulting and fluid interactions: a structural study from carbonated fault damage zones within ultramafic rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10158, https://doi.org/10.5194/egusphere-egu24-10158, 2024.

EGU24-10481 | ECS | Posters on site | TS1.5

Fluid-rock interaction in eclogite-facies meta-peridotite (Erro-Tobbio Unit, Ligurian Alps, Italy) 

Serena Cacciari, Giorgio Pennacchioni, Enrico Cannaò, Marco Scambelluri, and Giovanni Toffol

In subduction zones, fluids released by dehydration reactions strongly influence rock rheology and seismicity. In particular, the occurrence of deep Episodic Tremor and Slow Slip events (deep ETS) along the subduction interface, at 25-60 km depth1, is likely fostered by the simultaneous presence of fluctuating fluid pressure and rheological heterogeneities, that allow for strain partitioning into low-strain domains radiating tremor, and high-strain domains accommodating slow slip events.

The Erro-Tobbio meta-peridotite (Ligurian Alps) records fluid-rock interactions and associated deformation that occurred within the deep ETS depth range. Heterogeneous serpentinization of the original mantle peridotite resulted in partitioning of the eclogite-facies deformation into high-strain domains of antigorite mylonites and low-strain domains of undeformed meta-peridotites. Both mylonites and meta-peridotites contain veins/reaction bands of metamorphic olivine (Ol2) and Ti-clinohumite (Ti-chu), formed by breakdown of brucite (Brc) and antigorite (Atg) at estimated P-T of 1.5 GPa and 500 °C3. Ol2 + Ti-chu reaction bands are arranged into two main sets, mutually oriented at ~50°: (i) Set1, steeply-dipping around 320°, (ii) Set2, trending N-S and parallel to the mylonites. The mylonites include: (i) type1 mylonites, composed of a planar foliation marked by Set2 reaction bands, and (ii) type2 mylonites, displaying a chaotic structure.

Within the undeformed domains, hydration and dehydration events occurred statically. In such domains, Al-rich Atg (Atg1) epitaxially replaced mantle olivine (Ol1), and was in turn epitaxially overgrown by Ol2, that crystallized in radial aggregates and along Set1-Set2 reaction bands. Along the mylonitic horizons, Atg1 is affected by ductile deformation, and Set2 reaction bands mark a foliation parallel to that of Atg1. In this case, Ol2 is rarely crystallographically related to Atg1 and is mostly oriented with a-axis parallel to the reaction bands. Atg1 and Brc relics are preserved along Set1 and Set2. The absence of Brc in the wall rock suggests that formation of Ol2 localized along original Brc-rich layers. Later stage, Al-free serpentine locally extensively (up to 70% volume) replaces Ol2 along a pervasive network of microcracks that exploited the previous Set1-Set2 structures. These observations suggest the occurrence of localized Brc ± Atg1 dehydration to Ol2 along specific planes, likely related to Brc distribution and Atg deformation, and subsequent Ol2 hydration localized along serpentine-bearing microcracks.

In-situ LA-ICP-MS reveals an enrichment in fluid-mobile elements (As, Sb, Ba, W, Li, B) in prograde Ol2 and retrograde Al-free serpentine. This information provides evidence of infiltration of external fluids, indicating open system conditions during eclogite-facies deformation, in agreement with the literature2,4, and during retrogression.

References

1: Behr et al., 2021, What’s down there? The structures, materials and environment of deep-seated slow slip and tremor. Phil. Trans. R. Soc. A 379: 20200218.

2: Clarke et al., 2020, Metamorphic olivine records external fluid infiltration during serpentinite dehydration. Geochem. Persp. Let. 16, 25–29.

3: Hermann et al., 2000, The importance of serpentinite mylonites for subduction and exhumation of oceanic crust. Tectonophysics 327, 225±238.

4: Scambelluri et al., 2012, Boron isotope evidence for shallow fluid transfer across subduction zones by serpentinized mantle. Geology 40, 10,  907–910. 

How to cite: Cacciari, S., Pennacchioni, G., Cannaò, E., Scambelluri, M., and Toffol, G.: Fluid-rock interaction in eclogite-facies meta-peridotite (Erro-Tobbio Unit, Ligurian Alps, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10481, https://doi.org/10.5194/egusphere-egu24-10481, 2024.

EGU24-11900 | ECS | Posters on site | TS1.5

Frictional strength, healing behaviour and deformation mechanism of low-grade serpentinites at hydrothermal conditions 

Leonardo Salvadori, Telemaco Tesei, and Giulio Di Toro

Serpentinites are “weak” rocks that play a critical role in the nucleation and propagation of slow slip events, tremors and earthquakes due to their unique rheological properties that promote strain localization and are common in a variety of tectonic settings, from mid-ocean ridges, to transform faults and subduction zones. In this study we analyze the microstructures of natural and experimental faults made by low-grade serpentinites (chrysotile and lizardite ± magnetite) to infer the possible deformation mechanisms operating in nature at hydrothermal conditions.

The natural serpentinites pertain to the exhumed Monte Fico shear zone (Elba Island, Italy) that reached greenschist facies conditions during subduction related to the Apennine orogeny. The shear zone is made of dm-m scale lenses of massive and less deformed serpentines surrounded by foliated serpentinites and cut by brittle faults. Bulk deformation in the natural shear zones was accommodated by anastomosing and pervasive S/C foliation structures. Fault surfaces are covered with slickenfibers mostly composed of chrysotile and polygonal serpentine. The interpretation of the microstructural analysis indicates the coexistence of ductile pressure-solution within the massive lens with fracturing, veining and frictional slip along the faults bounding the lenses. This fault zone rock assemblage and microstructural association suggests that cycles of high fluid pressures are limited by dilatant slip along the faults.

To determine the frictional properties and deformation mechanisms of these serpentinite-bearing faults we performed experiments with a rotary shear apparatus equipped with an hydrothermal vessel (ROSA-HYDROS, Padua University, Italy). We conducted slide-hold-slide (SHS) experiments at an effective normal stress of 20 MPa, a fluid pressure of 6 MPa, constant sliding velocity of 10 µm/s and at four different temperatures (room, 100°C, 200°C and 400°C). Friction experiments allowed to determine the rheological difference between the massive lens and the bounding faults, which represents favorable sites for slip nucleation.  The frictional healing properties document how the strength of these heterogeneous brittle-ductile shear zones evolve during the interseismic period.

The combination of natural and experimental observation in our project aims at the understanding of the mechanical behaviour of such lithologically and geometrically complex fault zones and to elucidate slip processes during earthquakes and slow slip events.

How to cite: Salvadori, L., Tesei, T., and Di Toro, G.: Frictional strength, healing behaviour and deformation mechanism of low-grade serpentinites at hydrothermal conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11900, https://doi.org/10.5194/egusphere-egu24-11900, 2024.

This study demonstrates how the response of ultramafic lithologies to infiltrating H20-CO2 fluids depends on the primary mineralogy. This has major implications on fluid flow through the lower crust and upper mantle as mineral reactions control the permeability and rheology. The studied samples are from the hanging wall of a 2 kilometer-long transtensional shear zone within ultramafic-mafic rocks in the Reinfjord Ultramafic Complex (RUC), part of the Seiland Igneous Province (SIP) in Northern Norway.

Fluid-rock interaction surrounding shear zones with abundant pseudotachlylites is highly variable and depends on bulk rock compositions. Thermodynamic modelling demonstrates that mineral reactions involving hydration and carbonation differ between dunitic rocks and the pyroxenitic dykes which intersect them. Alteration of dunitic rocks results in the formation of dominantly magnesite-anthophyllite-talc and talc-magnesite assemblages causing approximately 12% volume expansion. This results in a sharp reaction front contacts with the host rock. When the alteration zones cross the dunite-pyroxenite boundary the associated alteration has a more gradual boundary towards the unaltered rock and the alteration zone widens by approximately 40%. In contrast to the simpler dunite alteration assemblage, the pyroxenetic dykes are altered to a complex mixture of cummingtonite-anthophyllite, magnetite and chlorite. Additionally, orthopyroxene is completely pseudomorphed by a mixture of cummingtonite and magnetite, whereas olivine xenocrysts are partly preserved and surrounded by a magnesite-anthophyllite assemblage. Other, open cavity-like areas are filled by chlorite, amphibole, and Mg-MgCa carbonates, indicating volume reduction during alteration of the pyroxene.

Accordingly, dunite alteration effectuates a significant volume expansion, and are therefore only altered locally during seismic creep events. The pyroxenites are near volume neutral throughout interaction with the same fluids, and are thus more homogeneously altered. The formation of chlorite in hybrid compositions, such as the dykes in the lower crust, may create weak permeable zones that are consequently exploited as pathways for fertile mantle fluids and will hence also be the locus of ore bearing fluids moving to the upper crust. Increased understanding of fluid mediated metamorphism increases our current knowledge on fluid flow and strain localization in the lower crust. We further suggest that the hydrothermal assemblages are closely related to deformation leading to the formation of grain size sensitive creep in olivine facilitated carbonation of olivine and clinopyroxene to form orthopyroxene and dolomite and associated pseudoctacylites in the peridotites (Sørensen et al., 2019) , commonly associated with volatile rich mafic dykes (Ryan et al., 2022). Either the ductile magnesite-chlorite-talc assemblages formed at the same time in a shear-related heat gradient or they formed during cooling and continued CO2 infiltration from depth through the shearzones.

 

Ryan E J, et al.  2022  Infiltration of volatile-rich mafic melt in lower crustal peridotites provokes deep earthquakes.  J. Struct. Geol. (https://doi.org/10.1016/j.jsg.2022.104708)

Sørensen, B.E., et al., 2019 In situ evidence of earthquakes near the crust mantle boundary initiated by mantle CO2 fluxing and reaction-driven strain softening. Earth and Planetary Science Letters (https://doi.org/10.1016/j.epsl.2019.115713 )

 

How to cite: Eske Sørensen, B., Ryan, E. J., Larsen, R., Lode, S., Drivenes, K., and Orvik, A. A.: Linkage between ductile deformation, pseudotachylites, strain softening and volume expanding carbonation reactions during mixed-volatile infiltration in ultramafic-mafic rocks from the Reinfjord lower crustal field laboratory , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13445, https://doi.org/10.5194/egusphere-egu24-13445, 2024.

EGU24-13986 | ECS | Orals | TS1.5

Dynamic and short-lived fluid flow in the high-grade metamorphic rocks related to seismic events in the middle crust. 

Diana Mindaleva, Masaoki Uno, and Noriyoshi Tsuchiya

Fluid flow in the crust induces fluid-rock reactions and contributes to earthquake triggering. However, there are limited numerical constraints on the fluid volumes with the available duration of fluid infiltration. There is also a gap in our knowledge of time-integrated fluid fluxes estimated from geological samples and their influence on controlling seismic/aseismic activity. Merging the timescales of fluid infiltration with the transport properties estimated from the geological samples such as metamorphic reaction zones is essential to understanding the fluid flux during crustal fracturing and its influence on controlling some characteristics of seismic/aseismic events.

This study focuses on fluid flow through a single fracture and the fluid-rock reaction zones and applies its results to low-magnitude fracturing events, such as tremors and low frequency earthquakes. Physical properties of fluid flow provide an opportunity to calculate the seismic moment and cumulative magnitude of the possibly triggered seismic/aseismic event.

Particularly, to examine the duration of fluid infiltration and time-integrated fluid fluxes we analyze amphibolite-facies fluid-rock reaction zones and then combine with estimates of possible associated seismicity and conclude that flow along a single fracture is compatible with seismicity of non-volcanic tremor and low frequency earthquakes. This study is based on evidence of rapid fluid infiltration (~10 h) caused by crustal fracturing and permeability evolution from low- to highly-permeable rocks (~10−9–10−8 m2).

Time-integrated fluid fluxes perpendicular to a given fracture and those through the fracture were estimated. Coupled methodology, including reactive-transport modeling and thermodynamic analyses, based on Si alteration processes within reaction zones is used to estimate fluid volumes involved in triggering seismic activity. Time-integrated fluid flux through the fracture results in 103-6 m3/m2. The lower range is similar to the fluxes through the upper crustal fracture zones (~103-4 m3/m2), while almost the whole range is comparable to the contact metamorphism zone (~102-5 m3/m2).

Fluid volumes transported through the fracture were compared with fluid injection experiment results. We also compare the durations of fluid infiltration to the durations of the slow slip events. There is no universal theory of slow slip phenomena from the perspectives of geological and geophysical properties. In terms of pressure and temperature, high-grade metamorphic rocks can be related to slow slip events. Our finding reveals that the transportation of voluminous fluid volumes through a fracture may be related to short seismic/aseismic events such as tremors and LFEs, as suggested from duration (~10 h) and cumulative magnitude, representing the maximum values as 2.0–3.8, the lower limit of the magnitude for a single fluid-driven seismic event as –0.6 to 0.2. Single fractures described in this study make it possible to transfer voluminous fluid flow. They could be an essential control on the generation of seismic activity above the tremor and slow slip events source regions in the lower–middle crust.

How to cite: Mindaleva, D., Uno, M., and Tsuchiya, N.: Dynamic and short-lived fluid flow in the high-grade metamorphic rocks related to seismic events in the middle crust., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13986, https://doi.org/10.5194/egusphere-egu24-13986, 2024.

EGU24-14313 | ECS | Orals | TS1.5

Brittle initiation of dissolution-precipitation creep in plagioclase-rich rocks: Insights from the Bergen arcs, Norway 

Jo Moore, Sandra Piazolo, Andreas Beinlich, Håkon Austrheim, and Andrew Putnis

The initiation of shear commonly occurs spatially associated with fluid-rock reactions along brittle precursors. In many cases the relative timing of fracturing, fluid infiltration, reaction, and recrystallisation is unclear, making it difficult to disentangle mechanisms of shear zone formation from subsequent deformation and recrystallisation. Here we present the transition from an anhydrous and relatively undeformed precursor rock into a highly deformed and hydrated plagioclase-rich rock. The studied outcrop remarkably preserves both (1) the interface between the anhydrous granulite-facies parent lithology and a statically hydrated amphibolite-facies rock, and (2) a transition from statically hydrated amphibolite to the sheared amphibolite-facies lithologies. Detailed study of plagioclase chemistry and microstructures across these two interfaces using Electron Backscatter Diffraction (EBSD) and wavelength dispersive spectrometry (WDS) allow us to assess the degree of coupling between deformation and fluid-rock reaction across the outcrop. Plagioclase behaves dominantly in a brittle manner at the hydration interface and so the initial weakening of the rock is attributed to grain size reduction caused by fracture damage at conditions of ca. 720°C and 10-14 kbar. Extensive fracturing induced grain size reduction locally increases permeability and allows for continuing plagioclase and secondary mineral growth during shear, as evidenced by a general increase in the amount of hydration reaction products across the shear zone interface. Due to the apparent coupling of deformation and reaction, and the plagioclase microstructures such as, an inherited but dispersed crystallographic preferred orientation (CPO), fine grain size (5-150 µm), and truncation of chemical zoning, we conclude that deformation is dominantly facilitated by dissolution-precipitation creep in the shear zone.

How to cite: Moore, J., Piazolo, S., Beinlich, A., Austrheim, H., and Putnis, A.: Brittle initiation of dissolution-precipitation creep in plagioclase-rich rocks: Insights from the Bergen arcs, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14313, https://doi.org/10.5194/egusphere-egu24-14313, 2024.

EGU24-14574 | ECS | Posters virtual | TS1.5

Relative significance of CO2 and silica on talc formation at slab-mantle interface: Insights from experiments on metasomatic boundary 

Shunya Okino, Atsushi Okamoto, Yukiko Kita, Sando Sawa, and Jun Muto

It is thought that the supply of Si-rich fluid from subducting slab results in the formation of talc, a mantle mineral lowest frictional coefficient, at the slab-mantle interface. In contrast, the exhumed metamorphic belts often contain serpentinite bodies with extensive carbonate veins accompanying with talc. Recent experiments showed that the interaction of mantle rocks and CO2 fluids rapidly produces the carbonate+quartz and carbonate+talc assemblage (Sieber et al., 2018). However, it is not well understood whether silica or CO2 contributes more significantly to talc formation at the mantle wedge condition. In this study, we conducted a new type of experiments on the metasomatic reactions at slab-mantle interface at the mantle wedge condition to evaluate the role of CO2 fluid relative to silica fluid on the formation of talc.

A Griggs-type piston cylinder apparatus was used for experiments on metasomatic reactions at the crust-mantle boundaries at 500°C, 1 GPa. We prepared the three layers of core samples; pelitic schist (the Sanbagawa belt, Japan) or quartzite was sandwiched between harzburgite (Horoman peridotite, dry mantle) and serpentinite (Mikabu belt, wet matle). Two types of fluids were introduced: pure H2O fluid and H2O-CO2 fluid. The latter produced by the decomposition of Oxalic Acid Dihydrate (OAD). We maintained 4wt% H2O and set the XCO2 = 0.2 for the H2O-CO2 experiments.

In all conditions, the alteration more proceeded in the mantle rocks (harzburgite or serpentinite) than on the crust side. In the experiment with H2O, talc was formed both in harzburgite and serpentinite at the contact with crustal rocks. In the pelitic schist at the contact with ultramafic rocks, albite was selectively replaced by Mg smectite, whereas in the quartzite, a small amount of talc was formed, indicating that counter diffusion of Si from crust to mantle, and Mg from mantle to crust. In the experiments with H2O-CO2 fluids, talc was formed with magnesite both in harzburgite and serpentinite with intense fracturing. The rough mass balance calculations reveal that the amount of talc in the ultramafic rocks can be explained solely by the reaction with CO2-fluid, even if quartz-bearing rocks existed at the contact.

These experimental results suggest that talc formation at the slab-mantle interface is greatly enhanced by the infiltration of CO2 fluids, at least, at the mantle wedge corner of the warm subduction zone, where the P-T conditions are similar to those of our experiments. In addition, not only silica but also other elements such as Mg and Al move significantly, which contributes to the various metasomatic reactions. Such heterogeneous metasomatic reactions could produce the rheological heterogeneities of the mantle wedge rheology at the slab-mantle interfaces, and may explain a wide spectrum of the slow slip events observed at the mantle wedge corner.

How to cite: Okino, S., Okamoto, A., Kita, Y., Sawa, S., and Muto, J.: Relative significance of CO2 and silica on talc formation at slab-mantle interface: Insights from experiments on metasomatic boundary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14574, https://doi.org/10.5194/egusphere-egu24-14574, 2024.

EGU24-15776 | ECS | Posters on site | TS1.5

Microcomputed Tomography Unravels CO2-fluid/rock Interaction in Elba's Carbonated Serpentinites 

Roberto Emanuele Rizzo, Samuele Papeschi, Edoardo Baroncini, and Paola Vannucchi

Carbonation of serpentinites is a crucial factor in controlling the earthquake cycle in subduction zones. Serpentinites are commonly found within subduction zones, both in the mantle wedge above subducting slabs and on the incoming plate, formed from peridotites exposed directly on the ocean floor. Carbonation of these serpentinites often results from the “contamination” of CO2-rich fluids derived from sediments involved in the subduction. This process leads to the formation of carbonate minerals within the serpentinite, which in turn influences the mechanical properties of the rock. A critical factor affecting the spatial and temporal progress of carbonation reactions - and thus their potential to trigger mechanical instabilities at the plate boundary - is the emergence of a permeable network of cracks and pores, which facilitates the interaction of CO2-rich fluids with the serpentinite rocks.

We present a detailed three-dimensional (3D) characterization of variously carbonated serpentinite samples through computed microtomographic (µCT) imaging integrated with a machine learning algorithm (i.e. Random Forest classifier) to segment the different mineral phases. Machine learning offers a robust and accurate means of identifying and quantifying the carbonate phases, leveraging the Random Forest capacity for handling complex, multidimensional data. This allows for a comprehensive 3D examination of the alteration phases affecting the serpentinite samples and provides quantitative insights into the volumes and geometries of the carbonate vein networks. Our focus is on samples from an exhumed subduction channel separating  the fossil Cretaceous – Eocene accretionary prism (Ligurian Units) from the continent-derived nappes of the Northern Apennines. The subduction channel, part of the Norsi – Cavo Complex, is exposed over approximately 10 km along the N-S strike on the Island of Elba, consisting of oceanic sediments and ultramafic rocks detached from the prism base. Our analyses reveal that carbonation preferentially follows pre-existing serpentine veins, exploiting inherent anisotropies in the rock. In addition, the geometry of the vein network, as illuminated by the µCT 3D data, can help us to correlate with the carbonation timescale and fluid fluxes, as inferred from geochemical data.

The presence of carbonate-rich fluids can be responsible for increasing pore-fluid pressure, pushing the rock toward failure. The formation of extensive carbonate vein networks can also lead to a net volume increase in the original serpentinite, thus increasing instability. The observed preferential distribution of carbonates along pre-existing structures not only provides crucial insights into the mechanics of subduction zones but also offers valuable implications for CO2storage models, highlighting potential fluid migration and reaction pathways.

How to cite: Rizzo, R. E., Papeschi, S., Baroncini, E., and Vannucchi, P.: Microcomputed Tomography Unravels CO2-fluid/rock Interaction in Elba's Carbonated Serpentinites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15776, https://doi.org/10.5194/egusphere-egu24-15776, 2024.

EGU24-16363 | Posters on site | TS1.5

Across the brittle-ductile transition: the role of fluids and anisotropy 

Giorgio Pennacchioni and Giovanni Toffol

The meta-granitoids of the Zillertal unit of the Tauern window (eastern Alps) record a sequence of Alpine deformations, developed during exhumation, ranging from ductile (at amphibolite-upper greenschist facies metamorphic conditions) to brittle (at conditions close to the base of the seismogenic crust).

In the core of the Zillertal unit, the high grade deformation (stage1) is common and localized to steeply-dipping strike-slip shear zones, mainly striking around E-W and hierarchically organized in thick (up to several metres), km-long mylonitic major shear zones (MSZs), and small-scale (mm-dm-thick) shear zones (SSZs). SSZs are strictly associated with precursor tabular heterogeneities (e.g. dykes) and fractures/veins1, 2. Stage1 deformation occurred (i) in presence of fluids, recorded by cyclic vein formation and extensive alteration haloes surrounding fracture/veins, (ii) at low differential stress, and (iii) during shortening at 345° (i.e. at a high angle to the orientation of most shear zones)3. Stage2 deformation is recorded by very discrete, local shear reactivation of the core of SSZs and of the mylonitic foliation of MSZs. Stage2 shear zones have a similar strike-slip shear sense as the overprinted stage1 shear zones, but developed (i) under fluid-deficient conditions, and (ii) high differential stress.

At lower temperature the meta-granitoids were involved into 2 stages of brittle deformation (stage3A and stage3B). Stage3A is represented by thin (mm-thick) cataclasites and pseudotachylyte veins formed by slip along the mylonitic foliation of MSZs with the same strike-slip kinematics of the exploited stage1 and stage2 shear zones. Cataclasites are not associated with any significant alteration and pseudotachylytes do not show ductile reactivation. Stage3B is represented by a pervasive system of vertical extensional chlorite-quartz-filled veins, epidote-filled hybrid fractures and faults, that crosscut and offset stage3A structures. The stage3B structures are surrounded by haloes of alteration of the host rock. The mineral filling of fractures (chlorite, epidote, albite) indicates conditions close to the base of the brittle crust. The orientation and kinematics of Stage3B structures constrain shortening as horizontal, oriented ca. N-S3.

We interpret this structural sequence as the result of deformation at decreasing temperature and, basically, under constant orientation of tectonic shortening. At ductile/brittle transition conditions yielding occurred by (i) seismic slip along the highly misoriented planes of anisotropy provided by the persistent (km-scale) foliation of MSZs, under fluid-deficient conditions and high differential stress (stage3A); and (ii) formation of new extensional and shear fractures, that disregard previous anisotropy, under fluid-present conditions and transient low differential stress (stage3B). This indicates that the fluid availability dramatically modifies the rock strength and the type of mechanical response of anisotropic rock systems.  

 

1Mancktelow, N.S., Pennacchioni, G., 2005. The control of precursor brittle fracture and fluid–rock interaction on the development of single and paired ductile shear zones. Journal of Structural Geology 27, 645–661.

2Pennacchioni, G., Mancktelow, N.S., 2007. Nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions. Journal of Structural Geology 29, 1757-1780

3Pennacchioni, G., Mancktelow, N.S., 2018. Small-scale ductile shear zones: neither extending, nor thickening, nor narrowing. Earth-Science Reviews 184, 1-12.

How to cite: Pennacchioni, G. and Toffol, G.: Across the brittle-ductile transition: the role of fluids and anisotropy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16363, https://doi.org/10.5194/egusphere-egu24-16363, 2024.

Deep slow earthquakes are commonly observed downdip from the seismogenic zone in relatively warm subduction zones. Most of these events occur close to the Moho depth of the overriding plate at depths of 30–40 km. Slow earthquakes show characteristics that can be related to both brittle and ductile behavior and their occurrence is thought to be closely related to the brittle-ductile transition. There is also good evidence that slow earthquakes develop in regions of high fluid pressure. The temperature of subduction zones is an important control on the location of the brittle-ductile transition and the release of fluid and healing of cracks along which fluids may move. However, temperature estimates along subduction zones are subject to considerable uncertainty. One of the main uncertainties is the amount of shear heating; many thermal models of subduction zones assume such shear heating is negligible. The Sanbagawa metamorphic belt of Southwest (SW) Japan formed along an ancient subduction boundary and now includes slivers of mantle wedge-derived serpentinite which are in direct contact with metasedimentary rocks derived from the subducted oceanic plate. These areas can be related to the ancient subduction plate interface. P-T paths from petrological studies combined with information on ancient plate reconstructions and thermal modelling suggest significant shear stresses developed along the subduction boundary and these strongly affect the thermal structure. Rocks originally located deep in subduction zones can record information about deformation processes, including shear stress. The estimated shear stress is likely to be representative of shear stress experienced over geological timescales and be suitable to use in subduction zone modelling over time scales of millions to tens of millions of years. Stress estimates based on quartz microstructure yield differential stresses of 30–80 MPa at depths close to the Moho of the overlying plate. Such stresses are compatible with the estimates from thermal modelling and imply shear heating needs to be considered when estimating the thermal structure in the domain of slow earthquakes.

How to cite: Wallis, S. R., Ishii, K., Koyama, Y., and Nagaya, T.: Shear heating along subduction zones and thermal structure in the domain of deep slow earthquakes: evidence from the exhumed subduction-type Sanbagawa metamorphic belt, SW Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16478, https://doi.org/10.5194/egusphere-egu24-16478, 2024.

EGU24-17072 | ECS | Posters on site | TS1.5

Temperature and strain-dependent healing of quartz gouges at hydrothermal conditions 

Giovanni Guglielmi, Telemaco Tesei, and Giulio Di Toro

The stick-slip model for earthquakes consists of slip instabilities due to elastic strain energy storage followed by sudden stress drops along seismogenic faults, phenomenologically representing the seismic cycle. During the interseismic time, the fault regains strength (healing) and stores elastic energy that will be partially released in the following earthquake. Fault healing has been consistently documented by field observations, geophysical studies, and laboratory experiments.

Despite the large focus on laboratory experiments in addressing this topic, observations of stress drops and recurrence intervals in natural earthquakes generally showed more pronounced fault healing in comparison to laboratory measurements. This discrepancy may arise from the difficulty of reproducing the natural conditions in the laboratory in terms of time, stress, fluids, and temperature. In particular, fluid-rock interaction and thermally-driven processes are widely accepted as crucial for faulting at seismogenic depths. For instance, the presence of pressurized fluids, at temperatures at the onset of crystal plasticity could lead to chemically assisted healing processes such as compaction and cementation. Although this mechanism finds support in a multitude of field observations, there have been only few systematic laboratory studies reproducing and quantifying the occurrence of incipient cementation in the laboratory seismic cycle. In addition, frictional healing has usually been experimentally measured at relatively low shear strain, often overlooking the “strain history” of laboratory faults.

We present a suite of 15 friction experiments in which we performed Slide-Hold-Slide (SHS) tests to evaluate the healing of quartz gouges under hydrothermal conditions. The temperature range investigated spans from 23 to 400 °C, at different effective normal stresses and fluid pressures. We also documented the role of shear strain in controlling the evolution of frictional healing through systematic repetitions of SHS tests at different amounts of strain of the laboratory fault. Our results indicate that frictional healing is positively dependent on temperature, especially at temperatures corresponding to the onset of crystal plasticity for quartz (> 350 °C). Best fit lines of healing measurements at 400 °C deviate from the classical log-linear time-dependent Dieterich-type healing, following an exponential relationship between ∆μ (frictional healing) and the logarithm of hold time. This suggests that incipient cementation processes play a major role during quasi-stationary, interseismic periods, better reflecting the higher fault healing usually observed in natural environments. In addition, experimental results relative to high strain SHS tests revealed that the “strain history” of laboratory faults exerts a strong control on the evolution of friction during the experiments. These results improve our understanding of a critical healing mechanism, constraining the dependence of frictional healing on temperature and shear strain.

How to cite: Guglielmi, G., Tesei, T., and Di Toro, G.: Temperature and strain-dependent healing of quartz gouges at hydrothermal conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17072, https://doi.org/10.5194/egusphere-egu24-17072, 2024.

Pseudotachylytes (frictional melts formed during seismic slip) in the metamorphosed anorthosites from Nusfjord (Lofoten, northern Norway) preserve a record of seismic rupture in the dry lower crust at 650–750 °C, 0.8 GPa. Field observations indicate that the Nusfjord pseudotachylytes represent single-earthquake events associated with large stress drops, on the order of hundreds of megapascal (MPa) to 1–2 gigapascal. Such large stress drops are interpreted to reflect the high strength of the intact anorthosite at the high confinement conditions of the lower crust. One important question is whether evidence of the high stresses necessary to initiate seismic rupture in the lower crust is preserved in the microstructure of the Nusfjord pseudotachylytes and of their damage zone.

Pyroxene deformation microstructures associated with preseismic loading and coseismic fragmentation reveal strongly localized transient stresses that presumably reached GPa-level magnitude. Here we use high-angular resolution electron backscatter diffraction (HR-EBSD) on diopside grains to obtain spatial datasets of residual stresses that are retained in the crystal lattice of diopside. We apply this method combined with microstructural analysis on diopside in a sample from a pseudotachylyte from Nusfjord to reconstruct the spatial heterogeneities of stress and link them to the earthquake cycle and associated coseismic thermal effects.

Diopside contains micro- to nanoscale deformation twins within 3 mm from the fault and in clasts in the pseudotachylyte. Strong lattice undulations are locally present in survivor clasts, indicating low-T plasticity at high stress. Residual stresses from the wall rock and in a survivor clast vary between ~600 and ~200 MPa and form a gradient of decreasing residual stress away from the pseudotachylyte, only elevated within 200 µm from the pseudotachylyte margin and with the highest values occurring within the clast. Microfaults crosscut the deformation twins, lattice undulations, and residual stress spatial heterogeneities within the clast. The latter appear strongly similar to the lattice undulations, in distribution and orientation.

The obtained stresses are lower than estimated stress drops for the locality and than stresses expected during rupture propagation (both >1 GPa). As alternative stress source, we investigated thermal stress introduced by coseismic frictional heating. Calculations demonstrate that this process is only significant over a distance of less than 100 µm in the wall rock for a stress drop of 100 MPa, and less than 10 µm for a stress drop of 1 GPa. Instead, because coseismic microfaults crosscut twinning, lattice undulations, and the spatial heterogeneities of residual stress, we interpret that these features correspond to the progressive build-up of stress during preseismic loading. An explanation for the discrepancy between the residual stresses and suggested stress drop is that the stress build-up in diopside was partially dissipated by the formation of twins. Additionally, the stress drop is estimated at the scale of the bulk fault, whereas the residual stresses are measured at the single grain scale and as such are likely to vary locally depending on the microstructure and on the different ability of different phases to dissipate the stress build-up via e.g. twinning and recovery of dislocations.

How to cite: van Schrojenstein Lantman, H. and Menegon, L.: Residual stress in diopside: insight into localized transient high stress in seismogenic faults in the lower crust, Lofoten, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17335, https://doi.org/10.5194/egusphere-egu24-17335, 2024.

EGU24-17448 | ECS | Posters on site | TS1.5

Hydrothermal Alteration-Induced Weakening in Experimentally Deformed Fault Gouges 

Weijia Zhan, Natalia Nevskaya, André Niemeijer, Alfons Berger, Christopher Spiers, and Marco Herwegh

In the granitoid crust, phyllosilicate-rich fault gouges are prevalent in mature fault zones undergoing hydrothermal alteration and often exhibit lower frictional strength compared to framework minerals (e.g., qtz, fds) under deformation at room temperature. However, the mechanical behavior and deformation mechanisms of altered gouges under hydrothermal conditions are not fully understood so far.

To investigate these effects, we conducted a series of experiments on three types of fault “gouge” material using a ring shear deformation apparatus. We used gouge mixtures obtained from (i) crushed granitoid ultramylonite, (ii) biotite- and (iii) muscovite-bearing gouges to represent quartzofeldspartic materials with (i) no alteration, (ii) high-temperature and (iii) low-temperature alteration, respectively (see Table 1 for the mineralogy). Deformation temperatures (T) ranged from 20-650°C, with a sliding velocity kept at 1 μm/s, and an imposed effective normal stress and pore fluid pressure at 100 MPa. At large shear strain (g ≈ 22-25) and T = 20-450°C, granitoid gouges consistently showed higher shear stresses (t = 73-81 MPa) than muscovite- (t = 47-69 MPa) and biotite-bearing gouges (t = 44-56 MPa). Granitoid gouges showed a decrease in t at T ≥ 450°C, while mica-rich gouges showed an increase in t with T at all tested conditions. Microstructurally, all gouges experienced strain localization into relatively fine-grained and dense principal slip zones (PSZs) at elevated T. The presence of newly percipitated minerals (e.g. bt, qtz) suggested the operation of dissolution-precipitation creep (DPC). However, the PSZs of granitoid and mica-rich gouges exhibited distinctive geometric features in their microstructure at 650°C. Granitoid gouges showed PSZs with ultrafine-grained (≤ 1 μm) relicts of porphyroclasts sparsely distributed within a dense matrix. In contrast, the PSZs of mica-rich gouges showed the anastomosing P-foliation of aligned micas with intervening shear band cleavages. Within these localized domains, quartz in mica-rich gouges exhibited larger grain sizes (1-4 μm) compared to those in granitoid gouges.  

Our observations indicate that in all tested gouges, frictional deformation gives way to grain-size sensitive creep mechanism as T rises, leading to the formation of fine-grained PSZs. We suggest that the ultrafine grain sizes in granitoid gouges promote DPC-accommodated viscous granular flow more efficiently, leading to the low shear stresses. In contrast, the strengthening of altered gouges with T was attributed to two factors: a less efficient DPC-assisted deformation due to generally larger grain sizes, and a less efficient viscous granular flow due to the development of foliation and shear bands inclined to the shear direction. Therefore, the mechanical behaviour of granitoids along the retrograde hydration-path depends not only on the evolving mineralogy, but also on microstructures and grain sizes.

Table 1. List of Samples Used in This Study and Their Mineralogy According to Quantitative XRD.

Sample

Composition (wt%)

Altreation type

Granitoid ultramylonite

37% qtz, 49% fds, 8% bt, 6% ep

No alteration

Biotite-bearing natural fault gouge

35% qtz, 4% fds, 37% phl, 21% mus, 3% smc

High-temperature

Muscovite-bearing natural fault gouge

39% qtz, 5% fds, 38% mus, 11% ser, 6% chl, 1% cal

Low-temperature

Qtz:quartz, fds: feldspar, bt: biotite, ep: epidote, phl: phlogopite, mus: muscovite, ser: sericite, smc: smectite, chl: chlorite, cal: calcite

How to cite: Zhan, W., Nevskaya, N., Niemeijer, A., Berger, A., Spiers, C., and Herwegh, M.: Hydrothermal Alteration-Induced Weakening in Experimentally Deformed Fault Gouges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17448, https://doi.org/10.5194/egusphere-egu24-17448, 2024.

EGU24-17549 | ECS | Orals | TS1.5

Paleo-seismic and aseismic processes and the role of fluids recorded in an exhumed carbonate fault  

Berit Schwichtenberg, Marco Herwegh, Alfons Berger, Christoph Schrank, Teo Neuenschwander, Sandro Truttmann, Michael W. Jones, Stefano M. Bernasconi, Dominik Fleitmann, and Cameron M. Kewish

Worldwide, fault zones in carbonates regularly host medium to large earthquakes including recent ones in the Mediterranean and Middle East. In addition to that, faults can control fluid flow by either acting as a conduit or seal for fluid pathways and should be considered in e.g., geothermal exploration. Hence, understanding the (micro-) structural evolution of these fault zones as well as fluid mediated geochemical processes involved in their dynamic deformation history allows to better address topics of societal and economic relevance ranging from seismic hazards to the exploitation of natural resources. Unfortunately, active in-situ deformation at depth is difficult to access, emphasising the need for investigations on suitable exhumed analogues.

This study focuses on the microstructural and geochemical record of a recently exposed seismogenic dextral strike-slip fault zone in the seismically active southwestern Swiss Alps. Due to excellent outcrop conditions on glacially polished rock surfaces and a wide range of preserved tectonites and associated deformation structures, this particular fault zone provides a valuable record of potential paleoseismicity in carbonates. We combined microstructural analyses with micro-chemical and isotope data in order to reconstruct the spatio-temporal evolution of high-strain domains at variable crustal levels throughout exhumation. While the microstructural record allows us to differentiate between rate-dependent brittle and viscous deformation phases, we use the geochemical fingerprint to distinguish and characterize individual fluid pulses.

Here, we present microstructural evidence of fast, possibly seismic, deformation along a principal slip zone. While injection structures containing fluidized material, suggest highest deformation rates as feasible for seismic events, repeated brittle deformation that was accompanied by the formation of cataclasites and calcite veins, hints towards fast seismic to sub-seismic rates.
We also found that newly formed calcite crystals, in veins and linkage zones, show significantly decreasing δ18OSMOWvalues, as low as 5 ‰ δ18OSMOW, implying an influence of meteoric water. Clumped isotope thermometry of such calcites resulted in temperatures of 65-95°C, which are approximately 100°C lower than Tmax in the area. This suggests that the analyzed material did not record any potential shear heating. Moreover, the investigated tectonites have most likely formed along a retrograde exhumation path. 

In combination with detailed observations on the m- to 10er-m-scale our observations provide a dataset that allows direct comparison of different deformation processes and correlation of paleo-seismicity to fluid flow in fault zones. Further, we contribute to the longstanding discussion of differentiating microstructural evidence for seismic slip from slow or aseismic slip in carbonate hosted fault zones.

How to cite: Schwichtenberg, B., Herwegh, M., Berger, A., Schrank, C., Neuenschwander, T., Truttmann, S., Jones, M. W., Bernasconi, S. M., Fleitmann, D., and Kewish, C. M.: Paleo-seismic and aseismic processes and the role of fluids recorded in an exhumed carbonate fault , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17549, https://doi.org/10.5194/egusphere-egu24-17549, 2024.

EGU24-17577 | ECS | Posters on site | TS1.5

Isotopic signatures of fluid inclusions from quartz veins record sub-surface fluid-rock interaction associated with the Variscan orogeny 

Akbar Aydin Oglu Huseynov, Jeroen van der Lubbe, Suzan Verdegaal - Warmerdam, Onno Postma, Klaudia Kuiper, and Jan Wijbrans

The presence of fluid inclusions in quartz veins is crucial to reconstruct fluid migration pathways in the subsurface. In this study, we provide an innovative approach to analyse  the hydrogen and oxygen isotopic composition of water fluid inclusions using cavity ring-down spectroscopy (CRDS). The CRDS is connected to a mechanical crusher in order to release fluid inclusion water from the host mineral. The evaporated fluid inclusion water from the crushed sample is added to a moistened background of nitrogen gas. For this purpose, we designed a temperature-regulated evaporation unit at Earth Science Stable Isotope Laboratory at the Vrije Universiteit Amsterdam (VU) to ensure that the isotopic composition and concentration of the background water vapour remains constant. The isotopic compositions of the fluid inclusions are calculated by subtracting the isotopic and concentration of the ‘wet’ background.

This newly designed setup allows for reliable measurements of the oxygen and hydrogen isotopic compositions of fluid-inclusions in quartz minerals. The objective of this study is to analyse the isotopic compositions of fluid-inclusions in quartz veins from distinct regions in Europe (Germany and Portugal), which are both linked to the Variscan orogeny. The isotopic data align with the modern Global Meteoric Water Line, providing evidence for the presence of meteoric fluids in the examined fold-and-thrust belts of the Variscan orogeny. Complementary microthermometry data, isotopic signatures of silicon and oxygen of  the quartz host mineral further document the cooling of hydrothermal systems under the influence of meteoric water at various geological events. This interpretation concords with the 40Ar/39Ar dating fluid rich fraction of quartz vein minerals.

How to cite: Huseynov, A. A. O., van der Lubbe, J., Verdegaal - Warmerdam, S., Postma, O., Kuiper, K., and Wijbrans, J.: Isotopic signatures of fluid inclusions from quartz veins record sub-surface fluid-rock interaction associated with the Variscan orogeny, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17577, https://doi.org/10.5194/egusphere-egu24-17577, 2024.

Geophysical observations have led to the conclusion that slow earthquakes (EQ) occur in the ductile realm at depths greater than ~20 km, in domains of low Vp and elevated Vp/Vs, consistent with high pore fluid pressure conditions and/or fluctuating fluid conditions. Furthermore, slow EQ are characterized by concomitant viscous aseismic slip and transient frictional slip responsible for tectonic tremors and low frequency earthquakes. Understanding the physics of slow earthquakes can be done by integrating geophysics, rock deformation experiments and numerical models with the observation and characterization of the possible rock record of slow earthquakes.

In this contribution, we contribute to the quest for geological records of slow EQ by adding a new example to the fast growing list of examples. Our approach is based on field observations, petrological and microtextural analysis carried out on exhumed shear zones in late Variscan volcanic rocks from the Suretta nappe (Central Alps, Switzerland). We propose that in continental collision settings, like the Alps, exhumed continental shear zones preserve geological evidence that may be related to paleo-slow earthquakes. We show that burial of continental units is characterized by concomitant frictional and viscous deformation in the ductile realm at temperature conditions above 450°C for a depth range between 18 and 25 km, which resembles those where slow earthquakes are expected. The finite geometry of the shear zone consists of a network of anastomosed mica-rich weak and high strain ductile shear zones of various size (m to km) bounding high strength and low strain domains, resulting in a “mélange” rheology. At a smaller scale, the localization of millimeter to centimeter wide ductile shear zones is controlled by the prior development of a damaged zone that has been detected by imaging volcanic quartz phenocrysts with cathodoluminescence. This damage zone is defined by a domain of high density healed cracks and fluid inclusion planes preserved only in volcanic quartz phenocrysts. These microcracks, follow a riedel-type geometry consistent with the ductile kinematics. The ductile shear zones are commonly crosscut by mono-mineralic quartz veins of a few millimeters in thickness parallel to the shear zone walls and localized in the middle of the shear zone. Quartz veins are characterized by a crack-seal texture with elongated blocky quartz grains perpendicular to the vein-wall interface suggesting that quartz was precipitated from a fluid in a dilatant fracture. These quartz veins are always overprinted by ductile deformation. Ductile deformation is characterized by dynamic recrystallization of the blocky quartz into small new grains formed by bulging recrystallization. When ductile deformation overprinting is high, quartz veins are sheared, isoclinally folded and almost entirely recrystallized into a fine grain aggregate.

How to cite: Goncalves, P., Leydier, T., Albaric, J., Trap, P., and Mahan, K.: Concomitant brittle-ductile deformation, fluid-flow and metamorphism during continental subduction : a slow earthquake rock record in the Suretta nappe (Central Alps, Switzerland) ?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17707, https://doi.org/10.5194/egusphere-egu24-17707, 2024.

EGU24-19532 | ECS | Orals | TS1.5

Seismic Mirror-like Surfaces in bituminous dolostones (Central Apennines, Italy) 

Miriana Chinello, Andrea Schito, Stephen A. Bowden, Telemaco Tesei, Elena Spagnuolo, Stefano Aretusini, and Giulio Di Toro

Mirror-like Surfaces (MSs) are ultra-polished fault surfaces that reflect visible light, thanks to their nanometer-scale surface roughness. They are often found in seismogenic fault zones cutting limestones and dolostones. Both natural and experimentally-produced fault-related MSs have been described in spatial association with ultrafine matrix (grain size <10µm), nanograins (<100nm in size), amorphous carbon, decomposition products of calcite/dolomite (i.e., portlandite, periclase), and larger but “truncated” clasts. However, the formation mechanism of MSs is still debated. Experiments show that MSs can develop both under seismic (slip rate ≈1 m/s; Fondriest et al., 2013; Siman-Tov et al., 2015; Pozzi et al., 2018) and sub-seismic (slip rate ≈0.1-10 µm/s; Verberne et al., 2014; Tesei et al., 2017) deformation conditions, involving various physical-chemical processes operating over a broad range of P-T conditions, strain, and strain rates.

To evaluate whether the MSs formed during the co-seismic (possibly associated with frictional heat pulses) or the inter-seismic (no heat pulses) phases where temperature might serve as a distinguishing factor, we assessed the thermal maturity of “bitumen” using biomarkers. We acquired data for natural and artificial MSs hosted within bituminous dolostones. We collected natural samples from faults with slip displacement from a few millimeters to a few meters, located in the Italian Central Apennines (Monte Camicia Thrust Zone, past burial depths up to ~3 km). We obtained experimentally-produced MSs by deforming powdered bituminous dolostones in a rotary shear apparatus (SHIVA, INGV) at sub-seismic (V = 10-4 m/s) and seismic (V = 1-3 m/s) slip rates for 1-3 m of slip, under room temperature and humidity conditions, and 20 MPa of normal stress.

We extracted solid bitumen of pre-oil window thermal maturity from the MSs and from the underlying slip zone of natural and artificial samples and we analyzed the bitumen using Gas Chromatography–Mass Spectrometry. We identified Steranes and other biomarkers based on relative retention time and measured peak heights to obtain thermal maturity parameters. By comparing different samples, changes in thermal maturity could be measured across slip zones bounded by the MS and possibly associated with frictional heat pulses during co-seismic slip.

Biomarker thermal maturity parameters are consistent with the immaturity of the host rock, which recorded a maximum ambient T < 100°C during diagenesis. In the experimental MSs produced at seismic slip velocity, where frictional heat pulses reached T∼400°C, thermal maturity of bitumen is higher than that of the entire slip zone and undeformed gouge. Higher thermal maturities were measured also in natural MSs but were not detected in the experimental MSs produced at sub-seismic slip velocity.

Chinello et al. (2023) proposed that the microstructures found in these slip zones recorded the main phases of the seismic cycle, from rapid co-seismic slip to post/inter-seismic viscous flow and fault strength recovery. The results presented here (1) confirm this interpretation, (2) show that the frictional heat pulse associated with seismic slip can be recorded by biomarkers thermal maturity of bitumen trapped in the fault MSs, and (3) some natural MSs are associated with heat anomalies caused by seismic ruptures.

How to cite: Chinello, M., Schito, A., Bowden, S. A., Tesei, T., Spagnuolo, E., Aretusini, S., and Di Toro, G.: Seismic Mirror-like Surfaces in bituminous dolostones (Central Apennines, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19532, https://doi.org/10.5194/egusphere-egu24-19532, 2024.

EGU24-428 | ECS | Orals | TS1.6

AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS 

Efe T. Ayruk, Muhammed Turğut, İlay Farımaz, Mehmet Köküm, Roger Bilham, and Uğur Doğan

The Mw 7.8 earthquake of 2023 ruptured the southern (main) branch of the East Anatolian Fault (EAF), followed by the Mw 7.6 earthquake on the northern (Çardak Fault) branch of the EAF nine hours later. In March, we installed ten carbon-rod extensometers across segments of the main and northern branches of the ruptured faults, where potential slip deficits were considered possible, to investigate if afterslip continues. It is important to measure afterslip to understand the behaviour of a fault, if any, resulting from stresses associated with local coseismic slip deficits.  Seven of these extensometers recorded less than a few millimetres of slip since March. In Göksun near the western end of the Çardak fault, we recorded more than a 25 mm of accelerating afterslip preceding local aftershocks of magnitude ≤Mw5.1.

The Mw 6.8 Elazığ-Sivrice earthquake of January 24, 2020, and the Mw 7.8 Kahramanmaraş earthquake of February 6, 2023, stopped in the Pütürge region, where it is named as Pütürge Gap. To understand why these two earthquakes terminated there, an array of five extensometers were ultimately deployed. One of the extensometers, which is 52 m long, shows that slip > 3.8 mm/yr continues at depth. Extensometers spaced 45 km apart recorded an eastward propagating subsurface creep event in September 2023. Four cGPS stations recording at 5 Hz were installed in an array to better investigate the subsurface evolution of aseismic slip on the Pütürge Fault in the village of Taşmış.

How to cite: Ayruk, E. T., Turğut, M., Farımaz, İ., Köküm, M., Bilham, R., and Doğan, U.: AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-428, https://doi.org/10.5194/egusphere-egu24-428, 2024.

EGU24-2299 | ECS | Posters on site | TS1.6

Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults 

Silvia Aldrighetti, Giulio Di Toro, and Giorgio Pennacchioni

Earthquakes are the result of propagation at ∽km s-1 of a rupture and associated slip at ∽m s-1 along a fault. The total energy involved in a seismic event is unknown, but qualitatively most of it is dissipated by rock fracturing and frictional heat. Seismic fracture energy G (J m-2) is the energy dissipated in the rupture propagation and can be estimated by the inversion of seismic waves. However, its physical significance remains elusive. G may include the contributions of both rock fracturing (energy to form new rock surfaces US, J m-2) and fault frictional heating (Q, J m-2) per unit fault area. Here we determine both US and Q in natural and experimental pseudotachylyte-bearing faults, following the approach used by Pittarello et al. (2008). In fact, in pseudotachylytes, or solidified frictional melts produced during seismic slip, (i) US is proportional to the surface of new fragments produced in both the slip zone and in the wall rocks, and (ii) Q is proportional to the volume of frictional melt.

The selected natural pseudotachylytes belong to the east-west-striking, dextral, strike-slip Gole Larghe Fault Zone (Adamello, Italian Alps). To estimate US we employed Electron Back-Scatter Electrons (EBSD), High Resolution Mid Angle Back-Scattered Electrons (HRMABSD) and Cathodoluminescence-Field Emission Scanning Electron Microscopy (CL-FESEM). In particular, CL-FESEM imaging reveals a microfracture network in the wall rocks that cannot be detected with the other techniques. In the pseudotachylyte-bearing fault, the microstructural analysis reveals (i) a high degree of fragmentation of the wall rock adjacent to the pseudotachylyte fault vein (formed along the slip surface), with clast size down to <90 nm in diameter, and (ii) a systematic difference in fracture density and orientation of the microfractures in the two opposite wall rock sides of the fault. In fact, in the northern wall rock the fracture density is low and the microfractures are oriented preferentially east-west, while in the southern wall rock the fracture density is high and oriented preferentially north-south. Instead, this asymmetric microfracture pattern is absent in the experimental pseudotachylytes produced by shearing pre-cut cylinders of tonalite (the rock that hosts natural pseudotachylytes) in the absence of a propagating seismic rupture. Thus, the formation of the asymmetric microfracture pattern is associated with the propagation of the seismic rupture and, therefore, can be used to estimate US.

In natural pseudotachylytes, fracture density decreases exponentially from the pseudotachylyte-wall rock contact towards the wall rock. The rock volumes with highest coseismic damage at the contact with the pseudotachylytes were assumed to represent the host-rock damage preceding frictional melting along the slip zone. Based on this assumption, US was estimated in the range 0.008-1.35 MJ m-2, while Q was estimated from the thickness of the pseudotachylyte vein to be ∽32 MJ m-2. In the case of the Gole Larghe Fault, numerical modelling of seismic rupture propagation yields fracture energies G in the range 8-67 MJ m-2 suggesting that US is a subordinate component of G and that most of the seismological fracture energy is heat.

How to cite: Aldrighetti, S., Di Toro, G., and Pennacchioni, G.: Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2299, https://doi.org/10.5194/egusphere-egu24-2299, 2024.

EGU24-3922 | ECS | Orals | TS1.6

Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence 

Fengjiang Ju, Haoran Meng, Xiaofei Chen, and Chunquan Yu

Advancing our understanding of earthquake nucleation process can shed lights on earthquake prediction, early warning, and hazard assessment. Foreshocks, which usually refer to smaller earthquakes that occur before an earthquake, exhibit good temporal and spatial correlations with the mainshock. Investigating the relationship between foreshocks and mainshocks can therefore provide valuable insights into earthquake nucleation mechanisms and contribute to the improvement of earthquake prediction and early warning capabilities.

A recent study on the 2019 Mw 7.1 Ridgecrest earthquake sequence suggests that immediate foreshocks often share similar waveforms to the P-waves of subsequent earthquakes, differing only in amplitude. This similarity is believed to arise from the fractal nature of fault fracture processes. Consequently, there might be many immediate foreshocks with similar waveforms hidden in ambient noise that have gone undetected. Two methods have been proved to be effective in detecting small events: the Matched Filter Technique (MFT) and the Source-Scanning Algorithm (SSA). The MFT relies on template events to detect small events by stacking cross-correlograms between the waveforms of the templates and potential events. The conventional MFT, however, requires that the small events be located in the vicinity of one of the template events and does not provide the accurate locations of detected events. On the other hand, SSA is a migration-based approach that involves stacking non-negative waveforms, envelopes, and their extended characteristic functions. However, due to their tendency to provide absolute locations, SSA are heavily influenced by the accuracy of the velocity model and struggle to accurately detect earthquakes that are obscured by noise.

In our study, we prioritize the accuracy of relative event locations when studying the relationship between foreshocks and mainshocks. To address this concern, we have developed an advanced method that combines the strengths of cross-correlation and beamforming analyses. This method allows us to detect and relatively locate small seismic events simultaneously using dense array data. For the 2021 Ms 6.4 Yangbi  aftershock sequence, we first compute the cross-correlograms of the contentious records with the P-waves/S-waves of the target earthquake, respectively. We then grid searches around the hypocenter using N-th root stacking to detect and locate the immediate foreshocks. Upon detecting numerous immediate foreshocks, we proceed to statistically quantify the earthquake nucleation process or investigate the nucleation mechanism.

How to cite: Ju, F., Meng, H., Chen, X., and Yu, C.: Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3922, https://doi.org/10.5194/egusphere-egu24-3922, 2024.

EGU24-4427 | Orals | TS1.6

Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults 

Kevin P. Furlong, Matthew W. Herman, and Kirsty A. McKenzie

A general correlation between maximum co-seismic fault slip and fault length has been well constrained by observations from numerous earthquakes occurring on many crustal faults. In spite of this global consistency, there are notable examples of co-seismic fault slip magnitudes that far exceed the expected maxima for the fault dimensions.  Two instances of extreme fault slip that occurred on short-to-moderate length upper-plate faults in subduction systems, where the megathrust lies at shallow depths are the 2016 Kaikoura (New Zealand) earthquake, and the 1855 Wairarapa (New Zealand) earthquake. In both cases, co-seismic fault slip was 5 to 10 times greater than expected from the rupture length - fault slip scaling relationships. The typical crustal fault model  is a fault with a brittle-to-ductile transition at depth; in this scenario, co-seismic slip is inhibited by viscous resistance from the deeper, ductile component of the fault.  In contrast, the tectonic characteristics of faults that experience extreme co-seismic slip, involve upper plate faults that truncate against the megathrust at seismogenic depths (i.e. are fully frictionally coupled over their entire depth extent). During a megathrust earthquake, the plate interface unlocks and upper-plate faults that extend to the ruptured plate interface transiently experience free-slip boundary conditions on both their upper (surface) and lower (megathrust) ends. As a result, such upper-plate faults can potentially experience full strain release (and therefore maximum slip), independent of their length. For appropriately oriented faults, this effect may be enhanced by co-seismic stress changes associated with the megathrust earthquake. 

Geologic evidence of large displacement (and/or displacement rate) upper-plate faults in other subduction systems indicates this process may commonly occur. One example is a set of upper-plate faults along the Cascadia margin (near Newport, Oregon), that have strike-slip geologic slip rates, averaged over 10s of thousands of years, exceeding tens of mm/yr and approaching local plate convergence rates. These upper-plate Cascadia faults are also located where the plate interface is sufficiently shallow and seismogenic, indicating that these high-slip, upper-plate faults are likely frictionally locked over their entire depth range. In spite of the high overall slip rates of these upper-plate faults, because they are locked along their entire depth extent between earthquakes,  they may be unrecognized by inter-seismic geodetic observations.

How to cite: Furlong, K. P., Herman, M. W., and McKenzie, K. A.: Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4427, https://doi.org/10.5194/egusphere-egu24-4427, 2024.

EGU24-4550 | Posters on site | TS1.6

Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations 

Yariv Hamiel and Roger Bilham

We use geodetic measurements to characterize aseismic deformation along the western boundary fault of the Dead Sea pull-apart basin, which is located at the southern part of the sinistral Dead Sea Fault. This research provides constraints on patterns and timescales of deformation and its dependence on regional tectonics and the rheology of the upper crust. We use creepmeter, GNSS, InSAR and airborne LiDAR observations and show transient aseismic slip on the western boundary fault of the Dead Sea basin. A biaxial creepmeter with a 30 s sampling interval was installed in early 2021 showing high extensional deformation (an average rate of ~8.6 mm/yr), which is consistent with the ~30 cm of subsidence recorded 2017-2019 differential LiDAR data. The data imply modulated slip on a 60° dipping normal fault with maximum slip rates of ~0.5 µm/hour starting in late August and varying close to zero in late April. We attribute these large movements to local tectonics, sediment compaction, thermo-elastic response and dissolution of subsurface salt responsible for the formation of sink-holes in the region. The creepmeter measurements also show some sinistral deformation with an average rate of ~2.1 mm/yr, comparable to the rate of 2.5±0.4 mm/yr that was observed for the Sedom Fault, the southernmost segment of the western boundary fault, using GNSS data. Several minor creep events were detected by the creepmeter. The 19 Feb 2022 creep event lasted more than an hour following heavy rain in this area with abrupt sinistral slip of ~2.5 mm preceding dilation and dip-slip by 20 minutes. Small Baseline Subset (SBAS) analysis of InSAR data reveals up to 7mm/yr of line-of-sight deformation across the western boundary fault, north of the creepmeter. It also reveals high subsidence rate (up to ~20 mm/yr) along the southern shores of the Dead Sea Lake that can be explained by high compaction rate of clay sediments and reduction of pore pressure along the lake shores. This high subsidence rate is also observed in our near shore GNSS stations. Our results indicate that deformation within the Dead Sea basin is not solely controlled by the active tectonics. The observed vertical deformation is apparently modulated by the response of sediments to seasonal variations of local conditions.

How to cite: Hamiel, Y. and Bilham, R.: Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4550, https://doi.org/10.5194/egusphere-egu24-4550, 2024.

EGU24-4561 | Orals | TS1.6

Boso seismicity swarm propagation driven by slow slip stress change 

Baptiste Rousset, Asaf Inbal, Roland Bürgmann, Naoki Uchida​​, Anne Socquet, Lou Marill, Takanori Matsuzawa, and Takeshi Kimura

The interactions between aseismic slip and seismicity is mostly studied during postseismic afterslip associated with the generation of aftershocks following large earthquakes. However because of the large stress perturbations produced by the coseismic rupture, it remains difficult to distinguish the contribution of the coseismic stress perturbation and the effects of stresses induced by the afterslip on the triggering of aftershocks. Studying seismicity triggered by slow slip events enables us to understand the direct effect of aseismic slip on the generation of the seismicity. While most subduction slow slip events are deep-seated, at the down-dip edge of seismogenic zones accompanied by tectonic tremors, some are also observed at shallower depths associated with seismic swarms. Among them are the well-studied Boso slow slip events located on the Sagami trough, between 10 and 20 km depth. Recorded every ~4 years since 1996, they are always accompanied by swarms of Mw 1 to 5 earthquakes on their northern and western flanks. Being located right beneath the Boso Peninsula coastline, the kinematics of these slow slip events is particularly well imaged by dense GNSS and tiltmeter networks. In this study, we model the time dependent aseismic slip of the 2018 Boso slow slip event, with the largest moment released of all Boso slow slip events, by inverting time step by time step the slip on the fault with joint GNSS and tiltmeter data. We do not impose arbitrary temporal smoothing in the inversion and find that the well constrained fault slip is first growing and then migrating southwestward with a migration speed of ~ 2 km/day. In order to model the interaction with the seismicity, we compute the Coulomb stress change due to the transient slip on receiver faults located in 9 cubes centered in the seismicity swarm and parallel to the subduction interface. From June 2nd to June 18th, the seismicity is migrating up-dip at a rate of 1 km/day. This migration period coincides with the peak slip rate and with Coulomb stress produced by the slow slip migrating updip together with the seismicity, indicating a causal relationship. Adopting a rate and state friction formalism to explain the nucleation of the seismicity, we finally investigate the ensemble of parameters, in particular the constitutive parameter that relates changes in stress to logarithmic changes of slip velocity, the effective normal stress and the tectonic stressing rates, that can explain the seismicity rate. 



How to cite: Rousset, B., Inbal, A., Bürgmann, R., Uchida​​, N., Socquet, A., Marill, L., Matsuzawa, T., and Kimura, T.: Boso seismicity swarm propagation driven by slow slip stress change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4561, https://doi.org/10.5194/egusphere-egu24-4561, 2024.

EGU24-5061 | ECS | Orals | TS1.6

Complex Frictional Behavior of Clay and Implications for Slow Slip  

Giuseppe Volpe, Cristiano Collettini, Jacopo Taddeucci, Chris Marone, and Giacomo Pozzi

The shallowest region of subduction megathrust accommodates deformation by a spectrum of seismic modes including continuous aseismic creep and peculiar seismic phenomena as slow slip events. However, the mechanisms behind these phenomena remain enigmatic because they are not explained by conventional frictional models. This because the shallowest regions of subduction zones are characterized by unconsolidated, clay-rich lithologies that, nominally, cannot nucleate seismic events due to their frictionally weak and rate-strengthening attributes. Here we present laboratory friction experiments showing that clay-rich experimental faults with bulk rate strengthening behavior and low healing rate can contemporaneously creep and nucleate slow slip events. These instabilities are self-healing, slow ruptures propagating within a thin shear zone and driven by structural and stress heterogeneities. We propose that the bulk rate-strengthening frictional behavior promotes the observed long-term aseismic creep whereas local frictional mechanism causes slow rupture nucleation and propagation. Our results illustrate the complex behavior of clay-rich lithologies, providing a new paradigm for the interpretation of the genesis of slow slip as well as significant implications for seismic hazard.

How to cite: Volpe, G., Collettini, C., Taddeucci, J., Marone, C., and Pozzi, G.: Complex Frictional Behavior of Clay and Implications for Slow Slip , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5061, https://doi.org/10.5194/egusphere-egu24-5061, 2024.

The acoustic emissions (AEs) produced during the shearing of granular materials reflect the accumulation and release of stress, offering valuable insights into the failure mechanisms of seismic faults and stick-slip-controlled landslides. While various characteristics such as amplitude, energy, counts, and frequency of AE signals generated by stick-slip have been studied, the stress changes corresponding to different frequency AEs at various stages of the stick-slip process remain unclear. This knowledge gap hinders our understanding of the precursory signals leading to stick-slip failure. In order to enhance our comprehension of the physical mechanisms underlying granular stick-slip, we conducted monitoring of both mechanical and AE signals using high-frequency (2 MHz) synchronous acquisition. This was done during the constant-speed shearing of packs containing uniform glass beads of different sizes under varying normal stresses. Our findings revealed an accelerated release rate of AE energy in tandem with sample volume dilatation. Additionally, the stress drop during stick-slip increased with higher normal stress and particle size. This study identified three distinct events during a single cycle of stick-slip: main slip, minor slip, and microslip. We analyzed the AE frequency spectra associated with each of these events. Main slip and minor slip correlated with stress drop, generating high-frequency AEs (approximately several hundred kHz). In contrast, microslip produced lower AE frequencies (around tens of kHz) and exhibited stress strengthening. These characteristics, overlooked in prior studies due to low-frequency acquisition, suggest that microslip is primarily a result of sliding on grain contacts, while main slip and minor slip arise from the breakage and reformation of force chains. The low-frequency AEs from microslip may serve as a crucial precursor to seismic faults and landslides, providing a deeper understanding of the granular stick-slip phenomenon.

How to cite: Gou, H. and Hu, W.: Detection of Stick-Slip Nucleation and Failure in Homogeneous Glass Beads Using Acoustic Emissions in Ring-Shear Experiments: Implications for Recognizing Acoustic Signals of Earthquake Foreshocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5252, https://doi.org/10.5194/egusphere-egu24-5252, 2024.

EGU24-5921 | ECS | Posters on site | TS1.6

Interaction of fault slip with fast fluid pressure transients in subduction zones 

Avinash Gupta, Nikolai M. Shapiro, Jean-Paul Ampuero, Gaspard Farge, and Claude Jaupart

This study investigates the dynamic interplay between fluids and fault slip transients in the portion of subduction zones subject to slow earthquakes. The permeable subduction interface in this region is believed to be saturated with fluids supplied by metamorphic dehydration reactions in the downgoing plate. Following Farge et al. (2021), we consider a model of a heterogeneous subduction channel filled with low-permeability plugs that behave as elementary fault-valves. Such a system is characterized by an intermittent fluid transport and rapid and localized pressure transients. Episodic rapid build-ups and releases of the fluid pressure affect the frictional strength on the fault and can result in transient slip accelerations. To study the possible effect of episodic fast fluid pressure variations on fault slip, we use numerical simulations in a 2D in-plane shear geometry. The fault is governed by rate-and-state friction, with velocity-strengthening steady-state properties, and is forced with time and spatially variable pore fluid pressure. In an initial set of tests, we show that periodic pore pressure oscillations can accelerate the fault slip akin to observed slow slip events. We then investigate how the fault slip responds to more complex and “realistic” pore pressure histories generated by the dynamic permeability model of Farge et al. (2021). Our results underscore the possible role of input fluid flux and permeability structure in determining the variations of fault slip and, in particular, in facilitating the slow slip events. 

How to cite: Gupta, A., Shapiro, N. M., Ampuero, J.-P., Farge, G., and Jaupart, C.: Interaction of fault slip with fast fluid pressure transients in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5921, https://doi.org/10.5194/egusphere-egu24-5921, 2024.

EGU24-7813 | Posters on site | TS1.6

The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia 

Manel Prada, Sara Martínez-Loriente, Jonas B. Ruh, and Valentí Sallarès

The present-day Eurasia-Africa plate convergence offshore SW Iberia gives rise to a diffuse plate boundary marked by deep lithospheric thrust and strike-slip faults. The Horseshoe Abyssal Plain Thrust (HAT) stands out as a key structure accommodating plate convergence, and it has been the site of deep (> 30 km depth) and large magnitude (Mw > 6) earthquakes. Additionally, the HAT has been proposed to be the source of the 1755 Lisbon earthquake (estimated Mw≥8.5), one of the most destructive earthquakes and tsunami in the history of Europe. The geometry of the fault and the physical properties of rocks surrounding it have been determined through tomographic models derived from controlled-source seismic data. Although large earthquakes along the HAT primarily occur at considerable depths within the peridotitic mantle (~40 km depth), the fault intersects a region of serpentinized mantle at shallower depths (10-20 km depth). In contrast to peridotite that undergoes seismic deformation, the frictional behaviour of serpentinized peridotite depends on factors such as pressure, water content, temperature, and slip velocity. Laboratory measurements indicate that serpentinite transitions from rate-strengthening behaviour at plate tectonic rates to rate-weakening at seismic slip rates. This dual nature suggests that large deep earthquakes, nucleated in pristine peridotite, could rupture seismically through the weaker serpentinized peridotite. While this mechanism has been proposed to explain the HAT's potential to generate large tsunamigenic earthquakes, it remains untested. In this study, we use dynamic rupture numerical simulations to investigate the role of serpentinized peridotite in the rupture process and the tsunamigenic potential of the HAT. In particular, we explore various frictional scenarios to determine the slip pattern necessary to account for the previously estimated tsunamigenic uplift associated with the 1755 Lisbon earthquake.

How to cite: Prada, M., Martínez-Loriente, S., B. Ruh, J., and Sallarès, V.: The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7813, https://doi.org/10.5194/egusphere-egu24-7813, 2024.

Topographic features such as seamounts can influence the buoyancy of the slab and the short- and long-timescale mechanical properties of the subduction interface. How seamounts in the trench interact with the upper plate accretionary wedge during subduction— their stress field, their potential for ‘decapitation’, and their ability to host large megathrust earthquakes— is not fully understood. We utilize exhumed rocks to investigate seamount–upper plate interactions at shallow subduction interface conditions. 

We focus on a 250-m-thick cross-section of deformed, weakly metamorphosed basalt, limestone, chert, argillite and greywacke exposed in the inboard part of the Chugach accretionary complex near Grewingk glacier, southern Alaska. Temperatures from Raman spectroscopy on graphite yield ~260°C, suggesting deformation and metamorphism down to ~15-20 km depth. Detrital zircon data from greywacke lenses within and outside the shear zone overlap within error suggesting emplacement over less than ~1 m.y. at ~167 Ma. 

Basalts in the shear zone are dismembered into ~3 slices up to 35 m thick, all of which contain limestone patches suggesting the basalt is derived from the seamount’s very top (limited decapitation). The basalt slices are bounded by high-strain melange-like shear zones up to 25 m thick, interpreted to represent décollements along which the seamount slices were underplated. These mélange belts exhibit a block-and-matrix texture with a macroscopically ductile argillite and chert matrix, and pervasively disaggregated and brittlely deformed greywacke and basalt lenses. Both the matrix and the blocks show several generations of dilational and shear veins, suggesting high fluid pressures and low differential stresses. Features suggesting deformation at fast (potentially seismic) strain rates include fluidized cataclasites, but these do not extend along strike for more than 0.25 m and do not occur within the larger (m-to-dm-scale) basalt lenses, suggesting that large-magnitude earthquakes were limited during seamount underplating. Instead, the observed mix of brittle and macroscopically ductile deformation at high fluid pressures is more consistent with a potential record of shallow tremor and slow slip.

Our findings support geophysical observations and numerical models that suggest relatively weak mechanical and seismic coupling between seamounts and the overriding plate, and are consistent with recent suggestions (e.g. for the Hikurangi margin) that sediment envelopes around subducting seamounts are conducive to slow slip and tremor.

How to cite: Behr, W., Akker, I. V., and Rast, M.: Deformation processes during seamount dismemberment and underplating along the shallow subduction interface: a case study from the Chugach Complex, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8244, https://doi.org/10.5194/egusphere-egu24-8244, 2024.

EGU24-8731 | ECS | Posters on site | TS1.6

Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet 

Xinze Li, Yongsheng Zhou, Lining Cheng, and Jianfeng Li

A large number of tourmaline fault mirrors are exposed in the north-south normal fault system in the southern part of the Tibetan Plateau. Microstructure analysis shows that the tourmaline fault mirror has the characteristics of co-seismic high speed friction sliding and high temperature plastic rheology. In order to reveal the mechanical process of friction-rheological strength and co-seismic slip of tourmaline fault, the frictional and rheological experiments were carried out on the gas-medium triaxial high temperature and high pressure experimental system using undeformed tourmaline in southern Tibet to determine the formation conditions of tourmaline fault mirror. The effective normal stress of frictional experiments is 100Mpa.The pore water pressure is 30MPa. The temperature is 25-500℃, and the shear slip rate is switched between 1μm·s-1, 0.2μm·s-1, 0.04μm·s-1. The experimental results show that stick-slip occurs at 200-350℃, and the speed weakens at 400℃ and 500℃. The rheological experiment temperature is 850-950℃. The pressure is 300MPa, and the strain rate is switched between 2*10-5s-1, 1*10-5s-1, 5*10-6s-1, 7.5*10-6s-1. The experimental results show that the natural tourmaline sample is mainly fractured flow under the experimental conditions. The strength of hot-pressed dry tourmaline sample decreases with increasing temperature. The rheological strength of water samples synthesized by hot pressing was significantly reduced.

How to cite: Li, X., Zhou, Y., Cheng, L., and Li, J.: Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8731, https://doi.org/10.5194/egusphere-egu24-8731, 2024.

EGU24-8767 | ECS | Posters on site | TS1.6

A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data 

Roxane Tissandier, Adriano Gualandi, Lauro Chiaraluce, Enrico Serpelloni, Mike Gottlieb, Catherine Hanagan, and Chris Marone

Low-angle normal faults (i.e. with a dip < 30°) were assumed to have a very low seismic potential (Sibson et al., 1985). However, several observations have shown that earthquakes and aseismic slip can occur along such faults. For instance, the Alto Tiberina Fault (ATF), a 60-km long normal fault with a 15° low angle dip located in the active sector of the Northern Apennines (Italy), is seismically active as well as is actively accommodating part of the Apennines extensional strain. However, the relative contribution of seismic and aseismic slip on it is still unclear. The central and northern Apennines experienced several seismic sequences in the recent decades and a Mw ∼ 4.6 aseismic event accompanied by a seismic swarm of similar or smaller size was also recorded in 2013-2014 along two synthetic and antithetic fault in the hanging-wall of the ATF (Gualandi et al., 2017). The interactions between such minor conjugate faults and the ATF compose a system undergoing complex behavior making the area an ideal candidate to improve our understanding of interactions between different slipping modes. We benefit from data of the Alto Tiberina Near Fault Observatory (TABOO-NFO; Chiaraluce et al., 2014) looking for aseismic events on the ATF and its surrounding faults. The dense network of GNSS, seismometers and borehole strainmeters provides a rarely attained high spatial (inter-distance < 10km) and temporal (from 2009 to nowadays) resolution framework enabling the study of the ATF fault system slip history. We search for transients with a semi-automatic detection tool of slow slip events based on kinematic inversions of strainmeters time series. We also test if these events interact with larger seismic events of the region. We present the strain time series processed with the EarthScope Strain Tools (EarthScope Consortium) and the preliminary signals detected with our tool. The fine analysis of the ATF would help better constraining the behavior of faults and more generally large events. 

How to cite: Tissandier, R., Gualandi, A., Chiaraluce, L., Serpelloni, E., Gottlieb, M., Hanagan, C., and Marone, C.: A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8767, https://doi.org/10.5194/egusphere-egu24-8767, 2024.

EGU24-9007 | Orals | TS1.6 | Highlight

A mechanical insight into the continuous chatter of a fault volume 

Harsha Bhat, Michelle Almakari, Navid Kheirdast, Carlos Villafuerte, and Marion Thomas

In recent decades, there has been a proliferation of observations related to spatiotemporally intricate slip events occurring in fault systems. These events encompass a spectrum of transient energy releases, ranging from slow slip events to low-frequency earthquakes (LFEs) and tremors, in addition to the more familiar creep and fast ruptures. The prevailing focus in recent research has been to interpret these events by considering variations in frictional behavior along the fault plane.

However, it is crucial to acknowledge the inherent geometric complexity of fault systems across multiple scales. Recent studies have illuminated the significance of incorporating a fault volume or damage zone surrounding the fault in the analysis of slip dynamics. In the context of this study, we endeavor to investigate the influence of "realistic" fault geometry on the dynamics of slip events. To achieve this, we approach the problem from three interrelated perspectives:

  • Forward Source Modeling: We employ forward source modeling techniques to simulate and understand the behavior of slip events.
  • Bridging Source Modeling and Observations: We establish a connection between our source modeling and observed data by generating synthetic surface records that can be compared to actual observations.
  • Energy Budget Analysis: We meticulously analyze the variations in the energy budget that occur throughout the earthquake cycles to gain insights into the mechanics of slip events.

Our primary objectives include deciphering how deformation within the volume is accommodated by both the off-fault damage zone and the primary fault. Specifically, we aim to determine the proportion of the supplied moment rate that is absorbed by off-fault fractures during an earthquake cycle. Additionally, we seek to unravel how the diverse sequences of complex behavior observed on the fault plane manifest in the signals recorded by seismic stations. This entails assessing the distinct contributions of the main fault and off-fault fractures to the radiated signals detected at the monitoring stations. Lastly, we delve into the evolution of the medium's energy budget throughout the earthquake cycles and evaluate the dissipative contribution of off-fault fractures to ascertain their energetic role in the context of earthquake cycles.

How to cite: Bhat, H., Almakari, M., Kheirdast, N., Villafuerte, C., and Thomas, M.: A mechanical insight into the continuous chatter of a fault volume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9007, https://doi.org/10.5194/egusphere-egu24-9007, 2024.

EGU24-9169 | ECS | Posters on site | TS1.6

A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle 

Silvio Pardo, Elisa Tinti, Martijn Van den Ende, Jean-Paul Ampuero, and Cristiano Collettini

Fluid induced seismicity represents a significant issue for numerous activities related to geo-energy production. Enhanced geothermal systems, enhanced oil recovery, disposal of wastewater and carbon dioxide capture and storage are associated with subsurface fluid injection that can change the state of stress within the crust and can induce or trigger earthquakes. In several regions, M>3 earthquakes occurred following fluid injection, whereas in others seismicity has been accompanied by slow slip events. Although several mechanisms have been proposed to explain slow slip associated with fluid injection, the conditions leading to the observed spectrum of fault slip behavior still remain elusive. Here we used a quasi-dynamic boundary element method, the QDYN earthquake cycle simulator, to model the response of a fault governed by rate-and-state friction to fluid injection within a reservoir. We imposed low long-term loading rates to simulate a fault located in an area of slow active deformation, leading to natural earthquake cycles with very long recurrence times. We then imposed fluid pressure perturbations (one-way coupling) at different stages of the seismic cycle, to evaluate pore-pressure effects on the triggering of the next event. 

Our results show that for injection at high fluid pressure, earthquakes are in general immediately triggered (during injection or soon after) irrespective of the stage (early or late) of the seismic cycle, whereas at lower fluid pressure fast triggering is observed only when injecting in the late stages of the seismic cycle. Our models produce a spectrum of fault slip behavior, from regular to slow earthquakes. The latter are observed for specific fluid pressure, flow rate and injection time relative to the seismic cycle. The physics underlying this complex slip behavior remain to be explained, and further studies are required to define the injection conditions that favor the occurrence of slow slip instead of regular earthquakes.

How to cite: Pardo, S., Tinti, E., Van den Ende, M., Ampuero, J.-P., and Collettini, C.: A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9169, https://doi.org/10.5194/egusphere-egu24-9169, 2024.

EGU24-9437 | Orals | TS1.6

Creeping sections on continental strike slip faults as the signature of deep fluid upwelling 

Romain Jolivet, Dmitry Garagash, Dublanchet Pierre, and Jorge Jara

Aseismic slip has been recognized over the last 50 years as one of the modes of elastic stress accommodation by large tectonic faults. Long strike slip faults have been imaged with InSAR and scrutinized with GNSS networks and creepmeters, revealing the strikingly ubiquitous occurrence of aseismic slip globally. From the 600-km-long creeping section of the Chaman to the 70 km-long Ismetpasa creeping section along the North Anatolian Fault, geodetic imaging illustrates the rich behavior of such aseismic slip, from mm-scale transient episodes of slip to seemingly continuously sliding fault segments.

Most models explaining the occurrence of aseismic slip along continental faults rely entirely on an ad hoc parameterization of the frictional rheology of the fault. While the friction law governing slip along faults has been determined from laboratory experiments, the inference of the constitutive parameters of such friction law entirely derives from reproducing geodetic data in most cases. In particular, most creeping sections are interpreted as the signature of rate-strengthening material, diffusing stress through stable sliding. However, most rocks at seismogenic depths exhibit a rate-weakening behavior and some even show transient episodes of slip incompatible with purely strengthening properties. In addition, other mechanisms, including complex geometric configuration of faults or fluid circulation may offer the conditions for slow slip. Therefore, the direct inference of constitutive properties of a fault zone from kinematic observations may not be simple.

We propose here a model in which upwelling of fluids sourced in the upper mantle through a vertical fault zone leads to the conditions for slow slip, irrespective of the fault constitutive properties. We map aseismic slip along three different fault zones, including the North Anatolian Fault (Turkiye), the San Andreas Fault (USA) and the Leyte fault (Philippines) and find a systematic relationship between the effective locking depth and the occurrence of aseismic slip. Our model explains this modulation of locking depth along strike and the subsequent modulation of surface shear stressing rate with the along strike variation in the mantle fluid source. This model applied to fault segments with relatively high mantle fluid source leads to low effective normal stress, large nucleation size of a frictional instability, and predicts occurrences of shallow aseismic slip. We perform numerical modeling to show that the critical parameter is the flux of upwelling fluid through the fault zone, which increase leads to the widening of the near-surface region of aseismic slip and transition to full-fault aseismic slip at large enough flux. We finally discuss the potential sources of fluids explaining such behavior.

How to cite: Jolivet, R., Garagash, D., Pierre, D., and Jara, J.: Creeping sections on continental strike slip faults as the signature of deep fluid upwelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9437, https://doi.org/10.5194/egusphere-egu24-9437, 2024.

EGU24-9595 | Orals | TS1.6

Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments 

Corentin Noël, Pierre Dublanchet, and François Passelègue

Deformation within the upper crust is mainly accommodated through slip on fault systems. These systems can accommodate slip via different modes, going from aseismic creep (i.e., stable motion) to dynamic earthquake (i.e., unstable motion). Notably, a single fault is not confined to a specific slip mode, as recent geodetic observations have indicated that a single fault can exhibit both stable and unstable motions. The distinct slip behaviours have been attributed to fault spatial heterogeneity of the frictional properties, rheological transitions, or geometrical fault complexities.

To comprehensively characterize the impact of frictional heterogeneities, we deformed heterogeneous fault samples in a triaxial apparatus, at confining pressure ranging from 30 to 90 MPa. The fault planes, sawcut at a 30° angle from the sample axis, consisted of two materials: granite and marble. Experiments were conducted for both marble asperities embedded in granite and vice versa, alongside homogeneous fault samples of single lithology. The selection of granite and marble was based on their different mechanical and frictional characteristics, with granite exhibiting seismic behaviour, while marble demonstrated aseismic behaviour across the pressure range tested.

Our findings reveal that the stress drops of seismic events are dependent on fault composition, with faults containing higher granite content exhibiting larger seismic events. In addition, by coupling the inversion of the kinematic slip from strain-gauge measurements and the records of acoustic activity during experiments, we demonstrate that the nucleation and propagation of seismic events are significantly influenced by lithological heterogeneity on the fault plane. In the case of homogeneous faults, the seismic event nucleation is relatively straightforward, initiating in the highest stressed region and propagating uniformly. Conversely, heterogeneous faults display more intricate nucleation patterns, often featuring multiple nucleation regions converging into a major dynamic event. The dynamic event propagation is expedited when traversing granite areas and more restrained within the marble. Remarkably, our experiments demonstrate that heterogeneities are required in order to induce earthquake afterslip. These results emphasize the crucial role of fault heterogeneity in earthquake nucleation and propagation, highlighting that even minor lithological heterogeneities are sufficient to complicate laboratory earthquake dynamics.

How to cite: Noël, C., Dublanchet, P., and Passelègue, F.: Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9595, https://doi.org/10.5194/egusphere-egu24-9595, 2024.

EGU24-9961 | Orals | TS1.6 | Highlight

Do earthquakes start with precursory slow aseismic slip? 

Quentin Bletery and Jean-Mathieu Nocquet

The existence of an observable precursory phase of aseismic slip on the faults before large earthquakes has been debated for decades. We conducted a global search for short-term precursory slip in GPS data. We summed the displacements measured by 3026 high-rate (5-minutes sample) GPS time series—projected onto the displacements expected from precursory slip at the hypocenter—during 48 hours before 90 (moment magnitude ≥7) earthquakes. Our approach revealed a ≈2-hour-long exponential acceleration of slip before the ruptures, suggesting that large earthquakes do start with a precursory phase of slip acceleration. The results have since been questioned as being due to an unfortunate combination of common mode noise in GPS time series. We investigate this possibility along with complementary tests to quantify the likelihood of the proposed pre-slip and the common mode hypotheses.

How to cite: Bletery, Q. and Nocquet, J.-M.: Do earthquakes start with precursory slow aseismic slip?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9961, https://doi.org/10.5194/egusphere-egu24-9961, 2024.

EGU24-10783 | Orals | TS1.6

Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening. 

Einat Aharonov, Pritom Sarma, Renaud Toussaint, and Stanislav Parez

Many previous studies have explored the role of granular media in controlling friction of faults. A gap exists though in understanding the failure process and sliding of a fluid-saturated fault gouge. Here we use a coupled 2D DEM-fluid code to simulate fault-gouge as a layer of grains, sheared by a constant stress boundary. We explore and compare two scenarios: 1) a dry granular layer, in which shear stress on the top wall is incrementally increased, or 2) a fluid-saturated granular layer, into which fluid is injected, so that fluid pressure is incrementally increased. Once the applied stress/pressure is high enough, the layer fails and starts accelerating, until it reaches a steady-state sliding rate (determined by the layers’ velocity-strengthening friction). We next incrementally step-down the shear stress or fluid pressure. Consequently, the slip-rate is observed to slow down linearly with decreasing stress/pore-pressure, until the layer finally stops, at a stress/pressure lower than that required to initiate the failure. Both the dry and fluid-saturated granular systems exhibit two main behaviors: 1) velocity-strengthening friction, following the mu(I) rheology, 2) a hysteresis effect between friction and velocity, porosity and grain coordination numbers. The hysteresis and strain-rate dependence agree with previous experimental, numerical and theoretical results in dry granular media, yet our work suggests these behaviors extend to fluid-filled granular media. We theoretically predict the transient and steady-state observations for dry and fluid-saturated layers, using the mu(I) friction rheology with an added component of hysteresis. Importantly, we show that fluid-filled faults exhibit a process which is absent in dry systems: fluid-injected layers may exhibit failure delay, with some time passing between pressure rise and failure. We link this delay to pre-failure creeping dilative strain, interspersed by small dilative slip events. Our numerical and analytical results may explain: (i) field measurements of fault creep triggered by fluid pressure rise (e.g. via injection), (ii) fault motion which is triggered by fluid-injection but continues even after fluid pressure returns to its pre-injection level. (iii) observed delay prior to failure in fluid-injection experiments.

How to cite: Aharonov, E., Sarma, P., Toussaint, R., and Parez, S.: Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10783, https://doi.org/10.5194/egusphere-egu24-10783, 2024.

EGU24-10887 | Orals | TS1.6

Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks 

Paul Antony Selvadurai, Antonio Felipe Salazar Vasquez, Patrick Bianchi, Claudio Madonna, Leonid Germanovich, Alexander M. Puzrin, Carlo Rabaiotti, and Stefan Wiemer

A growing number of observations made using geodetic approaches have been able to detect large preparatory regions that experience accelerated deformation prior to and in close proximity to an earthquake’s hypocenter. An uptick in localized seismicity has also been observed in these regions and represents an opposite end-member of the spectra of deformation, in both space and time, from the opposite broad and slow process. If and how these preparatory observations are linked are not well understood. To study this, we conducted a triaxial experiment on a granitic rock sample instrumented with calibrated acoustic emission (AE) sensors and a distributed strain sensing (DSS) method using fibre optics. These two technologies were sensitive to seismic (100 kHz to 1 MHz) and aseismic (DC to 0.4 Hz) deformation at our sample scale and these were monitored as it was loaded and experienced brittle shear failure. DSS measurement allowed us to visualize the emergence of slow, heterogeneous strain fields that localized well before the failure of the sample. In the early stages of localized deformation, the regions exhibiting preferential damage were growing and doing so without producing seismicity. However, when approaching failure, these regions accommodating slow deformation began to accelerate and now produced clusters of seismicity. The cumulative seismic moment of the precursory seismicity was a fraction of the total anelastic deformation (< 0.1%) precluding the runaway dynamic failure. We also examined the clustering and frequency-magnitude distribution of the seismicity with respect to the localized strain field. In the later stages, moments prior to nucleation, the b-value begins to drop and becomes anti-correlated to the rapidly accelerating average volumetric strain rate measured using the DSS array. This observation better constrains the hypothesis that dilation of the relatively large preparation zone can host larger precursory earthquakes therein. These findings can help constrain models that better replicate the physics associated with the large spectrum of brittle deformation and will in turn help with our understanding of preparatory earthquake processes.

How to cite: Selvadurai, P. A., Salazar Vasquez, A. F., Bianchi, P., Madonna, C., Germanovich, L., Puzrin, A. M., Rabaiotti, C., and Wiemer, S.: Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10887, https://doi.org/10.5194/egusphere-egu24-10887, 2024.

Natural fault zone are complex objects. They not only consist of a fine-grained narrow fault core where the extensive shearing is observed, but it is also surrounded by pervasively fractured rocks, within an intricate 3-D geometry. If fault slip behavior is intrinsically linked to the properties of the fault core, the complex structure of fault zone systems impacts the rheological properties of the bulk, which influence the modes of deformation, and slip, as underlined by recent observations. Fault zone structure is therefore of key importance to understand the mechanics of faulting. Within the framework of a micromechanics based constitutive model that accounts for off-fault damage at high-strain rates, this numerical study aims to assess the interplay between earthquake ruptures along non-planar fault and the dynamically evolving off‐fault medium. We consider 2D inplane models, with a 1D self-similar fault having a root mean square (rms) height fluctuations of order 10-3 to 10-2 times the profile length. We explore the dynamic effect of fault-roughness on off-fault damage structure and on earthquake rupture dynamics. We observe a high‐frequency content in the radiated ground motion, consistent with strong motion records. It results from the combined effect of roughness-related accelerations and decelerations of fault rupture and slip rate oscillations due to the dynamic evolution of elastic moduli. These scenarios underline the importance of incorporating the complex structure of fault zone systems in dynamic models of earthquakes, with a particular emphasis on seismic hazard assessment.

How to cite: Thomas, M. Y. and S. Bhat, H.: Combined Effect of Brittle Off-Fault Damage and Fault Roughness on Earthquake Rupture Dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12095, https://doi.org/10.5194/egusphere-egu24-12095, 2024.

EGU24-12752 | Posters on site | TS1.6

Healing of fault surfaces: a field vs. experimental perspective 

Telemaco Tesei, Giancarlo Molli, Silvia Mittempergher, Giacomo Pozzi, and Francesca Remitti

“Fault healing” is the ability of fault rocks to recover strength after rupture, due to a combination of several physical processes that include cementation, compaction, asperity growth etc. Healing is fundamental in the earthquake physics because it allows for the repeated accumulation of energy along faults over multiple seismic cycles. Fault healing is commonly studied in the laboratory, through Slide-Hold-Slide (SHS) tests and cementation experiments. However, laboratory measurements and the microstructures of experimental fault rocks are difficult to compare with natural rocks, due to the difference in kinetics of physical mechanisms and the small spatio-temporal scale of experiments.

Here, we review the field and microstructural evidence of various processes of fault healing along a carbonatic fault surface, taking advantage of an outstanding case study: the Pietrasanta Normal Fault (NW Tuscany, Italy). In the field, the most common evidence of fault healing is the occurrence of cohesive fault rocks (cataclasites) and veins, but other fault surface properties may influence the re-strengthening of fault surfaces: e.g. adhesion phenomena (sidewall ripouts and fault surface patches) and geometrical complexity.

We compare these observations with frictional healing experiments carried out on carbonatic fault rocks, in which both fault gouges and cohesive slip surfaces were used. We propose that a fault surface composed by “patches” of cohesive fault rocks bounded by anastomosing slip zones are the result of complex cycles of gouge formation and healing, which modulate the interplay of adhesion and localization along the fault surface.

How to cite: Tesei, T., Molli, G., Mittempergher, S., Pozzi, G., and Remitti, F.: Healing of fault surfaces: a field vs. experimental perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12752, https://doi.org/10.5194/egusphere-egu24-12752, 2024.

In earthquake research, the discovery and ongoing investigation of interseismic transient processes has revealed that faults are non-steady between large earthquakes. These transients are typically identified in continuously operating tectonic GNSS stations, whereby an acceleration away from the average interseismic rates of displacement can be identified with a variety of time series analysis methods. However, the features of these transients can vary depending on the processing strategy employed to derive displacement time series from the raw GNSS observables.

In the processing strategy, the definition of the geodetic datum is necessary to determine global terrestrial reference frames (TRFs), providing an accurate and stable absolute reference of Earth's locations. It is essential for comprehending the dynamic changes in Earth's geometry driven by factors like tidal and non-tidal loading, plate tectonic seismic activity, and ongoing climate change. Therefore, just as geodesy aims for accuracy and stability in the TRF, the datum definition—i.e., the realization of the TRF-defining parameters origin, orientation, and scale—may emerge as a critical factor in processing GNSS networks for geodynamic purposes.

The purpose of this study is to assess up to what extent the transient velocities obtained from GNSS-derived displacement time series change under different regional and global datum definitions for the Cascadia subduction zone and Hikurangi margin; regions with very well-known catalog of interseismic transient tectonic events. In our study, we process data from Cascadia to produce network solutions both NNR (No-Net-Rotation) and NNR+NNT (No-Net-Translation) constraint for regional and global datum definition, respectively. We employed dual-frequency ionosphere-free linear combination observations from 125 GNSS stations for the time between 2015 and 2020. The same GNSS processing strategy is then followed for the Hikurangi subduction zone using a set of 72 stations from the GeoNet project as well as the same control stations used for Cascadia spanning from 2002 to 2010.

For the Cascadia displacement time series, we find variations in transient velocities under different datum definitions emphasizing the need for a comprehensive understanding of its impact on dynamic geophysical processes. Processing and analyses of the New Zealand data is ongoing and results will be presented, along with recommendations for both regions on how to reduce the occurrence of likely non-tectonic transients in the displacement time series. Ultimately, our results may have implications for improving the estimate of the slip budget at plate boundaries that is released aseismically.

How to cite: Garcia, C., Bedford, J., Männel, B., and Glaser, S.: Impact of datum definition on transient velocities from GNSS displacement time series in Networks mode: A Case Study of Cascadia Subduction Zone and Hikurangi margin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12979, https://doi.org/10.5194/egusphere-egu24-12979, 2024.

EGU24-13514 | ECS | Posters on site | TS1.6

Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction 

Lin Zhang, Jianye Chen, Bowen Yu, and Miao Zhang

It is believed that seismic failure conditions are sensitive to strain-softening behavior of nominal rock or fault gouge, and that precursors prior to a big earthquake (i.e., tectonic trains, water level changes, and Vp/Vs anomalies, etc) are provided by the acceleration of local slip. Previous studies of earthquake nucleation on laboratory faults show that the initiation of unstable fault slip is spatiotemporal dependent and consists of an interval of fault preslip (or creep) that localizes and accelerates to a dynamically propagating rupture. We pose that perturbation-type experiments can provide a natural condition to help analyze the potential mechanisms between instability events and the stress loading. In this study, we conducted three sets of double-direct shear experiments on a 300 mm long fault filled with gypsum-rich gouges, under normal stress of 10 MPa superimposed with perturbations of various amplitudes (i.e., 0-0.5 MPa) and a fixed frequency (0.1 Hz). The result showed that during each cycle of the stick slip behavior, the applied normal stress perturbations were redistributed along the fault zone as revealed by the along-fault strain measurement in the normal direction. As such, the fault can be divided into different zones characterized by varied coupling with respect to the applied perturbations. We found, coincidently, nucleation of the final instability, as revealed by the strain measurement in the shear direction, tended to occur at the boundary between the so-called strong and weak coupling zones (‘Transition Zone). Moreover, local normal stress near the nucleation zone also showed some weakening prior to the instability, which was similar to that seen in the local shear stress, and hereafter referred to as ‘normal failure’. Based on these observations, we proposed an empirical equation to fit the normal strain or stress data, giving the distribution of the coupling coefficient (c-value) and the anomaly (a-value) along the simulated fault. Finally, we applied the proposed equation to fit the water level data from 6 monitoring stations along the fault that hosted a nature earthquake (~ML 4). The fitting results predicted a Transition Zone, which was close to the hypocenter. In the end, we propose that this approach can be tested widely to natural observations of various precursory signals, especially those considered to be sensitive to fault-normal deformation (“dilatation” or “compaction”), such as water level, soil gas, and Vp/Vs anomalies. Hopefully, the results can shed some lights on the location of the earthquake nucleation zone. 

How to cite: Zhang, L., Chen, J., Yu, B., and Zhang, M.: Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13514, https://doi.org/10.5194/egusphere-egu24-13514, 2024.

EGU24-13838 | ECS | Posters on site | TS1.6

Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones 

Jun Xie, Xiaotian Ding, and Shiqing Xu

A rich spectrum of slip behaviors, spanning from aseismic creep (mm/yr) to seismic slip (m/s), has been observed in many subduction zones and some strike-slip faults. Slow earthquakes, intermediate between these two end-member modes, exhibit transitional slip behaviors in fault sections adjacent to the seismogenic zone. Focusing on subduction zones, it is shown that they experience deformation not only along discrete fault planes but also over distributed frictional-viscous shear zones, the latter of which are thought to be responsible for the observed diverse slip behaviors. Here we employ a frictional-viscous mélange model consisting of brittle blocks surrounded by a viscous matrix to investigate its influence on slip behaviors. By varying the mélange's rheological and frictional properties, we observe a diverse range of slip behaviors. We also reproduce the source scaling relations observed in natural faults, including the relation between seismic moment and duration and that between moment magnitude and stress drop. Additionally, we find a close link between the modeled shear zone deformation patterns and the various geological structures observed in natural fault zones. Our study demonstrates that the interaction between the frictional and viscous compositions of the mélange is responsible for the resulting slip behaviors and their transitions under different compositional ratios. These results provide useful clues for constraining the environmental and rheological conditions of different subduction zone sections from the observed slip behaviors.

How to cite: Xie, J., Ding, X., and Xu, S.: Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13838, https://doi.org/10.5194/egusphere-egu24-13838, 2024.

EGU24-15197 | ECS | Posters on site | TS1.6

Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea 

Sejin Jung, Ji-Hoon Kang, Youngwoo Kil, and Haemyeong Jung

The 5.5 magnitude (Mw) earthquake in Pohang, South Korea in 2017 was one of the largest triggered earthquakes at an enhanced geothermal system (EGS) site. Faults that ruptured in Pohang were not identified by preliminary geological investigations or geophysical surveys, and the subsequent study of the fault rocks at the Pohang EGS site was limited to depths of 3790–3816 m. In this study, we present new observations of fault rocks from drill cuttings retrieved from the Pohang EGS. The drill cuttings obtained from 3256 to 3911 m contained “mud balls,” which showed a clay matrix with foliation and a cataclastic texture, indicating a typical fault gouge or breccia. Furthermore, the mud ball samples retrieved from depths of 3256 m and 3260 m contained black fragments. Scanning and transmission electron microscopy revealed that the black fragments consisted of glass-like material, which is indicative of frictional melting during coseismic slip (Jung et al., 2023). The presence of these black fragments suggests that at least one seismic event had occurred at the Pohang EGS site prior to the hydraulic stimulation test.

Jung, S., J. -H. Kang, Y. Kil and H. Jung, 2023, Evidence of frictional melting in fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea. Tectonophysics, 862, 229964.

How to cite: Jung, S., Kang, J.-H., Kil, Y., and Jung, H.: Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15197, https://doi.org/10.5194/egusphere-egu24-15197, 2024.

EGU24-15878 | ECS | Orals | TS1.6

Fault orientation in earthquake seismic precursors: insights from the laboratory 

Carolina Giorgetti and Nicolas Brantut

Faults in the brittle crust lie at any orientation to the far-field stress. However, laboratory experiments designed to investigate earthquake physics commonly simulate favorably oriented faults, potentially overlooking the complexity of natural fault behavior. Here, we assess the role of stress field orientation in fault reactivation and earthquake precursors by conducting triaxial saw-cut experiments with laboratory faults oriented at different angles to the maximum principal stress, ranging from 30° to 70°. The samples were instrumented with strain gauges and piezo-electric sensors. Laboratory well-oriented faults describe a rather simple system in which the elastic energy is stored via the deformation of the surrounding host rock during the inter-seismic period and released via on-fault slip during the co-seismic phase with associated precursor acoustic activity. Consistent with previous laboratory data, an abrupt increase in the on-fault acoustic emission rate occurs shortly before the laboratory earthquake. A more complex picture emerges when deforming laboratory misoriented faults. Particularly, acoustic emissions and strain gauge data indicate that when the fault is misoriented, off-fault permanent deformation occurs well before fault reactivation. The stress state in the host rock surrounding the fault is indeed far beyond the one required for the onset of inelastic deformation. In this case, acoustic activity distributed in the rock volume during the pre-seismic phase is associated with permanent deformation in the critically stressed host rock and is not a direct precursor to the following laboratory earthquake. Unlike well-oriented faults, laboratory mis-oriented faults lack detectable seismic precursors. The laboratory-observed increase in acoustic activity prior to, but not precursor of, mis-oriented fault reactivation impacts our understanding of earthquake precursors in natural faults.

How to cite: Giorgetti, C. and Brantut, N.: Fault orientation in earthquake seismic precursors: insights from the laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15878, https://doi.org/10.5194/egusphere-egu24-15878, 2024.

EGU24-16581 | ECS | Posters on site | TS1.6

Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series 

Rens Elbertsen, Ivan Vasconcelos, and André Niemeijer

Laboratory stick-slip experiments are a simple analogue for the earthquake cycle. The acoustic emissions (AE) of these experiments have been shown to contain hidden patterns. Machine Learning (ML) can extract these patterns and information on the fault state can be inferred (e.g. shear stress and time to failure). Two different ML approaches have been used in the past: 1) ensemble tree models, which are relatively easy to evaluate why they made a certain prediction, but only look at a snapshot in time and 2) deep neural networks using Long Short-Term Memory (LSTM), which have the ability to find patterns in the temporal changes in the signal, but act more as a black-box model, so the final predictions are hard to evaluate. Here we introduce an additional step in the workflow that can be used to allow the ensemble tree models information about the temporal changes of the input features. Furthermore, it is able to quantify and visualize whether a pattern is repetitive or not. Like earlier studies we start by calculating (statistical) features using a rolling window on the AE. The features are not directly used as the input of the model, but are placed in a larger Hankel matrix, where the consecutive time windows are the rows of the matrix. Using Principal Component Analysis (PCA) and Uniform Manifold Approximation and Projection (UMAP) we create an embedded version of this array that holds temporal information of features calculated in the previous step. Visual inspection of these embeddings shows that some features map to very distinct patterns that are repetitive over the majority of the stick-slip cycles. The advantage of this method is that an inverse mapping is easily available, allowing for an interpretable embedding of the data.

How to cite: Elbertsen, R., Vasconcelos, I., and Niemeijer, A.: Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16581, https://doi.org/10.5194/egusphere-egu24-16581, 2024.

EGU24-18746 | ECS | Posters on site | TS1.6

Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed 

Navid Kheirdast, Harsha Bhat, Michelle Almakari, Carlos Villafuerte, and Marion Thomas

Seismic observations confirm that natural fault systems radiate waves across a continuum of frequency and amplitude. Within this spectrum, faulted systems exhibit a continuous range of slip rates, allowing them to irreversibly dissipate energy stored in rocks over a broad range of seismic moment. Despite advancements in observations and numerical modeling models, the question on how a given fault system can host such a wide range of ruptures, including slow ruptures, VLFEs, LFEs, and fast earthquakes needs a careful attention. Addressing this question requires a framework rooted in fracture mechanics, which explores the rate at which energy provided to a crack drives the rupture front forward and how this process radiates energy throughout the medium.

This work delves into the question of how frictional instability and mechanical interactions between faults and fractures, particularly concerning the geometrical distribution of off-fault damage, can generate observed rupture patterns in seismic catalogs. A model of a representative fault system is proposed, featuring a main fault embedded within a fractured zone where all fractures can slip independently. The length distribution of the off-fault fractures follows a power-law. The study then explores the fracture processes within the system, examining rupture speed from an energetic standpoint and exploring the impact of the damaged zone on the supply or reduction of energy to the process zone, ultimately influencing whether ruptures propagate rapidly or slowly.

The influence of this process is further examined by analyzing the amount of energy radiated away from the fault system. Moment-radiated energy and moment-fracture energy scaling relationships will be presented as mechanical quantities that both slow and fast earthquakes adhere to on a common curve. We will discuss radiation efficiency as a function of rupture speed to illustrate how a fault adjusts its rupture speed according to the energy provided to it and the amount of its breakdown work. The effect of damage on the process zone of the rupture will be discussed to examine how interactions between multiple fractures supply or detract energy to an active process zone, affecting its rupture speed and, consequently, the fast or slow advancement of the front.

How to cite: Kheirdast, N., Bhat, H., Almakari, M., Villafuerte, C., and Thomas, M.: Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18746, https://doi.org/10.5194/egusphere-egu24-18746, 2024.

EGU24-20753 | Posters on site | TS1.6

Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System 

David Essing, Kaan Cökerim, Gian Maria Bocchini, and Rebecca M. Harrington

The Hellenic Subduction System (HSS) in the eastern Mediterranean is the oldest active subduction margin on earth. It is a segmented boundary that hosts the continuum of faulting styles over a ~200km range in depth and can generate large earthquakes with high tsunamigenic potential.  The complexity of deformation styles and rates leave key aspects of the system poorly understood. For example, historical records of Mw<8 earthquakes fail to explain the current observed convergence rate (~35mm/year), and recent geodetic measurements suggest that the degree of locking within the system is heterogeneous. The density of geodetic measurements is increasing rapidly, nevertheless, the inherent time lag required to accumulate data that will enable identifying regions that undergo slower (than seismic) deformation transients will necessitate inferences from seismic signals. In this work, we aim to further close the observational gap between heterogeneous deformation styles and rates using the features of seismicity distributions to infer where deformation rates, and by inference, locking, vary most.   

To that scope, we will present new results of an enhanced earthquake catalog that we will use to explore the spatio-temporal distribution of seismicity features (e.g., b-value, effective stress drop, seismic-moment-release skewness) to infer variability in deformation rates and loading. Catalog enhancement exploits data from the temporary (EGELADOS) broadband seismometer network that operated between 2005 until 2007 combined with permanent stations leading to a station spacing of ~40 km and covering the entire southern Aegean Sea. We first use the combined network to detect earthquakes using machine learning approaches (EQTransformer, PhaseLink) for detection, phase picking and association. After performing initial locations using NonLinLoc combined with a 1D velocity model and quality control procedure, we enhance the number of small-magnitude detections using a multi-station template-matching approach. Next, we scan the enhanced high-resolution catalog for distinct spatial and temporal patterns of seismicity using unsupervised clustering. We then quantify the clustered seismicity using b-value, effective stress drop, and seismic-moment-release skewness (among other parameters). We will present our clustering results in the context of the variability in slip phenomena related to earthquake-earthquake interactions (e.g., static and dynamic triggering) as well as in the context of external forcing (e.g., aseismic triggering or fluid migration).  

The preliminary results that we will present will provide a basis for our more broad-scale study of interplay between seismic and aseismic deformation. In particular, where the latter is gradually becoming increasingly resolvable using GNSS data within the HSS, this work will provide a basis for links with geodetically observed deformation in the future.  

How to cite: Essing, D., Cökerim, K., Bocchini, G. M., and Harrington, R. M.: Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20753, https://doi.org/10.5194/egusphere-egu24-20753, 2024.

EGU24-20908 | ECS | Posters on site | TS1.6

Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction  

Giacomo Mastella, Federico Pignalberi, Carolina Giorgetti, and Marco Scuderi

Double direct shear experiments serve as established methods for delving into the physics of laboratory earthquakes. Using a biaxial shearing apparatus with dual fault configurations, these friction experiments simulate real Earth faults' behaviors during loading and failure. 

Despite the presence of distinct layers, double direct shear experiments are commonly perceived as a unified fault system, where the evolution of fault zone properties captured through passive or active seismic imaging can be correlated with the instantaneous stress state affecting both layers uniformly. To further explore the physics of seismic cycles generated in this setup, we perform friction experiments aiming to independently monitor the behavior of each fault layer. In our experiments, we use granular quartz (medium grain size 40 µm) to simulate fault gouge, amd we vary the normal load and shear velocity, allowing us to modify the apparatus's loading stiffness, which relies on the critical fault rheologic stiffness (kc). In the Rate-and-State framework, increasing the normal load results in an  increase of kc, pushing the system towards instability, occurring when k/kc <1, where k is the fault stiffness. Under 50 MPa of  normal loads and 10 µm/s of loading rate, these conditions result in highly non-cyclic seismic cycles marked by significantly variable stress drops and recurrence times. This situation offers an exceptional opportunity to investigate stress partitioning between the two layers and understand their interactions. Experiments are monitored using high-frequency calibrated piezoelectric sensors with a sampling rate of 6 MHz, placed on each of the two forcing blocks. Such a sampling rate allows us to clearly distinguish the time delay between the Acoustic Emissions (AEs) generated from microslip events in different layers. Phase arrivals are detected using retrained, Deep Learning-based algorithms. By associating these phase arrivals using the DBSCAN clustering algorithm, we classify events as occurring on a single gouge layer or on both layers. Subsequently, we analyze the catalog of AEs,, and single seismic waveforms, in terms of general characteristics and frequency content, to look for differences in the physical sources generating them. Unsupervised clustering may help identify classes of AEs linked to specific stages within seismic cycles. By potentially using established supervised Machine Learning technique, it would be possible to verify the relation between AEs variance for each layer and macroscopic apparatus features, like instantaneous friction or time to failure. All of these techniques reveal differences in acoustic energy released before failure for each layer, observations that can be associated to changes in fault physical properties, asperity scale processes and/or  grains sliding or fracturing. In conclusion, our findings demonstrate that double-direct shear experiments can emulate a system of interacting double faults. In such a context, the continuous monitoring of AEs can provide insights into the stress partitioning between the two layers, a process that may guide the nucleation of major slip events as well as the long term behavior of the system. Additionally, our analysis may be helpful to investigate processes like fault interactions, faults synchronization, static, and dynamic stress triggering.

How to cite: Mastella, G., Pignalberi, F., Giorgetti, C., and Scuderi, M.: Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20908, https://doi.org/10.5194/egusphere-egu24-20908, 2024.

EGU24-685 | ECS | Posters on site | TS1.10

The internal deformation of the Praid salt diapir and implications for potential storage applications 

Daria Dohan, Dan Mircea Tamas, Alexandra Tamas, and Ioana Silvia Mihaela Tocariu

The Praid salt diapir is located in the Transylvanian Basin, Romania and it stands out as one of the earliest discordant salt structures to be described. The salt that forms this structure was deposited during the middle Miocene salinity crisis. Under geological conditions, rock salt exhibits plasticity, resembling a fluid, leading to highly intricate folding patterns in its deformation. Understanding the evolution of salt structures holds significant importance for a number of industries such as the hydrocarbon industry or hydrogen storage. To utilize such formations for storage purposes, a comprehensive understanding of the deformation processes, impurity distribution, and mineral composition becomes crucial. These factors wield considerable influence on the overall rock properties.

Certain diapiric salt formations within these areas hold potential as sites for hydrogen storage due to their substantial dimensions, reaching around ~3500m in size, and existing caverns within some of these formations. This investigation centers on analyzing the deformation of the Praid salt diapir. The site features a public-accessible salt mine and numerous surface salt exposures. Our study involves detailed mapping of both surface and subsurface areas, focusing on internal salt deformation, the nature and distribution of impurities, and exploring salt-sediment interaction where exposed.

In our research, we utilized surface and underground mapping within the accessible salt mine, coupled with photogrammetry and LiDAR technology, to construct detailed 3D models capturing complex large-scale deformation patterns. The majority of the salt layers exhibit steep to near-vertical inclinations, with diverse orientations that suggest curtain-fold-like structures. Certain areas notably display signs of refolding. Within the salt, various impurities of differing origins exist, predominantly large-scale blocks composed of siltstone to sandstone slabs that have undergone boudinage. This study is part of an ongoing initiative aimed at evaluating both the potential and associated risks of implementing hydrogen storage projects within these salt formations or similar structures.

Acknowledgements: The work of DD was financed through the Scientific Performance Scholarship, offered by Babes-Bolyai University, Cluj-Napoca.

How to cite: Dohan, D., Tamas, D. M., Tamas, A., and Tocariu, I. S. M.: The internal deformation of the Praid salt diapir and implications for potential storage applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-685, https://doi.org/10.5194/egusphere-egu24-685, 2024.

EGU24-709 | ECS | Posters on site | TS1.10

Resisting the unknown: Enhancing resistivity imaging of the crust through a multidisciplinary approach from µ- to km-scale at the DIVE DT-1B drill site 

Sören Tholen, Virginia Toy, Friedrich Hawemann, and Hadis Mansouri

Geophysical methods based on the conductivity of electrical currents through the subsurface (IP, ERT, magnetotellurics) are commonly used to identify mineral deposits or aquifers, for which large conductivity contrasts exist between host rock and target. These methods may also provide insights about tectonic processes, such as when rock masses contain partial melt, or are affected by active deformation. However, further advances in electrical imaging of rocks at depth are hindered by the lack of understanding of the relative contributions of paragenesis, fabric, and active processes to electrical conductivity. The ICDP project DIVE (Drilling the Ivrea-Verbano ZonE) provides a unique opportunity to evaluate these parameters by combining samples and measurements from up to ~580 m depth with a wide range of geophysical surface surveys.

The DT‑1B drill core comprises lower crustal rocks consisting mostly of metapelite and amphibolite with embedded pegmatitic lenses. We took 25 samples from these main lithologies that cover the major variations in fabric (e.g., foliation strength, continuity and style, grain size), as well as intervals rich in micro fractures, hydrous alteration, or highly conductive phases (graphite, sulfide). We focus on two main research questions: (1) How do aspects of rock fabrics such as style and strength of foliation or mineral content and the connectivity of conductive phases affect the electrical properties, and (2) can these micro-scale, fabric-induced electrical properties be extrapolated to larger scales?

Fabric analysis and quantification of mineralogy are carried out at thin-section scale by optical and electron microscopy (EDX, EBSD). Computed tomography (CT) performed on small cylinders drilled from the same samples allows the microstructural data to be extended into the third dimension. The CT ably reveals the elongation and alignment of sulfides, the style, and continuity of the foliation which is defined by biotite, and in places graphite- or sulfide-decorated fracture systems. Measurement of electrical properties of the same cylinders under various fluid saturation conditions and a wide frequency range completes the comprehensive database, enabling us to detect and model electrical pathways in the lower crust.

To scale from the micro to the macro scale, these results will be compared to the data from electrical surveys carried out around the DT-1B drill hole. Results will expand the applicability of resistivity imaging for a wide range of future, structural applications.

How to cite: Tholen, S., Toy, V., Hawemann, F., and Mansouri, H.: Resisting the unknown: Enhancing resistivity imaging of the crust through a multidisciplinary approach from µ- to km-scale at the DIVE DT-1B drill site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-709, https://doi.org/10.5194/egusphere-egu24-709, 2024.

EGU24-1059 | ECS | Posters on site | TS1.10

Competing development of S and C foliations in mylonites 

Pramit Chatterjee, Arnab Roy, and Nibir Mandal

Mylonites are characteristic rocks in ductile shear zones, and they contain two primary fabrics: i) C-fabrics, which are usually aligned parallel to the principal shear planes in the shear zones, ii) S-Foliations, which are oriented at angles to the shear plane, showing their vergence in the shear direction. Despite extensive studies of mylonite structures over several decades, the factors controlling the formation of S and C fabrics and their relative abundance in ductile shear zones are yet to be fully explored. This article investigates the competing development of S and C fabrics in ductile shear zones from two geological terrains of Eastern India. The shear zones offer macroscopic observations of various mylonitic rocks: i) C mylonites ii) S mylonites, and and iii) S-C mylonites.  Numerical simulations were performed to replicate them in model shear zones, considering a combination of transient visco-plastic rheology. The model study suggests that the growth of C- versus S- fabrics in mylonites depend on two fundamental non-dimensional parameters: imposed strain rate and bulk viscosity. It is observed that low bulk viscosity and strain rate conditions promoted the formation of S fabrics. With increase in bulk viscosity and strain rate, formation of C bands in the shear zones is facilitated leading to the localisation of strain in the form of narrow zones.

How to cite: Chatterjee, P., Roy, A., and Mandal, N.: Competing development of S and C foliations in mylonites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1059, https://doi.org/10.5194/egusphere-egu24-1059, 2024.

Salt tectonics and salt structures are attractive targets for hydrocarbon exploration since salt-related deformation can form hydrocarbon traps and influence hydrocarbon migration. Salt diapirs are considered a suitable site for reserving natural oil/gas, landfills, and hazardous wastes. Determination of the origin and age of salt diapirs, the diapir formation and evolution model, and their impacts on the surrounding structures are very necessary for hydrocarbon exploration. To characterize the structural and tectono-sedimentary evolution of the salt diapir at the Qom Kuh, located in the Qom basin (Central Iran), this research describes the origin, timing, and evolution history of the salt structure through the tectono-sedimentary analysis and field study. Moreover, the effect of salt diapirism on the surrounding structures is investigated in the study area. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth salt structure indicate that the salt extrusion occurred during two stages in the Qom Kuh. According to the structural evidence (e.g., hook and cusp) and the tectonic-sedimentary analysis, the first stage of salt extrusion happened in the Early Miocene concurrently with the extensional deformation event from the Eocene to the Early Miocene in the study area. The second stage of salt diapirism and its extrusion occurred during multi-stages of the Zagros orogenic compression from the Late Miocene to the present day. The final geometry of the salt diapir at the Qom Kuh formed along a releasing bend that was created by dextral transpressional strike-slip fault activity during the Zagros orogeny. Based on the lower thickness of evaporite units in the Upper Red Formation (Early Miocene) compared to the Lower Red Formation (Early Oligocene) and observing fragments of the Eocene volcanic rocks in the extruded salt on the ground surface, the Lower Red Formation salt along with the Upper Red Formation evaporites considered as the main source of salt diapirism in the Qom Kuh. Salt diapirism affected the surrounding structures of the Qom Kuh such as the Western Kuh-e-Namak and Western Alborz anticlines. The fold geometry and the hydrocarbon trap development in the Western Kuh-e-Namak and Western Alborz fields are controlled by salt tectonics and the occurrence of inversion tectonics. The results of this study could add data to worldwide examples of the impact of salt tectonics on the hydrocarbon trap development in collisional orogenic belts.

Keywords: Salt tectonics; Tectono-sedimentary analysis; Hydrocarbon traps; Qom Kuh; Central Iran

How to cite: Nikpoush, S. and Soleimany, B.: Control of salt tectonics on the hydrocarbon traps development: the surrounding structures of the Qom Kuh, Central Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2464, https://doi.org/10.5194/egusphere-egu24-2464, 2024.

EGU24-3225 | ECS | Orals | TS1.10

Full-Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration 

Baoqin Hao, Maria-Gema Llorens, Albert Griera, Paul D. Bons, Ricardo A. Lebensohn, Yuanchao Yu, and Enrique Gomez-Rivas

Full-field numerical modelling is a useful method to gain understanding of rock salt deformation at multiple scales, but it is quite challenging due to the anisotropy and complex plastic behavior of halite and other evaporite minerals at the single crystal level, together with dynamic recrystallization processes. We overcome these challenges and present novel results of full-field numerical simulation of dynamic recrystallization of halite polycrystalline aggregates during simple shear deformation, including subgrain rotation and grain boundary migration recrystallization processes. The results illustrate that the approach successfully reproduces the evolution of pure halite microstructures from laboratory torsion deformation experiments at 100-300℃ up to shear strain of four. Temperature determines the competition between (i) grain size reduction controlled by dislocation glide and subgrain rotation recrystallization (at low temperature) and (ii) grain growth associated with grain boundary migration (at higher temperature), while the resulting crystallographic preferred orientations are similar for all cases. The analysis of the misorientation reveals that the relationship between subgrain misorientation and strain follows a power law relationship with a general exponent of 2/3. However, with progressive deformation, dynamic recrystallization leads to a gradual deviation from this relationship. Therefore, predicting strain or temperature from microstructures necessitates careful calibration.

How to cite: Hao, B., Llorens, M.-G., Griera, A., Bons, P. D., Lebensohn, R. A., Yu, Y., and Gomez-Rivas, E.: Full-Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3225, https://doi.org/10.5194/egusphere-egu24-3225, 2024.

EGU24-3623 | ECS | Orals | TS1.10

The role of post-salt carbonates on salt tectonic minibasin formation 

Leonardo Muniz Pichel, Ritske Huismans, Rob Gawthorpe, and Jan Inge Faleide

Salt tectonics on passive margins is driven by sediment loading and gliding with minimal influence from basement-involved tectonics and is associated with variable and complex salt structures such as minibasins and diapirs. A major enigma in salt tectonics is the origin of load-driven diapir-flanked minibasins, synclinal depocenters formed by localized subsidence of syn-kinematic sediments into salt. How can less-dense clastic sediments sink into the denser salt promoting diapirism at their flanks? We use 2D numerical modelling of lithospheric extension including syn- and post-rift sedimentation to understand the evolution of salt-tectonic minibasins along rifted passive margins. Our results show that these minibasins are driven by the deposition of dense early post-salt carbonates and then amplified during the progradation of less dense and compacting clastics. In contrast, basin-scale salt flow driven by clastic progradation alone, without deposition of early post-salt carbonates, does not produce minibasins as observed on salt-bearing passive margins.

How to cite: Muniz Pichel, L., Huismans, R., Gawthorpe, R., and Faleide, J. I.: The role of post-salt carbonates on salt tectonic minibasin formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3623, https://doi.org/10.5194/egusphere-egu24-3623, 2024.

EGU24-4104 | Orals | TS1.10

Using salt diapirs and minibasins to constrain interpretations of crustal rifting and inversion in the Basque Pyrenees, Spain 

Mark G Rowan, Josep Anton Muñoz, Eduard Roca, Oriol Ferrer, Eloi Carola, and Iñaki Garcia

Published interpretations across the Basque Pyrenees vary significantly in their depictions of rifting and subsequent inversion. Major points of disagreement relate to: (i) the asymmetry of the margin, i.e., whether the major extensional and contractional detachment dipped toward the north or south; and (ii) the degree of decoupling between supra- and subsalt deformation and thus the amount of thin-skinned translation of the cover relative to basement. Here we use outcrop and subsurface data to analyze the salt structures along a regional transect in order to resolve this ongoing debate.

Several aspects of the salt-related geometries are diagnostic of thin-skinned deformation. First, Villasana de Mena diapir has significantly thicker synrift strata on its basinward (northern) flank, contains stringers of Paleozoic rocks, and was growing passively during crustal extension. Its origin was consequently related to an underlying basement fault, yet it is situated today above an unfaulted detachment, suggesting that the diapir was translated above the salt during rifting and/or shortening. Second, Salinas de Rosio diapir is located at the southern termination of landward-shifting synrift depocenters and developed as a postrift to synorogenic salt pillow and then diapir. Thus, thin-skinned translation over a fault-related ramp in the base salt created synrift ramp-syncline basins, with the basement fault subsequently localizing salt inflation due to differential loading and then contractional buttressing. Third, Poza de la Sal diapir is at the basinward end of another set of synrift ramp-syncline basins and along a thin-skinned fold and thrust structure that was active during the synrift. Fourth, the large-scale geometry from the Bilbao Anticlinorium to the south documents contractional translation above a continuous salt detachment with a ramp-flat geometry.

In summary, the salt and suprasalt geometries in a large part of the Basque Pyrenees demonstrate two phases of thin-skinned translation above a north-dipping salt detachment: (i) decoupled, basinward (northward) translation during rifting; and (ii) thin-skinned, southward-directed thrusting during inversion. The geometries are incompatible with thick-skinned inversion on a major south-dipping crustal detachment and smaller, basement-rooted faults that cut through the salt and its overburden.

How to cite: Rowan, M. G., Muñoz, J. A., Roca, E., Ferrer, O., Carola, E., and Garcia, I.: Using salt diapirs and minibasins to constrain interpretations of crustal rifting and inversion in the Basque Pyrenees, Spain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4104, https://doi.org/10.5194/egusphere-egu24-4104, 2024.

EGU24-4777 | ECS | Posters on site | TS1.10

Structural architecture of brittle-ductile mineralized veins in a Cenozoic orogenic gold deposit along the North Cycladic Detachment System, Greece 

Laurence Hamel, Taylor Ducharme, David Schneider, and Bernhard Grasemann

The Kallianos Au-Ag-Te deposit, located on southern Evia island in the NW Aegean Sea, is a Cenozoic orogenic gold deposit hosted in carbonate-epidote-phlogopite schists and phlogopite marbles of the Cycladic Blueschist Unit (CBU). Fluids that generated the deposit were channelized by a crustal scale post-orogenic extensional structure, the North Cycladic Detachment System (NCDS), which facilitated Miocene exhumation of the CBU into the brittle crust. Whereas ore deposits in the Cyclades have been broadly related to late Miocene granitic intrusions, magmatism of this age is notably undocumented on Evia. Field observations illustrate the connection between the structural architecture that host mineralization and deformation associated with the post-orogenic structures, refining the paragenetic model for Cenozoic gold deposits in the Cyclades. Mineralized veins, alongside unmineralized tension gashes, faults, conjugate faults, and joints, occur in parallel sets that locally define en-echelon arrays. Younger sub-vertical tension gashes cross-cut older boudinage mineralized veins. The vein orientations of the Kallianos deposit strike NW-SE and NNW-SSE, which is generally orthogonal to the sub-horizontal ~NE stretching lineations related to crustal extension and thinning accommodated by the NCDS. Brittle-ductile kinematic indicators such as shear bands exhibit top-NE displacement, consistent with footwall deformation related to the NCDS documented elsewhere along strike of the detachment. The two populations of vein orientations are not evident based on structural data alone, but field observations show clear cross-cutting of the earlier NW-striking vein set by later NNW-striking veins. The mineralization is hosted in subvertical mm- to m-scale veins composed of quartz, calcite, albite, with minor titanite and epidote and notable sulfide mineralization including pyrite, galena, chalcopyrite, bornite and hematite concentrated in cm-scale veins. Obvious native Au and Ag are not observed in the veins. The NNW-striking vein sets contain significantly more albite and mineralization than the NW-striking veins and generally exhibit greater evidence of strain, with an abundance of sutured and bulging grain boundaries preserved in the quartz. Vein arrays developed within the cataclastic deformation zone below the exposed NCDS detachment plane are parallel to those observed deeper in its footwall. Our structural data strongly imply a connection between mineralized veins of the Kallianos Au-Ag-Te deposit and the regional strain field imposed by displacement along the NCDS. Despite structural evidence linking the architecture of this Cenozoic gold deposit to the crustal scale NCDS, an origin for the mineralizing fluids remains equivocal due to the local absence of magmatism, and the distribution of brittle-ductile strain to significant depths in the footwall may implicate devolatilization reactions coinciding with exhumation through the brittle-ductile transition as an important fluid source.

How to cite: Hamel, L., Ducharme, T., Schneider, D., and Grasemann, B.: Structural architecture of brittle-ductile mineralized veins in a Cenozoic orogenic gold deposit along the North Cycladic Detachment System, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4777, https://doi.org/10.5194/egusphere-egu24-4777, 2024.

EGU24-5204 | ECS | Posters on site | TS1.10

Timing and rates of salt movement in the Romanian Eastern Carpathians: insights from Radiocarbon and OSL dating 

Dan Mircea Tamas, Alexandra Tamas, Gabriela Odilia Sava, Anca Avram, and Alida Timar-Gabor

Salt, an age-old resource, holds significance in human history and emerges as a potential solution in transitioning from fossil fuels to sustainable energy, due to its unique properties. Its geological fluidity results in formations like salt diapirs, influencing deformation in the past and present. Understanding the details and timing of such deformation is crucial for certain energy transition projects like hydrogen storage in salt caverns.

Salt tectonics in the Romanian Eastern Carpathians has long been studied. Initially, it was studied for its significance as a natural resource, but its implications for the hydrocarbon industry were later explored. Techniques such as seismic interpretation, well-log analysis, analogue and numerical modelling, and field observations are used to examine salt movement and interaction with sediment. In order to understand the Quaternary uplift rates of salt diapirs and the timing of salt movement in the Eastern Carpathians, we use radiocarbon and optically stimulated luminescence (OSL) dating.

This innovative combination of radiocarbon and OSL dating marks a breakthrough in understanding salt diapir uplift rates in the area of interest, shedding light on the historical dynamics of geological formations and erosion processes.

How to cite: Tamas, D. M., Tamas, A., Sava, G. O., Avram, A., and Timar-Gabor, A.: Timing and rates of salt movement in the Romanian Eastern Carpathians: insights from Radiocarbon and OSL dating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5204, https://doi.org/10.5194/egusphere-egu24-5204, 2024.

EGU24-6560 | ECS | Orals | TS1.10

Strain partitioning during 3D general shear in a heterogeneous low-angle shear zone: some hold strong, while the schists fall flat 

Taylor Ducharme, David Schneider, Bernhard Grasemann, Alfredo Camacho, Kyle Larson, and Victoria Scoging

General shear, wherein deformation incorporates elements of both coaxial and non-coaxial strain, is a prevalent strain regime in natural high-strain zones. In extensional tectonic settings, three-dimensional forms of general shear may enhance exhumation via additional crustal thinning (i.e., via pure shear or flattening strain components) or counteract it by inducing crustal thickening (i.e., via a constrictive strain component), without necessarily producing a conspicuous crustal-scale shear zone or fault. Schists and phyllonites demarcating a major tectonic boundary between thrust sheets on Evia in the NW Cyclades record structural evidence for general shear with a NE-directed non-coaxial component and contemporaneous flattening. The package of rock accommodating this strain is lithologically heterogeneous, comprising intercalations of carbonate-, quartz-, and phyllosilicate-dominated schist, as well as dispersed m- to hm-scale olistoliths and blocks of marble and metabasite. Flattening in these rocks is exemplified by foliation-oblique quartz ± calcite veins exhibiting pinch-and-swell or boudinage structure alongside dominant bidirectional dips perpendicular to the regional NE-SW stretching lineation. We combine in-situ 40Ar/39Ar and 87Rb/87Sr dating of white mica with quartz c-axis petrofabric analysis of the deformed quartz veins to elucidate the timing and styles of deformation recorded by these rocks. White mica provides mainly late Oligocene 40Ar/39Ar dates in samples with a single dominant foliation, whereas mica defining composite or crenulated foliations records late Eocene-early Oligocene dates, or age populations spanning the Oligocene. Some samples record dispersed Paleocene-Eocene dates older than the earliest proposed timing of metamorphism, although white mica from these rocks provides more geologically plausible early Oligocene 87Rb/87Sr dates. Vein quartz c-axis fabrics consist primarily of c-axis maxima or small-circle girdles centered about the Z-axis, with subordinate fabrics defining top-to-NE asymmetric type-I cross girdles or Y-axis maxima. Considered together with vein macro- and micro-structure, our data indicate that the deformed schists accommodated top-to-NE general shear at temperatures only slightly above 300°C, resulting in an oblate finite strain ellipsoid. Deformation over this interval produced differential transposition of earlier tectonic fabrics and structures into a sub-horizontal penetrative cleavage in the rheologically weak mica schists, whereas sections dominated by more quartzose- and carbonate-rich lithotypes display comparatively well-preserved older foliations and structures and a spaced secondary cleavage. The prevalence of late Oligocene 40Ar/39Ar dates in samples exhibiting a single, shallowly-dipping micaceous foliation implies that flattening general shear coincided with, and likely helped facilitate, exhumation. Our data indicate that unroofing may be partly facilitated by inconspicuous zones accommodating distributed inhomogeneous strain, a potentially important observation for exhumed subduction zones featuring prevalent block-in-matrix mélanges.

How to cite: Ducharme, T., Schneider, D., Grasemann, B., Camacho, A., Larson, K., and Scoging, V.: Strain partitioning during 3D general shear in a heterogeneous low-angle shear zone: some hold strong, while the schists fall flat, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6560, https://doi.org/10.5194/egusphere-egu24-6560, 2024.

EGU24-6744 | Posters on site | TS1.10

Deformation structures in the evaporitic melange. Case study from the Altaussee salt mine 

Marta Adamuszek, Marcin Olkowicz, Marcin Dabrowski, Mariusz Fiałkiewicz, Bartłomiej Grochmal, Thomas Leitner, and Oscar Fernandez

We investigated the salt deposits found within the Altaussee salt mine, which represent the Permian to Triassic evaporitic Haselgebirge Formation situated in the Northern Calcerous Alps (Austria). The extensive deformation of the evaporite sequence spanning from the Middle Triassic to Neogene periods led to the formation of a tectonic mélange. The sediments commonly comprise fragments of anhydrite, polyhalite, sandstone and limestone embedded in the halite-rich matrix. The dimensions of these blocks can exceed 10 meters in diameter, while the bulk volume of halite content in these layers is ranging from approximately 30 to 65 volume percent.

Our investigation focuses on the internal structure within the evaporite sequence. In particular, we examine various outcrops in caverns, galleries, and corridors that illustrate the role of block shape and size on the deformation pattern. Particularly noteworthy are findings from a large, well-exposed salt cavern ceiling covering approximately 4000 square meters. Utilizing tailored photogrammetric approach, image post processing techniques and using lidar data as reference, we generated detailed ortophoto map of 1000 square meters of cavern ceiling with resolution of 1 mm/pixel. This reveals intricate patterns around rigid blocks and their interactions at different scales. Fine layering within the rock salt allowed to illustrate spectacular structures that developed around the rigid blocks and also interaction between the blocks. Significantly, observations of layer deflection beneath blocks hint at potential block-sinking dynamics, offering valuable insights into the complex geological processes at play.

How to cite: Adamuszek, M., Olkowicz, M., Dabrowski, M., Fiałkiewicz, M., Grochmal, B., Leitner, T., and Fernandez, O.: Deformation structures in the evaporitic melange. Case study from the Altaussee salt mine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6744, https://doi.org/10.5194/egusphere-egu24-6744, 2024.

EGU24-8630 | Posters on site | TS1.10

Halokinetic growth wedges in platform carbonates: thoughts on subsidence and carbonate production rates 

Oscar Fernandez, Diethard Sanders, Hugo Ortner, Bernhard Grasemann, and Thomas Leitner

The Northern Calcareous Alps (NCA) in the Eastern Alps (Austria) developed during the Triassic as a Tethys-facing salt-rich passive margin. Extensionally-driven salt tectonics, mobilizing evaporites of Late Permian to Early Triassic age on the Tethyan passive margin, started as early as the early Middle Triassic and lasted through to the end of the Triassic. Here we document multiple examples of salt-related growth geometries in the central NCA, with specific emphasis on their dimensions and the implications these have on the balance between subsidence and carbonate production rates. The interaction between these two factors controlled the distribution of facies within the sedimentary growth wedges and the development of the transitions from shallow-water platforms into basinal domains >200 m in depth. The interplay between subsidence, carbonate production, and external factors (ocean currents) appear to have been critical for the persistence of long-lived intra-platform embayments, whose origin and development have long puzzled geologists.
The geometries and sedimentary architectures observed in the central NCA are directly comparable to those documented in other salt-rich basins such as the southern Atlantic passive margin or the (now inverted) Pyrenean rift. Excellent exposure and continuity over a large area render the Triassic of the central NCA an outstanding location for understanding the development of carbonate platforms above salt substrates.

How to cite: Fernandez, O., Sanders, D., Ortner, H., Grasemann, B., and Leitner, T.: Halokinetic growth wedges in platform carbonates: thoughts on subsidence and carbonate production rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8630, https://doi.org/10.5194/egusphere-egu24-8630, 2024.

EGU24-8722 | ECS | Orals | TS1.10

Evolution of a prograding shelf complex affected by salt tectonics, the case of the SW Valencia Trough 

Adrià Ramos, Menno J. de Ruig, Antonio Pedrera, Pedro Alfaro, and Iván Martin-Rojas

The Valencia Trough is a NE-SW trending sector of attenuated crust located between the Iberian Peninsula and the Balearic Islands in the western Mediterranean, bordered by the Catalan Coastal Ranges to the northwest, the Iberian Chain to the west, and the Balearic fold and thrust belt to the south. It includes several kilometers of Jurassic-Cretaceous rocks deposited over Upper Triassic salt associated with rifting in the western Tethyan margin. The Mesozoic deposits are deeply eroded as a result of basin inversion and uplift in Oligocene time, followed by extension in latest Oligocene-Early Miocene time. Overlying Middle-Late Miocene foreland basin sediments are associated with the subduction and rollback of the Tethyan oceanic lithosphere. During the Pliocene and Quaternary, a prograding shelf complex was established on the eastern margin of Iberia reaching 3000m in thickness and affected by extensional faulting.

The inspection of the available surface (geological maps and structural data) and subsurface data (2D seismic profiles and exploratory wells) allowed us to document the major role of the Triassic evaporitic sequence on the tectonic style and the configuration of the Pliocene to present-day sedimentary infilling in the Valencia Trough. Our results indicate that large N-S trending extensional faults, which control the depocentres of the Plio-Quaternary prograding shelf complex and offset underlying Mesozoic-Cenozoic sequence, detach into the salt layer. Supra-salt extensional deformation appears to be decoupled from extension in the sub-salt basement.

Sequential backstripping restorations also illustrate the evolution of the deformation and depositional space associated with the flexing down of diapiric structures, which are nucleated over inherited basement faults, parallel to the supra-salt ones. These diapirs were developed in the basin margin during the Mesozoic and Miocene times. The salt expulsion is mainly triggered by the overburden deposition of the prograding clinoforms wedges sourced from the rivers located to the west (e.g., Júcar, Túria and Serpis). Salt diapirs recording a Plio-Quaternary activity can be encountered in the surroundings of the basin, synchronously to the development of the withdrawal salt depocenters.

Moreover, the determination of the two extensional faults systems, salt-detached versus basement-involved, has significant implications on evaluating the structures responsible for the instrumental and historical seismicity in the area.

How to cite: Ramos, A., de Ruig, M. J., Pedrera, A., Alfaro, P., and Martin-Rojas, I.: Evolution of a prograding shelf complex affected by salt tectonics, the case of the SW Valencia Trough, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8722, https://doi.org/10.5194/egusphere-egu24-8722, 2024.

The Tyrrhenian Sea salt is part of the Messinian Mediterranean salt giant. Its regional distribution was mapped during the early exploration of the Tyrrhenian back-arc basin. More recently, detailed studies have focused on the reconstruction of the salt setting in the Sardinian offshore. A regional overview of salt tectonics character in the Tyrrhenian Sea is thus missing. With this in mind, we present the first basin-scale interpretation of a combined data set of multibeam bathymetry and seismic lines. In the relatively flat, proximal areas of the Cornalia and the Campania Terraces, vertical rise of diapirs is the dominant style of salt movement. Whereas most of the diapirs are buried, some of them emerge at the seafloor and their circular form of salt stocks is apparent. Widespread extensional faulting of the overburden is indicative of reactive diapiric rise and control the location and evolution of local depocentres. However, large parts of the Tyrrhenian Sea consist of areas dipping seaward, towards the centre of the Tyrrhenian Sea. Here, salt gliding is the prevalent style of salt deformation. In the Sardinian margin a belt characterized by salt gliding spans a length of 230 km and is up to 130 km wide, reaching the Vavilov Basin in the centre of the back-arc system. In the Campanian margin  a more equant salt gliding area has a length of 106 km and a width of 80 km. Smaller areas with evidence of salt gliding are located at the foot of the base-of-slope escarpment in the northern Sicilian margin to the south of the Vavilov Basin. Salt gliding results in discrete lobes with complex pattern of deformation. Deformation in the overburden often originates polygonal networks of grabens, scalloped scarps, circular or elongate minibasins, growth anticlines and synclines. When the halokinetic structures are present at the seafloor, their relative importance in the different sectors of the main lobes is apparent. Discrete zones of deformation, and a highly 3-D style of salt gliding and overburden deformation are thus recognized. Belts dominated by strike-slip deformation separate the different sectors of the main lobes and are often associated with salt stocks or faults. They are indicative of the linkage between discrete salt gliding systems with different movement direction. A complex deformation style and movement is thus evident in the Tyrrhenian Sea and the deformation of the overburden indicate the recent or active character of salt flow. Our analysis illustrate the processes and elements that characterize salt tectonics in irregular continental slope, with divergent gliding, and where different system interact.   At the basin-scale, salt deformation style does not comply with the simple patterns often observed in passive margins, consisting, moving seaward, of three domains: extensional, translational and contractional. In the Tryrrhenian Sea a more complex pattern is evident and can be related to the complex trend of the peripheral zone of the gliding salt masses inherited from the rifting stage. The crustal evolution and magmatic history of the basin also influences the discrete, but kinematically linked, slat gliding domains.

How to cite: Gamberi, F. and Ferrante, V.: Salt tectonics and gliding in the Tyrrhenian Sea: a centripetal salt deformation system in a back-arc basin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10801, https://doi.org/10.5194/egusphere-egu24-10801, 2024.

EGU24-10987 | Orals | TS1.10

Using crystal-lattice distortion data for geological investigations: the weighted Burgers vector method  

John Wheeler, Piazolo Sandra, David Prior, Patrick Trimby, and Jacob Tielke

Janos Urai made major contributions to our understanding of rock deformation and the microstructural fingerprints that can be used to investigate it.

One such fingerprint is intracrystalline distortion. Crystals can be distorted due to deformation or growth but the distortion gives insights into processes in either case. Distortion is generally due to the presence of dislocations which give information on slip systems, stress levels, growth mechanisms etc. Electron backscatter diffraction (EBSD) allows detailed quantification of distorted crystals, and we summarise here a method for extracting information on dislocations from such data. The weighted Burgers vector (WBV) method calculates a vector at each point on an EBSD map, or an average over a region. The vector is a weighted average of the Burgers vectors of dislocation lines intersecting the map surface. It is weighted towards dislocation lines at a high angle to the map but that can be accounted for in interpretation. The method is fast and does not involve specific assumptions about dislocation types; it assumes only that elastic strains have little effect on the calculation. It can be used, with care, to analyse subgrain walls (sharp orientation changes) as well as gradational orientation changes within individual grains. It can complement established methods for subgrain wall analysis and frees us from some assumptions made in other methods.

We give examples of its use applied to olivine and plagioclase. The magnitude of the vector relates to dislocation density but, as a vector, we find its directional information particularly informative. Code to implement this approach is available from the first author (“Crystalscape”), from Oxford Instruments (a commercial version) and aspects are implemented in MTEX.

Urai, J. L., Means, W. D. & Lister, G. S. 1986. Dynamic recrystallisation of minerals. In: Mineral and Rock Deformation: Laboratory Studies (edited by Hobbs, B. E. & Heard, H. C.). Geophysical Monograph 36. AGU, Washington, D.C., 161-199.

Urai, J. L. & Spiers, C. J. 2007. The effect of grain boundary water on deformation mechanisms and rheology of rocksalt during long-term deformation. In: 6th Conference on the Mechanical Behavior of Salt. Proceedings and Monographs in Engineering Water and Earth Sciences, Fed Inst Geosci & Nat Resources, Hannover, 149-+.

Wheeler, J., Piazolo, S., Prior, D. J., Trimby, P. W. & Tielke, J. A. 2024. Using crystal lattice distortion data for geological investigations: the Weighted Burgers Vector method. Journal of Structural Geology 179, 105040.

How to cite: Wheeler, J., Sandra, P., Prior, D., Trimby, P., and Tielke, J.: Using crystal-lattice distortion data for geological investigations: the weighted Burgers vector method , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10987, https://doi.org/10.5194/egusphere-egu24-10987, 2024.

EGU24-13072 | ECS | Posters on site | TS1.10

Poseidon’s seismic breadcrumbs: ultracataclasite vein evolution within a granodiorite along the Naxos Detachment System 

Olivia Rolfe, Renelle Dubosq, David Schneider, and Bernhard Grasemann

Ultracataclasites and pseudotachylytes often reflect localized deformation due to coseismic slip and the temporal evolution of seismogenic fault zones. Interaction of these structures and their mechanisms of nucleation and propagation into crustal rocks remain poorly constrained. Herein we conducted a microstructural analysis on a series of ultracataclasitic veins within a deformed granodiorite on Naxos, Greece. The island is a classical Miocene Cycladic metamorphic core complex, with migmatites and the granodiorite at its core. The Naxos detachment dissects the granodiorite, producing a strong N-S stretching lineation and SCC’ fabric indicating top-to-N kinematics. The granitoid cooled rapidly from crystallization (650-680°C) at c. 12 Ma to <60°C by c. 9 Ma. The investigated ultracataclastic veins are slightly anastomosing and oblique to the main foliation fabric in the granodiorite. Petrographic analysis of the granodiorite shows a coarse-grained (50 μm–2 mm) host rock matrix primarily composed of quartz, albite, orthoclase, hornblende and biotite, intersected by the fine-grained (5–60 μm) ultracataclasitic veins of the same composition. Quartz grains within the host rock occur as inequigranular, interlobate to amoeboid shaped grains exhibiting a shape preferred orientation that defines the foliation and appears to flow around larger feldspar porphyroclasts. Bulging and subgrains within the quartz grains are indicative of dynamic recrystallization. Albite occurs as subhedral porphyroclasts displaying undulose extinction, subgrains with fuzzy boundaries, tapered deformation twins, and bookshelf microfracturing. Orthoclase porphyroclasts within the host rock are subhedral to sigma-shaped, exhibiting undulose extinction with small subgrains (<50 μm) near the clast rims and vein margins. All feldspar porphyroclasts in the host rock are heavily fractured with increasing density proximal to the veins. Electron backscatter diffraction (EBSD) mapping of quartz, albite and orthoclase directly crosscut by the ultracataclastic veins reveals variations in relative phase deformation. Larger host rock quartz grains (50–300 μm) reveal internal lattice distortions (max. misorientations of ~20° relative to the grain average orientation) and low angle grain boundary (LAGB) development, with LAGB density and misorientation degree increasing towards grain edges. Smaller quartz grains (5–25 μm) display a moderate crystallographic preferred orientation and minimal misorientation (max. 8°). EBSD mapping of albite and orthoclase porphyroclasts (100 μm–1 mm) evinces crystal-plasticity in the form of a linear to heterogeneous misorientation pattern, with a maximum misorientations of ~38° and ~27°, respectively. Smaller grains of albite and orthoclase (<50 μm) with scattered orientations occur at clast rims and vein tips, and display a maximum misorientations of ~10° and ~15°, respectively. The localized subgrain structures observed in the feldspar are suggestive of dynamic recrystallization. The veins crosscut these recrystallized zones, suggesting propagation occurred after recrystallization of the feldspar. LAGB development is also observed in the feldspar clasts with increasing density towards the clast rims. The co-occurrence of fractures from dislocation and crystal-plastic microstructures in the feldspar porphyroclasts is indicative of fracture propagation in the brittle-ductile regime of feldspar (450–600°C). It remains equivocal whether the ultracataclastic material was injected into pre-existing fractures or the injection of the material induced fracturing within the host rock.

How to cite: Rolfe, O., Dubosq, R., Schneider, D., and Grasemann, B.: Poseidon’s seismic breadcrumbs: ultracataclasite vein evolution within a granodiorite along the Naxos Detachment System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13072, https://doi.org/10.5194/egusphere-egu24-13072, 2024.

EGU24-15737 | Posters on site | TS1.10

Quantification of the surface deformation on salt diapirs using high-resolution Persistent Scatterer Interferometry (PSI) and Multi-Spectral satellite imagery, Zagros mountains, southern Iran 

Stefanie Rieger, Prokop Závada, Jiří Bruthans, Mugabo Wilson Dusingizimana, Christina Plattner, Beth Kahle, and Anke Friedrich

Salt diapirs are ubiquitous in the Zagros Mountains, but salt-flow dynamics in their extrusive parts and interaction with their caprocks are complex and poorly understood. For a better understanding of the interaction between salt dynamics and the caprock on the surface of the salt extrusions, knowledge of high-resolution spatiotemporal surface deformation and multispectral satellite imagery analysis is essential. However, the contemporary vertical surface deformation pattern across salt diapirs is difficult to detect and interpret along disciplinary boundaries. With the aid of high-resolution PSI measurements and multispectral imagery analysis we detected high-precision spatiotemporal deformation patterns of the surfaces of salt diapirs and their caprocks. Furthermore, time-series analysis helped to distinguish between salt-supply-driven domal uplift and vertical surface modification induced by precipitation, dissolution, and erosion.

In this study, we analysed Sentinel-1 PSI time-series, processed by the German Aerospace Center (DLR), to obtain the highest available spatiotemporal resolution of the vertical surface-deformation pattern across three diapirs – Karmostaj, Siah Taq, and Champeh – in the Zagros.

Furthermore, the Persistent Scatterers are correlated to their lithological composition based on multispectral analysis of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite images. Preliminary results indicate that the deformation pattern of the salt diapirs does not correlate with seasonal effects, such as precipitation and heat. The vertical surface deformation pattern on these three diapirs implies that these diapirs are active and that caprock influences the salt flow pattern.

Unnderstanding the activity of salt diapirs in general is also important, for example, in the feasibility studies of salt diapirs as strategic storage facilities for hydrocarbons, waste material, and CO2 storage over longer time-scales worldwide.

How to cite: Rieger, S., Závada, P., Bruthans, J., Dusingizimana, M. W., Plattner, C., Kahle, B., and Friedrich, A.: Quantification of the surface deformation on salt diapirs using high-resolution Persistent Scatterer Interferometry (PSI) and Multi-Spectral satellite imagery, Zagros mountains, southern Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15737, https://doi.org/10.5194/egusphere-egu24-15737, 2024.

EGU24-16570 | ECS | Posters on site | TS1.10

Fabric and microstructural analyses of fine-grained glacier salt (Kuh-e-Namak, Dashti, southern Iran) 

Julia Schmitz, Prokop Závada, and Janos L. Urai

The Kuh-e-Namak diapir consists of a dome and two glaciers and displays flow structures along its profile. Microstructures in salt dome and glaciers are studied for deformation and recrystallization mechanisms in terms of the grain size reduction, grain fabric and its influence on the flow dynamics of the salt system. Using reflected and transmitted light microscopy of gamma-irradiated rock salt thin sections, electron backscatter diffraction and quantitative analysis of digitized microstructures, we show the transition of dislocation creep followed by fluid-assisted recrystallization from the extrusive dome into the glacier where solution-precipitation creep dominates. Along the profile of the glacier, the degree of recrystallization increases, while the porphyroclasts content progressively decreases in favor of the fine-grained matrix. Fabric analysis support the decreasing amount of porphyroclasts and rectangular halite grains. Porphyroclasts in domal salt show the highest misorientation values at the grain boundaries and are consumed by almost misorientation-free, rectangular grains. Further, a development of shape preferred orientation (SPO) in glacier salt is inferred from alignment of the long axes of elongated halite grains visible in the fabric and their rose diagrams. The microstructures are interpreted in terms of combined dislocation creep and solution-precipitation creep. Grain analyses give a mean grain size ranging between 180 and 508 µm and show a moderate aspect ratio around 2, whereas fabric analyses indicate increasing values from dome to glacier salt of up to 4. Subgrain piezometry infers differential stresses of 1.9 to 6.1 MPa, reflecting the high stress in the cold diapir stem, whereas the shear stresses estimated for the glacier are much lower. Estimation for strain rates based on the combination of dislocation creep and solution-precipitation creep are in the orders of magnitude of x10-10 to x 10-09. Well-developed SPO is interpreted to support the hypothesis that solution-precipitation creep is the dominant recrystallization mechanism in glacier salt. Since solution-precipitation creep dominates in salt glaciers at low deviatoric stress, the fine-grained salt deforms much faster than predicted by dislocation creep, allowing salt glaciers to flow.

How to cite: Schmitz, J., Závada, P., and Urai, J. L.: Fabric and microstructural analyses of fine-grained glacier salt (Kuh-e-Namak, Dashti, southern Iran), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16570, https://doi.org/10.5194/egusphere-egu24-16570, 2024.

EGU24-17484 | Orals | TS1.10

Folds in evaporites. What can we learn about the rock-salt rheology? 

Marta Adamuszek, Jessica Barabasch, Janos L. Urai, and Marcin Dabrowski

Due to the presence of low-viscosity rock-salt, evaporite sequences show a remarkable susceptibility to deformation across diverse geological settings. These sequences often exhibit intercalations of rock-salt with siliciclastic rocks, anhydrite, and sometimes various bittern salts like carnallite and bischofite. Their distinct layering serves as invaluable markers, facilitating a comprehensive analysis of internal salt deformation. The extensive deformation of the evaporites often gives rise to complex internal architectures within the salt body, characterized by commonly observed fold structures. The geometries of these structures are highly sensitive to the mechanical properties of the layers, thus offering profound insights into rock-salt rheology. Unravelling the rheological behaviour of rock-salt holds significant implications, particularly in salt mining, salt cavern operation, and advancing our understanding of salt tectonics.

In this project, we focus on specific outcrops within salt mines located in Romania, Austria, and Poland, where prominently exposed fold structures offer unique field laboratories. These sites hold significant potential for deciphering the mechanical behaviour of rocks during their long-term deformation. In our study, we combined field observations, detailed mapping and microstructural analysis of various single and multilayer folds complemented by numerical models of fold evolution. In our numerical simulations, we use the Carreau model for rock-salt, which captures two primary deformation mechanisms: pressure solution and dislocation creep. The mechanisms correspondingly result in the linear (Newtonian) and non-linear (power-law) rheological regimes, influenced by rock grain size and differential stress. Varying the rock-salt grain size enabled us to analyse fold evolution in both regimes as well as in the transitional domain. By systematically comparing our numerical analysis with field observations, we refine our understanding of the mechanical properties of evaporites, contributing to advancements in the study of rock deformation.

How to cite: Adamuszek, M., Barabasch, J., Urai, J. L., and Dabrowski, M.: Folds in evaporites. What can we learn about the rock-salt rheology?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17484, https://doi.org/10.5194/egusphere-egu24-17484, 2024.

EGU24-18140 | ECS | Posters on site | TS1.10

Evolution of fracture intensity and topology in granitic rocks: insight from Mt. Capanne Pluton, Elba Island, Italy  

Filippo Porta, Luigi Riccardo Berio, Cristian Cavozzi, Niccolò Menegoni, and Fabrizio Balsamo

Field analogue studies of fractured crystalline rocks are important for the clean energy transition and or better understanding the subsurface geothermal systems. In this contribution we present a workflow for multiscale quantitative analysis of fracture network and their connectivity in the monzogranitic pluton of Monte Capanne (Elba Island, Italy). Field structural analysis was integrated with Digital Outcrop Model (DOM) of a 1.5km-long outcrop and with microfracture analysis performed in thin section. The DOM was obtained from images acquired with UAV flights. Field analysis indicate the presence of three main fracture sets with different attributes and showing systematic crusscutting relationships. The quantitative analysis of the DOM was performed with QGIS software and allowed us to characterize the fracture length distributions, density (P20), intensity (P21), and topology (and their parameters). Data derived from field survey and DOM and analysis has been used to create a three-dimensional Discrete Fracture Network (DFN) using a DICE® (https:// github.com/nicmenegoni/DICE) algorithm in MatLab® to calculate the 3-dimensional fracture intensity (P32). In addition, we extended the two-dimensional topology concept in the third dimension. Thus, assuming circular fractures, new topology parameters have been calculated such as number of fracture intersection in volume and intersection fracture length in a volume, i.e., I30 and I31 respectively. Finally, based on the relative fracture chronology, we simulated the step-by-step evolution of 2- and 3-three-dimensional fracture density, fracture intensity and topology, describing the relationship between different fracture sets over time. The preliminary results show how fractures connectivity evolve over time. The ultimate goal of this work is to constrain the evolution of fracture porosity to enhance our ability for modelling fluid flow in crystalline rocks.  

How to cite: Porta, F., Berio, L. R., Cavozzi, C., Menegoni, N., and Balsamo, F.: Evolution of fracture intensity and topology in granitic rocks: insight from Mt. Capanne Pluton, Elba Island, Italy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18140, https://doi.org/10.5194/egusphere-egu24-18140, 2024.

EGU24-18516 | ECS | Posters on site | TS1.10

Megaflaps flanking salt walls: strain and stress distribution from field observations to numerical modeling. 

Marine Lartigau, Jean-Paul Callot, and Claude Gout

The megaflaps are halokinetic objects of multi-kilometer extension corresponding to vertical or overturned strata flanking salt walls or resulting welds. Although their geometry and mechanical behavior can be considered similar to detachment folds, their development mechanism and the consequences regarding strain record remain to be specified.

Megaflaps record strain before, during, and/or after tilting, and their development involves mechanisms specific to each megaflap (i.e. force folding with limb rotation or kink-band migration, passive folding), to their geological characteristics and the local and regional context. We highlight that the initial carapace, covering the evaporites and forming the future megaflap, constitutes a continuous mechanical unit allowing the transmission of an early homogeneous stress (either local or regional). Folding is then initiated by limb rotation, hinge migration or passive folding. During diapirism, the piercement of the salt structure generally accommodates the stress, that preserves the adjacent sediments from regional deformation. However, due to the evaporites loading, we observe a very localized compressive strain, which is perpendicular to the evaporite wall and results in the development of salt-related meso- and microstructures.

We compared the stress states determined on field analogs are with 2D uncoupled geomechanical models. The stress-strain distribution of two types of megaflaps were studied: a single development step megaflap, presenting a main mechanical unit (e.g. Karayün megaflap, Turkey), and a sequential development megaflap, presenting several mechanical units (e.g. Cotiella megaflap, Spain). Our models are based on well-defined geometries of known field analogs. In each model, the layers constituting the future megaflap record compressive strains, varying in extent and localized near the salt wall. Horizontal compression parallel to the layers, induced by salt push, is consistently observed and matches with field observations. Our models also depict layer folding, which can be accommodated through various mechanisms (extrados and intrados deformation, compressive mechanical guidance). Finally, it seems that the late stage tightening deformation would occur through an intensification of stress magnitude induced by complete welding. Our models show that welding significantly increases the maximum stress magnitude. The ratio between compressive stresses and background stresses is thus four to five after welding, compared to a ratio of two without welding. This matches our observations regarding the formation of new mesostructures during the late stage tightening within the Cotiella megaflap, induced synchronously in all layers (regardless their attitudes, already vertical and overturned, or gently dipping). In contrast, the preservation of salt bodies is correlated with the absence of late micro- and mesostructures perpendicular to the vertical layers as observed in other known field analogs (e.g., Sivas Basin, Paradox Basin, Witchelina diapir). Consequently, some megaflaps may remain unaffected by late-stage tightening even within a regional compressive system undergoing shortening.

How to cite: Lartigau, M., Callot, J.-P., and Gout, C.: Megaflaps flanking salt walls: strain and stress distribution from field observations to numerical modeling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18516, https://doi.org/10.5194/egusphere-egu24-18516, 2024.

EGU24-19007 | ECS | Orals | TS1.10

The microstructure of naturally deformed gneissic Zechstein 2 rock salt (Kristallbrockensalz) from the northern Netherlands – a review 

Jessica Barabasch, Joyce Schmatz, Jop Klaver, Alexander Schwedt, and Janos L. Urai

Janos Urai's contributions have significantly enhanced our understanding of salt deformation, particularly in predicting the long-term evolution of solution-mined caverns and radioactive-waste repositories in salt formations. His work delved into phenomena such as the weakening of rock salt by water during long-term creep at low differential stresses. Unlike most laboratory measurements, which are at higher differential stress, Urai's research considers dislocation creep and pressure solution (dissolution-precipitation creep), processes not commonly included in current engineering predictions.

Microstructural observations on Zechstein 2 (Z2) rock salt cores in the northern Netherlands reveal substantial grain-size-dependent differences in rock salt rheology. The study compares undeformed salt layers with strongly deformed diapiric ones, showcasing variations in megacrystals and fine-grained halite microstructures that point to different microphysical processes. The microstructural analysis, including optical microscopy of gamma-irradiated thin sections, recrystallized grain-size measurements, electron microscopy, and subgrain-size piezometry, indicates differential stresses between 0.5 and 2 MPa during deformation.

The findings highlight the importance of pressure solution creep at low differential stresses, demonstrating its significant impact on strain rate in rock salt. Integrating these results into constitutive flow laws reveals a four-order-of-magnitude difference in strain rates between halite types, emphasizing the role of different dominant deformation mechanisms. The study suggests that incorporating pressure solution creep and microstructural analysis can substantially enhance engineering and tectonic models of rock salt deformation in low-stress conditions.

How to cite: Barabasch, J., Schmatz, J., Klaver, J., Schwedt, A., and Urai, J. L.: The microstructure of naturally deformed gneissic Zechstein 2 rock salt (Kristallbrockensalz) from the northern Netherlands – a review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19007, https://doi.org/10.5194/egusphere-egu24-19007, 2024.

EGU24-20283 | Posters on site | TS1.10

The role of salt tectonics in the occurrence of the 2021 Central Adriatic seismic sequence 

Laura Scognamiglio, Francesca Di Luccio, Mimmo Palano, Alessandro Marchetti, Iva Dasović, Marija Mustać, Federica Magnoni, Pietro Artale Harris, Emanuele Casarotti, Alina Polonia, Luca Gasperini, Anke Dannowski, and Heidrun Kopp

On 27 March 2021 a three-months lasting seismic sequence struck the Central Adriatic Basin, part of Adria that is considered a relatively undeformed plate since recent times. Analyzing the waveform data acquired by the Italian and Croatian seismic networks, we computed the location parameters of 160 earthquakes and the focal mechanisms of the Mw5.2 mainshock and larger aftershocks. Most events align along a WNW-ESE, 30 km long, narrow belt. They form two clusters between 0-3 km and 4-14 km of depth, separated by a 1-2 km thick aseismic zone. Based on literature data, we suggest that such a seismic gap corresponds to a ductile salt layer, which constitutes the primary control factor for the evolution of the 2021 earthquake distribution. Moreover, the presence of a salt layer explains well the relatively high Vp/Vs ratio of 1.83 in the sediment rocks surrounding the salt bodies, as also observed in similar tectonic settings. We suggest that the seismogenic fault likely responsible for the 2021 events is an inherited SW-dipping normal fault, reactivated with prevalent reverse kinematics in response to the regional compressive stress. These results, and the recognition of a specific role of salt deposits in focusing deformation and seismogenesis represent a novel contribution to the long-standing problem of seismic hazard assessment of the Central Adriatic Basin, where moderate to large events could have devastating impacts along the highly populated coasts.

How to cite: Scognamiglio, L., Di Luccio, F., Palano, M., Marchetti, A., Dasović, I., Mustać, M., Magnoni, F., Artale Harris, P., Casarotti, E., Polonia, A., Gasperini, L., Dannowski, A., and Kopp, H.: The role of salt tectonics in the occurrence of the 2021 Central Adriatic seismic sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20283, https://doi.org/10.5194/egusphere-egu24-20283, 2024.

EGU24-249 | ECS | Posters on site | TS1.11

Competitive methane bubble growth in aquatic muds 

Xiongjie Zhou and Regina Katsman

Methane (CH4) bubbles developed in shallow aquatic muds present a significant environmental risk. Macroscopic CH4 gas content in the muds is accommodated in discrete bubbles that grow from below the pore scale size to the maximum size defined by muddy sediment mechanical properties. The bubbles force out the water within the pores and distort the structure of the muddy sediment by moving the grains apart at their growth above the pore scale. However, the interaction between growing bubbles was not understood. This study uses a mechanical/reaction-transport numerical model to simulate the interaction of competitive CH4 bubbles paired with fracture-driven growth of varying initial sizes in aquatic muds. It reveals that mechanical and solute transport dynamics play a crucial role at different stages of bubble growth, particularly hindering the development of smaller bubble growth in competition. The stress from the larger bubble impacts the inner pressure and diffusive CH4 flux to the smaller bubble, slowing its initial growth (at t < 40 s). Additionally, the larger bubble later diverts CH4 from the smaller one, further inhibiting its growth expansion. This interaction may cause more horizontally oriented smaller bubbles and significant deformations in the larger bubble, especially as the distance between the bubble pair decreases. Such competitive bubble growth may explain the bubble size distributions observed in lab experiments and in situ, promoting CH4 retention in muddy sediments and the formation of gas domes, which are precursors to pockmarks that can cause abrupt gas releases to the water and potentially the atmosphere. The study provides a foundation for upscaling to different models of gassy muddy sediment acoustic characteristics and models of gas retention evolution, while maintaining single bubble growth metrics. It contributes to better evaluating and potentially reducing long-persisting uncertainties around CH4 emissions from shallow aquatic sediments.

How to cite: Zhou, X. and Katsman, R.: Competitive methane bubble growth in aquatic muds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-249, https://doi.org/10.5194/egusphere-egu24-249, 2024.

EGU24-392 | Orals | TS1.11

Dykes and their magma overpressure 

Tridib Kumar Mondal and Sirshendu Kumar Biswas

Dykes are essentially magma filled fractures within the earth’s crust often formed by the pressure imparted by the intruding magma. Magnitude of the magma overpressure has been traditionally determined utilizing elastic properties of the host rock and the complete dimension i.e., full length and maximum width of the fractures. Full exposures of dykes (from tip to tip) are rare, however, as most of the dyke bodies encountered in the field are subject to erosion or disruption along its length as a result of geological time, making estimation of aspect ratios challenging.

We propose a new method of estimating total length and maximum width of dykes from their partial outcrops featuring at least one exposed tip. Taking into account the fact that majority of dykes form as dominantly opening mode fractures with an elliptical shape of opening, the method involves solving the equation of this ellipse using every conceivable combination of a pair of ground points recorded on the dyke margin considering the visible tip as the origin. Validity of the method has been checked using published data obtained from incomplete dyke outcrops exposed in the caldera walls of Miyake-jima volcano in Japan. The calculated estimates are in line with the results acquired through a previous published method. The present method has been effectively utilized to calculate the aspect ratios of partially exposed mafic dykes emplaced within the younger granite of the Chitradurga Schist Belt in the western Dharwar craton of peninsular India. We discuss the ranges of their magma overpressure and depths of origin as well as the stress intensity factors associated with the host granite.

 

How to cite: Mondal, T. K. and Biswas, S. K.: Dykes and their magma overpressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-392, https://doi.org/10.5194/egusphere-egu24-392, 2024.

EGU24-782 | ECS | Posters on site | TS1.11

(Un)certainties in tectonic stylolite stress inversion 

Saskia Köhler and Daniel Koehn

Over the last two decades application of stylolite roughness inversion has become a common tool to reconstruct paleostress-fields, stress magnitudes and burial depth. While the orientation of the highest principal stress is free of any doubt, there are uncertainties coming along with tectonic stylolite inversion that require a differentiated debate. This includes data quality, rock physical parameters, timing of stylolite growth and burial depth.

We present results of statistical data analysis, showing that data quality depends on the number of samples as well as on the sample size. Thus, the dataset can be of very high quality and stable in outcrop scale. This is faced by field and microscopic observations and results of the stress inversion itself, that demonstrate that some common assumptions, i.e. that modelled paleodepth can be used for tectonic stylolite inversion, are not generally valid. We want to open the discussion towards the question of how we can refine such assumptions and parameters for our paleo stress models and better prediction of recent deformations.

 

How to cite: Köhler, S. and Koehn, D.: (Un)certainties in tectonic stylolite stress inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-782, https://doi.org/10.5194/egusphere-egu24-782, 2024.

Observations of crustal stress orientation from the regional inversion of earthquake focal mechanisms often conflict with those from borehole breakouts. In particular, stress orientations from focal mechanism inversion tend to show little heterogeneity on length scales of kms to 10s of km, while borehole stress measurements often exhibit substantial short-length-scale heterogeneity.  Some of the difference may be because the two methods sample different locations within the crust, possibly indicating local stress heterogeneity, either laterally or with depth. We attempt to reconcile these two types of stress measurements, and investigate the implications for crustal stress heterogeneity. We compiled SHmax estimates from previous studies for 57 near-vertical boreholes with measured breakout azimuths across the Los Angeles region. We identified subsets of earthquake focal mechanisms from established earthquake catalogs centered around each borehole with various criteria for maximum depth and maximum lateral distance from the borehole. Each subset was independently inverted for 3-D stress orientation, and the SHmax direction compared with the corresponding borehole breakout-derived estimate. We find good agreement when both methods sample the basement stress (breakouts are close to the sediment-basement interface), or when both methods sample the mid- basin stress (sufficient earthquakes are present within a sedimentary basin). Along sedimentary basin margins, in contrast, we find acceptable agreement only when focal mechanisms are limited to shallow and close earthquakes, implying short-length-scale heterogeneity of <20 km. While the region as a whole shows evidence of both lateral and vertical stress orientation heterogeneity, we find a more homogeneous stress state within basement rock, over length scales of 1–35 km. These results reconcile the apparently conflicting observations of short-length-scale heterogeneity observed in boreholes, which sample primarily the basins, with the relative homogeneity of stress inferred from focal mechanisms, which sample primarily the basement.

How to cite: Hardebeck, J. and Luttrell, K.: A Unified Model of Crustal Stress Heterogeneity from Borehole Breakouts and Earthquake Focal Mechanisms , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3672, https://doi.org/10.5194/egusphere-egu24-3672, 2024.

EGU24-3863 | ECS | Orals | TS1.11

Mapping internal stress field in deforming rocks using synchrotron high-energy X-ray diffraction 

Jean-baptiste Jacob, Benoît Cordonnier, Jonathan Wright, and François Renard

Understanding the mechanisms controlling brittle rock failure at the grain to sub-grain scale is a fundamental challenge in geosciences. Recent advances in triaxial compression and dynamic shock experiments combined with dynamic X-ray microtomography provide unparalleled insights into the 3D strain field evolution within deforming rocks. However, these methods do not accurately predict the heterogeneous internal stress field prior to failure, which is crucial for predicting microfracture initiation and propagation, leading to macroscopic failure. In the past decade, efforts have focused on developing synchrotron X-ray diffraction techniques leveraging the high penetrative capacity of hard X-rays from the last generations of synchrotron light sources. These techniques offer spatially resolved information on crystal phase orientation and elastic strain within a 3D volume. The local orientation and elastic strain tensor is reconstructed grain-by-grain, with precision down to approximately 10-3 radian for orientation and 10-4 for strain. Stress is then calculated using Hooke's law for anisotropic materials and the elastic constants of the crystal phases. We employed 3D X-ray diffraction to investigate the internal stress field evolution in a rock core sample deformed under triaxial compression in the Hades apparatus. A 5mm-diameter core of Berea sandstone was subjected to axial step loading under constant radial stress of 10 MPa, reaching brittle failure at around 90 MPa differential stress. Elastic strain of individual quartz grains were measured at different load steps, and elastic stresses were calculated, providing maps of the internal strain and stress field in the sample. Results reveal progressive elastic shortening of quartz grains parallel to the compression axis and elongation in orthogonal directions due to the Poisson’s effect. Reorientation of principal stress components is also observed with increasing axial stress, which tend to align with the macroscopic stress field. Internal stresses distribution varies within a range of ca. 300 MPa, suggesting local stress amplifications occurred interpreted as force chains, potentially favoring crack nucleation. This experiment is among the first ones to characterize in-situ the stress distribution in a natural rock under compressive loading, and demonstrates the potential of synchrotron diffraction techniques for investigating strain and stress in geological materials.

How to cite: Jacob, J., Cordonnier, B., Wright, J., and Renard, F.: Mapping internal stress field in deforming rocks using synchrotron high-energy X-ray diffraction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3863, https://doi.org/10.5194/egusphere-egu24-3863, 2024.

Abstract

The shale reservoir in the Lower Permian Fengcheng Formation of Mahu Sag, the Junggar Basin is prospective in hydrocarbon exploration and development. Due to the complex structures of the study area and the strong heterogeneity of shale reservoirs, the distribution of in-situ stress in the research area has always been poorly understood. Previous studies on in-situ stress are mostly limited to mechanical experiments, logging calculation and simple 2D numerical simulations. Nevertheless, this study combines multiple technical means to simulate the complex 3D in-situ stress in a more accurate and precise way. In this study, a detailed geological model was established by utilizing the method of ant tracking. Post-stack acoustic impedance, logging data and acoustic emission tests were used to jointly invert the accurate 3D geomechanical model. The orientation of the in-situ stress in the study area was determined by digesting the information from FMI (Formation MicroScanner Image) while the boundary condition was fixed by acoustic emission experiments. Finally, the in-situ stress distribution of the study area was clarified through finite element numerical simulation. As is shown by the simulation results, the in-situ stress modeling revealed that the complicated stress state, stress differences, and stress difference coefficients, all of which can provide valuable guidance for well deployment optimization and hydraulic fracturing in the study area, are closely related to burial depth, faults, and rock mechanics parameters. The stress regime in the research area is mainly reverse faulting type. However, as the burial depth increases, the stress regime will change accordingly, transforming from reverse faulting stress regime to strike-slip faulting stress regime. In the same time, the existence of faults will also affect the stress regime to a certain degree. In addition, most faults in the research area are stable and show little tendency of slippage, but there may be a higher risk of slippage in the deep strata. Therefore, it is advisable to avoid these areas as much as possible during geological exploration.

Keywords: 3D in-situ stress field, numerical simulation, shale reservoir, Mahu Sag

How to cite: Chen, P., Qiu, H., and Chen, X.: 3D numerical simulation of complex in-situ stress fields in shale reservoirs: A case study in the northwestern Junggar Basin of China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4458, https://doi.org/10.5194/egusphere-egu24-4458, 2024.

Knowledge of the present‐day stress field in the Earth's crust is key for understanding the mechanical behaviour of rocks and structures under tectonic forces. The study of stress fields therefore remains a pivotal area for understanding the mechanical behaviour of rocks, fluid flow at depth and in revealing mechanisms that cause tectonic plates to creep, fail, or rupture. stress patterns in the Earth's crust appear on different scales: first order (plate scale), second order (regional scale), and third order (local scale). The latter is mainly controlled by basin geometry, topography, local inclusions, density contrasts, and active faults and can mask regional and plate stress patterns.

In this contribution, a couple of examples of stress states at the local, regional and large scale are presented using borehole breakouts as main stress indicator for the current stress field orientation.

In order to understand the influence of stress field evolution at local scale, a case study in Hawai´i concerns the effects of the two large overlapping shield volcanoes on the stress field at depth. The analysis reveals that the two-competing gravitational loads primary control the orientation of the present-day stress field, which deviates significantly from the plate and regional tectonic stress field. Therefore, knowledge of local and shallow stress fields can have a significant impact on future borehole planning. From a more regional point of view, an example of current stress orientation in Sweden is presented. The main objectives are to constrain the orientation of horizontal stresses using borehole data, and to discuss implications for geothermal exploration. Thus, obtaining detailed and accurate data on the stress state is of paramount significance to optimise the design of underground installations in order to maximise fluid flow and minimise the risks of wellbore instability. Finally, a large-scale study in Italy investigates the stress field at plate scale to reveal whether the orientation of horizontal stresses may change with depth or laterally indicating stress perturbations and heterogeneities related to areas with complex geo-tectonic setting.

In conclusion, this contribution aims to illustrate and emphasise the relevance of determining the horizontal stress orientation at depth in order to improve the understanding of subsurface stress fields and their applications in different fields of geosciences and different geological settings.

How to cite: Pierdominici, S.: Reconstruction of the state of stress in the upper crust by borehole breakouts stress indicators, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5744, https://doi.org/10.5194/egusphere-egu24-5744, 2024.

Transient stress perturbations caused by passing waves of distant earthquakes have been observed to activate fault slip. Observations of remotely triggered earthquakes at distances greater than ~2-3 mainshock fault lengths suggest that certain conditions promote fault activation, including large-amplitude shaking at periods below ~ 10 seconds within a geothermal setting and extensional and/or transtensional tectonics. Yet, it is still unclear if remote dynamic triggering is ubiquitous. An additional complication to determining the prevalence of triggering is that there are likely many small-magnitude earthquakes within sparsely instrumented regions that are uncataloged. Additionally, large mainshock signals can mask smaller local events that also are missing from the local catalogs. As a result, possible triggering mechanism(s) remain enigmatic. Bounding the necessary physical conditions for remote triggering, such as determining the upper or lower bounds of stress or strain amplitudes, the orientation of the seismic wave’s traversal with respect to the local stress field or fault geometry, or the geologic properties conducive to triggering can help provide clues about the physics of remote triggering. 

            The northern Chilean subduction margin provides an ideal setting to study remote dynamic triggering. Its dense instrumentation provides a long history of both seismic and aseismic deformation in both the subduction system and forearc faults, including the Atacama fault system. Our investigation combines a new, detailed regional earthquake catalog (2007-2021) from Sippl et al., (2023) and documented cases of triggered aseismic slip in the Atacama fault system (Victor et al., 2018). We use a twofold approach to determine the prevalence of earthquake triggering by candidate mainshocks that produce strains at our target location ranging from 1 to ~140 microstrain. The approach uses 1) a difference-of-means test of cataloged seismicity outside of the mainshock cluster (including foreshocks and aftershocks), and 2) a waveform-based approach to look for earthquake triggering at seismic stations located close to creepmeters that recorded triggered aseismic slip events.  We find a lack of evidence of persistent, statistically significant seismicity increases outside of the mainshock cluster associated with any of the candidate mainshocks.  Notably, there is an absence of significant seismicity changes outside of clustered foreshock or aftershock seismicity associated with the series of 11 M6.2-8.2 earthquakes that produced high-strain-rate events during the 2014 Iquique sequence. Seismic recordings of the 2011 M9.1 Japan earthquake at stations CX.PB01-CX.PB14 located near creep meter stations CAR3 and CH01 on the Mejillones peninsula near the Chomache fault reveal evidence of remote triggering. We observe local, uncataloged earthquakes that are only visible after applying a high pass filter that removes the mainshock signal that otherwise overprinted and swamped the local signals.  The uniformity of particle motions (circular or oblong) generated by local earthquakes on multiple stations (N=9) is lacking in most non-triggering mainshocks. This uniformity suggests that the orientation of transient stress perturbations imparted by the mainshock waveforms, in relation to the local fault orientations, may play a role in the triggering process. 

How to cite: Harrington, R. M., Kilb, D., Verdecchia, A., and Victor, P.: Putting faults into motion by remote dynamic triggering: local ground-motion orientations seem to eclipse strain in the northern Chilean subduction forearc crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6650, https://doi.org/10.5194/egusphere-egu24-6650, 2024.

EGU24-6837 | Posters on site | TS1.11

Neotectonic stress characterization of New Zealand along the Australia–Pacific plate boundary  

Mojtaba Rajabi, Moritz Ziegler, Oliver Heidbach, and Malte Ziebarth

The complex interplay between the Pacific and Australian plates in New Zealand offers a unique opportunity to investigate the present-day stress field in a tectonically active area. This study examines the present-day stress pattern of New Zealand through the analysis and compilation of data from 289 boreholes, 4291 earthquake focal mechanism solutions, and 72 neotectonic geological structures. Utilizing the Moho depth of New Zealand, we developed both crustal and mantle stress maps. Stress data above the Moho depth is categorized as the crustal stress map, while data below the Moho is classified as the mantle stress map.

The crustal stress map reveals a consistent ESE-WNW orientation of the maximum horizontal stress (SHmax) across much of the South Island, presenting a high angle to the strike of major active strike-slip faults. In the North Island, the crustal SHmax pattern is variable, highlighting the predominant role of the Pacific Plate subduction beneath the Australian Plate along the Hikurangi Margin. Within the Hikurangi Subduction Zone, both the crustal and mantle SHmax orientations are variable. However, the Taupo Rift Zone exhibits completely different stress pattern in mantle and crust, highlighting the Moho as a strong decoupling horizon in this region.

An examination of neotectonic stress regimes, derived from the neotectonic fault database, in comparison with the present-day stress regime from our stress database across 28 tectonic domains in New Zealand indicates a correlation between observed faults, faulting styles, and the stress field. Nevertheless, discrepancies emerge in certain domains, where the acting stress field diverges from the one expected according to the observed faults, suggesting non-optimal fault orientations.

How to cite: Rajabi, M., Ziegler, M., Heidbach, O., and Ziebarth, M.: Neotectonic stress characterization of New Zealand along the Australia–Pacific plate boundary , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6837, https://doi.org/10.5194/egusphere-egu24-6837, 2024.

The Sichuan-Yunnan region of the SE and E margin of the Tibetan Plateau, situated at the transitional nexus between the seismically-active intensely-deformed Tibetan Plateau and the tectonically stable Yangzi block with comparatively low seismicity, has experienced substantial geological transformations during the Quaternary. Given the pronounced seismicity, there is an escalating imperative for an accurate and refined distribution of the stress field in the region. To unravel the contemporary stress state within major active blocks and along active faults in the study area, an elaborate computation of their tectonic stress field is undertaken by comprehensive updated earthquake focal mechanisms catalog. The tectonic stress field in Sichuan-Yunnan region exhibits obvious lateral variations, with the principal compressive stress direction demonstrating a notable correlation with the azimuth of the P axis. The directions of the stress field show a variation from north to south at ~ 28°N. The directions of the maximum and minimum principal compressive stress in the north show nearly E-W compression and N-S tension, respectively. Conversely, in the south, there is a discernible clockwise rotation trend from east to west. Localized normal faulting stress regimes are observed in the middle section of Xianshuihe fault and southwest side of Litang fault. The extensional environment of the former may be attributed to the tectonic activities such as block translation, clockwise rotation and vertical uplift, as well as the clockwise rotation of the Xianshuihe fault from NW-SW to NNW-SSE. The latter may be related to the extensional structures, rift basins and the normal fault movements in the crust formed by the detachment of the plates and delamination of the mountain roots at the end of Triassic. We also found that the tectonic stress field under the large faults, such as Longmenshan fault, Red River fault, Xiaojiang fault and Lijiang-Xiaojinhe fault, show segmented variation. The findings yield invaluable insights into the intricate dynamics of tectonic deformation along the SE margin of the Tibetan Plateau [supported by NSFC Projects 42330311, 42074065 & 41730212].

How to cite: Tian, J., Gao, Y., and Li, Y.: Present-day stress field in Sichuan-Yunnan region based on comprehensive updated earthquake focal mechanisms catalog, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7176, https://doi.org/10.5194/egusphere-egu24-7176, 2024.

EGU24-7664 | Orals | TS1.11

Unusual fault kinematic behaviour and near-surface crustal stress variations before and during an earthquake series in the Vienna Basin (Austria) in spring 2021 

Rostislav Melichar, Ivo Baroň, Matt Rowberry, Jan Jelének, Ľuboš Sokol, Maria del Puy Papí Isaba, Christiane Freudenthaler, Helmut Hausmann, Lukas Plan, Bernhard Grasemann, Josef Stemberk, Richard A. Schultz, and Roland Bürgmann

Short-term earthquake prediction remains one of the primary goals of seismotectonics. Here detailed observations of unusual fault kinematic behaviour and near-surface crustal stress variations are presented from before, during, and shortly after an earthquake series which culminated with two Mw 4.6 and 4.4 events near Breitenau, Vienna Basin, Austria, on 30 March 2021 and 19 April 2021, respectively. The oblique normal NNE-SSW trending Pitten Fault is exposed in Altaquelle Cave close to the southern margin of the Vienna Basin in the eastern Alps, which is known to have hosted several historical earthquakes of Mw = > 5. This cave has developed in Triassic marbles of the Central Alpine Permomesozoic. The observed branch of this active steeply dipping fault is associated with the seismogenic sinistral Vienna Basin Fault and the NE-SW trending Mur-Mürz Fault. To investigate the fault activity, TM71 moiré extensometers have been used to obtain precise three-dimensional records of fault kinematic behaviour at the micron scale while the recently developed SMB2018 protocol has been used to define the stress state associated with each fault reactivation event. The observations were then compared to the Copernicus European Ground Motion Service InSAR time series derived from Sentinel-1 data. From late 2018 to early 2021, the three-dimensional kinematic behaviour of the fault comprised a variety of different on-plane as well as out-of-plane hanging block displacements ranging in magnitude from 3 to 19 μm. Then, around the time of the earthquake series in 2021, four significant displacement events were recorded: (i) 0.186 mm along a vector of 186/-12° (i.e. upward) on 16 March; (ii) 0.615 mm along a vector of 177/-88° (upward) on 26 March; (iii) 0.066 mm along a vector of 013/26° (downward) on 30 March; and (iv) 0.022 mm along a vector of 308/54° (downward) on 11 May. The third of these events occurred on the same day as the largest earthquake. These events are all much larger than any other record of fault displacement recorded in the Eastern Alps since 2013. This contribution details this unusual fault displacement behaviour and compares the calculated stress states with both the focal solutions for each earthquake and InSAR maps of E-W and vertical ground motion. A comprehensive understanding of this important seismotectonic event helps to shed further light on potential earthquake precursory phenomena.

How to cite: Melichar, R., Baroň, I., Rowberry, M., Jelének, J., Sokol, Ľ., del Puy Papí Isaba, M., Freudenthaler, C., Hausmann, H., Plan, L., Grasemann, B., Stemberk, J., Schultz, R. A., and Bürgmann, R.: Unusual fault kinematic behaviour and near-surface crustal stress variations before and during an earthquake series in the Vienna Basin (Austria) in spring 2021, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7664, https://doi.org/10.5194/egusphere-egu24-7664, 2024.

EGU24-9228 | Orals | TS1.11

Earthquake induced residual stresses preserved in fault rocks exhumed from the lower crust 

Luca Menegon, Giovanni Toffol, Hugo W. van Schrojenstein Lantman, David Wallis, Giorgio Pennacchioni, and Bjørn Jamtveit

Field studies established that seismicity in the lower crust is linked to brittle failure of dry, strong rocks. Failure of these strong rocks implies build-up of differential stresses to gigapascal (GPa) levels, but this requirement contrasts with current models of continental lithosphere deformation, which favour distributed flow of weak viscous lower crust. Although several mechanisms have been proposed to generate transiently high stresses, direct measurements are lacking. Recent advancements in microanalytical techniques (i.e., high-angular resolution electron backscatter diffraction, HR-EBSD) have proven successful at measuring the residual stress resulting from elastic strain retained in mineral grains.

We investigated with HR-EBSD the residual stresses in garnet and diopside from exhumed faults containing pseudotachylytes (quenched frictional melts produced during seismic slip). The samples come from Lofoten (Norway), Holsnøy (Bergen Arcs, Norway), and Musgrave Ranges (Central Australia). Pseudotachylytes from all three localities represent single earthquake events and formed at lower-crustal conditions (T = 500–720 °C, P = 0.5–1.0 GPa). Pseudotachylytes from Holsnøy show an asymmetric damage distribution, where host-rock garnet is pulverized nearby the fault on the side subjected to predominantly tensional stresses during rupture propagation, while garnet is intact on the other side. This asymmetry provides an opportunity to compare the residual stresses on both sides of the fault.

All samples preserve intragrain residual stress heterogeneities reaching 100s of MPa to GPa levels due to local high density of unrecovered lattice defects (dislocations). However, the timing of formation of lattice defects with respect to the seismic event differs. In samples from the Musgrave Ranges, the absence of any later deformation along with the sluggish mobility of dislocations in garnet at the ambient deformation conditions (500 °C, 0.5 GPa) allowed preservation of the high dislocation density produced during the earthquake rupture propagation, recording stress heterogeneities of as much as 6 GPa. In Holsnøy, residual stress heterogeneities of up to 1 GPa are only measured in pulverized grains and are also associated with unrelaxed dislocations generated during the earthquake rupture propagation. Intact garnet grains from the less damaged side of the fault show a limited range of intragrain stress heterogeneities, generally within 100 MPa, and a low density of dislocations. Residual stresses in diopside from Lofoten are only elevated (600 MPa) within 200 µm of the pseudotachylyte. Diopside recorded the progressive build-up of stress during interseismic loading, as suggested by the presence of coseismic cracks crosscutting lattice undulations that preserve the greatest stress heterogeneities. However, the ability of diopside to build up stress is limited, as stress is efficiently dissipated by the development of deformation twins.

In conclusion, great stress heterogeneities can be preserved in mineral grains that experienced the earthquake cycle in the lower crust. Different mineral phases can preserve stress heterogeneities to different extents, depending on the mobility of dislocations after their formation and on other relaxation mechanisms (e.g., twinning). Information on residual stress have important implications for the energy budget of an earthquake, the earthquake cycle deformation, and crustal rheology.

How to cite: Menegon, L., Toffol, G., van Schrojenstein Lantman, H. W., Wallis, D., Pennacchioni, G., and Jamtveit, B.: Earthquake induced residual stresses preserved in fault rocks exhumed from the lower crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9228, https://doi.org/10.5194/egusphere-egu24-9228, 2024.

EGU24-9630 | ECS | Posters on site | TS1.11

Quantitative constraints on crustal stress and strength from seismological observations in the Armutlu Peninsula (northwestern Türkiye) 

Gian Maria Bocchini, Patricia Martínez-Garzón, Armin Dielforder, Luca Smeraglia, Rebecca M. Harrington, and Marco Bohnhoff

The Armutlu Peninsula in north western Türkiye, a horst zone in an active transtensional pull-apart basin, is bounded by two major sub-branches of the North Anatolian Fault zone and host high rates of seismicity in the northern part. The ~25-station SMARTnet surface seismic network was installed in 2019-2020 with the purpose of augmenting permanent seismic stations in the northern part of the Armutlu Peninsula and to help increase the detection of small-magnitude earthquakes. Here, we employ a waveform-based clustering method that integrates detailed information from the seismicity and focal mechanism distribution enabled by the added station coverage to investigate the geometry and kinematics of the seismically active structures. We start by using an enhanced earthquake catalog of >4,000 double-difference-relocated events and >150 focal mechanisms obtained using P-wave polarities and amplitudes in the time period between January 2019 and February 2020. We perform a formal inversion of the stress field orientation from focal mechanisms to investigate the regional deviatoric stress field and its relation with activated fault structures. The stress-field inversion uses input data that combines the enhanced focal-mechanism catalog from background seismic events together with published focal mechanisms of M≥2.5 events that occurred between 1999 and 2019. Stress inversion results show an extensional stress regime for the broader northern Armutlu Peninsula and a transtensional stress regime for a narrow region of ~80 km2, referred to as the Esenköy Seismic Zone (ESZ). Within the ESZ, the minimum principal stress (σ3) is approximately horizontal and NE-trending, while the maximum (σ1) and intermediate (σ2) principal stresses are close in magnitude and vary between near vertical and near horizontal. We observe clusters of normal and strike-slip faulting events identified in the ESZ through waveform-based clustering analysis that are optimally oriented with respect to the stress field we derive for the area. The minimum principal stress in the ESZ is rotated clockwise by ~10-15° with respect to the minimum principal stress inferred for the broader Armutlu Peninsula and eastern Sea of Marmara. Based on the Mohr-Coulomb failure criterion, we quantify the relative and absolute magnitudes of the principal stresses, determine the local crustal stress and strength conditions, and will present a discussion of the implications for regional tectonic forces.

How to cite: Bocchini, G. M., Martínez-Garzón, P., Dielforder, A., Smeraglia, L., Harrington, R. M., and Bohnhoff, M.: Quantitative constraints on crustal stress and strength from seismological observations in the Armutlu Peninsula (northwestern Türkiye), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9630, https://doi.org/10.5194/egusphere-egu24-9630, 2024.

EGU24-10591 | ECS | Posters on site | TS1.11

Electrical conductivity in a Griggs apparatus: a new experimental geophysical tool to investigate geological processes 

Thomas P. Ferrand, Jacques Précigout, David Sifré, Frédéric Savoie, Rémi Champallier, and Fabrice Gaillard

Electrical conductivity measurements on well-characterized materials in the laboratory allow accurate interpretations of electrical anomalies within the lithosphere and asthenosphere. But so far, most measurements have been performed statically, and hence, the effect of deformation and/or differential stress on electrical conductivity remains largely unknown. Here we report the first successful deformation experiments performed in a new-generation Griggs-type apparatus adapted for electrical conductivity measurements. The experiments were conducted on samples of Åheim dunites at a confining pressure of 1 GPa and temperatures of 500, 650 and 800°C. In silicate polycrystals, electrical charges are known to preferentially travel through grain boundaries, which act as high-diffusivity pathways. Our results show that stress and strain can significantly impact the electrical conductivity of peridotites by changing the thickness and the number of grain boundaries, respectively. At fixed P-T conditions, the electrical conductivity varies within an order of magnitude during deformation. This motivates to reappraise interpretations of electrical anomalies in mantle rocks, at least in tectonically active regions. The design presented in this study is fully stable at 1 GPa (≈ 30 km depth) and should be stable up to 2 GPa at least, and to average temperatures as high as 1000°C. Further developments should soon enable similar measurements at pressures up to 4 GPa (120 km depth). These experimental achievements open a new research field, which will help to understand electrical anomalies and strain localization processes in rocks under stress at depth, notably within the lower crust, the upper mantle, and subducting slabs.

How to cite: Ferrand, T. P., Précigout, J., Sifré, D., Savoie, F., Champallier, R., and Gaillard, F.: Electrical conductivity in a Griggs apparatus: a new experimental geophysical tool to investigate geological processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10591, https://doi.org/10.5194/egusphere-egu24-10591, 2024.

EGU24-10900 | Orals | TS1.11

The development of kinematic shear-stress free faults  

Daniel Koehn, Daniel Hafermaas, and Saskia Koehler

Faults are normally thought to present shear fractures that develop at an angle to the main principal stresses, so that they have shear stresses active parallel to the fault plane and thus move. Here we present two “fault” features that deviate from this principle, they develop not due to stress but during kinematic movement, they are both oriented parallel to two of the main principle stresses and as such have no shear stresses in their planes. On the large tectonic plate scale one of these features are the well known transform faults between mid ocean ridges. The ridges themselves are extensional features with the lowest principle stress perpendicular to the ridge. Transform faults are oriented perpendicular to the ridges and show movement only or mainly between the ridges where the plates move in opposite directions. These are faults that do not develop due to shear stress, they develop only because of differential movement and are therefore only or mainly kinematic. On the small scale a very similar feature is the side of a stylolite tooth. Stylolites are dissolution features, they are thus in a way the opposite to mid ocean ridges and have the largest principal stress oriented perpendicular to the stylolite plane. Due to differential movement and growth of the stylolite roughness they develop steep teeth where the sides of teeth become oriented perpendicular to the stylolite plane. These are also movement surfaces or “faults” that have no shear stress.

What does this mean for stress inversion analysis? At least stylolite teeth show a quite pronounced set of striations on their sides and slikolites are also often developed on fault planes, at least in limestone. How do we separate a purely kinematic from a stress-related fault? This discussion and the potential consequences for stress inversion studies is not new, but remains to be very important and should be debated.

How to cite: Koehn, D., Hafermaas, D., and Koehler, S.: The development of kinematic shear-stress free faults , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10900, https://doi.org/10.5194/egusphere-egu24-10900, 2024.

Understanding the stress conditions of active subduction zones has been a longstanding hurdle with critical implications for natural disasters considering stress/strain orientations and magnitudes can control shallow earthquakes and tsunamigenesis. The Sestola-Vidiciatico Unit (SVU) in the Northern Apennines is an exhumed subduction channel with exposures of up to 9 km paleodepth, having reached up to 200°C. This unit experienced a relatively limited deformation history and serves as a rare analog to the shallowest portions of active subduction megathrusts. We use calcite twin data from shear veins along mineralized faults surrounding the exhumed subduction interface to reconstruct paleostress orientations through calcite twin stress inversion. Combining orientation data with calcite twin paleopiezometry and geothermometry, we are able to reconstruct the stress state of the SVU during peak subduction and subsequent exhumation.

During subduction, the maximum principal stress axis was oriented at a low angle to the subduction interface and the minimum principal stress axis oriented at a high angle, indicating N/NE directed compression. As subduction ceased and exhumation initiated, stress orientations inverted with the maximum principal stress axis becoming oriented at a high angle to the subduction interface and the minimum principal stress axis oriented at a low angle, indicating N/NE directed extension driven by primarily the weight of overburden material. These findings are consistent with theoretical orientations for both of these tectonic regimes and agree with previous studies interpreting subduction zone stress orientations. Calcite twin paleopiezometry and geothermometry suggests the rotation of principal stresses coincides with higher differential stresses during early exhumation. Based on the interpreted differential stresses and the reconstructed paleostress orientations, we model different possible explanations including contrasting mechanical strength between the contractional and extensional faults or changes in pore fluid pressure conditions between the two different tectonic regimes.

How to cite: Williams, S., French, M., and Rubin, C.: Determining the deformation temperatures and paleostress conditions of the Sestola-Vidiciatico Unit in the Northern Apennines, an exhumed shallow subduction zone, using calcite deformation twins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14306, https://doi.org/10.5194/egusphere-egu24-14306, 2024.

EGU24-15071 | Posters on site | TS1.11

Healing and strength cycling in a regional scale overthrust: insights from the Sestola Vidiciatico Unit in the Northern Apennines 

Silvia Mittempergher, Francesca Remitti, Telemaco Tesei, and Giancarlo Molli

During their activity, faults experience multiple seismic cycles, implying that faults recover strength between subsequent failures. Fault strengthening after failure (“fault healing”) occurs through processes having different space and time scales, including fault rock compaction, contact strengthening, contact area increase, fracture self-healing and precipitation of minerals in fractures (sealing). The efficiency of different processes varies depending on the geological setting, fault mechanics and availability and geochemistry of fluids. Here, we present preliminary data from a field-based study of the healing mechanisms of thrust faults inside the Sestola Vidiciatico Unit (SVU) in the Northern Apennines, a tectonic unit interpreted as the plate boundary shear zone between the Ligurian complex and the underthrusting Adria microplate during early-to-middle Miocene, active at temperatures up to 150°C.

The thrusts are sharp surfaces lined by calcite shear veins juxtaposing hectometer to kilometer-sized tectonic slices consisting of marls, shales, sandstones and mud-rich mass transport deposits. The marls and shales of the SVU bear a penetrative deformation pattern of fractures and incipient cleavage planes bounding oblate lithons, whose flattening planes define a foliation approximately parallel to the tectonic contacts. In the marls and shales adjacent to the main thrusts decimetric to metric-thick sheared domains may be observed showing an oblique foliation compatible with the sense of transport of the thrusts. Subvertical extensional calcite veins are common in the competent rock lithons. Multiple generations of normal faults lined by calcite shear veins crosscut the thrust faults, the oldest being rotated and deflected within the thrust-related shear zones. Calcite shear veins, in both thrusts and normal faults, display crack and seal domains and implosion breccias.

The lack of cataclastic rocks along faults indicates that the thrusts and normal faults were active at low differential stresses and high fluid pressures. Normal faults and subvertical extensional veins mutually crosscutting with thrusts are compatible with episodes of post-failure switching from reverse to normal fault stress regimes. Fault healing is dominated by calcite precipitation, which occurs both during fault slip (in crack and seal veins and implosion breccias), and after failure into subvertical extensional veins. Thrust compaction due to stress rotation is likely to be a factor promoting fault compaction and healing. Furter investigations will be conducted to constrain the origin of fluids involved in the vein cementation and the role of stress rotation in promoting different healing mechanisms.

How to cite: Mittempergher, S., Remitti, F., Tesei, T., and Molli, G.: Healing and strength cycling in a regional scale overthrust: insights from the Sestola Vidiciatico Unit in the Northern Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15071, https://doi.org/10.5194/egusphere-egu24-15071, 2024.

EGU24-15970 | Posters on site | TS1.11

Paleostress inversion of fault slip data: what is the problem? 

Christophe Pascal

Paleostress inversion methods based on fault slip data (i.e. “fault slip inversion methods” or FSIMs) were formalised fifty years ago to become, shortly after, classical tools in structural geology and tectonics. The great popularity quickly gained by the methods was as remarkable as the enduring scepticism they prompted in the geological community. FSIMs belong to the rather narrow collection of methods, which allow for bridging traditional field observations and measurements (of fault planes and their respective slickenlines in the present case) to the stress tensor, a complex mathematical object. The latter statement highlights the originality of the approach and, perhaps, the roots of FSIM scepticism: stress are “observed” (or derived from observation of the nature) and not “measured” with the help of physical instrumentation, as it is traditionally done.

FSIMs are thus methods that involve mathematical processing of field data after adequate encoding of these. They rely primarily on the so-called “Wallace-Bott hypothesis”, which assumes parallelism between the measured fault stria and the computed maximum resolved shear stress, and on additional background conditions. The purpose of the present contribution is to discuss the limits of FSIMs in the light of their theoretical background and of realistic geological situations. The discussion will mostly focus on key-issues (e.g. is the stress restored by FSIMs in agreement with the formal definition of mechanical stress?) and will try to propose some future research tracks.

How to cite: Pascal, C.: Paleostress inversion of fault slip data: what is the problem?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15970, https://doi.org/10.5194/egusphere-egu24-15970, 2024.

EGU24-16586 | Posters on site | TS1.11

The recent crustal stress state of Germany - results of a new geomechanical–numerical model 

Steffen Ahlers, Karsten Reiter, Andreas Henk, Tobias Hergert, Luisa Röckel, Sophia Morawietz, Oliver Heidbach, Moritz Ziegler, Birgit Müller, and Victoria Kuznetsova

Knowledge of the recent crustal stress state is crucial for a better understanding of crust stability. However, the amount of available stress data in Germany is low. Therefore, a reliable and comprehensive prediction of the complete stress tensor is not possible with these only. However, 3D geomechanical-numerical models, which represent the geometry of the subsurface and its mechanical properties and are calibrated to stress data, allow a continuum-mechanics based prediction of the complete stress tensor and its lateral and vertical variability. A new geomechanical-numerical model of Germany provides new insights into the recent crustal stress field. In contrast to previous models, an improved geological model with a significantly higher stratigraphic resolution is used, a high vertical resolution of ~40 m allows a better mechanical representation of individual units and mechanical inhomogeneities and new data records are used for calibration.

The results provide a comprehensive prediction of the complete stress tensor for Germany and can be used for a wide range of scientific questions and applications. Examples are the prediction of the fracture potential, the slip tendency of faults or as boundary conditions for small-scale models usable for example for engineering applications.

How to cite: Ahlers, S., Reiter, K., Henk, A., Hergert, T., Röckel, L., Morawietz, S., Heidbach, O., Ziegler, M., Müller, B., and Kuznetsova, V.: The recent crustal stress state of Germany - results of a new geomechanical–numerical model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16586, https://doi.org/10.5194/egusphere-egu24-16586, 2024.

Seismicity studies on both fast- and slow-spreading ridge systems have found along-strike variations in mantle mechanical behavior on oceanic transform faults (OTFs), at pressure and temperature conditions above the long-term brittle-ductile transition of peridotites at ~700°C. Plate motion on some sections of the fault is accommodated by aseismic slip only (ductile deformation), whereas motion on other sections is by slip and deep swarms of microearthquakes (semi-brittle deformation) of mantle rocks (e.g., McGuire et al., 2012; Yu et al., 2021). To explore the mechanisms responsible for lateral variations in mantle mechanical behavior and the occurrence of this deep mantle microseismicity, we carried out an integrated study on peridotite mylonites dredged from two OTFs on the Southwest Indian Ridge that record deformation at 700-1000°C.

The samples show variable degrees of deformation, ranging from proto- to ultra-mylonitic textures. The most deformed zones of the mylonites are characterized by an increase in the proportion of fine grained (<10 micron) mylonitic shear bands compared to coarse grained (millimeter) porphyroclasts inherited from the protolith. These shear bands contain syn-deformation chlorine-rich amphibole indicating seawater-peridotite interaction during shear band formation.

Olivine and pyroxene porphyroclasts in protomylonites contain evidence for intense brittle deformation. The presence of subgrain walls, high aspect ratios, and internal misorientations crosscut by fractures imply that they deformed by low-temperature plasticity before brittle deformation. Fractures are sealed by the fine-grained shear bands present in the samples. In (ultra)mylonites, porphyroclasts also show evidence of fracturing after flowing through low-T plasticity. Fracturing was coeval with viscous flow of surrounding weak and hydrated mylonitic shear bands and triggered by hardening of larger grains due to dislocation accumulation. From existing flow laws, such brittle deformation of peridotite minerals necessitates high strain rate deformation, from 10-9 to 10-5s-1, similar to strain rates associated with slow slip events.

From these results we propose that swarms of microseismicity on OTFs are triggered by deformation of a heterogeneous mantle. Seismic rupture occurs in lenses of coarse-grained peridotites, possibly driven by aseismic creep of surrounding hydrated mylonitic shear zones. Importantly, observations also suggest plastic flow of brittle (seismic) patches before rupture.

How to cite: Cécile, P. and Jessica, W.: Origin of brittle deformation and microseismicity in the ‘ductile’ mantle on oceanic transform faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16752, https://doi.org/10.5194/egusphere-egu24-16752, 2024.

EGU24-16807 | ECS | Orals | TS1.11

First-order global stress patterns inferred from hierarchies of upper mantle flow models 

Jorge Nicolas Hayek Valencia, Ingo Leonardo Stotz, Hans-Peter Bunge, Sara Carena, and Sia Ghelichkhan

Understanding the intricate dynamics of mantle flow and their influence on lithospheric stress patterns is critical for assessing reservoir responses to potential CO2 or nuclear waste storage, as well as for hazard and risk assessment. Stress patterns play a first-order control in the mechanical response within inherited tectonic structures, with varying stress sources governing different spatiotemporal scales. Our understanding of the present-day mantle flow state has much improved over the past decades, reflected in models that are consistent with first-order features. The World Stress Map (WSM) project serves as a primary observational dataset to validate our understanding of Earth's dynamics through a global compilation of crustal stress indicators.

Here we study mantle flow models as a simplified superposition of Couette and Poiseuille flow types, which have been useful in explaining sub-continental scale deformation in the lithosphere. We aim to understand the role of mantle flow as a stress driver by generating stress fields from an analytical representation of upper mantle flow, derived from the superposition of steady-state flow models. Our approach allows us to build first-order expectations and conduct fast hypothesis testing for upper mantle flow states.

How to cite: Hayek Valencia, J. N., Stotz, I. L., Bunge, H.-P., Carena, S., and Ghelichkhan, S.: First-order global stress patterns inferred from hierarchies of upper mantle flow models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16807, https://doi.org/10.5194/egusphere-egu24-16807, 2024.

EGU24-16849 | ECS | Orals | TS1.11

Subgrain-size piezometry of feldspar and quartz records a single paleostress from dry lower continental crust 

Alix Osinchuk, Brendan Dyck, Dave Wallis, and Alfredo Camacho

Strength-depth profiles for ductile portions of continental crust are derived from either extrapolation of flow laws from deformation experiments or paleopiezometric estimates in deformed and nominally hydrated plate margins. Lower continental crust in intracontinental settings, in contrast, is relatively dry and should be considerably stronger than the lower crust of hydrated plate margins. The relative strengths of dry quartz and feldspar are poorly constrained by experiments and paleopiezometric estimates from such rocks are sparse. As such, the strength of intracratonic lower crust is difficult to ascertain. Here, we use a recently calibrated subgrain-size piezometer to estimate paleostresses from feldspar and quartz deformed in relatively dry (<20 ppm H2O) lower continental crust of the Musgrave Ranges in central Australia. Neocrysts of plagioclase, K-feldspar, and quartz mantle partially recrystallized porphyroclasts, which is indicative of bulging and subgrain-rotation recrystallization. Using crystallographic preferred orientations and plotting misorientation axes of subgrain boundaries of each phase, we infer that dislocation creep involved the slip systems (010)[100] and (010)[001] for plagioclase, (010)[101] for K-feldspar, and (0001)<11-20> and {01-10}<0001> for quartz. Titanium in quartz and gradients in concentration of Ca and K in feldspars within neocrysts and along subgrain boundaries verify that subgrains in all three phases were formed at a temperature of ~650°C under dry, eclogite-facies conditions. Subgrain sizes of 10.6–18.1 µm in quartz, 11.5–16.9 µm in plagioclase, and 12.0–17.5 µm in K-feldspar correspond to differential paleostresses between 22–36 MPa and are consistent with a single mean paleostress of 28 MPa. Our results demonstrate that there is minimal stress partitioning between dry quartz, plagioclase and K-feldspar under typical crustal thermal gradients. Moreover, the differential stress accommodated by felsic rocks in the Davenport shear zone is lower than predicted by previous strength-depth profiles of lower cratonic crust.

How to cite: Osinchuk, A., Dyck, B., Wallis, D., and Camacho, A.: Subgrain-size piezometry of feldspar and quartz records a single paleostress from dry lower continental crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16849, https://doi.org/10.5194/egusphere-egu24-16849, 2024.

EGU24-16995 | ECS | Posters on site | TS1.11

Paleostress reconstruction from fault slip data along the Purulia Shear Zone, Chotanagpur Gneissic Complex, India   

Subha Kundu, Uddipta Mohanta, and Sudheer Kumar Tiwari

Paleostress analysis is commonly used to understand the brittle exhumation process of deeper crustal rocks to the surface. In this research, we have assessed different stress fields and associated tectonic events in the southern part of Chotanagpur Gneissic Complex (CGC) using fault slip data. The southern CGC comprises two significant crustal-scale shear zones: South Purulia Shear Zone (SPSZ) and the North Purulia Shear Zone (NPSZ), along and across which our fault slip data has been collected. These shear zones exhibit high-grade (amphibolite to granulite) facies Proterozoic rocks consisting mainly of felsic gneisses and migmatites in which low-grade metapelite of North Singhbhum Mobile Belt (NSMB), calc-silicate and mafic granulites of CGC occur as enclaves.

 There has not been any previous study to determine the major stress orientations during brittle exhumation acting upon the Proterozoic rocks in the study area. Thus, our main aim in this study is to understand the variation in stress regime along and across these shear zones and also try to reconstruct the paleostress orientation to determine the history of brittle exhumation of the lower crustal rocks during major orogenic stages of the Proterozoic period. Almost 1000 homogeneous fault slip data have been analyzed using Win-Tensor software. The primary fault data within both shear zones exhibits an approximate E-W orientation, whereas other sets range from NW-SE to NE-SW. Reconstructing stress fields using the age, overprinting relationship and sense of fault movements show that during the Neoproterozoic period (1.0-0.95 Ga), the direction of the compressional stress regime was in N-S orientation. This indicates an oblique-slip movement (thrusting and sinistral strike-slip fault) of the northern CGC block with respect to the NSMB resulting in crustal thickening. The evidence of E-W striking, orogen-parallel normal faults was produced from an N-S directed extensional stress and is primarily responsible for brittle exhumation of these widely distributed granulite facies rocks especially the CGC gneisses in the Purulia region through crustal extension and thinning at 0.95–0.85 Ga.

How to cite: Kundu, S., Mohanta, U., and Tiwari, S. K.: Paleostress reconstruction from fault slip data along the Purulia Shear Zone, Chotanagpur Gneissic Complex, India  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16995, https://doi.org/10.5194/egusphere-egu24-16995, 2024.

EGU24-17092 | ECS | Posters on site | TS1.11

Record of high-stress deformation before and during an earthquake at intermediate-depth conditions 

Giovanni Toffol, Giorgio Pennacchioni, Marco Scambelluri, and Luiz Fernando Grafulha Morales

Exhumed pseudotachylytes (quenched coseismic frictional melts) and their wall-rocks represent a source of information to investigate earthquake mechanics at hypocentre depth. Pseudotachylytes produced at eclogite-facies conditions in subducted oceanic rocks are of particular interest as they open a window into the elusive mechanics of intermediate-depth earthquakes1.

Here we present observations from pseudotachylytes hosted in oceanic gabbros and peridotites from Moncuni (Lanzo Massif, W Alps). These pseudotachylytes record seismic faulting occurred at ca. 70 km of depth during subduction of oceanic lithosphere and have been explained as the result of brittle failure under high differential stress in dry rocks2,3.

We focus on the pervasive damage surrounding pseudotachylytes within olivine-bearing gabbros. Brittle deformation comprises aseismic (cataclasite bands and foliated cataclasites) and coseismic (pulverized domains with shattering in-situ) features associated with the pseudotachylyte veins. Fluid-absent conditions promoted preservation of the pristine brittle features, including pseudotachylyte glass, throughout the exhumation path.

Pseudotachylyte veins and the associated sharp micro-faults are commonly bound by cataclastic domains. Locally, these domains develop an S-C fabric with ultracataclasites along the shear planes. This fabric shows a progressive localization of strain toward the core pseudotachylyte that cut through the S-C fabric, with the cataclastic aggregates proximal to the pseudotachylyte frequently impregnated by melt. Wall-rock olivine grains show evidence of low-temperature plasticity (deformation lamellae and undulatory extinction) and microfracturing. Both deformation lamellae and microfractures are oriented perpendicular to olivine c-axis. These deformation microstructures are also shown by olivine clasts within the cataclasites bounding the pseudotachylytes suggesting a temporal sequence of (i) crystal plastic deformation and (ii) shattering and pulverization. The small olivine clasts in contact with the sharp margin of the pseudotachylyte show substructures a few hundred nanometres in size and are characterized by absence of Kikuchi diffraction patterns. The lack of diffraction bands is interpreted as evidence of extremely high density of dislocations leading to amorphization of the material.

We interpret the low temperature plasticity of olivine and the progressive evolution of the S-C fabric to represent the precursory stage of stress localization predating the abrupt propagation of the seismic rupture, whose instantaneous high stress pulse is recorded by the shattered olivine clasts.

 

[1] Toffol et al., Earth and Planetary Science Letters, 2020, 578: 117289

[2] Scambelluri et al., Nature Geoscience, 2017, 10.12: 960-966

[3] Pennacchioni et al., Earth and Planetary Science Letters, 2020, 548: 116490

How to cite: Toffol, G., Pennacchioni, G., Scambelluri, M., and Grafulha Morales, L. F.: Record of high-stress deformation before and during an earthquake at intermediate-depth conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17092, https://doi.org/10.5194/egusphere-egu24-17092, 2024.

EGU24-17191 | ECS | Orals | TS1.11

Implications for the strength of the Earth’s middle crust from novel experiments on natural fine-grained granitoid rocks  

Natalia Nevskaya, Alfons Berger, Holger Stünitz, Weijia Zhan, Oliver Plümper, Marcus Ohl, and Marco Herwegh

To comprehend the rheology of the Earth's crust and the relevant rock properties, one key approach is to deform rocks and minerals at elevated pressures and temperatures and then extrapolate the measured stress and strain rate values to natural conditions using constitutive equations. Laboratory experiments are mostly conducted on monomineralic rocks, with quartz being considered as the weakest constituent of the middle continental crust. However, field observations suggest that this is an oversimplification, and polymineralic fault rocks may be weaker than monomineralic quartz rocks. This study presents the first experiments on fine-grained, solid, natural rock samples, containing their natural homogeneities and inhomogeneities, demonstrating that granitoid rocks may be weaker than quartz at mid-crustal conditions. It also highlights the importance of pre-existing faults and polymineralic fine-grained zones for strain localisation and proposes values for extrapolation to natural conditions and their use in numerical models of the deformation of the granitoid crust.

Cylindrical granitoid ultramylonite samples, composed of qtz + ab + K-fsp + bt + ep, with grain sizes of 125-15 μm are deformed in a Grigg’s type apparatus at T=650°C, confining P=1.2 GPa, strain rates=10-3 to 10-5s-1, and 0.2 wt% H2O added. Mechanical data are combined with light microscope, SEM, TEM, and quantitative image analysis to connect microstructures with stress and strain evolution. We show that polymineralic granitoid rocks deform through other mechanisms than monomineralic quartz aggregates at pressure and temperature conditions characteristic for the middle crust: Ultra-fine grain size reduction down to <50nm is developed by nucleation and growth of new grains in a polymineralic mixture. Grain size remains small because of pinning processes. We therefore refer to the deformation mechanism as pinning-controlled dissolution-precipitation creep (P-DPC).

Furthermore, we establish a new constitutive equation for this P-DPC, based on an exponential diffusion creep flow law, to model our experiments and tackle the extrapolation to various natural conditions. This flow law is supported by the microstructural evidence for the deformation mechanisms. Extrapolations show that the shear zones of the granitoid middle crust may be magnitudes weaker than extrapolated so far, and deformation may occur at magnitudes faster rates. The brittle to viscous transition may be shifted to shallower levels. This may have implications for the seismogenic zone and/or stress fields below geothermal reservoirs. Most importantly, we show the necessity to take polymineralic rocks into consideration for various numerical model applications.

How to cite: Nevskaya, N., Berger, A., Stünitz, H., Zhan, W., Plümper, O., Ohl, M., and Herwegh, M.: Implications for the strength of the Earth’s middle crust from novel experiments on natural fine-grained granitoid rocks , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17191, https://doi.org/10.5194/egusphere-egu24-17191, 2024.

EGU24-19186 | Orals | TS1.11

Could earthquakes cause rapid dehydration of serpentinite? 

Lucie Tajčmanová, Sebastian Cionoiu, and Dan Schuppenhauer

Dehydration reactions can influence the occurrence of earthquakes at a range of depths, highlighting the importance of understanding these reactions in the study of seismic activity. We have performed several pilot experiments that included the construction of a controllable fast pressure drop unit attached to the piston-cylinder apparatus. This setup makes it possible to simulate conditions that represent a fast pressure drop during an earthquake event. We focused on serpentinite dehydration because 1/ it plays an important link between the deep geodynamic processes occurring in subduction zones and the seismic and volcanic activity and 2/ the interplay between serpentinite dehydration and deformation during the earthquake cycle is not yet fully understood. To test the experimental setting, we first performed a series of static experiments under the conditions that are already in the olivine stability field. After the static experiments at high pressure (1.1 GPa), we performed the controlled fast pressure drop experiments to 0.3 GPa as well as the ramping experiments, in which a series of pressure build-ups and drops were performed maintaining the high temperatures (570 to 640 °C) to simulate the earthquake cycle. In these experiments, olivine was an order of magnitude more abundant than in the one-hour low-pressure static experiment. The pressure drop occurs in seconds. The ramping experiment lasted only 10 mins before cooling down. The results may challenge conventional wisdom about the timescales of mineral reactions under extreme conditions, such as during earthquakes.

How to cite: Tajčmanová, L., Cionoiu, S., and Schuppenhauer, D.: Could earthquakes cause rapid dehydration of serpentinite?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19186, https://doi.org/10.5194/egusphere-egu24-19186, 2024.

EGU24-19980 | ECS | Posters on site | TS1.11

Eurasian plate-scale stress model considering driving and resistive forces 

Renato Gutierrez Escobar and Rob Govers

Our goal is to constrain magnitudes and directions of forces that may explain present-day natural stresses within the Eurasian plate. Driving forces such as horizontal gravitational stresses (HGSs), mantle convective tractions including dynamic topography, and plate interaction tractions with bounding plates are considered. HGS resulting from lateral variations in gravitational potential energy are particularly relevant in the context of the Eurasian plate because there are no major slabs attached to it (i.e., no slab pull force). We illustrate that recently published models of lithospheric density including lateral variations in the lithosphere-asthenosphere boundary result in significantly different HGSs. Furthermore, we include observed major faults into a 2D spherical cap elastic model of the Eurasian plate. We present results of forward FEM calculations and compare them with observed stress directions from the world stress map. We propose different objective functions that determine the misfit of the modelled and observed stresses, fault slip directions, and magnitudes, the deviation of the net torque on the plate from zero, and the model representation error. Our analysis represents a first step towards a Bayesian inference workflow to constrain the dynamics of the Eurasian plate.

How to cite: Gutierrez Escobar, R. and Govers, R.: Eurasian plate-scale stress model considering driving and resistive forces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19980, https://doi.org/10.5194/egusphere-egu24-19980, 2024.

EGU24-20499 | Posters on site | TS1.11

Three-dimensional numerical modelling of drilling-induced tensile wall fractures 

Martin Schöpfer, Mario Habermüller, Nicola Levi, and Kurt Decker

Drilling-induced tensile fractures (DITFs) form due to stress concentrations around a wellbore and are in vertical wells typically parallel to the largest horizontal far-field stress and normal to the least horizontal far-field stress. The peak pressure in the wellbore exerted by the drilling mud that the wall rock can sustain is given by the so-called Hubbert-Willis (H-W) criterion, which predicts that wall rock failure takes place when the circumferential effective stress at the borehole wall reaches the tensile strength of the wall rock. However, even though the H-W criterion is a valuable fracture-initiation criterion, it cannot predict if and how an initiated fracture propagates. Linear elastic fracture mechanics (LEFM) can provide a solution to these questions under simple loading conditions, e.g. a vertical borehole in a rock mass that is under an Andersonian stress state. Predicting the initiation and propagation of DITFs in more complex settings, such as inclined boreholes or wellbores in mechanically layered sequences, however, necessitates three-dimensional numerical modelling.

Here we present results of three-dimensional numerical Rigid Body Spring Network (RBSN) lattice modelling. The model comprises so-called rigid blocks (tetrahedra in the present study), that interact with each other and can be bonded at their contacts; these bonds fail when the effective normal stress exceeds the bonds tensile strength, which corresponds to micro-fracture of the wall rock. Coalescence of these micro-cracks leads to the formation of macroscopic fractures. Wellbore failure is modelled by means of a hollow cylinder discretised by these bonded rigid blocks. The remote (tectonic) stress is applied to the hollow cylinder’s outer surface whilst the pressure exerted by the drilling mud is applied to its inner surface. Fractures connected to the wellbore receive the same internal pressure as the wellbore and quasi-static fracture propagation is achieved by gradually increasing the pressure on the borehole wall.

Validation of the numerical model under simple loading conditions illustrates that fracture lengths and associated aperture profiles as a function of wellbore pressure correspond well with LEFM predictions. Numerical models of moderately inclined boreholes exhibit stepping DITFs, where fracture stepping is most pronounced when the wellbore is inclined towards the least horizontal stress direction and no fracture stepping occurs when the wellbore is inclined towards the greatest horizontal stress direction. In mechanically layered sequences comprised of layers with different Young’s modulus, DITFs first nucleate in the stiff beds. Complex fracture geometries emerge in mechanically layered sequences, such as fracture stepping within individual beds or at layer boundaries. The detailed evolution of these more complex DITFs depends on several factors, such as the orientation of the remote principal stresses and layering relative to the wellbore axis. Our numerical modelling approach permits to systematically investigate the effects of these different factors on the geometry of DITFs and therefore offers a new tool that can assist in construing the mechanical genesis of fractures imaged in borehole logs and the current stress in the Earth’s crust.

How to cite: Schöpfer, M., Habermüller, M., Levi, N., and Decker, K.: Three-dimensional numerical modelling of drilling-induced tensile wall fractures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20499, https://doi.org/10.5194/egusphere-egu24-20499, 2024.

The 1D Geomechanical Models (1DGM) were done for four vertical boreholes in the Early Paleozoic shale sequences of the Baltic Basin in Poland. The models assumed an elastic rock behaviour with anisotropy in VTI symmetry. The far-field horizontal stresses were calculated as the sum of two components: the vertical stress derivative acting on the horizontally constrained rock column and the effect of elastic tectonic strains. Local stresses in the borehole wall were assumed to induce breakouts (BBs) and drilling-induced tensile fractures (DITFs). Hydraulic fracturing tests additionally validated the stress modelling results.

Micro-resistivity images from XRMI logging revealed irregular BBs, usually confined to individual layers, often non-symmetrical, and with a tendency to encompass the entire borehole wall. Despite their irregularity, statistical analysis of their orientation provides a good quality and stable stress orientation.

The initial modelling results, balancing the cumulative length of the modelled (BBM) and observed (BBO), revealed a systematic misfit between BBm and BBo locations. A detailed comparison between the BBm and BBo intervals concluded that the artificial degradation of Young's modulus and Poisson's ratio is caused by the perturbation of the velocity of the acoustic wave from the dipole acoustic tool passing through the intervals with irregular BBs. This makes it impossible to model the BBs in the places where they are present. To deal with this, the initial stress models were recalculated to the final models in which the BBm were avoided in intervals where there were no BBO.

The initial and final stress models differ significantly in terms of the tectonic strain values and the combined length of the BBm. Still, their stress profiles are similar due to the small contribution of tectonic strain to the far-field stresses. We concluded that irregular BBs developed due to small differential horizontal stresses, causing abrupt BB failure with rapidly growing angular width. The stress layering between lithostratigraphic units was obtained with a dominance of the normal faulting stress regime in the lower borehole sections and the reverse faulting present in the upper sections. The minor regional elastic tectonic strain value for the shale sequence was determined to be an order of magnitude lower than the strain in the crystalline basement, as determined from the satellite geodetic strain rate. We expect that this discrepancy could be explained by a higher rate of viscous relaxation in the shale sequence with > 60% of the clay mineral content. This suggests the need to implement the viscous relaxation into the 1DGM of sedimentary sequences.

How to cite: Jarosinski, M., Bobek, K., and Pachytel, R.: Geomechanical models of the shale sequence of the Baltic Basin (Poland): possible case of elastic properties degradation and viscous stress relaxation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20951, https://doi.org/10.5194/egusphere-egu24-20951, 2024.

EGU24-21427 | Orals | TS1.11

Combining synchrotron and acoustic emission techniques to reveal the secrets of high PT faulting 

Giulia Mingardi, Julien Gasc, Robert Farla, and Alexandre Schubnel

Numerous studies have illustrated that mineral transformations have the capability to induce faulting at elevated pressure and temperature (PT), circumstances in which ductile flow would typically dominate. This mechanism, commonly known as transformational faulting, emerges as a plausible explanation for the puzzling phenomenon of deep-focus earthquakes occurring at depths up to 700 km. Currently, the debate partly revolves around determining why certain phase transformations lead to faulting while others do not. To better understand this phenomenon, we can compare different transformations taking place in similar experimental conditions and see how they do or do not cause strain localization and faulting. In this regard, we conducted a series of five deformation experiments in the large volume press at the PB61 beamline at DESY synchrotron. Two of these experiments involved deforming germanium-olivine samples as they transformed into ringwoodite (the high-pressure phase). The other three experiments were carried out on quartzite (novaculite) samples while they were transforming to coesite. Throughout the experiments, we collected X-ray diffraction patterns and images concurrently with the collection of Acoustic Emissions (AEs).

The results indicate, in both quartz and olivine experiments, the growth of the high-pressure phase at various rates depending on PT conditions and equilibrium overstep. Specifically, we observed rapid olivine-ringwoodite kinetics at elevated PT, far from equilibrium, while slower kinetics were noted for the quartz-coesite transformation. Thousands of AEs were collected in each experiment, and their locations reconstructed using arrival times on the six transducers used. Interestingly, the spatial distribution of these AEs revealed that for some quartz-coesite experiments, AEs originated from fault planes that formed within the initially intact rock cores. Furthermore, an analysis of the AE catalogues, focusing on the magnitude-frequency distribution, revealed a wide range of b-values influenced by varying PT conditions and transformation kinetics. This observation underscores the different underlying mechanisms since the obtained b-values are high when transformation and strain are distributed and lower when strain is localized (i.e., when a fault plane develops).

Our study supports the major role of mineral transformations in inducing faulting under high PT. These findings will help better quantify the intricate relationships between mineral transformations and faulting and in turn contribute to a better understanding of the fundamental geological processes behind deep and intermediate earthquakes.

How to cite: Mingardi, G., Gasc, J., Farla, R., and Schubnel, A.: Combining synchrotron and acoustic emission techniques to reveal the secrets of high PT faulting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21427, https://doi.org/10.5194/egusphere-egu24-21427, 2024.

TS2 – Tectonics of Plate Boundaries: From Rifting to Orogenesis

EGU24-1239 | Posters on site | TS2.1

Constraints on the Formation Age of the Chukchi Basin, Arctic Ocean, inferred from Marine Heat Flow Measurements 

Young-Gyun Kim, Jong Kuk Hong, Young Keun Jin, and Byung Dal So

The Amerasia Basin, one of two major basins that comprise the Arctic Ocean, is thought to have a more complex formation history than its counterpart, the Eurasian Basin. Because the harsh conditions for marine expeditions last the entire year, there is a lack of observational data for constraining the tectonic history of the Chukchi Basin. Thus, there are multiple existing hypotheses for its tectonic history, with contrasting formation ages ranging from Mesozoic to Cenozoic and crustal types ranging from hyper-extended continental crust to oceanic crust. Recently, during the 2018 and 2021 Arctic expeditions of the Korean ice-breaking research vessel Araon, we obtained the new marine heat flow data along the east-west and northeast-southwest transect lines from the abyssal plain to the continental slope/shelf of the basin. These data may play an important role in constraining the formation age of the basin, as the extending axis among the hypotheses is likely oriented from north-south. Assuming an oceanic crust, the formation age can be inferred to be Late Cretaceous. This information concerning the formation age enhances our understanding of the underestimated complex tectonic history of the Amerasia Basin, because such inferred timing aligns with the formation age of the adjacent Chukchi Borderland.

How to cite: Kim, Y.-G., Hong, J. K., Jin, Y. K., and So, B. D.: Constraints on the Formation Age of the Chukchi Basin, Arctic Ocean, inferred from Marine Heat Flow Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1239, https://doi.org/10.5194/egusphere-egu24-1239, 2024.

EGU24-1615 | ECS | Orals | TS2.1

Evolution and activation of an orogen-scale shear zone in the northern Aegean Rift System: insights from the Mykonos Detachment, Cyclades, Greece 

Costantino Zuccari, Francesco Mazzarini, Enrico Tavarnelli, Giulio Viola, Luca Aldega, Roelant Van der Lelij, and Giovanni Musumeci

Extensional detachments are commonly considered key structures in accommodating the exhumation of deeply buried or subducted crustal slivers, and in facilitating the syndeformation emplacement of plutons during the evolution of wide rift systems (i.e., Basin and Range type). In those settings, ductile shear zones and brittle faults may act for several million years to accommodate important vertical and horizontal displacements such that multiply reactivated and highly complex shear zones and faults may form. The analysis of these complexities, together with the possibility to constrain the age of strain and deformation localisation, is thus pivotal in reconstructing the onset and evolution of the processes that steer(ed) the crustal extension.

Aiming at better understanding these structural/chronological intricacies, we have studied the brittle Mykonos Detachment (MD), which is thought to have facilitated the emplacement of the Mykonos granite starting in the Middle Miocene (~14-9 Ma) and following the activation of the earlier (ductile) Livada Detachment (LD) that would have favoured the beginning of pluton cooling during the structuring of the Aegean rifting. The Mid. Miocene age of the MD is, however, only loosely constrained by the stratigraphic age of syn-tectonic siliciclastic deposits in the hanging wall of the fault. No absolute ages exist yet on the activation of the brittle MD or the ductile LD, and a detailed description of the internal architecture of the MD is still not available.

Aiming to fill this gap(s), we carried out a detailed study that couples a Brittle Structural Facies – based structural analysis with K-Ar dating on authigenic illite from fault gouge(s) that compose the MD fault core. Fault gouges normally rest on and are cut by the MD principal slip surface (PSS), which reasonably postdates the gouge formation and represents the effects of the latest fault activity. We have obtained a 7.1 ± 0.1 Ma K-Ar age from a fault gouge suggesting that the MD activation postdated the widely accepted ~14-9 Ma of the granite cooling, also considering that the PSS postdates the 7.1 Ma gouge, as indicated by field evidence. On this ground, together with published thermochronological data showing that the granite experienced a rapid cooling from ~14 to ~11 Ma before experiencing slow cooling until ~9 Ma, we can state that most of the granite exhumation cannot be ascribed to the MD, the activation of which postdates the late stage of the granite cooling.

These new geochronological data (which are soon to be implemented with new K-Ar dates) and the description of the architectural evolution of the MD fault zone, stress the role of the detachment during the unroofing of the Mykonos granite in the Aegean rifting context. In this perspective, the granite exhumed is mostly assisted by the ductile LD, which acted before the MD. The latter acted instead only at a later stage when it juxtaposed the Miocene siliciclastic against an already cooled and unroofed granite, which had reached a temperature of ~40°C about 2Ma before the latest Late Miocene activation of the MD, as shown by our preliminary age constraint.

How to cite: Zuccari, C., Mazzarini, F., Tavarnelli, E., Viola, G., Aldega, L., Van der Lelij, R., and Musumeci, G.: Evolution and activation of an orogen-scale shear zone in the northern Aegean Rift System: insights from the Mykonos Detachment, Cyclades, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1615, https://doi.org/10.5194/egusphere-egu24-1615, 2024.

A new onshore-offshore 3-D constrained gravity inversion methodology that incorporates onshore topography and laterally variable inversion mesh depths is used to determine the crustal density distributions, Moho depths, and crustal thicknesses of Iberia, Morocco, and their respective rifted continental margins. The results largely show an excellent correspondence with crustal characteristics determined from sparsely distributed controlled-source and passive seismic experiments, while also allowing the layered density structure of the region to be explored and analyzed in terms of upper, middle, and lower crustal layers. These detailed regional views as a function of depth can improve characterization of crustal types (continental versus oceanic versus transitional), and the resulting interpretations can be directly compared against equivalently derived crustal characteristics for onshore-offshore Atlantic Canada, which encapsulates both Iberia’s and Morocco’s conjugate rifted margins. Collectively, the conjugate 3-D crustal-scale density models allow for the extraction of mega-transects across both sides of the southern North Atlantic, joined together back through geological time using kinematic plate reconstructions.

How to cite: Welford, J. K.: Crustal structure of onshore-offshore Iberia, Morocco, and their rifted continental margins, from constrained 3-D gravity inversion using variable mesh depths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3196, https://doi.org/10.5194/egusphere-egu24-3196, 2024.

EGU24-3979 | ECS | Posters on site | TS2.1

Three-dimensional crustal velocity structure of the north-eastern Gulf of Aden continental margin 

Jie Chen, Sylvie Leroy, Louise Watremez, and Adam Robinson

Continental rifting is the Earth’s fundamental tectonic process that may result in a new plate boundary, i.e., mid-ocean ridges, with the accretion of new oceanic crust. At present, continental rifted margins are classified into two end-members based on the amount of magmatism that occurred during the rifting process: magma-rich and magma-poor. However, various factors influence the formation of these margins, such as the inheritance of segmentation, extension obliquity, syn-rift magmatism, and sedimentation. The Gulf of Aden represents a good example for understanding such spatial variations in the formation of rifted margins. It consists of an oblique rifting system, with young and segmented margins (34-17.6 Ma) and thin sediments. In addition, the Gulf of Aden exhibits magma-rich margins in the west, related to the Afar hotpot, and magma-poor margins in the east, with a possible zone of exhumed continental mantle.

In this study, we develop a 3-D P-wave velocity model across the north-eastern Gulf of Aden continental margin, using wide-angle seismic refraction data from a combined onshore-offshore survey with 35 ocean-bottom seismometers and 13 land seismometers. Approximately 187,000 P-wave first arrivals were picked and inverted in 3-D, with the modelling informed by constraints from previously published 2-D velocity models. Here, we present our preliminary tomographic results that illustrate the spatial variations in the crustal velocity structure of the continent, continent-to-ocean transition (COT), and oceanic domains, as well as the comparison between our 3-D and the published 2-D velocity structures of the north-eastern Gulf of Aden continental margin.

How to cite: Chen, J., Leroy, S., Watremez, L., and Robinson, A.: Three-dimensional crustal velocity structure of the north-eastern Gulf of Aden continental margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3979, https://doi.org/10.5194/egusphere-egu24-3979, 2024.

During the final stages of breakup at magma-poor rifted margins, mantle rocks are commonly exhumed and altered to serpentinite due to the ingress of ocean water. This mantle exhumation phase is followed by an increase in magmatism as new oceanic crust begins to form. However, the degree to which serpentinisation is focused at faults and whether the onset of magmatism is abrupt or gradual are both unclear. These processes are difficult to untangle with seismic data alone because the P wave velocities of mafic crustal rocks and partially serpentinised mantle rocks can be similar. However, serpentinised mantle rocks are generally more conductive, often by about an order of magnitude, than mafic crustal rocks, so controlled source electromagnetic (CSEM) and magnetotelluric (MT) techniques provide a promising route to resolve controversies around the structure of lithosphere formed during the onset of seafloor spreading.

To take advantage of the complementary information provided by seismic and electromagnetic data, in September 2023 we acquired a coincident and densely sampled wide-angle seismic, CSEM and MT datasets across the continent-ocean transition at Goban Spur, southwest of the UK. Our c. 200-km profile is coincident with a pre-existing high-quality seismic reflection profile. It extends from thinned continental crust, whose nature is confirmed by drilling, across a broad zone that is inferred on the basis of a previous wide-angle seismic experiment to be composed of exhumed and serpentinised mantle, and into oceanic crust, evidenced by the presence of the prominent seafloor-spreading magnetic anomaly A34. Along this profile, we deployed 49 seafloor instruments at c. 4-km spacing that were each capable of recording seismic, electric field and magnetometer data, plus an additional two instruments recording the inline electric field on 200-m dipoles. These instruments were on the seafloor for about two weeks. During this time we acquired two wide-angle seismic profiles: one using a 5200 cu. in. airgun array shot at 90-s intervals and a second using a 3900 cu. in. airgun array shot at 30-s intervals. We also acquired a frequency-domain  CSEM profile using a transmitter towed c. 100 m above the seabed that powered a 300-m electric dipole with a c. 100-A current at a fundamental frequency of 0.25 Hz. Preliminary data analysis showed that seismic signals were recorded to c. 90 km offset and CSEM signals to c. 8 km offset, while high-quality MT data were recorded at periods of 20-10000 s.

Thus we expect to recover coincident high-resolution images of the seismic velocity and resistivity structure of the upper few km of the basement, sufficient to image patterns of serpentinisation and mafic intrusion. We also expect to recover lower-resolution images of the resistivity to tens of km below the seabed and thus to distinguish continental mantle lithosphere from depleted oceanic lithosphere. We will present examples of the data acquired and the results of some preliminary analysis.    

How to cite: Minshull, T., Bayrakci, G., and Constable, S.: An integrated seismic, controlled source electromagnetic and magnetotelluric study of the continent-ocean transition southwest of the UK, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6227, https://doi.org/10.5194/egusphere-egu24-6227, 2024.

EGU24-6331 | ECS | Orals | TS2.1

How developing grabens dictate volcanism shifts in rifts 

Gaetano Ferrante, Eleonora Rivalta, and Francesco Maccaferri

Volcanism in continental rifts is generally observed to shift over time from the inside of the graben to its flanks and back. These patterns are commonly observed across rifts from different tectonic contexts, different abundance of melt, and regardless of the rifts' specific complexities, suggesting a common control. However, despite recent advances, the mechanisms governing the spatio-temporal evolution of rift magmatism are still poorly understood. Here we test the hypothesis that the spatio-temporal evolution of rift volcanism is controlled by the crustal stresses produced during the development of the rift basin. To do so, we couple a gravitational unloading model of crustal stresses with a boundary element dike propagation code to investigate the effect of a deepening graben on the evolution of magma trajectories in rifts. We find that the progressive deepening of a graben rotates the direction of the principal stresses in the crust, deflecting ascending dikes. This causes a relatively sudden shift of volcanism from the inside of the graben to its flanks during the early stages of rifting. The intensification of this stress pattern, caused by further deepening of the basin, promotes the formation of lower crustal sill-like intrusions. These horizontal bodies can stack under the rift, shallowing the depth at which dikes nucleate, eventually causing a late stage of in-rift axial volcanism, which can alternatively be induced by compensation of graben unloading by sediment infill. Our model reproduces the general patterns of volcanism in rifts and provides a framework to explain their commonalities and account for possible differences. Given the agreement between our model results and observations, we conclude that the evolution of the stresses generated by a developing rift basin can account alone for the major aspects of the spatio-temporal evolution of rift magmatism.

How to cite: Ferrante, G., Rivalta, E., and Maccaferri, F.: How developing grabens dictate volcanism shifts in rifts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6331, https://doi.org/10.5194/egusphere-egu24-6331, 2024.

EGU24-6401 | ECS | Posters on site | TS2.1

Reactivation of inherited faults in rift basins: insight from analogue modeling 

Pauline Gayrin, Daniele Maestrelli, Giacomo Corti, Sascha Brune, and Chiara Del Ventisette

Continental rifts accommodate shallow extensional stresses both by brittle deformation (normal faulting) and volcanism (i.e. dykes and lava flows). Lava flows, together with clastic sedimentation reshape the topography of the rift floor, forming fresh new layers of rock that cover ancient faults. Therefore, the influence of the inherited buried faults on the development of the new faults and the processes of linkage at depth between them remain difficult to investigate. Here we use analogue brittle-ductile modeling with orthogonal extension to elucidate fault growth and reactivation modes, and then compare the results with data from natural rift systems.

In our models, deformation is produced above an elastic band placed between a fixed and a moving wall controlled by a stepper motor. A  layer of viscous material distributes the deformation within the model. On top of the viscous material we use a  layer of sand mixture to simulate the brittle properties of the upper crust. A first phase of extension develops an entire normal fault network, which is then carefully buried under a variable thickness of sand, simulating a cover of sedimentary or volcanic deposits. A second phase of extension allows us to study the mode of reactivation of the inherited faults.The progress of the deformation is tracked using top view images and digital elevation models interpolated from perspective images. At the very end of the model, cross sections cut at regular intervals show the faults at depth by overlaying coloured brittle layers. The high quality of the images allow us to map and analyze the network semi-automatically. We derive displacement/length profiles to characterize the style of fault growth and propagation mode.

Model results show the development of normal faults creating systems of fault-bounded basins, horst-graben structures and conjugated faults. The setup creates a gradient of deformation from the moving wall, where the faults nucleate first near the fixed wall. We thus observe the coexistence of faults of slightly different ages on the same model, as would occur in nature over time. The cross-section shows an upward propagation and the propagation of faults from depth to surface. The preliminary results indicate different styles of reactivation depending on the stage of fault development: reactivation according to a propagating fault mode where faults still have space at tips to develop and a constant-length fault mode where the network is already fully developed. In addition, we find that the surface overlying the inherited structures first bends, then fractures (without observable vertical displacement), and finally develops from the fracture into a proper fault before it finally propagates to connect laterally within the network. This latter growth mode is consistent with the process observed in Iceland by Braham et al. (2021). Understanding the processes of fault network inheritance holds broader applications to many areas where lava or sediments cover faults, layer after layer, such as magma rich rifts like the Eastern Africa Rift or Iceland.

How to cite: Gayrin, P., Maestrelli, D., Corti, G., Brune, S., and Del Ventisette, C.: Reactivation of inherited faults in rift basins: insight from analogue modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6401, https://doi.org/10.5194/egusphere-egu24-6401, 2024.

EGU24-6489 | Orals | TS2.1

Continental back-arc extension, molten lower crust and syn-kinematic granites: insights from Cycladic MCCs 

Laurent Jolivet, Laurent Arbaret, and Romain Augier

Rifting in back-arc basins is characterized by large extension rates, low-angle normal faults and metamorphic core complexes (MCC) displaying partially molten cores and granitic intrusions. The Aegean metamorphic core complexes (MCC) were exhumed underneath crustal-scale detachments accommodating large displacements of the order of 50-100 km and were intruded by Miocene syn-kinematic granites. A common finite geometry and kinematics of all these detachment/pluton systems is recognized with asymmetric intrusive bodies extracted from anatectic lower crust, whose internal structure is controlled by the large-scale dynamics, from the magmatic stage to mylonitization and final exhumation in brittle conditions. Detachments are organized in sets of structures working sequentially evolving from ductile to brittle, the successive branches of the detachment being progressively inactivated by emplacing plutonic batches. The Mykonos-Delos-Rheneia (MDR) MCC shows these interactions between lower crustal migmatites and different syn-kinematic plutons. Our new detailed map of Delos (1/5000) shows geometrical and kinematic relationships between the different magmatic venues during deformation. A strong internal orientation of granites is observed from the magmatic stage until the last ultramylonites below the upper detachments. The deepest magmatic batches are rich in high-grade rocks septae and mafic enclaves, also oriented parallel to regional stretching. Evidence for magma mixing and mingling further indicates interactions with mafic venues at the base of the crust from the mantle. Large high-grade rocks septae are intensely molten and the contact zone between host gneiss and plutons shows intense migmatitization with a foliation parallel to the granite magmatic foliation. Characteristic banded facies marking the contacts between the different intrusions result from high-temperature shearing at the magmatic stage. At all scales foliation and lineation in magmatic rocks and surrounding gneisses are parallel, suggesting a similar weak rheology. Delos shows the roots of these intrusions emplaced as a large-scale sheath-fold whose axis is parallel to the regional stretching direction. The quality of outcrops in Delos, Rheneia and Mykonos, as well as the links between magma emplacement and regional tectonics makes the MDR MCC a natural laboratory for studying the interactions between magmatic intrusions and crustal deformation in tectonically active and hot contexts. In such contexts magmatic and tectonic processes in the lower and middle crusts appear closely interconnected, working at a similar pace and interacting with mantle deformation and melting.

How to cite: Jolivet, L., Arbaret, L., and Augier, R.: Continental back-arc extension, molten lower crust and syn-kinematic granites: insights from Cycladic MCCs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6489, https://doi.org/10.5194/egusphere-egu24-6489, 2024.

EGU24-6912 | ECS | Orals | TS2.1

Upper mantle anisotropy under the strike-slip Dead Sea rift 

Huikai Xu, Youqiang Yu, and Jiaji Xi

Continental rifting is one of the fundamental tectonics of the Earth evolution while our current knowledge on the dynamic mechanism of the strike-slip ones are seriously limited. Here, a systematically shear-wave splitting investigation has been performed in the typical strike-slip Dead Sea rift to illuminate the upper mantle azimuthal anisotropic status across a transform boundary. Totally, 1855 well-defined anisotropic measurements are observed from 102 stations with dominantly N-S fast orientation, which is parallel to the rift strike but deviate from the absolute plate motion direction, mainly result from the plate-driven mantle flow deflected by the thick lithosphere of the eastern Arabian plate. Additionally, the significant fluctuation patterns of splitting times are identified on both the rift-parallel and rift-orthogonal profiles, among which the relatively large splitting times are generally concentrated at the rift zone and attributed to additional coupling lithospheric deformation from the shearing-oriented melt pockets. The consistent rift-parallel fast orientations, combined with the other geoscientific evidences, rule out the role of mantle plume or edge-driven convection in the rift development and further infer the Dead Sea rift to evolve in a passive mode.

How to cite: Xu, H., Yu, Y., and Xi, J.: Upper mantle anisotropy under the strike-slip Dead Sea rift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6912, https://doi.org/10.5194/egusphere-egu24-6912, 2024.

EGU24-7884 | ECS | Posters on site | TS2.1

A tale of two terrane boundaries – variable impact of terrane boundaries on rift geometry in the Great South Basin, New Zealand 

Malte Froemchen, Ken McCaffrey, Tom Phillips, Mark Allen, and Jeroen van Hunen

The evolution of continental rifts is influenced by the pre-rift rheology of the lithosphere and discrete lithospheric structures that segment the rift. The Great South Basin, offshore New Zealand, is a Cretaceous rift system that formed across heterogenous basement terranes which influence the rift architecture. Faults locally rotate or splay and segment along these terrane boundaries. While the impact of terrane boundaries on rift architecture is well understood, the temporal evolution of these rotated faults is poorly constrained. Here we use 3D reflection seismic data to investigate the timing and slip rate evolution of the rotated and segmented faults along two terrane boundaries. Our results show that these have a significant but variable impact on rift evolution and architecture: Faults in the Murihiku terrane show asymmetric throw-length profiles and are rotated along the terrane boundary to the Dun Mountain-Maitai terrane, as they detach into shallow crustal fabrics. Faults in the DMM terrane show less evidence of rotation and more symmetric throw-length profiles but are segmented along the DMM and Caples terrane boundary. The curving faults of the Murihiku terrane likely formed early on but remained as isolated segments only linking up during later stages of rifting when other faults became inactive. These results show the influence of the terrane boundaries was not only active early during initial segmentation but also during the linkage of curved fault segments in the later stages of rifting. These results may help understand the temporal evolution of lithospheric and crustal inheritance on rift evolution in other regions around the world like East Africa or North China.  

How to cite: Froemchen, M., McCaffrey, K., Phillips, T., Allen, M., and van Hunen, J.: A tale of two terrane boundaries – variable impact of terrane boundaries on rift geometry in the Great South Basin, New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7884, https://doi.org/10.5194/egusphere-egu24-7884, 2024.

Lithospheric extension leads to rift formation and may continue to the point of breakup, with oceanic ridge initiation and the formation of two conjugate rifted margins. In some settings, extension can cease, and the rift may be abandoned. These so-called failed rifts archive snapshots of early phases of deformation, with geometries that may help better constrain the parameters that can prevent a rift from reaching breakup, such as lithospheric rheology, thermal state, rift opening direction and rate, inheritance.

This contribution summarizes a study of the Norwegian Continental Shelf which includes the North Sea Rift and the Møre and Vøring rifted margins. We proceeded to the interpretation of a new dataset of deep penetrating seismic reflection profiles and worked at the regional scale, deliberately ignoring local particularities, to focus on the large-scale structural picture. The aim is to list architectural similarities and differences between the failed rift and the successful rifted margins.

The mapping shows that the North Sea structural geometries and basement seismic facies are very similar to the observations listed for the adjacent Møre and Vøring rifted margins. Various types of tectonic structures are observed, from thick anastomosing shear zones possibly evolving into core-complex geometries, to composite large-scale detachment faults and standard high-angle normal faults. These are categorized into five classes and interpreted as exemplifying the rift tectonic evolution through distinct generations of deformation structures that can activate, de-activate and re-activate. Based on these observations, rift failure dynamics are discussed, and it is proposed that the North Sea rift abandonment may not be related to pre-rift local conditions but rather to the ability to initiate specific tectonic structures such as distal breakaway complexes.

How to cite: Peron-Pinvidic, G.: Structural observations of the northern North Sea: insights into rift failure dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7915, https://doi.org/10.5194/egusphere-egu24-7915, 2024.

EGU24-8883 | Posters on site | TS2.1

Structural inheritance and the evolution of an incipient rift: interaction between the Eger Graben and the Elbe Zone, Central Europe 

David Ulicny, Vladimír Cajz, Karel Mach, Lenka Špičáková, Matěj Machek, Stanislav Čech, Radomír Grygar, Jan Mrlina, and Filip Havlíček

The present-day surface morphology and fabric of the lithosphere of west-central Europe in the foreland of the Alpine orogen have been significantly affected by formation of a system of rifts and associated volcanic domains during the Oligocene and Neogene, known as the European Cenozoic Rift System (ECRIS). In order to better understand the geodynamic causes of formation of ECRIS and its volcanism, it is important to improve the knowledge of chronology of tectonic events in the entire ECRIS, and to test the validity of existing palaeostress interpretations. The Oligo-Miocene Eger Rift, so far the least-studied part of ECRIS, has the potential to bring new clues to some persisting controversies.

The axis of the Eger Rift roughly follows the trend of a major Variscan lithosphere-scale boundary, the Teplá-Barrandian/ Saxothuringian suture (TSS) formed during the collisional phases about 380-320 Ma. Following the Variscan collision, the lithosphere of the Bohemian Massif was affected by formation of a Late Paleozoic extensional basin system which in the western part of the Bohemian Massif largely follows the NE strike of the TSS. Another major structure in the basement underlying the Eger Rift is the WNW-striking Elbe Zone, with main periods of activity during the Paleozoic and Mesozoic through early Cenozoic.

We present a synthesis of presently available structural and stratigraphic data and a resulting first-order interpretation of tectonic evolution of central and eastern Eger Rift. The main data sources were borehole, outcrop, seismic reflection data, targeted field mapping, digital elevation models, and gravity data from both public and industry sources. Several stratigraphic levels (within the Neogene, Cretaceous, and top of Late Palaeozoic) were used as structural datums.

Analysis of fault populations in central and eastern Eger Rift shows that overall, the Late Paleozoic fracturation of the upper crust of the Bohemian Massif was key for localization of the main fault systems of the Eger Rift. This includes dextral shearing within the Elbe Zone that affected the basement structural grain responsible for segmentation of the Eger Rift during the Cenozoic. Changes between oblique and orthogonal extension modes are interpreted from the geometries and temporal relationships of key structures - both in time, likely due to a changing regional paleostress field, and in space, due to different orientations of basement structures between the rift segments.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Ulicny, D., Cajz, V., Mach, K., Špičáková, L., Machek, M., Čech, S., Grygar, R., Mrlina, J., and Havlíček, F.: Structural inheritance and the evolution of an incipient rift: interaction between the Eger Graben and the Elbe Zone, Central Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8883, https://doi.org/10.5194/egusphere-egu24-8883, 2024.

Ocean closure and collisional orogeny frequently enrich the lithospheric mantle in incompatible chemical elements. The most intensive enrichment usually occurs during the subduction of continent-derived sediments and continental crust. Radioactive isotopes of uranium and thorium are part of the HFSE (high-field-strength elements) group of incompatible elements and, therefore, can be also characterized by increased concentration within the post-orogenic lithospheric mantle in comparison to the common lithospheric mantle. The anomalously high content of uranium and thorium within the post-orogenic mantle lithosphere is reflected by the composition of potassic and ultrapotassic magmas, which are sometimes extremely enriched in these radioactive elements. This enrichment is well documented by numerous studies and, therefore, cannot be ignored during the numerical modelling of rifting processes.

According to pure conductive thermal modelling, the anomalously increased content of radioactive elements within the post-orogenic lithospheric mantle causes a time-dependent rise in temperature, providing favourable conditions for intracontinental rifting more than 20-100 million years after the closure of the ocean. A time gap between the orogeny and highly increased temperature within the lithosphere is controlled by two major factors: (1) the amount of thorium and uranium and (2) the size of the anomalous lithospheric mantle. According to numerical thermo-mechanic modelling, the post-orogenic increase in temperature not only weakens the lithosphere but also causes thermal expansion of the lithosphere which can be sufficient to initiate the first stage of intracontinental rifting without involving regional extensional forces.

Therefore, we propose a new concept of intracontinental rift initiation as a result of time-dependent temperature increase and thermal expansion of the post-orogenic mantle lithosphere due to the decay of radioactive elements. The described rather simple mechanism of rift formation provides a significant advance in our understanding of both local rift processes and global tectonic cycles on our planet.

How to cite: Maystrenko, Y. and Slagstad, T.: Post-orogenic radiogenic initiation of intracontinental rifting within the lithospheric mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9325, https://doi.org/10.5194/egusphere-egu24-9325, 2024.

EGU24-9513 | Posters on site | TS2.1

Early relief growth at the edge of an incipient rift – the Eger Graben, Bohemia 

Michal Rajchl, Karel Mach, Filip Havlíček, David Uličný, and Matěj Machek

The present-day geological and morphological expression of the Cenozoic Eger Rift in central Europe is dominated by the faulted edge of the Krušné Hory (Erzgebirge) Mts., a plateau uplifted to c. 1 km above sea level following the mid-Miocene, resulting in partial deformation and erosion of parts of the Eger Rift sedimentary and volcanic infill. The main phase of the uplift is considered to have occurred in Plio-Quaternary times, but details of this process and its relation to the Eger Rift itself remain unclear.

The Oligo – Miocene Most Basin is the most extensive sedimentary basin preserved within the Eger Rift. The basin, bounded at the NW by the Krušné Hory uplift, is characterized by an economically important coal seam, up to 35 m thick. Previous research has shown that during the formation of the basinwide swamps in early Miocene the basin was hydrologically open, with at least one but probably more outlets draining its area toward the North and Northwest, across today’s Krušné Hory (Erzgebirge) Fault Zone (KHFZ). During the earliest Miocene times, most of the region of today’s Krušné Hory / Erzgebirge uplifted block was thus a generally low-relief area. Paleogeographic changes in the Most Basin suggest an increasing activity of its marginal faults, some of which were predecessors of the present-day KHFZ, still during the early to mid-Miocene. For understanding the formation of this major fault zone it is important to answer the question of the timing, magnitude and character of initial relief growth along the nw. edge of the Eger Rift.

The stratigraphic and structural record exposed recently at the KHFZ provides evidence of a small-scale relay ramp that formed between two overlapping normal faults of E-W general strike and breached later by a normal fault of NE strike. Debris-flows conglomerates were found interbedded with carbonaceous mudstones and lignite layers belonging to the early Miocene main coal seam, in the close vicinity of the lower bounding fault containing boulders from a tectonic breccia of the fault damage zone. This fact indicates the existence of a prominent fault scarp developed along the fault plane of the above fault and considered the source of coarse-grained clastics during the initial, coal-bearing, phase of the basin formation. The subsequent acceleration of the Most Basin subsidence that resulted in basin-wide expansion of the swamp environment, can be explained by linkage of the border faults accompanied by breaching and drowning of some relay ramps.

The studied sedimentary record provides evidence of faulted relief with an elevation of tens of metres that contributed to the supply of clastic material to the incipient rift during early Miocene time. The subsequent breakage and drowning of the relay ramp provide evidence for syn-sedimentary activity some of NE-SW segments of the KHFZ previously thought to be a manifestation of later, post-rift deformation.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S. We acknowledge support by the Severní energetická, a.s., and Ing. Petr Šulcek in conducting research in the Důl ČSA Mine.

How to cite: Rajchl, M., Mach, K., Havlíček, F., Uličný, D., and Machek, M.: Early relief growth at the edge of an incipient rift – the Eger Graben, Bohemia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9513, https://doi.org/10.5194/egusphere-egu24-9513, 2024.

EGU24-9770 | Posters on site | TS2.1

Modelling the effects of changing extension directions in a segmented rift: application to the Eger Rift, Central Europe 

Filip Havlíček, David Uličný, Ondřej Krýza, Matěj Machek, Michael Warsitzka, and Prokop Závada

Continental lithosphere undergoing the process of rifting has typically previously experienced a complex deformation history resulting in a highly heterogeneous mechanical structure. This structural inheritance can affect the developing continental rift across all scales, from rift localization and segmentation to individual fault geometries. Assessing the impact of such inherited structures on extensional basin geometries can be difficult, especially in the case of fossil rifts where uncertainties may arise about the orientation of regional stresses during extension. One such example is the Eger Rift which developed during the Oligocene to early Miocene as the easternmost branch of the European Cenozoic Rift System (ECRIS). Earlier interpretation proposed a two-phase extensional history for the rift.

We use a series of crustal-scale, brittle-viscous analogue models, based on the geometry of the central and eastern parts of the Eger Rift, to explore the development of a segmented rift in a multiphase setting with evolving extension direction. Our model crust rests on a basal velocity discontinuity (VD), a discrete boundary of a mobile base plate simulating a reactivated basement weakness localizing our model rift. The geometry of this weakness is a simplified representation of the geometry of older, mainly Upper Paleozoic basins, which are hypothesized to have greatly influenced the localization and geometry of principal fault systems and rift segments that they define. The VD thus consists of 3 segments oriented at various angles with respect to extension direction. The Model surface is imaged by stereoscopic cameras and analyzed by Particle Image Velocimetry (PIV) techniques to track surface deformation and topography evolution during the run.

Our results confirm that in a setting with an abrupt change in extension direction, the first extensional phase plays a key role in defining the final observed fault pattern with new second-phase faults generally being few in number and of limited length. This effect is enhanced above a segmented VD. If a larger portion of the VD is optimally oriented with respect to the first-phase extension, the final fault pattern is dominated by first-phase structures with the growth of second-phase faults being nearly inhibited. In a contrasting scenario, where most of the VD is initially oblique to extension direction, second-phase faults are more abundant, leading to a bimodal final fault pattern. By comparing our results with newly mapped fault populations in the Eger Rift we conclude that the proposed two-phase history for the rift is plausible with a major role of the initial phase of approximately N-S extension.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Havlíček, F., Uličný, D., Krýza, O., Machek, M., Warsitzka, M., and Závada, P.: Modelling the effects of changing extension directions in a segmented rift: application to the Eger Rift, Central Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9770, https://doi.org/10.5194/egusphere-egu24-9770, 2024.

EGU24-9947 | ECS | Orals | TS2.1

New results on the crustal configuration of the Newfoundland margin: Implications for rifting 

Laura Gómez de la Peña, César R. Ranero, Manel Prada, Donna Shillington, and Valentí Sallarès

Driven by discovery of contrasting structures of Continent to Ocean Transition (COT) discovered at rifted continental margins during the 90’s, several high-quality seismic datasets were acquired in these margins during the early 2000 to unravel the structure of unexplored regions. Despite the fact that some of these datasets are basically comparable to modern data in quality, the processing, imaging and modelling methodologies at the time of acquisition can be now refined and improved. Recent developments in parallel computing and novel geophysical approaches provide now the means to obtain a new look at the structure with enhanced resolution seismic models and a mathematically-robust analysis of the data uncertainty, that was formerly difficult, if not unfeasible, to achieve. 

We focused on the Newfoundland margin and applied up-to-date methodologies to the high-quality SCREECH dataset (2000). These data include three primary transects with coincident multichannel seismic (MCS) reflection data acquired with a 6-km streamer and wide-angle data recorded by short-period OBS and OBH spaced at ~15 km. We reprocessed the streamer data and also performed the join inversion of streamer and wide-angle OBS/OBH seismic data, using reflections and refraction arrivals, which significantly improved the resolution of the velocity model. We performed a statistical uncertainty analysis of the resulting model, supporting the reliability of the observed features. In particular the new velocity model provides a detailed definition of the top of the basement where the largest abrupt velocity change occurs. The comparatively high-resolution velocity model obtained from the joint tomography allowed to properly perform a Pre-Stack Depth Migration of the MCS. The improved velocity model and seismic images permit to characterize the different crustal domains of the margin with less uncertainty that previous attempts, and relate them to the tectonic structure.

The different domains reveal previously undetected crustal characteristics that change over short distances. The reprocessing of the MCS data allowed to a better understanding of the crustal structure, as the Moho is imaged for the first time under the slope domain.

Comparison of these new results on the Newfoundland margin with the most modern data on the West Iberian margin, acquired during FRAME (2018) and ATLANTIS (2022) cruises provides a new view of the evolution of the North Atlantic opening.

How to cite: Gómez de la Peña, L., R. Ranero, C., Prada, M., Shillington, D., and Sallarès, V.: New results on the crustal configuration of the Newfoundland margin: Implications for rifting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9947, https://doi.org/10.5194/egusphere-egu24-9947, 2024.

EGU24-11403 | Posters on site | TS2.1

The story of double spreading centers formed during continental rifting in 2D 

Laetitia Le Pourhiet and Fan Zhou

It is common wisdom, based on many years of published simulations of continental rifting followed by spreading that in 2D when a mid-oceanic ridge form in a numerical simulation of continental rifting, extension stops and spreading take over the extension. This is generally due to the complete loss of strength of the mantle lithosphere that cannot transmit forces horizontally across the spreading zone anymore. Actually, in general even the onset of mantle lithosphere necking in a simulation can cause the end of the extension and for many years, I actually claimed very load in the past that two active necking system must be the signature of some obliquity causing 3D extensional conditions. However, recently, a whole series of 2D simulations produced systematically two spreading centers active at the same time. These results surprised me a lot. These simulations were very complex, including a lot of inheritance, the first easy conclusion could have been to say that inheritance causes multiple spreading… But we spent some time and effort to understand if this behavior was due to inheritance or something else. Simplifying our model set-up to the strict minimum, we found it was not inheritance, but a quite cold mantle temperature which permitted a larger shear coupling between the upper mantle dynamics and the mantle lithosphere.  A 50°C difference in mantle temperature radically change the results of the simulation and thanks to our failure, we have found the embryo of an alternative explanation to 3D interactions for the occurrence multiple active necking zones.

How to cite: Le Pourhiet, L. and Zhou, F.: The story of double spreading centers formed during continental rifting in 2D, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11403, https://doi.org/10.5194/egusphere-egu24-11403, 2024.

EGU24-11494 | ECS | Posters on site | TS2.1

The seismic structure of the NW Moroccan margin, Gulf of Cadiz, from new high-quality multichannel seismic reflection data 

Silvia Foiada, Marta Neres, Pedro Brito, Laura Gomez de la Peña, Irene Merino, and César Ranero

The FRAME geophysical cruise, conducted in 2018 onboard the Spanish R/V Sarmiento de Gamboa, acquired new multichannel seismic reflection (MCS) data on the SW Iberia and NW Moroccan margins. MCS data were acquired with a 6 km long solid-state digital streamer Sercel SENTINEL towed at 19 m water depth, and a 3920 c.i. source with two sub-arrays with 20 guns towed at 10 m depth. The system was designed to provide high penetration and map the entire crust and the upper mantle structure and retain enough resolution to image well the stratigraphy.

In this work we present a 220 km long seismic line acquired on the NW Moroccan margin, from the shallow continental shelf across the continental slope and extending across the deep abyssal plain of the Gulf of Cadiz. The NW Africa margin was selected because the region was the focus of several geophysical campaigns, and several DSDP drill sites that drilled into the synrift strata.  However, limited modern data has imaged the crustal-scale tectonic structure to unravel the late Triassic - early Jurassic rift history of the region.

We applied a seismic processing flow tailored to the attenuation of the multiple energy, signal designature and for the creation of a detailed macro-velocity model to image the lateral changes of the synrift tectonic structure and stratigraphy. The high-quality image of the structure of this rifted margin reveals a complex tectonic structure from the shelf to the deep-water basin where a deep basement containing salt bodies across the entire profile extension. These new results are of high importance for the understanding of the rifting and continent-ocean transition (COT) processes on the northern Central Atlantic and Neothetys domains, as well as for the subsequent compressive deformation processes in the Gulf of Cadiz related to the Africa-Eurasia plate collision.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds through the project LISA (https://doi.org/10.54499/PTDC/CTA-GEF/1666/2020).

How to cite: Foiada, S., Neres, M., Brito, P., Gomez de la Peña, L., Merino, I., and Ranero, C.: The seismic structure of the NW Moroccan margin, Gulf of Cadiz, from new high-quality multichannel seismic reflection data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11494, https://doi.org/10.5194/egusphere-egu24-11494, 2024.

EGU24-11825 | ECS | Posters on site | TS2.1

Tectonostratigraphic evolution of the Tainan Margin (NE South China Sea): comparison with the Pearl River Mouth Basin 

Mateus Rodrigues de Vargas, Geoffroy Mohn, Julie Tugend, Nick Kusznir, and Andrew Lin

The wide rifting mode that preceded the opening of the South China Sea (SCS) in the Cenozoic generated a set of Paleogene rift basins presently buried under thick post-rift sedimentary infill. Much of the tectonostratigraphic evolution of the South China Sea is now relatively well-constrained (e.g., Pearl River Mouth Basin). However, the SCS's northeasternmost part (i.e., the Tainan margin sensu lato), which might represent the oldest passive margin segment, remains to be integrated into the framework of the rifting and opening of the SCS.

This work aims to review and revisit the tectonostratigraphic evolution of the Tainan margin. To do so, an integrative approach has been used combining the analysis of seismic reflection and gravity data. We use 3D gravity inversion to determine the distribution of Moho depth and crustal thickness within this margin segment. The gravity inversion scheme incorporates a lithosphere thermal gravity anomaly correction, which is critically important because of the elevated geothermal gradient within the young oceanic lithosphere of the South China Sea and its continental margins. In the Tainan margin, results show contrasted crustal domains from the continental shelf, to the distal margin and oceanic domain.

Only limited crustal thinning is observed over the continental shelf where a succession of rift basins is documented (i.e., Taihsi, Nanjihtao, and Penghu basins) that are part of the Northern Rift System. In contrast, the distal Tainan margin shows greater crustal thinning to less than 10 km thick under an aborted breakup basin, thereby forming the Southern Rift System. To the south, this basin is separated from the unambiguous oceanic domain (6 to 8 km thick) by a comparatively thicker crustal block (~ 10 to 15 km thick). This crustal block forms the Southern High where numerous volcanic edifices and magmatic intrusions are observed or inferred.

Half-grabens of the Northern Rift System are controlled by counter-regional faults and filled by Paleocene to Eocene syn-rift sediments. For the distal domain, no well calibration is available. There, we identified several seismic units bounded by regional unconformities. Our results show relatively thin syn-rift sediments locally controlled by a low-angle normal fault system in the Southern Rift System. In contrast, thick post-rift sequences are observed except over the Southern High.

Based on our results, we propose a review of structural style and age correlations from the continental shelf to the distal domains of the Tainan margin. To illustrate along-strike variations of the crustal structure and stratigraphic style, we build an array of regional geological cross-sections that are further compared with existing observations in the adjacent Pearl River Mouth Basin.

How to cite: Rodrigues de Vargas, M., Mohn, G., Tugend, J., Kusznir, N., and Lin, A.: Tectonostratigraphic evolution of the Tainan Margin (NE South China Sea): comparison with the Pearl River Mouth Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11825, https://doi.org/10.5194/egusphere-egu24-11825, 2024.

EGU24-11854 | Posters on site | TS2.1

Rifting style and continental breakup of Marginal Seas 

Geoffroy Mohn, Jean-Claude Ringenbach, Etienne Legeay, Julie Tugend, William Vetel, and François Sapin

Marginal Seas are extensional basins formed in a convergent setting near active subduction zones. They are characterized by a short life (<25 Ma), as well as unstable and changing directions of seafloor spreading. However, the processes related to their formation from rifting to seafloor spreading initiation remain debated (supra-subduction convection/extension, slab-pull). This problem is further compounded by the fact that our understanding of continental breakup used to be derived from the evolution of magma-poor and magma-rich Continent-Ocean Transitions (COT) of Atlantic margins.

Here, we describe and discuss the rifting style and the mode of continental breakup of three main Marginal Seas located in the Western Pacific, namely the South China Sea, the Coral Sea and the Woodlark Basin. All three examples formed under rapid extension rates and propagation of seafloor spreading.

In these three examples, continental extension is accommodated by a succession of hyper-extended basins controlled by low-angle normal faults that may form and be active at 30° (or less). These hyper-extended basins are filled by polyphase syn-rift sequences showing atypical geometries. These complex stratigraphic architectures result from the development of the low-angle normal faults interacting with antithetic faults, controlling the formation of extensional fishtails for example. The formation of such low-angle normal fault systems is enhanced by basement inheritance of the previous orogenic system.

Continental breakup and final extension are contemporaneous with an important magmatic activity emplaced in the distalmost part of these margins including volcanoes, dykes and sills. Continent-Ocean transitions (COTs) are characterized by a sharp juxtaposition of the continental crust against igneous oceanic crust suggesting that a rapid shift from rifting to spreading occurred. High extension rate prevents conductive cooling allowing the focusing of volcanic activity in sharp COTs, quickly evolving to magmatic accretion.

In conclusion, the rifting style and mode continental breakup are most likely associated with initial rheological conditions with hot geotherm combined with fast extensions rates likely directed by kinematic boundary conditions directly or indirectly controlled by nearby subduction zones.

How to cite: Mohn, G., Ringenbach, J.-C., Legeay, E., Tugend, J., Vetel, W., and Sapin, F.: Rifting style and continental breakup of Marginal Seas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11854, https://doi.org/10.5194/egusphere-egu24-11854, 2024.

EGU24-11873 | Posters on site | TS2.1

Palaeobathymetry of the Mid-Norwegian volcanic margin during continental breakup and paleoclimate implications 

Julie Tugend, Geoffroy Mohn, Nick Kusznir, Sverre Planke, Christian Berndt, Ben Manton, Dmitrii Zastrozhnov, and John, M. Millet

The Mid-Norwegian volcanic rifted margin and its NE-Greenland conjugate formed in relation to continental breakup in the latest Palaeocene to earliest Eocene during the emplacement of the North Atlantic Igneous Province (NAIP). The development of the NAIP and opening of the North Atlantic occurred contemporaneous to the Paleocene Eocene Thermal Maximum (PETM) which corresponded to a rapid 5-6 °C global warming episode.

The cause of this rapid global warming, explored as part of IODP Expedition 396, is thought to relate to the thermogenic gases released to the atmosphere via thousands of hydrothermal vents. The thermogenic gases were produced by contact metamorphism of carbon-rich sediments during widespread sill emplacement from the NAIP. The potential of hydrothermally-released greenhouse gases to influence climate depends strongly on the water depth at which they get released. Unless it is released in a shallow marine environment most methane will be oxidized before it reaches the atmosphere.

Early results from IODP Expedition 396 have documented that at least one of the Mid-Norwegian hydrothermal vents was emplaced in shallow marine to potentially sub-aerial conditions. The aim of this contribution is to constrain further the paleo-water depth at which hydrothermal vents formed along the other parts of the mid-Norwegian volcanic rifted margin. This study focuses on an integrated workflow of quantitative geophysical and geodynamic analyses calibrated by new IODP drilling results and structural and stratigraphic observations. We use a 3D flexural-backstripping, decompaction and reverse thermal subsidence modelling to predict the palaeobathymetry and palaeostructure at keys stages of the syn- to post-breakup evolution that can be compared with palaeo-water depths estimated from biostratigraphic data.

Results provide new constraints on the paleobathymetry of hydrothermal vent complexes required to confirm whether the global warming recorded by the PETM was triggered by the magma-rich continental breakup leading to the opening of the northeast Atlantic Ocean. 

How to cite: Tugend, J., Mohn, G., Kusznir, N., Planke, S., Berndt, C., Manton, B., Zastrozhnov, D., and Millet, J. M.: Palaeobathymetry of the Mid-Norwegian volcanic margin during continental breakup and paleoclimate implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11873, https://doi.org/10.5194/egusphere-egu24-11873, 2024.

EGU24-11877 | Orals | TS2.1

Along-strike magma-poor/magma-rich spreading transitions 

Michal Nemcok and Brian Frost

1D/2D data-based studies of active spreading centres brought the knowledge of extension ratedependent stretching-dominated v. buoyancy-dominated spreading. 3D reflection seismic data from the extinct centre of an initial oceanic corridor in the Caribbean allow us to see an along-strike transition between stretching- and buoyancy-dominated spreading where the spreading through detachment faulting is a precursor to the magma-assisted spreading. Studying progressively more evolved portions of the spreading centre, going from its end towards its centre, we see a progressively higher ascent of the asthenosphere, which heats the developing

core complex in the exhuming footwall of the initial stretching-dominated system. The asthenospheric ascent is associated with thermal weakening of the core complex, which eventually results in ductile deformation reaching the upper portion of the complex. Subsequently, the core complex is penetrated by the dyke located at the top of the asthenospheric body. The dyke, which subsequently evolves to a diapir-shaped body, reaches the sea floor

and establishes a magma-assisted steady-state seafloor spreading. These observations lead to a model explaining the initiation of the magma-assisted spreading in the initial oceanic corridor. Furthermore, they also improve our knowledge of multiple interacting mechanisms involved in the breakup of the last continental lithospheric layer, subsequent disorganized spreading and younger organized spreading.

How to cite: Nemcok, M. and Frost, B.: Along-strike magma-poor/magma-rich spreading transitions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11877, https://doi.org/10.5194/egusphere-egu24-11877, 2024.

EGU24-12130 | ECS | Posters on site | TS2.1

Structure and Dynamics of the Porcupine Magma-Poor Continental Margin from new Ocean Bottom Seismometer Data 

Ibrahim Yusuf, Stephen M Jones, Tim Reston, Thomas Funck, Brian M O'Reilly, and John R Hopper

The Porcupine Basin, situated in the North Atlantic, serves as a unique natural laboratory for investigating the temporal evolution of magma-poor rifts. Notably, the basin exhibits a progressive increase in the total degree of stretching from north to south, offering a valuable opportunity to interpret its structure in terms of the temporal evolution of magma-poor rifted margins. This study, as part of the broader PORO-CLIM project, focuses on Profile 2 to construct a whole-crustal seismic velocity model and integrate it with existing data to unravel the complete rifting history of the Porcupine Basin.

In the northern region, Reston et al. (2004) identified a detachment fault, the P-reflector, indicating substantial rifting  [1]. Recent analyses by Prada et al. (2017) extended this understanding to the central basin, revealing progressive crustal thinning and mantle serpentinization [2]. However, the southern sector remains largely unexplored. This project aims to capitalise on newly acquired Ocean Bottom Seismometer (OBS) data from PORO-CLIM Profile 2 to image the deep crustal structure and complement this with basement mapping of the southern Porcupine Basin using industry 2D seismic data.

Seismic refraction data from 20 OBS along a 226 km transect form the basis for constructing a comprehensive crustal velocity model. Utilising the RAYINV modelling package, a layer-by-layer forward modelling approach is employed to correlate calculated and observed travel times. Concurrently, structural mapping using long-offset 2D seismic reflection data assists in delineating major faults and regions of mantle unroofing, contributing to the understanding of the Porcupine Basin's subsurface. Preliminary findings reveal extreme crustal thinning and asymmetry, highlighting north-to-south crustal thinning and the emergence of the P-reflector in the southern region of the Porcupine Basin.

[1] Reston, T.J., Gaw, V., Pennell, J., Klaeschen, D., Stubenrauch, A. and Walker, I. (2004). Extreme crustal thinning in the south Porcupine Basin and the nature of the Porcupine Median High: implications for the formation of non-volcanic rifted margins. Journal of the Geological Society, [online] 161, pp.783–798.

[2] Prada, M., Watremez, L., Chen, C., O’Reilly, B.M., Minshull, T.A., Reston, T.J., Shannon, P.M., Klaeschen, D., Wagner, G. and Gaw, V. (2017). Crustal strain dependent serpentinisation in the Porcupine Basin, offshore Ireland. Earth and Planetary Science Letters, [online] 474, pp.148–159.

How to cite: Yusuf, I., M Jones, S., Reston, T., Funck, T., M O'Reilly, B., and R Hopper, J.: Structure and Dynamics of the Porcupine Magma-Poor Continental Margin from new Ocean Bottom Seismometer Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12130, https://doi.org/10.5194/egusphere-egu24-12130, 2024.

EGU24-12991 | ECS | Orals | TS2.1

Tectonic structure and evolution of Brazilian Equatorial Margin  

Julia Fonseca, César Ranero, Paola Vannucchi, David Iacopini, and Helenice Vital

The Brazilian Equatorial Margin (BEM) is classically interpreted as a transform margin formed during the last phases of the Atlantic rifting of Gondwana. However, rift kinematics and subsequent continental break up has not been constrained.

We present a new model based on the interpretation of a 2D seismic grid acquired along the BEM. The datasets, provided by the Brazilian National Agency for Petroleum (ANP), expand for ~600 km of the margin and consist of approximately 10.000 km of crustal scale 2D seismic reflection profiles which have been calibrated with industry drillholes. The integration of crustal-scale tectonic structures and age and distribution of synrift sediment deposits allowed to determine the style and the timing of the different tectonic phases and to define the crustal thinning evolution of the entire rift system along the Potiguar and East Ceará Basins (NE Brazil).

Our findings indicate that: 1. rifting started ~140-136 My, 2. extension stopped earlier (late Aptian) in the shallow sector of the basin than in the deep-water (early Albian) domains. The shallow basin domains presents minor crustal thinning (~35 thick crust over ~100 km wide), whereas in the deep-water domains, about ~60 km wide, the crust is 4-8 km thick and it extended into the early Albian (116-110 My).

The distribution of deformation structures supports a model of rift evolution where: deformation is initially distributed while forming a shallow basin; it evolves by focusing the extension; finally, extension migrates toward the basin centre to form the deep-water domain. Constraints from seismic reflection data and drillholes help define an abrupt continent to ocean transition (COT), and breakup occurred during the early Albian. Basin sedimentation from its onset to the late Aptian is terrigenous, indicating an isolated environment disconnected from the Northern and Southern Atlantic oceans. Sedimentation changed during the late-most Aptian to the early Albian when marine facies deposited during a rapid ocean water infill of a previously endorheic basin.

The seismic images document that rifting across the margin is not dominated by transcurrent deformation, with strike-slip faulting limited to a relatively small sector, whereas most of the margin extended through normal faulting deformation during opening.

From the interpretation of the 2D seismic reflection grid it was possible to distinguish abrupt lateral changes in the architecture of the basement. These changes defined three distinct, first order segments along the margin named Southern, Central, and Northern segments. The different evolution of the three segments throughout the rifting process is defined by thickness map of the basement. The Northern segment is the only region that shows evidence of potential late synrift magmatism, likely formed during the COT emplacement, which defines second order segmentation. Our interpretation suggests a spatial correlation between first-order tectonic segmentation and second-order magmatic segmentation during the embryonic formation of the spreading center with the definition of fracture zone/transform faults. These findings suggest that most transform faults formed on the spreading centers may have originated from the pattern of continental segmentation during rifting.

How to cite: Fonseca, J., Ranero, C., Vannucchi, P., Iacopini, D., and Vital, H.: Tectonic structure and evolution of Brazilian Equatorial Margin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12991, https://doi.org/10.5194/egusphere-egu24-12991, 2024.

EGU24-13269 | ECS | Posters on site | TS2.1

Crustal Structure of Continental Margin and Oceanic Basin at the Southern Mozambique Margin 

Wei Wang, Satish Singh, Zhikai Wang, Aiguo Ruan, Yong Tang, Jérôme Dyment, Sylvie Leroy, Louise Watremez, Zhaocai Wu, He Li, and Chongzhi Dong

During the Jurassic period, the Gondwana Continent progressively rifted from north to south along three huge transform faults (Davie Fracture Zone (DFZ), Mozambique Fracture Zone (MFZ) and Agulhas-Falkland Fracture Zone (AFFZ)), forming the northern, central and southern continental margins along Mozambique, producing a series of divergent and strike-slip margins. These margins are crucial areas for understanding the evolution of Gondwana as their crustal nature and geometry have strongly impacted the kinematic reconstruction of Gondwana. Especially, the debate about continental or oceanic crust for the Mozambique Coastal Plain (MCP) and North Natal Valley (NNV) at the southern Mozambique margin led to tens of kinematic reconstruction models of Gondwana. Based on the OBS and MCS data results of PAMELA MOZ3/5 Cruises, MCP and NNV were identified as continental crust. This has led the scientific community to reconsider the issue, for example, the opening time of the oceanic basin, the movement direction of rifting, and the intense magmatism during the rifting and break-up of Gondwana.

In June 2021, the Second China-Mozambique Joint Cruise was conducted onboard the R/V “Dayang hao”. Three wide-angle seismic OBS profiles were acquired where 70 four-component OBSs were deployed along profiles DZ02 and DZ04 oriented nearly W-E and DZ01 oriented nearly N-S. Four Bolt air guns with a total volume of 8000 in3 in total were towed at ~100 m behind the R/V “Dayang hao” at ~10 m below the sea surface. The shot interval was 200 m.

Here, we present the tomographic results of P-wave velocity along 442 km long profile DZ02, where 21 OBSs were deployed. It traverses through the Continent Ocean Transition (COT) and extends into the Mozambique ocean basin. Approximately 19,000 P-wave arrivals were manually picked, using the travel-time tomography inversion to get the velocity model. The tomographic result shows an apparent decrease in crust thickness from COT to the ocean basin, and the thickness of the oceanic crust is about 8 km. We also observe high-velocity anomalies up to 7.4 km/s in the lower crust above Moho, suggestive of more primitive melt. We will also present the S-wave velocity model for DZ02.  

How to cite: Wang, W., Singh, S., Wang, Z., Ruan, A., Tang, Y., Dyment, J., Leroy, S., Watremez, L., Wu, Z., Li, H., and Dong, C.: Crustal Structure of Continental Margin and Oceanic Basin at the Southern Mozambique Margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13269, https://doi.org/10.5194/egusphere-egu24-13269, 2024.

EGU24-13432 | Orals | TS2.1

Structural Evolution of the Black Sea Basin Using Sectioned Computational Models 

Armagan Kaykun and Russell Pysklywec

The tectonic formation of the Black Sea Basin (BSB) has been an ongoing debate: primarily, there is still not a consensus on whether the basin was rifted as one east-west oriented basin, or as two separate basins named Eastern and Western Black Sea Basins. These interpretations are based largely on deep-sea drilling projects and a growing dataset of seismic information (of variable access for academic use). Supporting the two-basin idea is the semi-parallel ridge and depression geometry of the BSB with NW-SE orientation in the Eastern portion of the Black Sea Basin; and W-E orientation in the Western portion of the Black Sea Basin. On the other hand, interpretations for a single basin are supported by the regional structure of the BSB being aligned with the geodynamic models of the basins rifted as a result of slab roll-back. Complicating the understanding of the basin extension and development is the inferred tectonic inversion to shortening in the region starting in the Late Eocene.

To propose a model to answer ongoing debates, we interpreted 24 long-offset 2D seismic lines acquired by GWL in 2011 in a structural geology context. We focused on the structural elements such as big scale normal faults, reverse faults, and tectonic inversion features to create a basis for our 2D computational models for both east and west portions of the BSB. One important finding was to determine the null points on basin bounding faults where the extensional tectonic movements stopped, and the compressional tectonic movements started. Utilizing the ASPECT geodynamic code, we built 2D computational models parallel to the selected two 2D seismic profiles. We compared our findings in our seismic interpretations with the results to understand the timing and basin-wide distribution of structural highs and the compressional tectonic features that shaped the BSB.

How to cite: Kaykun, A. and Pysklywec, R.: Structural Evolution of the Black Sea Basin Using Sectioned Computational Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13432, https://doi.org/10.5194/egusphere-egu24-13432, 2024.

Many orogenic belts today preserve evidence of past crustal rifting. During the syn-rifting, the crust undergoes thinning, forming rift basins with thick sedimentary deposits. The upwelling of the mantle during this extensional phase increases the geothermal gradient within the basin, affecting the crust and sedimentary rocks.

In this study, we used numerical models to simulate the temperature changes in sedimentary rocks within rift basins during both the active rifting phase and the passive continental margin phase after rifting cessation. We found that under a stretching rate of 0.7 cm per year, after 20 million years of continuous stretching, the geothermal gradient within the basin can reach 50-60°C per kilometer, with sedimentary rocks reaching temperatures as high as 450-500°C. After 20 million years of cooling following the end of stretching, the temperatures of the sedimentary rocks decrease by nearly 100°C, and the geothermal gradient reduces to approximately 30°C per kilometer.

We believe that these phenomena can be correlated with the evolution of the Hsuehshan Range in Taiwan, which experienced a transition from rifting to a passive continental margin. During the rifting phase, the temperatures of the sedimentary rocks within the basin reached high metamorphic temperatures of 450-500°C, as indicated by carbonaceous material Raman spectroscopy (RSCM). As the region entered the passive continental margin phase, the rocks gradually cooled, with a temperature decrease of nearly 100°C prior to the onset of mountain building in Taiwan. Similar high-temperature metamorphic temperatures were obtained through RSCM analysis along the Central Cross-Island Highway and Northern Cross-Island Highway, exceeding the closure temperatures of zircon core tracks. However, some zircon core tracks in certain areas did not yield closure ages, suggesting that the high metamorphic temperatures obtained from RSCM analysis were inherited from previous stretching events rather than occurring during the Penglai orogeny.

How to cite: zheng, M., Lee, Y.-H., and Tan, E.: Numerical modelling of continental margin of the Eurasian Plate Rifting and Tectonic evolution.Causes of the highest metamorphic temperature in the Hsuehshan Range and Backbone Range , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14297, https://doi.org/10.5194/egusphere-egu24-14297, 2024.

EGU24-14808 | Orals | TS2.1

Some evidence of a wide rotational extension in East Antarctica preceding Gondwana breakup 

Egidio Armadillo, Daniele Rizzello, Pietro Balbi, Alessandro Ghirotto, Davide Scafidi, Guy Paxman, Andrea Zunino, Fausto Ferraccioli, Laura Crispini, Andreas Läufer, Frank Lisker, Antonia Ruppel, Danilo Morelli, and Martin Siegert

Recent sub-ice topography compilations of East Antarctica have imaged a wide sector, spanning from 100° E to 160° E in longitude and from the Oates, George V and Adelie coastlines to 85° S in latitude, which contains numerous low-lying basins of variable size and uncertain origin. The sector shows a Basin and Range style tectonics comprising two major basins of continental proportions, the Wilkes Basin and the Aurora Basin complex, and many smaller basins such as the Adventure, Concordia, Aurora and Vostok trenches. The main longitudinal axes of the basins consistently point towards the South Pole and many exhibit intriguing distinct triangular shapes, sitting within an approximately 2000 x 2000 km fan-shaped physiographic region limited by a semi-circular coast line. We name this region as the East Antarctic Fan shaped Basin Province (EAFBP). To the West, this sector is limited by the intraplate Gamburtsev Mountains (GM) and to the East by the Transantarctic Mountains (TAM) constituting the uplifted shoulder of the Cenozoic West Antarctic Rift System (WARS).

Origins and inter-relationships between these four fundamental Antarctic tectonic units (WARS, TAM, EAFBP, GM) are still poorly understood and strongly debated. Very little is known about the mechanism generating the basins in the EAFBP, their formation time, whether they are all coeval and if and how they relate to Australia basins before Antarctica-Australia rifting. Present genetic hypotheses for some of the basins span from continental rifting to a purely flexural origin or a combination of the two. Also, post-tectonic erosional and depositional processes may have had a significant impact on the present-day topographic configuration.

Here we interpret the EAFBP as the result of a single genetic mechanism: a wide fan-shaped intra-continental extension around a near pivot point at about 135° E, 85° S that likely occurred at the Mesozoic-Cenozoic transition. We discuss evidence from the sub-ice topography and potential field airborne and satellite data. We have applied image segmentation techniques to the rebounded sub-ice topography to semi-automatically trace the first order shape of the sub-ice basins, that we assume to be fault controlled. Then we have fitted the edges of the basins by maximum circles and estimated the best Euler pole identified by their intersection. Potential field anomalies have been taken into account in order to enlighten major discontinuities not revealed by the sub-ice topography.

The reconnaissance of this large sector of East Antarctica as the result of rotational extension may have major implications on global and regional tectonics plate reconstructions, plate deformation assumptions and new tectonic evolutionary models of WARS, TAM, and GM.

How to cite: Armadillo, E., Rizzello, D., Balbi, P., Ghirotto, A., Scafidi, D., Paxman, G., Zunino, A., Ferraccioli, F., Crispini, L., Läufer, A., Lisker, F., Ruppel, A., Morelli, D., and Siegert, M.: Some evidence of a wide rotational extension in East Antarctica preceding Gondwana breakup, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14808, https://doi.org/10.5194/egusphere-egu24-14808, 2024.

EGU24-14829 | Orals | TS2.1 | Highlight

The November 2023 Grindavik dike injection in Iceland:  Implications for continental rifting, dike formation in extensional tectonic settings, and giant dike swarms 

Freysteinn Sigmundsson, Michelle Parks, Halldór Geirsson, Andrew Hooper, Vincent Drouin, Kristín Vogfjörð, Benedikt Ófeigsson, Sonja H. M. Greiner, Yilin Yang, Chiara Lanzi, Gregory Paul De Pascale, Kristín Jónsdóttir, Sigrún Hreinsdóttir, Valentyn Tolpekin, Hildur María Friðriksdóttir, Páll Einarsson, and Sara Barsotti

A 15 km long dike formed rapidly in the Reykjanes Peninsula oblique rift on 10 November 2023 and propagated under the town of Grindavík.  From just before noon on 10 November until midnight, around 25 MW≥4 earthquakes occurred, two of which were of MW~5.2. Three-dimensional ground deformation is well resolved both temporally and spatially with dense Global Navigation Satellite System (GNSS) geodetic observations, which record cumulative displacements up to about 80 cm occurring mostly over 6 hours in the evening of 10 November and continuing at much reduced rates in the following days. Interferometric analysis of synthetic aperture radar images using Sentinel-1, COSMO-SkyMed, and ICEYE satellites records also well the dike deformation, which occurred simultaneously with deflation over the nearby central part of the Svartsengi volcanic system. Geodetic modelling, assuming uniform elastic host rock behavior, infers a dike volume of (130-139)×106 m3, with up to ~8 m dike opening, as well as some strike-slip shear motion. Deflation at Svartsengi in our model is best fit using a spherical point source with a volume decrease of (76-82)×106 m3up until 12 November. The temporal evolution of the dike opening was further modelled using hourly GNSS displacements, allowing better derivation of the temporal evolution of the flow rate into the dike and the contraction volume of the subsidence source. The maximum flow rate into the dike is inferred to be ~9500 m3/s, between 18:00 and 19:00 on November 10. We infer that the massive magma flow into the dike was established with only modest overpressure in the feeding magma body, a sufficiently large pathway opening at the boundary of the magma body, and pre-failure lowering of pressure along the pathway that had occurred through gradual build-up of high tensile stress over the previous eight centuries. This explains the unprecedented fast maximum magma flow rates that we infer. Such high flow rates provide insight into the formation of giant dike swarms under conditions of high tensile stress, and imply a high hazard potential for dike intrusions, considering their potential to transition into eruptions.

 

How to cite: Sigmundsson, F., Parks, M., Geirsson, H., Hooper, A., Drouin, V., Vogfjörð, K., Ófeigsson, B., Greiner, S. H. M., Yang, Y., Lanzi, C., De Pascale, G. P., Jónsdóttir, K., Hreinsdóttir, S., Tolpekin, V., Friðriksdóttir, H. M., Einarsson, P., and Barsotti, S.: The November 2023 Grindavik dike injection in Iceland:  Implications for continental rifting, dike formation in extensional tectonic settings, and giant dike swarms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14829, https://doi.org/10.5194/egusphere-egu24-14829, 2024.

EGU24-14830 | Posters on site | TS2.1

High precision U-Pb geochronology of Cenozoic phonolite volcanic bodies in Cenozoic Eger rift basin (Bohemian Massif) 

Prokop Závada, Vladimír Cajz, Andrew Kylander-Clark, and David Uličný

A new set of high-precision U-Pb data was acquired for two groups of phonolite bodies emplaced in the volcano-sedimentary sequence of the Cenozoic Eger Rift in Bohemian Massif. The phonolites are located in the western (5 bodies) and eastern (3 bodies) edge of this monogenetic volcanic field, stretched along the central part of the Eger Rift system. The selected phonolite bodies represent lava flows, cryptodomes or extrusive domes emplaced in phreatomagmatic maar-diatremes, remnants of dykes, and a laccolith. The U-Pb dates were acquired using the Laser Ablation Split Stream system at Santa Barbara University geochronology lab, which provides the coupled geochronology and also REE and selected major element geochemistry. Despite the great variety of internal zircon textures from oscillatory zoning to complex patchy patterns with a large range of cathodoluminescence intensity, the groups of spots gained coherent and surprisingly precise ages for each sample. The western group of phonolite bodies, namely the Bořeň, Želenický vrch, Špičák, Hněvín, and Ryzelský vrch display clusters of ages ranging between 33Ma and 36Ma, while zircons of the eastern group of the phonolites, Krompach, Mariánská hora and Luž (Lausche) indicate ages between 30Ma and 32Ma. Terra-Wasserburg diagrams for individual samples revealed remarkable precision marked by errors of only 90-180 thousand years (5 samples) and 300-650 thousand years (2 samples). The U-Pb zircon ages are interpreted to reflect primarily the high-temperature overprint of inherited (and possibly newly crystallized) zircons before emplacement of the phonolite bodies in the upper crust. In addition, titanite grains measured alongside the zircon grains (in another run) either overlap (Bořeň) with the zircon age error on Terra-Wasserburg diagrams (geochrone) or are 2 Ma years younger than corresponding zircon ages (Špičák phonolite body). REE binary diagrams revealed separate clusters of Sm/Nd and also Hf content of the zircons, which can be attributed to different degrees of partial melting of parental magma in the source upper mantle or the lower crust for both groups of sampled phonolites. In summary, the results suggest that U-Pb geochronology using the LASS system is a powerful tool with a great potential for deciphering the evolution of phonolites in the Cenozoic Rift system in Bohemian Massif and possibly other rift systems in the foreland of the Alpine orogeny.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Závada, P., Cajz, V., Kylander-Clark, A., and Uličný, D.: High precision U-Pb geochronology of Cenozoic phonolite volcanic bodies in Cenozoic Eger rift basin (Bohemian Massif), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14830, https://doi.org/10.5194/egusphere-egu24-14830, 2024.

EGU24-15107 | ECS | Posters on site | TS2.1

The evolution of fault networks during multiphase deformation: An analogue modeling approach 

Jun Liu, Matthias Rosenau, Ehsan Kosari, Sascha Brune, Frank Zwaan, and Onno Oncken

It is well known that triaxial deformation is a common feature of continental tectonics, and is accommodated by complex polymodal fault networks. Field investigations confirm that multiple phases involving time-dependent three-dimensional strain conditions (e.g. constriction, plane, and flattening strain) affect the spatial and temporal interaction of polymodal fault systems. However, a key question remains: How do changing strain conditions affect the reactivation of fault systems that formed during a previous deformation phase? Here, we conduct scaled analogue models with time-dependent boundary conditions to investigate how fault networks evolve under changing boundary conditions, including  reactivation and formation of new faults.

We have developed a setup in which a basal rubber sheet is stretched in one direction, so that longitudinal extension and layer thinning are accompanied by lateral shortening, hence producing triaxial deformation (Liu et al. in revision). According to previous brittle-viscous experiments with this set-up, an increase in longitudinal extension velocity results in a higher coupling between the rubber base and brittle layer, generating increasing transmission of lateral shortening from the base into the brittle layer. We thus induce constriction-to-plane strain conditions in the brittle layer as a function of longitudinal extension velocity by varying the magnitude of lateral contraction. In a new set of experiments, by varying extension velocity either stepwise or continuously, we realize time-dependent kinematic boundary conditions including deformation phases and secular changes, respectively. Digital image correlation (DIC) and photogrammetry (structure from motion, SFM) are employed to track the 3D kinematic surface and topography evolution, respectively.

Preliminary observations show both the formation of new faults and the reactivation of early phase faults through a change from plane to constriction strain. Conversely, a change from constriction to plane strain conditions results in the abandonment of the early phase fault network as it becomes overprinted by fault systems of the subsequent phase. Moreover, early-phase fault systems influence the propagation and linkage of fault populations in subsequent phases. Our analogue models highlight the impact of strain conditions on the overall plan-view geometry of fault populations, providing alternative explanations for complex fault patterns and interactions (e.g. the Jeanne d’Arc basin, the North Træna Basin, and the Beagle Platform).

How to cite: Liu, J., Rosenau, M., Kosari, E., Brune, S., Zwaan, F., and Oncken, O.: The evolution of fault networks during multiphase deformation: An analogue modeling approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15107, https://doi.org/10.5194/egusphere-egu24-15107, 2024.

EGU24-15188 | Posters on site | TS2.1

Insights into Miocene paleostress history of the Eger Rift from mining-related structural datasets: the Most Basin, Bohemia 

Radomír Grygar, Karel Mach, Roman Gramblička, and Tomáš Novotný

The Most Basin is the largest and best-preserved of sedimentary basins formed within the Eger Rift, the easternmost part of the European Cenozoic Rift System. Previous work on the tectono-sedimentary history of the basin and its surroundings has led to an interpretation of two main extensional phases that governed the Oligo-Miocene rift initiation and subsequent evolution. That interpretation has been derived mainly from large-scale considerations of main fault geometries, while a satisfactory support by a large mesoscopic dataset from the basin infill was lacking.

 

Systematic acquisition of mesoscopic structural data in some of the open-cast coal mines operating in the Most Basin has been motivated by prevention of accidents of bucket wheel excavators, threatened by sliding of blocks of mainly clayey sediments. As a result, over 5 thousand mesoscopic measurements were acquired in the Bílina Mine alone and hundreds in other mines over the past 13 years. In the Most Basin, the main coal seam is located close to the base of the basin fill. Open-case mines thus expose a thick overburden and, locally, also the underlying basement. The structural measurements involved the superposition and evolution of mesoscopic structural features in geological time, from Variscan metamorphic rocks through Cretaceous sediments and Oligocene volcanics through the Miocene coals and clastics of the basin fill.

 

Structural analysis of the dataset and statistical comparison of specific regions focused on

spatial and stratigraphic distribution of fault directions and inclination arrays, resulting in interpretation of spatial and stratigraphic distribution of local paleostress. The principal results are as follows:

  • the number of detected mesoscopic fault populations, as well as of interpreted deformation phases decreases upward through the stratigraphic column;
  • orientation of faults generally changes from a dominant E-W and NW-SE strike of population in the pre-Miocene formations into dominant SW-NE up to WSW-ENE strike within the youngest Libkovice Member (Early Miocene);
  • a trend of decreasing fault inclination from older, more consolidated formations to younger ones, most probably linked to rheological (stage of lithification) on brittle deformations;
  • generally, data evaluation of inclination and direction of faults gave generally similar results for the Bílina and Libouš mines, in spite of the 60 km distance between them and their proximity to different leading fault systems (Bílina and Victoria faults in the former case and the Ahníkov and Kralupy faults in the latter);
  • the large dataset of mesoscopic fault-slip data shows a generally more complex picture of possible paleostress evolution than the one derived from the geometries of the main bounding fault systems, due to the influence of local stress fields of normal and transtensional faults. The general picture, however, implies a plausible gradual evolution of extension vector from NNE-SSW to NW-SE orientations. throughout the early Miocene.

 

The Severočeské doly, a.s., supported the long-term acquisition of the structural dataset and its utilization for basic research purposes. This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Grygar, R., Mach, K., Gramblička, R., and Novotný, T.: Insights into Miocene paleostress history of the Eger Rift from mining-related structural datasets: the Most Basin, Bohemia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15188, https://doi.org/10.5194/egusphere-egu24-15188, 2024.

EGU24-15268 | Orals | TS2.1

Shallow sources of upper mantle seismic anisotropy in East Africa  

Cynthia Ebinger, Miriam Reiss, Ian Bastow, and Mary Karanja

The East African rift overlies one or more mantle upwellings and it traverses heterogeneous Archaean-Paleozoic lithosphere rifted in Mesozoic and Cenozoic time. We re-analyze XKS shear wave splitting at publicly available stations to evaluate models for rifting above mantle plumes. We use consistent criteria to compare and contrast both splitting direction and strength, infilling critical gaps with new data from the Turkana Depression and North Tanzania Divergence sectors of the East African rift system. Our results show large spatial variations in the amount of splitting (0.1–2.5 s) but consistent orientations of the fast axes within rift zones: they are predominantly sub-parallel to the orientation of Cenozoic rifts underlain by thinned lithosphere with and without surface magmatism. The amount of splitting increases with lithospheric thinning and magmatic modification. Nowhere are fast axes perpendicular to the rift, arguing against the development of extensional strain fabrics. Thick cratons are characterized by small amounts of splitting (≤0.5 s) with a variety of orientations that may characterize mantle plume flow. Splitting rotates to rift parallel and increases in strength over short distances into rift zones, implying a shallow depth range for the anisotropy in some places. The shallow source and correlation between splitting direction and the shape of upper mantle thin zones suggests that the combination of channel flow and oriented melt pockets contribute > 1 s to the observed splitting delays. Enhanced flow, metasomatism, and melt intrusion at the lithosphere-asthenosphere boundary suggest that fluid infiltration to the base of the lithosphere may facilitate rifting of cratonic lithosphere. 

How to cite: Ebinger, C., Reiss, M., Bastow, I., and Karanja, M.: Shallow sources of upper mantle seismic anisotropy in East Africa , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15268, https://doi.org/10.5194/egusphere-egu24-15268, 2024.

EGU24-16081 | Orals | TS2.1

Reduced magmatism in the Turkana Depression: a consequence of inefficient melt transport 

Adina E. Pusok, Yuan Li, Richard F. Katz, Tim Davis, and Dave A. May

Geophysical studies along the Main Ethiopian Rift and Eastern Rift in Kenya indicate that strain accommodation is dominated by magmatic intrusion rather than tectonic extension (e.g., Ebinger and Casey, 2001). However, it remains unclear how magmatic extension developed in the Turkana Depression, the low-lying, broadly rifted region separating the Ethiopian and East African plateaus. We investigate the rifting dynamics of the Turkana Depression with two-phase flow numerical models of melt transport through the ductile–brittle lithosphere. These models suggest that the pre-rift rheological structure of the lithosphere exerts a counter-intuitive control on melt extraction, which can explain the character of the Turkana region.

Recent seismic imaging shows that both the Turkana Depression and the uplifted plateaus are underlain by deep-seated, hot, partially-molten, buoyant mantle that ponds below a thinned plate (Kounoudis et al., 2021). Yet, Ogden et al. (2023) estimated the Moho is 10–20 km shallower throughout the Turkana Depression (~20–25 km) than surrounding regions (~35–40 km). Here, we hypothesise that variations in lithospheric strength across the Turkana Depression and the Ethiopian Plateau have influenced magma transport across the lithosphere and rift development (Morley, 1994). 

Our models of melt extraction through the ductile–brittle lithosphere incorporate a new poro-viscoelastic–viscoplastic theory with a free surface (Li et al., 2023), designed and validated as a consistent means to model dykes. We initialise models with a source of partial melt in the asthenosphere and investigate how rheology of the overlying lithosphere impacts melt migration to the surface. Experiments are performed for buoyancy-driven magma transport under no tectonic extension, and for low background tectonic extension rates typical to the Turkana Depression (4 mm/yr; e.g., Knappe et al., 2020). Results indicate that both the rheology of lithosphere and extension rate control the efficiency of magma extraction. Magma transport across a thick, elastic lithosphere is more efficient than across a thin, more ductile lithosphere, and increases with extension. Our results suggest that surface volcanism in the Ethiopian Plateau is more likely to occur compared with the Turkana Depression, and at earlier times. 

References

Ebinger and Casey (2001), Geology, DOI: 10.1130/0091-7613(2001)029<0527:cbimpa>2.0.co;2

Kounoudis et al. (2021), G-cubed, DOI: 10.1029/2021GC009782

Ogden et al. (2023), EPSL, DOI: 10.1016/j.epsl.2023.118088

Morley (1994), Tectonophys., DOI: 10.1016/0040- 1951(94)90170-8

Knappe et al. (2020), JGR: Solid Earth, DOI: 10.1029/2019JB018469

Li et al. (2023), GJI, DOI: 10.1093/gji/ggad173

How to cite: Pusok, A. E., Li, Y., Katz, R. F., Davis, T., and May, D. A.: Reduced magmatism in the Turkana Depression: a consequence of inefficient melt transport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16081, https://doi.org/10.5194/egusphere-egu24-16081, 2024.

EGU24-16240 | ECS | Posters on site | TS2.1

Insights into the tectonic evolution of the northern Norwegian passive margin: Integrating field observations and plate modeling over 200 million years. 

Amber Distelbrink, Grace E. Shephard, Jean-Baptiste P. Koehl, Steffen G. Bergh, and Anouk Beniest

Constraining the evolution of the opening of the northernmost region of the Northeast Atlantic Ocean is of particular importance for understanding the diversity of ocean basin opening dynamics, including the development of oblique margins and shear zones. Accurately determining the timing and kinematics of the motion along the Senja Shear Zone and opening of the Fram Strait is of particular importance for climate research as this region forms the only deep-water gateway between the Northeast Atlantic Ocean and Arctic Ocean. This study combines new and legacy data and presents an analysis of the tectonic evolution of the northern Norwegian passive margin over the past 200 Ma, including integrating structural field observations and plate tectonics models.

Fieldwork took place on the islands of Senja and Kvaløya in Troms County of northern Norway. The field observations reveal four dominant brittle fault groups corresponding to four normal-oblique extension directions: E-W, NNW-SSE, NW-SE, NE-SW. In the Senja Shear Zone, the strike-slip faults are predominantly oriented NNW-SSE to NW-SE. Analysis of existing plate motion models for the region for 200 Ma to present day includes three prominent extension phases in chronological order: E-W, NNW-SSE, and NW-SE.

This study suggests that during the E-W oriented crustal thinning phase, normal faulting and minor strike-slip faulting dominated and gave way to basement-seated strike-slip faults during the NNW-SSE oriented extension phase. The presence of mid-upper crust faulting is argued by fault mineral striation assemblages and hydrothermal alteration. In the NW-SE oriented extensional phase, both normal faults and strike-slip faults were active. Comparisons to existing rigid plate tectonic models for the region suggest a revised deformable plate framework is required, and offers insights into the original thickness of the North-American and European plates and the role of mid-crustal tectonics in the breakup. The role of inheritance, including earlier shear zones and extensional phases will also be discussed. In addition, the present research encourages scientists to digitize analogue maps and data, preventing loss of knowledge during the analogue to digital transition.

How to cite: Distelbrink, A., Shephard, G. E., Koehl, J.-B. P., Bergh, S. G., and Beniest, A.: Insights into the tectonic evolution of the northern Norwegian passive margin: Integrating field observations and plate modeling over 200 million years., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16240, https://doi.org/10.5194/egusphere-egu24-16240, 2024.

EGU24-17089 | Posters on site | TS2.1

The ANR project “FirstMove”: first movements of divergence between future tectonic plates 

Julia Autin, Roxane Mathey, Harmony Suire, Mélanie Ballay, Marc Ulrich, Gianreto Manatschal, Daniel Sauter, Benoît Petri, Marc Schaming, and Luis Somoza Losada

As two tectonic plates drift away, the earlier movements, prior to oceanic crust formation, are ill-constrained. We are convinced that the kinematic models of plate movements could be significantly enhanced by focusing on the divergence before final lithospheric breakup. During this phase of transition several problems arise. Firstly, the classical interpretations of magnetic anomalies are not trustworthy (debated geometry and/or origin of anomalies). Secondly, the movements are more complex than in oceanic domain (polyphase deformation, obliquity, asymmetry). Those particularities occur especially if plate breakup happens in magma-poor conditions where mantle is exhumed at the surface (in about 50% of instances).

We focus on two pairs of conjugate magma-poor rifted margins: the Bay of Biscay and the Australia-Antarctica margins. In these areas, magnetic anomalies are controversial and seafloor formation started with large domains of hyperextended continental crust and exhumed mantle. Thus, the location and age of the LaLOC (landward limit of the oceanic crust) are uncertain. We aim to better define these domains in space, divergence direction and time through geophysical data and localized petrological observations and dating. This project is in its starting phase, it includes 2 PhD thesis. This presentation focuses on the general framework of the project and the preliminary results.

How to cite: Autin, J., Mathey, R., Suire, H., Ballay, M., Ulrich, M., Manatschal, G., Sauter, D., Petri, B., Schaming, M., and Somoza Losada, L.: The ANR project “FirstMove”: first movements of divergence between future tectonic plates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17089, https://doi.org/10.5194/egusphere-egu24-17089, 2024.

EGU24-17201 | ECS | Posters on site | TS2.1

Structural Mode and Evolution of Multi-stage Normal Fault Development in Jieyang Depression, NE South China Sea 

Chao-Hsun Wang, Ping-Rong Wu, Kenn-Ming Yang, Chih-Cheng Yang, and Bieng-Zih Hsieh

Jieyang Depression is located between the Southern Depression of the Taixinan Basin and the Chaoshan Depression of the Pearl River Mouth Basin in northern South China Sea. A series of NE-SW striking half graben developed in this area from late Mesozoic to early Paleogene, and then another two stages of normal faulting happened during Neogene. The development of these stages of normal faults are separated by the breakup unconformity and a post-rift truncation. The main purposes of this study are to investigate the evolutionary sequences of the multi-stages of normal faults and the truncations during the multi-stages of extension, the spatial distribution of each phase of normal faults, and how the younger normal faults were affected by the pre-existing ones.

The normal faults in the Jieyang Depression can be divided into three types. Type 1 faults are related to the Paleogene half graben formation and only cut through the pre-rift and syn-rift strata. Type 2 normal faults only developed and cut through the post-rift strata. Type 3 normal faults cut through the syn-rift and post-rift strata. In this study, we further divide the Type 2 normal faults into two different kinds. Type 2-1 faults developed above the Paleogene half graben and cut off by the post-rift truncation. Type 2-2 faults developed after the truncation. Type 3 normal faults can be divided into two different kinds as well. Type 3-1 faults developed in the syn-rift stage and yet were reactivated and linked with the faults developing in the later extension. Type 3-2 faults are the Type 2 faults that developed continuously cutting downward into the syn-rift strata.

In terms of spatial distribution, Type 1 normal faults strike NE-SW, forming the half grabens. Most of the Type 2 normal faults are located far away from continental shelf. Type 3 normal faults mostly distribute on the northeast and northwest sides of the study area, close to the continental shelf, and most of them are cut by the post-rift truncation.

As a result, from the late Mesozoic to the early Paleogene, the northern slope of the South China Sea experienced a NW-SE extension. At the end of the Paleogene, the extension ceased, forming the breakup unconformity. In the Neogene, the Jieyang Depression experienced second extension. In this time the extension orientation was NNW-SSE, developing Type 2-1 and Type 3 faults before the post-rift truncation. The subsequent truncation cuts Type 2-1 faults and the upper part of the Type 3 faults. After accumulating new strata above truncation, the third stage of extension happened and Type 2-2 faults developed after the post-rift truncation.

Key words: South China Sea, Jieyang Depression, normal fault, multi-stage extension, truncation

How to cite: Wang, C.-H., Wu, P.-R., Yang, K.-M., Yang, C.-C., and Hsieh, B.-Z.: Structural Mode and Evolution of Multi-stage Normal Fault Development in Jieyang Depression, NE South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17201, https://doi.org/10.5194/egusphere-egu24-17201, 2024.

EGU24-17395 | ECS | Orals | TS2.1

Structure and kinematics of the Danakil Depression, Afar, Ethiopia: insights into the formation of a magma-rich margin 

Valentin Rime, Anneleen Foubert, Derek Keir, and Tesfaye Kidane

The Danakil Depression is situated in the northern part of the Afar Depression in Ethiopia and Eritrea and is in an advanced phase of rifting close to continental breakup. It forms the equivalent of a magma-rich margin. As it is currently active and emerged, it offers a unique opportunity to study the processes of formation of these types of passive margins.

We combine seismic reflection data, field data, and remote sensing to constrain the structure and kinematics of this basin. Seismic data reveal the formation of Seaward Dipping Reflectors (SDRs). Surprisingly, field data show that these SDRs are dominated by clastic sediments and only contain relatively minor amount of magmatic material. Paleoshorelines and other proxies allow to quantify uplift and subsidence rates across the basin. These data highlight high spatial variability and allow to better understand the structure and evolution of older, deeply buried passive margins.

How to cite: Rime, V., Foubert, A., Keir, D., and Kidane, T.: Structure and kinematics of the Danakil Depression, Afar, Ethiopia: insights into the formation of a magma-rich margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17395, https://doi.org/10.5194/egusphere-egu24-17395, 2024.

EGU24-17937 | ECS | Posters on site | TS2.1

Using U-Pb geochronology of syn-faulting calcite-mineralised veins to track the evolution of superimposed rifting events: the Inner Moray Firth Basin. 

Alexandra Tamas, Robert E. Holdsworth, Dan M. Tamas, Edward D. Dempsey, Kit Hardman, Anna Bird, John R. Underhill, Dave McCarthy, Ken J.W. McCaffrey, and David Selby

Constraining the age of formation and movement along fault arrays in superimposed basins helps us to better unravel their kinematic history as well as the role of bounding faults or inherited structures in basin evolution. The Inner Moray Firth Basin (IMFB, western North Sea) comprises a series of superimposed basins overlying rocks of the Caledonian basement, the pre-existing Devonian-Carboniferous Orcadian Basin and a regionally developed Permo-Triassic North Sea basin system. The IMFB rifting occurred mainly in the Upper Jurassic – Lower Cretaceous after a long period of subsidence followed by localised uplift in its eastern parts due to thermal doming in the central North Sea (in the middle Jurassic). The rift basin later experienced further episodes of regional tilting, uplift and fault reactivation during Cenozoic.

New detailed field observations augmented by drone photography and creation of 3D digital outcrops, coupled with U-Pb geochronology of syn-faulting calcite-mineralised veins are used to constrain the absolute timing of fault movements and decipher the kinematic history of basin opening. It also helps to identify those deformation structures associated with earlier basin-forming events.

Five regional deformation events emerge: Devonian rifting associated with the older Orcadian Basin; Late Carboniferous inversion related to dextral Great Glen fault movements; Permian thermal subsidence with some evidence of minor fracturing; Late Jurassic – Early Cretaceous rifting and Cenozoic reactivation and local inversion. We were also able to isolate characteristic structures, fault kinematics, fault rock developments and associated mineralisation types related to many of these events.

How to cite: Tamas, A., Holdsworth, R. E., Tamas, D. M., Dempsey, E. D., Hardman, K., Bird, A., Underhill, J. R., McCarthy, D., McCaffrey, K. J. W., and Selby, D.: Using U-Pb geochronology of syn-faulting calcite-mineralised veins to track the evolution of superimposed rifting events: the Inner Moray Firth Basin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17937, https://doi.org/10.5194/egusphere-egu24-17937, 2024.

The presentation is based on the results of the research work of the Arktic-2011, Arktic-2014 and Arktic-2022 expeditions and contains the results of analysis of the structure of the sedimentary cover of the Eurasian basin of the Arctic Ocean. For the first time, the entire array of seismic data, including Russian and foreign seismic profiles, was used for tectonic constructions. The results obtained make it possible to reconstruct extensive areas of continental lithosphere development in the Eurasian basin. Based on the analysis of the structure of the sedimentary cover of the Amundsen Basin, four stages of the geological history of the formation of the sedimentary system of the Eurasian basin of the Arctic Ocean are substantiated. During the first (Cretaceous-Paleocene) stage, extensive axis-symmetric epicontinental paleo-basins of the Amundsen and Nansen Basins were formed on the shoulders of the continental rift, which were subsequently separated by seafloor spreading. Evidence of similar riftogenic settings in the second half of the Cretaceous is recorded along the entire periphery of the Arctic basin from Greenland to the Chukchi Rise. The second (Eocene)-spreading stage was characterised by stage accretion of the oceanic crust in the Gakkel Ridge and was accompanied by a gradual expansion of the sedimentary basin up to the present-day boundaries of the Eurasian basin. The third stage (Oligocene-Miocene) of sedimentary flexure corresponded to the accumulation of a thick undisturbed sedimentary cover over the entire Eurasian basin, indicating the temporary cessation of spreading in the Gakkel Ridge and the establishment of a tectonic quiescence regime. Similar conditions at this stage are recorded throughout the periphery of the Arctic basin. The resumption of spreading processes occurred at the fourth (Pliocene-Quaternary) neotectonic stage. As the result of the intensification of spreading processes in the Norwegian-Greenland Basin, tectonic stresses penetrated intothe Eurasian Basin along the axis of the Gakkel Ridge. The distinct morphological division of the Gakkel Ridge into Siberian-Marine and Atlantic segments is explained by the jump-like transmission of tectonic stresses of the North Atlantic, which is also confirmed by the anomalously high tectonic, volcanic and hydrothermal activity of the Gakkel Ridge.

How to cite: Neevin, I., Rekant, P., and Budanov, L.: MODEL OF THE FORMATION OF THE SEDIMENTATION SYSTEM OF THE EURASIAN BASIN OF THE ARCTIC OCEAN AS A BASIS FOR RECONSTRUCTING Its TECTONIC HISTORY, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18255, https://doi.org/10.5194/egusphere-egu24-18255, 2024.

EGU24-19671 | Orals | TS2.1

A generic crustal architecture data model for rift and passive margin analysis: Application to the conjugate South Atlantic margins 

Christian Heine, Ken McDermott, James Eldrett, Colin Grant, and Philip Thompson

The spatio-temporal analysis of rifts and passive margin evolution is often done based on regional case studies, using non-standardized terminology and classification models to characterize crustal boundaries and basin infill. As example, the use of “continent-ocean boundary” to delineate crustal types or “syn-rift” as basin infill characterization has proven to be no longer adequate, given our evolved understanding of passive margins. In general, such local approaches do not lean themselves to aggregate data for global and large-scale comparative analysis and often struggle to reconcile the spatially varying magmatic/weakly magmatic margin architecture in a rift system context. They also do not allow efficient deployment of spatio-temporal data analytic models due to a lack of standardized data classification.

To overcome these limitations, we have designed a novel “data science-ready” data model for crustal architecture that is based on commonly accepted terminologies, can be used independent of input data heterogeneity and can be deployed globally across the whole spectrum of margin types and complex 3D margin geometries/microplate settings. We classify two key crustal boundaries, the oceanward limit of continental crust ("OLCC") and the landward limit of oceanic crust ("LaLOC"), along with several key crustal interfaces, such as the top basement and base crust which are further subdivided into sub-categories. This approach allows us to easily generate standardized data products on rift system scale, which quantitatively describe key parameters relevant to understand lithosphere extension dynamics, such as volumes, ratio, and distribution of continental and magmatic crust, crustal stretching factors, and amount of crustal embrittlement. Coupled with plate kinematic models, these data products allow to build reproducible, extensible, and quantitative models of rift and margin evolution through time and highlight the dynamics of stretching, localization of deformation, the basin infill response, and spatio-temporally varying patterns and types of magmatism.

Applying this data model, we have characterized the crustal architecture of the conjugate South Atlantic passive margins, interpreting more than 100k line-kilometers of 2D and 3D seismic reflection data. Our findings highlight substantial shortcomings of current plate models to reconcile the crustal type distributions in the southern South Atlantic with a tight pre-breakup fit, the temporal emplacement dynamics of SDRs and plume-related magmatism along the whole South Atlantic rift, as well as the localization of deformation and dynamics of basin infill.

How to cite: Heine, C., McDermott, K., Eldrett, J., Grant, C., and Thompson, P.: A generic crustal architecture data model for rift and passive margin analysis: Application to the conjugate South Atlantic margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19671, https://doi.org/10.5194/egusphere-egu24-19671, 2024.

EGU24-19853 | Posters on site | TS2.1

Synrift and postrift thermal evolution of margins: a re-evaluation of classic models of rifting 

Marta Pérez-Gussinyé, Yangfan Xin, Tiago Cunha, Raghu Ram, Miguel Andres-Martinez, Dongdong Dong, and Javier Garcia-Pintado

The thermal history of margins controls the development of hydrothermal systems during rifting, diagenetic processes in the sediments and the generation and preservation of hydrocarbons. It also affects the depth of the oceanic gateways formed during continental break-up, thereby influencing ocean circulation and ultimately climate (Brune et al., 2023, Pérez-Gussinyé et al., 2023, Peron-Pinvidic et al., 2019). Observed heat-flow values however, do not always comply with classic rifting models. Here, we use 2D numerical models to investigate the relationship between rifting, sedimentation and thermal history of margins. We find that during the synrift, the basement heat flow and temperature are not only controlled by extension factor, but also by synrift sediment thickness and the evolution of deformation. As this progressively focuses oceanward, the proximal sectors thermally relax, while the distal sectors experience peak temperatures. This time lag is important for wide rifted margins. In the postrift, the lithosphere under the hyperextended margins does not return to its original state, at least for ~100 Myrs after breakup. Instead, it mimics that of the adjacent oceanic plate, which is thinner than that of the original continental plate. This results in heat flow values increasing oceanward at postrift stages where classic rifting theory predicts complete thermal relaxation. Our increased heat-flow estimations, may extend hydrocarbon plays into distal margin sectors and adjacent oceanic crust, previously discarded as immature. Finally, our models indicate that commonly used temperature approximations in basin analysis may strongly differ from those occurring in nature (Pérez-Gussinyé et al., 2024).

 

Brune, S., Kolawole, F., Olive, JA. et al. Geodynamics of continental rift initiation and evolution. Nat Rev Earth Environ 4, 235–253 (2023). https://doi.org/10.1038/s43017-023-00391-3

Pérez-Gussinyé, M., Collier, J., Armitage, J., Hopper, J. R., Sun, Z., and Ranero, C. R., Towards a process-based understanding of rifted continental margins, in Nature Reviews Earth and Environment, 2023, doi: 10.1038/s43017-022-00380-y

Marta Pérez-Gussinyé, Yanfang Xin, Tiago Cunha,  Raghu Ram, Miguel Andrés-Martínez, Dongdong Dong, Javier García-Pintado,Synrift and postrift thermal evolution of rifted margins: a re-evaluation of classic models of extension, in press, Geol. Soc Spec. Publ., 2024

Peron-Pinvidic, G., Manatschal, G., eta al. Rifted Margins: State of the Art and Future Challenges, Front. Earth Sci., 22 August 2019, Sec. Structural Geology and Tectonics, Volume 7 - 2, https://doi.org/10.3389/feart.2019.00218.

How to cite: Pérez-Gussinyé, M., Xin, Y., Cunha, T., Ram, R., Andres-Martinez, M., Dong, D., and Garcia-Pintado, J.: Synrift and postrift thermal evolution of margins: a re-evaluation of classic models of rifting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19853, https://doi.org/10.5194/egusphere-egu24-19853, 2024.

EGU24-19947 | ECS | Posters on site | TS2.1

Interactions between pre-existing fabrics and fault patterns during oblique rifting revealed by enhanced-gravity analog modeling 

Yaoyao Zou, Daniele Maestrelli, Giacomo Corti, Chiara Del Ventisette, Liang Wang, Xiaofan Wan, Yanjie Gao, and Chuanbo Shen

 

Multiple fault populations with different orientations and complex fault patterns can be observed during oblique rifting, conditions which result from a complex rift kinematics which combines dip-slip and strike-slip motion. Although analysis of different natural cases and analog or numerical modeling have shed light on the relations between rift obliquity and the related fault architecture, many aspects of the process remain poorly understood. One of these aspects is related to the existence of pre-existing fabrics in the upper crust, which may further complicate the fault pattern by forcing the development of faults with atypical geometries and orientation.

Here, we performed enhanced-gravity analog models of oblique narrow rifting to characterize the evolution and architecture of rift-related faults developing in a brittle upper crust characterized by inherited fabrics. The models reproduce a rift obliquity of 30° (angle between the rift trend and the orthogonal to the direction of extension), kept constant in all the experiments, and pre-existing vertical fabrics with variable orientation (from 0°, i.e. orthogonal to extension, to 90°, i.e. extension-parallel). Modeling results suggest that inherited fabrics have an important influence on rift-related faulting, with a significant correlation between the intensity of reactivation and their trend with respect to the extension direction. When the pre-existing fabrics trend perpendicular to the extension direction (obliquity 0°), they are strongly reactivated, localizing deformation and promoting the rapid development of faults and grabens perpendicular to the extensional direction. When the pre-existing fabrics trend at moderate obliquity (15°-45°), they are still reactivated and localize deformation causing the development of atypical fault trends and patterns. The degree of reactivation tends to gradually decrease with increasing obliquity; similarly, the influence of pre-existing structures decreases with progressive extension, and the fault pattern and evolution are progressively dominated by extension kinematics and crustal thinning. When the pre-existing fabrics trend at high obliquity (≥ 60°), they have almost no influence on the fault geometry and architecture.

This study has significant implications for explaining the fault geometry and evolution of some natural rift basins worldwide, such as basins of the East African Rift system, the North Sea Rift, and some offshore rift basins in eastern China.

How to cite: Zou, Y., Maestrelli, D., Corti, G., Del Ventisette, C., Wang, L., Wan, X., Gao, Y., and Shen, C.: Interactions between pre-existing fabrics and fault patterns during oblique rifting revealed by enhanced-gravity analog modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19947, https://doi.org/10.5194/egusphere-egu24-19947, 2024.

EGU24-20162 | ECS | Posters on site | TS2.1 | Highlight

 The Last Fissural Eruptions of the Manda Hararo Magmatic Segment, Central Afar (Ethiopia), Constrained from New cosmogenic Ages 

Yafet Gebrewold Birhane, Raphael Pik, Nicolas Bellahsen, Irene Schimmelpfennig, Lydéric France, Jessica Flahaut, Dereje Ayalew, and Gezahegn Yirgu

The Afar depression at the northern end of the East African Rift system is presently experiencing the final stage of continental break-up and progressive onset of steady magmatic spreading. The Magmatic Rift Segments in Afar broadly analogous to those observed within the mid oceanic ridges, offer the opportunity to study both mantle and crustal processes. Investigating the crustal architecture of those magmatic segments represents a key aspect to decipher fundamental parameters that control focussing of magmatic and tectonic activity during the generation of magmatic crust. Here, we present the typical organization of a 32 km long subsegment of the Manda Hararo magmatic rift system, with fissural activities symmetrical to an apparent mid segment magmatic reservoir and establish geochronology of the last eruptive history. We combine field investigations, precise mapping of volcanological and tectonic features, cosmogenic 36Cl exposure dating and geochemical analysis of lavas to constrain the temporal frame and the dynamics of magmatic processes. Our results show that the recent historical volcanic events (~ 500 to 2000 years) are sourced from calderas and fissures representing an alternating sequence of effusive and explosive (block fields) activities related to a coherent rifting episode along a single self-consistent magmatic sub-segment. Those recent fissural flows resurfaced a large portion of the segment and emplaced on older thick pahoehoe flows with a rather long lag-time of about 75 kyr separating the two episodes. Strongly contrasted geochemical signatures are also observed between those two volcanic episodes, with more differentiated and trace elements enriched basalts for the recent one, compared to the older one which are characterized by a unusual depleted signature. These new results for the Central Afar Manda Hararo rift have important implications for: (i) the local hazards along the segments, and (ii) the volcano-tectonic organization of the segment with coexistence of contrasted melt reservoirs on the underlying transcrustal plumbing system.

How to cite: Birhane, Y. G., Pik, R., Bellahsen, N., Schimmelpfennig, I., France, L., Flahaut, J., Ayalew, D., and Yirgu, G.:  The Last Fissural Eruptions of the Manda Hararo Magmatic Segment, Central Afar (Ethiopia), Constrained from New cosmogenic Ages, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20162, https://doi.org/10.5194/egusphere-egu24-20162, 2024.

EGU24-20218 | ECS | Posters on site | TS2.1

Unraveling Tectonic From Hydrological Subsidence Of The Okavango Graben (Botswana) Using FLATSIM InSAR Data. 

Louis Gaudaré, Cécile Doubre, Marc Jolivet, Olivier Dauteuil, Samuel Corgne, Raphaël Grandin, Marie-Pierre Doin, and Philippe Durand

Located at the southwestern terminus of the East African Rift System, the Okavango Rift System represents an opportunity to study the propagation of an active rift at its early stages (Gaudaré et al., in review). The Okavango Graben (northern Botswana) is an active half-graben of the Okavango Rift System, which shows normal to dextral strike-slip tectonic displacements of the order of 1 mm per year (Pastier et al., 2017). In addition to the impact of tectonics, large volumes of water (~10 km3 per year) brought in by the annual flood of the Okavango River generate seasonal subsidence of over 2 cm in the graben (Dauteuil et al., 2023). The prevalence of the hydrologic signal over the tectonic signal makes it challenging to provide clear interpretations of the Rift dynamics within the Okavango Graben. The previous studies are based on a network of GNSS stations, providing punctual data on displacements. To quantify the deformation field over the Okavango Graben, we analyze interferometric synthetic aperture radar (InSAR) data produced by the ForM@Ter LArge-scale multi-Temporal Sentinel-1 InterferoMetry service (FLATSIM, Thollard et al., 2021). FLATSIM automatically computes interferograms from Sentinel-1 synthetic aperture radar data and inverts them into displacement time series. The products span from April 2016 to April 2021 with a temporal resolution of 12 days, a spatial resolution of 115 x 115 m and cover the entire Okavango Rift System. We analyze and compare the seasonality of both the interferometric coherences and the InSAR displacement time series. Change detection in the interferometric coherence allows us to delineate flooded surfaces through time in the Okavango Graben, from which we deduce water loadings on the lithosphere and model the corresponding flexural response of the lithosphere. We then compare this response to the spatial distribution of annual vertical oscillations extracted from the displacement time series. Taking these seasonal signals into account, our objective is to estimate the rates of the tectonic subsidence in the Okavango Graben to better constrain the propagation of the East African Rift System at its southwestern end.

Dauteuil, O., Jolivet, M., Gaudaré, L., & Pastier, A.-M. (2023). Rainfall-induced ground deformation in southern Africa. Terra Nova, 00, 1–7. https://doi.org/10.1111/ter.12650

Gaudaré, L., Dauteuil, O., & Jolivet, M. Geomorphology of the Makgadikgadi Basin (Botswana): insight into the propagation of the East African Rift System. Tectonics, in review.

Pastier, A.-M., Dauteuil, O., Murray-Hudson, M., Moreau, F., Walpersdorf, A., & Makati, K. (2017). Is the Okavango Delta the terminus of the East African Rift System? Towards a new geodynamic model: Geodetic study and geophysical review. Tectonophysics 712–713, 469–481. https://doi.org/10.1016/j.tecto.2017.05.035

Thollard, F., Clesse, D., Doin, M.-P., Donadieu, J., Durand, P., Grandin, R., Lasserre, C., Laurent, C., Deschamps-Ostanciaux, E., Pathier, E., Pointal, E., Proy, C., & Specht, B. (2021). FLATSIM: The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service. Remote Sensing, 13(18), 3734. https://doi.org/10.3390/rs13183734

How to cite: Gaudaré, L., Doubre, C., Jolivet, M., Dauteuil, O., Corgne, S., Grandin, R., Doin, M.-P., and Durand, P.: Unraveling Tectonic From Hydrological Subsidence Of The Okavango Graben (Botswana) Using FLATSIM InSAR Data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20218, https://doi.org/10.5194/egusphere-egu24-20218, 2024.

EGU24-20223 | Posters on site | TS2.1

Interaction of tectonics and surface process during oblique rifted margin formation. Insights from 3-D forward coupled geodynamic-surface process modelling. 

Thomas Theunissen, Ritske S. Huismans, Delphine Rouby, Sebastian Wolf, and Dave A. May

The magma-poor passive rifted conjugate margins in the Southern Equatorial Atlantic, North Atlantic/Arctic oceans, and Northern Mozambique Channel display en-echelon extensional segments separated by long transform faults (>300 km), influenced by inherited weaknesses. Using advanced 3-D forward geodynamic modeling coupled with surface processes, we investigate the formation of oblique rifts and passive margins. Our focus is on pre-existing weaknesses parallel to the extension direction, exploring the system's sensitivity to various erodibility factors. Key findings include: (1) erodibility within a low to moderate range has limited influence on the morpho-structural evolution of the oblique continental rift, (2) pure-strike slip faults reactivating transform weaknesses result in reduced topography, (3) major catchments sink in the inner corner at the tip of each extensional segments, and (4) hinterland drainage network capture along extensional segments is absent, controlled by isostatic rebound during rift flank drainage divide migration. This study enhances our understanding of the complex interplay between inherited weaknesses, erodibility, and the evolving morphology of oblique rifted margins.

How to cite: Theunissen, T., Huismans, R. S., Rouby, D., Wolf, S., and May, D. A.: Interaction of tectonics and surface process during oblique rifted margin formation. Insights from 3-D forward coupled geodynamic-surface process modelling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20223, https://doi.org/10.5194/egusphere-egu24-20223, 2024.

EGU24-20850 | Posters on site | TS2.1

The Ross Sea formation: enquiring the sensitivity of basin architecture to prior conditions, with numerical models and a parameter search 

Martina Busetti, Alberto Pastorutti, Magdala Tesauro, Carla Braitenberg, Florence Colleoni, and Laura De Santis

The basins composing the 1000-km wide West Antarctica Rift System (WARS), derived from extensional dynamics lasting from the Cretaceous to the Middle Neogene, bear evidence of a peculiar evolution through time: a transition from a diffuse to a localized thinning style and a migration of the focus of deformation, which likely progressed towards the cratonic domains of West Antarctica. Using the current observations, we aim at identifying which inherited starting conditions [1] result in outcomes compatible with the present-time structures and which do not allow so, unless other factors are accounted for.

To this aim, we turn to an extensive grid search in the parameter space, running a large number of forward numerical models to cover the possible permutations of parameters under test. We use the open source Underworld2 code [2] with a simplified scheme of starting conditions and kinematics boundaries, for lithospheric-scale 2-D thermomechanical models. We analyse the results obtained by changing a great number of parameters, including initial geometries of the crust and lithosphere, different rheologies, inherited structures, such as strain-weakening scars and thermal remnants of slabs.

We identify that a high crustal thickness (more than 45 km) is required to accommodate the first rifting phase (170 km ca. of cumulated extension, [3]) without producing crustal necking and eventual ocean formation. Parameters that favour a weaker strength profile, chiefly temperature (due to a thicker crust and/or a shallow lithosphere-asthenosphere boundary), are also required to avoid an early transition to localized deformation, in agreement with previous studies [4]. Smaller scale features, such as partition in multiple sub-basins, require additional factors, such as inherited weak-zone seeds (“scars”) in the crust and mantle, which are likely remnants of previous compressive phases [5].

[1] Perron, P., Le Pourhiet, L., Guiraud, M., Vennin, E., Moretti, I., Portier, É., & Konaté, M. (2021). Control of inherited accreted lithospheric heterogeneity on the architecture and the low, long-term subsidence rate of intracratonic basins. BSGF - Earth Sciences Bulletin, 192. https://doi.org/10.1051/bsgf/2020038

[2] Mansour, J., Giordani, J., Moresi, L., Beucher, R., Kaluza, O., Velic, M., Farrington, R., Quenette, S., & Beall, A. (2020). Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud. Journal of Open Source Software, 5(47), 1797. https://doi.org/10.21105/joss.01797

[3] Brancolini, G., Busetti, M., Coren, F., De Cillia, C., Marchetti, M., De Santis, L., Zanolla, C., Cooper, A.K., Cochrane, G.R., Zayatz, I., Belyaev, V., Knyazev, M., Vinnikovskaya, O., Davey, F.J., Hinz, K., 1995. ANTOSTRAT Project, seismic stratigraphic atlas of the Ross Sea, Antarctica. In: Cooper, A.K., Barker, P.F., Brancolini, G., (Eds.), Geology and Seismic Stratigraphy of the Antarctic Margin. Antarctic Research Series, vol. 68, https://doi.org/10.1029/AR068

[4] Huerta, A. D., & Harry, D. L. (2007). The transition from diffuse to focused extension: Modeled evolution of the West Antarctic Rift system. Earth and Planetary Science Letters, 255(1–2), 133–147. https://doi.org/10.1016/j.epsl.2006.12.011

[5] Talarico, F., Ghezzo, C., & Kleinschmidt, G. (2022). The Antarctic Continent in Gondwana: a perspective from the Ross Embayment and Potential Research Targets for Future Investigations. In Antarctic Climate Evolution (pp. 219–296). Elsevier. https://doi.org/10.1016/B978-0-12-819109-5.00004-9

How to cite: Busetti, M., Pastorutti, A., Tesauro, M., Braitenberg, C., Colleoni, F., and De Santis, L.: The Ross Sea formation: enquiring the sensitivity of basin architecture to prior conditions, with numerical models and a parameter search, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20850, https://doi.org/10.5194/egusphere-egu24-20850, 2024.

EGU24-665 | ECS | Posters on site | TS2.2

First constraints on the timing of structural evolution of the north Sulaiman Fold-thrust belt, Pakistan  

Nowrad Ali, Edward R. Sobel, Humaad Ghani, and Anne Bernhardt

The Sulaiman and Kirthar fold-and-thrust belts constitute the western boundary of the India-Asia collision zone. The Sulaiman fold-thrust belt is composed of a passive margin sedimentary sequence of Mesozoic to Cenozoic platform carbonates and clastic sedimentary rocks overlain by younger Himalayan foreland basin molasse sediments. This study uses newly acquired zircon (U‐Th)/He (ZHe) data and surface geology observations to document the structural evolution of the north Sulaiman fold-thrust belt. The hinterland zone includes the Zhob Valley Suture thrust, emplaced ophiolites, and folded Mesozoic strata, while the foreland is characterized by folded Eocene to Pliocene strata and hinterland-verging back thrusts. The initial deformation of the North Sulaiman Fold-thrust belt was driven by an east-west compressional event, giving rise to structures oriented in a north-south direction. The formation of fault propagation folds such as the Drazinda Syncline and Domanda Anticline in the foreland region resulted from east-vergent deformational events. Following this eastward deformation, the west-verging East Domanda Fault was activated, forming a roof thrust within the tectonic wedge beneath the Domanda Anticline.

ZHe dates were obtained from Jurassic to Pliocene sandstone samples collected along the Drazinda-Zhob transect, crossing the Sulaiman Fold-thrust belt. ZHe ages from the Middle Jurassic (Chiltan Formation) and late Jurassic to early Cretaceous (Sembar Formation) samples are completely reset. ZHe ages from the late Cretaceous (Mughal Kot and Pab formations) to early Paleocene (Ranikot Formation) samples are partially reset to unreset; Eocene to Pliocene sample ages are unreset. ZHe ages for the Chiltan Formation range from 3.9-16.2 Ma with an average of 7.6 Ma. The ZHe ages for the Sembar Formation range from 5.5-41.4 Ma with an average of 15.2 Ma. The fully to partially reset ZHe ages for the Mughal Kot Formation range from 4.5 to 64.2 Ma with an average of 31.6 Ma. The ZHe ages of the Pab Formation samples range in age from 25.1-58.6 with an average of 44.9 Ma. A single partially reset ZHe age from the Ranikot Formation is 38.5 Ma. Thick and rapid sedimentation in the Late Cretaceous, Early Eocene and Miocene-Pliocene in the region resulted in sufficient burial of the Chiltan and Sembar formations to reset the ZHe system. Most of the reset ages from the Chiltan and Sembar formations range between 3.9-7.5 Ma, indicating rapid late Miocene to Early Pliocene uplift of the north Sulaiman Fold-thrust belt. This uplift is associated with development of the Sulaiman anticline and the associated Dhana Sar backthrust. Located along the western boundary of the Indian Plate, this area exhibits transpressional tectonics. The dominant east-west compression component coupled with left-lateral wrenching plays a key role in this rapid and young uplift in the north Sulaiman Fold-thrust belt.

How to cite: Ali, N., Sobel, E. R., Ghani, H., and Bernhardt, A.: First constraints on the timing of structural evolution of the north Sulaiman Fold-thrust belt, Pakistan , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-665, https://doi.org/10.5194/egusphere-egu24-665, 2024.

EGU24-771 | ECS | Orals | TS2.2

Analogue Modelling to Support Seismic Interpretation in the Eastern Carpathian Bend Zone, Romania 

Ioana Silvia Mihaela Tocariu, Alexandra Tamas, Dan Mircea Tamas, Daria Dohan, Alexandru Lapadat, Zsolt Schleder, and Csaba Krezsek

Studying the complex subsurface structures in fold-and-thrust belts, such as the Eastern Carpathian Bend Zone, remains challenging due to poor seismic data quality caused by steep and intricate structures alongside multiple detachment levels.

To address this, we have conducted eight analogue modelling experiments at the Structural Modelling Laboratory of Babes-Bolyai University with mechanical stratigraphy scaled to the area of interest. We used coloured quartz sand, glass microspheres and silicone to simulate brittle rocks, ductile shales, and salt, respectively. The materials were layered in a 120 cm long deformation box, which was shortened at a constant rate of one centimetre per hour. The experiments were monitored using timelapse photography and particle image velocimetry. The models were consolidated, serially sectioned, and photographed. MOVE software (Petroleum Experts) was used for importing the section images and interpreting the 3D structural style for the models.

The structural style of the experiments varied based on the change in parameters, such as layer thickness, materials, shortening amounts, as well as the timing of erosion and salt deposition. The following description will refer to the most common deformation features observed in the experiments but will use the equivalent formation names and ages. The most noteworthy features are the post-salt lower Miocene's decoupling from the pre-salt section, the lower Miocene upper Kliwa formation decoupling from the Oligocene lower Kliwa formation along the lower Miocene Podu Morii shales, and the distinct wavelengths for the post-salt, upper Kliwa, and pre-upper Kliwa structures.

Considering well data, outcrop data, analogue modelling observations, and the 3D model, we performed seismic interpretation. This guided seismic data interpretation revealed short-wavelength upper Kliwa disharmonic folding, Oligocene–Cretaceous thrust-related hanging-wall anticlines, and large thrust fault displacements leading to hanging-wall erosion and out-of-sequence reactivation of the thrust faults. The results of these experiments proved to be effective tools for comprehending the controlling factors of deformation in the Eastern Carpathian Bend Zone and can aid in the interpretation of subsurface data, especially in areas with poor seismic data quality.

How to cite: Tocariu, I. S. M., Tamas, A., Tamas, D. M., Dohan, D., Lapadat, A., Schleder, Z., and Krezsek, C.: Analogue Modelling to Support Seismic Interpretation in the Eastern Carpathian Bend Zone, Romania, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-771, https://doi.org/10.5194/egusphere-egu24-771, 2024.

Many arcuate orogenic belts display complex patterns of fold structures. However, the kinematics of their development is poorly understood. This study aims to explore the origin of complex fold structures in the Proterozoic mobile belt of Cuddapah in peninsular India. This is a N-S trending thin-skinned fold-thrust belt, showing a spectacular crescent shape with westward convexity. The tectonic reconstructions suggest that the Cuddapah fold-thrust belts (CFTB) evolved through westward indentation of the westerly convex Nellore-Khammam schist belts (NKSB) during the collision between the Indian shield and the Antarctic block, interpreted as a consequence of the Rodinia Supercontinental event in Neoproterozoic time. The westward convergence resulted in the development of highly deformed Nallamalai fold belt (NFB) in the eastern part of CFTB, consisting of orogen-scale overturned folds with arcuate trends as well as higher order west-verging F1 folds on a wide range of spatial scales. Inclined to recumbent F1 folds are coaxially refolded by orogen-parallel F2 folds in outcrop scale. However, the superposition of steeply inclined E-W trending cross-folds (F3) that produced culminations and depressions on F1 and F2 indicates that the belt underwent orogen-parallel shortening in the course of its evolution. We performed laboratory experiments on a scaled representative CFTB model to understand such spatiotemporal evolution of the strain field in the CFTB. Two sets of experiments were run with a constant (2 cm/yr) and a temporally varying (2 cm/yr in Stage I to 1 cm/yr in Stage II) convergence velocity. The experimental results show that the CFTB during the initial periods of shortening undergoes mainly flattening deformations with maximum horizontal instantaneous stretching axes (ISAHmax), describing an arcuate trajectory in the eastern part that conforms to the indentor shape. In the later periods of the experimental runs (albeit at different times in the two experiments), the arcuate shape of the fixed wall causes a SW and NE-directed upper crustal flows from the elevated NE and SW parts of the CFTB, respectively. The flow convergence causes the strain field in the central part of the CFTB to develop a horizontal constriction. This kinematic transition leads to superposition of cross-folds on orogen-parallel folds, manifested in culmination (domes) and depression (basins) structures.

How to cite: Patsa, A. and Mandal, N.: Development of fold styles in the strongly arcuate Cuddapah fold-thrust belt, India: new insights from analogue models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1068, https://doi.org/10.5194/egusphere-egu24-1068, 2024.

EGU24-3163 | ECS | Orals | TS2.2

Numerical modeling of basement inheritance and salt decoupling effects on the structural evolution of the Zagros Fold-Thrust Belt 

Fatemeh Gomar, Jonas B. Ruh, Mahdi Najafi, and Farhad Sobouti

Fold-thrust belts are complex tectonic domains formed in response to near- or far-field compressional stress fields in the Earth’s crust. The complexity of structural style in theses belts is controlled by multiple factors. The presence of mechanically weak layers, defined by rocks that exhibit lower strength than their surroundings, play a significant role in the formation and evolution of fold-and-thrust belts. In this research, a two-dimensional numerical finite difference model incorporating a visco-elasto-plastic/brittle rheology is utilized to investigate the structural evolution of the Fars arc in the southeast of the Zagros fold-thrust belt. The modeling includes the tectonic inversion process, from Permian-Triassic rifting of the Neo-Tethys Ocean to the Oligocene-to-present continental collision between the Arabian and Eurasian plates. The Eulerian grid dimensions were considered as 500 km in length and 60 km in thickness, respectively, comprising 1101×121 nodes. Each cell contains 16 Lagrangian markers that carry the information and properties of each layer. According to the stratigraphic column of the Fars arc, there are 30 km of basement overlain by a 2-km-thick salt layer with a 3-kilometer-thick Palaeozoic sedimentary sequence above the salt layer. Furthermore, to replicate the interplay between Earth's internal and surface dynamics, a 25-kilometer-thick layer representing air is incorporated at the uppermost part of the model to approximate a free surface. The experiments include three inherited basement faults. The role of pre-existing weak zones in extensional tectonics is the shaping of rift basin geometry, especially the formation of half grabens. In the convergence phase, fold-thrust-belts with a basal detachment layer and pre-existing faults produce folding at two distinct scales. The faulting in the basement develops long wavelength folds in the sedimentary cover, while the presence of a salt layer shapes the smaller wavelength folds and thin-skinned thrust faults that extend from the detachment layer to the surface. The reactivated faults play an important role in stress transfer, leading to the emergence of new faults and seismic events. The results indicate that deformed listric faults show a meaningful correlation with the depth distribution of earthquakes throughout the Fars arc. The outcome associated with the presence of a thick basal salt layer and involvement of the basement exhibit a correlation with the structural style of the Fars arc.

How to cite: Gomar, F., Ruh, J. B., Najafi, M., and Sobouti, F.: Numerical modeling of basement inheritance and salt decoupling effects on the structural evolution of the Zagros Fold-Thrust Belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3163, https://doi.org/10.5194/egusphere-egu24-3163, 2024.

EGU24-3200 | Orals | TS2.2

Thrust system growth by segment linkage in sedimentary multilayers 

Rob Butler, Francisca Robledo, Phoebe Sleath, and Clare Bond

This presentation challenges the conventional theory that thrust systems necessarily grow by the upward propagation of tip-lines of faults away from a basal detachment. The model underpins mechanical considerations of thrust belt dynamics, explanations of thrust-related folding and commensurate forecasting of distributed deformation in the surrounding strata. Yet there have been few tests of the paradigm at the cross-section scale – not least because the quality of seismic imagery in most foreland thrust belts is insufficient to resolve structural geometries. Rather, the widespread application of the upward propagation (conventional) theory results from a variety of cognitive biases, especially restrictive citation of published literature.

Here we present interpretations of exceptional 3D seismic imagery from the eastern, lateral termination of the Jura fold-thrust belt of Switzerland. The area (the Baden-Irchel-Herdern Zone, referred to here as the BIHZ - broadly overlying the eponymous basement lineament) shows relatively little horizontal shortening and therefore preserves structures that would otherwise be overprinted by more extensive thrusting.  Contractional structures are developed in a multilayer of Mesozoic strata that comprise competent carbonates and incompetent mudrocks and marlstones. Interpretations based on 2D seismic profiles display thrusts sweeping through the Mesozoic strata as simple, continuous ramps, splaying from a basal detachment in Triassic evaporites. However, the higher-quality 3D seismic imagery does not support this type of interpretation. Within the BIHZ, statal reflectors are offset by small-offset (<50m) thrust segments. These do not map out as continuous fault surfaces, either in depth or in map-view. Some thrusts dip forelandward, others towards the hinterland. Collectively, these thrusts are layer-confined and, in plan-view, have highly sinuous forms. These geometries are indicative of having formed by linkage of originally distinct fault segments. Collectively this zone of segmented/low-displacement thrusting represents a “bead” of distributed deformation, restricted to the BIHZ. Presumably, if the area then evolved with greater contraction, part of the thrust array will become fully-linked and develop as a continuous structure – perhaps as elsewhere along the Jura arc. Those fault segments not incorporated into the now-continuous thrust would remain, forming a broad halo of distributed faulting in the surrounding rock. In this spatial context, the swathe of distributed deformation might be designated as a “damage zone” with respect to the main thrust but in fact, the distributed faulting would have no causative relationship to this main thrust.

Our interpretation of thrust system evolution derives from the “ramps first” model of Eisenstadt & DePaor (1987) – a structural concept that has received substantially less attention that the “conventional theory”. We do not wish to imply that there is a single mechanism by which thrusts nucleate and grow – the “conventional” theory may well apply in some situations. So too, may others. We do however emphasise the importance of considering a range of different behaviours and their resultant structural geometries when interpreting thrust systems. Some of these may yet to be described!

How to cite: Butler, R., Robledo, F., Sleath, P., and Bond, C.: Thrust system growth by segment linkage in sedimentary multilayers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3200, https://doi.org/10.5194/egusphere-egu24-3200, 2024.

EGU24-3749 | ECS | Orals | TS2.2

Tectonothermal constraints on the early-stage orogenic wedge formation along the Arabia-Eurasia suture zone in the NW Zagros orogenic belt 

Renas Koshnaw, Jonas Kley, István Dunkl, Fadhil Ameen, and Davit Vasilyan

Deep earth geodynamic processes shape surface geology, topography, and the earth’s crust evolution with consequences on erosion, deposition, climate, and biogeography. This research investigates the early-stage growth of the NW Zagros belt in the Kurdistan region of Iraq after the early Oligocene Arabia-Eurasia collision and the geologic signatures of potential SE-ward propagating Neotethys slab tearing. We will test two end-member hypotheses: (i) the slab has already detached, causing subsidence before slab tearing, followed by rapid regional uplift in the vicinity of the suture zone afterward, or (ii) the slab is still attached, causing no pulse of significant hinterland uplift but continuous regional lower plate subsidence. In the NW Zagros belt, where the Arabian and Eurasian plates are sutured along the Main Zagros fault, allochthonous thrust sheets of ophiolitic and arc-related terranes were emplaced onto post-collisional autochthonous units of clastic and lower-middle Miocene shallow marine carbonate rocks, now at ~1-1.5 km elevation. The allochthonous thrust sheets host pre-collisional acidic and mafic intrusions that provide exhumation rate constraints throughout collision, whereas the post-collisional marine carbonate rocks attest to a significant suture zone subsidence and uplift. Thermal history modeling of bedrock samples using zircon and apatite (U-Th)/He thermochronometers suggests an early uplift during ~30-25 Ma, with most apatite (U-Th)/He samples being reset during ~15-10 Ma. To quantitatively determine the depositional age of the lower-middle Miocene marine carbonate rocks, 87Sr/86Sr isotope chronstratigraphy will be conducted. Furthermore, the isopach maps of the middle and upper Miocene foreland deposits show a notable shift in the depocenter axis and an enhanced subsidence toward the SE, concurrent with the arrival of the Afar plume to the suture zone in the NW. These preliminary results argue for the formation of the NW Zagros orogenic wedge as early as ~30-25 Ma, followed by suture zone subsidence during the early-middle Miocene and then uplift again during ~15-10 Ma, possibly due to initiation of Neotethys slab-tearing and its subsequent propagation along the suture zone from the NW to the SE. These findings have implications for investigating the role of the Arabia-Eurasia land bridge formation and deformation on vertebrate distribution and paleoclimate response to orographic barrier development since the late Miocene in the Middle East.

How to cite: Koshnaw, R., Kley, J., Dunkl, I., Ameen, F., and Vasilyan, D.: Tectonothermal constraints on the early-stage orogenic wedge formation along the Arabia-Eurasia suture zone in the NW Zagros orogenic belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3749, https://doi.org/10.5194/egusphere-egu24-3749, 2024.

The Pyrenees is a collisional orogen built by inversion of an immature rift system during convergence of the Iberian and European plates from Late Cretaceous to late Cenozoic. The full mountain belt consists of the pro-wedge and foreland of the southern Pyrenees and the retro-wedge and foreland of the northern Pyrenees, where the inverted lower Cretaceous rift system is mainly preserved. Due to low overall convergence and absence of oceanic subduction, this immature orogen preserves one of the best geological records of early orogenesis, the transition from early convergence to main collision and the transition from collision to post-convergence. During these transitional periods major changes in orogen behavior reflect evolving lithospheric processes and tectonic drivers. These records are best preserved in the North Pyrenean Zone (NPZ), the retrowedge thrust belt and its adjacent syn-orogenic basin. This paper reviews along strike variations in structural and stratigraphic characteristics of the NPZ and adjacent basin evolution and explores the changing role in space and time of rheological, thermal and structural Inheritance and local and plate scale drivers.

How to cite: Ford, M.: Lateral and temporal variations in thrust belt behaviour in a low convergence retrowedge, north Pyrenees. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4040, https://doi.org/10.5194/egusphere-egu24-4040, 2024.

EGU24-4663 | ECS | Orals | TS2.2

Multiple tectonic phases and fluids variability along transverse zones of the Central Southern Alps (Lombardy, Italy) 

Andrea Fiorini, Luca Aldega, Luigi Dallai, Eduardo Di Marcantonio, Martina Rocca, Stefano Tavani, Stefano Zanchetta, Andrea Zanchi, and Eugenio Carminati

Fold-and-thrust belts are usually deformed by major transverse zones oriented orthogonally to the main thrust faults. These structural discontinuities represent ancestral fault zones originated mainly during rifting and subsequently reactivated during orogenic shortening (Zanchi et al., 2012). Sectors displaying thicknesses and sedimentary facies changes within the syn-rifting successions are juxtaposed along transverse zones (Thomas, 1990). This variability results in diverse deformation and shortening styles, as thrusts exhibiting flat (detachment levels) or ramp (more competent lithologies) geometry occur at different depths.

Limited data exist on the origin of fluids circulating along transverse zones and how they control fluid flow at the regional scale. In this study, we analyse transverse zones in the Lecco area of the Central Southern Alps (Lombardy, Italy). This belt features N-S trending, km-scale transverse zones initiated as normal faults during Ladinian, Norian-Rhaetian and Early Jurassic rifting phases and subsequently reactivated as strike-slip faults and/or lateral ramps during the Alpine orogeny (Schönborn, 1992). Two transverse zones are foci of this work: the Lecco Line to the west, running along the southeastern branch of Como Lake, and the Faggio Line to the east.

Geological mapping and mesostructural analysis were conducted and geological cross sections were built to constrain the geometry and kinematics of such transverse zones. Inorganic thermal indicators were used to constrain the eroded overburden and the exhumation depth of the analysed fault zones. U-Pb radiometric dating on syntectonic calcite mineralizations allowed us to constrain the age of tectonic activity. Syntectonic calcite veins precipitated either during the Early Jurassic rifting phase or younger Alpine orogenic phases, testifying the complex and long-lasting tectonic history of these transverse zones. C and O stable isotopes analysis allowed us to assess the origin of fluids circulating within transverse zones and their degree of interaction with host rocks. Two significant findings emerged from these analyses: 1) calcite mineralizations with variable δ13C and δ18O values characterize these fault zones, pointing out different degrees of fluid-rock interactions and/or different origin of fluids circulating during rifting and orogenic shortening; 2) transverse zones and related structures bound sectors where mineralizations occasionally exhibit values within narrow ranges of δ13C and δ18O; conversely, in other sectors, isotopic values display significantly wider ranges. In conclusion, transverse zones in the Southern Alps are structural features with a complex tectonic and fluid flow history, as testified by the large variability of age and C-O stable isotopes values. Furthermore, they possibly exert a partial compartmentalization of fluid flow at the regional scale.

References:

- Schönborn, G. (1992). Alpine tectonics and kinematic models of the central Southern Alps. Memorie di Scienze Geologiche, 44, 229–393.

- Thomas, W. A. (1990). Controls on locations of transverse zones in thrust belts. Eclogae Geologicae Helvetiae, 83(3), 727-744.

- Zanchi, A., D’Adda, P., Zanchetta, S., & Berra, F. (2012). Syn-thrust deformation across a transverse zone: the Grem–Vedra fault system (central Southern Alps, N Italy). Swiss Journal of Geosciences, 105(1), 19-38.

How to cite: Fiorini, A., Aldega, L., Dallai, L., Di Marcantonio, E., Rocca, M., Tavani, S., Zanchetta, S., Zanchi, A., and Carminati, E.: Multiple tectonic phases and fluids variability along transverse zones of the Central Southern Alps (Lombardy, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4663, https://doi.org/10.5194/egusphere-egu24-4663, 2024.

EGU24-5837 | ECS | Orals | TS2.2

Rift inheritance in a fold-and-thrust belt evolution: Central Apennine crustal balanced cross-section 

Augusto Maresca, Pablo Granado, Josep A. Muñoz, Gianreto Manatschal, Kei Ogata, and Stefano Tavani

The Apennines fold-and-thrust belt builds part of the Africa-Eurasia convergent plate boundary. It developed due to the Neogene subduction of the Alpine Tethys underneath Europe and to the subsequent involvement of the Adria microplate rifted margin into the collisional process. Since the Miocene, eastward retreat of the slab caused extensional deformation of the thrust pile, eventually leading to the opening of the Tyrrhenian back-arc basin. Multiple schools of thought exist about the structural style of the Apennines, each of which proposes rather irreconcilable models. The amount of shortening, the involvement of the crystalline basement, the architecture of the inherited rifted system with its degree of reactivation during convergence, and the role played by compressive inheritance during back-arc extension, are still under discussion.

In this contribution we focus on the crustal structure of the central Apennines, along a transect that stretches from the Sardinian shelf (West) to the center of the Adriatic Sea (Est). Our aim is to critically evaluate prior models and contextually to illuminate the deeper part of the belt, which is still seldom considered in modern-day Central Apennines solutions. Based on the most recent ideas on rift inheritance and thrust tectonics, we present a brand-new crustal balanced cross-section. We employ well-constrained surficial geological data from available public maps, as well as the most recent deep-reaching geophysical data (especially, tomography and seismological data), which are supplemented by thermochronological, biostratigraphic, and Sr-isotope datings. On top of that, data are encompassed in a coherent geodynamic framework that is supported by a geometrically balanced and consistent kinematic model. This way, we provide a comprehensive explanation for the regionally observed coupled forward migration of compressional and extensional domains, which is related to the slab pull/trench retreat system.

Our results point to a predominantly thin-skinned style for the orogen with a secondary basement involvement in the later collisional stage. Inherited extensional faults, developed during the Mesozoic rifting of Adria, were partially reactivated during convergence, and influence spacing and geometry of the compressional features. The main thrusts of the area are characterized by significant displacements, ranging from 10 to >50 km, and sole out into a basal décollement located at the base of the post-Variscan sedimentary sequence. Finally, post-thrusting back-arc extension is accommodated by faults that either displace the compressional décollement levels or reactivate them with an opposing kinematics.

How to cite: Maresca, A., Granado, P., Muñoz, J. A., Manatschal, G., Ogata, K., and Tavani, S.: Rift inheritance in a fold-and-thrust belt evolution: Central Apennine crustal balanced cross-section, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5837, https://doi.org/10.5194/egusphere-egu24-5837, 2024.

EGU24-6533 | Posters on site | TS2.2

Triangle zones as mechanical gages - results from numerical models and the Alpine Carpathian Belt 

Christoph von Hagke, Arthur Bauville, Nils Chudalla, Sofia Brisson, Florian Wellmann, Dan Tamas, Alexandra Tamas, Piotr Krzywiec, and Alexander Malz

Fault vergence in fold-and-thrust belts and accretionary prisms is characterized by mainly forward verging thrusts and pop-up structures, and only few examples exist where backthrusting dominates. However, backthrusting and triangle zones are known from most if not all fold-thrust belts in the world. The circumstances under which backthrusts instead of forethrusts form are still incompletely understood. Previous studies suggest that the strength and dip of the basal décollement of Coulomb wedges plays a key role. However, a systematic study of these parameters is still missing. We present numerical models of brittle-ductile wedges, varying dip and strength of the basal décollement systematically. We show that a new parameter, cumulative vorticity, is well-suited to characterize wedges based on dominant fault vergence. We find that backthrust-dominated wedges form in setups of very low basal dip (≤ 0.5°) and a weak décollement. Increasing décollement strength or basal dip results in the formation of pop-up-dominated wedges, before forethrust dominated wedges form. While our models corroborate the idea that décollement strength and basal dip may control thrust vergence, comparison with natural examples indicates this cannot be the only explanation for the formation of backthrusts. We probe into this using a compilation of structures along strike the fold-thrust belt of the entire Alpine-Carpathian Belt. Our results show that indeed triangle zones are associated with weak décollements, while additionally syn-tectonic sedimentation, rheological changes across strike, or structural inheritance may play a role. In some cases, interpretations of backthrusts at depth is challenging due to geometric uncertainty. We show uncertainty modeling of triangle zones using a well-known example from the boundary between Eastern and Central Alps. These uncertainty estimates may be combined with thermochronological data with the goal to distinguish the presence or absence of triangle zones from exhumation estimates. When present, triangle zones and backthrusts may serve as mechanical gages, providing tight constraints on fold-thrust belt mechanics.

How to cite: von Hagke, C., Bauville, A., Chudalla, N., Brisson, S., Wellmann, F., Tamas, D., Tamas, A., Krzywiec, P., and Malz, A.: Triangle zones as mechanical gages - results from numerical models and the Alpine Carpathian Belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6533, https://doi.org/10.5194/egusphere-egu24-6533, 2024.

EGU24-6848 | ECS | Orals | TS2.2

Active tectonics within the southwestern edge of the Fars Arc, SW Iran 

Aram Fathian, Hemin Koyi, Stefan Back, Hamid Nazari, Dan H. Shugar, Mohammad Ali Shokri, and Klaus Reicherter

The Fars Arc constitutes the southeastern segment of a tectonic recessions and salients array that characterizes the Zagros orogen. The delineation of the Fars Arc's western boundary is attributed to the prominent Kazerun fault system. However, further to the west, the southwestern periphery of the Arc (i.e., the Bushehr area) remains relatively unexplored, lacking documented evidence of tectonically active structures, as well as significant historical and instrumental seismic events. We combined tectonic geomorphology, remote sensing, and Quaternary geochronology to comprehensively study and identify tectonically active structures within the onshore area. Investigating the offshore area, we utilized 2D seismic-reflection data to interpret and image active subsurface structures in the Persian Gulf. We mapped and introduced several active faults in the Bushehr area, some of which are closely associated with active Quaternary anticlines, e.g., the Bushehr and Abtavil anticlines. Two generations of uplifted marine terraces, Terrace-I and Terrace-II across the Bushehr anticline, reveal a local uplift rate of approximately 0.8 mm/yr across the Bushehr Peninsula. The offshore 2D seismic-reflection data indicate ongoing deformation in the study area and show evidence of a recent sedimentary depocenter offshore of the Bushehr Peninsula. These observations define the present-day active deforming structures along the Zagros orogenic front in the Persian Gulf. The 2D seismic-reflection interpretations have characterized the active folding of the Bushehr anticline, indicating a minimum age of approximately 600 ka BP. The integration of on- and offshore geological analysis has revealed contemporaneous incipient deformation and syn-kinematic sedimentation, which significantly contributes to our understanding of geodynamics of the Zagros deformation front.

How to cite: Fathian, A., Koyi, H., Back, S., Nazari, H., H. Shugar, D., Shokri, M. A., and Reicherter, K.: Active tectonics within the southwestern edge of the Fars Arc, SW Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6848, https://doi.org/10.5194/egusphere-egu24-6848, 2024.

The mechanisms of regional metamorphism in convergent orogens are still debated, with two perspectives on timing—either linked to convergence processes or pre-convergence rifting. The Hsuehshan Range in Taiwan experienced rifting from the Eocene to the Miocene, followed by a convergence since the late Miocene. In this study, we discuss the metamorphic mechanism of the Hsuehshan Range by combining Raman spectroscopy of carbonaceous material (RSCM) for the peak metamorphic temperatures and zircon fission track for the cooling ages, to constrain the burial temperature before the convergence.

In central Hsuehshan Range, RSCM temperatures peaked at 480°C, decreasing northward and southward. In the central-northern region, RSCM temperatures correlated positively with stratigraphic ages. However, in the southern region, east of the Tili Fault, temperatures increased eastward without matching stratigraphic ages.

In some areas, RSCM temperatures (260-300°C) indicate total reset during the late Cenozoic orogeny, while zircon fission-track ages show partial reset. Higher RSCM temperatures (>400°C) lack significant new biotite growth.

We propose that during the rifting stage, strata experienced peak metamorphism, followed by cooling before the late Cenozoic orogeny, thus explaining inconsistencies between RSCM temperatures and zircon fission track ages. The deposit thickness variations in the rifting basin that are contributed to the RSCM temperatures, show no apparent stratigraphic correlation.

How to cite: Hsieh, L.-C. and Lee, Y.-H.: Using Raman Spectroscopy of Carbonaceous Material to Explore the Metamorphic Temperature and its Tectonic Implications in the Southern Hsuehshan Range, Taiwan Orogen, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7239, https://doi.org/10.5194/egusphere-egu24-7239, 2024.

EGU24-7287 | Orals | TS2.2

Cover-basement relationships in a fold-and-thrust belt with inherited uneven weak horizons distribution: example from the southern Pyrenees across the Jaca basin 

Josep Muñoz, Esther Izquierdo, Rosibeth Toro, Pablo Santolaria, Pablo Granado, Emilio Pueyo, and Antonio Casas

We present a new cross-section across the Jaca basin in the southern Pyrenees, aiming to analyze the temporal and spatial distribution of deformation in a fold-and-thrust belt. In this study, we have integrated all available subsurface data, including seismic sections and well data, with surface data to construct a balanced cross-section and partial restored cross-sections that illustrate the evolution of the south-Pyrenean fold-and-thrust belt.

Contractional deformation, initiating the development of the Pyrenean Mountain belt, started during Late Cretaceous times due to the reactivation of the Early Cretaceous hyperextended margin. Subsequently, deformation progressed during the Paleogene within the unstretched Iberian plate. In this region, the kinematics of the thrust wedge was controlled by inherited extensional faults and the unevenly distribution of Triassic evaporites above the basement.

Although deformation progressed toward the foreland, synchronous thrusting characterized the internal deformation of the thrust wedge. The localization and switching of deformation along the fold-and-thrust belt resulted from the interaction of unevenly distributed weak layers, including salt, and syntectonic sedimentation.

This work illustrates how detailed fieldwork, when combined with subsurface data and news concepts and methodologies (such as the use of drone imagery and analogue and numerical modelling), can significantly improve the understanding of the structure and evolution of fold-and-thrust belts.

How to cite: Muñoz, J., Izquierdo, E., Toro, R., Santolaria, P., Granado, P., Pueyo, E., and Casas, A.: Cover-basement relationships in a fold-and-thrust belt with inherited uneven weak horizons distribution: example from the southern Pyrenees across the Jaca basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7287, https://doi.org/10.5194/egusphere-egu24-7287, 2024.

EGU24-7329 | ECS | Posters on site | TS2.2

Present-day quantification of seismic coupling along the décollement level beneath the Potwar Plateau region in Pakistan western Himalaya 

Pauline Meyer, Francois Jouanne, Marie-Pierre Doin, Awais Ahmed, Adnan Alam Awan, and Jean-Louis Mugnier

The northwestern syntax of the Himalaya is a very rapidly deforming area at the edge of the India-Asia collision zone. Therefore, we quantify the current velocity field of the Potwar Plateau – Salt Range fold-and-thrust belt using GNSS horizontal surface velocities and Sentinel-1 interferometry line-of-sight velocities. From this velocity field which indicates a creep of the Potwar Plateau along the Main Himalayan Thrust, we infer a weak subhorizontal décollement level formed by a massive Precambrian salt layer. South of the Plateau, the Salt Range is uplifted along the Salt Range Thrust up to 5 mm/yr. The Kalabagh Fault, which forms the western boundary of the Salt Range and the Potwar Plateau, exhibits a creep rate along fault of 3.3 mm/yr. To characterize the slip distribution and coupling along the faults, we use numerical modelling with a set of dislocations in an elastic half-space. The preferred model shows the presence of a large asperity along the décollement level beneath the Potwar Plateau and several smaller asperities along the eastern basal thrust. These observations are consistent with the occurrence of the 2029 Mirpur earthquake of Mw 5.9 along the eastern part of the décollement level. Along the southern and superficial parts of the Salt Range Thrust, the model indicates a slip rate of 20 mm/yr which is greater than the 14 mm/yr slip rate along the Main Himalayan Thrust at depth. This observation suggests the existence of an internal southward flow of the massive salt layer along the upper part of the Salt Range Thrust. For the Kalabagh strike slip fault, an alternation of coupled and decoupled zones is observed, meaning that this fault can be characterised by creep and asperities where earthquakes and/or slow slip events can occur. Considering the lack of instrumental and historical large magnitude earthquakes in the area since the AD 25 Taxila earthquake, it can be concluded that the Main Himalayan Thrust and the Kalabagh Fault are likely to be affected by large magnitude earthquakes.

How to cite: Meyer, P., Jouanne, F., Doin, M.-P., Ahmed, A., Alam Awan, A., and Mugnier, J.-L.: Present-day quantification of seismic coupling along the décollement level beneath the Potwar Plateau region in Pakistan western Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7329, https://doi.org/10.5194/egusphere-egu24-7329, 2024.

EGU24-8453 | ECS | Orals | TS2.2 | Highlight

The origin of tectonic mélanges and implication for the subduction interface processes 

Kristijan Rajič, Hugues Raimbourg, Vincent Famin, and Benjamin Moris-Muttoni

Tectonic mélanges, penetrative mixes of sediments and basalts, are often interpreted as fossil subduction plate interfaces. These formations, marked by intense deformation, contain witnesses of past earthquakes and commonly include remnants of the oceanic crust of the subducting plate. The original process that led to penetrative mixing of sediments and basalts is often controversial, and classically relies either on tectonic slicing of the downgoing plateduring subduction, or on pre-subduction, olistostrome-forming sedimentary mixing. In addition, magma emplacement in sediments of the downgoing plate may also explain the mixed lithologies of mélanges. This latter case should leave an aureole of contact metamorphism in sediments near basalts. In this work, we applied Raman Spectroscopy of Carbonaceous Material in the modern seafloor sediments where magmatism is reported, in order to evaluate the thermal influence from basalts onto carbonaceous material in the contacting sediments. Then, to check the potential contact metamorphism in mélanges, we employed the same methodology in several examples of sediment-basalt mélanges at (sub)-greenschist-facies conditions (Kodiak complex, Alaska; Shimanto Belt, Japan).

In modern ocean-floor settings, magmas intruding, and to a lesser extent, flowing onto sediments, resulted in higher crystallinity of carbonaceous material in a cm- to dm-thick contact aureole. In four of five studied mélanges, the crystallinity of carbonaceous material in metasediments increases toward basalts, indicating a ~1 cm-thick contact metamorphism aureole. Thus, we propose that for the studied mélanges the mixing likely occurred prior to subduction, with the preservation of contact metamorphism despite syn-subduction, low-temperature metamorphism.

As a consequence, the block-in-matrix structure observed in mélanges, as well as the occurrence of mafic bodies at seismogenic depths in accretionary prisms, is in many instances the result of pre-subduction structure, rather than tectonic slicing and step-down of the decollement into the oceanic crust. In particular, tectonic mélanges such as Mugi in Japan and Ghost Rocks in Alaska do not reflect simply the structure and thickness of the plate subduction interface, but a complex combination of pre-subduction geometry and tectonic processes during underplating and within the accretionary wedge.

Furthermore, in two studied paleo-accretionary complexes, deposition ages of the trench sediments forming the matrix of three examined mélanges overlap ages of magmatism within uncertainty. Considering that the basalts from these mélanges exhibit MORB signatures, this age overlap suggests that the mélanges possibly formed at the trench just before ridge subduction. We thus conclude that basalt-sediment mélanges stand as potential records documenting ancient ridge subduction events.

How to cite: Rajič, K., Raimbourg, H., Famin, V., and Moris-Muttoni, B.: The origin of tectonic mélanges and implication for the subduction interface processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8453, https://doi.org/10.5194/egusphere-egu24-8453, 2024.

EGU24-9604 | ECS | Orals | TS2.2

Penetrative strain of the Aragüés fault-propagating folds in the Southern Pyrenees revealed by magnetic fabric analysis 

Thorben Schöfisch, Hemin Koyi, Antonio Teixell, and Bjarne Almqvist

The Aragüés thrust system, in the Southern Pyrenees, is a superb and well-exposed sequence of thrust imbricates to study the deformation and development of fault-propagating folds. The mechanisms of folding and thrusting, including the importance of material contrast during the development of the thrust sequence, are well-studied in this area. However, insights into the distribution and magnitude of penetrative strain remain unknown. Therefore, analysis of anisotropy of magnetic susceptibility (AMS) is used to reveal penetrative deformation within the sedimentary rocks of the Aragüés thrust system. Rock samples from 66 locations are collected across the Aragüés thrust imbricates with a focus on the layered limestone unit. A total of 489 cylinders were retrieved from the oriented hand samples and their AMS signal was measured. Thermomagnetic and magnetic remanence measurements show that the magnetic susceptibility of the samples is dominated by paramagnetic minerals and the magnetic lineation (axis of maximum susceptibility) is mainly parallel to subparallel to bedding. However, the more strongly magnetic samples (kmean: 3-5 x 10-4SI) show a magnetic lineation parallel to the general NNE-SSW shortening direction at the back- and forelimbs of fault-propagation folds. In contrast, the samples with a lower magnetic susceptibility (kmean: 1-3 x 10-4 SI), which are also closer to fold hinges, reveal a magnetic lineation perpendicular to the main shortening direction. We interpret the differences in fabric alignment and magnetic susceptibility to mineral composition and structural evolution. For example, the magnetic lineation parallel to the shortening direction is a consequence of flexural slip and flow along bedding surfaces or incompetent beds of the layered limestone units in the fold limbs. Additionally, a relationship between the magnetic lineation and the development of cleavage and stylolites within the limbs can be identified, but is not consistent. The magnetic lineation at the fold hinge is perpendicular to the main shortening direction and needs further investigation for strain accommodation prior to folding, an effect of buckling and/or development as intersection lineation. These first interpretations of the magnetic fabric provide additional insights into the deformation of the Aragüés thrust system and the development of fault-propagating folds. Moreover, the AMS data adds new information on penetrative strain in this region of the Southern Pyrenees and reveals a general tectonic overprint on grain-scale within sedimentary rocks during deformation.

How to cite: Schöfisch, T., Koyi, H., Teixell, A., and Almqvist, B.: Penetrative strain of the Aragüés fault-propagating folds in the Southern Pyrenees revealed by magnetic fabric analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9604, https://doi.org/10.5194/egusphere-egu24-9604, 2024.

EGU24-10775 | Posters on site | TS2.2

Evidence for Eurekan deformation within and around the Yermak Plateau, Arctic Ocean 

Wolfram Geissler, Peter Klitzke, Graeme Eagles, Lutz Reinhardt, Maximilian Weber, Kai Berglar, and Antonia Ruppel

The Yermak Plateau is a submarine plateau that lies to the north of Svalbard. Strong magnetic anomalies over its northeastern part led early interpretations of an origin by volcanic processes in an oceanic setting, during the formation of the SW Eurasia Basin and the Fram Strait between Svalbard and Greenland. However, subsequent geophysical research delivered evidence that at least the southern and northwestern parts of the plateau might be underlain by extended continental crust. This implies that plate reconstructions for times before the opening of the Eurasia Basin should account for these continental fragments. Up until now, the true northward extent of this microcontinent and neighbouring parts of Svalbard, and their late Cretaceous and Paleogene relative locations, have been incompletely known.

Moreover, during the late Cretaceous and Paleogene, large areas along the Northern Canadian and North Greenland continental margins, as well as the West Svalbard and Southwest Barents Sea continental margins were affected by compressional and strike-slip deformation that culminated in at least two discrete phases together referred to as the Eurekan orogeny, which dates from 53 to 34 Ma. Considering that the continental fragments of Yermak Plateau were located to the north of Greenland or even north of the Canadian Arctic Islands, it is conceivable that the Eurekan deformation might have also left traces within or around the present-day Yermak Plateau.

Here we report on evidence from seismic reflection data from the Sophia Basin, which separates the Yermak Plateau from Svalbard. Evidence for compressional and transpressional features beneath a Neogene-Quaternary sedimentary cover can be correlated to the two Eurekan deformation phases. Reconstructing the Yermak Plateau towards the North Greenland margin by closing the Neogene-Quaternary Lena Trough spreading system based on aeromagnetic data, we also found further evidence for continuity of geological structures between North Greenland and the northwestern Yermak Plateau.

How to cite: Geissler, W., Klitzke, P., Eagles, G., Reinhardt, L., Weber, M., Berglar, K., and Ruppel, A.: Evidence for Eurekan deformation within and around the Yermak Plateau, Arctic Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10775, https://doi.org/10.5194/egusphere-egu24-10775, 2024.

EGU24-10919 | Orals | TS2.2

U-Pb calcite geochronology attests Late Cretaceous S-verging thrusting in the central Southern Alps, Italy 

Andrea Zanchi, Stefano Zanchetta, Martina Rocca, Chiara Montemagni, Luca Aldega, Andrew Kylander-Clark, Andrea Fiorini, and Eugenio Carminati

The central Southern Alps (cSA) form a complex south-verging polyphase fold-and-thrust belt developed from the Late Cretaceous onward due to the Alpine convergence (Schönborn, 1992; Zanchetta et al., 2015). The oldest ages related to thrust stacking have been obtained from pseudotachylythes along the Orobic Thrust exposed in the northern part of the belt (Zanchetta et al., 2011), stacking the Variscan basement onto the Permian-Triassic cover.

Aim of this contribution is to present new U-Pb radiometric ages of calcite tectonites obtained in the central and southern portion of the belt, where no precise time constrains of thrust stacking are available. E-W trending Eocene dike swarms crosscutting thrust planes are the only indirect evidence of a pre-Eocene age of the oldest stages of the Alpine contraction (D’Adda et al., 2011).

The central part of the cSA shows a thick pile of thrust sheets deforming the Lower to Middle Triassic carbonate successions. Our new U-Pb calcite ages obtained on growth fibers along fault planes, veins and calc-mylonites sampled along some of the most important regional thrust planes mainly result in Late Cretaceous ages. We obtained similar ages also within the southern portion of the belt, where the Norian “Dolomia Principale” thrust sheets, override the Rhaetian Riva di Solto Shale immediately to the north of the frontal portion of the belt. Younger ages resulted from the Paleogene units which are involved in the exposed frontal part of the belt, which is mostly buried under the recent infilling of the Po Plain forming the Milan Belt.

These data confirm previous interpretations of the central Southern Alps as part of a Late Cretaceous doubly vergent pre-collisional belt (Zanchetta et al., 2012). Research supported by the FAST PRIN Project (2021-NAZ-0299, Italian MUR).

D'Adda, P., Zanchi A., Bergomi M. A., Berra F., Malusà M. G., Tunesi A., & Zanchetta S. (2011) - Polyphase thrusting and dyke emplacement in the central Southern Alps (Northern Italy), International Journal of Earth Sciences, 100, 1095–1113.

Schönborn, G. (1992) - Alpine tectonics and kinematic models of the central Southern Alps. Memorie di Scienze Geologiche, 44, 229-393.

Zanchetta S., D'Adda P., Zanchi A., Barberini V. & Villa I.M. (2011) - Cretaceous-Eocene compressions in the central Southern Alps (N Italy) inferred from 40Ar/39Ar dating of pseudotachylytes along regional thrust faults. Journal of Geodynamics, 51, 245-263.

Zanchetta, S., Garzanti, E., Doglioni, C., and Zanchi, A. (2012). The Alps in the Cretaceous: a doubly vergent pre-collisional orogen, Terra Nova, 24, 351–356, 2012.

Zanchetta S., Malusà M. & Zanchi A. (2015) - Precollisional development and Cenozoic evolution of the Southalpine retrobelt (European Alps). Lithosphere, 7, 662-681.

How to cite: Zanchi, A., Zanchetta, S., Rocca, M., Montemagni, C., Aldega, L., Kylander-Clark, A., Fiorini, A., and Carminati, E.: U-Pb calcite geochronology attests Late Cretaceous S-verging thrusting in the central Southern Alps, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10919, https://doi.org/10.5194/egusphere-egu24-10919, 2024.

EGU24-11050 | Posters on site | TS2.2

Evidence for Eurekan deformation within and around the Morris Jesup Plateau, Arctic Ocean 

Peter Klitzke, Wolfram H. Geissler, Lutz Reinhardt, Antonia Ruppel, Martin Engels, and Rüdiger Lutz

The Morris Jesup Plateau is located offshore North Greenland and includes the Morris Jesup Rise in the west and the Morris Jesup Spur in the east. The Yermak Plateau north of Svalbard represents the conjugate margin of the Morris Jesup Plateau. Both margins are separated by the southernmost part of the Eurasia Basin with the Gakkel Ridge. The wider Eurasia Basin started to open in Paleocene-Eocene times. At those times, Greenland moved northwards due to active spreading both in the NE Atlantic and the Labrador Sea. This northward motion of Greenland resulted in the Eurekan compressional deformation between Greenland and Svalbard and limited or strongly influenced the opening of the Eurasia Basin towards the southwest. Only with the cessation of the Eurekan deformation in late Eocene times, the spreading system of the Eurasia Basin advanced southwards and finally separated the Yermak and Morris Jesup plateaus.

While Eurekan deformation is well documented onshore across the West Spitsbergen Fold-and-Thrust Belt and complex thrust and strike-slip zones in North and NE Greenland, only little is known about how these compressional/transpressional structures continue offshore across the North Greenland continental margin towards the Morris Jesup Plateau. Furthermore, the extent to which the Morris Jesup Plateau was affected by extension prior to its separation from the Yermak Plateau in the early Oligocene is poorly resolved. Answering these questions is essential to determine where the Morris Jesup and Yermak plateaus were situated along the North American margin in the late Mesozoic and earliest Cenozoic. Was the opening of the Eurasia Basin compensated by deformation within the plateaus, or did strike-slip movements reactivate the ancient Paleozoic Canadian Arctic transform system? Are there any indications for initial subduction to the North of Greenland as previously proposed on base of potential field data?

Here we report on the first multichannel seismic survey along with magnetic data of the southern Morris Jesup Plateau. The seismic data image transpressional and transtensional deformation likely associated with the two Eurekan deformation episodes, the transition to passive margin evolution as well as glacial sedimentation. We compare the results with two seismic lines of the northern Morris Jesup Plateau, which allow to discuss structural variations along the Morris Jesup Spur. 

How to cite: Klitzke, P., Geissler, W. H., Reinhardt, L., Ruppel, A., Engels, M., and Lutz, R.: Evidence for Eurekan deformation within and around the Morris Jesup Plateau, Arctic Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11050, https://doi.org/10.5194/egusphere-egu24-11050, 2024.

EGU24-11995 | ECS | Posters on site | TS2.2

Styles of deformation in the Umbria-Marche sector of the Apennines fold-and-thrust belt: new insights from balanced geological sections and 3D structural modelling 

Matteo Pedini, Federico Cella, Claudio Di Celma, Stefano Mazzoli, and Pietro Paolo Pierantoni

Understanding how orogenic shortening transfers from the basement to the sedimentary cover is crucial in fold-and-thrust belts. Transfer distance dictates the thrusting style. In cases of 'long-distance rooting' such as the Jura Mts.-Swiss Mollasse Basin-Alps system, the sedimentary cover's shortening leads to a thin-skinned deformation style. Conversely, 'short-distance rooting', as observed in the ramp-dominated sectors of the Southern Alps, results in thick-skinned deformation. However, the distinction of thin- vs. thick-skinned styles of thrusting may be ambiguous. 'Long-distance rooting' may cause thin-skinned deformation at the belt front and thick-skinned deformation where the basement underplates, as seen in the Alpine region. The crucial aspect in fold-and-thrust belt dynamics is whether the basement is extensively underthrust and processed in the orogen's interior ('long-distance rooting'), or if displacement directly transfers from basement thrusts to the sedimentary cover on a local scale ('short-distance rooting'). This fundamental issue is addressed here for the Umbria-Marche zone of the Apennines, which style of thrusting has been the subject of a long-lasting debate. Interpretations proposed in the last decades mostly range from pure thin-skinned to composite models of basement-involved deformation and detachment-dominated thrusting of the sedimentary cover.

We aim to investigate whether the sedimentary cover is more shortened than the basement (i.e., a substantial component of ‘long-distance rooting’ of thrust displacement of the sedimentary cover) or do shortening of basement and cover balance at the scale of the foreland fold-and-thrust belt (i.e., ‘short-distance rooting’ characterizes the Umbria-Marche zone). We integrate the updated 1:50,000 scale geological map (CARG Project) of the Sibillini area (Visso and Ascoli Piceno Sheets) with a 10 m cell-size digital elevation model, the interpretation of vintage seismic lines and gravimetric data. We present a series of new balanced and restored cross-sections, including a crustal section along the trace of available seismic lines covering the entire Apennine and foothills area to the coastline, validated by gravimetric modelling, and thirteen cross-sections used to verify the geometric viability of sedimentary cover structures in the study area. The results of our work suggest coupled deformation of basement and sedimentary cover, which are characterized by similar amounts of shortening (consistent with ‘short-distance rooting’ of thrust displacement). The balanced cross-sections, integrated with a dense grid of (n. 25) additional sections perpendicular to the main structural trends, were used to construct a 3D structural model calibrated by surface geology. This allowed us to reconstruct the main fault surfaces, accounting for the along-strike variability of geological features observed from the map and offering a detailed representation of the geometrical arrangement of key horizons (base-top Calcare Massiccio Fm, top Maiolica Fm, top Scaglia Rossa Fm, top Bisciaro Fm) and their relationships with major faults. Our structural model provides new insights into the architecture, timing of the deformation, and kinematic evolution of the Umbria-Marche sector of the Apennines. This has major implications for a better understanding of deformation style, the role of structural inheritance, and post-thrusting extensional tectonics (which controls the seismotectonic setting of the study area).

How to cite: Pedini, M., Cella, F., Di Celma, C., Mazzoli, S., and Pierantoni, P. P.: Styles of deformation in the Umbria-Marche sector of the Apennines fold-and-thrust belt: new insights from balanced geological sections and 3D structural modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11995, https://doi.org/10.5194/egusphere-egu24-11995, 2024.

EGU24-12111 | ECS | Orals | TS2.2

Sequential reactivation of the Billefjorden Fault Zone during evolvement of the West Spitsbergen Fold and Thrust Belt, Svalbard. 

Aleksandra Smyrak-Sikora, Alvar Braathen, Per Terje Osmundsen, and Kim Senger

The Paleogene West Spitsbergen Fold-and-Thrust Belt, WSFTB, is present in Svalbard (Norwegian High Arctic archipelago; 74-81°N, 15-35°E). The WSFTB’s contraction reflects the Eurekan Orogeny and transpressional continental breakup along a transform fault zone, followed by opening of a seaway between the North Atlantic and Arctic oceans. The overall timing of the contraction is not well constrained, and many authors link it to the development of a deep and narrow foreland basin system filled with Uppermost Paleocene and Eocene to Oligocene(?) deposits, while the Lower Paleocene deposits are considered to be deposited in a regional subsidence prior to Eurekan deformation. The WSFTB divides into a thick-skinned, basement-involved fold-thrust complex in the west, passing into a central zone of thin-skinned, fold-thrust units with associated detachments developed in Permian evaporites and Mesozoic organic-rich mudstones, separated by a prominent duplex system that reflects a thrust-ramp transferring movements from Permian to Mesozoic detachments eastwards. Stress transfer also reactivated the steep, basement rooted Billefjorden and Lomfjorden fault zones farther east, showing up to 200 m of reverse stratigraphic offsets. These fault zones are long-lived structural elements exposing multiple reactivation events since the Late Palaeozoic.

Our study targets the Paleogene reactivation and especially the sequence of deformation of the Billefjorden Fault Zone, based in detailed interpretations of onshore seismic lines, and field mapping supported by acquired and interpreted mountain-scale digital outcrop models. Results suggest initial shortening by reactivation of deep-rooted extensional faults, seen as reverse offsets of stratigraphic units and formation of fault-propagation monoclines as anticlines-synclines pairs. Subsequent deformation involved the regional-scale (tens of km long) decollement zones hosted by the Mesozoic mudstones. West of the Billefjorden Fault Zone, the decollement is seen in the Jurassic Agardhfjellet Formation. Crossing the Billefjorden Fault Zone, this decollement is seen truncating the reverse fault (digital outcrop data) and fault propagation fold (seismic data) and displacing them 2 km to the east, where the decollement continuous in the uplifted mid-Triassic mudstones of the Botneheia Formation. This sequence of deformation, with the reactivated deep-rooted faults truncated by the decollement, contradicts previously published models that advocate for reactivation of deep-rooted faults taking place late during the deformation, synchronised with an uplift of thick-skinned basement-involved thrusts.

The timing of the deep-rooted faults reactivation is poorly constrained. In this study, we hypothesise that it can be as early as the early to middle Paleocene, corresponding to phase of regional compression at 61 Ma indicated, by the recent studies, for the Lower Paleocene Firkanten Formation. This contraction could also be determined from the westward thickening and locally NE and E sourcing deposits of the Firkanten Formation and overlying Basilica and Grumantbyen formations, which indicate an existing topographic high or a foreland bulge as suggested by some of the authors. The timing of the second stage is consistent with the main shortening phase in the Eocene.

How to cite: Smyrak-Sikora, A., Braathen, A., Osmundsen, P. T., and Senger, K.: Sequential reactivation of the Billefjorden Fault Zone during evolvement of the West Spitsbergen Fold and Thrust Belt, Svalbard., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12111, https://doi.org/10.5194/egusphere-egu24-12111, 2024.

EGU24-12309 | ECS | Orals | TS2.2 | Highlight

Exploring mechanical stratigraphy's influence on deformation and seismicity: A 2D kinematic modelling study in the central External Dinarides 

Philipp Balling, Bruno Tomljenović, Marijan Herak, and Kamil Ustaszewski

The overall SW-vergent and in-sequence structural architecture of the Dinarides fold and thrust belt resulted from collision of the Adriatic Microplate with Eurasia in the Late Cretaceous. Throughout Eo-Oligocene times, the deformation front extended outward, causing substantial crustal shortening within the External Dinarides. This part of the orogen is predominantly composed of Mesozoic carbonate platform rocks, originally deposited in an external passive margin setting. Analysis of fault kinematics and two balanced cross-sections suggests a Cenozoic deformation characterized by along-strike contraction. The 250 km long dextral transgressive Split-Karlovac Fault acts as a boundary, separating a southern, SW-vergent nappe stack forethrust dominated domain (as observed in the Split cross-section) from a northern western NE-vergent backthrust dominated segment (as observed in the southern Velebit cross-section). To understand the reasons for the contrasting along-strike deformation, a reevaluation of the temporal and spatial distribution of Paleo-Mesozoic lithofacies along- and across-strike on both sides of the Split-Karlovac Fault was conducted. Additionally, an assessment of the impact of mechanical stratigraphy on deformation styles in this section of the fold-thrust belt was undertaken.

The best-fit kinematic forward model for the central Velebit Mtn. portrays a 75 km wide triangle zone, which took up at least 47 km of Eo-Oligocene shortening. The triangle structure comprises a SW-vergent thick-skinned duplex system detached in the lower Paleozoic Adriatic basement and five thin-skinned backthrusts detached in the upper Paleozoic basement. These backthrusts nucleated at lateral facies boundaries, related to extensional half grabens that formed due to passive margin extension in Middle Triassic and Late Jurassic times. During Cenozoic folding and thrusting these inherited Mesozoic half graben boundary faults were selectively inverted into the NE-vergent backthrusts. This process contributed to the observed along-strike variations in the deformation style of the External Dinarides.

An analysis of instrumentally recorded earthquakes within the northwestern structural domain unveils contrasting seismic activity along the central and southern Velebit transects. In the central Velebit Mountain, the triangle structure currently predominantly undergoes strike-slip motion, with reverse faulting predominantly occurring to the east of the Split-Karlovac Fault. Conversely, seismic activity along the southern Velebit cross-section is concentrated in the structurally lowermost parts of the triangle zone and the foreland, while its structurally higher sections exhibit lower seismic activity. The prevalence of reverse faulting along this transect suggests the ongoing accommodation of shortening in this region.

How to cite: Balling, P., Tomljenović, B., Herak, M., and Ustaszewski, K.: Exploring mechanical stratigraphy's influence on deformation and seismicity: A 2D kinematic modelling study in the central External Dinarides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12309, https://doi.org/10.5194/egusphere-egu24-12309, 2024.

EGU24-12571 | ECS | Orals | TS2.2

The Cala Viola-Torre del Porticciolo coastal area: classical geological survey and 3D digital outcrop models (DOMs) analysis to unravel the polyphase tectonics in NW Sardinia (Italy). 

Rudy Scarani, Angelo Cipriani, Niccolò Menegoni, Lorenzo Stori, Paolo Citton, Marco Romano, Umberto Nicosia, and Ausonio Ronchi

In the Nurra region (NW Sardinia), along the coast that stretches from Cala Viola to Cala del Turco bays, a stratigraphic sequence of continental sediments ranging from the upper Paleozoic to the lower Mesozoic is wonderfully exposed.

In the last twenty years this area has been a subject of renewed studies due to its exceptional stratigraphic and sedimentological features and thanks also to an exceptional paleontological record, encompassing trace fossils and body fossils, which provided key chronological data. The most recent investigations have been focused on stratigraphic and structural geology aspects, allowing to reconstruct the tectonic evolutionary history of Sardinia, from the middle Permian up to the Middle Triassic.

The redefinition of the stratigraphic and structural framework of the area became possible through integrating traditional geological surveys (mainly, field mapping, facies and structural analyses) with analyses conducted on 3D digital models of outcrops (DOMs) obtained via drone-based aerophotogrammetry. Investigations, both in the field and computer-based, have enabled the identification of the arrangement of cross-cutting relationships among fault systems.

Despite the absence of absolute geochronological constraints (e.g., dating of syn-kinematic mineralizations), it has nevertheless been possible to identify at least six to eight deformational events. These analyses have revealed the likely history of deformational processes in this sector of the Island, highlighting the tectonic events that have occurred from the Permian until at least the Pliocene, despite Pleistocene-Holocene tectonics cannot be excluded. The events can be summarized as follows:

  • Event 1: extensional tectonics related to the angular unconformity between Permian and Triassic deposits (age post early middle Permian to Early Triassic)
  • Event 2: extensional tectonics related to the rifting of the Ligurian-Piedmont Ocean and subsequent carbonates deposition (Middle Jurassic: Bajocian-Bathonian)
  • Event 3: extensional event related to the early Pyrenaic deformation and represented by an extensive angular unconformity/hiatus in carbonate platform (Early Cretaceous: Aptian-Albian)
  • Event 4: transpressive and compressive event related to deformative phase called “Laramian” tectonics (Late Cretaceous)
  • Event 5: compressive and consequent transcurrent tectonics related to the “Pyrenaic phase” (Eocene to Aquitanian age)
  • Event 6: extensional tectonics related to the opening of the Balearic basin and the rotation of the Sardinia-Corsica block (Burdigalian age)
  • Event 7: extensional tectonic phases occurred during two different sub-events (Serravalian age and the Pliocene age)
  • Event 8: extensional event occurred during the Pleistocene-Holocene

How to cite: Scarani, R., Cipriani, A., Menegoni, N., Stori, L., Citton, P., Romano, M., Nicosia, U., and Ronchi, A.: The Cala Viola-Torre del Porticciolo coastal area: classical geological survey and 3D digital outcrop models (DOMs) analysis to unravel the polyphase tectonics in NW Sardinia (Italy)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12571, https://doi.org/10.5194/egusphere-egu24-12571, 2024.

The Jura fold and thrust belt is characterised by dominant thin-skinned thrusting of the Mesozoic-Cenozoic sedimentary cover and variable interaction with inherited structures and deep-seated (i.e., sub-detachment) faults. In its central parts, this fold-and-thrust belt is detached from an underlying mechanically stiffer basement, along Triassic evaporites and displaced up to 30 km. The eastern termination of the fold and thrust belt is characterised by (i) a much lower amount of shortening (on the order of the hundreds of meters), (ii) a significant thickness reduction of evaporites of the Muschelkalk Group, and (iii) interaction of the décollement with steps associated with faults bounding an underlying Permo-Carboniferous graben (Constance-Frick Trough; CFT).

Using recently processed seismic data (Nördlich Lägern 3D), we document the role exerted by the inherited structures rooted in the Permo-Carboniferous basin fill and basement in the development of the different styles of deformation and structures in an area located northwest of the city of Zürich. The ENE-striking master normal fault bounding the CFT to the south displays evidence of reactivation, during both extensional and compressional episodes, illustrated by apparent normal steps, alignments with no apparent displacement, and gentle folding of the Permo-Carboniferous basin fill. The investigated seismic volume indicates that contractional deformation is concentrated in two major ENE trending fold-thrust zones involving the Triassic-Jurassic epicontinental platform succession and the stratigraphically overlying Cenozoic Molasse Basin deposits. The northern fold-thrust zone (NFTZ), manifested at the surface by the Siglisdorf anticline, consists of an up to 2 km wide pop-up structure linked to thrusting in the detached cover series. The structure is located in correspondence with steps in the topography of the base Mesozoic unconformity produced by south dipping ENE striking minor faults rooted in the Permo-Carboniferous sequence without affecting the detachment integrity. The southern fold-thrust zone (SFTZ), corresponding to the Baden-Irchel-Herdern Lineament, is located above a north dipping major fault of the Late Paleozoic half-graben. The overlying deformation structures in the SFTZ, comprising multiple thrusts and backthrusts, that form fish-tail structures in a narrow, steep zone involving the Mid-Triassic-Jurassic series, are interpreted as the result of layer-parallel shortening associated with buckling of the Mesozoic multilayer. In contrast, the Mesozoic succession is characterized by low deformation and absence of major faults in the area over the central part of the graben (comprised between the Weiach – Glattfelden – Eglisau Lineament – WGEL – to the north and the south fold-thrust zone). The WGEL separates a sub-horizontal to gently folded Mesozoic rock panel to the south from a gently dipping panel to the north. This suggests that fault reactivation may have been accompanied by mild basin shortening and inversion.

In conclusion, different modes of interaction between the Mesozoic multilayer (including the weak evaporite level at its base) and underlying Upper Paleozoic basin fill with inherited basement faults have produced a marked contrast in structural style among the detachment-dominated NFTZ, the buckling-dominated SFTZ, and a low deformation central area.

How to cite: Zambrano, M., Mazzoli, S., and Mosar, J.: Influence of Inherited Structures on Deformation Patterns in the Eastern Jura Fold and Thrust Belt: Insights from 3D Seismic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13025, https://doi.org/10.5194/egusphere-egu24-13025, 2024.

EGU24-13635 | ECS | Posters on site | TS2.2

 The northern Gondwana margin and Pangaea tectonics revisited: Preliminary results in the Ossa-Morena Zone (SW Iberian Massif) 

Lourenço Steel Hart, Ícaro Dias da Silva, Aitor Cambeses, João C. Duarte, and Manuel Francisco Pereira

Orogenesis involves a continuum of complex natural phenomena within the context of the Wilson Cycle, the backbone of modern plate tectonics. While topographic effects of present-day orogenic cycles are readily visible, eroded old orogens represent windows that expose the crust's interior and facilitate the study of complex lithospheric processes.

The object of this research lies within the Devonian-Carboniferous Variscan collisional orogen that extends from Southern Europe to Northern Africa. This orogenic belt resulted from the convergence and collision between the passive margin of north Gondwana and the active margin of southern Laurussia, forming the Pangea Supercontinent. The Iberian Massif, located in the core of Pangaea, is one of the best exposures of the Variscan orogen in Europe, and a unique natural laboratory to study deep-to-surface geodynamic phenomena. Studying this sector of the Pangea supercontinent raises new important questions about how modern collisional orogens evolve and how their crustal architecture develops.

Field and analytical data compiled in the last 20-30 years in Iberia has revealed a complex basin-cover architecture derived from the deformation and metamorphism of the Ediacaran to Carboniferous stratigraphy. Ongoing research in a critical and representative region of the SW Iberian Massif (i.e. Ossa-Morena Zone), reveals a close relationship between the deformation, metamorphism, magmatism and sedimentary processes involved in deep to shallow lithospheric dynamics, during both orogenic thickening and gravitational collapse. 

The systematic study of key outcrops was performed, to define first-order geological contacts between major tectono-metamorphic, stratigraphic and magmatic units. This information made it possible to define the architecture of the crust along a transverse across the central region of the Ossa-Morena Zone (Estremoz, Portugal). With the structural relationships well defined, the main units were sampled to control the ages of the orogenic events and to correlate the tectono-metamorphic fabrics found in the Variscan basement regionally. This research focused on SW Iberian Massif will give important constraints to develop state-of-the-art conceptual and numerical models of the tectonic evolution of the Variscan Orogen during the assembly of the Pangaea supercontinent. The combination of field and petrography data with numerical modelling can be very useful for better understanding the role of different lithospheric processes in orogenic building and gravitational collapse as Supercontinents are formed.

 

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), through the scholarship UI/BD/154616/2023 and through UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020), LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020) and DL57/2016/CP1479/CT0030 (https://doi.org/10.54499/DL57/2016/CP1479/CT0030). M.F. Pereira acknowledges financial support from the FCT project (grant No. FCT/UIDB/ 04683/2020-ICT).

How to cite: Steel Hart, L., Dias da Silva, Í., Cambeses, A., Duarte, J. C., and Pereira, M. F.:  The northern Gondwana margin and Pangaea tectonics revisited: Preliminary results in the Ossa-Morena Zone (SW Iberian Massif), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13635, https://doi.org/10.5194/egusphere-egu24-13635, 2024.

EGU24-16253 | Posters on site | TS2.2

Evolution in space and time of a regional-scale fault: example from the Orobic Thrust (European Alps, Southalpine Domain) 

Stefano Zanchetta, Martina Rocca, Chiara Montemagni, Giulio Viola, Luca Aldega, and Andrea Zanchi

Despite the small volume they occupy in the crust, fault zones are of striking importance as they localize both seismic slip and aseismic deformation, as well as fluid migration at middle to shallow crustal levels. Regional-scale fault systems may benefit of long-lived activity as, due to their rheological weakness, they can be also reactivated by weak far-field stresses in a variety of tectonic settings. The architecture of fault zones that experienced multiple re-activation is complex and accurate structural analyses, including also the identification of (micro)structural facies (Brittle Structural Facies, BSF) and their crosscutting relationships, is mandatory to solve the spatial evolution and relative chronology of the fault zone.

The Orobic Thrust is a regional-scale fault zone, more than 80 km in length, representing one of the largest structures in the European Alps retro-belt. Along the thrust plane the Variscan basement is thrusted southward over the Upper Carboniferous to Lower Triassic volcano-sedimentary cover of the Southalpine Domain. In several areas the fault zone, ca. 250-300 m thick, is continuously exposed, allowing the detailed reconstruction of the fault architecture. A narrow (20-25 m) protomylonitic band marks the top of fault zone suggesting temperature of at least 300°C in the early stage of fault activity. Temperature in excess of 200°C are also supported by analysis of the thermal maturity of clay mineral assemblages (<2 µm size fraction) in terrigenous rocks in the footwall of the thrust plane. Four distinct BSF have been recognized: cataclasites, foliated cataclasites, pseudotachylyte bearing cataclastic bands and incoherent fault gouges. Apart from fault gouges occurring along discrete plane that appear to be undeformed, all the other 3 BSF display mutual crosscutting relationships, testifying for multiple switching between seismic slip and aseismic creep during fault history. The occurrence of pseudotachyltes and fault gouge allow to obtain absolute age constraints with 40Ar-39Ar and K-Ar illite dating, respectively. The ages obtained from pseudotachylytes span from 83 to 64 Ma whereas illite (<0.1 µm size fraction), separated from the gouge along a fault plane with a reverse kinematic at the core of the Orobic Thrust fault zone, provided and age of 53 Ma. Pseudotachylyte age distribution shows older ages 79-83 Ma occurring both at the top and the bottom of the fault zone, with a superposed pattern that display instead a bottom forward younging direction of ages between 76 and 64 Ma. Discrete fault planes decorated with gouges mark the end of the activity of the Orobic Thrust in the early Eocene.

Detailed meso-and microstructural analyses combined by absolute age constraints of the BSF allowed the reconstruction in space and time of the Orobic Thrust fault zone through its 30 Myrs long fault activity.

How to cite: Zanchetta, S., Rocca, M., Montemagni, C., Viola, G., Aldega, L., and Zanchi, A.: Evolution in space and time of a regional-scale fault: example from the Orobic Thrust (European Alps, Southalpine Domain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16253, https://doi.org/10.5194/egusphere-egu24-16253, 2024.

EGU24-16686 | ECS | Posters on site | TS2.2

Kinematic modelling of fold and thrust structures in anisotropic layered rocks in examples from the Northern Calcareous Alps (Eastern Alps, Austria) 

Mariusz Fiałkiewicz, Marcin Olkowicz, Bartłomiej Grochmal, Marcin Dąbrowski, Bernhard Grasemann, and Oscar Fernandez

The presented study is a part of a broader project, which includes field as well as numerical investigations into the evolution of tectonic structures within fold-and-thrust belts, with a particular focus on the development of fault-related structures in layered rocks. The existing models for deformation in fold-and-thrusts belts predominantly adopt a kinematic approach, wherein layering is considered as passive. The kinematic approach neglects rheological effects such as mechanical anisotropy, which plays an important role in layered rocks commonly found within fold-and-thrusts belts.

To explore the role of mechanical anisotropy we have analysed folding and thrusting in the central Northern Calcareous Alps (NCA), which comprise the Permo-Mesozoic sediments of the Upper Austroalpine unit. The NCA represents a fold and thrust belt, in which folds are formed by processes along overthrusts (e.g. fault-bend folds or fault-propagation folds), but out-of-syncline overthrusts are also present. The tectonic evolution of NCA is strongly influenced by sedimentary facies. Nappes in the NCA were imbricated during Jurassic and Cretaceous thrusting. Our research has focused on the Scythian (Lower Triassic) mixed clastic-carbonate sediments of the Werfen Fm, located to the SW of Hallstatt at the base of the fold-and-thrust system, as well as on the Upper Jurassic limestones of the Oberalm Fm located SE of Bad Ischl that are deformed syndepositionally into thrusts and folds forming the shallowest part of the fold-and-thrust belt during the Jurassic deformation stage.

During fieldwork, documentation was gathered through the acquisition of orientation measurements of tectonic structures: folded bedding, faults with slickensides, fold axes, cleavage, joints, etc. Photographic documentation of tectonic structures was undertaken to produce georeferenced photogrammetric models. Digital outcrop models in the form of georeferenced textured polygon meshes, which allow the integration of spatial data with the results of detailed geological mapping, were created. All field observations, including outcrop images and measurements, were integrated in a 3D environment, which facilitated the collection of additional data from the digital models.

Sequential restoration and kinematic forward modelling of structures performed in Move software confirm the limitations inherent with kinematic modelling to represent real-world strain patterns. Hybrid modes of kinematic models provide more acceptable results and prove that rheological contrasts within the sedimentary pile exert a strong control in the distribution of folding and faulting. These observations made at the meter-scale, relate to structures that represent a scale of strain normally not represented in regional-scale (kilometer-scale) cross-sections and dealt with as ‘internal strain’. Our observations imply that strain distribution within sedimentary units can be strongly anisotropic and its distribution should be contemplated when performing kinematic modelling of regional-scale structures.

How to cite: Fiałkiewicz, M., Olkowicz, M., Grochmal, B., Dąbrowski, M., Grasemann, B., and Fernandez, O.: Kinematic modelling of fold and thrust structures in anisotropic layered rocks in examples from the Northern Calcareous Alps (Eastern Alps, Austria), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16686, https://doi.org/10.5194/egusphere-egu24-16686, 2024.

We present new zircon fission-track age and RSCM peak-metamorphic temperature estimates from the Taiwan slate-belt and northern Palawan. The two regions represent the conjugate margins of the South China Sea that have undergone inversion during two separate collisional episodes, from the latest Miocene until present-day (Taiwan) and in the Middle Miocene (Palawan). In both regions the slate/phyllite and (meta-) sandstone stratigraphic successions have undergone green-schist and sub-green-schist facies peak metamorphic temperatures with a consistent positive correlation between stratigraphic age and metamorphic grade. A similar pattern is observed in the resetting degree of ZFT-ages, with shallow stratigraphic levels displaying unreset to partially-reset ZFT ages, while older strata exposed at the core of regional anticlines are fully reset. Importantly, ZFT young-peak ages (i.e. pooled age of the youngest ZFT grain-age population) and fully reset ZFT-ages are consistent within error, and constrain the initiation of rock cooling and exhumation to 5.9±1.5Ma (weighted mean of 6 pooled ages) in the section studied in the Northern Hsuehshan Range (Taiwan), and to 14.7±0.5Ma (weighted mean of 7 pooled ages) in Northern Palawan. Taken together our data indicates that peak-metamorphic conditions in both regions were reached before the main exhumation event and precede thrust-stacking and topographic growth.  Metamorphism is possibly related to basinal evolution (“burial metamorphism”) during the opening of the South China Sea or to some other tectonothermal events unrelated to the late Cenozoic mountain building processes. Our findings have important implications for the commonly assumed orogenic origin of low-grade metamorphic belts, as this assumption is implicitly included in the tectonic evolutionary models of orogenic development and in models of orogenic gold deposits typically found in slate belts, to name a few.

How to cite: Mesalles, L. and Lee, Y.-H.: Chronology of deformation and metamorphism of an inverted passive margin: evidences of pre-orogenic peak-metamorphic conditions in Taiwan and Palawan island (The Philippines)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16812, https://doi.org/10.5194/egusphere-egu24-16812, 2024.

EGU24-17684 | ECS | Posters on site | TS2.2

Geodynamics and Structural Evolution of Makran Accretionary Prism, Arabian-Eurasian Convergent Plate Boundary 

Umair Khan, Majid Khan, Wu Shiguo, and Jinwei Gao

The complex interplay between thrust wedge deformation, tectonically-induced fluid overpressures, and the complex phases of wedge-top sedimentary depositional systems in accretionary prisms presents a formidable challenge. The offshore Makran accretionary prism is the world's largest, formed by the convergence of Arabian plate underneath Eurasian plate in the Early Cretaceous, followed by Middle Miocene renewed subduction. The substantial tectonic shortening, imbricate thrust faulting triggered by Middle Miocene renewed subduction, coupled with a continuous influx of sediments, synergistically contributed to the remarkable accumulation of ~7.5 km thick sedimentary succession. In this research, geological and geophysical constraints derived from seismic and borehole stratigraphy, seismic attributes, depth structural maps, isopach maps and 3D structural geological models reveal that Middle Miocene renewed subduction controls thrust wedge deformation, deep fluid overpressure and the deformational pattern of wedge-top sedimentary depositional systems. The seismic data analysis suggested that the basement pre-kinematic Himalayan turbidities depositional system (HTDs) have been tectonically incorporated into the accretionary prism by Middle Miocene renewed subduction, which gave rise to complex folding and N-dipping imbricate thrusting features. These N-dipping imbricate thrust faults initiated sediment underplating and served as major structural pathways for deep fluid overpressure migration, resulting in the formation of fluid escape pipes. The fluid escape pipes exhibit conical and bifurcating geometries with inclination angles of approximately 73°, 90°, and 100°, signifying the upward migration of deep overpressured fluids. Furthermore, the Middle Miocene to Pliocene syn-kinematic piggyback and growth depositional system (PGDs) show progressive thickening (Max ~3600m) towards onshore Makran accretionary prism. It lies unconformable above the pre-kinematic HTDs and carries valuable sedimentation records, growth stratal patterns, onlap terminations, and truncations against growing structures, revealed the timing and spatial deformation of thrust faults in 3D space. In contrast, the Pleistocene to Recent post-kinematic progradational depositional system (PDs) exhibits clinoforms marked by top-lapping, on-lapping, and down-lapping reflection, which are primarily controlled by sediment recycling dynamics and sea level change since Pleistocene. It shows progressive thickening (Max ∼1800m) towards the Makran subduction zone and lies unconformably above the syn-kinematic PGDs. Abridging the analyses, the tectonic reconstruction and deformation mechanisms model shows four phases, e.g. (1) initiation of subduction and accretionary prism formation in Eocene, (2) N-dipping imbricate thrust faults and deep fluid overpressure triggered by Middle Miocene renewed subduction, (3) development of piggyback basins and growth stratal geometries in Middle Miocene to Pliocene, (4) thrust deformation ceases and development of progradational depositional system. This research will provide a strong foundation for comprehending the convergent tectonic mechanisms that shape accretionary prism geometry, tectonically-induced fluid overpressure, and the deformational patterns of wedge-top sedimentary depositional systems in active convergent margins (e.g. Nankai Trough, Cascadia, Barbados, and Hikurangi).

How to cite: Khan, U., Khan, M., Shiguo, W., and Gao, J.: Geodynamics and Structural Evolution of Makran Accretionary Prism, Arabian-Eurasian Convergent Plate Boundary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17684, https://doi.org/10.5194/egusphere-egu24-17684, 2024.

EGU24-19457 | Posters on site | TS2.2

Basement geometry and cover-basement relationships in the central-western Jaca basin (southern Pyrenees): along-strike variations and role of structural inheritance 

Esther Izquierdo Llavall, Rosibeth Toro, Emilio Pueyo, Antonio Casas, Josep Antón Muñoz, Concepción Ayala, Félix Manuel Rubio, and The GeoEU Pyrenean Team

Pre- or syn-orogenic décollements in the external domains of fold-and-thrust belts enhance the decoupling between basement and cover folds and thrusts. In this structural setting, deciphering the degree of basement involvement and the kinematic relationship between thin- and thick-skinned structures can be challenging. This work addresses the study of basement/cover deformation in the central-western Jaca basin, in the southern Pyrenees. The Jaca basin represents the early South Pyrenean foreland basin that was latter deformed, piggy-back thrusted, and incorporated into the South Pyrenean fold-and-thrust belt. Its formation and deformation was coeval with the sedimentation of a thick syn-orogenic sequence consisting of early-middle Eocene turbidites (Hecho Group), late Eocene marls (Arguis Fm.) and late Eocene-Oligocene (Campodarbe Fm.) and Miocene continental units (Uncastillo Fm.). At surface, these syn-orogenic units are affected by a series of NE-SW and E-W-trending folds and thrusts that display frequent along-strike relays and geometrical changes. Debate exists on the geometry, timing and role of basement structures underlying these emerging thrusts and folds.

To shed some light in these discussed geometrical aspects, we carried out a combined structural and gravimetric study covering the central-western part of the Jaca basin. Four serial, seismic-based cross sections have been constructed (from East to West, the Hecho, Ansó, Roncal and Salazar cross-sections). In the cross-sections area, gravimetric data have been acquired along a homogeneous and dense grid, the spacing between gravity sites being ~ 1km.

Conversely to previous interpretations, seismic profiles depict a Paleozoic basement that is significantly faulted and involved in the deep structure of the Jaca Basin. Basement units are affected by numerous south-directed thrusts that partly result from the reactivation of inherited Permian-Triassic extensional faults. They provoke a significant basement uplift from East (Hecho cross-section) to West, with the shallowest basement being identified underneath the central part of the study area (Illón and Leyre surface thrusts). South of this basement uplift (Guarga syncline), the base of the Meso-Cenozoic sequence deepens drastically in the footwall of a main basement-involved structure that accommodates a significant shortening and connects with cover units through a long thrust flat along Middle-upper Triassic evaporites. Gravity data, although influenced by the non-coaxial crustal structure in the region, are consistent with the basement geometry deduced from seismic profiles. The Bouguer anomaly shows a prominent minimum along the Axial Zone and the eastern Jaca basin, a relative positive anomaly marking the central basement uplift (Illón-Leyre thrusts, central-western Jaca basin) and a relative minimum to the south of it, corresponding to the area where the denser basement units reach their deepest position. Both gravity and seismic data reveal a degree of cover/basement coupling which is greater than proposed in previous studies. Basement structures are not cylindrical along the study area, resulting in along-strike changes in outcropping folds and thrusts.

How to cite: Izquierdo Llavall, E., Toro, R., Pueyo, E., Casas, A., Muñoz, J. A., Ayala, C., Rubio, F. M., and Pyrenean Team, T. G.: Basement geometry and cover-basement relationships in the central-western Jaca basin (southern Pyrenees): along-strike variations and role of structural inheritance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19457, https://doi.org/10.5194/egusphere-egu24-19457, 2024.

EGU24-19944 | Posters on site | TS2.2

3D-seismic evidence for thick-skinned tectonics in a ‘classic’ thin-skinned tectonics region (external Alpine foreland, Switzerland) 

Kateřina Schöpfer, Kurt Decker, Fatemeh Nazari, and Herfried Madritsch

The northwestern Alpine foreland in Switzerland and France comprises the Late Miocene Jura Mountains, considered a type example for thin-skinned thrusting where deformation of the sedimentary cover is decoupled from the basement along a regional basal detachment. To what extent basement faults were involved during its deformation is a matter of debate. We use 3D seismic data to investigate the deformation style along the easternmost tip of the Jura range in an unprecedented detail. Here, basement-rooted normal faults were repeatedly reactivated before thrust belt formation but also contemporaneously active as reverse/transpressional faults. They either propagated up into the Mesozoic succession without interruption (“hard linkage”) or apparently controlled the localisation of Mesozoic faults via smaller-scale shear zones (“soft linkage”). Our analysis of the resulting fault geometries questions the existence of a large-scale basal detachment in this area and points out the importance of thick-skinned fault reactivation.

How to cite: Schöpfer, K., Decker, K., Nazari, F., and Madritsch, H.: 3D-seismic evidence for thick-skinned tectonics in a ‘classic’ thin-skinned tectonics region (external Alpine foreland, Switzerland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19944, https://doi.org/10.5194/egusphere-egu24-19944, 2024.

EGU24-1504 | Posters on site | TS2.6

Triassic-Jurassic ophiolites of Dinaridic Ozren and Borja-Mahnjača massifs in Bosnia and Herzegovina: Mineralogy, geochronology, and P-T estimates from subducted sole 

Marián Putiš, Ondrej Nemec, Samir Ustalić, Jiří Sláma, Dražen Balen, Elvir Babajić, Ján Soták, and Peter Ružička

The Ozren and Borja-Mahnjača ophiolite complexes in Bosnia and Herzegovina are part of the Dinaridic Triassic-Jurassic ophiolite belt (Putiš et al., 2022; Minerals). Triassic oceanic crust was dated at 242±1 Ma from a relic zircon population in a plagiogranitic layer of partially melted eclogitic sole by LA-ICP-MS U-Pb method, while the main zircon population of 176±1 Ma dates the crystallization of this layer from a metamorphic-anatectic melt. The host sole (Cpx-Grt-Rt) eclogite yielded metamorphic, most likely exhumation zircon age of 168±5 Ma, while rutile gave an age of 165±3 Ma. Jurassic lower oceanic crust was dated from an isotropic gabbro (178±1 Ma, zircon) and plagiogranite (177±1 Ma, zircon). The mantle spinel lherzolites, harzburgites, and dunites are crosscut by Cpx-Pl and Amp-Pl gabbroic, gabbro-pegmatitic, leuco-gabbroic (174±1 Ma, zircon), and doleritic (174±5 Ma, apatite) dykes, all suggesting an advanced evolutional stage and a shallower level of ophiolites due to extension and the deeper mantle melting. The upper oceanic crust pillow basalts are alternating with Bajocian to Callovian radiolarites (~171-162 Ma; Ustalić, Soták et al., 2023; Newsletter of the Slovak Geological Society). The dated N-MORB type sole eclogites-amphibolites indicate the intra-oceanic subduction of the Triassic gabbroic oceanic crust to about 55-60 km that was estimated from Perple_X modelling of 1.9-2.1 GPa and 780°C. Partial melting of subducted slab and a mantle wedge initiated the formation of Jurassic supra-subduction ophiolitic complex detected at ~178-162 Ma. Inferred slab roll-back enhanced the sole extension exhumation between ~170-160 Ma that was coeval with the formation of the upper oceanic crust basalt-radiolarite section. The mineral chemistry-based discrimination diagrams of ultramafic rocks constrain an evolutional trend from MORB to supra-subduction types of ophiolites. An increased depletion of ultramafic rocks is indicated by an increase of Cr# in spinel from ~30 to 60, exceptionally to 75, suggesting transitional abyssal to supra-subduction peridotites and dunites. Relatively thin, often hydrated (Amp-rich) gabbro-dolerite layer of this ophiolite complex may have formed in a fore-arc/back-arc slow-spreading ridge. Ophiolitic breccia, with fragments of the Jurassic oceanic crust and rare Triassic radiolarites, indicates the closure of the Jurassic Neotethys from approximately 160 Ma.

Funding from The Slovak research and development agency projects (APVV-19-0065, APVV-20-0079, APVV-22-0092), VEGA agency (1/0028/24, 2/0012/24), and the RVO67985831 program is acknowledged.

How to cite: Putiš, M., Nemec, O., Ustalić, S., Sláma, J., Balen, D., Babajić, E., Soták, J., and Ružička, P.: Triassic-Jurassic ophiolites of Dinaridic Ozren and Borja-Mahnjača massifs in Bosnia and Herzegovina: Mineralogy, geochronology, and P-T estimates from subducted sole, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1504, https://doi.org/10.5194/egusphere-egu24-1504, 2024.

EGU24-1523 | Posters on site | TS2.6

Magnetic characterization of the Ivrea-Verbano zone (NW Italy): A key to understand the magnetism and structure of the continental lower crust 

Liliana Minelli, Gaia Siravo, Fabio Speranza, Chiara Caricchi, Eugenio Fazio, Silvia Pondrelli, and Michele Zucali

The continental lower crust remains today the less known layer of the external Earth, and only relatively recently became the focus of researches addressing its structure, composition and magnetic characteristics as deduced from seismological, geophysical, geological, geochemical and petrological data. Particularly, very intense magnetic anomalies measured over cratons imply that strong magnetic source exists at lower crustal depths beneath the continents, but its nature has remained elusive so far.

One of the approaches to obtain valuable information on the continental lower crust is studying tectonically uplifted crustal cross-sections. The likely more complete continental lower crustal section exposed on Earth is the Ivrea-Verbano (IV) zone (NW Italy), considered as a petro-geophysical reference of the continental lithosphere. The IV exposes lower crust rocks of Adria (hence of African affinity) uplifted and tilted due to the Mesozoic and subsequent Alpine tectonics. Moving NW-ward along the section, originally deeper lower crust rocks are exposed, lying adjacent to the Insubric line marking the Alpine tectonic boundary. Three main lower crust types exist in the IV zone and their best exposures are along the Val d’Ossola, Val Strona and Val Sesia. Val d’Ossola and Val Strona outcrops show continental lithologies (mafic and felsic protoliths with few marbles) in both amphibolite and granulite metamorphic facies. The Val Sesia section hosts gabbros and diorites originated from a giant input of basaltic magmas underplated at crust-mantle interface in Permian times. Moving towards the Insubric line (lower part of the lower crustal section) few subordinate slices of peridotites are exposed (Megolo, Balmuccia and Finero, this latter in the northeastern most part of the IV zone). For instance, at Balmuccia (Val Sesia), a mantle slice of peridotites is tectonically embedded within the gabbros. Here seismic and gravimetric data suggest that paleo-Moho is very shallow.

We sampled the IV rocks along three sections exposed in the Val d’Ossola, Val Strona and Val Sesia at 34 paleomagnetic sites (eight oriented samples at each site) and 7 non-oriented sites (from two to eight hand-samples) for a total number of 306 samples and measured: 1) the magnetic susceptibility (k), 2) the direction and intensity of the natural remnant magnetization (NRM), 3) hysteresis loop parameters, and 4) density. These results will represent the input data for a forward magnetic model of the IV zone at a crustal scale, to be considered as an analogue for others lower continental crust settings.

These results were gathered in the frame of the Pianeta Dinamico "UNLOCK" INGV project, which aims at improving the knowledge on the structure, composition, magnetic properties and fluid content of the continental lower crust towards the mantle transition, by integrating new seismic, magnetic, mineralogical, petro-structural and geochemical data with unprecedented resolution from two worldwide known sampling localities, the Ivrea-Verbano and Serre (Calabria) lower crust sections.

How to cite: Minelli, L., Siravo, G., Speranza, F., Caricchi, C., Fazio, E., Pondrelli, S., and Zucali, M.: Magnetic characterization of the Ivrea-Verbano zone (NW Italy): A key to understand the magnetism and structure of the continental lower crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1523, https://doi.org/10.5194/egusphere-egu24-1523, 2024.

EGU24-3390 | ECS | Orals | TS2.6

Detrital rutile U-Pb geochronology as a tracer of convergence in the External Western Carpathians 

Ludwik de Doliwa Zieliński, Jakub Bazarnik, Ellen Kooijman, Karolina Kośmińska, Tomáš Potočný, Stanisław Mazur, and Jarosław Majka

The collision of Europe (Laurusia) and Alcapa (part of Adria) lead to the formation and later erosion of high-pressure rocks in the Carpathian arc. Since metamorphic rutile requires relatively high pressure to crystallize, its formation during orogeny is indicative for a subduction setting. To better understand the closure of the Alpine Tethys Ocean in the Western Carpathians, U-Pb geochronology was applied to detrital rutile from medium grained sandstones of the Magura and Silesian Nappes. Twelve samples were collected along a transect through the Magura Nappe and three samples from the Silesian Nappe were added as a reference. Approximately 200 rutile grains were separated from each sandstone and around half of them were selected for further analysis. The dated rutile shows significant differences in age, as well as in appearance (shape, inclusions, zoning etc.) suggesting derivation from various sources.

The most prominent age peaks represent the Variscan (c. 400-280 Ma) and Alpine (c. 160-90 Ma) tectonic events, which are well-represented in all but the oldest dated sample. It is noteworthy that four distinct Alpine maxima were detected in the rutile dataset. The two most prominent peaks of 137-126 Ma and 115-105 Ma are found in the majority of the samples. In two sandstone samples, deposited in the Eocene – Oligocene and the Late Cretaceous – Paleocene, the youngest peak of 94-90 Ma appears. Another peak of 193-184 Ma is also present in these two samples, as well as in another sandstone deposited between the Paleocene and Eocene. In addition, most of the dated sandstones show some Proterozoic ages (approx. 1770 Ma, 1200 Ma, 680 Ma and 600 Ma).

Tentatively, we propose that recognizable events include the Jurassic subduction of the Meliata Ocean (~180-155 Ma), and the Cretaceous thrust stacking and exhumation of the Veporic and Gemeric domains (140-90 Ma). The abundance of Alpine rutile in all but the oldest dated sandstone suggests no physical barrier for supply of detrital material derived from the southern and central Alcapa (part of Adria) to a sedimentary basin developed north of the alleged Oravic (Czorsztyn) continental sliver within the Alpine Tethys Ocean. The lack of young Alpine ages in the oldest sandstone could be a result of either a natural boundary between the basin and the orogen or a lack of rutile-bearing rocks at the surface at that time.

In a broader sense, we propose that synorogenic deposits of the Outer Western Carpathians contain detritus from the formerly subducted, exhumed and imbricated oceanic and continental crustal domains at the southern margin of the ALCAPA microcontinent.

This research is funded by the National Science Centre, Poland, project no. 2021/43/B/ST10/02312.

How to cite: de Doliwa Zieliński, L., Bazarnik, J., Kooijman, E., Kośmińska, K., Potočný, T., Mazur, S., and Majka, J.: Detrital rutile U-Pb geochronology as a tracer of convergence in the External Western Carpathians, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3390, https://doi.org/10.5194/egusphere-egu24-3390, 2024.

The change from a deep-marine, underfilled Flysch to a terrestrial and/or shallow-marine, overfilled Molasse stage of basin evolution is probably one of the major steps in the evolution of a foreland basin. Chrono-stratigraphic and sedimentologic data from the north Alpine foreland basin (NAFB), situated on the northern margin of the Alps, document that such a shift occurred at c. 30 Ma in the western (Swiss and German) part of the basin and c. 10 My later in the eastern (Austrian) segment. We relate these basin-parallel differences in the basin’s evolution to an orogen-parallel variation in subduction tectonics, that itself appears to be conditioned by the segmentation of the European plate during the Mesozoic phase of spreading preceding the build-up of the Alps (Schlunegger and Kissling, 2022). During the Mesozoic, the transition from the continental European plate to its extended margin farther South was most likely offset by a left-lateral fault in the vicinity of Munich, separating the future depositional realms of the NAFB into a western and an eastern segment. As a consequence, during the construction of the Alps from 35 Ma onward, continent-continent collision occurred earlier in the Western Alps (c. 32-30 Ma) than in the Eastern Alps (c. 20 Ma). This collision resulted in the delamination of the subducted European oceanic lithosphere from its continental counterpart beneath the Western Alps. As a consequence, the European continental plate beneath the Western Alps experienced a rebound, thereby causing the build-up of the Alpine topography and the increase in sediment supply to the foreland basin. This is recorded in the Western NAFB by a shift from Flysch- to Molasse-type of sedimentation at 30 Ma. Farther to the East, however, the subducted oceanic lithosphere slab of the European plate was still attached to the European continental plate, with the consequence that Flysch-type of sedimentation still prevailed in the Austrian part of the basin. The situation of sedimentation in an underfilled basin persisted until c. 20 Ma when the Austrian (eastern) part of the NAFB changed from a Flysch- to a Molasse-type of basin evolution. This is the main reason why we propose that continent-continent collision most likely occurred 10 My later in the Eastern Alps than in the Western Alps.

Schlunegger, F., Kissling, E. (2022). Slab load controls beneath the Alps on the source-to-sink sedimentary pathways in the Molasse Basin. Geosciences, 12, 226.

How to cite: Schlunegger, F. and Kissling, E.: Sedimentary records imply that continent-continent collision occurred later in the Eastern than in the Western Alps., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3428, https://doi.org/10.5194/egusphere-egu24-3428, 2024.

EGU24-4070 | ECS | Posters on site | TS2.6

High-resolution 3D geomodel of the central Po-Plain, Northern Italy. 

Daniel Barrera, Giovanni Toscani, Chiara Amadori, Roberto Fantoni, and Andrea Di Giulio

The Po Plain in Northern Italy constitutes an elongated alluvial valley characterized by an intricate geological evolution, extending from the late Paleozoic era to recent times. Notably densely populated, this region accommodates approximately one-third of the Italian population and hosts critical industrial facilities, coupled with a substantial history of oil and gas exploration and production. Given these factors, the creation of a high-resolution subsurface geomodel is imperative for various applications in this region.

Tectonically, the Po Plain is located in the Adria Microplate and is bounded by two opposite verging orogens sharing the same foreland: the Northern Apennines (NA) to the south, and the Southern Alps (SA) and the Western Alps to the north and the west. The SA are a south-verging fold-and-thrust belt, while the NA are a north-northeast-verging fold-and-thrust belt; both belts have their outer thrust front buried beneath the Neogene-Quaternary sediments of the Po Plain. The front of the Northern Apennines is structured into three different arcs with increasing amounts of shortening, from northwest to southeast: the Monferrato Arc, the Emilia Arc, and the Ferrara Arc. Along the Emilia Arc, the juxtaposition of the buried Southern Alps and the buried Northern Apennines is notably close, allowing for a more detailed analysis of their frontal convergence (a few kilometers). Moreover, the influence on the thrust(s) geometry from the inherited and inverted structural highs from the passive Mesozoic platform can be observed more clearly. This combination of factors, among others, makes the central area of the Po-Plain one of the most prolific for oil and gas production, hosting several productive fields.
Despite the long story of hydrocarbon exploration and production, a large-scale comprehensive 3D model using seismic lines and well information has not yet been published, apart from a couple of very good seismic sections, that have been studied and analyzed multiple times. In particular, the Plio-Pleistocene architecture of the basin has been only partially described. In this study, we have used an extensive database provided by ENI Spa to create a high-definition static model and several balanced cross-sections to understand better the distribution of the deformation along the Emilia arc and to comprehend how the complex relationship between NA, SA, and the inherited structural highs have driven the actual architecture of the central Po-Plain subsurface. This new highly detailed 3D geomodel provides the necessary base to implement renewable energy developments (geothermic) in one of the most populated areas in Italy.

How to cite: Barrera, D., Toscani, G., Amadori, C., Fantoni, R., and Di Giulio, A.: High-resolution 3D geomodel of the central Po-Plain, Northern Italy., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4070, https://doi.org/10.5194/egusphere-egu24-4070, 2024.

EGU24-4296 | Orals | TS2.6

Early Collisional Evolution of the Western Alps: how Important are Rift Inheritance and Paleogeography 

Gianreto Manatschal, Pauline Chenin, Gianluca Frasca, and Jean François Ghienne

The Western Alps, along the French-Italian border, are among the best investigated and imaged collisional belts worldwide. A major complexity of the Western Alps is their non-cylindricity and arcuate shape, as well as the occurrence of ultrahigh-pressure (UHP) metamorphic rocks. Our study shows that all these complexities are intimately linked to the interplay between the inherited rift architecture, the changing kinematics of convergence during the early stages of continental collision, and the complex 3D dynamics of the Alpine subduction system. Here we use a multi-disciplinary approach to investigate the evolution of the European/Briançonnais distal margin at the transition from subduction to early collision, which corresponds to the moment when rift inheritance and the paleogeographic configuration are the most important in controlling the orogenic structure and evolution.

In a first part, we reassess the architecture of the Western Alps based on a review of field and recent geophysical studies. This allows us to define the crustal architecture as well as the along and across strike position of the different Alpine units. The use of diagnostic petrologic, stratigraphic, and structural criteria allows us to identify the rift domains of the former European/Briançonnais margin, from which the different present-day orogenic units originated. This enables us to propose a first order, synthetic rifted margin template for the Western Alps. Of particular importance is the location of the necking zone, corresponding to the limit between the thick-crusted proximal and the thin-crusted distal margin. It also separates domains with different rheology and density/buoyancy/floatability, both of which control the subduction, exhumation and accretion behavior during subduction and early collision. We find that all units containing ultrahigh-pressure rocks derive only from the thin-crusted distal hyperextended domain.

In a second part, we revisit the paleogeography of the Alpine Tethys using a global kinematic restoration software (Gplates) and the new building block/rift domain concept that allows us to propose a tight fit restoration and evolution of the Atlantic Tethys junction during the Mesozoic.  In this restoration, the Briançonnais corresponds to a ribbon of slightly thinned continental crust that limits, along necking zones, two overstepping en-échelon rift basins, namely the Valais domain to the northwest and the Piemonte domain to the southeast. We affirm that this uneven-margin architecture can explain most of the Western Alps’ complexity. In our kinematic model, convergence between Adria and Europe was mainly accommodated by strike-slip movements until the late Eocene, which corresponds to the time of formation and exhumation of UHP metamorphic rocks. Early collision was diachronous along the margin and resulted first in the reactivation of the necking zone separating the Briançonnais and Prepiemonte domains. This fundamental structure, which we name the Prepiemonte Basal Thrust, floors the units preserving ultrahigh-pressure rocks. Once the distal margin was accreted, shortening mainly stepped inboard into the European necking domain, resulting in theformation of the Penninic Basal Thrust.

How to cite: Manatschal, G., Chenin, P., Frasca, G., and Ghienne, J. F.: Early Collisional Evolution of the Western Alps: how Important are Rift Inheritance and Paleogeography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4296, https://doi.org/10.5194/egusphere-egu24-4296, 2024.

EGU24-4686 | Posters on site | TS2.6

A new 4D model of Alpine orogenesis based on AlpArray 

Mark R. Handy and the members of the 4D-MB and AlpArray Groups

            Teleseismic Vp tomography from AlpArray suggests that the slab segment beneath the Central Alps comprises European lithosphere, is attached to its orogenic lithosphere and extends down to ~250 km depth, in parts possibly even to the Mantle Transition Zone. This marks a first phase of partial slab detachment, probably in late Paleogene time based on comparing slab length with shortening in the Central Alps and of Adria-Europe convergence since 35 Ma. In contrast, the slab segment beneath the Eastern Alps is detached between 80-150 km depth. The age of this second phase of slab detachment is bracketed at 23-19 Ma by criteria below and by comparing vertical detachment distance with global slab sink rates.

We propose a new model of Alpine mountain-building that features the northward motion of subduction singularities above delaminating and detaching Alpine slab segments, respectively in the Central and Eastern Alps, to explain E-W differences in Oligo-Miocene structure, magmatism, and foreland sedimentation. Mountain-building began at ~35 Ma with a decrease in Adria-Europe convergence to <1cm/yr collision, causing the European slab to steepen and detach beneath both the Central and Eastern Alps. Periadriatic magmatism may have initiated prior to slab detachment due to fluxing of the cold mantle wedge by fluids from devolatilizing crust along the steepened Alpine slab. Thereafter, the Central and Eastern Alps evolved separately. Northward motion of the singularity during slab delamination in the Central Alps increased both horizontal shortening and the taper angle of the orogenic wedge, with rapid exhumation and denudation in the retro-wedge. Slab steepening and delamination are inferred to have been more pronounced in the Eastern Alps, possibly due to the greater negative buoyancy of the slab in the absence of Brianconnais continental lithosphere in the eastern part of Alpine Tethys. Slab delamination in the east drove subsidence and continued marine sedimentation in the Eastern Molasse basin from 29-19 Ma, while the western part of the basin in the Central Alps filled with terrigeneous sediments. Slab detachment beneath the Eastern Alps at ~20 Ma coincided broadly with several dramatic events in the interval 23-17 Ma: (1) a switch from advance of the northern thrust front to indentation of the E. Alps by the eastern Southern Alps along the Giudicarie Fault; (2) rapid exhumation of Penninic nappes in the core of the orogen (Tauern Window) and orogen-parallel escape of orogenic crust toward the Pannonian Basin; (3) rapid filling of the Eastern Molasse basin. These events are attributed to a northward and upward shift of the singularity to within the orogenic crust during Adriatic indentation. Eastward propagation of the uplifting depocenter in the Eastern Molasse basin is interpreted to reflect orogen-parallel slab tearing beneath the Eastern Alps. This tearing ultimately accompanied Miocene rollback subduction in the Carpathians, as inferred from the migrating depocenter around the orogenic foredeep. An possible later slab detachment event (< 20 Ma) is inferred for the Eastern Alps from 3D-tectonic balancing of the Eastern and Southern Alps (McPhee et al., this session).

How to cite: Handy, M. R. and the members of the 4D-MB and AlpArray Groups: A new 4D model of Alpine orogenesis based on AlpArray, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4686, https://doi.org/10.5194/egusphere-egu24-4686, 2024.

EGU24-5390 | ECS | Posters on site | TS2.6

Pre-Alpine Metamorphism in Alpine low-grade metamorphic units in the Eastern Alps 

Kevin Karner-Ruehl, Walter Kurz, Hauzenberger Christoph A., Harald Fritz, Gallhofer Daniela, and Etienne Skrzypek

Pre-Alpine basement units, derived from the northeastern Gondwana margin, are incorporated within the Eastern Alps and were overprinted during Alpine nappe stacking. However, some of these units were only slightly affected by Alpine metamorphism and could therefore provide significant information about the pre-Alpine history of these basement units. The Kaintaleck Metamorphic Complex as part of the Eastern Greywacke Zone and the Silvretta-Seckau Nappe System experienced greenschist facies metamorphic conditions during Eo-Alpine times and are nowadays affiliated to the Upper Austroalpine Subunit.

The Kaintaleck Metamorphic Complex comprises a mafic suite of amphibolite, garnet-amphibolite, greenschist and serpentinite, and a felsic suite, mainly composed of gneiss and mica-schist, some of them garnet-bearing. Geochemical results of metabasites indicate a tholeiitic basalt source with MORB affinity. U-Pb zircon dating of a garnet-bearing amphibolite yields an Early Devonian age of 414 ± 5.6 Ma, interpreted as age of protolith formation. Chemical U-Th-Pb dating of monazites from the felsic suite revealed Late Devonian to Early Carboniferous ages of 362 ± 6 Ma, 358 ± 15 Ma, 351 ± 4 Ma and 349 ± 3 Ma, reflecting peak metamorphic conditions during Variscan orogeny. A two-stage metamorphic history of a HT/LP and a subsequent LT/HP metamorphic event, indicated by Zr-in-rutile thermometry and thermodynamic modeling, relates the Kaintaleck Metamorphic Complex to the opening and closure of the short-lived Balkan-Carpathian Ocean and implies a correlation to other ophiolitic relicts of Devonian age, exposed in the North-Gemeric Klatov and Rakovec Complexes in the Western Carpathians. The Seckau Complex, a part of the Silvretta-Seckau Nappe System is characterized by various metagranitoids, which have been extensively analyzed in recent studies. Based on these studies, the metagranitoids of the Seckau Nappe are subdivided into the Late Cambrian to Early Ordovican Hochreichart Plutonic Suite and the Late Devonian to Early Carboniferous Hintertal Plutonic Suite. The host rock for these large intrusions is the so-called Glaneck Metamorphic Suite, which is mainly composed of fine-grained paragneiss and mica-schist, some of them garnet-bearing. U-Pb zircon ages of the paragneisses indicate a detrital origin and ages of the cores cluster in the Neoarchean, Paleoproterozoic and Ediacaran, between 2.7 Ga and 559 Ma. A migmatized paragneiss yields an age of 505 Ma, which indicates, that migmatization was probably triggered by the intrusion of the Hochreichart Plutonic Suite. The timing of pre-Alpine metamorphism can therefore be constrained to have happened between 559 Ma and 505 Ma. Some samples do show a distinct two-phase garnet growth, suggesting an additional metamorphic event possibly during Variscan times. The Schladming Crystalline Complex, also part of the Silvretta-Seckau Nappe System, again comprises paragneisses, that were intruded by various metagranitoids. In contrast to the Seckau Complex, these metagranitoids do not only show Cambrian and Late Devonian to Early Carboniferous ages, but also Permian ages.

In order to complement the knowledge of the pre-Alpine metamorphic history of the Eastern Alps, new geochronological, geochemical and geothermobarometric data from various metapelitic and metabasic rocks within the Silvretta-Seckau Nappe system are being examined to reconstruct the tectonic development of these units in pre-Alpine times.

How to cite: Karner-Ruehl, K., Kurz, W., Christoph A., H., Fritz, H., Daniela, G., and Skrzypek, E.: Pre-Alpine Metamorphism in Alpine low-grade metamorphic units in the Eastern Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5390, https://doi.org/10.5194/egusphere-egu24-5390, 2024.

EGU24-5735 | ECS | Posters on site | TS2.6

Deep Structure of the Western Alps Derived from New Data — P and S wave velocity images from Finite Frequency Tomography 

Yuantong Mao, Xiaobing Xu, Xiaotian Tang, Liang Zhao, Lei Yang, Stefano Solarino, Anne Paul, Silvia Pondrelli, Coralie Aubert, Simone Salimbeni, Elena Eva, and Stephane Guillot

The Western Alps are a crucial region for studying subduction-collision processes. The deep structure beneath the orogenic belts has been a topic of ongoing debate and has undergone continuous refined investigations. In this study, we utilized the most extensive dataset available, covering the period from 2012 to 2020, with 1093 stations. This dataset comprises 659 permanent stations, 110 CIFALPS and CIFALPS-2 temporary stations, along with 324 AlpArray temporary stations.

We employed the finite-frequency method to conduct inversion of the regional deep velocity structure. Meticulous waveform analyses were performed across various frequency bands for both P and S waves (P: 0.1-0.5Hz, 0.5-2Hz; S: 0.05-0.1Hz, 0.1-0.5Hz). Additionally, for regions with insufficient ray coverage, we utilized the LSBP_Alpscrust1.0 model [Lu et al., 2020], derived from ambient noise tomography, to correct crustal velocities.

We have presented for the first time the deep velocity results of S-waves, demonstrating a good consistency with the P-wave velocity structure. Additionally, we re-selected the dataset pairs for the inversion of Vp/Vs images. Our findings provide further insight into the underground structure beneath the Western Alps, uncovering the presence of a continuous subducted slab. Furthermore, in the southern part of the Western Alps, there is a potential indication of high Vp/Vs ratios within the depth range of 100-150 km.

How to cite: Mao, Y., Xu, X., Tang, X., Zhao, L., Yang, L., Solarino, S., Paul, A., Pondrelli, S., Aubert, C., Salimbeni, S., Eva, E., and Guillot, S.: Deep Structure of the Western Alps Derived from New Data — P and S wave velocity images from Finite Frequency Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5735, https://doi.org/10.5194/egusphere-egu24-5735, 2024.

EGU24-5930 | Orals | TS2.6

Tectonic architecture of the northern Dora-Maira Massif (Western Alps, Italy): field and geochronological data 

Michel Ballèvre, Paola Manzotti, Francesco Nosenzo, Mikaela Krona, and Marc Poujol

High-pressure and ultra-high-pressure metamorphic terrains display an internal architecture consisting of a pile (or stack) of several coherent tectonic thrust sheets or units. Their identification is fundamental for understanding the scale and mechanisms active during subduction and exhumation of these crustal slices. This study investigates the geometry of the northern Dora-Maira Massif and the kinematics of the major tectonic boundaries, combining field and geochronological data. The tectonic stack of the northern Dora-Maira Massif comprises the following units. The lowermost unit (the Pinerolo Unit) is mainly characterized by Upper Carboniferous fluvio-lacustrine (meta-)sediments. The Pinerolo unit is overthrust by a pre-Carboniferous basement. The latter is subdivided in two tectonic units (the Chasteiran and Muret Units) with different Alpine metamorphism (ultra-high-pressure and high-pressure, respectively). The pre-Carboniferous basement of the Muret Unit is thicker than previously thought for two main reasons. Firstly, some paragneisses, traditionally assumed to be Carboniferous and/or Permian in age, display a dominant detrital zircon source at about 600 Ma. Secondly, three samples of the Granero Orthogneiss, previously assumed to be a Permian intrusive body, have provided zircon U-Pb ages of 447 ± 3 Ma, 456 ± 2 Ma and 440 ± 2 Ma, indicating a late Ordovician or early Silurian age for the protoliths. The uppermost unit (the Serre Unit) comprises porphyritic (meta-) volcanic and volcaniclastic rocks dated to the Permian (271 ± 2 Ma), on top of which remnants of the Mesozoic cover is preserved. Detailed mapping of an area about 140 km2 shows that (i) the ultra-high pressure Chasteiran Unit is localized at the boundary between the Pinerolo and Muret Units, (ii) the Granero Orthogneiss may be considered as the mylonitic sole of the Muret Unit, characterized by a top-to-W sense of shear, and (iii) the contact between the Muret and Serre Units displays ductile-to brittle structures (La Fracho Shear Zone), indicating a top-to-the-NW displacement of the hangingwall with respect to the footwall. A final episode of brittle faulting, cutting across the nappe stack (the Trossieri Fault), indicates an extensional stage in the core of the Alpine belt, as previously documented in more external zones. This work provides a necessary and robust basis for an accurate discussion of processes acting during continental subduction of the Dora-Maira Massif.

How to cite: Ballèvre, M., Manzotti, P., Nosenzo, F., Krona, M., and Poujol, M.: Tectonic architecture of the northern Dora-Maira Massif (Western Alps, Italy): field and geochronological data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5930, https://doi.org/10.5194/egusphere-egu24-5930, 2024.

EGU24-7625 | Posters on site | TS2.6

Deformation processes and origin of fluids during Oligocene-Miocene post-orogenic extension in Alpine Corsica 

Simone Masoch, Michele Fondriest, Nereo Preto, Francesca Prando, and Giulio Di Toro

Alpine Corsica is an accretionary wedge formed during the Alpine orogenesis and exhumed through Oligocene-Miocene lithospheric extension controlled by the eastward migration of Apenninic subduction. Here we integrate field geological surveys with microstructural and carbonate stable isotope (δ18O–δ13C) analyses of fault zone rocks to constrain the evolution of the W-dipping extensional Patrimonio Fault System (PFS). The PFS consists of multiple gouge-bearing fault core strands and splay faults in the footwall damage zone, and exhumed the Schistes Lustrés (e.g., impure quartzites, marbles, calcschists, serpentines) and slices of Hercynian granitoids in the footwall block, accommodating ~6 km of cumulative displacement.

We describe a deformation sequence during exhumation consisting of D1 mylonitic shearing, D2 seismogenic faulting and D3 shallow veining events. D1 mylonitic shearing produced a decameter mylonitic zone forming the roots of PFS, coeval with localized brittle-ductile shear zones and quartz ± chlorite vein arrays observed in the footwall metamorphic units. Ductile shearing was accommodated by low-temperature quartz and calcite crystal-plasticity, and pressure-solution mechanisms at greenschist conditions (i.e., 300-400 °C). D2 seismogenic faulting either overprinted or cut the D1 structures. Ancient seismic faulting is attested by occurrence of (i) altered pseudotachylytes and (ii) cockade-bearing fault-veins injecting into the host-rocks and mutually overprinting dolomite-rich veinlet mesh and mirror-like slip surfaces observed in the footwall splay faults. Seismic faulting is also accommodated by dolomite-quartz(-chalcedony) crack-seal veins, which have isotopic compositions similar to those of the carbonate-rich units of the Schistes Lustrés. These structural and geochemical observations indicate that ancient seismicity was cyclically modulated by overpressured fluids which isotopic composition was buffered by the host-rocks. The later D3 shallow (≤ 1 km depth) veining event consists of calcite-bearing veins and concretions filling open fractures, which have distinct isotopic compositions compared to the Schistes Lustrés units, suggesting percolation of meteoric fluids at depths. Based on these observations, we speculate that the D2 faults may represent a fossil analogue of the extensional faults active in the Apennines where seismicity is driven by CO2-rich deep-sourced fluids.

How to cite: Masoch, S., Fondriest, M., Preto, N., Prando, F., and Di Toro, G.: Deformation processes and origin of fluids during Oligocene-Miocene post-orogenic extension in Alpine Corsica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7625, https://doi.org/10.5194/egusphere-egu24-7625, 2024.

EGU24-8184 | ECS | Orals | TS2.6

Control of inherited structures on deformation and uplift in the European eastern Southern Alps: a multi-scale analogue modelling study 

Anna-Katharina Sieberer, Ernst Willingshofer, Thomas Klotz, Hugo Ortner, and Hannah Pomella

Neogene to ongoing N(W)-directed continental indentation of the Adriatic microplate into Europe controls the evolution of the European eastern Southern Alps (ESA). The Adriatic microplate, traditionally considered as a rigid indenter, demonstrates significant internal deformation, with mostly Miocene shortening being accommodated within a WSW-ENE striking, S-vergent fold-and-thrust belt. The latter overprints a compositionally heterogeneous upper crust linked to Permian intrusives and extrusives and a pre-existing platform-basin geometry related to Jurassic extension.

We present new, multi-scale physical analogue experiments, to address the effect of lateral crustal heterogeneities on strain localization and deformation geometries of the ESA, which is key for establishing causal relations between crustal and lithospheric deformation and surface uplift patterns associated with Miocene basin inversion.

Brittle crustal-scale analogue experiments with inversion of pre-scribed platform-basin geometries, indicate that variations in thickness, shape, and basement structure have impact on timing and uplift of the ESA’s upper crust. Our modelling results demonstrate that experiments with a stronger upper crustal domain (representing Permian volcanic rock on Jurassic platforms) show a smaller number of thrust sheets, being in line with thrust sheet geometries across the natural example of the ESA, and continuous uplift patterns. The latter is supported by continuous exhumation within the last 15 Ma documented by low-temperature thermochronology data between Mauls and Bassano east of the Giudicarie belt (see contribution of Klotz et al., this session). The topographic evolution of the experiments is sensitive to a variation in crustal composition; additional, e.g., basement structures (modelled using a fixed and rigid basal plate whose boundaries represent Permian faults) result in limited uplift of northern model parts, which is consistent with documented little vertical movement of the western ESA north of the Valsugana fault system between Jurassic and Neogene times.

On the scale of the lithosphere, new analogue experiments with pre-scribed platform and basin geometries in the upper crust show similar lateral variations in thrust fault orientation across transfer zones as crustal-scale experiments (Sieberer et al., 2023). Variations in lithospheric strength lead to increasing wavelengths between thrust sheets in models with stronger rheologies, pre-existing heterogeneities in the upper crust to strain localisation at boundaries of strong domains. Additionally, lateral variability of ductile lower crustal thickness predicts stronger uplift in areas of thicker lower crust. A similar relationship has been documented for the northwestern ESA, where Miocene thickening of the lower crust is expected to correlate with higher uplift in the Tauern window (Jozi Najafabadi et al., 2022).

Jozi Najafabadi, A., Haberland, C., Le Breton, E., Handy, M. R., Verwater, V. F., Heit, B., and Weber, M.: Constraints on Crustal Structure in the Vicinity of the Adriatic Indenter (European Alps) From Vp and Vp/Vs Local Earthquake Tomography, Journal of Geophysical Research: Solid Earth, 127, 10.1029/2021jb023160, 2022.

Sieberer, A.-K., Willingshofer, E., Klotz, T., Ortner, H., and Pomella, H.: Inversion of extensional basins parallel and oblique to their boundaries: inferences from analogue models and field observations from the Dolomites Indenter, European eastern Southern Alps, Solid Earth, 14, 647-681, 10.5194/se-14-647-2023, 2023.

How to cite: Sieberer, A.-K., Willingshofer, E., Klotz, T., Ortner, H., and Pomella, H.: Control of inherited structures on deformation and uplift in the European eastern Southern Alps: a multi-scale analogue modelling study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8184, https://doi.org/10.5194/egusphere-egu24-8184, 2024.

EGU24-8582 | ECS | Posters on site | TS2.6

Unraveling the collisional history of the Western Carpathians through deep geophysical sounding 

Tanishka Soni, Christian Schiffer, and Stanisław Mazur

The Pieniny Klippen Belt (PKB) in the Western Carpathian branch of the Alpine-Carpathian-Dinaridic orogenic system is considered to be the surficial representation of the Alpine-Tethys suture. It is a few kilometres wide and about 600 km long unit between the Outer Western Carpathians and Central Western Carpathians and does not show typical characteristics of a suture (Plašienka et al., 1997; Schmid et al., 2008). In fact, the structural relationship between the PKB and surrounding units is ambiguous. The PKB is a sub-vertical unit with mainly shallow marine limestone and flysch deposits in a conspicuous “block-in-matrix” structure (Plašienka et al., 1997). This structure has been explained mainly by two theories: sedimentary structures formed by gravity sliding; and post-sedimentation tectonic shearing due to strike-slip movement affecting the heterolithic composition of the unit (Plašienka et al., 2012; Golonka et al., 2015). The presence of “exotic” sediments in the PKB and the southernmost units of the OWC along with their shallow marine deposition environment led to the theory proposing the presence of a continental sliver called the Czorsztyn Ridge in the Alpine Tethys, dividing it into two oceanic/marine basins: the Magura Ocean to the north and the Vahic Ocean to the south (Plašienka, 2018).

A passive seismic experiment was designed and installed to provide insight into the deep lithospheric structure across the PKB, testing the presence of a tectonic suture along with relaminated remnants of the Czorsztyn Ridge, and potential remnants of subducted or underthrusted lithosphere. Eighteen broadband stations have been deployed in a ~N-S transect under the umbrella of the AdriaArray initiative, cutting across the PKB and the Neotethian Meliata suture to the south. The data obtained during up to three years will complement 10 other permanent and temporary broadband stations, forming an approximate 250 km long profile and will be primarily used to perform receiver function analysis and to build structural and velocity models of the lithosphere (i.e., Schiffer, 2014; Schiffer et al., 2023) beneath the Western Carpathians.

Gravity and magnetic data will be used to construct a 3-D model of the subsurface complementing the seismic experiment. Preliminary assessment of the data has shown that the PKB is represented by an anomaly reaching at least until the 15 kms depth and, therefore, is a deep-seated feature. It leads to a tentative conclusion that the PKB’s “block-in-matrix” structure is rather of tectonic origin. The qualitative analysis of potential field data reveals the presence of three major elements in the deep basement of the northern Carpathians corresponding to the ALCAPA, European Platform, and a previously undefined wedge-shaped block under the Eastern Carpathians. The PKB follows the boundary between the ALCAPA and the remaining two domains.

How to cite: Soni, T., Schiffer, C., and Mazur, S.: Unraveling the collisional history of the Western Carpathians through deep geophysical sounding, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8582, https://doi.org/10.5194/egusphere-egu24-8582, 2024.

EGU24-8854 | ECS | Orals | TS2.6

Mesozoic tectonic inheritance of the European crystalline basement (SE France) revealed by thermochronology 

Louise Boschetti, Frederic Mouthereau, Stephane Schwartz, Yann Rolland, Matthias Bernet, and Melanie Balvay

The Alpine orogenic belt in SE France is the result of the collision between the European, Adriatic and Iberian plates. The accreted Variscan continental crust, which now forms the external crystalline massifs (ECMs), recorded a complex Mesozoic thermal and tectonic evolution, that is not fully understood. In the Maures-Tanneron massif (MTM), the basement has undergone periods of subsidence and uplift, the latter indicated by stratigraphic gaps from the Albian and Upper Turonian to the Maastrichian. In the Ecrins-Pelvoux massif (EPM), differential subsidence is documented during Lower Jurassic by lateral variation from marine to continental environment, but most of the Cretaceous and Paleogene periods correspond to a stratigraphic hiatus that ends with the deposition of upper Eocene sediments. The link between these stratigraphic gaps and inheritance associated with the rifting, opening of the Alpine Tethys, and early convergence between Europe, Iberia and Adria is still not resolved. The goal of this study is to elucidate the thermal evolution of the European basement in SE France (EPM and MTM) during the Mesozoic using apatite and zircon fission track low-temperature thermochronology (AFT and ZFT). ZFT data from the southern EPM indicates a complex thermal history with central ages ranging from 158 to 45 Ma, thus revealing significant Jurassic to Eocene resetting and cooling. These ages are interpreted as resulting from several tectonic stages related to (1) Jurassic rifting (2) Mesozoic shortening and erosion and/or (3) incomplete Alpine reset during the main phase of underthrusting below the Penninic Frontal Thrust during the Oligocene. In contrast, the MTM shows several thermal events, comprising a major cooling stage at ca. 200 Ma coincident with the CAMP event preserved in the northern part of the massif. A final cooling event between 30 and 25 Ma, that is mostly represented to the South of the massif, is related to the opening of the Ligurian sea. Intermediate AFT ages between these two events are also identified, likely reflecting cooling events during the Mesozoic that can be resolved using thermal modelling. Finally, the long-term thermal evolution reported from SE France ECMs allows refining the geodynamics of this region from Pangea fragmentation to the onset of Alpine orogeny.

How to cite: Boschetti, L., Mouthereau, F., Schwartz, S., Rolland, Y., Bernet, M., and Balvay, M.: Mesozoic tectonic inheritance of the European crystalline basement (SE France) revealed by thermochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8854, https://doi.org/10.5194/egusphere-egu24-8854, 2024.

EGU24-9322 | Posters on site | TS2.6

3D thermo-mechanical modelling of oblique continental collision: relative role of slab tearing in along-strike topography evolution 

Giridas Maiti, Alexander Koptev, Paul Baville, Taras Gerya, Silvia Crosetto, and Nevena Andrić-Tomašević

It is assumed that slab tearing (or the lateral propagation of slab break-offs) in collisional belts controls the progressive along-strike uplift of mountains and the development of adjacent basins. However, differential continental collision due to obliquity or other irregularities of the original passive margin can introduce additional complications and influence the progressive topographic growth. Here, we use a 3D thermo-mechanical numerical modelling approach to distinguish the topographic response to slab break-off propagation from the surface uplift caused by along-strike differential collision. To this end, we examine the effects of several key factors, including (1) the obliquity of the passive margin, (2) the age of the oceanic slab, (3) the rate of convergence between colliding plates, and (4) the presence of a microcontinental block between passive and active margins. In all experiments, slab break-off initiates earlier than continental collision due to the transition from oceanic to continental subduction beneath the fore- and back-arc domain formed during the previous retreat of the subduction zone. The topographic uplift associated with slab tearing is more pronounced and spreads laterally much faster than in the subsequent collision phase. The parametric analysis shows that the lateral migration of the continental collision is controlled by the convergence rate, while the horizontal velocity of slab tearing depends mainly on the obliquity angle and slab age. The presence of additional structural complexity - a microcontinental block that has detached from the passive margin - leads to a transition from horizontal to vertical slab tearing and to more intense syn-collisional mountain growth.

How to cite: Maiti, G., Koptev, A., Baville, P., Gerya, T., Crosetto, S., and Andrić-Tomašević, N.: 3D thermo-mechanical modelling of oblique continental collision: relative role of slab tearing in along-strike topography evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9322, https://doi.org/10.5194/egusphere-egu24-9322, 2024.

EGU24-9371 | Posters on site | TS2.6

Kinematic restoration of the western Tauern Window 

Julia Rudmann, David Colin Tanner, Michael Stipp, Hannah Pomella, and Christian Brandes

The Tauern Window (TW) in the European Alps is one of the largest tectonic windows in the world. Its formation started in the Cretaceous with subduction of the Penninic realm beneath the northern margin of Adria leading to the collision between Europe (Subpenninic) and the Adria margin (Austroalpine). The resulting Penninic and Subpenninic nappe stack was exhumed by ca. 20 km by the approach of the Dolomites Indenter (Eastern Southern Alps) in the Miocene. This last deformation stage resulted in synkinematic N-S shortening of the western TW (ca. 70 km), W-E extension and lateral extrusion towards the east. However, how the Subpenninic core (Venediger Duplex; VD) and the Penninic and Austroalpine nappes (PN and AN, respectively) in the hanging-wall were tectonically stacked, upright folded and emplaced is poorly understood. This study investigates the deformation accommodated by each major tectonic basement unit of the western TW, and contributes to a better understanding of orogenic processes in general.

We kinematically restore the cross-section of [1] along the Brenner Base Tunnel (W of the TRANSALP seismic profile) using the software MOVEtm (Petroleum Experts), focusing firstly on the VD. We choose area balancing as minimum criteria, because we do not know how much material was transported out of the plane of cross-section by extension and lateral extrusion. We integrate zircon fission-track data (ZFT) as a temporal constraint and test different geothermal gradients. Petrological data are used to define the maximum depth the VD reached at the time of indentation and as marker for the transition from brittle to viscous conditions of the felsic rocks of the VD (lowest temperature for folding). Finally, we reconstruct the hanging-wall nappes above the restored VD, thereby precisely constraining the position of the AN at that time. The surface samples taken from the AN must have reached thermal conditions between the annealing zones of apatite fission-tracks and ZFT (115°C and 180°C, respectively) as only the former system was reset in the Miocene.

We first displace the entire VD down along the Sub-Tauern Ramp below the 300°C isotherm (brittle to viscous transition of felsic rocks). For this, the geothermal gradient of 50°C/km fits well to the petrological data. ZFT ages reveal upright folding of the VD terminated at ca. 17 +/- 2 Ma. Subsequent unfolding of the gneiss cores, while conserving surface area, reveals the model to be extended ca. 70 km to the south (i.e. thus equaling indenter shortening), which means that no material left the plane of cross-section by W-E extension or lateral extrusion. However, the situation for the hanging-wall nappes is different: The total thickness of the northern limbs of the AN and the PN together is twice as much after restoration compared to today. We postulate that the extension on the Brenner Normal Fault mainly caused this tectonic thinning, which is approximately 10 km.   

References

[1] Reiter, F., Freudenthaler, C., Hausmann, H., Ortner, H., Lenhardt, W., & Brandner, R. (2018). Tectonics, 37(12), 4625-4654.

How to cite: Rudmann, J., Tanner, D. C., Stipp, M., Pomella, H., and Brandes, C.: Kinematic restoration of the western Tauern Window, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9371, https://doi.org/10.5194/egusphere-egu24-9371, 2024.

EGU24-9709 | ECS | Orals | TS2.6

Dinarides slab gap - fact or fiction 

Lucija Golub, Stéphane Rondenay, and Josip Stipčević

Ever since the first regional teleseismic tomography images of the central Mediterranean region, one aspect that has stood out in nearly every model is the missing deep slab under the north and central Dinarides. In contrast, concurrent investigations of crustal formation have pointed to a deep crustal root under the whole of the Dinarides, supporting the hypothesis of a laterally continuous slab. In the last decade, several attempts have been made to untangle this conundrum but without much success. Nevertheless, these efforts have yielded some notable new findings, such as possible lithospheric delamination under the central Dinarides. This study aims to utilize all the available seismological results in combination with several new analyses to shed light on the upper mantle structure beneath the central Dinarides. We conducted the SKS shear-wave splitting analysis using 21 stations from the Croatian national seismic network and 7 stations from the AlpArray network. We considered events that occurred between 2010 and 2022 with magnitudes greater than MW = 6.0 and epicentral distances ranging between 85° and 120°. In parallel, a teleseismic Generalized Radon Transform (GRT) migration was conducted along a set of 2D profiles to provide structural insights into the subduction zone within the study area. Data from the Croatian national seismic network, the CRONOS temporary network, and the AdriaArray Temporary Network were used for the migration. For this approach, we considered events that occurred after January 2020 within the epicentral distance range of 30° - 100° and magnitudes greater than MW = 5.5. In addition to these two new analyses, we used other seismological results from previous investigations (including S-receiver functions and ambient noise tomography) to fill in the gaps in our investigation of the lithospheric structure under central Dinarides. Preliminary results exhibit distinctive patterns: the orientation of SKS fast axes, indicative of mantle flow, in the north and central External Dinarides aligns perpendicular to the mountain chain’s strike. However, this orientation abruptly transitions to a NW-SE direction further from the coast and continues in the northern part of Croatia. Results from converted/scattered-waves and ambient noise, for their part, point to a thickened crust under the central and southern External Dinarides, with a high-velocity anomaly reaching at least 100 km depth but a relatively thin lithosphere. Taken together these results suggest that the slab blocks the mantle flow up to depths of 100 – 150 km.

How to cite: Golub, L., Rondenay, S., and Stipčević, J.: Dinarides slab gap - fact or fiction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9709, https://doi.org/10.5194/egusphere-egu24-9709, 2024.

EGU24-9804 | ECS | Orals | TS2.6

AI based 3D P- & S-wave velocity model for the Alpine mountain chain from Local Earthquake Tomography 

Benedikt Braszus, Andreas Rietbrock, Christian Haberland, and Trond Ryberg

We present a new 3D P & S-wave model based on Local Earthquake Tomography (LET) of the European Alpine mountain chain using data from a total of more than 1100 broadband stations of the AlpArray Seismic Network and additional permanent and temporary stations. We use "SeisBench - A toolbox for machine learning in seismology" to assess the performance of the most commonly used AI pickers and find PhaseNet to be the most suitable. Our final data set comprises 2374 events of Ml >= 1.5 yielding 89,000 Pg-, 64,000 Pn-, 41,000 Sg- & 23,000 Sn-phases. Initially, we include observations from <130km epicentral distance to simultaneously relocate the quakes and invert for upper crustal velocity structure using the SIMUL2017 inversion algorithm. Subsequently, we add the remaining travel times to invert for velocities in the entire crust and upper mantle while fixing the hypocentres from the initial inversion run. 
First order features of our final vp model such as sediment basins and the Alpine orogenic root are in good agreement with previous tomographies and Moho studies of the area. In the Western Alps the well studied Ivrea Geophysical Body (IGB) is imaged as a high velocity anomaly where mantle velocities are present at depths of 15-20km. West of the IGB we find lower crustal velocities reaching depths of ~50km. Both observations are coinciding with the previously imaged Moho jump between deep European and shallow Adriatic Moho.
Similarly, we image the orogenic root in the Northern Apennines as an area of low vp with increased vp/vs-ratio. Beneath the Eastern Po plain we find mantle velocities at shallower depths than published Moho values would suggest. 

How to cite: Braszus, B., Rietbrock, A., Haberland, C., and Ryberg, T.: AI based 3D P- & S-wave velocity model for the Alpine mountain chain from Local Earthquake Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9804, https://doi.org/10.5194/egusphere-egu24-9804, 2024.

EGU24-10513 | Orals | TS2.6

Where data-based structure meets process simulation - how heterogeneities relate to lithosphere deformation in the Alps 

Leni Scheck-Wenderoth, Ajay Kumar, Mauro Cacace, Judith Bott, Hajo Götze, and Boris Kaus

To address the question of how the present-day architecture of the lithosphere and the heterogenous density configuration of the uppermost mantle influence deformation in the Alpine orogenic system we use data-derived 3D configurations as input to dynamic simulations. This includes on the one hand the consideration of a detailed crustal model of the Alpine region and its forelands that resolves first-order contrasts in the thermophysical properties of the crust consistent with available geoscientific observables (active and passive seismic, gravity, geological, geothermal). In addition, we tested an ensemble of configurations of upper mantle thermophysical properties derived from published seismic tomography models. Using a Gibbs-free energy minimization algorithm (https://zenodo.org/records/6538257) we convert the results of regional shear-wave seismic tomography models to temperature models and define the base of the lithosphere and the geometry of slabs in the asthenosphere with a threshold temperature of 1300°C. As a first step we model topography and deformation velocities as resulting from buoyancy-forces driven by a quasi-instantaneous flow resulting from the first-order rheological structure of the lithosphere-asthenosphere system using the open source geodynamic code LaMEM (https://github.com/UniMainzGeo/LaMEM). The simulation results indicate that a slab detached beneath the Alps, but attached beneath the Northern Apennines captures first-order patterns in topography, vertical surface velocities, and mantle flow. The presence of an attached slab beneath the northern Apennines also explains the observed sub-crustal seismicity in contrast to the seismicity in the Alps restricted to the upper-crustal domain.

How to cite: Scheck-Wenderoth, L., Kumar, A., Cacace, M., Bott, J., Götze, H., and Kaus, B.: Where data-based structure meets process simulation - how heterogeneities relate to lithosphere deformation in the Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10513, https://doi.org/10.5194/egusphere-egu24-10513, 2024.

EGU24-10762 | ECS | Orals | TS2.6

Submarine canyons cutting through the Annot Sandstones, a key-element of the evolution of the Alpine Foreland Basin during the Rupelian 

Louison Mercier, Sébastien Migeon, Jean-Loup Rubino, Jenny Trevisan, Speranta-Maria Popescu, Mihaela Carmen Melinte Dobrinescu, Miroslav Bubík, Yamirka Rojas-Agramonte, Anna Hagen, and Romain Bousquet

Submarine canyons are commonly controlled by tectonic structures and, therefore, are key elements of the evolution of convergent margins such as the Southern French Alpine Foreland Basin. Here we use the outcrops of Grès d’Annot and Schistes à Blocs formations of the Sanguinière-Restefond and Trois Eveches sub-basins, to study the morphology of ancient canyons respectively in relation to extensive and compressive tectonics. The Grès d’Annot Upper Erosion Surface (GAUES) and faults have been mapped in the field and using airborne and drone pictures. Moreover, the deposition age of the Schistes à Blocs Formation has been constrained by the analysis of calcareous nannofossils and benthic foraminifera coming from 9 samples. We also compared ages of detrital zircons by U-Pb thermochronology from 4 samples. One of them was sampled within Annot Sandstones while the other come from the turbidites of the Schistes à Blocs Formation that seals the GAUES.

The Colombart Structure in the Sanguinière-Restefond area is composed of two normal faults with a N80°E orientation and a southern vergence, bordering a northward dipping rollover anticline. The Colombart Structure axially controls the 700 m deep La Bonette Canyon cutting through the underlying Annot Sandstones. The submarine canyon is made of a succession of sharp erosive features, such as erosive walls, ramps and terraces. The cross-section profile of the canyon exhibits a tectonic control at several scales: it is asymmetric as well as the thalweg is. Faults also commonly control smaller scale morphologies, but also the capture of tributaries at right angles with the canyon axis, which testifies for a rectangular drainage pattern. The preliminary study of the GAUES in the Trois Eveches Sub-basin also exhibits a strong relationship between tectonics and submarine erosion. The last shows a 300 m-high scarp frontally eroding a NW-SE oriented thrust which affects the underlying sandstones. Moreover, biostratigraphic dating of the Schistes à Blocs Formation indicates NP22-lower NP23 biozones, i.e. the Early Rupelian. Detrital zircons analysis by U-Pb method show that Annot Sandstones and Schistes à Blocs Formation have the same signal. Finally, within both sub-basins, the thin bedded turbidites of the Schistes à Blocs Formation exhibit paleocurrent directions which are almost opposed to those measured within the Annot Sandstones. Paleocurrents within the Trois Eveches Sub-basin also locally change depending on which thrusts is located below the Schistes à Blocs Formation.

Consequently, the GAUES mainly results from retrogressive erosion affecting partially lithified turbidites following two main triggering factors which are: i) the foreland deformation with a deformation direction that potentially locally changes, and ii) the 3rd order eustatic fall linked to the Oi1a δ18O event. The creation of submarine canyons affecting previously deposited turbidite lobes testifies of a strong paleogeographical modification of the foreland before the Autapie nappe emplacement. This change is also evidenced by the paleocurrent reorganization after the submarine erosion. Nevertheless, the complete understanding of the whole Early Rupelian source-to-sink system would need to enlarge the study of the Schistes à Blocs Formation to the whole foreland, including the use of other methods.

How to cite: Mercier, L., Migeon, S., Rubino, J.-L., Trevisan, J., Popescu, S.-M., Melinte Dobrinescu, M. C., Bubík, M., Rojas-Agramonte, Y., Hagen, A., and Bousquet, R.: Submarine canyons cutting through the Annot Sandstones, a key-element of the evolution of the Alpine Foreland Basin during the Rupelian, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10762, https://doi.org/10.5194/egusphere-egu24-10762, 2024.

EGU24-10978 | ECS | Orals | TS2.6

Coesite in Alpine meta-ophiolites: hidden but widespread, and tectonically relevant  

Stefano Ghignone, Federica Boero, Marco Bruno, Mattia Gilio, Emanuele Scaramuzzo, and Alessia Borghini

The occurrence of coesite, a Ultrahigh Pressure (UHP) index mineral,  in tectono-metamorphic belts is of paramount importance to pinpoint the depths attained during subduction. Such minerals are generally found as inclusions within garnets and are often the sole remnants of an UHP mineralogy in largely re-equilibrated rocks. UHP tectonometamorphic units in subducted oceanic lithosphere are of particular interest because they are natural laboratories to study element-exchange and fluid rock interactions occurring in a subducting slab at depths > 80 km. In this context, the meta-ophiolites of the Western Alps are a perfect case study, as they offer a continuous outcrop along the entire belt. Here, we focus on the UHP meta-ophiolites of the Internal Piedmont Zone (IPZ) in the Western Alps, where coesite inclusions in garnet have recently been found (Ghignone et al., 2023 and Boero, 2023). These localities lay on the same structural position of the Lago di Cignana Unit, wherein coesite was discovered in the early 90’s (Reinecke, 1991). In addition, these three UHP localities share similar metamorphic peak conditions and their PT estimates lie on the same metamorphic gradient (roughly 6°C/Km).

A targeted sampling campaign along the entire Western Alpine meta-ophiolitic belt allowed to better understand the distribution of coesite-bearing rocks. Metasediments (Grt-quartzite, Grt-Cld micaschist, Grt-calcschist) are the best lithotypes that preserved coesite, but also some meta-mafic lithotypes (eclogite, Grt-metabasite) contain it. Usually, garnets within metasediments are strongly zoned, whereas in meta-mafic lithotypes they have a more constant composition. Coesite was identified via µ-Raman spectroscopy, showing the typical vibrational modes of the phase (521, 427, 271 and 180 cm-1), slightly shifted due to elastic residual strain. Coesite occur as pristine tiny crystals (<40 µm) entirely trapped in garnet, both isolated and clustered. Their shape varies from well-faceted to strongly anhedral with morphological evidence of resorption (i.e., lobed morphologies with rounded shapes and/or embayment). Bigger inclusions of quartz (>40 µm) present the typical features of re-equilibration after coesite (i.e., radial cracks, polycrystalline aggregates). 

Among the different UHP localities, the presence of coesite is limited to a specific garnet shell (e.g., core, mantle), identifying a specific moment of garnet growth in UHP metamorphic conditions. The other shells, contrarily, preserve inclusions of quartz. These differences allowed to reconstruct the prograde or retrograde evolution through a detailed inclusion study of their preserved elastic properties (i.e., elastic geobarometry).

Our results highlight that the entire IPZ eclogite-facies meta-ophiolites underwent UHP metamorphism in the coesite stability field. This suggests that a large volume of oceanic lithosphere was subducted at ca. 100 km depth and then returned to the surface. This is an important constrain to create  reliable tectonic models of  subduction and exhumation of the oceanic lithosphere in collisional subduction/accretionary systems.

 

Boero, F., 2023. Master Thesis, University of Turin. 115 pp.

Ghignone, S., Scaramuzzo, E., Bruno, M., Livio, F., 2023. Am Mineral, 108(7), 1368-1375.

Reinecke, T., 1991. Eur J Mineral, 3, 7-17.

How to cite: Ghignone, S., Boero, F., Bruno, M., Gilio, M., Scaramuzzo, E., and Borghini, A.: Coesite in Alpine meta-ophiolites: hidden but widespread, and tectonically relevant , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10978, https://doi.org/10.5194/egusphere-egu24-10978, 2024.

EGU24-11066 | Posters on site | TS2.6

New insights into seismic structures around the Tauern Window and the Periadriatic Fault System from reprocessing of TRANSALP seismic reflection data 

Klaus Bauer, Benjamin Schwarz, Rahmantara Trichandi, Britta Wawerzinek, Peter McPhee, and Mark R. Handy

The TRANSALP project carried out around the Millenium provided unique geophysical sections across the orogenic structure in the Eastern Alps. Active and passive seismic experiments were conducted along a 300 km long profile between Munich and Venice. From North to South, the transect covered parts of the eastern Molasse Basin, the Northern Calcareous Alps and European Alpine crust, the Peninnic units of the Tauern Window, the Periadriatic Fault System (PFS), the Dolomite Mountains and Adriatic crustal indenter, and the foreland basin of the Venetian-Friulian plain. The comprehensive data sets were used to derive seismic velocity models, structural images from processing of seismic reflection data and Receiver Function analysis, azimuthal anisotopy from shear wave splitting, and to provide constraints for density modelling with gravity data.

More recently, new geophysical, mostly seismological experiments were conducted in the Central and Eastern Alps within the framework of the priority programme "Mountain Building Processes in Four Dimensions" (4D-MB) as part of the AlpArray mission. The general scope of this programme is to image the structure of the Alps from their surface down to lithospheric depth. A multi- and interdisciplinary approach is used to improve understanding of linked processes between surface and mantle beneath mountain belts, where integration of geophysical and geological observations with modeling enable to look backward and forward in time during these processes.

In the Eastern Alps, the pre-existing geophysical transects along TRANSALP (around 12°E) and EASI (around 13.3°E) are often used as reference sections to compare and discuss new 3D and 4D models along these 2D high resolution profiles. However, there is still controversy on the interpretation of these previous cross-sections. Of particular interest are crustal structures which can be used to test the hypothesized change of subduction polarity from S-directed subduction along TRANSALP towards N-directed subduction along the EASI profile, more eastward. Hence, in our sub-project we reprocess the pre-existing seismic reflection data along TRANSALP with promising, more recently developed methods that were not applied to this data set so far. The first approach is based on the extraction and usage of diffractions for the seismic imaging of the subsurface. Controlled numerical simulations explain the workflow and demonstrate the performance of the method. Application to the northernmost part of the TRANSALP seismic line reveals a number of sub-vertical structures which match with the location of known faults and fracture systems both in the Molasse and the Northern Calcareous Alps. The second approach is based on coherency analysis of pre-stack data. For the subsequent depth migration we test a wide range of existing velocity models, both from previous work and new results from the 4D-MB project. Most prominent sub-vertical structures are imaged in the central part of the Tauern Window and around the PFS. Ongoing tests with different velocity models are used to derive robust images of these key structures in the central part of the TRANSALP profile. The results are reconciled with surface geology and other geophysical studies, and will ultimately provide additional constraints for 3D and 4D geological modeling.

How to cite: Bauer, K., Schwarz, B., Trichandi, R., Wawerzinek, B., McPhee, P., and Handy, M. R.: New insights into seismic structures around the Tauern Window and the Periadriatic Fault System from reprocessing of TRANSALP seismic reflection data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11066, https://doi.org/10.5194/egusphere-egu24-11066, 2024.

EGU24-12811 | Posters on site | TS2.6

SECOS24: New insights into seismicity, deformation and crustal stresses in the Central Alps Region from a baseline seismotectonic earthquake catalog 

Tobias Diehl, Julia Heilig, Carlo Cauzzi, Nicolas Deichmann, John Clinton, Sandro Truttmann, Marco Herwegh, and Stefan Wiemer

The base data for any seismotectonic study consist of accurate and precise hypocenter information, consistent magnitude estimates, and focal mechanisms derived either from the analysis of first-motion (FM) polarities or moment-tensor (MT) inversions. In this study, we present a new baseline seismotectonic earthquake catalog of Switzerland and surrounding regions (SECOS24), which covers the Central Alps (CA) region between 45.4°N/5.6°E and 48.4°N/11.1°E. The SECOS24 catalog includes instrumental seismicity routinely detected and located by the Swiss Seismological Service (SED) between 1975 and 2024 (about 49 years). For the digital era of the SED bulletin (phase picks and seismograms available in digital form) starting in 1984, hypocenters were consistently relocated in absolute terms using a recent Pg and Sg 3-D velocity model. Starting from these improved hypocenters, double-difference relative relocations were performed at different scales (single clusters as well as at regional scales), combining differential times from manual picks and waveform cross correlations. Based on available solutions and resulting location quality, a preferred solution was selected for each hypocenter of the SECOS24 catalog, in order to provide the maximum possible hypocenter accuracy and precision for each event. The SECOS24 catalog contains about 36,000 earthquakes with magnitudes ranging between ML -0.7 to 5.3. In addition to ML, the catalog reports complementary magnitudes for a subset of events. For 71 events, an MW magnitude was derived from a revised MT inversion for events starting in 1999. For events since 2009, a spectral MW was calculated if possible. This magnitude compilation allows for the assessment and improvement of existing ML-MW scaling relations. Finally, we linked each hypocenter with the revised MT catalog as well as solutions of an augmented FM catalog, which contains 492 high-quality, manually reviewed mechanisms based on P-wave first-motion polarities.

The SECOS24 catalog is used for down-stream seismotectonic analysis of the CA region. In this presentation, we show updated maps of seismicity and moment release in the CA and their foreland. In addition, we provide updated maps of deformation regimes and stress orientations derived from the analysis and inversion of the FM data. Besides previously known features, the SECOS24 catalog reveals several new features in the CA and their foreland like newly imaged seismogenic fault zones, lateral changes in the deformation regime along the Alpine Front of the CA, and ongoing shortening at shallow crustal levels in the Jura fold-and-thrust belt. In addition, the updated stress inversion provides more stable results and, in several places, higher spatial resolution in comparison to previous studies. The SECOS24 catalog therefore contributes to an improved understanding of present-day tectonic processes in the CA region and is crucial input for next-generation seismic hazard models of the region.

How to cite: Diehl, T., Heilig, J., Cauzzi, C., Deichmann, N., Clinton, J., Truttmann, S., Herwegh, M., and Wiemer, S.: SECOS24: New insights into seismicity, deformation and crustal stresses in the Central Alps Region from a baseline seismotectonic earthquake catalog, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12811, https://doi.org/10.5194/egusphere-egu24-12811, 2024.

Mt. Moslavačka Gora (MG) is a small crystalline exposure in the western segment of the Sava suture zone (SSZ) that divides the Europe-derived Tisia and Dacia from the Adria-derived units. The MG differs from other crystalline exposures of the SSZ by the presence of Cretaceous LP/HT metamorphic rocks and Alpine S-type granitic pluton. Our study of geochemical variability, source characteristics and geodynamic setting is based on geochemical dataset for the two predominant Late Cretaceous granite types sampled throughout the northern and central part of the pluton: two-mica granites (TMG; Bt>>Ms) that comprise the main plutonic body and subordinate muscovite (± tourmaline) granites i.e. leucogranites s.s. (LG) that crosscut the pluton. Most of the samples are highly peraluminos granites (ASI 1.1-1.6) with high SiO2 content (70-77 wt %). They correspond to magnesian to ferroan alkali-calcic and calc-alkalic granites. Major element characteristics show decreasing TiO2 (0.42-0.03 wt %), MgO (1.09-0.04 wt %), FeOtot (2.47-0.38 wt %), Al2O3 (15.34-13.18 wt %) and CaO (1.45-0.19 wt %) with increasing SiO2, with lowest abundances in the LG type. The Zr, Th and La quantities decrease from TMG toward the LG samples, consistent with petrological observations and fractionation of accessory phases (zircon, monazite and apatite). REE patterns point to vapour-absent partial melting of metasedimentary source, presence of residual feldspar during partial melting and retention of monazite within residual biotite in the source, more pronounced in the case of LG. Our data suggests that LG samples are generated as minimum melts by reactions involving predominantly breakdown of muscovite. TMG samples show geochemical variability indicative of involvement of biotite in melting reactions. Rb, Ba and Sr content are consistent with the observed mineralogy and further corroborate low melt fraction vapour-absent or vapour-deficient melting conditions. Multiple diagrams (e.g. Al2O3/TiO2 vs. CaO/Na2O, A-B discrimination diagram) point to Pl-enriched source and higher melting temperatures for the TMG source whilst LG source corresponds to Pl-poor/clay-rich source and lower melting temperatures which is in good agreement with Zr saturation temperatures for both types (c. 730 °C for TMG and c. 650 °C for LG, respectively). Based on geochemical, mineralogical and field characteristics of Bt-dominated (TMG) and Ms (±Tur)-dominated (LG) granites, partial melting of different portions of crustal source composed of felsic igneous rock or immature metasediments under similar melting conditions seems like a plausible genetic model. Studied samples categorize predominantly as collision-related peraluminous granites. Previous research tentatively ascribed the origin of MG granitoids to partial melting induced by (localized) mafic magma underplating in a subduction/collisional setting of the SSZ. However, the presence of regionally metamorphosed metasedimentary rocks of amphibolite to granulite facies in the parts of the pluton supports the idea that localized strain heating has also contributed to the Late Cretaceous crustal melting and granite magmatism in the studied area or even had a dominant role. This is further corroborated by our geochemical data that point to derivation of TMG and LG from metasedimentary source similar to the exposed metamorphic rocks.

How to cite: Petrinec, Z., Mureta, L., and Balen, D.: Late Cretaceous peraluminous collisional granites from the Sava Suture Zone (Moslavačka Gora, Croatia): geochemical variability, source characteristics and geotectonic interpretation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15277, https://doi.org/10.5194/egusphere-egu24-15277, 2024.

EGU24-15665 | ECS | Orals | TS2.6

The 2021 and 2023 Vienna Basin seismic sequences: Insights from earthquake relocation and moment tensor inversion 

María del Puy Papí Isaba, Elisa Buforn, Maurizio Mattesini, Gesa Petersen, Simone Cesca, Helmut Hausmann, and Wolfgang Lenhardt

Three peculiar seismic sequences occurred between March and May 2021 near Breitenau and Gloggnitz, about 50 km from Vienna, Austria. The seismic sequences’ mainshock epicentres are less than 15 km apart. In March 2023, seismic activity resumed in the Gloggnitz area and continued to be relatively high in comparison with the average background seismicity of the region.

The first of these sequences started on March 30th, 2021, with the occurrence of an ML4.6 and h = 9 km earthquake close to Breitenau. A period of increased seismic activity lasted ~2 weeks, before decreasing to the background seismicity rate by mid-April. On April 19th, 2021, an earthquake with similar magnitude and depth (ML4.4 and 9 km) occurred only 1 km northeast of the previous ML4.6. The following seismic sequence lasted until the end of May 2021. The third seismic sequence started on April 20th, 2021, ~15 km SW of the Breiteau sequences, with a shallow (h = 5 km) ML3.5 earthquake followed by the mainshock (ML3.8 and h = 5 km) on April 23rd, 2021 (ML3.8 and h = 5 km). Seismicity decayed to background rates by early May. On March 30th, 2023, the seismic activity resumed in the Gloggnitz area with a mainshock (ML4.2 and h = 10 km). Its epicentre was located between the 2021 Gloggnitz foreshock (ML3.5) and the mainshock (ML3.8). Compared to the 2021 Gloggnitz sequence, there was no significant surge in seismic activity following the ML4.2 event, and the seismicity levels remained moderately high, compared to the typical seismic activity observed in the year 2021, until the beginning of October.

In this study, we relocated all events using a non-linear location method and used a probabilistic full waveform inversion tool to derive full moment tensor solutions for the largest earthquakes of the sequences (ML4.6, ML4.4, ML4.2 and ML3.8). These neighbouring sequences, which cluster spatially along a narrow seismicity band, but show different focal mechanisms and different temporal evolutions, shed light on the segmentation of local seismogenic processes and complex fault system along the seismogenic lineament.

How to cite: Papí Isaba, M. P., Buforn, E., Mattesini, M., Petersen, G., Cesca, S., Hausmann, H., and Lenhardt, W.: The 2021 and 2023 Vienna Basin seismic sequences: Insights from earthquake relocation and moment tensor inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15665, https://doi.org/10.5194/egusphere-egu24-15665, 2024.

EGU24-16122 | ECS | Posters on site | TS2.6

Provenance analysis of the Permo-Triassic Lantschfeld quartzite in the Austroalpine of the Radstädter Tauern, European Eastern Alps 

Johannes Rembe, Edward Sobel, Susanne Schneider, and Axel Gerdes

The Permo-Triassic shallow marine to continental deposits of the Alpine Verrucano and the Lantschfeld quartzite discordantly overly the Variscan basement in the Eastern Alps. The late Permian Alpine Verrucano is characterized by fine- to coarse-clastic (meta-)sediments with local calcareous and/or conglomeratic layers. The well sorted and more mature, early Triassic Lantschfeld quartzite is carbonate free, shows pale green to white coloring and rare conglomeratic layers. Both provide an important detrital record of post-Variscan landscape evolution. Investigations on non metamorphic Permo-Triassic units of the Northern Calcareous Alps (Haas et al., 2020) provided zircons connected to processes of the Pan-African, Cadomian and Variscan Orogenies. However, they show large disparities between different nappes. This underlines the varied character of the Variscan basement units, and a better understanding may provide interesting hints for the assignment of tectonic slivers to certain nappe complexes.

In this contribution we present detrital age spectra from the metamorphic Lantschfeld quartzite of the Lower Austroalpine Radstadt Nappe and the Upper Austroalpine Silvretta-Seckau Nappe System. By combing detrital zircon U-Pb dating with detrital rutile U-Pb and rutile geochemistry data, we can better trace the metamorphic history of the Variscan basement units contributing to the early Triassic basin fill.

Haas I, Eichinger S, Haller D, Fritz H, Nievoll J, Mandl M, Hippler D and Hauzenberger C 2020 Gondwana Research 77 204–22

How to cite: Rembe, J., Sobel, E., Schneider, S., and Gerdes, A.: Provenance analysis of the Permo-Triassic Lantschfeld quartzite in the Austroalpine of the Radstädter Tauern, European Eastern Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16122, https://doi.org/10.5194/egusphere-egu24-16122, 2024.

EGU24-16199 | Posters on site | TS2.6

Seismicity recorded by DIVEnet, a temporary network covering the northern Ivrea-Verbano Zone 

Simone Salimbeni, Judith Confal, Silvia Pondrelli, and György Hetényi and the DIVENet Team

As part of the ICDP-DIVE project (www.dive2ivrea.org), the temporary seismic network DIVEnet has been installed across the northeastern part of the Ivrea Verbano zone (IVZ). The DIVE project aims to find answers to fundamental questions about the lower continental crust and its transition to the mantle with two scientific boreholes and a combination of geochemical, geological and geophysical analyses. Since due to Alpine collision lower crustal rocks are at the surface, and the Ivrea geophysical body is at a very shallow depth (locally ~1±1 km b.s.l.), the site is unique and offers an excellent frame for new discoveries. The DIVE project includes a first drillhole DT-1B which has been completed in Ornavasso, and a second, currently ongoing DT-1A in Megolo. To monitor natural seismicity as well as drilling-induced noise and possible signals in the area, we have deployed DIVEnet in Autumn 2021, a temporary seismic network consisting of 13 seismometers. In September 2023, a broadband borehole instruments has been lowered in the first, completed borehole and is now recording at 250 m depth. This long-term monitoring produced a catalog of local seismicity that shows that the main seismic activity is located around the well-known principal tectonic lines of the region, i.e. the Insubric Line, which, geologically speaking, are considered as inactive. Seismic monitoring techniques have been redefined to improve the detection ability, which has become possible thanks to tested and continuously improved quality checks. Additionally we use the data for various geophysical analyses. Together with other permanent and temporary seismic stations in the region, receiver function analysis and its back-azimuthal harmonics are being calculated to get a better image of the IVZ by checking the presence of anisotropy in this anomalous body and its surrounding lithosphere.

 

 

How to cite: Salimbeni, S., Confal, J., Pondrelli, S., and Hetényi, G. and the DIVENet Team: Seismicity recorded by DIVEnet, a temporary network covering the northern Ivrea-Verbano Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16199, https://doi.org/10.5194/egusphere-egu24-16199, 2024.

EGU24-16377 | ECS | Orals | TS2.6

The Alpine cooling history of the western Dolomites Indenter, European Southern Alps 

Thomas Klotz, Anna-Katharina Sieberer, Hugo Ortner, István Dunkl, and Hannah Pomella

The NW to N directed indentation of the Adriatic microplate into the European lithospheric domain, initiated in the upper Eocene following the closure of the Piemont-Liguria and Valais oceanic basins, constitutes a key feature of the Neoalpine orogenesis. The separation of the eastern Southern Alps (Dolomites Indenter) along the Giudicarie fault system from the late Oligocene (Middle Miocene at the latest) on and its increased northward push contributes significantly to major tectonic processes in the Eastern Alps north of the Dolomites Indenter: updoming, piggy-back top-N thrusting, and eastward lateral escape of the Tauern Window.

The interior of the Dolomites Indenter undergoes deformation as well, as documented, e.g., by the prominent, dominantly SSE-vergent fold and thrust belt of the Dolomites, as well as the top-WSW directed thrusts of the Dinaric chain and associated flysch sedimentation. New and compiled Apatite (U-Th)/He (AHe) and Fission Track (AFT) data allow the tracing of the exhumation history.

AFT data from the western Dolomites Indenter tend to cluster within consistent Dinaric and Neoalpine distinguishable tectonic blocks. However, the data are quite scattered. AHe data primarily indicate exhumation during the post-15 Ma Valsugana phase, showing a tendency of getting younger towards the east. A subordinate number of AHe datapoints document Eocene to Oligocene cooling as well.

Regional age-elevation profiles of consistent fault-delimited blocks exhibit (i) moderate cooling during the Mesoalpine Penninic subduction, (ii) fast Dinaric exhumation (in the Plose area), and (iii) fast Valsugana phase exhumation starting at approximately 15 Ma; Notably, this exhumation pulse starts earlier (Chattian/Aquitanian) in the northernmost tectonic block at the Indenter tip.

Time-temperature path modelling confirms the Valsugana phase as the most significant period of tectonic exhumation within the western Dolomites Indenter. According to the modeling, prior to this phase, a significant number of samples remained within the AFT annealing zone for an extended period of time, at least from Ladinian times onwards. This is due to a wide dispersion of single grain ages and suggests, the data does not necessarily represent a tectonic pulse. Moreover, many samples from sedimentary rocks of the Permian and Lower Triassic periods show a complete reset of the AFT system during the Middle Triassic, well before the maximum burial indicated by the stratigraphic record. This high-temperature anomaly could be attributed to the extensive Ladinian volcanism in the study area.

Based on the new thermochronological data, it can be inferred that the Middle Miocene Valsugana phase is the most significant exhumation phase in the Dolomites Indenter. Additionally, this phase begins earlier in the north than in the south. It is essential to consider the complex thermal history of the Dolomites Indenter and the possible long residence time of samples within the partial annealing zone prior to the Neoalpine exhumation when interpreting new data.

How to cite: Klotz, T., Sieberer, A.-K., Ortner, H., Dunkl, I., and Pomella, H.: The Alpine cooling history of the western Dolomites Indenter, European Southern Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16377, https://doi.org/10.5194/egusphere-egu24-16377, 2024.

EGU24-16390 | ECS | Orals | TS2.6

Subduction and exhumation of an Ultra-High Pressure oceanic slab in the Western Alps, new insights from the Lago Superiore Unit 

Emanuele Scaramuzzo, Franz Livio, Alessia Borghini, Mattia Gilio, Michele Locatelli, Federica Boero, and Stefano Ghignone

Ultra-high pressure (UHP) units sample the deepest portion of a subduction zone that returned to the surface, escaping their fate of disappearing deep into the mantle. Several mechanisms have been proposed for the exhumation of UHP units in collisional orogens but the topic remains still controversial and poorly understood.

The models invoked for the exhumation of UHP units generally require a positive buoyancy as trigger of exhumation. However, Ghignone et al. (2023) reported for the first time the occurrence of a slice tens of kilometres in length of oceanic slab, i.e., the Lago Superiore Unit (LSU), that reached UHP depth. This latter represents a portion of the former Alpine Tethys oceanic lithosphere now accreted within the Western Alpine collisional system (Ghignone et al., 2023).

In this contribution we present new insights on the subduction-accretionary processes preserved in the UHP Lago Superiore Unit. Our study is based on i) a new structural map of the LSU considering new data, ii) structural and kinematic field data, and iii) new prograde and retrograde P-T estimations calculated combining quartz-in-garnet elastic thermobarometry with Zr-in rutile and Ti-in-quartz thermometry.

Our new integrated kinematic and thermobarometric model suggests that the primary process driving the exhumation of the UHP Lago Superiore Unit was the progressive extraction of a composite metamorphic wedge. Final extension as revealed by thermobarometric constrain, allowed the exhumation of the Lago Suepriroe Unit at shallow crustal levels.

Ghignone, S., Scaramuzzo, E., Bruno, M., Livio, F., 2023. Am Mineral, 108(7), 1368-1375.

How to cite: Scaramuzzo, E., Livio, F., Borghini, A., Gilio, M., Locatelli, M., Boero, F., and Ghignone, S.: Subduction and exhumation of an Ultra-High Pressure oceanic slab in the Western Alps, new insights from the Lago Superiore Unit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16390, https://doi.org/10.5194/egusphere-egu24-16390, 2024.

EGU24-16584 | Posters on site | TS2.6

Seismicity clusters in the Eastern Alps: New insights from the large-N Swath-D seismic network 

Rens Hofman, Gesa Petersen, Jörn Kummerow, and Simone Cesca and the The AlpArray Swath-D Working Group

The installation of the temporary, large-N Swath-D seismic network in the years 2017-2019 (Heit et al., 2021) provided the basis for the recent compilation of a high-resolution, consistently processed seismicity catalogue for the eastern and southern Alps (Hofman et al., 2023). The catalogue contains more than 6,000 earthquakes with magnitudes down to −1.7 ML.

 

In the present study, we analyse in more detail several of the newly detected microseismic clusters in the study area, which includes the most active parts of the Alps as well as particularly quiet regions with very little previously reported seismicity. We combine inter-event waveform similarity clustering, catalogue statistics and rupture mechanisms to characterise the clustered seismicity swarms and mainshock-aftershock sequences. We apply a relative location technique based on differential Ts-Tp arrival times to better resolve the seismogenenic structures. For subgroups of microseismic events with magnitudes Mw 1.2-3.0, we obtain moment tensor solutions using the flexible probabilistic inversion framework Grond, which allows to combine different fitting targets and frequency bands, while providing meaningful estimates of uncertainties (Heimann et al., 2018, Petersen et al., 2021). This adds to resolve subtle, but systematic variations of the inner-cluster seismicity.

Thanks to the outstanding network density, we can report a variability of seismic sequences and microseismic event mechanisms across the study area and interpret them with in terms of long-term tectonic and intermediate triggering processes.

How to cite: Hofman, R., Petersen, G., Kummerow, J., and Cesca, S. and the The AlpArray Swath-D Working Group: Seismicity clusters in the Eastern Alps: New insights from the large-N Swath-D seismic network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16584, https://doi.org/10.5194/egusphere-egu24-16584, 2024.

EGU24-16705 | ECS | Posters on site | TS2.6

Changes in anisotropy with depth revealed by splitting intensity tomography beneath the Alps and surrounding regions 

Judith Confal, Paola Baccheschi, and Silvia Pondrelli

Complex tectonics and strong heterogeneity due to thickened crust, subducting lithosphere, and the movement of the surrounding asthenosphere can be well described by seismic anisotropy, a good indicator for active and past tectonic events. Most of methodologies adopted so far to reconstruct anisotropy have a poor depth resolution. To overcome this problem we are using splitting intensity, which is related to the energy on the transverse component of the waveform and is linearly related to the mediums elastic perturbations through 3D finite-frequency sensitivity kernels. Here, we have paid special attention to three regions: the Western Alpine orogen; the Upper Rhine Graben and the still active oceanic subduction in Southern Tyrrhenian region. We used 822 stations in the Central Mediterranean to compute 12480 splitting intensity measurements, afterwards they were inverted for depth dependent anisotropy. The 3D anisotropy models show a complex pattern in the shallower parts (60-100 km depth), becoming more aligned parallel to the slabs in the deeper parts (100-350 km depth) and influenced only by strong mantle flows. In the Upper Rhine Graben we are finally able to appoint an anisotropy pattern of NNW-SSE oriented fast polarisation directions, which are parallel to faults in the graben structure, to the lithosphere and a lower layer with orientations pointing NE-SW, to asthenospheric flow. While between 100 and 250 km depth the strength of anisotropy is very small. In the Western Alps we see complex shallow anisotropy pattern and possible mantle flow around the Alpine slab. Beneath the southern Tyrrhenian subduction system looking at the anisotropy tomography images we are able to identify circular mantle flow directions around the edge of the slab (beneath the Sicily Channel) and possible break-offs in the continuity of the slab.

How to cite: Confal, J., Baccheschi, P., and Pondrelli, S.: Changes in anisotropy with depth revealed by splitting intensity tomography beneath the Alps and surrounding regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16705, https://doi.org/10.5194/egusphere-egu24-16705, 2024.

EGU24-17724 | ECS | Orals | TS2.6

Late Cenozoic evolution of the Dent Blanche Tectonic Nappe in the Western Alps imaged by low-t thermochronology. 

Lorenzo Gemignani, Julian Hülscher, Michele Zucali, Edward R. Sobel, Klaudia Kuiper, and Irene Albino

The Cenozoic uplift evolution of the Western Alps has been examined from various perspectives. Several studies have suggested that a Late Miocene-Pliocene European slab break-off, coupled with increased erosion due to enhanced glaciation, serves as a driving factor controlling the Western Alps topography. Alternatively, strain partitioning resulting from Adriatic indentation and Oligocene clockwise rotation leads to contrasting kinematic regimes, segmenting the Western Alps into blocks with differential exhumation. Here, we analyze the evolution of the Dent Blanche Tectonic System (DBTS), an Austroalpine nappe in the Western Alps surrounded by oceanic units from the former Liguro-Piemontese ocean.

We apply Low-T thermochronology (apatite and zircon (U-Th)/He) and high resolution mica 40Ar/39Ar dating from the DBTS. ZHe sample ages from the DBTS are ~30 Ma, with an extremely low eU sample from the lower elevation of the Valpelline Valley as young as ~7 Ma. AHe samples are younger, ranging from ~20 Ma to ~3 Ma. Reliable mica Ar ages range from the Paleocene to Oligocene. Most of the samples' age distributions have low radiogenic Ar yields (low 40Ar*), and part of the analyzed muscovite shows low K/Ca ratios, likely indicating chloritization.

Inverse modelling of the cooling ages from selected samples from the core of the DBTS (Arolla Units) shows that the exhumation rate of the DBTS is one-fold lower than the exhumation rates derived in the units north of the nappe. These rates are comparable with slower exhumation rates south of the nappe.

We propose that the DBTS system underwent its highest exhumation rates in the Oligocene to Late Miocene, predating the proposed Pliocene slab break-off as well as Pliocene increased glaciation. The identification of Pliocene-Pleistocene ages from one sample is interpreted to reflect glacial erosion localized in the Valpelline Valley; this is aligned with similar increased denudation rates since Pliocene observed in other Western Alps regions. However, this single cooling age does not provide conclusive evidence that glaciation drove the DBTS’s exhumation from ~3 Ma ago.

How to cite: Gemignani, L., Hülscher, J., Zucali, M., Sobel, E. R., Kuiper, K., and Albino, I.: Late Cenozoic evolution of the Dent Blanche Tectonic Nappe in the Western Alps imaged by low-t thermochronology., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17724, https://doi.org/10.5194/egusphere-egu24-17724, 2024.

EGU24-18831 | ECS | Posters on site | TS2.6

A critical review of petrological data in the Penninic domain of the Central Alps (Lepontine dome and its E-NE metasedimentary covers)  

Alessia Tagliaferri, Enrico Pigazzi, Sabrina Morandi, Paola Tartarotti, and Filippo Luca Schenker

In the Central Alps, the Penninic domain is formed by Europe-derived crystalline basement units that experienced a complex geodynamic history. This geodynamic history spans from subduction-related HP-LT (high pressure-low temperature) at ca. 38 Ma up to Barrovian metamorphic conditions peaked at ca. 31 Ma, followed by a more or less pervasive greenschist facies re-equilibration more evident in the northern units. This history led to the piling of polymetamorphic crystalline basement nappes that nowadays are up arched forming the Lepontine dome.

The Lepontine dome is a structural and metamorphic dome characterized by a widespread Barrovian metamorphic imprint. The temperatures of the Barrovian metamorphism increment towards the south and have a concentric distribution, locally intersecting the nappe contacts.

Here, we present a critical review of petrological data from the literature within the Lepontine dome, coupled with new temperature data computed with Raman spectroscopy acquired on the E-NE margin (up to the Tambo nappe) of the Lepontine dome. This work aims to identify the finite shape of isotherms at the base and on the roof of the Adula HP nappe and to trace the peak temperature conditions according to their relation to the Adula nappe emplacement (pre-, syn- or post- deformation). Two endmembers are envisaged in the literature: (1) a history where the temperature peak is attained during deformation and, according to thermodynamic studies, evolves from a single prograde PT loop, and (2) a post-deformation thermal peak formed after the HP deformation. The spatial distribution of rocks recording these different thermo-mechanical histories and the geochronological ages of the peak thermal conditions will help to postulate coherent geodynamic scenarios.

Petrological data from the Lepontine crystalline basement nappes point to peak conditions developed during nappe emplacement. On the other hand, the metamorphism and deformation of the northern metasedimentary covers suggest that a second thermal imprint is responsible for the peak temperatures registered close to the Adula nappe. This might suggest that the heat surplus developed during deformation of the Adula nappe was diffused to the close units also after its emplacement.

How to cite: Tagliaferri, A., Pigazzi, E., Morandi, S., Tartarotti, P., and Schenker, F. L.: A critical review of petrological data in the Penninic domain of the Central Alps (Lepontine dome and its E-NE metasedimentary covers) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18831, https://doi.org/10.5194/egusphere-egu24-18831, 2024.

EGU24-18901 | ECS | Orals | TS2.6

Stable isotope paleoaltimetry reveals Early to Middle Miocene along-strike elevation differences of the European Alps 

Armelle Ballian, Maud M. J. Meijers, Isabelle Cojan, Damien Huygue, Katharina Methner, Daniel Boateng, Sebastian G. Mutz, Walter Kurz, Emilija Krsnik, Horst Zwingmann, Yann Rolland, Todd Ehlers, Jens Fiebig, and Andreas Mulch

The European Alps, one of the most studied mountain ranges worldwide, are hypothesized to have experienced diachronous surface uplift resulting from slab-breakoff (Schlunegger and Kissling, 2018; Handy et al., 2015). However their surface elevation history is yet not well constrained (Campani et al., 2012; Krsnik et al., 2021; Botsyun et al., 2020). Quantifying surface elevation of an orogen through geological time is essential for our understanding of the geodynamic drivers, as well as the paleoenvironmental impacts of surface uplift.

Here, we present Early to Middle Miocene stable isotope-based paleoelevation reconstructions of the Western, Central, and Eastern Alps. Stable isotope paleoaltimetry (the 𝛿-𝛿 approach) is based on the systematic decrease of oxygen (𝛿18O) and hydrogen (𝛿D) isotopic composition of precipitation with increasing elevation and strongly benefits from contrasting high and low elevation records of past rainfall.

Accordingly, contrasting temperature-corrected near sea level pedogenic carbonate 𝛿18O values with time-equivalent 𝛿D values of K-Ar dated clay minerals from fault gouges allows for the calculation of the differential elevation between a foreland basin and an orogen’s interior through time. Recent paleoaltimetry research with focus on the Middle Miocene Central Alps indicates elevations exceeding 4 km (Krsnik et al., 2021).

With a spatiotemporally enhanced coverage of the European Alps, we present estimates of paleoelevation covering the time interval between ca. 23 and 12 Ma. In addition, paleoclimate simulations for a number of topographic scenarios allow for the isolation of contribution of local elevation complex climate change, and regional topographic configuration signals (Boateng et al., 2023).

Our quantitative stable isotope paleoaltimetry estimates indicate peak elevations of >4km in the Central Alps already during the earliest Miocene (ca. 23 Ma). 𝛿D values from fault gouge-derived illites are up to 25 ‰ higher in the Eastern Alps than in the Central Alps for the time interval between 21-16 Ma and suggest that the Eastern Alps were significantly lower during that time interval. Our results from the Mont Blanc massif are in line with isotopic measurements from fluid inclusions in quartz veins, which highlight the Mont Blanc massif in the Western Alps, did not exceed an average elevation of ca. 1 km until the end of the Miocene (Melis, 2023). Collectively, these results confirm a scenario of west-to-east surface uplift as suggested on the basis of slab-breakoff and tearing.

How to cite: Ballian, A., Meijers, M. M. J., Cojan, I., Huygue, D., Methner, K., Boateng, D., Mutz, S. G., Kurz, W., Krsnik, E., Zwingmann, H., Rolland, Y., Ehlers, T., Fiebig, J., and Mulch, A.: Stable isotope paleoaltimetry reveals Early to Middle Miocene along-strike elevation differences of the European Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18901, https://doi.org/10.5194/egusphere-egu24-18901, 2024.

EGU24-20494 | ECS | Posters on site | TS2.6

Pre to syn orogenic evolution of the Piedmont-Ligurian oceanic covers: clues on the Flysch units of the Western Ligurian Alps (CARG project – Ormea sheet 244).  

Simone Lombardi, Lorenzo Stori, Laura Federico, Laura Crispini, Seno Silvio, and Maino Matteo

The evolution of the European margin before and during the collisional phase of the alpine orogenesis is still a debated topic. The Western Ligurian Alps are a complex key area that can help to better understand this tectonic evolution. Here the contact between two different domains crops out: Briançonnais domain (European passive margin) and the Piedmont-Ligurian sedimentary covers (oceanic domain). These last units are characterized by several deformation stages, presented by many thrust sheets and non-cylindrical folds that make difficult to understand their relationships and their three-dimensional setting. Moreover, they are characterized by low-grade metamorphism that often masks their sedimentary structures and features, resulting in a challenging reconstruction of the pre-orogenic stratigraphic and structural setting. Previous works have hypothesized that these turbidite systems have been deposited in an abyssal plain resulted from the Piedmont-Ligurian Oceanic rifting and spreading. They are characterized by a lower part of basal complexes with thin bedded and very-thin bedded turbidites and often containing olistostromes. These basal complexes are overlain by sand- or carbonate-rich turbidite systems (Decarlis et al. 2014; Lanteaume et al.1990) that are interpreted as trench environment deposits (Di Giulio, 1992; Mueller et al. 2017). During the progressive advance of the accretionary wedge towards the European foreland, these units have migrated and stacked in reverse order, with the oldest one in the topmost part. The aim of the study is to review and integrate the previous works with new data following a multidisciplinary approach with a particular focus on the basal complexes of the flysch units. The CARG project is focused on the detailed fieldwork mapping that is already in progress with the aim of realizing the geological map of Ormea Sheet 244. During this activity, samples are collected for laboratory analysis. Specifically, petrographic characterization of samples collected in the basal complexes is currently carried out to better understand the source area of the sediments. Geochemical analyses are also in progress on basalt clasts found in the chaotic bodies. Another aim is to investigate the metamorphic grade by analysing fluid inclusions and vitrinite reflectance. Geochronological analysis will be performed with U/Pb analytical techniques on zircons to compare the results with surrounding crystalline basements to put an additional time constrain to the poor biostratigraphic data.

REFERENCES

Decarlis A., Maino M., Dallagiovanna G., Lualdi A., Masini E., Toscani G., Seno S., 2014. Salt tectonics in the SW Alps (Italy-France): from rifting to the inversion of the European continental margin in a context of oblique convergence. «Tectonophysics» 636, 293-314

Di Giulio A., 1992. The evolution of the Western Ligurian Flysch Units and the role of mud diapirism in ancient accretionary prisms (Maritime Alps, Northwestern Italy) «International Journal of Earth Sciences (Geologische Rundschau)» 81, 655-668

Lanteaume M., Radulescu N., Gavos., Feraud J., 1990. «Notice explicative, Carte Géol. De France (1/50000), feuille Viève-Tende» 948, Orleans, BRGM. 139 pp.

Mueller P., Patacci M., Di Giulio A., 2017. A Hybrid event beds in the proximal to distal extensive lobe domain of the coarse-grained and sand-rich Bordighera turbidite system (NW Italy). «Marine and Petroleum Geology» 86, 908-931

How to cite: Lombardi, S., Stori, L., Federico, L., Crispini, L., Silvio, S., and Matteo, M.: Pre to syn orogenic evolution of the Piedmont-Ligurian oceanic covers: clues on the Flysch units of the Western Ligurian Alps (CARG project – Ormea sheet 244). , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20494, https://doi.org/10.5194/egusphere-egu24-20494, 2024.

EGU24-20770 | Posters on site | TS2.6

Tectonostratigraphy of the Koralpe Mountain ridge (Eastern Alps) 

Ralf Schuster, Gerald Schuberth-Hlavač, Tanja Knoll, Heinrich Mali, and Annika Geringer

The investigated area of the Eastern Alps consists of Austroalpine basement units composed of various types of mica schist and paragneiss with intercalations of amphibolites or eclogites, marbles and quartzites. Furthermore, Permian magmatic rocks are represented by gabbros, pegmatites and the Wolfsberg orthogneiss. All rocks belong to the Koralpe nappe system and are characterized by main imprints during Permian HT/LP metamorphism and Cretaceous LT/HP overprint and nappe stacking in the course of the Eoalpine orogenic event. Geological maps show only a rudimentary tectonic subdivision, although there are indications for a complex internal structure. To study the internal structure a W-E orientated section across the Großer Speikkogel (2140 m) is most suitable. Along this section the E-dipping Cretaceous schistosity is gently folded by WNW-ESE trending axes with steep axial planes. From bottom to the top two amphibolite-facies, three eclogite-facies and again amphibolite-facies nappes can be identified. This indicates an inverted metamorphic field gradient in the footwall and an upright gradient in the hanging wall.

The tectonically deepest part crops out in the Wolfsberg Window, where amphibolite-facies rock units of the northerly-situated Gleinalpe Mountains reappear at the surface. They comprise the Vordergumitsch nappe, which is mainly built up by biotite-rich mica schist, paragneiss and amphibolite of the Klining Complex. Additionally it includes the Wolfsberg orthogneiss. Above the Pusterwald nappe is situated. It is built up by the Rappold (Preims) Complex, mainly composed of garnet-bearing mica schist, paragneiss and marble with additional amphibolite, quartzite and pegmatites. The latter show relatively low grades of fractionation.

The lowermost eclogite-bearing unit is the several hundred meters thick Brandhöhe nappe. It represents an upright section through the lower and middle part of the Permian crust. Its lower part mainly consists of paragneiss, which experienced high amphibolite-facies and anatexis during the Permian event. Usually it contains several millimetres large aggregates of fine-grained kyanite ("Disthenflasergneis"). In the upper part paragneiss with up to several decimetres long kyanite pseudomorphs appears, which developed from Permian greenschist-facies schists with chiastolitic andalusite ("Paramorphosenschiefer”). Within the metasedimentary matrix some huge eclogite bodies appear. While pegmatitic mobilisates and weakly fractionated simple pegmatites occur in the lower part of the succession, fractionated pegmatites and spodumene pegmatite dikes of the Weinebene locality are situated in the upper part. Maybe the spodumene pegmatites from Trahütten and Klementkogel are also at this level. The overlying Hoher Speikkogel nappe is characterised by migmatic paragneiss again. Its upper boundary is masked by the Plattengneis shear zone. Therein, thick evolved pegmatites occur near the base, whereas above only millimetre thick pegmatitic mobilisates appear. This transition marks the base of the overlying Deutschlandsberg nappe. In its less deformed upper part bodies of Permian gabbro-eclogite, the leucogranite of Trahütten and most probably the spodumene pegmatite of the Gupper quarry are situated.

Along the western foothills of the Koralpe Mountain ridge amphibolite-facies rock assemblages are dominated by garnet mica schist. It is yet not clear whether they represent one continuous nappe sheet or several nappe sheets.

How to cite: Schuster, R., Schuberth-Hlavač, G., Knoll, T., Mali, H., and Geringer, A.: Tectonostratigraphy of the Koralpe Mountain ridge (Eastern Alps), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20770, https://doi.org/10.5194/egusphere-egu24-20770, 2024.

In Neogene time, the Eastern Alps underwent a profound tectonic reorganisation. This featured northward indentation of the Alpine orogenic wedge by the Adriatic plate, eastward lateral extrusion between conjugate strike-slip faults, and a shift from thrust propagation on the European lower plate to the Adriatic upper plate. We investigate the triggers of this reorganisation with new sequentially restored orogen-scale cross-sections along the TRANSALP (12°E, western Tauern Window) and EASI (13.3°E, eastern Tauern Window) transects, plus an E-W orogen-parallel cross-section (46.5°E). We use a map-view reconstruction to restore the effects of out-of-section transport by lateral extrusion and compare our results with P-wave local earthquake (LET) and teleseismic tomographic models of the crust and upper mantle.

The geologic record reveals two phases of indentation: Phase 1 (c. 23-14 Ma): The Adriatic Plate was an undeformed indenter, with northward motion relative to Europe accommodated by sinistral motion along the Giudicarie Fault and shortening within the Eastern Alps orogenic wedge. Upright folding of nappes mostly derived from the downgoing European Plate, and lateral extrusion of the entire metamorphic edifice and North Calcareous Alps accommodated this N-S shortening. This shortening required ongoing subduction of European lithosphere, ruling out previous models involving north-dipping Adriatic subduction. A purported detachment below the Venediger Nappes may have served as the base of the laterally extruding wedge.

Phase 2 (c. 14 Ma-Present): The leading edge of the Adriatic indenter has been deforming since c. 14 Ma, forming the thick-skinned South Alps fold-thrust belt. The onset of S-directed thrusting is recorded by Langhian-Serravallian flysch in the footwall of the Valsugana thrust. The Adriatic lower crust was decoupled and transported northwards into the orogenic wedge, indenting and exhuming the deeply buried equivalents of the Venediger Nappes in the Tauern Window. A high-velocity (6.8 - 7.25 km/s) bulge in LET models of the TRANSALP section images this indenter, which comprises mostly Adriatic lower crust, but possibly also includes some accreted European lower crust.

In P-wave teleseismic tomography along the EASI section, the European slab appears to be detached at a locus marked by a Moho gap and a shallow discontinuity in the positive velocity anomaly beneath the orogenic wedge. In contrast, no such discontinuity occurs beneath the TRANSALP section, where S-dipping European lithospheric mantle still extends beneath and south of the orogenic wedge. If the southern end of this relict slab segment marks the locus of a detachment, we find that the current slab length is less than the amount of N-S shortening in the TRANSALP section since 23 Ma. To explain this mismatch, we propose that the most recent slab detachment in the Eastern Alps event occurred after 23 Ma, and likely after 14 Ma (Phase 2 indentation). Note that this does not preclude earlier detachment events, notably at 22-19 Ma when the eastern Molasse Basin rapidly filled and orogenic vergence shifted from north to south (see Handy et al., this session).

How to cite: McPhee, P. and Handy, M.: Post-collisional reorganisation of the Eastern Alps in 4D – Crust and mantle structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21023, https://doi.org/10.5194/egusphere-egu24-21023, 2024.

EGU24-21804 | Posters on site | TS2.6

3D Geomodelling of Alpine structures: the Misox Shear Zone (Swiss) 

Riccardo Monti, Andrea Bistacchi, and Stefano Zanchetta

3D models are fundamental tools for studying the evolution of complex geological structures, such as shear zones in the metamorphic core of the Alps.
The study’s case is the area of the San Bernardino Pass (Swiss), focusing on the study of the structural and metamorphic evolution of HP units outcropping here.
The area of the San Bernardino Pass is part of the Penninic domain, an Alpine domain consisting of continental and oceanic crust derived from the distal margin of Europe, subducted during the Alpine orogeny.
In this area, the Adula nappe is in contact with the overlying Tambò nappe (part of the eastern flank of the Lepontine Dome) along a wide shear zone of several hundreds of metres.
This work is focused on the 3D modelling of the shear zone and the superposed fold system developed within the Adula nappe, in the hanging wall of the shear zone
Starting from original field data and available geological maps, structures were approximated and drawn using the open-source software QGIS to create a simplified geological-structural map.
These data are fundamental constraints for drawing geological sections using the open-source software PZero (https://github.com/andrea-bistacchi/PZero).
After careful reconstruction of serial geological cross-sections in PZero, advanced interpolation techniques such as implicit methods can be applied to develop accurate geological models.

PZero is an open-source software currently in development, dedicated to 3D geological modeling, featuring a user-friendly interface designed for structural geologists.

How to cite: Monti, R., Bistacchi, A., and Zanchetta, S.: 3D Geomodelling of Alpine structures: the Misox Shear Zone (Swiss), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21804, https://doi.org/10.5194/egusphere-egu24-21804, 2024.

EGU24-2622 | ECS | Posters on site | TS2.7

P and S Wave Anisotropic Tomography of the Banda Subduction Zone 

Yuanyuan Hua, Dapeng Zhao, and Yi-gang Xu

In subduction zones with slab-slab interactions, the pattern of mantle convection is very complex and still unclear. In this study, we jointly invert a large number of P and S wave arrival time data of local earthquakes for 3-D isotropic and anisotropic velocity structures of the Banda subduction zone. Along the curved Banda arc, the subducting Indo-Australian slab is detected clearly as a high-velocity zone, and its azimuthal anisotropy changes along the arc strike, representing fossil anisotropy within the slab and modified anisotropy by the subduction processes. Around the northern edge of the Banda slab, a semi-toroidal pattern of anisotropy appears in low-velocity anomalies, representing mantle flow extruded from the Banda arc and escaped from a gap of the Banda-Molucca slab toward the northeast. Our 3-D anisotropic tomography uncovers the mantle convection pattern induced by the slab-slab interactions, shedding new light on the complex dynamical processes in this curved subduction zone.

How to cite: Hua, Y., Zhao, D., and Xu, Y.: P and S Wave Anisotropic Tomography of the Banda Subduction Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2622, https://doi.org/10.5194/egusphere-egu24-2622, 2024.

The tearing of the subducting plate, which also named slab window, is prominent in the Java subduction zone. Mantle tomography data indicate plate tearing, supported by short-lived activity of K-rich volcanoes. Despite the acknowledged tearing phenomenon, the formation mechanism is less understood. Along the trench (95°E-120°E), we conducted 1707 profiles at 10 km intervals perpendicular to the subduction zone. Using five key parameters (1. Depth of the input oceanic plate; 2. Oceanic age of the input plate; 3. Trench depth; 4. Accretionary prism crest; 5. Accretionary prism slope), we illustrated bathymetric changes along each profile. Furthermore, utilizing data from over 40,000 earthquake depths, we imaged the subduction plate's configuration. Our study reveals distinct characteristics in the Java subduction system (110°-115°E). The input plate is 2500-3000 m shallower, the trench depth is 800-1200 m shallower, the accretionary prism crest is 1500-2000 m shallower, and the subduction angle is approximately 15° lower than surrounding subducting zones. A correlation between slab dip angles and the depth of the trench and prism crest indicates that the anomalous shallower bathymetry in the 110-115°E region is likely due to the decreased slab dip angles. This suggests that, at present, there is less likely thick buoyant oceanic crust is subducted beneath the Java trench, blocking its subduction and forming a slab window evident in tomography data.

How to cite: Tan, P. and Kong, F.: The mechanism of the tearing of the Java subducting plate comes from the constraints by surface bathymetry data and earthquake depth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3041, https://doi.org/10.5194/egusphere-egu24-3041, 2024.

EGU24-3107 | Posters on site | TS2.7

E-MORB glasses reveal a metasomatized mantle source of nascent oceanic crust in the Guaymas Basin, Gulf of California 

Wei Xie, Zhen-Min Ge, Xiao-Long Huang, and Tobias W Höfig

The formation of nascent ocean basins represents the beginning of the periodic Wilson cycle, and the geochemical characteristics of nascent oceanic crust are crucial for understanding how an ocean initially opens. The Gulf of California, which hosts young (<6 Ma) and active oceanic spreading centers (Lizarralde et al., 2007), is a prime example of a continental margin that has undergone oblique rifting and records the early stages of seafloor spreading. However, the mantle source composition of the nascent oceanic crust in the central part of the Gulf has not been comprehensively investigated yet. Here, we present major and trace element contents as well as B-Sr isotope compositions for basaltic glass samples from off-axis sills drilled by the International Ocean Discovery Program (IODP) Expedition 385 at Sites U1547 and U1548 in the intrusive sill-riddled Guaymas Basin. These glassy samples represent tholeiites and predominantly showtrace element patterns akin to enriched mid-ocean ridge basalts (E-MORBs), but with distinctive enrichments in Ba and K, as well as depletions in Nb, Ta, and Ti. They also have high B contents (3.07–3.67 ppm) with enriched Sr isotopes (87Sr/86Sr = 0.7032–0.7037) and heavy B isotopes (δ11B = -5.52‰ to 1.20‰), showing that the nascent oceanic crust in the Guaymas Basin might be generated through partial melting of a depleted MORB mantle (DMM) source, which has been metasomatized by melts from subducted slab materials including partially dehydrated sediment and altered oceanic crust components. Additionally, magmas in the Gulf of California show a systematic decline in their enrichment in fluid-mobile elements (Ba) and depletion in fluid-immobile elements (Nb, Ta, and Ti) from the northern (e.g., Isla San Luis volcanic center) to the central part (Guaymas Basin) and southward to the mouth (e.g., Alarcón Basin) of the Gulf. This suggests that the enriched (recycled) components in their mantle source were gradually extracted and exhausted during Gulf opening and oceanic crustal accretion that advanced in a northward direction. Our results indicate that the Guaymas Basin magmas were derived from a mantle that was fertilized by subduction components. The subduction signature is different from nascent ocean basins that evolved from intraplate rifting, such as the Red Sea, corroborating the Gulf opening as a process that started in response to long-term oblique convergence at the eastern Pacific plate margin without any influence from a mantle plume.

How to cite: Xie, W., Ge, Z.-M., Huang, X.-L., and Höfig, T. W.: E-MORB glasses reveal a metasomatized mantle source of nascent oceanic crust in the Guaymas Basin, Gulf of California, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3107, https://doi.org/10.5194/egusphere-egu24-3107, 2024.

Sulawesi Island is situated to the east of Kalimantan Island, composed of four branches. Throughout its tectonic evolution, influenced by both the Sulawesi Sea and the Banda Sea, Sulawesi Island involves the continental crustal fragment displacement and reorganization. Therefore, it is pivotal for studying geodynamic problems of ocean-continent coupling and subduction rollback. In this paper, combining dispersion data extracted from seismic surface wave and ambient noise with the satellite gravity anomaly data, we conducted a joint tomographic inversion to obtain a three-dimensional VS velocity model around Sulawesi. Combined with heat flow data, we derived a temperature structure and calculated the thickness and viscosity variation characteristics of the thermal rheological boundary layer at the bottom of the lithosphere by the thermal rheological method. The results suggest that: 1) The thickness of the rheological boundary layer in the southeastern part of Sulawesi Island, closer to the Banda Sea, is greater than that in the northern part, closer to the Sulawesi Sea. The different deformation rate, driven by lateral variations in rheological structure within the lithosphere, may control the continental crustal fragment displacement and reorganization in the Cenozoic, resulting in the maximum northward velocity in the eastern part of the East Branch of Sulawesi Island and the second in the western part of the North Branch of Sulawesi Island. 2) The low VS anomalous velocity zone, corresponding to the overlying crust of the subduction retreating plate of the North Sulawesi trench, likely represents a fluid-rich weak plate, leading to the extensional environment that contributes to the trench retreat. During the retreat, the area between the North Branch of Sulawesi Island and the Sulawesi subduction exhibits different rheological strengths under the influence of the surrounding tectonic stress field, resulting in the discontinuous Sulawesi subduction rollback.

How to cite: Zhang, J., Jiang, C., and Hao, T.: Thermal rheological structure analysis of crust and upper mantle in Sulawesi based on joint tomography of surface wave and gravity data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3281, https://doi.org/10.5194/egusphere-egu24-3281, 2024.

EGU24-3290 | Orals | TS2.7 | Highlight

Geodynamic and kinematic model of the South China Sea and regional plates since the end of seafloor spreading 

Minghui Zhao, Jean-Claude Sibuet, Jonny Wu, Siqing Liu, and Jinhui Cheng

The geodynamics and plate tectonics of the South China Sea (SCS)-Taiwan region since Miocene times are uncertain because the former extent and tectonic configuration of the subducted easternmost SCS along the Manila trench is uncertain. Here we unravel the regional kinematic context from main offshore constraints including published unfolding of the Manila slab from seismic tomography, which provides insight on restoring the subducted part of the SCS. We reconstruct a whole northern SCS continent-ocean boundary (COB) that consists of a northeastern SCS COB segment (called ‘S3’), trending N070° that roughly parallels the present SCS shelf; a 350-km long ~N-S trending segment S2 that steps north to Hualien; and, a third segment S1 that extends from east of Hualien beneath the Ryukyu subduction zone trending N085° that ends near Miyako Island in the Ryukyus.

We demonstrated that the two-plate kinematic model is the best framework to explain the existing data. The boundary between Eurasia and Philippine Sea plate is a ~NS oriented left-lateral lithospheric shear fault called the Manila transcurrent fault (MTF). The MTF initiated ~18 Ma at the onset of the tear and progressively moved eastward, creating the intra-oceanic Luzon arc. The MTF ancestor was a N337° oriented left-lateral shear fault, while the HB-PSP/EU motion was changing to N307°, allowing the HB-PSP plate to subduct between the two lips of a westward propagating tear fault until ~7 Ma. Since ~7 Ma, the MTF-PFZ constantly moved westward and 23° clockwise rotated from N337° to ~NS, which began collision ~7 Ma ago along the EU margin. Plate kinematic reconstructions from ~18 Ma to Present are synthesized in terms of continental or oceanic nature of the main PSP-HB and EU entities before their subduction that provide new understanding on Taiwan, PSP-SCS kinematics, and regional histories. This work is supported by Key projects of the Chinese National Natural Science Foundation (contracts 91958212, 42106078).

How to cite: Zhao, M., Sibuet, J.-C., Wu, J., Liu, S., and Cheng, J.: Geodynamic and kinematic model of the South China Sea and regional plates since the end of seafloor spreading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3290, https://doi.org/10.5194/egusphere-egu24-3290, 2024.

This study explores the formation of Oceanic Core Complexes (OCCs), hypothesized to arise from long offset, active normal faults that exhume the lower crust and upper mantle to the ocean floor. OCCs are predominantly observed in asymmetric crustal accretion zones, especially where magma supply is limited, such as in slow-spreading mid-ocean ridges. Traditional observational approaches, mostly perpendicular to these ridges, have suggested that spreading rates are a critical factor in OCC genesis. However, a lack of comprehensive data along the strike of mid-ocean ridges has limited our understanding of the interaction between tectonic and magmatic processes in OCC formation.

Our investigation commenced with the utilization of recently acquired seismic data from the spreading center of the West Philippine Basin. This exceptional dataset has allowed us to chronologically trace the development of multiple distinct OCC structures along the mid-ocean ridge. Complemented by satellite gravity data, we further verified the interpretation of the OCC. The results indicate significant density variability within OCCs, ranging from 2.55 to 3.3 g/cm^3, in contrast to the narrower range of 2.74 to 3.1 g/cm^3 observed in normal oceanic crust. The integration of seismic interpretation and gravity data inversion exposes an alternating sequence of magma-poor and magma-rich segments along the ridge axis. This sequence demonstrates a shift in magmatic activity, transitioning from Penrose-type to Chapman-type crust, characterized by the sequential development of detachment faults and OCCs, ultimately reverting to Penrose-type in the eastern segment. Consequently, our findings propose that, in addition to spreading rates, the localization and delocalization of strain along structural strikes play a pivotal role in OCC evolution. This perspective provides a nuanced understanding of the dynamic interactions between tectonic and magmatic processes that shape the oceanic crust.

How to cite: Zhao, J., Zhao, Y., Ding, W., and Manatschal, G.: Seismic and Gravity Data Analysis of Oceanic Core Complexes in the West Philippine Basin: Insights into Along-Strike Variations and Formation Processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3335, https://doi.org/10.5194/egusphere-egu24-3335, 2024.

EGU24-3360 | ECS | Orals | TS2.7

Lithospheric velocity structure of South China Sea basin from ocean bottom seismometer ambient noise tomography 

Liqun Cheng, Yinxia Fang, Xiongwei Niu, Tingzi Li, Chongzhi Dong, Yanghui Zhao, Hao Hu, Fansheng Kong, Pingchuan Tan, Aiguo Ruan, Shaoping Lu, Jianke Fan, Hafeez Jeofry Muhammad, Weiwei Ding, Jiabiao Li, and Xinguang Du

The South China Sea (SCS) located at the intersection of the three intercontinental plates of Eurasia, IndiaAustralia, and the Pacific Oceanis, is a typical marginal sea basin formed by the seafloor spreading under the tectonic background of plate convergence. Many crustal-scale studies indicate that the SCS basin has undergone asymmetric spreading, multi-phase ridge jumps, and intense post-spreading volcanic activity. Due to the lack of seismic data in the oceanic basin of the SCS, it remainsunclear about the scale and basin control of the Zhongnan fault, the magma source depth of the SCS basin, and the transport channel after the cessation of seafloor spreading. Phase velocity derived from ambient noise surface wave tomography may provide useful information to shed light on the mechanisms of the aforementioned problems. From October 2019 to July 2020, a 3D Ocean Bottom Seismometers (OBS) passive seismic observation experiment was carried out by the Second Institute of Oceanography, Ministry of Natural Resources (SIOMNR) in a broad area of the SCS. Based on the seismic ambient noise data recorded by 16 OBSs in the SCS basin, we inverted the phase velocity images over a period range of 10–20 s using ambient noise surface wave tomography. Our results indicate that the Zhongnan fault zone is a lithospheric-scalefault, which played a regulating role in the last oceanic ridge transition of the SCS basin from the East Subbasin to the Southwest Subbasin. In addition, the low-velocity body in the north flank of the Southwest Subbasin extends from the post-spreading seamounts on the ocean crust to the uppermost mantle (i.e., about 10–30 km), which indicates an oblique magma migration during the postspreading volcanism.

How to cite: Cheng, L., Fang, Y., Niu, X., Li, T., Dong, C., Zhao, Y., Hu, H., Kong, F., Tan, P., Ruan, A., Lu, S., Fan, J., Muhammad, H. J., Ding, W., Li, J., and Du, X.: Lithospheric velocity structure of South China Sea basin from ocean bottom seismometer ambient noise tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3360, https://doi.org/10.5194/egusphere-egu24-3360, 2024.

EGU24-3791 | Orals | TS2.7

Crustal structures and Cenozoic magmatism in the northwestern South China Sea 

Jinwei Gao, Thomas Lüdmann, Chun-Feng Li, Lin Li, Liyan Tian, Yongpeng Qin, and Taoran Song

This study investigates the crustal structure and Cenozoic magmatism in the northwestern South China Sea (SCS), based on the long-cable multi-channel seismic reflection profiles, together with gravity and magnetic data, and adjacent wide-angle refraction profiles. Basins/sags are bounded by large listricnormal faults (fault throws ≥ 0.5 km) and massifs are cut off by normal faults with small offsets (fault throws < 0.5 km) in the northwestern SCS. These structures are penetrated by magmatic edifices showing positive gravity and magnetic anomalies. Syn-rift magmatic intrusions/extrusions were intense in the basins/sags and continent-ocean transition zone while post-rift magmatism was widespread from basins/sags to massifs with the most intense stage occurring from 5.5 to 2.6 Ma. Based on previous geophysical and geochemical results, we suggest that syn-rift mantle upwelling from partial melting initiated seafloor spreading magmatic activities, whereas plume-related mantle upwelling contributed to the magmatism during and after seafloor spreading in the northwestern SCS. Stretching factors show that the upper and lower crusts have experienced differential extension from basins/sags to massifs. The nonuniform crustal extension resulted from upper crustal faulting and lower crustal flow. Particularly, the lower crustal flow was probably linked with the combined action of magmatic heating, mantle flow shearing stresses, and sediment loading, resulting in crustal boudinage and reestablishment of an equilibrium state over long distances.

How to cite: Gao, J., Lüdmann, T., Li, C.-F., Li, L., Tian, L., Qin, Y., and Song, T.: Crustal structures and Cenozoic magmatism in the northwestern South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3791, https://doi.org/10.5194/egusphere-egu24-3791, 2024.

In the regime of plate tectonics, subduction of an oceanic plate generally terminates with the collision and accretion of continental terranes. Then, a new subduction zone may form in the neighboring oceanic plates, which is defined as the terrane collision-induced subduction initiation (SI). Based on the analyses of western Pacific subduction system in the Cenozoic, three types of collision-induced SI have been observed: subduction polarity reversal, subduction transference and far-field subduction. However, the dynamics and controlling factors of SI mode selection after terrane collision are not clear. In this study, a multi-terrane collision model has been conducted with variable rheological strength of continental terranes and different convergence velocities. The model results indicate that the relative strength of the terranes controls the SI mode selection, with the new subduction zone tending to form beneath weaker terranes. In addition, the higher convergence velocity can facilitate the collision-induced SI. An analytical study of force balance has been further conducted, which provides the mechanical explanation for the numerical prediction of weak overriding terrane as a favorable SI site. The numerical models and force balance analyses are further compared with the natural cases in the western Pacific subduction system. It indicates that subduction polarity reversal is the most favorable mode after terrane collision in the western Pacific, possibly due to the weakness of overriding plate during the preceding subduction-induced fluid/melt activity. This comprehensive study provides systematic constraints for the dynamics of collision-induced subduction jump, especially for the western Pacific subduction zones in the Cenozoic.

How to cite: Cui, F. and Li, Z.-H.: Terrane collision-induced subduction initiation: Mode selection and implications for western Pacific subduction system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4872, https://doi.org/10.5194/egusphere-egu24-4872, 2024.

EGU24-5331 | Posters on site | TS2.7 | Highlight

Compositional heterogeneity within the mantle beneath the South China Sea 

Xiao-Long Huang, Fan Yang, Yu-Xin Cai, Yi-Gang Xu, and Zhen-Min Ge

The recycling of crustal materials is widely recognized as the primary mechanism driving compositional heterogeneity within the mantle. Seismic tomography has revealed stagnant slabs in the mantle transition zone (MTZ) beneath the South China Sea (SCS), indicating the significant presence of recycled oceanic crust (ROC) in its upper mantle. However, the extent to which recycled crustal materials contribute to the mantle source of mid-ocean ridge basalts (MORBs) remains a subject of debate, as radiogenic isotopes alone yield ambiguous insights. Here, we present comprehensive data on whole-rock major element, trace element, and Mo–Sr–Nd–Hf–Pb isotopic compositions for MORB samples from International Ocean Discovery Program Expedition 349 sites U1431E and U1433B in the eastern (ESB) and southwestern (SWB) subbasins, respectively, of the SCS. The δ98/95Mo values of the SCS MORBs exhibit a significant range (from −0.80‰ to +0.05‰), in contrast to the restricted composition observed in MORBs (δ98/95Mo = −0.19‰ ± 0.01‰). Specifically, the ESB MORBs display extremely light Mo isotopic compositions with Nd–Hf isotopic compositions similar to those of Pacific MORB, whereas the SWB MORBs show slightly higher δ98/95Mo values and depleted Nd–Hf isotopic compositions. The subbasin-scale mantle heterogeneity in the SCS can be best explained by varying degrees of interaction between a mantle plume and stagnant slabs in the mantle transition zone. The rigid stagnant slab in the mantle transition zone beneath the SWB largely impeded the upwelling of the mantle plume, whereas the slab beneath the ESB was disrupted by the plume and subsequently transported into the upper mantle. Furthermore, the SCS MORBs exhibit enriched Sr and Pb isotopes, indicating the incorporation of terrigenous sediment components in the upper mantle beneath the SCS. Continuous subduction preceding seafloor spreading has facilitated the substantial incorporation of subducted crustal materials into the upper mantle or as stagnant slabs within the MTZ of the SCS. The SCS underwent a rapid transition from continental rifting to seafloor spreading, enabling significant preservation of ROC in the upper mantle or as stagnant slabs in the MTZ. Therefore, mantle recycling in marginal sea basins exhibits distinct characteristics compared to that occurring in open oceans.

How to cite: Huang, X.-L., Yang, F., Cai, Y.-X., Xu, Y.-G., and Ge, Z.-M.: Compositional heterogeneity within the mantle beneath the South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5331, https://doi.org/10.5194/egusphere-egu24-5331, 2024.

International Ocean Discovery Program (IODP) Expeditions on the northern continental margin of the South China Sea (SCS) have nullified the early notion that the SCS is a magma-poor margin. However, there are continuing debates on how the rapid transition from continent to ocean is supported by geochemical and petrologic data, and whether such a process was related to plate subduction or mantle plume activities. Here we present the bulk-rock and plagioclase phenocryst geochemistry of basalts generated during the early spreading (initial and steady ocean) stage of SCS basin extension, which were drilled at IODP Sites U1500 and U1503, respectively. Combined with published data from the late spreading stage of the basin, the new measurements provide an excellent opportunity to examine the magmatic processes associated with the evolution of the SCS basin. Our results reveal that SCS basalts generally exhibit higher Al contents than global mid-ocean ridge basalts, particularly at lower MgO contents, similar to the characteristics of modern arc basalts. Nevertheless, their origins are site-specific and complex. Some U1503 basalts display strong subduction signals in terms of trace elements, and their correlations with Al2O3 content suggest that they are products of partial melting of the mantle wedge, closely related to the northward subduction of proto-SCS. This subduction had a significant effect on triggering the opening of the SCS, rather than by a mantle plume. Basalts from the other sites, including Site U1500, exhibit significant accumulation of plagioclase. Moreover, the An values of the plagioclase in Site U1500 basalts increase with the increase of host magma Al contents, indicating that the floatation mechanism cannot account for plagioclase accumulation. Therefore, we propose that the high abundance of plagioclase in Site U1500 basalts requires rapid ascent of magma, supporting a rapid rifting and strong magmatism during the initial opening of the SCS.

How to cite: Tian, L., Wang, W., Castillo, P. R., and Wu, T.: Petrogenesis of high-alumina basalts in South China Sea: Implications for magmatic processes associated with the opening of an oceanic basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6883, https://doi.org/10.5194/egusphere-egu24-6883, 2024.

From the Late Cretaceous to the Quaternary, the northeastern end of the Eurasian margin experienced a complicated tectono-magmatic history including the subduction of the Izanagi-Pacific ridge in the Eocene time, the opening of the Japan and Kuril basins and the associated trench migration in the Oligocene to Miocene time, the possible collision of the Eurasian plate and the North American (Okhotsk) plate around the Oligocene to Miocene time, and subduction zone magmatism in all periods.

In central Hokkaido (Japan), Eocene-Miocene plutonic bodies are distributed along the north-south orientated Hidaka Magmatic Zone (HMZ). We report new zircon U-Pb ages and geochemical data from plutonic rocks in the HMZ, which reveal Miocene compositionally bimodal magmatism; the felsic magmatism present is characterized by island-arc geochemical signatures. Trace element compositions of the Miocene mafic-intermediate plutonic rocks of the HMZ appear as a mixture between typical N-MORB and island-arc compositions. Trace element profiles from HMZ plutonic rocks are similar, albeit with less pronounced arc signatures, to the Miocene volcanic rocks formed along the Paleo-Japan Trench. Together, these data suggest the coexistence and mixing of N-MORB-type primitive magma, with the parental magmas of the HMZ mafic rocks, implying petrogenesis of a different nature than typical subduction zone magmatism.

The cause of the north-south orientation of the Miocene plutono-volcanic rocks from central Hokkaido to its northern extension into Russia (Sakhalin) is probably along some kind of tectonic/structural boundary. However, the inferred paleo-position of the HMZ is very close to the trench and far from the volcanic front at that time and the existence of N-MORB-type primitive magma cannot be explained by subduction magmatism. The newly proposed possible geodynamic setting in this study that can reasonably explain the distribution and geochemical signature of these rocks is the simultaneous opening of the Japan and Kuril basins at different rates. In the Japan Trench, the Pacific plate was subducted at a relatively shallow angle and the magmatic arc forcibly moved eastward due to the opening of the Japan Basin. In the Kuril Trench, the rollback corresponding to the steep subduction of the plate and the associated opening of the Kuril Trench occurred simultaneously in a short period of time. If the Paleo-Kuril Trench retreated rapidly relative to that of the Paleo-Japan Trench, a horizontal propagating tear that cuts the slab horizontally is estimated to have occurred at the bend of both trenches, together with a (vertical) slab tearing and blocky opening of the subducting oceanic plate on the Paleo-Japan Trench side. At the western margin of the Kuril Basin, the N-MORB magma and hot asthenosphere inflow induced remelting of the mantle already contaminated to various degrees at the subduction zone.

How to cite: Yamasaki, T., Schaen, A., Ibanez-Mejia, M., Schoene, B., and Maeda, J.: Bimodal Miocene magmatism at the northeastern end of the Eurasian margin in response to horizontal propagating tear of slabs due to the simultaneous opening of the Japan and Kuril basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6889, https://doi.org/10.5194/egusphere-egu24-6889, 2024.

EGU24-6931 | ECS | Orals | TS2.7

The Nature and the response characteristics of the Roo Rise to subduction zone in the eastern Indian Ocean 

Weimin Ran, Yintao Lu, Tao Jiang, Hong Liu, and Luning Shang

The Sunda arc convergent plate subduction tectonic system in Southeast Asia is one of the most active convergent plate boundary zones in the world. Early studies suggest that the Sunda arc subduction system is mainly characterized by subducted accretionary plate margin and typical accretionary prism forearc uplift landform. The latest research found that the Roo Rise, the most eastern section of the Christmas Island Seamount Province in the Wharton Basin of the eastern Indian Ocean, has reached the Java Trench region with plate movement. Compared with the “normal” oceanic crust subduction process in other regions of the Sunda arc, the Roo Rise “Uplift” structure triggered different subduction geological processes in the Sunda arc system. Combined with previous research results, the nature of Roo Rise are comprehensively summarized and understood, including the lithology and chronological origin, and the deep subduction structure characteristics of the “Rise-Trench” area. To further enhance the understanding of the early forearc subduction erosion process, including local accretionary prism front edge collision “concave”, differential uplift of forearc uplift, the compression and narrowing of the forearc basin. We discuss the response characteristics of the backarc basin to the new subduction tectonic framework of “Rise-Trench-Arc-Basin” by using two-dimensional multichannel seismic data interpretation for the first time. At present, a new stage of compressional tectonic movement is taking place in the backarc Kendeng-Madura strait basin. We believe that the characteristics of the shallow compressional anticline are the direct tectonic deformation response in the backarc basin under the new “vertical orthogonal fast and high angle” subduction structure framework formed by the Roo Rise.

How to cite: Ran, W., Lu, Y., Jiang, T., Liu, H., and Shang, L.: The Nature and the response characteristics of the Roo Rise to subduction zone in the eastern Indian Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6931, https://doi.org/10.5194/egusphere-egu24-6931, 2024.

Nansha Trough, located in the southern part of Nansha Block, is an important boundary of the southern continental margin of the South China Sea, which has undergone complex tectonic superposition process, and is an important area for studying the subduction extinction of the Proto-South China Sea and the current expansion of the South China Sea. In this study, we make use of a new multi-channel seismic profile, which is almost parallel to the distribution of Nansha Trough, to systematically identify and analyze the magmatic activity in Nansha Trough for the first time, and combine the geophysical data such as gravity and magnetism to determine the attributes of seamounts in the trough. We found that all the seamounts in the trough were formed by magmatism, and underwent multiple episodes of magmatism, some of the seamounts were deposited with huge thick carbonate layers on the top. The magmatic rock mass in the trough shows different gravity and magnetic anomaly characteristics on the east and west sides, which may be related to magmatic stage, magmatic source and magmatic differentiation. Unlike the widely developed post-rift magmatism in the northern passive margin of the South China Sea, most magmatic activities in the Nansha Trough seem to ceased around 16Ma, which may be related to the dehydration and melting caused by the subduction plate rotation in the Proto-South China Sea.

How to cite: Guo, C. and Tang, Y.: Magmatism in the Nansha Trough on the southern continental margin of the South China Sea: Recent evidence from seismic profiles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7401, https://doi.org/10.5194/egusphere-egu24-7401, 2024.

EGU24-7595 | ECS | Orals | TS2.7

Shallow tremors in the northern sulawesi subduction zone 

Chenghao Jiang, Jian Zhang, and Tianyao Hao

Tectonic tremors (TTs), composed of a swarm of low-frequency earthquakes (LFEs), constitute a type of slow earthquakes characterized by a lack of high-frequency energy. Previous studies have suggested that slow earthquakes, which usually occur near the megathrust earthquake rupture zones, are crucial for deepening our understanding of seismic activity. The Northern Sulawesi subduction zone (NSSZ) is situated at the convergence of the Eurasian, Australian, and Philippine Sea plates, experiencing frequent earthquakes that may trigger local tsunamis due to the complex tectonic setting. Until now, the lack of shallow observations has limited the understanding of the shallow tectonic structure beneath the NSSZ. We observe episodic shallow TTs using 8 Ocean Bottom Seismometers (OBS) deployed near the NSSZ, indicating the presence of stable sliding near the subduction boundary. Our research results reveal that the locations of shallow TTs align with the boundary of the weakly coupled plate interface where the relative Coulomb stress is weaker. Additionally, we discover that the sedimentary environment in the shallow subduction zone and the dehydration of serpentinite within the plates provide favorable conditions for high pore fluid pressure, thereby promoting the occurrence of shallow TTs. Furthermore, we try to establish a connection between deep earthquakes and shallow TTs, exploring the possibility of deep-seated stress propagating from the deep crust to the shallow seismic zone through faults or plate boundaries.

How to cite: Jiang, C., Zhang, J., and Hao, T.: Shallow tremors in the northern sulawesi subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7595, https://doi.org/10.5194/egusphere-egu24-7595, 2024.

Crustal thickness (H) and bulk Vp/Vs ratio (k) are widely used to understand crustal deformation and probe tectonic evolution of plates. In the study, 17 pairs of H and k are obtained based on the H-k stacking of receiver functions in the Java subduction zone, among which 14 pairs are corrected for sedimentary effect by applying a resonance removal procedure. The measured crustal thicknesses of Java Island range from 30.2 to 36.5 km, with an average of 32.5 km, and the crustal thicknesses of the Lesser Sunda Islands are strongly variable, ranging from 20.1 to 34.1 km. The crust thickness in the island arc is consistent with that of the extended crust, and the crust thickness of Java Island is on average thicker than that of the Lesser Sunda Islands. This characteristic is consistent with the current extension environment caused by trench retreat and crustal movement, and the stretching stress increases from west to east. The study area has extremely high Vp/Vs ratios, ranging from 1.80 in western Java, to an average of 2.0 in central and eastern Java, and up to 2.2 on average in the Lesser Sunda Islands. The Vp/Vs ratios increase from west to east, which we attribute to: (1) The history of block collision and volcanic activity of the Java subduction zone gradually decrease from west to east, resulting in relatively weak crustal magmatic activity in western Java; (2) The crust of the Lesser Sunda Islands is subjected to the stronger stretching stress, which makes it easier for the mantle material intrusion; (3) The significant variation of crustal thicknesses and widespread lateral crustal dips and faults of the Lesser Sunda Islands provide good vertical channels for the intrusion of basic mantle materials.

How to cite: Liu, Z., Kong, F., Yu, Y., and Li, J.: Crustal structure along the island arc of the Java subduction zone from receiver functions and its tectonic implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8227, https://doi.org/10.5194/egusphere-egu24-8227, 2024.

EGU24-11171 | ECS | Orals | TS2.7 | Highlight

Subduction of Seamounts and Ridges along the Java Margin, Indonesia: Impacts on Structural Geology and Seismic Activity 

Yueyang Xia, Heidrun Kopp, Dirk Klaeschen, Jacob Geersen, Bo Ma, and Michael Schnabel

The Java-Lesser Sunda margin exhibits different topography of subducting oceanic basement relief and diverse upper plate tectonic processes, ranging from neutral characteristics offshore Lombok and Sumbawa to erosional features offshore Central Java to Bali, distinct from its accretionary counterpart off Sumatra. Despite this classification, a comprehensive understanding of how the subduction of oceanic basement relief influences the plate boundary and upper plate structure across the transition from neutral to erosional remains elusive. In our investigation, we illuminate the tectonic parameters governing the margin's classification by integrating multi-channel reflection seismic images obtained through a grid-based P-wave velocity inversion and high-resolution multibeam bathymetric maps. Our dataset reveals the nuanced modifications to seafloor morphology, upper plate structure, and décollement position brought about by various scales of subducting topography. Large-scale subducting features prompt a landward shift of the deformation front, leading to a shortened accretionary wedge and heightened seafloor incline at the relief's trailing edge. Conversely, small-scale subducting ridges predominantly impact the frontal prism, causing over-steepening at the trench and localized slope failures. Deformation of the accretionary wedge ahead of subducting relief is characterized by intensified compression and reduced seafloor slope, seemingly independent of the relief's size. Ridge and seamount subduction induce frontal erosion and basal erosion offshore Lombok and Bali, respectively. Our P-wave velocity models reveal a notably lower rigidity of the upper plate's base along the eastern Sunda margin compared to the global trend. This lower rigidity is a crucial factor favoring the occurrence of tsunami earthquakes on the Java margin. In conclusion, our study provides a comprehensive analysis of the complex interplay between subducting oceanic relief and tectonic processes, shedding light on the factors that dictate the margin's transition from neutral to erosional characteristics and the associated seismic implications.

How to cite: Xia, Y., Kopp, H., Klaeschen, D., Geersen, J., Ma, B., and Schnabel, M.: Subduction of Seamounts and Ridges along the Java Margin, Indonesia: Impacts on Structural Geology and Seismic Activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11171, https://doi.org/10.5194/egusphere-egu24-11171, 2024.

EGU24-13639 | Orals | TS2.7

Cyclical continental extension reworks and destructs the cratonic lithosphere of South China 

Yang Chu, Tanjie Liu, Wei Lin, Faure Michel, Lingtong Meng, Wei Wei, Weibin Ji, and Zhenhua Xue

Continents with cratonic cores can resist deformation, and thus survive billions of years in the geological record. Tectono-thermal reworking is a key process in continental evolution because it alters composition and structure of some continents, weakens, and finally destructs or even dismembers them. Typical examples of reworked continents develop in subduction or collision settings, mostly situating in East Asia, Western North America, or the Tethyan collisional zones. 

In western Pacific, East Asian continental margins suffered extensive continental reworking and lost part of their continental lithosphere and developed a wide (>1000 km) extensional province. Across the South China Block, Mesozoic cyclical tectonics destructed a large portion of its cratonic lithosphere. Such strongly modified continent represents an ideal target to reveal the process and mechanism of continental reworking.

We analyzed and synthesized the structural evolution of extensional domes and illustrated the process of lithospheric thinning of Mesozoic South China before Cenozoic rifting of the large marginal seas. Structural and geochronology data of the extensional domes in the SCB indicate Cretaceous two-stage extension, a weaker extension during the early extension, and a faster and stronger extension in the later extension. Unlike the previous rapid, one-cycle delamination model occurred in the North China Craton, the destruction process of South China operates in a cyclical, progressive manner in which compression destabilized the edge of the cratonic lithosphere and the following extension destructs the unstable part to thin the lithosphere. This process, as an endmember of lithospheric destruction mechanisms, requires cyclical tectonics of the subduction zone and the overriding plate, which has been widely reported in the Cordilleras of the eastern Pacific margin. The progressive lithosphere destruction model may also explain how ancient cratons shrink by subduction-related tectonics.

How to cite: Chu, Y., Liu, T., Lin, W., Michel, F., Meng, L., Wei, W., Ji, W., and Xue, Z.: Cyclical continental extension reworks and destructs the cratonic lithosphere of South China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13639, https://doi.org/10.5194/egusphere-egu24-13639, 2024.

EGU24-13946 | ECS | Orals | TS2.7

The Geometry and Thermal Fault Models of Flores Thrust 

Harisma Andikagumi and Kyle Bradley

The 2018 Lombok earthquake demonstrated the hazard that the Flores Thrust possesses and highlighted our lack of knowledge on this crustal scale backarc thrust. The Flores Thrust extends from west to east, located at the backarc of the Lesser Sunda Islands, Indonesia. Here we construct the geometry model of the Flores Thrust by fitting the best surface on the relocated and filtered intraplate seismicity using simulated annealing and interpolating using the FastRBFTM algorithm. The thrust has a flat and a ramp component where the flat is generally constant, inclined ~5° southward, but limited between eastern Bali and western Sumbawa due to the sediment-filled North Bali-Lombok Basin. The ramp of the thrust is dipping southward with a 38° average dip, where the dip increases eastward from Bali (27°-37°) to Lombok (28°-38°), Sumbawa (30°-50°), and western Flores (40°-58°), but then shallower in central Flores (29°-39°). The segmented geometry of the Flores Thrust with varying dips from west to east might be related to the complex geological history and the heterogeneity of both the upper and lower plates in the Lesser Sunda region. Based on our analysis of the volcano distribution, the seismogenic zone of Flores Thrust is constrained by arc volcano distribution; bounded by volcanoes at the western tip (Raung, Ijen, and Baluran in Java) and the eastern tip (Lereboleng and Lewotobi in Flores) while the deeper part is terminated by the along-arc distribution of volcanoes or where the temperature exceeds the brittle-ductile transition zone (>450°C). The proximity between the Flores Thrust and the volcanism might also suggest its interplay during the thrust development. The presence of high-K backarc volcanoes, Tambora and Sangeang Api, to the north of the low-K basaltic-andesitic dominated volcanoes in Sumbawa (e.g., Sangenges and Sorumundi) suggest a possible northward arc migration, closer to the thrust, and a complex interaction between arc volcanism and thrust development. Therefore, the complexity of the Flores Thrust geometry and its interplay with the volcanism should be investigated further, to mitigate the greater effects of any geological hazards in the region.

How to cite: Andikagumi, H. and Bradley, K.: The Geometry and Thermal Fault Models of Flores Thrust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13946, https://doi.org/10.5194/egusphere-egu24-13946, 2024.

EGU24-14004 | Posters on site | TS2.7 | Highlight

Lithosphere structure beneath the Philippine Sea plate and adjacent regions caused by eastward mantle flow 

Cuilin Li, Jianke Fan, Dongdong Dong, and Xiaoyang Wu

The Philippine Sea Plate (PSP) is the largest trench-arc-basin system in the Western Pacific, which is completely surrounded by convergent boundaries and characterized by a complex evolution of back-arc systems and marginal basins involving lithospheric processes. The azimuthally anisotropy structure can be employed to reflect the deformation histories of the lithosphere mantle and help us to reveal the influencing factors of the marginal basins formation especially the West Philippine Basin (WPB). However, seismic anisotropic velocity structures have not been established reasonably due to lack of seismic stations in the interior of the PSP. In this study, high resolution 3-D shear-wave velocity structures and azimuthal anisotropy of the lithosphere mantle beneath the PSP are estimated using the continuous waveform data recording by broadband passive OBS stations and seismic stations surrounding the PSP. Strong and consistent N-S fast directions in the crust beneath the southern WPB are approximately perpendicular to the magnetic anomaly strips and subparallel to the seafloor spreading direction, which may be contributed to the remnant anisotropy accompanying with oceanic crust formation induced by the seafloor spreading. Whereas, relatively weak and inconsistent azimuthal anisotropy beneath the northern WPB might indicate that the oceanic crust was modified controlled by the subduction of the Pacific Plate. Prominent E-W fast direction in the lithosphere mantle beneath the northern WPB may be responsible for the eastward mantle flow triggered by the retreating of the Pacific plate along a stationary Marianas trench since the Miocene. While NE-SW fast direction beneath the southern WPB may correspond to the deformation filed controlled by the interactions both the eastward mantle flow and the collision between the Caroline Plate and PSP. Furthermore, anisotropy images reveal that lithosphere deformation and low-velocity zone in the asthenosphere beneath the marginal basins around the PSP including the Japan Sea and the South China Sea are controlled by the eastward mantle flow as a result of the retreat of the Pacific plate.

How to cite: Li, C., Fan, J., Dong, D., and Wu, X.: Lithosphere structure beneath the Philippine Sea plate and adjacent regions caused by eastward mantle flow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14004, https://doi.org/10.5194/egusphere-egu24-14004, 2024.

EGU24-14171 | ECS | Posters virtual | TS2.7

Teleseismic imaging results reveal Proto-South China Sea subduction remnants 

Shi Huiyan and Li Tonglin

The subduction and disappearance process of the Proto-South China Sea is closely related to the opening of the South China Sea. Studying its subduction process and dynamic mechanism helps to explore the Cenozoic evolution model of the South China Sea. We collected teleseismic travel time data from Southeast Asia over the past 20 years, preprocessed the original data through data filtering, picking first arrival , and crustal correction, and obtained a three-dimensional velocity model of Southeast Asia using the Fast Marching Teleseismic Tomography(FMTT) method. The velocity imaging results reveal the presence of high-velocity anomalies in the mantle and mantle transition zones beneath Borneo and the Philippines. It is worth noting that the distribution range of serpentinite and serpentinite belt discovered in this area is highly consistent with the range of high-velocity anomaly bodies. Therefore, it is highly likely that the high-velocity anomalous bodies discovered in this area are remnants of the Proto-South China Sea subduction plate in the mantle transition zone. The morphology of residual subduction plates indicates that the Proto-South China Sea was subducted and closed from south to north, which may have had a certain impact on the Cenozoic seafloor spreading of the South China Sea; The detailed distribution range of residual plates further delineates the location of the disappearance of the Proto-South China Sea.

How to cite: Huiyan, S. and Tonglin, L.: Teleseismic imaging results reveal Proto-South China Sea subduction remnants, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14171, https://doi.org/10.5194/egusphere-egu24-14171, 2024.

EGU24-14474 | Posters virtual | TS2.7

New insights on the structural configuration and evolution of the deepwater offshore margin of Sabah, Borneo 

Anne Domzig, Mei Lu Lee, Jyoti Shah Jaiswal, M Hisham Ismail, Lucy MacGregor, and Ahmad Shahir Saleh

Offshore Borneo in the South China Sea has a complicated structural setting resulting from complex regional geodynamics, marginal basins subductions and openings. Here we present a model for the tectonic evolution of the deepwater offshore Sabah region, North-West Borneo, based on recent observations on seismic and integration of multiphysics data in the Sabah trough (also called Nansha trough) and the Dangerous Grounds. In this work we look at the basin architecture, structural style, and evolution of the margin and well as discussing the nature of the crust in the study area.

The area of interest experienced rifting from Palaeocene-early Eocene to the Oligocene when the South China Sea starts opening. We look at the early configuration of the basin, the rifting style and fault systems involved in the rifting stages. At the end of the rifting there is evidence of volcanic activity across the margin, then starts a sag phase and the buildup of carbonate mounds on topographic highs. Subsidence continues in the Sabah trough during the Miocene, which causes carbonate mounds, which are at the edge of the trough, to be drowned and a more siliciclastic sedimentation takes the relay. A fold-and-thrust belt starts forming to the South-East and puts the trough in a position of foreland basin.

The reason and modalities for the presence of compressional structures West of Borneo are still debated and various tectonic models exist. Nonetheless, recent paleomagnetic studies have proposed that Borneo started to rotate anticlockwise since the late Eocene and this results in compressional features on the west margin of Borneo. We investigate the possible scenarios of crustal configurations associated with the structures visible on seismic. The integration of magnetotelluric (MT) data to seismic, gravity and magnetic data allows us to draw a new picture of this part of the margin, showing crustal thickness variations and nature, and the implications for the regional tectonics.

How to cite: Domzig, A., Lee, M. L., Shah Jaiswal, J., Ismail, M. H., MacGregor, L., and Saleh, A. S.: New insights on the structural configuration and evolution of the deepwater offshore margin of Sabah, Borneo, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14474, https://doi.org/10.5194/egusphere-egu24-14474, 2024.

EGU24-20275 | ECS | Posters virtual | TS2.7

Complex mantle flows caused by multiple subducting slabs: P-wave tilting-axis anisotropic tomography of the Molucca Sea subduction zone 

Tianmeng Yuan, Zewei Wang, Dapeng Zhao, Rui Gao, and Xiaofei Chen

The Molucca Sea subduction zone is famous for its active divergent double subducted slab and located on the north side of the ongoing Java and Banda subduction zones. The spatial closeness of the subduction zones would causes a complex mantle flow field. To clarify the mantle dynamics, in this study, we present a P-wave tilting-axis anisotropic tomography by inverting a large number of local and teleseismic travel-time data recorded at 254 seismic stations in eastern Southeast Asia. Our anisotropic tomographic result shows that the mantle structure of the western Molucca Sea subduction zone is probably affected by the remote controls of the Java and Banda subduction zones. The mantle convection in the big mantle wedge west of the Molucca Sea subduction zone is possibly influenced by the east-west mantle flow associated with the compression of the Indo-Australian slab, as well as the north-south mantle flow related to the rollback of the Indo-Australian slab. In contract,  the eastern Molucca Sea subduction zone is virtually unaffected by other subduction zones, probably due to the domination of its still ongoing subduction.

How to cite: Yuan, T., Wang, Z., Zhao, D., Gao, R., and Chen, X.: Complex mantle flows caused by multiple subducting slabs: P-wave tilting-axis anisotropic tomography of the Molucca Sea subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20275, https://doi.org/10.5194/egusphere-egu24-20275, 2024.

EGU24-2122 | ECS | Orals | GD5.1

Oxide gabbro: from detachment/transform faults to subduction. 

Thomas Gyomlai and Cecile Prigent

Along slow and ultra-slow spreading detachment and transform faults, a large abundance of oxide gabbro is documented and thought to represent the injection of a differentiated Fe-Ti-(V)-(P) saturated nelsonitic melt in gabbroic mushes. The oxide-rich gabbro carapace observed on detachment faults is interpreted as a deformation-assisted melt migration playing a critical role in rock weakening, strain localization, exhumation and evolution of core complexes. Fe-Ti-rich metagabbros are also often found in exhumed high-pressure low-temperature oceanic metamorphic units which allow to understand how they transform during subduction. The aim of this study is to constrain the composition and deformation of oxide gabbros from transform faults and to compare it to (1) oxide gabbros and processes at detachment faults and (2) subducted and exhumed oxide gabbros to characterize their variability and infer their chemical and rheological impacts on the subduction system.

This study focuses on samples collected in the Atlantic Ocean with the submersible Nautile along the northern and southern Vema transform valley walls during the Vemanaute campaign. The nelsonitic melt led to the crystallization of large amount (~10-60%) of V-rich ilmenite and titanomagnetite, F-rich amphibole, olivine and variable amount of apatite, which pervasively intrude the primary gabbro. Thermometric estimates on amphiboles suggest a crystallization at around 800-900°C. Some samples are mylonitic and textures suggest that deformation was coeval with melt infiltration and crystallization. Fe-Ti oxides do not show any internal deformation suggesting rock hardening following melt-rock reaction. Vema oxide gabbros are nonetheless impacted by subsequent hydrothermal alteration with the pseudomorphic replacement of pyroxene into Cl-rich amphibole (~500-700°C) and late alteration phases (e.g., clay).  

Oxide gabbros therefore play a similar role in weakening the oceanic lithosphere on both transform and detachment faults. However, apatite-rich oxide gabbros (with apatite content up to 50% of the melt products) found at the Vema transform fault are not described in detachment faults. Furthermore, melt-rock interactions produce amphibole and olivine in transform faults whereas pyroxene is formed at detachment faults. This indicates important differences on the composition of the nelsonitic melt, with potential differences on the melt source or degree of differentiation. In the case of transform faults, the presence of hydrated phases indicates a hydrated source.

In both cases, the nelsonitic melt intrusion induces a localized drastic change in the rheology and bulk composition of gabbros which will likely hold significant chemical and rheological implications during subduction, particularly along the subduction interface. This phenomenon can be further explored in exhumed ophiolite, such as in Syros, Greece, interpreted as a preserved coherent fragment of a discontinuous, slow-spreading oceanic domain. There, Fe-Ti-rich gabbros consist of blocks distributed in a serpentinite matrix. They play a major role as a calcium source and as a lithological discontinuity localizing fluid pathways which allow to pervasively metasomatize the serpentinite matrix (half of it) into a tremolite-chlorite-talc schist. Such diffuse transformation of a serpentinite unit is bond to impact the chemical and rheological behavior of the subduction interface.

How to cite: Gyomlai, T. and Prigent, C.: Oxide gabbro: from detachment/transform faults to subduction., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2122, https://doi.org/10.5194/egusphere-egu24-2122, 2024.

Rock types of basement determine the magnetic signature of hydrothermal fields. Low magnetization zone (LMZ) is commonly observed at the basalt-hosted hydrothermal fields due to the fluid-rock interaction destroying the magnetic minerals inside basalt. We here report a near-seafloor magnetic survey conducted by the Autonomous Underwater Vehicle (AUV) over a basalt-hosted hydrothermal field on the East Pacific Rise (EPR). Inversed magnetization and Reduced-To-the-Pole (RTP) magnetic anomaly both show negative reduced magnetic signature centered on the hydrothermal field, reflecting enhanced demagnetization alteration process. Meanwhile, we delineate the range of the LMZ and compare it with the previous high-resolution near-seafloor magnetic studies on the fast-spread EPR, slow-spread Mid-Atlantic Ridge, and ultra-slow-spread Southwest Indian Ridge and Mohns Ridge. The statistical result shows that the diameter of LMZ increases with the decreasing spreading rate, suggesting the stable tectonic environment and focused melt supply at slower spreading ridge favor the birth of larger hydrothermal field.

How to cite: Zhou, F., Tao, C., Wu, T., and Dyment, J.: A near-seafloor study reveal a smaller low magnetization zone of a basalt-hosted hydrothermal field at East Pacific Rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2899, https://doi.org/10.5194/egusphere-egu24-2899, 2024.

EGU24-4461 | ECS | Posters on site | GD5.1

Global variations in the dip geometry of oceanic transform faults 

Alexandre Janin, Mark D. Behn, and Xiaochuan Tian

Little is known about the geometry of oceanic transform faults.  Although their surface trace and curvature along kinematic small circles has been known since the advent of plate tectonics, their structure at depth remains poorly constrained. The classical assumption is that oceanic transform faults are vertical and delimited at depth by the 600°C isotherm. It is only recently that the deployment of local OBS arrays on major oceanic transform faults have allowed us to investigate their geometry at depth and the link with their seismicity.  Seismic moment tensors of teleseismic events also contain first order information about the geometry of oceanic transform faults, giving us access to the dip of the fault plane that has ruptured.  Abercrombie and Ekström (2001) investigated focal mechanisms along the Chain transform fault (TF) in the equatorial Atlantic Ocean, which indicated a consistent northward dip of the fault along its entire 300-km length.
In this study, we take advantage of the increasing data from global seismic catalogs and conduct a statistical exploration of the dip variations of strike-slip focal mechanisms along more than 80 oceanic transform faults.  Most of them are either vertical to subvertical, depending on the local variability of the data, or show no preferential dip towards a given side of the fault. Although the optimal dip for a strike-slip fault in a classical Andersonian stress state is vertical, we show here that the case of the Chain TF is not isolated and several other oceanic transform faults show a similar deviation to the vertical, including Owen TF in the Indian Ocean, Vema TF in the Atlantic Ocean, and Tharp TF along the Pacific-Antarctic ridge. The measured deviations to the vertical show a maximum at ~20° (dip 70°).   We discuss our observations within the tectonic setting and history of each of these plate boundaries, and speculate on the implications of this maximum dip for the mechanical properties and/or stress conditions in oceanic lithosphere. 

How to cite: Janin, A., Behn, M. D., and Tian, X.: Global variations in the dip geometry of oceanic transform faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4461, https://doi.org/10.5194/egusphere-egu24-4461, 2024.

EGU24-4970 | Posters on site | GD5.1

Extensional tectonics at ridge-transform intersections – constraints from micro-seismicity and bathymetric data 

Ingo Grevemeyer, Dietrich Lange, Lars Ruepke, Ingo Klauke, Anouk Bienest, Laura Gómez de la Peña, Yu Ren, Helene-Sophie Hilbert, Yuhan Li, Louisa Murray-Bergquist, Katharina Unger Moreno, Thor Hansteen, and Colin W. Devey

Fracture zones were recognized to be an integral part of the seabed long before plate tectonics was established. Later, plate tectonics linked fracture zones to oceanic transform faults, suggesting that they are the inactive and hence fossil trace of transforms. Yet, scientist have spent little time surveying them in much detail over the last three decades. Recent evidence (Grevemeyer, I., Rüpke, L.H., Morgan, J.P., Iyer, K, and Devey, C.W., 2021, Extensional tectonics and two-stage crustal accretion at oceanic transform faults, Nature, 591, 402–407, doi:10.1038/s41586-021-03278-9) suggests that the traditional concept of transform faults as being conservative (non-accretionary) plate boundary faults might be wrong. Instead, transform faults are always deeper than the associated fracture zones and numerical modelling results suggest that transform faults seem to suffer from extensional tectonics below their strike-slip surface fault zone. In 2021, we tested this hypothesis by collecting, in a pilot study, micro-seismicity data from the Oceanographer transform fault which offsets the Mid-Atlantic Ridge by 120-km south of the Azores near 35°N. Analysis of 10-days of seismicity data recorded at 26 ocean-bottom-seismometers and hydrophones showed 10-15 local earthquakes per day. Furthermore, a sparse network recorded micro-earthquakes for three months. Joint interpretation of the data shows that earthquakes away from the ridge-transform intersections cluster along the fault trace imaged in bathymetric data and focal mechanisms support strike-slip motion. However, at the ridge-transform intersections seismicity does not mimic a right-angular plate boundary; instead, seismicity occurs below the inside corner and focal mechanism indicate extensional tectonics. In addition, we put published micro-earthquake data from surveys conducted in the 1970 to 1980s from the Oceanographer, Kane and Vema transform fault in a new context by plotting them onto modern swath-bathymetric data. In concert, micro-seismicity supports features found in numerical simulations, revealing that transform faults have an extensional as well as a strike-slip component.

How to cite: Grevemeyer, I., Lange, D., Ruepke, L., Klauke, I., Bienest, A., Gómez de la Peña, L., Ren, Y., Hilbert, H.-S., Li, Y., Murray-Bergquist, L., Unger Moreno, K., Hansteen, T., and Devey, C. W.: Extensional tectonics at ridge-transform intersections – constraints from micro-seismicity and bathymetric data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4970, https://doi.org/10.5194/egusphere-egu24-4970, 2024.

EGU24-5134 | Posters on site | GD5.1

Role of lithosphere and mantle composition on tectonic and magmatic variability of oceanic accretion at slow spreading ridges 

Remisha Rajeevan, Marcia Maia, Mathieu Rospabé, Jean Arthur Olive, and Ewan Pelleter

The Mid-Atlantic Ridge (MAR) is a complex system comprising spreading centers, transform faults and associated volcanic features, and it is divided into distinctive accretionary segments by axial discontinuities (Sempere et al., 1990). Our focus is on two specific sections of the MAR recently surveyed during several cruises, the central MAR and the equatorial MAR. Our aim is to investigate the complex interplay between tectonics, volcanism and hydrothermal processes in the building of the axial lithosphere.

At present, our investigation focuses on the central Mid-Atlantic Ridge (24° N to 24°40’ N), surveyed by the HERMINE 1 & 2 cruises. This area is characterized by extensive faulting demonstrating a broad spectrum of lengths and thrust magnitudes. The fault lengths vary from tens of meters to several kilometers, while thrust ranges from a few meters to 1.2 kilometers. The volcanic characteristics in this area encompass narrow, axis-parallel ridges emplaced on the rift valley floor as well as a range of volcanic features, from minor cones to substantial volcanoes.

The rift valley comprises a sequence of intermittent deep basins featuring minor linear topographic elevations on the valley floor associated with recent volcanism, suggestive of recent dike emplacement. The terrain is notably uneven, particularly in the northern section, where talus accumulates adjacent to a large normal fault of 9.2 kilometers long with a vertical offset of 930 meters, located at the segment end, possibly a detachment fault. Volcanic summits are present near this fault, suggesting a potential failed detachment. The spreading axis exhibits a slight clockwise rotation at 24°30’ N. Samples collected during the HERMINE 1 and 2 cruises through dredging and dive methods include various rock types such as basalts, gabbros and serpentinized/mineralized peridotites. The presence of serpentinized/mineralized peridotites provides clues about hydrothermal circulation and exhuming mantle rocks to the seafloor.

By addressing a joint study of the bathymetry and the sample petrology, we will study the evolution of this portion of the ridge axis in connection with tectonic, magmatic, and hydrothermal processes.

How to cite: Rajeevan, R., Maia, M., Rospabé, M., Olive, J. A., and Pelleter, E.: Role of lithosphere and mantle composition on tectonic and magmatic variability of oceanic accretion at slow spreading ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5134, https://doi.org/10.5194/egusphere-egu24-5134, 2024.

EGU24-5337 | Orals | GD5.1

Seismic velocity structure of the 25 °S OCC north of the Rodriguez Triple Junction at the Central Indian Ridge extracted from ocean bottom seismometer 

Anke Dannowski, Martin Engels, Bettina Schramm, Michael Schnabel, Oscar Lucke, Udo Barckhausen, Ingo Heyde, Stefan Ladage, Rüdiger Lutz, Christian Filbrandt, Anna Jegen, and Ingo Grevemeyer

Three tectonic plates meet at the Rodriguez Triple Junction in the Central Indian Ocean. The plates are separated by the Central Indian Ridge (CIR), the South-East Indian Ridge (SEIR) and the South-West Indian ridge (SWIR), which all show highly different spreading behaviours. While the northernmost segment of the SEIR is magmatically robust, the eastern tip of the SWIR is highly amagmatic. The CIR appears to oscillate between opening mechanisms, associated either with magmatic or magma-starved spreading processes, which can be observed over a very confined stretch of crust. Even though the area has been studied thoroughly, using a variation of geophysical and geological methods in the past decades, seismic images of the region were missing. From November 2023 to January 2024, RV Sonne (SO301 - SCIROCCO) set out for a seismic reflection and refraction survey to fill this gap and to provide a database for a better understanding of the tectonic setting and evolution of the area. A special focus was put on studying the structure and extent of the Oceanic Core Complex (OCC) at 25 °S.

Here we present preliminary results of an east-west trending 150 km long profile crossing the OCC and the CIR. Along the profile, 33 ocean bottom seismometers were deployed with a spacing of 4-5 km that grew denser over the OCC. The shot spacing was between 50-110 m. Clear crustal refracted P- and S-phases were observed to offsets of up to 40 km in the shot sections and mantle reflections, as well as Pn-phases could be identified sporadically. First results of travel time tomographies, which were executed separately for P- and S-waves, and used for the calculation of a Vp/Vs-ratio section indicate a strongly variable crustal construction. Highly fractured areas seem to interchange with highly hydrated areas within short distances. Correlations of the new bathymetric data to the seismic images and the integration of the new gravimetric and magnetic data will sharpen the geophysical image and its tectonic interpretation along the profile.

How to cite: Dannowski, A., Engels, M., Schramm, B., Schnabel, M., Lucke, O., Barckhausen, U., Heyde, I., Ladage, S., Lutz, R., Filbrandt, C., Jegen, A., and Grevemeyer, I.: Seismic velocity structure of the 25 °S OCC north of the Rodriguez Triple Junction at the Central Indian Ridge extracted from ocean bottom seismometer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5337, https://doi.org/10.5194/egusphere-egu24-5337, 2024.

EGU24-6198 | ECS | Posters on site | GD5.1

The impact of brittle and ductile weakening mechanisms on strain localization and the stabilization of transform fault zones 

Sandrine Ritter, Attila Balázs, and Taras Gerya

Rheological weakening mechanisms play a crucial role in plate tectonics by locally dropping lithospheric strength and leading to the formation of new plate boundaries, including new subduction zones or transform boundaries. Despite the abundance and persistence of large-offset oceanic transform faults, understanding their formation, the role of their preceding continental rifting history and their preservation is less understood. Furthermore, the role of different rheological weakening mechanisms is still debated.

In this study, we aim to better understand the contribution of different rheological weakening mechanisms, including both brittle and ductile processes, to the development of rifts and transform fault zones. To achieve this, we are running a comprehensive series of high-resolution 3D petrological-thermomechanical models (i3ELVIS). These models include elasto-visco-plastic rheology with strain-rate induced weakening, partial mantle melting, oceanic crustal growth, thermal contraction and mantle grain size evolution. To investigate the influence of weakening processes, we compare model evolutions that include strain-induced and strain-rate induced plastic weakening parameters. A particular focus is made on the evolution of locally high plastic strain rate values during the evolution and stabilization of transform faults following rifting and during oceanic spreading. New insight from this study can then be applied on a natural example such as the Romanche Transform Fault Zone located in the equatorial Atlantic.

How to cite: Ritter, S., Balázs, A., and Gerya, T.: The impact of brittle and ductile weakening mechanisms on strain localization and the stabilization of transform fault zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6198, https://doi.org/10.5194/egusphere-egu24-6198, 2024.

EGU24-7463 | ECS | Posters on site | GD5.1

A comparative study of mineral-melt interactions at Kane Megamullion and Atlantis Massif: Identifying universal processes building the slow-spreading lithosphere 

Marine Boulanger, Marguerite Godard, Benoit Ildefonse, and Malissa Bakouche

The structure of the lithosphere and the associated magmatic systems found in different locations along slow-spreading ridges can vary dramatically, from melt-starved to magmatically robust segments. A growing number of studies suggest that the evolution of the magmatic crust being governed solely by fractional crystallization is too simplistic. Reactions between migrating melts and their surroundings play a key role during accretion, yet the full extent of their impact is still to be resolved. We present here the results of a petrological, microstructural, and in situ geochemical study of two drilled magmatic sequences from the Kane Megamullion and Atlantis Massif oceanic core complexes. Our results show that mineral-melt interactions generate locally strong textural and/or geochemical heterogeneity at the cm-scale, but their impact can also be reconstructed at the 100m-scale. We found evidence for assimilation at various degrees of primitive lithologies of potential mantle origin within gabbros (sensu lato) at both locations, in addition to typical melt-mush reactions previously described in other slow-spread magmatic systems. Numerical modeling shows the sameness of the reaction equations to be considered for both sequences. Yet, the regime of the reactions (ranges of assimilation over crystallization ratios) varies between Kane Megamullion and Atlantis Massif, variations which likely result from differences in melt fractions present during mineral-melt interactions. We infer, relying on our observations, available thermodynamic modeling, and previous studies, that the regime of the reactions is most likely controlled by the melt flux during the formation of the two sections.

How to cite: Boulanger, M., Godard, M., Ildefonse, B., and Bakouche, M.: A comparative study of mineral-melt interactions at Kane Megamullion and Atlantis Massif: Identifying universal processes building the slow-spreading lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7463, https://doi.org/10.5194/egusphere-egu24-7463, 2024.

EGU24-7543 | Orals | GD5.1 | Highlight

Magma-induced tectonics at the East Pacific Rise 9º50’N: Evidence from high-resolution characterization of seafloor and subseafloor  

Milena Marjanovic, Jie Chen, Javier Escartín, Ross Parnell-Turner, and Jyun-nai Wu

Mid-ocean ridges host the most extensive magmatic system on Earth, where ~60% of the lithosphere is formed. Fast spreading segments such as the East Pacific Rise (EPR) 9º50’N (full spreading rate >80 mm/yr) represent only ~20% of the global ridge network, but contribute ~50% of the total oceanic crustal accretion.  At these ridge segments, magma accumulates in on-axis, quasi-steady-state axial magmatic lenses (AML), typically found 1-2 km below the seafloor, 2 km wide on average, and <0.1 km thick. AMLs are highly three-dimensional in geometry, marked by alternating lineated ridges and troughs where dikes originate and connect with the seafloor through the systems of the faults and fissures (Marjanović et al., 2023). A couple of kilometers away from the ridge axis, the seafloor is dominated by abyssal hills, which are bounded by faults resulting from unbending, cooling, and extension of the lithosphere. Within the critical region between the axial summit trough (AST) and the first abyssal hill bounding faults, sparse mapping has shown that prominent faults can exist, but the mechanism for their origin and contribution to tectonic strain has remained elusive.

At the EPR 9º50’N, we combine meter-scale bathymetric mapping with the highest-resolution seismic imagery of an AML to date (horizontal resolution 25 x 25 m2) to reveal a remarkable vertical alignment between the AML and seafloor fault scarps. This genetic link we observe for four distinct cases. Each AML-fault pair is aligned asymmetrically with respect to the ridge axis and is associated with confirmed and possible records of hydrothermal venting observed in the results of recent seafloor and water column mapping (Wu et al., 2023). Along most of such faults’ scarps, the emplacement of magma through various eruption episodes is evident, helping build the crust outside the AST. Our observations at 9º48’N support a mechanism by which these asymmetric, tectonic-magmatic features originate from shallow magma injection sites. After initial magma injection, the surrounding crustal stresses are perturbed thus promoting further crack propagation aligned with the orientation of the underlying magma body. Finally, by joint analyses of faults exposed on the seafloor and seismically-imaged in the subsurface, we also show that their collective contribution to the overall tectonic component of seafloor spreading is less than 0.5%, with a close to negligible role of the lava-covered faults, much smaller than previously proposed.

Marjanović, M. et al., 2023, Insights into dike nucleation and eruption dynamics from high-resolution seismic imaging of magmatic system at the East Pacific Rise: Science advances, v. 9, p. eadi2698, doi:10.1126/sciadv.adi2698.

Wu, J.-N., Parnell-Turner, R., Fornari, D.J., Barreyre, T., and McDermott, J., 2023a, Oceanic heat transfer by diffuse and focused flow through off-axis vents at 9°50’N, East Pacific Rise, in AGU Fall Meeting Abstracts, v. 2023, p. V43B-0174.

How to cite: Marjanovic, M., Chen, J., Escartín, J., Parnell-Turner, R., and Wu, J.: Magma-induced tectonics at the East Pacific Rise 9º50’N: Evidence from high-resolution characterization of seafloor and subseafloor , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7543, https://doi.org/10.5194/egusphere-egu24-7543, 2024.

EGU24-7636 | ECS | Posters on site | GD5.1

Near vent seismicity at the Tour Eiffel vent site, Lucky Strike hydrothermal field, Mid-Atlantic Ridge 

Soumya Bohidar, Wayne Crawford, and Mathilde Cannat

Intense discharge of high temperature fluids through focused vents at black smoker hydrothermal fields creates local entrainment of cold seawater into the shallow sub-seafloor. This secondary hydrothermal circulation generates lower temperature diffuse vents that surround the black smokers, carry a large part of the total hydrothermal heat flux, and facilitate mineral precipitation in the substratum. Pontbriand and Sohn (2014) constrained this secondary circulation beneath the Trans-Atlantic Geotraverse (TAG), by characterizing shallow microearthquakes which were located by a small ~200 m aperture short-period Ocean Bottom Seismometer (OBS) network. These microearthquakes were proposed to have been triggered by reaction-driven cracking in response to anhydrite precipitation from heated seawater in the secondary circulation system.

To detect possible shallow microearthquakes associated with the secondary circulation at the Tour Eiffel (TE) vent site, a small-scale ~150 m aperture 4 hydrophones network was deployed in 2016 as part of the EMSO-Azores observatory. TE is the largest vent site of the Lucky Strike hydrothermal field. It has a massive ~15 m high sulfide edifice, bearing several black smokers and surrounded by diffuse flow areas. The total heat flux, including both discrete and diffuse venting, from the TE vent site is estimated to be at least 20 MW, with more than 95% of the heat coming from diffuse venting.

The first one year of data (September 2016 - September 2017) recorded by the hydrophone network includes shallow near vents events, whale songs and earthquakes originated outside the network. We therefore developed criteria based on waveform characteristics, number of phases, frequency spectra and synthetic waveform modelling to select only the shallow microearthquakes. We detected only 740 shallow microearthquakes, yielding a seismicity rate of only ~3 events/day and an average local magnitude of -2.48. The number of shallow events, and their magnitudes, are much smaller than those documented beneath the TAG hydrothermal mound (~ 243 events/day with average local magnitude = -0.95). The small number of shallow microearthquakes detected near TE over the one-year survey suggests that heating of entrained seawater and anhydrite precipitation are less prevalent than at TAG. This hypothesis is supported by time-series analysis of diffuse fluid samples, which mostly show no chemical evidence for anhydrite precipitation. It is also consistent with the TE vent site being smaller and having a lower estimated heat flux compared to the TAG mound (~1 GW).

How to cite: Bohidar, S., Crawford, W., and Cannat, M.: Near vent seismicity at the Tour Eiffel vent site, Lucky Strike hydrothermal field, Mid-Atlantic Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7636, https://doi.org/10.5194/egusphere-egu24-7636, 2024.

EGU24-7861 | Posters on site | GD5.1

Hydration of the Oceanic Lithosphere: Impact on Hydrothermal Fluid Chemistry and Seismicity. 

Leila Mezri, Thomas P. Ferrand, Alexander Diehl, Javier García-Pintado, Manon Bickert, and Marta Pérez-Gussinyé

Slow and ultraslow spread oceanic lithospheres consist of a mixture of magmatic rocks and mantle rocks with variable alteration degrees. However, the nature, extent and distribution of alteration mineral assemblages are not well constrained. Understanding this alteration pattern at ridges is key to determining the nature of hydrothermal fluids and the seismic structure of the oceanic lithosphere, with implications for seismogenesis at ridges, transform fault zones, and subduction zones. Here, we present 2D numerical models that aim to explore the nature of alteration mineral assemblages and the seismic structure of the oceanic lithosphere during ultraslow magma-poor spreading. For this, we couple thermodynamic calculations with a visco-elasto-plastic model. We simulate the formation of the oceanic lithosphere, ongoing faulting, magmatism, hydrothermal cooling and hydration reactions, starting from continental extension to oceanic spreading. We compare our results with the Gakkel Ridge and the magma-poor section of the Southwest Indian Ridge at 64°30’ East; as both present similarities in the magma production rate and mineral assemblages suggesting similar conditions of hydrothermal alteration [1-3]. Our model reproduces the observed seismic structure of this part of the oceanic lithosphere and its alteration mineral assemblages. Importantly, we show that the interaction between faulting, hydrothermal cooling and hydration reactions results in a complex compositional nature of the oceanic lithosphere. In particular, we find a correlation between the spatial distribution of seismicity peaks and changes in mineral stability fields at mid-ocean ridges. We discuss the impact of such a compositional complexity on hydrothermal vent chemistry and the seismogenic behavior of the oceanic lithosphere.

1- Patterson, S.N., et al., High temperature hydrothermal alteration and amphibole formation in Gakkel Ridge abyssal peridotites. Lithos, 2021. 392: p. 106107. 

2- Bickert, M., M. Cannat, and D. Brunelli, Hydrous fluids down to the semi-brittle root zone of detachment faults in nearly amagmatic ultra-slow spreading ridges. Lithos, 2023. 442: p. 107084.

3- Dessimoulie, L., et al., Major and trace elements exchanges during fluid-rock interaction at ultraslow-spreading oceanic lithosphere: Example of the South West Indian Ridge (SWIR). Lithos, 2020. 352: p. 105233.

 

How to cite: Mezri, L., Ferrand, T. P., Diehl, A., García-Pintado, J., Bickert, M., and Pérez-Gussinyé, M.: Hydration of the Oceanic Lithosphere: Impact on Hydrothermal Fluid Chemistry and Seismicity., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7861, https://doi.org/10.5194/egusphere-egu24-7861, 2024.

Emplacement of magmatic crust at mid-ocean ridges (MORs) is confined in a narrow neovolcanic zone on the seafloor, whereas geophysical observations suggest that mantle melting occurs over a broad region. How melt is transported horizontally towards the ridge axis, i.e. melt focusing, remains incompletely understood. Here we present numerical models, theoretical decomposition, and scaling analysis, to isolate melt focusing mechanisms, and focus in particular on ridge suction and on the permeability barrier. We show that shear deformation induced dynamic pressure leads to large decompaction pressure, which increases porosity, instead of generating ridge suction as previously expected. We further demonstrate that a permeability barrier resulting from cold lithosphere systematically leads to a horizontal compaction pressure gradient that focuses melt toward the ridge axis, which may explain widespread melt focusing at global MORs as well as the three-dimensional melt distribution at ultra-slow spreading centers.

How to cite: Lu, G., Huismans, R., and May, D.: On the causes of melt focusing at mid-ocean ridges: Ridge suction versus permeability barrier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7999, https://doi.org/10.5194/egusphere-egu24-7999, 2024.

After nearly 50 years of research on hydrothermal circulation, the global hydrothermal on-axis element turnover is still not well constrained. Existing estimates of hydrothermal element fluxes typically invoke a basalt-hosted black smoker archetype hydrothermal vent fluid that is imposed to be responsible for the global hydrothermal cooling of oceanic lithosphere. The diversity of hydrothermal vent fluid compositions, especially to be found at slow to ultra-slow spreading mid-ocean ridges (due to varying degrees of fluid rock interaction with peridotites), has not been properly addressed yet.

Here we present a study that for the first time considers the diversity of hydrothermal vent fluids by analyzing a global database of hydrothermal vent fluid compositions (MARHYS Database Version 3.0). We derive a proper weighting of these fluid types by analyzing strike lengths and substrate types of the mid-ocean ridge system and estimate the partitioning of these hydrothermal fluid types to improve quantification of hydrothermal element fluxes at mid-ocean ridges. We show that the element‑to‑energy flux ratio in peridotite-hosted (or peridotite-influenced) hydrothermal vent fluids is significantly different to the one in purely basalt-hosted fast spreading ridges. Consequently, for many compounds significantly higher (e.g. H2, CH4, Fe) or lower (e.g. H2S, CO2) element fluxes are found to be associated with hydrothermal cooling at slow- and ultra-slow spreading ridges. Our results show that, despite their lower power output (compared to fast spreading ridges), slow and ultra-slow spreading centers, with their serpentinization‑derived hydrothermal fluids, play a major role for the element transfer between the ocean crust and the ocean.

How to cite: Diehl, A. and Bach, W.: Revising hydrothermal element fluxes at mid-ocean ridges: The role of slow and ultra-slow spreading centers regarding the global hydrothermal element budget., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8149, https://doi.org/10.5194/egusphere-egu24-8149, 2024.

In the quest to deepen our understanding of mid-ocean ridge dynamics, this study presents coupled numerical simulations focused on the intricate processes of ridge formation and propagation leading to micro-plate creation, their rotation and the formation of transform faults. Our numerical approach to the problem is based on a 2.5D approximation with a fracturing brittle and a ductile viscous layer coupled to a temperature field. The growth of new oceanic material is modelled by the introduction of new hot particles in opening fractures and the plates cool by temperature diffusion. Thermo-mechanical coupling is induced by a reduction of breaking strength, elastic constants and viscosity of the solid as a function of temperature leading to weakening of material whereas a healing function that is reconnecting broken bonds leads to hardening. Initially we are inserting seeds for offset ridges so that overlaps and potential transform faults are predefined, however, we also observe the first self-developing transform faults in the system. The model is not as complex as some existing full 3D models, however it offers to study the complexity of the brittle processes and the growth of ridges in detail.

Central to our investigation is the comprehensive simulation of mid-ocean ridge systems under varying spreading rates and the creation of micro-plates versus stable transform faults as well as the comparison to natural settings. Fast spreading rates lead to hot ridges in nature and in the model, because hot material is added faster than the heat can diffuse, whereas slow ridges remain relatively cool. Higher temperature is thought to lead to faster healing in our model, which counteracts the weakening induced by higher temperature. We modelled the formation and evolution of microplates and transform faults, uncovering the critical role of healing and weakening rates in shaping these features. Faster healing leads to micro-plate formation whereas more weakening, especially the reduction of the breaking strength, induces stable transform faults. The interplay between ridges is very dynamic with a continuous process of microplate rotation versus micro-plate splitting, their integration in the mid-ocean ridge and their destruction when transform faults form. The important parameters in the simulations that prefer micro-plate formation are higher breaking strength, fast healing, low viscosity and larger lateral distance between opening ridges.

The integrated analysis from our numerical simulation enriches the existing understanding of mid-ocean ridge dynamics. It highlights the nuanced interplay between spreading rates, lithospheric stress, and thermo-mechanical coupling in shaping the oceanic crust. The findings from our study, particularly the spinning of microplates and the formation of transform faults, provide a new dimension to our comprehension of these geological features.

This research contributes significantly to marine geology, offering a framework for future explorations and a benchmark for comparison with natural ridge systems. The detailed insights gained from our simulation pave the way for more informed interpretations of mid-ocean ridge processes and underscore the potential of numerical modelling in advancing our knowledge of Earth's dynamic systems.

How to cite: Hafermaas, D. and Koehn, D.: Bridging Theory and Nature: Numerical Simulations to Understand Mid-Ocean Ridge Formation, Transform Faults and Microplates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10389, https://doi.org/10.5194/egusphere-egu24-10389, 2024.

EGU24-10653 | Orals | GD5.1

Mercury fluxes from hydrothermal venting at mid-ocean ridges constrained by measurements 

Lars-Eric Heimbürger-Boavida, Natalia Torres-Rodriguez, Jingjing Yuan, Sven Petersen, Aurélie Dufour, David Gonzalez-Santana, Valerie Chavagnac, Hélène Planquette, Milena Horvat, David Amouroux, Cecile Cathalot, Ewan Pelleter, Ruoyu Sun, Jeroen Sonke, and George Luther

The UNEP Minamata Convention on Mercury aims to reduce human exposure to toxic mercury through the reduction of anthropogenic emissions. We are primarily exposed via the consumption of fish that bioaccumulate mercury from the ocean. The current paradigm is that anthropogenic mercury emissions (present-day 3,100 tons per year) have increased the global oceanic mercury reservoir by 21%. This estimate is flawed because we do not know how much natural mercury resided in the ocean before anthropogenic emissions started. We are similarly unable to quantify how anthropogenic emissions have affected fish mercury levels. Hydrothermal venting is the only direct source of natural mercury to the ocean. Previous studies, based on vent fluid measurements alone, suggested that hydrothermal mercury inputs could range from 20 and 2,000 tons per year. We use observations of vent fluids, plume, sea water and rock cores from the Trans-Atlantic Geotraverse (TAG) hydrothermal vent at the Mid-Atlantic ridge aquired during three dedicated oceanographic cruises. The combined observations suggest that the majority (67–95%) of the mercury enriched in the vent fluids (4,966 ± 497 picomoles per litre) is diluted into sea water  to reach background seawater levels (0.80 picomoles per litre) and a small fraction is scavenged locally (2.6–10%). An extrapolation of our results suggests that the global hydrothermal mercury flux from mid ocean ridges is small (1.5 - 65 tons per year) compared to anthropogenic mercury missions. While this suggests that most of the mercury present in the ocean is of anthropogenic origin, it also gives hope that the strict implementation emission reductions in the framework of the Minamata Convention could effectively reduce fish mercury levels and human exposure.

Torres-Rodriguez, N., Yuan, J., Petersen, S., Dufour, A., González-Santana, D., Chavagnac, V., Planquette, H., Horvat, M., Amouroux, D., Cathalot, C., Pelleter, E., Sun, R., Sonke, J. E., Luther, G. W., and Heimbürger-Boavida, L.E.: Mercury fluxes from hydrothermal venting at mid-ocean ridges constrained by measurements, Nat. Geosci., 1–7, https://doi.org/10.1038/s41561-023-01341-w, 2023.

 

How to cite: Heimbürger-Boavida, L.-E., Torres-Rodriguez, N., Yuan, J., Petersen, S., Dufour, A., Gonzalez-Santana, D., Chavagnac, V., Planquette, H., Horvat, M., Amouroux, D., Cathalot, C., Pelleter, E., Sun, R., Sonke, J., and Luther, G.: Mercury fluxes from hydrothermal venting at mid-ocean ridges constrained by measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10653, https://doi.org/10.5194/egusphere-egu24-10653, 2024.

EGU24-11449 | ECS | Posters on site | GD5.1

A 3-D Seismic Tomographic Study of Spreading Structures and Smooth Seafloor Generated by Detachment Faulting – the Ultra-Slow Spreading Southwest Indian Ridge at 64˚30’E 

Adam Robinson, Louise Watremez, Sylvie Leroy, Timothy Minshull, Mathilde Cannat, and Ana Corbalán

At ultra-slow spreading ridges, with full spreading rates less than ~15-20 mm/yr, spreading is accommodated both by limited, highly spatially and temporally segmented magmatism, and by tectonic extension along large-scale oceanic detachment faults, which cut from the seafloor through into the upper mantle and exhume ultramafic material to the seafloor. Detachment faulting is highly asymmetric and alternates in polarity over time, producing a “flip-flopping” effect of subsequent detachment dips. The resulting seafloor in these regions displays a morphology termed “smooth seafloor” comprising elongate, broad ridges, which have peridotite/serpentinite lithologies distinct from the typical basalt-gabbro layered oceanic crustal structure. We refer to the outer layer, above the mantle, in this case as the “crustal section”.

We conducted tomographic travel-time inversion of a 3-D wide-angle seismic dataset acquired over a region of smooth seafloor around 64˚30’E along the Southwest Indian Ridge (SISMOSMOOTH; Cruise MD199), to produce a seismic velocity volume through the crustal section and into the uppermost mantle. The resulting velocities support a non-magmatic origin for the crustal section, up to 100% alteration of originally ultramafic compositions to serpentinite, and a near-constant thickness of ~3.4 km into a transitional Moho zone which overlies the unaltered mantle. Patterns of velocity anomalies are interpreted as changes in the degree of alteration with depth resulting from spatial and temporal variations in fluid-rock interaction, controlled by faulting and tectonic damage processes and progressive porosity infill. The detachment faults show limited along-axis extent and are not simple planar structures at depth, instead mirroring the shapes of the bathymetric ridges they exhume. The boundaries between smooth seafloor and adjacent more magmatic segments are not vertical at depth, suggesting that detachment processes extend laterally at depth beyond their mapped extent seen at the seafloor. Magmatic input is overall highly limited and dominantly takes the form of individual flows forming superficial veneers, but there is one region on the lower part of an exhumed detachment footwall where the magmatic section is up to ~1.5 km thick, which may reflect changes in larger-scale magma segmentation which could contribute to detachment abandonment.

How to cite: Robinson, A., Watremez, L., Leroy, S., Minshull, T., Cannat, M., and Corbalán, A.: A 3-D Seismic Tomographic Study of Spreading Structures and Smooth Seafloor Generated by Detachment Faulting – the Ultra-Slow Spreading Southwest Indian Ridge at 64˚30’E, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11449, https://doi.org/10.5194/egusphere-egu24-11449, 2024.

EGU24-11890 | ECS | Orals | GD5.1

Continental slivers in oceanic transform faults controlled by tectonic inheritance 

Attila Balázs, Taras Gerya, and Gabor Tari

The ocean floor shows variable morphological features, transtensional and transpressional structures, magmatic and amagmatic domains. Surprisingly, continental blocks separated from the continental margins from 100s or 1000s km distance have been occasionally reported, however, their origin remains debated.

We conducted 3D magmatic-thermo-mechanical numerical experiments with the code I3ELVIS to simulate the dynamics of continental rifting, continental proto-transform fault zones, and eventually the formation of persistent oceanic transform faults and their connection to mantle melting. Numerical modelling results allow to analyze the first order features of passive and transform margins and oceanic basins. Our models explain the evolution of continental blocks entrapped between oceanic spreading ridges bounded by strike-slip fault zones inherited from the preceding continental rifting stage. The formation of such continental slivers is controlled by the relative timing between the onset of oceanic spreading and strain localization along strike-slip fault zones. This is connected to the rheology of the plates and also linked to different thermal gradients, divergence velocities, melting conditions and surface processes. Furthermore, we discuss the formation of zero-offset V-shaped oceanic fracture zones and the along-ridge variation of oceanic crustal thicknesses. Our model results are compared with observational data from the Romanche transform of the Equatorial Atlantic, the East Greenland Ridge and Newfoundland Ridge in the northern Atlantic, the Zabargad Islands in the Red Sea and the Davie Fracture Zone.

How to cite: Balázs, A., Gerya, T., and Tari, G.: Continental slivers in oceanic transform faults controlled by tectonic inheritance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11890, https://doi.org/10.5194/egusphere-egu24-11890, 2024.

The 70-km long Lucky Strike segment at 37oN on the Mid-Atlantic Ridge is characterized by a well-defined median valley bounded by ridge-ward dipping faults and a volcano located at the segment centre. The central volcano is fed by an axial magma chamber at ~3 km depth below seafloor. Away from the axial valley, the seafloor morphology is dominated by fault-controlled abyssal hills. Several active hydrothermal vents have been observed on the summit of the Lucky Strike volcano, and the axial magma chamber has been suggested to be the source supplying heat. Seismic velocities of the subsurface provide constraints on porosity and thus permeability, as well as the distribution of hot or molten rock. Therefore, determining fine-scale velocity structure of crust formed on the Lucky Strike segment is critical for understanding the interactions between magmatic, tectonic and hydrothermal processes during crustal accretion.

We performed two-dimensional elastic full waveform inversion (FWI) to wide-angle ocean bottom seismometer (OBS) data to constrain the velocity of the crust beneath a profile along the entire Lucky Strike segment and another across the axis extending to ~50 km distance on both flanks. The seismic data were acquired during the SEISMOMAR survey in 2005. The OBS intervals vary between 4.5 and 14.0 km, with denser OBS deployed around the central volcano. Both profiles were shot multiple times, with shot spacings of 425 m and 150 m. Starting models for FWI were obtained from travel time tomography of the OBS dataset. The FWI results show a low velocity anomaly (LVA) beneath the Lucky Strike volcano at ~3 km depth below seafloor, just below the axial magma chamber reflector imaged in seismic reflection data. The LVA extends ~10 km along axis and ~4 km across axis and is ~0.7-1 km thick in depth. Taking the depth of 6.5 km/s velocity contour as the base of upper crust, the upper crust thickens along the axis from 2.2 km at segment centre to 3.5 km at the segment ends. In contrast, the crustal thickness reduces from ~8.3 km at the segment centre to 4.0-4.5 km at distal ends, assuming the 7.1 km/s velocity contour corresponds to the crustal base. This contrast is due to the significant reduction in lower crustal thickness towards the segment ends, where the upper-to-lower crustal thickness ratio increases from ~0.4 to >3.5 from segment centre to ends. These observations suggest the presence of focused magma supply to the segment centre along the Lucky Strike segment and that the igneous crust at the segment ends is formed primarily by magma eruption and/or diking. The upper crustal thickness has smaller variations in the across-axis direction to ~40 km distance, suggesting the current magmatic accretion mode could have been going for ~3.5 Myr. Beneath the central volcano, the crustal velocity is higher in the along axis direction above the LVA, suggesting seismic heterogeneity in the upper crust.

How to cite: Wang, Z., Minshull, T. A., and Singh, S. C.: Fine-scale crustal velocity structures along and across the Lucky Strike segment of Mid-Atlantic Ridge from full waveform inversion of wide-angle seismic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12161, https://doi.org/10.5194/egusphere-egu24-12161, 2024.

EGU24-12596 | Orals | GD5.1

Smokers under stress: new insights into the tectonic, magmatic and oceanic modulation of hydrothermal discharge at mid-ocean ridges 

Thibaut Barreyre, Lars Rüpke, Jean-Arthur Olive, Eoghan Reeves, Lars Ottemöller, Jill McDermott, Ross Parnell-Turner, and Daniel Fornari

Hydrothermal systems along mid-ocean ridges (MORs) are a crucial interface between Earth’s deep interior, the seafloor, and the overlying ocean. Although hydrothermal systems are typically thought of as steady-state flow environments, field-based observations indicate that flow rates and temperatures are highly variable over a wide range of spatial and temporal scales. These observations show that flow systems respond to sub-surface processes such as earthquakes, magmatic activity, dissolution/precipitation of fluid minerals, and tidal loading of the oceanic crust and sediments. This variability in subsurface phenomena associated with seafloor flow systems directly impacts both the transfer of heat and matter and therefore, productivity of associated hydrothermal ecosystems.

Moving beyond an empirical assessment, however, remains challenging because a complete theoretical framework relating tectonic and magmatic fluctuations to hydrothermal output is currently lacking. Understanding the relationship between tectonic- and magma-induced stress and strain transients, crustal permeability, and the thermo-chemical state of hydrothermal fluids before, during and after an earthquake and magmatic emplacement event is particularly crucial. To address this issue, we curated time series of vent temperatures at the Loki’s Castle and EPR 9°50'N hydrothermal systems, and analyzed them alongside microseismicity catalogs, intermittent sampling of vent fluid chemistry, and a large body of geological, geophysical and biological observations, including proxies for crustal permeability.

Results suggest that both short-term (sec to hours) and long-term (decadal) variability in hydrothermal venting is controlled by fluctuations in the permeability field of the underlying crust, which can itself be related to changes in the crustal stress regime. We capture co-seismic, dike-induced and inter-eruptions changes in the fluid flow records indicating tectonic and magmatic control on hydrothermal vent temperature and flow discharge. Using simple analytical models for hydrothermal discharge temperature, elastic stress changes, and permeability-stress relations, we argue that temperature fluctuations can result from changes in permeability caused by either passing seismic waves, magmatic reservoir inflation (/deflation), or intrusions. Our observations and models further imply that short- and long-term fluctuations in tectonic and magmatic activity can modulate hydrothermal output, with potential consequences for deep sea ecosystems. This methodology has the potential to track tectonic and magmatic induced deformation transients in the sub-seafloor from hydrothermal flow records. 

How to cite: Barreyre, T., Rüpke, L., Olive, J.-A., Reeves, E., Ottemöller, L., McDermott, J., Parnell-Turner, R., and Fornari, D.: Smokers under stress: new insights into the tectonic, magmatic and oceanic modulation of hydrothermal discharge at mid-ocean ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12596, https://doi.org/10.5194/egusphere-egu24-12596, 2024.

EGU24-13004 | ECS | Posters on site | GD5.1

Evolution history of the Knipovich-Mohns ridge intersection (Artic Ocean) during the last 20 Ma 

Eleonora Ficini, Cuffaro Marco, Ligi Marco, Miglio Edie, and Sanfilippo Alessio

Mid-ocean ridges (MORs) form as a result of upwelling and partial melting of the underlying mantle, leading to seafloor spreading and new lithosphere formation. They result from an interplay between different geological forces shaping ocean seafloors and offer insights into Earth's mantle convection and lithospheric evolution. Recent advances in numerical models contributed to describe oceanic rift processes, although complex geodynamic settings remain relatively unexplored.
Knipovich and Mohns ultraslow spreading ridges are located in the Arctic Ocean, separated from Kolbensey and Gakkel ridges by the Jan Mayen transform and Lena Trough. They do not present any evidence of transform fault along their entire length and are characterized by a high obliquity (~35°-50°) with respect to their spreading direction, constituting some of the most intriguing MORs worldwide. At their intersection, geophysical data revealed a focused mantle upwelling along a narrow, oblique, and strongly asymmetric zone, coinciding with uneven surface uplift. These asymmetrical features have been associated to i) the control on passive upwelling of slow and asymmetric motion of the North America and Eurasia plates, or ii) the results of a major spreading reorganization in the area. However, asymmetries are tipically observed in other geodynamic settings, such as for example subduction zones, where they have been related to the relative motion of lithospheric plates with respect to the asthenosphere. In this work we carried out 3D numerical models reproducing the geodynamic evolution of a ~800-km long segment of the Knipovich and Mohns ridges (extending from ~76°N to ~71°N), including their migration with respect to the asthenosphere. The model uses a visco-plastic rheology which approximate both the asthenospheric and the lithospheric mantle, providing information on the temperature and deformation patterns within the mantle. We also computed the degrees of melting beneath each area of the MOR segment. In agreement with previous geophysical and petrological data, our results suggest that mantle upwelling is focused in a narrow zone, where the MOR makes a sharp bend, providing the inferred asymmetric patterns. On this basis, we propose a mechanism which could have led to the asymmetrical features (e.g., topography, spreading rate, mantle temperature and composition, etc.) characterizing the Knipovich-Mohns segments area. 

How to cite: Ficini, E., Marco, C., Marco, L., Edie, M., and Alessio, S.: Evolution history of the Knipovich-Mohns ridge intersection (Artic Ocean) during the last 20 Ma, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13004, https://doi.org/10.5194/egusphere-egu24-13004, 2024.

EGU24-13609 | Orals | GD5.1 | Highlight

Geochemical insights into conditions of vent fluid origin and water-rock interaction over two eruptive cycles at 9° 50´N East Pacific Rise 

Jill M. McDermott, Connor C. Downing, Jada M. Siverand, Esmira Bibaj, Thibaut Barreyre, Daniel J. Fornari, Ross Parnell-Turner, Jeffrey S. Seewald, Eoghan P. Reeves, Drew D. Syverson, Dalton S. Hardisty, and Alysia D. Cox

Multidisciplinary studies at the 9°50’N East Pacific Rise (EPR) hydrothermal field span three decades and encompass two periods of volcanic activity in 1991-1992 and 2005-2006. Shifts in the pressure and temperature of hydrothermal circulation induced by the magmatic cycle drive changes in the composition of venting fluids. Previous geothermobarometric model approaches used quartz solubility and fluid Cl concentrations to estimate pressure and temperature conditions in the zone where hydrothermal fluids originate [1, 2]. A geothermometer based on dissolved Fe/Mn [3] now provides additional insight on fluid origin temperatures. Consequently, application of an updated geothermobarometric model is possible.

We estimate the pressure and temperature conditions of fluid formation at historic high temperature vents in the 9°50’N EPR area between 2018 and 2023 and compare them with time series data since 1991. These calculations focus on six vents that span 7 km north to south along the axial summit trough, including M, Bio9, P, V, L, and L-Hot8 vents.

Immediately following eruptions, fluid origin pressures are considerably shallower at Bio9, M, and P vents (25-27 MPa) than during periods of lower magmatic activity (30-35 MPa). Additionally, fluid origin temperatures at the same vents rise from 390-400 °C for 1-2 years after eruptions to 410-430 °C during the periods between eruptions. Despite repeated observation of a continuous warming trend in vent fluid exit temperatures in the years preceding eruptions, fluid origin temperatures are relatively stable at a given vent location over the same time periods. 

These results support previous assertions that the upflow zone may experience enhanced permeability immediately following an eruption, leading to seawater entrainment, and cooling prior to venting. These inferences are also supported by a significantly greater proportion of radiogenic, seawater-derived Sr isotope input to circulating fluids in the 1-2 years after eruptive events, followed by a shift toward less radiogenic, more basalt-derived Sr isotope signatures.  The vent fluids are presently circulating into the sheeted dikes and attaining maximum depths and temperatures similar to those previously observed leading up to the 2005/2006 eruption. The chemical behavior and formation conditions of these hydrothermal fluids will be tracked through 2025, with the goal to understand the hydrothermal response preceding the next magmatic event. 

[1] Von Damm (2004) AGU Mono; [2] Fornari et al. (2012) Oceanography; [3] Pester et al. (2011) Geochim. Cosmochim. Acta.

How to cite: McDermott, J. M., Downing, C. C., Siverand, J. M., Bibaj, E., Barreyre, T., Fornari, D. J., Parnell-Turner, R., Seewald, J. S., Reeves, E. P., Syverson, D. D., Hardisty, D. S., and Cox, A. D.: Geochemical insights into conditions of vent fluid origin and water-rock interaction over two eruptive cycles at 9° 50´N East Pacific Rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13609, https://doi.org/10.5194/egusphere-egu24-13609, 2024.

EGU24-14965 | ECS | Orals | GD5.1

Revealing mantle heterogeneity in a cold intra-transform spreading segment (7-8°N at Mid Atlantic Ridge) 

Camilla Sani, Alessio Sanfilippo, Sergey Skolotnev, Marco Ligi, Felix Genske, and Andreas Stracke

The Doldrums transform system (TS), located in the Equatorial Mid Atlantic Ridge (MAR) at 7-8°N, is a 110 km-wide multi-fault shear zone, with five active transform faults separated by four short intra-transform ridge segments (ITRs). The medial ITRs are substantially deeper than the peripheral rift segments, which indicate differences in the thermal conditions of the sub-ridge mantle. New chemical and radiogenic isotope data from on-axis lavas erupted across the entire transform domain reveal that the basalts from the shortest and deepest ITRs are enriched comparatively in alkalis (Na2O+K2O= 4.3 wt%; Na8 up to 3.7) and light rare earth elements (La/Sm)N = 0.86 -0.97), likely suggesting the presence of an extremely cold mantle region characterised by low degrees of partial melting. The enriched incompatible element compositions, however, are coupled with the lowest Sr and Pb isotopes in the Equatorial Atlantic magmatism (i.e., 87Sr/86Sr ~ 0.70237 and 206Pb/204Pb ~ 18) and relatively high Nd and Hf isotope ratios (143Nd/144Nd = 0.51315-0.51325; 177Hf/176Hf = 0.2832-0.28325), which indicates that incompatible element enriched components are less abundant in the mantle source of the central ITRs. Hence we infer that the mantle under the central ITRs has been melted at the MAR axis before being transported laterally into the central ITR domain during the formation of the Doldrums transform system. This mantle portion melted a second time, and to a low extent, during the opening of the cold ITR, revealing its depleted geochemical character. Therefore, MORB from intra-transform ridge segments provide a rare opportunity to constrain the isotopic composition of the depleted peridotitic mantle, a ubiquitous, but otherwise often concealed component of Earth’s mantle.

How to cite: Sani, C., Sanfilippo, A., Skolotnev, S., Ligi, M., Genske, F., and Stracke, A.: Revealing mantle heterogeneity in a cold intra-transform spreading segment (7-8°N at Mid Atlantic Ridge), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14965, https://doi.org/10.5194/egusphere-egu24-14965, 2024.

The Central Atlantic oceanic crust documents the evolution of seafloor spreading along the Central Mid-Atlantic Ridge. Previous works have identified marine magnetic anomalies (i.e., isochrons) every ~7 Myr for the pre-Neogene time, thus, the existing Nubia-North America plate kinematic models suffer from rather crude temporal resolution. Here, we present preliminary results from a detailed plate kinematic investigation aiming to reconstruct the kinematics of seafloor spreading at ~1.5 Myr time intervals. Our model is constrained by ~11000 identifications of 40 magnetic reversals younger than C34y (83.6 Ma) and older than C6no (19.7 Ma). We also investigated the fracture zones using multibeam bathymetry and satellite-derived gravity data. These identifications are confined by the Fifteen-Twenty fracture zone in the south and the Azores triple junction in the north. We invert these identifications and fracture zone crossings to estimate a set of finite rotation poles and stage rotations. We confirm the validity of our plate kinematic solutions by comparing a set of synthetic flowline tracks to the location of fracture zone traces. Based on these new poles, we present a detailed kinematic analysis that sheds new light on the evolution of the Central Atlantic since the Late Mesozoic.

 

How to cite: Granot, R. and Gaina, C.: High-resolution kinematic study of the Late Mesozoic to Late Cenozoic seafloor spreading at the Central Mid-Atlantic Ridge., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14978, https://doi.org/10.5194/egusphere-egu24-14978, 2024.

EGU24-15593 | Posters on site | GD5.1

Modes of detachment faulting at slow and ultraslow mid-oceanic ridges 

Antoine Demont, Mathilde Cannat, and Jean-Arthur Olive

Large-offset detachment faults are commonly observed at slow-spreading mid-ocean ridges (MORs), typically in areas with a moderate to low magma supply (e.g., 13º20'N on the Mid-Atlantic Ridge). Detachments are also found at nearly amagmatic sections of ultraslow MORs (e.g., 64ºE on the Southwest Indian Ridge), where the seismogenic lithosphere is unusually thick (> 15 km). There, detachments of opposing polarity form in sequence and cross-cut each other in a "flip-flop" regime. Prior studies have shown that marked strength contrasts, resulting from reduced cohesion and/or friction in fault zones, promote stable detachments. Here we present 2-D thermo-mechanical models based on geological observations to examine how strength contrasts between fault zones and the adjacent lithosphere impact the modes of faulting at an ultraslow and nearly amagmatic ridge axis.

We model the brittle lithosphere as a Mohr-Coulomb elasto-plastic material, where cohesion and friction diminish with increasing plastic strain. We explore a broad range of cohesion and friction contrasts between deformed and intact material. We also consider the influence of a strong, viscous lower lithosphere on the brittle deformation of the upper lithosphere by comparing simulations that use a dry olivine flow law with models where the brittle lithosphere sharply transitions into a low-viscosity asthenosphere. Fluid circulation in the shallow axial lithosphere is also considered, parameterizing both the cooling and the mechanical effect of hydrothermal circulation.

Our simulations produce three distinct regimes: (1) sequential development of horsts bound by two active antithetic faults, (2) formation of intersecting “flip-flopping” detachments, (3) runaway detachments. The latter case describes models in which a single detachment remains active. In nature, this endmember case is not observed, probably because it results in an excessive migration of the detachment toward its hanging wall. We show that these 3 regimes transition over a narrow range of cohesion and friction contrasts between deformed and intact material (the contrast in friction coefficient over which our simulations transition from regimes 1 to 3 is only 0.1- 0.2). Distributed footwall damage produces antithetic proto-faults, but their ability to mature as major seafloor-breaching faults depends on the degree of rheological weakening. A stronger lower lithosphere promotes such distributed faulting and modifies the onset of the persistent detachment regime to greater strength contrasts. The impact of hydrostatic fluid pressure on tectonic styles is relatively minor compared to fault weakening.

The results of these simulations are consistent with an analytical force balance model that compares the (localizing) loss of fault strength in the detachments to the (delocalizing) flexural force that develops in the surrounding lithosphere. Detachments persist when the magnitude of fault strength loss exceeds the maximum bending force. We find that runaway detachments require a total loss of integrated strength in excess of 1.5e12 N.m, equivalent in our models to a drop in friction coefficient by ~0.25–0.3 in fault zones. Thus, even a moderate frictional weakening, such as that allowed by the presence of lizardite in the fault zone (frictional strength of 0.45) enables large-offset (>15 km) faulting.

How to cite: Demont, A., Cannat, M., and Olive, J.-A.: Modes of detachment faulting at slow and ultraslow mid-oceanic ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15593, https://doi.org/10.5194/egusphere-egu24-15593, 2024.

Ultra-slow spreading ridges are unique in global ridges in its highly heterogeneous crustal thickness, numerous economically significant hydrothermal vents despite of extremely limited melt supply, and exposure of lower crust gabbro and mantle peridotite at seafloor particularly at amagmatic spreading segments. Although amagmatic accretionary segments are considered to be the key component of ultraslow-spreading ridges (Dick et al., 2003), how limited melt supply accommodates such a tectonically-dominated spreading system and heats the hydrothermal system remain unclear. And the key resides in the evolution of gabbro sills which preserves the history of frozen melt in the cold lithosphere and also provides the heat necessary for hydrothermal systems at such a condition. Therefore, for a better understanding of the lithosphere accretion history of amagmatic segments, we conduct systematic petrographic and geochemical analyses on a variety of samples collected from so far the best sampled and mapped amagmatic segment -- 53°E Southwest Indian Ridge, including abyssal peridotite, primitive to evolved cumulates (olivine-rich troctolite, gabbro, and oxide gabbro) and MORB.

We identify several unique chemical compositions of the minerals which was never reported in ocean ridges before, especially in the olivine-rich troctolite located to the south of rift valley within a massive exposure of peridotite up to ~3200 km2 (Zhou and Dick, 2013). 1. Unique NiO vs. Fo for olivine in the olivine-rich troctolite record the reaction between highly evolved magma (with Mg#~20) and dunitic mush. 2. Highly evolved trace element signatures with high Mg# for clinopyroxene and orthopyroxene in the gabbro vein cutting the troctolite confirm that the highly evolved magma intruding into the dunitic mush is felsic in composition. 3. The occurrence of oxide gabbro in the gabbro core complex (~380 km2) to the north of the rift valley indicates the presence of highly evolved gabbro sill in the north, which is most likely the parental magma of the evolved felsic melt invading the primitive troctolite in the south. 4. The occurrence of small volume of primitive troctolite with a crystallization temperature of ~1192°C in the massive peridotite in the south, and large volume of variably differentiated gabbro in the gabbro core complex with crystallization temperature as low as 998°C in the north reveal the unique cooling history of gabbro sills with different size in the newly-formed lithosphere in the amagmatic spreading segment.

The unique chemical compositions and 200°C variation in temperature suggests two juxtaposed gabbro sills in the lithosphere in amagmatic segments can vary greatly with different cooling and crystallization history. We propose that bigger gabbro sills in amagmatic spreading systems would more likely have a prolonged cooling history to crystallize more evolved lithologies, which would provide the necessary heat supply for potential hydrothermal systems. Future exploration on the occurrence of gabbro sills beneath hydrothermal systems is recommended to better understand how varied cooling history of individual gabbro sill control the formation and evolution of hydrothermal systems at ultraslow-spreading ridges.

References:

Dick, H. J. B., et al. (2003). Nature 426(6965): 405-412.

Zhou, H. Y. and H. J. B. Dick (2013). Nature 494(7436): 195-200.    

How to cite: Yang, A. Y., Huang, X., Zhao, S., and Zhao, T.: Unique chemical compositions of cumulates from 53°E Southwest Indian Ridge reveal distinct evolution and cooling history of gabbro sills in amagmatic accretionary segments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16093, https://doi.org/10.5194/egusphere-egu24-16093, 2024.

Mid-ocean ridge (MOR) systems form multi-layered mechanical structures, constituted by a solid elastic crustal layer and an underlying melt-rich mush complex (MC) in the mantle. This article presents a new integrated solid-fluid modelling approach to show the development of complexly heterogeneous stress field in MORs. The modelling is implemented in two steps: 1) simulation of multi-ordered 3D convective circulations, produced by decompression melting in the mushy region, subjected to random thermal perturbations, and 2) mechanical coupling of the sub-ridge mushy regions with the overlying elastic crustal layer within a mathematical framework of fluid-structure interaction (FSI) mechanics. Using an enthalpy-porosity-based fluid-formulation of uppermost mantle the model accounts for a one-way FSI interaction for transmission of viscous forces of the MC region to the overlying upper crust. It is demonstrated from the model runs that a MOR spontaneously develops strongly heterogeneous stress fields on a time scale of million years, characterized by their segmented patterns. The stress mapping reveals a distinct 30 km wide axial zone of ridge-normal tensile stresses ( < 250 MPa), flanked by ridge-parallel linear belts of ridge-normal compression (median < 100 MPa). The FSI model results suggest that ridge-parallel compression belts can develop in MORs without involving flexural bending of lithospheric plates. In addition, a MOR system produces narrow along-axis compressional zones transverse to the ridge axis, resulting in segmentation of the stress field on a wavelength of 40-150 km. These segmented stress fields conforms to the second-order magmatic segmentation patterns of MORs, as reported in the literature.

How to cite: Mandal, N., Sen, J., and Sarkar, S.: Calculations of the 3D stress fields in mid-ocean ridge systems: a fluid-structure interaction (FSI) modelling approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16143, https://doi.org/10.5194/egusphere-egu24-16143, 2024.

EGU24-17326 | Posters on site | GD5.1

Fault scarps and tectonic strain in young seafloor 

Mathilde Cannat, Jie Chen, and Javier Escartin

Fault scarps at Mid-Ocean Ridges (MOR) are well recognized on the seafloor and often measured to estimate the tectonic component of plate spreading. However, tectonic strain estimates based on the dimensions of fault scarps that can be traced on seafloor topographic maps (which we refer to as apparent tectonic strain) differ from the actual whole tectonic strain. This is clearly the case at relatively melt-poor slow-ultraslow ridge segment ends, where strain is accommodated by detachment faults that do not produce linear fault scarps at the seafloor. This contribution explores the relation between actual and apparent tectonic strain in magma robust MOR regions (at fast, intermediate spreading ridges, and in the magmatically robust segment centers of slow-ultraslow ridges). We use high-resolution (1-2 m) bathymetry data at 8 MOR sites, which span a broad range of spreading rates (14-110 km/Ma) and melt fluxes. To the first degree, apparent tectonic strain is highest at slow spreading ridges, which have the lowest melt fluxes, and decreases as melt flux increases (fast spreading ridges). We examine how faults nucleate and evolve on the young axial seafloor, while establishing the relationships to volcanism. Apparent tectonic strain derived from the dimensions of fault scarps on the young seafloor is reduced due to lava flows that cover pre-existing faults. Apparent tectonic strain also includes a component of strain that is not related to far-field tectonic stresses but to stalled dike intrusions that induce extensional faults in the shallow crust. This mechanism is probably responsible for the high apparent tectonic strain estimated at domal volcanos found at the center of intermediate-slow-ultraslow ridge segments. Apparent tectonic strain at and near MOR thus poorly reflects the real tectonic component of plate divergence, instead relating to the interplay between tectonic and magmatic processes over different time scales.

How to cite: Cannat, M., Chen, J., and Escartin, J.: Fault scarps and tectonic strain in young seafloor, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17326, https://doi.org/10.5194/egusphere-egu24-17326, 2024.

EGU24-17466 | Posters on site | GD5.1

Hydrothermal processes at the Pompeii hydrothermal field: insights from the association of a large sulfide deposit and talc-rich hydrothermal mounds (Mid-Atlantic Ridge)  

Ewan-Loiz Pelleter, Cecile Cathalot, Mathieu Rospabe, Thomas Giunta, Stephanie Dupre, Marcia Maia, Audrey Boissier, Sandrine Cheron, Mickaël Rovere, Yoan Germain, Vivier Guyader, and Jean-Pierre Donval

The Pompeii hydrothermal field was discovered in July 2022 during the HERMINE2 cruise [1]. It is located on an inside corner high (21°20 N) at the northern end of a “doomed” ridge segment [2] located just south of the TAMMAR propagating rift. The inside corner high is a domal bathymetric high with gentle slope ridgewards and spreading-parallel lineations (corrugations) characteristic of an oceanic core complex (OCC). The OCC is dissected by several faults including a ridge-perpedicular fault and a series of smaller ridge-parallel faults.

The main Pompeii hydrothermal site is located on the corrugated surface atop a spreading-perpendicular rubble ridge. The mound is about 150 m in diameter and 30-40 m high and mainly composed of sulfide-bearing rocks partly covered by Fe-Mn hydrothermal crusts. Sulfide-bearing mineralization mainly consist of quartz and pyrite and are characterized by low copper and zinc concentrations (i.e. <0.1 wt.%). At least three smaller satellite mounds (< 40m in diameter) located north, south and west of the main site are composed of silica-rich slabs and/or talc-rich mineralizations. Talc-dominated mineralizations are composed of talc with variable amount of microcistalline silica and rare fully-oxidized sulfides. Mineralogy and chemistry of the talc-rich mineralization is similar to that described for the deep active Van Damm hydrothermal field [3]. The main hydrothermal still exhibit a very weak hydrothermal activity (up to 4.25 °C) with H2 concentrations ranging from 45 to 90 nmol/L indicating interaction with a gabbro-peridotite basement. While sulfide-rich mineralization suggest high-temperature interaction in the reaction zone, talc-rich hydrohtermal deposits point out moderate-temperature interaction with mafic/ultramafic rocks [3]. The tight spatial association between these two different types of deposits (i.e. talc-rich and sulfide-bearing deposits) within the Pompeii hydrothermal field raises the question of the evolution and dynamics of hydrothermal circulation over time in an OCC setting.

 

[1] Pelleter and Cathalot (2022),

https://doi.org/10.17600/18001851

[2] Dannowski et al., (2018) J. Geophys. Res. 123, 941-956

[3] Hodgkinson et al. (2015) Nat. Commun 6:10150

doi: 10.1038/ncomms10150 .

How to cite: Pelleter, E.-L., Cathalot, C., Rospabe, M., Giunta, T., Dupre, S., Maia, M., Boissier, A., Cheron, S., Rovere, M., Germain, Y., Guyader, V., and Donval, J.-P.: Hydrothermal processes at the Pompeii hydrothermal field: insights from the association of a large sulfide deposit and talc-rich hydrothermal mounds (Mid-Atlantic Ridge) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17466, https://doi.org/10.5194/egusphere-egu24-17466, 2024.

EGU24-17664 | ECS | Posters on site | GD5.1

More magmatic versus less magmatic oceanic detachment fault zone anatomy 

Souradeep Mahato and Mathilde Cannat

Oceanic detachment faults (ODFs) are critical drivers of plate separation in slow-to-ultraslow spreading mid-ocean ridges (MORs). Numerous previous studies have shown that the anatomy of ODFs varies significantly between more magmatic and nearly amagmatic ridges sections. More magmatic ODFs are typically dome-shaped, corrugated, and face volcanic seafloor on the hanging wall side, while the footwall exhumes upper crustal and mantle-derived rocks, including gabbro, serpentinized peridotite, basaltic breccia, and diabase. In contrast, nearly amagmatic ODFs (e.g., at 64°E Southwest Indian Ridge SWIR) are characterized by long (up to ~95 km) broad and smooth ridges with no visible corrugations in the shipboard bathymetry. These ODFs form in alternate polarity and exhume serpentinized peridotite to the seafloor on both plates. Here, we present the anatomy of the exposed fault zone in the footwall of D1, a young active ODF in the nearly amagmatic 64°35'E region of the SWIR, utilizing shipboard bathymetry, micro-bathymetry, and ROV dive observations to document their footwall geology, deformation patterns, and along-strike variations.

The axial valley wall in the study area corresponds to the footwall of D1, and high-resolution bathymetry shows that it exposes two distinct domains. The western domain displays corrugations similar to those documented in more magmatic, domal ODFs, while the eastern domain is smooth. The western, corrugated domain also displays small offset ESE-trending antithetic normal faults and several hecto-to-kilometers-wide NNE-trending ridges, interpreted as mega-corrugations that formed due to hecto-to-kilometer-scale phacoids between linked fault splays in the detachment damage zone. These ridges and the antithetic minor faults are absent in the smooth eastern domain. Outcrop scale ROV dive observations show one significant difference in the geology of the exposed fault zone between the two domains: in the east, the fault zone comprises up to 10 m-thick intervals of serpentine microbreccia and chrysotile gouge, while in the west, these highly deformed horizons are a few decimeter-thick at the most, surrounding phacoids of less deformed serpentinites and therefore less pervasive at the outcrop scale. These observations suggest a stronger fault and footwall in the corrugated region. Microstructural observations also suggest that hydrous fluids facilitated the formation of the gouges and that non-brittle mechanisms (serpentine dissolution and precipitation) were involved.

Compared with more magmatic, domal corrugated ODFs, the smooth eastern part of our study area exposes thicker and more pervasive intervals of cataclastic microbreccia and gouge. In contrast, previous work on domal ODFs shows that strongly deformed intervals there consist mostly of talc±tremolite±chlorite±serpentine schist. Experimental studies suggest that the frictional strength of talc and chrysotile gouge at the sample scale are comparable. However, the gouge outcrops in the eastern part of the D1 footwall are thick and promote the formation of a planar (smooth) exposed fault surface. By contrast, highly deformed talc-bearing schists at domal ODFs are found around meter to decameter-scale phacoids of less deformed rocks, which are probably the cause of the observed corrugations.

How to cite: Mahato, S. and Cannat, M.: More magmatic versus less magmatic oceanic detachment fault zone anatomy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17664, https://doi.org/10.5194/egusphere-egu24-17664, 2024.

EGU24-20491 | ECS | Posters on site | GD5.1

Modeling the Evolution of Transform Faults: Influence of Mid-Ocean Ridge Spreading Dynamics 

Yinuo Zhang, Lars Ruepke, Fan Zhang, Sibiao Liu, and Ingo Grevemeyer

The role of transform faults, significant plate boundaries located on the seafloor, in influencing and modifying the spreading processes of adjacent mid-ocean ridges has long been a subject of investigation. However, the reciprocal impact of spreading rate and magma supply on the development and demarcation of transform faults has not been fully addressed. Observations from the Atlantic further suggest that long offset transform faults tend to remain stable upon variations in magma supply at the adjacent ridge segments, while shorter transforms are frequently abandoned during axis reorganizations by e.g. propagating ridges. In this study, we developed a three-dimensional model to examine the response of transform faults to variations in magma supply at the adjacent ridges.  In a suite of model runs, we change offset, transform fault rheology, and magma supply to evaluate if shorter transforms are more likely to be abandoned or replaced by non-transform offsets than longer transforms. We confront our modeling insights with observations from the North Atlantic, particularly between latitudes 30°N and 35°N, where the Atlantis, Hayes, and Oceanographer transforms appear to have been stable on long time scales, while the shorter segmentations in between have experienced multiple reorganizations.

 

How to cite: Zhang, Y., Ruepke, L., Zhang, F., Liu, S., and Grevemeyer, I.: Modeling the Evolution of Transform Faults: Influence of Mid-Ocean Ridge Spreading Dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20491, https://doi.org/10.5194/egusphere-egu24-20491, 2024.

EGU24-20662 | ECS | Orals | GD5.1

2-D Oceanic Core Complex Structure at the Semenov hydrothermal field on the Mid-Atlantic Ridge from New Wide-Angle Seismic Data 

Szu-Ying Lai, Gaye Bayrakci, Bramley Murton, Tim Minshull, Emma Gregory, and Isobel Yeo

We presented results from a new seismic refraction experiment at the Semenov hydrothermal area at 13°30’ N on the western flank of Mid-Atlantic Ridge. The survey was carried out on Cruise JC254 on RRS James Cook in November 2023. Semenov is a typical ultramafic-hosted field consisting of five active and extinct hydrothermal sites (Semenov-1 to 5) associated with massive sulphide mounds (SMS), hosted on a 20-km-long oceanic core complex (OCC). The OCC offers an exceptional opportunity to observe deep-seated ultramafic rocks exposed on the seafloor by detachment faulting. Semenov field is an ideal location to investigate the link between OCC-related detachment and SMS deposit formation. Here, we aim to determine the Semenov OCC crustal structure, geometry, and extent of subseafloor SMS mineralisation.

Our seismic refraction survey revealed a detailed 2-D P-wave velocity structure beneath Semenov. We target the Semenov-3 and Semenov-4 hydrothermal sites sitting at either side of the seabed termination of the detachment fault. We focused on profiles crossing the OCC in E-W and N-S directions, shot with two GI guns (250G and 105I cubic inch) every 30 m. The data were recorded by a network of 18 ocean bottom nodes (OBX) at 0.4 to 1 km spacing, showing clear first-arrival refractions from beneath the OCC and the hanging wall. We expect to define the seismic structure down to 2 km beneath the seabed. The derived velocity model could give information to the lithology beneath the Semenov OCC-related detachment and possibly driving source for the hydrothermal circulation. Lastly, we compare our result with another detachment-related hydrothermal system at TAG, where the OCC is thought to be at the initial stage and the hydrothermal system is basalt-hosted.

How to cite: Lai, S.-Y., Bayrakci, G., Murton, B., Minshull, T., Gregory, E., and Yeo, I.: 2-D Oceanic Core Complex Structure at the Semenov hydrothermal field on the Mid-Atlantic Ridge from New Wide-Angle Seismic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20662, https://doi.org/10.5194/egusphere-egu24-20662, 2024.

EGU24-21861 | ECS | Posters on site | GD5.1

Local seismicity surrounding the Atobá Ridge in the slow-slipping St. Paul transform system, equatorial Atlantic 

Guilherme Weber Sampaio de Melo, Marcia Maia, Simone Cesca, Ingo Grevemeyer, and Aderson do Nascimento

The equatorial Atlantic transform faults are among the largest and most complex in the world’s oceans. Among them, the St. Paul Transform System (SPTS) is a large multi-faulted system formed by four slow-slipping transform faults (Transforms A, B, C, and D), accumulating ∼630 km of axial offset (Maia et al., 2016). Transform A is the northernmost fault which contains the Atoba Ridge Zone (ARZ), a large transpressive ridge formed at a large stepover (Maia et al., 2016). St. Peter and St. Paul (SPSP) islets sit at the ARZ summit, where is installed a single broadband seismograph (ASPSP) recording local seismicity since 2011 (de Melo and do Nascimento., 2018). Here, we produce a new catalog of the local seismicity recorded around the ARZ between 2011 and 2016. For the epicenter location, we process an initial picking of the P and S waves referent to 359 earthquakes identified manually using SEISAN package applying a 2-12 Hz band-pass filter. Next, we follow a single station approach to locate the epicenters. We estimate the source-receiver distance based on the differential S-P time and the back azimuth from the polarization of P wave recordings, whenever this shows a high rectilinearity coefficient (Montalbetti and Kanasewich., 1970; Cesca et al., 2022). A total of 245 earthquakes were cataloged again using the new improved location process. 54 earthquakes were also identified also by EquatorialAtlanic hydroacoustic catalog (Parnell-Turner et al., 2022) and 12 by the International Seismological Centre. Our results reveal that a large part (174 earthquakes) of the local seismicity is clustered on the west flank of the ARZ, located from 2.18 to 22.58 km southwest of the SPSP islets. Rocks sampled along the ARZ are peridotite mylonites exhumed during the transpressional push-up tectonism of the ARZ. Other minor events are located on the east flank of the ARZ where sample deformation shows strong control of seawater fluid percolation (Bickert et al., 2023), enabling weakening of the rheology and possibly contributing to maintain an aseismic behavior on the faults.

 

Bickert, M., Kaczmarek, M. A., Brunelli, D., Maia, M., Campos, T. F., & Sichel, S. E. (2023). Fluid-assisted grain size reduction leads to strain localization in oceanic transform faults. Nature Communications14(1), 4087.

Cesca, S., Sugan, M., Rudzinski, Ł., Vajedian, S., Niemz, P., Plank, S., ... & Dahm, T. (2022). Massive earthquake swarm driven by magmatic intrusion at the Bransfield Strait, Antarctica. Communications Earth & Environment3(1), 89.

de Melo, G. W., & Do Nascimento, A. F. (2018). Earthquake magnitude relationships for the Saint Peter and Saint Paul archipelago, equatorial atlantic. Pure and Applied Geophysics175, 741-756.

Maia, M., Sichel, S., Briais, A., Brunelli, D., Ligi, M., Ferreira, N., ... & Oliveira, P. (2016). Extreme mantle uplift and exhumation along a transpressive transform fault. Nature Geoscience9(8), 619-623.

Montalbetti, J. F., & Kanasewich, E. R. (1970). Enhancement of teleseismic body phases with a polarization filter. Geophysical Journal International21(2), 119-129.

Parnell‐Turner, R., Smith, D. K., & Dziak, R. P. (2022). Hydroacoustic monitoring of seafloor spreading and transform faulting in the equatorial Atlantic Ocean. Journal of Geophysical Research: Solid Earth127(7), e2022JB024008.

How to cite: Sampaio de Melo, G. W., Maia, M., Cesca, S., Grevemeyer, I., and do Nascimento, A.: Local seismicity surrounding the Atobá Ridge in the slow-slipping St. Paul transform system, equatorial Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21861, https://doi.org/10.5194/egusphere-egu24-21861, 2024.

EGU24-22120 | Orals | GD5.1

Abiotic synthesis of volatile and condensed organic compounds in the deep oceanic lithosphere  

Muriel Andreani, Clément Herviou, Gilles Montagnac, Clémentine Fellah, Bénédicte Ménez, Céline Pisapia, Marvin Lilley, and Gretchen Früh-Green

In nature, very few organic compounds are recognized as abiotic. Abiotic methane (CH4) is the most abundant, and can be accompanied by short-chain hydrocarbons (ethane, propane) or organic acids (formate, acetate) in fluidsoccurring in molecular hydrogen (H2)-enriched hydrothermal systems where olivine-bearing rocks are altered via serpentinization reactions, such as along slow and ultra-slow spreading ridges. In addition to those volatiles and dissolved organic species, studies of oceanic serpentinites have highlighted low temperature (T), abiotic formation of organic compounds such as amino acids or various carbonaceous compounds within the rock substrate. This suggests the availability of more diverse abiotic organic reactants than previously expected on Earth, notably in the subseafloor, and questions the reaction paths at their origin.

Here we present an rocky road to abiotic organic synthesis and diversification in hydrothermal environments, which involves magmatic degassing and water-consuming mineral reactions occurring in olivine fluid inclusions. This combination gathers key gases (N2, H2, CH4, CH3SH) and various polyaromatic materials associated with nanodiamonds and mineral products of olivine hydration (serpentinization). This endogenous assemblage results from re-speciation and drying of cooling C-O-S-H-N fluids entrapped below 600°C-2kbars in rocks forming the present-day oceanic lithosphere. Samples have been drilled at the Atlantis Massif (30°N Mid-Atlantic Ridge) during IODP Expeditions 304-305, five km to the north of Lost City hydrothermal field where the discharge of abiotic H2, CH4 and formate have been observed in fluids. Fluid inclusions served as a closed microreactor in which serpentinization dries out the system toward macromolecular carbon condensation, while olivine pods keep ingredients trapped until they are remobilized for further reactions at shallower levels. Results greatly extend our understanding of the forms of abiotic organic carbon available in hydrothermal environments and open new pathways for organic synthesis encompassing the role of minerals and drying. Such processes are expected in other planetary bodies wherever olivine-rich magmatic systems get cooled down and hydrated.

How to cite: Andreani, M., Herviou, C., Montagnac, G., Fellah, C., Ménez, B., Pisapia, C., Lilley, M., and Früh-Green, G.: Abiotic synthesis of volatile and condensed organic compounds in the deep oceanic lithosphere , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22120, https://doi.org/10.5194/egusphere-egu24-22120, 2024.

EGU24-22147 | ECS | Posters on site | GD5.1

Interpretation of a second-order discontinuity at 1°N latitude of the Mid-Atlantic Ridge 

Raissa Francicleide Sousa da Silva, Helenice Vital, and Aderson Farias do Nascimento

Understanding the depths of the marine substrate is of vital importance for an increasing variety of fundamental purposes that contribute to the comprehension of our planet's functioning. The primary objective of this research was to map the seafloor through multibeam bathymetry, at Latitude 1º N of the mid-Atlantic ridge, NW of the Archipelago of São Pedro and São Paulo. Data were collected aboard the Hydrographic and Oceanographic Research Ship (NpqHOc) Vital de Oliveira, within the scope of the QWHALES, SeabedMap and PQ MapMar projects. An EM-122 multibeam echosounder was used, in the 12 kHz frequency range, with an opening of 60º and at a speed of 7 knots. Raw data processing was performed with Caris HIPS & SIPS version 11.4.24 software. Until this study, the selected area had not been mapped, meaning that mapping a previously unexplored region of the ocean floor represents a crucial advancement, highlighting the importance of understanding the complexity of the marine environment. The obtained results allowed the generation of a bathymetric surface map at a pixel resolution of 50 meters. With the bathymetric map, it was possible to identify the morphology of slow-spreading mid-ocean ridges. Through elevation profile, an axial valley delimited by edge faults to the axial valley was interpreted. Along the valley, there is a discontinuity with an offset of approximately 17 km from the axis in the mapped area. This metric, associated with the morphology of the expansion axis that develops a narrow and deep axial valley, allowed the classification of non-transforming displacement or second-order displacement. Finally, it was also possible to identify that this discontinuity is located between the South American and African tectonic plates. 

How to cite: Francicleide Sousa da Silva, R., Vital, H., and Farias do Nascimento, A.: Interpretation of a second-order discontinuity at 1°N latitude of the Mid-Atlantic Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22147, https://doi.org/10.5194/egusphere-egu24-22147, 2024.

Abstract: The study of K-enriched intrusive rocks is essential for deciphering mantle metasomatism beneath active continental arcs. In this contribution, high-precision zircon U‒Pb‒Hf isotope, whole-rock geochemistry, Sr‒Nd isotope, and mineral chemistry analyses were performed to evaluate the petrogenesis and geodynamic system of the Yunnongfeng intrusion on the southwestern margin of the Yangtze Block. The Yunnongfeng intrusion consists of a high-K to shoshonitic rock assemblage with variable lithology from gabbro-diorite to granite. Zircon U‒Pb dating gives concordant crystallization ages of ca. 782.5 ± 3.8 Ma for gabbro-diorite, ca. 774 ± 4.1 and 776 ± 4.1 Ma for diorite, ca. 770 ± 4.7 Ma for quartz monzonite, ca. 763 ± 3.4 Ma for quartz syenite, and ca. 764 ± 16 Ma for granite. These samples also show similar Sr‒Nd, and Lu‒Hf isotopic compositions, implying a common magma source. The similar crystallization age and regular variation of major and trace element contents suggest that these rocks were formed through fractional crystallization of cogenetic primitive mantle magmas. The enriched εNd(t) (−5.7 to −5.1) and εHf(t) (−6.7 to −1.2) values, high Rb/Y and Th/La ratios, slight Nd‒Hf decoupling, and high-K and Th contents demonstrate that their lithospheric mantle source was enriched by slab-related fluid and sediment-related melt. The samples also exhibit remarkable enrichment in large-ion lithophile elements and depletion in high-field-strength elements, indicative of subduction-related arc magmatism. Taking into account previous studies, we suggest that the western margin of the Yangtze Block experienced a long-term subduction process during the Neoproterozoic, and the Yunnongfeng intrusion formed in an extensional back-arc basin. Based on the K-enriched mafic‒intermediate rocks from the western margin of the Yangtze Block commonly show high K2O/Na2O, Rb/Sr, low Ba/Rb ratios, and enriched εNd(t) values, our study, coupled with numerous previous reports, proposes that the K-enrichment resulted from the breakdown of phlogopite, owing to subduction-related sediment melt reacting with peridotite in the mantle source area.

Keywords: Potassium-enriched intrusive rocks; Southwestern Yangtze Block; Fractional crystallization; Lithospheric mantle; Sediment melt

How to cite: Jiang, X. and Lai, S.: Petrogenesis of Neoproterozoic high-K intrusion in the southwestern Yangtze Block, South China: Implication for the recycled subducted-sediment in the mantle source, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-253, https://doi.org/10.5194/egusphere-egu24-253, 2024.

EGU24-330 | Orals | GD4.1

The Role of Upper Mantle Forces in Post-subduction Tectonics: Insights from 3D Thermo-mechanical Models in the East Anatolian Plateau 

Ebru Şengül Uluocak, Russell N. Pysklywec, Andrea Sembroni, Sascha Brune, and Claudio Faccenna

Post-subduction tectonics can involve a wide range of spatiotemporal processes associated with regional and large-scale upper mantle forces. To better understand the interaction between these forces in collisional settings, we focus on active mantle dynamics beneath the East Anatolian Plateau, a well-documented segment of the Arabian-Eurasian continental collision zone. In detail, we use state-of-the-art instantaneous thermomechanical models by combining the advantages of 3D numerical modeling with high-resolution imaging techniques. We analyze the model’s outputs, such as 3D stress-strain and temperature variations of upper mantle convection and reconcile them with numerous geological and geophysical observations. Our results show prominent northward-directed channel flow in the mantle that cuts across the plateau and surroundings, from the Arabian foreland to the Greater Caucasus domain. This result reproduces and elucidates the proposed ~SW-NE-oriented Anatolian Background Splitting pattern and recent seismic low-ultra low-velocity anomalies. We argue that this large-scale upper mantle flow constitutes the engine for the long-wavelength dynamic topography (~400 m) in the region and promotes the relatively small-scale convection pattern by supporting intraplate rift tectonics in the extensional Van Lake zone.

How to cite: Şengül Uluocak, E., Pysklywec, R. N., Sembroni, A., Brune, S., and Faccenna, C.: The Role of Upper Mantle Forces in Post-subduction Tectonics: Insights from 3D Thermo-mechanical Models in the East Anatolian Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-330, https://doi.org/10.5194/egusphere-egu24-330, 2024.

  Yanshanian magmatic rocks are widely distributed in the northern margin of the South China Sea and the continental margin of South China. These magmatic rocks are generally believed to have been formed by the subduction of the Paleo-Pacific plate to the South China Plate from Late Jurassic to Early Cretaceous. Due to the small number of wells drilled to the basement, most predecessors have studied on the distribution range, origin and tectonic setting of Yanshanian magmatic rocks by geophysical means(magnetic anomalies and seismic data). At present, The reported ages of basement magmatic rocks in the Pearl River Mouth Basin are mainly concentrated in Zhu 1 Depression and Panyu Low Uplift, and there is no petrological evidence in other regions.Baiyun Depression, as the largest hydrocarbon generating depression in the Pearl River Mouth Basin, has important oil and gas significance. In order to better define the spatial and temporal distribution of Yanshanian magmatic rocks, nearly 30 basement drilling samples in the periphery of Baiyun Depression and 8 onshore outcrop samples were collected. The genesis and tectonic significance of Yanshanian magmatic rocks are discussed through 76 thin sections, 7 U-Pb zircons dating, 26 major elements analysis, 16 trace elements analysis and 4 Sr-Nd-Pb isotope analysis.The results show that the magmatic rocks in the study area are concentrated in the J3-K1 and mainly developed S-type granite. These magmatic rocks are basically derived from the crust, and a few magmatic rocks or a small amount of mantle-derived materials are mixed in. The trace element discrimination diagram indicates that all samples belong to volcanic island arc type granite. The distribution curve of rare earth elements shows that light rare earth elements are enriched and heavy rare earth elements are low and stable.According to the above results, these magmatic rocks are part of the NE-trending continental margin magmatic arc formed by subduction and accretion of the paleo-Pacific plate to the South China Plate during the Yanshanian.Combined with the previous research results, it is believed that the extensional action caused by subduction and retreat of the Paleo-Pacific plate migrated to the ocean direction in the late stage of tensile rupture, and magmatism also migrated to the ocean, so the intrusion time of the magmatic rocks from continental to marine along the NW-SE direction gradually became late.This study adds important petrological evidence to clarify the genesis and tectonic setting of Yanshanian magmatic rocks in the northern margin of the South China Sea and the South China continent, and also has important application value for oil and gas exploration of buried hills in the Pearl River Mouth Basin.

How to cite: lu, F. and zhao, J.: Genesis and Tectonic Setting of Yanshanian Magmatic Rocks in the Northern Margin of South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-339, https://doi.org/10.5194/egusphere-egu24-339, 2024.

EGU24-568 | ECS | Posters on site | GD4.1

Trans-Lithospheric Diapirism as a Possible Mechanism for Ophiolite Emplacement? 

Nikola Stanković, Taras Gerya, Vladica Cvetković, and Vesna Cvetkov

Oceanic obduction and ophiolite emplacement are processes which result in positioning of more dense oceanic lithosphere on top of less dense continental crust. It is known that obduction is related to the closure of oceanic realms, however exact mechanisms that lead to the obduction of these ophiolite rocks, and more importantly, their permanent emplacement onto the continental crust is still controversial.

Although many mechanisms for ophiolite emplacement have been proposed, there have been substantial difficulties in modelling the ophiolite emplacement by means of numerical simulations. Creating physically viable simulations of the ophiolite emplacement is of paramount importance for better understanding of the process itself. There have been some notable successful attempts. For example, [1] succeeded in emplacing ophiolites by artificially reversing the velocity conditions once the ophiolite block is already obducted. More recently, [2] have shown that continental extrusion mechanism, which is a result of the activation of subducted continental crust at higher P-T conditions, can account for the emplacement of far-travelled ophiolites.

In this communication, we report interim results of our attempt to explain spontaneous emplacement of large ophiolite blocks by means of trans-lithospheric diapirism of continental crust. This phenomenon has recently been modelled [3] in the context of continental collision and the formation of the European Variscides. However, in this study, we produce a spontaneously induced intra-oceanic subduction. This model involves a retreating subduction with trench reaching the passive continental margin, leading to the continental subduction under very young oceanic lithosphere. Consequently, subducted crust is activated in deeper regions and forms a diapiric upward flow. This trans-lithospheric diapirism reaches the surface, thus separating the already obducted parts of the oceanic lithosphere from the rest of the oceanic domain, resulting in permanent ophiolite emplacement.

The presence of crustal rocks in such deep environments of ultra-high pressure certainly leads to their metamorphism. In the scope of our simulations we are monitoring the P-T paths of relevant crustal markers and propose rough estimates of the P-T conditions of metamorphic peak. For the calculations of the numerical simulations we utilize marker-in-cell method with conservative finite differences [4].

 

[1] T. Duretz, P. Agard, P. Yamato, C. Ducassou, E. B. Burov, and T. V. Gerya, “Thermo-mechanical modeling of the obduction process based on the oman ophiolite case,” Gondwana Research, vol. 32, pp. 1-10, 2016.

[2] K. Porkoláb, T. Duretz, P. Yamato, A. Auzemery, and E. Willingshofer, “Extrusion of subducted crust explains the emplacement of far-travelled ophiolites,” Nature Communications, vol. 12, no. 1, p. 1499, 2021.

[3] P. Maierová, K. Schulmann, P. ’Štípská, T. Gerya, and O. Lexa, “Trans-lithospheric diapirism explains the presence of ultra-high pressure rocks in the european variscides,” Communications Earth & Environment, vol. 2, no. 1, p. 56, 2021.

[4] T. V. Gerya and D. A. Yuen, “Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties,” Physics of the Earth and Planetary Interiors, vol. 140, no. 4, pp. 293-318, 2003.

How to cite: Stanković, N., Gerya, T., Cvetković, V., and Cvetkov, V.: Trans-Lithospheric Diapirism as a Possible Mechanism for Ophiolite Emplacement?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-568, https://doi.org/10.5194/egusphere-egu24-568, 2024.

EGU24-700 | ECS | Posters on site | GD4.1

The British Virgin Islands in the Caribbean Evolution: Petrogeochemical and geochronological constraints 

Noémie Bosc, Delphine Bosch, Mélody Philippon, Mélanie Noury, Olivier Bruguier, Lény Montheil, Douwe van Hinsbergen, and Jean Jacques Cornée

The British Virgin Islands (BVI) is a NE-SW trending archipelago located in the northeastern corner of the Caribbean plate. Exposing volcanic arc rocks, it is located at the junction between the old arc of the Greater Antilles to the Northwest and the active arc of the Lesser Antilles to the South. The BVI are a key location to study the geodynamical evolution of the northeastern boundary of the Caribbean plate. In order to understand its significance into the overall Caribbean evolution, a set of 16 igneous samples from seven islands was studied for petrology, geochemistry (major and trace elements, and Pb-Sr-Nd-Hf isotopes), thermobarometry (Al-in-hornblende) and U-Pb geochronology on accessory minerals (zircon, titanite and apatite). The studied rocks show a typical volcanic arc signature and correspond to a calc-alkaline series, differentiated along a NE/SW gradient. Trace elements patterns show strong negative HFSE anomalies and LILE enrichments. ɛHfi are homogeneous ranging from +11.4 to +14.1 typical of a MORB-type mantle. Magmas were thus originated from a homogeneous mantle corresponding to the mantle wedge, with participation of a slab component. The slab component contribution is estimated to be less than 2% and is dominated by aqueous fluids, except for Peter and Norman Islands. U-Pb ages emphasize an active magmatic period spanning between ~43 Ma and ~30 Ma along a NE-SW younging gradient. This age range and strong geochemical similarities with arc lavas exposed in St Martin and St Barthélémy suggest that the BVI represent the northern continuity of the Eo-Oligocene extinct branch of the Lesser Antilles arc. Crystallization depth of the studied plutonic bodies, estimated by thermobarometric constraints, supports a NE-SW increasing emplacement depth from ~7km to ~13km. The oldest plutonic bodies at NE thus experienced less total exhumation than the youngest plutonic bodies at SW (maximum rate of ~2.2 mm/yr at SW and minimum rate of ~0.2 mm/yr at NE). From Eocene to Oligocene it has been recently demonstrated that the block from Puerto Rico-Virgin Islands (PRVI) rotated 45° counter clockwise (Montheil et al., 2023). Previous thermochronological data shows that the BVI exhumation occurred synchronously along the archipelago between ~25 and ~21 Ma (Román et al., 2021). Together these observations suggest a regional tilt of the BVI block that occurred between plutons crystallisation and their exhumation at ~2 km depth. We propose that the tilting and the fast exhumation of the BVI, that are synchronous with counterclockwise rotation of the PRVI block, are the consequence of subduction locking generated by the Bahamas bank accretion to the northeastern Caribbean plate.

How to cite: Bosc, N., Bosch, D., Philippon, M., Noury, M., Bruguier, O., Montheil, L., van Hinsbergen, D., and Cornée, J. J.: The British Virgin Islands in the Caribbean Evolution: Petrogeochemical and geochronological constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-700, https://doi.org/10.5194/egusphere-egu24-700, 2024.

EGU24-1044 | ECS | Orals | GD4.1

The role of hydration-induced processes in the deformation of the North China craton 

Açelya Ballı Çetiner, Oğuz Göğüş, Jeroen van Hunen, and Ebru Şengül Uluocak

Numerous previous studies have been conducted in the North China Craton to investigate its anomalously thin lithosphere, high magmatism, and extensional tectonics along its eastern margin. Based on petrological analyses it has been suggested that the cratonic mantle lost its root (~100 km) with multiple tectonic processes during the late Jurassic – Early Cretaceous. The weakening and erosion of the North China craton is often attributed to its high water content and lower viscosity of the lithosphere associated with the movement and position of the Paleo-Pacific plate. However, other mechanisms and control parameters for the craton destruction have been proposed, and the thinning of the North China craton remains an enigmatic process.

To have a better understanding of the dynamics of the lithospheric deformations beneath the North China Craton that changes over time, we conducted a series of 2D geodynamic models. Specifically, we investigate the impact of hydration-induced processes on the lithosphere and the overriding plate and focus on parameters such as external tectonic forcing, the rheology and the strength of the overriding plate. Moreover, the effect of the angular position of the oceanic plate, and the existence of the mid-lithosphere discontinuities was also examined. Our results reveal that the destruction of North China Craton is more complex and heterogeneous than is often assumed in modelling studies. Furthermore, we find that without significant weakening, the mantle lithosphere is unlikely to delaminate. Extensive hydrous weakening may account for this, but external tectonic forcing in combination with non-linear rheology and eclogitization of the lower crust may have played an important role too.  

How to cite: Ballı Çetiner, A., Göğüş, O., van Hunen, J., and Şengül Uluocak, E.: The role of hydration-induced processes in the deformation of the North China craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1044, https://doi.org/10.5194/egusphere-egu24-1044, 2024.

EGU24-3010 | ECS | Posters on site | GD4.1

Thermo-mechanical models on the missing forearc basement in Taiwan 

Chih-Hsin Chen, Eh Tan, Shu-Huei Hung, and Yuan-Hsi Lee

Taiwan is located at the edge of the Eurasian plate and borders the Philippine Sea plate. The Philippine Sea plate is moving northwestward at a speed of 70 to 80 mm/yr and is converging with the Eurasian plate, forming the Luzon arc and the Taiwan orogenic belt. However, in the middle section of the Taiwan orogenic belt, the Luzon arc is directly adjacent to the edge of the Eurasian continental margin, and the forearc basement is missing. This phenomenon of missing forearc basement is also widely observed in similar plate convergence zones. Previous studies have suggested that this forearc basement has subducted between the Philippine Sea plate and the Eurasian plate. In order to explore the mechanism of forearc basement subduction, we used thermal-mechanical coupled numerical simulations combined with geological data to simulate the dynamic mechanism of forearc basement subduction in the middle section of the Taiwan orogenic belt.

 

The simulation results show that when the subducting plate transitions from oceanic crust to continental crust, the continental crust has a lower density and is not easily subducted. The huge mass formed by the orogeny blocks the Philippine Sea plate from moving northwestward, causing the forearc crust to bend concavely and form a forearc basin. The basin begins to accumulate a large amount of sedimentary material. Later, the center of the basin breaks to form the Longitudinal Valley fault, the island arc to the east of the basin thrusts over the forearc basement, pushing the basin sediment to uplift rapidly, and finally the forearc basement subducts below the Philippine Sea plate.

 

This model explains the mechanism for the missing forearc basement, the timing of the formation of the Longitudinal Valley fault, and the dramatic up and down movements recorded in the sedimentary rocks of the Coastal Mountains. It also explains the spatial pattern of the surface heatflow.

How to cite: Chen, C.-H., Tan, E., Hung, S.-H., and Lee, Y.-H.: Thermo-mechanical models on the missing forearc basement in Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3010, https://doi.org/10.5194/egusphere-egu24-3010, 2024.

EGU24-4122 | ECS | Orals | GD4.1

Investigating Interactions between Subduction Initiation and Plate Reorganizations From A Global Perspective 

Xin Zhou, Nicolas Coltice, and Paul Tackley

Subduction initiation (SI) creates new subduction zones and provides driving forces for plate tectonics, being a key process of theplate tectonic regime on Earth. Although SI has been extensively studied in 2D regional numerical models, obtaining a global perspective on SI remains elusive. Geological observations and plate reconstructions both suggest that SI is coeval with the global or local plate reorganizations. The tectonic plate reorganizations are marked by rapid changes of plate motions occurring over a few million years and are recurrent throughout Earth’s history.  One of the most well-known plate reorganization events occurred at approximately 53-47 Ma ago, characterized by the bending of Hawaii-Emperor Seamount Chain. Simultaneously, several SI events occurred in the Pacific Plate, such as Izu-Bonin-Mariana (~52 Ma) and Tonga-Kermadec (~50 Ma). The relationship between SI and plate reorganizations, as well as their collective impacts on continental evolution, is poorly understood. It is also unclear whether these processes are dominated  by a “top-down” or “bottom-up” mechanism. This study is committed to exploring the interaction between SI and plate reorganizations using 3D global mantle convection models. We reproduce SI coeval with plate reorganizations in these numerical models. We analyze the changes of stress distribution in the lithosphere during the plate reorganizations and their effects on SI. A variety of different interplays between SI and tectonic plates reorganizations have been identified based on their chronology and driving mechanisms. We also investigate their influences on the supercontinental breakup and assembly. Two major plate reorganization events, occurring at 100 Ma and 50 Ma ago respectively, are used to compare with the numerical modeling results. The effects of key parameters, such as lithosphere thickness and strength, will be examined. Plate reconstruction models will also be included to study the interaction between SI and plate reorganizations in the future.

How to cite: Zhou, X., Coltice, N., and Tackley, P.: Investigating Interactions between Subduction Initiation and Plate Reorganizations From A Global Perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4122, https://doi.org/10.5194/egusphere-egu24-4122, 2024.

Subduction initiation remains one of the least understood global processes of plate tectonics.  Prominent models have been cast in terms of two broad classes: “spontaneous” cases due to lithospheric gravitational instabilities and “induced” cases due to forced plate convergence. Yet gravitationally unstable lithosphere is old, strong, and difficult to begin to bend into a subduction zone and convergent forces necessary to begin subduction are often too large given the plates involved. These models also consider the asthenospheric mantle as passive, even though relative motion between slabs and the asthenosphere has long been regarded as a strong control on subduction dynamics. Here I propose that subduction-transform edge propagator (STEP) faults can initiate subduction depending on the absolute motion of the STEP fault with respect to the asthenosphere. STEP faults form where subduction zones end and the subducting plate tears forming a down flexed transcurrent plate boundary at the surface shearing against the adjacent rear arc lithospheric plate. However, STEP faults are not simple transcurrent boundaries. Absolute motion of the down flexed STEP fault edge with respect to the surrounding asthenosphere can produce a strong “sea anchor” force that either continues to bend the edge downward, initiating subduction, or opposes slab bending, inhibiting subduction. In the south Pacific, the southern end of the New Hebrides Trench and the northern end of the Tonga Trench are type-example STEP faults with opposite senses of dip but both moving northward with respect to the asthenosphere. The northward dipping New Hebrides STEP fault moves northward in a mantle reference frame creating a strong asthenospheric flow against the STEP fault edge, inducing active subduction at the Matthew-Hunter trench. In contrast, the Tonga STEP fault dips southward but also has a northward component of motion with respect to the mantle. Asthenosphere thus flows southward beneath the down flexed Tonga STEP fault edge opposing further bending.  Subduction does not initiate at the Tonga STEP fault despite a ~100 Myr age contrast between the Pacific and north Fiji and Lau basin lithospheres. Since absolute plate motions reflect the sum of all forces acting on the entire lithospheric plate, a strong sea anchor mantle force may be generated at a STEP fault edge, initiating subduction (or inhibiting it), even where lithosphere is old, strong, and resists bending and without requiring large convergent forces between plates, overcoming these objections to previous models.

How to cite: Martinez, F.: Subduction initiation (or not) due to absolute plate motion at STEP faults: The New Hebrides vs. the Tonga examples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4189, https://doi.org/10.5194/egusphere-egu24-4189, 2024.

The migration and character of magmatism over time can provide important insights into the tectonic evolution of an orogen. We present evidence for three separate episodes of compositionally distinct granitoid magmatism associated with the Acadian orogenic cycle in the eastern and southern Newfoundland Appalachians. The interpretations are based on new zircon U-Pb ages, geochemical data, and Sr-Nd-Hf-O isotopic data for 18 samples from 15 Silurian and Devonian granitoid plutons, combined with previously published data. The three episodes outline hinterland and foreland-directed migration trends and represent subduction (435-420 Ma), syn-collision (415-405 Ma), and post-collision (395-370 Ma) settings in the Acadian orogenic cycle. The Silurian plutons (435-420 Ma) consist mainly of quartz diorite, tonalite, granodiorite, monzogranite, and syenogranite, with high-K calc-alkaline and enriched Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = -5 to -2; εHf[t] = -3 to -1; δ18O = +6 to +8). They are interpreted to record the subduction of oceanic lithosphere of the Acadian seaway that separated the leading edge of composite Laurentia represented by the Gander margin and Avalonia. The Early Devonian plutons (415-405 Ma), containing more voluminous monzogranite and syenogranite, have calc-alkaline to high-K calc-alkaline features, adakite-like compositions, and more-depleted Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = -6 to 0; εHf[t] = +1 to +3; δ18O = +5 to +6). This stage occurs mostly to the northwest of the Silurian, indicating a regional scale northwestward (hinterland-directed) migration of magmatism with a rate of > 9 km/Ma. The migration is interpreted to be related to the progressive shallow underthrusting of Avalonia beneath the Gander margin (composite Laurentia) at least as far as 90 km inboard. The Middle to Late Devonian plutons (395-370 Ma) consists mainly of monzogranite, syenogranite, and alkali-feldspar granite, which are silica- and alkali-rich with large negative Eu anomalies. These rocks are concentrated along both sides of the Dover - Hermitage Bay fault zone, which represents the boundary between Avalonia and composite Laurentia, to the southeast of the Silurian-Early Devonian igneous rocks. This stage of magmatism represents a foreland-directed (retreating) migration. The Early Devonian and Middle to Late Devonian magmatism were separated by a gap between 405 and 395 Ma, and recorded an evolution from (high-K) calc-alkaline to alkaline compositions, which is ascribed to partial delamination of Avalonian lithospheric mantle in a post-collisional setting.

How to cite: Wang, C., Wang, T., Cees, V. S., Hou, Z., and Lin, S.: Evolution of Silurian to Devonian magmatism associated with the Acadian orogenic cycle in Newfoundland Appalachians: Evidence for a three-stage evolution characterized by episodic hinterland- and foreland-directed migration of granitoid magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4216, https://doi.org/10.5194/egusphere-egu24-4216, 2024.

Convergent continental margins are the major sites for the formation, differentiation, preservation, and destruction of continental crust. This article focuses on the Mesozoic crustal modification history of northeastern China from a magmatic perspective. During Mesozoic times, NE China was influenced by three convergent systems, namely the Paleo-Asian Ocean (PAO) regime to the south, the Mongol-Okhotsk Ocean (MOO) regime to the northwest, and the Paleo-Pacific Ocean (PPO) regime to the east. This study comprehensively synthesizes information on Early Triassic to Early Cretaceous magmatic rocks. We unravel the spatiotemporal effects of the above-mentioned convergent regimes by evaluating the migration of major magmatic belts and other geological and geophysical evidence. The PAO regime is confined to the southernmost part of NE China and exerted influence during pre-late Late Triassic times. The MOO regime-related magmatism lasted until the early Early Cretaceous and occurred throughout the Great Xing’an Range and adjacent regions. The spatial effect of the PPO did not exceed the eastern margin of the Songliao Basin until the Early Jurassic; low-angle to flat subduction of the PPO slab led to the westward migration of continental arc front in the Middle Jurassic and the waning of PPO regime-related magmatism in the Late Jurassic. Since the earliest Cretaceous, the rollback and retreat of the PPO slab became the predominant geodynamic control in NE China, but the superposition of the MOO regime played a role during the early Early Cretaceous. Employing whole-rock Nd and zircon Hf isotope spatial imaging, this study elucidates that, although the pre-Mesozoic lithospheric heterogeneity provides first-order control, the Mesozoic crustal architecture of NE China was further carved by Mesozoic tectonics. Retreating subduction (slab rollback) and post-collisional lithospheric delamination resulted in the prolonged extensional background and crustal growth (rejuvenation); on the contrary, low-angle subduction and syn-collisional compression could cause transient periods of ancient crust reworking. Our results also estimate the high altitude of the Great Xing’an Range and adjacent regions in the Early Cretaceous. This study opens new possibilities to explicitly document crustal modification processes in fossil orogens from a magmatic perspective.

How to cite: Huang, H., Wang, T., and Guo, L.: Crustal modification influenced by multiple convergent systems: Insights from Mesozoic magmatism in northeastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4240, https://doi.org/10.5194/egusphere-egu24-4240, 2024.

EGU24-4319 | Posters virtual | GD4.1

Towards understanding the interplay between tectonics, magmatism, and sedimentation in the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians 

Uros Stojadinovic, Marinko Toljić, Branislav Trivić, Radoje Pantović, Danica Srećković-Batoćanin, Nemanja Krstekanić, Bojan Kostić, Miloš Velojić, Jelena Stefanović, Nikola Randjelović, and Maja Maleš

Among the many examples observed worldwide, the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians represents an excellent area for a process-oriented study on the interplay between tectonics, sedimentation, and magmatism in continental back-arc basins above evolving subducted slabs. The TMC is a segment of the larger Late Cretaceous Apuseni-Banat-Timok-Srednogorie (ABTS) magmatic belt, formed in response to the subduction of the Mesozoic Neotethys oceanic lithosphere beneath the Carpatho-Balkanides of south-eastern Europe. However, despite many qualitative studies, the quantitative link between the subducted slab's mechanics and the overlying basins' evolution is less understood. Within the scope of the newly funded TMCmod project, supported by the Science Fund of the Republic of Serbia (GRANT No TF C1389-YF/PROJECT No 7461), coupled field and laboratory kinematic and petrological investigations will be focused on creating a conceptual definition of the TMC geodynamic evolution, by combining near-surface observations with the known evolution of the subduction system. This definition will be subsequently validated through analogue modelling and integrated into a coherent geodynamic model of tectonic switching in basins driven by the evolution of subducted slabs. The new geodynamic model coupling the TMC basin with its Neotethys subduction driver will quantitatively advance the strategy of prospecting and exploration of world-class porphyry copper-gold deposits, which have been actively exploited in this region for more than a century. Furthermore, reconstructed regional kinematic evolution will improve seismic hazard assessment during industrial and societal infrastructure planning and construction.

How to cite: Stojadinovic, U., Toljić, M., Trivić, B., Pantović, R., Srećković-Batoćanin, D., Krstekanić, N., Kostić, B., Velojić, M., Stefanović, J., Randjelović, N., and Maleš, M.: Towards understanding the interplay between tectonics, magmatism, and sedimentation in the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4319, https://doi.org/10.5194/egusphere-egu24-4319, 2024.

Previous subduction thermal models are inconsistent with the values of forearc heat flow (50-140 mW/m2) and global P‒T conditions of exhumed rocks, both suggesting a shallow environment 200~300°C warmer than model predictions. Here, we revaluate these problems in Kuril-Kamchatka using 3-D thermomechanical modeling that satisfies the observed subduction history and slab geometry, while our refined 3-D slab thermal state is warmer than that predicted by previous 2-D models and better matches the observations involving exhumed rock records. We show that warmer slabs create hierarchical slab dehydration fronts at various forearc depths, causing fast and slow subduction earthquakes. The multilayered subduction regime and a large downdip thermal gradient of > 5°C/km beneath Kuril-Kamchatka indicate a stratified characteristic effect on slab dehydration efficiency. We conclude that fast-to-slow subduction earthquakes all play a key role in balancing plate coupling energy release on megathrusts trenchward of high P‒T volcanism.

How to cite: Zhu, W. and Ji, Y.: Reestimated slab dehydration fronts in Kuril-Kamchatka using updated three-dimensional slab thermal structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4972, https://doi.org/10.5194/egusphere-egu24-4972, 2024.

Oceanic Core Complexes (OCCs) are peridotite and serpentinite rich geological features, commonly located at the external intersections of slow-spreading mid-oceanic accreting ridges (MORs) with transform faults (TFs). The peridotites of these complexes are commonly considered to derive from the upper mantle while the serpentinites are attributed to chemical weathering that affected rock-mass during its ascent through the lithosphere. Description of cores drilled into OCCs commonly describes in detail the various peridotites but ignores the serpentinites, which are considered secondary additions. However, this presumption seems flawed due to the absence of high-pressure rocks such as eclogites, therefore it seems that the origin of the various peridotite minerals were formed concurrently with the serpentinites from pyroxenes under constrains of moderate geological pressures and temperatures, and various availabilities of H2O.

The intersections between slow MORs and TFs, where most OCCs occur, are characterized by steep thermal gradients and by distinct density contrasts. The thermal gradients in the upper crust of the MOR axial rift are nearly 1300/km, due to the shallow depth of the upper mantle there. The density of the fresh basaltic lava at the MOR is ca. 2700 kg/m3, because the temperature of the fresh basalt is some 1100oC. However, the density of the older basalt that builds the older plate across the transform fault is 2900 kg/m3. It is plausible that at fast-spreading MORs the plate juxtaposed against the active spreading rift would still be warm and its density would too light to initiate the spontaneous subduction. Tectonic experiments showed that at least 200 kg/m3 density contrast between lighter and denser crustal slabs would be sufficient to initiate spontaneous subduction. Furthermore, geochemical experimentation shows that under 500oC temperatures, namely at depths of ca. 4 km under the MOR, minerals of the pyroxene group in the oceanic basalts, are likely to be altered either into peridotites under dry conditions or into serpentinites under wet constraints at such temperature. These constraints suggest that the serpentinites in OCCs are generic and not erosional features, and their light densities and plasticity could have generated the diapiric ascent of the OCCs. The density contrast between the fresh and the old basalts, juxtaposed at the ridge – transform junctions, could take place if the spreading rate of the MOR is slow and the older slab has the time required to cool and reach the density of 2900 kg/m3.

 Keywords: Ridge-transform intersection, oceanic core complexes, spontaneous subduction, peridotites, serpentinites, diapirs.

How to cite: Mart, Y.: Oceanic core complexes: Serpentinite diapirs at slow ridge - transform fault intersections?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5261, https://doi.org/10.5194/egusphere-egu24-5261, 2024.

EGU24-5274 | ECS | Orals | GD4.1

Investigating the plate motion of the Adriatic microplate by 3D thermomechanical modelling 

Christian Schuler, Boris Kaus, Eline Le Breton, and Nicolas Riel

The geodynamic evolution of the Alpine-Mediterranean area is complex and still subject to ongoing debate. The Adriatic microplate motion is of particular interest as it is influenced by three distinct subduction systems: the Alpine subduction in the north, the Dinaric-Hellenic subduction in the east, and the Calabrian-Apenninic subduction in the west. Additionally the system is influenced by the northward movement of the African continent, which further contributes to the geodynamic complexity of the region.

In this study, 3D thermomechanical simulations of the Alpine-Mediterranean region are performed using the code LaMEM (Kaus et al., 2016). The simulations employ a viscoelastoplastic rheology and an internal free surface to investigate the internal dynamics of the mantle. The initial plate configuration for the simulations is based on the kinematic reconstructions of Le Breton et al. (2021) at 35 Ma. The objective is to identify the controlling factors that drive the motion of the Adriatic microplate. This is achieved by investigating the role of various model parameters, such as the thermal structure of the lithosphere, the geometry and strength of the continental margin, the mantle viscosity, brittle parameters of the crust and the location of crustal heterogeneities.

Results show that Adria undergoes two distinct phases of plate motion over the past 35 million years. Between 35 Ma and 20 Ma, the African plate moves northward, pushing Adria in the same direction. However, once the Hellenic slab rolls back from the east and the Calabrian and Apenninic slabs roll back from the west, the Adriatic microplate decouples from the African plate, resulting in an anticlockwise rotation of Adria. Overall, this study provides valuable insights into the parameters that affect subduction dynamics in the Mediterranean and the independent motion of the Adriatic microplate.

Kaus, B. J. P., A. A. Popov, T. S. Baumann, A. E. Pusok, A. Bauville, N. Fernandez, and M. Collignon, 2016: Forward and inverse modelling of lithospheric deformation on geological timescales. Proceedings of NIC Symposium.

Le Breton, E., Brune, S., Ustaszewski, K., Zahirovic, S., Seton, M., & Müller, R. D. (2021). Kinematics and extent of the Piemont–Liguria Basin–implications for subduction processes in the Alps. Solid Earth, 12(4), 885-913.

How to cite: Schuler, C., Kaus, B., Le Breton, E., and Riel, N.: Investigating the plate motion of the Adriatic microplate by 3D thermomechanical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5274, https://doi.org/10.5194/egusphere-egu24-5274, 2024.

Fluid release from dehydration reactions and subsequent fluid migration in the subducting slab control the distribution of fluids in subduction zones, impacting many subduction processes, such as intraslab earthquakes, megathrust earthquakes, episodic slip and tremor, mantle wedge metasomatism, and arc-magma genesis.  Previous numerical models of two-phase flow indicate that compaction-pressure gradients induced by the dehydration reactions could drive updip intraslab fluid flow near the slab surface (Wilson et al., 2014). However, how the initial hydration in the incoming oceanic mantle prior to subduction impacts the updip fluid flow has not been investigated. Here, we use a 2-D two-phase flow model to investigate this effect under various initial slab-mantle hydration states and slab thermal conditions, the latter of which impact the depth extent of the stability of hydrous minerals. We especially focus on quantifying the lateral shift between the site of dehydration reactions and the location at which the fluids reach the slab surface due to their updip migration within the slab. The modeling results show that the most favourable path for updip flow is the antigorite dehydration front, the spatial extent of which depends on the slab-temperature and the thickness of the hydrated slab mantle. Our models predict that slab-derived fluids can travel over tens of km updip within the slab before reaching the slab surface. Such updip migration is more likely in warm(ish)-slabs, in which the formation of the antigorite dehydration front in the slab mantle does not require deep hydration of the incoming oceanic mantle prior to subduction.

How to cite: Cerpa, N. and Wada, I.: Role of degree and depth extent of slab-mantle hydration in controlling the intraslab fluid flow upon dehydration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6007, https://doi.org/10.5194/egusphere-egu24-6007, 2024.

EGU24-6290 | Orals | GD4.1

Can we identify evidence of subduction initiation beneath the Macquarie Ridge Complex from teleseismic tomography? 

Jifei Han, Nick Rawlinson, Hrvoje Tkalčić, Caroline Eakin, Mike Coffin, and Joann Stock

Subduction is a key process in both the recycling and creation of new oceanic crust, the exchange of water between the Earth, oceans and atmosphere, and the distribution of earthquakes and volcanoes. However, the formation of new subduction zones - or subduction initiation - remains a poorly understood process. Macquarie Island, which lies along the Macquarie Ridge Complex (MRC) that forms the transpressional boundary between the Australian and Pacific plates in the southwest Pacific, is one location on Earth where subduction initiation is thought to be taking place. Several studies have suggested that the northern and southern segments of the MRC may be experiencing incipient subduction, but it is unclear what is happening in the central section, which includes Macquarie Island.


Indirect evidence for at least incipient subduction beneath Macquarie Island includes (i) ophiolite (oceanic crust) being exposed above sea level; (2) extreme topography, with Macquarie Island lying  ~5 km above the surrounding ocean basin; (3) thrust faults on either side of the island. To help investigate whether subduction may have been initiated in the neighborhood of Macquarie Island, we analyze teleseismic body wave data recorded by a network consisting of land stations and oceanic bottom seismometers deployed between October 2021 and November 2022. We extract teleseismic P-wave arrival time residuals across the combined array from ~20 events with epicentral distances between 30 and 90 degrees and invert them using FMTOMO to obtain 3-D P-wave velocity anomalies in the upper mantle. Preliminary results indicate that higher velocities are present to the east of the MRC in the vicinity of Macquarie Island, although further refinement is required before a detailed interpretation is possible.

How to cite: Han, J., Rawlinson, N., Tkalčić, H., Eakin, C., Coffin, M., and Stock, J.: Can we identify evidence of subduction initiation beneath the Macquarie Ridge Complex from teleseismic tomography?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6290, https://doi.org/10.5194/egusphere-egu24-6290, 2024.

The spinel phase (wadsleyite, ringwoodite) in the mantle transition zone (MTZ), can contain up to 1–2 wt% of water. However, whether these water reservoirs in the MTZ are filled is debated and, as the result, water content estimates in the MTZ range from less than 1 to up to 11 surface oceans (Ohtani, 2021 and references therein). I test water stability in the MTZ numerically by using 2D hydro-thermomechanical-chemical upper-mantle scale models with phase transitions and water diffusion and percolation in the mantle. Initial conditions correspond to a hydrated stagnant slab segment placed on top of 660 km discontinuity. Numerical model predicts that water diffusion from thermally relaxing slab triggers development of cold hydrous plumes from the slab surface, which are driven by the water-induced buoyancy (Richard and Bercovici, 2009). These plumes rise to and interact with olivine-spinel transition at 410 km. Positive Clapeyron slope of this transition causes cold plume upwellings to spread under it until their temperature rises enough to allow hydrated material to cross the transition. This crossing triggers aqueous fluid release, which rapidly rises upward in form of porosity waives. Relatively low water content and cold temperature of the wet plumes rising from stagnant slabs in the mantle transition zones may suppress hydrous melting above the 410 km discontinuity, thereby disabling the transition-zone water filter effect (Bercovici and Karato, 2002) at this boundary. Based on the results of experiments, we conclude that, due to the intrinsic positive buoyancy of hydrated mantle compared to dry rocks, mantle transition zone can only serve as a transient water reservoir. The duration of water residence mainly depends on the characteristic thermal-chemical relaxation time of subducting slabs in the mantle transition zone. Therefore, average water content in this zone should mainly depend on the average amount of water brought into it by subducting slabs globally during the characteristic relaxation time.

 

References

Bercovici, D., Karato, S., 2003. Whole-mantle convection and the transition zone water filter. Nature, 425, 39–44.

Ohtani, E., 2021. Hydration and Dehydration in Earth's Interior. Annual Review of Earth and Planetary Sciences, 49, 253-278.

Richard, G.C., Bercovici, D., 2009. Water-induced convection in the Earth’s mantle transition zone. J. Geophys. Res. 114, B01205.

How to cite: Gerya, T.: Is mantle transition zone a water reservoir? Yes, but only transient, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6602, https://doi.org/10.5194/egusphere-egu24-6602, 2024.

EGU24-6689 | Orals | GD4.1

Hoop Stresses in Free Subduction on a Sphere 

Neil Ribe, Stephanie Chaillat, Gianluca Gerardi, Alexander Chamolly, and Zhonghai Li

Because Earth's tectonic plates are doubly curved shells, their mechanical behavior during subduction can differ significantly from that of flat plates. We use the boundary-element method to study free (gravity-driven) subduction in 3-D spherical geometry. The model comprises a shell with thickness h and viscosity η1 subducting in a viscous planet with radius R0. Our focus is on the magnitude of the longitudinal normal membrane stress (`hoop stress'), which has no analog in Cartesian geometry. Scaling analysis based on thin-shell theory shows that the resultant (integral across the shell) of the hoop stress obeys the scaling law Tφ ∼ (η1h W/R0) max(1, cotθ) where θ is the colatitude and W is the velocity of the shell normal to its midsurface that is associated with bending. We find that the state of stress in the slab is dominated by the hoop stress, which is 3-7 times larger than the downdip stress. Because the hoop stress is compressive, it can drive longitudinal buckling instabilities. We perform a linear stability analysis of a subducting spherical shell to determine a scaling law for the most unstable wavelength, which we compare with observed shapes of trenches in the Pacific ocean. 

How to cite: Ribe, N., Chaillat, S., Gerardi, G., Chamolly, A., and Li, Z.: Hoop Stresses in Free Subduction on a Sphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6689, https://doi.org/10.5194/egusphere-egu24-6689, 2024.

The dynamics of subducting lithosphere with an embedded continental fragment is complex, with rapid changes in plate kinematics, mantle flow and uplift of the overriding plate as the fragment impacts the trench. However, the sequence and timing of the effects is often difficult to constrain, leading to uncertainties in the exact causes for particular subduction zones. We conducted 2D and 3D numerical modelling of subduction with Underworld2.0 to investigate the interactions between the subducting lithosphere and an embedded continental fragment, the Eratosthenes Seamount in the Cyprus subduction zone. Due to the uncertainty in the size of the continental crust around the Eratosthenes Seamount, we varied the size of the fragment from 200 km to 400 km (trench perpendicular) and compared to 3D model with a fixed seamount. The 3D model matches the regional seismic tomography models that show the absence of lithosphere on the subducting slab ahead of the continental fragment. In all the models, the subduction zone first develops as expected as the continental fragment approaches the trench. As the fragment contacts the trench at 6.5 Ma, the first uplift in Anatolia is experienced. However, the pace of uplift increases dramatically at 450 ka as the slab tear develops and the mantle flow pattern changes. The observed uplift rate before 450 ka is 0.07 mm/yr while after 450 ka, the uplift rate increases to 3.21 – 3.42 mm/yr. The model that best matches the size of the fragment is 200 km with a rate of 0.04 mm/yr before 450 ka and 1.76 mm/yr after 450 ka. The reference uplift rate from the model without the slab break-off from 450 ka is only 0.02 mm/yr.  The models demonstrate that the slab tear and break-off caused by the impact of the Eratosthenes Seamount causes the uplift observed and in particular is responsible for the more rapid uplift rates observed since 450 ka in the Central Taurides. 

How to cite: Clark, S. and Lou, P.: The Acceleration of Uplift in the Central Taurides due to Continental Fragment Collision in the Subduction Zone of the Eastern Anatolian Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7174, https://doi.org/10.5194/egusphere-egu24-7174, 2024.

EGU24-7864 | Orals | GD4.1

Folding of subducting slabs controls their deep thermal structures in the mantle transition zone  

Fanny Garel, Nestor Cerpa, Hana Čížková, Xavier Vergeron, Diane Arcay, Serge Lallemand, and Cécilia Cadio

The thermal structure of slabs is thought to be a key parameter for deep-focus earthquakes in subduction zones, since most proposed mechanisms, such as transformational faulting, dehydration reactions or shear instabilities, are controlled by temperature. However, the classical (shallow) thermal parameter "phi", associated to the downward advection of isotherms and approximated as slab age x sinking velocity (Kirby et al., 1996), does not explain deep-focus seismicity occurring in relativelty “hot” subduction zones, e.g. under Bolivia.

 

On the other hand, the various morphologies if subducting slabs imaged by seismic tomography reveal reveal the diversity of slab deformation histories in the transition zone as they reach the high-viscosity lower mantle, e.g. folding, deflection, vertical piling.

 

Using numerical models of subduction dynamics, we propose here to characterize the spatio-temporal evolution of deep thermal structures of subducted slabs throughout various subduction scenarios. We investigate how the maximum depth reached by a given isotherm vary through time (up to 200 km for a given subduction zone). In particular, we evidence the key control of the history of slab-folding in the transition zone (folding amplitude and frequency), associated to e.g. slab viscosity and buoyancy.

 

Hence the past dynamics of subduction zones, in addition to present-day subduction parameters, has to be taken into account to predict slabs thermal structures.

 

This work is part of ANR project RheoBreak (ANR-21-CE49-0009).

How to cite: Garel, F., Cerpa, N., Čížková, H., Vergeron, X., Arcay, D., Lallemand, S., and Cadio, C.: Folding of subducting slabs controls their deep thermal structures in the mantle transition zone , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7864, https://doi.org/10.5194/egusphere-egu24-7864, 2024.

EGU24-8053 | Posters on site | GD4.1 | Highlight

Gibraltar subduction zone is invading the Atlantic 

Joao C. Duarte, Nicolas Riel, Filipe M. Rosas, Anton Popov, Christian Schuler, and Boris J.P. Kaus

Subduction initiation is a cornerstone of the Wilson cycle. It marks the turning point in an ocean’s lifetime, allowing its oceanic lithosphere to be recycled back into the mantle. However, forming new subduction zones in Atlantic-type oceans is challenging, as it commonly involves the action of an external force, such as the slab pull from a nearby subduction zone, a far-field compression or the impact of a mantle plume. Notwithstanding, the Atlantic Ocean already has two fully developed subduction zones, the Lesser Antilles and the Scotia arcs. These subduction zones have been forced from the nearby Pacific subduction zones. The Gibraltar Arc is another place where a subduction zone is invading the Atlantic. This corresponds to a direct migration of a subduction zone that developed in the dying Mediterranean basin. Nevertheless, few authors consider the Gibraltar subduction zone as still active because it has significantly slowed down in the last millions of years. Here, we present new 3D buoyancy-driven geodynamic models, using the code LaMEM, that reproduce the first-order evolution of the Western Mediterranean, show how the Gibraltar Arc may have formed and test if it is still active. The numerical simulations are validated using geological and geophysical data. The results suggest that the Gibraltar arc is still active and will propagate further into the Atlantic after a period of tectonic quiescence. The models also show how a subduction zone starting in a closing ocean (the Ligurian) can migrate on its own into a new opening ocean (the Atlantic) through a narrow oceanic corridor. Subduction invasion is likely a common mechanism for introducing new subduction zones in Atlantic-type oceans and a fundamental process in the recent geological evolution of Earth.

 

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). JCD also acknowledges FCT a CEEC Inst. 2018, CEECINST/00032/2018/CP1523/CT0002 (https://doi.org/10.54499/CEECINST/00032/2018/CP1523/CT0002).

How to cite: Duarte, J. C., Riel, N., Rosas, F. M., Popov, A., Schuler, C., and Kaus, B. J. P.: Gibraltar subduction zone is invading the Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8053, https://doi.org/10.5194/egusphere-egu24-8053, 2024.

EGU24-8155 | ECS | Posters on site | GD4.1

Insights into Asymmetric Back-Arc Basin Formation in the Mariana Trough at 17°N from Traveltime Tomography 

Helene-Sophie Hilbert, Anke Dannowski, Ingo Grevemeyer, Christian Berndt, Shuichi Kodaira, Gou Fujie, and Narumi Takahashi

The Mariana Trough is the youngest back-arc basin in a series of basins and arcs that developed behind the Izu-Bonin-Mariana subduction zone in the western Pacific. In addition to active seafloor spreading, the Mariana Trough also exhibits a pronounced asymmetry, with the spreading axis closer to the Mariana Arc. The formation and development of this back-arc basin and its predecessor is controlled by a complex interplay of temporal mantle heterogeneities, subduction dynamics of the Pacific Plate and large-scale tectonics since ~50 Ma. Here, we present new insights into the development of the central Mariana Trough at ~17°N from analyses of a 2-D P-wave traveltime tomography together with high-resolution bathymetric data. The refraction and wide-angle reflection data have been recorded by R/V KAIYO (JAMSTEC) on 41 ocean bottom seismometers (OBSs) along a 250 km profile in 2003. The results allow a subdivision of the Mariana Trough into different stages of back-arc basin opening and seem to imply a transition from symmetric rifting to asymmetric seafloor spreading. Fast-velocities in the lower crust in the rifting domain indicate that magma generation and crust formation was highly affected by hydrous melting from the subducting slab during this stage. This slab contribution decreases with the onset of active seafloor spreading due to a change in mantle flow and hence seems to be accompanied by a tectonic rearrangement of the eastern side of the basin.

How to cite: Hilbert, H.-S., Dannowski, A., Grevemeyer, I., Berndt, C., Kodaira, S., Fujie, G., and Takahashi, N.: Insights into Asymmetric Back-Arc Basin Formation in the Mariana Trough at 17°N from Traveltime Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8155, https://doi.org/10.5194/egusphere-egu24-8155, 2024.

EGU24-8282 | ECS | Orals | GD4.1 | Highlight

A twisted ribbon of subducted lithosphere beneath southeast Anatolia and its seismotectonic implications 

Sonia Yeung, Gordon Lister, Wim Spakman, Oğuz Göğüş, Marnie Forster, Adam Simmons, and Hielke Jelsma

Forensic analysis of the geological architecture in the aftermath of destructive earthquakes is an essential step to identify controlling structures that need to be monitored. Here we suggest the sequence of events during the February 2023 Turkey–Syria earthquakes was driven by the roll back of a twisted ribbon of subducted lithosphere beneath southeast Anatolia. We assume that the February 2023 Turkey–Syria earthquakes were short-term manifestations of a longer-term tectonic process. To investigate, we built a three-dimensional (3D) mesh frame defining the geometry of subducted Tethyan lithosphere in the Eastern Mediterranean, using the UU-P07 global tomography model, and where appropriate, earthquake hypocentre sets from the Global Centroid Moment Tensor project (GCMT) and from the International Seismic Centre (ISC). The 3D model of the subducted Tethyan lithosphere exhibits three variably twisted ribbons. The Cyprus ribbon is subducted to ~280 km depth and is ~120 km wide, and it twists and curls parallel to its length by ~20 degrees anticlockwise.

The geometry prior to subduction can be estimated by floating the mesh back to the surface using the Pplates program. The process of subduction can be visualised by incorporating the floated mesh into a 2D+time tectonic reconstruction from 125 Ma to the present. This leads to the inference that the ribbons are associated with slab tearing during roll back of the Tethyan lithosphere, due to the accretion of the Lycian block and the Cyprus promontory. The twisting motions can be related to a lateral push sideways caused by anticlockwise vertical axis rotation of the Arabia indenter during opening of the Red Sea rift and the Gulf of Aden. We suggest that the Anatolian lithosphere is being stretched by ongoing differential roll back caused by drag of the Cyprus ribbon through the asthenosphere underlying southeast Anatolia. This motion continually triggers failure along strike-slip faults while facilitating the continued indentation of Arabia. Seismotectonic analysis of aftershock sequences highlights the underlying geodynamics.

How to cite: Yeung, S., Lister, G., Spakman, W., Göğüş, O., Forster, M., Simmons, A., and Jelsma, H.: A twisted ribbon of subducted lithosphere beneath southeast Anatolia and its seismotectonic implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8282, https://doi.org/10.5194/egusphere-egu24-8282, 2024.

EGU24-8760 | ECS | Orals | GD4.1

Mantle Oxidation Driven by the Redox Dynamics of the Mariana-Type Subduction 

Wenyong Duan, James Connolly, Peter van Keken, Taras Gerya, and Sanzhong Li

Oceanic plates descending into subduction zones transport a significant amount of oxidized material to both the subduction zone and the Earth's deeper layers (Wood et al. 1990). However, the specific mechanism of mass transfer and the corresponding flux released at different depths remains unclear. Through the use of numerical modeling and a coupled geochemical database, we examined redox dynamics in subduction zones, particularly focusing on Mariana-type subduction zones, representative of the modern plate tectonic regime (Yao et al., 2021).

Our findings highlight two primary mechanisms in the mantle oxidation processes related to subduction. Firstly, desulfurization enables subduction fluids to carry substantial oxidation fluxes into the sub-arc mantle. Mass balance calculations emphasize the sufficiency of these fluxes in oxidizing both the arc magma and mantle wedge, with the hydrated mantle being the primary fluid contributor, followed by the altered oceanic crust. Secondly, partial melting of slab-top rocks, where Fe3+-rich melts from sediments and altered oceanic crust play a predominant role in the oxidation of the back-arc mantle. Importantly, during Mariana-type subduction, the majority of oxidation fluxes penetrate the deeper mantle with subducting slabs. According to our models, we illustrate that during the modern era of plate tectonics, the oxidation fluxes generated by Mariana-type subduction zones had a significant global impact on Earth's mantle redox evolution and the oxygenation of our planet.

References

Wood, B. J., Bryndzia, T., Johnson, K. E. Mantle oxidation state and its relationship to tectonic environment and fluid speciation. Science 248, 337-345 (1990).

Yao, J., Cawood, P. A., Zhao, G., Han, Y., Xia, X., Liu, Q., Wang, P. Mariana-type ophiolites constrain the establishment of modern plate tectonic regime during Gondwana assembly. Nat. Commun. 12(1), 4189 (2021).

How to cite: Duan, W., Connolly, J., van Keken, P., Gerya, T., and Li, S.: Mantle Oxidation Driven by the Redox Dynamics of the Mariana-Type Subduction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8760, https://doi.org/10.5194/egusphere-egu24-8760, 2024.

EGU24-8783 | Posters on site | GD4.1

Unveiling parental compositions in Andean-type intrusions through magma mingling zones 

Daniel Gómez Frutos and Antonio Castro

An important task in petrology is the successful identification of the parental that birthed the magmas constituting the continental crust. Among these, an intermediate parental to subduction related magmas, often referred to as Andean-type, has been determined experimentally in various works. However, identification of a natural rock matching the model compositions has not been accomplished. This difficulty arises primarily from prolonged cooling times, leading to large-scale fractionation and impeding the preservation of the parental magmas. In this regard, quenching becomes a valuable phenomenon, precluding differentiation and thereby preserving the initial compositions. This highlights the relevance of magma mingling zones, a common feature of Andean-type batholiths, as optimal places to probe for parental compositions. Following these considerations, a new set of geochemical analyses from the Gerena magma mingling zone, an Andean-type intrusion in southwest Iberia, is presented to address this problematic. Sampling focused on dark bodies, presumed to be mafic to intermediate in composition. Interestingly, combined evidence from major, trace element and Sr and Sm isotopes suggest that the smaller dark bodies have undergone precluded differentiation. Moreover, according to geochemical modelling their composition can reproduce the neighbouring granites and cumulates through differentiation. These findings emphasize the importance of magma mingling zones as valuable sources of information and shed new light in the identification of the parental composition to Andean-type magmatism.

How to cite: Gómez Frutos, D. and Castro, A.: Unveiling parental compositions in Andean-type intrusions through magma mingling zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8783, https://doi.org/10.5194/egusphere-egu24-8783, 2024.

        The East Kunlun orogenic belt represents a typical accretionary orogenic belt and has undergone an evolutionary process from the Proto-Tethys to the Paleo-Tethys oceans. The Late Triassic period witnessed the East Kunlun transitioning into the post-collisional extensional tectonic setting. However, there is ongoing debate regarding the dynamic mechanism responsible for the post-collisional extension. This study conducts the lithological, geochronological, and geochemical characteristics of the Yeniugou gabbros to shed light on the dynamic mechanism. Zircon geochronology suggests that the gabbros formed in the Late Triassic, ca. 207–209 Ma. Furthermore, the positive εHf (t) values (0.1–5.7), the relatively high values of Mg# (42.2–59.4), as well as the elevated contents of the compatible element (V, Cr, Co, Ni), suggest a mantle source with the contributions from asthenospheric mantle constituents. Additionally, gabbros are enriched in LREE and LILEs (Rb, Ba, Th, U, Sr), and depleted in HFSEs (i.e., Nb, Ta, Ti, Zr), suggesting the incorporation of arc-related enrichment components. The higher values of La/Sm, Th/Yb, Th/La, and lower values of Ba/Th, Ba/La, and Lu/Hf indicate that the enriched components are derived from the melting of the terrigenous sediment. The higher Zr/Y ratios, Nb contents, moderate Zr, Y contents, and the positive correlation between clinopyroxene Alz and TiO2, imply that these rocks were formed within an extensional tectonic setting, where upwelling of asthenospheric mantle caused partial melting of metamorphosed lithospheric mantle. Our new investigations support the interpretation that E-KOB experienced the thickening lithospheric delamination during the Late Triassic.

How to cite: Zhang, B., Dong, Y., Sun, S., and He, D.: Petrogenesis and tectonic implications of the late Triassic gabbro in southern East Kunlun Orogenic Belt, northern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10243, https://doi.org/10.5194/egusphere-egu24-10243, 2024.

EGU24-10304 | Orals | GD4.1

Dynamics of subducting slabs and origin of deep-focus earthquakes 

Hana Čížková, Jakub Pokorný, Craig Bina, and Arie van den Berg

Most earthquakes are associated with subduction zones. While earthquakes occur on very short time scales, they reflect thermal conditions and stress state attained in the subducted slab during its long term evolution. The source models of deep earthquakes thus might provide unique information about stress distribution in subduction zones which could be used to constrain geodynamic models.  

In the Tonga region, ordinary deep (620-680 km) earthquakes exhibit down-dip compressional stresses as expected, but unusually deep (≥680 km) earthquakes have unique focal mechanisms with vertical tension and horizontal compression. Here we employ geodynamic slab models to investigate the effects of the phase transitions and rheology on the stress and thermal state in Tonga slab in the transition zone and shallow lower mantle and we discuss its relation to deep earthquakes. We show that the direct buoyancy effects of the endothermic transition at 660 km depth are overprinted by bending-related forces and resistance from the more viscous lower mantle transmitted by a strong slab up-dip. The stress pattern that best fits seismogenic stresses is found for the cold plate (150 Myr old) and a viscosity increase at 1000 km depth. An abrupt change in stress orientations occurs as the slab temporarily deflected by the endothermic phase transition penetrates the shallow lower mantle while the fold in the flat-lying part tightens.

How to cite: Čížková, H., Pokorný, J., Bina, C., and van den Berg, A.: Dynamics of subducting slabs and origin of deep-focus earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10304, https://doi.org/10.5194/egusphere-egu24-10304, 2024.

EGU24-10345 | ECS | Orals | GD4.1

Subduction initiation, propagation and progression recorded along the Sulu and Celebes seas (SE Asia) 

Patricia Cadenas Martínez and César R. Ranero

The inception of a subduction system delineates the birth of a destructive plate boundary that constrains the closure of Earth´s oceans. Material and structures of the transient stage between the reactivation of a passive margin and the establishment of a self-sustaining subduction zone are rarely-preserved in the geological record of fossil subduction zones, and natural examples of currently ongoing subduction initiation are scarce. Reported Cenozoic fossil examples have been interpreted to illustrate successive immature stages of plate rupture, underthrusting and the formation of a volcanic arc, all prior to the formation of a mature self-sustained subduction zone. However, many uncertainties about the processes and the kinematics of subduction initiation remain, due to the scarcity- and lack of recent studies- of examples recording the plate rupture and decoupling, the transition to underthrusting, and the formation of the mega-thrust fault.

We use seismic images to study active subduction initiation and plate-boundary propagation in the Sulu and Celebes seas located in SE Asia. The two basins formed in Paleogene to Lower Miocene time and since possibly late Miocene, a phase of contractional deformation has led to the creation of the subduction trenches. The Sulu Trench is growing and laterally propagating along the SE margin of the Sulu Sea basin, and the Cotobato and North Sulawesi trenches propagate along the northeastern and southern margins of the Celebes Sea basin.

We reprocessed and interpreted >4857 km of 2D seismic reflection profiles that image the structure across three active trenches and the regions where the trenches are laterally propagating and display likely related deformation. We identified and mapped subduction-related structural domains of the downing and overriding plates. The megathrust plate boundary reaching the surface separates a trench filled with turbidites from the thrusts sheets of accretionary prisms, overlain with a forearc basin. The images show pre-existing faults and first-order seismo-stratigraphic horizons along the continental margins away from the trench, and the deformation structures associated to their reactivation and possibly linked to either lateral propagation of the subduction trenches or perhaps the local formation of a new trench.

The images illustrate the transition from diffuse deformation to two decoupled plates and to along-strike structural variations of subduction-related structural domains. We show for the first time how the three trenches record the spatial variability of currently active deformation associated to stages of passive margin reactivation, subduction initiation, propagation and progression. These results provide novel insights to further investigate and constrain unsolved questions about the initiation and development of subduction zones.

How to cite: Cadenas Martínez, P. and R. Ranero, C.: Subduction initiation, propagation and progression recorded along the Sulu and Celebes seas (SE Asia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10345, https://doi.org/10.5194/egusphere-egu24-10345, 2024.

EGU24-10454 | Orals | GD4.1

Compaction pressure goes global: Investigating fluid release and flow in subduction zones worldwide 

Peter E. van Keken, Cian R. Wilson, and Geoff A. Abers

Subduction of oceanic slabs causes the influx of fluids through hydrated phases. Fluids are released by metamorphic dehydration reactions particularly when the slab comes in contact with the hot mantle wedge at depths greater than ~80 km. Fluid release can be diverse and occur at different depths inside the oceanic slab with sediments and uppermost oceanic crust generally dehydrating before the serpentinized mantle and gabbroic sections.

Significant progress has been made in recent years on geophysical imaging of subduction zones that highlight the thermal structure, the location of metamorphic dehydration reactions, and the presence of fluids in slab and mantle wedge (e.g., Kita et al., Tectonophysics, 2010; van Keken et al., Solid Earth, 2012; Shiina et al., GRL, 2013; Pommier and Evans, Geosphere, 2017, Abers et al., Nature Geoscience, 2017). In a complimentary fashion, geodynamical modeling provides first principles constraints on how fluids are released and transported.

Using a simplified modeling geometry, Wilson et al. (EPSL, 2014) showed the importance of compaction pressure gradients as an oft cited, but also frequently ignored, driving force for fluids in the slab. The inclusion of compaction pressure gradients causes the fluids to both be driven from their source to the arc and flow up in part parallel to the slab surface, explaining to at least some extent geophysical observations.

We have modeled the effects of compaction pressure gradients in a global set of subduction zone models (van Keken and Wilson, PEPS, 2023) and show that focusing of the fluids below the typical arc location (at where the slab is at about 100 km depth) is a common feature and that therefore the compaction pressure effects, along with the geometry of the cold corner in the mantle wedge, can naturally explain the position of the arc above subduction zones globally.

How to cite: van Keken, P. E., Wilson, C. R., and Abers, G. A.: Compaction pressure goes global: Investigating fluid release and flow in subduction zones worldwide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10454, https://doi.org/10.5194/egusphere-egu24-10454, 2024.

EGU24-10800 | ECS | Orals | GD4.1

Gravimetric signature of subducted slabs’ deep thermal structures. 

Xavier Vergeron, Cécilia Cadio, and Fanny Garel

At subduction zones, cold lithospheric plates dive deep into the hotter Earth’s mantle. Earthquakes can occur at depths of hundreds of kilometers in these cold subducted slabs, apparently related to their thermal structures. Seismic tomography provides a first-order information on slab morphology but cannot discriminate « cold » from « warm » slabs partly due to the inhomogeneous repartition of seismic sources and surface sensors. This study investigates the potential of the gravity data from the GOCE mission to infer deep slabs’ inner thermal structures (> 200 km depth). Thermal structures of slabs with various morphologies are derived from dynamic subduction zones models. We convert temperature field into density assuming mineralogical phases at thermodynamical equilibrium for pyrolite mantle using HeFESTo model (Stixrude and Lithgow-Bertelloni 2011). We then use the freeware DynG3 (Cadio et al. 2011) to predict surface and CMB deflections due to slab dynamic sinking – depending on the radial mantle viscosity – and calculate the corresponding synthetic signals (geoid, gravity disturbance, gravity gradients). Our parametric study considers various radial mantle viscosity profiles, slab morphologies and slabs inner thermal structures (SITS). As expected, geoid and gravity gradients are sensitive to density anomalies at different depth ranges. We highlight linear relationships between both these signal for a given viscosity profile and a given slab’s morphology :

  • First, the colder an isothermal slab, the higher the geoid and gravity gradients anomalies.

  • Second, for a given shallow temperature, the colder the deep slab (>500 km), the lower the gravity gradient anomaly and the higher the geoid anomaly.

This last, counter-intuitive, result is explained by the fact that the long wavelength component associated to deep density anomaly overprints, for colder slabs, the short wavelength component associated to surface deflection. Thus, for a known viscosity profile and slab morphology, both shallow (~ 200-500 km depth) and mean slab thermal structures could be inverted from the combination of geoid and gravity gradients anomalies.

How to cite: Vergeron, X., Cadio, C., and Garel, F.: Gravimetric signature of subducted slabs’ deep thermal structures., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10800, https://doi.org/10.5194/egusphere-egu24-10800, 2024.

Subduction zone plate boundary shear zones are often heterogenous, polyrheological units with a block-in-matrix structure analogous to exhumed mélanges. Field study of these units reveal extreme variability in block and matrix lithologies, geometries, and internal structures. Subduction zone plate interfaces are host to a wide range of slip magnitudes and velocities, including some of the largest earthquakes on our planet.

Previous studies on the mechanical behaviour of these mélange units in shear zones have shown that the material properties of the blocks and matrix, as well as the proportions of each, strongly influence the rheological behaviour of the zone. Analysis of the Osa Mélange in SW Costa Rica has also shown that blocks may be weakened by alteration and brecciation, and/or the matrix strengthened by diagenesis/metamorphism, such that the blocks become weaker than their surrounding matrix at shallow depths of subduction. Rheological inversion may also occur at greater depths by processes such as heterogenous dehydration of serpentinite. Such an inversion of the typically-envisaged rheological relationship can have a profound influence on the distribution of stresses, location of ruptures, and the resultant slip behaviour. 

Using COMSOL Metaphysics, we conducted a systematic series of finite element numerical experiments of simple-shear in models consisting of one or multiple inclusions. The geometry, arrangement, number, and material properties of these inclusions were varied systematically — as was the material properties of the surrounding matrix — and the magnitude and location of von Mises stress minima and maxima were recorded. These experiments assessed varying the Young’s Modulus of blocks and matrix from Eblock > Ematrix to Ematrix > Eblock in comparison to varying block proportion, block aspect ratio, block angularity, block rotation angle, and the difference in Poisson’s ratio between the blocks and the matrix. 

Our data shows that the difference in Young’s Modulus between the blocks and the matrix has a greater influence on the magnitude and structure of the stress field than any other studied factor and that weak blocks in a strong matrix lead to significantly greater accumulated stresses in all geometrical configurations. Whether the blocks or matrix are expected to yield first will depend on the interplay between the difference in strength and the difference in Young’s Modulus of the two materials. In the inverted rheological relationship, failure in one block leads to greater increases in the stresses in neighbouring blocks than in the normal rheological relationship.

Clustered failure of blocks in a subduction channel has been proposed as a causal mechanism for non-volcanic tremor, with the accompanying accelerated strain being analogous to slow slip events. Rheological inversion markedly increases the likelihood that blocks fail before the matrix and that failure of one block triggers a cascade of similar failure events. This study demonstrates the significance of rheological inversion to considerations of the mechanics of subduction zone plate boundary shear zones.

How to cite: Clarke, A., Vannucchi, P., and Morgan, J.: Weak Blocks in a Strong Matrix: Exploring parameter-spaces for the biggest controls on subduction interface mechanics , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11199, https://doi.org/10.5194/egusphere-egu24-11199, 2024.

EGU24-12008 | ECS | Posters on site | GD4.1

On The Timing of Collision Induced Slab Break-Off and Polarity Reversal 

Erkan Gün, Philip Heron, Russell Pysklywec, Gültekin Topuz, and Oğuz Göğüş

The subduction process is the main driver of tectonic plate movements and can carry different-sized, thick crustal materials (i.e., continents, oceanic plateaux, seamounts, volcanic arcs) to the subduction trenches through the consumption of oceanic plates. The arrival of these allochthonous terranes to the subduction channel and their accretion to the overriding plate (fully or partly) can often halt the subduction process. Such a subduction-choking event is usually followed by slab break-off or polarity reversal if an ocean-ocean subduction setting is present. While these two types of post-subduction termination events are well-documented in the literature, their timing following a collision is often overlooked.

Here, we present an extensive compilation of scientific literature that shows slab break-off and subduction polarity reversal (flip) events following a collision can happen in a very short time interval. Evidence from contemporary and paleo-subduction zones (i.e., Ontong Java Plateau, Taiwan/Ryukyu Arc, Banda Arc, Philippine Trench, Caribbean Oceanic Plateau, Central Apennines, India-Asia collision) suggests that these major subduction dynamic changes can occur, on average, in 2.5 to 4.5 Myr. The findings of our numerical subduction models are in accordance with the literature and demonstrate that the required time for collision-induced break-off and polarity flip can be as short as ~2 Myr. Our recent numerical modeling work, focusing on allochthonous terranes (microcontinents and oceanic plateaux), explains a potential mechanism for these fast geodynamic events. The slab pull force can stretch and weaken the trench side of drifting terranes. Following arrival in the subduction channel, this weakened portion of terranes is easier to break, yielding a fast detachment of subducting slabs.

How to cite: Gün, E., Heron, P., Pysklywec, R., Topuz, G., and Göğüş, O.: On The Timing of Collision Induced Slab Break-Off and Polarity Reversal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12008, https://doi.org/10.5194/egusphere-egu24-12008, 2024.

EGU24-12731 | Orals | GD4.1

The Seismic Expression and Tectonomagmatic Evolution of Subduction Termination along the Anatolian Margin  

Jonathan Delph, Mary Reid, Daniel Portner, Susan Beck, A. Arda Ozacar, W. Kirk Schleiffarth, Michael Darin, Donna Whitney, Michael Cosca, Christian Teyssier, Nuretdin Kaymakci, and Eric Sandvol

The geological expression of subduction termination is poorly understood due to overprinting during the collisional stage of the Wilson Cycle. The Anatolian domain of the eastern Mediterranean represents a modern system where spatial variability can be interpreted in terms of the transition from subduction to collision. Convergence in the west is accommodated by the subduction of the last remnants of Neotethyan oceanic lithosphere, while in the east, the margin has transitioned to complete continent-continent collision. In central Anatolia, however, the expression of convergence is complicated by the underthrusting of small continental fragments and attenuated continental lithosphere. By investigating variations in the geological expression of convergence across this system, we can investigate the processes that accompany the transition from subduction to collision.

Spatially variable tectonomagmatic and seismic characteristics along the Anatolian margin reflect this transition. Seismic images reveal a disjointed and disaggregating subducting slab beneath central Anatolia that interacts with, and in some cases induces, mantle flow. This spatially corresponds with Miocene-to-recent volcanism that is sourced from very shallow depths (<60 km) and has a southwestward younging pattern to the initiation of magmatism. Primitive melts in the region contain metasomatized lithospheric mantle and asthenosphere signatures resulting from the long-lived subduction history of the margin combined with recent slab rollback and mantle upwelling around the subducting slab edge based on seismic images. Superimposed on regional magmatic trends, local spatiotemporal patterns show subtle southward and westward younging and/or broadening, perhaps associated with thermomagmatic erosion of the lithosphere along relict structures and/or slab edge-induced flow. Conversely, seismic images in eastern Anatolia reveal a nearly uniform mantle flow and no discernable evidence for subduction. Interestingly, magmatic patterns in central and eastern Anatolia bifurcate in the early to mid-Miocene, interpreted as the time when a vertical slab tear developed along the once continuous Tethyan slab. These results indicate that expressions of subduction termination can be very heterogenous along the strike of a margin.

How to cite: Delph, J., Reid, M., Portner, D., Beck, S., Ozacar, A. A., Schleiffarth, W. K., Darin, M., Whitney, D., Cosca, M., Teyssier, C., Kaymakci, N., and Sandvol, E.: The Seismic Expression and Tectonomagmatic Evolution of Subduction Termination along the Anatolian Margin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12731, https://doi.org/10.5194/egusphere-egu24-12731, 2024.

EGU24-12869 | Posters on site | GD4.1

Deep lithospheric controls on the formation and evolution of the East Anatolian Fault Zone and Anatolia-Arabia-Africa Triple Junction 

Jonathan Delph, Michael Darin, Donna Whitney, Michael Cosca, Christian Teyssier, Tuna Eken, Nuretdin Kaymakci, Mary Reid, and Susan Beck

The North and East Anatolian Fault Zones represent plate-bounding transform faults that enable the westward tectonic escape of the Anatolian Plate away from the Arabian-Eurasian collisional zone. These fault zones are both capable of hosting large (Mw > 7) seismic events, as most recently demonstrated by the extremely damaging February 2023 Kahramanmaraş earthquake sequence. This earthquake sequence highlighted that plate boundary forces in this area are distributed over a very broad region, however what controls the location, distribution, and character of this plate-bounding strike-slip system remains enigmatic. To better understand potential contributions to deformation, we compare seismic images of the lithosphere (e.g., crustal and lithospheric mantle thickness and velocity) to deformational features and seismicity near the EAFZ, as well as further west where it joins with the Anatolia-Arabia-Africa (A3) triple junction along the southeastern margin of the Anatolian escape system. We interpret that although controls on surface deformation are commonly linked to stress in the brittle upper crust, the complex deformation and seismicity patterns in this region are likely related to variations in the location and extent of the strong lithospheric mantle of the Arabian plate, which currently underthrusts Anatolia as far north as the Sürgü-Çardak fault zone (~50 km). In addition, the Arabian lithospheric mantle extends at least as far west as at least the central Adana Basin, coincident with a zone of relatively deep (>30 km) strike-slip seismogenesis that has produced Mw > 6 earthquakes. By investigating the relationship between recent geological deformation since the inception of the East Anatolian Fault (ca. 5 Ma) and the modern record of seismic structure and seismicity, we infer that the Sürgü-Çardak fault zone and its associated near-orthogonal bend reaching into the Adana Basin will be the future southeastern boundary of the Anatolian Plate escape tectonic system.

How to cite: Delph, J., Darin, M., Whitney, D., Cosca, M., Teyssier, C., Eken, T., Kaymakci, N., Reid, M., and Beck, S.: Deep lithospheric controls on the formation and evolution of the East Anatolian Fault Zone and Anatolia-Arabia-Africa Triple Junction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12869, https://doi.org/10.5194/egusphere-egu24-12869, 2024.

EGU24-14322 | ECS | Posters on site | GD4.1

The metamorphic dehydration of subducted metabasalts in the Catalina Schist: Does epidote record fluid production at the depths of deep slow slip and tremor? 

Peter Lindquist, Cailey Condit, William Hoover, and Victor Guevara

Dehydration reactions in the subducting slab have been suggested as a fluid source for high pore fluid pressures that are inferred in the environment that hosts deep slow slip and tremor in subduction zones. Using petrography, major and trace element geochemistry, and petrologic modeling, we study the record of dehydration reactions in exhumed metabasalt from the Catalina Schist in southern California, USA to explore potential sources of the fluids that produce high pore fluid pressures at the plate interface. The Catalina Schist comprises tectonic slices that were underplated in a subduction zone at lawsonite blueschist to amphibolite facies conditions. Metabasalts from the epidote-amphibolite facies unit here represent a coherent section of oceanic crust that was underplated during subduction at ~550°C and ~1 GPa, and are  ~100 m structurally below an ultramafic-metasedimentary mélange unit interpreted to be a paleosubduction interface from ~35 km paleodepth. Previous thermodynamic modelling suggests that epidote minerals may be common reaction products during prograde dehydration reactions along typical warm subduction geotherms, particularly at the conditions of slow slip and tremor. We therefore focus on epidote textures and trace-element compositions to provide insights into the metamorphic reactions experienced by these metabasalts, and by extension reconstruct the dehydration history of this subducted slab. Pairing these analyses with phase equilibrium modeling, we estimate the P-T path experienced by these metabasalts and the conditions at which epidote may be growing or reacting out. Epidote textures vary significantly across outcrops and appear in various settings including: epidote-rich veins and vein-like dehydration networks, and porphyroblastic epidote in surrounding host rocks. Oscillatory zoning in synkinematic epidote porphyroblasts further suggests episodic growth under varying conditions or fluid compositions. Variations in the major element and trace element geochemistry of epidote across these domains, coupled with petrologic modeling helps to reveal the metamorphic reactions that occurred in these rocks, and allows us to begin quantifying the volumes of fluids that may be released during prograde metamorphism near the conditions of deep slow slip and tremor.

How to cite: Lindquist, P., Condit, C., Hoover, W., and Guevara, V.: The metamorphic dehydration of subducted metabasalts in the Catalina Schist: Does epidote record fluid production at the depths of deep slow slip and tremor?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14322, https://doi.org/10.5194/egusphere-egu24-14322, 2024.

Elastic/viscoelastic dislocation theory is a fundamental tool in computing crustal deformation due to fault motion, not only for instantaneous coseismic deformation but also for gradual postseismic and interseismic deformation. Expressing the kinematic interaction between the subducting and overriding plates by dislocation along the plate interface, our group has developed a crustal deformation model due to plate subduction, named "dislocation model for plate subduction" (Matsu'ura & Sato 1989, GJI), which is a generalization of Savage's back slip model (Savage, 1983, JGR), including the effect of deformation due to steady plate subduction. Hashimoto et al. (2004, PAGEOPH) demonstrated that the pattern of uplift rates in and around Japan computed by this model shows excellent coincidence to the observed free-air gravity anomalies. Fukahata and Matsu‘ura (2016, GJI), using the 2D model, explained the physical mechanism of island-arc uplift, trench subsidence, and outer rise uplift by combining the effects of lithospheric rotation and gravity.

   In this study, we develop a 3D numerical model and compute vertical displacement rates in a subduction zone caused by steady slip along a plate interface, in which the trench axis has a bend convex toward the island arc. Computation results show that the island arc lithosphere significantly subsides around the bend, and that the subsidence is larger for a larger bend angle.

   This subsidence can be physically understood by mass deficit in the island arc lithosphere, as explained below. When a plate subducts along a trench with a bend convex toward the island arc, mass excess inevitably occurs in the subducting slab, which can be understood from an analogy of a tablecloth draped at a corner of a table. In the dislocation model, the motion of plate subduction is expressed by displacement discontinuity along the plate interface. The displacement discontinuity, which is equivalent to a force system of a double couple, requires two surfaces that sandwich a fault to move in exactly opposite directions each other, which results in mass deficit in the island arc, because mass excess occurs in the subducting slab.

   Along the main Japanese islands, we observe significant invasions of negative free-air gravity anomalies into the forearc around the Hidaka Trough, the Kanto Plain, and the Bungo Channel, which correspond to the junctions of the trench axes. In brief, these forearc negative free-air gravity anomalies can commonly be understood by the above mechanism. We also observe similar invasions of negative free-air gravity anomalies around the Arica bend, South America, and Cascadia, though the signals of negative gravity anomalies are smaller in these regions, reflecting gentler changes of the strikes of the trench axes.

How to cite: Fukahata, Y. and Mori, Y.: 3-D Numerical Simulation of Island Arc Deformation based on the Dislocation Model for Plate Subduction and its Insight into Topographic Evolution of Island Arcs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14479, https://doi.org/10.5194/egusphere-egu24-14479, 2024.

EGU24-14482 | ECS | Posters on site | GD4.1

An alternative mode of slab deformation in the mantle transition zone: segmentation and stacking 

Keqing Li, Jiashun Hu, Yida Li, Hao Zhou, and HaiJiang Zhang

The contradiction of high subducting plate speed (ranging from 4-9 cm/yr on Earth’s surface) and slow slab sinking rate (about 1-2 cm/yr in lower mantle) is intimately related to the subduction dichotomy of strong plates and weak slabs. The significant difference in the two rates indicates significant slab deformation in the mantle transition zone. However, the way and mechanism by which this deformation occurs have not been fully understood. Slab buckling has been frequently invoked to explain the deformation, but it is insufficient to accommodate the large difference in slab sinking rates across the mantle transition zone, even if an extremely low yield stress  100 MPa is applied.

Using 2-D numerical models that incorporate composite viscosity and grain size evolution, we propose a new mode of slab evolution, slab segmentation and stacking, to accommodate the differential slab sinking rates between the upper and lower mantle. The segmentation of slab is facilitated by the serpentinization of the normal faults at the outer rise and the grain size evolution, confirming the results of earlier studies (Gerya et al., 2020). More interestingly, we find periodic tearing and stacking of slab when it encounters the high viscosity lower mantle. Stacked slabs slowly sink in the lower mantle, while periodic slab tearing hinders stress transimission upward, allowing shallow plates to subduct at a higher rate. This model not only explains the high plate subduction rate observed at present day, but also the thickening of slab in the lower mantle. In addition, it provides a mechanism for slab to tear in the mantle transition zone, and thus may explain the enigmatic slab geometry beneath the Izu-Bonin-Mariana subduction zone.

How to cite: Li, K., Hu, J., Li, Y., Zhou, H., and Zhang, H.: An alternative mode of slab deformation in the mantle transition zone: segmentation and stacking, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14482, https://doi.org/10.5194/egusphere-egu24-14482, 2024.

EGU24-14498 | ECS | Posters on site | GD4.1

Numerical modelling of dynamic fluid-rock reactions in subduction settings 

Kevin Wong, Alberto Vitale Brovarone, Simon Matthews, Guillaume Siron, Valeria Turino, Adam Holt, and Andrew Merdith

At subduction zones, geophysical and petrological observations suggest that forearc mantle wedges may be serpentinised by fluids released from the devolatilization of subducting slabs [1]. This pervasive serpentinisation of the wedge may be a substantial source of abiotic hydrogen (H2) and methane (CH4): gases with the potential to feed extremophile microorganisms in the deepest parts of the continental lithosphere that overlie the wedge. Characterisation of mantle wedge serpentinisation is therefore paramount to constraining the limits within which this deep biosphere can exist. However, the geochemical and geodynamical controls on wedge serpentinisation remain a subject of immense uncertainty. The magnitude of H2 and CH4 concentrations and fluxes generated from wedge serpentinisation are therefore poorly constrained at present.

Owing to the inaccessibility of the mantle wedge, constraints on H2 and CH4 generation within the mantle wedge must be predicted through geochemical models. In this contribution we present the preliminary results of an ongoing modelling study into mantle wedge serpentinisation. Our approach utilises the Deep Earth Water model [2] to calculate fluid-rock reactions at relayed pressure-temperature conditions in the wedge, which are dictated by geodynamical models of subduction zone thermal structure [3]. The resultant fluids of prior reactions are used as reactant fluids for subsequent reactions at new pressures and temperatures; a chain of individual reactions therefore simulates the whole-scale serpentinisation of a column of mantle rock by slab fluid as the fluid migrates upwards through the wedge. By recording the composition of the overall mantle column at each pressure-temperature step, the introduction of new fluid to the resultant column provides a time element, which we use to track the evolution of bulk mantle mineralogy as subduction progresses.

Our preliminary results suggest that a heavily serpentinised layer forms rapidly at the slab-wedge interface, thereby strongly shielding the overlying mantle from significant alteration. Over more time steps, while bulk mantle density continues to decrease with time and increasing serpentinisation, our model suggests that new fluid does not significantly alter the mineralogical composition of the bulk mantle as observed within the first few time steps, and H2 and CH4 concentrations remain invariant throughout the column. However, the rate at which this fluid equilibration is achieved is strongly dependent on the initial conditions applied to the model. Our approach therefore provides a means to test multiple different parameters on H2 and CH4 generation at subduction zones, with scope for investigating the impact of variable fluid-rock ratio, initial mantle wedge and slab fluid compositions, and mantle wedge thermal structure.

[1] Vitale Brovarone et al., 2020. Nature Comms. 11(1), 3880.
[2] Sverjensky et al., 2014. Geochim. Cosmochim. Acta 129, 125-145.
[3] Holt and Condit, 2021. Geochem. Geophys. Geosyst. 22(6), e2020GC009476.

How to cite: Wong, K., Vitale Brovarone, A., Matthews, S., Siron, G., Turino, V., Holt, A., and Merdith, A.: Numerical modelling of dynamic fluid-rock reactions in subduction settings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14498, https://doi.org/10.5194/egusphere-egu24-14498, 2024.

EGU24-14820 | Orals | GD4.1

Subduction dynamics and overriding plate deformation 

Wouter P. Schellart

Many subduction zones on Earth experience active overriding plate deformation. Most experience extension, resulting in the formation of a backarc basin (e.g. East Scotia Sea, North Fiji Basin, Aegean Sea), while some experience shortening, resulting in a massive cordilleran mountain range (e.g. Andes). It is unclear why some overriding plates experience shortening and others extension, and why extension occurs more frequently than shortening. Numerical geodynamic simulations of subduction are presented investigating the control of slab width and subduction depth on overriding plate deformation. The numerical models demonstrate that shortening only occurs at very wide subduction zones that have subducted into the lower mantle, while overriding plate extension occurs more frequently, taking place both for narrow and intermediate size subduction zones throughout their evolution, and for wide subduction zones in the early (upper mantle) stage of their evolution as well as near their lateral slab edges during the middle stage of their evolution. The model results are compared with a global dataset of all active subduction zones on Earth (about 51,600 km of subduction zones), providing an explanation for the present-day deformation style at these subduction zones. In particular, the comparison between models and the global dataset provides an explanation for the more frequent occurrence of extension in the overriding plate compared to shortening.

How to cite: Schellart, W. P.: Subduction dynamics and overriding plate deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14820, https://doi.org/10.5194/egusphere-egu24-14820, 2024.

EGU24-15803 | ECS | Posters on site | GD4.1

Slab window geodynamics: towards an integrated understanding of upper mantle dynamics and observations 

Jorge Sanhueza, Attila Balázs, Taras Gerya, Gonzalo Yáñez, and W. Roger Buck

The generation of a slab window impacts the spatio-temporal evolution of subduction zones and promote complex mantle flow pattern where slabs once descended. The origin of slab windows is attributed to processes such as mid-ocean ridge subduction, slab tearing and/or break-off. The interaction between mid-ocean ridges and trenches is a common process affecting the geodynamic history of the margins around the Pacific, at least, during the Cenozoic and generated several modern slab windows. These intriguing features have notable effects on the upper mantle where temperature anomalies develop due to the asthenospheric upwelling and complex toroidal flow patterns through and around slab windows. There are profound effects on the overriding plate for the surface heat flow, geochemistry and spatial distribution of magmatic activity, seismicity and topographic relief. However, these manifestations evolve through space and time depending on the ridge axis-trench geometry, inducing the continuous slab window opening during its subduction.

In this contribution, we derived a simplified expression for the slab window angle and then conducted 3D geodynamic modeling to link slab windows dynamics with geochemical and geophysical observables. The numerical models were conducted with fixed geometries in steady-state (using finite elements), compared with time-dependent solutions (using the I3ELVIS code) and then compared with observations from modern slab windows along the eastern Pacific. The analytical solution for the plan projection of the slab window depends on three parameters: the ratio between the half-spreading rate to the velocity of the overriding plate, the subduction angle and the obliquity of the ridge axis respect to the trench.

Fast spreading or slow plate convergence promotes a wide (> 90°) slab window while slow spreading or fast convergence narrows this gap (< 90°). The slab dip and ridge obliquity have a second order control on the plan projection of the slab window but affect the existence of a steady-state solution. The implementation of this geometry into 3D steady-state models was used to generate a novel methodology to estimate mantle/melt upwelling and temperature anomalies in the upper mantle for a wide range of tectonic settings. Preliminary results on 3D time-dependent models reproduce a self-consistent opening of the slab window by only imposing spreading at the mid-ocean ridge and a subduction velocity with respect to the overriding plate. The ratio and absolute magnitude of these velocities controls the timing of the opening as well as the lateral and depth extent of the subducting plates. This timing also influences the development of upwelling and toroidal flow patterns around the slab edges. Finally, observations in modern slab windows along the eastern Pacific are consistent with the temperature and velocity field of the models. Variations in temperatures in the upper mantle are consistent with mantle shear wave speeds anomalies, while the flow field is correlated with the azimuthal anisotropy. In terms of magmatism, variables degrees of melting are consistent with the generation of tholeiitic to alkaline magmas in backarc areas.

How to cite: Sanhueza, J., Balázs, A., Gerya, T., Yáñez, G., and Buck, W. R.: Slab window geodynamics: towards an integrated understanding of upper mantle dynamics and observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15803, https://doi.org/10.5194/egusphere-egu24-15803, 2024.

EGU24-15924 | Posters on site | GD4.1

The Mussau Ridge and Trench – news from an infant subduction zone 

Philipp Brandl, Christoph Beier, Leon Waßmund, Jacob Geersen, and Felix Genske

The Mussau Trench between Papua New Guinea and the Federated States of Micronesia is considered as the type locality for induced subduction initiation through transference. Despite its significant role for studying and understanding global plate tectonic cycles, little is known about its tectonic  geomorphology, lithostratigraphy, and geodynamic evolution. During research expedition SO299 DYNAMET with the German RV SONNE, the morphology and shallow structure of the Mussau Ridge was mapped along its entire length and sampled at representative locations. At the central segment, the ridge was visually mapped and stratigraphically sampled using the ROV. Here we present the first results from petrology, geochemistry and structural mapping of the ridge. Preliminary glass major and trace element data indicate a depleted MORB-like nature of the exposed crust that is in agreement with previous findings. Stratigraphically, lavas (layer 2A) and sheeted dykes (layer 2B) of the oceanic igneous crust are exposed. Whole rock trace element and radiogenic isotopes analyses are currently underway to further constrain the geochemical character of the crust and its associated mantle sources. Initial results from hydroacoustic and visual mapping indicate the presence of an active thrust system based on pristine fault scarps and large rubble piles lacking any sediment cover. However, shape and structure of the ridge vary along strike, and only the central portion holds indications for tectonic uplift. In the south and in the north, the ridge shows evidence for a strong lateral shear component. We combine the obtained results into an initial model of the tectonic evolution of the ridge and how this fits into regional plate tectonic models.

How to cite: Brandl, P., Beier, C., Waßmund, L., Geersen, J., and Genske, F.: The Mussau Ridge and Trench – news from an infant subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15924, https://doi.org/10.5194/egusphere-egu24-15924, 2024.

EGU24-16152 | Posters on site | GD4.1

Balance of solid and fluid transfers near the updip limit of the seismogenic zone at the scale of all subduction zones in a revised kinematic framework 

Serge Lallemand, Michel Peyret, Diane Arcay, Nestor Cerpa, and Arnauld Heuret

The nature and amount of sediments transferred from one plate to the other near the subduction interface partly determine the tectonic and seismogenic regime of a margin. Examination of over 500 multichannel seismic lines has enabled us to build a global database of subduction zone front characteristics at unprecedented spatial resolution. The total thickness of sediments in the trench below the deformation front, as well as that of the subduction channel at a distance from the trench, combined with other indices, such as the tectonic regime of the forearc or the migration of the volcanic front, are used to revisit the accretionary or erosional character of active margins.

The integration of our observations over the last million years has been achieved in parallel with a revision of the kinematics of subduction zones, taking into account deformation at the front of the thrust plate. Indeed, subduction zones are often the site of distributed or localized deformation up  to several hundred kilometers away from the plate boundary. Taking the "arc sliver zone » deformation into account yields a more accurate estimate of the effective long-term slip velocities (modulus, azimuth) on the subduction interface, which is fundamental to properly estimate material flow transiting towards the mantle.

Preliminary conclusions, based on ∼3/4 of sufficiently documented subduction zones, show a predominance of the erosive character of subduction over the last million years. The flux of solid sedimentary matter through the shallow part of the subduction channel is approximately 1.5 km3/yr, and that of pore fluids 0.4 km3/yr. Some subduction zones, such as the Aegean-Cyprean one, are characterized by exceptional solid flux in the channel, whereas the fluid flux is comparatively moderate. This is because channel sediments are compacted even before being subducted. Indeed, porosity has a major influence in estimating these fluxes, maximum porosity in the channel being reached when there is neither accretion nor tectonic erosion. Overall, fluid flux in the channel is greater under erosive margins, due both to the higher rate of subduction and often higher porosity. The data are displayed over 260 transects across subduction zones thanks to the Submap web-tool (www.submap.fr).

How to cite: Lallemand, S., Peyret, M., Arcay, D., Cerpa, N., and Heuret, A.: Balance of solid and fluid transfers near the updip limit of the seismogenic zone at the scale of all subduction zones in a revised kinematic framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16152, https://doi.org/10.5194/egusphere-egu24-16152, 2024.

EGU24-16410 | ECS | Orals | GD4.1 | Highlight

H2 formation in subduction zone 

Alexis Gauthier, Tiphaine Larvet, Laetitia Le Pourhiet, and Isabellle Moretti

Dihydrogen (H2) is a promising decarbonized energy source, but traditional artificial production methods emit CO2 and/or consume a lot of energy. However, there are natural sources of H2 on Earth originating from diverse geochemical processes. A recent study above the Nazca plate subduction in the Andes, detected variations in the H2 emanation function on the slab dip angle. This H2 release is likely the result of peridotite hydration in the mantle wedge, notably through serpentinization. The water required for peridotite hydration is sourced from dehydration of the subducting plate as it sinks into the Earth's mantle.

This study aims to understand the influence of slab dip angle on H2 production in the mantle wedge using the pTatin2D code. Fluid circulation were implemented based on two principles:

  • The hydration and dehydration capacity of rocks under varying pressure and temperature conditions is predicted using tables from the thermodynamic software PerpleX.
  • The velocity of free water is equivalent to that of surrounding rocks, with a vertical component related to percolation.

Numerical simulations show that in the case of flat subduction, the mantle hydration zone, where H2 is produced, is wide and extending up to 500 km from the trench. On the other hand, in the case of a steep subduction, the zone is narrower, and is located between the trench and the volcanic arc. Magma formation competes with H2 generation for the use of water released from the subducting plate. During the transition from steep to flat subduction, the mantle hydration zone undergoes widening while the volcanic zone migrates significantly away from the trench. This transition may also trigger oceanic crust melting, resulting in a shift in magma composition before the volcanism intensity diminishes and then disappears.

How to cite: Gauthier, A., Larvet, T., Le Pourhiet, L., and Moretti, I.: H2 formation in subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16410, https://doi.org/10.5194/egusphere-egu24-16410, 2024.

EGU24-17659 | ECS | Posters on site | GD4.1

Dynamics of Plateau Growth: Geodynamic Modeling of the East AnatolianPlateau Uplift Through Double Subduction Processes 

Uğurcan Çetiner, Jeroen van Hunen, Andrew P. Valentine, Oğuz H. Göğüş, and Mark B. Allen

The Turkish–Iranian Plateau was formed by the collision between the Arabian and
Eurasian plates, commencing along the Bitlis-Zagros suture in the Late Eocene (~30-
35 Ma). This region, commonly partitioned into the East Anatolian Plateau and the
Iranian Plateau, is associated with significant differences in terms of lithospheric
structure despite an overall average of ~2 km. The geodynamic evolution of East
Anatolia is represented by a double subduction system, where the two branches of
Neo-Tethys were subducting beneath Eurasia, constantly accumulating accretionary
material that forms the bulk of the plateau today (i.e., East Anatolian Accretionary
Complex). Seismic evidence demonstrates that the region has unusually thin MOHO
(~35 km around Lake Van region) while the whole area is formed mostly by oceanic
(accretionary) material and is underlain by no or very thin mantle lithosphere. The
uplift of East Anatolia is attributed to slab break-off and slab peelback (delamination),
combined with crustal shortening. However, the intricate plate dynamics arising from
such a double subduction system, controlling plateau formation remains unclear.
Here, we conducted 2D numerical experiments and comparative model sets indicate
that, in a double subduction system like Eastern Anatolia, the mechanisms of slab
break-off and peelback heavily depend on the rheology of the subducting plates and
the coupling between the overlying and subducting plate along the trenches. In cases
of strong coupling between subducting and overlying plates, we observed an
amalgamation of the two subducting plates as they converge, potentially resulting in
a break-off as a single blob, depending on plate rheology. Conversely, in models with
weaker coupling along the trenches, peelback along the northern slab creates a thin
lithosphere along the accretionary prism, such as in the evolution of the Eastern
Anatolian Plateau. Our results highlight the important interaction between the
subduction systems where rheological constraints of the lithosphere, among other
model parameters, exert a first-order control for plateau formation.

How to cite: Çetiner, U., van Hunen, J., Valentine, A. P., Göğüş, O. H., and Allen, M. B.: Dynamics of Plateau Growth: Geodynamic Modeling of the East AnatolianPlateau Uplift Through Double Subduction Processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17659, https://doi.org/10.5194/egusphere-egu24-17659, 2024.

EGU24-17823 | Posters on site | GD4.1

Influence of the fluid pressure ratio on accretionary wedge evolution over long timescales 

Derek Neuharth, Whitney Behr, Adam Holt, and Jonas Ruh

Accretionary wedges are regions of off-scraped and underplated sediment and oceanic crustal materials formed along subduction zones. Many modeling studies investigate accretionary wedge mechanics on a crustal scale, or on a larger scale using kinematic boundary conditions. However, in fully dynamic systems subduction velocity can change through time in response to variations in large-scale subduction dynamics (e.g., as the slab travels rapidly through the upper mantle vs. slower sinking through the transition zone). How this time-dependence affects an evolving accretionary wedge and subduction interface properties, and the resulting effect on subduction speeds, is not well understood.

To understand how accretionary wedges evolve during different stages of subduction, we develop fully dynamic 2D subduction models using the finite element code ASPECT. The visco-plastic model setup consists of a dense subducting plate and a buoyant overriding plate coupled with a 6-km thick wet quartzite sediment interface. A fluid pressure ratio profile is prescribed within the sediment that varies from 0.4 at the surface to 0.9 at depths greater than 4-km. Between 50 to 100 km depth, the fluid pressure ratio is linearly tapered from 0.9 to 0. We run models for 30 Myr where we vary 1) the initial sediment thickness, 2) frictional strength, and 3) the depth needed to reach the maximum fluid pressure ratio. We explore how these parameters affect the thickness of the accretionary wedge, the amount of sediment that enters the subduction channel, and the resulting subduction speed.

Preliminary results suggest that an accretionary wedge will initially frontally accrete as the wedge thickens. Over time, the faults forming these slivers are rotated towards vertical and moved towards the subduction zone along a basal decollement. Eventually, a second decollement forms along the overriding plate interface and links to the first decollement through backthrust faulting, creating a series of accretionary wedge blocks that are underthrust into the subduction interface. Increasing the depth to the maximum fluid pressure ratio leads to a larger accretionary wedge, and a deeper basal decollement. A deeper decollement results in greater sediment underplating due to the backthrust faulting, resulting in more sediment within the subduction interface.

How to cite: Neuharth, D., Behr, W., Holt, A., and Ruh, J.: Influence of the fluid pressure ratio on accretionary wedge evolution over long timescales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17823, https://doi.org/10.5194/egusphere-egu24-17823, 2024.

EGU24-18222 | ECS | Posters on site | GD4.1

Variability of lower continental crust constrained by drill core data of the Ivrea Zone (DIVE project DT-1B, Ornavasso, Val d’Ossola, Italy) 

Alexia Secrétan, Sarah Degen, Luca Pacchiega, Jörg Hermann, and Othmar Müntener

The estimates of the chemical composition of the lower continental crust ranges from predominantly mafic to felsic. The Ivrea Zone in the Southern European Alps provides insight into this variability, featuring a pre-Permian mostly felsic lower crust modulated by additions of mafic rocks during Permian underplating. The Ivrea zone is an ideal location to examine major, trace, and volatile elements over the full range of proposed lower crustal compositions. Our study presents whole-rock data derived from a drill core of the first hole (DT-1B) of the ICDP-funded project DIVE (Drilling the Ivrea-Verbano Zone). The drilled section spans nearly 600 m, representing an upper part of the Ivrea lower continental crust. Logging of the drill core showed that biotite-gneisses (Qtz + Pl + Bt ± Gt ± Kfs ± Sil – 75 vol%) and metamafic rocks (Amp + Pl + Qtz ± Px ± Bt ± Gt – 21 vol%) are the main rock types with minor calcsilicate rocks (Cc + Gt + Px + Ttn + Qtz + Pl ± Amp – 2 vol%), and some minor pegmatites (2 vol%). Both targeted and grid sampling strategies aimed to minimize sampling bias, providing a reliable basis for understanding the Ivrea lower continental crustal composition and extrapolating the results toward a realistic assessments of the LCC composition in general.

Amphibolite facies metasediments (34 samples) range from calc-silicates to pelites and psammites, exhibiting a wide range of major element compositions (32 - 89 wt.% SiO2; 0.5 - 5.8 wt.% K2O; 0.35 - 0.54 Mg#). Metamafic rocks (16 samples) cover a more restricted compositional range (43 - 57 wt.% SiO2; 0.1 - 5 wt.% K2O; 0.3 - 3 wt.%; 0.36 - 0.61 Mg#). Most mafic rocks are LREE enriched, but a few resemble MORB-like compositions. A preliminary comparison of the bulk rock estimate of the entire drill core relative to the integrated composition derived from geological maps indicates that deviations between the two approaches are considerable, ranging from <10% up to 30% difference for major elements (calculated bulk vs compiled data from the literature: 62.8 vs 57.6 wt.% SiO2; 2.3 vs 1.95 wt.% K2O; 0.47 vs 0.50 Mg#). Results also indicate that fluid-mobile elements are mostly conservative with respect to potential protoliths. The chemical variability points to a possible origin of sediments derived from an accretionary wedge. The evaluation of bulk trace element ratios (i.e., Th/La, Sm/La, Nb/K2O) suggests that the drilled sequence likely originated from (Paleozoic?) turbidites. Subduction of sediments and accretion to the lower continental crust are the most likely processes to explain the predominance of metasediments in this part of the Ivrea lower continental crust.

How to cite: Secrétan, A., Degen, S., Pacchiega, L., Hermann, J., and Müntener, O.: Variability of lower continental crust constrained by drill core data of the Ivrea Zone (DIVE project DT-1B, Ornavasso, Val d’Ossola, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18222, https://doi.org/10.5194/egusphere-egu24-18222, 2024.

EGU24-18579 | ECS | Posters on site | GD4.1

Complex subduction and mantle dynamics induced by along-strike variations in overriding plate structure 

Pedro José Gea Jódar, Ana M. Negredo, Flor de Lis Mancilla, Jeroen van Hunen, and Magali Billen

Subduction zones are intrinsically three-dimensional and present a huge variability in observables along the trench, such as deformation style of the overriding plate, trench velocity, slab depth and mantle flow patterns. Geodynamic models commonly rely on factors such as external mantle flow and/or along-strike variations in the properties of subducting slabs to account for these variations in the trench-parallel direction, often ignoring the role of the overriding plate, which has been proven to strongly affect subduction dynamics. In this work, we investigate through self-consistent 3D subduction models how along-strike variations in the overriding plate structure can induce along-strike variations in subduction dynamics and mantle flow. Our results show that variations of the overriding plate thickness along the trench-parallel direction result in large along-strike variations of the trench retreat velocities, leading to highly arcuated trenches. This difference in trench retreat velocities along the trench induce complex mantle flow patterns, with the toroidal flow cells that surround the slab converging below the thin part of the overriding plate. Due to this complex mantle flow, regions of maximum localised extension are found within the thin portion of the overriding plate. Overall, our results contribute to a better understanding of seismic anisotropy observations at subduction zones on Earth.

How to cite: Gea Jódar, P. J., Negredo, A. M., Mancilla, F. D. L., van Hunen, J., and Billen, M.: Complex subduction and mantle dynamics induced by along-strike variations in overriding plate structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18579, https://doi.org/10.5194/egusphere-egu24-18579, 2024.

EGU24-19448 | ECS | Posters on site | GD4.1

Bending-related faulting, hydration, and mantle serpentinization in the incoming Cocos Plate at Middle America Trench: Evidence from wide-angle seismic refraction data 

Yuhan Li, Ingo Grevemeyer, Adam Robinson, Timothy J. Henstock, Milena Marjanović, Anke Dannowski, Helene-Sophie Hilbert, and Damon A.H. Teagle

At subduction zones, the bending of incoming plates and associated extensional stresses resulted in strong fault activity in the crust and upper mantle. The severe fracturing of the subducting slab in the trench outer rise facilitates the entrain of seawater into the lithosphere, leading to the serpentinization of peridotite in the upper mantle. Therefore, subduction zones are an important setting, nurturing material exchange between the hydrosphere and the solid earth, affecting the water cycle.

To investigate the behavior of the subducting plate, during the experiment conducted aboard RRS JAMES COOK in the Guatemala Basin where the Cocos plate enters the Middle America Trench, we collected a wide-angle seismic refraction profile and coincident multi-channel seismic profile. Here, we present a seismic velocity model derived from a joint refraction and reflection seismic tomography using 10,508 crustal refraction arrivals, 6,533 Moho reflection arrivals, and 7,769 upper mantle refraction arrivals recorded by 37 ocean-bottom-seismometers. The spacing of instruments is ~7.5 km on the unaltered incoming plate and decreases to half of that from the outer rise into the trench. The results show that the unaltered oceanic crust is ~5-6 km thick and features a typical two-layer oceanic structure, ranging from ~4-5 km/s at the basement top to ~7 km/s at the bottom of the crust. Closer to the trench, at ~70 km away, we observe a prominent velocity reduction with lower-crustal velocities dropping to <6.8 km/s, indicating a strong impact of bend-faulting and/or hydration of the crust. However, the onset of normal faulting is observed in the coincident seismic reflection profile at ~100 km away from the trench axis. The observed faulting may indicate an evolutionary process with the progressive development of bending-related faults. At the outer rise, a seamount rising ~1 km above the seafloor is characterized by extremely low crustal velocities of only <6.5 km/s at the bottom of the crust, suggesting that the seamounts facilitate hydration. Further east, the lower crustal velocities are reduced to ~6.5-6.7 km/s beneath the outer trench wall. In the upper mantle, velocity reduction is observed ~100 km away from the trench axis and reaches its minimum beneath the seamount at the outer rise with ~7.2 km/s, which may indicate up to ~20% of mantle serpentinization. Based on our velocity modeling results, we conclude that the intensity of bend-related faulting, hydration, and mantle serpentinization is not only controlled by the distance from the trench axis but also by seamounts ventilating the oceanic crust.

How to cite: Li, Y., Grevemeyer, I., Robinson, A., Henstock, T. J., Marjanović, M., Dannowski, A., Hilbert, H.-S., and Teagle, D. A. H.: Bending-related faulting, hydration, and mantle serpentinization in the incoming Cocos Plate at Middle America Trench: Evidence from wide-angle seismic refraction data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19448, https://doi.org/10.5194/egusphere-egu24-19448, 2024.

EGU24-19465 | Posters on site | GD4.1

Parametric study for self-sustained Andean-type subduction speed 

Jamison Assunção, Nicolas Riel, Andrea Piccolo, and Victor Sacek

The relation between subduction dynamics, plate rheology and geometry is still not well understood. To numerically assess how subduction convergence velocity develops, a wide range of simulations is required to quantify any correlation between physical parameters and kinematic behavior of a subduction system. In this study, we performed a set of 2D numerical simulations designed to better constrain the range of rheological and geometrical conditions necessary to model subduction dynamics. We used the parallel numerical code LaMEM to simulate thermo-mechanical convection. In addition, we coupled these numerical simulations with MAGEMin to compute a self-consistent mineral assemblage of the asthenospheric mantle and the plates, and we parameterized the lower mantle using a linear equation, following the Clapeyron slope from Faccenda and Zilio (2017). The modeled region is 9300 km wide and accounts for both the upper and whole lower mantle. We consider an Andean type subduction system where our baseline scenarios are defined by a partially subducting oceanic plate beneath a continental plate. Once the simulation starts, the subducted portion of the oceanic plate triggers the subduction thanks to a weak zone between the lower and upper plate. The subduction is sustained by the negative buoyancy of the lower plate with respect to the surrounding mantle. We aim to simulate subduction dynamics that exhibit convergence velocities and long term behavior, including lower mantle penetration, similar to what is observed in nature. We investigate the role of the length of the subducting plate, the geometry of its composing lithological units, and the viscosity of the asthenosphere and the lower mantle. We find that the subduction velocity is inversely correlated with the non subduction length of the oceanic plate, and that a less viscous asthenospheric mantle increases the subduction speed. 

How to cite: Assunção, J., Riel, N., Piccolo, A., and Sacek, V.: Parametric study for self-sustained Andean-type subduction speed, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19465, https://doi.org/10.5194/egusphere-egu24-19465, 2024.

EGU24-19667 | ECS | Posters on site | GD4.1

Dynamical evolution of forearc subsidence controlled by slab geometry 

Francisco Bolrão and Wouter Schellart

The forearc is the region of the overriding plate (OP) that physically interacts with the subducting plate (SP) and is expected to record critical information about subduction dynamics. A way to access such information is through its topography, which presents a wide variability across the natural prototypes. Some forearcs show a peculiar topography characterised by a forearc high next to the trench and a forearc basin in between this high and the magmatic arc (e.g. Alaska, Java, Central Chile). Previous studies have proposed that such topographic signature is a consequence of the gradient of the vertical component of the suction force along the plate interface (e.g., Hassani et al. 1997, Chen et al. 2017). 
Our study focuses on the role of several subduction parameters in shaping the topography of the forearc, namely the OP and SP thicknesses, OP viscosity, and slab dip angle. To carry out this investigation, we developed a series of buoyancy-driven and isoviscous models using analogue techniques, where we applied a stereoscopic particle image velocimetry technique to monitor the topography of the forearc.
So far, we have analysed the impact of the OP thickness, which shows a negative correlation with the magnitude of the forearc basin. Thicker OPs constrain trench retreat, which forces the SP to move trenchward,with subduction occurring mostly through down-dip slab sinking. Consequently, the suction force created at the plate interface by hinge retreat will decrease, resulting in shallower forearc basins. Moreover, the wavelength of the forearc basin is also affect, with thicker OP producing wider basins. Such observation suggests that the previously proposed mechanism that shapes the forearc topography is correlated with the subduction partitioning so that the magnitude of the forearc basin increases as the subduction is increasingly accommodated by slab retreat.

How to cite: Bolrão, F. and Schellart, W.: Dynamical evolution of forearc subsidence controlled by slab geometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19667, https://doi.org/10.5194/egusphere-egu24-19667, 2024.

EGU24-20470 | Orals | GD4.1

Storage and fate of volatiles in the shallow mantle: Insights from fluid mobile elements and light element (B, Li) isotopes in serpentinites 

Ivan Savov, Samuele Agostini, CeesJan DeHoog, William Osborne, Andrew McCaig, Detlef Rost, Jeff Ryan, Roy Price, Dyonisis Foustoukos, Haiyang Liu, and International Ocean Discovery Program Expedition 399 Sci. Party

We will present whole rock and mineral chemistry insights into the systematics of light elements (B, Li) and their isotopes during the serpentinization processes at both divergent and convergent plate margins. For the divergent plate case we have selected Site 1309D and some from the recently drilled (IODP Expedition 399, Atlantis Massif, Mid-Atlantic Ridge 30N) Site 1601C as the deepest in situ gabbo-peridotite drill cores ever recovered from the ocean floor. The downcore variation in fluid mobile elements and the vast Sr and light element isotope fractionations highlight the important role of seawater infiltration and seawater-crust interactions taking place at depth. However, it appears that the role of seawater is gradually diminishing with depth, where rather unaltered lithologies may still be involved in active metamorphic (hydration) reactions. For the convergent plate margin serpentinization we have selected to present the fascinating case of the Mariana serpentinite mud “volcanism” in the W. Pacific. Several key cores were recovered during ODP Legs 125 and 195, as well as during the IODP Expedition 366. The rocks and fluids at these forearc sites also show very large downcore elemental and isotope fractionations. In contrast to the oceanic intraplate sites, these are associated with fluids produced by metamorphic dehydration reactions occurring at blueschist and amphibolite facies conditions as a consequence of subduction of old and cold Pacific slabs. We will attempt to contrast the different tectonic settings and speculate on the importance of variously hydrated ocean crust as a volumetrically important carrier of volatiles from the surface to the deep mantle and back. Serpentinites may be important to kick-start subduction initiation.

How to cite: Savov, I., Agostini, S., DeHoog, C., Osborne, W., McCaig, A., Rost, D., Ryan, J., Price, R., Foustoukos, D., Liu, H., and Ocean Discovery Program Expedition 399 Sci. Party, I.: Storage and fate of volatiles in the shallow mantle: Insights from fluid mobile elements and light element (B, Li) isotopes in serpentinites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20470, https://doi.org/10.5194/egusphere-egu24-20470, 2024.

EGU24-20684 | ECS | Posters on site | GD4.1

Subduction polarity reversal facilitated by plate coupling during arc-continent collision 

Zaili Tao and Jiyuan Yin

Subduction polarity reversal usually involves the break-off or tearing of downgoing plates (DPs) along the continent-ocean transition zone, in order to provide space for the overriding plate (OPs) to descend. Here we propose that subduction polarity reversal can also be caused by DP-OP coupling and that it can account for the early Paleozoic geological relationships in the West Kunlun Orogenic Belt (WKOB). Our synthesis of elemental and isotopic data reveals transient (~5 Myr) changes in the sources of the early Paleozoic arc magmatism in the southern Kunlun terrane. The early stage (530–487 Ma) magmatic rocks display relatively high εNd(t) (+0.3 to +8.7), εHf(t) (−3.6 to +16.0) values and intra-oceanic arc-like features. In contrast, the late-stage (485–430 Ma) magmatic rocks have predominantly negative εNd(t) (−4.5 to +0.3), εHf(t) (−8.8 to +0.9) values and higher incompatible trace elements (e.g., Th), similar to the sub-continental lithospheric mantle (SCLM) beneath the Tarim Craton. This abrupt temporal-spatial variation of arc magmatism, together with the detrital zircon evidence, indicate that subduction polarity reversal of the Proto-Tethys Ocean occurred in a period of ~10 Ma, consistent with migration of the magmatic arc. This rapid polarity reversal corresponds with the absence of ultra-high-pressure metamorphic [(U)HP] and post-collisional magmatic rocks, features normally characteristic of the slab break-off or tearing. Numerical modeling show that this polarity reversal was caused by plate coupling during arc-continent collision without slab break-off and tearing. This prevented rebound of the positively buoyant relic rocks and asthenosphere upwelling. This model successfully explains the early Paleozoic orogenesis in the WKOB and may be applied elsewhere where post-collisional magmatic and (U)HP rocks are absent.

How to cite: Tao, Z. and Yin, J.: Subduction polarity reversal facilitated by plate coupling during arc-continent collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20684, https://doi.org/10.5194/egusphere-egu24-20684, 2024.

EGU24-21046 | ECS | Orals | GD4.1

On the iron isotope systematics of subducted oceanic gabbros 

Alex Churchus, Oliver Nebel, Yona Jacobsen, Xueying Wang, Massimo Raveggi, Marianne Richter, and Roland Maas

Oceanic gabbros represent a voluminous part of oceanic crust and are to a large degree cumulative mineral assemblage composed of olivine-pyroxene-feldspar and iron oxides. As such, oceanic gabbros represent a large Fe isotope reservoir in the global Fe cycle. During recycling into the mantle, oceanic gabbros undergo metamorphic reactions but are often considered a small contributor to the subduction component in arcs (e.g., slab-derived fluids) due to their relatively dry and refractory nature. Instead, fluids released from serpentinite as a result of slab devolatisation are considered to be the main source of deep mantle wedge fluids and considerably contribute to arc-lava chemistry and the redox state of metasomatised mantle wedge. However, serpentinite-derived fluids will, by default, pass through overlying gabbroic sequences when ascending to the mantle wedge with a potentially considerable contribution to the Fe isotope budget of the mantle wedge and arc lavas.

Here, we investigate the Fe isotopic signature of gabbroic rocks exposed on the seafloor along the Southwest Indian Ridge and collected during IODP scientific ocean drilling expedition leg 118 from the Atlantis Bank Gabbro Massif (IODP Site 735B). Site 735B is composed of intrusive lower crustal and upper mantle rock exhumed to the surface by detachment faulting. Iron was chemically leached, simulating passing fluids, with both leachate and residue analysed for their Fe isotope composition. Our samples display large variation in isotopic composition ranging from mantle to extreme values of δ57Fe = -0.07 to +0.68‰ (relative to IRMM-524a) for the leachate, and MORB-like δ57Fe = -0.1 to +0.21‰, for the residue, respectively. Our results imply that the leached isotopically heavier Fe from oceanic gabbros can be a significant contributor to the Fe isotope composition of the subduction component in arcs and counterbalance the light Fe isotopes derived from serpentinites. Considering the oxidation state of Fe in magnetite, this may further add to the oxidized nature of arc lavas. If such fluids remain in the mantle, they can potentially be a very heavy Fe isotope reservoir, which may explain some exotic signatures observed in ocean island lavas or transition zone diamond inclusions. Gabbroic residues deprived of any such leachate resembles Fe isotope signatures of the upper mantle and MORB and thus does not change the Fe isotope composition of the mantle significantly after subduction. 

How to cite: Churchus, A., Nebel, O., Jacobsen, Y., Wang, X., Raveggi, M., Richter, M., and Maas, R.: On the iron isotope systematics of subducted oceanic gabbros, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21046, https://doi.org/10.5194/egusphere-egu24-21046, 2024.

EGU24-990 | ECS | Posters on site | GD9.1

Quirquincho and Pampeano-Chaqueño Highs: forebulge or Palaeozoic structures? 

Valentina Cortassa, Robert Ondrak, Stefan Back, Cecilia del Papa, and Eduardo Rossello

The Andean Foreland Basin in the Chaco-Pampean Plain of North-West Argentina is thought to have been tectonically inactive during the Cenozoic. However, re-interpreted industry seismic-reflection data and borehole information document a complex tectonic history in the subsurface at least until Palaeogene times. Data synopsis and re-analysis reveal two regionally extensive and approximately NW-SE-oriented basement highs beneath the flat present-day surface, the Quirquincho (or Rincón Caburé) High and the Pampeano-Chaqueño High. These large geological structures were described previously, but the mechanism that elevated these features relative to the surrounding stratigraphy and the timing of uplift has remained elusive.

This study documents and describes of the Quirquincho and Pampeano-Chaqueño Highs and their relationship to the depocenters around and the sedimentary successions of the Chacoparanaense, Salta Rift and Andean Foreland Basins. We studied palaeo-basin morphology, stratigraphy, stratal terminations and distance to the Andes to unravel viable mechanisms that influenced the genesis of the two structural highs. The work presented is based on the re-interpretation of a large set of subsurface information (2D seismic-reflection profiles and well reports) using a regional approach that considers the Chacoparanaense, Salta Rift and Andean Foreland Basins as a complex lateral arrangement of basins varying in activity through time, depending on their relative location concerning orogens and rifted ocean margins.

Our research reveals that the Quirquincho and Pampeano-Chaqueño Highs were elevated features from the Late Palaeozoic to the Palaeogene, strongly influencing the deposition of Mesozoic and Palaeogene sediments. The tectonic mechanism controlling the rise of the Quirquincho and Pampeano-Chaqueño Highs was initially flexural deformation in the foreland of the Gondwanide orogen in the Permian, subsequently influenced in the Mesozoic by the opening of the Southern Atlantic Ocean.

How to cite: Cortassa, V., Ondrak, R., Back, S., del Papa, C., and Rossello, E.: Quirquincho and Pampeano-Chaqueño Highs: forebulge or Palaeozoic structures?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-990, https://doi.org/10.5194/egusphere-egu24-990, 2024.

EGU24-5394 | ECS | Orals | GD9.1

Comprehensive two-dimensional structural-geological model of the Nazca Ridge subduction zone 

Sara Ciattoni, Federico Cella, Stefano Mazzoli, Miller Zambrano, Robert Butler, Stefano Santini, Antonella Megna, and Claudio Di Celma

The Nazca Ridge's thickened subduction beneath the South American continental margin (10° to 15° S) is characterised by a flat-slab configuration. This peculiar geological setting strongly influences upper plate dynamics, significantly impacting stress distribution and seismicity in the South American plate. However, the effects of the Nazca Ridge subduction on the Peruvian forearc and Andean Cordillera development remain subjects of extensive debate. In this study we thoroughly investigate the general structure of the Nazca Ridge subduction zone producing an integrated two-dimensional structural-geological model of the south-Peruvian Andes. Combining surface geological data and geophysical information from existing literature, we delineated the crustal structure up to a depth of about 130 km along a ca. 1000 km-long transect, encompassing the Peruvian Forearc System and the Andean Cordillera. In order to improve the characterization of geological features and validate the model, we carried out forward modelling of the Bouguer anomaly in the region, integrating four distinct datasets. Subsequently, we formulated a two-dimensional density model to reproduce the observed gravity field, taking into consideration the petrological properties of the materials and the P-T condition in each area of the crustal section. The geometry of the structures was assessed by choosing the configuration that, honouring the geological and geophysical constraints upon which the initial model was based, also allowed maximising the fit between observed Bouguer anomaly values and the values computed during the forward modelling process. Our exhaustive approach allowed us to obtain a comprehensive model of the Nazca Ridge subduction zone, accurately defining both the deep lithosphere-asthenosphere system and shallow geological structures. This contribution will substantially enhance the ongoing debate on the tectonic evolution and geodynamics of Andean orogeny.

How to cite: Ciattoni, S., Cella, F., Mazzoli, S., Zambrano, M., Butler, R., Santini, S., Megna, A., and Di Celma, C.: Comprehensive two-dimensional structural-geological model of the Nazca Ridge subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5394, https://doi.org/10.5194/egusphere-egu24-5394, 2024.

EGU24-5730 | ECS | Posters on site | GD9.1

Combining local earthquake tomography and petrological models to constrain wavespeeds in the subducting Nazca Plate 

Nazia Hassan, Sally Henry, and Christian Sippl

Intermediate-depth seismicity in Northern Chile shows a pattern which is distinct from a conventional double seismic zone (DSZ) setting. While two distinct seismicity planes are present in the updip part of the slab, there is a sharp transition to a highly seismogenic cluster of 25–30 km thickness at 80-90 km depth, extinguishing the gap between the two seismicity planes. As seismic velocities can be used to constrain mineralogy and fluid content, characterizing seismic wavespeeds of this subduction zone segment using local earthquake tomography can provide important constraints on the mineralogical processes that produce the seismicity pattern seen here.

We used the catalog of Sippl et al. (2018), which contains arrival time data from permanent stations of IPOC (Integrated Plate Boundary Observatory Chile), complemented by several temporary deployments spanning shorter time sequences. The catalog contains more than 100,000 earthquakes and 1,200,404 P- and 688,904 S-phase picks for the years 2007 to 2014. In order to use the best available picks for tomography, we limit our analysis to events that have more than 14 P-arrivals as well as more than 7 S-arrivals, leading to a total of 8883 events with 213,908 P- and 99466 S-arrivals.

Parallelly, we also attempt to obtain an estimate of the possible mineral compositions at the depths and P-T conditions relevant to our study in the DSZ setting. For this, we assume a simple model where the upper plane of the DSZ is considered to be evolving from MORB-like composition and the lower plane of the DSZ from depleted-mantle composition. These global average compositions are then fed into Perple X (Connolly & Kerrick, 1987) as starting compositions and pseudosections of possible mineral assemblages are constructed for P-T conditions significant to this study. We calculate the theoretical Vp and Vp/Vs values for those P-T conditions using the same software.

We present 3D models of P- and S-wavespeeds from the Northern Chile forearc between about 20.4° S and 22.5° S, as well as images of ray coverage, relocated seismicity, and synthetic resolution tests. Tomography models for different choices of grid spacing and damping-smoothing parameters are compiled and compared to derive the optimal settings for the inversion. The seismic velocity distribution obtained through tomography is compared with the aforementioned theoretical wavespeeds to narrow down the range of possible reactions occurring at depth.

How to cite: Hassan, N., Henry, S., and Sippl, C.: Combining local earthquake tomography and petrological models to constrain wavespeeds in the subducting Nazca Plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5730, https://doi.org/10.5194/egusphere-egu24-5730, 2024.

EGU24-5819 | ECS | Orals | GD9.1

Structure and geometry of the Chilean subduction zone near Copiapó (~27°S) based on an amphibious seismic refraction experiment 

Arne Warwel, Dietrich Lange, Anke Dannowski, Sara Aniko Wirp, Eduardo Contreras-Reyes, Ingo Klaucke, Marcos Moreno, Juan Diaz-Naveas, and Heidrun Kopp

The subduction of the oceanic Nazca plate beneath the continental South American plate shapes the Chilean margin and is known to generate large megathrust earthquakes. Our study focuses on the region defined by the pre-collision and subduction of the Copiapó Ridge with the Chilean margin at ~27°S. This area has been a seismic gap since 1922, and little is known about the geometry and deep structures of the incoming plate, the overriding plate, and the processes related to the subduction of the Copiapó Ridge. 

We model the seismic structure in the region by using wide angle seismic data from a recent amphibious seismic refraction experiment. Thereby, we utilize seismic signals from both offshore airgun-shots and onshore mining blasts. Overall, we use 36 Ocean-Bottom-Seismometers and 10 temporal seismic land stations along an approximately 420 km long profile ranging from more than 300 km offshore up to more than 100 km landwards.

Our P-wave velocity model images the geometry and velocity structure of the incoming oceanic plate, including three seamounts belonging to the Copiapó Ridge, the marine and continental forearc, and the upper part of the downgoing slab. The model shows an oceanic crust with hardly any sediment cover (generally less than 10 m) and an average oceanic Moho depth of about 6.2 – 6.9 km below the seafloor, which increases to over 10 km below the seamounts of the Copiapó Ridge. The velocities beneath the seamounts are similar or slightly slower compared to the adjacent upper oceanic crust (Vp ranging from 3.5 to 6 km/s). This suggests that the Copiapó Ridge was predominantly formed by extrusive processes. In addition, the velocity model reveals a significant thinning (to less than 4 km) of the oceanic crust landwards of the trench axis.

Together with recently acquired bathymetry data, we will compare our findings to other studies north and south of the Copiapó region and discuss the structural and geometric along-strike variations of the northern Chilean subduction zone.   

How to cite: Warwel, A., Lange, D., Dannowski, A., Wirp, S. A., Contreras-Reyes, E., Klaucke, I., Moreno, M., Diaz-Naveas, J., and Kopp, H.: Structure and geometry of the Chilean subduction zone near Copiapó (~27°S) based on an amphibious seismic refraction experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5819, https://doi.org/10.5194/egusphere-egu24-5819, 2024.

EGU24-5820 | Orals | GD9.1

Spanning the Arc: Margin Geometry and Topography Control Upper Plate Deformation in the Central Andean Subduction Zone 

Bernd Schurr, Armin Dielforder, Lukas Lehmann, and Claudio Faccenna

Subduction zone forearcs deform transiently and permanently due to the frictional coupling with the converging lower plate. Transient stresses are mostly the elastic response to the seismic cycle. Permanent deformation is evidenced by forearc topography, upper plate faulting, and earthquakes; its relation to the megathrust seismic cycle is debated. Here we study upper plate seismicity, interplate earthquake slip vectors, and the GNSS strain field in the northern Chile subduction zone to deduce the stress field and to separate elastic and permanent strain. We find that seismicity is distributed unevenly and that high seismicity rates concur both with a break in the forearc topography and tectonics of the Coastal Cordillera and the onset of a change in subduction obliqueness. Earthquakes in the South American crust under the sea and the Coastal Cordillera show a remarkably homogenous north-south, i.e., trench-parallel, compressional stress field. The trench-parallel compression above the plate coupling zone, almost perpendicular to plate convergence direction, may be explained by strain resulting from a change in subduction obliqueness due to the concave shape of the plate margin, which we demonstrate by investigating inter-plate earthquake slip vectors. From these, we derive a strain rate estimate (-5×10e-8 /a) and compare it to one derived from upper plate earthquakes (-8×10e-9 /a). We argue that the dominance of trench-parallel compressive stresses over trench-perpendicular ones is due to canceling of the latter by tensional gravitational stresses due to the topographic gradient between the Andes and the Nazca trench. Based on the distribution of the type of faulting we investigate the trench-perpendicular stress field with a force-balance model. The observed deep strike-slip earthquakes, expression of trench-perpendicular tension, require the deepest extent of the megathrust to be very weak.

How to cite: Schurr, B., Dielforder, A., Lehmann, L., and Faccenna, C.: Spanning the Arc: Margin Geometry and Topography Control Upper Plate Deformation in the Central Andean Subduction Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5820, https://doi.org/10.5194/egusphere-egu24-5820, 2024.

EGU24-6860 | ECS | Orals | GD9.1

Phase stability and metamorphic reactions related to intraplate seismicity in the Nazca Plate 

Martin Riedel, Andrés Tassara, Nicole Catalán, and Rodolfo Araya

Subduction zones are complex geotectonic environments where multiple processes interact resulting in different kinds of seismicity. Among them is intermediate depth intraplate seismicity, which occurs within the subducting plate in conditions that should favor ductile shear rather than fragile faulting. A high variability in focal mechanisms and spatial distribution has been observed globally for this kind of events. In some subduction zones a double seismicity zone develops while in others not. Moreover, these earthquakes may occur in dry and hydrated conditions. Therefore, there is no consensus on the process that originate them.

In the context of hydrated subductions, such as is the Chilean case, the influence of fluids liberated through the metamorphism of the slab is generally considered as the main triggering factor. It is therefore important to know at what pressure and temperature and between which mineral associations these reactions occur.

Hacker et al. (2003) compiled information on average mineralogy and whole rock composition to create phase diagrams which have allowed the study of dehydration reactions and intraplate seismicity around the world. However, their work is based on data from the FAMOUS area in the Atlantic Ridge for the MORB and the Semail ophiolite for ultramafic rocks, which do not correlate to compositions in the Nazca Plate.

To better constrain the conditions on which dehydration reactions take place within the Nazca slab, we used PERPLE_X to calculate pseudosections with geochemical data more representative of it. We created a simple model of the plate consisting of a top layer with MORB compositions from drilled and dredged samples for the crust and a bottom layer with ultramafic rock compositions obtained from ophiolites from a geotectonic context consistent with that of the Nazca Plate. We then coupled the pseudosections with a kinematic thermal model of the Chilean subduction zone to create profiles of stable mineral associations and hydration gradient along the subducted slab.

We observe that, for constant PT, hydrated mineral stability is mainly controlled by the initial (pre-subduction) slab hydration percentage and in a much lesser extend by slab composition. For areas where slab hydration is constrained by geophysical data, we tested different slab compositions and found that modelling with data from Nazca Plate layer 2 basalts and a mid ocean ridge type ophiolites provides the best fit to seismic data. It appears that intraplate seismicity nucleates along areas with strong hydration gradients, i.e. where dehydration reactions occur. We then extrapolated these compositions to the rest of the plate and with the assumption that the correlation observed between hydration gradient and intraplate seismicity hypocenters is maintained along the margin, we estimated hydration percentages along 5 latitudinal profiles.  Although further work remains to improve our seismic catalogues and spatial resolution of the thermal model, preliminarily it seems that the Nazca Plate is more hydrated in northern Chile (~2.5%) and less to the south (~1%) and that the Chilean double seismicity zone only occurs where hydration is above ~2%.

How to cite: Riedel, M., Tassara, A., Catalán, N., and Araya, R.: Phase stability and metamorphic reactions related to intraplate seismicity in the Nazca Plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6860, https://doi.org/10.5194/egusphere-egu24-6860, 2024.

The use of machine-learning based tools for phase picking and association is in the process of revolutionizing the field of seismicity analysis, leading to the simplified creation of “deep” seismicity catalogs often containing 10s or 100s of thousands of events. Having such catalogs as an available resource opens the field for novel ways of combining seismicity information with other types of datasets. At the same time, the sheer amount of data poses challenges for the visualization as well as joint analysis with other constraints.

In this contribution, I want to explore different ways of using and visualizing large seismicity catalogs, using a range of different recently compiled earthquake catalogs from the Chilean margin as showcase examples. Moreover, I attempt to find efficient ways of cross-plotting seismicity data from “deep” catalogs with other datasets such as interplate coupling maps, seismic velocity distributions, temperature models or inferred mineralogy maps.

How to cite: Sippl, C.: Using large microseismicity catalogs to constrain subduction zone processes – examples from the Chilean margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7484, https://doi.org/10.5194/egusphere-egu24-7484, 2024.

EGU24-7958 | ECS | Posters on site | GD9.1

Towards 3D attenuation tomography of the Northern Chile forearc 

Ignacio Castro-Melgar and Christian Sippl

In subduction zones, intermediate-depth earthquakes typically occur in two discrete layers, delineating an upper and a lower seismicity plane with a separating aseismic or minimally seismic region, a phenomenon named Double Seismic Zone (DSZ). However, the seismicity pattern in Northern Chile features two parallel planes of seismic activity only in the shallower section of the slab. Around depths of 80–90 km, the seismicity undergoes a transition to a significantly seismogenic zone approximately 25–30 km thick, effectively connecting the initial seismicity planes. This variation presents a distinct form of intraslab seismicity that deviates from the traditional DSZ structure and prompts further investigation into its underlying mechanisms and implications for regional seismic hazard assessment. Insights derived from this region's seismicity could provide pivotal constraints and enhance our understanding of the complex interplay between geological processes, mineral transformations, and fluid migrations in shaping subduction zone seismicity.

The attenuation of seismic waves in a rock volume is a property that is highly sensitive to the presence and concentration of fluids as well as spatial variations of temperature. As intermediate-depth seismicity is thought to originate from dehydration processes in the downgoing slab, along-strike or along-dip changes in slab seismicity should have a signature in seismic attenuation of the slab as well as the overlying mantle wedge. We hence aim at better understanding the aforementioned seismicity configuration in Northern Chile by acquiring a 3D image of its attenuation signature. 

The primary dataset for our analysis comes from the seismic stations of the Integrated Plate boundary Observatory Chile (IPOC) network in Northern Chile's forearc, augmented by additional data from different temporary deployments. Using the extensive seismicity catalog of Sippl et al. (2023), we have about 180,000 events at over 50 seismic stations at our disposal from the period 2007 to 2021; we select only the high quality traces for the analysis. The rays are traced in a 3D velocity model. We invert the spectral ratios obtained with the coda normalization method to obtain total-Q values. We present images of the 3D attenuation structure of the Northern Chile Forearc between 21ºS and 23ºS, which are obtained with measurements of the coda normalization method using the Multi-Resolution Attenuation Tomography algorithm (Sketsiou et al., 2021).

How to cite: Castro-Melgar, I. and Sippl, C.: Towards 3D attenuation tomography of the Northern Chile forearc, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7958, https://doi.org/10.5194/egusphere-egu24-7958, 2024.

EGU24-8006 | ECS | Posters on site | GD9.1

Towards a 3D integrated geophysical model of Northern Chile 

Dominika Godová and Christian Sippl

The South American active margin is one of the most important and well-studied subduction zones on the Earth. In the last decade, our knowledge about the geometry of its respective constituent parts in Northern Chile has been significantly expanded thanks to seismicity data from a large network of permanent seismic stations. That calls for an effort to summarize these diverse constraints in a single 3D model, which can be validated and optimized using satellite gravity data.

Integrated geophysical modelling is primarily based on gravity data, which bring information about different crustal density inhomogeneities and their sources. As an inverse geophysical problem, gravity modelling is ambiguous, and therefore it is necessary to include geometry constraints from other geophysical data as well as geological information. Different types of seismic data offer the most commonly used constraints due to their depth range and the relatively well-described relation between seismic velocities and densities.

We aim to compile a 3D integrated geophysical model for Northern Chile in the IGMAS+ software, based on gravity data of the global gravitational (or geopotential) model EIGEN-6C4, which include terrestrial, satellite and altimetry data to a high degree and order of spherical harmonic expansion. As the main geometry constraints of the model, we use the newest available seismicity catalogs in the study area together with crustal thickness values from receiver functions. Starting with the geometries of previously published density models in the area of the Central Andes, especially those located at least partly in Northern Chile, we will modify these models guided by the geometry constraints from seismic data and will also use regional and global models of crustal and lithospheric interfaces, such as the top of basement in sedimentary areas, plate interface geometry, depth to continental Moho, and the lithosphere-asthenosphere boundary (LAB). Densities of the modeled bodies will be selected based on previously published models or estimated from seismic velocities. We also plan to study the gravity effect of the different geometries deduced from different generations of seismic data.

Our contribution provides an overview of evidence compiled in previous studies and adds new information on the deep lithospheric structure of the North Chilean margin by integrating them into a single model.

How to cite: Godová, D. and Sippl, C.: Towards a 3D integrated geophysical model of Northern Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8006, https://doi.org/10.5194/egusphere-egu24-8006, 2024.

We derive a co-seismic slip model of the 2015 Mw 8.3 Illapel, Chile earthquake constrained by line-of-sight displacements from Sentinel-1 interferograms. Greens functions are calculated with 3D finite element models (FEMs). The FEMs simulate a non-uniform distribution of elastic material properties and a precise geometric configuration of the irregular topographical surface. The rupturing fault follows the curvilinear Peru-Chile Trench and Slab1.0. The optimal model that inherits heterogeneous material properties, provides a significantly better solution than that in a homogenous domain at the 95% confidence interval. The best-fit solution for the domain having a non-uniform distribution of material properties reveals a triangular slip zone. Slip is concentrated near the trench with a dip-slip up to 7.75 m, giving rise to a moment magnitude of Mw8.22 in general agreement with the seismological estimate. This methodology allows us to integrate multiple datasets of geodetic observations with seismic tomography, to achieve a better understanding of seismic ruptures within crustal heterogeneity and fault curvature.

How to cite: Tung, S. and Masterlark, T.: Revisit the coseismic slip model of the 2015 Mw 8.3 Illapel, Chile earthquake with curvilinear fault rupture, finite element model, and InSAR observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8443, https://doi.org/10.5194/egusphere-egu24-8443, 2024.

EGU24-8472 | ECS | Orals | GD9.1 | Highlight

Crustal Deformation Associated with the Seismic Cycle in the Central Andes from InSAR and GNSS Geodetic Time Series 

Bertrand Lovery, Anne Socquet, Mohamed Chlieh, Marie-Pierre Doin, Mathilde Radiguet, Juan Carlos Villegas-Lanza, Juliette Cresseaux, and Philippe Durand

The Central Andes subduction has been the theater of numerous large earthquakes since the beginning of the 21th Century, notably the 2001 Mw8.4 Arequipa, 2007 Mw8.0 Pisco, and 2014 Mw8.1 Iquique earthquakes. A better knowledge of the interplate coupling distribution and seismic cycle in this area is thereby fundamental for improving our understanding of large earthquakes segmentation, and ultimately improving our knowledge of the seismic potential in the area. Interseismic models from inversions of 80 GNSS velocities in Central and South Peru (12–19°S) on a 3-D slab geometry indicate that the locking level is relatively high and concentrated between 20 and 40-km depth. Locking distributions indicate a high spatial variability of the coupling along the trench, with the presence of many locked patches that spatially correlate with the seismotectonic segmentation. Our study confirms the presence of a creeping segment where the Nazca Ridge is subducting, we also observe a lighter apparent decrease of coupling related to the Nazca Fracture Zone (NFZ). However, since the Nazca Ridge appears to behave as a strong barrier, the NFZ is less efficient to arrest seismic rupture propagation. Considering various uncertainty factors, we discuss the implication of our coupling estimates with size and timing of large megathrust earthquakes considering both deterministic and probabilistic approaches. We estimate that the South Peru segment, from the Nazca Ridge to the Arica bend, could have a Mw=8.4-9.0 earthquake potential depending principally on the considered seismic catalog and the seismic/aseismic slip ratio (Lovery et al., 2024).

We use large-scale InSAR Sentinel-1 time series, processed in the frame of the FLATSIM-Andes project (Thollard et al., 2021), encompassing the Central Andes (7–26°S) on the 2015-2021 period. These InSAR data provide a useful complementarity to the GNSS data, with a higher spatial resolution in exchange for a lower temporal resolution. Subsequently, it allows to better define the contours of the asperities, or the maximum locking depth. We modelled the effects of non-tectonic processes such as solid earth tides (SET), ocean tide loading (OTL), and ionospheric electronic content (TEC) on the ramps in range and azimuth, in order to measure ground deformation in a stable reference frame, with sufficient accuracy for large-scale tectonic applications, allowing vertical and horizontal decomposition.

In order to perform joint inversions of GNSS and InSAR interseismic velocities, we also develop finite element models of the subduction zone with more complex viscoelastic rheology (Maxwell and Burger laws). Viscoelastic models are expected to produce a broader displacement, with horizontal displacements extending further inland. Higher magnitudes of deformation in the late-stage of the interseismic period and a shallower optimal locking depth have also been reported for viscoelastic models. These features are key factors to make the link between short-term and long-term deformation, and to discriminate the slip on the slab interface from internal deformation. We investigate the viscoelastic effects associated with the great 2001 Mw8.4 Arequipa earthquake, in order to assess its impact on the interseismic loading estimate on the subduction megathrust.

How to cite: Lovery, B., Socquet, A., Chlieh, M., Doin, M.-P., Radiguet, M., Villegas-Lanza, J. C., Cresseaux, J., and Durand, P.: Crustal Deformation Associated with the Seismic Cycle in the Central Andes from InSAR and GNSS Geodetic Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8472, https://doi.org/10.5194/egusphere-egu24-8472, 2024.

EGU24-8641 | ECS | Posters on site | GD9.1

Joint inversion for Vp, Vs, and Vp/Vs of subduction zone in northern Chile 

Zixin Chen, Haijiang Zhang, and Lei Gao

We collected earthquake waveform data recorded by permanent seismic stations in northern Chile from 2014 to 2019 to construct a new earthquake catalog, and integrated them with the previous catalog data. In total, the new catalog consisted of 536342 P and 453920 S arrival times from 52165 earthquakes and 245 stations. We resolved Vp, Vs, and Vp/Vs models and seismic locations for northern Chile by using a new version of double-difference seismic tomography method based on Vp/Vs model consistency constraint (Guo et al., 2018). The new velocity models provide a refined structure of the subducting slab down to 350 km.

The earthquake relocations reveal a distinct double seismic zone in northern Chile, but the gap between the two seismic planes disappears at a depth of approximately 100 km and replaced by a concentration of seismic cluster. Under this intermediate-depth seismic cluster, several isolated small seismic clusters remain. The tomography results indicate a strong correlation between seismicity distribution and high-velocity anomalies. The subducting Nazca Plate presents stripe-like high-velocity anomalies with clear segmentations, potentially related to the weakening at the outer-rise of the trench. Furthermore, our Vp/Vs model indicates that the upper seismic plane exhibits high Vp/Vs anomalies, which may indicate the presence of fluids released from dehydration reactions of various hydrous minerals. In contrast, lower seismic plane and deep seismic clusters are associated with low Vp/Vs anomalies, which could be related to supercritical fluids. Additionally, the enhanced seismicity and velocity anomalies in the region of 21-22ºS along the strike suggest a potential influence of the subduction of the Iquique Ridge of the Nazca Plate.

How to cite: Chen, Z., Zhang, H., and Gao, L.: Joint inversion for Vp, Vs, and Vp/Vs of subduction zone in northern Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8641, https://doi.org/10.5194/egusphere-egu24-8641, 2024.

EGU24-9019 | ECS | Posters on site | GD9.1

The IPOC catalog goes deep: preliminary results 

Nooshin Najafipour, Jorge Antonio Puente Huerta, Christian Sippl, Javad Kasravi, Jonas Folesky, and Bernd Schurr

Northern Chile is one of the most seismogenic regions on the planet, and has been monitored by a permanent network of seismic stations since 2007. We here present a first step towards a new, more complete seismicity catalog for this region, leveraging modern deep-learning based algorithms for phase picking and association.

We first assessed the performance of EQTransformer, a deep learning based phase picker, in detecting and phase picking seismic data from the Northern Chile Subduction Zone by comparison with a large, meticulously handpicked dataset. We found that the "INSTANCE" model within SeisBench yielded the best performance for our study area. Through systematic threshold variations, we determined the optimal values using Precision-Recall curves (0.4 for event detection, 0.1 for P and S picks). Subsequently, we applied GaMMA, identified as the best performing phase associator in synthetic tests, coupled with NonLinLoc for initial event location. One of GaMMA's key operational criteria is the association threshold, where we required a minimum of five seismic phases to define an event, which yielded a high reliability in the phase association process. Moreover, we refined the catalog by automatically identifying and removing duplicate events. All associated events were consecutively relocated in a 1D and a 2D velocity model, using the VELEST and simul2000 algorithms. Events with disproportionally high RMS residuals as well as single picks with high residuals were removed in the process. In a final step, events were relocated with a double-difference approach.

A first application of this combined approach for the year 2020 yielded 2,838,080 P and S picks in the picking stage, with a total of 83,194 events after association and relocation. This is a nearly tenfold increase in event numbers compared to the IPOC catalog of Sippl et al. (2023), which contains 8,716 events for the same time interval.

In this contribution, we present results from a larger-scale application of our procedure to several years of IPOC data, and compare retrieved geometries as well as event numbers to the previously published IPOC catalog. Our findings demonstrate the potential of modern deep-learning algorithms in the creation of larger and more complete earthquake catalogs. Moving forward, our goal is to extend this preliminary catalog to span the entire 15 years of IPOC operation, facilitating in-depth analysis of regional processes.

How to cite: Najafipour, N., Puente Huerta, J. A., Sippl, C., Kasravi, J., Folesky, J., and Schurr, B.: The IPOC catalog goes deep: preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9019, https://doi.org/10.5194/egusphere-egu24-9019, 2024.

EGU24-9376 | Posters on site | GD9.1

Joint Tomographic Inversion of the Pampean Flat Slab: Insights from Extensive Archived Seismic Data 

Ariane Maharaj, Steve Roecker, Diana Comte, Mauro Saez, Sol Trad, Gustavo Ortiz, and Martin Fernadez

The Andean Margin hosts alternating regions of “flat” and “normal” subduction, which includes the Pampean flat slab that extends from central Chile to Argentina. The discovery of an unusual travel time anomaly beneath the high Andes above the flat slab motivated a study to investigate the lithosphere in this region. Leveraging extensive archived seismic data from both Chile and Argentina, we performed a large-scale joint inversion of P and S body wave arrival times from earthquakes, and surface wave dispersion measurements from earthquakes and ambient noise. We created 3D Vp, Vs and Vp/Vs models using at least an order of magnitude more data than previous studies with about an 80% reduction in grid spacing. Our models corroborate results from previous studies: (1) a high velocity, high Vp/Vs region associated with a cool, slightly hydrated and depleted mantle above the flat slab, and (2) a low velocity structure beneath the high Andes interpreted as an overthickened crustal root, with our results showing that the root extends to just above the flat slab. Curiously, our models also reveal two low velocity zones within and below the flat slab seismic zone that have not been previously reported. Notably, the decrease in velocity is more pronounced in Vp than Vs. We postulate that the eastern low velocity anomaly is likely due to hot asthenosphere heating the slab, although no melting is occurring as the Vs is not significantly reduced. The western low velocity anomaly, which spatially correlates with the Juan Fernandez Ridge (JFR), we postulate is either due to the presence of supercritical fluids trapped within the JFR or an increase in silica content possibly linked to petit spot volcanism.

How to cite: Maharaj, A., Roecker, S., Comte, D., Saez, M., Trad, S., Ortiz, G., and Fernadez, M.: Joint Tomographic Inversion of the Pampean Flat Slab: Insights from Extensive Archived Seismic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9376, https://doi.org/10.5194/egusphere-egu24-9376, 2024.

EGU24-11322 | ECS | Orals | GD9.1 | Highlight

What repeating earthquakes can tell us about postseismic slip and fluid circulation in the Ecuadorian subduction zone 

Caroline Chalumeau, Hans Agurto-Detzel, Louis De Barros, and Philippe Charvis and the Rapid Response Team of the 2016 Pedernales Earthquake

The Ecuador-Colombia subduction zone is a complex and spatially heterogeneous region that hosts both shallow aseismic slip and large megathrust earthquakes, and where both  inter-seismic and post-seismic seismicity have been linked to aseismic slip. Repeating earthquakes, which are the result of repeated loading and failure of single asperities on a fault, are a valuable tool in studying aseismic slip as well as in monitoring the evolution of fault properties over time. In this study, we search for repeating earthquakes within one year of aftershocks following the April 16th, 2016 Mw 7.8 Pedernales earthquake, and we analyze their relationship to afterslip and the evolution of their source properties. 

We calculate waveform cross-correlation coefficients (CC) on 4762 catalog events, and use a threshold CC of 0.95 to sort events into preliminary families, which are then completed using template-matching and relocated using HypoDD. In total, 376 earthquakes were classified into 62 families of 4 to 15 earthquakes. Additionally, the magnitudes, corner frequencies and stress drops of 136 repeaters were determined using spectral ratios.

We find an increase in the recurrence time of repeating events with time after the mainshock, highlighting a possible timeframe for the afterslip’s deceleration. However, repeating earthquakes appear to concentrate around the areas of largest afterslip release, where afterslip gradient is the highest. This suggests that while most repeating aftershocks are linked to afterslip release, the afterslip gradient may play a bigger role in determining their location than previously thought. We also find that repeaters in the region near the trench are unusual, in that their stress drops are anomalously low and systematically decrease over the postseismic period, hinting at a potential increase in pore fluid pressure in this region over time. 

How to cite: Chalumeau, C., Agurto-Detzel, H., De Barros, L., and Charvis, P. and the Rapid Response Team of the 2016 Pedernales Earthquake: What repeating earthquakes can tell us about postseismic slip and fluid circulation in the Ecuadorian subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11322, https://doi.org/10.5194/egusphere-egu24-11322, 2024.

EGU24-11363 | Orals | GD9.1 | Highlight

Tectonics and exhumation processes in the northern Andes 

Audrey Margirier, Manfred R. Strecker, Stuart N. Thomson, Peter W. Reiners, Ismael Casado, Sarah George, and Alexandra Alvarado

The Cenozoic growth and uplift of the Andes has been strongly influenced by the subduction dynamics and the superposed effects of climate. Previous studies have shown that the arrival of oceanic ridges and slab flattening triggered regional uplift and exhumation in Peru and Chile. Recent studies suggest that the subduction of the Carnegie Ridge below the Ecuadorian Andes controlled the formation of a crustal sliver moving northward. However, the timing of the ridge’s arrival at the trench and its effect on topographic growth remain unclear.

New geo-thermochronological data allows us to investigate the possible role of ridge subduction in prompting the growth of the Ecuadorian Andes and to pinpoint the timing of the Carnegie Ridge subduction. Time-temperature inverse modeling of this new thermochronological dataset constrained two cooling phases in the Western Cordillera. The first phase occurred after the emplacement of intrusions, likely associated with magmatic cooling. The second phase began ~6 Ma, coinciding with the last cooling phase observed in the Eastern Cordillera and is likely to be associated with exhumation of the Western Cordillera. Based on our results and existing geological cross-sections we propose that recent crustal shortening and rock uplift led to exhumation of Ecuadorian Andes at ~6 Ma. We suggest that the onset of Carnegie Ridge subduction at ~6 Ma increased the coupling at the subduction interface, promoting shortening and rock uplift in the region.

How to cite: Margirier, A., Strecker, M. R., Thomson, S. N., Reiners, P. W., Casado, I., George, S., and Alvarado, A.: Tectonics and exhumation processes in the northern Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11363, https://doi.org/10.5194/egusphere-egu24-11363, 2024.

EGU24-12727 | Posters on site | GD9.1

Characterizing past earthquakes through historical observations and logic tree approximation 

Ignacia Calisto, Rodrigo Cifuentes, Javiera San Martín, Javiera Alvarez, Lisa Ely, Breanyn MacInnes, Jorge Quezada, and Daniel Stewart

Characterizing the spatial distribution of ruptures from historical and recent earthquakes is key to understanding the seismic cycle of large earthquakes in subduction zones, and thus to assessing the potentialrisks associated with future earthquakes. Central Chile (35°S - 38°S) has been continuously affected by large earthquakes, such as the 2010 Maule (Mw 8.8) and the 1835 earthquakes witnessed by Robert Fitzroy (HMS Beagle captain). Here, we identify the rupture pattern and tsunami propagation of the 1751, 1835, and 2010 mega-earthquakes, events that overlapped in central Chile, by  compiling historical records and applying robust statistical tools. We used an adaptation of a logic tree methodology to generate random sources of slip distribution for each event, constrained by tsunami and deformation data. We find that the three events studied have different slip peaks. The 1751 earthquake has the largest slip with a maximum patch of ∼ 26 m, while the 2010 and 1835 earthquakes reach slips of ∼ 16 m and ∼ 10 m, respectively. Our results show that a part of the segment between 36◦S and 37◦S was consistently affected by large earthquakes, but with different slip and depth. The northern part of the segment accumulated energy for at least 300 years and was released by the 2010 earthquake. This work provides important information for identifying rupture patterns between historical and recent earthquakes, and highlights the importance of extending the time scale of earthquake slip distribution analyses to multiple cycles to describe both earthquake characteristics and their spatial relationship, and thus gain a better understanding of seismic hazard.

How to cite: Calisto, I., Cifuentes, R., San Martín, J., Alvarez, J., Ely, L., MacInnes, B., Quezada, J., and Stewart, D.: Characterizing past earthquakes through historical observations and logic tree approximation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12727, https://doi.org/10.5194/egusphere-egu24-12727, 2024.

EGU24-12800 | ECS | Posters on site | GD9.1

Interaction between historical earthquakes in the seismic gap of central Chile and the Marga-Marga crustal Fault: The seismic potential of the Valparaiso region. 

Javiera Álvarez, Ignacia Calisto, Jorge Crempien, Joaquín Cortés, Claudio Faccenna, and Rodolfo Araya

The characterization of the spatial distribution of historical earthquake ruptures in a seismic segment plays a fundamental role in our understanding of the seismic cycle of significant earthquakes and in assessing the potential hazards associated with future events of this nature.

Due to its tectonic behavior, Chile has been impacted by megathrust earthquakes of considerable magnitude, such as the Valdivia 1960, Maule 2010, and more recently, the Illapel 2015 events. However, there are certain areas where no large earthquakes have occurred and are thus considered to be in a seismic gap. Despite experiencing some significant events, they do not manifest the required energy release properties and depth to compensate the accumulated friction. All these earthquakes, which represent varying stages of the seismic cycle, interact with different geological characteristics of the segment. This is evident in the central zone of Chile, specifically in the Valparaíso region, which has been in a seismic gap since the last major surface-rupturing earthquake of 1730.

During the Maule 2010 and Illapel 2015 earthquakes, rupture occurred only in the southern and northern segments in the mentioned area. Despite seismic activity in 1822, 1906, 1985, and 2017, and the presence of the Marga-Marga crustal fault in Viña del Mar, the energy release has not been sufficient to trigger the expected seismic sequence. It is worth noting that the fault is dangerously located in the most densely populated and frequented area of the city of Viña del Mar, presenting a threat to the surrounding population greater than what could be expected from a subduction earthquake itself.

This research aims to identify and quantify the interaction between the subducting and the Marga-Marga faults in order to assess the potential seismic activity in the area, considering that the crustal earthquakes caused by faults such as Marga-Marga are potentially more destructive than subduction earthquakes of equal magnitude. A relevant precedent is the interaction between the rupture of the Maule 2010 earthquake and the active fault segment of Pichilemu, which triggered a seismic swarm in 2011.

To achieve this, a study was conducted to characterize the slip associated with tsunamigenic events that occurred in the Central Chile segment in 1730, 1906, and 1985. The study revealed deformation patterns, indicating that the last shallow movement occurred in 1730, followed by deep patterns along the coast for subsequent events. Historical data was collected, and a stochastic modeling methodology was applied to comprehensively reconstruct the events. The Coulomb stress transmission between the Marga-Marga fault and subduction events, such as the one in 1906, was then characterized using the newly acquired information from historical deformation to identify potential activation zones of the crustal fault. Currently, efforts are underway to implement a methodology that uses computational simulation tools to visualize the impact of a coseismic event, such as the one in 1730, on the crustal fault and the surrounding region. The aim is to understand the past behavior of the region to be prepared for potential future activations.

How to cite: Álvarez, J., Calisto, I., Crempien, J., Cortés, J., Faccenna, C., and Araya, R.: Interaction between historical earthquakes in the seismic gap of central Chile and the Marga-Marga crustal Fault: The seismic potential of the Valparaiso region., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12800, https://doi.org/10.5194/egusphere-egu24-12800, 2024.

EGU24-12834 | Posters on site | GD9.1

Lower plate retreat and opening of a Cretaceous forearc basin, Northern Andes 

Andreas Kammer, Camilo Andrés Betancur, and Camilo Conde

The tectonic setting of the Northern Andes is delineated fundamentally by a western oceanic terrane that was juxtaposed to the continental margin along the now fossilized interandean Romeral suture since the Early Cretaceous. This constellation and the connection to the Caribbean Large Igneous province have been attributed to a far-travelled and now partially subducted, formerly coherent terrane with a trailing edge represented by the Panama-Choco block. A former disconnection between oceanic terrane and South American plate may, however, be contended by considering continental provenance data of siliciclastic and volcanic rock units and a widely distributed geochemical arc signature of the effusive rock series. Moreover, the emplacement of the basic igneous sequences was strongly controlled by extensional tectonics and subduction correlates in its lifetime with the production of oceanic crust, suggesting a coupling between intrusive activity and convergence. In this contribution, we examine apparently conflicting structural deformations that may be reconciled, however, with the opening of a forearc basin and a deformational imprint that affected extensively the continental margin, supposing the existence of a subduction system composed of two continentward dipping slabs.

How to cite: Kammer, A., Betancur, C. A., and Conde, C.: Lower plate retreat and opening of a Cretaceous forearc basin, Northern Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12834, https://doi.org/10.5194/egusphere-egu24-12834, 2024.

EGU24-12909 | ECS | Posters on site | GD9.1

Microplate behaviour of the Andes during co- and early postseismic phases of the seismic cycle 

Mara A. Figueroa, Franco S. Sobrero, Demián D. Gómez, Robert Smalley Jr., Michael G. Bevis, Dana J. Caccamise II, and Eric Kendrick

The Central and South-Central Andes form a “two-sided” mountain belt bounded by distinct zones of convergence in the western forearc and eastern foreland flanks. Previous geodetic studies of interseismic deformation in the Bolivian Subandes and the Argentine Precordillera found that the forearc to foreland velocity field decayed too slowly to be explained purely by elastic shortening driven by locking of the Nazca megathrust. The velocity field is more precisely explained if elastic deformation is augmented by eastward displacement of the entire Andes. Here, we extend the earlier interpretation of interseismic motion and argue that foreland décollements can participate in the co- and postseismic phases of the earthquake deformation cycle associated with the Nazca megathrust. These findings have direct implications in estimating recurrence interval, slip rate, and probabilistic seismic hazard analysis on both sides of the orogen.

How to cite: Figueroa, M. A., Sobrero, F. S., Gómez, D. D., Smalley Jr., R., Bevis, M. G., Caccamise II, D. J., and Kendrick, E.: Microplate behaviour of the Andes during co- and early postseismic phases of the seismic cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12909, https://doi.org/10.5194/egusphere-egu24-12909, 2024.

EGU24-13804 | Orals | GD9.1

3D-time slab deconstruction and ore deposit localization in South America 

Nipaporn Nakrong, Marnie Forster, Wim Spakman, Hielke Jelsma, and Gordon Lister

Here we present a 3D-time reconstruction of the tectonic evolution of the Nazca and South American plates. The geometry of subducted slabs was modelled down to a depth of ~1950km using UU-P07 global tomographic model. Our approach integrated geochronological records, geological history, and seismotectonic data. Furthermore, our proposed slab models incorporated both velocity and temperature gradients to determine the mid-slab surface accurately. To reconstruct these slabs with minimal distortion back to the Earth's surface, we employed a reverse engineering method. The positions of potential tears in the subducted slabs can then be recognized by the induced distortions. We identified at least three down-dip tears, which significantly influence subduction behaviour. We then integrated the floated or pre-subducted slabs into a 2D-time tectonic reconstruction and tracked the subduction interface over time. Our reconstruction reveals that the pre-subducted slabs accurately mimic the shape of the Andes during the Oligocene-Miocene boundary. However, the remnants of slabs subducted before that time are no longer connected to the entire slab. To the north of the Nazca tear, which coincides spatially with the Nazca fracture zone, the continuous slab has subducted to a depth of ~1950km. To the south, the downgoing slab has been segmented into three distinct zones, with tears localized along the two arms of the extrapolated Juan de Fernández ridge and the inferred Challenger fracture zone. Moving from north to south, the slab in these zones detached at some point after 22Ma, 15Ma, and 12Ma, respectively. Each slab segment exhibits variations in geometry, with flat slab and steep slab portions, as well as differences in penetration depth. Notably, the location of the Nazca down-dip tear coincides with the initial location of the eastward spanning of the Cu belts.

How to cite: Nakrong, N., Forster, M., Spakman, W., Jelsma, H., and Lister, G.: 3D-time slab deconstruction and ore deposit localization in South America, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13804, https://doi.org/10.5194/egusphere-egu24-13804, 2024.

EGU24-13893 | ECS | Posters on site | GD9.1

Stochastic Strong-Motion Simulation of Valparaiso 1985 Mw 8.0 Chile Earthquake 

Rogelio Torres and Sergio Ruiz

In recent years, several historical earthquakes have been studied in Chile to understand the seismotectonic context and anticipate the ground motion of these natural phenomena. One of the first great earthquakes documented by the Global Digital Seismographic Network (GDSN) occurred on March 3, 1985, off the coast of Valparaiso, with a moment magnitude (Mw) 8.0.

Several researchers have modeled the slip distribution at the seismic source, obtaining satisfactory results and fits, mainly at low frequencies and in far field. However, a discrepancy has been observed between the areas of maximum slip and the accelerations recorded in the near field.

In this study, the code proposed by Ruiz and Otarola (2016) was employed to stochastically generate synthetic accelerograms capable of accurately replicating the accelerations observed during near-field ground motion. This approach provides a realistic simulation of earthquake characteristics, source, path, and site.

The importance of generating synthetic accelerograms extends to critical sectors such as civil engineering, geophysics, construction, and urban planning. These simulations play a critical role in understanding ground behavior, predicting large seismic movements, and improving the development of earthquake-resistant structures. Furthermore, in the fields of construction and urban planning, synthetic accelerograms are essential for assessing the vulnerability of specific areas, diversifying applications in industry, and facilitating a more resilient design approach for future seismic events.

The results obtained by generating synthetic accelerograms can replicate the spectral and temporal shape, in agreement with the records provided by the National Seismological Center (CSN) network. Stochastic simulations have been run both in rocky environments and in areas with site effects.

How to cite: Torres, R. and Ruiz, S.: Stochastic Strong-Motion Simulation of Valparaiso 1985 Mw 8.0 Chile Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13893, https://doi.org/10.5194/egusphere-egu24-13893, 2024.

EGU24-14050 | Posters on site | GD9.1

Nature of asperities and barriers along the Chilean megathrust unveiled by an integrated analysis of seismicity, gravity, geodetic locking and wedge geometry 

Andres Tassara, Christian Sippl, Martin Riedel, Catalina Castro, and Favio Carcamo

Asperities inside the seismogenic zone of subduction megathrust are regions where specific frictional properties allow a stick-slip behavior characterized by the accumulation of slip deficit over decades to centuries and its sudden release during earthquakes. Despite its major role on the occurrence of the most devastating earthquakes and tsunamis on the planet, the physical nature of asperities and their limiting barriers is still unclear. This is partially due to an, often, ambiguous interpretation of individual geophysical proxies that are theoretically connected with the frictional structure of the megathrust at quite different time scales, ranging from 100-102 yrs (seismicity patterns, geodetic locking, Vp/Vs and MT anomalies) to 105-107 yrs (coastal geomorphology, forearc wedge geometry and associated basal friction, magnetic and gravity anomalies). If transient phenomena, like slow slip events (SSEs) or stress shadows created by previous earthquakes, do not dominate the seismogenic behavior of the megathrust, then short- and long-term frictional proxies should coincidently illuminate the location of asperities and barriers. Moreover, this would imply that the nature of this features must be connected to the geology structure of both converging plates, with strong implications to seismic hazard assessment. A number of previous studies have explored a combination of several geophysical proxies for megathrust frictional structure, most of them along the Chilean margin. Here we expand over the work of Molina et al. (2021) and Sippl et al. (2021) by performing an integrated analysis of gravity anomalies, friction from critical wedge theory, geodetic locking and seismicity patterns for the entire 4000-km long Chilean megathrust. Particularly, we use available (micro)seismicity catalogues to compute maps of the b-value of the frequency-magnitude relationship. This parameter contributes with an independent short-term proxy for the stress state of the megathrust and we treat it as an additional continuous field into a principal component analysis (PCA) similar to Molina et al. (2021) that aims to quantify the main spatial correlation between the proxies. We will also test other techniques to measure the degree of spatial correlation, like AI-based pattern recognition methods. This integrated analysis will also consider rupture length of historical earthquakes over the last 500 yrs and slip distribution of instrumental earthquakes and SSEs. This will allow us to test contrasting hypothesis about the nature of seismic asperities and barriers along the Chilean megathrust and elsewhere.

How to cite: Tassara, A., Sippl, C., Riedel, M., Castro, C., and Carcamo, F.: Nature of asperities and barriers along the Chilean megathrust unveiled by an integrated analysis of seismicity, gravity, geodetic locking and wedge geometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14050, https://doi.org/10.5194/egusphere-egu24-14050, 2024.

EGU24-17042 | ECS | Posters on site | GD9.1

Search for repeaters in the central part of the Chilean subduction zone  

Audrey Chouli, Lucile Costes, David Marsan, Jannes Münchmeyer, Sophie Giffard-Roisin, and Anne Socquet

Repeating earthquakes, corresponding to the rupture of the same asperity over time at more or less regular intervals, can be used to estimate the slip rate on a subduction plate interface. The purpose of this work is to build a catalog of repeaters for the central part of the Chilean subduction zone, extending from 24°S to 33°S latitude and centered on the Copiapo seismic gap. As a basis for our study, we used the seismicity catalog from the Centro Sismológico Nacional (CSN).

The similarity between waveforms gives a good criterion to assign earthquakes to a similar asperity. To measure it, we calculated for each pair of events the coherency, correlation and associated time lag between the vertical components of their P waves, on a 5 s window starting 1 s before the P arrival. We tested different frequency bands (1-4 Hz, 3-12 Hz, 5-20 Hz, ...) and kept each time the one with the best coherency value. We selected all pairs of earthquakes with coherency higher than 0.95, at three or more stations. To ensure a stable measurement, we imposed that the time lags from cross-correlation and coherency differ by less than 0.01 s. To verify that the earthquakes of a repeaters family take place at the same location, we relocated the events using a double-difference method and created clusters based on both coherency and location similarity. As coherency values are calculated on a 5 s window, we relocate the centroids of the events, i.e. the center of mass of the rupture. To estimate the surface rupture, we calculate the rupture radius based on the seismic moment and stress-drop values (Eshelby 1957), estimating the stress-drop and seismic moment with SourceSpec (Satriano 2023).          

As preliminary results, we found 347 families, mostly located between 30-60 km deep, and between 29-33.5°S. Almost no repeaters were found before 2015 due to the lack of available stations. Obtained families contain a few events, with 11 earthquakes in the biggest one. We compared the obtained repeaters with the coupling along the plate interface.  Most repeaters are located at the transition between strong and low coupling zones in the Illapel area, making a circle shape around the deep part of the Illapel coseismic slip. Furthermore, we investigated the evolution of the number of repeaters with time in different areas and found potential aseismic slip marked by repeaters' activity consistent with previous observations, such as before the 2017 Valparaiso sequence (Ruiz et al., 2017) or after the Atacama sequence (Klein et al., 2021).

In order to obtain more complete repeaters families, we created a new machine learning based earthquake catalog for the study area with SeisBench (Woollam et al., 2022), using data from permanent and temporary networks in Northern and Central Chile. We are currently applying our analysis to this new catalog.

How to cite: Chouli, A., Costes, L., Marsan, D., Münchmeyer, J., Giffard-Roisin, S., and Socquet, A.: Search for repeaters in the central part of the Chilean subduction zone , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17042, https://doi.org/10.5194/egusphere-egu24-17042, 2024.

EGU24-20233 | ECS | Orals | GD9.1 | Highlight

Structural control on aseismic and seismic slip interactions during the 2020 SSE in the Atacama region, Chile. 

Diego Molina, Jannes Münchmeyer, Mathilde Radiguet, Anne Socquet, and Marie-Pierre Doin

While subduction earthquakes are widely recognized for releasing seismic slip, aseismic slip can also be hosted on the megathrust by the occurrence of postseismic phase or Slow Slip Events (SSEs). SSEs have been reported along several subduction zones, preferably on the deeper zone and usually lasting months or even years (Draguert et al., 2001). Notably, in the Chilean subduction zone, deep SSEs have been observed in only a reduced area in Central Andes, specifically close to the Copiapo city. Recent studies report that this area is prone to host regular SSEs with a recurrence time of ~5 years and variable duration (Klein et al., 2021), which was confirmed by a new detected SSE in 2020 and 2023.

Notably, during the 2020 SSE, a seismic crisis with a main shock of Mw 6.9 took place on the zone (September 2020), likely provoking an interaction between the different slip modes.  In this work, we attempt to enhance the characterization of the temporal and spatial pattern-evolution of the SSE to elucidate whether there was a trigger mechanism for the seismic crisis or if the earthquake affected the SSE evolution.

To describe the seismic behavior of the area, we recur to the analysis of distinct data sets. On one hand, GNSS stations deployed by different institutions are used to characterize the temporal evolution and amplitude of the 2020-SSE and respective seismic crisis. On the other hand, the spatial pattern is recovered by InSAR data recorded by Sentinel-1 mission. Additionally, a seismicity catalogs coming from machine learning approach is used to investigate aseismic-seismic interactions.

Our analysis shows that the 2020 SSE triggered the seismic sequence in September of that year. We also observed that the aseismic deformation migrates, resulting in a total cumulative slip pattern similar to another SSE detected in 2014. Remarkably, our study evidences a clear segmentation along dip and strike affecting both, aseismic and seismic slip, which correlates with gravity anomalies.

This study suggests a tectonic control on the slip behavior characterizing the area and highlights the cinematic between slow and fast earthquakes hosted along the plate interface.

 

 

How to cite: Molina, D., Münchmeyer, J., Radiguet, M., Socquet, A., and Doin, M.-P.: Structural control on aseismic and seismic slip interactions during the 2020 SSE in the Atacama region, Chile., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20233, https://doi.org/10.5194/egusphere-egu24-20233, 2024.

EGU24-20700 | ECS | Posters on site | GD9.1

From regional to local structures imaged by seismic tomography at the Atacama seismic gap, Central-Northern Chile (24.5-29°S) 

Nicolás Hernádez-Soto, Matthew Miller, Marcos Moreno, Dietrich Lange, Anne Socquet, Christian Sippl, and Diego González-Vidal

Between 2020 and 2022 the ANILLO+DEEPtrigger (Y6+XZ) Seismic Network, comprising 108 seismic stations, operated for eighteen months in Northern-Central Chile (24.5°S - 29°S). Employing Deep Learning (EQTransformer, Mousavi et al., (2022)) and Phase Association (GaMMA, Zhu et al. (2021)) algorithms, we identified over 30,000 seismic events in an area with a notable absence of moderate-to-large events in the past century, since the 1922 M8.5 Atacama earthquake.  
From the initial catalog, we selected a well-distributed subcatalog of 1000 earthquakes, consisting of 26,570 P- and 22,109 S-wave arrival times, by selecting for events with an optimal spatial distribution, small residuals, and abundant P- and S-arrivals. These selected events served as input for VELEST (Kissling et al., 1994) to compute a new 1-D velocity model representative of this region by minimizing the subset residuals. To reduce both residuals and location errors associated with the seismicity, we relocated the entire catalog using staggered tomographic inversions based on SIMUL2000 (Thurber & Eberhart-Phillips, 1999), simultaneously inverting for seismic velocity models and hypocentral parameters within the iterative damped least squares method. Following the proposed method, we gradually increased model complexity, transitioning from 2-D Vp and Vp/Vs to ultimately a 3-D fine Vp and Vp/Vs solution with low node separation.
Next, synthetic resolution tests were conducted to assess the reliability of the spatial limits and boundaries within the solutions. In this context, distinctive patterns were identified for each profile of the three-dimensional model, revealing enhanced horizontal and vertical resolution in the central region beneath the network. Conversely, a decline in resolution was noted at the peripheries, primarily attributable to reduced station coverage causing poorer seismic event relocations.
Our results reveal both regional and local patterns. We observed a mantle wedge with vertical thicknesses ranging from ~35km in the southernmost profiles less than 25 km in the northern region, consistent with previous seismic tomography observations in northern Chile (Pastén-Araya et al., 2021). The Vp/Vs ratio and Vp values allow us to discern the distribution of the hydrated slab, which, spatial correlated with seismicity, provides evidence of irregular dehydratation processes along both dip and strike directions.
Relocated seismicity exhibits some noteworthy features. Shallower crustal sesmicity is predominantly related to high rates of mining activity. In the subduction areas, the most prominent cluster is located at depths of 20-50 km, delineating the seismogenic zone. At greater depths, double and even triple seismic bands add structural complexities to the observations.
From 26.5°S to 29.5°S, between 20 km and ~75 km depth, seismicity predominantly aligns with the interplate contact defined by SLAB2 (Hayes et al., 2018). In contrast, northward from 26.5°S, our deepest seismicity, situated between 75 and 125 km depth, diverges from SLAB2, depicting a steeper dip angle.
Lastly, we recommend integrating OBS and back-arc stations, whose data would improve off-shore and back-arc resolution, contributing to a more comprehensive understanding of seismotectonic environments. Non-supervised Deep Learning results can provide exceptional databases for tomographic studies, yielding residuals similar to human-picked databases but within shorter timeframes.

How to cite: Hernádez-Soto, N., Miller, M., Moreno, M., Lange, D., Socquet, A., Sippl, C., and González-Vidal, D.: From regional to local structures imaged by seismic tomography at the Atacama seismic gap, Central-Northern Chile (24.5-29°S), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20700, https://doi.org/10.5194/egusphere-egu24-20700, 2024.

EGU24-20861 | Orals | GD9.1

The effect of subduction relief on megathrust slip properties in Ecuador, constraints from gravity anomalies and seismic tomography 

Michele Paulatto, Yueyu Jiang, Audrey Galve, Mireille Laigle, Andreas Rietbrock, Monica Segovia, and Sandro Vaca

The subduction margin in Ecuador is dominated by the subduction of the Carnegie Ridge and associated oceanic plate relief. This region is also affected by complex slip behaviour including aseismic deformation, slow slip, and large earthquakes. We present new seismic and gravity data collected as part of the HIPER campaign in 2020 and 2022, covering the subduction margin at the northern edge of the Carnegie Ridge. Traveltime tomography of dense active source wide-angle seismic data from a trench perpendicular profile reveals the structure of this part of the margin. The slab crust thickens from 7.5 km at the western end of the profile to 15 km at the eastern end. The profile crosses two seamounts (Atacames seamounts), one currently impinging onto the margin (AS2) and the other already buried beneath the accretionary prism (AS1). The seamounts have low P-wave velocity roots and are associated with gravity anomaly highs. The forearc is uplifted in front of the subducted seamount AS1 and is affected by gravitational collapse in its wake. In the area affected by the seamounts, the interseismic plate coupling is reduced to almost zero likely because of the fracturing and disruption of the forearc and lubrication induced by enhanced fluid input. Further downdip the profile extends into the rupture area of the 2016 M7.8 Pedernales earthquake. This part of the plate interface is more laterally homogeneous and characterised by higher Vp. Our results confirm that rugged plate relief is associated with reduced interseismic coupling and that megathrust earthquake rupture areas tend to have high Vp and laterally homogeneous properties.

How to cite: Paulatto, M., Jiang, Y., Galve, A., Laigle, M., Rietbrock, A., Segovia, M., and Vaca, S.: The effect of subduction relief on megathrust slip properties in Ecuador, constraints from gravity anomalies and seismic tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20861, https://doi.org/10.5194/egusphere-egu24-20861, 2024.

EGU24-1771 | Posters on site | GD5.2

Rifting in the presence of accreted terranes – a numerical modelling study 

Zoltán Erdős, Susanne Buiter, and Joya Tetreault

Many rifted margins have formed in areas that have previously experienced subduction and orogenesis, completing the Wilson cycle of closing and opening oceans. Often the subduction phase is accompanied by the accretion of bathymetric highs, such as oceanic plateaus, continental fragments, seamounts and microcontinents. Such accretionary orogeneses result in a more complex structural, rheological and thermal inheritance than continent-continent collision without terranes. Here we use 2D thermo-mechanical numerical models to investigate how accretionary, rather than collisional orogens, affect a subsequent phase of continental rifting. Our models build an orogen through subduction, terrane accretion and collision before the onset of rifting. We examine the structure of the resulting rifted margins and the degree in which inherited compressional structures are utilized.

For rifting of collisional systems without terrane accretion, we find that there is a competition between structural and thermal inheritance that has a first order control on rifted margin architectures. For smaller, colder collisional systems, localized reactivation of the old subduction interface promotes the formation of narrow margins. Conversely, in larger, hotter collisional orogens, wide margins develop through distributed extension, initiating away from the inherited suture in the hot, weak regions of the pre-rift orogen. This dynamic persists even in the presence of accreted terranes, where the orogens preserve multiple suture-zones that dissect the lithosphere. In smaller orogens, the optimally oriented, steepest and as a result shortest, and hence weakest suture experiences the highest degree of inversion, localizing the rifting.. In larger, hotter accretionary orogens, deformation is not primarily focused on inherited shear zones but is instead concentrated in the thickest, hottest part of the orogen. We interpret this as thermal inheritance dominating over the influence of structural inheritance. Depending on the pre-rift lithosphere configuration, accreted terranes can be preserved in one or both rifted margins. Our results show that the size of the accretionary orogen prior to extension has the strongest influence on the style of the resulting rifted margins and that the presence of multiple sutures between the accreted terranes plays a smaller role in localizing extension.

Our experiments demonstrate that a wide range of features such as continental fragments, allochthons or hyper-extended segments that can form in the presence of inherited compressional structures and emphasize the importance of the deformation history in the evolution of continental rifting. These results can be further used to understand how various stages of the Wilson cycle affect each other. 

How to cite: Erdős, Z., Buiter, S., and Tetreault, J.: Rifting in the presence of accreted terranes – a numerical modelling study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1771, https://doi.org/10.5194/egusphere-egu24-1771, 2024.

EGU24-2366 | ECS | Posters on site | GD5.2

The role of velocity and thermal structure in the construction of asymmetric rifted margins 

Sara dos Santos Souza, Claudio Alejandro Salazar-Mora, and Victor Sacek

The development of asymmetric conjugate rifted margins has been explained by processes such as rift migration and sequential faulting (Brune et al., 2014; Ranero & Pérez-Gussinyé, 2010), and by the effects of lithospheric strength and strain-softening (Svartman Dias et al., 2015; Huismans & Beaumont, 2003) during rifting. Briefly, rift migration consists of sequential faulting of the upper crust that moves oceanward and is associated with lower crustal flow. Nonetheless, there are other thermal and dynamic parameters that might either facilitate or hinder the construction of an asymmetric margin, also depending on the coupling degree between the continental and mantle lithosphere. Since there are a considerable number of asymmetric margins around the world, mostly associated to petroleum fields, and more recently emerging as green hydrogen reservoirs, there is a need to understand which and how much the parameters influence the construction of asymmetric margins during the rifting phase. For that reason, this work aims to contribute to the understanding of this subject through thermo-mechanical numerical models. Velocity and thermal structure were the principal factors considered in the context of a decoupled lithosphere. Our models show that rift velocity is the principal parameter that controls width and margin asymmetry, being followed by thermal structure. High rift velocities (~5 cm/year) developed wide and asymmetric margins, while a thick upper crust is shown to be crucial to develop the distal domain in the late stages of rifting. When both parameters are combined, the generated margins can reach about 360 km long. In some scenarios, the margin width is up to 550 km, with a distal domain which exceeds 130 km long.

Funded by Petrobras Project 2022/00157-6.

 

Brune, S. et al. Rift migration explains continental margin asymmetry and crustal hyper-extension. Nature communications, v. 5, n. 1, p. 4014, 2014.

Huismans, R. S. & Beaumont, C. Symmetric and asymmetric lithospheric extension: Relative effects of frictional-plastic and viscous strain softening. Journal of Geophysical Research: Solid Earth, v. 108, n. B10, 2003.

Ranero, C. R. & Pérez-Gussinyé, M. Sequential faulting explains the asymmetry and extension discrepancy of conjugate margins. Nature, v. 468, n. 7321, p. 294-299, 2010.

Svartman Dias, A. E. et al. Conjugate rifted margins width and asymmetry: The interplay between lithospheric strength and thermomechanical processes. Journal of Geophysical Research: Solid Earth, v. 120, n. 12, p. 8672-8700, 2015.

How to cite: dos Santos Souza, S., Salazar-Mora, C. A., and Sacek, V.: The role of velocity and thermal structure in the construction of asymmetric rifted margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2366, https://doi.org/10.5194/egusphere-egu24-2366, 2024.

EGU24-2390 | Posters on site | GD5.2

The role of pre-rift tectonic quiescence on rifted margins configuration 

Claudio A. Salazar-Mora and Victor Sacek

During the breakup of the Pangea Supercontinent, rifting localized in portions of the continental lithosphere that comprised orogenic structural inheritances. This heterogeneous orogenic lithosphere is a result of mountain-building processes followed by post-orogenic tectonic quiescence. In the case of the Atlantic Ocean opening in its North, Central, and South segments, the time span between Gondwana-Pangea amalgamation and the onset of rifting is largely different, ranging from tens of Myrs to hundreds of Myrs. In this contribution, we discuss the effects of different tectonic quiescence periods of time on the pre-rift continental lithosphere and consequent variable conjugate rifted margin configurations. Here we present 2D thermo-mechanical numerical models that simulate a sequence of extension, contraction, quiescence, and final extension (i.e. accordion-like models). Through this process, our models self-consistently create the orogenic inheritance that undergoes quiescence and final rifting. We explored wide orogenic structures (i.e. without erosion) and narrow ones (i.e. with erosion). In the case of wide orogens, our models showed that tectonic quiescence periods between 30-60 Myrs developed symmetric conjugate rifted margins, where the lithospheric mantle broke up before the continental crust, which, in turn, hyperextended. Nearly 50% of the previously subducted continental crust remained in the fossil subduction zone after rifting. In the case of wide orogens with 100-300 Myrs of tectonic quiescence, the conjugate rifted margins are strongly asymmetric with one ultra-wide side. Nearly 80% of the previously subducted crust was educted during extension. Still in the wide orogens, but now with less than 30 Myrs of quiescence, the resulting rifted margins are asymmetric, not developing ultra-wide sides and having up to 90% of the previously subducted crust educted. Finally, the narrow orogens were not significantly influenced by tectonic quiescence periods in the construction of the final rifted margins, which resulted all asymmetric and rather narrow. In this case, the longer the quiescence, the more continental crust was preserved in the fossil subduction zone. These simulations show that the final rifted conjugates are strongly affected by an interplay between structural and thermal inheritances in the orogenic lithosphere. Wide orogens are hot due to high concentrations of heat-producing elements and grow laterally by orogenic spreading during longer periods of quiescence. Contrastingly, narrow orogens are cold and lack crustal material for wide rifted conjugates.

Funded by Petrobras Project 2022/00157-6.

How to cite: Salazar-Mora, C. A. and Sacek, V.: The role of pre-rift tectonic quiescence on rifted margins configuration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2390, https://doi.org/10.5194/egusphere-egu24-2390, 2024.

EGU24-3455 | Posters on site | GD5.2

Ocean Bottom Seismic Model in the Knipovich Ridge area 

Wojciech Czuba, Rolf Mjelde, Yoshio Murai, and Tomasz Janik

The structure of the oceanic crust generated by the ultraslow-spreading mid-ocean Knipovich Ridge still remains relatively uninvestigated compared to the other North Atlantic spreading ridges further south. The complexity of the Knipovich Ridge, with its oblique ultraslow-spreading and segmentation, makes this end-member of Spreading Ridge Systems an important and challenging ridge to investigate. At spreading rates below 20 mm/y, ultraslow spreading ridges are characterized by a low melt supply. The Ocean Bottom Seismometer (OBS) data along a refraction/reflection profile (~280 km) crossing the Knipovich Ridge off the western Barents Sea was acquired by use of RV G.O. Sars on July 24 - August 6, 2019. The project partners are University of Bergen, Institute of Geophysics, Polish Academy of Sciences, and Hokkaido University. The seismic energy was emitted every 200 m by an array of air-guns with total volume of 80 l. To receive and record the seismic waves at the seafloor, ocean bottom seismometers were deployed at 12 positions with about 15-km spacing in 2 deployments. All the stations were recovered and correctly recorded data. Seismic energy from airgun shots were obtained up to 50 km from the OBSs. The profile provides information on the seismic crustal structure of the Knipovich Ridge and oceanic and continental crust in the transition zone. Seismic record sections were analyzed with 2D trial-and-error forward seismic modeling. This profile is a prolongation of the previously acquired profile AWI-20090200 (Hermann & Jokat 2013) and together will allow to interpret of ~535 km long transect crossing the Knipovich Ridge from the American to the European plate. This work is supported by the National Science Centre, Poland according to the agreement UMO-2017/25/B/ST10/00488. The cruise was funded by University of Bergen.

 

Hermann, T. and Jokat, W., 2013. Crustal structures of the Boreas Basin and the Knipovich Ridge, North Atlantic. Geophys. J. Int., 193, 1399–1414, doi: 10.1093/gji/ggt048

How to cite: Czuba, W., Mjelde, R., Murai, Y., and Janik, T.: Ocean Bottom Seismic Model in the Knipovich Ridge area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3455, https://doi.org/10.5194/egusphere-egu24-3455, 2024.

EGU24-3982 | Orals | GD5.2

Different Wilson Cycle styles in Western Europe: the key role of inheritance 

Pauline Chenin, Gianreto Manatschal, Gianluca Frasca, Rodolphe Lescoutre, and Emmanuel Masini

In the classical Wilson Cycle concept, orogeny is assumed to follow protracted subduction of a wide oceanic domain. Such subduction systems form magmatic arcs associated with high-temperature and low-pressure metamorphism in the subduction upper plate, and depletion of the mantle wedge above the slab. Since its emergence, the Wilson Cycle concept has been largely used to study collisional orogens in general, and yet, in Western Europe, the Pyrenees and the Alps are both devoid of magmatic arc remnants.

Recent field studies and paleogeographic restorations suggest that both the Pyrenees and the Alps resulted from the closure of narrow proto-oceanic domains that may have never reached the stage of steady-state seafloor spreading. This would imply that rift systems may be inverted at any stage of their development, including prior to the onset of steady-state seafloor spreading. Inversion of such a rift system would not form a magmatic arc due to the limited length of the slab, and hence orogeny would essentially be a mechanical process mainly controlled by the inherited rift architecture.

In this presentation, we first describe the paleogeographic settings of the Alpine Tethys–Pyrenean rift systems. We show the results of an innovative kinematic reconstruction approach that integrates field observations, realistic margin widths and pre-rift tight full fit restorations.

Second, we discuss how the margins along-dip architecture has controlled the two-dimensional architecture of the Pyrenean and Alpine orogens. We show that the major escarpments inherited from rifting and separating the thick-crusted and buoyant proximal domain from the thin-crusted and denser distal domain have become first-order ramp structures that today separate the external- from the internal part of both orogens.

Finally, we explore how the along-strike segmentation of the Pyrenean and Alpine rift systems have controlled the three-dimensional architecture of the subsequent orogens. We show that the segmentation of the Pyrenean and Alpine rift systems, which both used to display ribbons of thick continental crust between overstepping rift basins, can explain most of the non-cylindricity observed today in both the Pyrenean and Alpine orogens.

How to cite: Chenin, P., Manatschal, G., Frasca, G., Lescoutre, R., and Masini, E.: Different Wilson Cycle styles in Western Europe: the key role of inheritance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3982, https://doi.org/10.5194/egusphere-egu24-3982, 2024.

Transform faults most commonly exhibit offsets of 100 to 200 km, with a minority defined as mega-transforms with >200 km offsets. Consequently, these mega-transforms represent a relatively understudied feature of plate tectonics with our understanding of their formation and development currently incomplete. In this study, we use the numerical modelling software ASPECT (Advanced Solver for Problems in Earth's ConvecTion) to create high resolution 3D simulations of mega-transforms following oblique changes in plate motion. Specifically, we determine how inducing transpression and transtension across a mega-transform fault affects the development of new transforms and mid-ocean ridge segments. Our numerical models all implement an initial stage of orthogonal extension and continental break up along an offset rift, followed by a second stage of oblique extension across a wide range of extension azimuths (-75° to 75°). Here, we find that small transpressional changes in plate motion (-15°) lead to the development of a short 130 km long transform, whilst larger (-75°) changes in plate motion led to the development of a longer 300 km transform. Alternatively, increasingly oblique, transtensional deformation leads to increased rifting between the offset ridges with a >60° change in the extension orientation leading to continental rifting across the old transform margin. These results are analogous to real world examples such as the Davie (West Somali Basin) and Ungava Fault Zones (Davis Strait) where we also highlight the role of plate motion changes on continental cleaving. Additionally, the orientation of mid-ocean ridges and transforms in the Labrador Sea suggests a late phase of E-W extension prior to the cessation of spreading.

How to cite: Longley, L., Phethean, J., and Heron, P.: Deciphering the Role of Plate Motion Changes and Inherited Structures in Mega-Transform Fault Development Using Geodynamic Numerical Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4090, https://doi.org/10.5194/egusphere-egu24-4090, 2024.

In this field-based study, we investigate the Notre Dame Bay Magmatic Province (NDBMP) located in the Dunnage Zone, north-central Newfoundland, Canada. The NDBMP is a collection of rift-related intrusions dated at ca. 148 Ma (Late Jurassic, Tithonian), including the gabbroic Budgell Harbour Stock (BHS) and an associated lamprophyre dyke swarm. The host rock, composed of Ordovician-aged sedimentary and volcanic back-arc sequences, is metamorphosed to greenschist and locally amphibolite facies. The host rocks were deformed during the Ordovician-Silurian closure of the Iapetus Ocean. The primary Iapetus suture divides peri-Laurentian and peri-Gondwanan terranes in the Newfoundland Appalachians, and forms a Z-shaped flexure across the study area.

Our research focuses on three primary aspects: 1) investigating the relationship between pre-existing orogenic structures and rift-related magmatism, 2) assessing the impact of this magmatism on the host rock, and 3) analysing the post-intrusive deformation of lamprophyres. The dataset includes 178 structural measurements of lamprophyres, and host rock structures, petrographic analysis of thin sections of the BHS, lamprophyres, and host rocks, and 3D structural models created from drone-based photogrammetry for selected outcrops.

Our findings indicate that structures dating from the Ordovician to Silurian, associated with the Iapetus suture and Notre Dame Bay oroclinal flexure, significantly impacted the location and pathways of magmatism. This influence occurred at local scales, where dykes were deflected along bedding, foliation, and fold hinges, and on a larger scale along the Iapetus Suture. Additionally, multiple instances of magmatism affecting the host rock, including fracturing occurring subparallel to dykes, hydrothermal alteration, and brecciation were observed. Our investigation also identified three instances where dykes underwent brittle and ductile deformation due to the reactivation of pre-rift south-east dipping thrust faults with an oblique dextral motion towards the northeast. This movement is consistent with the direction of extensional forces the region experienced during Mesozoic rifting.

Preliminary findings suggest that the reactivation of these Ordovician-Silurian thrust faults reflect larger scale transtensional reactivation of the Iapetus suture zone during Mesozoic rifting and opening of the Atlantic Ocean. These results enhance our understanding of structural inheritance, which is essential for accurately modelling rifting processes and reconstructing the opening of the North Atlantic Ocean.

How to cite: Keefe, E., Peace, A., Guna, A. G., and McCausland, P.: Impact of pre-existing structures on the emplacement and post-intrusion deformation of the Late Jurassic rift-related Notre Dame Bay Magmatic Province, Newfoundland, Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4212, https://doi.org/10.5194/egusphere-egu24-4212, 2024.

EGU24-4308 | Orals | GD5.2

Timing and Volume of Magma Emplacement During Rifting, Breakup, and Initial Spreading: from Simple Endmember Models to Overlooked Complexities 

Gianreto Manatschal, Pauline Chenin, Nick Kusznir, Daniel Sauter, and Cuimei Zhang

A major achievement in the study of rifted margins was the establishment of the “magma-poor” vs. “magma-rich” archetypes distinguishing between margins with exhumed mantle and margins whose continental crust is heavily intruded and overlain by extrusive magmatic flows (e.g., seaward dipping reflections (SDRs)). However, this binary approach, mostly dictated by the magmatic budget/mantle potential temperature, cannot account for observations made at high-resolution, wide-angle seismic data. These data show markedly variable along and across strike volumes of magmatic products from the intra-segment scale (< 100 km) to the margin scale (> 100 km). These observations highlight that the binary magma-rich vs. magma-poor classification is only a first order simplification and other factors that so far have been overlooked control the timing and volume of magma emplacement during rifting, breakup and initial seafloor spreading.

Two main limitations exist when describing magmatic systems at rifted margins: 1) distinguishing among inherited continental crust, newly created magmatic crust and serpentinized mantle in seismic data is challenging due to their comparable geophysical properties (density and seismic velocity); and 2) modelling magmatic systems is limited by the poor knowledge of their initial conditions (mantle potential temperature and inherited compositional variations in the subcontinental mantle). The study of magma-rich margins is challenging as different factors may control the timing and volume of magma emplacement, and hence control their crustal shape. These factors include: (1) the initial conditions mentioned above; (2) the mode of lithosphere extension (e.g., pure shear vs. depth-dependent lithosphere thinning); and (3) external rift-independent factors (e.g., strain rates or elevated temperature linked to mantle plumes). Thus, new observational approaches are needed to describe the tectono-magmatic evolution of margins and unravel the spatio-temporal evolution of magmatic processes at the transition from rifting to seafloor spreading.

In our presentation, we first present along and across strike seismic observations that show evidence for variability in the timing and volume of the first magmatic addition with respect to the onset of steady-state seafloor spreading. These observations allow us to explore and discuss the importance of strain rate and initial conditions and provide insights into the dominant processes controlling the tectono-magmatic evolution during rifting, breakup, and initial spreading. Finally, we propose a simple approach that focuses on the mapping of first order interfaces. This approach allows us to determine the crustal shape and the nature of top basement, both of which are diagnostic for extensional and/or magmatic processes. We combine this approach with a simple geometric/kinematic/isostatic model, which allows us to calculate the relative timing and volume of magma emplacement and its subsequent isostatic equilibration.

How to cite: Manatschal, G., Chenin, P., Kusznir, N., Sauter, D., and Zhang, C.: Timing and Volume of Magma Emplacement During Rifting, Breakup, and Initial Spreading: from Simple Endmember Models to Overlooked Complexities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4308, https://doi.org/10.5194/egusphere-egu24-4308, 2024.

EGU24-4479 | Posters on site | GD5.2

Slab pull drives IBM Trench advance despite the weakened Philippine Sea Plate 

Huizi Jian and Ting Yang

The Izu-Bonin-Mariana (IBM) subduction zone has one of the most significant advancing trenches on Earth, but the mechanism responsible for its trench advance remains in dispute. Slab pull from the Ryukyu subduction zone may have provided the main driver for this significant trench advance. However, it is unclear whether this slab-pull force can transmit through the weak zones, such as the young Shikoku and Parece Vela basins, the active Izu-Bonin rifts, and the continuous spreading Mariana Trough, and then act on the IBM trench. To figure out this issue, we conduct slab subduction numerical models to reproduce the spatio-temporal tectonic evolution of the Philippine Sea Plate. Model results show that the stretching rate of 2.5 cm/yr during rifting/spreading represents the critical threshold for the transmission of slab pull. Additionally, the lithospheric strengthening and weakening effects cancel out each other during the rift stage so that the slab pull from the Ryukyu Trench can transmit through the weak fossil spreading centers and intra-arc rifts and drive the Izu-Bonin Trench's advance. In contrast, lithospheric weakening overwhelms lithospheric strengthening and impedes stress transfer in the back-arc spreading stage, suggesting that the slab pull cannot directly pull the Mariana Trench to advance at present. We suggest that the Mariana Trench advance is driven by the continuous Izu-Bonin Trench advance from the north, which is supported by the fact that the Mariana Trench is further east than the Izu-Bonin Trench and that the IBM trench advance rate decreases southward.

How to cite: Jian, H. and Yang, T.: Slab pull drives IBM Trench advance despite the weakened Philippine Sea Plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4479, https://doi.org/10.5194/egusphere-egu24-4479, 2024.

EGU24-5920 | ECS | Orals | GD5.2

Revisiting the exhumed mantle at the Iberia margin to get new insight about break-up processes 

Harmony Suire, Marc Ulrich, and Gianreto Manatschal

Previous studies from the Western Iberia magma-poor rifted margin enabled to describe the evolution of the mantle lithosphere during rifting and breakup based on the study of dredged and drilled magmatic and mantle samples. These data together with those from the present-day Australia-Antarctica and the fossil Alpine Tethys rifted margins and Pyrenean hyperextended basins provide insights about the role of the mantle processes and inheritance on the tectono-magmatic evolution of rift systems during rifting and breakup. However, key questions remain in understanding lithospheric breakup such as when, where, and how much magma is produced during breakup; how first magma interacts with the percolated subcontinental mantle and how these mantle-melt processes interrelate with the extensional processes operating during breakup.

This study focuses on samples drilled during ODP Legs 103, 149, 173 and 210 from the conjugate Iberia-Newfoundland margins and included also previously little studied dive-recovered samples from the Galicia Bank (Galinaute I and II). Bulk-rock, in-situ chemical and isotopic analysis of ultramafic rocks are used to constrain mantle dynamics during final rifting and breakup along the southern North Atlantic margins. Major and trace-element concentrations of primary minerals like olivine, pyroxenes and spinel are used to distinguish between different mantle domains, i.e., depleted oceanic or refertilized and/or inhertited subcontinental mantle. Thermo-barometry calculations are applied to define rates and thermal conditions during mantle exhumation.

Preliminary results from textural observations and geochemical data from Galinaute ultramafic rocks show two mantle types: subcontinental and refertilized mantle (T1/T2 mantle types). Indeed, plagioclase texture in corona around spinel together with spinel compositions are consistent with lherzolite formation by sub-solidus re-equilibration, similar to those of subcontinental mantle exposed in the Alps (Tasna and Malenco). However, some clinopyroxene compositions show evidence of low pressure mantle-melt interaction, which may indicate a refertilization process by ascending MORB-type melts. Diffusion modeling of sub-solidus major element and REE re-equilibration between OPX and CPX from Galinaute peridotites show that the exhumed mantle along the Galicia Bank cooled at rates between 10-6 and 10-4°C/yr across the sp-pl peridotite facies transition, slower than cooling rates determined for samples from the Alpine Tethys and the present-day Australia-Antarctica magma-poor rifted margins.

How to cite: Suire, H., Ulrich, M., and Manatschal, G.: Revisiting the exhumed mantle at the Iberia margin to get new insight about break-up processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5920, https://doi.org/10.5194/egusphere-egu24-5920, 2024.

Abstract:

Deciphering inversion tectonics and identification of inverted structures are very important in the petroleum industry due to the positive or negative impacts they can exert on the hydrocarbon traps. The proper understanding of structures related to inversion has implications for geo-energy exploration. In order to characterize the occurrence of inversion tectonics and its effect in the Western Alborz Oilfield, located in the Qom-Saveh area (Central Iran), this research describes the structural style and deformation history through structural and tectono-sedimentary analyses based on the surface data (geological map and satellite image) and subsurface data (seismic data and well data). The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth structures indicate that the Western Alborz anticline is created from multiple fault-propagation folds. The final shape and geometry of the Western Alborz anticline are affected by thrust fault with the ram and flat geometry, reversed normal fault, and steeply dipping normal fault activity. The Western Alborz structure evolved at least during six tectonic phases. Three stages of the extensional deformation occurred from the Eocene to the Early Miocene. Moreover, three compressional phases happened in the Late Miocene and continued to the present day. During the Middle Miocene (Langhian-Serravallian), the tectonic quiescence period prevailed in this Oilfield. Multiple fault-propagation folding and the fold axis rotation in the Western Alborz anticline are controlled by the presence of décollement surfaces, the salt diapirism, and the occurrence of inversion tectonics along the pre-existing basement structure. Based on the structural evidence of inversion tectonics and the deformation history in the study area, the positive inversion tectonics occurred at the Middle to Late Miocene boundary and modified the evolutionary history of the sedimentary basin. Inversion affected hydrocarbon trap development at the Late Miocene and controlled their current conditions in Central Iran. Considering the hydrocarbon migration after the Late Miocene in the Central Iran basin up to the present day, the inversion tectonics event has a positive impact on the hydrocarbon trap development in the Western Alborz Oilfield. The results of this study could add data to worldwide examples of the positive impacts of tectonic inversion on the hydrocarbon trap development in collisional orogenic belts.

 

Keywords: Inversion tectonics; Tectono-sedimentary analysis; Hydrocarbon trap; Western Alborz Oilfield; Central Iran

How to cite: Tajmir Riahi, Z., Nikpoush, S., and Soleimany, B.: Impact of inversion tectonics on the hydrocarbon trap development in the Qom-Saveh area: Insights from the Western Alborz Oilfield, Central Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6165, https://doi.org/10.5194/egusphere-egu24-6165, 2024.

EGU24-7743 | ECS | Posters on site | GD5.2

Numerical modelling of the Wilson Cycle: effects of orogenic inheritance on the formation of rifted continental margins 

Kai Li, Sascha Brune, Zoltán Erdős, and Anne Glerum

The Wilson Cycle describes the repeated opening and closure of oceanic basins from continental rifting to continent-continent collision. The correlation between ancient orogenic belts and young rift systems highlights the significance of orogenic inheritance in shaping the complexities of rifted margins. Orogenic belts can be classified as either pure shear double-vergent or simple shear single-vergent orogens based on their rheological properties and lithospheric deformation mechanisms during lithospheric shortening. Therefore, their resulting pre-rift conditions differ significantly by providing varying inherited structure. The actual inversion from orogen to rift remains poorly understood. For instance, how does inheritance from orogenic processes affect the evolution and final architecture of rifted margins? 
To investigate this, a numerical forward model was applied that integrates geodynamic thermo-mechanical and landscape evolution software. The simulations include continental collision, post-orogenic collapse and continental rifting, and breakup, through velocity boundary conditions that vary from compression to extension over time. The two end-member orogens are generated by the adjustment of crustal rheology and erosion efficiency. For comparative analysis, we also simulate the extension of laterally homogeneous lithosphere without orogenic inheritance.
Results show that collision in cold and strong continental crust generally produces single-vergent orogens. The double-vergent orogen is formed in weak and hot continental crust with low erosional efficiency. However, a transition in the orogenic dynamics occurs under high erosional efficiency, leading to the development of single-vergent orogens for weak and hot crust. The double-vergent orogen features a wide zone of shortening (~350 km) with a large number of conjugate thrust faults. These faults all tend to reactivate as normal-faults during the subsequent phase of rifting and breakup generally occurs around an inherited, overthickened crustal root. These orogens produce largely symmetric rifts. In contrast, the single-vergent orogen is asymmetric with most shortening accommodated along one dominant interface during the orogenic stage. During rifting, this subduction interface is fully reactivated, accommodating most of the extension and determining the crustal breakup location. These orogens produce an asymmetric rift. In conclusion, orogenic inheritance controls the localization of deformation along pre-existing structural weaknesses and reactivation mechanisms, resulting in complex rifted margins.

How to cite: Li, K., Brune, S., Erdős, Z., and Glerum, A.: Numerical modelling of the Wilson Cycle: effects of orogenic inheritance on the formation of rifted continental margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7743, https://doi.org/10.5194/egusphere-egu24-7743, 2024.

EGU24-9359 | ECS | Posters on site | GD5.2

From intraplate weakening to plate boundary: New diagnostics to quantify rheological controls on deformation localization in a simple extension set-up at lithospheric scale 

Etienne Van Broeck, Catherine Thoraval, Fanny Garel, Diane Arcay, and Rhodri Davies

Initiation of new plate boundary can be related to a spatio-temporal evolution of an intraplate vast diffuse deformation towards a narrow highly deforming boundary. It can also occur by reactivation of an inherited weak zone. In all cases, breaking a plate requires a weakening of the lithospheric cold mantle, whose rheological parameterisation often features a « yield strength » formulation that is not clearly related to actual deformation mechanisms. On the other hand, the bulk effective viscosity for mantle rocks, either cold lithospheric mantle or the hotter asthenosphere underneath, have multiple dependencies, that may co-evolve in geodynamic settings, e.g. temperature and strain rate increase during asthenosphere upwelling associated with plate extension.

In dynamic models, the (output) pattern of deformation localization cannot be directly predicted from the (input) flow laws governing material weakening, e.g. viscosity decrease when strain-rate or temperature increase. We currently lack diagnostics to quantify which rheological dependency weakens lithosphere through time.

Using finite-element Fluidity code, we designed 2-D upper-mantle thermomechanical models of plate extension. Simulations were run for various background strain rates (associated to various horizontal velocity profiles imposed along vertical sides) and for various rheological parameterizations featuring Newtonian diffusion creep, non-Newtonian low/high temperature dislocation creep, and/or yield stress. We propose diagnostics to quantify, through space and time, the weakening efficiency associated to thermomechanical parameters (here either strain-rate, or temperature) . The weakening efficiency is defined as the temporal variation of viscosity relative to only strain rate (or only temperature), normalized to the total viscosity variation. It is used to characterize the chronological sequence and feedbacks leading to deformation localization, and compare them for different rheological parameterizations. From these diagnostics, we discuss which deformation mechanisms are activated during plate extension and thinning, and the characteristic time-scale of successful or failed localization for various rheologies. We compare especially simulations featuring an ad hoc yield strength parameterization vs. low-temperature dislocation creep.

How to cite: Van Broeck, E., Thoraval, C., Garel, F., Arcay, D., and Davies, R.: From intraplate weakening to plate boundary: New diagnostics to quantify rheological controls on deformation localization in a simple extension set-up at lithospheric scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9359, https://doi.org/10.5194/egusphere-egu24-9359, 2024.

EGU24-9699 | Posters on site | GD5.2

Understanding Volcanic Margin Evolution through the Lens of Norway's Youngest Granite discovered by IODP Expedition 396 

Laurent Gernigon, Jochen Knies, Jasmin Schönenberger, Alejandro Piraquive, Roelant van der Lelij, Magdalena H. Huyskens, Sverre Planke, Christian Berndt, Morgan Jones, John M. Millett, Geoffroy Mohn, and Carlos A. Alvarez Zarikian

Three boreholes drilled during the International Ocean Discovery Program (IODP) Expedition 396 have yielded unexpected findings of altered granitic rocks covered by basalt flows, interbedded sediments, and glacial mud on the Kolga High situated near the continent-ocean transition on the mid-Norwegian margin.  To assess basin and basement structures near Kolga High in relation to the broader regional setting, a potential field forward modelling study was conducted. One specific goal was to evaluate the density distribution beneath the Kolga granite. The necessity of low-density crustal material beneath the Kolga High challenges the hypothesis of an old, thick, dense, and inherited basement high directly beneath the basalt, given the low gravity signal observed. In our potential field model, the rock density underneath the basalt remains relatively low (2.4 g.cm-3 in average). Based on onshore measurements, Caledonian or Precambrian ‘fresh’ granitoids and other inherited basement rocks typically exhibit bulk densities usually exceeding 2.65-2.75 g.cm-3. The gravity signal observed on Kolga High, along with the low-density necessary to fit it, suggests that the inherited basement should be situated at a considerably greater depth (~up to 10 km), which is approximately 5-7 km deeper than the drilled Kolga granite/basalt interface. To unravel the weathering chronology for this enigmatic granite, the K-Ar method was selected to date fine-grained clay minerals. X-ray diffraction was performed on different grain size fractions to identify both protolithic and authigenically formed K-bearing minerals derived from the IODP rock samples (Holes U1565A and U1566A). K-Ar geochronology was then performed on five grain size fractions (<0.1, 0.1-0.4, 0.4-2, 2–6, and 6–10 µm).  Finally, the crystallisation age of the granite was verified by conducting mineral analysis on 104 zircons using laser ablation inductively coupled with mass spectrometry (LA-ICP-MS). The K-Ar dating indicates that the alteration of the Kolga granite occurred between 54.7 ± 1 and 37.1 ± 1 Ma suggesting a long period of near surface exposure after the breakup. Based on U-Pb dating of zircon, the granite’s crystallization age is determined at 56.3 ± 0.2 Ma, which aligns with the Paleocene-Eocene Thermal Maximum (around 56 Ma). Collectively, insights from the gravity model and geochronology indicate that the Kolga granite is a Paleocene intrusion, likely emplaced under exceptionally shallow conditions, possibly preceding the breakup and opening of the Norwegian-Greenland Sea. The geochronological results indicate a remarkably short period of time between the granite emplacement, its near surface weathering, and the basaltic lava flows emplacement above the paleosurface. Incidentally, this intrusion also represents the most distal and youngest granite discovered in Norway. This study provide crucial paleogeographic constraints and helps to refine the mode of breakup of a nascent volcanic margin.

How to cite: Gernigon, L., Knies, J., Schönenberger, J., Piraquive, A., van der Lelij, R., Huyskens, M. H., Planke, S., Berndt, C., Jones, M., Millett, J. M., Mohn, G., and Alvarez Zarikian, C. A.: Understanding Volcanic Margin Evolution through the Lens of Norway's Youngest Granite discovered by IODP Expedition 396, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9699, https://doi.org/10.5194/egusphere-egu24-9699, 2024.

EGU24-10289 | Orals | GD5.2

Quantitative characterization of orogenic evolution within the Wilcon cycle 

Tao Wang, Jianjun Zhang, He Huang, Chaoyang Wang, and Yi Ding

Orogens are mostly composite and experience multiple stages of the orogenic processes, such as the accretion of relatively small terranes (or soft collision) and continental collision, and these orogens are commonly called composite orogens, Thus, orogens vary in their nature and style, defining a broad spectrum of types that encompass the Wilson Cycle.

 From the point of view of the Wilson Cycle, orogens begin as accretionary and evolve into collisional, culminating in the termination phase during supercontinent amalgamation. Thus, each orogen may be viewed as having reached a certain stage of its evolution path in the Wilson Cycle. Moreover, active accretionary orogens will continue to evolve; for instance, the active accretionary orogenic systems around the margins of the Pacific Ocean, such as the North and South American Cordillera, may evolve or be reformed into collisional or even intracratonic orogens if the Pacific Ocean closes in the future. Based on this expected orogenic evolution, we use the decrease in the juvenile crustal areal proportions to semi-quantitatively trace the orogenic stages. Our research, part of the IGCP-662 project, "Orogenic Architecture and Crustal Growth from Accretion to Collision," investigates these orogen progresses, and characterization of orogens through comparative studies on the lithospheric architecture and crustal growth patterns of Phanerozoic orogens. A global igneous rock database, in collaboration with the Deep-time Digital Earth (DDE), provides the foundation for our analyses. The juvenile crustal areal proportions can be determined Quantitatively through isotopic mapping (Wang et al., 2023). This innovative approach enhances our understanding of orogenic processes, shedding light on the intricate relationships between orogenesis and continental growth within the framework of the Wilson Cycle.

How to cite: Wang, T., Zhang, J., Huang, H., Wang, C., and Ding, Y.: Quantitative characterization of orogenic evolution within the Wilcon cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10289, https://doi.org/10.5194/egusphere-egu24-10289, 2024.

EGU24-10658 | ECS | Orals | GD5.2

Birth and death of a triple junction: The example of the Bay of Biscay 

Roxane Mathey, Julia Autin, Gianreto Manatschal, Daniel Sauter, Marc Schaming, and Luis Somoza Losada

The Bay of Biscay fossil triple junction separated three tectonic plates: North America, Europe and Iberia. It is defined by three pairs of conjugate margins: Armorican-North Iberian margins, the Goban Spur-Flemish Cap margins, and the West Iberia-Newfoundland margins. In this area, although it was proposed that steady-state spreading started in Aptian/Albian times and ceased around 80 Ma (Verhoef et al., 1986), the timing and opening directions during rifting and spreading remain uncertain. Indeed, oceanic magnetic isochrones are badly constrained. Moreover, exhumed mantle is exposed, so the Ocean-Continent Transition (OCT) of the three conjugate margins is difficult to localize (Boillot et al., 1988; Sibuet et al., 2007; Thinon, 1999; Tugend et al., 2015).  As a result, there is no consensus on kinematic reconstructions.

This work, in the context of my PhD thesis, is part of the ANR project “FirstMove”. It is based on a multidisciplinary approach using geological data (wells, dives) and geophysical data (seismic reflection, magnetic, gravity and bathymetry data). Notably, we integrate the Breogham seismic reflection profiles which cross the fossil spreading ridge. We aim to redefine, map and date the different rift domains (necking, hyperextended, exhumed mantle and oceanic domains), in order to better constraint the evolution of the Bay of Biscay triple junction. Indeed, the Iberia plate kinematic is a keystone to understand the global kinematic of the whole Atlantic-Tethys system.

 

Boillot, G., Winterer, E. L., & et al. (Eds.). (1988). Proceedings of the Ocean Drilling Program, 103 Scientific Results (Vol. 103). Ocean Drilling Program. https://doi.org/10.2973/odp.proc.sr.103.1988

Sibuet, J., Srivastava, S., & Manatschal, G. (2007). Exhumed mantle‐forming transitional crust in the Newfoundland‐Iberia rift and associated magnetic anomalies. Journal of Geophysical Research: Solid Earth, 112(B6), 2005JB003856. https://doi.org/10.1029/2005JB003856

Thinon, I. (1999). Structure profonde de la Marge Nord Gascogne et du Bassin Armoricain. Ifremer-IUEM, Brest, France.

Tugend, J., Manatschal, G., Kusznir, N. J., & Masini, E. (2015). Characterizing and identifying structural domains at rifted continental margins: application to the Bay of Biscay margins and its Western Pyrenean fossil remnants. Geological Society, London, Special Publications, 413(1), 171–203. https://doi.org/10.1144/SP413.3

Verhoef, J., Collette, B. J., Miles, P. R., Searle, R. C., Sibuet, J.-C., & Williams, C. A. (1986). Magnetic anomalies in the northeast Atlantic Ocean (35°-50° N). Marine Geophysical Researches, 8(1), 1–25. https://doi.org/10.1007/BF02424825

How to cite: Mathey, R., Autin, J., Manatschal, G., Sauter, D., Schaming, M., and Somoza Losada, L.: Birth and death of a triple junction: The example of the Bay of Biscay, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10658, https://doi.org/10.5194/egusphere-egu24-10658, 2024.

EGU24-11398 | Orals | GD5.2

The seismic velocity structure and tectonic features of the Africa-Europe plate boundary region in the Atlantic: new high-quality geophysical data 

Marta Neres, Manel Prada, Ingo Grevemeyer, Laura Gomez de la Peña, Irene Merino, Pedro Brito, Pedro Terrinha, and César Ranero

The LISA and ATLANTIS geophysical cruises were conducted in 2021 onboard the Spanish R/V Sarmiento de Gamboa. We collected wide-angle seismic reflection and refraction (WAS) data (ATLANTIS) and coincident streamer data (FRAME) to constrain the seismic velocity structure on the region to the west of the Gorringe Bank (West Iberia Margin), where the nature and structure of the lithosphere are mostly unknown. The LISA profile runs across different geological domains: from the Ampère seamount at SE, the West Horseshoe Abyssal Plain, the region of the Josephine seamount (at the intersection of the Tore-Madeira Rise with the Gloria fault) and the undisputed North Atlantic oceanic domain to the NW.

WAS data were acquired with 21 ocean bottom hydrophones (OBH) spaced at ~15 km, along a NNW-SSE oriented, ~400 km long profile, at 250 Hz sampling frequency. The seismic source was designed to provide high penetration and map the entire crust and the upper mantle structure and consisted of two sub-arrays of 16 airguns with total volume of 5200 c.i., towed at 15 m depth. Multichannel seismic reflection (MCS) streamer data were also acquired with a 6 km long streamer towed at 23 m and using the same seismic source.

OBH sections were analyzed for picking of Ps, Pg, PmP and Pn phases, and show high variability along the profile. Joint inversion of refraction and reflection travel times of key boundaries observed in the WAS and MCS data were used to build a final P-wave velocity (Vp) model, following a layer stripping strategy, and Vp uncertainty was evaluated using Monte Carlo analysis.

In this work we focus on the northern part of the profile, sampled by the 14 northernmost OBH, to present the velocity structure and a seismic image across the region of the contact of the plate boundary and the Tore-Madeira Rise, near the Josephine seamount. A vertically and laterally complex velocity distribution is observed. An apparently low velocity (<4 km/s) from the top of the basement extends ~5 km underneath. There is a significant lateral variation of velocity within the lower crust and upper mantle. Wide-angle Moho reflections could be identified and modeled, in some places marking the transition to 8 km/s mantle, and in others to lower velocity mantle, implying the occurrence of serpentinization. We discuss the role of magmatic intrusion and tectonic deformation processes in the crustal structure, as well as implications for plate boundary activity, and for the isostatic equilibrium of this important bathymetric feature.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) –  UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and projects LISA (https://doi.org/10.54499/PTDC/CTA-GEF/1666/2020) and RESTLESS (http://doi.org/10.54499/PTDC/CTA-GEF/6674/2020). Support from the Spanish Ministry of Science and Innovation (CTM2015-71766-R, PID2019-109559RB-I00) and Spanish Research Agency (CEX2019-000928-S) is also acknowledged.

How to cite: Neres, M., Prada, M., Grevemeyer, I., Gomez de la Peña, L., Merino, I., Brito, P., Terrinha, P., and Ranero, C.: The seismic velocity structure and tectonic features of the Africa-Europe plate boundary region in the Atlantic: new high-quality geophysical data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11398, https://doi.org/10.5194/egusphere-egu24-11398, 2024.

EGU24-12369 | Posters on site | GD5.2

Fracture zones and rift systems of eastern Iceland: Tectonic and geodynamic links to extinct rifts on the Iceland-Faroe Ridge and Iceland Plateau 

Anett Blischke, Bryndís Brandsdóttir, Jeffrey A. Karson, and Ögmundur Erlendsson

In the wake of the North-Atlantic Geoscience Tectonostratigraphic Atlas (NAGTEC) project and the mapping of the Jan Mayen microcontinent and Iceland Plateau region a comprehensive study of re-processed and new geological and geophysical data is needed to establish a detailed kinematic model of the NE-Atlantic region, linking the tectonic evolution of Iceland to the offshore Iceland Plateau Rifts, the Iceland-Faroe Ridge, and the Iceland-Faroe Fracture Zone regions. Acquisition of new tectonic and structural data from extinct rift zones on land is required to further our understanding of offshore rift systems. Kinematic models indicate that Northeast Iceland and its insular shelf formed by asymmetric spreading similar to the Iceland Plateau Rift under the influence of the Iceland mantle plume. These processes created multiple volcanic rift zones, fracture zones, and strike-slip elements that accommodated the breakup and formation of crustal domains north of Iceland, such as the Iceland-Faroe Fracture Zone (IFFZ), and along the Iceland-Faroe Ridge. Recent structural mapping within the Tröllaskagi-Flateyjarskagi region and the Tjörnes Fracture Zone have revealed stress-field variations within an overall right-lateral obliquely opening rift zone that includes N-S to NNE-SSW striking left-lateral strike-slip fault systems that serve as an analogue case. This corresponds to changes and rotations in dyke strike directions adjacent to the Dalvík lineament of the Húsavík-Flatey Fault system since the Mid-Miocene. To map out structural evidence and geometries for old and abandoned propagating rift systems onshore NE Iceland, we conducted preliminary fieldwork in the Vopnafjörður region, which we aim to continue within the next three years. Our goal is to delineate abandoned rift segments within NE Iceland and model the evolution of individual rift systems with time, to determine if younger rifts cut through or have discordant trends in respect to older rift structures. We plan to assess, how onshore Miocene rift systems (~15-6 Ma) align to older Miocene systems offshore and whether the IFFZ is a pseudo-fault that developed gradually during rift propagation or a prominent feature along the NE insular margin of Iceland, within a segmented Tertiary transform zone system. Our multidisciplinary approach will thus further our understanding of the dynamics of rift zone development and transfer in proximity to the Iceland mantle plume.

How to cite: Blischke, A., Brandsdóttir, B., Karson, J. A., and Erlendsson, Ö.: Fracture zones and rift systems of eastern Iceland: Tectonic and geodynamic links to extinct rifts on the Iceland-Faroe Ridge and Iceland Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12369, https://doi.org/10.5194/egusphere-egu24-12369, 2024.

EGU24-12945 | ECS | Posters on site | GD5.2

A recipe for continental fragment formation: big data analysis of rift models 

Alan Yu, Erkan Gün, Ken McCaffrey, and Philip Heron

Former plate boundaries (sutures) are usually considered to be future locations for continental breakup, but this is not always the case. For example, continental rifting can generate a crustal fragment, where a sliver of a plate diverges from its component part and remains attached to another plate. Despite the prevalence of continental fragments and accreted terranes in the geological record, the underlying tectonic processes leading to their formation remain poorly understood. Previous geodynamic models have indicated structural and rheological heterogeneities inherited from past tectonic events as a key mechanism driving the initiation of continental breakup. Most of these studies have primarily focused on the styles of rifted margins, but limited attention is given to the mechanism of continental fragment formation.

In this study, we present a suite of over 100 different numerical models of inherited structures with the tectonic potential to generate a new continental fragment during continental extension. Our models show the first-order impact of structural inheritance on the evolution of rifting and continental fragmentation. Here, the size of the fragment is influenced by the extent and geometry of the inherited structures. By analyzing our models using novel data science techniques, we are able to quantify the impact of different initial conditions on generating a continental fragment. Our models provide a range of new physical constraints for the formation of continental fragments. Most importantly, they highlight the potential role of different forms of structural inheritance in controlling deformation within complex tectonic plate margins. Finally, we apply these findings to some real-world examples of continental fragments.

How to cite: Yu, A., Gün, E., McCaffrey, K., and Heron, P.: A recipe for continental fragment formation: big data analysis of rift models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12945, https://doi.org/10.5194/egusphere-egu24-12945, 2024.

Continental rifting is a fundamental process of plate tectonics and the Wilson Cycle where weak zones within the continental lithosphere are exploited by both far-field and near-field forces to break-up the continental lithosphere (e.g Molnar et al., 2019). These pre-existing weak-zones are remnants of past tectonic deformation, delineated by shear zones, faults, and/or mobile belts. Reactivation of such inherited structures from previous tectonic phases has been attributed to several continental rift systems, for example, the Rhine graben, Rio Grande rift, Main Ethiopian Rift, Malawi Rift, and the Red Sea. In geodynamic modeling of continental rifts, these weak zones are often approximated by lithospheric thermal perturbation or a weak seed/fault to facilitate strain localization and initiate rifting in response to uniform stretching of the lithosphere. Here, we adopt a different approach building upon models by Salazar-Mora and Sacek (2022) and Peron-Pinvidic et al. (2022) to implement the inherited structures. We start with a geodynamic simulation of continental collision and orogenesis prior to extension but include the effect of temperature-dependent strain healing in the mantle (e.g. Fuchs and Becker, 2021) and time dependent plastic strain healing in the crust (e.g. Olive et al., 2016). We use a 2D geodynamic model ThermoMech (e.g. Xue et al., 2023) coupled to a landscape evolution model FastScape (Yuan et al., 2019), to explore the parameter space in an effort to understand the longevity of weak zones and their implications for rift initiation.

 

Fuchs, L. & Becker, T. W. (2021). Deformation Memory in the Lithosphere: A Comparison of Damage-dependent Weakening and Grain‐Size Sensitive Rheologies. J. Geophys. Res.: Solid Earth 126.

Molnar, N. E., Cruden, A. R., & Betts, P. G. (2019). Interactions between propagating rifts and linear weaknesses in the lower crust. Geosphere, 15(5), 1617–1640.

Olive, J.-A., Behn, M. D., Mittelstaedt, E., Ito, G. & Klein, B. Z. (2016). The role of elasticity in simulating long-term tectonic extension. Geophys. J. Int. 205, 728–743.

Peron-Pinvidic, G., Fourel, L. & Buiter, S. J. H.  (2022). The influence of orogenic collision inheritance on rifted margin architecture: Insights from comparing numerical experiments to the Mid-Norwegian margin. Tectonophysics 828, 229273.

Salazar-Mora, C. A. & Sacek, V. (2023). Effects of Tectonic Quiescence Between Orogeny and Rifting. Tectonics 42.

Xue, L., Muirhead, J. D., Moucha, R., Wright, L. J. M. & Scholz, C. A. (2023). The Impact of Climate-Driven Lake Level Changes on Mantle Melting in Continental Rifts. Geophys. Res. Lett. 50.

Yuan, X. P., Braun, J., Guerit, L., Rouby, D., & Cordonnier, G. (2019). A New Efficient Method to Solve the Stream Power Law Model Taking Into Account Sediment Deposition. J. Geophys. Res.: Earth Surface, 124(6), 1346–1365.

How to cite: Moucha, R. and Xue, L.: Modeling inherited structures and their effects on strain localization during continental rifting , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13268, https://doi.org/10.5194/egusphere-egu24-13268, 2024.

EGU24-14404 | Orals | GD5.2

How do the Red Sea and Gulf of Aden rifts connect?  

Ameha Muluneh, Sascha Brune, Carolina Pagli, Alessandro La Rosa, Derek Keir, Derek Neuharth, and Giacomo Corti

The Afar rift in East Africa is a classic natural laboratory where we can directly observe tectonic processes related to the ongoing deformation between the Red Sea and Gulf of Aden rifts. While there have been several geophysical studies conducted in the region, we know surprisingly little about the mechanism of connection between the two rifts. Earlier studies suggest that the two rifts form an overlap zone within which crustal blocks rotate in a clockwise sense via rift parallel strike slip faults. In contrast, geodetic data indicate a direct linkage via a zone of extension with dextral shearing at the lateral tips of the zone of extension and minimal vertical axis block rotation. Here we combine high-resolution 3D lithospheric scale geodynamic models using ASPECT and strain rate derived from geodesy to fully capture the evolution of deformation between the Red Sea and Gulf of Aden rifts as they evolve. Our results demonstrate that the two rifts link via a transtensional deformation zone, where incipient transform faulting, overlapping en-echelon basins and vertical axis block rotation play roles at different stages of the evolution. We argue that the discrepancy between the proposed models for the Red Sea and Gulf of Aden rift connection can be reconciled when considering the spatial and temporal evolution of the rifts.

How to cite: Muluneh, A., Brune, S., Pagli, C., La Rosa, A., Keir, D., Neuharth, D., and Corti, G.: How do the Red Sea and Gulf of Aden rifts connect? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14404, https://doi.org/10.5194/egusphere-egu24-14404, 2024.

EGU24-15801 | ECS | Posters on site | GD5.2

Rapid Along-strike Variation of Breakup Volcanism on the Pelotas Margin, Offshore SE Brazil, South Atlantic and its Control by Lithosphere Inheritance 

Marlise Colling Cassel, Nick Kusznir, Gianreto Manatschal, and Dan Sauter

The southern rifted margins of the South Atlantic are commonly regarded as some of the best examples of magma-rich margins with the Pelotas, Uruguay, Argentine and Namibia margins showing prominent Seaward Dipping Reflectors (SDRs). These volcanic SDRs are commonly interpreted as resulting from enhanced decompression melting during rifting and breakup from regionally elevated asthenosphere temperatures associated with the Parana-Etendeka mantle plume. We investigate the lateral variability of breakup volcanic addition along-strike of the Pelotas segment of the southern South Atlantic rifted margin offshore SE Brazil. Our analysis of regional seismic reflection profiles shows that magmatic addition on the Pelotas margin varies substantially along strike from extremely magma-rich to magma-normal within a distance of approximately 300 km.

In the north of the Pelotas margin, where SDRs are thickest, the Torres High shows SDRs up to  20 km thickness. In contrast, in the south of the Pelotas margin, the magmatic addition is normal and SDRs are very thin or absent. Further south of the Pelotas margin, offshore Uruguay and northern Argentina, margins are again magma-rich with SDRs thickness reaching 10 km or more.The very thick SDRs of the northern Pelotas margin lay offshore of the thick Serra Geral volcanics of similar Cretaceaous age found onshore in the Santa Catalina, Parana, Sao Paulo and northern Rio Grande do Sul states of SE Brazil. Further south, Serra Geral volcanics are absent in the cratonic southern Rio Grande do Sul, which is onshore of the southern Pelotas margin with thin or absent SDRs and normal magmatic addition. The abrupt decrease in rift and breakup decompression melting from north to south along the Pelotas margin, and its increase to the south on the Uruguay and northern Argentina margins is inconsistent with the simple Parana-Etendeka mantle plume model. The correlation of magma-normal breakup in the southern Pelotas margin with cratonic geology onshore implies a significant contribution of lithosphere inheritance to decompression melting during rifting and breakup to form the southern South Atlantic margins.

A relationship is observed between the amount of volcanic material and the two way travel time (TWTT) of first proximal volcanics in seismic sections.  First volcanics are observed at 1.25s TWTT for the highly magmatic Torres High profile while, in contrast, for the normally magmatic profiles in the south, first volcanics are observed at 4.2s TWTT or deeper. The observed inverse relationship between post-breakup accommodation space and SDR thickness is consistent with predictions of a simple isostatic model of continental lithosphere thinning and decompression melting during breakup. This relationship between TWTT of first volcanics in seismic sections and the magnitude of magmatic addition may provide an effective means of mapping the distribution of breakup magmatic volume for the southern South Atlantic margins and its correlation with onshore geological inheritance.

How to cite: Colling Cassel, M., Kusznir, N., Manatschal, G., and Sauter, D.: Rapid Along-strike Variation of Breakup Volcanism on the Pelotas Margin, Offshore SE Brazil, South Atlantic and its Control by Lithosphere Inheritance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15801, https://doi.org/10.5194/egusphere-egu24-15801, 2024.

Recent 3D seismic reflection imaging has provided new insights into lithosphere extensional deformation processes in the hyper-extended domain of magma-poor rifted margins where extensional faults penetrate through the thinned continental crust into the topmost mantle. Seismic analysis shows that high-angle extensional faults sole out into a sub-horizontal reflector (the S-type reflector) in the top-most mantle. This reflector is interpreted as a horizontal detachment and has been shown to develop progressively oceanward with the in-sequence extensional faulting above.

We examine the evolution of fault geometries during extensional faulting in the hyper-extended domain. We show that the predictions of a recursive flexural rolling-hinge model  of planar faulting of thinned continental crust soling out into a horizontal detachment in the top-most mantle are consistent with the seismic interpretations. Our modelling shows that initially high-angle extensional faults are isostatically rotated to low-angle by oceanward in-sequence faulting and that their deeper segments form a continuous sub-horizontal structure in the top-most mantle corresponding to the S-type reflector imaged by seismic data.

Both 3D seismic interpretation and our modelling indicate that the sub-horizontal detachment imaged as the S-type reflector, and forming an apparent regional detachment, is not active simultaneously over its whole length in the dip-direction but that it developed oceanward incrementally together with the in-sequence high-angle extensional faulting above.

How to cite: Kusznir, N. and Gomez-Romeu, J.: A “Rolling Hinge” Model of the Incremental Oceanward Development of the S-type Reflector Horizontal Detachment at Magma-Poor Rifted Margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15890, https://doi.org/10.5194/egusphere-egu24-15890, 2024.

The Borborema province is a mobile belt that was established at the end of the Brasiliano orogeny (600±50 Ma) as a consequence of the collision among the West African, São Luiz, Congo-Kasai and São Francisco cratons. Its basement comprises vast blocks of Archean and Paleo-Proterozoic ages. The Borborema province is crossed by several mantle-scale shear faults, with eastward extension into Africa. During the opening of the South Atlantic, the Borborema Province played a key role, initially through extensional deformation that allowed the formation of several basins, and later acting as a lock during Albian times. Indeed, its northeasternmost portion at the contact between the South Atlantic and the Equatorial Atlantic was the last to split from Africa. It has been suggested that internal block rotation provided by the shear zones absorbed deformation, and that the final split from Africa provided the connection between the Equatorial and South Atlantic oceans only after thinning of the lithosphere and oceanic rifting. With the goal to study the resistivity structure at lithospheric depths of the Borborema Province, a 3D long- period MT survey was conducted in NE Brazil in 2016 and 2017. The 3D inversion model revealed an unexpectedly resistive, therefore thick lithosphere along the continental margin of the study area, narrowing towards the SW. This finding suggests that the current Borborema continental margin endured segmented extensional deformation during the opening of the South Atlantic Ocean, and that deformation probably focused on a narrow continental block currently offshore and in select internal areas.

How to cite: Garcia, X. and Julià, J.: Thick lithosphere in NE Brazil: Implication for lithospheric stretching during South Atlantic opening, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18485, https://doi.org/10.5194/egusphere-egu24-18485, 2024.

EGU24-20596 | Orals | GD5.2

Late Cretaceous reactivation of a Paleo-Tethyan suture zone in Xizang of western China: extensional collapse of the proto-Tibetan plateau? 

Xiao Liang, Genhou Wang, Paul Bons, Bo Zhang, Wentao Cao, Yilong Zheng, and Zhongbao Zhao

The deformation of the Himalaya-Tibetan plateau remains one of the hottest examples of Earth's tectonics and dynamic evolution. What drives deformation and growth of the plateau, and how this is partitioned into diverse structural styles and mechanisms remain heated discussions. Mesozoic orogens also contributed to crustal thickening of the plateau prior to the Cenozoic India-Asia collision and notably, they were reactivated due to its structural inheritance and low viscosity since the collision, for example, the first uplift in Qiangtang and the Paleo-Tethyan suture zone in its interior. However, few attention was paid to pre-collision reactivation and structural superimposition of Mesozoic orogens. The newly discovered NWW-trending Ejiumai shear zone with biotite 40Ar/39Ar and zircon and monazite U-Pb ages of ca. 80-70 Ma flanks the northern border of the Paleo-Tethyan suture zone and mainly includes reactivated Triassic basement gneisses and syntectonic pegmatite. Combined with the oblique moving kinematics including both sinistral and normal-sense shear, a transtension regime with lower crustal anatexis can be concluded for the genesis of Ejiumai shear zone. Concurrent granitic plutons were also found in the suture hundreds of kilometers to the east. Based on these observations, we present a schematic model of extensional collapse of the proto-Tibetan plateau induced by far-field northward indentation of Neo-Tethyan suture zone to the south in Late Cretaceous.

How to cite: Liang, X., Wang, G., Bons, P., Zhang, B., Cao, W., Zheng, Y., and Zhao, Z.: Late Cretaceous reactivation of a Paleo-Tethyan suture zone in Xizang of western China: extensional collapse of the proto-Tibetan plateau?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20596, https://doi.org/10.5194/egusphere-egu24-20596, 2024.

EGU24-20807 | ECS | Posters on site | GD5.2

Dry ocean formation: Might some SDRs represent post-breakup non-classical oceanic crust? 

Jordan J. J. Phethean and Alexander L. Peace

During continental breakup, the width of a developing rift system is thought to be primarily controlled by crustal rheology, where weak and decoupled crust may develop into a wide (up to 300 km) rift system and strong crust can lead to localised thinning. Simultaneously, the development of magma-rich margins is increasingly being recognised to result from lithospheric mantle thinning prior to crustal thinning, allowing the development of both narrow and wide magma-rich continental margin systems. Seaward Dipping Reflectors (SDRs) and flat lying flows (FLFs) at magma-rich margins are generally considered to develop above rifting upper continental crust and flowing ductile lower continental crust, respectively, which in many instances contribute to isostatic buoyancy and therefore the subaerial eruption of lavas. Subsequent to continental breakup, therefore, ocean basin flooding readily occurs, leading to the production of classical oceanic crustal structure in a submerged basin (i.e. pillow basalts, sheeted dykes, and gabbro). What happens, however, if basin flooding is significantly delayed relative to breakup of the continental lithosphere? Here, we review evidence from the Mozambique Basin (and other magma-rich basins around the globe) to understand if basin flooding can postdate continental breakup and lead to the development of SDRs outboard of the continent ocean transition. In the Mozambique Basin, we find this unusual situation may have occurred locally despite the basin likely residing below sea level. This circumstance was facilitated by long-offset continent-continent transform faults isolating the basin within the continent interior during plate separation. Our findings have implications for the development of appropriate models of crustal structure at magma-rich continental margins and, therefore, our ability to appropriately interpret geophysical datasets, which often permit contrasting interpretations of crustal composition and distribution.

How to cite: Phethean, J. J. J. and Peace, A. L.: Dry ocean formation: Might some SDRs represent post-breakup non-classical oceanic crust?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20807, https://doi.org/10.5194/egusphere-egu24-20807, 2024.

TS3 – Active tectonics, seismicity, kinematics, and dynamics

EGU24-1801 | Posters on site | TS3.1

Strong (Mw>6.0) earthquakes along the KTFZ: implications for recurrence pattern and seismic coupling 

Eleftheria Papadimitriou and Vassilios Karakostas

The Kefalonia Transform Fault Zone (KTFZ) in central Ionian Islands (Kefalonia and Lefkada Islands), Greece, exhibits the fastest rates of relative plate motion in the Mediterranean. It constitutes an active boundary and comprises five manor fault segments with a total length of nearly 120km, and are characterized by fast long–term rates of displacements of about ~25mm/yr for Kefalonia segments and ~15 mm/yr for Lefkada segments. Strike slip faulting with moment magnitudes Mw up to 7.0 characterizes the largest earthquakes, whereas the five almost along strike faults have been the sites of numerous earthquakes of moment magnitude, Mw, 5.0–7.0 during the past 50 years. The KTFZ in its entire length is much more active at the Mw>6.0 level than a comparable length of either the North Aegean Trough or Corinth rift, which are the most fastly deforming areas in the area of Greece. Alteration of active periods comprising multiple earthquakes with much longer quiescent periods is the mode of strong earthquake occurrence, with prevailing clustering over the period when historical information is available. The fast rate of plate motion, maximum size of earthquakes and relatively short repeat times make these fault segments suitable to seek for recurrence behavior that approaches quasi–periodic and its potential implications to the cyclic mode of seismogenesis. Recurrence of M6.0 earthquakes along nearly the same fault segment is attempted after evaluating the location of the historical events, based on all available macroseismic descriptions. These estimations are then compared with computed simulated catalogs.

The computed depths of earthquakes along the KTFZ are accurate enough to ascertain centroid depths as indicators of the downdip width of seismic faulting. With aftershock relocation we constrained the seismogenic layer in Kefalonia and Lefkada segments equal to 14 km (between depths of 3 and 17 km) and 10 km (between depths of 5 and 15 km) respectively, corresponding to downdip widths of 19 and 12 km, respectively. We compared these constraints with the calculated downdip width from a segment’s length along strike, moment release and relative plate motion ‘assuming’ full seismic coupling. The good correlation between the two support the high degree of coupling along the KTFZ.

Acknowledgments: Funded by the European Union. Views and opions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Commission – Euratom. Neither the European Union nor the granting authority can be held responsible for them.

 

 

How to cite: Papadimitriou, E. and Karakostas, V.: Strong (Mw>6.0) earthquakes along the KTFZ: implications for recurrence pattern and seismic coupling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1801, https://doi.org/10.5194/egusphere-egu24-1801, 2024.

EGU24-2188 | ECS | Posters on site | TS3.1

Bridging geological and geodetic observations for the 1700 Cascadia earthquake with an earthquake cycle model 

Weilun Qin, Rob Govers, Mario D’Acquisto, Natasha Barlow, and Riccardo Riva

Subduction earthquake cycles are known to produce distinctive patterns of crustal motion, providing critical insights into the details of plate interface coupling and rupture behavior. Retrieving these patterns in the Cascadia subduction zone poses a significant challenge, particularly because the 1700 great Cascadia earthquake (Mw>=9.0) occurred more than three centuries ago.

Previous studies of the megathrust earthquake cycle along the Cascadia margin focused on either the geologically constrained coseismic rupture, or on the present-day interseismic coupling patterns based on geodetic observations. There thus is a gap in the comprehensive understanding of the earthquake cycle, particularly in the integration of available geological and geodetic evidence.

Our study aims to bridge this gap and unify the insights preserved in both records. To do so, we develop a three-dimensional viscoelastic earthquake cycle model with realistic slab geometry, crustal thickness, and topography. We simulate the coseismic, postseismic, and interseismic stages of the earthquake cycle by alternately locking and releasing asperities, which are derived from geodetic coupling (Li et al., 2018) and geological rupture (Wang et al., 2013) studies.

Our results show a good match to convergence-parallel interseismic velocities from the geodetic observations of McKenzie and Furlong (2021). Considering the subsidence signal in the geological record, a good fit can be obtained by a combination of coseismic slip and early afterslip. We find that our results are largely determined by the slab geometry, although factors like asperity configurations, downdip limits of the slab-crust interface, and mantle viscosity structure influence the model predictions.

How to cite: Qin, W., Govers, R., D’Acquisto, M., Barlow, N., and Riva, R.: Bridging geological and geodetic observations for the 1700 Cascadia earthquake with an earthquake cycle model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2188, https://doi.org/10.5194/egusphere-egu24-2188, 2024.

The 2021 Maduo MS7.4 earthquake occurred in the Jiangcuo fault with left-lateral strike-slip movement. In order to study the movement and deformation characteristics of the Jiangcuo fault before the Maduo earthquake and further analyze the seismogenesis process of the continental strong earthquake, the large-scale strain rate field distribution in western China, the locking degree and the evolution of slip deficit rate of the Jiangcuo fault, and the rupture mechanism of seismogenic fault are analyzed and discussed in this paper using the GPS velocity field on a long time scale and InSAR dynamic velocity field. The results show that: (1) The strain rate field in EW direction shows that the Maduo earthquake is located at the edge of the EW direction strong compression zone of Bayanhar block. The eastern part of the Maduo earthquake is a compression strain accumulation zone, and the western part is a gradual transition from weak compression to tension strain. The results of the maximum shear strain rate field show that the Maduo earthquake is located at the edge and high gradient zone of the high value area of the maximum shear strain rate field. (2) The inversion results of the locking degree show that deep unlocking occurs in some regions in the east and west of the epicenter of the fault during 2015-2021, gradually transitioned to a completely locked state in the middle of the fault, and the focal point of Maduo earthquake is at the edge of the completely locked region in the transition region. The dynamic results from 2015 to 2017 and 2017 to 2019 were basically stable. The whole fracture plane was basically in a state of strong locking, and only partial unlocking with a depth below 15km existed in local areas. From 2019 to 2021, some faults in the east and west of the epicenter have deep and shallow unlocking phenomena, including the overall unlocking of most areas of the western section and the local deep unlocking of the East section of the ruptured fault, while the rapid unlocking of the two sides of the epicenter may contribute to the occurrence of the main earthquake. This work was supported by Science for earthquake resilience (XH23047A).

How to cite: Zhao, J., Yuan, Z., and Wang, Y.: The movement and deformation of the Jiangcuo fault before the 2021 MS7.4 Maduo earthquake reflected by GPS and InSAR data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2226, https://doi.org/10.5194/egusphere-egu24-2226, 2024.

EGU24-2385 | ECS | Posters on site | TS3.1

Do Faults Localize as They Mature? Insight From 17 Continental Strike-slip Surface Rupturing Earthquakes (Mw > 6.1) Measured by Optical and Radar Pixel Tracking Data. 

Chris Milliner, Jean-Philippe Avouac, Saif Aati, James Dolan, and James Hollingsworth

As faults accumulate displacement, they are thought to mature from disorganized and distributed fracture networks to more simplified throughgoing fault structures with a more localized zone of inelastic strain. Understanding the degree of inelastic strain localization holds importance for seismic hazard, as smoother faults are thought to host faster rupture velocities and have different seismic shaking intensities from ruptures along rougher, less mature faults. However, quantifying this evolutionary process of strain localization along major fault systems has been difficult due to a lack of near-field coseismic measurements. Here we test if such an evolutionary process exists by measuring the near-field surface deformation pattern of 17 large (6.0 < Mw < 7.9) continental strike-slip surface ruptures. To do this we use a range of geodetic imaging techniques including, a new 3D optical pixel tracking method, and pixel tracking of radar amplitude data acquired by satellite and UAVSAR platforms. With these geodetic imaging data we measure the total coseismic offset across the surface rupture and difference them from the displacements recorded by field surveys, which we assume captures the on-fault, discrete component of deformation. This differencing allows us to obtain an average magnitude of off-fault deformation for each surface rupturing event, which we compare to a number of known source parameters to test the notion of progressive fault localization. Our results show that progressively smaller amounts of off-fault strain occur along fault systems with higher cumulative displacements, supporting the notion that faults systems localize as they mature. We also find strong correlations of off-fault deformation with the long-term fault slip-rate and the geometrical complexity of the mapped surface rupture, and a moderate correlation with rupture velocity. However, we find a weak-no correlation of off-fault deformation with the fault initiation age and the moment-scaled radiated energy. We also present comparisons of off-fault strain with other known seismic source parameters.

How to cite: Milliner, C., Avouac, J.-P., Aati, S., Dolan, J., and Hollingsworth, J.: Do Faults Localize as They Mature? Insight From 17 Continental Strike-slip Surface Rupturing Earthquakes (Mw > 6.1) Measured by Optical and Radar Pixel Tracking Data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2385, https://doi.org/10.5194/egusphere-egu24-2385, 2024.

EGU24-2389 | ECS | Orals | TS3.1

Decoding inter-seismic deformation: Insights from viscoelastic modeling 

Hugo Boulze, Luce Fleitout, Emilie Klein, and Christophe Vigny

GPS positioning offers millimetric precision in measuring deformation of the lithosphere during the seismic cycle. In particular, during the post-seismic phase, long-lasting and large-scale deformation are measured. They result from the viscoelastic relaxation in the asthenosphere. Consequently, the post-seismic phase is currently modeled using viscoelastic rheologies (e.g., Maxwell or Burgers viscous models). On the other hand, the inter-seismic phase is mainly modeled using purely elastic models. In particular, coupling models, widely used to quantify the accumulation of deformation on the subduction fault, are therefore used to evaluate earthquake hazard. However, such elastic models fail to explain mid-field deformation without the use of an external hypothesis (e.g., a third plate called sliver).

The study of post-seismic deformation has provided important insights into the rheological properties of the asthenosphere during the post-seismic phase. For example, viscous creep has been found Newtonian since the cumulative post-seismic displacements normalized by the co-seismic offset, as a function of distance to the trench, superimpose very well for earthquakes of different magnitudes [Boulze et al. 2022].

By incorporating these different results and using the backslip theory [Savage 1983], we model the inter-seismic phase using viscoelastic models. We explore the impact on coupling distribution along the Chilean subduction zone, in particular discussing differences with the elastic model in terms of depth and lateral extension. We also examine the impact of viscoelastic models in a region of Chile (Taltal region, 25.2°S) where elastic models currently fail to reproduce deformation in the near-field [Klein et al. 2018]. Finally, we show that a 2-Burgers viscous model is necessary to reproduce deformation in Argentina in 2010, before the Maule earthquake.

How to cite: Boulze, H., Fleitout, L., Klein, E., and Vigny, C.: Decoding inter-seismic deformation: Insights from viscoelastic modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2389, https://doi.org/10.5194/egusphere-egu24-2389, 2024.

We have developed a 3D viscoelastic finite element model to study processes that control the postseismic deformation due to the 2021 M8.2 Chignik, Alaska earthquake. Our model employs a bi-viscous Burgers rheology to represent the viscoelastic relaxation of the upper mantle and the first two years GPS data after Chignik event as constraints.

Initially, we investigated the viscoelastic relaxation mechanism and stress-driven afterslip mechanisms individually. We then attempted to reconcile their contributions by assessing the misfit between observed and simulated displacements. And, it is assumed that the afterslip evolution is governed by rate-strengthening friction. The results show that there exists a substantial misfit between the simulated and the observed value of the optimal model under the viscoelastic relaxation mechanism. Notably, at one observation site in the near-field, the observed displacement exceeds 200 mm, whereas the simulated value only less than 5 mm. Similarly, the optimal solution of simulated value under the afterslip mechanism does not align well with the observed value. Furthermore, we also utilized different frictional properties on updip (0-40 km) and downdip (40-100 km) regions of the coseismic rupture. The preferred misfit in this model is lower than that obtained using the model with a uniform friction parameter, but there is still a discrepancy between the simulated and observed values. These results indicate that neither the afterslip nor viscoelastic relaxation mechanisms alone can fully explain the total postseismic deformation.

Subsequently, we utilized an integrated model to simultaneously extract the contributions from both mechanisms. The combined modeling results indicate that the near-field postseismic displacements are dominated by both mechanisms together. However, in the far-field, deformation is primarily controlled by afterslip, with minimal influence from the viscoelastic relaxation mechanism. The inferred frictional properties on the updip and downdip regions of the coseismic rupture exhibit significant differences, which likely reflect variations in fault zone materials at different depths. And the optimal model supports a viscoelastic rheology for the continent mantle, with a steady-state viscosity is 1×1019Pa•s and the transient viscosity is 1×1018Pa•s. 

How to cite: Dong, P. and Zhao, B.: Afterslip and viscous relaxation on the postseismic deformation following the M8.2 Chignik, Alaska earthquake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2967, https://doi.org/10.5194/egusphere-egu24-2967, 2024.

EGU24-6640 | ECS | Orals | TS3.1

Unveiling the Activity of a Young Fault: Insights from the 2021 Maduo Earthquake 

Wenqian Yao, Jing Liu_Zeng, Yann Klinger, Guiming Hu, Yanxiu Shao, Xiaoli Liu, Kexin Qin, Zhijun Liu, Zijun Wang, Yunpeng Gao, and Longfei Han

Faults grow through fault lengthening and slip accumulation, which are episodic processes related to the repetition of earthquakes. It is most often recorded in geomorphology. Meanwhile, the activity and seismic hazard of the ‘slow-moving’ faults are often overlooked due to their weak imprints in landforms, especially at their initial formation stage. The 2021 Mw 7.4 Maduo earthquake triggered a ~158-km long surface rupture along the poorly-known and geomorphically subtle Jiangcuo fault, which is one of the distributed faults in the Bayan Har block and splays that merge with the Kunlun Pass fault. The slip rate of the Jiangcuo fault is thus crucial for comprehending how the strain is distributed between the major and subsidy faults in the complete fault system of the Bayan Har block, as well as the broader deformation process at a large scale. In this study, we present three sites where the Jiangcuo fault left-laterally displaces Holocene geomorphic features (e.g., terraces, fans, and channels). Through the detailed interpretations of high-resolution Digital Elevation Models (DEMs), field investigations, and credible Optically Stimulated Luminescence (OSL) dating of displaced geomorphic features, we document an average left-lateral slip rate of 2.1 ± 0.2 mm/yr since ~12 ka of the Jiangcuo fault. Furthermore, we conservatively updated existing slip rates of the large strike-slip faults (East Kunlun fault, Ganzi-Yushu-Xianshuihe fault) bounding the Bayan Har block. Synthesizing the slip rate of the Jiangcuo fault with the updated rates of the bounding faults, our findings suggest that the Jiangcuo fault accommodates ∼10% of the total deformation in the Bayan Har block. This study provides valuable insights into the impact of younger faults on regional deformation processes.

How to cite: Yao, W., Liu_Zeng, J., Klinger, Y., Hu, G., Shao, Y., Liu, X., Qin, K., Liu, Z., Wang, Z., Gao, Y., and Han, L.: Unveiling the Activity of a Young Fault: Insights from the 2021 Maduo Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6640, https://doi.org/10.5194/egusphere-egu24-6640, 2024.

Strike-slip faults of considerable scale play a pivotal role in accommodating crustal deformation resulting from the Cenozoic India-Eurasia collision. The manner in which strike-slip motion is transferred along faults remains a topic of ongoing debate. In this study, we have meticulously compiled millennial strike-slip rates and GPS-derived strike-slip data along the extensive ~1800 km East Kunlun Fault (EKF). Our objective is to discern the slip distribution pattern and evaluate the mode of strike-slip transfer. The findings reveal a segmented pattern of strike-slip activity, characterized by a consistently high strike-slip rate exceeding 10 mm/yr along the central segments. In contrast, the eastern segment exhibits a reduced slip rate, measuring less than 5 mm/yr, and further diminishes to approximately 1 mm/yr along its eastern fault tip zone. Notably, strike-slip drop events occur within the fault bending zone, or in areas where the fault bifurcates, forming a horsetail structure. To complement our observational insights, numerical modeling has been employed to validate that the fault geometry may serve as a crucial controlling factor in the observed variation of strike-slip rates, Additionally, it influences the local stress situation along the fault, further contributing to the earthquake risk along the fault and the associated hazards impacting the local area.

How to cite: Zhang, Y. and Jiao, L.: Mechanism of Strike-slip Transfer along the East Kunlun Fault in Northern Tibet, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7062, https://doi.org/10.5194/egusphere-egu24-7062, 2024.

EGU24-7436 | ECS | Orals | TS3.1

Strain partitioning and fault kinematics in the Northern Qilian Shan (NE Tibet) determined from Bayesian inference of geodetic data  

Yingfeng Zhang, Sam Wimpenny, Luca Dal Zilio, and Xinjian Shan

Strain partitioning between strike-slip faults within mountain ranges and thrust faults along their margins is a common process that accommodates oblique plate convergence in continental collision zones. In these settings accumulated strain is periodically released by earthquakes on the strain-partitioned fault systems, which threatens the densely populated foreland areas. An extreme earthquake rupture scenario in these settings is that multiple faults rupture simultaneously releasing the built up strain – an example being the 2016 Mw 7.8 Kaikoura earthquake where a cascading rupture occurred on many separate faults with different kinematics. Recent work suggests that such cascading ruptures may occur in fault systems that are coupled in the shallow crust that are being loaded by a deeper, creeping fault.

 

This study focuses on understanding earthquake risks in the northern Qilian strain-partitioned fault system, which is important due to the populated areas nearby. We investigate its 2-D kinematic models using available geodetic measurements under a Bayesian inversion frame. Our results prove that the kinematic models of the northern Qilian strain-partitioned fault system can be well determined, and compatible of the geological measurement and seismicity distribution. In contrast to the frequent thrust earthquakes, any thrust faults are not required to explain the available geodetic data indicating that the short-term geodetic measurements cannot reflect the thrust fault kinematics of the northern Qilian Shan in the geological time-scale. The non-thrust fault involved model also present a highly locked wedge beneath the foreland area, reconciling the supposed historical cascading earthquake ruptures in north Qilian Shan.

How to cite: Zhang, Y., Wimpenny, S., Dal Zilio, L., and Shan, X.: Strain partitioning and fault kinematics in the Northern Qilian Shan (NE Tibet) determined from Bayesian inference of geodetic data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7436, https://doi.org/10.5194/egusphere-egu24-7436, 2024.

Geometric complexity plays an important role for a fault’s seismotectonic behavior as it affects the initiation, propagation and termination of an earthquake and influences stress-slip relationships, fault-segment size, and the probability of multi-segment rupture. Consequently, geometric fault complexity is studied intensively and increasingly incorporated into computational earthquake rupture simulations. These efforts reveal a problem: While a natural fault’s geometry may be well quantifiable at the surface (i.e., the fault trace), its down-dip buried portion cannot be well constrained. At this point, it is not clear how this epistemic uncertainty affects the propagation of individual ruptures and a fault’s seismotectonic behavior (e.g., large-earthquake recurrence).

We address this issue computationally with a physics-based multi-cycle earthquake rupture simulator (MCQsim), enabling us to investigate various aspects of rupture propagation and earthquake cycle in a controlled environment (e.g., with well constrained fault geometry). We approximate fault geometric complexity as a 2-D random field using the “random midpoint displacement” method which allows us to represent fault roughness (i.e., incorporate its epistemic uncertainty) while keeping the fault surface trace unchanged. 

Using MCQsim, we create 20kyr-long synthetic earthquake catalogs for strike-slip faults that share the same complex fault surface trace but have different sub-surface fault geometries. We analyze the resulting variations in single-event rupture propagation (i.e., the kinematic source model) and long-term seismotectonic behavior. We find that kinematic source models of individual events differ substantially between different realizations of sub-surface geometry. However, the long-term seismotectonic behavior (e.g., large-earthquake recurrence) does not differ as much and is less sensitive to the epistemic uncertainties of sub-surface fault geometry.

How to cite: Zielke, O. and Mai, P. M.: Exploring the effects of sub-surface fault geometry on rupture propagation and long-term fault behavior, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7556, https://doi.org/10.5194/egusphere-egu24-7556, 2024.

EGU24-7990 | ECS | Orals | TS3.1

Development of a Bayesian non-planar fault geometry inversion using geodetic seismic cycle deformation data 

Guoguang Wei, Kejie Chen, and Luca Dal Zilio

The geometry of faults regulates the spatial patterns of interseismic, coseismic, and post-seismic surface deformation. Geodetic techniques can measure these deformation patterns during a seismic cycle and are expected to constrain the geometry of  seismogenic faults. However, the conventional linear inversion of geodetic data is unable to simultaneously estimate the fault slip distribution and the fault geometry. In this study, we propose a Bayesian framework that treats fault geometry as a time-invariant parameter. It can individually use coseismic deformation data or simultaneously utilize interseismic, coseismic, and post-seismic deformation data to invert for both fault slip distribution and non-planar fault geometry. Within this framework, geometry evidence informed by geophysical imaging, geological surveys, and microseismicity forms the basis for establishing the prior probability density function, while geodetic observations constitute the likelihood function. Our methodology provides an ensemble of plausible geometry parameters by sampling the posterior probability distributions of the parameters using Markov Chain Monte Carlo simulation. The performance of the developed method is tested and demonstrated through inversions for synthetic oblique-slip faulting models. Results demonstrate that assuming constant rake can significantly bias fault geometry estimates and data weighting. Additionally, considering the variability of slip orientations allows for plausible estimates of non-planar fault geometry with objective data weighting.We applied the method to the 2013 Mw 6.5 Lushan earthquake in Sichuan province, China. The results reveal dominant thrust slips with left-lateral components and a curved fault geometry, with the confidence interval of the dip angles ranging between 20° and 25° and 56° and 58°. Furthermore, the application of this method to the 2015 Gorkha earthquake in Nepal sheds light on the Main Himalayan Thrust, which serves as the interface between the Indian Plate and Eurasia. This may provide new insights into future seismic potential and topographic growth in the Nepal Himalaya.

How to cite: Wei, G., Chen, K., and Dal Zilio, L.: Development of a Bayesian non-planar fault geometry inversion using geodetic seismic cycle deformation data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7990, https://doi.org/10.5194/egusphere-egu24-7990, 2024.

EGU24-8280 | ECS | Orals | TS3.1

Kinematics of the Southeastern Tibetan Plateau from Sentinel-1 InSAR and GNSS: Implications for Seismic Hazard Analysis 

Jin Fang, Tim Wright, Kaj Johnson, Qi Ou, Richard Styron, Tim Craig, John Elliott, and Andy Hooper

Earthquakes release strain energy that has accumulated between seismic events. Measuring strain accumulation rates is critical for understanding earthquake cycle and assessing earthquake potential, with fault slip rates serving as essential inputs for seismic hazard models. However, the Tibetan Plateau has been lacking comprehensive estimates of geologic slip rates on numerous faults. To address this gap, geodetic data have been invoked to derive fault slip (or slip deficit) rates using various methodologies. These include the commonly adopted classic and deformable block modelling approaches (Meade & Loveless, 2009) and the newly developed direct inversion of geodetic strain rates (Johnson et al., 2022), which has the advantage of not requiring blocks to be defined.  A comprehensive comparison of slip rates obtained from these different geodetic methods has been notably absent.

In this study, we focus on the southeastern Tibetan Plateau, utilising Sentinel-1 satellite data from 35 ascending and 32 descending frames spanning the period between 2014 and 2023, along with published GNSS velocities. We constructed high-resolution (1 km) maps of velocity and strain rate fields covering 1.3 million km2. Using these maps, we derived slip rates on newly mapped faults (Styron, 2022) using classic block modelling, “deformable block” modelling, and by the direct inversion of strain rates. Our strain rate fields reveal a partition through focused shear on the Kunlun fault, the Xianshuihe-Xiaojiang fault system, the Longriba fault, the Longmenshan fault possibly influenced by the ongoing postseismic deformation of the 2008 Mw 7.9 Wenchuan earthquake, and the Lijiang-Xiaojinhe fault. On the deforming plateau there is diffuse deformation away from the major faults, with average shear strain and dilatation rates of 14.3 and 13.1 nanostrain/year, compared to 9.4 and 11.1 nanostrain/year in the Sichuan basin (which likely reflects the noise floor in the data). The geodetically-determined slip rates from the three methods generally align with available geologic rates, particularly along-strike variations on the Kunlun fault and the Xianshuihe-Xiaojiang fault system. Our block model consists of 103 blocks bounded by 326 fault sections in the southeastern Tibetan Plateau. The model is constrained by the combined geodetic horizontal velocities from 6617 observation points. Classic block modelling without considering internal strain tends to overestimate slip rates on faults that slip faster than 5 mm/yr, compared to deformable block model that accounts for homogeneous intrablock strain, constituting 5% of the total. The two block models explain approximately 45-50% of the geodetic strain, predicting focused strain on block boundaries even in the absence of observed strain concentrations. By directly inverting strain rates, we suggest that 40-50% of the geodetic strain is attributable to elastic coupling (back slip) on faults, while the remaining can be explained by off-fault distributed moment sources (body forces) in a thin elastic plate. We discuss limitations of different geodetic approaches in modelling deformation (velocities or strain rates) and implications for seismic hazard by comparing the seismic moment release rate from earthquakes and the geodetic moment accumulation rate from our geodetic models.

How to cite: Fang, J., Wright, T., Johnson, K., Ou, Q., Styron, R., Craig, T., Elliott, J., and Hooper, A.: Kinematics of the Southeastern Tibetan Plateau from Sentinel-1 InSAR and GNSS: Implications for Seismic Hazard Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8280, https://doi.org/10.5194/egusphere-egu24-8280, 2024.

EGU24-9097 | ECS | Posters on site | TS3.1

Understanding strain partitioning, segmentation, and the slip-rate history of the Middle Branch of the Northern Anatolian fault, Turkey 

Nicolas Harrichhausen, Julia de Sigoyer, Yann Klinger, Cengiz Yildirim, Melike Karakaş, and Baptiste Camus

We present preliminary results from a paleoseismic study of the middle branch of the Northern Anatolian Fault (MNAF) in Turkey. Despite low instrumental seismicity and geodetic slip rates (~2.5 mm/yr) relative to the northern branch, historical, archeological, and paleoseismic studies indicate the MNAF has hosted several damaging earthquakes in the last two millennia. Recent geomorphic and bathymetric analyses reveal segmentation of the MNAF that may indicate strain partitioning of normal and strike slip along parallel fault strands. However, it remains uncertain whether these fault segments have ruptured simultaneously. Geologic studies have constrained right-lateral slip rates to between 2 and 5.3 mm/yr, with most results contrasting against the present-day geodetic slip rate of ~2.5 mm/yr. Whether this represents a reduction in strain rate along this branch of the Northern Anatolian fault is not clear. Our study has two main objectives: first, to delineate the earthquake history along the newly identified segment of the MNAF beneath Lake Iznik and map its onshore extensions to the east and west of the lake; second, to determine the right-lateral slip rate of the MNAF across different temporal scales. We will present preliminary results from geomorphic mapping, electromagnetic conductivity and ground penetrating radar surveys, and paleoseismic trenching aimed at achieving these objectives. By further establishing the earthquake history and length of the new branch beneath Lake Iznik, we aim to ascertain whether this segment has ruptured concurrently with parallel and along-strike segments, allowing us to estimate paleo-earthquake magnitudes and maximum rupture lengths. Concurrently, by constraining the slip rate of the MNAF over time, we seek to understand whether slip along this branch has decreased and if this reduction is linked to a subsequent increase in slip rate on either the northern or southern branch of the Northern Anatolian Fault.

How to cite: Harrichhausen, N., de Sigoyer, J., Klinger, Y., Yildirim, C., Karakaş, M., and Camus, B.: Understanding strain partitioning, segmentation, and the slip-rate history of the Middle Branch of the Northern Anatolian fault, Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9097, https://doi.org/10.5194/egusphere-egu24-9097, 2024.

EGU24-9399 | ECS | Posters on site | TS3.1

A new deep-learning approach for the sub-pixel correlation of optical images in the near-field of earthquake ruptures 

Tristan Montagnon, Sophie Giffard-Roisin, James Hollingsworth, Erwan Pathier, Mauro Dalla Mura, and Mathilde Marchandon

Precise estimation of ground displacement from correlation of optical satellite images is fundamental for the study of natural disasters. In the case of earthquakes, characterizing near-field displacements around surface ruptures provides valuable constraints on the physics of earthquake slip. Recently, image correlation has been used to investigate the degree of slip localization, and how it may vary as a function of geological parameters (such as fault structural maturity), raising the possibility that slip localization (vs distribution) may be predictable, with important implications for seismic hazard assessment.

Current sub-pixel correlation methods (frequency or spatial domain) all rely on the same general approach: they work at a local scale, with small sliding windows extracted from a pair of co-registered satellite images acquired at different times, and they assume a rigid uniform shift between the two correlation windows. However, in the near-field of fault ruptures, where the correlation window spans the fault discontinuity, this hypothesis breaks down, and may bias the displacements. Additional smoothing associated with the correlation window further complicates the interpretation of sharp features in the displacement field, artificially shifting displacement to the off-fault region.

We developed a U-net-based method to solve the sub-pixel displacement estimation problem at a global scale. Such architecture is able to retrieve full scale surface displacement maps, making use of both global and local features, and potentially tackling different noises of the input images. We trained our model with real satellite acquisitions, warped with ultra-realistic synthetic displacement maps representing realistic faults. The model exhibits promising preliminary results, showcasing its capability to retrieve full-scale surface displacement maps with high accuracy. While direct comparisons with other state-of-the-art approaches (COSI-Corr and MicMac) are pending, our findings suggest that our proposed U-net-based approach has the potential to compete or even outperform these correlators. 

How to cite: Montagnon, T., Giffard-Roisin, S., Hollingsworth, J., Pathier, E., Dalla Mura, M., and Marchandon, M.: A new deep-learning approach for the sub-pixel correlation of optical images in the near-field of earthquake ruptures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9399, https://doi.org/10.5194/egusphere-egu24-9399, 2024.

Geometrical irregularities of faults drive stress heterogeneities that strongly affect the seismic rupture. Here we analyze the effect of fault topography and remote stresses during the interseismic phase on the static stress pattern around faults and on the onset of failure. The analytical solution is derived using perturbation theory for a defined interface topography. We apply our solution for the static stress field near the East Anatolian Fault and we show that a large stress barrier is developed around the segment that ruptured during the Mw 7.8 Kahramanmaraş Earthquake. Considering stress field conditions that are associated with left-lateral strike slip on the fault, we show how the barrier location is affected by the fault geometry, while the amplitude of stress variations are sensitive to the background stress values and their directions. The solution predicts that the value of the accumulated elastic energy in the host rock around the fault is maximal in the barrier region suggesting that in this area the elastic energy available for potential slip is the largest. We therefore suggest that the length of the ruptured segment and magnitude of the strong Kahramanmaraş Earthquake were greatly influenced by the stress heterogeneity generated by the fault geometry during the long interseismic period. This example of the East Anatolian Fault shows that the geometry of the fault is crucial for the location and the extent of earthquakes along it. We further suggest that the presented analytical approach provides a simple yet powerful new tool for assessing seismic hazards before earthquakes occur.

How to cite: Sagy, A., Morad, D., and Lyakhovsky, V.: Stress, energy, and the onset of failure around geometrically irregular faults: Example from the East Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9615, https://doi.org/10.5194/egusphere-egu24-9615, 2024.

EGU24-9782 | Orals | TS3.1

Detection of slow slip events along the southern Peru - northern Chile subduction zone 

Jorge Jara, Romain Jolivet, Anne Socquet, Diana Comte, and Edmundo Norabuena

Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at the global scale. However, no such event has been described in the south Peru - north Chile subduction zone so far, except for the early preparatory phase of the 2014 Iquique earthquake. We use geodetic template matching on GNSS-derived time series of surface motion in Southern Peru - Northern Chile to extract SSEs hidden within the geodetic noise. We detect 33 events with durations ranging from 9 to 40 days and magnitudes from $M_w$~5.6 to 6.2. The moment released by these aseismic events seems to scale with the cube of their duration, suggesting a dynamic comparable to that of earthquakes. We compare the distribution of SSEs with the distribution of coupling along the megathrust derived using Bayesian inference on GNSS- and InSAR-derived interseismic velocities. From this comparison, we obtain that most SSEs occur in regions of intermediate coupling where the megathrust transitions from locked to creeping or where geometrical complexities of the interplate region have been proposed. We finally discuss the potential role of fluids as a triggering mechanism for SSEs in the area. 

How to cite: Jara, J., Jolivet, R., Socquet, A., Comte, D., and Norabuena, E.: Detection of slow slip events along the southern Peru - northern Chile subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9782, https://doi.org/10.5194/egusphere-egu24-9782, 2024.

EGU24-11002 | ECS | Posters on site | TS3.1

Simulating normal fault interactions during complex seismic sequences in the southern Apennines 

Constanza Rodriguez Piceda, Zoë K. Mildon, Yifan Yin, Billy J. Andrews, Claudia Sgambato, Martijn van den Ende, and Jean Paul Ampuero

Active faults with low extension rates can generate large magnitude earthquakes with severe damages, as exemplified in the southern Apennines (Italy) by the Irpinia earthquake (Mw 6.8) in 1980 and the Val D’Agri earthquake (Mw 7.1) in 1857. These earthquakes occur within a network of faults, and geological evidence (e.g. paleoseismic trenching) suggest that earthquake activity varies from decennial to millennial time scales on such fault systems. Therefore, improving our understanding and forecasting capabilities of seismic sequences in these areas is crucial. However, studying fault behaviour in slowly deforming regions can often prove challenging due to the long recurrence intervals and low slip rates of these faults, which results in limited instrumental, historical and paleoseismological records.

To address this issue, we use physics-based numerical models, since they allow for controlled experiments that can span thousands of years with relatively low computational costs, thus they are valuable tools to investigate the causal dynamics between seismic events. Here, we model a system of NW-SE oriented normal faults in the southern Apennines, accounting for the variable slip rates and geometry of the faults. The study region is characterized by areas with variable number of across-strike faults, thus it is suitable to study the effects of fault network geometry (across-and along-strike interaction) on the seismic cycle and earthquake statistics (e.g. recurrence time, coefficient of variation) of a geologically realistic fault network. We use the boundary-element code QDYN which incorporates rate-and-state friction and elastic interactions to examine relevant inputs for seismic hazard assessment, including inter-event time within and between faults, magnitude-frequency distribution, and nucleation location. We are able to simulate spontaneous ruptures following power-law relationships of frequency-magnitude distribution. Differences in the recurrence time (periodic vs. aperiodic cycles) and rupture extent (characteristic vs. non-characteristic seismicity) in the fault planes seem to correlate with the number of faults that exist across strike. Our simulations demonstrate how quasi-dynamic earthquake simulators can provide insights into how fault network geometry impacts earthquake occurrence and seismic hazard assessment.

How to cite: Rodriguez Piceda, C., Mildon, Z. K., Yin, Y., Andrews, B. J., Sgambato, C., van den Ende, M., and Ampuero, J. P.: Simulating normal fault interactions during complex seismic sequences in the southern Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11002, https://doi.org/10.5194/egusphere-egu24-11002, 2024.

EGU24-12582 | ECS | Orals | TS3.1

Deformed Holocene coastal notches reinforce the validity of earthquake slip histories implied by in-situ 36Cl exposure fault scarp dating. 

Jenni Robertson, Claudia Sgambato, Gerald Roberts, Zoe Mildon, Joanna Faure Walker, Francesco Iezzi, Sam Mitchell, Athanassios Ganas, Ioannis Papanikolaou, Elias Rugen, Varvara Tsironi, Joakim Beck, Silke Mechernich, Georgios Deligiannakis, Steven Binnie, Tibor Dunai, and Klaus Reicherter

We report the first example where the timing of earthquake slip from in situ 36Cl cosmogenic exposure dating of an active normal fault scarp can be verified using independently 14C dated Holocene coastal notches which are deformed along the strike of the fault. We have remodelled 36Cl data from the active Pisia-Skinos normal fault, Greece, published by Mechernich et al. (2018), which indicates that the fault slip rate fluctuated through time. We model the expected coastal uplift and subsidence induced by slip on the fault using elastic half-space models and surface ruptures observed following the 1981 Pisia-Skinos earthquakes. Coastal uplift is constrained by elevation measurements of Holocene coastal notches that have previously been dated using 14C by Pirazzoli et al. (1994) and agree with time periods consistent with Holocene climate stability. We mapped the elevations and numbers of notches along the strike of the Pisia-Skinos fault, including measurements made underwater for locations where fault slip has submerged the notches below the present-day shoreline. We show that the spatial patterns and timing of uplift and subsidence from the notches agrees with the timing of periods of high slip associated with earthquake clusters and quiescence associated with anti-clusters from the slip histories derived from 36Cl data, and with the uplift and subsidence derived from elastic half-space modelling. In particular, where modelled subsidence is highest, Holocene notches that formed between 6-2 ka can be preserved but are submerged. Notches could form at this time because the 36Cl data show that the Pisia fault had entered a period of relative quiescence with a slip-rate of <0.1 mm/yr, accompanied by uplift from the offshore Strava fault. In contrast, rapid slip on the Pisia fault at 1.4 mm/yr between 2 ka and the present-day did not allow notches to form during this time period in the location of highest subsidence. Our example is the first that independently calibrates the timing of slip derived from 36Cl on a fault plane using 14C dates on a deformed coastline, and is consistent with the idea that slip-rate variations can be measured and should be incorporated into seismic hazard assessment.

How to cite: Robertson, J., Sgambato, C., Roberts, G., Mildon, Z., Faure Walker, J., Iezzi, F., Mitchell, S., Ganas, A., Papanikolaou, I., Rugen, E., Tsironi, V., Beck, J., Mechernich, S., Deligiannakis, G., Binnie, S., Dunai, T., and Reicherter, K.: Deformed Holocene coastal notches reinforce the validity of earthquake slip histories implied by in-situ 36Cl exposure fault scarp dating., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12582, https://doi.org/10.5194/egusphere-egu24-12582, 2024.

The seismic chronicle, derived from the analysis of 14 short sediment cores and three long cores from Lake Iznik (NW Turkey), along with the identification of a subaquatic fault segment belonging to the Middle Strand of the North Anatolian Fault (MNAF), provides insights into both local seismicity and the regional seismic activity over the last 6000 years.

The integration of this seismic chronicle with ground-motion estimations at the core locations for all historical earthquakes, together with the evolution of sedimentation rate through time, allow to discuss the epicentral region and epicentral intensity of each historical earthquake in the western NAF system. This analysis also helps us to discriminate which earthquake is likely to generate an event deposit in the case of several historical earthquake candidate, especially when chronological uncertainty are larges

This approach allows a discussion of the factors influencing the threshold (sedimentation rate, ground motions at different spectral frequencies ) for triggering an event deposit in the Lake Iznik and the type of slope destabilization that can be triggered .

Thanks to these finding and through the established scaling relationship it is then possible to infer a minimum intensity for prehistoric earthquakes recorded in Lake Iznik at a given period.

Combining these data with paleoseismological data from the region allows us to propose a scenario for the long-term seismic cycle of the western NAF system.

How to cite: de Sigoyer, J., Domenge, J., Céline, B., Gastineau, R., Sabatier, P., and Duarte, E.: Information on past seismicity of the western NAF system (Turkey) combining ground-motion models with historical earthquakes and event deposits recorded in the sediments of Lake Iznik (NAF system, Turkey), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12894, https://doi.org/10.5194/egusphere-egu24-12894, 2024.

EGU24-13043 | ECS | Posters on site | TS3.1

PyMDS, a Bayesian inversion algorithm for chlorine 36 dating based on the last No-UTurn Sampler (NUTS) 

Maureen Llinares, Lucilla Benedetti, Ghislain Gassier, and Sophie Viseur

Markov Chain Monte Carlo (MCMC) algorithms are sampling approaches relying on Bayesian inference, theorized in the late 1940s and used in many applications (multi-dimensional integral computations, probability law explorations, inversion problems, etc.). MCMC methods are computationally expensive and many variants have been proposed to optimize them Today, MCMC algorithms are used as inversion tools in different contexts: from receiver functions in seismology . The success and efficiency of those methodologies depends on: the complexity of the forward function, the efficiency of the MCMC strategy and the implementation language. The last MCMC sampler is the No U-Turn Sampler or NUTS (Hoffman and Gelman, 2011), an evolution of the Metropolis Hastings (HMC).

Estimating seismic history along fault scarps from 36Cl profiles is a typical inversion problem. Thus, previous studies have proposed MCMC routines to the forward function described in (Schlagenhauf et al., 2011), to invert 36Cl data and to infer seismic histories on fault scarps  (Beck et al., 2018; Mechernich et al., 2023; Tesson and Benedetti, 2019). The complexity of the forward function implies the necessity of a powerful MCMC sampler such as NUTS (Liesenfeld and Richard, 2008).

Here, we discuss these different approaches and present a new approach, termed as PyMDS, which relies on the NUTS algorithm. We implemented the code in python and performed synthetic tests to evaluate the algorithm ability to retrieve seismic histories.The results for three earthquakes synthetics tests will be presented and show that the algorithm is capable of finding the seismic scenario (ages, slips and slip rate) with a precision of few hundred years on the ages, 10 to 30 cm on the slips and inferior 0.05 mm/yr on the slip rate with a runtime of 4 hours (faster than the previous Fortran code published by Tesson & Benedetti (2019) that required 3 days to complete). We will also present preliminary results obtained on the five sites located on the Velino-Magnola fault system and the implication on seismic cycle. Finally, we will discuss potential improvement and development perspectives, such as the optimization of the forward function, the necessity to invert slips and the parametrization of the NUTS algorithm.

How to cite: Llinares, M., Benedetti, L., Gassier, G., and Viseur, S.: PyMDS, a Bayesian inversion algorithm for chlorine 36 dating based on the last No-UTurn Sampler (NUTS), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13043, https://doi.org/10.5194/egusphere-egu24-13043, 2024.

EGU24-13133 | ECS | Orals | TS3.1

Slip localization on multiple fault splays accommodating distributed deformation across normal fault complexities. 

Francesco Iezzi, Marco Francescone, Alberto Pizzi, Anna Maria Blumetti, Paolo Boncio, Pio Di Manna, Bruno Pace, Tommaso Piacentini, Felicia Papasodaro, Francesco Morelli, Marco Caciagli, Massimo Chiappini, Francesca D’Ajello Caracciolo, Valerio Materni, Iacopo Nicolosi, Vincenzo Sapia, and Stefano Urbini

Features such as fault geometry and slip-rates are key inputs to assess the seismic hazard imposed by either ground motion or fault displacement. However, complexities in the geology of faults, such as relay zones and along-strike fault bends, could lead to settings characterized by high segmentation, with multiple splays arranged both along and across strike. In order to assess the seismic hazard associated with such fault sectors, it is necessary to establish whether the 3D shallow deformation is equally spread over the multiple fault splays or the activity tends to localise on specific splays. This problem is enhanced when these faults are located within urban areas, and therefore their surface expression is altered by intense anthropic activity.

Within the framework of a work on the mitigation of the fault displacement hazard associated with the Mt. Marine active normal fault (Central Italy), we have performed two paleoseismological surveys within the town of Pizzoli (about 10 km NW of L’Aquila), where the fault is expressed with several splays arranged both along and across-strike. The trenches were planned to explore (i) potential fault scarps altered by human activity, identified through aerial photographs, LiDAR and fieldwork analysis, and (ii) discontinuities in the stratigraphic record highlighted by geophysical investigations (ERT, GPR) and borehole data.

The paleoseismological surveys intercepted five fault splays arranged across-strike, three synthetic and two antithetic to the main Mt. Marine fault. The fault splays show evidence of multiple Late Pleistocene/Holocene surface-rupturing seismic events, marked by colluvial wedges and infilled fractures. Moreover, we constrained the Late Pleistocene slip-rate of the Mt. Marine fault splays by dating and correlating Late-Pleistocene paleosols found (1) outcropping in the footwall of one of the inner fault splay and (2) in a borehole located just at the hangingwall of the outermost splay.

Our results show that the fault splays exhibit different and variable activity rates, suggesting that fault activity is localized on specific fault splays through space and time with the potential to rupture simultaneously during large earthquakes. Our findings have strong implications on fault-based seismic hazard assessments, as they imply that data collected on one splay may not be representative of the behaviour of the entire fault.

How to cite: Iezzi, F., Francescone, M., Pizzi, A., Blumetti, A. M., Boncio, P., Di Manna, P., Pace, B., Piacentini, T., Papasodaro, F., Morelli, F., Caciagli, M., Chiappini, M., D’Ajello Caracciolo, F., Materni, V., Nicolosi, I., Sapia, V., and Urbini, S.: Slip localization on multiple fault splays accommodating distributed deformation across normal fault complexities., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13133, https://doi.org/10.5194/egusphere-egu24-13133, 2024.

Previous studies have constrained the fault slip rates and block geometries of the SoutheasternTibetan Plateau (SETP) with contradictory results due to complex deformation patterns, limited datasets, and subjective choices of block boundaries. In this work, we address the issue of uncertain block geometries by employing an unsupervised machine learning (Euler pole clustering) algorithm that automatically resolves regions that behave as rigid blocks (clusters) using ~1000 GNSS velocity vectors. The optimal clustering results, determined by F-test and Euler-vector overlap analyses, indicate 4 elongated blocks exist in the SETP that are approximately parallel and delineated by a set of arcuate sinistral-slip faults. Our clustering results redefine the kinematicsof the SETP region with new block definitions which elucidate the dominance of sinistral-slipfaults.

How to cite: Xu, R. and Liu, X.: Clustering of GNSS Velocities Using Unsupervised Machine Learning in the Southeastern Tibetan Plateau: Block Identification and the Dominance of Sinistral-slip Faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13534, https://doi.org/10.5194/egusphere-egu24-13534, 2024.

EGU24-14326 | Orals | TS3.1

Low-angle normal faulting triggered by fluids 

Carolina Pagli, Alessandro La Rosa, Derek Keir, Gareth Hurman, Hua Wang, Cecile Doubre, Renier Viltres, Martina Raggiunti, and Atalay Ayele

In extensional settings under Andersonian mechanics, low-angle normal faults should not form in favour of steeply dipping normal faults. However, InSAR shows that a seismic sequence including an earthquake with magnitude Mw 5.6 on August 1st, 2023 (NEIC - National Earthquake Information Center) at the northern end of the Afar rift was caused by normal faulting on a low-angle 35° dipping plane. Our best-fit InSAR model shows that the low-angle normal fault occurred on the west margin of the rift axis, it was relatively deep (6.7 km) and it slipped fully seismically, having a geodetic magnitude of Mw 5.66 in agreement with the global seismic recordings (NEIC). Temporally, the faulting occurred at the end of a one-year period (December 2022-December 2023) of increased seismicity in the northern sector of Afar, with swarms of seismicity migrating northward along the rift. The seismic characteristics, fault location and kinematics are consistent with the low-angle normal fault being triggered by fluids that locally could be released by a deep magmatic heat source along the rift axis under high extensional stresses. Our observations show that low-angle normal faults can form in rifting settings, are activated seismically and are likely fluid-induced.

How to cite: Pagli, C., La Rosa, A., Keir, D., Hurman, G., Wang, H., Doubre, C., Viltres, R., Raggiunti, M., and Ayele, A.: Low-angle normal faulting triggered by fluids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14326, https://doi.org/10.5194/egusphere-egu24-14326, 2024.

EGU24-16153 | ECS | Posters on site | TS3.1

Transient aseismic vertical deformation during the interseismic cycle across the Pisia-Skinos normal fault (Gulf of Corinth, Greece) 

Zoe Mildon, Manuel Diercks, Gerald Roberts, Joanna Faure Walker, Athanassios Ganas, Ioannis Papanikolaou, Vassilis Sakas, Jennifer Robertson, Claudia Sgambato, and Sam Mitchell

Loading and deformation during the interseismic period of the earthquake cycle is often considered to be constant for continental faults, therefore assuming that the short-term (annual-decadal) deformation is representative of longer-term deformation. Based on this assumption, geodetically-derived deformation rates are sometimes used to infer the slip-rates and thus seismic hazard of faults. However geological observations indicate that deformation and slip rates are variable over a range of timescales, and we present an observation of variable deformation across an active normal fault occurring on an annual timescale. The Pisia-Skinos normal fault in the Gulf of Corinth, Greece, is a well-known fault which slipped most recently during a sequence of damaging earthquakes in 1981. Using vertical deformation data, available from the European Ground Motion Service (EGMS), we observe uplift/subsidence of the footwall/hangingwall of the Pisia fault between 2016-2021. Of particular interest is our observation that the deformation is not uniform over the 6 year time period, instead there is an up to 7-fold increase in the vertical deformation rate in mid-2019. We hypothesise that this deformation is aseismic as there is no temporally correlated increase in the earthquake activity (M>1). We explore four possible causative mechanisms  for observed deformation; shallow slip, post-seismic after-slip, deep slip on an underlying shear zone, and post-seismic visco-elastic rebound. Our preferred hypothesis is that the transient deformation is caused by centimetre-scale slip in the upper 5km of the Pisia fault zone, based on the magnitude and spatial extent of the deformation. Our results suggest that continental normal faults can exhibit variable deformation over shorter timescales than previously observed, implying that the interseismic period of the earthquake cycle on continental faults may be more variable than previously hypothesised. This also highlights potential pitfalls of using slip rates measured over short-timescales to infer seismic hazard.

How to cite: Mildon, Z., Diercks, M., Roberts, G., Faure Walker, J., Ganas, A., Papanikolaou, I., Sakas, V., Robertson, J., Sgambato, C., and Mitchell, S.: Transient aseismic vertical deformation during the interseismic cycle across the Pisia-Skinos normal fault (Gulf of Corinth, Greece), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16153, https://doi.org/10.5194/egusphere-egu24-16153, 2024.

EGU24-16171 | Orals | TS3.1

Fast stress-loading and -unloading below the seismogenic zone 

Claudia Trepmann, Lisa Brückner, and Fabian Dellefant

At depth just below the seismogenic zone of the continental crust, i.e. at greenschist facies conditions, stresses increase during seismic rupturing within minutes from differential stresses on the order of a few tens of MPa to several hundreds of MPa. These fast stress-loading rates are manifested in characteristic microfabrics in fault rocks (cataclasites and pseudotachylytes) exhumed from these depths. The microfabrics indicate quasi-instantaneous cataclasis of almost all rock-forming minerals including garnet and quartz, as well as mechanical twinning of pyroxenes, amphiboles and titanite. In combination with experiments, the microfabrics can be used as paleo-stress gauges, i.e., paleopiezometers. The characteristic microstructures can occur distributed over the whole width of large-scale thrust faults, as the Silvretta basal thrust in the Central European Alps. There, twinned amphiboles record transient differential stresses of more than 400 MPa in a rock volume to about 300 m above the basal thrust exposed at the contact to the Penninic units of the Engadine window over several tens of km. Fast stress-unloading is indicated by growth of new undeformed quartz grains along cleavage cracks in host quartz generated coeval with seismic rupturing and missing evidence of quartz dislocation creep after pseudotachylyte formation. This fast stress-loading and unloading is recorded in pseudotachylytes, i.e., close to the seismic rupture, whereas at larger distance to the seismic rupture accelerated creep at hundreds of MPa occurs on a longer time scale. 

How to cite: Trepmann, C., Brückner, L., and Dellefant, F.: Fast stress-loading and -unloading below the seismogenic zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16171, https://doi.org/10.5194/egusphere-egu24-16171, 2024.

EGU24-16276 | ECS | Orals | TS3.1

Triggered and recurrent slow slip in North Sulawesi, Indonesia 

Nicolai Nijholt, Wim Simons, Taco Broerse, and Riccardo Riva

Nearby faults interact with each other through the exchange of stress. However, the extent of fault interaction is poorly understood. In particular, closely tied tectonic systems like crustal-scale faults that are right next to subduction zone interfaces are likely to express such interactions. Interactions may lead to slow-slip activity, resulting in episodes of transient surface motion.

Our study concentrates on Northwest Sulawesi (Indonesia), which hosts two fault zones with potential for major earthquakes and tsunamis: the strike-slip Palu-Koro fault and the Minahassa subduction zone. Both fault zones accommodate 4 cm/yr of interseismic relative motion. Thanks to a 20-year-long effort in geodetic monitoring, we are able to identify multiple periods during which surface velocities deviate from their interseismic trend. The most recent episode followed the 2018 Mw7.5 Palu earthquake.

We use a Bayesian methodology with forward predictions of slip on the two fault interfaces to match the observations following the 2018 Mw7.5 Palu earthquake, and infer that both deep afterslip on the Palu-Koro fault and slow slip on the Minahassa subduction interface have caused the observed transient surface motion. This finding represents the first recording of a slow slip event on the Minahassa subduction interface. We also speculate that the subduction interface and the strike-slip fault are likely interacting on a regular basis, affecting the seismogenic potential of both parts of this tectonic system.

How to cite: Nijholt, N., Simons, W., Broerse, T., and Riva, R.: Triggered and recurrent slow slip in North Sulawesi, Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16276, https://doi.org/10.5194/egusphere-egu24-16276, 2024.

EGU24-16670 | Orals | TS3.1

Bayesian Inference of Rheological Parameters from Observations Before and After the Tohoku Earthquake 

Rob Govers, Celine Marsman, Femke Vossepoel, Ylona van Dinther, and Mario D'Acquisto

Geodetic data covering different phases of the earthquake cycle provide a great opportunity to improve our understanding of the processes and parameters governing the dynamics at subduction margins. However, quantifying the individual contributions of physical processes such as viscoelastic relaxation, afterslip, and (re)locking throughout the earthquake cycle remains challenging. Moreover, it is relevant to account for these processes within a rheological framework that is consistent over the entire earthquake cycle. We address this using Bayesian inference in the form of an ensemble smoother, a Monte Carlo approach that represents the probability density distribution of model states with a finite number of realizations, to estimate geodynamic model parameters. Prior estimates of the imperfect physical model are combined with the likelihood of noisy observations to estimate the posterior probability density distribution of model parameters.

 

We construct a 2D finite element seismic cycle model with a power-law rheology in the mantle. A priori information, such as a realistic temperature field and a coseismic slip distribution, is integrated into the model. Model pre-stresses are initialized during repeated earthquake cycles wherein the accumulated slip deficit is released entirely. We tailor the last earthquake to match the observed co-seismic slip of the 2011 Tohoku earthquake. The heterogeneous rheology structure is derived from the temperature field and experimental flow laws. Additionally, we simulate afterslip using a thin, low-viscosity shear zone with a Newtonian rheology. We focus on constraining power-law flow parameters for the mantle, and the shear zone viscosity.

 

We assimilate 3D GEONET GNSS displacement time series acquired before and after the 2011 Tohoku earthquake. The data require separate viscoelastic domains in the mantle wedge above and below ~50 km depth, and in the sub-slab mantle. Power-law viscosity parameters are successfully retrieved for all three domains. The trade-off between the power-law activation energy and water fugacity hinders their individual estimation. The wedge viscosity is >1019 Pa·s during the interseismic phase. Postseismic afterslip and bulk viscoelastic relaxation can be individually resolved from the surface deformation data. Afterslip is substantial between 40-50 km depth and extends to 80 km depth. Bulk viscoelastic relaxation in the wedge concentrates above 150 km depth with viscosities <1018 Pa·s. Landward motion of the near-trench region occurs during the early postseismic period without the need for a separate low-viscosity channel below the slab.

How to cite: Govers, R., Marsman, C., Vossepoel, F., van Dinther, Y., and D'Acquisto, M.: Bayesian Inference of Rheological Parameters from Observations Before and After the Tohoku Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16670, https://doi.org/10.5194/egusphere-egu24-16670, 2024.

Shallow creep, as a widespread phenomenon in the earthquake cycle, plays an important role in understanding the behavior of faults and seismic hazards. However, it is still under debate whether creeping is an inherent behavior of fault or is a form of afterslip following large earthquakes. The East Anatolian Fault was recently ruptured by the 2020 Mw6.8 Elazig, and 2023 Mw7.8/Mw7.6 Kahramanmaras earthquake sequence, providing a unique opportunity to investigate the relation between shallow creep and earthquakes along strike-slip fault. Here, we show the spatial distribution and temporal evolution of creeping segments along the EAF using the InSAR phase-gradient stacking method. We derive the shear-strain rates in three periods – before the 2020 earthquake, between the 2020 and 2023 earthquakes, and after the 2023 earthquake sequence. By comparing the spatial distribution of the interseismic strain rates, the coseismic slip, and the post-seismic strain rates, we document a tight connection between creeping and coseismic slip on the two recent earthquakes. We also investigate the temporal behavior of faults following the two earthquakes using time-series shear strain analysis. The results reveal behaviors of shallow creep on different segments of the EAF with different statuses before the earthquakes. Our results shed new light on understanding the mechanism of creeping and its relation with large earthquakes during the earthquake cycle.

How to cite: Liu, Z. and Wang, T.: Shear-strain rates across the East Anatolian Fault (EAF) response to the 2020 Mw6.8 Elazig, and 2023 Mw7.8/Mw7.6 Kahramanmaras earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18092, https://doi.org/10.5194/egusphere-egu24-18092, 2024.

EGU24-18562 | Posters on site | TS3.1

Insights into the site-to-site correlation of paleoseismic data  

Nicolás Pinzon and Yann Klinger

Integration of paleoseismic data from multiple sites is important to assess the past fault rupture scenarios and determine an earthquake chronology for the entire fault system. However, the current methods used to combine paleoseismic data are diverse and lack theoretical foundations from a mathematical perspective. We present a method to evaluate and integrate paleoseismic event data from multiple sites into a single earthquake time history. We apply this method to the central-eastern fault sections of the Altyn Tagh Fault using data from ten fault trenches. Applying a Bayesian approach we constructed time-stratigraphic models that yield the probability density functions corresponding to the age of individual earthquakes at each site. Then, our method to integrate these data consists of two main steps: 1) we constructed a rupture pool with all the modeled event ages, and we evaluated the overlapping degree between the site PDFs; 2) For sufficiently contemporary PDFs we combine them by computing the weighted-mean method which emphasizes the overlap in the site earthquake times. The weighted-mean method yields smaller earthquake-time uncertainties compared to the rupture-mean approach and is consistent with the earthquake rupture assumptions behind the integration of paleoseismic data and the probability theory of density functions. This approach helps to clarify the timing and rupture extent of past earthquakes along central-eastern ATF and is essential to improve the earthquake probability assessment for the region.

How to cite: Pinzon, N. and Klinger, Y.: Insights into the site-to-site correlation of paleoseismic data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18562, https://doi.org/10.5194/egusphere-egu24-18562, 2024.

Following large earthquakes, postseismic crustal deformations are often observed. They include the afterslip and the viscoelastic deformation of the crust and the upper mantle, activated by the coseismic stress change. In order to predict the future deformations, and the stress change distributions, it is important to divide each deformation. The physical parameters; frictional properties of the fault and the rheological properties are the key to determining the slip behavior, but they are generally unknown.

Data assimilation (DA) studies have attempted to estimate the frictional properties directly from the observational data. DA incorporates the observed data into the physics-based model to construct a more plausible model. When DA works well, we can obtain the physics-based model, including the physical properties, that can quantitatively explain the observed data. The constructed physics-based model can be used to simulate the slip evolution beyond the data period, i.e., prediction of the deformation.

There are two types of DA technique applying to nonlinear system, the sequential method called as Ensemble Kalman filter method (EnKF) and the variational method called as 4DVAR. For the fault system, EnKF is applied to the deformation data to estimate the physical variables (van Dinther et al., 2019, Hirahara and Nishikiori, 2019). 4DVAR is also applied to the afterslip assuming elastic medium to estimate the fault frictional properties (Kano et al., 2015; 2020). If the physics-based model under consideration is linear, the sequential and the variational methods are consistent, but this is not the case for fault systems.

In this presentation, I construct a simple model that include the fault slip that follows the rate- an state- friction law and the viscoelastic deformation. Then I apply both EnKF and 4DVAR, and compare the results to discuss the characteristics of the methods.

How to cite: Ohtani, M.: Numerical experiments on estimating the fault frictional properties and the viscosity from the postseismic deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19405, https://doi.org/10.5194/egusphere-egu24-19405, 2024.

EGU24-20077 | ECS | Orals | TS3.1

Co-seismic fault offsets of the 2023 Türkiye earthquake ruptures using Sentinel-2 satellite imagery and field observations 

Floriane Provost, Volkan Karabacak, Jean-Philippe Malet, Jérôme Van Der Woerd, Mustapha Meghraoui, Frédéric Masson, Matthieu Ferry, David Michéa, and Elisabeth Pointal

On February 6, 2023, southern Türkiye was hit by two major earthquakes at 01:17 UTC (Mw 7.8, Pazarcık, Kahramanmaraş) and at 10:30 UTC (Mw 7.6, Elbistan, Kahramanmaraş) leading to severe damages at the complex junction of the Dead Sea Fault (DSF), the Cyprus arc and the East Anatolian fault zone (EAFZ). The ruptures propagated along several known strands of the southwestern termination of the EAFZ, the main Pazarcık and Karasu valley faults and the Çardac-Sürgü fault. The spatial extent of the impacted zone (300 x 300 km) supports the use of satellite images to map ruptures and damages and measure the co-seismic displacement over the whole region. Among the different satellite constellation available nowadays, Sentinel-2 presents the advantages of offering high-resolution images (10 m), global coverage with frequent revisit time and open access policy to the images. We here present the high-resolution mapping of the entire coseismic surface ruptures derived from image correlation of optical Sentinel-2 satellite acquisitions. We further estimated the rupture width, the total and on-fault offset, and of the diffuse deformation obtained a few days after the two mainshocks along the two main ruptures at 50 m resolution along the rupture. The mapping and the estimation of the offset are validated with the location of the rupture and the offset measurements collected on the ground. We found that the ruptures extend over lengths of 310 km and 140 km, with maximum offsets reaching 7.5±0.8 m and 8.7±0.8 m near the epicenters, for the Mw 7.8 and Mw 7.6 mainshocks, respectively. We propose a segmentation of the two ruptures based on these observations, and further discuss the location of potential supershear rupture. The use of optical image correlation complemented by field investigations along earthquake faults provides new insights into seismic hazard assessment.

How to cite: Provost, F., Karabacak, V., Malet, J.-P., Van Der Woerd, J., Meghraoui, M., Masson, F., Ferry, M., Michéa, D., and Pointal, E.: Co-seismic fault offsets of the 2023 Türkiye earthquake ruptures using Sentinel-2 satellite imagery and field observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20077, https://doi.org/10.5194/egusphere-egu24-20077, 2024.

EGU24-20361 | ECS | Posters on site | TS3.1

3D discrete element modeling for the simulation of seismic cycles on a strike-slip fault 

Adélaïde Allemand, Liqing Jiao, and Yann Klinger

Knowing about the geometry of both (i) ruptured zones during seismic events, and (ii) faults throughout seismic cycles, as well as the evolution of this geometry, is important to understand what is controlling the start and the ending of large earthquakes. In this study, we use 3D Discrete Element Modeling (DEM) in order to simulate a strike-slip fault, formed from an initially homogeneous, intact medium representing brittle rock that is submitted to tectonic loading. Indeed, this numerical method models the crust as an assembly of rigid spheres which are linked by user-defined interactions and reconfigurate very naturally when subjected to loading. Therefore, such approach is adapted to study the evolution of fault geometry through earthquake cycles, since it permits to simulate large displacements of the particles, while avoiding prescribing fault location and geometry, and letting such geometry evolve freely.

A 3D parallelepipedic model is designed and then indefinitely sheared by assigning periodic boundary conditions. The particular feature of our model is the implementation of a healing phenomenon, a key process which allows fractured zones to restrengthen after a slip event. During the simulation, the position of particles and the state of their bonds are recorded at regular time intervals; consequently, the shape and dimension of deformation are evaluated, the evolution of fault geometry is monitored, and the stresses in the domain can be measured. Results show a stick-slip behaviour which can be identified as earthquakes separated by locking periods. In addition, the amount of displacement and the rupture surface can be estimated and enable the computation of a magnitude-like quantity. Thus, earthquake-like events seem to follow a magnitude-frequency relationship, and earthquake-like surface deformations are comparable to observations of ground deformation after real size earthquakes. Eventually, the evolution of the fault geometry during the simulation is also scrutinized.

How to cite: Allemand, A., Jiao, L., and Klinger, Y.: 3D discrete element modeling for the simulation of seismic cycles on a strike-slip fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20361, https://doi.org/10.5194/egusphere-egu24-20361, 2024.

EGU24-179 | Posters on site | TS3.2

The 1928 – 1937 Oaxaca Earthquake Sequence (Mexico) 

Francisco J Nunez-Cornu and Diana Nunez

Oaxaca is the most seismically active region in Mexico and one of the most studied using different methodologies. This seismic activity is due to the subduction of the Cocos Plate beneath the North American Plate, which is considered an anomalous subduction zone since it is a truncated continental margin. Seventy-four earthquakes (M> 7.0) have been identified in the last 510 years, which is an average of one earthquake every 6.8 years. The seismic sequence occurred between 1928 and 1937 is the key to understand the regional seismotectonics. The locations of these nine events (M>7.0) reported by different authors differ by more than 100 km for the same earthquake. We relocated the aftershocks of these earthquakes using the seismograms from TAC (Tacubaya) and VCM (Veracruz) stations available at the Seismological Seismic Network (Mexico) archive reading pre-phases S-P.  To calibrate these readings, we relocate the seismicity in the region between 1950 and 1982 with the JHD Method using 1978, 1982, 1965 and 1968 earthquakes as Master Events. We look from this catalog the earthquakes registered in TAC and VCM in the period 1950 - 1982 and whose seismograms were in the archive were selected. The S-P prephases in TAC and VCM were read with the same criteria used previously. With these data we fitting a time-distance curve for each station. These curves were used to obtain more reliable aftershock area for each of the coastal earthquakes occurred during the 1928 – 1937 sequence.

How to cite: Nunez-Cornu, F. J. and Nunez, D.: The 1928 – 1937 Oaxaca Earthquake Sequence (Mexico), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-179, https://doi.org/10.5194/egusphere-egu24-179, 2024.

EGU24-1460 | ECS | Posters on site | TS3.2

Seismogenic structures and stress state of the Puysegur Subduction Zone (Fiordland, New Zealand) from detailed earthquake observations. 

Cédric De Meyer, Calum J. Chamberlain, and Martha K. Savage

The formation of new subduction zones, termed Subduction Zone Initiation (SZI), has a large influence on global plate tectonics. However, how stresses within the plate boundary region evolve throughout the evolution of nascent subduction zones remains unresolved. The Puysegur Subduction Zone in Fiordland, near the southern tip of New Zealand’s South Island, is a young, steeply dipping subduction zone and a key site for studying such incipient stages of subduction. Despite the global significance of the Puysegur Subduction Zone, it has received relatively little attention, mostly due to its remote location. Few passive seismic studies have been carried out in the region, and the continuous GeoNet network is too sparse to detect and accurately resolve seismicity around the Puysegur Subduction Zone. Because of this, the present-day structure and stress state of the Puysegur Subduction Zone remain poorly resolved.

We aim to study these two unresolved characteristics by using a combination of temporary seismic networks and the permanent GeoNet network to increase station coverage in the region. We have developed a Puysegur-appropriate workflow consisting of automated earthquake detection and association, manual event evaluation and P-wave polarity determination. Highly accurate earthquake locations are obtained using NonLinLoc and a 3D velocity model. Focal mechanism analyses and stress inversion are conducted using Bayesian approaches. Currently, we have obtained a preliminary catalogue for the period between 02/2018 and 10/2018, which shows that the developed methodology is capable of producing more complete earthquake catalogues compared to the national GeoNet catalogue. Preliminary precise hypocentral locations and well- constrained focal mechanisms for moderate-to-large magnitude events are used to constrain the region’s seismogenic structures, such as the subduction interface and major active faults, as well as provide preliminary constraints on the region’s stress state.

How to cite: De Meyer, C., Chamberlain, C. J., and Savage, M. K.: Seismogenic structures and stress state of the Puysegur Subduction Zone (Fiordland, New Zealand) from detailed earthquake observations., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1460, https://doi.org/10.5194/egusphere-egu24-1460, 2024.

EGU24-1542 | ECS | Posters on site | TS3.2

Neotectonics in southern Ontario: Pop-up structures and their implications for seismic hazards in intraplate settings 

Abigail Clark, Alexander Peace, Carolyn Eyles, and Ethan Davies

Intraplate neotectonism is generally not well documented and understood despite its significance for seismic hazards in areas such as eastern Canada. This study aims to provide an in-depth structural analysis of potential neotectonic pop-up structures in southern Ontario, Canada, leading to a more comprehensive definition of pop-up structures, and ultimately constrain the processes involved and extent to which neotectonism impacts the region. Three locations in Southern Ontario were documented using a combination of ground and drone-based structural analysis: 1) Fletcher Creek Ecological Preserve, 2) Wainfleet Wetlands, and 3) multiple sites on Manitoulin Island. Sites were chosen where previous work had documented neotectonic activity, and/or where initial geomorphic analyses indicated the possibility of pop-up structures. The locations are all located within the Ordovician to the Devonian Niagara Escarpment stratigraphy. Fracture patterns at each site were analyzed using ground-based measurements or drone-based photogrammetry (DJI Phantom 4 V2 and Phantom 4 Pro acquisition followed by analysis in Pix4D), where applicable. Orthomosaics were then analyzed using FracPaq to determine fracture statistics including orientation, intensity, and density. Where access permitted, ground-based structural measurements were also obtained on structures such as fractures and folds, in addition to RTK-DGPS (real time kinematic differential-global positioning system) profiles over potential pop-up structures. The analysis revealed inconsistencies in the definition of a "pop-up", prompting further inquiry into the definition of a pop-up versus stress relief features more generally. To address this ambiguity, a classification system was developed to differentiate between pop-ups and other tectonic stress relief features. It was concluded that pop-up structures exhibit a distinct geomorphic expression, manifesting as a linear elevated ridge. In southern Ontario, regardless of whether a feature is identified as a stress relief feature or a pop-up, it nonetheless demonstrates that the region is tectonically active despite often being characterized as a stable continental interior. This study adds to a growing body of work documenting neotectonic activity in southern Ontario, with the several stress-related structures documented for the first time in this study showing their prevalence over a wide area.

How to cite: Clark, A., Peace, A., Eyles, C., and Davies, E.: Neotectonics in southern Ontario: Pop-up structures and their implications for seismic hazards in intraplate settings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1542, https://doi.org/10.5194/egusphere-egu24-1542, 2024.

The characteristic stress drop of an earthquake is indicative of its slip to fault dimension. Its value is affected by fault strength, fault topography, the presence of fluids, and other properties. By estimating stress drops throughout an entire subduction zone, namely for the seismically highly active northernmost part of Chile, and combining it with mapped b-values and their corresponding magnitude distribution, this work aims to better constrain the conditions under which earthquakes of different provenances may nucleate.
Database is a recent seismicity catalog, containing over 180,000 events and covering 15 years of seismicity, for which more than 50,000 stress drop estimates were computed. Their class wise spatial average segments the subduction zone into different parts. This difference, however, is small compared to the natural scatter of stress drop values. 
By considering stress drop variations, b-value map, magnitude distribution, and thermal modeling, I describe a variety of mechanisms of earthquake nucleation which might explain the observed stress drop variation. This is done for 1) the plate interface in general; 2) local shallow interface features, i.e., asperities and creeping sections; 3) the highly active intermediate depth seismicity region. In all three cases, the combination of stress drop distribution and b-value mapping helps to better understand the differences in earthquake nucleation and to formulate hypotheses on the controlling factors of earthquake nucleation.

How to cite: Folesky, J.: From stress drop mapping to earthquake nucleation conditions in the northern Chilean subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1741, https://doi.org/10.5194/egusphere-egu24-1741, 2024.

EGU24-2612 | ECS | Posters on site | TS3.2

Probabilistic Assessment of Slip Rates Over Time of OffshoreBuried Thrusts: A Case Study in the Central Adriatic Sea(Italy) 

Ada De Matteo, Daniel Barrera, Francesco Maesano, Giovanni Toscani, Silvio Seno, and Roberto Basili

Understanding the recent tectonic activity and seismotectonics of inaccessible buried faults requires the development of feasible and robust approaches. The foredeep deposits of the northern and central Apennines (an offshore area in the central Adriatic Sea, Italy) blanket the active buried frontal thrusts of the Apennines and the Dinarides orogens. Detecting recent-to-ongoing tectonic activity of these thrusts is particularly challenging because sedimentation rates easily exceed the very slow tectonic rates.
In this work, we combine seismic reflection profile interpretation, sediment decompaction, kinematic restoration and balancing to quantitatively analyse the Plio-Pleistocene tectonic activity of the Apennines and Dinarides buried thrusts in the central Adriatic Sea and calculate the slip rates of the major faults. The northern and central Apennines foredeep is filled by a thick Messinian to Quaternary sedimentary wedge, unconformably resting on a Meso- Cenozoic carbonatic and siliciclastic passive margin succession, which is in turn involved in the east-northeast propagation of the fold-and-thrust belt from onshore to offshore (Adriatic Sea). As suggested by previous studies, the region is in a substantial tectonic activity decrease, but local and qualitative observations on specific structures show evidence of recent tectonic activity. The frontal thrusts of both the Apennines and the Dinarides are active, as also demonstrated by the moderate seismic activity historically (few past centuries) recorded in the region and by the recent earthquakes, followed by rather rich aftershock sequences that occurred in this region and nearby (e.g. the Porto San Giorgio earthquake Ml 5.0 in 1987; the Jabuka earthquake Mw 5.5 in 2003, the Pesaro earthquake Ml 5.7 in 2022). We interpreted, depth converted, and restored two northeast-trending regional seismic reflection profiles, thus roughly orthogonal to the main strike of the buried thrusts. We then used the inverse trishear approach to determine the slip necessary to recover the residual tectonic deformation (after decompaction) of four stratigraphic horizons with well-constrained age determinations (Zanclean to Middle Pleistocene). We then calculated and reported the slip rates using probability density functions, considering the uncertainties associated with both horizon ages and the restoration process. All together, our results show a progressive reduction of slip rates over time, with a main slowdown around 1.5 Ma. Reporting slip rates with probabilistic distributions is useful for incorporating epistemic uncertainty on the total seismic moment release in earthquake hazard analyses.

How to cite: De Matteo, A., Barrera, D., Maesano, F., Toscani, G., Seno, S., and Basili, R.: Probabilistic Assessment of Slip Rates Over Time of OffshoreBuried Thrusts: A Case Study in the Central Adriatic Sea(Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2612, https://doi.org/10.5194/egusphere-egu24-2612, 2024.

EGU24-3071 | Posters on site | TS3.2

Virtual outcrop models of geological structures: problems and best practices related to extraction of 3D structural data 

Amerigo Corradetti, Stefano Tavani, Marco Mercuri, Lorenzo Bonini, and Thomas Seers

The advancement of computer vision–based photogrammetric image processing pipelines, particularly Structure from Motion–Multi-View Stereophotogrammetry (SfM-MVS), has rapidly evolved. This evolution, coupled with the accessibility of low-cost and portable acquisition tools such as DSLR and mirrorless cameras, Uncrewed Aerial Vehicles (UAVs) and smartphones, has transformed outcrop studies in structural geology, propelling traditional field geology into the digital era. Notably, this revolution has significantly impacted Virtual Outcrop Models (VOMs), elevating them from mere visualization media to fully interrogable quantitative objects. 

Among the various applications of VOMs in structural geology, the extraction of near-planar features, including fracture and bedding surfaces, stands out as crucial. Numerous procedures exist for this purpose, ranging from fully automated segmentation and best-fitting of point clouds to the manual picking of 3D traces on both point clouds and textured meshes.

In this work, we explore the advantages, disadvantages, best practices, and drawbacks associated with the principal procedures for extracting near-planar geological data from VOMs. While automated or supervised recognition and subsequent best-fitting of coplanar patches in point clouds have garnered significant attention, their application is generally limited to specific case studies. Geological outcrops commonly lack patches of sufficiently large near planar surfaces for robust best fitting, necessitating manual picking procedures based on visual and/or structural interpretation. In such cases, the use of textured meshes is preferred over point clouds, and consideration must be given to the accuracy of the textured mesh during digitization, as well as the intrinsic roughness of geological surfaces. 

The analysis of coplanarity and collinearity of picked point sets aids in identifying traces deviating from idealized configurations. However, commonly suggested threshold values often result in small datasets. Nevertheless, relying on the visual inspection of the best-fit plane and real-time computation of best-fit planes from picked point sets generally yields acceptable results, handling coplanarity and collinearity dynamically during the extraction process.

How to cite: Corradetti, A., Tavani, S., Mercuri, M., Bonini, L., and Seers, T.: Virtual outcrop models of geological structures: problems and best practices related to extraction of 3D structural data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3071, https://doi.org/10.5194/egusphere-egu24-3071, 2024.

EGU24-3277 | ECS | Posters on site | TS3.2

Impact of outer-rise slab hydration on the intermediate-depth seismicity: Evidence from near field OBS observation in the southernmost Mariana subduction zone 

Han Chen, Gauhua Zhu, Hongfeng Yang, Shaoping Lu, Chuanxu Chen, and Jian Lin

Intermediate-depth earthquakes (IDEs), i.e., earthquakes at depths of 70 to 300 km, have been observed in subduction zones globally and extensively investigated. However, the seismogenic mechanism of IDEs is still controversial, especially in the southern end of the Mariana Trench, where near-field observations are lacking. By using machine-learning-based methods in three sets of near-field Ocean Bottom Seismogram (OBS) network data, we detected and located more than 1,000 intraplate and interplate earthquakes. The seismogenic volumes in different regions of the subducted plate are different, showing the character of double seismogenic zones (DSZ) and single seismicity layer (SSZ). The seismicity features coincide well with the regional landform, development of outer-rise faults, and hydration scenarios, suggesting a dehydration-related mechanism for the generation of IDEs. The subducted slabs experience different degrees of slab hydration, leading to various seismic behaviors.

How to cite: Chen, H., Zhu, G., Yang, H., Lu, S., Chen, C., and Lin, J.: Impact of outer-rise slab hydration on the intermediate-depth seismicity: Evidence from near field OBS observation in the southernmost Mariana subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3277, https://doi.org/10.5194/egusphere-egu24-3277, 2024.

EGU24-4320 | ECS | Orals | TS3.2

Relationships between seismicity and geological structures at the hanging-wall of a low-angle normal fault (Alto-Tiberina fault system, Northern Apennines of Italy). 

Federica Riva, Simone Marzorati, Nicola Piana Agostinetti, Elham Safarzadeh, Diana Latorre, Lauro Chiaraluce, and Massimiliano Rinaldo Barchi

One of the most seismically active areas in Central Italy is located within the Pre-Apennine Umbria region, between the Tiber Valley, the town of Gubbio and the main mountain ridge of the Umbria-Marche Apennines. The fault system that characterizes this region is dominated by a 60 km long low-angle normal fault (Alto Tiberina, ATF), active since the Late Pliocene-Early Pleistocene. This area is mainly monitored and studied though the Alto Tiberina Near Fault Observatory (TABOO-NFO), a multidisciplinary monitoring infrastructure composed of dense arrays of seismic, geodetic, strain , geochemical and electromagnetic sensors deployed both at the surface and on boreholes. This infrastructure is fundamental to investigate the principal geophysical and geochemical processes occurring in this complex geological area (https://www.ont.ingv.it/infrastrutture-di-ricerca/sismologia/taboo). Besides the high rate of micro-seismicity nucleating along the ATF (ML<3.0), there is also a considerable number of synthetic and antithetic faults (e.g., Gubbio Fault, GuF) located in the hanging-wall of the ATF that produced historical and most recent earthquakes of moderate magnitude (e.g., MW 5.1 1984 Gubbio earthquake).

Our study focuses on the most recent seismic sequences, occurred in this area between 2010 and 2023, that produced main shocks of magnitude > 3 (Mw= 3.6 - Pietralunga 2010, Mw= 3.6 - Città di Castello 2013, Mw = 3.9 - Gubbio 2021, Mw = 4.5 - Umbertide 2023).

These seismic events have been registered, located and published in the Database of the Central Eastern Italy by the INGV office in Ancona (https://doi.org/10.13127/resiico/eqs). From these data, all the considered sequences are characterised by dominant normal fault kinematics, coherent with the regional SW-NE active extension. Moreover, they occurred at relatively shallow depth (< 7 km), at the hanging-wall of the ATF, and their location cannot be directly referred to any extensional fault, mapped in the studied area. The aim of our work is to investigate the potential relationship between the cited 2010-2023 seismic sequences and the occurrence of still unknown causative minor faults, at the hanging-wall of ATF. To reach the goal, we propose a revised detailed interpretation of a set of 2D-seismic reflection profiles, calibrated by few deep boreholes, acquired in the 80s for hydrocarbon exploration purposes. Previous studies of these data have been focussed on the ATF and on its major antithetic splay, i.e. the SW-dipping Gubbio normal fault. In this study, we want to explore the presence of other, synthetic and/or antithetic splays, visible at the seismic scale and possibly connected with the 2010-2023 seismic sequences. In order to improve the comparison between the geological structure at depth and the seismicity distribution, we decided to relocate the 2010-2023 catalogue of seismicity for the study area, following two innovative strategies: a 3D velocity model created on purpose for the ATF area and a Markov chain Monte Carlo algorithm for events location.

By combining interpretation of active seismic data with innovative strategies of earthquake re-location, our study proposes as a pivotal experience for seismo-tectonic interpretation of low-magnitude seismic sequences.

How to cite: Riva, F., Marzorati, S., Piana Agostinetti, N., Safarzadeh, E., Latorre, D., Chiaraluce, L., and Barchi, M. R.: Relationships between seismicity and geological structures at the hanging-wall of a low-angle normal fault (Alto-Tiberina fault system, Northern Apennines of Italy)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4320, https://doi.org/10.5194/egusphere-egu24-4320, 2024.

EGU24-6030 | ECS | Orals | TS3.2

Geological and Seismotectonic Analysis of the area struck by the November 2022 Mw 5.5 Offshore Pesaro Earthquake (Northern Adriatic Sea Region, Italy).  

Elham Safarzadeh, Massimiliano Rinaldo Barchi, Assel Akimbekova, and Francesco Mirabella

On the 9th of November 2022, a Mw 5.5 earthquake occurred near the Northern Adriatic coast, between Ancona and Pesaro (Marche region, Italy), as part of a complex seismic sequence, including six M>4 events, with NW-SE striking thrust fault focal mechanisms. This study is aimed at reconstructing the subsurface geological setting of the area struck by the seismic sequence, focusing on the active thrusts responsible for the observed seismicity. We interpreted previously unpublished 2D seismic reflection profiles integrating with deep wells, covering approximately 1500 km2.

We analysed the stratigraphic and geophysical log data from eight deep wells. This analysis defined the local stratigraphy, comprising a Late Triassic-Paleogene multilayer of evaporites, carbonates and Tertiary marls, overlain by Pliocene-Quaternary syn-tectonic clastic sediments. Wells data were used to calibrate the strong reflections recognized along the 2D seismic profiles. These profiles include six cross-lines (i.e. SW-NE), connected by three strike-lines (i.e. NW-SE).

Five key-horizons were distinguished: Top Pleistocene unconformity, Base of Pliocene -Pleistocene unconformity, Top of Middle Pliocene, Top of Messinian, and Top of Oligocene. The Messinian's prominent reflection, specifically, played a pivotal role in interpreting and identifying these horizons. These stratigraphic markers are cut and displaced at depth by two major thrust-fault segments, affecting the Mesozoic-Cenozoic carbonate succession.  Along-strike geometry of these major, SW gently dipping thrusts has been identified across four seismic reflection profiles, along a distance of about 24 km. A set of more complex, shallower thrusts, affecting the Tertiary marls and the overlying, syn-tectonic clastic sediments, splays out from these major structures. Time to depth-converted structures were derived by establishing a proper velocity model based on both local and regional log data. The location and depth of the seismic events were plotted along the depth-converted seismic profiles, demonstrating a good correlation with the geometry and kinematics of the deep thrust-fault segments. The interpretation of the deformation observed in the overlying strata suggests a strong Pliocene-Pleistocene contractional phase, up to the end of the Early Pleistocene. In recent times, the increased sedimentation rate masks the continuing tectonic activity.

This study contributes to a deeper understanding of the location, geometry, and kinematics of potentially active buried faults, sheding light on the seismotectonic setting of the study area, leading to a better understanding of the geological structure of the active external thrust in the Northern Adriatic region. The study contributes not only to a better knowledge of the seismotectonic setting of the region, but also plays an important role in formulating effective strategies for seismic hazard assessment and regional seismic risk management.

How to cite: Safarzadeh, E., Barchi, M. R., Akimbekova, A., and Mirabella, F.: Geological and Seismotectonic Analysis of the area struck by the November 2022 Mw 5.5 Offshore Pesaro Earthquake (Northern Adriatic Sea Region, Italy). , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6030, https://doi.org/10.5194/egusphere-egu24-6030, 2024.

EGU24-7352 | Orals | TS3.2

Subduction thermal structure and megathrust earthquakes under the Mariana arc 

Yingfeng Ji, Rui Qu, and Weiling Zhu

Due to the steep subduction of a highly concave slab, researchers have characterized megathrusts under the Marianas as among the coldest and curviest plate coupling interfaces in various circum-Pacific subduction zones. Seismic tomography indicates that the heterogeneous underlying plate varies markedly in its subduction angle, velocity, and flexure along the strike and dip, while their effects on the thermal structure and intraslab earthquake occurrence remain enigmatic. By incorporating the 3-D MORVEL velocity and state-of-the-art slab geometry into thermomechanical modeling, we estimated the 3-D subduction thermal state and hydrothermal regime below the Marianas. We find that (1) the concave slab geometry and the complexity of the intraslab velocity variation in the Marianas are associated with a heterogeneous along-strike thermal regime and a cold mantle wedge beneath the central Marianas; (2) amphibolitization and eclogitization of subducted oceanic crust cause variations in fluid pressure and fluid release from the subduction interface, which may influence the distribution of interface seismicity in the Mariana system; (3) the concentration of active hydrothermal vents in the trench > 8 km deep is accompanied by a large temperature gradient and subsequent remarkable slab dehydration in the southern Marianas; and (4) slab dehydration (> 0.02 wt%/km) from 30 to 80 km indicates notable fluid release and potential fluid migration in subduction channels, which may correspond to the large water flux at depth beneath the Marianas.

How to cite: Ji, Y., Qu, R., and Zhu, W.: Subduction thermal structure and megathrust earthquakes under the Mariana arc, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7352, https://doi.org/10.5194/egusphere-egu24-7352, 2024.

EGU24-7886 | Posters on site | TS3.2

Predicting the fault beneath a newly-created earthquake-related landform: A case study of Leader Fault rupture during the 2016 Kaikōura Earthquake, New Zealand 

David Tanner, Christian Brandes, Andy Nicol, Jan Igel, Sumiko Tsukamoto, and Julia Rudmann

In outcrops, the hanging-wall and/or footwall structure around a fault are often exposed, while the underlying fault is poorly resolved. In these cases, it is desirable to estimate the location and shape of the fault at depth, especially if it belongs to an active fault system prone to large earthquakes. The Mw 7.8 Kaikōura earthquake occurred two minutes after midnight on 14th November 2016, causing at least 17 faults in the northeast South Island of New Zealand to rupture, including a number of faults that had not been previously mapped. One of these smaller new faults is the Leader Fault, which at the surface displaces Mesozoic interbedded greywacke and argillite. In outcrop, the fault rupture caused an over 3 m high, 20-30 m wide, and over 120 m long hanging-wall fold to appear at the surface.

In September 2022, we used a differential global navigation satellite system to map the topography of the fold. We collected a total of 1493 points over a map area of 4526 m², i.e. an average point density of ca. 1 point per 3 m². The data were meshed into a three-dimensional triangular surface, which was then sectioned into ten cross-sections, each 10 m apart and perpendicular to the fold axes. We present fault-prediction modelling of two of these sections. In the Movetm software (Petroleum Experts), we used two methods of fault prediction; constant heave and constant slip. Both methods require implicit information about the hanging-wall shape, the position of the fault at the surface and the “regional”, i.e. the position of the hanging wall before deformation. Before the modelling, all this information was known apriori; i.e. we mapped the shape of the ground surface, we knew the fault to outcrop at the break of slope at the front of the leading edge, and the regional is an extension of the undeformed footwall. Both modelling techniques require a seed, i.e., a small portion of fault at the surface with a certain angle of dip. We use a horizontal and a 60° dipping seed.

We can estimate the fault geometry down to a depth of 20-25 m. For both sections, we predict the fault is steep, greater than 60°. Using a flat seed gives a slightly listric fault geometry, but in any case, the fault is steep down to 20 m depth before flattening out slightly. Compared to a small (15 cm) outcrop of the fault plane (dipping 75° WNW) at the surface at the northern end of the outcrop, the best matches are given by modelling with constant slip. The steep fault geometry is governed by the basement rock that has steep bedding that also dips ca. 70° WNW.

How to cite: Tanner, D., Brandes, C., Nicol, A., Igel, J., Tsukamoto, S., and Rudmann, J.: Predicting the fault beneath a newly-created earthquake-related landform: A case study of Leader Fault rupture during the 2016 Kaikōura Earthquake, New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7886, https://doi.org/10.5194/egusphere-egu24-7886, 2024.

EGU24-9421 | ECS | Posters on site | TS3.2

Active deformation in Tunisia from GNSS measurements 

Hamza Kristou, Frédéric Masson, Néjib Bahrouni, Mustapha Meghraoui, and Patrice Ulrich

Tunisia lies at the centre of the East-West trending convergence zone between the Nubian and Eurasian plates, at the eastern end of the large tectonic structures of the Atlas and Tell mountains and to the west of the Pelagian block and Sicily. As a result, its complex tectonics along the plate boundary show N-S to NW-SE oblique convergence expressed by E-W- to WNW-ESE-trending right-lateral strike-slip faults associated with E-W- to NE-SW-trending thrust faults that affect the Neogene and Quaternary units of the Tell and Sahara Atlas of Tunisia.

Although this region is generally characterized by moderate seismicity, it is known for its historical and instrumental seismic activity that has resulted in human and materiel losses, such as in Utique 408 AD, Kairouan 859 AD, Tozer 1997 and recently in March 2018 an earthquake felt between Tunis and Bizerte and in April 2023 an earthquake felt in Metlaoui, both earthquakes registered (Mw 5).

A partnership between the National Office of Mines ONM-Tunisia and ITES-Strasbourg is being set up to develop spatial geodesy work using GNSS measurements to characterize and quantify the active deformation of Tunisia alongside previous tectonic and seismotectonic works.

A network of already existing 21 GNSS stations spread over the Tunisian territory is managed by OTC (Office of topography and cadaster) so in the framework of this project 6 days/year of records from 2012 to 2019 has been purchased.

To improve the resolution of the acquired data and fill the gaps between the OTC stations, a national network consisting of 24 mobile stations is set up and three campaigns of 3 days of records in 2019, 2021 and 2023 have already been carried out.

Between 2022 and 2023, five more permanent stations have been installed to provide a continuous flow of data.

Two target areas, Gafsa and Kairouan have been chosen to install regional networks consisting of 16 sites each around active faults. Three campaigns in 2021, 2022 and 2023 have been carried out and one more is planned in 2024 to detect the deformation in those areas.

All these data allowed the calculation of a precise velocity field of Tunisia based on GPS trends and the establishment of the strain rate distribution across continental Tunisia. These new data will be analyzed in the light of existing knowledge, in particular the recent seismotectonic and paleoseismological work carried out as part of our project.

How to cite: Kristou, H., Masson, F., Bahrouni, N., Meghraoui, M., and Ulrich, P.: Active deformation in Tunisia from GNSS measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9421, https://doi.org/10.5194/egusphere-egu24-9421, 2024.

The 2007 Mw8.4 southern Sumatra earthquake provides an opportunity to understand the rheological properties in the southern Sumatra, particularly in the Mentawai gap. In this study, we have derived the first 3-year GPS postseismic observations to study deformation processes based on a three-dimensional viscoelastic finite element model. In the model, a 2-km-thick shear zone attached to the fault is used to simulate the time-dependent and stress-driven afterslip. Model results indicate that a model with a heterogenous shear zone better fits the horizontal GPS observations than a model with a uniform shear zone. This heterogenous shear zone is divided into the southern shear zone and northern shear zone (Mentawai gap), which is separated by the southern edge of the Mentawai gap. The southern shear zone is further divided into an upper (depths of ≤ 20 km) and lower shear zone (depths of > 20 km). The viscosities in these three shear zones are determined to be 5 x 1017 Pa s, 1016 Pa s and 1018 Pa s, respectively. Model results indicate that a weakened mantle wedge is required to better explain the observed uplift in vicinities of the rupture area.

How to cite: Yang, S. and Yan, H.: Rheological structure beneath the southern Sumatra constrained from postseismic deformation of the 2007 Mw8.4 Sumatra earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11015, https://doi.org/10.5194/egusphere-egu24-11015, 2024.

EGU24-11125 | ECS | Orals | TS3.2

Seismological evidence for a multi-fault network at the Ecuadorian subduction interface 

Caroline Chalumeau, Hans Agurto-Detzel, Andreas Rietbrock, Michael Frietsch, Onno Oncken, Monica Segovia, and Audrey Galve

The simplified view of the subduction interface is that of a single plane along which seismic and aseismic deformation occurs. In reality, however, exhumed subduction zones and geophysical imaging have shown that the seismogenic plate interface is a deformed, 100m-1km thick tabular region. Within this region, we currently do not know if seismic slip is localized on a single fault or distributed over several active faults, and how this impacts seismogenesis and the timing of deformation. Here, we use high-resolution earthquake locations to shed light on these questions.

We focus on the aftershock sequence of the March 27th 2022, Mw 5.8 Esmeraldas earthquake which occurred at 19 km depth at the plate interface in Ecuador, and which was recorded by the dense temporary seismic network deployed during the HIPER2 marine campaign. We use machine learning to detect and pick over 1700 earthquakes (Mw 0-3), which we then locate using a double difference algorithm with cross-correlation times and a 3D velocity model. This allows us to obtain an exceptionally detailed image of the seismicity at the plate interface, which falls into a 200-400 m thick zone, comparable to plate interface thicknesses observed in exhumed subduction zones. Using a cross-correlation threshold of 0.75, we extract families of similar earthquakes, whose geometry we investigate using the 3-point method. These families generally occur on subparallel, sometimes superposed planes with a thickness of 0-40 m that is comparable to the thickness of individual fault zones observed within fossil subduction shear zones. These individual fault zones appear to form a network whose geometry impacts the aftershock expansion, itself controlled by afterslip rather than diffusive processes, thus demonstrating the importance of considering the 3D structure of the plate interface when modeling slip.

How to cite: Chalumeau, C., Agurto-Detzel, H., Rietbrock, A., Frietsch, M., Oncken, O., Segovia, M., and Galve, A.: Seismological evidence for a multi-fault network at the Ecuadorian subduction interface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11125, https://doi.org/10.5194/egusphere-egu24-11125, 2024.

The Indo-Burma subduction zone (IBSZ) is an entirely subaerial plate boundary, where the Indian plate obliquely converges with the Burma microplate. Because the incoming plate includes the 16-20 km thick sediment of the Ganges-Brahmaputra Delta, the accretionary prism is over 250 km wide with numerous active splay thrust faults and strike slip faults. Accurately assessing the long- and short-term dynamics of this complex region is critical for determining its earthquake hazard.

However, due in part to insufficient geodetic observations in the region to constrain the 3D shape of the megathrust and upper plate deformation, the kinematics of this plate boundary zone remain controversial. Ongoing debates focus on how strain is partitioned between the megathrust and strike-slip and oblique faults, whether the subduction zone is locked, and whether the multiple anticlines of the accretionary prism foldbelt are locked or actively deforming aseismically.

In this study, we present the first large-scale Interferometric Synthetic Aperture Radar (InSAR) velocity field over the IBSZ. Considering the operational nature and radar characteristics of different satellites, we processed datasets of multiple satellites spanning from late 2014 to 2023, including Sentinel-1, ALOS-2, and the newly launched L-Band differential InSAR satellite of China, LuTan-1. This approach allows us to more accurately constrain deformation across such a heavily vegetated and topographically-varied region. We incorporated updated horizontal and vertical GNSS velocities from 60 sites obtained from 2003 to 2023 to derive a three-dimensional decomposed velocity field, and then we investigated faults activities by estimating interseismic strain rates across the IBSZ. Our preliminary results reveal how strain is distributed in the region, shedding light on seismic hazard across this densely populated area.

How to cite: Shen, L., Steckler, M., Lindsey, E., Oryan, B., and Chong, J. H.: Large-scale geodetic deformation measurements of the Indo-Burma Subduction Zone from multi-sensor InSAR and GNSS: implications for strain partitioning and earthquake hazard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11641, https://doi.org/10.5194/egusphere-egu24-11641, 2024.

EGU24-12143 | ECS | Orals | TS3.2

Seismotectonics of the Southwestern Swiss Alps – Revisiting Faults, Earthquakes, and Crustal Stresses 

Sandro Truttmann, Tobias Diehl, Giovanni Luca Cardello, and Marco Herwegh

The Alps are a dynamic orogen, as evidenced by recent crustal uplift and seismic activity. Earthquakes are primarily occurring along the many pre-existing Neogene faults formed during the Alpine orogeny, making it challenging to predict which faults are being reactivated. Limited geophysical data, low strain rates, high erosion rates, and widespread faulting complicate the detection of active faults in low-strain regions. Currently there is a lack of knowledge about the abundance, architecture, and properties of active faults in the Alps, which is however critical for evaluating the regional seismic hazard.

This study adopts an interdisciplinary approach to identify and characterize active faults in the Rawil depression and surrounding areas north of the Rhône-Simplon fault system, located in the southwestern Swiss Alps. A comprehensive seismotectonic description of the region is achieved by combining information from recent high-precision earthquake catalogs derived from relative relocations covering about 40 years, new fault maps using remote sensing and field surveys, updated stress inversion from extended focal mechanism catalogs and paleostress inversion from fault slip data, as well as GNSS data. Results from 3D imaging of active faults at depth, based on the high-precision hypocenter catalogs, reveal that subvertical faults, striking E-W, host most of the present-day earthquakes in the region. This imaging also uncovers previously unknown NW-SE striking active faults potentially contributing to the overall strain distribution in this part of the Alps. Compared to principal stress orientations in the upper crust derived from focal mechanisms, faults striking in both E-W and NW-SE directions appear to be optimally oriented for reactivation in the current stress field. Recent crustal stresses, consistent with the results obtained from paleostress inversion indicating NE/SW-directed transtension, suggest a relatively constant stress regime over the last couple of million years. This implies similarities between exhumed and seismically active faults at depth. The agreement between fault geometries exhumed at the surface and reconstructions of active faults at depth, as determined by hypocenter-based 3D imaging of active faults, support these findings. In conclusion, our study demonstrates that such interdisciplinary studies provide valuable insights into the deformation processes in tectonically active regions, contributing to refined seismic hazard assessments.

How to cite: Truttmann, S., Diehl, T., Cardello, G. L., and Herwegh, M.: Seismotectonics of the Southwestern Swiss Alps – Revisiting Faults, Earthquakes, and Crustal Stresses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12143, https://doi.org/10.5194/egusphere-egu24-12143, 2024.

EGU24-12240 | ECS | Posters on site | TS3.2

Unveiling subduction-related seismicity: towards a new global database 

Silvia Brizzi, Arnauld Heuret, Claudia Piromallo, Fabio Corbi, Francesca Funiciello, and Serge Lallemand

Subduction zones host the world’s largest earthquakes. Recent studies suggest complex interactions between megathrust, upper plate and intraslab seismicity. Understanding the spatio-temporal relationships of seismicity within subduction zones is challenging, yet essential for accurate seismic hazard assessment. A prerequisite for conducting these analyses involves the availability of a reliable and readily updatable dataset that classifies subduction seismicity into the three categories above.

In this work, we compile a comprehensive global database of subduction-related earthquakes from 1976 to 2023, using the ISC-GEM catalog (Storchak et al., 2013; 2015; Di Giacomo et al., 2018) for events with magnitude Mw ≥ 5.5. Building on Heuret et al. (2011), we define 505 trench-normal transects across all active subduction zones, spaced at 1-degree intervals along the trench, partially overlapping and extending 120 km on both sides of a vertical plane. The seismicity in each transect is initially categorized into shallow (≤ 70 km) and deep (> 70 km) events. We then focus on the megathrust region, identifying earthquakes exhibiting a thrust focal mechanism with the  azimuth and dip of the focal planes aligning with the strike and dip of the megathrust along the transect. Subsequent steps involve categorizing the remaining earthquakes in the transect as either upper or subducting plate events. The classification uses the Slab 2.0 model (Hayes et al. 2018) when available, determining whether each earthquake occurs above or below the slab top surface.  In regions lacking Slab 2.0 data, geometric criteria are applied, considering the distance of the hypocenter to the trench. For each transect, this workflow yields three distinct seismicity classes: megathrust, upper plate, and intraslab earthquakes. Subsequently, seismicity from individual transects is merged into 62 broader segments (Heuret et al., 2011), ensuring the uniqueness of earthquakes in each segment.

This automated workflow ensures the application of objective classification criteria and facilitates efficient analyses with each update of the ISC-GEM catalog. We compare key seismic parameters (e.g., maximum magnitude, number of events, cumulated seismic moment, recurrence time) across the different categories and segments. Additionally, we evaluate the correlation with a wide range of geological, geophysical, and geodynamical factors. This process not only provides an overview of the global behavior of subduction-related seismicity but also allows for the statistical identification of the combination of factors influencing subduction seismicity.



How to cite: Brizzi, S., Heuret, A., Piromallo, C., Corbi, F., Funiciello, F., and Lallemand, S.: Unveiling subduction-related seismicity: towards a new global database, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12240, https://doi.org/10.5194/egusphere-egu24-12240, 2024.

EGU24-13263 | Posters on site | TS3.2

Fault pattern and kinematics at the Tyrrhenian-Ionian transition zone (northern Messina Strait) 

Alessia Conti, Marco Cuffaro, Eleonora Ficini, Patrizio Petricca, Andrea Billi, Alessandro Bosman, Valentina Ferrante, Filippo Muccini, Valentina Romano, Marco Ligi, Carlo Doglioni, and Sabina Bigi

The Messina Strait and surrounding areas are one of the most interesting regions of the western Mediterranean Sea, characterized by the complex interplay between the Mesozoic-Paleogene Ionian basin, where the Calabrian Arc accretionary prism extends towards the southeast, and the Neogene Tyrrhenian back-arc basin to the northwest.

Complex fault networks with different kinematics, running from the inner side of the Calabrian arc through the Messina Strait and the Ionian coast of Sicily, as far as the Hyblean Plateau, result from the coexistence of different geodynamic settings in the area. Some of these faults are responsible for several of the largest earthquakes occurred in southern Italy and the Mediterranean Sea in recent times. Different works aimed at establishing a relationship between seismogenic sources and mapped faults, defining the location and rupture mechanism of some of these fault lineaments. Even tough, many uncertainties still exist for earthquakes occurred in offshore areas, where the fault kinematics and geometry are in some cases still poorly constrained.

In this work, we focus on a group of offshore faults located between the northern sector of the Messina Strait and the Gioia Basin (southern Tyrrhenian Sea). We aim at understanding the kinematics and the style of deformation in this area, and to investigate the role played by the main fault networks in the framework of the regional complex geodynamic setting of the Ionian-Tyrrhenian transition zone. This study is based on the interpretation of a multichannel seismic dataset (TIR10 survey), combined with the analysis of morpho-bathymetric and geodetic data, and with numerical modeling. This multidisciplinary and multiscale approach can contribute to unravel the particular role of this region in the context of a stepwise migrating subduction system and provides new constrains for the study of this highly populated area characterized by severe seismic and tsunamigenic hazard.

How to cite: Conti, A., Cuffaro, M., Ficini, E., Petricca, P., Billi, A., Bosman, A., Ferrante, V., Muccini, F., Romano, V., Ligi, M., Doglioni, C., and Bigi, S.: Fault pattern and kinematics at the Tyrrhenian-Ionian transition zone (northern Messina Strait), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13263, https://doi.org/10.5194/egusphere-egu24-13263, 2024.

EGU24-13305 | Posters on site | TS3.2

Retracing the Africa-Eurasia convergent boundary in the western Mediterranean based on seismic, geodetic and tectonic data 

Marco Cuffaro, Andrea Billi, Barbara Orecchio, Mimmo Palano, Debora Presti, and Cristina Totaro

In the western Mediterranean, the subduction of the Tethyan ocean has progressively come to an end, following the intervening continent-continent collision. Compressional deformation connected with the ongoing Africa (AF) – Eurasia (EU) convergence has therefore progressively resumed mostly along the southern passive margins of the Mediterranean back-arc basins. The use of geodetic, seismological, and pre-existing tectonic data recorded between the Gulf of Cadiz and the Ionian Sea helps to trace this nascent AF-EU boundary and constrain its kinematics. Based on these data, this plate boundary is detected, kinematically defined, and compared with the previously identified boundaries in the same region. The nascent boundary is articulated and formed by variably oriented inherited structures. It is characterized by a discrepancy between the general motion of Africa with respect to Eurasia and the local contractional/compressive axes deduced from geodetic and seismic data. The oblique convergence along the nascent boundary matches that recorded in other instances of subduction initiation elsewhere, but the average convergence rate equal to 5 mm/yr in the Mediterranean seems currently too small for such a subduction initiation. Based on the assumption of a future northward tectonic vergence (i.e., Eurasian foreland), the Tyrrhenian, Algerian, and Betic salients, the Oran and Fès recesses, and the Ionian, Trans-Alboran, and Gibraltar transfer zones are identified along the nascent boundary. The latter zones connect salients and recesses through strike-slip displacements. The Algerian offshore hosts a long segment of the boundary characterized by locally increased seismic rate and actual northward vergence that would suggest this area being the first nucleus of subduction initiation in the western Mediterranean.

How to cite: Cuffaro, M., Billi, A., Orecchio, B., Palano, M., Presti, D., and Totaro, C.: Retracing the Africa-Eurasia convergent boundary in the western Mediterranean based on seismic, geodetic and tectonic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13305, https://doi.org/10.5194/egusphere-egu24-13305, 2024.

EGU24-13308 | ECS | Posters on site | TS3.2

Present-day crustal deformation of the Caucasus and Northern Iran constrained by InSAR time series   

Zaur Bayramov, Renier Viltres, Cecile Doubre, Alessia Maggi, Frederic Masson, Behzad Zamani, and Marie-Pierre Doin

The Caucasus and Northern Iran lie within the central part of the Alpine-Himalayan belt, where the Arabian and Eurasian plates started colliding over 100 My ago and caused the building of mountain chains associated with complex tectonics, including transform faulting systems. The region contains many tectonic features including the EW-trending Greater Caucasus and the NW-trending Lesser Caucasus thrust belt separated by the Kura basin. In the southern part of the region, the tectonics are complicated by the Anatolia-Eurasia-Arabia triple junction and the northern end of the Talysh and Alborz thrust belts. There have been several destructive earthquakes in the region, including the Shamakhi earthquake sequences in 1667(8) and 1902 at the junction of the controversial and mostly a-seismic West-Caspian Fault and the Eastern Greater Caucasus and the 1721 and 1780 earthquakes on the North Tabriz fault in NW Iran. 

Investigations of the few publicly available seismic catalogs of the region have been insufficient to understand the seismo-tectonic behavior of the regional structures due to sparse existing seismic networks. To better characterize the active structures in the Caucasus and  Northern Iran we produced  regional-scale mean line-of-sight velocity maps and time-series of the surface displacement from the north-eastern Caucasus to northern Iran. To obtain this dataset we performed Synthetic Aperture Radar interferometry using the NSBAS processing (Doin et al., 2011) of Sentinel-1 images along both ascending and descending tracks for 9-years (2015 to 2023). Main processing steps (such as atmospheric correction, multilooking and filtering) were applied to counter biases and loss of coherence due to the snow and vegetation coverage in the Greater Caucasus mountains. We produced two regional-scale interseismic velocity maps that highlight crustal motions of the large-scale tectonic structures. Moreover, we have identified coseismic deformation due to the 5.2 ml Shamakhi earthquake in the SE Caucasus mountains (Feb. 2019), the 5.9 Mw Torkamanchay earthquake in the Bozgush mountains of NW Iran (Nov. 2019), and possible aseismic strike-slip along the West Caspian fault after the large seismic events in Türkiye in February, 2023. Our results can also be used to study the local deformation of mud volcanoes in the Eastern part of Azerbaijan.

How to cite: Bayramov, Z., Viltres, R., Doubre, C., Maggi, A., Masson, F., Zamani, B., and Doin, M.-P.: Present-day crustal deformation of the Caucasus and Northern Iran constrained by InSAR time series  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13308, https://doi.org/10.5194/egusphere-egu24-13308, 2024.

EGU24-14378 | Posters on site | TS3.2

Shallow geological structure by applying H/V method in volcanic area in northern Taiwan 

Chia-Han Tseng, Po-Yu Chu, Cheng-Feng Wu, and Ruei-Juin Rau

The Taiwan Island is the product of the orogeny resulting from the collision of the two tectonic plates, the Eurasia Continent Plate and the Philippine Sea Plate. The Philippine Sea Plate has subducted the Eurasia Continent Plate and formed Ryukyu Volcanic Arc in northern and northeastern Taiwan. The Datun Volcano Group (DVG) being located in northern Taiwan is the westernmost member of the Ryukyu Volcanic Arc and has the widest extent and largest eruption amount among the volcanic rock areas. About 1 Ma, compressional stress transformed into extensional stress in northern Taiwan, and magma from the depth erupted to form younger volcanoes (~20) in the same area. During this period, the Taipei Basin and the Jinshan Basin gradually formed as half grabens on a normal fault, namely the Shanjiao Fault.

The DVG and the Shanjiao Fault have been identified to be active for micro-earthquake activities and topographical features, respectively, revealed by dense and high-resolution surficial monitoring systems in the Datun Mountain area. However, owing to rugged landscape and dense vegetations, geological boreholes are few and shallow (10 to 20 meters) so that the underground geological structures in the Datun Mountain area are still unclear. In this study, microtremor cross the presumed fault trace of the Shanjiao Fault are recorded and analyzed by applying the horizontal-to-vertical (H/V) spectral ratio method, and the H/V spectrum is further decomposed into E-W and N-S components.

The H/V spectral ratio reveals different dominant frequency for different volcanic products. The results indicate that the stations on thin loose deposits (pyroclastic debris) underlying by lava flow (andesite) show the higher dominant frequency, and these stations are near crater, while the stations farther from the craters have lower dominant frequency with thick loose deposits. And these results are also consistent with the topography revealed by high-resolution digital terrain model of the Datun Mountain area.

Based on the results, the future work of this study will be describing spatial geometry of the Shanjiao Fault by distinguishing different dominant frequencies corresponding to the footwall and hanging wall.

How to cite: Tseng, C.-H., Chu, P.-Y., Wu, C.-F., and Rau, R.-J.: Shallow geological structure by applying H/V method in volcanic area in northern Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14378, https://doi.org/10.5194/egusphere-egu24-14378, 2024.

The seismicity in the back arc of the Mexican subduction zone is relatively low.  An exception to this is the seismic activity observed in the Isthmus of Tehuantepec, where shallow earthquakes take place mostly along the coast of the Gulf of Mexico.  The largest recorded earthquake occurred on 26 August 1959 (Mw 6.9).  Other moderate earthquakes are recorded also in the southeastern margin of the Gulf of Mexico with magnitudes ranging from 5.3 to 5.9.  Data from the VEOX experiment that registered seismic data continuously on a cross-section across the Isthmus of Tehuantepec were analyzed.  Shallow earthquakes were culled from the continuous records, eliminating events within the subducted slab.  A total of ~40 shallow earthquakes were identified.  The linear geometry of the VEOX array made it difficult to locate the earthquakes.  Thus, additional stations from the Seismological Service of Mexico were used in the analysis.  Hypocentral locations were improved using the double-difference hypocentral algorithm.  The focal mechanisms obtained show consistently reverse faulting, where the axes of maximum compression are oriented NE – SW, like the 1959 earthquake.  This indicates that the lithosphere is deformed by compressive stress oriented in the direction of relative plate motion.  The best-located earthquakes show focal depths ranging from 20 to 50 km.  The depth of the Moho in the Isthmus of Tehuantepec is well controlled by receiver function results.  Therefore, it is possible to identify where the earthquakes occur relative to the depth of the Moho.  Unlike most upper plate deformation in the back arc of the subduction zones, earthquakes in the Isthmus of Tehuantepec occur both in the crust and the upper mantle.    Rheological models suggest that shallow earthquakes occur mostly in the seismogenic part of the upper crust and the upper mantle.  Our observations clearly show that in this region earthquakes reflect lithospheric deformation involving the crust and the upper mantle.  We are currently exploring rheological models that may help explain earthquakes in both the crust and upper mantle. The focal mechanisms suggest that the deformation may be induced by the subduction of the aseismic Tehuantepec Ridge in the Mexican subduction zone.

How to cite: Suarez, G. and Aguilar, S.: Rheological Behaviour of  the Deformation of the Back Arc in the Isthmus of Tehuantepec in South-eastern Mexico, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14489, https://doi.org/10.5194/egusphere-egu24-14489, 2024.

EGU24-15223 | ECS | Posters on site | TS3.2

Local scale of ground deformation along faults in area and vicinity of one possible Einstein Telescope location 

Karolina Owczarz, Romy Schlögel, Anne Orban, and Hans-Balder Havenith

The Einstein Telescope area was a research site of a project called Ground Deformation from Meteorological, Seismic and Anthropogenic Changes Analyzed by Remote Sensing, Geomatic Experiments and Extended Reality (GERMANE), which aimed to analyze ground deformation hazards induced by meteorological changes and seismotectonic conditions in eastern Belgium, western Germany and the south-eastern Netherlands. Within the project we proposed and applied an approach based on various Synthetic Aperture Radar Interferometry (InSAR) processing methods to detect and measure ground motions in time series. We focused on the Persistent Scatterer Interferometry (PSI), Small Baseline Subset (SBAS)  and Parallel Small BAseline Subset (P-SBAS) methods. An important issue was that the current neotectonic activity in the target area was not well known, but through spatiotemporal analysis of ground deformation we investigated behavior along NW-SE trending normal faults, where karst also develops, as well as along Variscan  NE-SW trending thrust faults. Time series analyzes were performed along Gueule fault and Gulp fault, which cross the Einstein Telescope area in the Pays de Herve (Belgium) and Heerlerheide fault in the Roer Valley Graben (Germany). We calculated the relative double difference (RDD) of Line of Sight (LOS) displacements to estimate relative deformation of one point with respect to the other. Additionally, we detected regression lines with Bayesian information criterion (BIC) that enables to choose the model which represents better the set of data points corresponding to specific InSAR techniques in double difference. In results, annual velocity rates of the benchmarks extracted along the Gueule and Gulp faults were less than -2mm/yr – which are insignificant value. However, comparing the velocity values for the extracted benchmarks along the faults, it can be seen that the Gulp fault is characterized by slightly higher annual velocities than the Gueule fault. Our time series analyses results along the Heerlerheide fault indicated that its eastern face is uplifting with velocity rates of up to 8 mm/yr. The obtained InSAR results are very small and can be described as insignificant, therefore we cannot find increased seismic activity of the analysed faults, especially the Heerlerheide and Gueule ones, as old mining activity may be responsible for the observed deformation. In sum, the faults crossing the Einstein Telescope area do not show significant displacements, which confirms the initial hypothesis of their low seismotectonic activity. Therefore, we consider the possible Einstein Telescope location as being relatively stable.

How to cite: Owczarz, K., Schlögel, R., Orban, A., and Havenith, H.-B.: Local scale of ground deformation along faults in area and vicinity of one possible Einstein Telescope location, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15223, https://doi.org/10.5194/egusphere-egu24-15223, 2024.

EGU24-15633 | ECS | Orals | TS3.2

An integrated multi-proxy approach to characterize the southern part of the Al Idrissi strike-slip fault system, Alboran sea 

Léa Vidil, Elia d'Acremont, Sara Lafuerza, Laurent Emmanuel, Alain Rabaute, and Sylvie Leroy

In the Alboran Sea, oblique convergence between the African and Eurasian plates led to establishing the active Al Idrissi sinistral strike-slip fault system 1 Ma ago. Several moderate magnitude earthquakes (Mw > 6) have been recorded on different segments of this fault system.

The objective of this study is to analyse the dynamics of this nascent plate boundary by studying the seismic events recorded in sedimentary series. We focused on a key transtensive fault transect, namely the Bokkoya fault system, shifting the small Al Idrissi volcano. This fault has a lateral extent of 11km along strike. Sedimentation is strongly affected by the circulation of deep Mediterranean water masses resulting in contouritic deposits, and likely mass movement during seismic events.

We used a panel of geological, geophysical, geotechnical and geochemical tools acquired during the ALBACORE oceanographic campaign (R/V Pourquoi pas? 2021). This work is part of the ANR ALBANEO project, which aims to understand the dynamics of this new plate boundary and to assess the hazards in this area of the western Mediterranean Sea. The data analysed are derived from (i) 4 sediment calypso cores (ALB_CL26, ALB_CL54, ALB_CL53 and ALB_CL52) from 10m to 16m (analysed with a multi-sensor core logger – MSCL and X-Ray Fluorescence-XRF), (ii) piezocone tests (CPTU) with the Ifremer Penfeld as well as (iii) multibeam bathymetry data and (iv) seismic reflection/sub-bottom profiles. This multi-proxy dataset provided detailed lithological and geophysical stratigraphy, calibrated with the picked seismic horizons, and sediment cores dating along a transect perpendicular to the Bokkoya fault system.

Isotopic analysis of 3 cores provided 𝛿18O evolution curves, identifying a thermal anomaly in each of them, and in particular in the one penetrating the fault plane. Oxygen isotopic curves were calibrated using 14C radiocarbon analysis, enabling sedimentary series to be dated up to 40 ka. Accordingly dated, representing the first 16 m of sediment cores: the cold stadials, with the Younger Dryas; the Heinrich Stadials 1 and the Last Glacial Maximum. The sedimentation rate is about 30 cm/kyr in the depression zone whereas on either side of the contourite drift, it is about 20-25 cm/kyr.

The recognition of seismic events in the past is attempted by comparing sedimentary successions in different fault compartments. The active Bokkoya fault appears to offset the sedimentary series with a normal component and a vertical throw of 1 m, evaluated between the seabed and the dated YD reflector.

The results from the different datasets allow us to identify (1) syn-tectonic deposits that may be associated with past co-seismic events (2) intense erosional events that may be associated with localized water masses currents (3) a thermal anomaly whose origin is to be determined. This dataset highlights the complex interaction between tectonics and sedimentation/erosion along this segment of the Bokkoya fault over at least 60 ka.

How to cite: Vidil, L., d'Acremont, E., Lafuerza, S., Emmanuel, L., Rabaute, A., and Leroy, S.: An integrated multi-proxy approach to characterize the southern part of the Al Idrissi strike-slip fault system, Alboran sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15633, https://doi.org/10.5194/egusphere-egu24-15633, 2024.

EGU24-16945 | Orals | TS3.2

Interactions between deep seismicity and shallow deformation in the Japan trench and Chile subduction zones  

anne socquet, Audrey Chouli, Blandine Gardonio, Jorge Jara, Sophie Giffard Roisin, David Marsan, and Michel Bouchon

Recent great subduction earthquakes have been preceded by an accelerated rate of both interface seismicity along the megathrust and intermediate depth seismicity within the slab at ~100km depth (e.g. Bouchon et al., 2016, 2018), sometimes along with seismicity lineaments along dip over some hours (Bouchon et al., 2022, 2023). These may also be associated with large-scale gravity and mass changes in the subduction zone (Panet el al. 2018). Such interactions between deep and interface seismicity can last several years and can be associated with deformation within the upper plate (Durand et al., 2014; Jara et al. 2018, Rousset et al. 2023, Mitsui et al. 2021).

However such interactions between deep seismicity and shallow deformation have been observed only on rare occasions. In addition, assessing better how they relate to fluid transfer and slab force balance is key to improved understanding of the driving mechanisms of the plate interface destabilization.

Here we present some intriguing examples of interactions between intraslab seismicity and shallow deformation, and assess their statistical significance. We show that the occurrence of the Tohoku earthquake significantly changed the deep (>150km) seismicity rate, suggesting that this major megathrust event modified the slab equilibrium down to the lower mantle.

We also revisit the interactions between intermediate-depth and shallow seismicity in the Japan trench and the northern Chile subduction zone, during the decade preceding the Tohoku-oki (Mw 9.0, 2011) and Iquique (Mw 8.2, 2014) megathrust events. Cross correlations highlight different periods with significant interactions between intermediate-depth and shallow earthquakes, including the 8 months before the Tohoku-Oki megathrust in Japan, over which multiple bursts of ~7 days are synchronized. In Chile, the 4 months preceding the Iquique megathrust also show strong interactions, with successive bursts of ~4 days. Unlike some other periods, no stress transfer implied by Mw>6 earthquakes can explain the correlations observed before both megathrust events. Clustering of the seismicity allowed to identify along-dip lineament patterns. Their occurrence rate shows a significant increase when approaching the date of the megathrusts. If only a few are observed in Chile, the numerous lineaments downdip Tohoku highlight some structures along which lineaments concentrate. These elongated seismicity features seem to connect intermediate-depth and shallow seismicity and could be explained by fluid migrations.

How to cite: socquet, A., Chouli, A., Gardonio, B., Jara, J., Giffard Roisin, S., Marsan, D., and Bouchon, M.: Interactions between deep seismicity and shallow deformation in the Japan trench and Chile subduction zones , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16945, https://doi.org/10.5194/egusphere-egu24-16945, 2024.

EGU24-17556 | Posters on site | TS3.2

The active frontal sector of the offshore Northern Apennine thrust belt: insights from an interdisciplinary approach following the 2022 Mw 5.5 Costa Marchigiana Pesarese earthquake (Italy) 

Lorenzo Petracchini, Andrea Billi, Eugenio Carminati, Claudio Chiarabba, Alessia Conti, Roberto Devoti, Mimmo Palano, Giuseppe Pezzo, Laura Scognamiglio, Stefano Tavani, and Elisa Tinti

Identifying seismogenic faults in offshore regions presents significant challenges, particularly in achieving their precise geometry and kinematics. Geological data derived from deep-sea exploration and geophysical surveys are commonly used to characterize offshore active faults together with earthquake hypocentral locations. However, limitations may arise in the quantity and quality of geophysical available data, inhibiting the realization of accurate 3D models. Furthermore, the precise relocation of seismic events is demanding, especially in the depth domain, due to the limited azimuthal coverage and the minimum station-event distance that is well beyond the mean depth of the events. In this context, an interdisciplinary approach becomes imperative to mitigate over-interpretation and over-simplification in defining the seismogenic sources and establishing an all-encompassing rupture model.

By means of an interdisciplinary (geological, seismological, and geodetic) approach, we investigate the outermost Northern Apennines fold-and-thrust belt front in the Adriatic Sea (Italy) involved in the Costa Marchigiana Pesarese seismic sequence started with the 9 November 2022 Mw 5.5 mainshock. Given the proximity of the mainshock and the subsequent seismic sequence to the urbanized coastline, where several cities are situated, characterizing the activated faults and the related estimation of ground displacement becomes crucial for seismic risk assessment and the tsunamigenic potential.

We analysed the geological setting of the area by means of an accurate interpretation of numerous seismic reflection profiles and well data acquired over the past decades, which complemented the publicly available seismic data. The interpretation of this dataset, provided by oil companies, led to an accurate definition of the thrust systems highlighting both the geometry of the activated sector of the thrust front and its relation to potentially active adjacent faults. Moreover, the results show the strong influence of past paleogeography and paleomorphology on the evolution and geometry of this sector of the fold-and-thrust belt, including the buttressing effect of carbonate platforms and inherited highs.

The resulting 3D model was integrated with seismological data and geodetic observations allowing us to well highlight the activated portion of the fault plane: strong motion data and continuous GNSS stations hosted by onshore (storage centers) and offshore (seabed-anchored hydrocarbon platforms) infrastructures were jointly inverted to retrieve the Mw 5.5 coseismic rupture history.

How to cite: Petracchini, L., Billi, A., Carminati, E., Chiarabba, C., Conti, A., Devoti, R., Palano, M., Pezzo, G., Scognamiglio, L., Tavani, S., and Tinti, E.: The active frontal sector of the offshore Northern Apennine thrust belt: insights from an interdisciplinary approach following the 2022 Mw 5.5 Costa Marchigiana Pesarese earthquake (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17556, https://doi.org/10.5194/egusphere-egu24-17556, 2024.

EGU24-17839 | ECS | Orals | TS3.2

Insights into fault behaviour and seismic hazard from studying active and inactive faults over a range of timescales 

Zoe Mildon, Billy Andrews, Constanza Rodriguez Piceda, and Manuel Diercks

Tectonics and active faults are studied using a broad range of techniques and observations, and each of these datasets have both strengths and limitations. Ideally, a multidisciplinary approach should be used when studying active faults, to mitigate against gaps in data and knowledge, and to span the spatial scales of deformation. Furthermore different approaches can provide insights into how faults and fault networks behave over a wide range of timescales, from annual behaviour (e.g. geodesy, seismology) to millennia (e.g. paleoseismology) and millions of years (e.g. seismic reflection). By using a range of techniques to study fault behaviour over a range of timescales, we gain insights into how faults behave and interact, which ultimately can improve our understanding of the resultant seismic hazard.

For seismic hazard studies, it is important to quantify fault geometry, dimensions and connectivity as these factors influence the magnitude and propagation of earthquakes. However these are typically difficult to constrain from onshore continental faults where  sub-surface information is often limited. Another important aspect to consider for seismic hazard studies is the slip rate of faults, but an aspect that is rarely considered is how slip rates vary spatially and temporally. Using seismic reflection datasets of inactive normal faults, we can study how slip rates vary over far longer timescales than can be considered from field studies alone. While it is challenging to study onshore faults using the same approach, what our findings indicate is that slip rates can vary by more than an order of magnitude over the lifetime of a single fault. Additionally, faults are almost never a single isolated structure, and instead form fault networks, with variable spacing, orientation and lengths. Understanding how a fault network behaves and interacts over time is also important to gain insights into seismic hazard.

Ultimately to gain a comprehensive understanding of fault behaviour in time and space, a range of complementary studies, including observations and modelling, are needed to span the broad range spatial and temporal scales that need to be considered when assessing active faults.

 

How to cite: Mildon, Z., Andrews, B., Rodriguez Piceda, C., and Diercks, M.: Insights into fault behaviour and seismic hazard from studying active and inactive faults over a range of timescales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17839, https://doi.org/10.5194/egusphere-egu24-17839, 2024.

EGU24-19217 | Posters on site | TS3.2

The potential of high density seismic arrays to elucidate distributed deformation in the Dinarides and Hellenides 

Frederik Tilmann, Andreas Rietbrock, Bernd Schurr, Ben Heit, Michael Frietsch, Hans Agurto-Detzel, Ya-Jian Gao, Sofia-Katerina Kufner, Edmond Dushi, Besian Rama, Damiano Koxhaj, Dinko Sindija, Gesa Petersen, Efthimios Sokos, Claudio Faccenna, Thomas Meier, and Petr Kolinský

The eastern Adriatic margin with the Dinarides and Hellenides orogens is one of the most hazardous areas in Europe from an earthquake hazard perspective in spite of only moderate shortening rates (e.g. less than 0.5 cm/yr across the Dinarides), as exemplified by the recent highly damaging earthquakes in Durrës, Albania (2019, M6.4) and Petrinja, Croatia (2020, M6.4). Deformation is both fairly localised on shallowly NE dipping thrust faults near the coast, and distributed, with a transition to spatially extended extensional deformation in the southern Dinarides and Northern Hellenides. and a complex regime involving strike-slip and obblique mechanisms in the eastern part of the Northern Dinarides. Making sense of this distributed deformation requires highly accurate locations both horizontally and in depth, which can only be achieved with dense seismic observations.

This region is thus being explored with multi-scale dense seismic deployments. On one hand, the multi-national AdriaArray initiative has combined temporary and permanent broadband stations to achieve a nearly-uniform coverage with typical inter-station distances of 30-40 km. In Albania, where the transition of the Dinarides to the Hellenides is occurring, this regional coverage is complemented by a ultra-dense deployment of nearly 400 stations (mostly geophones with a few broadband sensors) with a nominal spacing of 5 km, which was later rearranged into three orogen-perpendicular profiles, and one along-strike profile with 1 km station spacing. Such large numbers of stations require automated processing approaches leveraging recently developed machine learning-based techniques. The presentation will review the tectonic context for these surveys and share some preliminary results from these deployments as well as an earlier more localised deployment in the area of the Durrës earthquake.

How to cite: Tilmann, F., Rietbrock, A., Schurr, B., Heit, B., Frietsch, M., Agurto-Detzel, H., Gao, Y.-J., Kufner, S.-K., Dushi, E., Rama, B., Koxhaj, D., Sindija, D., Petersen, G., Sokos, E., Faccenna, C., Meier, T., and Kolinský, P.: The potential of high density seismic arrays to elucidate distributed deformation in the Dinarides and Hellenides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19217, https://doi.org/10.5194/egusphere-egu24-19217, 2024.

EGU24-19684 | ECS | Orals | TS3.2

DInSAR coseismic surface deformation of the 2023 Mw 6.8 Al Haouz earthquake(High Atlas Mountains, Morocco) 

Riccardo Lanari, Martina Occhipinti, and Massimiliano Porreca

On 8th September 2023, the Al Haouz province in Morocco was struck by a strong earthquake of 6.8 Mw. The mainshock was generated by a reverse fault with an ENE-WSW orientation, as suggested by the derived focal mechanism.  

To obtain preliminary information of a seismic event, and to characterize the associated seismotectonic framework, in the last decades, the combination of field geology with satellite observations is becoming gradually more frequent. In particular, the DInSAR technique can be a powerful method of analysis to have an initial detailed information on the deformation field produced by the earthquake.  

In the present study, to understand the deformation field induced by the event and the structures involved, the DInSAR technique has been applied to obtain displacement maps in LOS, vertical, and horizontal (E-W) directions. On these maps, the geological meaning of both the vertical and horizontal displacement components is interpreted in the framework of the known tectonic structures of the Western High Atlas Belt. The inferred coseismic deformation along its vertical component shows a wide antiform characterized by an overall E-W trend and a slight southward vergence. On the other side, the horizontal (E-W) component of the deformation seems to be affected by the flexuring of the antiform flanks.  

Integrating the retrieved DInSAR maps with published geological observations and preliminary seismological data, it is possible to demonstrate how the coseismic deformation pattern may be affected not only by a possible activity of the main Tizi n’test fault but also by the far western High Atlas frontal thrust and by possible blind faults, better oriented to the vertical deformation field. 

How to cite: Lanari, R., Occhipinti, M., and Porreca, M.: DInSAR coseismic surface deformation of the 2023 Mw 6.8 Al Haouz earthquake(High Atlas Mountains, Morocco), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19684, https://doi.org/10.5194/egusphere-egu24-19684, 2024.

EGU24-19788 | Posters on site | TS3.2

Land-sea mapping and deformation kinematics in the Cape Gris-Nez fault zone (Dover Strait, Eastern Channel)  

Dibousse Aboubacar, Olivier Averbuch, and Virginie Gaullier

The Dover Strait, at the transition between the Eastern English Channel and the North Sea, lies on a complex faulted bedrock, making it a potential seismic risk area. Resulting from recent periglacial processes, it cross-cuts the geological structures inherited from the major tectonic deformations that affected the West European margin at the Late Jurassic-Early Cretaceous (extension and subsidence due to the propagation of the opening of the North Atlantic Ocean) and during the Cenozoic (compression causing the inversion of basins linked to the African-Eurasian convergence). Cape Gris-Nez is one of the most striking features of the fault system bordering the inverted Weald-Boulonnais basin. The Sirène beach, which has been heavily cleared of sand over the past 20 years, reveals the complexity of the folded and faulted geological structures associated with the development of this deformation zone. Over the last few years, detailed structural surveys have been carried out on land, using GNSS layer-to-layer mapping, and at sea, using very high-resolution SPARKER seismic profiles, providing an overall land-sea map of this fault zone. This first-rate mapping was recently supplemented by photogrammetric surveys by drone at very high spatial resolution (5 cm) making it possible to obtain an ortho-mosaic and a digital terrain model of the foreshore and cliffs of Cap Gris Nez. The interpretation of these very high-resolution images, adopted in a new structural survey campaign, leads to an optimization of the mapping of structures and a better understanding of the geometry and kinematics of deformations at the fault zone preliminary data for a better definition of seismic risk in the sector.

How to cite: Aboubacar, D., Averbuch, O., and Gaullier, V.: Land-sea mapping and deformation kinematics in the Cape Gris-Nez fault zone (Dover Strait, Eastern Channel) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19788, https://doi.org/10.5194/egusphere-egu24-19788, 2024.

EGU24-19891 | ECS | Orals | TS3.2

Insights the transpressioanl deformation patterns in the western zone of Sulaiman Fold-and-Thrust belt from spaceborne geodesy 

Muhammad Tahir Javed, Sylvain Barbot, Farhan Javed, and Carla Braitenberg

Continental convergence of Indian and Eurasian plates produces Himalayas in the north, while tectonically complex transpressional zones of the Sulaiman Fold and Thrust (SFT), and Kirthar Fold and Thrust (KFT) belts in the East. Seismic hazards in the zones are very high and less understood due to complex tectonic settings, and lack of GPS network. Here, we take advantage of spaceborne SAR interferometry and use the Sentinel-1, and ALOS-2 ScanSAR satellite observations to estimate the coseismic deformation caused by the 2021 Mw 6.0 Harnai earthquake in the western zone of the SFT belt. We find the line-of-sight (LOS) displacement of ~80 and ~70 mm from Sentinel-1 descending and ascending interferograms respectively. We find the ~50 mm of LOS displacement from ALOS-2 descending interferogram, but it is majorly biased by lower and upper atmospheric noises even after the GACOS and ionosphere corrections. In order to avoid the major noise components in inversions that may affect the accuracy, we discarded the ALOS-2 LOS displacement and relied only on the ascending and descending interferograms of Sentinel-1data. The deformation has an oblique component, but mostly dominated by thrusting on the NW-SE trending Harnai fault. First, we invert the LOS displacement using geodetic Bayesian Inversions approach, and find two plausible fault plane the NW-SE trending, and the NE-SW trending solutions. The simplified fault parameters have a strike of 327° ± 12, a dip of 31° ± 9, the length of 8.3 ± 2.1 km, and the width of 2.5 ± 2.0 km, which fits well the ISC and USGS fault models. Then, we determine the finite slip distributions on both plausible faults.  The NW-SE trending fault shows the maximum slip is found to be 70 cm at around 8 km depth. The slip distribution along the down dip and strike of the fault shows that 85% of the slip is concentrated in an area of (9 × 9) = 81 km2 at a down dip distance of 3 - 12 km. Furthermore, the results show the earthquake is propagated equally along strike and dip. For the NE-SW trending fault the maximum slip is similar but has higher residuals and scattered slip along depth. Therefeore, we preferred the NW-SE trending fault plane solution because based on the compatibility with fault structures in the region, and higher accuracy in the inversions. We also determine postseismic movement using time series analysis of spaceborne Sentinel-1 SAR data, but no significant afterslip and viscoelastic relaxation signals is found on the fault after the earthquake.

How to cite: Javed, M. T., Barbot, S., Javed, F., and Braitenberg, C.: Insights the transpressioanl deformation patterns in the western zone of Sulaiman Fold-and-Thrust belt from spaceborne geodesy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19891, https://doi.org/10.5194/egusphere-egu24-19891, 2024.

EGU24-20437 | ECS | Posters on site | TS3.2

Direct dating of active faults using luminescence: A case of study in New Zealand 

Andrés Melo, Sumiko Tsukamoto, Margret Fuchs, David Tanner, Christian Brandes, Uwe Kroner, Andrew Nicol, and Richard Gloaguen

The Alpine Fault in New Zealand is one of the world’s major active crustal-scale faults. It builds the boundary between the Pacific and the Australian plate, and branches into strike-slip faults known as the Marlborough fault system. The northeastern region of the southern island of New Zealand has a historical record of large, shallow earthquakes with magnitude (Mw > 6.5) since the Nineteenth Century. The most recent event, the 2016 Kaikōura earthquake, with a magnitude (Mw) of 7.8, is among the strongest. The severe impact on society and landscape explain the importance of a better understanding of the Quaternary activity of these active faults. Recent investigations in other tectonically-active settings worldwide indicate the potential feasibility of applying luminescence dating to unravel the timing and hence, re-occurrence of fault activity as a source for earthquakes.

We aim to test the potential of luminescence dating to determine the relative activity of three active faults in New Zealand. To this end, we collected four dark-gray, fine to very fine grain-size samples classified as cataclasite and gouge from outcrops situated along the fault traces of the Alpine Fault, Hope Fault, and Hundalee Fault. Through sample processing, we obtained polymineral fine grains, ranging from 4 to 11 µm, to conduct post-infrared infrared stimulated luminescence (pIRIR225) dating. The method applied on faults is the signal-resetting event of the fault movement, and if the signal is not saturated in nature, this implies that frictional heating was enough to at least partially reset the system; for feldspar the closure temperature is 40-90 °C.

The growth curves of the pIRIR225 signals reveal that the gouge samples extracted from the Hope fault and Hundalee fault approach saturation levels with equivalent doses around 850 Gy and 900 Gy, respectively. In contrast, the equivalent dose of cataclasite samples from the Alpine Fault was clearly below saturation ranging from 220 Gy to 410 Gy. All assessment criteria, including recycling ratio and recuperation rate, meet the rejection criteria for all samples, indicating a reliable signal to dose relationship. These results suggest there were events, which thermally eroded the pIRIR225 signal at the Alpine Fault. The comparison of the equivalent doses from the three faults also indicates that the method is applicable to evaluate the relative fault activity; the Alpine Fault is more active than the Hope and Hundelee faults. However, micro-structural analysis also indicated differences in brittle deformation mechanisms, differences that also potentially influence the variations between the pIRIR225 signals of individual samples. Observed features comprise, for example, grain fracturing, frictional sliding, pressure solution, and twinning. The micro-structural variation suggest differences in deformation, stress and pressure-temperature (P-T) conditions experienced by the studied cataclasite and gouge samples.

This study presents the first findings of pIRIR225 dating on feldspar in active faults in New Zealand and points at the success of luminescence dating. However, we strongly emphasize the importance of combining luminescence analysis with microstructural and mineralogical data obtained through Scanning Electron Microscope (SEM)-Mineral Liberation Analysis (MLA) to better understand the P-T conditions and resulting degree of luminescence signal reset.

How to cite: Melo, A., Tsukamoto, S., Fuchs, M., Tanner, D., Brandes, C., Kroner, U., Nicol, A., and Gloaguen, R.: Direct dating of active faults using luminescence: A case of study in New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20437, https://doi.org/10.5194/egusphere-egu24-20437, 2024.

EGU24-20926 | Posters on site | TS3.2

Similarities and differences between natural and simulated slow earthquakes 

Adriano Gualandi, Luca Dal Zilio, Davide Faranda, and Gianmarco Mengaldo

Earthquakes are understood as frictional instabilities taking place in weak zones of the Earth crust called faults. On the one hand, the lengthy recurrence time of earthquakes makes numerical simulations an invaluable tool to study consecutive ruptures of a given fault. On the other hand, it makes a direct comparison with nature difficult, if not currently impossible. Slow earthquakes, exhibiting lower recurrence times, serve as a viable alternative for validating models against real-world observations. We investigate similarities and differences between natural and simulated slow earthquakes using nonlinear dynamical system tools. We focus on slow earthquakes derived from Global Navigation Satellite System (GNSS) position time series in Cascadia and numerical simulations intended to reproduce their pulse-like nature and scaling laws. We provide metrics to evaluate the accuracy of simulations in mimicking slow earthquake dynamics, and we investigate the influence of spatio-temporal coarsening as well as observational noise. Findings indicate that numerical simulations exhibit average properties akin to natural occurrences. In addition, despite the usage of many degrees of freedom in numerical simulations, we retrieve a low average dimension, like the one obtained for Cascadia slow earthquakes, suggesting that a reduced order model may be a viable representation of slow slip events. Time-dependent, instantaneous properties show strong dependence on the variable considered for the analysis for numerical simulations, but not for natural observations. Our exploration show a possible way to extract dynamic attributes from kinematic information, and enriches the picture that we have of natural-scale friction We propose to use the suggested metrics as an additional tool to narrow the divergence between slow earthquake observations and dynamical simulations.

How to cite: Gualandi, A., Dal Zilio, L., Faranda, D., and Mengaldo, G.: Similarities and differences between natural and simulated slow earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20926, https://doi.org/10.5194/egusphere-egu24-20926, 2024.

EGU24-21021 | Posters on site | TS3.2

Geophysical constraints on intraplate deformation in southern Africa 

Alastair Sloan, Beth Kahle, Robert Muir, Diego Quiros, Khumo Leseane, Shaakirah Adams, Timothy Jones, Anele Matsebula, Anzani Ramagadane, Guy Salomon, and Benjamin Whitehead

The hazard posed by large intraplate earthquakes is relatively well-known in the Global
North, but Sub-Saharan Africa is poorly represented in compilations of such events, and the
hazard they may pose in this region is not well understood. Much of southern Africa is an
unusual example of an intraplate region undergoing predominantly extensional
deformation, complicating comparisons with otherwise similar regions. Here we present the
locations of moderate magnitude instrumentally-recorded seismicity, as well as eight major
paleoseismic fault scarps across South Africa, Namibia and Botswana. We focus on regions
generally considered to be stable, and compare these data to available aeromagnetic and
seismic tomographic datasets. Major events are primarily focussed on either the boundaries
of the cratonic cores in the region, or in the vicinity of large igneous complexes, suggesting
that variations in large-scale lithosphere rheology provide a first-order control on their
occurrence. Aeromagnetic lineaments, associated with Jurassic-Cretaceous normal faults or
ancient shear zones within mobile belts, are associated with almost all of the major
paleoseismic ruptures, and appear to control fault bends and terminations. Significant
differences in strike over relatively short length-scales suggest the orientation of the faults
are controlled by crustal anisotropy rather than variations in stress orientation. Some of the
scarps are likely to be associated with M7+ events, suggesting that such events can occur in
stable regions experiencing extensional stresses. The association with major crustal
structures likely explains their great length, relative geometric simplicity and unexpectedly
large magnitudes, despite limited recent brittle offset. While intraplate events are relatively
poorly studied in southern Africa the excellent preservation potential of landscape, and the
rarity of extensional events in other comparably stable regions, mean that this region has
excellent potential to increase our understanding of these phenomena.

How to cite: Sloan, A., Kahle, B., Muir, R., Quiros, D., Leseane, K., Adams, S., Jones, T., Matsebula, A., Ramagadane, A., Salomon, G., and Whitehead, B.: Geophysical constraints on intraplate deformation in southern Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21021, https://doi.org/10.5194/egusphere-egu24-21021, 2024.

EGU24-21217 | ECS | Posters on site | TS3.2

Faults segmentation in active external extensional front: insights from seismicity in the Sant'Anna Pelago area, North Apennines 

Simone Lenci, Derek Keir, Giancarlo Molli, Paola Vannucchi, Chiara del Ventisette, and Carolina Pagli

The Neogene-to-Recent tectonic evolution of the Northern Apennines has been characterized by contraction in the foreland, accompanied by extension in the internal domain. While the architectural and kinematic aspects of these two distinct sectors are better-known, uncertainties persist regarding the transition between them. Understanding the tectonics is made more complex since the width of the internal extensional domain increases south-eastward as the Northern Apennines steps eastward across Italy.

The Sant'Anna Pelago area, located on the Tuscan-Emilian ridge between Alpe di Succiso (NW) and Monte Cimone (SE), exhibits pronounced instrumental seismicity with over a thousand recorded events over the last ~15 years, forming the focus of this study. Sant'Anna Pelago represents a critical zone as the extensional front is situated near the outermost out-of-sequence contractional front affecting the Tuscan Nappe. The region locates close to the orographic divide, and also where the width of the internal extension starts widening significantly eastward. Seismicity in Sant’Anna is expressed through three major seismic sequences over a 10-year period from 2012 to 2022, with events concentrated in 2013, 2018, and 2022. P and S arrival times from 56 evenly distributed stations within 130 km radius from the publicly available INGV database were utilized to perform a preliminary relocation of seismic clusters using NonLinLoc and a local velocity model. Subsequent precise relocations were conducted using differential arrival times through HypoDD.

The relocation revealed three primary deep clusters and several minor aligned ones. The 2013 sequence is 8-km-long, 10-17 km deep, strikes parallel (NW) with the Apenninic trend, and dips 50 degrees towards the SW. This structure aligns prominently with the southern tip of the Zola master fault, surfacing near Pieve Pelago. Earthquakes are particularly dense at the southern tip of this structure. The subsequent clusters are in the footwall of the 2013 sequence, and at similar depths. These show several discrete, sub-vertical structures oriented E-W, each approximately 3 km long. These clusters geometrically resemble synthetic en-echelon faults situated in the footwall of the Zola fault. The western tips of these structures align along a potential envelope segment linking them to the 2013 cluster, a transverse SW-NE structure orthogonal to the Apenninic structure and the Zola Fault. We interpret the 2013 sequence as normal slip on a reactivated NW striking Apenninic contractional structure, and the subsequent en-echelon sequences on E-W faults as mostly normal slip in a dextral stepping zone of local re-orientation of stress. The interpretations will however, be tested with earthquake focal mechanisms and field structural geology. 

How to cite: Lenci, S., Keir, D., Molli, G., Vannucchi, P., del Ventisette, C., and Pagli, C.: Faults segmentation in active external extensional front: insights from seismicity in the Sant'Anna Pelago area, North Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21217, https://doi.org/10.5194/egusphere-egu24-21217, 2024.

EGU24-293 | ECS | Orals | TS3.3

Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya 

Jyoti Tiwari, Surendra S. Bhakuni, Pradeep Goswami, and Anil Tiwari

Understanding the geodynamics and seismotectonic characteristics of a region requires an integrated approach involving the analysis of structures, active deformations, seismicity, and tectonic stress conditions. Analysing the links between ongoing seismic activities and the development of the landscape provides a deeper understanding of the dynamic interplay between tectonic forces and geological formations. This study focuses on the Kullu-Larji-Rampur (KLR) window in the NW Himalaya, situated just south of the Main Central Thrust (MCT), where seismicity is notably frequent. The primary objective is to comprehensively analyse parameters in this region, located in Himachal Pradesh, India. Extensive fieldwork involved scaling and mapping active deformation and geomorphological features along major transverse routes of the Sutlej and its tributaries in Himachal Pradesh. Structural data collected encompass measurements of foliation/schistosity, lineations, bedding planes, fold hinge lines, limb of folds, axial planes, shear zones/planes, kinematic indicators, and more. Results from structural data, remote sensing data and field investigations indicate active footwall duplexing or faults along bounding surfaces of tectonic horses, including younger thrust splays within the footwall block of the Jutogh Thrust (JT) or within the KLR window. Additionally, the study assesses localized stress behaviour and seismicity parameters (b-value and source mechanisms) in this seismically active region using background seismicity. Notably, significant depth variations and anomalies in stress conditions are observed, interpreted as a brittle-semi-brittle and stress transition zone. The south-eastern section of the KLR window is identified as a high-stress accumulation zone. We have established a correlation between present-day seismicity and the evolving landscape of the region. The study concludes that continuous interseismic and co-seismic deformation, along with the active footwall duplex in the Lesser Himalayan Sequence (LHS), play pivotal roles in shaping the growth of the KLR window and driving active in-sequence thrusting along the younger splays of the Jutogh Thrust.

How to cite: Tiwari, J., Bhakuni, S. S., Goswami, P., and Tiwari, A.: Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-293, https://doi.org/10.5194/egusphere-egu24-293, 2024.

There is a growing interest among seismologists on the nonlinearity of seismic processes, corresponding to the synergetic approach to the development of the Earth as a nonlinear, open, self-organizing system. In the analysis of very complex multi-component geological-geophysical systems, it is important to assess the degree of their nonlinearity based on a set of control parameters. For the analysis of the seismic process, we propose to use seismic-tectonic stress in the Earth's crust and lithosphere as a control parameter. Also, in the analysis of processes releasing tectonic stresses in the form of earthquakes, the synergetic of choosing the initial state becomes important.

To choose the initial state of the Earth's crust and lithosphere, we consider them as an oscillatory block-hierarchical system, interconnected and developing over time but differing in various layers of the Earth's crust – sedimentary, consolidated crust, lower crust, and mantle beneath the Moho boundary, as each layer has its lithological properties and is in different physical conditions, at least due to the change in pressure. Block sizes are determined based on the thickness of the layer, and vertical planes of the block are determined based on the morphology of the layer, as well as the presence of a fault inside the block. Changes in the seismic-tectonic deformation vector indicate a change in the initial state of seismic-tectonic deformation of each block. Thus, for the analysis of the nonlinear seismic process, we obtain a continuous series of changes in seismic-tectonic stresses in different layers and for each block of the layer. Thanks to the known time of deformation changes, as well as the known size of each block, we have an approximation of the nonlinear oscillatory process in the block-hierarchical system of the Earth's crust and lithosphere, manifested as seismicity. Within the designated time interval, the seismic-tectonic deformation process in each block follows a linear law. We have tested our methodological approaches to the analysis of the nonlinear seismic process in the example of the Crimean-Black Sea region. We have processed earthquakes contained in the new catalog of seismic events for the period 1970-2012, recalculated according to the Seismological Bulletins of the USSR and Ukraine. The method of Aki was used to determine the seismic-tectonic deformation regime by constructing averages foci by the signs of the first arrivals of P-waves taken from the bulletins. Time series of changes in seismic-tectonic deformation regimes in different layers of the Earth's crust and lithosphere show that each layer has its peculiarities of deformation but fits into the general context of tectonic processes in the region. One of the interesting features of the tectonic process in the region turned out to be the unexpected variability of regimes and their duration from 2 to 10 years in different areas of the Crimean-Black Sea region. An important consequence of our study is the definition of clear spatial-temporal frameworks for the analysis of the amounts of seismic energy release in each of the blocks, which will improve the quality of seismic risk assessment for individual regions.

How to cite: Shumlianska, L. and Vilarrasa, V.: Approximation of nonlinear seismic processes based on space-time series of changes in seismotectonic deformation regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-641, https://doi.org/10.5194/egusphere-egu24-641, 2024.

The faults and the fault zones are essential to determine the seismotectonic features and the regime of a region and to produce seismic hazard and risk maps. Many geophysical methods, such as seismic, magnetic and gravity are used to determine the location and direction of faults. This study aims to detect potential fault edges located in the south-southwest of Nisyros Island and west of Tilos Island in the southeastern Aegean Sea and to interpret the seismic activity and faulting characterization. To this end, the potential fault edges were initially detected using the total horizontal derivative method on the gravity dataset collected from the WGM2008 database. The obtained spatial locations were combined with the seismicity and the focal mechanisms of the earthquakes. The detected fault has a northeast-southwest orientation with normal faulting. It was proved that this obtained fault is not included in the active faults of the Eurasia database (AFEAD), European Fault - Source Model 2020 (EFSM20) database and the Mineral Research and Exploration General Directorate (MTA) active fault map. Moreover, this observed fault was detected as longer than the fault shown on the National Observatory of Athens (NOAFAULTs) in terms of length. Consequently, it is highly recommended that this potential fault, which produces earthquakes with a moment magnitude greater than 4.0 (on instrumental period) must be added to such fault databases to increase and spread the knowledge of seismological and seismotectonic research.

How to cite: Tamtaş, B. D. and Toktay, H. D.: Seismotectonic interpretation and edge detection of the potential fault on the SE Aegean Sea using the total horizontal derivative method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-785, https://doi.org/10.5194/egusphere-egu24-785, 2024.

EGU24-1278 | ECS | Posters on site | TS3.3

Active triangle zones within the two orogens convergence zone, central Caucasus, Georgia 

Tamar Shikhashvili, Mariam Mariam Bekurashvili, Anzor Giorgadze, Aleksander Razmadze, Onise Enukidze, and Victor Alania

Collision and subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the Caucasus region (e.g., Cavazza et al., 2023). Inversion of back-arc basins, exhumation, and crustal thickening took place in the far-field zone, forming two orogens, and leading to a convergence between the Lesser Caucasus (LC) and Greater Caucasus (GC). Continuous convergence between the LC and GC caused incremental deformation of the Kura foreland basin (Alania et al., 2023). Our study area is located within the LC-GC convergence zone in the western Kura foreland basin and is represented by the lenticular-shaped compressional basin formed by northward and southward-directed thrusting. 2D seismic reflection profiles revealed the presence of triangle zones at the frontal part of the LC retro-wedge and GC pro-wedge. According to analog, seismic, and sequential kinematic modeling results, the frontal part of the GC is represented by a double wedge-dominated triangle zone and is characterized by the presence of passive, active wedges and passive-forethrust. In the frontal part of the LC orogen, the syn-kinematic (Middle-late Miocene) strata have been deformed and uplifted by passive-back thrusting at the triangle zone. Seismic reflection profiles show north-vergent duplex and structural wedge at the triangle zone beneath the thrust front monocline and is represented by Cretaceous-Paleogene strata. Western part of the triangle zone of the Kavtiskhevi-Akhalkalaki area is introduced by south-vergent imbricated fan (passive-back thrusts). The imbricated fan is characterized by fault-propagation folding. The kinematic evolution of south-vergent fault-propagation folds is related to northward propagating duplex. Recent and historical earthquakes and paleoseismic data indicate that the frontal part of LC and GC is tectonically active (e.g., Stahl et al., 2022; Tsereteli et al., 2016).

 

Reference

Alania, V., et al. (2023). Interpretation and analysis of seismic and analog modeling data of triangle zone: a case study from the frontal part of western Kura foreland fold-and-thrust belt, Georgia. Frontiers in Earth Sciences 11, 1195767.

Cavazza, W., et al. (2023). Two-step exhumation of Caucasian intraplate rifts: a proxy of sequential plate-margin collisional orogenies, Geoscience Frontiers 15, 101737.

Stahl, T. A., et al. (2022). Recent Surface Rupturing Earthquakes along the South Flank of the Greater Caucasus near Tbilisi, Georgia. Bull. Seism. Soc. Am. XX, 1–19.

Tsereteli, N., et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328-344.

How to cite: Shikhashvili, T., Mariam Bekurashvili, M., Giorgadze, A., Razmadze, A., Enukidze, O., and Alania, V.: Active triangle zones within the two orogens convergence zone, central Caucasus, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1278, https://doi.org/10.5194/egusphere-egu24-1278, 2024.

EGU24-1557 | Posters on site | TS3.3

Structural architecture of the active eastern Achara-Trialeti fold-and-thrust belt (Tbilisi urban area), Georgia 

Mariam Bekurashvili, Tamar Shikhashvili, and Victor Alania

Our study area, Tbilisi urban area is located in the eastern Achara-Trialeti fold-and-thrust belt. The Achara-Trialeti fold-and-thrust belt, which is one of the good examples of collision-driven far-field deformations, is located within the northernmost part of the Lesser Caucasus orogen and is associated with Arabia-Eurasia convergence. Our interpretation has integrated seismic reflection profiles, several oil wells, and surface geology data to reveal the deformation structural style of the eastern Achara-Trialeti fold-and-thrust belt. Fault-related folding theories were used for seismic interpretation. Seismic reflection data reveal the presence of south-vergent and north-vergent fault-propagation folds, duplexes, and structural wedge. Interpreted seismic reflection profiles, structural cross-section, and recent earthquakes reveal the presence of an active blind thrust fault and structural wedge(s) beneath Tbilisi and the surrounding area. The structural model shows that the 2002 Mw 4.5 Tbilisi earthquake was related to a north-vergent blind thrust and the Kumisi and Teleti earthquakes are related to a north-vergent blind wedge thrust system.

How to cite: Bekurashvili, M., Shikhashvili, T., and Alania, V.: Structural architecture of the active eastern Achara-Trialeti fold-and-thrust belt (Tbilisi urban area), Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1557, https://doi.org/10.5194/egusphere-egu24-1557, 2024.

EGU24-1713 | Posters on site | TS3.3

The Valsugana area (TN, Italy): a structural knot 

Silvana Martin, Laura Montresor, Pina Zambotti, Giovanni Monegato, Guido Roghi, Gianluca Piccin, Alessia Modesti, and Francesco Gosio

In the Valsugana area (Southern Italian Alps) a NE-SW trending pre-permian Southalpine phyllitic basement is intruded by an Early to Middle Permian granitoids (Cima d’Asta,190 km2) and includes volcanic calderas of the Athesian Volcanic Group (125 km2) of the same age, and is locally covered by Upper Permian to Miocene sedimentary sequences. A complex system of faults juxtaposes these different geological domains. In particular, the Permian tectonic structures have been repeatedly reactivated during Mesozoic and Tertiary. The phyllitic basement, which suffered Variscan metamorphism and deformation, and the granitoids were dismembered by NNW-SSW and N-S tectono-magmatic faults associated with the opening of permian calderas. The main tectonic system of this area is the ENE-WSW oriented Valsugana fault system of Middle-Late Miocene age (Heberer et al., 2017 ). The master fault separates the metamorphic basement from the sedimentary sequences (e.g., M. Armentera, M. Civerone and M. Lefre). At the footwall of the master fault, other faults deformed in a compressive to transpressive regime the sedimentary sequences. Some of these are extensional faults were reactivated many times from Triassic to Lower Jurassic. The Valsugana fault system ends against the Permian to Mesozoic Calisio fault to the SW, while it continues to the NE towards Brocon and Cereda Passes (Gianolla et al. 2022). The Valsugana fault system is cut across by the Val di Sella fault of Late Miocene-Pliocene age, oriented c.a. E-W which deformed the northern walls of the Asiago Plateau (Barbieri & Grandesso, 2007), transporting slices of metamorphic basement and Permo-Mesozoic sequences to the north, over the Middle Miocene sandstones and marls of Valsugana. The most recent tectonic system consists of a set of NNW-SSE to N-S faults which cut across the ENE-WSW Valsugana and E-W Val di Sella fault systems. The N-S Grigno-Tolvà fault cuts across the Cima d’Asta magmatic complex from Val Vanoi to the north to Asiago Plateau to the south over XX km, and dislocates the Belluno and Val di Sella thrust faults at the footwall of the Valsugana fault system. All these faults are still seismically active.

Barbieri G. & Grandesso P. (2007) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 082, Asiago.

Heberer B., Reverman R.L., Fellin M.G., Neubauer F., Dunkl I., Zattin M., Seward D., Genser J. & Brack P. (2017) - Postcollisional cooling history of the Eastern and Southern Alps and its linkage to Adria indentation. International Journal of Earth Sciences (Geologische Rundschau), 106:1557–1580.

Gianolla G., Caggiati M. & Riva A. (2022) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 046, Longarone.

How to cite: Martin, S., Montresor, L., Zambotti, P., Monegato, G., Roghi, G., Piccin, G., Modesti, A., and Gosio, F.: The Valsugana area (TN, Italy): a structural knot, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1713, https://doi.org/10.5194/egusphere-egu24-1713, 2024.

EGU24-1794 | Orals | TS3.3

Disaggregation bands as indicator for active blind faults 

Christian Brandes, David Tanner, Haakon Fossen, Matthias Halisch, and Katharina Müller

The identification of active faults is an important step in the seismic hazard evaluation process. However, this task is often difficult because many faults are unknown, buried below younger sediments. Especially in slowly-deforming intraplate areas with long recurrence intervals between individual seismic events, the detection of hidden blind faults is a major challenge. Furthermore, active faults can undergo long episodes of aseismic creep and thus do not produce typical earthquake-related, soft-sediment deformation structures, which also hinders the detection of these faults. Consequently, there is the demand for a robust universal geological indicator for active blind faults. Based on outcrop studies, we are able to show that disaggregation bands (near-surface deformation bands that develop in unconsolidated sediments due to reorganization of the grain fabric) are such an indicator. Disaggregation bands are developed at several locations in Central Europe and Scandinavia, in near-surface sandy sediments above the tip lines of blind faults. The strike of these bands is parallel to the strike of the underlying faults, which indicates that the disaggregation bands formed as a consequence of fault movement. The disaggregation bands internally show a pore-space reduction and in some cases a clear alignment of elongated grains. The thickness of the disaggregation bands increases with the amount of offset along the bands. Based on these observations, we infer that the bands formed in the process zone of propagating faults due to a shear-related reorganization of the grain fabric that leads to strain-hardening and a growth of the bands into centimetre-thick tabular structures. With analogue shearing experiments we show that disaggregation bands can form at a wide range of deformation speeds, even down to speeds several orders of magnitudes lower than seismogenic fault-slip velocities. Thus, disaggregation bands are key structures that record large parts of the seismic cycle and represent a very suitable indicator for active blind faults, even if the related fault creeps without emitting seismic waves. Disaggregation bands can easily be recognized in outcrops and artificial trenches, and previous studies showed that it is possible to even image them with ground-penetrating radar.

How to cite: Brandes, C., Tanner, D., Fossen, H., Halisch, M., and Müller, K.: Disaggregation bands as indicator for active blind faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1794, https://doi.org/10.5194/egusphere-egu24-1794, 2024.

EGU24-1802 | Posters on site | TS3.3

The shear deformation zone along the KTFZ: implications for faulting properties 

Vasileios Karakostas and Eleftheria Papadimitriou

The Kefalonia Transform Fault Zone (KTFZ) in central Ionian Islands (Kefalonia and Lefkada Islands), Greece, a dextral strike slip transform zone, exhibits the fastest rates of relative plate motion in the Mediterranean. Strong (Mw>6.0) earthquakes associated with the fault segments comprised in KTFZ are frequent as historical information and instrumental record reveals. Four main shocks of this order magnitude, among other earthquakes of Mw>5.0 occurred since 2003 on almost along strike adjacent fault segments, with high aftershock productivity extended far beyond the fault tips forming aftershocks zones remarkably wider than expected of strike slip faulting. This enhanced aftershock seismicity is associated with the shear deformation zone surrounding the mainshock rupture plane. It has been suggested that it results from the reactivation of secondary faults, its width decreases as a power law with cumulative fault displacement being narrower around mature faults than around immature faults. As the structural maturity may have a strong impact on earthquake behavior, such as magnitude, stress drop, distribution of slip, rupture velocity, ground motion amplitude, and number of ruptured segments, as prior studies have suggested, we aim at investigating the shear deformation zone along KTFZ. We used the relocated aftershock seismicity of the four recent (2003 – 2015) strong (Mw>6.0) main shocks that occurred on almost along strike positioned strike slip faults for defining the fault width in conjunction with the fault length, as we have already done in the case of the 2015 Lefkada main shock, and the activation of secondary faults, most probably triggered by stress changes and stress redistribution due to the main shock coseismic slip. Detailed slip models, when available, are engaged for this scope for investigating possible triggering of the secondary fault segments taking part in each seismic excitation, due to the stress transfer, taking also into account the stress sensitivity on the geometry and faulting properties of the minor faults, along with the accurately relocated aftershock seismicity. After the main fault width definition, we investigated the decrease of aftershock frequency and spatial density as a function of distance from the main fault.

Acknowledgments: Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Commission – Euratom. Neither the European Union nor the granting authority can be held responsible for them.

How to cite: Karakostas, V. and Papadimitriou, E.: The shear deformation zone along the KTFZ: implications for faulting properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1802, https://doi.org/10.5194/egusphere-egu24-1802, 2024.

EGU24-2168 | Posters on site | TS3.3

Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review 

Federico Pasquaré Mariotto, Alessandro Tibaldi, Fabio Luca Bonali, Noemi Corti, Martina Pedicini, Babayev Gulam, and Tsereteli Nino

The convergence between the Arabian and the Eurasian plates resulted in the development of the Greater Caucasus (GC) and the Lesser Caucasus fold-and-thrust belts, separated across most of their length by the Transcaucasian depression. The whole sub-horizontal shortening of the Caucasus was quantified at hundreds of kilometers and, according to several studies, reached its maximum rate in the Miocene-Pliocene. At present, convergence between the Eurasian and African-Arabian plates is still active, producing widespread deformation within the mountain belt and in surrounding regions, as testified to by seismological, paleoseismological and GPS data.

Understanding the active tectonics of the Caucasus is of paramount importance for a better assessment of geohazards, especially seismic hazard. Moreover, there is a major concentration of residents in Tbilisi, the capital of Georgia, hosting 1.2 million citizens, and in Baku, the capital of the Azerbaijan Republic, with over 2.3 million citizens; both cities are located in active tectonic basins at the southern foothills of the GC. Hundreds of rural villages are scattered in the mountain regions, and all were built without taking into consideration antiseismic criteria. All the above shows that the Caucasus and Transcaucasus regions are subject to an extreme seismic hazard and risk.

Here, we describe the active kinematics of the Greater Caucasus (territories of Georgia, Azerbaijan and Russia) through an integrated analysis of seismological, structural-geological and GPS data. Alignments of crustal earthquake epicentres indicate that most seismic areas are located along the southern margin of the mountain belt and in its north-eastern sector, in correspondence of major, activeWNW-ESE faults, parallel to the mountain range. Focal Mechanism Solutions (FMS) delineate dominant reverse fault kinematics in most sectors of the mountain belt, although swarms of strike-slip FMS indicate the presence of active transcurrent faulting, especially along the southeastern border of the Greater Caucasus. The mountain belt is characterized by dominant NNE-SSW-oriented P-axes. In the central-southern sector, in correspondence of the local collision between the Lesser and Greater Caucasus, P-axes are mainly NNW-SSE oriented. GPS data show dominant motions to the NNW, with rates increasing in eastward direction. All observations are consistent with a component of eastward escape of the central-eastern part of the Greater Caucasus.

How to cite: Pasquaré Mariotto, F., Tibaldi, A., Bonali, F. L., Corti, N., Pedicini, M., Gulam, B., and Nino, T.: Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2168, https://doi.org/10.5194/egusphere-egu24-2168, 2024.

EGU24-3078 | Orals | TS3.3 | Highlight

Differences in earthquake size distributions for thrusts and normal faults: the case of Italy 

Michele M. C. Carafa and Matteo Taroni

The earthquake size distribution is characterized by an exponential function determined by the b-value parameter. Previous studies have demonstrated the dependence of the b-value on both the differential stress and tectonic settings. This study proposes a novel approach to categorize earthquakes based on the kinematics of interseismic geodetic strain rates and horizontal stress directions. When combined with other geological or geophysical information, incorporating stress directions and geodetic data enhances seismotectonic models, reducing arbitrariness in delineating seismic zones.

Using the Italian peninsula as a case study, we observe a significantly larger b-value for extensional faults than thrusts, albeit with smaller differences than previously reported. Additionally, our findings reveal that the spatial fragmentation of uniform tectonic regimes can lead to inaccurate b-value estimates for single faults due to the undersampling of earthquake size distribution.

How to cite: Carafa, M. M. C. and Taroni, M.: Differences in earthquake size distributions for thrusts and normal faults: the case of Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3078, https://doi.org/10.5194/egusphere-egu24-3078, 2024.

In this research, we combine seismic and tectonic approaches in an attempt to apply the empirical relationships between fault parameters and earthquake magnitudes aiming to assess the maximum possible magnitude for the prediction of intensity ground motion in the areas close to active faults. The case we study is the Talysh area in southern Azerbaijan with the total area of 3960 km². It stretches to 38054'N northern latitude and 48035'E eastern longitude and spreads to the north through the Alborz mountains of Iran. The earthquakes with a higher depth are concentrated mainly in the central part of the Talysh zone (up to 70 km) and in the southwestern part of the Caspian Sea (up to 55 km), with the local magnitude range of up to M5.5.

The earthquake magnitudes calculated on the basis of the surface fault length were compared with the catalogued magnitudes. As a procedure, (1) a comprehensive catalogue of all available known faults was compiled; (2) earthquake magnitude is then derived from fault length; (3) the resulting fault-length-earthquake-magnitudes were compared by the mathematical difference with catalogued earthquake magnitudes; and (4) as a final, intensity simulation of ground motion on near-fault areas was plotted. The results show the approximate consistence of the calculated fault-length-earthquake-magnitude with the catalogued seismicity. The map shows that the highest intensity areas of VII are observed in the central and western parts of the zone. An intensity VI covers majority of the Talysh zone. The results will contribute to the implementing more solid analyses for advancing seismic hazard analysis. Our research emphasizes the seismotectonic areas in southern Azerbaijan where further comprehensive studies on faults are required.

How to cite: Babayev, G., Aliyev, Y., and Aliyev, M.: Magnitude and intensity simulation of ground motion on near-fault areas: the case of Talysh (southern Azerbaijan), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3646, https://doi.org/10.5194/egusphere-egu24-3646, 2024.

EGU24-5338 | ECS | Posters on site | TS3.3

A dynamic identification of continuous discontinuities in geodynamic numerical models 

Valeria Fedeli and Anna Maria Marotta

 Discontinuities affect the Earth’s dynamics, yet the Earth is often represented in geodynamical models as a continuous material. The challenge of representing discontinuities in numerical models has been addressed in several ways in literature. The split node method, originally introduced by Jungels (1973) and Jungels and Frazier (1973) for elastic rheology and then modified by Melosh and Raefsky (1981) to simplify its implementation, allows the introduction of discontinuity into a finite element model by imposing an a-priori slip at a designated node, where the displacement depends on the element which the node is referred to. Originally, this method requires that the discontinuity’s geometry and slip are pre-established.

More recently, Marotta et al. (2020) modify this approach by introducing a coupling factor that indicates the percentage difference between the velocities of the element to which the slip node belongs, while the velocity consistently derives from the dynamic evolution of the system. However, this method still requires the pre-establishment of the discontinuity’s geometry.

We here present a new technique that enables the dynamic identification of the discontinuity’s during the thermomechanical evolution of the system, based on physical parameters and without predefining the slip or the geometry.

We have implemented a new algorithm that identifies one or more discontinuities in a finite-element scheme operating through two phases: nucleation and propagation. Nucleation involves selecting a yield physical property and identifying the potential slip nodes, i.e., nodes on which the chosen physical property exceeds a yield value. The nucleus is then identified as the potential slip node where the chosen property most exceeds the yield. Propagation can be performed by choosing between three approaches of propagation: single simple fault, multiple simple fault and single double fault; and three schemes for the identification of neighboring nodes: grid-bounded, pseudo-free and free. The resulting discontinuity is the line connecting the nucleus and the propagation nodes.  Once the discontinuity has been identified, a coupling factor is introduced and the algorithm continues to operate following the Marotta et al., (2020)’s scheme.

The results of several benchmark tests, performed through both simple and complex finite-elements models, confirm the success of the algorithm in recognizing yield conditions and introducing a discontinuity into a finite-element model and demonstrate the correctness of the propagation’s geometry.

References

Jungels P.H.; 1973: Models of tectonic processes associated with earthquakes. PhD thesis.

Jungels P.H., Frazier G.A. Frazier; 1973: Finite element analysis of the residual displacements for an earthquake rupture: source parameters for the San Fernando earthquake. Journal of Geophysical Research.

Marotta A.M., Restelli F., Bollino A., Regorda A., Sabadini R.; 2020: The static and time-dependent signature of ocean-continent and ocean-ocean subduction: The case studies of Sumatra and Mariana complexes. Geophysical Journal International.

Melosh H.J., Raefsky A.; 1981: A simple and efficient method for introducing faults into finite element computations. Bulletin of the Seismological Society of America.

How to cite: Fedeli, V. and Marotta, A. M.: A dynamic identification of continuous discontinuities in geodynamic numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5338, https://doi.org/10.5194/egusphere-egu24-5338, 2024.

EGU24-6061 | Orals | TS3.3

Kinematics of active deformation and possible segmentation of seismic slip along the foothills of the Western Kunlun (China). 

Martine Simoes, Christelle Guilbaud, Jérôme Van der Woerd, Guillaume Baby, Laurie Barrier, Haibing Li, and Jiawei Pan

The Tibetan Plateau stands as a prominent topographic feature at the Earth’s surface, characterized by intense seismic activity, in particular along the mountain ranges that form its bounding edges. To the northwest, the Western Kunlun Range has received increasing attention since the 2015 Mw 6.4 Pishan earthquake but its kinematics of deformation remain to be properly documented. Here, we analyse the terrace record of active deformation along the Karakash River, where it crosses the Hotan anticline. We date terraces using in-situ produced cosmogenic isotopes, and show that terrace incision and uplift are spatially correlated with blind duplex ramps beneath the anticline. From there, we quantify the overall slip rate of the duplex to be 1.2-2.8 mm/yr over the last ~250 kyr. Our data are not able to resolve the detailed kinematics on each blind ramp and we cannot exclude that several of them are active at places along the anticline. By comparison to the data available west of our study area, we propose that the blind structures all along the foothills of the Western Kunlun range have an overall slip rate of ~2 mm/yr. However, the way this slip rate is to be partitioned on one or several blind ramps is expected to vary along strike, generating a certain structural and kinematic segmentation of active deformation, and from there possibly explaining the moderate recorded seismicity in this region. Because this slip is transmitted upward and forward onto the Mazar Tagh wide and geometrically simple frontal thrust sheet, we question the possibility of large – but rare – earthquakes rupturing this structure. From there, we propose the idea of a bimodal seismicity in the region, as a mirror of the structural segmentation of active faults.

How to cite: Simoes, M., Guilbaud, C., Van der Woerd, J., Baby, G., Barrier, L., Li, H., and Pan, J.: Kinematics of active deformation and possible segmentation of seismic slip along the foothills of the Western Kunlun (China)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6061, https://doi.org/10.5194/egusphere-egu24-6061, 2024.

EGU24-6563 | Orals | TS3.3

Meta-analyzing geological data for seismic hazard assessment: the case study of central Apennines 

Deborah Di Naccio, Cinzia Di Lorenzo, Marco Battistelli, Simona Miccolis, Vanja Kastelic, and Michele MC Carafa

In the past decade, seismic hazard assessment has progressively relied on innovative approaches based on seismotectonic models for robust physical-based short-term and long-term estimations. For this reason, consistency and homogenization are crucial in collecting data for a scientifically sounding seismotectonic model, especially when dealing with large amounts of information at different temporal and spatial scales. Additionally, a solid probabilistic approach is needed to correctly explore the uncertainties of the seismotectonic model components (e.g., offset, age, long-term slip rate). In this contribution, we focus on the active tectonics of the central Apennines because they have been repeatedly investigated in past decades, and a significant amount of complementary data is available. In such a case, we can define an innovative fault database for seismic hazard assessment, exploring in a probabilistic sense the deformation data (age and offset) and rate (long-term slip rate). Our approach provides a substantial methodological upgrade to fault-based input for seismic hazard assessment. The proposed methodology can be easily exported to zones with scarce data availability.

How to cite: Di Naccio, D., Di Lorenzo, C., Battistelli, M., Miccolis, S., Kastelic, V., and Carafa, M. M.: Meta-analyzing geological data for seismic hazard assessment: the case study of central Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6563, https://doi.org/10.5194/egusphere-egu24-6563, 2024.

EGU24-6771 | Posters on site | TS3.3

Active crustal-scale duplexes and structural wedge in the central part of Greater Caucasus orogen pro-wedge, Georgia 

Victor Alania, Onise Enukidze, Nino Kvavadze, Anzor Giorgadze, Demur Merkviladze, Alexander Razmadze, and Tornike Xevcuriani

The Greater Caucasus orogen is a typical active double wedge orogen that accommodates the crustal shortening due to far-field effects of the collision between the Arabian and Eurasian plates. Our study area is a central part of the Greater Caucasus pro-wedge and represented by the Dzirula-Imereti Uplift zone and epicentral area of Racha 1991 (MW=7) and 2009 (MW=6) earthquakes - Southern Slope of Greater Caucasus. Here we present a new structural model based on interpreted seismic profiles and regional balanced cross-sections. Seismic reflection data reveals the presence of a basement structural wedge, fault-related folds, triangle zones, and active- and passive-roof duplexes. The most important observation from our study is that the Dzirula massif is a basement wedge and forms a triangle zone. The Dzirula structure is defined by mid-crustal detachment and a roof thrust, constituting a tectonic wedge with a passive back thrust. The regional balanced cross-sections show that the Racha earthquakes are related to crustal-scale duplexes.

Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

How to cite: Alania, V., Enukidze, O., Kvavadze, N., Giorgadze, A., Merkviladze, D., Razmadze, A., and Xevcuriani, T.: Active crustal-scale duplexes and structural wedge in the central part of Greater Caucasus orogen pro-wedge, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6771, https://doi.org/10.5194/egusphere-egu24-6771, 2024.

EGU24-7249 | Orals | TS3.3

Insights into the September 8, 2023, MW 6.8 earthquake in Morocco: a deep transpressive fault along the High Atlas Mountain belt 

Daniele Cheloni, Nicola Angelo Famiglietti, Cristiano Tolomei, Riccardo Caputo, and Annamaria Vicari

On September 8, 2023, a magnitude 6.8 earthquake impacted the High Atlas Mountains in western Morocco, approximately 70 km southwest of Marrakesh, resulting in significant devastation and casualties. This study delves into a comprehensive geodetic dataset, utilizing interferometric synthetic aperture radar (InSAR) measurements to analyze the fault segment accountable for the seismic occurrence. Our findings propose two potential fault scenarios: a transpressive NNW-dipping high-angle fault (70°), associated with the Tizi n’Test alignment, or a transpressive SSW-dipping low-angle fault (22°) linked to the North Atlas Fault, where slip (up to 2.2 m) is observed predominantly in deeper sections of the fault. Although seismic catalogs were inconclusive regarding the dip direction of the fault, evidence from mainshock locations, gravity and heat-flow data, along with modeling, and the active shortening direction, collectively indicate the activation of a low-angle, southwesterly dipping oblique thrust of the North Atlas fault during the 2023 Moroccan earthquake. Integrating interferometric analyses with geological, tectonic, and seismological data could be crucial for resolving ambiguities in satellite-based models. This study therefore underscores the complexity of fault identification and the need for a multidisciplinary approach in understanding seismic events.

How to cite: Cheloni, D., Famiglietti, N. A., Tolomei, C., Caputo, R., and Vicari, A.: Insights into the September 8, 2023, MW 6.8 earthquake in Morocco: a deep transpressive fault along the High Atlas Mountain belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7249, https://doi.org/10.5194/egusphere-egu24-7249, 2024.

EGU24-7666 | ECS | Orals | TS3.3

Progressive development of an accretionary wedge margin from oblique thrust to strike-slip fault (Mikulov Fault, Outer Western Carpathians). 

Martin Šutjak, Rostislav Melichar, Ivo Baroň, Yi-Chin Chen, Jan Černý, Jia-Jiyun Dong, Václav Dušek, Filip Hartvich, Lenka Kociánová, Tung Nguyen, Matt Rowberry, and Chia-Han Tseng

The Outer Western Carpathians are fractured by several syn-thrust and post-thrust faults. One of them, the Mikulov Fault, has been studied using a combination of surface and subsurface methods. The former comprised the analysis of a LiDAR digital terrain model and aerial photographic interpretation while the latter comprised the analysis of ERT profiles and 2D seismic reflection profiles interpreted with the aid of borehole data. Paleostress analysis has also been used to understand the stress history and progressive development of the fault. By combining these methods it has been possible to define a distinct N-S directed fault zone that intersects or delineates the majority of the Jurassic limestone nappe outliers around the highlands of Pavlov Hills. This almost continuous fault zone runs for several kilometers on the Czech side of the border and extends further south into Austria. The thrusted Jurassic limestone bodies are cut by the fault zone, which tectonically crushed the limestone in its core and the cores of the secondary fault branches. The mapped pattern of the fault zone suggests branching and reattaching with the production of lenticular tectonic slices. Consequently, we interpret the fault as a prominent sinistral shear zone. This is indicated on the surface by block displacement on Svatý kopeček Hill and by the orientation of the accompanying subvertical Riedel shears with identified horizontal lineation. Subsurface kinematic indication derives from the interpretation of a prominent negative flower structure in the deep seismic profiles, just beneath the fault zone. The ERT profiles have revealed that the limestone bodies are tectonically bound by accompanying fault branches. Moreover, paleostress analysis suggest that fault zone activity can be divided into three main stages: (i) NE-SW thrust faults indicate thrusting of the Carpathian accretion wedge over the Bohemian Massif; (ii) NE-SW strike-slip faulting, during which the fault blocks moved along the faults in the direction of propagating wedge; (iii) N-S strike-slip faulting, marking the change in compression direction and transition from thrusting to a strike-slip regime. The main movement along the fault is probably of the late Miocene age and probably continues to the present day.

 

The research was funded by the Grant Agency of the Czech Republic (GC22-24206J).

How to cite: Šutjak, M., Melichar, R., Baroň, I., Chen, Y.-C., Černý, J., Dong, J.-J., Dušek, V., Hartvich, F., Kociánová, L., Nguyen, T., Rowberry, M., and Tseng, C.-H.: Progressive development of an accretionary wedge margin from oblique thrust to strike-slip fault (Mikulov Fault, Outer Western Carpathians)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7666, https://doi.org/10.5194/egusphere-egu24-7666, 2024.

EGU24-7731 | ECS | Posters on site | TS3.3

Complex fault-zone structure of the 2021 Yangbi Earthquake sequence revealed by dense array observations 

Xianwei Zeng, Chunquan Yu, and Gongheng Zhang

The 2021 MS 6.4 Yangbi earthquake occurred near the southwestern boundary of the Chuandian block in the SE Tibetan Plateau. Previous studies found that the mainshock occurred to the west of the main boundary fault – the Weixi-Qiaohou-Weishan fault, but the detailed seismogenic structure of the Yangbi earthquake sequence remains unclear. Accurate spatiotemporal characteristics of aftershocks and precise fault-zone structure are crucial for a more thorough understanding of the seismogenic structure and nucleation mechanisms of the Yangbi earthquake. Five days after the mainshock, we deployed a dense array with 200 short-period nodal seismometers spaced approximately 2 to 3 km in the vicinity of the Yangbi earthquake source region. In this study, we use the three-month-long continuous recordings of the dense array to study aftershock source parameters and fault-zone structures. We first obtained an earthquake catalog containing 88934 high-resolution event locations and 625 high-quality focal mechanisms. The entire aftershock sequence has a complete magnitude of -0.2, and a b-value of 0.97, with earthquake depths concentrated between 1 and 7 km below sea level. Combining precise aftershock locations and focal mechanisms, we constructed a detailed three-dimensional fault-zone structure model for the Yangbi earthquake sequence. The results reveal significant geometric variations in both strike and dip directions of the main fault. Along the dip direction, a conspicuous flower-like structure is present in the shallow part, transitioning to a listric structure inclined to the southwest at deeper levels. Along the strike direction, a noticeable bend exists in the central part. Several conjugate or intersecting faults are also present around the main fault. One of these faults, intersecting the main fault at a depth of about 4 km and dipping to the northeast, is likely the seismogenic fault of the largest foreshock. Additionally, below the main fault, there is another listric fault which appears to connect to the known Weixi-Qiaohou-Weishan fault at the surface. Our study provides new insight into the mechanism of the 2021 Yangbi earthquake sequence. The 3D fault-zone geometry can potentially be used for dynamic source modeling to better understand the initiation and rupture process of the mainshock.

How to cite: Zeng, X., Yu, C., and Zhang, G.: Complex fault-zone structure of the 2021 Yangbi Earthquake sequence revealed by dense array observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7731, https://doi.org/10.5194/egusphere-egu24-7731, 2024.

EGU24-7828 | Orals | TS3.3

3-D structural model of the Rioni foreland fold-and-thrust belt, Georgia  

Onise Enukidze, Victor Alania, Nino Kvavadze, Alexandre Razmadze, Anzor Giorgadze, and Demur Merkviladze

The Rioni foreland basin system is located between the Lesser Caucasus (LC) and the Greater Caucasus (GC) orogens. Deformation of the Rioni double flexural foreland basin was controlled by the action of two opposing orogenic fronts, the LC retro-wedge to the south and the GC pro-wedge to the north (Alania et al., 2022). The Rioni foreland fold-and-thrust belt (RFFTB) is part of the Greater Caucasus pro-wedge.  Here we show the deformation structural style of the RFFTB based on seismic reflection profiles and serial structural cross-sections. On the basis of serial structural cross-sections, 3-D structural models. 2-3D structural models show that the Rioni foreland is a thin-skinned fold-and-thrust belt and the main style of deformation within the RFFTB is represented by a set of fault-propagation folds, duplexes, and triangle zones. The presence of two detachment levels in the RFFTB raises important questions about the deformation sequence. The serial structural cross-sections show that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. The formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. Recent earthquake data indicate that the RFFTB is still tectonically active and earthquake focal mechanisms within the RFFTB are thrust faults (Tsereteli et al., 2016), and active structures are mainly represented by thrust faults, blind thrusts, and blind wedges. 

Acknowledgments. This work was funded by the Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

References

Alania, V., et al. (2022). Deformation structural style of the Rioni foreland fold-and-thrust belt, western Greater Caucasus: Insight from the balanced cross-section. Frontiers in Earth Science 10, 10968386.

Tsereteli, N., et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328–344.

How to cite: Enukidze, O., Alania, V., Kvavadze, N., Razmadze, A., Giorgadze, A., and Merkviladze, D.: 3-D structural model of the Rioni foreland fold-and-thrust belt, Georgia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7828, https://doi.org/10.5194/egusphere-egu24-7828, 2024.

EGU24-8289 | ECS | Orals | TS3.3

Unrevealing Seismogenic Sources of Historical Earthquakes: New Insights from the Elusive 1706 Maiella Earthquake (Abruzzi Region, Central Italy) 

Tiziano Volatili, Veronica Gironelli, Lucia Luzi, Paolo Galli, Michele Carafa, and Emanuele Tondi

The Inner Abruzzi region ranks among Italy's highest seismic hazard areas, hosting a system of SW-dipping normal faults historically active with moderate-to-large earthquakes (Mw ≥ 5.5). The L’Aquila earthquake in April 2009 (Mw = 6.3) intensified interest in assessing active fault seismogenic potential. Despite extensive studies, the Maiella Massif's historical seismicity, notably the 1706 and 1933 earthquakes (Mw ~6.8 and 5.9, respectively), causing severe damage, remains elusive. The investigation of historical seismic events, such as the 1706 earthquake within the Maiella area, aligns with the pressing need to identify and characterize potential seismogenic sources of future seismic activity. This task is often hindered by the scarcity of unambiguous evidence or quantitative data at both near-surface and seismogenic depths. Many source hypotheses, possibly related to the 1706 earthquake, are present in the literature. These structures, with different geometrical parameters, depths, and kinematics, characterized the tectonic setting of this region.

This study offers a comprehensive overview of these hypotheses in assessing the 1706 earthquake’s source. Their 3D geometrical representation was modelled, considering the available geological and geophysical information. The resultant seismic scenarios were estimated in terms of macroseismic intensity by calculating peak ground motion values (i.e., PGV, PGA) for each point within the 1706 macroseismic field. This procedure incorporates site amplification effects into the synthetic ground motion calculations at each site within the macroseismic field, coupling a Vs,30 map of the Italian territory. Finally, the determination of the best source model involves assessing the misfit (residuals) between the simulated macroseismic intensities and the observed ones. The accuracy of the simulated macroseismic field in reproducing the real field is evaluated by calculating the residual mean and the root-mean-square error (RMSE).

The study outcomes highlight the complexities in determining the exact source of the 1706 earthquake. Despite detailed modelling efforts, discrepancies in intensity distributions and the absence of recent seismic activity on specific faults pose uncertainties in understanding seismicity in the Inner Abruzzi area. While contributing to the ongoing debate, the research underscores the need for further investigations to better constrain the seismic hazard of this region.

How to cite: Volatili, T., Gironelli, V., Luzi, L., Galli, P., Carafa, M., and Tondi, E.: Unrevealing Seismogenic Sources of Historical Earthquakes: New Insights from the Elusive 1706 Maiella Earthquake (Abruzzi Region, Central Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8289, https://doi.org/10.5194/egusphere-egu24-8289, 2024.

EGU24-9839 | ECS | Posters virtual | TS3.3

Geometrical characteristics of buried fault damage zones in the Bohai Basin, eastern China 

Nianfa Yang and Zonghu Liao

Characterizing the structures of buried faults is inherently challenging due to a lack of data. However, the seismic survey has demonstrated the potential to reveal geometrical features of faults in the subsurface. In this study, we utilized three-dimensional seismic data and its associated attributes of variance, edge detection, and azimuth for investigating the distribution and structural characteristics of the buried faults in the Bohai Basin, eastern China. The results indicate: (1) there are two 7-km NNE strike-slip carbonate faults (F1, F2, in the Figure) dominated in this region, with fault sub-systems of horst and graben, stepped combinations, and "Y"-shaped; (2) F1 fault is approximately 6.5km with a fault damage zone of about 0.75km in width, and F2 fault is about 7.5km with a fault damage zone of 1.0km in width; (3) The width of fault damage zones increases from south to north, with increasing fault displacement. The maximum fault displacements of F1 and F2 are estimated at 420m and 700m, respectively. We argue that fault displacement leads to the growth of fault damage zones, which potentially controls the evolution of fault architecture. The geometrical information from the subsurface may provide crucial insights for understanding the fault mechanisms and associated earthquakes.

Figure 1. (A) Seismic attribute map of edge detection and time structure showing the two carbonate faults (F1, F2); (B) Measured fault displacement and damage zone width along the fault striking direction of F1 and (C) F2.

How to cite: Yang, N. and Liao, Z.: Geometrical characteristics of buried fault damage zones in the Bohai Basin, eastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9839, https://doi.org/10.5194/egusphere-egu24-9839, 2024.

EGU24-10101 | Posters on site | TS3.3

Structure, morphology and seismicity of the frontal part of a propagating fold-and thrust belt: The Holocene 123-km-long Kur Fault, Greater Caucasus, Azerbaijan  

Alessandro Tibaldi, Fabio Bonali, Federico Pasquaré Mariotto, Paolo Oppizzi, Nino Tsereteli, Hans Havenith, Gulam Babayev, and Tomáš Pánek

We present the main features of the frontal structure, known as Kur Fault, of the Plio-Quaternary Kura fold-and-thrust belt in the Greater Caucasus (Azerbaijan). The Kur Fault has been analysed thanks to geological-structural and geomorphological surveys of its whole length, integrated by a relocation of instrumental seismicity, data on historical seismicity, new focal mechanism solutions, and ambient vibration measurements across the fault trace. The in-depth study of the frontal structure can: i) provide insights into the shallow propagation of a regional reverse fault, ii) contribute to a better understanding of the earlier stage of development of a young continent-continent collision, and iii) have implications for seismic hazard assessment because the area is seismically active and hosts the most important infrastructure for energy production in the country. The results show that the fault deforms the surface for a total length of 123 km. The shallow expression is given by four main scarp segments, with a right-stepping arrangement, which have different structural significance; they are represented by an alternation of fault-propagation folds, folds with offset frontal limbs, and shallow faulting. Analyses of the age of deformed deposits and landforms suggest activity from Mid-Late Miocene times to the Holocene. The fault attitude and its reverse kinematics are coherent with the Holocene and present-day state of stress, characterised by a N-S to NNE-SSW horizontal s1, suggesting the capability for seismic reactivation. Earthquake focal mechanism solutions indicate from pure reverse motions to transpressional kinematics in the area. Calculation of potential Mw indicates values in the range 7.5-7.9 if we consider its entire fault length, 6.1-7.2 if we consider the single segments.     

How to cite: Tibaldi, A., Bonali, F., Pasquaré Mariotto, F., Oppizzi, P., Tsereteli, N., Havenith, H., Babayev, G., and Pánek, T.: Structure, morphology and seismicity of the frontal part of a propagating fold-and thrust belt: The Holocene 123-km-long Kur Fault, Greater Caucasus, Azerbaijan , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10101, https://doi.org/10.5194/egusphere-egu24-10101, 2024.

EGU24-10669 | Posters on site | TS3.3

Fault offset rate and historic earthquake catalogue-based seismic coupling estimate for the central Apennines (Italy) 

Cinzia Di Lorenzo, Michele Carafa, Deborah Di Naccio, and Vanja Kastelic

The large amount of long-term fault slip rate measurements allows for determining the long-term tectonic moment rate for the central Apennines (Italy). Converting the long-term moment rate in seismicity rates requires a correct estimation of the long-term seismic coupling due to aseismic creep, possibly responsible for some of the observed dislocations. Ignoring this issue could induce a gross overestimation of the regional seismic hazard. Consequently, we must quantify the fraction of tectonic deformation released as earthquakes to correctly use the fault-based approach for forecasting long-term seismicity and assessing the seismic hazard of a region. To this aim, we introduce the seismic coupling in the calculation and treat it as a statistical variable. The probabilistic approach also considers the uncertainties in each parameter of active faults (depth of seismicity cutoff, length, and slip rate). The parameters of a regional Tapered Gutenberg-Richter distribution are determined to reproduce the observed earthquake size distribution. We found that about three-quarters of the long-term tectonic moment rate goes into earthquake activity, suggesting a non-marginal role of aseismic deformation for active faults in the central Apennines.

How to cite: Di Lorenzo, C., Carafa, M., Di Naccio, D., and Kastelic, V.: Fault offset rate and historic earthquake catalogue-based seismic coupling estimate for the central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10669, https://doi.org/10.5194/egusphere-egu24-10669, 2024.

EGU24-11665 | Posters on site | TS3.3

Dual Role of Fluids in Activating Extensional Seismicity at Middle and Lower Crust Depth: the Deformation Corridor Throughout the Southern-Central Apennines (Italy) 

Rita de Nardis, Alessandro Vuan, Luca Carbone, Donato Talone, Maria Adelaide Romano, and Giusy Lavecchia

Our study extensively explores the analysis of successive swarms and seismic sequences that followed the 2009 L'Aquila mainshock (Mw 6.3) in the southern-central Apennines of Italy—a region historically recognized for seismic events, some reaching ~M7.

The study area is characterized by active fault alignments well-documented in the geological literature. Bounded eastward by the Fucino-Marsicano-Barrea SW-dipping faults and westward by the southern termination of the Ernici NE NNE-dipping fault systems, it is also crosscut by the Villavallelonga-Pescasseroli–San Donato-Val Comino and the innermost right-stepping en-echelon Balsorano-Posta Fibreno sets, as well as the Sora fault.

Despite its active fault systems, the study area exhibits a low level of seismicity, prompting extensive investigation in previous experiments conducted by temporary seismic networks (Bagh et al., 2007; Romano et al., 2013) and more recent contributions by Frepoli et al. (2017). Notwithstanding, the paucity of seismicity, coupled with the deep geometry of faults and their association with historical earthquakes, remains a topic of ongoing debate in the literature.

Through the application of template matching techniques (Vuan et al., 2018) to enhance the available seismic catalog, we unveil previously undetected low-level seismicity with a completeness magnitude ML ~ 0.0. The space-time evolution of the intense seismicity, along with the characterization of each seismic episode, migration velocity, and Vp/Vs ratios, combined with the 3D distribution of seismicity and geological data, revealed both a clear tectonic influence and the role of fluids in seismic processes. This exploration illuminated previously unknown geometric aspects and provided the first evidence of the WNW-ESE deformation zone in the southernmost segment of the Villavallelonga fault at depths ranging from 11 to 15 km. Our results indicate that deeper seismicity (>16 km) suggests an ascending trend of possible mantle-derived CO2.

These findings significantly contribute: (1) to the understanding of tectonic seismic swarms in extensional domains, (2) to provide insights into fluid involvement in seismic processes, and (3) to the discussion of the seismotectonic setting in high seismic-risk areas. The acknowledgment of the value of microseismicity for regional seismotectonic studies serves as a compelling conclusion, underscoring the broader significance of these findings.

 

Bagh, S., Chiaraluce, L. et al. 2007. Background seismicity in the Central Apennines of Italy: The Abruzzo region case study. Tectonophysics, 444,80–92.

Frepoli, A, Cimini, G.B et al., 2017. Seismic sequences and swarms in the Latium-Abruzzo-Molise Apennines (central Italy): New observations and analysis from a dense monitoring of the recent activity, Tectonophysics, 312-329.

Vuan, A., Sugan, M., et al., 2018. Improving the Detection of Low‐Magnitude Seismicity Preceding the Mw 6.3 L’Aquila Earthquake: Development of a Scalable Code Based on the Cross Correlation of Template Earthquakes. BSSA 108, 471–480.

Latorre, D., Di Stefano, R., et al., 2023. An updated view of the Italian seismicity from probabilistic location in 3D velocity models: The 1981–2018 Italian catalog of absolute earthquake locations (CLASS): Tectonophysics, 846, 229664.

Romano, M. A., de Nardis, et al., 2013. Temporary seismic monitoring of the Sulmona area (Abruzzo, Italy): A quality study of microearthquake locations. NHESS, 13, 2727–2744.

How to cite: de Nardis, R., Vuan, A., Carbone, L., Talone, D., Romano, M. A., and Lavecchia, G.: Dual Role of Fluids in Activating Extensional Seismicity at Middle and Lower Crust Depth: the Deformation Corridor Throughout the Southern-Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11665, https://doi.org/10.5194/egusphere-egu24-11665, 2024.

EGU24-12862 | ECS | Posters on site | TS3.3

Active deformation within the slow-straining northernmost Africa region constrained by InSAR time-series 

Renier Viltres, Cécile Doubre, Marie-Pierre Doin, and Frédéric Masson

The present-day tectonics of the northernmost Africa region is dominated by the oblique convergence
between the Nubia and Eurasia plates initiated 35 Ma ago. GNSS-derived velocities indicate that the
relative plate motion of only ~5 mm/yr is accommodated within a wide region involving inland
and offshore tectonic structures, from Morocco to Tunisia and from the Mediterranean Sea to the Sahara
platform. Due to limited and sparse geodetic measurements, the main zones of strain accommodation as
well as the strain partitioning between thrust and strike-slip faults remain unresolved. However, despite
the low strain budget, significant seismicity and destroying earthquakes have been recorded in the region
with five M>6 events nucleated on both inland and offshore faults during the last decade.

To better identify the active inland faults and constrain their interseismic behavior for a better seismic
hazard assessment in northernmost Africa, we used multi-temporal InSAR analysis to produce the first
regional-scale interseismic velocity map of the region. The primary data consists of up to ~8 years of
SAR imagery from the Sentinel-1 satellite constellation for 6 tracks in both the ascending and descending
orbits. The data processing and the generation of InSAR-based time series describing the spatio-temporal
evolution of surface deformation were performed using the New Small Baselines Subset processing chain
(NSBAS, Doin et al. 2011). We followed a three-blocks processing strategy leading to (1) interferograms
generation, (2) phase unwrapping, and (3) time series estimation. Within the first block, interferometric
networks combining image pairs with short and long temporal baselines were defined to mitigate potential
bias introduced by changes in soil properties (e.g., snow, vegetation growth, dunes). Before unwrapping,
interferograms flattening, multi-looking, and atmospheric phase screen (APS) corrections based on the
ECMWF ERA-5 atmospheric model were implemented. The resulting time series of surface displacement
along the line-of-sight direction (LOS) for the 2014-2022 period were decomposed into the near-vertical
and horizontal (E-W) components and expressed into a Eurasia-fixed reference frame using the GNSS
velocities in Billi et al. (2023).

Our estimated deformation maps reveal multi-scale present-day motions, with large- and small-scale
signals suggesting tectonic origin and ground response to anthropogenic activity or landslides, respectively.
The oblique plate convergence involves the interseismic loading of a series of E-W oriented right-lateral
strike-slip inland faults. Between the longitudes ~3°W and ~9°E, this inland deformation is localized
within a 25-75 km wide zone consistent with a unique linear strike-slip fault without any clear uplift related
to thrusting on already mapped transfer structures. The rates and directions of surface displacements
suggest that the shortening component of the Nubia-Eurasia relative plate motion is almost entirely
accommodated by offshore tectonic structures which has an important impact on the assessment of
seismic and tsunamigenic hazards.

 

 

How to cite: Viltres, R., Doubre, C., Doin, M.-P., and Masson, F.: Active deformation within the slow-straining northernmost Africa region constrained by InSAR time-series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12862, https://doi.org/10.5194/egusphere-egu24-12862, 2024.

EGU24-13778 | Orals | TS3.3

Inversion tectonics and dual decollements in southwestern Taiwan: implication from a dense seismic array 

Wei-Hau Wang, Yi-Shen Lin, Wei-Cheng Huang, and Strong Wen

We employed dense seismic arrays to reveal the seismogenic zones beneath the foreland basin and the foothills in southwestern Taiwan. We used EqTransformer to pick earthquakes and P and S wave arrival time, GaMMA to associate earthquakes, and NonLinLoc to locate the earthquakes. Our results show that the thin-skinned thrust belts were mostly locked above a shallow decollement at a depth of ca. 6 km. Below it, a foreland-dipping seismogenic belt extends from the base of the shallow decollement to a depth of about 15 km, the deep decollement, beneath the coastal plain. We interpret this westward-dipping seismogenic belt as a passive roof duplex by inversion of the pre-existing graben-and-horst structure sliding along a ductile shear zone at a depth of 15 km during the ongoing orogeny.

How to cite: Wang, W.-H., Lin, Y.-S., Huang, W.-C., and Wen, S.: Inversion tectonics and dual decollements in southwestern Taiwan: implication from a dense seismic array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13778, https://doi.org/10.5194/egusphere-egu24-13778, 2024.

EGU24-13981 | Posters on site | TS3.3

Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence 

Chung-Hsiang Mu, Ching-Chou Fu, Hao Kuochen, Kuo-Hang Chen, and Kuo-Wei Chen

Our goal is to comprehend fluid circulation within fault zones and its impact by monitoring hydrochemical and hydrophysical aspects across multiple dimensions. We also monitor nearby micro-seismicity and surface deformation. MAGIC (Multidimensional Active fault of Geo-Inclusive observation Center) is located at the Chihshang creeping fault, situated at the boundary of tectonic plates in eastern Taiwan. This fault exhibits aseismic creep at a rate of 2 cm per year, alongside high seismic activity.

The earthquake sequence of 2022 began with a magnitude 6.4 event on September 17 (local time), followed by a magnitude 6.8 earthquake the next day. The epicenters were within the Central Range fault system, positioned to the west of our monitoring network. This presents a significant opportunity to observe co-seismic changes in pore pressure within the footwall and fault zone.

The findings revealed that after the initial earthquake in the adjacent fault system, the pore pressure within the footwall swiftly decreased by nearly 100 cm within 15 hours. Simultaneously, the pore pressure within the fault zone increased by approximately 25 cm during the same period. Subsequently, the footwall's pore pressure continued to decrease with the second earthquake and then slowly recovered. These alterations in pore pressure suggest that fractures underwent both opening and closure during stress migration.

How to cite: Mu, C.-H., Fu, C.-C., Kuochen, H., Chen, K.-H., and Chen, K.-W.: Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13981, https://doi.org/10.5194/egusphere-egu24-13981, 2024.

EGU24-14319 | Posters on site | TS3.3

Paleoseismic records around epicenter of the 2017 Pohang earthquake, SE Korea 

Seongjun Lee, Youngbeom Cheon, Jong-won Han, Sangmin Ha, Jeong-Heon Choi, Yeong Bae Seong, Hee-Cheol Kang, and Moon Son

The 2017 Pohang earthquake (ML 5.4) ranked as the second-largest instrumental earthquake in Korea and the most destructive seismic event. Before this event, the absence of documented instrumental seismic activity and no mapped Quaternary faults near the epicenter raised questions about the paleoseismic history of the region. This study aims to gather and trace evidences of the paleoseismic ruptures along the surface projection of seismogenic fault, reported by previous study, and interpret their implications. To achieve it, we conducted comprehensive paleoseismological investigations, including geomorphic analysis, fieldwork, drilling survey, trench excavation and numerical age dating. Through geomorphic analysis and drilling survey, we identified two lineaments: NNE–SSW-striking Fault-1 and NE–SW to NNE–SSW-striking Fault-2. In the excavation site of fault-1, stratigraphic features and numerical ages indicate that the PE event occurred between 11±1 ka and 2.6±0.1 ka, and then the MRE event activated after 0.17±0.01 ka.  On the other hand, the combined results of two outcrops of Fault-2 show that the MRE and PE of Fault-2 could be constrained to have occurred between 148±7 ka and ca. 40 ka and around 200 ka, respectively. Our findings present that even before the 2017 Pohang earthquake, seismic events causing surface ruptures of moderate to large magnitude have occurred at least three times in this area during the late Quaternary.

This work was supported by a grant (2022-MOIS62-001) of National Disaster Risk Analysis and Management Technology in Earthquake funded by Ministry of Interior and Safety (MOIS, South Korea).

How to cite: Lee, S., Cheon, Y., Han, J., Ha, S., Choi, J.-H., Seong, Y. B., Kang, H.-C., and Son, M.: Paleoseismic records around epicenter of the 2017 Pohang earthquake, SE Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14319, https://doi.org/10.5194/egusphere-egu24-14319, 2024.

Kvarner area belongs to the External Dinarides fold-and-thrust belt that is characterized by intensive tectonic deformations of a few kilometers thick sedimentary cover of the central part of the Adriatic microplate. The main deformations occurred predominantly during Eocene to Oligocene thin-skinned tectonics, while late-orogenic thick-skinned deformations and wrenching resulted in the exhumation of the orogenic belt. The latter tectonic mechanism is supposed to be still active, but there is no reported evidence of active faults on the surface of predominantly karstic terrain. Nevertheless, seismological data reveal subsurface activity along various fault plane solutions, and crucial evidence of possible active deformations on the surface is expected within stratified superficial deposits in the area. However, stratified Quaternary sediments are rare onshore and on the Kvarner islands but are widespread on the bottom of the surrounding Adriatic Sea. During the targeted high-resolution sub-bottom geoacoustic seismic survey we focused on the zones that are characterized by earthquakes and on the previously arbitrarily recognized regional seismogenic sources. However, only shallow seismic profiles along and across the Vinodol and the NW part of the Velebit channel revealed clear evidence of fault-related deformations of the youngest Quaternary sediments. The fault zone is up to hundreds of meters wide, limited by parallel sub-vertical fault planes, and characterized by deformations of the strata between the planes either in a positive (uplifted) or a negative (downthrown) manner along the strike, which are typical for strike-slip faults. Besides, the disturbed layering of the uppermost well-stratified unit (Late Pleistocene) resembles fluid/sediment escape structures that could be related to strong shaking during prehistorical earthquakes. The fault zone is also tentatively recognized in the onshore bedrock along the strike of the submerged fault, where it appears as an indistinct fractured zone that is more corroded than surrounding bedrock carbonates. Therefore, sub-bottom profiling has been proven to be a useful tool for identifying active faults and should be used as a key method in future seismotectonic research of submerged seismogenic zones.

How to cite: Korbar, T., Hasan, O., Brunović, D., and Markušić, S.: High-resolution seismic imaging of the sub-bottom Quaternary deposits revealed an active fault in the Vinodol-Velebit channel (Kvarner, Croatia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14660, https://doi.org/10.5194/egusphere-egu24-14660, 2024.

To better understand seismotectonic processes and the associated seismic hazards within a region, it is imperative to explore the causality between earthquakes, active tectonics, and individual fault structures. Hypocenter locations represent a well-established method to identify active faults, their spatial geometry and temporal evolution. First motion focal mechanisms provide insights into source processes and fault kinematics, aiding in the reconstruction of seismic strain and seismogenic stress regimes. Waveform modelling is key to refine earth structure models and constrain source process parameters.

Here, we present the challenging case of the seismic sequence of Saint-Ursanne of March and April 2000 in Switzerland, where we applied advanced seismological analyses to reduce uncertainties in hypocenter locations and focal mechanisms, commonly encountered in shallow seismicity. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (ML) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which has been approved as a site for the development of a deep geothermal project. Our results, combined with geological data, suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the sequence. These new findings provide new insights into the present-day seismotectonic processes of the Jura fold-and-thrust belt (FTB) of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely <0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement. This transpressive regime is confirmed by the ongoing Réclère earthquake sequence, ca. 20 kilometres west of St. Ursanne, which initiated with a reverse event of ML 4.1 on December 24, 2021, and was followed by few aftershocks in January 2022. Seismic activity started again in March 2023 with another ML4.3 reverse event, which activated a left-lateral strike-slip secondary fault just west of the reverse fault. This fault seems to be more active in terms of microseismicity and is responsible for the increased activity over the last years.  

How to cite: Lanza, F. and Diehl, T.: Deciphering seismic sequences with high-precision hypocenter locations, focal mechanisms, and waveform modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14739, https://doi.org/10.5194/egusphere-egu24-14739, 2024.

EGU24-14973 | Orals | TS3.3

Deformed archeological remains at Lilybaeum in Western Sicily (southern Italy) as possible ground signatures of coseismically-slipped fault in the area 

Barreca Giovanni, Pepe Fabrizio, Sulli Attilio, Morreale Gabriele, Gambino Salvatore, Gasparo Morticelli Maurizio, Grassi Sabrina, Monaco Carmelo, and Imposa Sebastiano

Archaeoseismic analysis performed in Western Sicily point to deformed archeological remains at Lilybaeum, a Punic coastal city founded in 397 B.C. at the Island’s westernmost edge. Starting from the direct observation of deformed ruins, an interdisciplinary work-strategy, which has included field-structural analysis, drone-shot high-resolution aerial photogrammetry, and geophysical prospecting, was employed to investigate whether the identified deformations may represent the ground effects of a previously unknown large earthquake in the area. Among the unearthed remains, some mosaics and a stone-paved monumental avenue show evidence of tectonic deformation being fractured, folded, and uplifted. Trend of folding and fracturing is consistent with the NNW-SSE oriented tectonic max stress axis to which western Sicily is currently undergoing. Displacement along a fracture deforming the Decumanus Maximus together with the finding of a domino-type directional collapse, enable us to interpret the observed deformation as the ground signature of a coseismic slip. Seismic rupture occurred along a previously unmapped deformation front that well fits in the seismotectonic context of Western Sicily. Measured offset, geophysical prospecting, and age-constraints all point to the possibility that a highly-energetic earthquake nucleated in the area following a coseismic rupture along a NE-SW trending back-verging reverse fault towards the end of the IV century A.D. Since seismic catalogs do not provide evidence of such a large earthquake, the latter might represent a missed event in the historical seismic record. This finding provides constraints to redefine the seismic hazard of Western Sicily, a region where recurrence-time intervals for large earthquakes are still unknown.

How to cite: Giovanni, B., Fabrizio, P., Attilio, S., Gabriele, M., Salvatore, G., Maurizio, G. M., Sabrina, G., Carmelo, M., and Sebastiano, I.: Deformed archeological remains at Lilybaeum in Western Sicily (southern Italy) as possible ground signatures of coseismically-slipped fault in the area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14973, https://doi.org/10.5194/egusphere-egu24-14973, 2024.

EGU24-15305 | Posters on site | TS3.3

Multidisciplinary geophysical approach to investigate the deeper portion of the Central Apennines (Italy) 

Mara Monica Tiberti, Francesco Emanuele Maesano, Mauro Buttinelli, Pasquale De Gori, Fernando Ferri, Liliana Minelli, Maria Di Nezza, and Chiara D'Ambrogi

In the Central Apennines (Italy), the project RETRACE-3D provided a reliable 3D model of the crust in the area affected by the 2016-17 Amatrice-Visso-Norcia seismic sequence, highlighting that the coseismic rupture at the surface can involve old inherited normal faults while the seismogenic sources lay at depth, possibly reactivating and inverting previous thrust faults, as in the case of the Mw 6.5 Norcia earthquake (30 october 2016). Here we present a 2D gravity model across the Central Apennines, spanning from the Tyrrhenian coast to the Adriatic Sea, aimed at completing and verifying the crustal geometries resulting from the 3D model itself. The cross-section was built integrating different types of data, such as surface geology, hydrocarbon wells, seismic lines, and results from receiver function analysis. It was then checked against gravity anomalies and the velocity distribution from Local Earthquake Tomography (LET), adding further details, and, finally, against seismicity recorded during the 2016-2017 sequence. The results substantiate the reliability of the geometries proposed in the RETRACE 3D model, as they fit well, except for some local misfits, with the other independent data, such as the Bouguer anomalies and the velocity distribution from LET. Furthermore, the integration of different types of data allowed us to describe in detail the structural setting of the Apennine chain also in the surroundings of the RETRACE study area, where the cross-section length exceeds the 3D model, and to add some new elements at seismogenic depths, that exceed those typical of hydrocarbon exploration. In particular, we were able to investigate the nature of the basement top and its relationship with seismotectonics.

How to cite: Tiberti, M. M., Maesano, F. E., Buttinelli, M., De Gori, P., Ferri, F., Minelli, L., Di Nezza, M., and D'Ambrogi, C.: Multidisciplinary geophysical approach to investigate the deeper portion of the Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15305, https://doi.org/10.5194/egusphere-egu24-15305, 2024.

Outer Albanides experienced a seismic sequence starting on 21 September 2019, with an Mw 5.6 earthquake, followed by an Mw 5.1 aftershock 10 minutes later considered as foreshocks, and culminated with the main shock Mw 6.38 on 26 November 2019, preceded by several immediate foreshocks (Mw 2.0-4.4), followed by numerous aftershocks (Mw > 5.0). We model the co-seismic slip distribution using InSAR, permanent and campaign GNSS measurements. Two hypotheses are tested: an earthquake on a thrust plane with direction N160°, and an earthquake on a backthrust. Varying the depth and dip angle for the first hypothesis and only the dip angle for the second, it is concluded that the optimal solution is a blind thrust at a depth of 15 km with an eastward dip of 40°, a maximum slip of 1.4 m and a Mw of 6.38. The GNSS time series obtained after 2020 shows two slow slip events (SSE): the first 200 days after the main shock up to about 26 days, and the second 300 days after the main shock up to about 28 days. We tested three hypotheses: SSE occurred along the basement thrust where the main shock was localised, SSE occurred along the flat formed by the detachment layer of the cover, and SSE occurred along these two faults. It has therefore been concluded that SSE has occurred along the detachment layer or along both the detachment layer and the basement thrust activated during the Mw 6.38 Durres earthquake.

How to cite: Matraku, K., Jouanne, F., and Dushi, E.: The 26 November 2019 Durres earthquake, Albania: coseismic displacements and occurrence of slow slip events in the year following the earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15944, https://doi.org/10.5194/egusphere-egu24-15944, 2024.

EGU24-16075 | ECS | Posters on site | TS3.3

Earthquake data analysis in the Racha region, Georgia: Implication for 3D structural model active faults 

Nino Kvavadze, Victor Alania, and Onise Enukidze

The Caucasus region, which is one of the good examples of collision-driven far-field deformations, is located in the northernmost part of the Arabia/Eurasia collision zone and is classified with moderate seismic activity. Racha region, a part of Greater Caucasus orogen, in particular is characterized with the highest activity. In recent year several moderate earthquakes were observed in the region, notably 2009 September 7 (Mw = 6.0), 2011 August 18 (Mw = 4.8), and also 2024 January, 2 (Mb = 4.4), with depths varying from 10 to 15 km. The strongest event during the instrumental period recorded in Racha was observed in 1991 April 29, with magnitude Mw=7.0 and Depth = 17.2 km. Which was the largest earthquake recorded in the region, causing casualties. This event caused a number of fore- and aftershocks. Following the Racha 1991 earthquake temporary, dense seismic network was installed around the area to study aftershock activity, around 2000 aftershocks of different magnitudes were recorded by this network in total. This data was analyzed in several papers (for example Triep, et al., 1995, Fuenzalida, et al., 1997), including hypocenters and focal mechanisms. Depths of the aftershocks were observed ranging from 0 to 15 km. The mechanism of Racha 1991 main shock was shown to be reverse faulting on a gently sloping (35°) plane. Also, strong earthquake mechanisms show reverse faulting with strike-slip components. This work was oriented to analyze existing earthquake data and see its correlation to a 2-3D structural model created for the area.

Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

How to cite: Kvavadze, N., Alania, V., and Enukidze, O.: Earthquake data analysis in the Racha region, Georgia: Implication for 3D structural model active faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16075, https://doi.org/10.5194/egusphere-egu24-16075, 2024.

EGU24-16527 | ECS | Posters on site | TS3.3

First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses 

Giulia Patricelli, Maria Eliana Poli, Emanuela Falcucci, Stefano Gori, Giovanni Paiero, Enzo Rizzo, Andrea Marchesini, and Riccardo Caputo

We present the findings of a multimethodological study made on the Budoia-Aviano Thrust System conducted as part of the NASA4SHA PRIN Project “Fault segmentation and seismotectonics of active thrust systems: the Northern Apennines and Southern Alps laboratories for new Seismic Hazard Assessments in northern Italy”.

The NW dipping, SW-NE striking Budoia-Aviano Thrust System represents the southeast-verging external front of the Plio-Quaternary Eastern Southalpine Chain, occurring at the front of the western Carnic Pre-Alps, between Polcenigo and Montereale (PN).

The recent activity of the Budoia-Aviano thrust is evidenced by numerous geological and morphostructural features, including the exposure of Mio-Pliocene reliefs emerging from the Last Glacial Maximum alluvial plain, the upwarping of the LGM fan of the Artugna stream, and geomorphic anomalies of the surface hydrographic network (Poli et al., 2014).

Moreover, to identify sites to perform excavation aimed at exploring the Holocene movements of the thrust system, we performed multiscale geophysical investigations, such as Deep Electric Resistivity Tomography, Electric Resistivity Tomography and Ground Penetrating Radar across the entire thrust system. They revealed the presence of a series of possible north-verging shear planes, whose trace seemed to correspond to the more pronounced up-ward convex profile of the Artugna alluvial fan.

Based on geophysical results, two NNW-SSE paleoseismological trenches were excavated along selected GPR profiles. The trenches exposed late LGM-to-Holocene alluvial fan deposition of the Artugna stream. Notably, a paleosoil embedded in alluvial sequence yielded a 14C age interval between 16 Ky and 5 ky BCE.

In both trenches, the entire excavated late Quaternary succession was affected by a set of north-verging reverse planes, coinciding with the discontinuities identified in GPR profiles. In each trench, the total vertical displacement measured across all thrust planes is of about 4.5 meters, resulting from at least three displacement events occurred in the last 7,000 years. Moreover, the involvement of the bottom of the ploughed soil supports the hypothesis of the backthrust being activated during the MW 6.3 Alpago-Cansiglio earthquake (Rovida et al., 2022) as suggested by Galadini et al. (2005).

The integration of paleoseismology, photogrammetry, and high-resolution geophysics enabled the construction of a detailed 3D model of the Budoia-Aviano Thrust System, revealing a 20-meter-wide deformation zone on the hanging wall of the main south-verging Budoia-Aviano Thrust. In the perspective of seismic hazard assessment and regional planning, it is worth to consider the proximity of this active and capable fault to industrial complexes, urban centres, and vulnerable structures characterizing the Budoia and Aviano area.

REFERENCES

  • Galadini, M.E. Poli, Zanferrari, A. (2005). Seismogenic sources potentially responsible for earthquakes with M≥ 6 in the eastern Southern Alps (Thiene-Udine sector, NE Italy). Geophysical Journal International161(3).
  • M.E. Poli, G. Monegato, A. Zanferrari, E. Falcucci, A. Marchesini, S. Grimaz, P. Malisan, E. Del Pin (2014). Seismotectonic characterization of the western Carnic pre-alpine area between Caneva and Meduno (Ne Italy, Friuli). DPC-INGV-S1 Project.
  • Rovida, M. Locati, R. Camassi, B. Lolli, P. Gasperini, A. Antonucci (2022). Catalogo Parametrico dei Terremoti Italiani (CPTI15), versione 4.0. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/CPTI/CPTI15.4

How to cite: Patricelli, G., Poli, M. E., Falcucci, E., Gori, S., Paiero, G., Rizzo, E., Marchesini, A., and Caputo, R.: First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16527, https://doi.org/10.5194/egusphere-egu24-16527, 2024.

EGU24-17289 | ECS | Orals | TS3.3

Off-fault damage in the 2023 Kahramanmaraş (Türkiye) earthquakes from SAR images 

Jihong Liu, Sigurjón Jónsson, Xing Li, and Yann Klinger

Large strike-slip earthquakes are usually modeled as slip on localized planar fault planes within a homogeneous or layered elastic half-space. However, geodetic fault-slip inversions often show a shallow slip deficit, where the maximum slip is found at a depth of several kilometers with gradually decreasing slip towards the surface. High-resolution satellite images of earthquake surface ruptures also suggest a reduction in on-fault slip, often termed as off-fault damage or distributed deformation. In this study, we refer to this reduction in near-fault deformation as surface absent deformation (SAD). The presence of coseismic SAD, due to off-fault damange and/or compensated for by shallow interseismic fault creep and afterslip, holds significance for earthquake rupture processes, paleoseismology, and earthquake hazard assessments.

In our study, we quantify the SAD along the main ruptures of the magnitude 7.8 and 7.6 Kahramanmaraş earthquakes, which occurred on 6 February 2023 near the Türkiye-Syria border, by mapping coseismic three-dimensional (3D) surface displacements using differential interferometry and pixel tracking of satellite synthetic aperture radar (SAR) images. The two earthquakes had a combined rupture length of approximately 500 km, exhibiting multi-meter surface fault offsets and diverse fault geometries, necessitating high-resolution deformation mapping near and away from the fault. We obtained the SAD distribution by analyzing fault-perpendicular profiles of fault-parallel displacement from the SAR-derived 3D displacements. For each profile, an arctan function was used to predict the near-fault (e.g., 0-5 km) elastic displacement based on the far-field (e.g., 5-50 km) observations, yielding an estimate of the lack of deformation close to the fault (i.e., the SAD). The results reveal a clear correlation between SAD and geometrical complexities along the two co-seismic ruptures. Using this strategy to determine the SAD, we find that about 35% of the surface fault slip is “missing” and expressed as SAD within a distance of 5-7 km from the coseismic surface ruptures. By comprehensively analyzing the interseismic, coseismic, and postseismic deformation in this area, we find that shallow interseismic fault creep and afterslip cannot explain the coseismic SAD and that it appears to be dominated by off-fault damage. Notably, existing research on off-fault damage has been concentrated within a range of only 1-2 km. Our results therefore underscore the significance of extending investigations of off-fault damage to 5-10 km from fault ruptures, and suggest that relying solely on on-fault offset measurements may lead to an underestimation of fault slip rate estimations by as much as one third.

How to cite: Liu, J., Jónsson, S., Li, X., and Klinger, Y.: Off-fault damage in the 2023 Kahramanmaraş (Türkiye) earthquakes from SAR images, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17289, https://doi.org/10.5194/egusphere-egu24-17289, 2024.

EGU24-19541 | Orals | TS3.3

Active faulting and seismogenic potential in low-strain rate southern Tuscany (Italy) 

Pierfrancesco Burrato, Andrea Brogi, Paola Vannoli, Martina Zucchi, Umberto Fracassi, Gianluca Valensise, Hsun-Ming Hu, and Chuan-Chou Shen

We explored the behaviour and earthquake potential of an active fault system in the slowly deforming part of southern Tuscany. This region corresponds to the eastern margin of the Siena Basin, a Neogene structural depression that developed during the extensional tectonics that affected the inner northern Apennines. Here, N-, NE- and WNW-trending faults were active during the Zanclean-Latest Quaternary. Clear evidence of the activity of these faults, particularly the most recent WNW-striking ones, is represented by faulted Late Pleistocene-Holocene travertine deposits that preserve also evidence of active seismogenic faulting. Indeed, this area in recent times was mostly interested by low-magnitude seismic sequences that occurred in the uppermost 10 km of the crust, mainly characterized by transcurrent and transtensive faulting mechanisms. However, the historical record includes also damaging earthquakes in the 5.0-6.0 Mw range, such as the 7 August 1414, Mw 5.7, Colline Metallifere, 13 April 1558, Mw 6.0, Valdarno Superiore, and 25 August 1909, Mw 5.3, Crete Senesi events, but, to date, very little is known about the geometry, maximum earthquake potential and slip rate of their causative faults.
In this study, we characterize an active, capable, and seismogenic fault system identified in the saw-cut walls of an active travertine quarry near Serre di Rapolano, a few kilometres south-east of the city of Siena. To document the geometric and kinematic features of the active faults, we carried out a detailed geological and structural field survey of the quarry outcrop, collected samples for U-Th dating and constructed a virtual outcrop model. We found compelling evidence for nearly SW-NE surface-breaking faulting, perpendicular to the main structural fabric of the central and northern Apennines, whose activity extends at least into the Upper Pleistocene. The peculiar geology of the area also suggests that these faults have generated earthquakes associated with surface faulting, namely the occurrence of clastic dykes injected within the fault zones during earthquake-induced liquefaction.
Our results may help to address the current lack of understanding concerning earthquake activity in the slowly deforming region, and improve the current knowledge of the seismotectonic setting of the Siena Basin and the corresponding part of the inner northern Apennines. Our findings hint to a still unexplored tectonic mechanism, which suggests that the earthquakes affecting this part of southern Tuscany may be caused by segments of rather elusive, very long, SW-NE and WNW-ESE lineaments crossing the entire Apennine stack.

How to cite: Burrato, P., Brogi, A., Vannoli, P., Zucchi, M., Fracassi, U., Valensise, G., Hu, H.-M., and Shen, C.-C.: Active faulting and seismogenic potential in low-strain rate southern Tuscany (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19541, https://doi.org/10.5194/egusphere-egu24-19541, 2024.

EGU24-20372 | Orals | TS3.3

FRAME – a Fast Response Aftershock network for the Moroccan Earthquake (Mw 6.9, 08.09.2023) 

Martin Zeckra, Lahcen El Moudnib, Abderrahime Nouyati, and Sebastián Carrasco

The 2023 Mw 6.9 Al Haouz Earthquake in the Moroccan High Atlas mountains is the most recent example of a destructive event in an intraplate setting under the absence of a causative plate boundary. Their large inter-event times in such seismotectonic regimes hinders the study of single focus regions and apparently underestimates their larger seismic hazard potential, leaving local communities unaware of the scale of their exposure to these risks. One major shortcoming in the immediate scientific analysis of this unprecedented earthquake is the lack of (publicly) available seismic waveform recordings in the source area.

An immediate impact is displayed in the source location uncertainty, including a high variability in focal depth estimations. Associating the earthquake origin to a causative fault remains puzzling, bearing in mind the deeper-than-average focal depth of around 32 km. The complex tectonic history of the Atlas mountain chains is depicted in a plethora of active, reactivated and abandoned faults. In addition, prior studies noticed a lithospheric anomaly underneath the High Atlas mountain range, that lacks a classical mountain root. Thus, this event raise questions on the thermo-elastic parameters at depth in order to support a large seismogenic thickness of the crust.

In the immediate aftermath of the Al Haouz, we initiated a rapid-response task force for setting up a temporal seismic network in the High Atlas. Within two weeks, six autonomous seismological stations have been installed between 20 and 80 km from the estimated epicenter. Due to the large degree of destruction, problematic access and absence of major infrastructure in the epicentral region, we relied on autarkic and robust sensors. As a novelty, the stations consisted of SmartSolo® three component 5 Hz geophone sensors. These industrial-level instruments are light-weight and easy to deploy in any terrain. In a compact casing, the passive sensors host digitizer, data storage, GPS and battery life-time of up to 30 days.

Here, we present the first data of this 2 months temporary network. Based on preliminary analysis, we could obtain more than 1000 events recorded on all stations of the network during the 54 recording days. The largest recorded events had an assigned magnitude of ML 4.5. Considering single stations detections as well, we estimate more than 10,000 earthquake detections overall. This catalog will greatly expand the scientific insight into the mechanisms of this exceptional earthquake in the near-future.

Further, through the use of simple geophone sensors this study presents a proof of concept for rapid response installations of temporary aftershock network. These sensor types strongly outperform the fully elaborated counterparts in installation speed, transportability and external requirements for potential installation sites without large drawbacks in data quality.

How to cite: Zeckra, M., El Moudnib, L., Nouyati, A., and Carrasco, S.: FRAME – a Fast Response Aftershock network for the Moroccan Earthquake (Mw 6.9, 08.09.2023), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20372, https://doi.org/10.5194/egusphere-egu24-20372, 2024.

EGU24-20764 | Orals | TS3.3

POSEIDON Project: Seismic Hazards in the western Peloponnese - Ionian Islands Domain 

César R. Ranero, Paraskevi Nomikou, Filomena Loreto, Irene Merino, Valentina Ferrante, Danai Lampidou, Elisavet Nikoli, and Serafeim Poulos

The cruise POSEIDON from 10-22 June 2023, mapped the tectonic structure of the region extending from the western Peloponnese across the Ionian Islands. This is one of the most complex and comparatively little evaluated regions, with demonstrated seismic hazard, in the Mediterranean.

The region contains a complex fault system with numerous strands controlling much of the submarine and subaerial relief and with dramatic lateral changes in deformation rates. The fault system has produced large earthquakes, mostly offshore, recorded during the past few decades in the Greek national seismological network. However, the largest recent Mw~6.8-7.0 Kephalonia 1953 event was recorded in few stations available then. This earthquake - possibly the most destructive in recent Greek history - cause the collapse of ~85% of all buildings on Kephalonia Island, ~1k deaths, and ~145k people homeless. However, the 1953 earthquake is poorly understood compared with more recent, albeit less destructive events. The epicentre of the 1953 event is not well constrained, and the location and dimensions of the causative fault are unknown. Likewise, the hypocenter depth of the 1953 event thrust-fault focal mechanism, that occurred E or SE of Kefalonia, is defined from <50 km to <20 km, depending on the analysis. Studies in the islands interpret active shallow thrusting to propose that the 1953 event ruptured the upper 5 km of several shallow faults, but such a rupture cannot explain a Mw~6.8-7.0 even.

The goal of POSEIDON is to define the regional fault system structure and kinematics and to place it in the proper geodynamic context that helps understand hazards and eventually evaluate associated risks. The DEM displays a rugged terrain from the Ionian Islands to the Peloponnese Peninsula, with numerous features that indicate active deformation across the entire region. Major submarine tectonic structures around the islands trend from NE-SW to NNW-SSE, similar to the basins and ranges on the islands. Elongated shallow troughs offshore laterally project to the relief trends on the islands, supporting widespread active faulting.

A further complication in the research area is that the upper-crust fault system, might be located above, or sole into, a mega-thrust plate boundary fault of the Hellenic subduction zone, inferred -in publications- to dip in a NE direction at ~25-40 km depth under the surface. However, the location of a mega-thrust seismogenic zone is yet not well constrained. POSEIDON seismic data image the tectonic features in the crust and integrated with the high-resolution bathymetry allow to define the main faults across the offshore region in unprecedented detail.

Acknowledgements

We acknowledge the professional and dedicated work of the National Institute of Oceanography and Applied Geophysics (OGS-Trieste) technical party and the technical party of the Marine Technology Unit (UTM) from the Spanish National Research Council (CSIC) to make the experiment a success. We also acknowledge the professional and dedicated work of the master, officers and crew of the R/V Laura Bassi during the POSEIDON experiment.

How to cite: Ranero, C. R., Nomikou, P., Loreto, F., Merino, I., Ferrante, V., Lampidou, D., Nikoli, E., and Poulos, S.: POSEIDON Project: Seismic Hazards in the western Peloponnese - Ionian Islands Domain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20764, https://doi.org/10.5194/egusphere-egu24-20764, 2024.

EGU24-378 | ECS | Orals | TS3.4

Constraining the <500 Ka faulting history of the Central Taurides above the Cyprus Subduction Zone: Insights from U-Th carbonate geochronology 

Tunahan Aykut, Cengiz Yıldırım, I. Tonguc Uysal, Uwe Ring, and Jian-xin Zhao

The Central Taurides is located at the southern margin of the Central Anatolian Plateau with a high relief up to a 2 km topography. This plateau margin rises in the upper plate north of the Cyprus Arc where the African Plate subducts beneath the Anatolian Plate. Although the relationship between regional surface uplift and mantle-driven processes, such as slab tearing/break-off and asthenospheric upwelling are well constrained in this area, the Quaternary faulting history and the seismic hazard potential remain hardly known. The Central Taurides between Alanya and Seydişehir (from the coast to the plateau), presents a series of NW-SE striking faults that control the topography across the highly erosional and karstified orogenic plateau margin. In this study, we utilize U-Th carbonate geochronology, microstructural analysis and fault-slip data to decipher the timing and mechanism of upper crustal brittle deformation. We date fault-related calcites and examine fault kinematics to constrain the <500 Ka faulting history of the overriding Anatolian Plate (southern part) that has uplifted 1.5 km since 450 Ka. Our kinematic measurements of the youngest generation of the brittle structures indicate widespread normal faulting due to NE-SW horizontal tension in the upper crust. Microscopy and scanning electron microscope analyses on calcite samples show twinning, brecciated zones, calcite gouges, slickenlines, slickenfibres, fault grooves, microfractures and displaced dilation veins; underlining microstructural footprints of faulting-related deformation. U-series dating of fault-related calcites yielded twenty-eight U-Th ages ranging between 714±285 ka and 18.76±0.53 ka. The results of this study constrain the temporal relationships between surface uplift, upper crustal brittle deformation and mantle-rooted processes above active subduction zones. This study is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) “2232 International Fellowship for Outstanding Researchers Program” (Grant No: 118C275), and TUBITAK “2214-A International Research Fellowship Programme for PhD Students” (Grant No: 1059B142200520).

How to cite: Aykut, T., Yıldırım, C., Uysal, I. T., Ring, U., and Zhao, J.: Constraining the <500 Ka faulting history of the Central Taurides above the Cyprus Subduction Zone: Insights from U-Th carbonate geochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-378, https://doi.org/10.5194/egusphere-egu24-378, 2024.

EGU24-950 | ECS | Posters on site | TS3.4

The Narlı Fault: the characteristics of the surface rupture that initiated the 6 February 2023 Kahramanmaraş Earthquake Sequence (Türkiye) 

Havva Neslihan Kıray Canik, Cengiz Zabcı, Hüsnü Serdar Akyüz, Erdem Kırkan, Gürsel Sunal, Nurettin Yakupoğlu, Asen Sabuncu, and Ahmet Murat Akoğlu

The south-southeastern Türkiye was struck by a series of earthquakes in February 2023 causing the death of more than 50,000 people and billions of USD of economical loss. The largest of these events, the February 6th Mw 7.8 Pazarcık and Mw 7.5 Ekinözü earthquakes occurred only 9 hours apart of each other generating surface ruptures of about 450 km and the majority of the destruction. All these events took place in a complex tectonic system where the boundary structures of the Anatolian Block, the Arabian Plate and the Adana-Cilicia-Hatay Basin merge together. The Pazarcık earthquake was initiated along a subsidiary splay, the Narlı Fault (NF), and continued with the bilateral rupturing of faults over a length of 300 km.

In this study, our aim is to document the surface deformation along the NF in order to have a better understanding of the initiation mechanism of the ‘multi-segment’ Pazarcık earthquake. In addition to our field observations, we operated a sUAS to map the rupture and measure offsets. We used a tape measure to determine the magnitude of slip across the well-established offset markers in the field, while the ultra-precise rupture mapping and a vast number of displacement measurements were made by using sUAS-based digital surface models (DSM) and orthophotos with a ground pixel resolution of ~3–5 cm.

We mapped two sets of continuous surface ruptures, the 14 km-long southern and the 10 km-long northern parts, separated by a ‘gap’ of 8 km. The average sinistral offset along the ~N20-30°–striking southern rupture is about 2 m, whereas the maximum value reaches up to 3.7 ± 0.7 meters. On the other hand, the horizontal slip along the N25-35°–striking northern rupture barely exceeds 1.2 m. In this section, it is highly probable that a large portion of the total horizontal deformation is shared by widely distributed surface shears within the wedge between the East Anatolian Fault and the NF, which can be an analogue to a variant of a Prandtl Cell Model. In addition, we identified semi-circular/elliptical surface cracks at more than 10 locations to the south of the NF rupture. These are interpreted as seismically induced sink-holes, given the widely distributed Eocene limestones in the region. The preliminary analysis of the time series of interferograms between 2015–2022 suggests a long-term systematic subsidence, supporting our hypothesis.

How to cite: Kıray Canik, H. N., Zabcı, C., Akyüz, H. S., Kırkan, E., Sunal, G., Yakupoğlu, N., Sabuncu, A., and Akoğlu, A. M.: The Narlı Fault: the characteristics of the surface rupture that initiated the 6 February 2023 Kahramanmaraş Earthquake Sequence (Türkiye), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-950, https://doi.org/10.5194/egusphere-egu24-950, 2024.

EGU24-992 | ECS | Orals | TS3.4

Unveiling the Kinematics of the 2022 Düzce Earthquake (Mw 5.9) and Its Impact on Regional Tectonics 

İlay Farımaz, Seda Özarpacı, Alpay Özdemir, Efe Turan Ayruk, Simon Orrego Astudillo, Figen Eskiköy, Havva Neslihan Kıray, Cengiz Zabcı, Semih Ergintav, and Uğur Doğan

In 1999, The North Anatolian Fault (NAF) generated two destructive earthquakes, namely, the Mw 7.4 Izmit earthquake and the Mw 7.1 Düzce earthquake, in the western part of Türkiye and broke more than 180 km of NAF. After 22 years of silence, at the overlapping section of these ruptures,  the region produced two earthquakes: one with a magnitude of 5 and another, a year later, with a magnitude of 5.9. In this study, we aim to examine the role of these recent earthquakes in terms of slip deficit between two ruptures.

Our primary focus is on the Düzce earthquake (Mw 5.9) that occurred on 23 November 2022.  Here we use a novel method to reconstruct the coseismic deformation field by  enhancing the signal-to-noise ratio (SNR) from ~3 years of Interferometric Synthetic Aperture Radar (InSAR) Sentinel-1 TOPS data spanning the earthquake. We estimate a coseismic surface displacement of ~2 cm for this event.

Furthermore, data from the stations belonging to the Turkish National GNSS Network and data from eight new cGPS sites that we have established in the area have been processed to observe coseismic and postseismic displacement. Postseismic deformations are estimated for one month interval after the earthquake, maximum postseismic deformation is observed on the site named AKSU: 18.6 ± 2.18 mm at east and -1.5 ± 2.28 mm at north direction.

A joint inversion model was developed using the aforementioned geodetic and seismological data to estimate the region's final state and was linked to the potential slip deficit of previous major earthquakes in 1999.

How to cite: Farımaz, İ., Özarpacı, S., Özdemir, A., Ayruk, E. T., Astudillo, S. O., Eskiköy, F., Kıray, H. N., Zabcı, C., Ergintav, S., and Doğan, U.: Unveiling the Kinematics of the 2022 Düzce Earthquake (Mw 5.9) and Its Impact on Regional Tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-992, https://doi.org/10.5194/egusphere-egu24-992, 2024.

EGU24-1284 | Posters on site | TS3.4

Identification of Source Faults of Large Earthquakes in the Turkey-Syria Border Region Between AD 1000 and the Present, and their Relevance for the 2023 Mw 7.8 Pazarcık Earthquake 

Sara Carena, Anke Maria Friedrich, Alessandro Verdecchia, Beth Kahle, Stefanie M. Rieger, and Simon Kübler

The February 6th, 2023, Mw 7.8 Pazarcık earthquake in the Turkey-Syria border region raises the question of whether such a large earthquake could have been foreseen, as well as what is the maximum possible magnitude (Mmax) of earthquakes on the East Anatolian fault system and on continental transform faults in general. To answer such questions, knowledge of past earthquakes and of their causative faults is necessary. Here, we integrate data from historical seismology, paleoseismology, archeoseismology, and remote sensing to identify the likely source faults of fourteen Mw ≥ 7 earthquakes between AD 1000 and the present in the region. We conclude that, based on the historical seismic records of the region, the 2023 Mw 7.8 Pazarcık earthquake was foreseeable in space and time, but not in size. Mmax for the EAF is likely ~ 8.2, with the limit rupture length being the distance between the Karliova and Amik triple junctions. The 2023 earthquake may not have reached Mmax simply by a fortuitous combination of factors: if the 2020 Elȃziǧ earthquake had not happened where and when it did, would the 2023 rupture have continued propagating towards the northeast? This is a question that could be answered by combining Coulomb stress models and dynamic rupture models. If nothing else, what we have learned from the 2023 Mw 7.8 Pazarcık earthquake is that segmentation of continental transform faults is not relevant for calculating Mmax, because some earthquakes can jump across segment boundaries. Such earthquakes are so infrequent, however, that they are difficult to study, and therefore hard to foresee.

How to cite: Carena, S., Friedrich, A. M., Verdecchia, A., Kahle, B., Rieger, S. M., and Kübler, S.: Identification of Source Faults of Large Earthquakes in the Turkey-Syria Border Region Between AD 1000 and the Present, and their Relevance for the 2023 Mw 7.8 Pazarcık Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1284, https://doi.org/10.5194/egusphere-egu24-1284, 2024.

EGU24-4163 | Orals | TS3.4

Geologic, Topographic, and Seismic Characteristics of Large Landslides Triggered by 2023 Kahramanmaras Earthquakes, Türkiye 

Tolga Gorum, Hakan Tanyas, Abdussamet Yilmaz, Furkan Karabacak, and Gonghui Wang

The devastating Kahramanmaras earthquake sequence occurred on February 6, 2023. Two main events, Mw 7.8 and Mw 7.5, occurred 9 hours apart, affected 11 cities in Türkiye, and affected an area of ∼90,000 km2. This was the strongest historical earthquake doublet of magnitudes above 7.5 ever recorded in this region, and the consequences were catastrophic. The earthquake doublet triggered more than 3,600 landslides. Among these landslides, 35 of them have an area greater than 50,000 m2. Here, we focus on those largest coseismic landslides and show that 21 of them are pre-event landslides reactivated during the earthquake. They concentrate along a 5km-wide buffer zone around the surface rupture. Approximately 90% of these large landslides are distributed along the western section of the Eastern Taurus Mountain Belt, which is highly deformed and results in numerous overthrusts extending for 50 to 100 km. The geologic units in this part of the Taurus Mountain Belt consist of sedimentary, metamorphic, and igneous autochthonous and allochthonous units. The spatial distribution of landslides closely coincides with the topographic differences. They mostly (>82%) occurred on hillslopes where local relief varies between 500 and 700 m, and slope steepness ranges from 20° to 45°. Our preliminary analyses also revealed a relationship between the fault rupture dynamics and the distribution of large landslides. In addition to the rupture dynamics and topographic contrasts in the area, vertical lithological differences and the long-term tectonic deformations affecting autochthonous and allochthonous units have primary controls on the distribution of large landslides triggered by this earthquake doublet.

How to cite: Gorum, T., Tanyas, H., Yilmaz, A., Karabacak, F., and Wang, G.: Geologic, Topographic, and Seismic Characteristics of Large Landslides Triggered by 2023 Kahramanmaras Earthquakes, Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4163, https://doi.org/10.5194/egusphere-egu24-4163, 2024.

The eastern Mediterranean hosts complex tectonic units with multiple strike-slip and collision plate boundaries. The Anatolian plate is being pushed away from the Eurasian plate and Arabian plate via two left-lateral transform faults with uncoupled crust and upper mantle inferred from anisotropy studies. The rheological structure is thus important to better understand the plate dynamics of the Anatolian and its surrounding plates. The 2023 Mw7.8 and Mw7.6 earthquake doublet in the East Anatolian Fault zone provides a unique opportunity to study viscoelastic relaxation of the upper mantle and time-dependent afterslip over the crustal faults. Here we have derived the first 3-month postseismic displacements from GNSS time series of 94 stations after the events to investigate the early postseismic deformation processes through a three-dimensional viscoelastic finite element model. Afterslip in the model is simulated through a 2-km thick weak shear zone attached to the fault. Viscoelastic relaxation is represented by the bi-viscous Burgers rheology. We find that the observed long-wavelength displacements is dominated by the viscoelastic relaxation even in this early postseismic stage, and the contribution from the afterslip is spatially limited. The viscosity of the Anatolian upper mantle should be lower than 1019 Pa s to better fit the observed horizontal and vertical displacements. This inferred weak upper mantle may result from the upwelling mantle due to the tearing African slab.

How to cite: Wang, K. and Hu, Y.: Weak Anatolian upper mantle inferred from postseismic deformation of the 2023 Türkiye earthquake doublet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4865, https://doi.org/10.5194/egusphere-egu24-4865, 2024.

EGU24-8446 | Posters virtual | TS3.4

Geological Effects and Constructional Properties Controlling Structural Damage triggered by the 6 February 2023 Kahramanmaraş Earthquakes in Southeastern Turkey 

Spyridon Mavroulis, Emmanuel Vassilakis, Ioannis Argyropoulos, Panayotis Carydis, and Efthymios Lekkas

On 6 February 2023, the Eastern Anatolia experienced significant devastation due to two major seismic events, leading to the collapse of hundreds of thousands of structures and causing tens of thousands of human casualties, injuries, and homeless people. The substantial magnitude of these impacts is attributed to the extensive occurrence of heavy and very heavy structural damage, categorized as damage grades 4 and 5 according to the European Macroseismic Scale EMS-98, within the earthquake-affected area.

The discernible factors contributing to the disaster encompassed the substantial magnitude of the earthquakes, the occurrence of the initial seismic event during nighttime, thereby locating a considerable portion of the population within their residences, and the demographic attributes of the region characterized by densely constructed and populated zones, coupled with the close proximity of numerous residential areas to the ruptured faults. Additionally, the confluence of significant factors, closely associated with the seismotectonic context of the region, the effects of earthquake environmental effects, and the characteristics of the impacted structures, culminated in one of the most extensive earthquake disasters in the recent history of Turkey.

This study aims to highlight the factors controlling associated with building properties and the manifestation of earthquake environmental effects that govern the severity and spatial dispersion of structural damage within the earthquake-affected regions under study in the southeastern Turkey. The findings presented herein derive from field surveys undertaken by the authors in the immediate aftermath of the seismic events (7th to 11th February) and subsequently, almost two months later (31st March to 6th April). The field surveys included conventional techniques of geological mapping alongside innovative methodologies, including the deployment of Unmanned Aerial Systems (UAS).

With regard to building construction characteristics, insufficient adherence to building codes, arbitrary urban planning solutions, and substandard construction practices constitute primary deficiencies contributed to the disaster. Concerning geological factors, the generation of both primary and secondary earthquake environmental effects significantly influenced the intensity and distribution of damage. Locations where coseismic surface ruptures intersected with built-up areas exhibited heavy to very heavy structural damage, as evidenced along the ruptured segments of the East Anatolian Fault Zone. Liquefaction proximal to water bodies resulted in damage indicative of building foundation load-bearing capacity. Earthquake-triggered landslides predominantly impacted mountainous and semi-mountainous villages and areas characterized by pre-existing susceptibility. The substantial susceptibility to EEEs generation was extensively corroborated in numerous cases, leading to widespread damage. The presented information highlights the pivotal role of such studies in informing hazard mitigation and facilitating disaster risk reduction measures.

How to cite: Mavroulis, S., Vassilakis, E., Argyropoulos, I., Carydis, P., and Lekkas, E.: Geological Effects and Constructional Properties Controlling Structural Damage triggered by the 6 February 2023 Kahramanmaraş Earthquakes in Southeastern Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8446, https://doi.org/10.5194/egusphere-egu24-8446, 2024.

EGU24-12188 | Posters on site | TS3.4

Investigation of the Active Deformation in the Caucasus Region from Seismic and Geodetic Observations 

Hayrullah Karabulut, Vadim Milyukov, Sezim Ezgi Guvercin, Seda Ozarpaci, Mironov Alexey Pavlovich, Semih Ergintav, Volkan Özbey, Cengiz Zabci, Ali Ozgun Konca, Ruslan Diyagilev, and Steblov Grigory Mikhailovich

The deformation and shortening in the Caucasus region are predominantly driven by the collision of Arabian and Eurasian plates with a possible contribution of the lithospheric deformation beneath the Caucasus.  The tectonic uplift/inversion, along with the formation of the Greater and Lesser Caucasus fold and thrust belts, is driven and maintained by the continental collision of the Arabian and Eurasian plates. However, the dominant factor for the regional variations of surface deformation and sub-crustal seismic activity, whether lithospheric delamination or slab detachment beneath the Caucasus region, is not well understood. Moreover, the variations in shortening along the Caucasus cannot be solely explained by plate boundary forces without constraints from lithospheric dynamics. The large uncertainties of the models lead to limited understanding of the formation and active deformation of this fold and thrust belt. The main reason for this shortcoming is the limited access to the seismic and geodetic data in the region. In this study, we merged seismic and geodetic data from Russia and surrounding countries.  We constructed a joint database for the period between 2007 and 2010 and updated 1D crustal velocity models for four sub-regions. We obtained the relocated seismicity within each region using the local velocity models. In addition, we updated the earthquake source mechanisms catalog in the Caucasus region.  A new Pn tomography model is computed using the new catalog. The crustal thickness variations are recomputed from receiver function analysis using the broad-band stations of Russia. We also update block boundaries and corresponding slip rates in the study region using both seismicity and geodetic data.

How to cite: Karabulut, H., Milyukov, V., Guvercin, S. E., Ozarpaci, S., Pavlovich, M. A., Ergintav, S., Özbey, V., Zabci, C., Konca, A. O., Diyagilev, R., and Mikhailovich, S. G.: Investigation of the Active Deformation in the Caucasus Region from Seismic and Geodetic Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12188, https://doi.org/10.5194/egusphere-egu24-12188, 2024.

EGU24-12525 | ECS | Posters on site | TS3.4

Post-seismic analysis of the Kahramanmaraş triple junction using GNSS data acquired following the 2023 Kahramanmaraş earthquakes 

Volkan Özbey, Pierre Henry, Mehmet Sinan Özeren, Elliot C. Klein, Alan John Haines, Lifeng Wang, Anke Maria Friedrich, and Ali Mehmet Celal Şengör

Understanding the evolution of the crustal kinematic/dynamic response of the Kahramanmaraş triple junction after the occurrence of the destructive earthquake doublet on 6 February 2023 is of great interest to seismologists and geodesists. Along with the near-field postseismic effects such as the afterslip, it is also essential to study relatively far-field effects where the interaction of the brittle upper crust with the lower crust and upper mantle can be relevant in how the stress is redistirbuted during the months/years following the earthquake. The latter seems to be a particularly interesting problem for this case because the earthquake perturbation to the interseismic velocity field is very significant and extends approximately 400 km to the west of the rupture zone.  The affected region seemingly comprises a large part of the Central Anatolian Block where the interseismic internal deformation was less than 10 nanostrain/yr prior to the large event. Most tomographic studies show that the lithospheric mantle beneath Central Anatolia is either very thin or absent. This indicates a necessity to test various upper mantle and lower crust viscosity scenarios for the far-field effects.

We conducted a GNSS (Global Navigation Satellite System) campaign in July 2023, reoccupying 18 sites around the triple junction area to monitor the intermediate and far-field post-seismic effects caused by the ruptures and the subsequent loading behavior of the faults therein. Our primary aim was to characterize: (1) the postseismic effect on the relatively far-field, which likely includes viscoelastic responses in central Anatolia where the lower crust and mantle are presumably weak; (2) variations of the strain field stemming from aftershocks of the large earthquakes; and (3) the response of secondary faults such as the Ecemiş, Deliler, and Sariz faults in Adana and Kayseri provinces. 1-year GNSS time series of continuous stations broadly reveal the postseismic field behavior. The occurence of a postseismic signal is clear northwest of the rupture zone however, the signal is weak for the stations southwest of the earthquake area. The preliminary analysis of the survey mode sites is in agreement with continuous stations. Here we present the resulting post-seismic velocity, the strain rate field and its contrast from the pre-event strain rate field and a preliminary viscoelastic model to shed light onto the underlying physical processes.

How to cite: Özbey, V., Henry, P., Özeren, M. S., Klein, E. C., Haines, A. J., Wang, L., Friedrich, A. M., and Şengör, A. M. C.: Post-seismic analysis of the Kahramanmaraş triple junction using GNSS data acquired following the 2023 Kahramanmaraş earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12525, https://doi.org/10.5194/egusphere-egu24-12525, 2024.

EGU24-13021 | Posters on site | TS3.4

Investigating the Seismicity of Eastern Marmara Using Machine Learning Algorithms 

Ali Özgün Konca, Birsen Can, Arkadaş Özakın, and Mustafa Aktar

In this study we explore the seismicity along the Eastern Marmara Sea using machine learning techniques to improve the detection threshold and improve the earthquake locations. The Sea of Marmara comprises network of faults including the northern strand of the North Anatolian Fault, the Main Marmara Fault (MMF). MMF features a ~150 km seismic gap that did not rupture in the last 250 years. In addition to the MMF, other normal and strike-slip faults generate seismicity in the vicinity especially to the south of the Princes’ Islands.  It is therefore crucial to understand whether this seismicity is related to the MMF or other faults.

Here by employing a convolutional neural network detection and phase picking algorithm (Mousavi et al., 2020) and using a phase associator based on a grid search of locations (Zhang et al., 2019) we show that we can increase the detected number of earthquakes significantly and obtain a catalog with very low travel time residuals. Our primary objective is to acquire an improved earthquake catalog to facilitate subsequent clustering and focal mechanism analysis, thereby illuminating the underlying fault system responsible for these seismic events.

(This study is funded by TÜBİTAK Project No 121Y407).

How to cite: Konca, A. Ö., Can, B., Özakın, A., and Aktar, M.: Investigating the Seismicity of Eastern Marmara Using Machine Learning Algorithms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13021, https://doi.org/10.5194/egusphere-egu24-13021, 2024.

EGU24-13350 | Posters on site | TS3.4

Primary Surface Rupture and Slip Distribution Associated with the Mw 7.6 06 February 2023 Elbistan Earthquake, Turkey 

Sinan O. Akciz, Taylan Sançar, Havva N. Kıray, Cengiz Zabcı, Mehmet Köküm, Musa Balkaya, Davaasambuu Battogtokh, and H. Serdar Akyüz

The February 06, 2023, Kahramanmaraş earthquake sequence started with an earthquake with magnitude Mw 7.0 on the Narlı Fault and continued on the tectonic boundary between the Anatolian and Arabian plates. The main event, the Mw 7.8 Pazarcik earthquake, ruptured the East Anatolian Fault (EAF) bilaterally for over 300 km. This main event was followed nine hours later by the Mw 7.6 Elbistan earthquake, with the epicenter near the town of Ekinözü, about 100 kilometers away from the epicenter of the Pazarcik earthquake. The Elbistan earthquake also ruptured bilaterally, resulting in approximately 140 km of co-seismic surface rupture along a set of faults that form a major splay of the East Anatolian Fault Zone. Field investigations supplemented with interpretations of high-resolution photographs from small unmanned aircraft systems and helicopters show that the surface rupture associated with the Elbistan earthquake occurred on two different left-lateral strike faults: The first, known as the Çardak fault, extends from the town of Göksun in the west to Bıçakçı village in the east. The second is the newly identified Yeşilyurt Fault, an NE-SW-striking left-lateral fault with a subtle topographic expression that strikes parallel to the EAF.

 

The surface trace of the Çardak Fault can be divided into two geometric sections: The arc-shaped western section extends nearly 80 km between Göksun and Nurhak where the rupture was continuous and focused within a narrow zone. Horizontal slip along the eastern half of this section was typically over 6 meters, reaching over 8 meters at the maximum slip location just east of the epicenter. The average lateral slip drops to approximately 4 meters west of Ericek before decreasing uniformly to the west from Fındık until the surface rupture ends in Göksun. The second fault section extends nearly E-W between Nurhak and Bıçakçı for almost 20 km, including the structurally complex region associated with the Nurhak restraining bend, where only a handful of field slip measurements were made in this broadly deformed section. The average minimum horizontal slip measurements in this section of the Çardak fault is around 2.5 m. Our field investigations indicate that the rupture established a new trend parallel to the East Anatolian Fault instead of using the E-W-oriented Sürgü Fault to connect with it. The average slip along this new 40 km-long fault zone, here named Yeşilyurt Fault, is about 1m, with maximum left-lateral slip reaching  ~2.5m. Unlike the nearly continuous rupture along the Çardak fault, the rupture zone of the Yeşilyurt Fault generally consists of a series of right-stepping en-echelon arrays of discontinuous sinistral fault traces of various lengths and stepovers that range between tens of meters to several hundred meters.

How to cite: Akciz, S. O., Sançar, T., Kıray, H. N., Zabcı, C., Köküm, M., Balkaya, M., Battogtokh, D., and Akyüz, H. S.: Primary Surface Rupture and Slip Distribution Associated with the Mw 7.6 06 February 2023 Elbistan Earthquake, Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13350, https://doi.org/10.5194/egusphere-egu24-13350, 2024.

EGU24-14308 | Orals | TS3.4

3D Dynamic Rupture Modeling of the 6 February 2023, Kahramanmaraş, Turkey Mw 7.8 and 7.7 Earthquake Doublet Using Early Observations 

Alice-Agnes Gabriel, Thomas Ulrich, Mathilde Marchandon, James Biemiller, and John Rekoske

The 2023 Turkey earthquake sequence involved unexpected ruptures across numerous fault segments. We present 3D dynamic rupture simulations to illuminate the complex dynamics of the earthquake doublet. Our models are constrained by observations available within days of the sequence and deliver timely, mechanically consistent explanations of the unforeseen rupture paths, diverse rupture speeds, multiple slip episodes, heterogeneous fault offsets, locally strong shaking, and fault system interactions. Our simulations link both earthquakes, matching geodetic and seismic observations and reconciling regional seismotectonics, rupture dynamics, and ground motions of a fault system represented by 10 curved dipping segments and embedded in a heterogeneous stress field.

The first, Mw 7.8 earthquake features delayed backward branching from a steeply branching splay fault, not requiring supershear speeds. The asymmetrical dynamics of the distinct, bilateral second Mw 7.7 earthquake are explained by heterogeneous fault strength, prestress orientation, fracture energy, and static stress changes from the previous earthquake. Our models explain the northward deviation of its eastern rupture and the minimal slip observed on the Sürgü fault. 3D dynamic rupture scenarios can elucidate unexpected observations shortly after major earthquakes, providing timely insights for data-driven analysis and hazard assessment toward a comprehensive, physically consistent understanding of the mechanics of multifault systems.

Our models illustrate the predisposition of complex fault geometries, prevalent in tectonically complex immature fault systems, for cascading multi-fault and multi-event earthquake sequences. The unexpected doublet dynamics maybe explained by stress and strength heterogeneity, and include branching and delayed triggering in backward direction; triggered high-stress drop events, a single fault system with variable relative strength hosting rupture propagating at highly variable rupture speeds across different segments and in different directions.

How to cite: Gabriel, A.-A., Ulrich, T., Marchandon, M., Biemiller, J., and Rekoske, J.: 3D Dynamic Rupture Modeling of the 6 February 2023, Kahramanmaraş, Turkey Mw 7.8 and 7.7 Earthquake Doublet Using Early Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14308, https://doi.org/10.5194/egusphere-egu24-14308, 2024.

EGU24-15112 | ECS | Posters virtual | TS3.4

Effects of the 2023 Kahramanmaraş Earthquake Sequence on the Palu Segment of the East Anatolian Fault 

Muhammed İbrahim Hoşses, Seda Özarpacı, Alpay Özdemir, Efe Turan Ayruk, Muhammed Turğut, İlay Farımaz, Uğur Doğan, and Semih Ergintav

The East Anatolian Fault (EAF) is an approximately 420 km long sinistral strike-slip fault extending between Karlıova (Bingöl) in the northeast and Türkoğlu (Kahramanmaraş) in the southwest. The earthquake in Sivrice (Elazığ) on January 24, 2020, with a magnitude of Mw 6.8, along with the earthquakes in Pazarcık (Kahramanmaraş) on February 6, 2023, with a magnitude of Mw 7.8, and Elbistan (Kahramanmaraş) with a magnitude of Mw 7.6, has increased the seismic potential of the left-lateral strike-slip East Anatolian Fault.

This study involved a total of 12 campaign measurements conducted at a GNSS network consisting of six sites in Palu (Elâzığ) segment of EAF  between the years 2015 and 2023. The distance of the survey GNSS sites and continuous GNSS stations from the fault varies between approximately tens of meters to hundred of kilometers. Before and after the earthquakes on February 6, 2023, near field GNSS data were utilized in the analysis of crustal movements related with  the earthquakes in 2020-2023. The estimated deformation in the GNSS network campaign results between September 2021 and September 2023, varies from approximately 10 ± 2.6 mm to 40 ± 2.9 mm in Palu segment. These estimations include not only the postseismic effects of the 2020 Sivrice (Elaz) earthquake, but also the coseismic and early postseismic effects of the 2023 Kahramanmaraş earthquake sequence, along with ongoing shallow creep observations.

How to cite: Hoşses, M. İ., Özarpacı, S., Özdemir, A., Ayruk, E. T., Turğut, M., Farımaz, İ., Doğan, U., and Ergintav, S.: Effects of the 2023 Kahramanmaraş Earthquake Sequence on the Palu Segment of the East Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15112, https://doi.org/10.5194/egusphere-egu24-15112, 2024.

EGU24-15534 | Orals | TS3.4

Post-orogenic extension in Kos Island (Greece): geodynamic implications 

Vincent Roche, Bernhard Grasemann, David Schneider, Konstantinos Soukis, and Michael Pichler

Despite significant differences in the early tectonic histories, rocks in the eastern Mediterranean region partly share a common Cenozoic history characterized by several tectonic events including subduction, collision and extension. The correlations between the Aegean domain and the Menderes Massif have often been proposed, but few studies have considered the geology of the central Dodecanese Islands, which are located at the transition between the Aegean and Anatolian plates. In this study, we focus on the poorly studied island of Kos and investigate the tectonic history of the central Dodecanese Islands, as well as the general correlation with the Aegean and western Anatolian. Raman Spectroscopy of Carbonaceous Material (RSCM) analyses combined with white micas 40Ar/39Ar and zircon (U-Th)/He geochronology were carried out to determine peak temperatures and the timing tectonothermal events recorded by the various units. Three different tectonic units were identified from bottom to top: (1) the Paleozoic Unit overlain by the Permo-Triassic Wildflysch Unit in which primary sedimentary structures are well preserved. The units consist of low-grade meta-sediments including bedded meta-sandstones, meta-arkosic sandstones, meta-pelites and subordinate impure marble layers, bedded meta-chert with chaotic polymictic conglomerates containing huge blocks of metavolcanites, dolomitic limestones and marbles. Tmax of a graphitic phyllonite located in the Wildflysch Unit is 299 ± 14°C, confirming low-grade metamorphism. (2) The Marina Basement Unit consists of coarse-grained pure marbles, impure marbles with metachert layers, garnets, andalusite-mica schists, and quartzites, which was thrusted onto the Paleozoic and Wildflysch units with top-to-N kinematics during the Paleocene. Tmax from the Marina Basement are around 565 ± 35°C, suggesting a temperature difference of over 250°C with the previous units. (3) The Marina Cover Unit consists of unmetamorphosed dolomites, dolomitic limestones, and micritic limestones. Rocks of this unit are only preserved as isolated klippen juxtaposed onto the metasediments of the Paleozoic/Wildflysch Unit along the Oligocene Kos Detachment that exhibits an overall top-to-SSE shear sense. The western part of the Paleozoic Unit was intruded by a c. 10 Ma quartz-bearing biotite-hornblende monzonite intrusion which cooled until 5 Ma. The metamorphic aureole is a few 100 meters wide, which is similar in size to metamorphic aureole of other Miocene granitoids in the Cyclades. N-S extension is recorded after the intrusion as testified by cataclasites and W-E striking high-angle faults that control the current geomorphology of the island. At the regional scale, we propose that Oligocene extension occurred along the top-S Kos-Kalymnos Detachment System, and was localized in the Pelagonian Unit. Further west and a few million years later, the deformation started to propagate to deeper structural levels within the base of the Pelagonian, affecting the rocks of the Cycladic Blueschist Unit and favoring their relatively fast exhumation. Conversely, deformation in southwestern Turkey appears to record only compressional tectonics. Here, the Lycian nappes – the Turkish equivalent of the Pelagonian – were thrust to the SE upon the Menderes Massif and the Bey Daglari platform. This implies that the subduction dynamics differ from east to west in the eastern Mediterranean region.

How to cite: Roche, V., Grasemann, B., Schneider, D., Soukis, K., and Pichler, M.: Post-orogenic extension in Kos Island (Greece): geodynamic implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15534, https://doi.org/10.5194/egusphere-egu24-15534, 2024.

EGU24-17052 | Orals | TS3.4 | Highlight

6 February 2023 Kahramanmaraş Earthquake Sequence: ‘supercycle’ events within a complex tectonic setting 

Cengiz Zabcı, Taylan Sançar, Havva Neslihan Kıray, H. Serdar Akyüz, Gülsen Uçarkuş, Erdem Kirkan, Gürsel Sunal, M. Ersen Aksoy, Nurettin Yakupoğlu, Musa Balkaya, Mehmet Köküm, Asen Sabuncu, Bahadır Seçen, and Ahmet M. Akoğlu

On 6 February 2023, a series of earthquakes struck south-eastern Türkiye and northern Syria, causing a death toll of more than 50.000 people and an economic loss of billions of US Dollars. The devastating sequence started with the Mw ~7.0 Narlı Earthquake along a subsidiary splay, which was then instantly followed by the Mw 7.8 Pazarcık Earthquake bilaterally rupturing multiple structural elements in a complex triple junction system. These were followed ~9 hours later by the Mw 7.6 Elbistan Earthquake that took place on the Çardak and the Yeşilyurt faults. The involvement of multiple faults and the immense size of the affected region raise multiple questions such as the controlling factors, especially on the extent of the rupture length, slip distribution, width of the rupture zone, and any potential seismic gaps that were brought closer to failure.

This study aims to present our field investigations and measurement for the 6 February 2023 earthquakes with a particular emphasis on the tectonic complexity of the region. We have constructed a detailed surface rupture map and documented hundreds of offset measurements that suggest up to ~7 and ~8.5 meters of maximum sinistral displacements, for the Pazarcık and Elbistan earthquakes, respectively. The co-seismic slips differ from the offsets of the penultimate event in places, suggesting a variable slip behaviour, especially for the Çardak Fault. Our map does not only include the Principal Displacement Shear (PDS), but also almost all the secondary shears that provide an opportunity to determine the deformation width along the faults. One of the widest zones of surface breaks is observed within the Palaeozoic metamorphics and Mesozoic limestones of the Nurhak Mountain along the Çardak rupture, highlighting the influence of structural complexities on the distribution of deformation. A similar control occurs at the northeastern tip of the Pazarcık Rupture, which terminates in another structural complexity where the left-lateral East Anatolian Fault (EAF) connects with the Bitlis-Zagros suture zone. Field data suggests that this structural junction is responsible for arresting the rupture along the EAF, not the southern termination of the 24 January 2020 Mw 6.8 Sivrice (Elazığ) Earthquake rupture, producing a ‘seismic gap’ of about 20 km. To the south, the Pazarcık rupture reached the Dead Sea Fault, which has not had a significant surface rupturing earthquake to the north of Aqaba since the early 11th century.  Despite the widespread destruction that razed several towns to the ground, the 2023 Kahramanmaraş Earthquake Sequence provides invaluable information on understanding the geometry and kinematics of active faulting that accommodate the Eurasia-Africa-Arabia convergence in the eastern Mediterranean.

How to cite: Zabcı, C., Sançar, T., Kıray, H. N., Akyüz, H. S., Uçarkuş, G., Kirkan, E., Sunal, G., Aksoy, M. E., Yakupoğlu, N., Balkaya, M., Köküm, M., Sabuncu, A., Seçen, B., and Akoğlu, A. M.: 6 February 2023 Kahramanmaraş Earthquake Sequence: ‘supercycle’ events within a complex tectonic setting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17052, https://doi.org/10.5194/egusphere-egu24-17052, 2024.

EGU24-17305 | ECS | Orals | TS3.4

The slow slip events cycle along the Izmit segment of the North Anatolian Fault  

Estelle Neyrinck, Baptiste Rousset, Cécile Doubre, Cécile Lasserre, Marie-Pierre Doin, Philippe Durand, and Flatsim Team

The detection and analysis of transient aseismic slip events is crucial for a better understanding of the seismogenic behavior of major active faults and the associated seismic hazard. The North Anatolian Fault (NAF) in Türkiye has ruptured from east to west since the 1930’s with a Mw 7+ earthquake sequence involving seven events. The two last events ruptured the Izmit and Düzce segments close to Istanbul in 1999, with Mw 7.6 and Mw 7.2 respectively. Postseismic studies of the Izmit earthquake reveal first a rapid and logarithmic decay of the afterslip, followed by a viscoelastic relaxation of the lower crust and upper mantle. Estimates of the mean shallow creep more than 20 years after the rupture using Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data show an average velocity of 2.7 cm/year. An InSAR time series analysis of the aseismic behavior from Aslan et al. [2019], based on 2014-2017 Sentinel 1 data,  enabled the detection of a slow slip event modulating the creep in December 2016. This event was also observed by creepmeters. In this study, we used InSAR data over the extended period 2015-2021, from the Sentinel-1 A and B acquisitions, to analyze the aseismic slip dynamics of the Izmit segment. The InSAR data were processed with the FLATSIM workflow [Thollard et al., 2021] based on the NSBAS processing chain [Doin et al., 2011]. To extract the tectonic signal of the time series, we corrected for the annual seasonal components on each track, we decomposed the residual line of sight signals of the ascending and descending tracks into vertical and east-west (E-W) deformation fields and performed an Independent Component Analysis (ICA) decomposition on the Izmit sedimentary basin to correct for a high frequency signal. In the post-processed time series, we detect three main slow slip events in December 2016, March 2018 and November 2019, the first one corresponding to that  already detected by Aslan et al., [2019]. The average recurrence interval between the three events is 1.5 years. We extracted the E-W surface static displacements associated with each slow slip event and modeled the slip distribution at depth on a 2D-fault interface in a layered elastic half space. The slip associated with the transient slip pulses is localized at a depth of ~ 2 km, at the basis of the sedimentary basin. We estimated that along the central part of the Izmit segment, 50% of the total observed creep is occurring during the three 20 days-long slow slip events, and only 25-30% at the extremities of the segment. The characterization of a succession of slow slip events two decades after a Mw 7.6 earthquake on the Izmit segment and 70 years after a Mw 7.4 earthquakes on the Ismetpasa segment of the NAF [Rousset et al., 2016; Jolivet et al., 2023] question the logarithmic decay of postseismic slip and suggest a more transient and intermittent slip release, at least along some segments of the fault. 

How to cite: Neyrinck, E., Rousset, B., Doubre, C., Lasserre, C., Doin, M.-P., Durand, P., and Team, F.: The slow slip events cycle along the Izmit segment of the North Anatolian Fault , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17305, https://doi.org/10.5194/egusphere-egu24-17305, 2024.

EGU24-17400 | ECS | Posters on site | TS3.4

The Early Cretaceous to Miocene tectonic evolution of NW Cyclades based on 40Ar/39Ar multiple single crystal dating from Andros 

Shijie Shang, Bertram Uunk, Klaudia Kuiper, Fraukje Brouwer, and Jan Wijbrans

The Cycladic Archipelago in Greece preserves widespread evidence for high-pressure (HP) metamorphism and subduction and extension tectonics, during the evolution of a NE dipping subduction zone. How and at what rates various HP rocks were subducted and exhumed and how the associated complex deformation patterns originated remains controversial. We collected 26 samples from the Cycladic Blueschist Unit (CBU), the overlying Makrotantalon Unit (MU) and their contact zone on Andros for white mica single grain 40Ar/39Ar dating and combined the results with field and petrological observations to constrain the tectonic evolution of the NW Cyclades. To investigate the thermal state during tectonic evolution and the duration of deformation, we conducted 40Ar/39Ar multiple single crystal dating on different grain size fractions of white mica from the same sample.

Our results show three distinct episodes of deformation:

  • D0 is only locally preserved within the MU and the underlying contact zone and derives from the Early Cretaceous (128-119 Ma) Vardar ophiolite obduction above the Pelagonian margin, driving metamorphism and deformation of the passive margin. The white mica grains from the MU present Early Cretaceous ages of ~128 Ma (500-1000 mm) and ~117 Ma (120-250 mm). We suggest that the 11 Ma difference indicates a slower cooling rate.
  • D1 recorded in the contact zone and in the CBU, indicating that the CBU was exhumed along this contact zone from subduction depths during the Eocene (52-48 Ma). The white mica grains from the CBU present Eocene ages of ~52 Ma (500-1000 mm) and ~48 Ma (120-250 mm), with a gap of 4 Ma suggesting a faster cooling rate.
  • D2 is characterized by ductile-to-brittle deformation preserved in the contact zone and within the CBU, indicating they accommodated extension from around 28 Ma, with the initiation of slab rollback in the eastern Mediterranean. The contact zone between the MU and CBU exhumed greenschist-facies rocks of the CBU as a detachment until 21 Ma, when the rocks crossed the brittle-ductile transition and initiated brittle deformation, characterized by top-to-NE normal faulting.

We further redefine the structure of North Andros. In our study, we merge the MU and the ophiolites of the upper unit exposed in North Andros, previously thought to be separate units, in one unit equivalent of the Pelagonian unit. The contact between the MU and CBU, previously thought to be a thrust, is remapped as a brittle-ductile detachment fault between this one Pelagonian unit and the lower CBU and represents the NW extension of the Tinos, Mykonos detachments. This contact has accommodated syn-orogenic exhumation the CBU below the Pelagonian unit during Eocene HP metamorphism, and accommodated regional extension as part of the North Cycladic Detachment System during the Miocene.

How to cite: Shang, S., Uunk, B., Kuiper, K., Brouwer, F., and Wijbrans, J.: The Early Cretaceous to Miocene tectonic evolution of NW Cyclades based on 40Ar/39Ar multiple single crystal dating from Andros, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17400, https://doi.org/10.5194/egusphere-egu24-17400, 2024.

EGU24-17515 | ECS | Orals | TS3.4

Structures and kinematics of the Cephalonia-Lefkada Transform Fault zone 

Silvia Crosetto, Claudio Faccenna, Paolo Ballato, Vasiliki Mouslopoulou, John Begg, and Sabrina Metzger

The Cephalonia-Lekfada Transform Fault Zone (CLTFZ) lies at the transition between the continental subduction of Adria microplate underneath Eurasia to the north, and the oceanic subduction of the Nubian plate along the Hellenic Arc to the south.

Since its onset, estimated around the Late Miocene-early Pliocene, the CLTFZ is considered to have accumulated between 40 and ~80 km right-lateral displacement, with most of the offset occurring in the last ~5 Ma. Currently, the intense crustal deformation characterising the area results in high seismicity affecting the western part of Lefkada and Cephalonia islands, as demonstrated by several Mw>6 earthquakes that struck this narrow region in the last two decades (Mw 6.2 Lefkada, 2003; Mw 6.1 and Mw 5.9 Cephalonia, 2014; Mw 6.4 Lefkada, 2015).

We use conventional structural mapping and geomorphic analysis to identify and measure the main onshore faults and their kinematic evolution along the western coast of Cephalonia and Lefkada islands.

We observe that the topography of the islands is mostly tectonically controlled: right-lateral transpression is expressed as elongated ridges, trending ~N15 and delimited by thrusts. Transtensive, NE-SW-trending en échelon faults develop on the ridge crests, where measured fault throw indicates up to 1.5 km NW-SE-directed extension on a single ridge. Similar structures have been recently observed in analogue modelling experiments, forming as Riedel-shears in the later stages of the transpressional system evolution.

Inactive, and hence older faults seem to have formed as opening fractures in an extensional regime (~W-E). The fractures are filled with calcite veins displaying multiple growth generations, which suggests formation in a fluid-rich environment. Active faults display at least two generations of striae indicating pure dip-slip and strike-slip/oblique movement. Where visible, the cross-cutting relationship between the two generations indicates a first phase of normal faulting followed by more recent transcurrent faulting. This is in agreement with geodetic data, reporting a dominant horizontal component of movement during the recent earthquakes.

The overall fault analysis indicates an important strain partitioning along the CLTFZ, providing relevant constraints to the seismotectonic pattern of the region.

How to cite: Crosetto, S., Faccenna, C., Ballato, P., Mouslopoulou, V., Begg, J., and Metzger, S.: Structures and kinematics of the Cephalonia-Lefkada Transform Fault zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17515, https://doi.org/10.5194/egusphere-egu24-17515, 2024.

EGU24-18328 | Posters on site | TS3.4

6 February 2023 Mw 7.8 Pazarcık (Kahramanmaraş) Earthquake: the rupture geometry and slip distribution 

Cengiz Zabcı, Havva Kıray, H. Serdar Akyüz, Taylan Sançar, Sinan O. Akçiz, Gülsen Uçarkuş, Erdem Kırkan, Gürsel Sunal, M. Ersen Aksoy, Davaasambuu Battogtokh, Nurettin Yakupoğlu, Mehmet Köküm, Musa Balkaya, and Asen Sabuncu

6 February 2023 Mw 7.8 Pazarcık (Kahramanmaraş) Earthquake generated about a 300 km-long surface rupture between the Antakya airport to the south and the Karaköse and Yarpuzlu villages (Sincik, Adıyaman) to the north and strong ground motions, resulting in extensive property damage and loss of lives. We rapidly started to document the deformation structures on the surface by the second day of the event, spreading into smaller mapping teams and covering nearly the entire rupture zone. In addition to walking the rupture and recording locations with GPS waypoints, we made surface offset measurements with a standard tape measure. We used several sUAS’ to acquire high-resolution Digital Orthophoto Maps and Digital Surface Models (between 3 to 5 cm pixel resolution) to map the coseismic slip and surface rupture zone details. We utilized high resolution stereo aerial images with 10 or 30 cm ground pixel resolution, collected by the General Directorate of Mapping, in areas where we could not collect high-quality sUAS imagery.

This poster presentation aims to show the full extent of our field and sUAS-based rupture map and horizontal slip measurements of the Pazarcık Earthquake. At the most southern section, the rupture along the Hatay Rift is ~115 km long with a maximum sinistral offset of about 4.5 m between Nurdağ and Şekeroba towns. Between Türkoğlu and Gölbaşı, the rupture is 85 km long and the maximum slip reaches up to ~7m to the north of the Pazarcık town, close to the junction of the East Anatolian and Narlı faults. Farther to the NE, between Gölbaşı and Çelikhan, the slip first decreases to a mean value of ~2.5 m, but then it increases again to ~6.5 m at Kurucaova village. This section of the fault zone is nearly one km wide and is characterized by numerous sub-parallel surface breaks. To the north east of Çelikhan, the slip drops to less than one meter. It diminishes to the north of the Karaköse village (Sincik, Adıyaman), leaving of about 20 km-long unbroken fault section at the surface until the southwest termination of the 2020 Mw 6.8 Sivrice Earthquake rupture.

How to cite: Zabcı, C., Kıray, H., Akyüz, H. S., Sançar, T., Akçiz, S. O., Uçarkuş, G., Kırkan, E., Sunal, G., Aksoy, M. E., Battogtokh, D., Yakupoğlu, N., Köküm, M., Balkaya, M., and Sabuncu, A.: 6 February 2023 Mw 7.8 Pazarcık (Kahramanmaraş) Earthquake: the rupture geometry and slip distribution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18328, https://doi.org/10.5194/egusphere-egu24-18328, 2024.

EGU24-18563 | ECS | Posters on site | TS3.4

Fostering an Earthquake Culture: Towards Enhancing Seismic Resilience in Türkiye 

Deniz Ertuncay, Ezgi Karasözen, Pınar Büyükakpınar, Elif Oral, and Emre Havazlı

The recent M 7.5 earthquake that struck Japan on January 1st, 2024, marked a significant event due to its substantial magnitude and surprisingly minimal damage. This occurrence serves as a stark contrast to Türkiye's experience, notably the devastating Kahramanmaraş earthquake of February 2023. Japan's impressive success in earthquake resilience, achieved through strict building code enforcement and effective public awareness campaigns, stands in sharp contrast to Türkiye's ongoing struggle with seismic vulnerability. This discrepancy underscores the urgent need to bridge the gap between scientific knowledge and societal preparedness in Türkiye.

To address this pressing issue, we propose a set of actionable guidelines. Firstly, there is a need to integrate geoscience into Türkiye's educational system, thereby enhancing public understanding of earthquake risks. Simultaneously, opportunities for geoscientists should be expanded to facilitate expertise growth. Establishing local earthquake centers is paramount to improving seismic monitoring, research, and outreach efforts, bolstering the nation's preparedness for seismic events. Furthermore, geoscientists should prioritize science communication training to effectively engage the public and combat misinformation, thereby fostering a more informed and proactive society. In addition to these measures, implementing earthquake scenario modeling and regular preparedness exercises are instrumental in enhancing nationwide earthquake readiness and preparing Türkiye for future seismic events. Lastly, we emphasize the importance of fostering an earthquake culture through memory and awareness initiatives. This approach will instill a collective consciousness about seismic risks and responses, creating a more resilient society.

It is essential to recognize that the successful implementation of these guidelines will require active participation from scientists, institutions, and the public. By following these recommendations, Türkiye can build resilience and mitigate the impact of future earthquakes, ultimately ensuring a safer future for its citizens.

How to cite: Ertuncay, D., Karasözen, E., Büyükakpınar, P., Oral, E., and Havazlı, E.: Fostering an Earthquake Culture: Towards Enhancing Seismic Resilience in Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18563, https://doi.org/10.5194/egusphere-egu24-18563, 2024.

The 6 February 2023 sequence that was initiated by the failure of the <40 km-long Narlı fault turned out to be the biggest seismic event to occur in and around Türkiye during the modern times. While reaching a total rupture length of almost 450 km, the two separate sinistral events of Mw 7.7 and Mw 7.6 that took place 9 hours apart on the very same day also gave rise to an extremely heavy aftermath: loss of >50.000 lives and > USD 100 billion in economic damages.

We have analysed the first 12 months of postseismic movements following the February 2023 sequence using both Sentinel-1 and ALOS2 radar imagery. Movement along both the East Anatolian and Çardak fault zones are evident with the latter being more pronounced owing (probably) to the line-of-sight N-S insensitivity of the satellites. The time series analysis also shows movement along the westernmost part of the Sürgü fault and a ~20 km N-S oriented fault towards the western end of the Çardak rupture. The continuation of the dominantly E-W oriented Çardak rupture to northeast towards the city of Malatya is also evident in the postseismic data emphasizing once again the elevated seismic risk posed on the city.

Apart from the postseismic activity associated with the 2023 sequence another prominent feature observable in the radar data is the continuing aseismic movement along the Pütürge segment of the East Anatolian Fault Zone which was reported earlier by Çakır et al. (2023). Taking into account moderate earthquakes like the August 4th, 2020 Mw 5.6 earthquake that took place in between the 2020 Mw 6.8 Sivrice-Elazığ earthquake rupture zone and the Yarpuzlu restraining bend where the Mw 7.7 event of the 2023 sequence has terminated; we propose that at least 20 km of the segment could still be unbroken.

 

How to cite: Akoğlu, A. M., Zabcı, C., and Çakır, Z.: Analysis of the First Year of Postseismic Movements Following the 2023 Kahramanmaraş (Türkiye) Earthquake Sequence Using InSAR Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18791, https://doi.org/10.5194/egusphere-egu24-18791, 2024.

EGU24-18829 | Posters on site | TS3.4

Monitoring Tectonic Movements with Low Cost GNSS Measurement Systems 

Burak Akpinar, Seda Özarpacı, Cüneyt Aydın, Nedim Onur Aykut, Alpay Özdemir, Güldane Oku Topal, Özge Güneş, Fahri Karabulut, and Uğur Doğan

Geodetic GNSS (Global Navigation Satellite Systems) measurement systems play a crucial role in studies aimed at monitoring crustal movements. From the past to the present, GNSS measurement systems have served as active measurement tools within the scope of these studies. In these studies, geodetic GNSS measurement systems can be used as continuous reference stations and are primarily employed in campaign-type measurements. However, the setup and operation of continuous reference stations require a significantly high financial budget. On the other hand, campaign-type measurements necessitate simultaneous data collection using multiple GNSS measurement systems, depending on criteria such as the size of the field and the number of points. This, in turn, increases the overall measurement costs. Today, due to the high expenses associated with geodetic GNSS measurement systems, research is being conducted on the use of low-cost GNSS systems in structural health monitoring, displacement determination, and other applications. Since the studies conducted so far have generally been limited to short-term observations at short baselines, there remain questions about the performance of low-cost GNSS measurement systems in monitoring crustal movements. In this study, the objective is to determine the performance of GNSS measurement systems, whose unit costs are considerably lower compared to geodetic GNSS systems, in monitoring crustal movements. For this purpose, two low-cost GNSS measurement systems will be deployed on the northeastern edge of the surface rupture caused by the earthquakes of Mw7.8 and Mw7.6 that occurred in Kahramanmaraş on 06.02.2023. This will enable the continuous monitoring of the post-earthquake effects in the Çelikhan segment on the East Anatolian Fault (DAF). Furthermore, the performance of low-cost GNSS measurement systems will be assessed. In addition to the measurements taken at permanent stations, campaign-type GNSS measurements will be conducted at four different points using both geodetic and two low-cost GNSS measurement systems throughout the project. By processing the data obtained from geodetic GNSS measurement systems and the data acquired from low-cost GNSS measurement systems in the same region, the results will be analyzed. This analysis aims to determine the performance of low-cost systems in monitoring tectonic structures through continuous measurements and campaign-type measurements. This is work is supported by TUBITAK project number 123Y147.

How to cite: Akpinar, B., Özarpacı, S., Aydın, C., Aykut, N. O., Özdemir, A., Oku Topal, G., Güneş, Ö., Karabulut, F., and Doğan, U.: Monitoring Tectonic Movements with Low Cost GNSS Measurement Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18829, https://doi.org/10.5194/egusphere-egu24-18829, 2024.

EGU24-18974 | Posters on site | TS3.4

6 February 2023 Kahramanmaras, Turkey Earthquakes: Microtremor Measurement, Extensive Field Survey On Seismic Intensity  And Structural Damage Correlations To Develop The New Intensity Formula For The Region 

Nurcan Meral Ozel, Shinichiro Mori, Hitomi Murakami, Maki Koyama, Dilek Kepekçi, Gulten Polat, Yasemin Korkusuz Ozturk, Saki Yotsui, Hiroyuki Goto, Shigeto Osato, Tatsuro Chiba, Koji Hada, Masayuki Yamada, Takumi Hayashida, and Mayumi Sakamoto

The research conducted on the 6th of February 2023 Mw7.8 Kahramanmaraş earthquake represents
a comprehensive study aimed at understanding the distribution of seismic intensity in the affected
areas and developing a novel intensity calculation formula for Eastern-Southeastern Turkey. This
seismic event, the most catastrophic in Turkey&#39;s last century, was initiated on the Narli splay fault
and propagated bilaterally along the East Anatolian Fault (EAF). The rupture extended over a
significant seismic gap of the EAF and the Amanos Fault, affecting 11 provinces in Turkey&#39;s Southeast
region and bordering areas of Syria, resulting in a total rupture length exceeding 300 km and causing
over 50,000 fatalities.
The study evaluates seismic intensity distribution across seven cities: Hatay, Gaziantep,
Kahramanmaraş, Adıyaman, Malatya, Osmaniye, and Şanlıurfa. An online intensity questionnaire
survey was distributed to educational institutions in these provinces. In October 2023, a Turkish-
Japanese reconnaissance team collaborated with the National Education Directorate of the seven
provinces to disseminate the questionnaire format and URL link to all public high schools, middle
schools, and elementary schools, garnering responses from 14,739 participants. Geocoordinate
inputs were accurately assigned using the ArcGIS survey123 system, contributing to the preliminary
survey results which included damage observations.
Microtremor observations were conducted in Hatay, Gaziantep, Kahramanmaraş, and Adıyaman
using the Kinkei seismic measuring device developed in Japan. The research involved single-point
microtremor measurements at 20 locations within the earthquake zone, fault-fracture zones,
damaged residential areas, particularly near the AFAD seismic stations. Additionally, array
microtremor measurements were made at 31 AFAD station locations with strong motion records.
The analysis of 39 microtremor measurements revealed preliminary results indicating a correlation
between heavily damaged buildings and areas where the Vs30 values are less than 180 m/s. The
finding suggests that areas with lower Vs30 values may be more susceptible to damage during
earthquakes.

These observations, combined with the result of the online intensity questionnaire surveys and local
soil amplifications, are utilized to assess the correlation between microtremor amplification and
seismic damage. The objective is to formulate a new intensity calculation formula tailored to the
Eastern-Southeastern part of Turkey. This research&#39;s findings are anticipated to offer significant
contributions to earthquake intensity assessment methodologies, particularly in regions with distinct
geological and seismic profiles. The collaboration between Turkish and Japanese experts adds an
international dimension to the study, potentially leading to improved seismic risk assessment,
preparedness strategies, and recovery measures on a broader scale in the future.

How to cite: Meral Ozel, N., Mori, S., Murakami, H., Koyama, M., Kepekçi, D., Polat, G., Korkusuz Ozturk, Y., Yotsui, S., Goto, H., Osato, S., Chiba, T., Hada, K., Yamada, M., Hayashida, T., and Sakamoto, M.: 6 February 2023 Kahramanmaras, Turkey Earthquakes: Microtremor Measurement, Extensive Field Survey On Seismic Intensity  And Structural Damage Correlations To Develop The New Intensity Formula For The Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18974, https://doi.org/10.5194/egusphere-egu24-18974, 2024.

EGU24-19513 | ECS | Posters on site | TS3.4

Akyaka-Ula Region Tectonics based on Geodetic Observations 

Muhammed Turgut, Seda Özarpacı, Alpay Özdemir, Efe T. Ayruk, İlay Farımaz, Uğur Doğan, and Aynur Dikbaş

The Aegean region is under the influence of tectonic extension due to subduction zone along the Hellenic Arc. This extension leads to many earthquakes of magnitude 6 and above in the region. The earthquake that occurred on July 21, 2017, in Bodrum Mw 6.7 increased curiosity about the region due to the seismic activities in the Gulf of Gökova and the absence of an active fault in the area according to the active fault map published by the General Directorate of Mineral Research and Exploration (MTA). In the nearby region of the 2017 earthquake, there are the Gökova Fault Zone and the Fethiye-Burdur Fault Zone. Morphological linearity and the seismicity are observed between these two fault zones, and some recent studies indicate the existence of active faults. The aim of this study is to determine whether there are active faults in the Akyaka-Ula region with geodetic measurements. For this purpose we started to observe the area with GNSS campaigns and continuous data since 2021.

For this purpose, the data of Turkish National Permanent GNSS Network (CORS-TR) continuous stations, Turkish National Fundamental GNSS sites campaign measurements and survey data of a GNSS network established by our research group were processed together. The GNSS network stations were strategically placed in both near field and far field to the potential fault. GNSS data processed by using Bernese 5.2 software. According to the calculations based on the data from TNPGN-Active and TNFGN stations, the region exhibits an southwestward movement at a rate of approximately 3cm/year.

This work is supported by TUBITAK Project Number 121Y300

How to cite: Turgut, M., Özarpacı, S., Özdemir, A., Ayruk, E. T., Farımaz, İ., Doğan, U., and Dikbaş, A.: Akyaka-Ula Region Tectonics based on Geodetic Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19513, https://doi.org/10.5194/egusphere-egu24-19513, 2024.

EGU24-19720 | ECS | Posters on site | TS3.4

Creeping Pütürge Segment with Geodetic Evidence 

Seda Özarpacı, Celeste Hofstetter, Gareth Funning, Ugur Dogan, Semih Ergintav, Ziyadin Çakır, Cengiz Zabcı, Alpay Özdemir, Efe Turan Ayruk, and İlay Farımaz

On January 24, 2020 the Mw 6.8 Sivrice (Elazığ) earthquake was arrested by the ~80 km long Pütürge segment. On February 6, 2023, the first earthquake of the Kahramanmaras Earthquake Sequence, also ended at the southwest end of this segment. Is it creep also that arrest 2023 Pazarcik rupture? We analyzed InSAR data over the Pütürge segment to answer this question. We used over 5000 ARIA standard product interferograms from two ascending and two descending tracks of the Sentinel-1 satellites and the MintPy software to produce InSAR time series and velocity maps for the area. Also we processed both survey and continuous GNSS data with GAMIT/GLOBK GNSS software (v10.7) from 2014. We analysed the results in three time periods – before, between, and after the two earthquakes. InSAR shows that before both earthquakes the segment was creeping and GNSS data is confirming that outcome. We also are searching for any unbroken part of this segment and if this could be another danger in the future.

This work is supported by TUBITAK project numbers 114Y250, 118Y435 and 121Y400.

How to cite: Özarpacı, S., Hofstetter, C., Funning, G., Dogan, U., Ergintav, S., Çakır, Z., Zabcı, C., Özdemir, A., Ayruk, E. T., and Farımaz, İ.: Creeping Pütürge Segment with Geodetic Evidence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19720, https://doi.org/10.5194/egusphere-egu24-19720, 2024.

EGU24-19798 | Orals | TS3.4

Resolving the Slip-Rate Inconsistency of the Northern Dead Sea Fault  

Sigurjon Jonsson, Xing Li, Shaozhuo Liu, Zhangfeng Ma, Nicolas Castro-Perdomo, Simone Cesca, Frédéric Masson, and Yann Klinger

Geological studies, GPS observations, and plate motion models consistently show that the slip rate for most of the Dead Sea Fault (DSF) is 4-5 mm/year. However, for the northernmost DSF, just south of where the 2023 Kharamanmaraş earthquakes occurred, results differ, with GPS results from Syria (from before 2010) indicating a lower rate of only 2-3 mm/year. Conventional InSAR observations have not provided useful information about the present-day strain accumulation on the DSF, due to the fault’s north-south orientation and the insensitivity of InSAR to north-south displacements. Therefore, to study this slip-rate inconsistency and overcome limited access to the northern DSF in Syria, we employed time-series analysis of along-track burst-overlap interferometric (BOI) observations from 2014-2021 Sentinel-1 data to retrieve the interseismic horizontal fault-parallel displacements in the burst-overlap areas. Elastic modeling based on the BOI velocities indicates the fault slip rate decreases from ~5 mm/year in the south to only 2.8 mm/year at the northern DSF in Syria, in agreement with the GPS observations. Using what we know about earthquake clustering statistics on the DSF, we also demonstrate that the higher paloseismological slip rate on the northern DSF, which primarily comes from offset markers in the past 3500 years, could by chance be inflated by earthquake clustering. Furthermore, we suggest that the northern Sinai plate, west of the northern DSF is its own micro-plate (Latakia-Tartus plate), separated from the main Sinai plate in the south by a diffuse offshore plate boundary zone between Lebanon the Cyprus arc. This interpretation is supported by elevated offshore seismicity and the several moment tensor solutions we could determine. Together, our results resolve the long-standing slip-rate inconsistency along the northern DSF and indicate lower earthquake hazard for that part of the fault than previously thought.

How to cite: Jonsson, S., Li, X., Liu, S., Ma, Z., Castro-Perdomo, N., Cesca, S., Masson, F., and Klinger, Y.: Resolving the Slip-Rate Inconsistency of the Northern Dead Sea Fault , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19798, https://doi.org/10.5194/egusphere-egu24-19798, 2024.

The Mw 7.7 Ekinozu Earthquake is the second shock of the devastating 2023 Kahramanmaraş earthquake doublet. It ruptured bilaterally along a ~150 km-long stretch of the Cardak-Surgu fault. Along its eastern section, instead of propagating along the Surgu fault to connect with the main East Anatolian Fault where the Mw7.8 shock occurred, the rupture unexpectedly turned to the northeast to propagate along a secondary structure. Surface ruptures and assessment of displacement along that section of the fault have been challenging to map, and these are less documented. This is crucial for unraveling the entire rupture process, fault growth, and related seismic hazards. In this study, we focus on the eastern end of the ~57-km long surface rupture caused by the Mw 7.7 Ekinozu Earthquake. By correlating high-resolution optical images SPOT (pre-earthquakes, resolution 1.5m) and Pléiades (post-earthquakes, resolution 50 cm), we computed displacement maps at 1.5 m ground resolution for the study area. In addition, using the post-event Pleiades images, we meticulously characterized the coseismic surface ruptures in detail. Our mapping presents a segmented surface rupture trace with azimuth variations and several distinguishably complex geometries, such as double bends and branches. Furthermore, our investigation includes precise measurements of on- and off-fault surface displacement with sub-pixel detection over the ~57-km long section. Our findings underscore the significance of detailed interpretations of coseismic surface rupture and coseismic displacement measurements in comprehending the propagation of the seismic rupture.

How to cite: Delorme, A., Yao, W., and klinger, Y.: Imaging the Northeastern End of the Mw7.7 Ekinozu Earthquake Rupture along the Çardak-Surgu Fault during the 2023 Kahramanmaraş, Türkiye, Earthquake Doublet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20732, https://doi.org/10.5194/egusphere-egu24-20732, 2024.

EGU24-22128 | ECS | Posters on site | TS3.4

The seismic cycle of the Hatay Triple Junction from GNSS analysis: interseismic, coseismic and postseismic deformations 

Ali Özkan, İbrahim Tiryakioğlu, Halil İbrahim Solak, Göksu Uslular, Baptiste Rousset, Frédéric Masson, and H. Hakan Yavaşoğlu

The East Anatolian Fault Zone (EAFZ) is a major tectonic feature in Anatolia, moving westward relative to the Eurasian plate, primarily due to the compressional behavior of the African, Sinai, and Arabian plates. The EAFZ has been historically significant as the epicenter of several major seismic events, including the recent devastating earthquakes in Kahramanmaraş on February 06, 2023. In this study, we provide a comprehensive tectonic analysis of the EAFZ, focusing specifically on the Hatay Triple Junction (HTJ), where the EAFZ meets with the continuation of the Dead Sea Fault Zone and the Cyprus Arc. Through the synthesis of pre-seismic evaluations and co-seismic data derived from our comprehensive geodetic network, we aim to extend the understanding of the seismic cycle and fault behavior in this tectonically complex region.

In the pre-seismic phase, we employed a dense GNSS network, including the Turkish National Fundamental GPS Network (TUTGA) and various campaign sites, to analyze the strain accumulation and fault kinematics at the HTJ. Analyses revealed that the EAFZ and Karataş-Osmaniye fault exhibit complete locking at depths of 15 km and 7 km, respectively, while the Karasu Fault (KF) demonstrates locking up to a depth of 7 km. Our kinematic models indicated significant slip rates, suggesting a high potential for large earthquakes. Remarkably, during the revision of our manuscript in “Tectonophysics”, two major earthquakes (Mw 7.7 and Mw 7.6) occurred near the KF and EAFZ in Pazarcık and Elbistan, Kahramanmaraş, respectively. These earthquakes, happening in close succession, dramatically corroborated our predictions for seismic activity near the HTJ. 

In the co-seismic phase, following the Kahramanmaraş earthquakes, we utilized a high-resolution GNSS network with 73 permanent and 40 campaign stations to assess surface displacements and fault slip distributions. Significant displacements were recorded, with the largest being 466 cm, and substantial fault ruptures were observed along the EAFZ and Çardak fault segment, including the left-lateral slips of 494 cm and 391 cm in the first and second earthquakes, respectively.  

Our ongoing projects will integrate pre-earthquakes geodetic data with new GNSS measurements to analyze the postseismic deformation following the Kahramanmaraş earthquakes, including afterslip and its relation with aftershocks, as well as stress perturbations on the neighboring faults. This integrated approach is expected to further refine our ability to understand the behavior of the fault in the post-seismic phase and delineate the complete seismic cycle along the EAFZ.    

How to cite: Özkan, A., Tiryakioğlu, İ., Solak, H. İ., Uslular, G., Rousset, B., Masson, F., and Yavaşoğlu, H. H.: The seismic cycle of the Hatay Triple Junction from GNSS analysis: interseismic, coseismic and postseismic deformations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22128, https://doi.org/10.5194/egusphere-egu24-22128, 2024.

EGU24-1045 | ECS | Posters on site | TS3.5

Tectono-Geomorphic Studies along the Khetpurali Taksal Fault, Northwestern Himalayas 

Poorvi Narayana and Javed N Mailk

The Northwestern Himalayas have been host to many earthquakes, with the recent 1905 Kangra Mw 7.8. Studies suggest the seismic gap in the Northwestern Himalayas to be more than Mw 7.8 in general, and of about Mw 8.4 in the Nahan region of the Northwestern Himalayas. There are studies suggesting the rupture of the Himalayan Frontal Thrust (HFT) and hinterland subsidiary faults by the Earthquakes in the region. In this study, we focused the Khetpurali Taksal Fault (KTF), which is one of the corroboration. It is an out-of- sequence ~ 250 km long dextral strike-slip fault with an NNW-SSE trend. KTF, which is bounded to the west by the Nahan Salient, and in the east by the Dehradun re-entrant; marks the boundary between the Central Himalayas (convergence rate ~ 18 ± 1 mm/y and obliquity ~0°) and the Northwestern Himalayas (convergence rate ~13.6–14 ± 1 mm/yr and obliquity ~ 15°-30°), which runs through the ~ 100km locked width of the Main Himalayan Trust (MHT). The dextral strike-slip motion has caused the displacement of some quaternary deposits along the KTF. It plays a key role in the slip partitioning between the active thrust and the oblique faults with the HFT displaying the thrusting and oblique component in the Pinjore Garden fault, Jhajra fault, and Barsar fault of the same region in the Northwestern Himalayas. This study is focused on the active fault along the KTF. We prepared the geomorphic map and delineated the extent of the KTF using the high-resolution Cartosat-1 data. Our studies show the presence of displaced terraces, lateral offset of streams, sag ponds, and pressure ridges along the KTF. A displacement of 250m to 1350m has been observed. Samples from the displaced terraces are analyzed by OSL dating technique to find out the slip along the KTF. Understanding the slip along KTF will enhance the understanding of slip partitioning taking place in the Nahan Region as a whole, which will help understand the geodynamics of the region and thus in seismic hazard assessment.

How to cite: Narayana, P. and Mailk, J. N.: Tectono-Geomorphic Studies along the Khetpurali Taksal Fault, Northwestern Himalayas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1045, https://doi.org/10.5194/egusphere-egu24-1045, 2024.

EGU24-1056 | ECS | Posters on site | TS3.5

Active Fault and Paleoseismological studies in the hinterland region of NW Himalaya 

Rukhshar Husain and Javed N Malik

The Indian plate is currently underthrusting beneath the Tibetan plateau along the Main Himalayan Thrust (MHT). The strain is getting accumulated during the inter-seismic period on MHT due to this ongoing convergence. The accumulated strain energy is released in a stick-slip fashion on MHT causing destructive earthquakes. Several strong earthquakes within the Himalayan zone have been reported in previous studies such as 1897 at Shillong (Mw 8.2), 1905 at Kangra (Mw 7.8), 1934 at Bihar-Nepal (Mw 8.1), 1950 at Assam (Mw 8.4), 2005 at Muzaffarabad (Mw 7.6), 2015 at Gorkha (Mw 7.8), and 2015 in Afghanistan (Mw 7.6). Based on the distribution of recent and historic earthquake activity in the Himalayas, three seismic gaps can be distinguished from west to east: the Kashmir Seismic Gap (west of the 1905 Kangra earthquake), the Central Seismic Gap (between the 1905 and earthquakes), and the Assam Seismic Gap (between the 1897 and 1950 earthquakes). The major objective of this study is to investigate the hinterland region in the NW Himalaya, which is relatively less explored in terms of its Active Tectonics & Paleoseismology as compared to the deformation front along the Main Himalayan Thrust (MFT). The Nahan salient and Kangra re-entrant are characterised by a complicated pattern of fault distribution which has been proposed in previous studies to get activated, either individually or alongside the Main Frontal thrust, during past large to great-magnitude earthquakes. A detailed tectono-geomorphic map has been prepared using the Cartosat-1 dataset, and geomorphic markers suggestive of recent tectonic activity have been identified in the study region. An exhaustive fieldwork has been conducted, during which a total of 13 samples were collected for Optically Stimulated Luminescence (OSL) dating and Carbon dating to identify signatures of past earthquakes and assess the possibility and degree to which the 1905 earthquake has affected the region. Based on the detailed tectono-geomorphological and paleoseismological investigations, we will be able to assess regional seismic hazards.

(*Author RH aka Rukhshar)

How to cite: Husain, R. and Malik, J. N.: Active Fault and Paleoseismological studies in the hinterland region of NW Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1056, https://doi.org/10.5194/egusphere-egu24-1056, 2024.

EGU24-2671 | ECS | Orals | TS3.5

Seismic risk microzonation mapping using microtremor recordings for an urban area in the vicinity of Lamni Fault, southern Kashmir Basin  

Falak Zahoor, Villayat Ali, Bashir Ahmad, and Inaam ul Haq Jeelani

A high-angle reverse fault was identified near the Aharbal Falls in the Shopian District of the southern Kashmir Basin and was subsequently named as Lamni Fault by Zahoor et al. (2023). The rise of the Pir Panjal range due to the higher tectonic activity in the southern part of Kashmir (Dar et al., 2014) has led to the overthrusting of the Early Permian Panjal Traps over the Pleistocene Fluvio-Glacial Deposits. The presence of the fault was experimentally validated through the conduction of single-station microtremor horizontal-to-vertical spectral ratio (MHVSR) method, supported by the results from multichannel simulation with one-receiver (MSOR) surface wave tests across the suspected fault zone in Shopian. The fault zone was demarcated at the location by identifying anomalously high H/V amplitudes (>8) at high frequencies (>4Hz) as opposed to the low values (2-3) in the surrounding host rock. As an extension of the work, we seek to conduct the microzonation of the region laced by the Lamni Fault in the Sedow area of Shopian, Kashmir, using the atypical HVSR amplitudes as the markers of high risk. The MHVSR method has been successfully employed for investigating buried and exposed faults like Erft-Sprung normal fault, Tremestieri normal fault, southern Crete of Greece, Longmen Shan fault zone, etc. (Hinzen, 2004; Lombardo and Rigano 2006; Moisidi et al., 2012; Zhang et al., 2019). The low-velocity fractured fault zone is known trap seismic waves and hence lead to large amplifications of the waves which is thus reflected in the HVSR curves as well as in earthquake recordings e.g., in San Andreas fault zone (Li et al., 2000) and San Jacinto fault zone (Roux et al., 2016). Utilising this behaviour of the fractured fault zones, microzonation of the Sedow locality which lies in the vicinity of the detected Lamni Fault was conducted by performing about 50-60 single-station MHVSR tests over an area of about 2 km x 2 km. The area has several residential buildings along with local government school buildings as well as a mosque, thus demanding serious consideration of the increased seismic hazard due to the presence of the fault. Zones of anomalous H/V amplitudes were found in the region surrounded by stable low estimates. This may have serious implications for the seismic hazard estimates in the region surrounding the fault zone also supported in earlier studies in other regions of the world (e.g., Spudich and Olsen, 2001; Donati et al., 2001; Rovelli et al., 2002). It is recommended that a zone be defined at a significant width around the fault zone in which constructions may be avoided or else special considerations for the increased seismic hazard be considered for the existing buildings. Such a buffer zone has been named the Alquist-Priolo zone, APZ in earlier studies (Spudich and Olsen, 2001; Bryant, 2010). The APZ is considered an important inclusion in seismic hazard and microzonation process to aid in urban planning and development in a region.

How to cite: Zahoor, F., Ali, V., Ahmad, B., and Jeelani, I. U. H.: Seismic risk microzonation mapping using microtremor recordings for an urban area in the vicinity of Lamni Fault, southern Kashmir Basin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2671, https://doi.org/10.5194/egusphere-egu24-2671, 2024.

The January 10, 2022, MS 6.9 Menyuan, China, earthquake occurred caused by strike-slip faulting in the tectonically complex region of the northeastern Tibetan Plateau, and ten people were injured in Menyuan City. The September 8, 2023, MS 6.9 Morocco, earthquake occurred in the African Plate at shallow depth with oblique-reverse faulting. At least 2,900 people were killed and more than 5,000 injured in Morocco till to September 13, 2023. International media reports of such kind of disasters by the Morocco earthquake only resulted from poor building structure design and low-solidity housing, such as in Marrakech, southwest of the epicenter. The surface wave magnitude (MS) of the two earthquakes is the same, and the moment magnitude (MW) and energy magnitude (Me) of the Menyuan mainshock are slightly lower than those of the Morocco event. Although the scalar moment and radiated seismic energy from Morocco dynamic rupture are only 2~3 times of the Menyuan earthquake, the density of urban residents nearby and around the epicenter of the Morocco mainshock is at least more than a hundred times higher than that around the epicenter of the Menyuan even. For the Morocco sequence, the USGS reported the number of aftershocks higher than MW4.0 is only seven and the largest is 4.9. In contrast, there are two aftershocks higher than MS5.0 in the Menyuan sequence recorded by the China Earthquake Networks Center, 5.1 and 5.2, respectively. Normally, a similar magnitude does not reflect the equivalent seismic moment, release of radiated energy, and the occurrence of strong aftershocks. Meanwhile, devastating loss of life and injuries are not only due to the design of the building and the quality of the house.

Acknowledgment: This research is supported by the Spark Program of Earthquake Sciences (XH22012YC)

How to cite: Meng, L., Zang, Y., and Xie, M.: The Differential of Casualties, Energy Radiation, and Characteristics of Sequences from the Same MS: The Menyuan MS 6.9 2022 and Morocco MS 6.9 2023 Earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3159, https://doi.org/10.5194/egusphere-egu24-3159, 2024.

EGU24-5155 | Posters on site | TS3.5

Empirical scaling correlations between fault lengths and fault slip-rates in seismically-active extensional regions: The Calabria and Messina Strait region (southern Italy) as case study 

Marco Meschis, Gerald Roberts, Claudia Sgambato, Alessandro Maria Michetti, Franz Livio, Zoe Mildon, Joanna Faure Walker, Francesco Iezzi, Jennifer Robertson, Alessandro Gattuso, Marino Domenico Barberio, Paolo Randazzo, and Antonio Caracausi

In this study, we present scaling relationships between fault lengths, fault slip-rates and historical seismicity for an active normal fault system, seismically accommodating crustal extension within the upper plate of the Ionian subduction zone (southern Italy). This crustal extension is confirmed by historical seismicity and instrumental geodesy, with GNSS-derived values of horizonal deformation within a range of 2-3 mm/yr throughout Calabria and the Messina Strait region. We collated data for fault slip-rates, fault lengths and historical earthquakes for a given fault to explore whether fault slip-rates are correlated with fault size and their geometric moment.

We present new results showing a robust correlation between fault lengths and fault slip-rates, which supports the idea of a relationship for a given fault between fault slip-rates and the geometric moment.

We discuss our results in terms of how these correlations should be used if regional deformation is accommodated by localised strain on faults mostly arranged along strike rather than distributed strain on multiple faults across-strike. For instance, we compare our empirical correlation between fault lengths and fault throw-rates over the Middle-Late Pleistocene in Calabria and the Messina Strait with those from Central and Southern Apennines over the Holocene, characterized by strain distributed on multiple faults across-strike and strain localised on faults mostly arranged along-strike, respectively.

Tectonic and seismic hazard implications are discussed for future investigations based on fault slip-rates, fault size and historical seismicity.

How to cite: Meschis, M., Roberts, G., Sgambato, C., Michetti, A. M., Livio, F., Mildon, Z., Faure Walker, J., Iezzi, F., Robertson, J., Gattuso, A., Barberio, M. D., Randazzo, P., and Caracausi, A.: Empirical scaling correlations between fault lengths and fault slip-rates in seismically-active extensional regions: The Calabria and Messina Strait region (southern Italy) as case study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5155, https://doi.org/10.5194/egusphere-egu24-5155, 2024.

EGU24-7698 | Posters on site | TS3.5

Exploring the uncertainties of the fault source parameters in the Alboran Sea for seismic hazard using earthquake rate modelling tools 

Hector Perea, Octavi Gómez-Novell, María José Jiménez, Mariano García, Lucía Lozano, Julián García-Mayordomo, José Luis Sánchez-Roldán, Ariadna Canari Bordoy, and Sara Martínez-Loriente

The Alboran Sea is one of the most seismically regions of Western Europe, accommodating an important part of the current NW-SE convergence between the African and Eurasian plates (4-5 mm/yr). Despite the Alboran Sea is considered as a region of relatively low tectonic deformation and diffuse seismicity, the major faults within have been responsible of large earthquakes (IEMS>IX) since historical times (e.g., 1522 Almería, 1790 Oran, 1804 Alboran, 1910 Adra or 2016 Al-Idrissi earthquakes). One of the main issues for the characterization of the seismic hazard in the Alboran Sea, common to many low-deformation regions, lies in accurately constraining the seismic parameters that define fault activity and their behavior (i.e., slip rates, earthquake recurrence and multi-fault rupture capability, among others). This issue is further aggravated by the fact that these faults are mostly located offshore, making their investigation more challenging. As a result, most faults in the Alboran Sea have poor slip and activity rate estimates, while their capability to interact and rupture in complex rupture patterns has not been explored yet. In this study, we compute several models of earthquake rupture rates for the Alboran Sea with the SHERIFS code and using a systematic parameter exploration tree to determine the parameters of each model. We base the exploration tree on the slip rate and multi-fault rupture scenarios, allowing us to investigate the epistemic uncertainty linked to these parameters. To check the feasibility of the computed earthquake rates of each model, we compare them with the observed seismicity rates in the region. As a result, this enables us to identify which parameter combinations best match the recorded seismicity, prioritizing those that perform better for the hazard assessment. In addition, these optimal values might be used as indicators for further studies focused on better constraining the fault parameters in some faults, as well as for preliminary fault-based seismic hazard assessments. By extension, the limitations of the modelling in terms of slip rate budget distribution and fault rupture scenarios can also be used to determine which areas should be prioritized for further research. We expect that the results of our work enhance discussion among researchers working in the area and motivate further investigations into fault dynamics.

How to cite: Perea, H., Gómez-Novell, O., Jiménez, M. J., García, M., Lozano, L., García-Mayordomo, J., Sánchez-Roldán, J. L., Canari Bordoy, A., and Martínez-Loriente, S.: Exploring the uncertainties of the fault source parameters in the Alboran Sea for seismic hazard using earthquake rate modelling tools, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7698, https://doi.org/10.5194/egusphere-egu24-7698, 2024.

EGU24-7956 | ECS | Posters on site | TS3.5

A Millennial Perspective on Coulomb Stress Transfer Impact in the seismicity of the Central Apennine Fault System 

Giorgio Valentini, Tiziano Volatili, Paolo Galli, and Emanuele Tondi

This research examines the influence of static Coulomb Stress Transfer (CST) in shaping the seismic cycles associated with the Central Apennine Fault System (CAFS), an active tectonic region that witnessed numerous destructive seismic events over the last millennium.

We selected 15 seismic events in the CAFS, dating from 1279 CE to the present, all exceeding Mw 6.0. Out of these, 9 events were specifically chosen for CST analysis, based on their spatial-temporal proximity to later activated faults. The study not only investigates static stress transfer for each event, but also considers the cumulative CST from recent earthquakes, providing a holistic view of the current stress environment. Following a novel approach, we utilized a three-dimensional fault modeling technique, with ellipses representing the 2D geometry of faults at depth. This approach accounts for strike variations and employs a variable strike three-dimensional elliptical model for enhanced precision in CST calculations.

Our case studies within the CAFS suggest that CST might have been a critical factor in either triggering or inhibiting fault activities. Instances of fault reactivation following high stress transfers and scenarios showing the dampening effects of stress shadows were observed. This intricate understanding of CST has practical implications, offering insights into potential future earthquake patterns and aiding in devising targeted risk mitigation strategies.

The complexity of CAFS reveals intricate stress patterns emerging from the interplay of different seismic episodes. These patterns of stress lobes interact in complex ways, influencing adjacent faults by amplifying, neutralizing, or diversifying their CST impacts. Through detailed analyses and cutting-edge modeling techniques, our study provides valuable insights for future research directions and practical approaches to seismic risk reduction. It underscores the strong impact of CST on shaping a region's seismic history and highlights the necessity of ongoing research in this vital area of geosciences.

How to cite: Valentini, G., Volatili, T., Galli, P., and Tondi, E.: A Millennial Perspective on Coulomb Stress Transfer Impact in the seismicity of the Central Apennine Fault System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7956, https://doi.org/10.5194/egusphere-egu24-7956, 2024.

EGU24-9870 | Orals | TS3.5

Characteristics of slip-rate variability and temporal earthquake clustering across a distributed network of active normal faults from in situ 36Cl cosmogenic dating of fault scarp exhumation. 

Gerald P. Roberts, Claudia Sgambato, Ioannis Papanikolaou, Zoe Mildon, Joakim Beck, Alessandro Michetti, Joanna Faure Walker, Sam Mitchell, Marco Meschis, Richard Shanks, Richard Phillips, Ken McCaffrey, Eutizio Vittori, Francesco Iezzi, Jennifer Robertson, Francesco Visini, and Maz Iqbal

We present an in situ 36Cl dataset recording the exhumation of 27 active normal fault planes by earthquake slip for the central Apennines, Italy. We do this to constrain the characteristics of earthquake clustering and anticlustering across the entire extending orogen, and in an attempt to constrain the reasons why clustering and anticlustering occurs. We show that duration and magnitude of clustering and anticlustering, and their characteristics, can be explained by a model where the transfer of differential stress between faults and their underlying shear-zones, and between neighbouring fault/shear-zone structures, produces changes in strain-rates on underlying viscous shear zones which drive periods of rapid or reduced slip-rate on their overlying faults. We suggest that stress increase on an underlying shear zone produced by coseismic slip on its overlying fault could be the mechanism that initiates an earthquake cluster. We suggest that stress reductions on shear-zones from coseismic slip located across strike could be the mechanism that initiates an earthquake anticluster. The durations of anticlusters are controlled by the summed stress decreases through time on shear zones, because although these shear zones are slipping relatively slowly, eventually they will load their overlying fault to failure initiating a new cluster, with anticlusters induced across strike. Thus, there is dynamic feedback both up and down dip between faults and their underlying shear zones and crucially across strike between neighbouring fault/shear-zone structures. If the dynamics producing clustering and anticlustering can be constrained, it may be that observations of these phenomena should be included in probabilistic seismic hazard assessments (PSHA) and also interpretations of regional deformation rates and crustal rheologies based on geodetic data. Multi-millennial clustering and anticlustering should become a subject for discussion in these scientific communities.

How to cite: Roberts, G. P., Sgambato, C., Papanikolaou, I., Mildon, Z., Beck, J., Michetti, A., Faure Walker, J., Mitchell, S., Meschis, M., Shanks, R., Phillips, R., McCaffrey, K., Vittori, E., Iezzi, F., Robertson, J., Visini, F., and Iqbal, M.: Characteristics of slip-rate variability and temporal earthquake clustering across a distributed network of active normal faults from in situ 36Cl cosmogenic dating of fault scarp exhumation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9870, https://doi.org/10.5194/egusphere-egu24-9870, 2024.

We investigate the Coulomb stress changes due to 30 strong earthquakes occurring on normal faults since 1509 A.D. in Calabria, Italy, including the influence of both coseismic and interseismic loading in our modelling. We compare the results to existing studies of stress interaction from the Central and Southern Apennines, Italy. The three normal fault systems have different geometries and long-term slip-rates. The Central Apennines hosts a complex fault system, with many faults across strike, so that when an earthquake occurs, many of the surrounding faults experience a stress decrease. The Southern Apennines and Calabria have a simpler geometry, with fewer faults, and faults are located predominantly along strike, therefore when an earthquake occurs the dominant process on the neighbouring faults is stress increase. We investigate how stress transfer may influence the occurrence of future earthquakes and what factors may govern the variability in earthquake recurrence in different fault systems. Within the analysed time period, the Calabrian, Central Apennines, and Southern Apennines fault systems have 91%, 73% and 70% of faults with a mean positive cumulative Coulomb stress change, respectively; this is due to fewer faults across strike, more across strike stress reductions, and greater along-strike spacing in the three regions respectively. In regions with close along strike spacing or few faults across strike, such as Calabria and Southern Apennines, the stress loading history is mostly dominated by interseismic loading and most faults are positively stressed before an earthquake occur on them (96% of all faults that ruptured in Calabria; 94% of faults in the Southern Apennines), and some of the strongest earthquakes occur on faults with the highest mean cumulative stress of all faults prior to the earthquake. In the Central Apennines, where across strike interactions are the predominant process, 79% of the earthquakes occur on faults that are positively stressed. The results highlight that fault system geometry plays a central role in characterizing the stress evolution associated with earthquake recurrence, and can possibly influence the occurrence of propagating triggered earthquake sequences.

How to cite: Sgambato, C., Faure Walker, J. P., Roberts, G. P., Mildon, Z. K., and Meschis, M.: Influence of fault system geometry and slip rates on earthquake triggering and recurrence variability, insights from Coulomb stress interactions during historical earthquake sequences in Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10100, https://doi.org/10.5194/egusphere-egu24-10100, 2024.

EGU24-10122 | ECS | Orals | TS3.5

Using fracture-scarp lineations as kinematic indicators on active normal fault scarps 

Billy Andrews, Zoë Mildon, Manuel Lukas Diercks, Sam Mitchell, Gerald Roberts, Constanza Rodriguez Piceda, and Jenni Robertson

To undertake fault-based seismic hazard assessment, we need to accurately identify source faults and assess their slip-rate and kinematics through pertinent data collection. For example, converging slip vectors may be used to deduce whether isolated fault strands are connected at depth. Kinematic (slip vector) data can be collected through offset piercing points or from striations preserved on fault scarps. However, striations are surficial features and may therefore be readily eroded and not preserved or visible on degraded scarps. Tensional fracture networks are ubiquitous on bedrock fault scarps and extend deeper into the scarp, and therefore have a greater preservation potential when compared to striations. In this work we characterise fracture-scarp (F-S) lineation patterns across eight faults in Italy (Central Apennines) and Greece (Perachora Peninsula) to explore how these patterns relate to fault plane geometry and slip-vector.

Various fracture-scarp (F-S) lineation patterns (including sinistral/dextral en-echelon arrays, slip-parallel/-perpendicular fractures, and conjugate sets) are recognised. These patterns show evidence of progressive growth during exhumation. This suggests F-S lineations formed near the surface as the footwall uplifts, with larger features becoming more connected and smaller ones remaining ‘isolated’. The orientations of F-S lineations align within a pure or Riedel shear geometry where the shear sense is related to the rake of the slip vector. We propose that the observed patterns are controlled by fault plane orientation relative to a 3D strain ellipsoid and the progressive reduction of effective normal stress during footwall exhumation. As fractures form under the same stress regime as striations, they can serve as a kinematic indicator even on highly degraded active fault scarps.

How to cite: Andrews, B., Mildon, Z., Lukas Diercks, M., Mitchell, S., Roberts, G., Rodriguez Piceda, C., and Robertson, J.: Using fracture-scarp lineations as kinematic indicators on active normal fault scarps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10122, https://doi.org/10.5194/egusphere-egu24-10122, 2024.

EGU24-10216 | ECS | Posters on site | TS3.5

Fault interactions and Coulomb stress-triggering in complex fault networks 

Manuel Diercks, Zoe Mildon, Sarah Boulton, Ekbal Hussain, Cihat Alçiçek, Tunahan Aykut, and Cengiz Yıldırım

Earthquakes on normal faults cause negative Coulomb stress transfer (CST) onto receiver faults located across-strike, which, in theory, delays or prevents rupture. Nevertheless, earthquakes on such across-strike faults are frequently observed. This study explores why, and how, large earthquakes can be triggered on faults repeatedly receiving negative coseismic CST. Two triggering mechanisms are hypothesised: (1) Positively stressed patches or segments of faults, resulting from heterogeneous stress transfer, act as triggers to rupture earthquakes on faults that are on average negatively stressed. (2) Negative coseismic CST is compensated by interseismic loading and other processes building up positive stress on the source faults. To test both hypotheses, a 400-year earthquake sequence is modelled, located in the fault network of the Western Anatolian Extensional Province (SW Türkiye). The fault network features multiple active faults located along-strike and across-strike of another, as well as faults in a variety of orientations, suitable to explore stress-triggering mechanisms in a structurally complex setting. Detailed information on fault location, geometry, and mechanism is compiled from field investigations, literature review, and geodetic data. Based on instrumental and historical earthquake catalogues, and the suitability of the source fault network, a sequence of earthquakes is determined to investigate the two hypotheses by comparing the effects of coseismic CST and interseismic loading.

Results show that, out of 28 modelled large (MW ≥6) earthquakes, 6 were triggered on faults receiving significant negative coseismic CST. For five of these, negative coseismic CST is compensated by processes increasing CST. Only for one studied example, highly stressed positive fault segments on an otherwise negatively stressed fault could have been the driving mechanism leading to rupture of a large earthquake. Given all model uncertainties, stress-heterogeneities cannot be validated as a probable triggering mechanism for faults in the stress shadow of neighbouring faults. In contrast, earthquakes on normal faults located across-strike of another can only delay, but in most cases not prevent failure, as interseismic loading usually exceeds negative coseismic CST.

To reinforce these results, the impact of the modelled fault geometry and slip rates, used to calculate interseismic loading, is evaluated. Models of strike- and dip-variable faults, following the actual surface fault traces, are compared with simplified, planar fault models. Simplified models feature exaggerated areas of positive and negative CST on source faults prior to earthquakes, essentially distorting the stress field and causing stress-heterogeneities that are less pronounced in more realistic models. This observation highlights the necessity of modelling fault geometry as realistic as possible, especially when models are used in fault-based SHA. The impact of slip rates on model results is less drastic, so long as slip rates are used that are determined on similar time scales as the model duration. For the studied fault network short-term (geodetic) and long-term (‘geologic’) slip rates vary from the ‘Holocene’ slip rates by an order of magnitude. If used for modelling interseismic loading, the stress state and recurrence intervals of faults would be drastically under- or overestimated.

How to cite: Diercks, M., Mildon, Z., Boulton, S., Hussain, E., Alçiçek, C., Aykut, T., and Yıldırım, C.: Fault interactions and Coulomb stress-triggering in complex fault networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10216, https://doi.org/10.5194/egusphere-egu24-10216, 2024.

Understanding earthquake initiation, propagation, and arrest is critical for mitigating seismic risks, yet these processes remain among the most complex natural phenomena to decipher. The ERC-Synergy project FEAR (Fault Activation and Earthquake Ruptures), conducted within the Bedretto Underground Laboratory for Geosciences and Geoenergy (BedrettoLab), offers a pioneering approach to investigate these intricate mechanics. Here, we highlight the unique challenges and opportunities presented by the FEAR project, with a particular focus on computational earthquake physics and its potential to enhance our understanding of fluid-induced seismic events on broadband seismic arrays. Located ~1.5 kilometers beneath the Swiss Alps, BedrettoLab provides an unparalleled setting for a detailed study of earthquake mechanics. The FEAR project utilizes this exceptional environment to induce and monitor small-scale seismic events. By employing hydraulic stimulation on selected faults near the BedrettoLab tunnel, the project aims to initiate and observe earthquakes of approximately magnitude ~1.0. These refined methods provide a controlled setting to study the intricate details of earthquake processes closely, offering a chance to push the boundaries of current understanding of earthquake physics.

Central to the FEAR project is the development and testing of hydro-mechanical computational methods capable of replicating various injection protocols. These methods systematically test a range of constitutive laws that govern the evolution of fault friction, integrating insights from laboratory experiments with fully inertial elastodynamic modeling of earthquake processes. This approach allows us to investigate the poroelastic response of the rock mass, examining how seismic and aseismic slip interact in space and time, and assessing the dynamic evolution of pore-fluid pressure due to processes such as shear-induced dilatancy and compaction. Furthermore, we employ 3D dynamic rupture simulations to explore conditions controlling either self-arresting or run-away rupture. These simulations provide critical insights into wave spectrum and attenuation near BedrettoLab, enabling us to predict the peak ground velocity (PGV) of anticipated magnitude ~1 earthquakes. This innovative modeling approach represents a significant opportunity to advance our understanding of fault mechanics and the influence of fluid interactions.

In conclusion, the FEAR project within BedrettoLab provides a unique and controlled environment to study the mechanics of earthquakes. The challenges posed by this research are matched by the significant opportunities it offers for advancing our understanding of seismic phenomena. By focusing on innovative modeling techniques and integrating multidisciplinary data, this project aims to shed light on the complex dynamics of fault activation and rupture, ultimately contributing to more accurate seismic hazard assessments and safer geoenergy practices.

How to cite: Dal Zilio, L. and the FEAR team: Modeling Earthquake Dynamics and Fault Poromechanics in the BedrettoLab FEAR Project: Opportunities & Challenges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11726, https://doi.org/10.5194/egusphere-egu24-11726, 2024.

Himalayan seismicity exhibits a bimodal mechanism with great earthquakes (+M8) rupturing the upper locked segment of the Main Himalayan Thrust (MHT) and blind earthquakes (up to Mw ~ 7.8) rupturing the down-dip section of the decollement. However, few imbricate and out-of-sequence active structures have been overlooked with limited research in the hinterland regions with respect to active fault mapping and paleoseismological trench excavations. The present study focusses on the western section of the Trans-Yamuna Active Fault (TYAF) in northwestern Sub-Himalaya, hosting the Sirmurital Active Fault (SAF). The SAF exhibits a distinctive south-side up trace, obliquely cross-cutting the Main Boundary Thrust (MBT).

Satellite data, coupled with detailed field investigation confirms that the above fault dips 60˚ to the north, with a fault scarp of 40 m height. Minor strike-slip component is also confirmed with the presence of a subtle pressure ridge, and preliminary fluvial terrace mapping. Generation of a high-resolution Digital Elevation Model (DEM) from Cartosat-1 stereo pairs, and quantification with total station mapping of fault scarp further confirmed the terrace displacement. Subsequently, trench excavation (31 m in length) across the SAF at Sirmurital village provided compelling evidence of atleast two paleoearthquakes displacing and deforming Quaternary sediments along two identified fault strands. Soft-sediment deformation features complemented with injection features suggests its genetic link with paleoearthquakes. Radiocarbon dating analysis offers insights into the probable timing of the faulting events. Overall, the tectonic placement of the SAF provides a unique opportunity to document the occurrence of a normal fault in the hanging wall of a megathrust system and its potential to generate earthquakes in the highly populous mountainous belt of NW Sub-Himalaya. Therefore, the SAF along with the other associated faults, in the hinterland calls for detailed evaluation for a more comprehensive seismic hazard assessment.

 

Keywords: Out of sequence; Sirmurital Active Fault; Cartosat-1; Paleoearthquakes; Soft-sediment deformation; Seismic hazard 

 

How to cite: Ghosh, S., Philip, G., and Narayanapanicker, S.: Evidence of surface rupture associated with paleoearthquakes in the Trans Yamuna Segment of Northwestern Sub-Himalaya, India - Focus on the Sirmurital Active Fault , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12101, https://doi.org/10.5194/egusphere-egu24-12101, 2024.

EGU24-14251 | Orals | TS3.5

Palaeoseismology and tectonic geomorphology for detecting the seismic behaviour of the Pidima-Anthia Fault, south Greece 

Ioannis Koukouvelas, Athanassios Ganas, Vasiliki Zygouri, and Christina Tsimi

Geomorphologic analysis and data from paleoseismological sites across segmented active faults help the evaluation of past and future seismic faulting. The study of paleo-earthquakes on the Pidima-Anthia Fault provides an opportunity to unravel the seismic behaviour of the Eastern Messinia Fault Zone (EMFZ) that defines the western border of the N-S trending Taygetos Mtn range in Peloponnese (southern Greece). This fault zone is segmented and includes a complex system of primarily normal fault- segments dipping westwards, with a traceable length from 6-10 km. We applied geomorphological and palaeoseismological analysis across the Pidima-Anthia Fault segment. The palaeoseismological trench data provide evidence for five M >6.4 earthquakes and indicate an apparent slip rate of 0.23 mm/a. Geomorphologically, the modelling of a footwall series of triangular facets, attest to a slip-rate estimation in the order of 0.28-0.44 mm/a. These data highlight that the slip rate of the fault is remarkably stable for the Quaternary period but particularly over the last 17 ka period, as well as that this duration is enough for a morphogenic active fault to create seismic landscapes. The Holocene earthquake history of the Pidima-Anthia Fault allows its comparison with six other known active normal faults of southern Greece. The overall data indicate a pattern of earthquake clustering in the southern Greece faults ("Wallace-type" behaviour). In particular, the Pidima-Anthia Fault's seismic history resembles with time predictable earthquakes and clustering during the Holocene. However, the Pidima-Anthia Fault during the current period (i.e., post 1 Ka AD) does not display cluster time-predictable behaviour, and a strong earthquake can happen at any time.

How to cite: Koukouvelas, I., Ganas, A., Zygouri, V., and Tsimi, C.: Palaeoseismology and tectonic geomorphology for detecting the seismic behaviour of the Pidima-Anthia Fault, south Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14251, https://doi.org/10.5194/egusphere-egu24-14251, 2024.

EGU24-15619 | ECS | Posters on site | TS3.5

Deciphering the recent activity of normal faults in the Hellenic Volcanic Arc from combined morpho-tectonics analysis and TCNs method dating (36Cl), Amorgos Island (Greece)  

Sylvain Palagonia, Frédérique Leclerc, Christophe Larroque, Lucilla Benedetti, Nathalie Feuillet, Paraskevi Nomikou, Maxime Henriquet, Valery Guillou, and Fabio Manta

The study of normal fault-generated landforms, such as fault scarps, is commonly performed to investigate fault evolution and the recurrence and magnitude of earthquakes. The Amorgos region (Cyclades, Greece), located in the central part of the Aegean Sea, is structured by ~70km large NE-SW normal faults accommodating the back-arc extension of the Hellenic arc and the Anatolian extrusion. These faults are able to generate large earthquakes such as the Amorgos event (Ms=7.8) on July 09, 1956, followed by a second shock (Ms=7.2) 12 minutes later. This destructive event was the largest Mediterranean earthquake of the 20th century and caused severe damage, especially on Santorini Island. It also triggered a tsunami with reported run-ups reaching locally 30m along the southern coast of Amorgos Island. The submarine Amorgos fault, structuring the island’s southern coast and cumulating a ~2 km high vertical offset, is suggested to be the source of the 1956 main shock and tsunami. However, the accurate position of the 1956 rupture and the magnitude of the slip at surface are unknown, as the fault outcrops at 700m below sea level, as well as the pace at which this fault breaks. Considering that normal faults frequently accommodate the deformation on multiple splays, and within their damage zone, we searched whether the onland faults found within the cumulative scarp of the Amorgos fault ruptured during the 1956 event. We first performed a morphological study of the Chozoviotissa fault segment with satellite imagery, Structure-from-motion modelling, and field observations. We found evidence of recent deformation along this fault, in particular a ~70 cm high fresh ribbon at the base of the fault scarp. To provide chronological constraints, we sampled along-dip the carbonate-rich fault scarp for TCNs (Terrestrial Cosmogenic Nuclides) dating using the chlorine-36 element. This paleoseismic approach provides new insights on the recent slip history of this secondary fault, which is important to better evaluate the activity of the Amorgos fault system and improve the hazard assessment of the archipelago.

How to cite: Palagonia, S., Leclerc, F., Larroque, C., Benedetti, L., Feuillet, N., Nomikou, P., Henriquet, M., Guillou, V., and Manta, F.: Deciphering the recent activity of normal faults in the Hellenic Volcanic Arc from combined morpho-tectonics analysis and TCNs method dating (36Cl), Amorgos Island (Greece) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15619, https://doi.org/10.5194/egusphere-egu24-15619, 2024.

EGU24-16169 | ECS | Posters on site | TS3.5

Analysis of active and fossil seismic structures: a multidisciplinary study for the seismic risk assessment in low-seismicity regions 

Michele Locatelli, Laura Crispini, Marco Scambelluri, Laura Federico, Daniele Spallarossa, Danilo Morelli, and Paola Cianfarra

Understanding the source processes and wave propagation in heterogeneous rock media is one of the most challenging frontiers to improve the seismic risk assessments in densely populated areas. In this framework, the sector of the Voltri Massif (NW Italian Alps) forming the hinterland of the city of Genoa is a natural laboratory to investigate (i) the interaction between rock faulting and fluid circulation during (potential) paleo-seismic activity and (ii) the detection, location, and source characterization of micro-earthquakes along tectonic lineaments developed inland and offshore the city area (i.e., in the Ligurian Sea). Our multi-scale and multidisciplinary study is part of the PNRR research program RETURN (“Multi-risk science for resilient communities under a changing climate”): it will include the structural and petrographic characterization of fault rocks (i.e., serpentinite breccias), the quantification of serpentinite carbonatization and its impact on the fault strength, and the analysis of the network of inland-offshore tectonic lineaments. This work, coupled with the analysis of historical seismic clusters, is crucial to identify suitable areas for the deployment of high-resolution seismometers and for tracing the spatial-temporal evolution of micro-earthquakes and their static and dynamic source parameters.

The detailed structural mapping of selected fault zones has revealed a complex, multi-stage deformation history, with older ductile structures (paragenesis: antigorite + ilmenite ± chlorite ± pyrite ± chalcopyrite, likely ascribed to the alpine-subduction and collision stages) cut by steeply dipping fault planes NNE-SSW striking. These latter are subparallel with the (low magnitude) seismic clusters detected in the area and develop multiple, anastomosed fault cores consisting of serpentinite-rich ultracataclasites, locally bound by chrysotile-rich shear bands. The faults damage zones textures (e.g., breccias and microbreccias), the paragenesis of newly formed shear bands and associated veins (chrysotile + chlorite) and the orientation of these faults (NNE-SSW striking, subparallel to the Miocene-age lineaments detected in the Gulf of Genoa) suggest recent tectonic reactivation at the regional scale.

Future developments of the research project will include more detailed, high-magnification microscopy of selected samples (e.g., raman, field emission SEM, EBSD and microprobe), regional scale morphotectonic characterization by satellite image analysis, and integration of field and seismic data. This will clarify the link between inland-offshore tectonic lineaments and the (low magnitude) seismicity of the area.

How to cite: Locatelli, M., Crispini, L., Scambelluri, M., Federico, L., Spallarossa, D., Morelli, D., and Cianfarra, P.: Analysis of active and fossil seismic structures: a multidisciplinary study for the seismic risk assessment in low-seismicity regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16169, https://doi.org/10.5194/egusphere-egu24-16169, 2024.

EGU24-16516 | ECS | Orals | TS3.5

Characterisation of strike-slip fault offsets using convolutional neural networks 

Sarah Visage, Léa Pousse, Sophie Giffard-Roisin, Margaux Mouchené, Laurence Audin, and Sarah Perrinel

The understanding of seismic recurrence relies on the chronology and magnitude of earthquake ruptures that have occurred in the past along a given fault. Knowledge of the rupture history of a fault provides valuable insights into its potential future behavior, aiding in the assessment of seismic hazard. Geomorphic evidence of faults is thus crucial for constraining models of seismic recurrence through surface rupture. The advent of remote sensing and other high-resolution datasets (such as Pleiades and SPOT satellite images) has improved tectono-geomorphological studies, promising to improve earthquake recurrence models. While manual or semi-automatic measurements of fault offsets using topographic markers like rivers have been conducted (Manighetti et al., 2015, 2020; Zielke et al., 2012), recent advances in artificial intelligence (AI) open new avenues for geoscientific applications (Ren et al., 2020) to handle the amount of high-resolution datasets.

This study takes on the challenge of measuring slip offsets of faults using a Convolutional Neural Network (CNN) applied to synthetic Digital Elevation Models (DEM). The methodology involves generating realistic synthetic landscape models (DEM) using the Landlab software (Hobley et al., 2017), simulating slip faults based on the method of Reitman et al. (2019). The approach includes creating synthetic DEMs with Landlab, incorporating fault effects such as erosion, slip rates, and variable fault zone widths. Preliminary work in this study involves automating the creation of synthetic DEMs for a 2D prototype with a variable slip fault. A regression CNN model (with three convolutional layers followed by max-pooling layers and fully connected layers) is trained on these synthetic datasets, achieving slip offsets of ±3 meters on validation data. The model is then tested on real data labeled by experts, yielding satisfactory preliminary results.

This study demonstrates the potential of CNNs for measuring slip offsets of faults using synthetic DEMs. The successful application of AI to geosciences paves the way for more efficient and automated analysis of fault activity in landscapes, thereby contributing to an enhanced assessment of seismic risks.

How to cite: Visage, S., Pousse, L., Giffard-Roisin, S., Mouchené, M., Audin, L., and Perrinel, S.: Characterisation of strike-slip fault offsets using convolutional neural networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16516, https://doi.org/10.5194/egusphere-egu24-16516, 2024.

EGU24-18480 | ECS | Posters on site | TS3.5

Evaluating probabilities of earthquake fault jumps from 2D numerical simulation of seismic cycles 

Sylvain Michel, Oona Scotti, Sebastien Hok, Harsha Bhat, Navid khairdast, Michelle Almakari, and Jinhui Cheng

The efficiency of an earthquake to cross a barrier can be evaluated based on geometric and frictional properties of faults, and specific seismic parameters such as the stress drop during an earthquake. Numerical modelling of seismic cycles allows to generate thousands of seismic events and to explore the effect of the physical properties with respect to a barrier effectiveness criteria. The probability of an event passing a barrier can thus be evaluated on the basis of this barrier effectiveness criteria. Such approach has been used for frictional barriers and fault bends. In this study we focuses on earthquake fault jumps which has been observed on multiple occasions such as the latest 2024 M7.5 earthquake in Japan. We use the quasi-dynamic algorithm VEGA, which numerically simulates seismic cycles of 2D fault networks and is based on rate and state friction. The problem is simplified to two planar faults separated by a gap. Among other parameters, we explore the effect of the overlap, distance and angle between the two faults. The loading of a fault network can be done in multiple ways. We thus explore the impact on the dynamics of sequences of earthquakes either from a far-field stress loading or from imposing a back slip rate loading on each fault. We also look at the effect of adding creeping - velocity strengthening - sections at the borders of the faults. We finally compare our results with the statistics of jump probabilities from published observed seismic events. Our study allows for a rapid assessment of thousands of earthquake scenarios and is a promising approach to facilitate the integration of earthquake physics into seismic hazard.

How to cite: Michel, S., Scotti, O., Hok, S., Bhat, H., khairdast, N., Almakari, M., and Cheng, J.: Evaluating probabilities of earthquake fault jumps from 2D numerical simulation of seismic cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18480, https://doi.org/10.5194/egusphere-egu24-18480, 2024.

EGU24-18523 | ECS | Posters on site | TS3.5

Review of methods that implement active faults characterization for PSHA in Southern Spain. Preliminary results of the application of the FAMS method. 

Adriana Fatima Ornelas-Agrela, Carlos Gamboa-Canté, María Belén Benito, Alicia Rivas-Medina, and Ligia Quirós-Hernandez

Incorporating faults as independent seismic sources in Probabilistic Seismic Hazard Assessment (PSHA) significantly influences the ground motion values when compared to classical zoning methods (CZM). This practice holds particular relevance for populations situated top or near active faults. Some hybrid methods (HM) and fault-based methods, implemented in Spain, show that Peak Ground Acceleration (PGA) values increase in the vicinity of the fault traces. In some cases the hazard levels may double, consistent with the PGA observed in recent earthquakes (Rivas-Medina, A., 2018; Gómez-Novell O., 2020). Despite the existence of methods that combine zones and faults in seismic sources characterization, there is a lack of allocation of seismic potential between these two types of sources. Additionally, there is an increasing use of geological data since seismic catalogs alone are insufficient to fully characterize the seismic potential of faults. This limitation becomes particularly evident in slow deformation zones, such as southeastern Spain, where the recurrence period of faults exceeds the temporal coverage of the seismic catalog.

The present investigation addresses two key aspects: how to quantify the geological information of the faults and transfer it to recurrence models, and how to distribute the seismic potential of the region between faults and zone. This research contemplates two steps. In the first step, four methods were applied: 1) Moment rate-based method, 2) Slip rate-based method, both proposed by Bungum (2007); 3) the hybrid method developed by Rivas-Medina et al. (2018), which considers both zone-type and fault-type sources; and 4) SHERIFS, a fault system-based assessment proposed by Cartier et al. (2019). In the second step, Faults and Area Moment Sharing (FAMS) (Ornelas-Agrela et al., 2022*) is applied. This new method enables characterizing the faults based on their associated seismicity, improving the distribution of seismic potential between faults and zones. The five methods were applied to multiple seismogenic zones within southeastern Spain, recognized as one of the most seismically active areas in the country. An analysis was conducted, highlighting the sensitivity of the results of PSHA implementation. The preliminary results of the FAMS method application are presented.

* first presented by Ornelas-Agrela, A. et al. at the Iberfault2022 congress in Teruel, Spain.

How to cite: Ornelas-Agrela, A. F., Gamboa-Canté, C., Benito, M. B., Rivas-Medina, A., and Quirós-Hernandez, L.: Review of methods that implement active faults characterization for PSHA in Southern Spain. Preliminary results of the application of the FAMS method., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18523, https://doi.org/10.5194/egusphere-egu24-18523, 2024.

EGU24-18876 | ECS | Orals | TS3.5

A simple yet effective method to rank the performance of physics-based earthquake simulations 

Octavi Gómez-Novell, Francesco Visini, Bruno Pace, José Antonio Álvarez-Gómez, and Paula Herrero-Barbero

The use of physics-based earthquake simulators is increasingly common in earthquake forecasting for seismic hazard. Their popularity is related to their ability to overcome completeness limitations of real seismicity catalogues, while reproducing complex earthquake rupture behavior and interaction patterns through the modelling of the physical processes involved in earthquake nucleation and rupture propagation. One common challenge when designing earthquake simulations is the selection of the input parameters that will produce the most feasible models in terms resemblance to natural earthquake processes and relationships, e.g., the rate-and-state frictional parameters – a, b – and the initial normal stress. The frequent lack of empirical data on such parameters, often bases their selection on non-systematic testing and qualitative model performance analysis, thus potentially reducing the objectivity of the modelling. We present a new quantitative approach to evaluate and rank the performance of multiple earthquake simulation models based on a workflow that scores each synthetic catalog according to their combined fit to objective seismological benchmarks. These benchmarks rely on widely used empirical earthquake data: 1) scaling relationships, 2) shape of the magnitude-frequency distribution and 3) rates of surface ruptures from paleoseismology. The approach permits an objective and effective approximation to model performance evaluation, allowing to easily identify which models (and input parameter combinations) simulate better natural earthquake relations and behavior. The algorithm-based approach also facilitates the exhaustive analysis of many input parameter combinations and allows the identification of systematic correlations between parameters and model performance. We validate the approach with earthquake simulations on a theoretical planar fault and with published simulations at the Eastern Betics Shear Zone (EBSZ) in southeastern Spain. In both cases, the method successfully ranks the models with better resemblance to natural catalogues, while avoiding self-correlation of the benchmark scores, i.e., the best model is not the best in all benchmarks but the better balanced across them. In the case of the EBSZ, our ranking analysis replicates the qualitative and manual analyses previously published, which reinforces the usefulness of the approach. We also identify very clear correlations between the model performance and the rate-and-state a and b parameters. In particular, we observe that larger differences between a and b tend to better model performance. Conversely, the initial normal stress does not correlate with the performance. Overall, we estimate that the approach can ease researchers on earthquake simulation design and building, and on better understanding the impact of selected input parameters into the physics-based models. Moreover, the model ranking results can be employed to drive further analysis such as weighting of earthquake forecast models in seismic hazard logic trees.

How to cite: Gómez-Novell, O., Visini, F., Pace, B., Álvarez-Gómez, J. A., and Herrero-Barbero, P.: A simple yet effective method to rank the performance of physics-based earthquake simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18876, https://doi.org/10.5194/egusphere-egu24-18876, 2024.

TS4 – Tectonics and its interaction with surface processes and life

The Eastern European Alps formed during two orogenic cycles, which took place in the Cretaceous and Cenozoic, respectively. In the Ötztal-Stubai Complex – a thrust sheet of Variscan basement and Permo-Mesozoic cover rocks – the record of the first (Eoalpine) orogeny is well preserved, because during the second (Alpine) orogeny the complex remained largely undeformed. We use new zircon (U-Th)/He (ZHe) ages and thermo-kinematic modeling to constrain the cooling and exhumation history of the central part of the Ötztal-Stubai Complex since the Late Cretaceous. The ZHe ages from two elevation profiles increase over a vertical distance of 1500 m from 56±3 to 69±3 Ma (Stubaital) and from 50±2 to 71±4 Ma (Kaunertal), respectively (Hölzer et al., accepted by Lithosphere). These ZHe ages and few published zircon and apatite fission track ages were used for inverse thermo-kinematic modeling. The modeling results show that the age data are well reproduced with a three-phase exhumation history. A first phase with relatively fast exhumation (~250 m/Myr) during the Late Cretaceous ended at ~70 Ma and is interpreted to reflect the erosion of the Eoalpine mountain belt. As Late Cretaceous normal faults occur at the margins of the Ötztal-Stubai Complex, normal faulting may have also contributed to the exhumation of the study area. Subsequently, a long period with slow exhumation (<10 m/Myr) prevailed until ~16 Ma. This long-lasting phase of slow exhumation suggests a rather low topography with little relief in the Ötztal-Stubai Complex until the mid-Miocene, even though the Alpine orogeny had already begun in the Eocene with the subduction of the European continental margin. Accelerated exhumation since the mid-Miocene (~230 m/Myr) is interpreted to reflect the erosion of the mountain belt, due to the development of high topography in front of the Adriatic indenter and repeated glaciations during the Quaternary.

How to cite: Hölzer, K., Wolff, R., Hetzel, R., and Dunkl, I.: The long-lasting exhumation history of the Ötztal-Stubai Complex (Eastern European Alps): New constraints from zircon (U-Th)/He age-elevation profiles and thermo-kinematic modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1495, https://doi.org/10.5194/egusphere-egu24-1495, 2024.

Constraints on the continental weathering feedback on carbon-cycle perturbations on northern Pangea during the end Triassic extinction (ETE) are sparse. Here, we use hyperspectral core imaging (HSI) applied to conglomeratic beds offshore central Norway which shows that enhanced degassing of basalt flows from the Central Atlantic magmatic province (CAMP) was concurrent with intense continental transformation during the ETE. We use well-constrained mercury pulses emitted in gaseous form during volcanism, and subsequently deposited in near-coastal sediments, to identify the ETE. Parallel to mercury pulses, HSI derived smectite was immediately replaced by kaolinite at the extinction level corroborating increased radiogenic run-off from the hinterland as inferred from osmium isotopes. Our new results suggest that, parallel with CAMP activity and with atmospheric carbon dioxide (pCO2) up to four times the pre-extinction level, continental weathering instantaneously intensified, providing novel empirical knowledge that can be integrated in carbon-cycle models to underpin future warming assessments.

How to cite: Knies, J.: Instant weathering response to carbon-cycle perturbations during the end-Triassic extinction , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3024, https://doi.org/10.5194/egusphere-egu24-3024, 2024.

In this study, we employed low-temperature thermochronology to investigate the depositional source and exhumation rates of the mountain belt in central Taiwan. We collected four sedimentary rock samples from the Chiunkongliao River and one sample from Wuxi. Utilizing zircon fission-track (ZFT) dating and uranium-lead (U-Pb) dating, we observed an increase in the percentage of partially reset zircon from the Chinshui Shale to the Toukoshan Formation. Additionally, we identified total reset zircon in the Toukoshan Formation. Furthermore, the probability density of U-Pb dating in the Toukoshan Formation leans more towards the Oligocene than the Miocene.

Through double-dating, we determined that ZFT ages less than 65 Ma are not the result of Cenozoic volcanic activity. These findings suggest a change in the origin of the depositional source from the Cholan Formation to the Toukoshan Formation. According to the lag time curve, the exhumation rate accelerated during the time period from 1.1 Ma to 0.5 Ma.

Comparing our results with previous studies in the Western Foothills of central Taiwan, we observed that the annealing zone was exposed earliest in the middle part than in the southern one. This may indicate that, in central Taiwan, the exhumation rate in the middle part was the fastest.

 

How to cite: Hsu, W.-C., Lee, Y.-H., Yang, K.-M., Lin, K.-W., and Chang, S.-P.: Study of Plio-Pleistocene Foreland Basin Provenance and Orogenic Exhumation History in Central Taiwan: Fission-Track and U-Pb Dating Analyses of Detrital Zircon from Western Foothills, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3322, https://doi.org/10.5194/egusphere-egu24-3322, 2024.

EGU24-3969 | Posters on site | TS4.2

Jurassic heritance of the geomorphology in Mid Norway 

Odleiv Olesen, Håkon Gunnar Rueslåtten, Jasmin Schönenberger, Morten Smelror, Roelant van der Lelij, Bjørn Eskil Larsen, Lars Olsen, and Arne Bjørlykke

The age and formation of the Scandinavian mountains and the western coastal areas (the ‘strandflat’)  have long been the subject of debate. Some suggest that the present-day mountains are remains of the Caledonian orogen while others claim that the Caledonian nappes after denudation were covered by Mesozoic sediments and subsequently exhumed. We have tried to clarify these issues by studying remains of chemically weathered rocks (saprolites) along two profiles from the coast to the interior of central Norway. This multidisciplinary study includes the following data: digital topography, electrical resistivity tomography (ERT), XRD, XRF, palynological analyses and K–Ar dating of samples from outcrops, trenches and core drilling. The coastal areas are dominated by an outer ‘strandflat’ and an inner ‘joint-valley’ landscape, while the interior and mountainous areas are  characterised by smoother landscapes referred to as ‘palaeo-surfaces’. Remnants of pre–Tertiary weathering occur in the joint-valley landscape as well as on the palaeo-surfaces. The deep saprolites are found within fault- and fracture-zones and at depths exceeding 50 m in drillholes. It is suggested that the old saprolites were strongly eroded along the coast and in the fjords and valleys like Orkdalen and Sunndalen. K–Ar dating of clay from saprolites on the mainland commonly show Jurassic ages, seen along a profile that stretches from the coast to the Dovrefjell (approx. 1400 m a.s.l.).The age of the smectite- and kaolinite-containing saprolites seems to be almost contemporaneous along this profile, implying that the entire area was subject to weathering in a warm and humid climate, such as prevailed during the Late Triassic and Jurassic. Palynological remains in the clayey saprolites contain thermally altered pollen and spores from the Triassic and Jurassic, which supports the interpretation and dating of the saprolites.  It is therefore suggested that the Mesozoic landscape in central Norway was shaped by uplift and deep weathering in the Jurassic. However, saprolites occurring along a second profile south of the Trondheimsfjord show Carboniferous and Permian K-Ar ages, indicating that this area constitute a Permian or Triassic sediment basin that was eroded during the late Cenozoic. Thus, it is likely that the entire Trøndelag county was covered by Mesozoic sedimentary rocks, right up to the start of the Cenozoic erosion. Important processes that governed the shaping of the landscape were tectonic uplift and erosion throughout the Cenozoic, followed by extensive abrasion and erosion by glaciers and meltwater during Pleistocene. We therefore conclude that both the studied saprolites and the shape of the present-day landscape in central Norway are characterized by the landscape formed during the Jurassic. This includes the deep profiles of chemical weathering and a drainage pattern that changed in the Pleistocene.

How to cite: Olesen, O., Rueslåtten, H. G., Schönenberger, J., Smelror, M., van der Lelij, R., Larsen, B. E., Olsen, L., and Bjørlykke, A.: Jurassic heritance of the geomorphology in Mid Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3969, https://doi.org/10.5194/egusphere-egu24-3969, 2024.

EGU24-4635 | ECS | Orals | TS4.2

Starting of Qilianshan’s uplift since Cenozoic and its implications for Tibetan mantle dynamics 

Jianzhang Pang, Dewen Zheng, and Yan Ma

The Qilian Shan, located at the northeastern edge of the Tibetan Plateau, plays a crucial role in understanding the Plateau's uplift and expansion processes. There are two classical models, one proposes a progressive expansion of the thickened crust, while the other suggest that the northern extent of the Plateau was established soon after the collision between India and Eurasia around 50 Ma ago. Nevertheless, a recent study introduces a more complex scenario, proposing a pulsed uplift of the northern Tibetan Plateau starting around 30 Ma (Wang et al., 2022). These models heavily rely on the spatial and temporal evolution of the Qilian Shan. Nevertheless, the exact timing and mechanisms of its evolution remain elusive.

To delve into the growth history of the southern Qilian Shan, we have obtained apatite fission track data from the Dachaidan Shan and the northern Qaidam basin. Notably, AFT ages from the Dachaidan Shan transect (ranging from 35 Ma to 10 Ma) vary significantly with elevation. An intriguing observation is a possible break in slope at 18±2 Ma, which is interpreted as indicating the onset of intense exhumation in the southern Qilian Shan. Furthermore, within the Qaidam basin, a total reset AFT age group of 14.8±3.8 Ma was found in Jurassic strata but not in Cretaceous and Cenozoic strata. This suggests a rapid cooling event occurred at that time, which we interpret as marking the initial deformation of the northern margin of the Qaidam basin.

In combination with previous studies on the deformation time of the Qilian Shan, our findings suggest that the initial deformation of the Qilian Shan occurred in the Middle Miocene, followed by a multi-step outward expansion. This synchronized expansion might have been triggered by the removal of mantle beneath northern Tibet.

Wang, W., Zhang, P., Garzione, C.N., et al., 2022. Pulsed rise and growth of the Tibetan Plateau to its northern margin since ca. 30 Ma. Proceedings of the National Academy of Sciences 119, e2120364119.

This research was supported by the State Key Laboratory of Earthquake Dynamics (LED2021A05) and the National Natural Science Foundation of China (42272269).

How to cite: Pang, J., Zheng, D., and Ma, Y.: Starting of Qilianshan’s uplift since Cenozoic and its implications for Tibetan mantle dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4635, https://doi.org/10.5194/egusphere-egu24-4635, 2024.

Understanding how the interplay between tectonics, climate, and surface processes reflects the Earth’s endo- and exogenic dynamic behaviour, inevitably requires studying the nucleation, growth and development of faults. Faults shape the plumbing system of the Earth’s crust, promoting mass and heat transfer and steering fluid migration, storage and mineralizations. They control landscape evolution and impact society because, although they only occupy a small volume of the crust, they govern its modes of deformation by localizing earthquake slip, thus being sources of seismic hazard. To improve our understanding of faulting and produce time-constrained models firmly based on physical and chemical constraints, a deep knowledge of the structural, mechanical, hydrogeological and petrophysical properties of faults is thus required.

Long-lived, multiply reactivated faults can be architecturally complex, with every new deformation episode adding to this complexity by forming new brittle structural facies, altering the bulk and local permeability and steering the rheology of the deforming rock volume. This complicates the interpretation of the brittle archive of fault zones, which impacts on the interpretation of the local and regional deformation history. It also impacts on the seismogenic style associated with faulting (with coseismic rupturing and aseismic creep variably occurring in time and space), on modes of fluid ingress and circulation and formation of geofluid reservoirs. Recent studies have documented that this complexity is the norm rather than the exception and that it may result from deformation histories lasting many millions of years. The outcrops we study, therefore, only represent snapshots of this long history and rushed interpretations of their complexity and/or its downplaying may be grossly misleading.

To better understand the architecturally complex geometry and evolution in time and space of mature fault zones, the methodological approach to- and the first results from an ongoing study of the Carboneras Fault (CF) in the Betic Cordilleras of Spain are discussed. The CF is a NE-SW striking, 100 km long, upper crustal sinistral strike-slip fault that is described as accommodating c. 40 km offset with still ongoing distributed seismicity. It exhibits a complex architecture defined by strands of phyllosilicate-rich fault gouge enveloping domains of variably reworked host rock. Up to 14 brittle structural facies have been identified at four key outcrops. Structural analysis, X-ray diffraction and isotopic analysis of fault rocks have been systematically carried out. Sampling of each facies made it possible to define their mineralogical composition, the maximum temperature they were subjected to during faulting, their isotopic signature and the deformation mechanisms responsible for their formation. In-situ outcrop air-permeametry helped constrain the present-day permeability and its heterogeneity at the scale of the fault zone. K-Ar illite dating of eight gouge samples shows that faulting has been ongoing for >20 Myrs, and provides a comprehensive timeline for deformation localization down to the microscopic scale. Results from this high-resolution approach offer a comprehensive work protocol to untangle the spatiotemporal evolution of long-lived mature fault zones elsewhere.

How to cite: Viola, G.: High-resolution multidisciplinary studies of fault zone architecture: Insights into deformation histories, fault mechanics, fluid circulation, weathering and…, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4676, https://doi.org/10.5194/egusphere-egu24-4676, 2024.

In sedimentary basins, the basement typically exhibits non-conformable contact with the overlying sedimentary strata. The basement surface undergoes a complex history of uplift, weathering, erosion, and sediment burial, all of which contribute to its reservoir structural composition. This study integrates microscopic observations, macroscopic well logging data, and seismic data to analyze the physical and weathering effects on the basement reservoirs with different lithologies and distinct structural features within the Erlian Basin. The basement rock types in the study area mainly include tuff, limestone, granite, cataclastic rock, and the basement has been affected by weathering, denudation, dissolution and structural transformation during the evolution of the basin. The basement has been subjected to long-term tectonic modification, forming network cracks on the macro scale and micro-fractures on the micro scale. Weathering and underground fluids along the fractures dissolve the matrix of tuff rock, feldspar in granite and limestone, thus forming dissolution fractures and dissolution pore in the basement rocks. These fractures and dissolution pores make the porosity and permeability of the basement rocks surface show obvious heterogeneity. According to the microstructure and physical property changes, the structure of different lithology basement surface is analyzed. Among them, the surface of the tuff basement rock has undergone multi-stage volcanic eruptions and weathering leaching, with a structure of multi-stage ancient weathering crust reservoir superposition, and the porosity and permeability of the gentle slope at the structural high part is large. The surface of granite and cataclastic rock basement is controlled by tectonic activity, weathering leaching, and formation fluid action. The double-layer structure comprises the top paleo-wind crust reservoir and the middle and lower fracture dissolution reservoirs, exhibiting high porosity and permeability in the elevated structural positions and the region proximate to the fault zone. Controlled by karstification, tectonic activity, and ancient landform, the limestone basement rock surface displays longitudinal variations in reservoir storage space types, featuring a structure with multiple sets of vertically arranged reservoirs, particularly characterized by high porosity and permeability in elevated structural positions and near fault zones. The concept and results of this work can be used for future studies on unconventional basement reservoirs in other regions.

How to cite: Shen, C. and Jiang, Y.: The reservoir development model of different lithology basement rocks in Erlian Basin,Northeast China., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4821, https://doi.org/10.5194/egusphere-egu24-4821, 2024.

EGU24-6716 | ECS | Orals | TS4.2

Helium diffusion systematics in apatites: lessons from Continuous Ramped Heating analysis 

Hongcheng Guo, Peter Zeitler, Bruce Idleman, and Marissa Tremblay

There is now a growing body of literature that reports over-dispersed (U-Th)/He ages from apatites. To address this challenge, we have performed continuous ramped heating (CRH) experiments on apatites from various geologic settings to characterize grain-specific helium (4He) diffusion behavior. Several first-order results emerge from our CRH analyses. (1) It became clear that simple volume diffusion, even accounting for radiation damage, cannot completely describe the diffusion of 4He in apatite. Two major types of 4He degassing behavior were broadly observed. Apatites with good (U-Th)/He age reproducibility show simple and unimodal incremental degassing curves that are similar to those predicted by volume diffusion, whereas samples exhibiting greater age dispersion, often accompanied by anomalously old ages, have complex gas-release curves that feature secondary gas-release peaks deferred to higher temperatures. (2) In practice, CRH can serve as a screening tool to reduce the dispersion of apatite (U-Th)/He ages, especially for those obtained from samples that have experienced slow-cooling. (3) Even among apatites in which 4He does show broad volume diffusion behavior (i.e., size and radiation-damage modulated volume diffusion), CRH analysis reveals kinetic variability of 4He diffusion. (4) Diffusion sinks, which are capable of trapping radiogenic 4He during both geologic processes and laboratory heating, can explain the observed high-temperature gas release during CRH analyses. CRH results of a sample suite from an active helium partial retention zone demonstrate that the release of sink-trapped 4He is temperature dependent rather than being controlled by a threshold mechanism. The results from our CRH analyses carry two critical implications. First, CRH is suitable for routine implementation that enables thermochronology practitioners to focus their measurement and interpretation on apatites in which 4He diffusion obeys volume diffusion. Second, diffusion sinks provide opportunities to extract additional thermal-history information providing a description of grain-specific trapping dynamics. Work in this area is ongoing via 4He/3He diffusion experiments, through which degassing of proton-irradiated 3He in a sample provides information trapping dynamics and degassing of radiogenic 4He constrains the sample’s thermal history.

How to cite: Guo, H., Zeitler, P., Idleman, B., and Tremblay, M.: Helium diffusion systematics in apatites: lessons from Continuous Ramped Heating analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6716, https://doi.org/10.5194/egusphere-egu24-6716, 2024.

EGU24-7700 | Orals | TS4.2

The relationship between brittle tectonics and bedrock morphology of Central Fennoscandia 

Nicklas Nordbäck, Pietari Skyttä, and Nikolas Ovaskainen

The bedrock of Central Fennoscandia has been shaped by a long and complex geological history involving ductile deformation and metamorphism which dates back at least to the 1.9–1.8 Ga Svecofennian orogeny. Subsequent geological processes including Precambrian brittle faulting and fracturing, younger fault reactivations and several stages of hydrothermal activity and alteration processes, provided further contribution to defining the present-day bedrock structure and mechanical properties. Eventually, extensive glaciation affected the exposed upper part of the bedrock through structurally selective erosion, which is largely responsible for the morphology of the bedrock erosion surface. As such, the brittle tectonic history, involving faulting and fracturing near the Earth’s surface, has played a significant role in shaping the current bedrock topography. However, also the preceding ductile structures played a role as they caused the localisation of the brittle deformation through the process of structural inheritance.

Based on previously published results the brittle tectonic development within Central Fennoscandia initiated in response to N–S compression at around 1.75 Ga. Based on our new datasets, consisting of isotopically dated fault gouge samples and brittle structural observations (Nordbäck et al., 2022), N–S extension at around 1.65 Ga and a E–W extension at around 1.6 Ga were associated with 1) reactivations of previously formed major structures of the bedrock, 2) rapakivi magmatism and 3) the development of a (failed) continental rift between Finland and Sweden. Our structural data from within the 1.58 Ga rapakivi granites indicate that strike-slip tectonics prevailed during Mesoproterozoic times. According to isotopic and structural data from Olkiluoto in southwestern Finland, thrust faults were generated in response to E–W compression during the Sveconorwegian orogeny between 1.1–1.0 Ga. The younger stress changes that induced faulting activity, have been found to cause merely reactivations of the fault systems that were formed already by late Mesoproterozoic times. Based on our structural datasets from the 1.58 Ga rapakivi granites, paleostress analysis and observed relative age relationships between faults and joints, Neoproterozoic exhumation of the bedrock appears to have resulted in extensional bedrock stresses and the development of Precambrian bedrock joints.        

Erosional processes during the Quaternay glaciations interacted strongly with the existing brittle structures which were preferably eroded during the glacial advances and retreats. Especially the intensely fractured major fault zones greatly impacted the current bedrock morphology while smaller structures, such as individual joints or shear fractures, only have a local impact (Skyttä et al., 2023).

References:

Nordbäck, N., Mattila, J., Zwingmann, H., Viola, G., 2022. Precambrian fault reactivation revealed by structural and K-Ar geochronological data from the spent nuclear fuel repository in Olkiluoto, southwestern Finland. Tectonophysics 824, 229208. https://doi.org/10.1016/j.tecto.2022.229208

Skyttä, P., Nordbäck, N., Ojala, A., Putkinen, N., Aaltonen, I., Engström, J., Mattila, J., Ovaskainen, N., 2023. The interplay of bedrock fractures and glacial erosion in defining the present-day land surface topography in mesoscopically isotropic crystalline rocks. Earth Surface Processes and Landforms. https://doi.org/10.1002/esp.5596

How to cite: Nordbäck, N., Skyttä, P., and Ovaskainen, N.: The relationship between brittle tectonics and bedrock morphology of Central Fennoscandia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7700, https://doi.org/10.5194/egusphere-egu24-7700, 2024.

EGU24-8170 | Orals | TS4.2

Physical erosion rates in Ogooué and Mbei Rivers (Gabon, Western Central Africa): insights for Cratonic Catchments. 

Vincent Regard, Sébastien Carretier, Moquet Jean-Sébastien, Sandrine Choy, Pierre-Henri Blard, Sakaros Bogning, Auguste Paulin Mbonda, Emmanuel Mambela, Marie Claire Paiz, Michel Séranne, Julien Charreau, Delphine Rouby, Julien Bouchez, Jérôme Gaillardet, and Jean-Jacques Braun

We measured the long term physical denudation of the Ogooué River catchment using 10Be. These measurements are averaged over 25-200 ka (average 40 ka), depending on the physical denudation rate. The denudation rate of the Ogooué River catchment is slow (38 t/km2/a, 15 m/Ma), slightly higher than the Equatorial West Africa (from Senegal to Angola, 26 t/km2/a, 10 m/Ma). Physical denudation and chemical weathering fall within the same order of magnitude. Thus, although low, chemical weathering, is substantial compared to physical denudation, its contribution is likely over 30% of the total denudation.

Denudation rates are spatially variable (from 10 to 60 t/km2/a) within this large Ogooué River catchment. Over the long term, this variability exhibits a fairly close match of physical denudation/chemical weathering, except in the Batéké Plateaux area, because they are made up of already weathered detrital material and their modern flux of solutes is therefore very low (~9.5 t/km2/a). The spatial distribution is similar to the one described in Moquet et al. (2021)'s work, i.e. the southern part of the catchment is denuding twice as fast as the northern part. We show here that the whole picture did not vary much since 100 ka, as shown by both methods giving consistent results. Faster denudation in the south of the catchment may be related to some more uplift than in the north caused by the south African superswell.

 

How to cite: Regard, V., Carretier, S., Jean-Sébastien, M., Choy, S., Blard, P.-H., Bogning, S., Mbonda, A. P., Mambela, E., Paiz, M. C., Séranne, M., Charreau, J., Rouby, D., Bouchez, J., Gaillardet, J., and Braun, J.-J.: Physical erosion rates in Ogooué and Mbei Rivers (Gabon, Western Central Africa): insights for Cratonic Catchments., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8170, https://doi.org/10.5194/egusphere-egu24-8170, 2024.

The distribution of oil and gas resources in the Upper Paleozoic of the Ordos basin is extensive, with well-developed source rocks. However, there is currently a lack of systematic research on source rocks in the Wuqi area, which greatly limits the oil and gas exploration work in this area. This study aims to restore the burial and thermal evolution history of the region, clarify the accumulation periods of source rocks, and promote the fine exploration and development process of oil and gas. It provides a basis for understanding and improving the oil and gas accumulation laws of the Upper Paleozoic in the entire basin. Research suggests that the Wuqi area has undergone four periods of erosion since the Upper Paleozoic, including the end of the Triassic, middle Jurassic, end of the Jurassic, and end of the Cretaceous. The first three periods of erosion were relatively small, mainly distributed between 100-200m, and the end of the Cretaceous period was characterized by significant erosion, which was the main erosion event. The interval transit time method was used to recover the erosion thickness at the end of the Cretaceous period in this study, mainly distributed in the range of 600-1500 m, and the overall erosion amount gradually decreased from east to west. We used vitrinite reflectance to restore palaeogeotherm and PetroMod software combined with parameters such as stratigraphy, lithology, erosion thickness, and boundary condition to reconstruct the burial history and thermal evolution history of the Wuqi area by basin simulation methods. Microscopic observation and combined with fluid inclusion homogenization temperature data were used to further determine the oil and gas accumulation period through a combination of forward and reverse analysis. According to the inclusions and homogenization temperature, it is reflected that there are mainly early and late inclusions in the Upper Paleozoic mudstone in the Wuqi area. Early fluid inclusions are mainly distributed on the secondary enlargement edge of quartz, with temperatures mainly ranging from 110 to 140 ℃; The late stage fluid inclusions are mainly distributed in quartz particle fractures, with temperatures mainly ranging from 100 to 160 ℃, which is the main charging period. The temperature distribution of the two phases of inclusions is continuous process. In conclusion, there were two consecutive oil and gas changes in the Upper Paleozoic in the Wuqi area of the Ordos basin: the first oil and gas charging period was in the Middle Jurassic; The second oil and gas charging period was in the Early Cretaceous.

How to cite: Zhao, F. and Cui, J.: Analysis of Thermal Evolution History of Source Rocks and Natural Gas Accumulation Periods of Upper Paleozoic in the Wuqi Area of the Ordos Basin,China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9333, https://doi.org/10.5194/egusphere-egu24-9333, 2024.

EGU24-10436 | ECS | Posters on site | TS4.2

Evolution of brittle-ductile deformation to brittle fault zones and the role of fluid migration in Cruzeiro do Nordeste shear zone, Borborema Province, NE Brazil 

Tiago Miranda, Daniel Barbosa, Osvaldo Correia Filho, Acaua Silva, Gustavo Viegas, Sergio Pacheco, and Bruno Carvalho

The Borborema Province in northeastern Brazil is an ideal location for investigating the tectonic evolution of crustal-scale strike-slip shear zones. These structures exhibit an anastomosing network with numerous well-exposed mylonitic belts linked to the Neoproterozoic Brasiliano-Pan-African Orogeny. However, there is a gap in information on fluid-rock interaction related to both brittle-ductile and brittle deformation. This work aims to describe the control of brittle-ductile structures on the development of brittle fault zones with significant fluid interaction associated with the Cruzeiro do Nordeste shear zone, which limits the northern border of the Jatobá Basin. Our study is based on multiscale structural analyses, integrating aeromagnetic data, UAV images, outcrop-based measurements and microstructural characterization. We documented that the mylonitic foliation is represented by ENE-WSW magnetic positive anomalies (~14 nT/m) and is characterized by S-C fabrics indicating dextral kinematics. Brittle-ductile deformation is marked by dextral C'-type shear bands (WNW-ESE) and mesoscopic strike-slip faults (NW-SE and N-S). These structures exhibit bulges defined by fine-grained, peripheric quartz grains. C’ shear bands evolve into brittle fault zones composed of mosaic and chaotic breccias, veins filled by epidote, epidote+calcite, and calcite, which are associated with hydraulic brecciation. Cathodoluminescence analysis revealed variations in luminescence along the calcite-filled veins, suggesting at least two phases of fluid interaction. The older phase exhibits higher luminescence and is brecciated by the younger calcite fluid, which displays lower luminescence activation. This fluid-rock interaction can modify the permoporous system of analog reservoirs, which can be observed through the variation in cementation intensity in the Tacaratu Formation, sandstones of the Paleozoic sequence of the Jatobá Basin. Our results indicate that the Cruzeiro do Nordeste shear zone is an excellent example that preserves the record of ductile, brittle-ductile and brittle deformation due to exhumation. Furthermore, enhancing our knowledge of brittle deformation associated with the late stages of the Brasiliano-Pan-African cycle (Cambrian?) at shallow crustal levels may be the key to understanding the tectonic evolution of Paleozoic and Cretaceous sedimentary basins in northeastern Brazil. 

How to cite: Miranda, T., Barbosa, D., Correia Filho, O., Silva, A., Viegas, G., Pacheco, S., and Carvalho, B.: Evolution of brittle-ductile deformation to brittle fault zones and the role of fluid migration in Cruzeiro do Nordeste shear zone, Borborema Province, NE Brazil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10436, https://doi.org/10.5194/egusphere-egu24-10436, 2024.

EGU24-10890 | ECS | Posters on site | TS4.2

Evaluating the classic and distal Fish Canyon Tuff localities with apatite 4He/3He thermochronology 

Cody Colleps, Peter van der Beek, and Julien Amalberti

The late Oligocene Fish Canyon Tuff (FCT)—preserved within the San Juan volcanic field of southern Colorado—has long served as a reliable source of multiple accessory minerals for geochronology and thermochronology age standards. Whereas the ‘classic’ FCT sampling locality preserves near consistent ages of ~28–29 Ma across the sanidine 40Ar/39Ar, zircon U-Pb, zircon fission track, zircon (U-Th)/He, and apatite fission track systems, the average single-grain apatite (U-Th)/He (AHe) age at this site is notably younger at 20.8 ± 0.4 Ma. Considering that the classic sampling site is positioned at the bottom of a deeply incised valley with ~800 m of local relief, this AHe age has been proposed to record burial of the basal tuff to depths exceeding ~1000 m, with subsequent Early Miocene cooling reflecting valley incision. In contrast, an average single-grain AHe age of 28.5 ± 0.1 Ma was previously recorded from a newly proposed distal FCT locality where the upper-most tuffs are freshly preserved within a quarry. This AHe age is consistent with higher temperature geochronological ages from the same locality, which suggests that the distal FCT experienced no post-emplacement thermal disturbance. The observed, locality-specific difference in AHe ages provides a unique opportunity to calibrate and assess the potential of apatite 4He/3He thermochronology to (1) quantify the degree of post-emplacement burial and the rate of subsequent cooling at the classic FCT locality, and (2) record rapid late Oligocene cooling at the distal FCT locality. We respectively test the hypothesis that the classic FCT apatite will yield a comparatively diffusive 4He/3He degassing spectra, whereas the distal FCT apatite will preserve a near-uniform 4He/3He spectra that is solely affected by alpha-ejection. We consider and discuss newly derived 4He/3He results in light of (1) the geological history and landscape evolution of southern Colorado, (2) the potential use of distal FCT apatite as a coupled AHe and 4He/3He thermochronology reference material, and (3) the reproducibility of FCT apatite 4He/3He spectra using differing proton-irradiation procedures. 

How to cite: Colleps, C., van der Beek, P., and Amalberti, J.: Evaluating the classic and distal Fish Canyon Tuff localities with apatite 4He/3He thermochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10890, https://doi.org/10.5194/egusphere-egu24-10890, 2024.

EGU24-11185 | ECS | Posters on site | TS4.2

New Constraints on Late Cenozoic Convergence between the Pamir and South Tianshan from Apatite (U-Th-Sm)/He Thermochronology 

Fujun Wang, Edward R. Sobel, Peter van der Beek, Wenbin Zhu, Cody Colleps, Lingxiao Gong, Johannes Rembe, Guangwei Li, and Johannes Glodny

Cenozoic collision between the Indian and Eurasian plates instigated significant intracontinental deformation in Central Asia, giving rise to the Tibetan Plateau and the Himalayan orogen. Simultaneously, it compelled the Pamir to undergo extensive northward movement, accompanied by tens to hundreds of kilometers of crustal shortening. Ultimately, this geological activity culminated in the collision of the Pamir with the South Tianshan. This collision may be a key factor influencing topography and climate change in Central Asia, yet comparatively little is known about the details of the tectonic evolution of the collision zone. In particular, precise determination of the timing of activation of different thrusts in the Main Pamir thrust (MPT), Pamir fold-and-thrust (PFT), and South Tianshan thrust (STT) system remains lacking. Here, we report new apatite (U-Th-Sm)/He (AHe) dates from fourteen samples collected from the hanging walls of these thrusts, situated at the westernmost tip of the Tarim Basin, NW China. Samples collected from the MPT record rapid cooling at ~ 11 ± 1 Ma, samples from the PFT show rapid cooling at ~ 7 ± 2 Ma and ~4-3 Ma, while samples from the STT reveal accelerated cooling at ~11 ± 1 Ma, ~7-6 Ma and ~3-2 Ma. We propose that the observed rapid cooling was caused by thrust-induced exhumation in this region, thus the rapid cooling represents the activity time of thrusts. Combined with previous studies on the onset deformation in the MPT and STT, we develop a model of the convergence between the North Pamir and South Tianshan in our study region since the late Oligocene. Late Oligocene to early Miocene (~20 ± 5 Ma) cooling ages from the MPT and STT hanging walls date the onset of thrusting, indicating the initiation of this convergence. Afterward, the MPT and STT experienced northward and southward propagation during the late Miocene (~11 ± 1 Ma), respectively. Subsequently, during the latest Miocene (~7 ± 2 Ma), the PFT started to form, while simultaneously, the STT propagated southward, resulting in the contact of these two thrusts at the Wuheshalu section. We suggest that the timing of contact of PFT with the STT represents the surface expression of the onset of collision between the Pamir and South Tianshan in the western Tarim basin. Following the initial collision, the PFT gradually propagated northward while the STT propagated southward during the Pliocene to Pleistocene (~3 ± 1 Ma), establishing the present-day superimposed and imbricated thrust system in the Pamir-South Tianshan convergence zone.

How to cite: Wang, F., R. Sobel, E., van der Beek, P., Zhu, W., Colleps, C., Gong, L., Rembe, J., Li, G., and Glodny, J.: New Constraints on Late Cenozoic Convergence between the Pamir and South Tianshan from Apatite (U-Th-Sm)/He Thermochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11185, https://doi.org/10.5194/egusphere-egu24-11185, 2024.

EGU24-12215 | ECS | Posters on site | TS4.2

Apatite U-Pb, fission-track, and trace element provenance constraints on Oligocene-Miocene northeastern Tibetan Plateau growth and dynamics 

Chao Guo, Zhiyong Zhang, Richard Lease, Marco Malusà, David Chew, Bernhard Grasemann, and Wenjiao Xiao

Understanding the geodynamics of plateau evolution necessitates careful consideration of the spatial and temporal constraints associated with mountain building on the northeastern Tibetan Plateau. However, when and how the northeastern Tibetan Plateau grew remains highly debatable. Here we integrate apatite U-Pb, fission-track, and rare-earth element provenance indicators from the Oligocene-Miocene continental succession of the Xunhua Basin to establish a framework of drainage reorganization and topographic evolution of the Xunhua region. The results suggest three provenance changes at ca. 28 Ma, ca. 20 Ma, and ca. 12 Ma, that not only indicate topographic growth of the West Qinling, Laji Shan, and Jishi Shan, respectively, but emphasize the significance of apatite for provenance analysis. The compilation of our findings and deformations within the northeastern Tibetan Plateau reveals the Oligocene-Miocene stepwise expansion and the Middle Miocene stress reorganization within the northeastern Tibetan Plateau. Combined with regional evidences, we propose that the Early Cenozoic northward compression of the Indian continent shortened and thickened Tibetan lithosphere, and subsequently triggered the removal of thickened lithosphere beneath south-central Tibet in the Oligocene. This process not only induced Oligocene-Miocene progressive expansion across the northeastern Tibetan Plateau, but also facilitated the continuous northward injection of the Indian lithosphere. Simultaneously, accompanied by the southward insertion of the North China craton, the underthrusting of both the India and North China initiated sinistral strike-slip faults in the middle Miocene, driving a change in stress directions. The results of this study underline the contribution of both the lithospheric removal and continental underthrusting geodynamic processes in driving outward growth of plateau. 

How to cite: Guo, C., Zhang, Z., Lease, R., Malusà, M., Chew, D., Grasemann, B., and Xiao, W.: Apatite U-Pb, fission-track, and trace element provenance constraints on Oligocene-Miocene northeastern Tibetan Plateau growth and dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12215, https://doi.org/10.5194/egusphere-egu24-12215, 2024.

How did the continent-oceanic plate interact, and when did the initial west paleo-Pacific plate subduction beneath Eurasian continent occur, are still unknown. NE China deformation, volcanic eruptions and magmatic intrusions can give some constraints. Muling located in the Dunhua-Mishan fault zone in NE China, is a key area where the E-W-trending Eurasian domain changed to NE-trending west Pacific Plate domain in NE China. During the Mesozoic time, at least three stages of deformation occurred, including: (1) E-W-trending structures with extensive ductile shear deformation and south-verging folds which result from thrusting towards the south, followed the emplacement of granitic rocks. (2) NE- or NNE-trending thrust faults and strike-slip movement, accompanied by the formation of west-verging inclined and recumbent folds. This phase deformation changed the whole tectonic framework of eastern China from an E-W-trending Eurasian domain to a NE-trending west Pacific Plate domain. (3) NE-trending strike-slip faults and E-W-trending strike-slip motion. Field investigations of Mesozoic ductile shear zone and faults, granitic intrusions and dykes, combined with zircon U-Pb dating and muscovite 40Ar/39Ar plateau ages, reveal the age of the E-W-trending structures as ~254-209Ma, and NE–SW-trending tectonic belts as ~182–170 Ma. The tectonic transformation of the eastern China continent involved a change from E-W to NE-SW-trending structures was a response to the initial subduction of paleo-Pacific plate.

How to cite: Zhou, L. and Wang, Y.: Middle-late Mesozoic tectonic evolution of the NE China—corresponding to westward subduction of the paleo-Pacific plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13898, https://doi.org/10.5194/egusphere-egu24-13898, 2024.

EGU24-13936 | Posters on site | TS4.2

Overview of thermochronological studies in and around the Japan Arc; towards Thermo2025 Conference in Kanazawa, Japan 

Takahiro Tagami, Noriko Hasebe, and Shigeru Sueoka

Recent progress of low-temperature thermochronology enables to analyze uplift-exhumation-cooling histories of the island-arc mountains with good confidence. This is particularly fruitful for studying the topographic evolution of the Japan Arc, because many of the Japanese mountains are started to uplift in recent time (e.g., late Pliocene to Quaternary) after an extended period of tectonic quiescence, and hence the resultant amount of total denudation is relatively small. The utility of the approach was first demonstrated by elucidating the uplift-exhumation-cooling process for some of the Japan Alps, in which average topographic changes of the tilted mountain block were quantitatively reconstructed by low-temperature thermochronology (Ref. 1-2). Such analyses also allow to estimate the background paleo-depth of neo-tectonic faulting episodes.

In this presentation, we highlight recent and ongoing important thermochronological research in and around the Japan Arc (Ref. 3-5). In addition, we will promote the Thermo2025 conference and introduce its preliminary plans. The International Conference on Thermochronology has been held biyearly around the world and the International Standing Committee on Thermochronology (ISCT) determined that the 19th conference (Thermo2025) will be held in Kanazawa, Japan, on September 14-20th, 2025 (https://isct.sedoo.fr/meetings-2/). Then, the local organizing committee, including the authors, have promoted the preparation of the conference in partnership with the domestic geoscience societies and international thermochronological communities. Pre-registration of Thermo2025 is now being accepted at the website (https://smartconf.jp/content/thermo2025). Those who are interested in the conference can soon receive the announcements by pre-registration.

References

1. Sueoka, S. et al. Island Arc 21, 32-52 (2012).

2. Sueoka, S. et al. Journal of Geophysical Research: Solid Earth 122, 6787-6810 (2017).

3. Sueoka, S. and Tagami, T., Island Arc 28, 1-8 (2019).

4. Fukuda, S. et al. Earth Planet Space, 72, 1-19 (2020).

5. King, G.E. et al. Geology, doi.org/10.1130/G50599.1 (2022).

How to cite: Tagami, T., Hasebe, N., and Sueoka, S.: Overview of thermochronological studies in and around the Japan Arc; towards Thermo2025 Conference in Kanazawa, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13936, https://doi.org/10.5194/egusphere-egu24-13936, 2024.

EGU24-14281 | Orals | TS4.2

Silicate weathering estimates from paleogeographic and biogeochemical cycling models of orogens and ophiolite obduction during the Phanerozoic 

Sabin Zahirovic, Tom Schmaltz, Addison Tu, Rafael Pinto Cherene Viana, Kevin Hao, Jonathon Leonard, Claire Mallard, and Tristan Salles

Collisional settings that terminate subduction are most often associated with orogenesis, and in many cases are also associated with the obduction of oceanic crust into the suture zone. These events are key components of the planetary carbon cycle, where the subduction-related volcanic outgassing is generally shut down, and instead dominated by processes of erosion and silicate weathering and carbon dioxide drawdown. This is particularly intense where silicate rocks are being exhumed, and especially where fresh ophiolitic crust is exposed, to intense weathering in the near-equatorial humid belts.

Here we use a new compilation of Phanerozoic orogens and ophiolites in a (py)GPlates workflow to analyse the distribution of these orogenic and obduction events in time and space. We test different tectonic reference frames, as well as explore different assumptions of the distribution of the near-equatorial humid belt through time. We compare our datasets and analysis with previously published models, and link the time series to the COPSE biogeochemical cycling model. In addition, we evaluate the implications of erosion and weathering from recent global landscape evolution models to explore the role of the near-equatorial humid belt precipitation and mountain areas.

The analysis suggests that large areas of mountains resided in the near-equatorial regions in the late Cambrian to Ordovician, late Carboniferous, the Cretaceous, and in the Neogene. One obvious challenge that emerges is the need to designate actively-uplifting versus inactive orogens, as the paleogeographic reconstructions do not yet discriminate between these categories. However, using our (py)GPlates workflows and other geological data (such as magmatic zircons), we can use the plate tectonic reconstructions to infer which orogens are proximal to plate boundaries and more likely to be actively uplifting, in contrast to mountains that are passively being denuded.

Although this approach sees an improvement to the constraints on the areas of elevated crust for the use in biogeochemical cycling, it remains challenging to infer the paleo-altimetry of these orogens in deep time. In addition, other geological time series inputs require further work (e.g., volcanic and orogenic/metamorphic degassing). Ongoing work is quantifying self-consistent tectonic parameters that can be incorporated into the biogeochemical cycling models to help improve the constraints on these models. More broadly, this approach provides a pathway towards more robust and geologically-constrained Earth Systems Models that have implications for our understanding of paleo-climate and carbon cycling in deep time.

How to cite: Zahirovic, S., Schmaltz, T., Tu, A., Pinto Cherene Viana, R., Hao, K., Leonard, J., Mallard, C., and Salles, T.: Silicate weathering estimates from paleogeographic and biogeochemical cycling models of orogens and ophiolite obduction during the Phanerozoic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14281, https://doi.org/10.5194/egusphere-egu24-14281, 2024.

EGU24-14975 | ECS | Posters on site | TS4.2

Impact of magmatic intrusions on metamict zircon annealing as constrained by Raman spectroscopy in the eastern Adamello batholith (Central Alps) 

Silvia Favaro, Alberto Resentini, Massimo Tiepolo, Marco Giovanni Malusà, and Stefano Zanchetta

The impact of a magmatic polyphasic intrusion on the empirical relationship between zircon metamict state as revealed by Raman spectroscopy (Zhang et al., 2000) and α-damage accumulation of the same grains is investigated in the eastern Adamello batholith (Central Italian Alps). Eighteen samples, spanning the contact between the Val di Genova pluton, the Sostino-Corno Alto pluton, and their host rocks – including Permian intrusives, were examined.

Zircons were analysed with a 100mW Nd:YAG solid state laser emitting at 532 nm Raman spectrometer to assess their metamict state based on the position and full width at half maximum of different Raman bands. For each zircon, on the same spot, LA-ICP-MS analyses were performed to determine the crystallization age and U, Th, and Pb concentrations. Crystallization ages and actinides content were used to calculate α-damage since zircon crystallization.

Magmatic zircon ages display a south to north younging trend from the Sostino pluton (44.79±0.35 Ma) to the Val di Genova pluton (34.18±0.20 Ma), consistent with literature data (Schaltegger et al, 2009 and 2019; Ji et al., 2019 and references therein). Moreover, magmatic zircons from the Adamello batholith exhibit a metamict state roughly consistent with calculated α-doses, indicating nearly full retention of decay-related damage. In contrast, zircons from the Paleozoic country rocks and Permian plutons show a nearly crystalline state conflicting with calculated high α-doses, thus suggesting a thermal overprint that annealed their crystalline structure, here identified with the thermal aureole of the Adamello magmatic intrusions. In fact, the measured metamict state of zircons in the host rocks is in overall agreement with α-damage accumulation calculated since intrusion rather than crystallization ages.

Raman analysis of radiation damage in zircon is being currently investigated as a new thermochronological method (Pidgeon, 2014; Nasdala et al., 2001; Nasdala et al., 2002; Hartel, 2021) with particular emphasis on unannealed zircons to test its feasibility. With this study, we present an application of Raman analysis of radiation damage in annealed zircons to trace their thermal history, thus providing independent validation of contact-metamorphic overprints.

How to cite: Favaro, S., Resentini, A., Tiepolo, M., Malusà, M. G., and Zanchetta, S.: Impact of magmatic intrusions on metamict zircon annealing as constrained by Raman spectroscopy in the eastern Adamello batholith (Central Alps), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14975, https://doi.org/10.5194/egusphere-egu24-14975, 2024.

EGU24-15953 | Posters on site | TS4.2

Some thoughts on the usefulness of Lineament Maps 

Thomas F. Redfield, Espen Torgersen, Anna K. Svendby, Karl Fabian, Anna M. Dichiarante, and Volker Øye

“Of what use at all is a lineament map?” constitutes a fair question posed with positively indecent irregularity, if ever at all. Here we suggest that because topographically derived lineament maps depict landscape elements that form under physically differing processes at different rates and times, they have historically conflated time-transgressive morphological evolution of the region at hand with a simplistic message, stated or implied, akin to “this map, then, represents the structural framework underlying such-and-such geological province.” This slippery slide down the razor presupposes two essential conditions: That incision occurs only where the substrate is most easily eroded and that all faults, fractures, and shear zones are less resistant than undeformed rock. It is a demonstrable fact that neither condition is necessarily true. Yet lineament mapping persists, from Earth to Mars and by now, presumably, on even more distant planets. What can we do with these things, and why do we bother?

Whilst quantifiable linearity does convey information that may be useful for landscape classification, abstracting topographic surfaces into lineaments does not, a priori, expose the structural template of the underlying bits of any given planet. Analyses of azimuth, density, length, or any other quantity provide little benefit unless one can constrain exactly what it was that one measured. Digital vectorization of modern DTM data does offer hope. Furthermore, linearity can be expressed in topographically positive features such as ridgelines. Individual vectors can (must!) be given local attributes (depth… width… sinuosity… slope…) that may be coupled to a postulated (theoretical, probably optimistic, and in most cases surely a relative) morphologically dependent ‘age’ of incision. Regional (‘environmental’) attributes pertaining to bulk properties of the area traversed by that very same vector (flat… inclined… U or V shape… carbonate… granite…) can be collected to provide external context. Equally important is a careful inventory of bias such that the mapping method generates reproducible vectors with representative and homogeneous coverage from the upper left-hand corner of the dataset to both the penultimate and ultimate pixels at the (assume southeastern) End Of File. Absent these, a lineament map is not dissimilar to a basket of tropical fruits plucked from one’s local Arctic haberdashery at or around Christmastime.

Because she exhibits a wide range of topographic styles, human-generated lineament maps have struggled to extract unbiased, homogeneous signals from Baltica’s tired old bones. Having experimented for some years with algorithms designed to map lineaments automatically from (x, y, z) data we feel inclined to present a few observations, interpretations, confessions of bias, and recommendations for how we might possibly do better. We will briefly describe one successful algorithm for computerized lineament mapping, present results that purportedly describe distinctly different Norwegian landscapes, illustrate some connections to certain known structures and disconnections with others, and attempt a sort of general, undoubtably conflicted synthesis of the potential use of lineament maps in assessing the landscape evolution of certain small parts of the Norwegian rifted margin.

“There are more things in heaven and Earth than are dreamt of in our Science….”

How to cite: Redfield, T. F., Torgersen, E., Svendby, A. K., Fabian, K., Dichiarante, A. M., and Øye, V.: Some thoughts on the usefulness of Lineament Maps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15953, https://doi.org/10.5194/egusphere-egu24-15953, 2024.

EGU24-16090 | Posters on site | TS4.2

Lineament analysis for characterizing regional fracture system – A case study from the Oslo region, Norway 

Anne Kathrine Svendby, Espen Torgersen, Tim Redfield, Anna Maria Dichiarante, and Karoline Arctander

Lineament analysis from topographic maps is a well-known method to identify regional fracture systems and the potential for weakness zones, but the significance of lineaments can easily be misinterpreted. A topographic lineament (topolineament) is just an elongated depression, which may or may not contain important structural information. In which case lineaments represent faults or fractures, and do all brittle structures appear as a lineaments? This is the focus of our project.

In this study, we investigate the applicability of lineament analysis to characterize the fracture system in the Oslo region, Norway. Topolineaments, derived by automatic detection using an in house-developed algorithm (OttoDetect) on a 10x10m digital elevation model, are combined with field structural observations and measurements. Special emphasis was placed on comparing the orientation of brittle structures from field data with that of the detected topolineaments.

The fieldwork was carried out by measuring fractures at selected locations both along and away from larger topolineaments. In some areas, data collection also included measuring scanlines parallel and orthogonal to selected topolineaments. Structural measurements were split into different geographical areas of Oslo and plotted on stereonets. The topolineaments were analyzed and classified by parameters such as orientation, length, density (number of lineaments over a given distance) and width-depth ratio (within the lineament), etc. Rose diagrams of all lineaments within a given radius from a geographical center point were used to show the dominant lineament orientations in the studied area. We pay especially close attention to lineaments in regions dominated by bedrock, in order to represent only bedrock-incised topolineaments, so that the rose diagrams could be used to compare with fracture orientations.

Preliminary results show that both field data and topolineaments are dominated by two orthogonal sets: E-W and N-S. However, the relative dominance of either set in the two datasets seems less correlated. Further analysis is ongoing to also constrain the relationship between fracture and lineament densities.

How to cite: Svendby, A. K., Torgersen, E., Redfield, T., Dichiarante, A. M., and Arctander, K.: Lineament analysis for characterizing regional fracture system – A case study from the Oslo region, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16090, https://doi.org/10.5194/egusphere-egu24-16090, 2024.

EGU24-16413 | Posters on site | TS4.2

From Margin to Menace: the role of structural inheritance in the geohazards distribution in Norway   

Per Terje Osmundsen and Thomas F. Redfield

Formation of the Norwegian rifted margin in the Mesozoic and Early Cenozoic and denudation of adjacent onshore areas resulted in preferential reactivation of regionally important Paleozoic faults and shear zones as indicated by a variety of published geochronological data. Lithospheric-scale necking impacted the later topographic evolution of the present onshore areas, including an escarpment topography and incision pattern that correlates with the seawards taper of the crystalline crust. The density of large, mapped landslides in turn reflects topographic and structural signals and tend to cluster inboard of sharply tapered areas. Margin formation also resulted in the impregnation of crystalline basement by swarms of smaller structures around multiply reactivated structures that made the bedrock prone for coastal erosion as well as onshore slope instability, with apparent maxima in glacially incised topography in areas inboard of sharply tapered margin segments in North- and Mid Norway as well as inboard of parts of the northern North Sea. Offshore, the sharply tapered Møre segment contains stacked submarine slide deposits in an anomaleously short progradational Quaternary wedge, illustrated spectacularly by the Holocene Storegga slide.  An important part of the geohazards distribution onshore and offshore Norway can thus be viewed as long-term responses to the rifting process through an interplay between crustal-scale inheritance, structural reactivation and saturation and mass redistribution by erosion, especially glacial transport. Other rifted margins that evolved by multiphase extension may display similar relationahips between ancient structural templates and the modern distributiion of geohazards.    

How to cite: Osmundsen, P. T. and Redfield, T. F.: From Margin to Menace: the role of structural inheritance in the geohazards distribution in Norway  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16413, https://doi.org/10.5194/egusphere-egu24-16413, 2024.

EGU24-16717 | ECS | Orals | TS4.2

Unravelling the Tectonic History of an Intraplate Region: A Geochronological Study of the Danube Fault, Bavarian Forest, Germany 

Alina Lucia Ludat, Anke M. Friedrich, Florian Hofmann, Robert Bolhar, and Torsten Hahn

Deformation in the Earth’s upper crust is typically accommodated by faults, which can range from microscopic displacements to regional tectonic features. Despite being located in the continental interior of the Eurasian plate, Central Europe displays notable evidence for recent activity, including active faulting, even along fault lines previously presumed inactive. This intraplate region has experienced multiple phases of fault reactivation, which provide the basis for debate regarding the underlying causative deformation mechanisms and driving forces. Determining the timing of episodic fault activity and their deformation rates is crucial to investigating the mechanisms behind Cretaceous to Paleocene exhumation and its relationship to more recent fault activity.

An excellent region for this purpose is the Bohemian Massif, which is characterized by a complex structural and lithological architecture recording a long history of deformation. This area hosts significant fault zones, such as the NW–SE-striking Pfahl and Danube faults. Despite being one of the largest faults in Central Europe with a prominent scarp and young morphology, the ages of inception and reactivation of the Danube fault remain poorly constrained. Furthermore, therefore, seismic risks associated with these significant intraplate faults are difficult to include in earthquake hazard catalogs.

To determine the timing of fault-slip and re-activation of the intracontinental Danube fault system in the Bavarian forest, we designed a sampling strategy involving multiple radiometric geochronometers and judiciously sampled transects across minor faults exposed in numerous quarries. We are currently dating authigenic and synkinematically recrystallized minerals, including U-Pb dating of slickenfiber calcite and K-Ar dating of illite. We also employ 40Ar/39Ar thermochronology and multi-domain diffusion modeling of potassium-bearing minerals of the granitoid host rocks to determine the timing of exhumation and re-setting of this system due to fault activity.

The earliest time constraint for the initiation of the Danube fault was established by using published U-Pb zircon ages of deformed granites (310 to 342 Ma) (Klein et al. 2008 Lithos 102). We anticipate the K–Ar ages of illite and U–Pb ages of calcite to be significantly younger, which would confirm potential phases of reactivation accompanied by fluid alteration during cataclastic deformation. These fluid-infiltration events could potentially serve as markers for dating various phases of fault reactivation, which, along with information from frictional resetting, offer insights into the dynamic evolution of the Danube fault over time.

How to cite: Ludat, A. L., Friedrich, A. M., Hofmann, F., Bolhar, R., and Hahn, T.: Unravelling the Tectonic History of an Intraplate Region: A Geochronological Study of the Danube Fault, Bavarian Forest, Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16717, https://doi.org/10.5194/egusphere-egu24-16717, 2024.

EGU24-17264 | ECS | Orals | TS4.2

Chemical weathering processes of Himalaya-river systems since Miocene recorded by bulk and clay mineralogy of deep-sea sediments from IODP Expedition 354   

Joffrey Bertaz, Pascale Huyghe, Christian France-Lanord, Albert Galy, Mara Limonta, and Aswin Tachambalath

The Ganga-Brahmaputra river system transports up to 600 million tons of sediment annually from the Himalayan range to the Bengal Fan. The catchment of the Ganga-Brahmaputra river system is characterized by highly contrasting lithologies and exhumation rates which strongly influence erosion and chemical weathering processes. Recent studies have emphasized the importance and role of floodplains for the chemical weathering of sediments eroded from Himalayan mountains. Changes in sediment chemical weathering are controlled by climatic changes, such as variations in Indian summer monsoon precipitation and glacial interglacial cycles. However, further exploration is needed to understand the impact of anthropic changes and long-term climatic and tectonic forcings on the chemical weathering regime of the Ganga-Brahmaputra system. We present the bulk and clay mineralogy, obtained with XRD, of turbiditic sediments collected from the Bengal Fan in the Indian Ocean during the IODP Expedition 354. The clay mineralogical assemblages of IODP Expedition 354 present a dominance of illite and chlorite throughout the record with a relative increase of smectite and kaolinite content during the Miocene. Such clay mineralogy is consistent with the clay mineralogy of sediments from Leg 22 site 218 from DSDP (which was reoccupied for  IODP Expedition 354). Miocene bulk sediments are relatively enriched in smectite, kaolinite, goethite, and terrigenous carbonates (calcite and dolomite). Therefore, our mineralogy results are showing a change in chemical weathering regime affecting the Himalaya system between the Miocene and Quaternary.  The Quaternary is characterized by a lower content of smectite, kaolinite and carbonates, the presence of amphiboles and an enrichment in micaceous minerals (muscovite/illite, biotite, chlorite) and plagioclases as also inferred from Raman spectroscopy (Limonta et al., 2023). This indicates that during the Miocene the chemical weathering of ferro-magnesian minerals and calco-sodic feldspars was more efficient as shown by geochemical data (Tachambalath, 2023). The decrease in chemical weathering intensity from Late Miocene is consistent with the concurrent Late Cenozoic global cooling and drying of Himalayan front associated with the decrease in Indian monsoon seasonality and/or precipitation after 10-8 Ma (Clift and Webb, 2019). Here, we show that the change in the Indian monsoon system from 10-8 Ma is marked in the Bengal Fan turbiditic sediments mineralogy.

How to cite: Bertaz, J., Huyghe, P., France-Lanord, C., Galy, A., Limonta, M., and Tachambalath, A.: Chemical weathering processes of Himalaya-river systems since Miocene recorded by bulk and clay mineralogy of deep-sea sediments from IODP Expedition 354  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17264, https://doi.org/10.5194/egusphere-egu24-17264, 2024.

EGU24-19032 | ECS | Posters on site | TS4.2

Effective Etch Times and compositional effects on the etching of Fossil Fission Tracks in Geological Apatite Samples 

Florian Trilsch, Hongyang Fu, Raymond Jonckheere, Bastian Wauschkuhn, Carolin Aslanian, and Lothar Ratschbacher

Apatite fission-track modelling reconstructs the low-temperature histories of geological samples based on measurements of the lengths of etched confined fission tracks and counted surface tracks. We investigate the influence of the chemical composition of apatite on the etching of fossil confined fission tracks, and its consequences for the apatite fission-track method, to optimize the track-length distribution for modelling apatites with varying chemical compositions. The duration for which each confined track was etched can be calculated given the apatite etch-rate νR. We conducted step-etch experiments on samples with etch pit diameters (Dpar) spanning most of the range for natural apatites (1.4–4.6 μm), including four gem-quality apatites (Panasqueira, Slyudyanka, Brazil, Bamble) and fourteen samples from the igneous and metasedimentary basement of the Tian Shan, Central Asia, in or­der to determine the apatite etch rate vR as a function of crystallographic orientation for each. To a first order, νR correlates with the size of the track intersections with the mineral sur­face for all hexagonal apatites. For the gem-quality apatites we fitted three-parameter exponential functions (vR = a 𝜙’ × e b𝜙 + c); a and b both exhibit a linear correlation with Dpar. Combin­ing these results gives one equation (vR = a(Dpar) 𝜙’ × e b(Dpar)𝜙 + c) giving the apatite etch rate vR in a giv­en orientation (ϕ’) for hexagonal apatites with a specified chemical com­position (Dpar). Bamble exhibits a different - bimodal - relationship between vR and ϕ’. In all cases, including Bamble, there is a striking parallelity between the angular frequencies of horizontal con­fined tracks and the magnitude of the apatite etch rate vR per­pendicular to the track axes. This shows that the sample of confined tracks selected for measurement and modelling is to a much greater degree de­termined by the etching properties of the apatite sample than by geometrical or subjective biases. The mean track-etch-rate vT correlates with Dpar, so that tracks etch to their full lengths in a shorter time in faster etching apatites. The mean rate of length increase between etch steps, vL, also correlates with Dpar. For the Tian Shan samples we use νR for calculating the effective etch time tE of confined tracks measured after 20 to 60 s immersion in 5.5 M HNO3 at 21 °C. Considering only tracks within a predetermined etch-time window for length measurement improves the reproducibility of the track-length distributions. Because an etch-time window allows excluding under- and over-etched tracks, sample immersion times can be optimized to increase the number of confined tracks suitable for modelling. If vT correlates with Dpar as our data indicate, future studies need to investigate how such an effective etch time window should be scaled by chemical composition as well. An alternative approach for selecting an appropriate etch time for each sample is to look on the track length anisotropy. We finally compare thermal histories obtained with a conventional 20 s immersion protocol, without tE selection, with those using the length of tracks within the range tE = 15–30 s.

How to cite: Trilsch, F., Fu, H., Jonckheere, R., Wauschkuhn, B., Aslanian, C., and Ratschbacher, L.: Effective Etch Times and compositional effects on the etching of Fossil Fission Tracks in Geological Apatite Samples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19032, https://doi.org/10.5194/egusphere-egu24-19032, 2024.

EGU24-20432 | Posters on site | TS4.2

Development and implications of a new open-source time-temperature inversion program 

Brenhin Keller and Kalin McDannell

Time-temperature inversion is a critical step in the interpretation and application of thermochronologic data. However, the computational source code for such programs has typically not been freely available, limiting reproducibility. Here we present a new fully open-source (GPL-3.0) time-temperature inversion program, Thermochron.jl, developed in the Julia programming language. This program initially aims to invert zircon helium and apatite helium data via a Markov chain Monte Carlo approach, and allow for the propagation of uncertainty in diffusion parameters. Here we will present the testing and validation of this model, and consider the implications for some open problems in thermochronology, including the limits of resolution for deep-time thermochronology.

How to cite: Keller, B. and McDannell, K.: Development and implications of a new open-source time-temperature inversion program, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20432, https://doi.org/10.5194/egusphere-egu24-20432, 2024.

Measuring the topographic relief evolution over hundreds of thousands to million-year timescales remains challenging. Current approaches use a mix of basin stratigraphy, numerical modelling of terrestrial cosmogenic nuclide (TCN) exposure ages on strath terraces, and exhumation histories based on thermochronology or drainage basin evolution. Yet, even a combined mix of these methods is incapable of quantifying the rate changes with precisions needed to differentiate climate from tectonic drivers over multiple glacial cycles and longer timescales.

The recently conceived muon-paleotopometry (MPT) approach is tailored to close the methodological gap of determining relief generation. MPT exploits the dependence of cosmic ray muon flux on crustal shielding depth. The spatial concentration pattern of multiple muon-induced TCN measured along a near-horizontal transect under valleys and peaks relates directly to the history of changes (positive or negative) in crustal thickness. MPT allows paleotopometry measurements above the sample datum over an isotope-specific monitoring duration. By sampling at depths of hectametres, long-lived TCN (e.g., 10Be, 26Al) are not sensitive to minor short-term (<105-yr) changes owing to cut and fill terraces or transgressions. For instance, the horizontal samples will have similar muon production histories. At this depth, only fast muon interactions and radiogenic or nucleogenic pathways are likely, and only high-energy cosmic ray particles can penetrate, dodging variations in geomagnetic and solar effects and simplifying the interpretation of concentrations along the transect.

We provide an overview of this new method, starting with the theoretical concept, the encouraging proof-of-concept results by Dalhousie (M. Soukup, Hon. Thesis, 2017), the laboratory needs for measuring low TCN concentrations at great depths (>150 m) and update on the progress for the current large-scale relief investigation of the European Alps.

How to cite: Raab, G., Gosse, J., and Hidy, A.: Conceptual proof, current application, and lab procedures to quantify crustal thickness variations with muon paleotopometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1067, https://doi.org/10.5194/egusphere-egu24-1067, 2024.

In contrast to the mountainous topography and high relief of the eastern Tauern window, the adjacent Nock Mountains (Gurktal Alps, Austria) are characterized by hilly topography, lower relief and rounded summits with elevations of ca. 2000 m. Although the unusual landforms in the Nock Mountains have long been recognized (Hejl, 1997; Frisch et al., 2000, and references therein), little is known about rates of landscape evolution in this area, which was deglaciated ~15 ka ago (Wölfler et al., 2022). Here we present a new set of 16 catchment-wide erosion rates from the Nock Mountains derived from cosmogenic 10Be concentrations in stream-sediment samples. Samples from 10 major streams that drain the Nock Mountains toward the Mur-Mürz valley, the Katschberg-Lieser valley and the Drau valley range between ~130 and ~300 mm/ka. Smaller subcatchments with low relief located in the upper part of the larger catchments erode at lower rates between ~80 and ~160 mm/ka. A comparison between 10Be-derived erosion rates and exhumation rates obtained from low-temperature thermochronology and thermokinematic modelling reveals that short-term and long-term erosion rates are remarkably similar. In the central Nock Mountains, 10Be-derived erosion rates of 110-160 mm/ka are similar to the long-term exhumation rate of ~160 m/Ma since ~34 Ma (Wölfler et al., 2023). The southern Nock Mountains (Millstatt Complex) show higher short-term erosion rates of 170-300 mm/ka and also a higher long-term exhumation rate of ~270 m/Ma since 18 Ma (Wölfler et al., 2023). The similarity between short-term and long-term erosion rates suggests that the pace of erosion in the Nock Mountains did not change significantly during the late Cenozoic. A comparison of our data with 10Be erosion rates from the eastern Tauern Window (>500 m/Ma) and the Lavanttal Alps (<125 m/Ma) (Dixon et al., 2016; Delunel et al., 2021), which are located west and east of the Nock Mountains, respectively, reveals that erosion rates in the Eastern Alps decrease from west to east.

  • References
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  • Dixon JL, von Blanckenburg F, Stüwe K, Christl M (2016) Earth Surf. Dyn. 4:895909.
  • Frisch W, Székely B, Kuhlemann J, Dunkl I (2000) Zeitschr. f. Geomorph. 44:103–138.
  • Hejl E (1997) Tectonophysics 272:159–173.
  • Wölfler A, Hampel A, Dielforder A, Hetzel R, Glotzbach C (2022) J. Quat. Sci. 37:677-687.
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How to cite: Hampel, A., Wölfler, A., Wolff, R., and Hetzel, R.: 10Be-derived catchment-wide erosion rates from the Nock Mountains (Gurktal Alps, Austria): comparison with thermochronological data and implications for landscape evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1362, https://doi.org/10.5194/egusphere-egu24-1362, 2024.

EGU24-4640 | Orals | TS4.3 | Highlight

New constraints on the Neo-Tethyan carbon cycling and its forcing of early Cenozoic climate 

Pietro Sternai, Sébastien Castelltort, Pierre Bouilhol, Lucas Vimpere, Léa Ostorero, Mubashir Ali, Luca Castrogiovanni, Bram Vaes, and Eduardo Garzanti

Cenozoic climate trends are classically ascribed to variations of the geological carbon cycle related to Neo-Tethyan geodynamics. It is widely agreed that the collision of India and Arabia with Asia and associated mountain uplift enhanced erosion and global silicate weathering rates, ultimately driving post-50 Ma climate cooling. Cenozoic climate trends, however, involve major events of global warming in the early Paleogene (~60-50 Ma), a period that preceded rapid mountain uplift by about 30 Ma and that was characterized by a climax of arc magmatism profoundly affecting the surface CO2 budget and consequently climate. We present new measurements of mercury and carbon-isotope anomalies documented in the sedimentary archive, together with pre-eruptive CO2 budgets of Neo-Tethyan magmas encompassing the India-Asia and Arabia-Asia collision. We also show new forward modeling of the Neo-Tethyan geodynamics and inverse modeling of the Cenozoic surface CO2 budget which, tied to these new observational constraints, allow us to quantify magmatic CO2 emissions associated with the collision of India and Arabia with Eurasia. We demonstrate through such comprehensive and interdisciplinary approach that CO2 emissions associated with magmatic pulses induced by subduction of Neo-Tethyan lithosphere as well as of Indian and Arabian passive-continental-margin successions exerted a primary control on early Cenozoic climate changes.

How to cite: Sternai, P., Castelltort, S., Bouilhol, P., Vimpere, L., Ostorero, L., Ali, M., Castrogiovanni, L., Vaes, B., and Garzanti, E.: New constraints on the Neo-Tethyan carbon cycling and its forcing of early Cenozoic climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4640, https://doi.org/10.5194/egusphere-egu24-4640, 2024.

EGU24-5514 | ECS | Orals | TS4.3

Dynamic Evolution of the Northern Carnarvon Basin: An Integrated Kinematic Approach 

Patrick Makuluni, Juerg Hauser, and Stuart Clark

The geological histories of passive margin basins are dominated by tectonically induced vertical and lateral motions that control sediment transport and the development and distribution of resource systems within the basins. However, the upward (uplift and exhumation), downward (burial and subsidence) and lateral (extension, rifting and potential inversion) motions are rarely analysed together. Exploration models built from basin evolution models that include only the vertical dimension may contain larger uncertainties than those that combine lateral and vertical motions. Based on a case study, our research suggests that the combination of analyses can improve the accuracy of basin evolution models and help optimise exploration models. 

Here, we present a case study for the basin evolution model for the Northern Carnarvon Basin that incorporates data from such a combined vertical and lateral motion analysis. Backstripping and decompaction techniques were used to analyse subsidence in more than 200 wells to build the basin’s subsidence and sediment evolution maps. These maps were then used to analyse lateral motions associated with the intraplate rift development in the region. In parallel, we analysed exhumation using compaction and vitrinite reflectance analysis techniques on porosity, sonic logs and paleotemperature data from 210 wells. Our combined analyses revealed seven critical periods of basin development from the Triassic to the present. The Triassic Period was dominated by thermal subsidence and sedimentation within the south-western parts. High subsidence (~ 90 m/Ma) and sedimentation were dominant in the Early and Mid-Jurassic, coinciding with the intraplate rifting of up to ~8 mm/yr, which produced the major sub-basins in the southern and southeastern parts of the basin. This was followed by Callovian exhumation that removed up to 1500 m of sediments from the western part of the basin. The Cretaceous was dominated by rifting and breakup-related subsidence, truncated by exhumation episodes that removed up to 1000 m of sediment thickness in the southeastern parts of the basin. In the Cenozoic, the basin experienced subduction-related tilting that exhumed the southern part while the northeastern parts subsided. Our study has shown that integrating the vertical and lateral motions presents a more accurate and complete basin evolution model with the potential for improving the optimisation of basin exploration.

How to cite: Makuluni, P., Hauser, J., and Clark, S.: Dynamic Evolution of the Northern Carnarvon Basin: An Integrated Kinematic Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5514, https://doi.org/10.5194/egusphere-egu24-5514, 2024.

EGU24-8880 | ECS | Posters on site | TS4.3

Tectonic driving mechanism of Quaternary rock-uplift and topographic evolution in the northern-central Apennines from linear inversion of the drainage system 

Simone Racano, Peter van der Beek, Claudio Faccenna, Victor Buleo Tebar, Domenico Cosentino, and Taylor Schildgen

The study of rock-uplift variations in time and space can provide insights into the processes driving the topographic evolution of mountain belts. The Apennine mountain chain of Italy, one of the more recently developed mountain belts in the Mediterranean region, has undergone a strong Quaternary rock-uplift phase, particularly in the north-central sector, which has shaped the present-day topography. It has long been recognized that drainage systems can record temporal and spatial variations in rock-uplift rates. Specifically, in detachment-limited systems with simple settings (e.g., no significant variations in drainage area over time, and catchments mostly draining perpendicular to regional structures), river profiles can be inverted to reconstruct their history of rock uplift. In this study, we present linear inversions of river profiles from 28 catchments along the eastern flank of the northern-central Apennines. These results are calibrated to infer rock-uplift rates by estimating the value of an erodibility parameter (K) from short-term incision rates and catchment-averaged erosion rates obtained from cosmogenic-nuclide data. Different approaches with constant and variable K have been applied to produce the rock-uplift model that best fits independent geochronological constraints about the uplift of the Apennine belt. Our findings suggest a spatially and temporally variable rock-uplift event that started around 2.5 to 3 Ma, following the last compressional orogenic phase and coinciding with the onset of extension. Furthermore, this rock-uplift pulse migrated southward at a rate of approximately 115 km/Myr. The highest rock-uplift rates (higher than 1.2 km/Myr) are observed in the region encompassing the highest Apennine massifs, such as the Laga Massif and the Gran Sasso Range. These results align with previous studies on Apennine paleoelevations, and they are consistent with numerical models and field evidence from other regions exhibiting rapid rock-uplift pulses and the migration of uplift related to slab break-off. Our results support the hypothesis of a break-off of the Adria slab under the central Apennines and its southward propagation over the last few million years.

How to cite: Racano, S., van der Beek, P., Faccenna, C., Buleo Tebar, V., Cosentino, D., and Schildgen, T.: Tectonic driving mechanism of Quaternary rock-uplift and topographic evolution in the northern-central Apennines from linear inversion of the drainage system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8880, https://doi.org/10.5194/egusphere-egu24-8880, 2024.

EGU24-8980 | Orals | TS4.3

Mechanisms and effects of Tarim rotation: 3-D thermo-mechanical modeling 

Qihua Cui, Pengpeng Huangfu, and Zhong-Hai Li

The rotational of rigid blocks within continental interiors, distant from plate convergence boundaries, represents a peculiar phenomenon with unclear dynamics. The Tarim block, characterized as a rigid Precambrian entity in Central Asia, is surrounded by the Tibetan–Pamir plateau to the south and the Tian Shan mountains to the north. Geophysical data strongly indicate a significant clockwise rotation of the Tarim block during the Cenozoic era. Simultaneously, distinctive deformation patterns and associated topographic responses are observed between the western–central and eastern Tian Shan regions. The intricate relationship among the India-Asia collision, Tarim's rotation, and Tian Shan's responses remains insufficiently constrained. In this study, we constructed a series of large-scale, high-resolution 3-D numerical models to study the mechanisms and effects of Tarim rotation. Our model results reveal that the collision between the advancing Indian lithosphere and the southwestern rim of the Tarim block triggers a clockwise rotation of the Tarim block. Subsequently, this rotation induces varied deformation responses along the strike of Tian Shan—resulting in heightened compression and significant uplift in central Tian Shan due to convergence, while eastern Tian Shan experiences less compression and moderate uplift attributed to divergence. Thus, the Tarim rotation emerges as an essential linkage, connecting the evolutionary dynamics of the Tibetan plateau with the far-reaching activation of Tian Shan. This research provides valuable insights into the geodynamic processes shaping continental interiors, with implications for broader tectonic frameworks and technological applications.

How to cite: Cui, Q., Huangfu, P., and Li, Z.-H.: Mechanisms and effects of Tarim rotation: 3-D thermo-mechanical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8980, https://doi.org/10.5194/egusphere-egu24-8980, 2024.

EGU24-9089 | Posters on site | TS4.3

Variscan olistostromes and the geological history they tell… unraveling the tectonic evolution of the Pangea supercontinent  

Ícaro Dias da Silva, Manuel Francisco Pereira, Emílio González-Clavijo, José Brandão Silva, and Lourenço Steel Hart

Mass transport deposits or olistostromes, carrying large-sized blocks or olistoliths, are related to active and passive margin tectonics. Information on how they are produced is critical to understanding the tectonically driven topographic dynamics in the source areas, and the tectonic evolution of sedimentary basins and their shoulders. The geological record of these mass transport deposits is commonly well preserved onshore, in orogenic regions where continental margins uplift was influenced by the gradual movement of continents.

The Iberian Massif is one of the World’s key areas for studying ancient orogenies, like the Late Paleozoic Variscan belt, to understanding the formation of olistostromes, and developing provenance studies on such complex tectonic fold and thrust belts. Structural relations between the basement and overlying Mississippian synorogenic marine basins were recently examined in the lower plate (Gondwana side) of the Variscan collisional orogeny in Iberia. The stratigraphy of these Variscan synorogenic basins is quite complex and includes: a) sedimentary melánges (e.g., related to submarine mudflows and turbidites) that carried or were formed by different-sized blocks of different age metamorphic, volcanic, siliciclastic and carbonated rocks derived from the nearby pre-Mississippian basement; b) partially or completely dismantled Devonian and/or Mississippian carbonate platforms; and c) syn-sedimentary bimodal calc-alkaline volcanism. Geochronology data show that Mississippian sedimentation and volcanism occurred simultaneously with regional high temperature-low pressure metamorphism, associated with the formation of gneiss domes, bounded by extensional shear zones and faults, during crustal thinning and plutons emplacement. Mapping of shear zones and faults on the Iberian Variscan basement provided crucial information for better comprehending Mississippian synorogenic basin architecture. Our study demonstrates that there is a spatial and temporal relationship between the generation of olistostromes (including large olistoliths) and the development of first-order extensional structures in the pre-Mississippian basement.

Given that the collision between Laurussia and Gondwana had already occurred, it seems that these Mississippian synorogenic basins were not formed in a foreland, backarc, or forearc setting related to the subduction of the Rheic oceanic lithosphere, and thus, other geodynamic hypotheses need to be set. Two tectonic models have been discussed to explain the occurrence of a significant thermal anomaly beneath the lower plate (Gondwana side) and the formation of the Mississippian synorogenic basins in Iberia: Model A) considers that the roll-back of the lower plate was responsible for the formation of an orogenic plateau, the lateral flow of partially molten orogenic roots, and peel-back tectonics, after the subduction of the Rheic Oceanic lithosphere under the upper plate (Laurussia side) and the subsequent continental collision. In this case, the Mississippian synorogenic basins would be of peel-back type; Model B) invokes the subduction of the Paleotethys oceanic lithosphere beneath the Variscan collisional orogen, and the Mississippian synorogenic basins would be of backarc type but developed later than the Rheic Ocean closure.

This work was supported by FCT I.P./MCTES (Portugal) through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020), LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), DL57/2016/CP1479/CT0030 (https://doi.org/10.54499/DL57/2016/CP1479/CT0030), FCT/UIDB/ 04683/2020-ICT and by the Spanish Agency of Science and Technology MCIN/AEI/10.13039/501100011033 and TED2021- 130440B-I00

How to cite: Dias da Silva, Í., Pereira, M. F., González-Clavijo, E., Silva, J. B., and Steel Hart, L.: Variscan olistostromes and the geological history they tell… unraveling the tectonic evolution of the Pangea supercontinent , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9089, https://doi.org/10.5194/egusphere-egu24-9089, 2024.

EGU24-10486 | Posters on site | TS4.3

Central Anatolian (Turkey) and Aegean (Greece) soil carbonate δ18O values reveal Late Miocene surface uplift of the southern plateau margin and post−Miocene aridification of the northeastern Mediterranean region 

Maud J.M. Meijers, Tamás Mikes, Bora Rojay, Erkan Aydar, H. Evren Çubukçu, Thomas Wagner, and Andreas Mulch

In recent years, numerous studies focused on reconstructing the surface uplift history of the Central Anatolian Plateau (CAP) and the associated driving mechanisms such as slab breakoff, removal of lithospheric mantle, or crustal thickening (e.g. McPhee et al., 2021). The CAP forms the westward portion of the Turkish−Iranian plateau and has mostly been above sea level since ca. 41 Ma (Okay et al., 2020). Most of its present-day topography, featuring mean elevations of ca. 1.0-1.5 km, however, has been shaped since the Late Miocene (e.g. Meijers et al., 2018; Schildgen et al., 2012a,b). Perhaps the most spectacular discovery is the recognition of 2 km of surface uplift of a portion of the southern plateau margin, the Tauride Mountains, since ca. 0.5 Ma (Öğretmen et al., 2018).

Here, we provide stable isotope paleoaltimetry estimates for the Late Miocene for the southern CAP margin. The method is based on the inverse relationship between the oxygen isotopic composition (δ18O) of meteoric waters and elevation. We therefore contrast the δ18O values of age−equivalent low and (potential) high elevation soil carbonates (the δ−δ method; Mulch, 2016) from central Anatolia with published Anatolian and Aegean soil carbonate δ18O values (Böhme et al., 2017; Meijers et al., 2018; Quade et al., 1994). Our results reveal a low (ca. 0.5 km) orographic barrier between the Aegean and Mediterranean coastlines and central Anatolia at ca. 10 Ma, which increased to an elevation of ca. 1 km by ca. 8−6 Ma. This trend in increasing surface elevations during the Late Miocene is in agreement with stable isotope−derived paleoelevation estimates from Anatolian lacustrine carbonate records (Meijers et al., 2018). Given proposed post−0.5 Ma surface uplift of the southernmost plateau margin (Öğretmen et al., 2018), our results imply a phase of significant local subsidence bracketed between the latest Miocene and ca. 0.5 Ma. From the Pliocene onward, we also observe long-term trends toward higher δ18O values in soil carbonate data sets from the Aegean Sea and CAP region, which indicate increased aridification and possibly seasonality of rainfall in the region since the Pliocene. Additionally, our ‘modern’ soil carbonate records from central Anatolia underestimate the elevation of the modern Tauride orographic barrier (ca. 2.2 ± 0.5 km) at the southern plateau margin by ca. 0.5 to 1.0 km (non−linear vs. linear lapse rate, respectively). We attribute this underestimation to the mixing in of higher δ18O atmospheric moisture derived from the Black Sea compared to atmospheric moisture derived from the Mediterranean Sea during spring and early summer, a signal that is likely incorporated into soil carbonates that form at the onset of the dry summer season. Although atmospheric moisture derived from the Black Sea yields lower δ18O values than Mediterranean atmospheric moisture at sea level (Schemmel et al., 2013), the former undergoes less distillation across the significantly lower northern plateau margin (the Pontide Mountains). The presently observed mixing of Black Sea and Mediterranean Sea moisture sources might have also led to an underestimation of southern orographic barrier elevations in the geologic past.

How to cite: Meijers, M. J. M., Mikes, T., Rojay, B., Aydar, E., Çubukçu, H. E., Wagner, T., and Mulch, A.: Central Anatolian (Turkey) and Aegean (Greece) soil carbonate δ18O values reveal Late Miocene surface uplift of the southern plateau margin and post−Miocene aridification of the northeastern Mediterranean region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10486, https://doi.org/10.5194/egusphere-egu24-10486, 2024.

EGU24-11203 | ECS | Posters on site | TS4.3

What controls the migration rate of divides? Insights from morphometry and 10Be and 26Al cosmogenic nuclides analysis applied to the Vosges massif 

Bastien Mathieux, Jérôme van der Woerd, François Chabaux, Philippe Steer, Julien Carcaillet, and Thierry Perrone

The Vosges massif is a mid-altitude mountain range located northeast of France. It extends latitudinally for 250 km north of the Alps and is characterized by topographic, geological and geomorphological north-south and east-west gradients. In the south, the exhumed Paleozoic basement culminates at about 1400 m asl while in the north, river valleys incise Mesozoic sandstones with summits ranging between 400 and 700 m asl. The relief is intricately linked to the Eocene-Oligocene formation of the Rhine graben and the Mio-Pliocene deformation of the Alpine foreland. The present-day slow deformation rates in the Rhine graben, coupled with the region’s moderate seismicity characterized predominantly by strike-slip mechanisms, raise questions about the current driving forces behind the Vosges’ topographic evolution.

The evolution of drainage divides provides a window into the complex interrelations among tectonic forces, surface erosion processes and climatic influences that contribute to shaping a mountain range. In this study, we combine morphometric and cosmogenic nuclides (10Be and 26Al) analyses to assess the migration of the Vosges’ main drainage divide. Gilbert’s metrics (elevation, relief and gradient) alongside χ-index reveal a strong eastward gradient across the divide suggesting a migration away from the Rhine graben margin. To provide a quantification of this migration, a dataset of in-situ cosmogenic nuclides whose concentrations are erosion-dependent has been measured in samples collected across various segments of the divide. Cosmogenic nuclide analysis reveals a robust set of 10Be/26Al ratios falling within the steady-state denudation curve and denudation rates, ranging from 30 to 90 mm/kyr in the south and 40 to 70 mm/kyr in the north. Notably, both regions display an eastward trend in denudation, corroborating the gradient observed in the morphometric analysis.  A geometric approach was used to translate cross-differences in denudation rates and topographic gradients into migration rates of the main drainage divide, showing a westward shift of 20-70 mm/kyr in the south and 3-30 mm/kyr in the north.

Expanding our analysis, we examined the correlation between the calculated denudation rates and the hilltop curvatures derived from high-resolution DEMs (1m). A relation appears in the south, whereas no relationship has been found in the north, suggesting additional complexities in controlling morphogenetic processes. This finding allows us to use hilltop curvature as a proxy for denudation rates, particularly within mono-lithologic soil-mantled basins along the southern Vosges drainage divide. These insights offer a valuable conceptual framework for constraining numerical simulations at the mountain range scale aimed at unravelling the external forces that shape the highest Vosges relief.

How to cite: Mathieux, B., van der Woerd, J., Chabaux, F., Steer, P., Carcaillet, J., and Perrone, T.: What controls the migration rate of divides? Insights from morphometry and 10Be and 26Al cosmogenic nuclides analysis applied to the Vosges massif, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11203, https://doi.org/10.5194/egusphere-egu24-11203, 2024.

EGU24-12254 | Posters on site | TS4.3

Relief stability of western Europe middle mountains from morphometry and 10Be denudation rates: the Strengbach catchment case in the central Vosges massif 

Jérôme van der Woerd, Daniel S. Moreno Martin, Raphaël di Chiara Roupert, Bastien Mathieux, Thierry Perrone, Gilles Rixhon, Silke Merchel, Anne-Sophie Mériaux, and François Chabaux

Assessing the Quaternary topographic stability of western Europe middle mountains characterized by low tectonic activity remains challenging. We suggest to tackle this question in the Vosges – Upper Rhine Graben system where elevation reach up to 1400 m asl. This study is focused on the Strengbach catchment, that flows from the Vosges massif towards the Rhine graben, upstream of Ribeauvillé in the central Vosges. The catchment reaches 29 sq.km between 500 to 1200 m elevation. Morphometric analysis of the main trunk and tributaries is performed to constrain the areas of topographic disequilibrium along the valleys (knickpoints). 10Be cosmogenic isotope analysis in river sediments from various sites in the catchment is used to constrain the migration rates of these topographic instabilities at the millennial scale.

The morphometric analysis performed in the Strengbach catchment (catchment topography - χ-elevation profiles) provide evidence of relic topographic surfaces upstream of a 2 km-long convex knick-zone located at about 700 m. Below this zone, the catchment is deeply incised and ramified with knick-points in the tributaries at about 500 m. Above the knick-zone, fluvial incision is reduced with a high-standing knickpoint at about 950 m marking the upper section of the Strengbach stream. 10Be denudation rates points to relatively small variations along the main trunk upstream (36 ± 2 - 44 ± 3 mm/ka), while denudation rates derived from the tributaries range from 38 ± 2 mm/ka to 75 ± 5 mm/ka. We show that these variations are primarily controlled by topographic and lithologic factors, namely the presence of sandstones in the sub-catchments, characterized by higher erodibility than crystalline rocks. The 10Be cosmogenic isotope concentrations in sediments from both upstream and downstream of the knickpoints, and in the tributaries, constrain at first order the migration rate of the knickpoints along the river profile and the retreat rate of sandstone cliffs upstream some tributaries. Migration rates on the order of 100-200 m/Ma suggest that at the millennial scale, the topography is relatively stable. These data will be used to discuss the source of topographic disequilibrium present in the catchments.

How to cite: van der Woerd, J., Moreno Martin, D. S., di Chiara Roupert, R., Mathieux, B., Perrone, T., Rixhon, G., Merchel, S., Mériaux, A.-S., and Chabaux, F.: Relief stability of western Europe middle mountains from morphometry and 10Be denudation rates: the Strengbach catchment case in the central Vosges massif, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12254, https://doi.org/10.5194/egusphere-egu24-12254, 2024.

EGU24-13770 | ECS | Posters on site | TS4.3

The Northward Expansion of the Tibetan Plateau: Topographic Evidence from the Bogda Mountains—Junggar Basin Coupling system, Northwest China 

Mengyue Duan, Franz Neubauer, Jörg Robl, Xiaohu Zhou, and Moritz Liebl

Distinct Mountain–Basin coupling systems were formed during the expansion of the Tibetan Plateau into the surrounding low elevation regions in the north, northeast and east. In this study, we focus on the topographic features of the Bogda Mountains–Southern Junggar Basin coupling system on the north of the Tibeau Plateau, which influenced by the N-S orthogonal shortening caused by the uplift of the Tibetan Plateau and northward propagation of deformation away from the India-Asia collision zone. We mainly quantify the influence of uplift of the Tibetan Plateau on the formation of the Bogda Mountains–Junggar Basin coupling system by fluvial geomorphologic analysis based on the digital elevation model analysis and the optically stimulated luminescence (OSL) dating on the Dalongkou river terraces on the northern slope of Bogda Mountains. Together, these morphological analyses show that the high normalized steepness index (ksn) and knickpoints mainly distributed in the western Bogda Mountains. The normalized steepness index (ksn) gradually decreased from west to east, which indicated that the tectonic activity of the western Bogda Mountains is higher. The compiled low-temperature thermochronology data of the Bogda Mountains show a younging trend from west to east, which indicates that the western Bogda uplift started earlier than in eastern Bogda. The difference of the χ values on both sides of the Bogda Mountains is similar, which means the drainage divide of the Bogda Mountains is stable. There are five river terraces distributed on both side of the Dalongkou River. The optically stimulated luminescence (OSL) dating results show that the ages of the T2 river terrace, T3 river terrace, T4 river terrace of the Dalongkou river are 6.2±1.3 ka, 13.1±1.7 ka, and 14.2±2.5 ka, respectively. The incision rate of the Dalongkou river increases upstream from ~1.22 mm/yr close to the southern Junggar Basin, to ~2.1 mm/yr, and to ~6.33 mm/yr in front of the higher Bogda Mountains, which means that the uplift rate of the Dalongkou river increases upstream. We propose a model of upbending of central Bogda Mts. by ongoing Holocene folding, with an inflection point close to the southern boundary to the Junggar Basin. By comparing the geomorphological features of the Bogda Mountains with the North Tianshan Mountains, we conclude that the tectonic uplift intensity gradually decreased from the North Tianshan Mountains to the Bogda Mountain, as well as the gradual accelerated uplift rate of the Bogda Mountains, are influenced by the N-S orthogonal shortening caused by the uplift of the Tibetan Plateau, which is gradually decreasing from west to east.

How to cite: Duan, M., Neubauer, F., Robl, J., Zhou, X., and Liebl, M.: The Northward Expansion of the Tibetan Plateau: Topographic Evidence from the Bogda Mountains—Junggar Basin Coupling system, Northwest China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13770, https://doi.org/10.5194/egusphere-egu24-13770, 2024.

Quantifying rates and magnitudes of topographic change across timescales requires diverse observational and modeling techniques.  Low-temperature thermochronometer methods are a powerful tool for quantifying denudation rates, paleotopography, and/or the kinematic history of orogens over geologic timescales.  Parallel to thermochronometer technique development, a range of thermal, kinematic, and erosion modeling approaches are available to interpret tectonic and surface processes from thermochronometer data. However, differing thermal modelling approaches exist in the literature and often lead to the question of which approach is most appropriate, and when?

This presentation addresses the diversity of thermo-kinematic and erosion modelling approaches available to quantitatively interpret topographic change or tectonic processes from thermochronometer data. Emphasis is placed on deciphering the different approaches available and which approach is suitable for the scientific questions asked (e.g., topographic change, tectonic/faulting history, etc.) in diverse geologic settings.  Thermo-physical factors explored include the appropriate model spatial dimension (e.g., 1D, 2D, vs. 3D); the influence of model geometry on geotherms; the importance of constant basal temperature vs. flux basal boundary conditions; transient vs. steady-state geotherms, and how tradeoffs in different parameters (exhumation rate, material properties, boundary conditions) can produce similar thermochronometer ages. The presentation focuses on examples from the literature, ranging from William Thompson’s (Lord Kelvin) founding work on continental geotherms to contemporary numerical modeling approaches.

How to cite: Ehlers, T. A. and Willett, S. D.: Appropriate Thermal Modelling Approaches for Interpreting Topographic and Tectonic Change from Thermochronometer Data (Remembering the Geotherm and 200 years of Lord Kelvin’s legacy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13841, https://doi.org/10.5194/egusphere-egu24-13841, 2024.

EGU24-15024 | Orals | TS4.3

Direct evidence of drainage divide migration reveals intermittent dynamics linked to 100 kyr climate oscillations 

Liran Goren, Elhanan Harel, Tianyue Qu, Onn Crouvi, Naomi Porat, Hanan Ginat, and Eitan Shelef

It is common to assume that when there are erosion rates and slope gradients across a drainage divide, the divide is prone to migrate and change the drainage area distribution of its bounding catchments. However, direct records of divide migration are exceptionally rare. This raises the following questions: Could the assumption be wrong, and can divides sustain topographic and erosion rate asymmetry over geomorphic and geologic (104– 106 yrs) timescales? And when divides eventually migrate, is the migration driven by endogenic feedback within the basin, or by exogenic forcing, such as climate change?

To address these issues, we study a field area along the escarpments of the Dead Sea plate boundary, Israel, where direct records for divide migration are present in the form of terraces that grade opposite to the channel flow direction. These terraces are interpreted as a record of the divide’s paleo-locations, such that terraces are formed when the divide migrates inland from the edge of an escarpment, inducing drainage reversal and gradually extending the reversed channel that drains toward the escarpment.

Absolute dating of these terraces using luminesces techniques and relative dating using soil chronosequence markers reveal that the terraces become older from the present locations of the divide toward the escarpment, consistent with the interpreted process of their formation. Terrace ages show an average divide migration rate of ~1100 m myr-1 over the past ~230 kyr, supporting active divide migration over timescales of 105 yrs or shorter.

Terrace groups with similar ages indicate ~100 kyr cycles of periods of divide stalling and episodes of rapid divide migration with rates up to fourfold relative to the average rate. We use numerical simulations to explore possible drivers for the inferred divide intermittent dynamics. Simulations show that the dynamics are inconsistent with landscape evolution under uniform environmental conditions due only to internal basin dynamics. Instead, the inferred intermittency is best explained with time-dependent erosional efficiency that is sensitive to global climate change and correlates with regional paleoclimate proxies.

This study provides the first detection of divide migration rate intermittencies at timescales of 104-105 yrs, and the association between divide dynamics and changing climatic conditions. This highlights the potentially significant impact of climate changes on the plan-form evolution of drainage basins.

How to cite: Goren, L., Harel, E., Qu, T., Crouvi, O., Porat, N., Ginat, H., and Shelef, E.: Direct evidence of drainage divide migration reveals intermittent dynamics linked to 100 kyr climate oscillations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15024, https://doi.org/10.5194/egusphere-egu24-15024, 2024.

EGU24-15751 | Posters on site | TS4.3

3D interaction of tectonics with surface processes explains fault network evolution of the Dead Sea Fault 

Sascha Brune, Esther L. Heckenbach, Anne C. Glerum, Roi Granot, Yariv Hamiel, Stephan V. Sobolev, and Derek Neuharth

Releasing and restraining bends are complementary features of continental strike-slip faults. The Dead Sea Basin of the strike-slip Dead Sea Fault is a classical example of a releasing bend with an asymmetric, deep basin structure. However, the intrinsic relationship to its northern counterpart, the restraining bend that created the Lebanese mountains, remains unclear.

Here, we present 3D coupled geodynamic and landscape evolution models that include both the releasing and the restraining bend in a single framework. These simulations demonstrate that the structural basin asymmetry is a consequence of strain localization processes, while sediments control the basin depth. Local extension emerges due to strength heterogeneities and a misalignment of faults and the overall stress field in an area where regional tectonics are dominated by strike-slip motion. Furthermore, we reveal a crustal thinning and thickening pattern that intensifies with surface process efficiency. Along-strike deformation is linked through coupled crustal flow driven by gravitational potential energy which is opposed by deposition at the releasing bend and enhanced by erosion around the restraining bend. Due to the generic nature of our models, our results provide templates for the evolution of fault bends worldwide.

How to cite: Brune, S., Heckenbach, E. L., Glerum, A. C., Granot, R., Hamiel, Y., Sobolev, S. V., and Neuharth, D.: 3D interaction of tectonics with surface processes explains fault network evolution of the Dead Sea Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15751, https://doi.org/10.5194/egusphere-egu24-15751, 2024.

EGU24-17337 | Orals | TS4.3

Landscape response at the edge of a tearing slab 

Jose Miguel Azañon, Jorge Pedro Galve, Daniel Ballesteros, Jose Vicente Perez-Peña, Patricia Ruano, Fernando Garcia-Garcia, and Guillermo Booth-Rea

Tearing at the edges of subducted slabs permits the migration of narrow orogenic arcs. Dynamic models predict that the active segment of subvertical tears migrates in the sense opposite subduction modifying the topography and tectonic regime along its path. However, the effects of slab tearing on surface deformation and landscape evolution, remains virtually unexplored. Here we show the landscape response to slab tearing, including drainage development and reorganization in the Betics, with analogies to the southern Caribbean arc. After approximately 400 km of slab tearing since 10 Ma the Betics show a transient topography with positive residual values over regions stripped from their subcontinental lithospheric mantle and negative anomalies outboard of the tear. The landscape evolves through crustal shortening and flexural uplift in the foreland of the active tearing segment producing land emergence and drainage development, with fluvial diversion around uplifting structures. Slab pull and orogen transverse extension inboard the active-tearing segment foster basin development followed by emergence and drainage reorganization by fluvial incision and capture. Mantle upwelling, flexural rebound and further extension affects teared regions, driving positive residual topography amplified in the footwall of extensional domes. Mantle flow around the slab drives uplift hundreds of km away from the slab edges.

How to cite: Azañon, J. M., Galve, J. P., Ballesteros, D., Perez-Peña, J. V., Ruano, P., Garcia-Garcia, F., and Booth-Rea, G.: Landscape response at the edge of a tearing slab, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17337, https://doi.org/10.5194/egusphere-egu24-17337, 2024.

EGU24-17907 | Orals | TS4.3

3D Velocity field of Romania derived from more than 20 years of continuous GPS observations 

Alexandra Muntean, Boudewijn Ambrosius, Eduard Ilie Nastase, and Ioan Munteanu

Abstract

      The Earth's surface is continuously transformed, with deep and superficial processes contributing to the present-day morphology. Evaluating the contribution of each process and interaction between tectonics, climate, and human activities is difficult, especially in areas with relatively low crustal deformation.

      With this study, we aim to better understand the tectonic and sub-surface geodynamic processes that result in (small) surface motions in Romania. We are particularly interested in the Eastern Carpathians Bending Zone (Vrancea region), where strong deep earthquakes occur. Furthermore, we are focused on the interaction between the Eurasian, and Aegean tectonic plates. For this purpose, we processed more than 20 years of cGPS data from various networks in Romania (more than 100 stations), using the GipsyX software. To put our results in a broader perspective, we also included similar results published in open-source online literature including countries around Romania. Combining all these solutions we generated a velocitiy horizontal and vertical velocity fields for this extended region. All solutions were converted to the Eurasian tectonic reference plate in the ITRF14 plate rotation model.

      We find that in general, the horizontal velocity vectors in Romania have small values, ranging from 0.0 mm/yr in the north to 1.5 mm/yr in the south, and notably, the majority of stations indicate a subtle yet significant downward motion of 1.0 -2.0 mm/yr. In contrast, to our expectations, we did not find any significant horizontal and vertical motions in the Vrancea region. The horizontal motions exhibit a strong, generally southward, and gradually increasing trend, starting south of the South Carpathians. The trend is in the direction of the tectonic plates in southeast Europe. It means that the intraplate deformation zone extends to south Romania. The observed patterns contribute to our understanding of intraplate deformation and emphasize the need for continued regional research.

Keywords: crustal deformations, GPS, geophysics, tectonics 

 

Acknowledgments

This paper was carried out within Nucleu Program SOL4RISC, supported by MCI, project no PN23360101, and PNRR- DTEClimate Project nr. 760008/31.12.2023, Component Project Reactive, supported by Romania - National Recovery and Resilience Plan

How to cite: Muntean, A., Ambrosius, B., Nastase, E. I., and Munteanu, I.: 3D Velocity field of Romania derived from more than 20 years of continuous GPS observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17907, https://doi.org/10.5194/egusphere-egu24-17907, 2024.

EGU24-18362 | ECS | Posters on site | TS4.3

The role of tectonic, volcanic, and fluvial processes as controls of Neogene intermontane basin evolution in the western Colombian Andes 

Santiago León, Claudio Faccenna, Ethan Conrad, and Víctor A. Valencia

The sediment dispersal patterns at active orogens are highly sensitive to changes in the landscape configuration triggered by the combined effects of deformation, volcanism, and geomorphological processes. Hence, reconstructing source-to-sink systems provides valuable insights into the interplay between deep-seated and surface processes as controls of the coupled development of mountain ranges and intermontane sedimentary basins.

The Oligocene-Miocene evolution of the Colombian Andes has been shaped by subduction tectonics and the collision of an oceanic terrane, which are linked to changes in the kinematics of crustal deformation and the tectono-magmatic history of continental arcs. Nevertheless, the combined effect of such processes on the growth of the Western and Central Cordilleras and the associated intermontane basins remains elusive.

Here, we use a large dataset of detrital zircon U-Pb ages from Oligocene-Pliocene strata of intermontane basins of western Colombia, and available (bio)stratigraphic and structural constraints to reconstruct: i) the regional-scale configuration of source areas and accumulation settings, ii) the sediment routing systems, and iii) the history of basin connectivity. We interpret the sediment dispersal patterns as controlled by the pulsed uplift of the Central and Western Cordilleras linked to a syn- to post-collisional transpressional tectonic regime, and to changes in the drainage network driven by intra-basinal arc-related magmatic activity

How to cite: León, S., Faccenna, C., Conrad, E., and Valencia, V. A.: The role of tectonic, volcanic, and fluvial processes as controls of Neogene intermontane basin evolution in the western Colombian Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18362, https://doi.org/10.5194/egusphere-egu24-18362, 2024.

EGU24-20268 | Orals | TS4.3

Discovery of lithospheric drip explains topographic rejuvenation of the Uinta Mountains, USA 

Adam Smith, Matthew Fox, Scott Miller, and Leif Anderson

Densification at the base of thickened crust drives lithospheric dripping or delamination. Mountain ranges form due to crustal thickening, and so represent locations where dripping and delamination are likely to occur. Recent studies have implicated dripping continental crust with a variety of different surface expressions, from driving surface uplift to initiating rifting, highlighting the uncertainty associated with our ability to predict the surface consequences of dripping continental crust. The Uinta Mountains in Utah formed during the Laramide orogeny, and despite this period of crustal shortening ending ~50 mya, the elevation of the range, and the form of the river networks draining the range suggest the range has undergone topographic rejuvenation. To investigate the cause of this rejuvenation, we extract map of recent surface uplift from the river networks of the Uintas, and use previously published seismic tomography to investigate the structure of the mantle beneath the range. We identify dripping lithospheric crust beneath the Uintas, and, using a simple isostatic model, are able to reconcile the observed surface uplift with a prediction of surface uplift based on isostatic compensation. The agreement between our observations and our predictions allow us to present a compelling case for delamination driven surface uplift of the Uintas, and show that simple isostatic compensation can explain the surface expressions of delaminated crust. Our observations therefore have important implications for the history of the Uinta Mountains and more generally for our understanding of the long-term evolution of the continents.

 

How to cite: Smith, A., Fox, M., Miller, S., and Anderson, L.: Discovery of lithospheric drip explains topographic rejuvenation of the Uinta Mountains, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20268, https://doi.org/10.5194/egusphere-egu24-20268, 2024.

EGU24-412 | Posters on site | TS4.5

Paleozoic evolution in the Alborz: Continuous extension from the Gondwanan active margin to Paleotethys post-rift passive margin 

Asghar Dolati, Jeroen Smit, Amin Behrooz, Akbar Jabbari, and Alireza Shahidi

The transition from the Ediacaran-Cambrian Gondwana active margin to the rifting and opening of the Rheic and Paleotethys Oceans forms a turning point in the history of the Peri-Gondwanan Terranes. There are few better places to study the Pre-Cambrian and Paleozoic evolution of the northern Gondwana margin better than in the Central Iranian Microplate (CIM). The Alborz Mountains of northern Iran, formed by inversion of the Paleozoic Paleotethys passive margin of the Central Iranian Plate during successive collision phases since the Late Triassic, is one of the places where Paleozoic rocks are well exposed. The aim of this study is to elucidate the Paleozoic structural-tectonic framework and the transition of geodynamic regimes. We present the first paleostress analysis of the Paleozoic evolution of Alborz, were carried out for 49 sites, ranging from Cambrian to Permian outcrops in the Central and Eastern Alborz.

We focus on the orientation of the pre-orogenic Paleotethys margin and the evolution of the Paleozoic stress field by inversion of fault slip data, starting with the Central and Eastern Alborz. Syn-sedimentary faults, i.e. those not reactivated by later tectonic events, were the main target of measurements for the paleostress analysis. Calculated paleostress tensors show a constant north-south extension stress regime throughout the Paleozoic during successive geodynamic regimes, from the Gondwana active margin to the Paleotethys post-rift passive margin. The extension was accommodated by east-west oriented (current reference frame), margin-parallel normal faults. These intra-formational faults are parallel to the main basin-bounding faults, which were repeatedly reactivated during later inversion and extension phases.

How to cite: Dolati, A., Smit, J., Behrooz, A., Jabbari, A., and Shahidi, A.: Paleozoic evolution in the Alborz: Continuous extension from the Gondwanan active margin to Paleotethys post-rift passive margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-412, https://doi.org/10.5194/egusphere-egu24-412, 2024.

EGU24-1308 | Orals | TS4.5

Evidences for Neoproterozoic fragments with Indian origin in Oman and northern Madagascar 

Wilfried Bauer, Imboarina T. Rasaona, Joachim Jacobs, Alan Collins, Lesley Ellen Edwards, Ivan Callegari, and Andreas Scharf

Newly obtained geochemical and geochronological data from the Saih Hatat Dome in northeastern Oman and the Betsiaka Group in northern Madagascar reveal compelling similarities in the Neoproterozoic geological evolution of these geographically distant regions. The Saih Hatat Dome serves as a tectonic window with a NW-SE extension of <95 km and an E-W extension of <50 km. It is encircled by the allochthonous Samail Ophiolite and the underlain nappes consisting of mostly sedimentary rocks from the Neo-Tethyan Hawasina Basin. The rocks within this window underwent Late Cretaceous high-pressure/low-temperature eclogite- and blueschist-facies metamorphism.

In contrast, the Betsiaka Group of northern Madagascar, located between the Neoproterozoic Bemarivo Belt (750-720 Ma) and the Permo-Mesozoic cover, includes amphibolites, garnet-sillimanite micaschists, quartzites, and rare calc-silicate rocks.

New U-Pb zircon LA-ICP-MS data from a quartzdiorite dyke, intruding the basal part of the Hatat schists of the Saih Hatat Dome, yielded a crystallization age of 845 +2/-4 Ma. Similarly, a U-Pb zircon age of 841 ± 5 Ma was determined from an orthogneiss within the Betsiaka Group. Both igneous suites exhibit a calc-alkaline geochemical signature characteristic of volcanic island arcs.

The quartzdiorite in the Saih Hatat intruded a volcanosedimentary sequence and is covered by Cryogenian to Ediacaran metasedimentary and metavolcanic formations. Two metatuffites contain igneous and detrital zircons with ages ranging from approximately 530 to 2872 Ma, featuring clusters around 750 to 850 Ma and 1010 to 1164 Ma. Ages exceeding 1.1 Ga are unprecedented from an Arabian Plate source. Conversely, a quartzite from the Betsiaka Group displays a youngest >90% concordant zircon age of 1771 ± 28 Ma, with age peaks at around 2.5, 2.4 Ga, 1.8 Ga, and 1.85 Ga, pointing towards a Late Paleoproterozoic deposition age. Zircon ages between 1.77 and 1.85 Ga are also absent from central Madagascan igneous rocks. We propose that these crustal fragments in Oman and Madagascar originated from an area previously proximate to the Aravalli Craton in NW India.

How to cite: Bauer, W., Rasaona, I. T., Jacobs, J., Collins, A., Edwards, L. E., Callegari, I., and Scharf, A.: Evidences for Neoproterozoic fragments with Indian origin in Oman and northern Madagascar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1308, https://doi.org/10.5194/egusphere-egu24-1308, 2024.

EGU24-1476 | Posters on site | TS4.5

The geometry of the Main Himalayan Thrust in Central Nepal (85°E) derived from thermo-kinematic modeling of thermochronological data in the Gyirong region (southern China) 

Ralf Hetzel, Kyra Hölzer, Reinhard Wolff, Qiang Xu, István Dunkl, Aneta Anczkiewicz, and Zhenyu Li

The subsurface structure of the Himalaya is dominated by the seismically active Main Himalayan Thrust fault, which accommodates about half of the plate convergence between India and Asia. In Central Nepal, geological, geophysical, and geodetic studies indicate that the Main Himalayan Thrust has a flat-ramp-flat geometry, which causes cooling, erosion, and exhumation of rocks to be faster above the mid-crustal ramp than above the adjacent upper and lower flats (Brewer & Burbank 2006; Robert et al. 2011; Hubbard et al. 2016). However, in the northern High Himalaya the ramp geometry, in particular its width and depth are not well resolved. To place further constraints on the northward extent and depth of the ramp, we present low-temperature thermochronological data and U-Pb zircon ages from the Gyirong region, China. Our zircon U-Pb data show that the protolith of the High Himalayan orthogneisses is 478±4 Ma old, and was intruded by a large leucogranite at 19.5±0.7 Ma. The Pliocene-Quaternary cooling of the study area is constrained by apatite fission track ages and apatite and zircon (U-Th)/He ages between ~5 Ma and ~0.5 Ma, which show a marked trend of southward-younging ages (Wolff et al. 2022). Together with published cooling ages from Nepal farther south, the ages define a U-shaped pattern across the Main Himalayan Thrust, with ages increasing to the north and south from a minimum in the High Himalaya. A thermo-kinematic model, in which the geometry of the mid-crustal ramp was varied, explains the age data and suggests that the ramp has a dip of ~22°N. Compared to previous models, our new ages require that the ramp has a greater width (~55 km) and reaches a greater depth (~34 km) below the northern High Himalaya. Still farther north, the fault is presumably developed as a gently-dipping ductile shear zone, which forms the prominent reflector visible in seismic reflection data.

References

Brewer, I.D., Burbank, D.W. (2006). J. Geophys. Res. 111, B09409.

Hubbard, J., Almeida, R., Foster, A., et al. (2016). Geology 44, 639-642.

Robert, X., Van der Beek, P., Braun, J., et al. (2011). J. Geophys. Res. 116, B05202.

Wolff, R., Hölzer, K., Hetzel, R., et al. (2022). Tectonophysics 834, 229378.

How to cite: Hetzel, R., Hölzer, K., Wolff, R., Xu, Q., Dunkl, I., Anczkiewicz, A., and Li, Z.: The geometry of the Main Himalayan Thrust in Central Nepal (85°E) derived from thermo-kinematic modeling of thermochronological data in the Gyirong region (southern China), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1476, https://doi.org/10.5194/egusphere-egu24-1476, 2024.

EGU24-2532 | ECS | Orals | TS4.5

Carbonate U-Pb ages constrain Paleocene initiation along the Altyn Tagh fault in response to the India-Asia collision 

Kexin Yi, Feng Cheng, Marc Jolivet, Jiaming Li, and Zhaojie Guo

The formation of the Tibetan Plateau as a result of the Cenozoic India-Asia collision had a profound impact on the Asian tectonics configuration and climate dynamics. The kinematics and deformation pattern along the Altyn Tagh fault (ATF), marking the Plateau’s northern boundary, is of great significance for resolving the dispute on the deformation mechanisms of the Tibetan Plateau. However, the timing and configuration of the initial rupture along the ATF remains debated given the limited constraints on the depositional age of associated Cenozoic syntectonic strata.

Here we investigated the syntectonic Cenozoic strata in the Xorkol Basin, the pull-apart basin of the ATF. New uranium-lead analyses of the carbonate deposits yield dates of 58.9 ± 1.29 Ma. Therefore, we propose that the initiation of strike-slip motion along the ATF occurred no later than 58.9 Ma, leading to the formation of the Xorkol Basin as a composite pull-apart basin. This finding clarifies the timing and location of the initial ATF activity, indicating that the modern configuration of the ATF was established as early as the early Cenozoic.

This research provides the first yet oldest radioisotopic age along the ATF and surrounding area. This age estimate is also indicative of the depositional age of the Lulehe Formation in the Qaidam Basin, suggesting that the syntectonic sedimentation in the northern Tibetan Plateau initiated during the Paleogene. This timing coincides with the ca. 60 Ma onset timing of India-Asia collision, highlighting its far-field effect. We infer stress triggered by the India-Asia collision has propagated across the entire plateau in ca. 1-2 Ma, resulting in Paleocene strike-slip faulting along the ATF and other deformation in North Tibet.

How to cite: Yi, K., Cheng, F., Jolivet, M., Li, J., and Guo, Z.: Carbonate U-Pb ages constrain Paleocene initiation along the Altyn Tagh fault in response to the India-Asia collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2532, https://doi.org/10.5194/egusphere-egu24-2532, 2024.

EGU24-2576 | Posters on site | TS4.5

Protolith age and composition of the north Shahrekord Jurassic eclogite in SW Iran: Correlation with the Permian flood basalts across Asia 

Rezvaneh Jamali Ashtiani, Axel K. Schmitt, Jamshid Hassanzadeh, and Arash Sharifi

The Zayanderud high-pressure metamorphic complex in the Sanandaj-Sirjan zone, north of the Neotethyan Zagros suture in Iran, includes Jurassic eclogites that have been the subject of multiple studies aiming at deciphering their metamorphic history. However, determination of the protolith age has remained ambiguous due to subsequent thermal overprint. This study investigates the protolith ages and characteristics of metabasites from outcrops north of Shahrekord that are older than the Zagros blueschist association. Through U-Pb zircon ages, whole rock analysis, and Sr-Nd-Hf isotope data for metabasites, new insights into their age, chemical composition, and tectonic setting have been achieved. Ion microprobe U-Pb geochronology of rare zircons in thin section permits extracting Early Permian protolith ages for eclogite, despite textural evidence for metamorphic, low-U zircon overgrowths on the zircon crystals. These protolith ages align with the well-studied Permian flood basalts associated with Pangea breakup and Neotethys opening. Remnants of coeval flood basalts are preserved in Oman, the Himalayas, and the Asian Large Igneous Provinces in Tarim, Tianshan, and Emeishan. Elemental and Sr-Nd-Hf isotopic compositions of Zayanderud eclogites and amphibolites confirm a continental flood basalt affinity. Earlier investigations suggested that the eclogitization occurred in the Early- to Middle Jurassic time. Our findings put forward a scenario that the Permian volcanic passive margin of this Neotethyan segment sank into the mantle at the onset of subduction in the Jurassic. The studied example advocates a previously unexplored possibility of deep sinking of a passive continental margin at the beginning of subduction. Another important aspect of the studied metabasites is that they have recorded two major rifting events in the history of Pangea, namely the Permian rifting which caused the separation of the Cimmeria continental ribbon and the Jurassic opening of the southern hemisphere oceans in connection with initiation of subduction within the Neotethys domain.

How to cite: Jamali Ashtiani, R., Schmitt, A. K., Hassanzadeh, J., and Sharifi, A.: Protolith age and composition of the north Shahrekord Jurassic eclogite in SW Iran: Correlation with the Permian flood basalts across Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2576, https://doi.org/10.5194/egusphere-egu24-2576, 2024.

EGU24-4262 | Posters on site | TS4.5

Late Neogene hydrothermalism in the Central Oman Mountains 

Andreas Scharf, Robert Bolhar, Tonguc Uysal, Frank Mattern, Ivan Callegari, Gülcan Bozkaya, and Kim Baublys

The Jabal Akhdar Dome of the Central Oman Mountains provides insights into the autochthonous Neoproterozoic to Cretaceous Arabian rocks. A superbly exposed outcrop of the dark carbonate Ediacaran Hajir (or Khufai) Formation displays NW/SE-trending, non-plunging tight folds and SW thrusts. As the Permo-Mesozoic rocks lack this deformation pattern, the folds/faults are inferred to have formed during the Infracambrian Cadomian Orogeny. White calcite veins in fold hinges and within faults/calcmylonites provide U-Pb ages of 8.95 ±0.92, 7.71 ±1.44, 5.91 ±2.92, 4.89 ±6.1, 2.41 ±1.46 and 2.03 ±0.78 Ma (all 2 SE). These ages do not match the field observation, indicating that pre-existing Cadomian(?) calcite veins were overprinted at a later stage. Geochemically, almost all carbonates from the veins display strongly positive Eu values in shale normalization ([Eu/(0.5*Sm+0.5*Gd]MUQ=1-8.4) indicative of precipitation from hydrothermal fluids at temperatures >200-250°C under non-oxidizing conditions. The δ13C and δ18O values of the limestone host rocks range between +3.93‰ to +5.93‰ and between +19.8‰ to +23.3‰, respectively. In contrast, vein calcites show considerably higher δ13C values, varying between +5.85‰ to +7.01‰ and slightly lower δ18O values from 16.5‰ to 20.7‰. Fluid inclusion homogenization temperatures of vein calcite suggest two phases of precipitation, with values of 125-150°C and 160-260°C. Based on fluid inclusion data, two phases of fluid entrapment can be discerned, consistent with two different calcite generations or recrystallization events. Stable isotope data seem to be a product of one calcite precipitation or recrystallization event, rather than a mixture of two different generation, because δ18O values of vein calcites define a fairly narrow range, requiring precipitation from fluids at similar temperatures and oxygen isotope compositions, during a time of similar palaeohydrological conditions. Fluid inclusions from primary inclusions in calcite indicate relatively high temperatures (at ~225°C) and are possibly a product of the fluid-flow event in response to the Cadomian Orogeny. Since the U-Pb isotopic system of the calcites was reset, providing late Cenozoic ages (<10 Ma), δ18O, values of vein calcites are most likely the product of the younger calcite recrystallization event that must have occurred at relatively shallow depths at temperatures between 125 and 150°C.

Our U-Pb vein calcite ages, combined with geochemical, stable O-C isotopes and fluid inclusion data reveal that former Cadomian(?) calcite veins formed at temperatures of ~225°C, which was subsequently overprinted by near-surface hydrothermal activity at <10 Ma. This study highlights and dates a hydrothermal event in the Jabal Akhdar Dome. The inferred hydrothermal event correlates with an undated thermal overprint of Mesozoic shelfal rocks from the Jabal Akhdar Dome (Pracejus et al., 2022) and a hydrothermal-fluid flow east of the dome, which is related to listwaenite formation and Arabia-India convergence.

 

Pracejus, B., Scharf, A. & Mattern, F. (2022) Thermal overprinting of Mesozoic shelfal limestones on Jabal Akhdar, Oman. European Geosciences Union (EGU), Vienna, Austria, vEGU 2022-3985.

How to cite: Scharf, A., Bolhar, R., Uysal, T., Mattern, F., Callegari, I., Bozkaya, G., and Baublys, K.: Late Neogene hydrothermalism in the Central Oman Mountains, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4262, https://doi.org/10.5194/egusphere-egu24-4262, 2024.

EGU24-4386 | Orals | TS4.5

The sedimentary record of ophiolite obduction in North Oman 

Henk Droste, Bruce Levell, and Mike Searle

The Late Cretaceous emplacement of the Semail ophiolite and underlying thrust sheets onto the Arabian continental margin is well constrained by geochronological data. The stratigraphy and the development of the foreland basin in front of the advancing nappes is still poorly understood. This study aims to unravel the tectonostratigraphy of the foreland basin and link this to different stages of the nappe emplacement.

Obduction is associated with a major regional Turonian (92Ma) unconformity that ended the middle Cretaceous shallow water carbonate deposition on the passive margin. Locally this is related to the development of a foreland bulge in front of the southward advancing nappes. It caused collapse and erosional recession of the platform margin; the platform top was subaerially exposed and was incised by fluvial valley systems some 150 m deep.

Along the collapsed margin, a sedimentary mélange formed with re-deposited platform sediments and blocks. These were later incorporated into the thrust complex and returned tectonically onto the margin. The subaerial unconformity on the exposed carbonate platform was onlapped during the initial phase of foredeep development by a thin (150 m thick 150km wide) transgressive carbonate ramp as it subsided into a starved foredeep. Further forebulge onlap was by fine-grained coastal clastics that were sourced laterally from local uplift of the Huqf Basement along the eastern margin of the Arabian Plate.

Transgression ended in the Santonian (85Ma) and is followed by some 250 km northward progradation of a mud-prone delta complex of more than 1 km thick into the southeastern part of the foredeep. This deltaic wedge has been incised by deep canyons and slump scars suggesting slope collapse and sediment by-pass during the Early Campanian (83Ma). The eroded slope is onlapped by a sequence of laterally-derived siliciclastic turbidite siltstones and sands which onlap the nappes to the north demonstrating that nappe emplacement ended in the early Campanian. The clastics are sourced from exposed Upper Paleozoic clastics in the Huqf area. There is very little detritus from the orogen.

The Late Campanian to Maastrichtian deposition in the foredeep consists of hemipelagic chalks and marls which can be more than 1300 m thick. Influx of detrital sediments from the orogen is restricted to a strip just a few kilometers wide in front of the thrusts.  This sequence is affected by a latest Campanian tectonic uplift associated with incisions up to 150 m deep filled with redeposited hemipelagic carbonates. This event may be related to inversion in eastern Oman coinciding with slab break-off (ca 75Ma) and exhumation of the subducted continental margin in the northeast.

The foredeep along the ophiolite obduction complex was a persistently underfilled basin:  filled by hemipelagic carbonates and local clastic detritus from the forebulge. Lack of sediment input from the orogen suggest that this was mostly subaqueous. Limited uplift may be related the high density of the ophiolite slab and could be a general feature of obduction orogens. Erosion by dissolution could help explain the lack of sediment input from both the forebulge and the orogen.

How to cite: Droste, H., Levell, B., and Searle, M.: The sedimentary record of ophiolite obduction in North Oman, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4386, https://doi.org/10.5194/egusphere-egu24-4386, 2024.

EGU24-4476 | Orals | TS4.5

Discrete Element Modelling of Southeast Asia’s 3D Lithospheric Deformation during the Indian Collision 

Liqing Jiao, Frederic-Victor Donze, Paul Tapponnier, Luc Scholtes, Yves Gaudemer, and Xiwei Xu

The Indian collision has deformed the eastern Asian continent in a multifaceted way, uplifting Tibet and surrounding mountains, activating ≥ 1000 km-long strike-slip faults, and opening Tertiary rifts and oceanic basins up to ≈ 3000 km away from the Himalayas. Modelling such broad-scale tectonics has been challenging. While continent-scale, lithospheric deformation appears to have been primarily taken-up by long, narrow, inter-connected shear-zones with large offsets, the contribution of processes such as channel-flow, collapse, delamination, etc… has remained contentious. Here, based on increasing 4G (Geological, Geophysical, Geochronological, Geodetic) evidence including kinematic and timing constraints on the main mechanisms at play, we use Discrete Element (DE) Modelling to simulate and further understand the evolution of 3D strain across east Asia since the onset of collision, ≈ 55 Ma ago. The planar, 50 million km2, 125 km-thick models are scaled for gravity. The approach permits mega-fault generation and evolution without pre-arranged initial settings. The results provide insight into fault birth, propagation, and motion, as well as mountain building and plateau growth. They corroborate that continental crustal thickening across Tibet alternated with the extrusion of large blocks that rifted apart in the far field. Remarkably, without changes in boundary conditions or indentation rate, the DE model also vindicates slip reversal along initial strike-slip shear zones.

How to cite: Jiao, L., Donze, F.-V., Tapponnier, P., Scholtes, L., Gaudemer, Y., and Xu, X.: Discrete Element Modelling of Southeast Asia’s 3D Lithospheric Deformation during the Indian Collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4476, https://doi.org/10.5194/egusphere-egu24-4476, 2024.

The Tibetan Plateau has been characterized by orogen-wide crustal thickening and surface uplift, partially attributed to the underthrusting Indian model. In addition, the underthrusting Indian crust has been proposed to promote the predominant E-W extension and N-S rifting in southern Tibet. However, the influence of the underthrusting processes of the Indian crust on crustal deformation in the Tibetan Plateau remains debated. Here, we construct a series of 2D thermo-mechanical models to investigate the mechanical interactions between the rigid underthrusting Indian lower crust and its overlying Tibetan crust. The preliminary results show that pronounced decrease in N-S compressional rates in the upper crust above the front edge of the underthrusting Indian lower crust, which moves northwards with the northward slab indentation. In contrast, the shear tractions on the overlying upper crust from the interior of the underthrusting plate, alleviating the N-S compression, are relatively slight. Therefore, the numerical results indicate locally accelerated extension in the middle-upper crust of the southern Tibet in response to the northward indentation of the Indian lower crust.

How to cite: Pang, Y.: Mechanical interactions between the underthrusting Indian crust and overlying Tibetan crust: insight from 2D numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4854, https://doi.org/10.5194/egusphere-egu24-4854, 2024.

EGU24-5218 | Orals | TS4.5

High-Precision Vertical Movement of the Tibetan Plateau 

Yanqiang Wu, Guangli Su, Jingwei Li, Yajin Pang, Changyun Chen, Zaisen Jiang, and Wanju Bo

Quantitative and high-precision vertical movements are indispensable for resolving the geological diversity of the Tibetan Plateau. In this study, we proposed a joint geodetic adjustment with Helmert iteration algorithm, systematically analyzed its merits with simulated data, and then jointly processed the datasets, including 116,000 km of leveling data, 21 continuous GNSS data sets, and their connecting surveying data, to get a high-precision vertical velocity field for the Tibetan Plateau. The primary results are as follows: (a) Compared with the single leveling data adjustment, the joint Helmert adjustment results of leveling data (i.e., the leveling data and errors are generated by simulation under the first order leveling regulations, which includes 55,708 km, 4605 segments, 4584 points, 22 loops and 40 nodes) and 500 geodetic simulated data (including 2–4 mm/yr errors) demonstrate that the Helmert adjustment can reduce the residual distribution range by roughly 46%; (b) Vertical uplift is dominant on the southern, northeastern, and southeastern margins of the plateau, with uplift rate ranges of 2.0–3.0, 1.0–3.8, and 1.0–2.0 mm/yr, respectively; (c) Conspicuous subsidence is located along the southern portion of the Ganzi fault, with vertical rates ranging from −3.3 to −0.5 mm/yr; (d) Velocity profiles show that vertical deformation varies in different parts of the Tibetan Plateau, which is mostly accommodated by large strike-slip and thrust faults, such as the Kunlun, Ganzi, and Longmenshan faults. Most of the surface uplift is accommodated by crustal shortening in the interior of the Tibetan Plateau; abrupt changes in vertical rates in eastern Tibet and the widely distributed surface subsidence of southeastern Tibet are consequences of crustal flow and gravitational collapse. Overall, the Tibetan Plateau is characterized by continuous deformation, with large spatial variations accommodated by complicated tectonic processes.

How to cite: Wu, Y., Su, G., Li, J., Pang, Y., Chen, C., Jiang, Z., and Bo, W.: High-Precision Vertical Movement of the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5218, https://doi.org/10.5194/egusphere-egu24-5218, 2024.

EGU24-8376 | Posters on site | TS4.5

Numerical Simulation of the Contribution of the Longmenshan Fault to the Uplift Mechanism of Tibetan Plateau 

Wei Tao, Zhengkang Shen, and Xuhang Yang

Tibet Plateau is bordered to the east by the Longmen Shan Fault, adjacent to Sichuan Basin of the stable Yangtze Block. Across the Longmen Shan Fault zone, the topographic differential extends to 5 km, with the deep lithosphere varying by nearly 20 km. In contrast to the large strike-slip faults found within the plateau, the Longmen Shan Fault is an oblique thrust fault that shapes the plateau's boundary, enveloped in a more intricate structural and dynamic environment.

The role of the Longmen Shan Fault remains a pivotal point in the ongoing debate regarding the formation of the Tibet Plateau. We have developed a two-dimensional viscoelastic finite element model, encompassing the Longmen Shan Fault, the Tibet Plateau, and the Sichuan Basin on either side. The model simulates, over geological timescales, the thickening process of the Tibet Plateau and the activity of the Longmen Shan Fault under the influence of gravity and the pushing of the Indian plate. The results demonstrate the adjusting role of the Longmen Shan Thrust Fault in the deformation pattern at the eastern edge of the plateau, explaining the difference in the topographic and lithosphere thickness between the Tibet and Sichan Basin. The thrust Longmen Shan Fault not only contributes to cumulative crustal thickening but also plays a role in the thickening of the mid-lower crust and upper mantle viscoelastic media on the Tibet Plateau side.

How to cite: Tao, W., Shen, Z., and Yang, X.: Numerical Simulation of the Contribution of the Longmenshan Fault to the Uplift Mechanism of Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8376, https://doi.org/10.5194/egusphere-egu24-8376, 2024.

EGU24-8861 | Orals | TS4.5

Stratigraphic and tectonic setting of the Rus Formation at Jebel Hafeet, UAE. 

Alessandro Decarlis, Dominik Hennhöfer, Francesco Arboit, and Andrea Ceriani

The Rus Formation consists of a succession of carbonate rocks deposited in the Southeastern Arabian foreland system during the Paleocene-Ypresian. Throughout the UAE, the Rus Formation is commonly restricted to the subsurface of the Abu Dhabi Emirate territory, with the exception near the western front of the Hajar Mountains close to Al Ain city. At this location, the Rus Formation is exposed and forms the core of the Jebel Hafeet km-scale anticline fold. This large-scale exposure allowed us to study its stratigraphic and tectonic evolution from deposition to the present-day tectonic framework. Lithostratigraphic and facies analyses of the outcropping portion of the Rus Formation at Jebel Hafeet identified a succession of approximately 150 m of limestones and dolostones characterized by three main depositional facies:

  • platform facies, characterized by thick to massive carbonate beds with abundant shallow-water bioclasts;
  • ramp facies, showing evidence for syn-depositional instability, with mass flows and collapse structures;
  • ramp-basin facies, characterized by thin beds with marked downlapping geometries.

Thus, the studied succession forms a complete platform-to-foreland basin transition that is well-exposed along the hinge of the fold structure. The base of the Rus Formation is concealed beneath the widespread quaternary cover, whereas the top of the Rus consists of unconformable stratigraphic contact with the Dammam Formation.

During the Early Cenozoic, the depositional environment of the Rus Formation was probably subjected to far-field stress due to the migration of the foreland depocenter in response to the obduction of the ophiolite slabs onto the Arabian continental margin successions. Structural analyses of deformation features such as faults and folds and geochronological/geochemical analysis of the correlated calcite veins (U-Pb on calcite) within the Rus Formation revealed that compressive tectonics generated the main folding event and drove subsequent exhumation from c. 20 to 2 Ma. Thus, these new data suggest that the deformation and uplift of Jebel Hafeet succession occurred in the context of post-Oligocene tectonics simultaneously with the Zagros collision but were likely developed along a strike-slip system accommodating the push of the Eastern Makran Belt.

How to cite: Decarlis, A., Hennhöfer, D., Arboit, F., and Ceriani, A.: Stratigraphic and tectonic setting of the Rus Formation at Jebel Hafeet, UAE., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8861, https://doi.org/10.5194/egusphere-egu24-8861, 2024.

EGU24-9668 | Orals | TS4.5

Slab tear of subducted Indian lithosphere beneath the Eastern Himalayan Syntaxis region 

Bo Zhang, Ziqing Li, and Jinjiang Zhang

In the southeastern Tibetan Plateau, a series of region-scale dextral strike-slip shear zones play important roles in accommodating the continental collision and continental subduction during India-Asia convergence. This study provides structural, kinematic and geochronological data along the Dulongjiang shear zone, a newly recognized region-scale dextral strike-slip zone around the Eastern Himalayan Syntaxis (EHS) region. The structures and kinematic indicators record dextral lateral shearing within the zone in the Dulongjiang and Nabang regons of western Yunnan, China. The temperature range for dextral ductile shearing is estimated to be between 550 and 450 ℃, based on ductile feldspar deformation and CPO patterns of quartz in the granitic mylonites. Zircon U-Pb dating of syn-shearing leucogranites indicateds a period of dextral strike-slip movement between 30 and 18 Ma. The 40Ar/39Ar dating results from the mica fragments in mylonitic granites suggest rapid cooling since approximately 17-14 Ma. Combining these findings with previously published data on other dextral strike-slip faults/shear zones around the EHS and southeastern Asia, it is concluded that the Dulongjiang shear zone is connected with the Parlung shear zone in Tibet, the Nabang shear zone in western Yunnan and Sagaing Fault in the southeastern Asia. The Parlung-Dulongjiang-Nabang shear zone, along with other dextral strike-slip zones, forms a regional-scale Cenozoic dextral shear system around the EHS, extending into southeastern Asia. In addition, our study, in conjuncation with high wavespeed tomographic anomalies beneath the India-Asia collision zone, emphasizes the distinct evolution at lithospheric scales in  the southeastern and eastern parts of the collision zone. The intracontinental continuous strike-slip shearing indicates a tectonic transformation from extension in Tibet to block rotation around the EHS. From 30 to 18 Ma, the slab tear is associated, spatially and temporally, with a clockwise rotation and dextral strike-slip shearing around the EHS. These characteristics suggest a warmer geodynamic setting during the rotation and the influence of  a hot mantle flow associated with the tear in ongoing India lithosphere subduction. The Oligocene-Miocene dextral strike-slip shearing around the EHS and their linkage southwards with the dextral Sagaing Fault may correspond to the rotation required for the slab to bend, stretch and eventually tear beneath the EHS region.

How to cite: Zhang, B., Li, Z., and Zhang, J.: Slab tear of subducted Indian lithosphere beneath the Eastern Himalayan Syntaxis region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9668, https://doi.org/10.5194/egusphere-egu24-9668, 2024.

Anatexis (i.e., partial melting) commonly occurs during crustal thickening, post-collisional collapse or exhumation and tectonic regime transition. It plays a crucial role in the evolution processes of tectono-thermal, rheological, and deformation behavior of the continental crust in orogenic belts. Continental-scale strike-slip shear zones often record significant tectono-magmatism and dynamic deformation processes of the crustal lithosphere. However, the genetic relationships and timing among the anatexis, deformation, and initial shearing along a strike-slip shear zone have not been well defined. The Chongshan shear zone (CS-SZ) is an important hundred-kilometer-long continental scale strike-slip shear zone on the Southeastern Tibetan Plateau. The CS-SZ involved contemporaneous activity with the adjacent sinistral Ailaoshan–Red River shear zone and dextral Gaoligong shear zone during the Cenozoic. In this study, we present a combined result of detailed field, microstructural, zircon U–Pb geochronology, geochemical and EBSD texture analyses of leucogranites and migmatites in the CS-SZ. The results indicate that most migmatites and leucogranites exhibit strong shear deformation and well-developed high-temperature mylonitic microstructures. The quartz aggregated from foliated leucogranites developed dominant high-temperature prism and prism

How to cite: Li, W., Cao, S., Dong, Y., Zhan, L., and Tao, L.: Deep crustal deformation, anatexis and rheological significance of the Continental-Scale Chongshan Strike-Slip shear zone on the Southeastern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11406, https://doi.org/10.5194/egusphere-egu24-11406, 2024.

EGU24-13521 | Orals | TS4.5

Himalayan deformation and its connection to geologic hazards: cross fault examples 

Mary Hubbard, Malay Mukul, and Ananta Gajurel

As a product of continental collision, the Himalaya developed major thrust and fold structures to accommodate convergence.  With the continental subduction of the Indian continent beneath Asia, the deformation front has migrated southward over time.  The result of these tectonic and structural processes is the world’s highest mountain belt that exposes rocks of a large span of ages and has had a dynamic geomorphological evolution for the past 50-60 million years.  The Himalaya is now home to more than 53 million people.  These people face the ongoing threat of earthquakes, landslides, and floods due the active landscape in which they live.  While most earthquake events are caused by thrust fault activity, it has been recognized that there are faults that cut across the range, cross faults, that also play a role in hazards.  In the central and eastern Himalaya, cross faults have been identified where the range front transitions from salients to recesses.  Examples of these structures in Sikkim and Nepal include the Gish and Kosi faults.  Similar structures have also been identified north of the range front in the Lesser and Greater Himalayan regions.  A map of aftershock data from the 2015 earthquake shows an abrupt termination of aftershocks in the region east of Kathmandu that aligns with a proposed cross fault known as the Gaurishankar lineament.  Geophysicists suggested that a cross fault could be responsible for blocking of the lateral propagation of the thrust rupture.  The Dudh Kosi valley that drains the Khumbu or Everest region has had historic and pre-historic large landslides that may have originated on the Benkar cross fault structure.  In 2021, the Melamchi valley east of Kathmandu experienced a devastating flood that was in part tied to the reactivation of a large landslide.  That landslide site is co-located with north-south striking shear zones or cross fault structures.  While cross faults are not the major structures accommodating convergence, our work suggests that there are implications for hazard occurrence due to the presence of these structures.

How to cite: Hubbard, M., Mukul, M., and Gajurel, A.: Himalayan deformation and its connection to geologic hazards: cross fault examples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13521, https://doi.org/10.5194/egusphere-egu24-13521, 2024.

EGU24-13574 | Orals | TS4.5

Cenozoic growth of the Tibetan Plateau: insights from exhumation and geomorphology along the eastern margin 

Eric Kirby, Kevin Furlong, Xuhua Shi, Martin Danisik, Peter Kamp, Kip Hodges, and Huiping Zhang

In the nearly 50 years since Paul Tapponnier first recognized that eastward motion of Asian lithosphere played a key role in accommodating ongoing convergence between India and Eurasia (Molnar and Tapponnier, 1975, Science), the debate over the mechanical processes governing plateau growth have been a source of both inspiration and controversy.  Along the eastern margin of the Tibetan Plateau, adjacent to and north of the Sichuan Basin, a robust debate continues as to whether massifs substantially elevated above the plateau interior developed largely along upper-crustal faults or, alternatively, were built by flow and thickening in the lower crust.  We explore constraints on the timing, rates, and patterns of mountain building along the eastern margin of the Tibetan Plateau provided by over two decades of thermochronologic and geomorphologic studies.  Early models attributed mountain building along the plateau margin to extrusion along the left-lateral Kunlun fault; however, recent work has shown that slip along the Kunlun fault dies out eastward and is absorbed by deformation and rotation about the fault tip.  Rates of shortening across the plateau margin in the Longmen Shan region are low (< 1-2 mm/yr), but multi-thermochronometer relief transects (age-elevation) from three separate localities across the plateau margin imply that moderate to high rates of rock uplift and exhumation have been sustained along the plateau margin since ~30 Ma.  Forward modeling of the thermal response to exhumation reveals details of spatial differences in the exhumation history.  In the Pengguan Massif, immediately adjacent to the Sichuan Basin, these data require a two-phase exhumation history, separated by a hiatus or significant reduction in exhumation rate (Wang et al., 2012).  To the west, however, in the Xuelongbao Massif, new thermochronologic data require continuous (but temporally variable) exhumation rates >500 m/Myr during the entire late Cenozoic (Furlong et al., 2021).  Such rapid, localized exhumation coincident with high relief along the plateau margin requires a sustained influx of crustal mass at depth.

North of the Sichuan Basin, the topographic margin of the plateau is defined by the Min Shan.  The lack of a direct association between topography and upper crustal faults affords an opportunity to evaluate the patterns of differential rock uplift in the absence of inherited crustal anisotropy.  Here, correlations among topography, channel steepness, and erosion rate indicate a locus of moderate (300-500 m/Myr) erosion rate coincident with the Min Shan.  Fluvial incision rates inferred from dated strath terraces along the Bailong Jiang confirm spatial gradients in fluvial incision, with the highest incision rates (1000-2000 m/Myr) localized along the axis of the range.  This locus of incision has been sustained for 80-100 ka, and we interpret it to reflect differential rock uplift along the plateau margin.  The wavelength of rock uplift is consistent with thickening in the deep crust.  Collectively, the spatial patterns and rates of exhumation and erosion along the eastern margin of the plateau suggest that crustal thickening in the deep crust is ongoing today and may have been sustained since the late Oligocene.

How to cite: Kirby, E., Furlong, K., Shi, X., Danisik, M., Kamp, P., Hodges, K., and Zhang, H.: Cenozoic growth of the Tibetan Plateau: insights from exhumation and geomorphology along the eastern margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13574, https://doi.org/10.5194/egusphere-egu24-13574, 2024.

EGU24-14336 | ECS | Orals | TS4.5

Environmental change and stratigraphy of the Upper Triassic sediment succession in Ras Al-Khaimah, UAE 

Azeem Shah, Dominik Hennhoefer, Aisha Al-Suwaidi, Mohammed Alsuwaidi, and Thomas Thomas Steuber

In the United Arab Emirates, the Late Triassic events including the Carnian Pluvial Episode are relatively poorly studied compared to the carbon isotope excursion and extinction event at the Triassic-Jurassic boundary. This study presents an integrated approach using geochemical and sedimentological data to investigate the depositional and environmental changes through the Late Triassic into the earliest Jurassic. Upper Triassic sediments exposed in Wadi Milaha consists of the marine Milaha and Ghalilah formations. The upper part of the Milaha Formation comprises limestone (predominantly mudstones and wackestones), with subordinate sandstone, marl and shale deposited in a shallow marine environment with some evidence of high-energy shoal deposition represented by ooidal and bioclastic grainstones and packstones. Clastic input varies cyclically and correlates with higher-order sea-level fluctuations. Faunal content includes bivalves, green algae, echinoderms, and benthic foraminifers, and suggests deposition in a shallow semi-restricted to open marine environment. Elemental proxies including Fe and Mn enrichment factors show widespread oxygen deficiency during the Late Norian on this equatorial shelf of Panthalassa. The Late Norian-Hettangian Ghalilah Formation is further broken into the Asfal and Sumra members. The first of these members is dominated by floatstones and rudstones with a higher content of coarse siliciclastics, indicating deposition in regressive conditions. The Sumra Member shows a decrease in coarse siliciclastics and an increase in mudstones, wackstones and packstones indicating a transgressive sea level cycle following the sequence boundary at the top of Asfal. The XRF elemental data also indicate fluctuations in clastic input throughout the Asfal and Sumra members indicative of increased weathering fluxes likely associated with a change to more humid conditions through the Late Triassic. A loss of fauna as well as ooidal grainstones are present at the top of the Sumra Member and continue into the Sakhra Member of the Ghalilah Formation indicating the well-documented extinction at the Triassic–Jurassic boundary. These new data from the equatorial margin of Panthalassa highlight significant environmental and climatic shifts through the Late Norian to Hettangian.

 

How to cite: Shah, A., Hennhoefer, D., Al-Suwaidi, A., Alsuwaidi, M., and Thomas Steuber, T.: Environmental change and stratigraphy of the Upper Triassic sediment succession in Ras Al-Khaimah, UAE, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14336, https://doi.org/10.5194/egusphere-egu24-14336, 2024.

EGU24-16878 | ECS | Orals | TS4.5

Fracture network analysis of Jebel Madar (North Oman): new perspectives from very-high resolution Digital Outcrop Modelling 

Niccolò Menegoni, Yuri Panara, Regina Iakusheva, Juliette Lamarche, Pascal Richard, and Thomas Finkbeiner

Jebel Madar is located in the Adam Foothills of North Oman. It has been interpreted as a salt-cored, faulted anticline caused by the movement of the Precambrian-Cambrian Ara salt Fm, during the orogeny of the Oman mountains. The out-cropping Shuaiba and Natih carbonate rocks are reservoirs analogues for numerous Omani hydrocarbon fields. The maximum depth of burial is interpreted to be similar to those observed in the sub-surface fields. Therefore, Jebel Madar is considered a perfect structural analogue of fracture and fault dominated reservoirs above a salt dome in sub-surface conditions. Previous fracture studies focused mostly on the peripheral parts of Jebel Madar (i.e., Natih Fm.). Thus, fracture patterns are described as being radial, independent from regional fault and fracture pattern, and therefore, hypothesized as controlled by salt doming.

Recently, we conducted a high-resolution drone photogrammetry survey focused on the central parts of the jebel, in order (1) to update and detail fault and fracture patterns; (2) to refine our understanding of its structural evolution model; (3) to serve as a foundation for virtual reality field trips and courses.

The dataset comprises ~ 37,000 drone photographs with a total aerial coverage of ~ 6 km2 and a resolution between 3cm and 1 mm. This enables us to develop 44 Digital Outcrop Models (DOMs), with a total of ~ 10.2 billion points. This unique database allows us to quantify the fault and fracture networks of Jebel Madar, in terms of orientation, intensity and 3D arrangement. The DOMs also provide a unique opportunity to map, analyze and interpret fractures and faults that are not accessible by field geology, but only accessible by drone.

This contribution shows early results of the high-resolution Digital Outcrop Model-based fault and fracture analysis. We will illustrate the impact of mechanical stratigraphy on fracture distributions in 3D and re-evaluate the impact of regional tectonics on the structural rise of the dome.

How to cite: Menegoni, N., Panara, Y., Iakusheva, R., Lamarche, J., Richard, P., and Finkbeiner, T.: Fracture network analysis of Jebel Madar (North Oman): new perspectives from very-high resolution Digital Outcrop Modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16878, https://doi.org/10.5194/egusphere-egu24-16878, 2024.

EGU24-18476 | Orals | TS4.5

Working with Paul Tapponnier on the Structure, Age and Evolution of the Red Sea 

Jerome Dyment, Aboud Afifi, and Anne Briais

As part of his sabbatical at Schlumberger in the ARAMCO in 2008-2009, Paul Tapponnier started a complete reassessment of the plate tectonic structure, age and evolution of the Red Sea.  Public and industrial geophysical data, including gravity, magnetics, and seismics, covering the whole Red Sea, have been (re)interpreted in view of recent concepts.  This study concluded that oceanic lithosphere covers a large part of the Red Sea, although the expression of seafloor spreading in the whole ultraslow-spreading northern Red Sea and on the earlier stage of opening in the central and southern Red Sea is hidden by the thick salt cover.  We have been associated to this research between 2009 and 2013 and beyond, and will present some highlights of this exciting period.

How to cite: Dyment, J., Afifi, A., and Briais, A.: Working with Paul Tapponnier on the Structure, Age and Evolution of the Red Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18476, https://doi.org/10.5194/egusphere-egu24-18476, 2024.

EGU24-18578 | ECS | Orals | TS4.5

Testing high-resolution block modeling of the India-Eurasia collision zone with GPS, InSAR and geological fault slip rate data 

Gang Zheng, Tim Wright, Richard Styron, Jin Fang, Qi Ou, Dehua Wang, Jianghui Geng, Bin Zhao, Dongzhen Wang, and Jingnan Liu

The India-Eurasia collision zone is the largest deforming region on the planet with numerous faults and widespread earthquakes, extending from the Himalayan Front to north of the Tien Shan. Developed from plate tectonic theory, block models have long been used to describe the crustal deformation in the collision zone, and GPS data are often invoked to constrain and test the models. Although previous block models perform well against GPS data on the whole, the detailed performance in many areas of the collision zone remains uncertain due to sparsity of GPS data and the low resolution of the fault database used to define the blocks.

In this study, we process the raw GPS data collected via regional continuous GPS observation networks and Crustal Movement Observation Network of China (CMONOC) up to 2021, mainly located in Tibet, and obtain our core GPS velocity field with 420 continuous and 872 campaign stations. We further incorporate published GPS velocities, mainly located in the Himalaya and Tien Shan regions. We convert these velocities into our core solution to keep all the velocities in a consistent reference frame. As a result, we provide the densest and up-to-date GPS velocity field in the India-Eurasia collision zone including 2811 stations. Although the stations from CMONOC have been presented before, our updated velocities are more robust as they are derived from a longer time span, e.g., 5 years more than Wang and Shen [2020]. Also, we add an extra 351 stations for the collision zone compared to Wang and Shen [2020], most of which are continuous stations, over 300 of which have never been published. Wright et al. [2023] presented the first high-resolution InSAR velocity field for whole Tibet. Constraints from the InSAR data enable us to effectively evaluate the detailed performance of block modeling in Tibet, especially in the remote regions where the GPS data are sparse.

We incorporate the GPS and InSAR velocity fields, and 170 Quaternary fault slip rates into a recently-developed high-resolution block model with 237 blocks by Styron [2022] to predict block motion and fault slip rates throughout the collision zone. The block model fits the data well in general, although there are some significant residuals. The predicted slip rates along ~900 faults from the model are generally small except for those along several major faults, including the major Tibetan strike-slip faults, which have larger slip rates but still within the level of 10 mm/yr, and the Main Himalayan Thrust, which has a convergence rate at the level of about 15 mm/yr. The predicted slip rates show along-strike variations, and are consistent with previous geodetic studies. We then use our results to assess the limitations of tectonic block modelling for applications in seismic hazard assessment and in understanding the geodynamics of continental tectonics. The results suggest that tectonic strain has two modes: a few major faults exhibit focused strain and high slip rates; between these major structures, deformation is more continuous.

How to cite: Zheng, G., Wright, T., Styron, R., Fang, J., Ou, Q., Wang, D., Geng, J., Zhao, B., Wang, D., and Liu, J.: Testing high-resolution block modeling of the India-Eurasia collision zone with GPS, InSAR and geological fault slip rate data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18578, https://doi.org/10.5194/egusphere-egu24-18578, 2024.

EGU24-18604 | Orals | TS4.5

Present-day deformation rates across Oman based on space Geodesy  

Amir M. Abolghasem, Anke M. Friedrich, Faisal Al Balushi, Ismail Al Sheidi, Aseel Al Musalhi, and Yousuf Al Wardi

Oman is situated in the southeastern Arabian plate, just behind the Makran subduction zone. The internal stability of this portion of the Arabian plate must be questioned, however, based on recent studies focusing on long-term observations. These studies provide evidence of active deformation in the Hajar mountains of northern Oman and the UAE. Specifically, recent studies that focused on vertical deformation, yielded temporally and spatially variable vertical rates ranging from 0.01 to 0.89 mm/a in northeastern region of the Arabian Peninsula (Hoffman et al., 2020). Others presented evidence of the continuing uplift of some domes in the Hajar mountains. Furthermore, a significant seismic contrast is well-documented along the Makran subduction zone in Iran and Pakistan. This provides an opportunity to study whether the regional-scale uplift pattern of the Hajar mountains correlates with the variability in deformation style along the Makran plate interface or is caused by driving forces unrelated to horizontal plate motion and subduction. Monitoring the contemporary motions of the northeastern boundary of the Arabian plate can, therefore, enhance our understanding of the complex kinematics of the Makran region. Here, we provide first results of our space-geodetic study in which we combine, both, vertical and horizontal motion analysis to determine the present-day 4D-temporal and spatial strain variability across Oman.

The National Survey Authority (NSA) that runs the GNSS reference network across the Sultanate of Oman, established a continuously operating network of 47 sites in 2016. Since its establishment, the network served numerous positioning and mapping activities within the country, providing a precise tool to study the internal deformation of the southeastern Arabian plate. Six-and-a-half years of continuous data acquisition were utilized in our study, combined with 26 IGS stations, to derive horizontal and vertical displacement rates, initially in ITRF20.

A new regional reference frame for Oman was realized by rotating ITRF20 so that the horizontal velocities of the Oman CORS stations are minimized in the new reference frame ONGD23. As a result of this process, the average rigid-body rotation of the Arabian plate was estimated and eliminated. The residual velocities illustrate internal horizontal and vertical deformation across Oman, ranging from fractions of millimeters per year to a few millimeters per year. The spatial pattern varies from 1.5 mm/a subsidence in the north to 0.1 mm/a uplift in the northeast. Subsidence of 1.2 to 1.8 mm/a is documented around oil fields. The results also yield uplift rates of up to 0.8 mm/a near certain domes of the Hajar mountains. A noticeable pattern of subsidence transitioning to uplift, from west to east, is observed across the Hajar mountains. Surprisingly, however, the southern flanks of the mountains yield gradual uplift rates. The Arabia – Eurasia plate convergence cannot be directly responsible for such regional scale uplift. Additional mechanisms must be invoked to explain this enigmatic intra-plate strain.

How to cite: Abolghasem, A. M., Friedrich, A. M., Al Balushi, F., Al Sheidi, I., Al Musalhi, A., and Al Wardi, Y.: Present-day deformation rates across Oman based on space Geodesy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18604, https://doi.org/10.5194/egusphere-egu24-18604, 2024.

The geology of northern Oman and eastern Arabia is distinctive because of the emplacement of the Semail Ophiolite onto the stable Arabia platform in the late Cretaceous followed by the later development of the Jebal Akhdar and Saih Haitat domes. East of Muscat, the Wadi Kabir Fault forms an important structure along which the northern edge of the Saih Hatat domes was unroofed.  In the Bandar Jissah area, Triassic carbonates occur in the footwall of the NNE-dipping Wadi Kabir Fault while rocks of the Semail Ophiolite, newly discovered rocks of the metamorphic sole, and a sequence of Paleogene sedimentary rocks crop out in the footwall.  Some workers posit that the Wadi Kabir and associated faults form basin-bounding faults for the Bandar Jissah rift basin and that folds in the hanging wall cover sequence are the product of rollover during basin formation.

However, our detailed mapping and kinematic analysis illustrates that folds in the hanging wall are actually contractional structures that formed due to tectonic inversion along the Wadi Kabir and other faults.  The overall shortening is modest (~10%) and primarily confined to the hanging wall rocks, consistent with buttressing against mechanically rigid rocks in the footwall of the Wadi Kabir Fault.  These structures require an interval of N-S directed shortening in northern Oman  that post-dates the deposition of mid-Eocene marine sediments in the Seeb Formation. The Wadi Kabir Fault also has localized zones of listwaenite preserved in its damage zone derived from ophiolitic rocks. Collectively, the Wadi Kabir Fault is a long-lived structure that’s experience multiple episodes of extensional and contractional slip since the Paleocene.

How to cite: Bailey, C. and Driscoll, E.: Tectonic inversion in the Bandar Jissah Area: evidence for Cenozoic contraction in northern Oman, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18950, https://doi.org/10.5194/egusphere-egu24-18950, 2024.

EGU24-19309 | Orals | TS4.5

Enigmatic Kilometric Scale Diagenetic Structures of the Haushi-Huqf High, Central Oman 

Thomas Seers, Juan Carlos Laya, Amerigo Corradetti, Ryan Ewing, and Brent Miller

In this study, we present enigmatic exposures of suspected Cambrian age deposits of the Haushi-Huqf High, Central Oman. The present study area is an uplifted horst-block bounded by north-south oriented normal faults, with onlapping Mesozoic carbonate deposits on its western and eastern flanks, covering an outcrop area of ~1 km2. This exposure reveals decameter to kilometer-scale concentric, nested and coalescing ring-like structures superimposed within a clastic host rock, forming regularly spaced structural highs with lateral thicknesses and heights of one to several meters bounded by several meter wide troughs infilled with recent sediments. The host rock comprises fine to coarse grained, cross stratified quartz arenites, with basal pebbly lags, and with paleocurrents indicating a W-SW paleo-transport direction. The significant textural/mineralogical maturity of these sandstones suggests extensive recycling of older sediments, with the presence of frosted, well rounded grains signifying aeolian input. Establishing the stratigraphic position of the deposit within the regional context is challenging, owing a lack of body fossils, datable strata or correlatable stratigraphy proximal to the study site. However, Uranium-Lead Zircon dating of the host rock does reveal two geochronological populations: Neoarchaean to Paleoproterozoic (2.8-2.5 Ga), likely sourced from Precambrian basement rocks of Northern and Eastern Yemen, and Early Cambrian (~530 Ma), likely sourced from Cambrian-aged alkaline magmatism located within close proximity to the study site. Based upon the above, coupled with the observed textural, mineralogical and depositional characteristics of the deposit, we postulate that a Lower Paleozoic origin (esp. Amin Fm. Of the Haima Supergroup) is likely.

Interpreted as fluivial-plain / fluvio-deltaic in origin, these rocks exhibit bioturbation within a select interval in the form of large horizontal/vertical calcite cemented burrows, indicating marine influence and colonization by benthic macrofauna. Furthermore, a thin, laterally continuous deposit of botryoidal calcite is observed, which commonly pinches out between reactivation surfaces. We interpret this deposit as recrystallized bacterially induced precipitates of calcium carbonate, signifying the presence of microbial mats developed during a short-lived period of marine incursion. Petrographic analysis reveals that there is a strong association between the pronounced diagenetic overprint of the study area and the occurrence of this deposit. Ridges structural highs exhibit major chemical compaction and porosity collapse via the development of quartz overgrowths. Conversely, topographic lows between these structures are generally porous and poorly consolidated, being characterized by the presence of calcite cementation and hematite grain coatings. The contrasting mechanical competence of the sandstones forming the topographic highs and lows offer spatial controls over differential weathering and erosion of the study area, resulting in the remarkable diagenetic architecture observed therein. It is proposed that spatially disparate early calcite cementation associated with microbial mat colonization protected the pore system from pervasive chemical compaction, which was extensively removed by meteoric dissolution post-exhumation. The pronounced spatial organization of calcite precipitation and cementation controlling these structures poses fascinating questions regarding the self-organization of microbial mat communities during the Cambrian substrate revolution, hinting at the influence of internal feedback and environmental controls in their nucleation and propagation.

How to cite: Seers, T., Laya, J. C., Corradetti, A., Ewing, R., and Miller, B.: Enigmatic Kilometric Scale Diagenetic Structures of the Haushi-Huqf High, Central Oman, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19309, https://doi.org/10.5194/egusphere-egu24-19309, 2024.

EGU24-20189 | ECS | Posters virtual | TS4.5

Active fault growth with geologic inheritance –through the lens of earthquake rupture 

Jing Liu-Zeng, Zhijun Liu, Xiaoli Liu, Chris Milliner, Alba M. Rodriguez Padilla, Shiqing Xu, Jean-Philippe Avouac, Wenqian Yao, Yann Klinger, Longfei Han, Yanxiu Shao, Xaiodong Yan, Sarif Aati, and Zhigang Shao

Fault maturity has been proposed to exert a first-order control on earthquake rupture, yet direct observations linking individual rupture to long-term fault growth are rare. The 2021 Mw 7.4 Maduo earthquake ruptured the east-growing end of the slow-moving (~1 mm/yr) Jiangcuo fault in north Tibet, providing an opportunity to examine the relation between rupture characteristics and fault structure. Here, we combine field and multiple remote sensing techniques to map the surface rupture at cm-resolution and document comprehensively on-fault offsets and off-fault deformation. The 158 km-long surface rupture consists of misoriented structurally inherited N110°-striking segments and younger optimally oriented N093°-striking segments, relative to the regional stress field. Despite being comparatively newly formed, the ~N093°-striking fault segments accommodate more localized strain, with up to 3 m on-fault left-lateral slip and 25-50% off-fault deformation, and possibly faster rupture speed. These results are in contrast with previous findings showing more localized strain and faster rupture speed on more mature fault segments; instead, our observations suggest that fault orientation with respect to the regional stress can exert a more important control than fault maturity on coseismic rupture behaviors when both factors are at play.

How to cite: Liu-Zeng, J., Liu, Z., Liu, X., Milliner, C., Padilla, A. M. R., Xu, S., Avouac, J.-P., Yao, W., Klinger, Y., Han, L., Shao, Y., Yan, X., Aati, S., and Shao, Z.: Active fault growth with geologic inheritance –through the lens of earthquake rupture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20189, https://doi.org/10.5194/egusphere-egu24-20189, 2024.

EGU24-20331 | Posters on site | TS4.5

Building the Tibetan orogenic plateau : the dominant role of faults 

Anne Replumaz, Cédric Thieulot, Marie-Pierre Doin, and Paul Pitard

Despite decades of controversy, our understanding of the formation of the Tibetan Plateau remains limited. The role of competing mechanisms, such as distributed crustal thickening versus lateral propagation of thrust faulting at crustal or lithospheric scales, is still poorly understood. Conceptual models explaining observations at the continental scale are based on hypotheses that are hard to reconcile, on the one hand buoyancy forces dominating with low influence of upper crustal faulting, on the other hand faults dominating by favour discrete propagation of rigid upper crustal thickening since the onset of collision at ~50 Ma. However, in view of the 3D nature and temporal complexity of the involved deformation processes, it remains difficult to test the mechanical and rheological consistency, and the ability to explain observations, of end-member conceptual models at the scale of the Tibetan Plateau.

In order to generate new insights in deformation modes in Tibet, models to study the mechanical behaviour in the lower crust of the upper crustal thrust faults observed along the Tibet eastern edge, have been made, based upon recent thermo-kinematic modelling of thermochronology data (Pitard et al., 2021). We made schematic 2-D viscous models of thrusts embedded in the crust, to study eastern Tibet thrust activity in the building of the topography through time (Pitard et al., 2023). We show that both the high viscosity upper crust in which the fault is embedded and more surprisingly the low viscosity lower crust with no fault, are driven toward the surface by the fault. This generates along the fault a parallel zonation of the vertical velocity field, with high velocities close to the fault, decreasing away from it, fitting well the rejuvenation of cooling ages observed toward the thrust of SE Tibet. On the contrary, by using a model driven by an overpressure in the lower crust, we show that the obstacle halts the viscous lower crustal flow and generates a smooth exhumation gradient at the edge of the plateau, not observed in Eastern Tibet. Furthermore, in the Yalong margin region, the channel flow scenario has been related to a regional uplift of low-relief surfaces where exhumation is mainly driven by deeply entrenched river incision. By testing such scenario on the complete thermochronologic data set available for the Muli thrust, we show that incision alone is not reproducing the thermochronologic ages.

References

Pitard, P., A. Replumaz, M.-L. Chevalier, P.-H. Leloup, M. Bai, M.-P. Doin, C. Thieulot, X. Ou, M. Balvay, and H. Li (2023), Exhumation History Along the Muli Thrust—Implication for Crustal Thickening Mechanism in Eastern Tibet, GRL, 48, doi: 10.1029/2021GL093677

Pitard, P., Replumaz, A., Thieulot, C., & Doin, M.-P. (2023). Modeling deep rooted thrust mechanism of crustal thickening in Eastern Tibet. Geophysical Research Letters, 50, doi: 10.1029/2023GL104134

How to cite: Replumaz, A., Thieulot, C., Doin, M.-P., and Pitard, P.: Building the Tibetan orogenic plateau : the dominant role of faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20331, https://doi.org/10.5194/egusphere-egu24-20331, 2024.

EGU24-20743 | ECS | Posters virtual | TS4.5

 Quaternary foreland tectonics and geomorphic landscape evolution- A case study of North East Himalayan Piedmont zone, India 

Mery Biswas, Adrija Raha, and Suvashree Das

The Main Boundary Thrust (MBT) and Main Frontal Thrust (MFT) along the east–west direction have been reanalysed under the frame of the Jiti–Khuji Diana interfluve of the Himalayan foreland basin. This area is sharply dissected by three main streams under the Jaldhaka system, i.e. river Jiti, Khuji Diana, and Thaljhora, amongst which the Thalhjora flows from east to west and the other two rivers flow roughly from NNE (north-north-east) to SSW (south-south-west). The present research focuses on the control of active Thaljora and Chalsa fault scarps, which predominantly represent the monocline fault on the landscape deformation. This fault was propagated by the folding of two opposite limb directions, forming a synform that uplifted over time and formed river terraces by incision process. The linear and basin morphometric indices confirm the neotectonic activeness in addition to the deformed landform, which emerges as terrace and Doon-shaped valley in between Jiti fault (JF) and Thaljhora fault (TS). In the studied area, Thaljhora Fault Scarp is noted as Main Boundary Thrust (MBT) and Main Frontal Thrust has been noted near Chalsa (Kar et al. 2014). This study has deciphered the application of morphometric indices to indicate active tectonics with well-exposed landforms. The two tire river terraces and the reframed alluvial fans were caused by uplift and erosion sequences that were assembled by slope differentiation and flow/velocity alteration. The alluvial fan in a fan formation stretched southward and featured three well defined geomorphic units: lobes, mid-fan, and apex. These fans are categorised as mega fans and range in size from meso to micro.To ensure that the morphological units of the study's results are clearly understood, the results are summarised in a single graphical image. Artificially induced water flow with variable discharge (Q) has been tested in the field to establish a notion of an enlarged coverage area during the monsoon and flood season

How to cite: Biswas, M., Raha, A., and Das, S.:  Quaternary foreland tectonics and geomorphic landscape evolution- A case study of North East Himalayan Piedmont zone, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20743, https://doi.org/10.5194/egusphere-egu24-20743, 2024.

In seminal papers Paul Tapponnier revealed the existence of several hundred-km-long active strike-slip faults in and around the Tibetan plateau where, the India-Asia collision was expected to only produce reverse faults and folds (e.g., Tapponnier et Molnar, 1977). He latter further stressed out the role of such large strike-slip faults in the long-term building of the plateau, especially on its eastern side, (e.g., Tapponnier et al., 1982; 1990; 2001). the so-called extrusion tectonics model rises major discussions in particular on how SE Tibet evolved through time and in a more general way how the continental crust deforms. Completely different, sometime antagonistic, models have since been proposed for the geological and topographic evolution of SE Tibet, such as the channel flow hypothesis (e.g.; Royden et al., 1997; Clark and Royden, 2005). Central to this discussion are the Ailao Shan – Red River (ASRR) metamorphic belt and the eastern topographic margin of the Eastern Tibetan plateau.

The ASRR has been interpreted as a major left-lateral faults allowing the ≥500 km lateral escape of Sundaland toward the SE during the Miocene (e.g.; Tapponnier et al. 1990, Leloup et al., 1995, 2001), linked with the opening of the South China Sea (Briais et al., 1993). On the other hand, other propose that the ASRR as a limited offset and / or is an exhumed piece of a lower crustal channel (e.g. Searle, 2006; Mazur et al., 2012; Chen et al., 2023).

The eastern margin of the Tibetan plateau geological history is also disputed. It has been interpreted as a topographic step passively uplifted by eastward propagation of lower crustal channel flow during the Upper Miocene (e.g., Clark et al., 2005; Royden et al., 2008; Burchfiel et al., 2008). Other favour the existence of a ~800 km long thrust belt where thrusting take place since the Oligocene linked to crustal shortening (e.g.; Tapponnier et al., 2001; Liu-Zeng et al., 2008; Zhu et al., 2021; Pitard et al., 2021; Ge et al., 2023) in complex interaction with the Xianxuihe left-lateral fault since ~9 Ma (e.g.; Zhang et al., 2017).

At the light of the thermochronological and geochronological data allowing to better constrain the timing of exhumation and deformation in the ASRR, the Xianshuihe fault and along the Eastern Tibetan margin we will discuss how the channel flow model appear flawed and how large strike-slip fault have interacted with reverse faults to shape eastern Tibet since the Oligocene.

How to cite: Leloup, P. H.: Interaction between large strike-slip faults and reverse faulting shapes East Tibet since the Oligocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21522, https://doi.org/10.5194/egusphere-egu24-21522, 2024.

In the first phase of the International Deep Profiling of Tibet and the Himalaya the INDEPTH project an over 90 km long deep seismic reflection profile was acquired. This was an interdisciplinary program of geophysical and geological studies focus to increase the understanding of the internal architecture and mechanics of the Himalaya-Tibet region. Reprocessing of INDEPTH-I deep seismic reflection image resolves the South Tibetan Detachment System (STDS) as composed by few laterally displaced ramp structures. These can be interpreted to be structurally related to the outcropping gneiss domes. The STDS is recognized as complex extensional shear zone most probably coeval with the emplacement of the leucogranitic bodies. Geologic data indicates that the latter are pre-, syn- and post- kinematic with the deformation and, are generally controlled by the system of detachment faults (including the STDS). The interpreted STDS is broken up, and the individual segments are tilted revealing compressional deformation. Underneath, and down to 42 km depth, two prominent high amplitude, multi cyclic, north dipping events are imaged: the Tethyan Himalayan Sequence (THS) and, the Greater Himalayan Sequence (GHS). Above the GHS the north-dipping reflection fabrics appear imbricate and are seldom interrupted by weak/transparent zones. The existing geological knowledge and, the geometrical relationships (unraveled by the internal architecture constrained by the seismic image suggest that the transparent areas in the GHS could be indicative of leucogranite emplacements. Thus, the latter can be interpreted as the product of rapid exhumation of the upper GHS together with magma along the High Himalayan Thrust (HHT), repeated in-situ remelting due to strain heating by exhumation of the lower GHS and Lesser Himalayan Sequence (LHS), and extension of the South Tibetan Detachment System (STDS). This mechanism is consistent with interpretation of seismically transparent zones as the seismic response of granitic plutons.

How to cite: Carbonell, R., Li, H., Gao, R., and Lu, Z.: Revisiting the INDEPTH-I Deep seismic profile in Himalayan Orogen: Constraints on structure and leucogranites emplacement, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22363, https://doi.org/10.5194/egusphere-egu24-22363, 2024.

EGU24-193 | ECS | Orals | GM8.1 | Highlight

Repeated failures of the giant Beshkiol landslide and its impact on the long-term Naryn Basin flooding, Kyrgyz Tien Shan 

losen julie, rizza magali, nutz alexis, henriquet maxime, schuster mathieu, Rakhmedinov erkin, Baikulov sultan, Abdrakhmatov kanatbek, fleury jules, Rinterknecht vincent, and siame lionel

Earthquake-triggered landslides pose significant hazards and their long-term effects can radically reshape the local physiography but also may generate cascading risks. Indeed, a landslide could dam the river, having for consequence the formation of an upstream lake, which in turn makes the dam unstable, leading to cataclysmic flooding in the case of sudden failure. The Naryn River is one of the most important rivers in the Western Tien Shan, and major changes in its dynamics could have a significant economic impact in Central Asia and lead to political tensions over water management. Our study focuses on the Beshkiol paleo-landslide (>10km3), one of the largest in Central Asia, an overlooked hazard along the Naryn River.
Through a multi-disciplinary approach that combines detailed geomorphological, sedimentological and chronological (luminescence, cosmogenic and radiocarbon) analysis over a study area more than 130 km-long, we determined the different phases that affected the evolution of this landslide from the late Pleistocene to the late Holocene. First of all, two lacustrine sequences have been identified in the Naryn Basin, illustrating two successive periods of river damming and a lake outburst flooding. The triggering of the Beshkiol landslide occurred ~52 ka ago, led to the damming of the Naryn River and the formation of an 80 km-long lake upstream. Our chronological constraints highlight a residence time of 36,000 years, one of the longest ever documented in the world for a natural dammed-lake. This lake then drained in a cataclysmic event around 15 ka, which most likely led to the flash flooding of the downstream basin of the Naryn River (Kazarman Basin), as evidenced by very high energy deposits identified upstream of the landslide. However, shortly afterwards (less than 1,500 years), the foot of landslide was reactivated, causing the formation of a second lake, with a residence time estimated at ~7,600 years. This period was followed by a gradual emptying, and a phase of erosion that shaped the present landscape. Our results highlight that cascading events took place over the last 50,000 years and show complex interactions between the Naryn River and the largest landslide in Central Asia. Today, this landslide is categorized as inactive, but in view of the large volumes of material that can be reactivated by earthquakes or changes in precipitation, it is necessary to take this hazard into account as several thousand people living in the region could be impacted

How to cite: julie, L., magali, R., alexis, N., maxime, H., mathieu, S., erkin, R., sultan, B., kanatbek, A., jules, F., vincent, R., and lionel, S.: Repeated failures of the giant Beshkiol landslide and its impact on the long-term Naryn Basin flooding, Kyrgyz Tien Shan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-193, https://doi.org/10.5194/egusphere-egu24-193, 2024.

EGU24-426 | ECS | Orals | GM8.1

Late oligocene elevation of the Himalaya recorded by O and H isotopes of fluid inclusions 

Raphaël Melis, Gweltaz Mahéo, Véronique Gardien, Philippe-Hervé Leloup, Stéphane Scaillet, Patrick Jame, and Erik Bonjour

Since the Earth’s topography is shaped by both tectonic and climatic processes, measuring land surface elevation variations through time is of critical importance for the investigation of the multiple interactions between mountain building (orogenic) processes and long-term climate change. With a total surface area of over 5 million km2, an average elevation of 5000 m and 14 peaks over 8000 m, the Tibetan Plateau (TP) and adjacent Himalaya are particularly well suited to this research, as many models attempt to explain the growth of these high elevation regions in the context of the continental collision between India and Asia and their feedback on the Asian climate. However, the evolution of surface elevation (paleoaltimetry), whilst essential, is still elusive in the Himalaya. A number of published paleoaltimetric data hinges on the relationship between the stable isotopic composition of precipitation (δ18O and δD) and altitude. However, these methods, based on the stable isotopic composition of carbonates and phylosilicates, do not provide both δ18O and δD values and involve the use of an isotope exchange equation to calculate the composition of paleoprecipitation. To avoid such calculation, we use a method developed at LGL-TPE, which directly measure the isotopic composition (δ18O and δD) of paleoprecipitation trapped in fluid inclusions of hydrothermal quartz veins.

We measured the δ18O and δD of fluid inclusions in quartz veins within the Main Central Thrust shear zone in the Jajarkot klippe (Central Himalaya, Nepal). The δ18O of fluid inclusions varies between -3.69‰ and -9.01‰ and the δD between -43.11‰ and -74.24‰, which are consistent with meteoric water compositions. Stable isotope analysis were coupled with Ar-Ar geochronology on hydrothermal white micas that co-crystallized with quartz and indicates an age of 24.7 ± 0.2 Ma for vein formation. Taken together, these data allow us to calculate a mean elevation of the Central Himalaya of 2771 +286/-403 m at the end of the Oligocene, a period for which no previous paleoaltimetric data are available. Although already significant 25 Myr ago, the mean elevation of the Central Himalaya was nevertheless lower than the average elevation of the present topography (~5000 m), which formed at least ~16 Myr ago (e.g., Gébelin et al., 2013, Melis et al., 2023). Collectively, our data as well as previous paleoaltimetric studies provide a valuable contribution to the assessment of deformation models for the Himalayan range.

 

How to cite: Melis, R., Mahéo, G., Gardien, V., Leloup, P.-H., Scaillet, S., Jame, P., and Bonjour, E.: Late oligocene elevation of the Himalaya recorded by O and H isotopes of fluid inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-426, https://doi.org/10.5194/egusphere-egu24-426, 2024.

EGU24-682 | ECS | Orals | GM8.1

Lithological influence on bedrock incision and transience: Insights from the Aparados da Serra Escarpment, southeast Brazil 

Maurício Haag, Lindsay Schoenbohm, Scott Jess, Carlos Augusto Sommer, and Gabriel Endrizzi

Bedrock strength is widely regarded to exert major control over fluvial incision and landscape evolution. Despite that, quantifying lithological effects on natural landscapes has been extremely difficult due to limited continuous exposure at a watershed scale, especially in vegetated environments. Recent numerical models emphasize the pivotal role of rock strength in steering long-term landscape evolution, causing deviations from steady-state conditions, the formation of knickpoints, and biased erosion records. Situated along the southeast coast of Brazil, the Aparados da Serra Escarpment (lat. 28–29°S) represents a prominent geomorphological feature (>1,500 m asl) in the passive margin section of South America. Marked by a sequence of relatively weak sedimentary units overlain by relatively strong volcanic rocks, the escarpment exhibits gradual changes in the strong/weak ratio along its length due to a regional south-dipping contact. The well-constrained stratigraphy (stacked sedimentary and volcanic rocks), climatic conditions (uniform rainfall and temperature), and tectonic setting (regionally uniform and low uplift rates) make this region an ideal laboratory for investigating the influence of rock strength on river profiles. This study conducts a comprehensive series of in-situ rock strength measurements at closely spaced intervals (15 m vertical intervals between each site) along three sections across the escarpment (Rocinha at 28.8°S, Rio do Rastro at 28.4°S, and Corvo Branco at 28.0°S), covering a total escarpment segment > 100 km along strike and providing near-continuous exposure from sea level to 1,500 m asl. To this end, we perform detailed mapping along each section and use a Schmidt hammer type N to record the compressive strength of each lithological unit in the area. In addition, we also record the weathering state and fracture spacing for each site, allowing us to build the first continuous rock strength suite for a major geomorphological feature. Our resulting dataset (> 200 sites with > 30 measurements for each site) allows us to examine a long-postulated but rarely documented relationship between rock strength and bedrock channel steepness. Comparative analysis of normalized river steepness (Ksn) from adjacent watersheds (<5 km away) reveals that: (i) Ksn closely follows rock strength in all escarpment sections, and most of the major knickpoints and steepened reaches can be explained by lithological effects alone, (ii) for the same lithology/geological unit, absolute Ksn and rock strength values are the same across all the sections, (iii) even modest rock strength differences, as little as 30%, can induce changes in Ksn values and the development of knickpoints, and (iv) sedimentary rocks exhibit an increase in rock strength with age. Our results have implications for both forward and inverse landscape evolution models since autogenic knickpoints and transient reaches have the potential to mask uplift signals, particularly for slow-uplifting areas such as passive margins and cratons. These findings largely support the parametrization of lithological heterogeneities in bedrock incision models, as well as a detailed mapping when conducting relatively small-scale (< 10,000 km2) landscape evolution studies.

How to cite: Haag, M., Schoenbohm, L., Jess, S., Augusto Sommer, C., and Endrizzi, G.: Lithological influence on bedrock incision and transience: Insights from the Aparados da Serra Escarpment, southeast Brazil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-682, https://doi.org/10.5194/egusphere-egu24-682, 2024.

EGU24-714 | ECS | Orals | GM8.1

Uplift history and landscape evolution along the northwest margin of the Iranian Plateau (Talesh Mountains) in the Arabian–Eurasian collision zone 

Mohammad Moumeni, Marta Della Seta, Michele Delchiaro, Paolo Ballato, Reza Nozaem, Dmitry Tikhomirov, Marcus Christl, and Markus Egli

To comprehend the evolution of a landscape in response to intraplate crustal deformation over long timescales, it is necessary to investigate the interactions between tectonics, climate, and lithology. Isolating the role of each factor gives rise to a better understanding of landscape evolution. In this respect, the Talesh Mountains, which are a prominent tectonic range in the NW of the Iranian Plateau and formed by compressional stresses owing to the Arabia-Eurasia continental collision, provide a unique case study to explore the interplay between tectonics and surface processes. The range shows a transient landscape resulting from a combination of several tectonic events from the Eocene to the Pliocene, rainfall variability and rock strength contrasts. To date, the main governing agents of the present-day architecture of landscape have not been fully studied. We therefore combined geomorphological field surveys with quantitative analyses of the regional topography, geomorphology and stability of the main drainage divide, stream profile analysis and denudation rates using meteoric 10Be to decipher the surface deformation, uplift mechanism and drainage divide evolution. Additionally, an inverse modelling of the river longitudinal profiles was performed to reconstruct the base level fall history of the region, providing insights into the timing of the rock uplift rates and geodynamics of the NW margin of the Iranian plateau. Our results document contrasting erosion rates ranging from ⁓ 100 to 400 m/Myr, with lower values in the more arid plateau interior, and higher values on the wetter plateau exterior. These rates correlated well with topographic metrics. The spatial pattern of erosion rates showed that the drainage networks of the eastern flank of the range, and along the plateau margin are eroding about twice as fast as those in the plateau interior. These contrasting erosion rates triggered the divide migration towards the plateau interior. Our inverse modelling of river longitudinal profiles of the plateau exterior indicated a progressive increase in the relative rock-uplift rates which reached its peak to ⁓0.5 mm/yr from ⁓5 to 3 Ma. For these documented uplift rates there are two different processes: (i) a kilometer-scale base level drop of Caspian Sea driven by eustasy and changes in regional tectonics, and (ii) localized thrusting and rock uplift along the eastern flank of the range. The combined effect of these processes results in a significant relative base level fall. This event accelerated the bedrock river incision in the Talesh Mts. The differences in erosion rate across the divide are indicative of a long-wavelength morphological disequilibrium and landscape transience in response to asymmetric uplift and feedback of surface processes driven by climate together with lithological characteristics.

How to cite: Moumeni, M., Della Seta, M., Delchiaro, M., Ballato, P., Nozaem, R., Tikhomirov, D., Christl, M., and Egli, M.: Uplift history and landscape evolution along the northwest margin of the Iranian Plateau (Talesh Mountains) in the Arabian–Eurasian collision zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-714, https://doi.org/10.5194/egusphere-egu24-714, 2024.

EGU24-953 | ECS | Posters on site | GM8.1

Tectonic and climatic controls on terrace preservation in a large Himalayan river catchment 

Eliot Weir, Fiona Clubb, Alex Densmore, and Martin Hurst

Terraces are important archives of past environmental conditions, recording variations in both climate and tectonics on thousand-to-million-year timescales. For example, fill terraces in large mountain ranges may contain repeated deposits from large scale debris flow or landslide events, or may deform in response to gradients in tectonic uplift rate. However, our knowledge of the geographical extent of Himalayan terraces is currently very limited. This hinders our understanding of the spatial and temporal patterns of extreme hazard events such as large landslides, major earthquakes, and glacial lake outburst floods. Our limited understanding of Himalayan terraces may be a consequence of low preservation potential due to erosional processes within a rapidly uplifting mountain range. Even a comprehensive assessment of terraces in an area may not provide a complete archive of depositional processes as terraces can be destroyed or modified. Alternatively, terraces may be present, but difficult to recognise in the field or to manually identify from aerial photographs or satellite imagery. An automatic method for identifying river floodplains and terraces has recently been developed (Clubb et al, 2017). Using this method, we identify terraces at a catchment scale for the first time within the Gandaki catchment of central western Nepal using the 12m TanDEM-X digital elevation model. We explore the spatial pattern of terraces along the long profiles of each major river within the catchment by calculating the total terrace area adjacent to the channel. We then attempt to link terrace preservation to tectonic drivers by analysing the relationship between terrace exposures and channel steepness, knickpoints and major structural boundaries along the river profile. Coupling an analysis of spatial patterns in terrace preservation with the shape of terrace profiles downstream compared with the modern channel allows for investigation into whether terrace preservation is controlled by long term tectonic forces or stochastic high magnitude flooding events. We find that terrace preservation within the Gandaki catchment is largely tectonically controlled, with terraces mostly preserved directly upstream of major tectonic structures such as the Main Frontal Thrust, the Main Boundary Thrust and within the Thakkhola-Mustang Graben. However, we link a pattern of preserved terraces directly south of the Main Central Thrust to the stochastic occurrence of high magnitude debris flow events. These highly elevated terraces decrease in downstream elevation compared with the modern channel, are unconstrained by downstream tectonic structures and source from the steep topography of the High Himalaya. Our work demonstrates the potential of automated terrace extraction techniques for understanding controls on sediment storage and dynamics across actively uplifting mountain ranges.

How to cite: Weir, E., Clubb, F., Densmore, A., and Hurst, M.: Tectonic and climatic controls on terrace preservation in a large Himalayan river catchment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-953, https://doi.org/10.5194/egusphere-egu24-953, 2024.

The Himalayan-Tibetan Plateau presents an exemplary setting to explore the intricate interactions among tectonics, erosion, and climate. Since achieving its elevated stature in the Miocene, the plateau's landscape has undergone significant transformation, largely influenced by several major rivers. The Yarlung Tsangpo River, the largest river on the plateau, has been instrumental in this geomorphic evolution. Throughout the Neogene and Quaternary periods, this river has facilitated the extensive removal and transportation of massive rock volumes from the plateau into the southern Himalayas. Consequently, it has profoundly affected the patterns and intensities of erosion and uplift within the orogenic system, contributed to the reorganization of river networks, and influenced sedimentary processes in the adjacent foreland basin. Nevertheless, the specifics of river erosion evolution process in southeast Tibet and its driving factors remain a subject of considerable debate.

 

In this study, we present an in-depth analysis of both long- and short-term denudation processes in southeast Tibet, particularly along the Yarlung Tsangpo River. The long-term denudation history is elucidated through exhumation rate simulations derived from published low-temperature thermochronological data. Near the hanging wall of the Woka normal fault (upstream), the data indicates an average exhumation rate of 0.23 km/Ma, predominantly from samples older than 10 Ma. In contrast, the footwall experienced an initial rapid exhumation phase around 10.25 ± 0.81 Ma, with rates approximating 0.53 km/ myr. This rate was comparatively steady at 0.31 ± 0.01 km/ myr further from the fault. Subsequently, at 7.12 ± 0.36 myr, the exhumation rate increased to 0.42 ± 0.02 km/myr. Post 5 Ma, rapid exhumation, reaching rates of 0.57 ± 0.05 km/ myr, was confined to the Jiacha Gorge, continuing up to ~1 Ma as indicated by AHe dating. Short-term erosion processes were assessed through millennium-scale catchment erosion rates, determined by cosmogenic nuclide analyses of river sediments. A sample from the hanging wall of the Woka normal fault indicated a catchment-wide erosion rate of 19.9 m/myr. Conversely, samples from outside the Jiacha Gorge, including two from main river tributaries and two from secondary tributaries, demonstrated significantly higher erosion rates, ranging from 47.5 to 67.3 m/myr.

 

Subsequently, we employed 3D thermo-kinematic modeling to reconstruct the region's topography as it appeared approximately 15 million years ago, integrating both long-term exhumation and short-term erosion rates. The model suggests the formation of a peneplain in southern Tibet around 15 Ma, after notable uplift in the early Miocene and substantial exhumation between 20 and 15 Ma. The drainage patterns during this period in southern Tibet likely differed markedly from the present, as the eastward-flowing Yarlung Tsangpo River had not yet formed. It is hypothesized that the river flowed directly towards the Himalayan foreland until around 6 Ma. At this time, the river channel was altered through capture by the Jiacha Gorge, redirecting its flow eastward.

How to cite: Shen, T., Wang, G., and Miao, S.: Multi-stage river incision processes since 15 Ma and the formation of the Yarlung Tsangpo River in the southeast Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2715, https://doi.org/10.5194/egusphere-egu24-2715, 2024.

EGU24-2774 | ECS | Posters on site | GM8.1

Hillslope-controlled incision thresholds shape mountain range topography of the Northern Andes 

Richard Ott, Dirk Scherler, Kimberly Huppert, Jean Braun, and Mauricio Bermudez

Rivers have long been regarded as the drivers of mountain landscape evolution, with hillslopes following suite. In this view, rivers set the rate of base-level change at the bottom of hillslopes that passively adjust their geometry to attain a matching hillslope denudation rate. Hence, most large-scale landscape evolution studies focus on analyzing metrics of the river network, such as normalized river steepness (ksn). More recently, it has been recognized that ksn may depend on incision thresholds, a critical shear stress or unit stream power required to erode bedrock, which depend on sediment cover. In this study, we use previously published cosmogenic-nuclide derived erosion rate data from the Northern Andes to investigate how hillslope sediment delivery, controls incision thresholds and the first-order topography of two adjacent mountain ranges with different lithology.

Our results suggest that the exponent of the power law between ksn and erosion rate, which we refer to as topographic insensitivity, is twice as high in the sedimentary rock-dominated Eastern Cordillera compared to the crystalline rock-dominated Central Cordillera. This generally means that in the Eastern Cordillera, spatial differences in erosion rate, e.g. induced by tectonic gradients, will only result in minor differences of river steepness compared to the Central Cordillera. We use river width measurements, discharge data, and channel grain size data to constrain a stochastic threshold incision model. Our results indicate that the difference in the erosion rate- ksn relationship can be explained by a 26 times higher incision threshold in the Eastern Cordillera. This difference in topographic insensitivity caused by incision thresholds cannot solely be explained by factors such as discharge variability, river width to discharge scaling, or channel grain size. However, we find a significantly higher landsliding frequency in the Eastern Cordillera that causes transient channel covering and damming, leading to a lower sensitivity of ksn to erosion rate. These findings highlight how hillslope-controlled sediment delivery can modify the stream response to tectonic uplift and exhibit a first-order control on the landscape evolution of adjacent mountain ranges.

How to cite: Ott, R., Scherler, D., Huppert, K., Braun, J., and Bermudez, M.: Hillslope-controlled incision thresholds shape mountain range topography of the Northern Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2774, https://doi.org/10.5194/egusphere-egu24-2774, 2024.

EGU24-4046 | ECS | Posters on site | GM8.1

The influence of sediment isostatic adjustment on sea-level change and its records along the coast of Taiwan 

Andrew Ho, J. Bruce H. Shyu, Eh Tan, and Ken L. Ferrier

Information of sea-level change history is crucial for the understanding of tectonic movements along coastal areas.  Locally, changes in sea-level may be influenced by sediment isostatic adjustment (SIA) that results from erosion and deposition and perturbs crustal elevation and the Earth’s gravitational field.  However, many previous studies on coastal uplifts neglected such effects.  In this study, we utilized gravitationally self-consistent sea-level model to quantitatively analyze how SIA affected the sea-level during the last glacial-interglacial cycle around Taiwan, where erosion and deposition are among the fastest in the world.  We constructed a time-variant sediment transfer history for Taiwan and used it, together with published ice loading history over the past 122 kyr, as input to drive the sea-level model.  To build a comprehensive sediment model, we combined erosion and exhumation rate data derived from cosmogenic nuclides, detrital zircon fission-track, and fully reset apatite fission track ages to construct the erosion rate map.  In addition, we compiled age data from both on-land and offshore sediment cores, and isopach map derived from submarine seismic profiles to generate the deposition rate map.  The modeling results show that SIA would cause significant spatial variations in sea-level history along the coast of Taiwan.  For example, along the eastern coast, isostatic uplift due to the high rate of erosion of nearby mountains induces sea-level fall, whereas isostatic subsidence resulting from deposition may surpass the effect of erosion and lead to sea-level rise along the southwestern coast.  This may be the first observation of completely different isostatic patterns of coastlines occurring in such a short distance, likely owing to the extremely rapid sediment redistribution and the relatively thin elastic lithosphere of Taiwan.  Furthermore, the effects of SIA may produce sea-level variations in the order of meters to tens of meters since 10 ka, and up to tens to more than two hundred meters since 122 ka along Taiwan’s coast.  Without the consideration of SIA effects, the estimation of tectonic coastal uplift rates may be overestimated or underestimated by up to 60% and 90%, respectively, along some coast of Taiwan.  Our results highlight the importance of considering SIA processes when using paleo-sea-level indicators to characterize tectonic movements along the coast, especially in regions with rapid erosion or deposition.

How to cite: Ho, A., Shyu, J. B. H., Tan, E., and Ferrier, K. L.: The influence of sediment isostatic adjustment on sea-level change and its records along the coast of Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4046, https://doi.org/10.5194/egusphere-egu24-4046, 2024.

EGU24-4055 | ECS | Posters on site | GM8.1

Formation of the Hukou waterfalls by entrenchment due to a downstream integration process 

Hao Liang and Ke Zhang

Waterfall represents a pulse of erosion by lowering the local base level, and produces fluvial terraces that serve as an agent to transfer tectonic, climatic, or autogenic signals upstream through a catchment. Although widespread creation, well-dated waterfalls in the trunk of world’s large river are numbered. This has led to rarity of trunk waterfall case studies, obscuring the resulting landform impacts during waterfall migration and therefore, hindering the exploration of their origins and mechanism. The Hukou Waterfall, situated downstream of the Jinshaan Gorge in the middle reach of the Yellow River, is a unique trunk waterfall. With its homogenous tectonic and bedrock conditions, no anthropogenic activities, and preserved fluvial terraces by retreating waterfall, the Hukou Waterfall provide opportunities to replicate the upstream migration process and associated landform response. Herein, we applied detailed field and DEM-based measurements and age constraints to construct dated longitudinal profiles throughout the Hukou Waterfall and downstream Jinshaan Gorge. We replicate two paleo-trunk in longitudinal profiles: (1) relatively low diachronous trunk (Ta) aged headward from ca. 245 ka to present-day with an average retreating rate and incision rate of 24.5 cm/a and 27.5 cm/ka, representing waterfall migration; and (2) relatively high isochronous trunk (Tb) aged ca. 2.5 Ma throughout the downstream of the gorge with a slow incision rate (8.0-8.7 cm/ka) occurred between Ta and Tb, suggesting a slow slip rate of bounding fault at the outlet of the Jinshaan Gorge. Replication of Ta shows analogous slope of riverbeds with Tb, implying that no waterfall commenced until ca. 245 ka in the downstream of Jinshaan Gorge. This study hypothesizes the Hukou Waterfall to have formed as a mid-Pleistocene rapid base-level-lower event. This event is likely ascribed to the entrenchment due to an integration process between the Fenwei Basin (local base level of the Jinshan Gorge) and the Sanmen Gorge (further downstream of the Fenwei Basin), which exposed the subsurface bedrock scarp produced by the faults accumulate slip.

How to cite: Liang, H. and Zhang, K.: Formation of the Hukou waterfalls by entrenchment due to a downstream integration process, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4055, https://doi.org/10.5194/egusphere-egu24-4055, 2024.

EGU24-4481 | Posters on site | GM8.1

A Comparative Analysis of Fluvial Propagation and Divide Migration in the Liqiu River Basin, Eastern Tibet 

Wei Wang, Jinyu Zhang, and Jing Liu-Zeng

     The assessment of rock uplift and climatic conditions through channel profiles traditionally relies on the assumption of topographic equilibrium. Nevertheless, there is a growing acknowledgment that landscapes frequently transition away from this equilibrium as a result of shifts in boundary parameters, such as base-level changes, climatic fluctuations, drainage network reconfigurations, or tectonic activities. Notably, the dynamic nature of drainage divides can introduce substantial disequilibrium into the profiles, severing the tight linkage between channel morphology and the spatiotemporal distributions of tectonic uplift, climatic conditions, or lithologic resistance. It is therefore vital to quantify the rates of river network adjustment and drainage divide migration to fully unravel the complex narratives of landscape evolution, as well as evaluate the influence of mobile divide mobility on the interpretation of river profiles in tectonically active settings.

      In the context of this research, we utilized a topographic index alongside 10Be-derived catchment-wide denudation rates to explore how river channels and drainage divides of the Liqiu River in Eastern Tibet adapt to environmental and tectonic forces. Our discovery reveals a significant temporal lag, with divide migration occurring at a pace roughly tenfold slower than that of river channel adjustments. Despite the continuous movement of divides, the channels' swift morphological response broadly maintains their fidelity as indicators of regional uplift, climatic perturbations, and bedrock characteristics.

How to cite: Wang, W., Zhang, J., and Liu-Zeng, J.: A Comparative Analysis of Fluvial Propagation and Divide Migration in the Liqiu River Basin, Eastern Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4481, https://doi.org/10.5194/egusphere-egu24-4481, 2024.

EGU24-5153 | ECS | Orals | GM8.1

Monazite fission-track thermochronology as a possible proxy for low-magnitude erosion 

Gilby Jepson, Barbara Carrapa, Sean Jones, Barry Kohn, Andrew Gleadow, Sarah George, George Gehrels, Caden Howlett, and Antoine Triantafyllou

Conventional low-temperature thermochronology can resolve cooling typically associated with ~2 – 6 km of erosion. Lower magnitudes of erosion produced by surface processes and climatic variations are often difficult to quantify. Here, we apply a new, low-temperature thermochronometer (closure temperature <50 – 25 °C), monazite fission-track (MFT), to the Catalina-Rincon metamorphic core complex, Arizona, USA which has a well-constrained tectonic and paleoclimatic history. In the Catalina-Rincon, traditional low-temperature thermochronology (apatite and zircon fission-track and apatite and zircon [U-Th-Sm]/He) record timing of cooling related to metamorphic core complex detachment faulting and subsequent Basin and Range normal faulting (26 – 20 Ma and 15 – 12 Ma, respectively). We collected two monazite fission-track age-elevation profiles across southwestern and northeastern extent of the Catalina-Rincon. The southwestern profile (~ 1000 m relief) records a Plio-Pleistocene age-elevation trend, with older ages at higher elevations (4.5 – 1.5 Ma). Whereas the northwestern profile (~ 500 m) records a late Miocene-Pleistocene age-elevation trend, also with older ages at higher elevations (8.1 – 2.0 Ma). Across the two profiles these ages do not correlate with known tectonic activity in the region, they are consistent with Pliocene intensification of the North American Monsoon. However, such a low closure temperature could suggest that fission-tracks in monazite are not stable at surface temperatures and lie in the partial annealing zone.  Despite this concern, we attribute Plio-Pleistocene thermochronometric ages to record climate-enhanced erosion during a known period of enhanced precipitation. These results suggest that MFT has potential for dating low-magnitude erosion associated with climate and relief-forming processes.

How to cite: Jepson, G., Carrapa, B., Jones, S., Kohn, B., Gleadow, A., George, S., Gehrels, G., Howlett, C., and Triantafyllou, A.: Monazite fission-track thermochronology as a possible proxy for low-magnitude erosion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5153, https://doi.org/10.5194/egusphere-egu24-5153, 2024.

Force-balance models show that the stress state at active continental margins is largely controlled by the gravitational force and the megathrust shear force and remains unchanged as long as subduction proceeds undisturbed. Glacially induced changes in mountain topography and mass redistribution by glacial erosion, sediment transport and deposition alter the force balance but the impact on the upper-plate stress state and tectonics remains quantitatively poorly constrained. Here, we use numerical force-balance models (Matthies et al., 2024) and investigate upper-plate stress changes resulting from (i) a reduction in mountain height in the arc by glacial erosion, (ii) a steepening of the arc front, (iii) a decrease in the megathrust shear force due to increased sediment subduction and fault weakening, (iv) an increase in sediment thickness in the trench, and (v) the load of an ice cap. Our model results show that each process causes distinct stress changes that affect different parts of the upper plate. The largest stress changes result from a reduction in mountain height, which increases the deviatoric compression in the arc, and a decrease in megathrust shear force, which reduces the deviatoric compression in the entire upper plate. Smaller stress changes occur for a steepening of the arc front, increased sediment deposition in the trench and the load of an ice cap. The different stress changes may promote or suppress faulting in different parts of the upper plate. Application of our model to the North Patagonian Andes indicates that glacial erosion during late Cenozoic cold periods may have localized the deformation in the arc interior but did not significantly reduce the mean elevation of the mountain range. Moreover, the reduced activity of thrust faults in the forearc and backarc likely reflect reduced compression of the upper plate due to a decrease in megathrust shear force.

 

Matthies, F., Dielforder, A., & Hampel, A. (2024). Force-balance modelling of the impact of glacial erosion, trench sedimentation, megathrust weakening and glacial loading on the stress state of the crust at active continental margins. Tectonophysics, 871, 230180. https://doi.org/10.1016/j.tecto.2023.230180. 

How to cite: Dielforder, A., Matthies, F., and Hampel, A.: Effects of glaciations on the tectonics of active continental margins: Insights from force-balance models and implications for the North Patagonian Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5229, https://doi.org/10.5194/egusphere-egu24-5229, 2024.

EGU24-5304 | ECS | Posters on site | GM8.1

The validity of river steepness as a proxy for erosion rates 

Xianjun Fang and Sean D. Willett

River steepness (Ks) is a crucial geomorphic metric used to characterize river slope, normalized by local river drainage area. According to many erosion laws, Ks should be proportional to erosion rate, offering insights into the dynamic processes of landscape evolution. This relationship is complicated by spatial and temporal variations in precipitation rate. To address this issue, modern precipitation-corrected river steepness (Ksp) has been adopted and used as a proxy for erosion rates. However, the utilization of modern precipitation rates may not be entirely suitable to assess erosion rates over the timescales at which river profiles form, spanning thousands or even millions of years, due to temporal changes in precipitation rate, including those driven by glacial-interglacial cycles. To test the viability of river steepness as a proxy for erosion rates under conditions of time-dependent precipitation, we develop a 1-D longitudinal river profile model incorporating periodic precipitation fluctuations and apply this analysis to river profiles of the Three Rivers Region (TRR) in the Southeastern Tibetan Plateau. 

This model calculates Ks and Ksp as well as instantaneous erosion rates(Ein) and erosion rates as measured by time-averaging cosmogenic isotope concentrations (Ecos) on river profiles subjected to Milankovic-cycle precipitation fluctuations. Based on this model, we propose a new metric, mean precipitation-corrected river steepness (Kspm), which is corrected by both local river drainage area and mean precipitation over glacial-interglacial cycles. We find that the precipitation oscillation introduces scale-dependent effects on Ksp, Ein, and Ecos with the variation in Ecos being smaller than in Ein. Ks is largely unaffected by cyclic changes in precipitation but is dependent on mean precipitation levels. In contrast, Kspm remains constant despite fluctuations in precipitation and is not dependent on mean precipitation rates. Hence, Kspm emerges as a preferable indicator to correct precipitation dependence on river steepness. There remains a bias in the measured erosion rates that is dependent on the phase of the imposed precipitation rate.

We examine the three kinds of river steepness to the rivers in the TRR and compare the steepnesses of the trunk rivers and the major tributaries. The south-north trends in tributary basin-averaged river steepness and trunk river steepness are generally similar in pattern, but the tributaries are steeper than the corresponding trunks unless an unusually large concavity parameter is selected for the analysis. The steepest segments of normalized Ksp and normalized Kspm are located further south than those of normalized Ks. This observation suggests an influence of precipitation on river steepness, pointing out the potential bias on measured Ks. For the same trunk segments, the variation of the corresponding tributary basin-averaged normalized Kspm is smaller than that of normalized Ksp, which suggests that some noise in the tributary steepness is a consequence of glacial-interglacial precipitation variation, which can be removed through the use of Kspm. We propose that normalized Kspm is a better metric for long-term erosion rates, but more erosion data are still needed to confirm the use of these metrics as proxies for erosion rates. 

How to cite: Fang, X. and Willett, S. D.: The validity of river steepness as a proxy for erosion rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5304, https://doi.org/10.5194/egusphere-egu24-5304, 2024.

EGU24-5314 | ECS | Orals | GM8.1

Increasing fluvial incision rate in the southern Jinshan Gorge from tributary terraces and river network analysis 

Yuezhi Zhong, Vincenzo Picotti, Jianguo Xiong, Sean Willett, Christoph Schmidt, and Georgina King

Base level fall on a tributary is genetically related to its trunk channel incision, and analysis of tributaries thus provides information of the trunk channel evolution history. In the middle Yellow River, for example, several integration processes were proposed and should be consistent with river terrace data from the trunk channel. We investigate the rates and spatiotemporal variations of incision along the Jinshan Gorge in the middle Yellow River with dated strath terraces from its tributaries. The incision rate for six tributaries along the Jinshan Gorge is constrained using mapped and dated terraces. By comparing terraces of similar age, we find generally decreasing incision rates from the confluence with the trunk river to upstream within a tributary in the southern Jinshan Gorge. Decreasing incision rates are also observed among tributaries from south to north along the gorge. The results independently confirm the spatial pattern from “pseudo-terraces” derived from channel profile modeling. This interpretation reinforces the previous proposal that paleo-lake regressions in the Weihe Graben or integration with the Hetao Graben are unlikely to have been responsible for recent incision. An estimation method with terrace data within a tributary of erodibility coefficient, K, a crucial parameter for river profile inversion analysis, is also provided. K is recalibrated to be 1.03 10-5 m0.3/a with all terrace data. With an assemblage of published terrace data along the Jinshan Gorge, we suggest a re-examination of published terrace ages, which may help unravel the mysterious evolution history of the middle Yellow River.

How to cite: Zhong, Y., Picotti, V., Xiong, J., Willett, S., Schmidt, C., and King, G.: Increasing fluvial incision rate in the southern Jinshan Gorge from tributary terraces and river network analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5314, https://doi.org/10.5194/egusphere-egu24-5314, 2024.

EGU24-6089 | Posters on site | GM8.1

The rapid surface uplift of the Eastern Alps. Evidence from cosmogenic nuclides and mapping of elevated low relief surfaces 

Kurt Stüwe, Jörg Robl, Lukas Plan, Derek Fabel, Fin Stuart, and Gerit Gradwohl

Surface uplift of the Eastern Alps is generally considered to have occurred more or less continuously over the last 30 Ma. During this period, the interplay of many kilometres of rock uplift and erosion has resulted in surface uplift of some 2-3 kilometres. However, reference frames that allow rock uplift and surface uplift to be distinguished are often hard to identify. Surface uplift rates can be determined in regions where erosion did not occur. That is classically done by the identification and dating of relicts of ancient base levels. In the Eastern Alps a suite of discrete elevated low relief landscapes (ELRLs) are present up to 3000 m surface elevation that have been identified as relicts of base levels.

 

In this contribution we present a map of these ELRL landforms for much of the Eastern Alps and report cosmogenic 10Be, 21Ne and 26Al nuclide data from fluvial sediments sampled from 50 caves that are interpreted to have formed at the same time as the ELRL paleosurfaces. The samples that are interpreted to have been deposited during cave formation at the vadose-phreatic transition. As such, they form markers for base level and the time of their deposition in the cave may be interpreted as the time the cave was at base level. Our data indicate that the uplift rate of the Eastern Alps may be in the order of 200 – 500 m per million years for much of the Pliocene. This is significantly faster than previously thought and implies that much of the surface uplift of the Eastern Alps may have occurred since the late Miocene.

How to cite: Stüwe, K., Robl, J., Plan, L., Fabel, D., Stuart, F., and Gradwohl, G.: The rapid surface uplift of the Eastern Alps. Evidence from cosmogenic nuclides and mapping of elevated low relief surfaces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6089, https://doi.org/10.5194/egusphere-egu24-6089, 2024.

EGU24-6121 | Posters on site | GM8.1

Old orogen - young topography: erodibility contrast as superior control of relief rejuvenation in the Bohemian Massif? 

Jörg Robl, Kurt Stüwe, Fabian Dremel, Christoph von Hagke, and Derek Fabel

Although the topography of the Variscan orogen was largely leveled in the Permian, outcrops of Variscan rocks occur in the form of several low mountain ranges forming tectonic windows framed by Neogene sediments. The Bohemian Massif is one of these low mountain ranges and consists of high-grade metamorphic rocks and magmatic intrusions that dip towards the south under the weakly consolidated Neogene sediments of the Molasse Basin. Timing and rates of Neogene uplift of the region are largely unconstrained, but the occurrence of marine sediments several hundred meters above sea level is a clear indication of significant surface uplift during the last few million years. Morphologically, the Bohemian massif is characterized by rolling hills and extended planation surfaces above 500 m that are contrasted by deeply incised gorges with steep and morphological active valley flanks. The central ridge of the Bohemian Massif forms a continental divide with the Vlatava and the Danube draining the northern and southern part of the mountain range. To constrain the pattern of landscape change and its rates, we computed topographic metrics and determined catchment-wide erosion rates from the concentration of cosmogenic 10Be in river sands.

The morphometric analysis indicates an out-of-equilibrium landscape. River length profiles feature knickpoints abundantly at elevations of about 500 m separating steep channel segments at lower elevations from less steep channel segments at higher elevations. Hypsometric maxima near knickpoint elevations along with high and low values in geophysical relief down- and upstream of major knickpoints testify of a bimodal landscape. The continental divide shows a distinct asymmetry, which is expressed by across-divide gradients in channel steepness.  The higher average channel steepness within the southerly Danube catchment predicts the northward migration of the Danube-Vltava drainage divide. Erosion rates of 20 to 50 m per million years in the 20 catchments studied are very low compared to the Alps and appear to contradict the steep topography close to the receiving streams. The lowest erosion rates occur in catchments with a large proportion of low relief areas at medium altitudes. The highest erosion rates occur in elongated catchments of Danube tributaries whereby these basins also have a large proportion of low gradient topography.

Based on our results we suggest that the Bohemian Massif was affected by low but long-lasting uplift without significant gradients between the Bohemian Massif and the nearby Molasse Basin. In our model, the occurrence of contrasting bedrock properties between Neogene sediments of the Molasse Basin and the crystalline basement represents the superior control on the topographic evolution of the entire region. As the river incision progresses, there is a transition from easily erodible sediments to the much less erodible crystalline rocks below, which abruptly reduces the ability of a river to incise. Consequently, relief forms and channel gradients increase until the erosion rate can balance out the uplift rate. We suggest that the Bohemian Massif is currently at such a transient state, which is expressed by landscape bimodality, where the two contrasting landscape types are separated by upstream migrating knickpoints.

How to cite: Robl, J., Stüwe, K., Dremel, F., von Hagke, C., and Fabel, D.: Old orogen - young topography: erodibility contrast as superior control of relief rejuvenation in the Bohemian Massif?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6121, https://doi.org/10.5194/egusphere-egu24-6121, 2024.

The rapid collision between the continental margin of the Eurasia Plate and the Luzon Arc on the Philippine Sea Plate has built the island of Taiwan. The suture zone of the arc-continental collision that divides the Coastal Range to the east and the Central Range to the west is called the Longitudinal Valley. The Central Range and the Longitudinal Valley are bound by the Central Range Fault, which has long been proposed as an active fault. Still, limited field evidence of its activity has prevented us from comprehensively understanding its fault trace, geometry, and faulting mechanism. Surface ruptures caused by the 2022 Taitung Earthquakes revealed that the Yuli Fault, which also ruptured in the 1951 earthquakes, is a west-dipping fault and belongs to the Central Range Fault. This event thus brought the Central Range Fault back into the spotlight. In this work, we looked for potential geomorphic signatures associated with the fault activity using geomorphic indicators such as channel steepness, channel width, and grain size distribution of sediments in the main drainage basins along the middle part of the eastern Central Range. The channel width was determined by mapping the channel borders using SPOT images captured in 2003 and 2022 to determine the potential variance induced by recent mass-wasting events. In addition, we collected detrital sediment samples from these basins to derive basin-wide erosion rates based on in-situ 10Be concentrations. We combined all these results to discuss the evolution of the landscape in response to the activities of the Central Range Fault.

How to cite: Chen, C.-Y., Willett, S., Haghipour, N., and Christl, M.: The tectonic activity of the Central Range Fault in Taiwan: insights from patterns of erosion rate and geomorphic evidence in the eastern Central Range, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6234, https://doi.org/10.5194/egusphere-egu24-6234, 2024.

EGU24-6732 | Posters on site | GM8.1

Temporal deceleration of fluvial incision since the Middle Pleistocene along the Salween-Nu River in southeast Tibet 

Jinyu Zhang, Wei Wang, Huili Yang, Xianyang Zeng, and Zhaowu Guo

Fluvial terraces record intermittent river aggradation and down cutting regulated by the competition between stream power and sediment supply. Therefore, reconstructing the magnitude and rate of fluvial incision can provide insights into the interaction of tectonics, surface processes and climate change in shaping the landscape. The southeast Tibetan plateau is characterized by gently-dipping topography and deeply incised valleys with inset levels of fluvial terraces along the Salween, Mekong, and Yangtze Rivers. In this study, we focused on fluvial terraces well preserved at the two steeper segments of the Salween-Nu River (Bingzhongluo and Exi) to reconstruct the aggradation and incision history by integrating field investigation, unscrewed aerial vehicle (UAV) photogrammetric survey, and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating. For the downstream Bingzhongluo reach with higher steepness, three levels of strath terraces at 20-160 m above the trunk river are overlain by three episodes of fluvial deposits at 370 ka, 275 ka, and 130 ka, and this yield the incision rates decreasing from 0.4 to 0.2 mm/yr with time. For the upstream Exi reach with lower steepness, five levels of strath terraces occurs at 10-350 m high, and the middle three terrace deposits are dated at 430 ka, 380 ka, and 300 ka. The corresponding incision decelerated from 0.6 mm/yr to 0.1 mm/yr. To summarize, fluvial terraces along two steeper reaches of the Salween-Nu River reveal temporal deceleration of river incision since the Middle Pleistocene varying at 0.6-0.1 mm/yr. Field investigation for terrace deposits revealed that there occur thick alluvial deposits overlying fluvial deposits by the Salween-Nu River, either tributary-derived boulder conglomerates or hillslope-derived angular conglomerates. We tend to believe that the large amounts of sediment supply may protect the underlying bedrock strath from erosion for a certain interval of time, and therefore slow the pace of river incision and regional landscape evolution in southeast Tibet.

How to cite: Zhang, J., Wang, W., Yang, H., Zeng, X., and Guo, Z.: Temporal deceleration of fluvial incision since the Middle Pleistocene along the Salween-Nu River in southeast Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6732, https://doi.org/10.5194/egusphere-egu24-6732, 2024.

EGU24-6811 | Orals | GM8.1

Climatic controls on the stream network topology 

Minhui Li, Hansjörg Seybold, Xudong Fu, Baosheng Wu, and James Kirchner

Stream networks are striking expressions of how Earth’s hydraulic cycle shapes topography, yet the degree to which different geomorphological processes are visible in their ramified structure remains debated. Here we analyzed 18,030 river networks across the contiguous United States as mapped by the high resolution National Hydrographic Dataset, measuring the Tokunaga parameter c, which characterizes the degree of side-branching, in order to quantify the stream networks' topologies. We find that stream networks with more side branches tend to occur in wetter climates while channel networks in arid regions are less "feathered". As side branches tend to be steeper than the main channel, the aridity-induced dependence of slope ratio identified in recent studies may indicate inherent topological differences between stream networks in arid and humid regions. Such climatic signatures in the planform morphology of stream networks may help to better understand landscape evolution on the continental scale, and may also hold clues for the climatic history of other planetary bodies such as Mars or Titan.

How to cite: Li, M., Seybold, H., Fu, X., Wu, B., and Kirchner, J.: Climatic controls on the stream network topology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6811, https://doi.org/10.5194/egusphere-egu24-6811, 2024.

Drainage systems are highly sensitive to landform changes, and their formation and evolution history are of great significance for understanding regional tectonic-climatic processes and ecological environmental changes. Since the Cenozoic, the uplift and expansion of the Tibetan Plateau have profoundly influenced the landforms and drainage patterns in its surrounding area. The Qinling-Daba Mountains are located on the northeastern margin of the Tibetan Plateau, and the Han River, as the largest tributary of the Yangtze River, originates from the southern flank of the Qinling Mountains and flows from west to east between the Qinling and Daba Mountains, whose evolution history may document abundant clues of the expansion of the Tibetan Plateau and regional tectonic-climatic responses. Previous studies suggested that a significant river reorganization event may have occurred in the upper reaches of the Han River. However, the timing and mechanism are still vague. In this study, the evolution history of the upper reaches of the Han River is reconstructed through terrace mapping, paleocurrent measurements, K-feldspar Pb isotope provenance analysis, and quartz electron spin resonance (ESR) dating. Combined with the fault kinematic analyses, it is believed that before 0.4 Ma, the Paleo-Han River flowed directly eastward along the Ankang Basin. Between 0.4-0.15 Ma, the continuous left-lateral strike-slip movement along the Ankang Fault resulted in vertical uplift at its compressional bend and caused the Han River to flow southward and bypass into the Daba Mountains. This river evolution event within the Qinling region reflects the adjustment process of the peripheral water systems and landforms under the influence of the expansion of the Tibetan Plateau.

How to cite: Ju, D. and Yang, Z.: Pleistocene drainage reorganization of the upper reaches of the Han River and its tectonic significance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7041, https://doi.org/10.5194/egusphere-egu24-7041, 2024.

Climate contrasts across drainage divides, such as orographic precipitation, are ubiquitous in mountain ranges, and as a result, mountain topography is often asymmetric. Asymmetric glaciation arising from climate gradients across divides can cause topographic asymmetry that is potentially different from fluvial landscapes, causing divide instability during glacial-interglacial cycles. In this study, we quantified topographic asymmetry caused by asymmetric glaciation and assessed its sensitivity to different climate scenarios. Using an analytical model of a steady-state glacial profile, we find that the degree of topographic asymmetry is primarily controlled by differences in the Equilibrium Line Altitude (ELA) across the divide. When the ELA differences are caused by precipitation variations across the divide, glacial topography exhibits greater asymmetry than fluvial topography. These results suggest that glacial erosion responds differently to the same climate asymmetry from fluvial erosion, and therefore, intermittent glaciations may have promoted drainage reorganization and landscape transience in glaciated mountain ranges. Preliminary model results indicate that the rate of divide migration caused by asymmetric glaciation is several millimeters per year and the timescale of migration is several million years.

How to cite: Lai, J. and Huppert, K.: Climate-driven topographic asymmetry enhanced by glaciers: Implication for divide stability in glacial landscapes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7438, https://doi.org/10.5194/egusphere-egu24-7438, 2024.

EGU24-7762 | Orals | GM8.1

Downstream versus upstream propagation of fluvial erosion in orogenic plateaus: Example of the eastern Tibetan Plateau 

Xiaoping Yuan, Ruohong Jiao, Jing Liu-Zeng, Guillaume Dupont-Nivet, Sebastian Wolf, and Xiaoming Shen

Fluvial erosion of small mountain belts is widely represented as a wave of upstream migration of knickpoints, starting from a stationary boundary of a high topography created by increased rock uplift rates. However, mountain belts such as the Tibetan Plateau and the central Andes are large, and fluvial erosion remains poorly constrained when orogens expand in width with their boundaries continuously advancing towards the foreland. Here we propose a simple analytical solution for a laterally expanding orogen dominated by fluvial erosion, and apply it to the propagation of Eastern Tibet where the plateau margin is characterized by widespread low-relief surfaces incised by steep river valleys. Our analytical solution is based on the assumption that the topography of Eastern Tibet was built by high uplift rates located in a belt along the plateau margins migrating outwards during plateau growth, as well as carved by erosion of large rivers originating from the interior of the plateau. We validate our analytical solution by comparing it to numerical models and various types of data from five large rivers in Eastern Tibet (Salween, Mekong, Yangtze, Yalong, and Dadu Rivers). The results show that the models with optimized parameters are generally consistent with the observed river-profile morphologies, exhumation magnitudes, and low-temperature thermochronometric ages. We also tested whether the observations on topography and exhumation could also be explained by a period of headward erosion and plateau retreat, the consequence of an early formation of the Tibetan Plateau. By testing various fluvial erodibilities and model durations, we could not reproduce the observed topographies, river profiles, and exhumation magnitudes. The tested model also predicts an increase in thermochronometric ages from the center to the margin of the plateau, opposite to the observed trend of ages. Our results thus show that the long-term fluvial erosion in Eastern Tibet features mainly a downstream migration of high erosion rates, which is fundamentally different from the headward erosion of most of small mountain rivers and a major plateau margin retreat. The characteristics described by our simple analytical solution may represent a common pattern of outward growing mountains and plateaus in tectonically active regions on Earth.

How to cite: Yuan, X., Jiao, R., Liu-Zeng, J., Dupont-Nivet, G., Wolf, S., and Shen, X.: Downstream versus upstream propagation of fluvial erosion in orogenic plateaus: Example of the eastern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7762, https://doi.org/10.5194/egusphere-egu24-7762, 2024.

EGU24-7773 | ECS | Posters on site | GM8.1

Multi-stage Cenozoic exhumation history of southern Central Tian Shan: implications for geodynamic and sedimentary evolution 

Lixing Lyu, Tao Li, Yingying Jia, and Jie Chen

Despite important implications for tectonic, sedimentary, geodynamic and climatic evolution in central Asia, Cenozoic exhumation history of the Tian Shan remains highly debated. Here, we report unexpectedly young zircon fission-track and zircon (U-Th)/He dates from the Tomor Peak region in southern Central Tian Shan. Together with new and published biotite 40Ar/39Ar and apatite (U-Th)/He data, the exhumation history since latest Jurassic is reconstructed. An initial increase in exhumation rate from ≤0.01 to ~0.1-0.2 km/Myr occurred at ~25-20 Ma, which is thought to be a response to changed regional stress field due to growth of the Tibetan-Pamir Plateau driven by deep geodynamic processes relating to India-Asia convergence. The second stage of exhumational acceleration took place at ~12-6 Ma, with an apparent rate of ~1.0 km/Myr, which probably relate to the “hard collision” between the Indian lithospheric mantle and the Tarim-Tajik lithospheric mantle beneath the Pamir and western Tibet. After ~5 Ma, the mean exhumation rate of sampled rocks dropped to be ~0.5 km/Myr due to drier climate condition and redistributed strain accompanying the formation of Kuqa foreland thrust system. Finally, based on the presented bedrock exhumation history and available sedimentary records from foreland basins, we propose a coupled tectono-sedimentary evolution model to reconcile the conflicting tectonic interpretations between low temperature thermochronological and sedimentological studies.

How to cite: Lyu, L., Li, T., Jia, Y., and Chen, J.: Multi-stage Cenozoic exhumation history of southern Central Tian Shan: implications for geodynamic and sedimentary evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7773, https://doi.org/10.5194/egusphere-egu24-7773, 2024.

EGU24-8974 | ECS | Orals | GM8.1 | Highlight

The stratigraphic and orogenic response to the Middle Miocene Climatic Optimum in the southern Central Andes 

Sarah W.M. George, Barbara Carrapa, Peter G. DeCelles, Gilby Jepson, Hamida Nadoya, Clay Tabor, Caden J. Howlett, Chance B. Ronemus, Mark T. Clementz, and Lindsay Schoenbohm

Changes in precipitation can drive major shifts in stratigraphy and fold-thrust belt behavior. We investigate the stratigraphic and orogenic response to pronounced climatic warming during the Middle Miocene Climatic Optimum (ca. 17-14 Ma) in the southern Central Andes.  New and compiled stratigraphic and geochronologic data come from depocenters at ~25-35°S; these basins would have occupied both high and low elevation positions during the middle Miocene. Regionally ubiquitous eolianite deposition from ca. 22-17 Ma supports arid conditions on the eastern flank of the Central Andes preceding the Middle Miocene Climatic Optimum. Eolian facies are replaced by fluvial-lacustrine strata near the onset of the Middle Miocene Climatic Optimum over 1000 km along-strike. These results support a change from arid to more seasonal and humid conditions during the Middle Miocene Climatic Optimum. New climate models also support increased seasonality and moisture availability on the eastern flank of the Andes during the Middle Miocene Climatic Optimum, which we attribute to intensification of the South American Monsoon. We compare our results with published sequentially restored, regional cross-sections to explore linkages between the climatic shift and orogenic growth. A more seasonal climate should drive increased erosion, which in turn should drive the wedge into sub-critical state as predicted by critical taper theory.

How to cite: George, S. W. M., Carrapa, B., DeCelles, P. G., Jepson, G., Nadoya, H., Tabor, C., Howlett, C. J., Ronemus, C. B., Clementz, M. T., and Schoenbohm, L.: The stratigraphic and orogenic response to the Middle Miocene Climatic Optimum in the southern Central Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8974, https://doi.org/10.5194/egusphere-egu24-8974, 2024.

EGU24-9234 | Posters on site | GM8.1

Interactions between tectonics, climate and surface processes over the last 200,000 years in the Naryn Basin (Kyrgyz Tien Shan). 

Magali Rizza, Julie Losen, Alexis Nutz, Maxime Henriquet, Mathieu Schuster, Sultan Baikulov, Erkin Rakhmedinov, Kanatbek Abdrakhmatov, Jules Fleury, Vincent Rinterknecht, and Lionel Siame

Geomorphological markers such as alluvial fans, fluvial or lacustrine terraces, and landslides reflect the interaction among tectonics, climate, and surface processes in mountain belts and basins. To understand the evolution of the Tien Shan Range, which is located in Central Asia, the study of intramontane basins may provide insights on the rate of the deformation as active faults and folds commonly deform both Cenozoic and Quaternary deposits. In this active orogen, the intramontane Naryn Basin is the right place to study tectonic deformations recorded by fluvial deposits as well as changes in fluvial networks since the Pliocene-Pleistocene. Based on analysis of high-resolution topographic data and field investigations, we propose a revised mapping of the western Naryn Basin and a new evolutionary model for the chronology of its Quaternary deposits. Indeed, the use of several Quaternary dating methods (luminescence, cosmogenic nuclides, radiocarbon) enables us to better constrain the evolution of the landscape at different time scales, highlighting drastic changes over the last 200,000 years.

First, the western Naryn Basin was characterised by fluvial dynamics with deep fluvial incisions, aggradation of large alluvial fans and terraces, likely controlled by glacial/interglacial cycles. These deposits were deformed by several deep-seated, relatively steeply dipping thrust faults during the Pliocene-Pleistocene. During the late Pleistocene, a major earthquake probably triggered the giant Beshkiol landslide which blocked the Naryn River, having a major impact on the sedimentary dynamics of the entire upstream basin. A large lake more than 80 km long and lake sedimentation lasted around 36,000 years, changing the base level of the Naryn river and reshaping the surrounding paleotopography. This lake was probably emptied during a cataclysmic event (dam breach) with evidence found both in the Naryn and the downstream Kazarman basins. The external factors that led to the dam's failure are still debated, but they are contemporary with the Bølling-Allerød interstade. Fluvial conditions prevailed for a short period of time before a second damming of the Naryn basin by the Beshkiol landslide, and the subsequent restoration of lake conditions for a period of ~7 600 years. This second lake was gradually emptied and formed large geomorphological flats, which have long been wrongly interpreted as fluvial top surfaces. In the late Holocene, the rapid incision of the Naryn river to restore its base level has strongly reshaped the Naryn basin, erased large volumes of sediments and new fluvial terraces are emplaced. Weak evidence of tectonic deformation is noted along the thrust faults, which raises the question of possible inhibition of tectonic activity by the long residence time of the two lakes.

How to cite: Rizza, M., Losen, J., Nutz, A., Henriquet, M., Schuster, M., Baikulov, S., Rakhmedinov, E., Abdrakhmatov, K., Fleury, J., Rinterknecht, V., and Siame, L.: Interactions between tectonics, climate and surface processes over the last 200,000 years in the Naryn Basin (Kyrgyz Tien Shan)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9234, https://doi.org/10.5194/egusphere-egu24-9234, 2024.

EGU24-9308 | Orals | GM8.1

Geomorphological evolution of the Eastern Sardinian Margin (Western Tyrrhenian) from the Messinian to the Plio-Quaternary: New evidence for post-rift deformation from bathymetric and seismic data. 

Romain Sylvain, Virginie Gaullier, Frank Chanier, Louise Watremez, Fabien Caroir, Fabien Graveleau, Johanna Lofi, Agnès Maillard, Françoise Sage, Isabelle Thinon, and Gaia Travan

The hyper-extended Eastern Sardinian margin is due to the eastward migration of the Appennine-Calabria subduction zone, creating the Neogene back-arc Tyrrhenian Basin. This area was affected by strong erosion during the Messinian Salinity Crisis (MSC, 5.97 - 5.33 Ma) on the continental shelf and slope leading to a major discontinuity, known as the Messinian Erosion Surface (MES), constituting, therefore, a remarkable stratigraphic marker. It is also a powerful paleo-topographic marker of the MSC times and can be used as a marker of the deformation during Plio-Quaternary times. The end of the rifting phase in the Eastern Sardinian margin is dated during the Tortonian (11.63 - 7.25 Ma) attested by the occurrence of a relatively thick syn- and post-rift sequence pre-dating the MES.

The “METYSS 4” cruise led to the acquisition of more than 2,000 km of very high-resolution (VHR) seismic reflection data, following a dense grid, on the Eastern Sardinian continental shelf and slope, which has been little explored until now. Seismic interpretation allowed for mapping the major erosion surface, the MES, across the continental shelf and slope. At the base of the PQ sequence, the MSC paleo-topography highlights a hydrographic paleo-network identical to the current one and a general progradation of the shelf-break toward the east during the Plio-Quaternary. In the southern part of the study area, several east-dipping normal faults, oriented N-S, significantly shift the MES (between 5 and 55 m; assuming sound wave velocity of 1700 m/s in Plio-Quaternary sediments). The MES is tilted toward the fault and is covered by Plio-Quaternary deposits, which display a fan-shaped geometry (eg. 50 m thick on the hanging wall). These NS-trend faults are cross-cut by E-W trending messinian canyon and this fault pattern is also observed on the other flank of the canyon. The along-strike geomorphological analysis of canyons reveals the occurrence of knickpoints (slope breaks) coinciding with the front of the two fault patterns. Moreover, the shifts in water depth of most knickpoints are at the same order of amplitude than fault offsets (ie. 10 to 50 m). These geomorphologic markers reinforce the hypothesis that the fault activity is recent (ie. less than 5 Ma). We interpret these observations as markers of a recent reactivation of the structures inherited from the rift in the western part of the Tyrrhenian Sea.

How to cite: Sylvain, R., Gaullier, V., Chanier, F., Watremez, L., Caroir, F., Graveleau, F., Lofi, J., Maillard, A., Sage, F., Thinon, I., and Travan, G.: Geomorphological evolution of the Eastern Sardinian Margin (Western Tyrrhenian) from the Messinian to the Plio-Quaternary: New evidence for post-rift deformation from bathymetric and seismic data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9308, https://doi.org/10.5194/egusphere-egu24-9308, 2024.

EGU24-9632 | Orals | GM8.1

Late Miocene evolution of Jordan Rift Valley recorded on its eastern flank 

Giancarlo Scardia, João Carlos Cerqueira, Francisco Ladeira, Fabio Parenti, and Walter Neves

The Jordan Rift Valley (JRV) is a depression produced by the active Dead Sea Transform (DST), separating the Sinai subplate and the Arabian Plate. Its beginning is related to the late Miocene (~6 Ma), when sinistral displacement of the DST gained an extensional component, thus accentuating the subsidence of the JRV. This shift is recorded by Messinian basalt flows that cover JRV eastern slopes (Zerqa Ma, Mujib, and Tafila basalts; 6–3.4 Ma) and the Cover basalt (5.8–3.6 Ma) in the Galilee region. Sediments from the Sedom Lagoon since ~12 Ma suggests that the JRV was already a shallow depression connected with the Mediterranean Sea, which at the early Pliocene (5–4 Ma) lost permanently this connection due to the uplift of the JRV flanks. More information about geomorphology and drainage pattern of the region during the Late Miocene is limited to information available along the western side of the JRV, including the fluvial/lacustrine Hazeva Fm (~20–6.4 Ma) in the Arava region and lacustrine/marine formations in the lower Galilee (~17–5 Ma). Here we discuss the implications of Zarqa Valley geomorphological features and its volcano-sedimentary infill to the Miocene evolution of the JRV. The Zarqa Valley is carved into Cretaceous/Paleogene bedrocks at the Eastern Flank of the JRV, and it hosts a perennial water drainage system flowing westward to the Jordan River. The oldest dated filling of the Zarqa Valley is represented by a series of late Miocene lava flows, named collectively as “Lower Basalt” (LB), spanning 5.82 to 5.51 Ma. It records the existence of a pre-existing valley in the late Miocene, with already at least 300 m of incision, observed by the difference of the base of the LB and the bedrock summits surrounding the valley. The LB outcrops ca. 40 km east of JRV axis and its thickness increases eastward to more than 100 m. W-NW paleocurrent data in conglomerates underlying the LB indicate that the Zarqa River maintained the same flow towards the JRV since the Late Miocene. The occurrence of the LB in the Zarqa Valley is synchronous with the dramatic sea level fall of Messinian Salinity Crisis (MSC, 5.97–5.33 Ma), when the Sedom Lagoon lost temporarily the connection to the Mediterranean Sea. Opposite to what is observed throughout the Mediterranean Sea, where rivers underwent a profound incision phase, the Zarqa Valley experienced aggradation of conglomerates and thick basalt flows. We propose that this is an indication that Sedom Lagoon acted as local base level of an endorheic drainage by the time when the MSC started, possibly with an increasing water table, necessary to produce the accumulation space to account for the Zarqa Valley deposition. We hypothesize that a highstand of the base level in the JRV during the MSC can be explained by a favorable climate and several stream capture in the Levant that caused rivers to migrate to the endorheic drainage of the Sedom Lagoon.

How to cite: Scardia, G., Cerqueira, J. C., Ladeira, F., Parenti, F., and Neves, W.: Late Miocene evolution of Jordan Rift Valley recorded on its eastern flank, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9632, https://doi.org/10.5194/egusphere-egu24-9632, 2024.

EGU24-10477 | ECS | Orals | GM8.1

Unraveling rapid exhumation: Insights into the increase of exhumation rates in the Sutlej River anticline (NW Indian Himalaya) over the last 200 kyr. 

Marie Genge, Chloé Bouscary, Alex Webb, Georgina King, Blessing Adeoti, Ari Ganbat, and Dominik Vlaha

Estimating exhumation rates on Pleistocene-Holocene time scales presents a challenge due to the scarcity of suitable low-temperature thermochronometers. Apatite helium (AHe) dating is unable to precisely differentiate cooling ages <1 Ma and whilst optically stimulated luminescence (OSL) thermochronometry resolves younger ages (104-105 years timescale), it is limited in regions with lower exhumation rates (<2-3 mm/yr). These restrictions limit our ability to accurately study exhumation rates on such time scales, thus hindering our understanding of the implications of tectonics, climate, and hydrology. To address this challenge and gain insights into the dynamics of rapid exhumation, we conducted our study in the Sutlej River valley (northwest Indian Himalaya), which features a prominent river anticline with exceptionally high exhumation rates locally reaching up to 12 mm/yr (OSL data from a previous study). For this purpose, we collected 10 samples, including 5 from a 2200 m vertical profile in the Sutlej valley, and 5 from the main tributaries. The new OSL analysis of these samples reveals high exhumation rates at lower altitudes (<2500 m), ranging from 6-8 mm/yr, 350 m above the river, and from 3-5 mm/yr, 720 m above the river. Furthermore, OSL ages of samples from lower elevations along the tributaries were not saturated, also pointing to rapid exhumation in these areas. In contrast, all samples from higher elevations (>2500 m) reach field saturation, indicating lower average exhumation rates that cannot be recorded using OSL thermochronometry. Although the vertical profile data exhibit a significant increase in exhumation rates over the past 200 kyr, this region lacks glaciated landscapes, suggesting a feedback loop within the river anticline. The river incision promotes the development of the anticline, which, in turn, amplifies the river incision, leading to accelerated exhumation over time. By demonstrating the importance of the interplay between river incision and anticline development in driving the progression of exhumation rates in the Sutlej River region, this study offers a new perspective on Late Pleistocene exhumation rates in the Himalayas.

How to cite: Genge, M., Bouscary, C., Webb, A., King, G., Adeoti, B., Ganbat, A., and Vlaha, D.: Unraveling rapid exhumation: Insights into the increase of exhumation rates in the Sutlej River anticline (NW Indian Himalaya) over the last 200 kyr., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10477, https://doi.org/10.5194/egusphere-egu24-10477, 2024.

EGU24-10609 | Posters on site | GM8.1

River terrace formation in response to climate, regional uplift and local normal faulting: The Danube terrace staircase in Vienna 

Bernhard Salcher, Stephanie Neuhuber, Jan-Christoph Otto, Tom Payer, Christopher Lüthgens, Sebastian Fuchs, Adrian Flores-Orozco, Zsofia Ruszkiczay-Rüdiger, Sabine Grupe, and Markus Fiebig

The formation of impressive Quaternary terrace sequences along many mid to high latitudinal rivers is the consequence of surface uplift and a strong climate related impact on the fluvial system. Glacial and periglacial processes may amplify events of aggradation thereby providing clear stratigraphic markers in the fluvial terrace record. Terrace sequences are essential landforms in many continental basins even though local subsidence may counteract the regional uplift trend. We explore these opposing lithospheric forces, regional uplift vs. local normal faulting along the perialpine section of the Danube River that is supposedly strongly affected by a 100-kyr depositional cyclicity during the Quaternary. Within the city of Vienna, the Danube forms an impressive terrace staircase which is impacted by a continental scale normal fault at the transition Alps – Vienna Basin crossing the city right in its central parts. Hydrocarbon exploration indicate a vertical offset of up to c. 4 km that accumulated during the Miocene, but its recent activity remined so far ambiguous.

Anthropogenic overprint led to the obliteration of terrace morphology and solifluction resulted in thick soil bearing colluvial deposits along slopes. To constrain fault activity, kinematics and stratigraphic information from terrace elevation, we used electrical resistivity tomography and analyzed data from numerous drill logs and outcrops. We applied terrestrial cosmogenic burial and luminescence dating to derive rates of vertical velocities and to support morphostratigraphic age modelling. We show how long-wavelength uplift and concomitant normal faulting controls terrace formation and landscape evolution under periods of aggradation and incision. Our study provides the largest set of cosmogenic derived depositional ages of perialpine fluvial sediments of the Eastern Alps and provides unambiguous evidence of active faulting within the city of Vienna.

How to cite: Salcher, B., Neuhuber, S., Otto, J.-C., Payer, T., Lüthgens, C., Fuchs, S., Flores-Orozco, A., Ruszkiczay-Rüdiger, Z., Grupe, S., and Fiebig, M.: River terrace formation in response to climate, regional uplift and local normal faulting: The Danube terrace staircase in Vienna, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10609, https://doi.org/10.5194/egusphere-egu24-10609, 2024.

EGU24-10973 | ECS | Orals | GM8.1

Tectonic advection controls drainage divide asymmetry patterns in the Longmenshan, SE Tibet, China 

Katrina Gelwick, Yanyan Wang, Sabrina Metzger, Kimberly Huppert, Rong Yang, and Sean Willett

The lateral movement of Earth’s crust through tectonic advection plays an important role in shaping topography in many active orogens worldwide. Numerical modelling and select field studies have shown that tectonic advection can alter topography and thereby create asymmetric drainage divides. Divide migration typically occurs opposite to the direction of tectonic advection, however, in many mountain belts, the wedge-tip propagation towards the foreland outpaces the rate of convergence, in which case the direction of topographic asymmetry should be reversed. 

We combine geomorphic and geodetic analyses with numerical models to test whether topographic asymmetry in the Longmenshan region of Southeast Tibet is dominated by advection of the crust from the ongoing India-Eurasia collision, movement of river base-level with the propagation of the thrust front into the Sichuan Basin, or other tectonic and climatic factors. We measure the magnitude and direction of drainage divide asymmetry using geomorphic metrics and compare these to horizontal GNSS velocities, which measure tectonic advection and shortening relative to the stable Sichuan Basin block. Geologic studies estimate that wedge-tip propagation toward the Sichuan Basin has been negligible since ~5-10 Ma.

Our results show that drainage divide asymmetries in the Longmenshan and Bayankala tectonic blocks indicate a dominantly northwest divide migration direction relative to the underlying rock. This is opposite to the dominantly southeast-pointing GNSS rates and suggests that within-wedge shortening and southward surface advection are more important than wedge-tip propagation. These findings also indicate that topography in the Longmenshan and Bayankala blocks has already adjusted to the current kinematics. Inconsistencies in the signal can be explained by localized deformation and uplift from faulting and other small-scale transient adjustments in the river network, such as those caused by stream captures. We compare these results to a series of numerical model scenarios with varying advection and wedge-tip propagation velocities to discern the relative influence of tectonic advection and thrust-front dynamics on the region’s topography. Our study highlights the critical role tectonic advection plays in shaping topography on the Southeast Tibetan Plateau and it provides a comparative framework for distinguishing the relative rates of advection and wedge-tip propagation.

How to cite: Gelwick, K., Wang, Y., Metzger, S., Huppert, K., Yang, R., and Willett, S.: Tectonic advection controls drainage divide asymmetry patterns in the Longmenshan, SE Tibet, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10973, https://doi.org/10.5194/egusphere-egu24-10973, 2024.

EGU24-11491 | Posters on site | GM8.1

Late-Neogene to Quaternary uplift, relief and drainage evolution in the western French Alps: new insights from surface and underground karst archives in the subalpine massifs 

Pierre Valla, Vivien Mai Yung Sen, Yann Rolland, Stéphane Jaillet, Xavier Robert, Julien Carcaillet, Christian Crouzet, Olivier Bruguier, Edwige Pons-Branchu, Emmanuel Malet, Nouméa Boutin Paradis, and Léo Moiret

The late-Neogene to Quaternary evolution of the western European Alps has been marked by major changes in geodynamic, tectonic and climatic forcing. The complex interplay between endogenic and exogenic processes has resulted in rock-uplift changes, topographic relief development and major drainage pattern reorganizations. However, quantitative estimates on these interrelated mechanisms have remained scarce due to the poor preservation on surface geological archives in the alpine massifs. This is the case for the frontal part of western Alps, i.e. the subalpine massifs, for which the overall tectonic architecture and total deformation/uplift are well constrained but the timing and rates remained poorly known.

Here, we focus on the Vercors subalpine massif and specifically target karstic systems in the upper Bourne catchment that have been developed and potentially preserved over million-year timescales. Our study combines karst network analysis with the investigation of surface geomorphological markers (abandoned canyons) to provide an incision history and integrated geomorphic evolution of the Bourne catchment from the late Neogene to Quaternary. We develop an innovative multi-method approach with 3D mapping of both surface and underground markers associated to geochronological investigation of preserved detrital sediments (26Al/10Be burial dating, U/Pb dating, paleomagnetism) and speleothems (U-Th dating). Our results show first changes in the surface drainage pattern at ~10 Ma for the Bourne catchment, in agreement with tectonic deformation and topographic uplift at that time. The Bourne incision history reveals a multi-stage complex evolution, with a late Neogene incision phase followed by relative quiescence during the Pliocene. The late-stage history of the Bourne is marked by a second incision phase since ca. 2 Ma that could be linked to isostatic response to relief development during major Alpine glaciations. Our new results nicely complement recent data from the nearby Devoluy massif, and indicate a late-Neogene structuration and uplift of the subalpine massifs which has been relatively contemporaneous with the exhumation of the external crystalline massifs (Belledonne, Ecrins-Pelvoux). This tectonic structuring resulted in the present-day “plateau” configuration of the subalpine massifs, and their uplift led to a major change from an earlier radial into the modern “orogen-parallel” drainage system, which was then marked by the Quaternary alpine glaciations.

How to cite: Valla, P., Mai Yung Sen, V., Rolland, Y., Jaillet, S., Robert, X., Carcaillet, J., Crouzet, C., Bruguier, O., Pons-Branchu, E., Malet, E., Boutin Paradis, N., and Moiret, L.: Late-Neogene to Quaternary uplift, relief and drainage evolution in the western French Alps: new insights from surface and underground karst archives in the subalpine massifs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11491, https://doi.org/10.5194/egusphere-egu24-11491, 2024.

EGU24-11613 | Orals | GM8.1

Mantle-related late Cenozoic surface uplift in NW Iberia revealed by 10Be cosmogenic nuclide dating and non-linear river profile inversion 

Julien Babault, Paula Figueiredo, Lewis A. Owen, Javier Fullea, Ana Negredo, Pierre Arroucau, Ludovic Bodet, María Charco, Jean Van Den Driessche, and Marc Caffee

During the last decade there has been an increase in the study of transient topography because it gives information about surface uplift history. The onset of transient topography forms after a gain in potential energy which leads to the creation of slopes at the outlet of catchment. It is followed by a wave of transient erosion that propagates upstream along the main river, then across tributaries, and from the tributaries to the hillslopes. Records of incision history such as topographic data and landform dating can be gathered into inversion schemes to reconstruct base-level fall and uplift history. In this study, we employ a reversible jump Markov chain Monte Carlo Bayesian algorithm to perform an inversion of topographic data, landform dates, and erosion rates in order to unravel surface uplift history. By adopting a probabilistic approach, we generate an ensemble of solutions that comprise various combinations of model parameters. This methodology enables us to estimate uncertainties in the timing and amount of changes in uplift rates. In the forward model we use the non-linear analytical solutions of the stream power incision model that states that incision I = KAmSn is simply a function of S, the local channel gradient, and A, drainage area above that point and K incapsulates climatic conditions, geometrical and hydraulic characteristics of the stream, bedrock resistance to erosion. Our inversion is constrained by new river-sands 10Be cosmogenic nuclide data, and by incision rates derived from river terraces from the literature. Millennial scale erosion rates and topographic metrics helps us to calibrate the empirical scaling parameters of the stream power incision law. We apply our model to the Atlantic rivers draining NW Iberia where canyons are incised in low-relief erosional surfaces that developed in the last 100 Ma. We show that the transient topography is compatible with a regional late Cenozoic uplift of several hundreds of meters, most likely in response to a mantle-related continental-scale uplift.

How to cite: Babault, J., Figueiredo, P., Owen, L. A., Fullea, J., Negredo, A., Arroucau, P., Bodet, L., Charco, M., Van Den Driessche, J., and Caffee, M.: Mantle-related late Cenozoic surface uplift in NW Iberia revealed by 10Be cosmogenic nuclide dating and non-linear river profile inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11613, https://doi.org/10.5194/egusphere-egu24-11613, 2024.

EGU24-11794 | Posters on site | GM8.1

Impact of glaciations on the exhumation history of the Kyrgyz Range – Western Tien Shan (Kyrgyzstan). 

Apolline Mariotti, Taylor Schildgen, Edward R. Sobel, Maxime Bernard, Lingxiao Gong, Peter van der Beek, and Johannes Glodny

Constraining the effect of global climatic changes on Earth-surface processes is crucial to our understanding of landscape evolution. One debated question is the impact of Cenozoic cooling and subsequent glaciations on the spatial and temporal distribution of erosion in mountain ranges. The apatite (U-Th-Sm)/He thermochronometric system can record low temperature (<100 ◦C) cooling histories and thus potentially has the sensitivity to detect million-year timescale changes in exhumation rates in glaciated regions.

Previous thermochronology studies in the Kyrgyz Range (Western Tien Shan, Kyrgyzstan) have identified an increase of exhumation rates over the last 3 Ma, which have been hypothesized to result from enhanced glacial erosion (Bullen et al., 2003; Sobel et al., 2006). Furthermore, an analysis of published global thermochronology data identified the Kyrgyz Range as one of the few locations globally with the potential to record the effect of Pleistocene glaciations (Schildgen et al., 2018).

In this study, we present new AHe ages for 3 samples collected along the main trunk of the Ala Archa valley and 6 samples collected in a tributary valley exhibiting clear glacial imprint. The samples were collected from granite outcrops over an elevation range of 1850 m (lowest sample: 1792 m – highest sample: 3634 m).

These new samples exhibit: (1) an onset of cooling at 12 - 10 Ma, in agreement with published work and interpreted as the start of exhumation in the Kyrgyz Range; (2) a rapid increase in cooling rates between 2 and 3 Ma recorded in the lower elevation samples (1792 – 2240 m), which could have been caused by glacial incision and valley widening during the onset of Pleistocene glaciations (2.6 Ma) and; 3) a negative age-elevation relationship above 3600 m (5.6 ± 0.7 Ma) potentially demonstrating valley widening due to lateral glacial erosion.

These results suggest that the onset of the Pleistocene glaciations had a strong impact on the Western Tien Shan, both at higher and lower elevations.

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Bullen, M. E., Burbank, D. W., and Garver, J. I.: Building the Northern Tien Shan: Integrated thermal, structural, and topographic constraints, Journal of Geology, 111, 149–165, https://doi.org/10.1086/345840, 2003.

Schildgen, T. F., Van Der Beek, P. A., Sinclair, H. D., and Thiede, R. C.: Spatial correlation bias in late-Cenozoic erosion histories derived from thermochronology, Nature, 559, 89–93, https://doi.org/10.1038/s41586-018-0260-6, 2018.

Sobel, E. R., Oskin, M., Burbank, D. W., and Mikolaichuk, A.: Exhumation of basement-cored uplifts: Example of the Kyrgyz Range quantified with apatite fission track thermochronolgy, Tectonics, 25, https://doi.org/10.1029/2005TC001809, 2006.

How to cite: Mariotti, A., Schildgen, T., Sobel, E. R., Bernard, M., Gong, L., van der Beek, P., and Glodny, J.: Impact of glaciations on the exhumation history of the Kyrgyz Range – Western Tien Shan (Kyrgyzstan)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11794, https://doi.org/10.5194/egusphere-egu24-11794, 2024.

EGU24-11893 | Orals | GM8.1

Enhanced exhumation in the East Karakoram during themid-Pleistocene climate transition: A detrital provenance assessment 

Chris Mark, Peter Clift, Célia Paolucci, Anwar Alizai, and Eduardo Garzanti

Around the Nanga Parbat-Haramosh massif in the west and the Namche Barwa massif in the east, the Himalayan orogen exhibits an abrupt strike change from roughly E-W to N-S, forming two structural syntaxes. Each syntaxis is drained by a major trans-orogenic river system: the Indus and Ganges-Brahmaputra, respectively. The syntaxial massifs record rapid exhumation rates (up to c. 10 mm/a), together with Plio-Pleistocene mineral (re)crystallisation and cooling ages (Bracciali et al, 2016; Crowley et al., 2009; Zeitler et al., 1993). The Namche Barwa massif supplies c. 65-74% of Brahmaputra bedload (Enkelman et al., 2011; Dong et al., 2023). In contrast, the Nanga Parbat massif supplies c. 10% of modern Indus bedload, which instead is dominantly sourced from the East Karakoram (Clift et al, 2022).

We present detrital rutile and zircon U-Pb data from the Indus fan, sampled by IODP expedition 355 and ODP leg 117. These data record abrupt increases in the proportion of sediment sourced from the Nanga Parbat massif between c. 8-6 Ma and again at c. 2 Ma, coherent with bedrock studies (Crowley et al., 2009; Zeitler et al., 1993). The Nanga Parbat massif then dominates sediment supply until c. 1.5-0.6 Ma, followed by an abrupt switch to East Karakoram sourcing.

The East Karakoram includes some of Earth’s highest peaks, and largest extra-polar glaciers. Therefore, a provocative possibility is that the jump in erosion focus was driven by the switch from c. 41 ka, obliquity-dominated, to 100 kyr, eccentricity-dominated orbital forcing (the Mid-Pleistocene Transition). This transition occurred at c. 1 Ma (Clark et al., 2006), and could have driven enhanced glacially-mediated erosion in the east Karakoram, outpacing Nanga Parbat exhumation. Approximately synchronous increases in exhumation rate are also documented at Nanga Parbat-Haramosh massif, and the Namche Barwa massif (Guevara et al., 2022; Govin et al., 2020; King et al., 2016;).   

Bracciali, L., et al., 2016, Earth-Sci. Rev., 160, 350-358, doi: 10.1016/j.earscirev.2016.07.010; Clark, P., et al., 2006, Quat. Sci. Rev., 25, 3150-3184, 10.1016/j.quascirev.2006.07.008;; Clift, P., et al., 2022, Earth Plan. Sci. Lett., 600, 117873, 10.1016/j.epsl.2022.117873; Crowley, J., et al., 2009, Earth Plan. Sci. Lett., 288, 408-420, doi: 10.1016/j.epsl.2009.09.044; Dong, X., et al., 2023, Basin Res., 35, 2193–2216, doi: 10.1111/bre.12795; Enkelman, E., et al., 2011, Earth Plan. Sci. Lett., 307, 323-333, 10.1016/j.epsl.2011.05.004; Govin, G., et al., 2020, Geology, 48, 1139-1143, doi: 10.1130/G47720.1; Guevara, V., et al., 2022, Science Advances, 8, eabm2689, 10.1126/sciadv.abm2689;King, G., et al., 2016, Science, 353, 800-804, doi: 10.1126/science.aaf2637; Zeitler, P., et al., 1993, Geology, 21, 347-350, doi: 10.1130/0091-7613(1993)021<0347:SAMARD>2.3.CO;2

How to cite: Mark, C., Clift, P., Paolucci, C., Alizai, A., and Garzanti, E.: Enhanced exhumation in the East Karakoram during themid-Pleistocene climate transition: A detrital provenance assessment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11893, https://doi.org/10.5194/egusphere-egu24-11893, 2024.

During the Cenozoic, the formation of the Andean Cordillera had a profound effect on the drainage evolution in the South America continent. The load of the Andes induced the bending of the lithosphere, creating foreland basins adjacent to the cordillera. Additionally, an increase in orographic precipitation along the eastern flank of the Andes amplified the erosion of the cordillera and the sedimentation rate in the foreland and other interior basins. As a result, the drainage pattern changed from parallel to the cordillera to a system perpendicular to the orogen. This led to the development of the Amazon drainage system in northern South America and guided the formation of the present Paraguay-Paraná Basin in southern South America. Concurrently, dynamic topography induced by the subduction of the Nazca plate under the western margin of the continent created long-wavelength topographic perturbations throughout the continent, partially modulating the generation of accommodation space in interior sedimentary basins and allowing intermittent marine incursions in lowland regions. In this work, we present this complex evolution based on numerical models dedicated to simulating the tectono-sedimentary evolution of the entire South America continent, coupling surface processes, lithospheric flexure, sea-level oscillations, and dynamic topography. This project represents an expansion of the works developed in our research group, previously focused only on the drainage dynamics of northern South America.

How to cite: Sacek, V. and Bicudo, T.: Drainage dynamics of the entire South American continent during the Andean Orogeny: Results from tectono-sedimentary numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11931, https://doi.org/10.5194/egusphere-egu24-11931, 2024.

EGU24-12433 | ECS | Posters on site | GM8.1

The Atacama Desert rock coast: an underrated witnesses of long-term wave erosion 

Camila Arróspide, Germán Aguilar, Hugo Carrillo, María Pía Rodríguez, and Vincent Regard

The Atacama Desert rock coast has allowed for the study of tectonic and climate influences on landscape construction and evolution. This rock coast features important morphologies such as: (1) the Great Coastal Cliff, which runs parallel to the coastline for almost 1000 km, reaching heights between 800 and 2000 m a.s.l.; and (2) shore platforms and staircased marine terraces, which are discontinuously recognized along the extension of the Atacama Desert coast. These morphologies, especially marine terraces, have been studied to estimate rates of uplift in order to constrain the history of the Chilean forearc deformation. However, they have received little attention about the influence of surface processes such as wave erosion on their development and preservation. Certainly, it has been largely proven that wave erosion plays an important role in the development of shore platforms and the evolution of coastal areas. Despite this, its effects on the development of shore platforms and marine terraces and, thus, the landscape construction of the Atacama Desert coast have been scarcely investigated. In this work, we developed a numerical model to understand the influence of a set of processes on the long-term landscape evolution (104-106 years) on rocky coasts. The set of processes involves relative changes in sea level due to eustatic cycles and vertical landmass movements, as well as surface processes such as wave erosion and intertidal weathering. This model allows us to estimate rates of coastal erosion and, thus, morphology development (e.g., platforms and cliffs) to provide new insights for one of the longest but underrated erosive rock coasts. The research design consisted of two stages: (1) model development and testing, and (2) model validation. The model was validated using Atacama Desert coast geomorphology, including field data and morphometric analysis from high-resolution digital elevation models. The model results and the research itself are used to understand the influence of surface processes on the evolution of rock coasts in a tectonic uplift and hyperaridity context.

How to cite: Arróspide, C., Aguilar, G., Carrillo, H., Rodríguez, M. P., and Regard, V.: The Atacama Desert rock coast: an underrated witnesses of long-term wave erosion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12433, https://doi.org/10.5194/egusphere-egu24-12433, 2024.

EGU24-14635 | Orals | GM8.1

Late Cenozoic deformation and glacial imprint on the Terskey Range, Kyrgyzstan 

Lingxiao Gong, Peter van der Beek, Edward Sobel, Taylor Schildgen, Apolline Mariotti, Maxime Bernard, and Johannes Glodny

It is widely recognized that the topography of the Earth's surface records coupling between tectonics, climate and surface processes. However, the relative contributions of tectonic and climatic drivers to the observed topography, rates and patterns of erosion remain poorly constrained in many mountain regions. The Terskey Range, located in the Kyrgyz Tian Shan, is an ideal natural laboratory to investigate this question because of its well-documented structure, kinematics and denudation history. Cenozoic deformation of the Terskey Range is mainly characterised by southward tilting associated with thrusting along the Main Terskey Fault; this fault delimits the mountain range to the north. Tilting can be reconstructed using relict low-relief surfaces that have undergone minimal Cenozoic erosion. Slip along the Main Terskey Fault initiated in the early Miocene and accelerated at around 10 Ma. A comparison between short- and long-term denudation rates suggests a significant increase during the Quaternary, which has been linked to glaciation of the range. The geomorphology of the range, with deeply incised, highly concave main valleys contrasting to less incised and concave minor valleys, suggests significant but variable ice dynamics.

We focus here on the reanalysis of published low-temperature thermochronology data (apatite fission-track, apatite and zircon (U-Th-Sm)/He) of two elevation transects from the glacially affected Barskoon Valley, one of the main valleys draining the Terskey Range to the north. We collected three new valley-bottom samples from the Barskoon Valley to better constrain differential erosion along the valley, with the aim to discriminate between tectonic, fluvial and glacial drivers of valley incision. Inverse thermal-history modelling of the elevation profiles, combining new and existing data, indicates a significant increase in exhumation rate since around 3 Ma in the northern transect. We suggest that this signal records the initiation of efficient glacial erosion in Terskey Range. Future studies will include higher resolution 4He/3He thermochronology of the valley-bottom samples and inversion of the preglacial topographic relief using thermal-kinematic Pecube.

How to cite: Gong, L., van der Beek, P., Sobel, E., Schildgen, T., Mariotti, A., Bernard, M., and Glodny, J.: Late Cenozoic deformation and glacial imprint on the Terskey Range, Kyrgyzstan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14635, https://doi.org/10.5194/egusphere-egu24-14635, 2024.

EGU24-15067 | ECS | Orals | GM8.1

Periodic climatic variations during collisional orogenesis – insights from coupled tectonic-surface-process models 

Sebastian G. Wolf, Jean Braun, and Ritske S. Huismans

Mountain building through continent-continent collision is typically accommodated by crustal thickening and creates topography as a consequence of isostatic compensation. Precipitation-fueled erosion, in-turn, counteracts orogen growth and provides a feedback-loop between tectonics, surface processes, and climate. Climate on Earth varies on different timescales and with variable dominant periodicity. Orbital forcings, e.g. Milankovitch cycles, change climate with periods up to in the order of 1e5 years, while internal “tectonic” forcings change climate on longer timescales in the order of (several) Myrs. The feedback between tectonics and climate-fueled erosion raises the question: How do collisional mountain belts respond to climatic variations on Earth? Here, we use numerical coupled tectonic-surface processes models to explore the influence of periodic climatic variations on collisional mountain building on Earth, specifically focusing on the evolution of sediment flux and topography. Our results from the coupled numerical models are compared to and supported by a simple analytical solution. We find that climatic forcings with a short period have a small effect on orogen height (Gain G < 0.1), that is lagging by 1/4 phase, while the effect on the sediment flux is in phase and strong (G 1). These results are independent of orogen type and expected to be observable in orogens limited in height by crustal strength or erosional efficiency. Climatic forcings with a long period result in a low gain in sediment flux (G < 0.3), that is lagging by up to 1/4 phase. The effect on topography is in phase and with a high gain of up to G 1. However, the effects of long-period forcings are not well expressed in strength-limited orogens and can primarily by observed in erosion-limited orogens. Comparing our modelling results with typical tectonic and surface processes timescales of orogens on Earth shows that variations in erosional efficiency due to orbital forcings, i.e. Milankovitch cycles, are likely detectable in the sedimentary record, while it is challenging to disentangle the autogenic dynamics of mountain building and periodic long-term climatic forcings.

How to cite: Wolf, S. G., Braun, J., and Huismans, R. S.: Periodic climatic variations during collisional orogenesis – insights from coupled tectonic-surface-process models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15067, https://doi.org/10.5194/egusphere-egu24-15067, 2024.

EGU24-15427 | ECS | Posters on site | GM8.1

River long profile modelling since the Mid-Pleistocene for the Río Santa Cruz, Southern Patagonia. 

Andreas Ruby, Fergus McNab, Taylor Schildgen, Andrew Wickert, and Victoria M. Fernandes

Alluvial rivers connect sediment sources in mountain belts to depositional basins. They not only transport water and sediment, but also adjust to changing forcing conditions by aggrading or incising their beds, a process potentially recorded by fluvial terraces. The formation of stepped terrace sequences is commonly thought to be driven by cyclic changes in sediment and water supply, but may be modulated by rock uplift or sea-level changes.

The Río Santa Cruz in Southern Patagonia, Argentina, flows ca. 250 km from its glacial headwaters in the Andes eastward to the Atlantic Ocean. There are no major tributaries or substantial anthropogenic impacts along its course. A set of at least six exceptional fluvial terraces stretches along ca. 230 km and rise up to 110 m above the river. Our preliminary 10Be cosmogenic nuclide exposure dates show that river incision began at ca. 1 Ma, and that terrace formation proceeded in roughly 100-ky intervals, suggesting control by orbital climate cycles, likely through their impacts on the sediment-to-water supply ratio. However, a step in the terrace age-elevation sequence between 700 and 300 ky points to a change in net incision rate at that time. Particularly at the upstream end of the river, terraces have been uplifted at a rate nearly twice as high compared to the rest of the river.

While it is likely that multiple factors affected the evolution of the Río Santa Cruz over the last 1 Myr, the magnitude and spatial pattern of impacts from these different drivers is unclear. We apply a recent numerical model (GRLP), implemented here as a simple single-thread channel, to solve for the channel long profile evolution under different forcing scenarios. This approach allows us to test the impacts of individual, or combinations of, drivers on river-profile evolution.

Our results suggest that Late Pleistocene 100 ky climate cycles have had the main impact on long profile evolution, especially along the upper 70 km of the river, with aggradation-incision cycles of up to an order of 10 m in magnitude. In contrast, sea-level change does not seem to influence significantly long profile evolution, as the exposed offshore slope does not change significantly compared to that onshore. To match the vertical distribution of terrace surfaces requires a long-term uplift rate of around 0.2 mm/yr, but with a hiatus between 700 and 300 ky. To accurately simulate the full terrace sequence, enhanced uplift is required upstream, decreasing exponentially towards the middle reaches.

How to cite: Ruby, A., McNab, F., Schildgen, T., Wickert, A., and Fernandes, V. M.: River long profile modelling since the Mid-Pleistocene for the Río Santa Cruz, Southern Patagonia., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15427, https://doi.org/10.5194/egusphere-egu24-15427, 2024.

EGU24-15722 | Posters on site | GM8.1

Quaternary evolution of the Danube along Lower Danube Gorge (Iron Gates) and Oltenia Plain (Romania, SE Europe) – a literature review 

Ioana Perșoiu, Nicolae Cruceru, Maria Rădoane, Luminița Preoteasa, and Zsófia Ruszkiczay-Rüdiger

Recent investigations on the sedimentary infill of the western Dacian Basin suggest that between ~4.8 Ma and 4.2 Ma (Dacian) the Danube and its tributaries formed a deltaic front at the exit from the Lower Danube Gorge (LDG) known also as Iron Gates. The appearance of a large fluvial system (the proto-Danube) connecting the two basins was dated to ~4.0 Ma with the water course becoming fully formed and discharging into the Black Sea after ~3.7 Ma.

In the present paper, the emphasis falls on the Quaternary history of the Danube in the area of the LDG and the Oltenia Plain, the western extremity of the Dacian Basin. The proposed review summarizes investigations of geomorphology and fluvial sedimentology in the region performed during the last 100 years. Morphological, sedimentological, tectonic, and relative chronological information is brought together to advance an overview of the spatial distribution of terrace fragments, their relative altitudes, associated sedimentary structures, available relative chronological frameworks (based mainly on macro- and microfossils) and documented minor deformations associated with local tectonic structures.

During the Quaternary, incision of the Danube at the LDG was estimated to be over 250 m. This incision corresponds to a number of at least 7 levels of strath terraces, preserved in a fragmentary way along the narrow passages but better conserved in the successive local tectonic depressions along the LDG. Here 7-10 terraces have been described, among which the lowest 5-6 were attributed to the Quaternary.

Downstream of the LDG, the Danube developed a large alluvial fan during the Early Quaternary, the remains of which are currently located at over 180 - 200 m r.a., while in the last ~1 Ma it developed a system of 7 (8?) terraces from ca. 140 - 170 m to 4-7 m r.a. These alluvial terraces attest for a constant southward migration of the Danube to its current position, under the influence of local subsidence and/or of large amount of incoming sediments deposited by the tributaries arriving from the north, draining the southern flanks of the uplifting Southern Carpathians.

Through this analysis, we aim to highlight the characteristics of the Quaternary history of the Danube in two distinct sectors: the LDG and the area downstream to it, the Oltenia Plain down to Jiu River, the first important tributary of the Danube downstream to the LDG. The final objective of this exercise is to create the framework for the first investigations of numerical age determination of terraces along the lower sector of the Danube.

Funding: PNRR-III-C9 2022 - I8, project code CF 253/29.11.2022, no: 760055/23.05.2023.

How to cite: Perșoiu, I., Cruceru, N., Rădoane, M., Preoteasa, L., and Ruszkiczay-Rüdiger, Z.: Quaternary evolution of the Danube along Lower Danube Gorge (Iron Gates) and Oltenia Plain (Romania, SE Europe) – a literature review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15722, https://doi.org/10.5194/egusphere-egu24-15722, 2024.

EGU24-16248 | Posters on site | GM8.1

Quaternary denudation rates in the Tianshan 

Jérôme Lavé, Julien Charreau, Pierre-Henri Blard, Etienne Large, Catherine Zimmermann, Stéphane Dominguez, and Wang Sheng Li

The Earth surface, where life develops and stands, is strongly affected by denudation which is the sum of physical erosion and chemical weathering. Denudation impacts soil formation and agriculture, affects the relief stability and, at the geological time scale, controls the atmospheric CO2 via the weathering of silicates and the production of sediments that later bury organic matter in the oceans. In the context of global warming, it is particularly important to predict how denudation will change and hence impact the Earth Surface where we live. This requires to understand the links between past climate variability and denudation changes, especially during the Quaternary when Earth experienced rapid climate oscillations of amplitude similar to what is expected in the future due to anthropic impact. To reach this goal, quantitative estimate of past denudation rates during the Quaternary are needed.

In this study, we reconstruct Quaternary paleo-denudation rates in the Tianshan range located in Central Asia because (1) it is a major orographic barrier that likely played an important role during the onset of Quaternary glaciations, (2) regional climate variations have been well documented by the geochemical and isotopic analyses of speleothems in caves and (3) well dated Quaternary deposits are abundant in the piedmonts

To reconstruct basin average paleo-denudation rates we used the inherited 10Be concentrations derived from the inversion of 10Be cosmogenic depth profile collected across abandoned alluvial surfaces. We used a unique inversion technique to reprocess preexisting data and also analyze 5 new cosmogenic depth profiles located in the northern Tianshan. In this region, to extend the dataset we have also collected 9 ancient river sand samples along the magnetostratigraphically dated Jingou He section. For comparison between all data, paleo-denudation rates are normalized to modern 10Be derived denudation rates across the same drainage basin. This yields to a 0-1.5Ma record of paleo-denudation rates that is compared to climate variations to discuss the potential links between the two.

How to cite: Lavé, J., Charreau, J., Blard, P.-H., Large, E., Zimmermann, C., Dominguez, S., and Sheng Li, W.: Quaternary denudation rates in the Tianshan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16248, https://doi.org/10.5194/egusphere-egu24-16248, 2024.

EGU24-16382 | Orals | GM8.1

Quaternary intraplate surface uplift and opening of the Cenozoic Madrid Basin (Central Iberia) 

Manuel Montes, Julien Babault, Elisabet Beamud, Miguel Garcés, Aratz Beranoaguirre, and Pablo Pelaez-Campomanes

The Central Range, the Iberian Chain and the Toledo Mountains in central Iberia were built during the Paleogene and Neogene alpine deformation, in response to shortening and thickening of the crust. The Cenozoic Madrid Basin in central Iberia was filled under endorheic conditions, fed by clastic sediments supplied from these mountains. This sediment influx led to the accumulation of over 3km of clastic sediments, primarily occurring during the Oligocene and early Miocene epochs. Presently, the river network, connected to the Atlantic Ocean, has carved into the sedimentary basin, resulting in an incision exceeding 200 meters.

The most recent endorheic lacustrine sediments in the center of the Basin are commonly believed to have been deposited during the late Miocene (~6 Ma). Recently published dating of alluvial pediments in the northwestern part of the Basin using the cosmogenic nuclide method suggests that the basin experienced a semi-endorheic period lasting around 3 Ma (~6.4 Ma to >2.4 Ma). It is proposed that the onset of glacial/interglacial oscillations at ~3.35 Ma (M2 event) would have driven the overspilling of the closed sedimentary Basin, establishing its connection to the Atlantic River network (Karampaglidis et al., 2020).

We present a new stratigraphic framework based on a new magnetostratigraphic analysis of the Plio-Quaternary deposits located in the center of the Madrid sedimentary Basin, incorporating new paleontological data and absolute U-Pb carbonate dating. Our findings indicate lacustrine endorheic conditions prevailed at least until 2.6 Ma. Moreover, on top of the lacustrine deposits, an accumulation of clastic deposits and carbonated paleosoils persisted until 1.7+-0.3 Ma. Modeling the transient incision within the Basin revealed a subsequent wave of incision propagating from the South to the North along the Central System mountains. Consequently, the onset of river incision appears to be more recent than previously acknowledged and unrelated to the onset of Quaternary climate oscillations. The long-wavelength deformation and the southward tilting of the youngest lacustrine deposits, combined with the age of the overlying paleosoils, suggest a mantle-driven surface uplift of Central Iberia during the last 1.7+-0.3 Ma. Previous studies suggested that regional surface uplift and the building of the Iberian Meseta began either at 20 Ma or after 3 Ma, depending on the methodology employed. The observed incision history in the Madrid Basin aligns with the latter estimation and even suggests a more recent age for a mantle-related surface uplift and the opening of the Cenozoic Madrid Basin.

 

Reference:

Karampaglidis, T., Benito-Calvo, A., Rodés, A., Braucher, R., Pérez-González, A., Pares, J., Stuart, F., Di Nicola, L., and Bourles, D., 2020, Pliocene endorheic-exhoreic drainage transition of the Cenozoic Madrid Basin (Central Spain): Global and Planetary Change, v. 194, p. 103295.

How to cite: Montes, M., Babault, J., Beamud, E., Garcés, M., Beranoaguirre, A., and Pelaez-Campomanes, P.: Quaternary intraplate surface uplift and opening of the Cenozoic Madrid Basin (Central Iberia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16382, https://doi.org/10.5194/egusphere-egu24-16382, 2024.

River terraces form as a response to regional uplift and climatic fluctuations (Bridgland & Westaway, 2008). While the intensity of climatic oscillations controls trends of aggradation and incision, it is uplift that determines the amplitude of the vertical spacing between consecutive terraces (Demoulin et al., 2017). Glacial and periglacial processes may amplify these trends providing distinct stratigraphic markers on climate and tectonic processes in the fluvial terrace record. Over several glacial-interglacial cycles, terraces can form complex sequences often referred to as a river 'terrace staircase'. Terrace staircases are not necessarily limited to mid- and high latitudes and do often lack (consistent) age models, as accurate radiometric and biostratigraphic time constraints are lacking when records extend into the Mid- and Early Pleistocene. Morphostratigraphy can thereby add valuable information if data on terrace strath (base unconformity) or tread (top unconformity) elevation are available. However, elevation information alone may not be sufficient. Especially for old terraces, that may be patchily preserved, a synopsis of sedimentologic and age data in a morphologic context may be necessary, to uncover stratigraphic questions.

We present a GIS based toolset for R, that is designed to i) detect and map potential terrace surfaces from digital elevation data (3D view, mapping), ii) statistically evaluate potential terraces together with additional geological information along 2D profiles (2D view, modelling), iii) transform resulting models in a map view.

The toolset allows a semiautomated workflow, optimized, to deliver quick results, enabling mapping and correlation of terraces at mountain range scale. Central part for data evaluation and illustration are 2D profiles. To minimize potential projection artifacts, the profile lines are optimized in a 3D view, by detecting the orientation with best correlation of terrace top elevation data, indicative for paleo-flow and thus ideal local profile line orientation. In the 2D view terrace elevation data is statistically evaluated and models, including error estimation, are fitted to each terrace stratigraphic unit. Additional control is contributed via including outcrop and geologic map information in the profile views.

We tested the toolset in the North Alpine Foreland, where more than a century of extensive Quaternary research lead to a vast resource of available geodata and detailed terrace stratigraphic maps. Terraces of up to postulated Early Pleistocene age are partly preserved well and over large areas. However, despite the abundance of data, stratigraphic inconsistencies exist in the current foreland wide terrace stratigraphic model. These need to be addressed, when using local terrace staircases as an archive of geodynamic information. This qualifies the North Alpine Foreland as an ideal test site for our code.

References:

Bridgland, D., Westaway, R. (2008): Climatically controlled river terrace staircases: A worldwide Quaternary phenomenon. Geomorphology 98, p. 285-315. Elsevier. doi:10.1016/j.geomorph.2006.12.032

Demoulin, A., Mather, A., Whittaker, A. (2017): Fluvial archives, a valuable record of vertical crustal deformation. Quaternary Science Reviews 166, p. 10-37. Elsevier. https://doi.org/10.1016/j.quascirev.2016.11.011

How to cite: Pollhammer, T., Salcher, B., and Fuchs, S.: MAMU: an R package for GIS-based river terrace mapping, morphostratigraphic evaluation of terrace maps and outcrop data and river long profile modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16766, https://doi.org/10.5194/egusphere-egu24-16766, 2024.

EGU24-17993 | Posters on site | GM8.1

Recent denudation rates of southwestern Madagascar from a 10Be analysis of river sand samples 

Pierre-Henri Blard, Etienne Large, Julien Charreau, Alfred Andriamamonjy, and Amos Fety Michel Rakotondrazafy

Many regions, though tectonically inactive, present significant reliefs of elusive origins. In these areas, it is critical to constrain denudation rates to assess the long-term evolution of these reliefs, but data and thus information on what controls their spatiotemporal evolution are scarce, especially in the Southern Hemisphere.

In this study, we present in-situ cosmogenic 10Be data from 14 new sand samples of main rivers and their tributaries of southwestern Madagascar, a subtropical island of southeastern Africa (Indian Ocean). This island presents in its central part a low relief high plateau composed of Mesoarchean to Neoproterozoic crystalline basement, a narrow coastal plain in its eastern part, separated from the central plateau by a great escarpment, and two large sedimentary basins of Carboniferous to Neogene ages in its western part. Its recent (i.e., past 15 Ma) tectonic activity and associated uplift is mainly attributed to mantle upwelling, probably related to the East African Rift System, creating long-wave uplift of 1 to 2 km. Limited seismicity associated with extensive settings is measured on the island. In terms of climate, Madagascar undergoes a monsoon type of climate with a strong gradient in humidity from northeast to southwest.

Our new cosmogenic 10Be data comes in complement of an important dataset of 99 samples previously published in three different studies. This brings the total dataset to 116 samples, covering over 50% of the total island surface. Our results are in good agreement with the previously published data with overall low denudation rates (4 ± 1 to 30 ± 6 mm/ka). This dataset allows exploring how the island erodes and calculating and comparing sediment fluxes from the eastern and western sides. Our results show that, although the eastern great escarpment is retreating at rates of 182 to 1886 m/Ma, average denudation rates of the basins draining it (16.6 mm/ka) are comparable, though slightly lower than the average denudation rates we measured in the southwestern basins (17.2 mm/ka).

How to cite: Blard, P.-H., Large, E., Charreau, J., Andriamamonjy, A., and Rakotondrazafy, A. F. M.: Recent denudation rates of southwestern Madagascar from a 10Be analysis of river sand samples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17993, https://doi.org/10.5194/egusphere-egu24-17993, 2024.

EGU24-18199 | ECS | Orals | GM8.1

Quaternary incision dynamics of the western to central Alpine valleys from cave systems investigations 

Vivien Mai Yung Sen, Pierre Valla, Yann Rolland, Stéphane Jaillet, Xavier Robert, Miguel Borreguero, Christian Crouzet, Julien Carcaillet, Edwige Pons-Branchu, Olivier Bruguier, Nouméa Boutin-Paradis, Emmanuel Malet, and Christophe Gauchon

Plio-Quaternary global climate changes had major impacts on landscape dynamics and relief evolution worldwide. The Quaternary onset and intensification of the glaciation in the European Alps greatly reshaped the mountainous reliefs with deep glacial carving of the modern main valley systems. Quantifying this climate forcing on the long-term relief evolution is challenging because of the poor preservation of the surface geomorphic markers in a context of strong landscape rejuvenation. Previous studies have shown that a major incision phase occurred for the Aare and upper Rhône valleys (Switzerland) since the mid-Pleistocene transition (onset of the 100-ka glacial-interglacial cycles). But the dynamics of this incision phase remains poorly constrained in both time and space across the Alpine realms. Moreover, the Pliocene to Lower Pleistocene Alpine relief dynamics is still largely unknown. To fill this current knowledge gap, we study cave systems in karst environments which are widespread in the frontal part of the western to central Alps. Karst network development and associated cave sediment records are closely coupled with valley evolution and can be preserved for timescales of million years. They are therefore ideal proxies for quantifying long-term relief dynamics.

This study focuses on 3 cave systems nearby the Isere valley (western French Alps) and 1 cave system at the head of the Sarine valley (central Swiss Alps). We apply a multi-method approach that combines 3D analysis of the cave networks with geochronological data on both the detrital sediments (26Al/10Be burial dating and paleomagnetism) and speleothems (U/Th and U/Pb dating).

Our results show a significant development of the major Alpine cave systems during the Pliocene, in agreement with previous studies. The abandonment of the perched networks around the Isère valley highlights a first incision phase in the frontal part of the Alps at the Pliocene-Quaternary transition. The apparently later abandonment of the cave system in the upper Sarine valley (~1.8 Ma) suggests an apparent lag in the incision onset for the upper Alpine watersheds. The main incision phase of the Isère valley to its modern base level (i.e. not considering the overdeepened section) took place in the early Middle Pleistocene from ~800 ka up to 450 ka, therefore occurring over only few glacial cycles. Our results imply thus a rapid response time (i.e. few 100 ka) of the major Alpine glacial valleys physiography to the Plio-Quaternary climatic forcing.

How to cite: Mai Yung Sen, V., Valla, P., Rolland, Y., Jaillet, S., Robert, X., Borreguero, M., Crouzet, C., Carcaillet, J., Pons-Branchu, E., Bruguier, O., Boutin-Paradis, N., Malet, E., and Gauchon, C.: Quaternary incision dynamics of the western to central Alpine valleys from cave systems investigations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18199, https://doi.org/10.5194/egusphere-egu24-18199, 2024.

EGU24-18699 | ECS | Orals | GM8.1

A landscape evolution model of how uplift has shaped drainage patterns in Central Europe 

Maximilian Rau, Wolfgang Schwanghart, and Michael Krautblatter

The large-scale reorganization of drainage patterns is one of the most enigmatic events in the landscape history of Central Europe. In particular, the rivers Main and Neckar show a reversal of the flow direction from southeast to northwest. Historically, this has been interpreted as a consequence of the subsidence of the Upper Rhine Graben (URG) and the subsequent lowering of the base level. However, the high uplift rates along the shoulders of the URG, which suggest an increased southeastward tilt, raise questions. This prompts the investigation of alternative uplift patterns contributing to the observed river reversals.

This study uses a new version of the landscape evolution model TTLEM and river analyses with TopoToolbox to investigate the potential role of large-scale lithospheric folding resulting from the collision of the Alps. Our research challenges the conventional narrative by examining whether such folding could be a driving force behind the enigmatic flow reversals in the Main and Neckar rivers.

During the transition from the Cretaceous to the Paleocene, a dome-shaped exhumation event in Europe led to the establishment of a radial river network originating in higher regions. Some rivers still have their original flow directions, such as the Wörnitz and the Brenz, or the Neckar, which now flows in the opposite direction. In southern Germany, a network of rivers flowed in a southward or southeastward direction. The Eocene marked the beginning of the formation of the URG, accompanied by a marked uplift of the Graben shoulders and a tilting of southern Germany to the east-southeast. During this period, the flow directions of the rivers remained constant, and the sinking URG initially failed to extend its drainage basin beyond the graben shoulders.

The pivotal moment in the redirection of the rivers has been evident since the Miocene when lithospheric folding occurs parallel to the Alpine front. This previously unnoticed event highlights a crucial link between the collision of the Alps and the redirection of the Main and Neckar rivers. Our findings shed light on the complex interplay of tectonic forces, landscape evolution, and river dynamics, challenging existing paradigms and contributing to a deeper understanding of the geomorphic history of Central Europe.

How to cite: Rau, M., Schwanghart, W., and Krautblatter, M.: A landscape evolution model of how uplift has shaped drainage patterns in Central Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18699, https://doi.org/10.5194/egusphere-egu24-18699, 2024.

EGU24-20314 | ECS | Orals | GM8.1

Climate storminess as a driver of surface processes and a limiting factor for topographic responses to rock uplift 

Rebekah Harries, Sim Reaney, Germán Aguilar, and Linda Kirstein

In the south-central Andes, a long-term persistent pattern in climate aridity has been linked to sediment storage in mountain valleys and the resultant delaying of river steepening in response to rock uplift over millennia. This conceptual model implies that the landscape has a long-term trajectory for sediment export that may be sped up or slowed down by projected climate change. With this framing, we seek to investigate how changes in precipitation patterns and discharge regimes impact the transient evolution of a semi-arid, post glacial landscape and its physical processes. Changes in precipitation patterns and discharge regimes are understood to drive substrate erosion, sediment transport and changes in channel patterns and dimensions. They also alter vegetation, weathering regimes and catchment morphologies that influence sediment supply and slope-channel coupling.  

Using field data, we investigate how a sequence of floods has driven the conveyance of sediment through a semi-arid, postglacial landscape. Along the Rio Teno in Central Chile, we quantify changes in vertical bed structure, bed surface grain size, clast lithology, river morphology and slope-channel connectivity in March 2021 and again following an extreme and a large flood event in 2023. Our findings highlight the importance of including the full range of flood magnitudes that exceed critical entrainment thresholds in models of sediment export and landscape evolution. While extreme events do significant work in redistributing sediment within a catchment, it is the higher frequency, lower magnitude events and snowmelt cycles that evacuate sediment and reset base levels. In the context of climate change, a hydroclimate dominated by extreme floods in this landscape would likely result in greater sediment export from postglacial upper reaches, sediment storage within valleys in mid-reaches and lateral erosion and sediment export along the lowest reaches. This potential change has significant implications for understanding the fate of mountain landscapes and their human populations over the next century. 

How to cite: Harries, R., Reaney, S., Aguilar, G., and Kirstein, L.: Climate storminess as a driver of surface processes and a limiting factor for topographic responses to rock uplift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20314, https://doi.org/10.5194/egusphere-egu24-20314, 2024.

Rifted margins include the Earth’s most voluminous sediment accumulation, host important energy and natural resources providing a rich archive for global environmental changes. However, revealing the deep structure within rifted basins is challenging, because their deep part is commonly vogue in seismic images and their structure is complex because it is usually affected by several deformation phases that occurred during their long history. The Levant Basin is a good example for a deep Tethyan basin that formed alongside Gondwana breakup. Unlike many Tethyan basins that were eroded and/or severely deformed during the Alpine orogeny, the Levant Basin has preserved a thick (>15 km), long-lived (>250 Myr), and continuous sedimentary record providing a world-class archive to study the role of post-rift subsidence and sediment supply on depocenter evolution.

We synthesize regional seismic interpretations from previous studies utilizing thousands of kilometers of seismic lines and tens of wells in a unified dataset. By applying a low pass post-stack filtering on 2D seismic reflection surveys covering the Israeli economic water, we improved the imaging of the deeper reflectors and enabled the distinction of the deep units, which otherwise appeared blurred at conventional industry processed data. Based on thickness analysis, we identify the syn-rift to post rift transition. The regional seismic horizon marking this transition is tied to dated horizons in wells providing a concrete age constraint of pre- 163 Ma (end of Callovian) for the end of rifting, which was previously debated. In addition, we show that rifting comprises at least two phases, which are equivalent to three extensional phases documented onshore: Permian, Mid-Late Triassic and Early-Mid Jurassic.

Analysis of 11-thickness maps showcase the 250 Myr evolution of sedimentary filling, opening a discussion about the parameters that controlled depocenter migration in relation to tectonic subsidence and sediment supply. We distinguish between periods during which near margin accumulation dominated versus periods during which more sediments accumulated in the deep basin. We explain these variations in light of sediment sources in surrounding continents and paths of transport. Marginal accumulation periods (syn-rift, early post-rift, and Pliocene-Quaternary) represents dominance of shallow biogenic and nearby terrestrial (silisiclastic) sources, whereas, deep basin accumulation periods represent sediment supply that was either provided from the water column (pelagic micro- and nano-fossils, Santonian to Mid-Eocene), or transported mostly from Africa with minimal accumulation along the Levant margin (during the Late-Eocene to Miocene).

How to cite: Sagy, Y. and Gvirtzman, Z.: Interplay between early rifting and sedimentary filling along 250 Myr of a long-lived Tethys remnant: the Levant Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20660, https://doi.org/10.5194/egusphere-egu24-20660, 2024.

TS5 – Modelling, Imaging and Methodological Developments

EGU24-496 | ECS | Orals | TS5.1

Rayleigh and Love Wave Tomographic Imaging of Heterogeneous Crust in a magmatic rift: the Turkana Depression, East Africa 

Martin Musila, Francesco Civilini, Cynthia Ebinger, Ian Bastow, Rita Kounoudis, Finnigan Illsley-Kemp, and Chris Ogden

Theory and geoscientific observations demonstrate that plate stretching, heating, faulting, active and frozen magma intrusions, and extrusive eruptive products are consequences of mantle upwelling mechanism driving continental rifting. Problematic to this picture is the lack of consensus on how, when and where these processes modify the crust’s thermal and mechanical structure. We use data from East Africa’s 300-km wide Turkana Depression to investigate how the superposition of these rift processes and the spatial migration of the active plate boundary through time within one geodynamic setting modify the crust’s structure. Utilizing ambient noise seismic methods and data from the 34 station Turkana Rift Arrays Investigating Lithospheric Structure (TRAILS) seismic network, we invert for Rayleigh and Love tomographic models and overlay results with our local earthquakes crustal splitting results. Preliminary results show that regions that experienced Eocene flood magmatism have localized high Vs of > 3.4 km/s at mid-lower crustal depths implying that flood magmatism is fed by unknown localized centers and/or dike swarms. Quaternary eruptive centers with Vs < 3.4 km/s at mid-lower crustal depths are punctuated and irregularly spaced suggesting that bottom-up mantle upwelling influence their location. Regions with superposed Cretaceous-Paleogene and Miocene-Recent rift phases have persistent low velocities (Vs ≥ 3.8 km/s) to the mid-crust with thinner crust (~ 20 km); the active Miocene-Recent rift structures are oblique to the largely inactive Cretaceous-Paleogene rift structures implying no reactivation of pre-existing structures during modern-day rifting.

How to cite: Musila, M., Civilini, F., Ebinger, C., Bastow, I., Kounoudis, R., Illsley-Kemp, F., and Ogden, C.: Rayleigh and Love Wave Tomographic Imaging of Heterogeneous Crust in a magmatic rift: the Turkana Depression, East Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-496, https://doi.org/10.5194/egusphere-egu24-496, 2024.

EGU24-608 | ECS | Posters on site | TS5.1

Miocene to Quaternary Seismic Stratigraphy and Tectonic Evolution of the Marine Area Between Çandarlı Bay and Lesbos Basin, Northeastern Aegean Sea 

İrem Elitez, Tuba İslam, Derya İpek Gültekin, and Cenk Yaltırak

This study focuses on the marine area located between Çandarlı Bay and Lesbos Basin in the Northeastern Aegean Sea. The high quality multibeam bathymetry data, their processing and interpretation with the onshore structures and an integrated interpretation with seismic reflection profiles allowed to map the offshore active faults, to prepare the seismic stratigraphy and to evaluate the tectonic evolution of the marine area between Çandarlı Bay and Lesbos Basin. In addition, thickness maps were generated from seismic reflection profiles and seismic stratigraphic units were correlated with the Foça-1 well to reveal the characteristics of the deposited strata in this region. The seismic stratigraphic units were also compared with onshore geological units.

Five major seismic stratigraphic units were identified and all of which are compatible with each other from the Çandarlı Bay to the Gulf of Izmir. The findings suggest continuous sedimentation from the Burdigalian (Lower Miocene) to the present day. A predominantly volcaniclastic sequence deposited in the Burdigalian-Serravalian period rests on basement rocks. This unit is overlain by Tortonian clastics and carbonates interbedded with volcanic rocks. Tortonian sediments are followed by about 300-500 m thick clastics and anhydrites, which were deposited in an environment corresponding to the Messinian salinity crisis in the Mediterranean Sea. The post-Messinian unit is of Pliocene age and starts with upper Miocene limestones at the base and transitioning upwards into clastic rocks. The stratigraphy concludes in the upper part with a Quaternary unit, which is mainly composed of fine-grained clastics and has been influenced by sea-level changes.

The study area is dominated by both NW-SE and NNW-SSE-striking normal faults and two distinct tectonic phases have been identified. The first phase spans from the Miocene to the end of the upper Miocene and is characterized as a supra-detachment basin associated with the development of core complexes in the region. These faults do not extend to the surface in seismic sections and are indicative of an early-stage tectonic activity. The homogeneity of the sediment thickness suggests a slowdown in tectonic activity during the Tortonian-Messinian period. In the Plio-Quaternary period, the sediment thicknesses indicate uplift in the surrounding region. Additionally, the bathymetric traces of faults shaping the Lesbos Basin to the west of Çandarlı Bay indicate the presence of a new tectonic system.

How to cite: Elitez, İ., İslam, T., Gültekin, D. İ., and Yaltırak, C.: Miocene to Quaternary Seismic Stratigraphy and Tectonic Evolution of the Marine Area Between Çandarlı Bay and Lesbos Basin, Northeastern Aegean Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-608, https://doi.org/10.5194/egusphere-egu24-608, 2024.

The seismically active Andaman-Sumatra subduction zone hosts a prolonged back-arc basin, with the Andaman Sea encompassing several volcanoes, notably the active Barren volcano and the dormant Narcondam volcano. Metamorphic features like the Alcock Rise and Sewell Rise are prominent in this region, experiencing oblique subduction between the Indo-Australian and Eurasian plates alongside backarc seafloor spreading. This convergence has led to significant crustal-scale fault systems like the Great Sumatra Fault, the Andaman Nicobar Fault, and the Sagaing faults. Due to limited geophysical datasets, particularly offshore Narcondam, we utilized three reflection lines (Line 1: 30 km, Line 2: 36 km, and Line 3: 36 km) derived from industry and corresponding satellite gravity data to complete the objectives of this study. We employed F-K and parabolic Radon filtering methods on the seismic data, eliminating noise and seawater multiples from the lengthy east-west 2D seismic profile lines. Subsequently, semblance-based conventional processing techniques were applied to visualize the subsurface. The water depths in the basin range from 1262 to 1554 meters along the profile, with the thickest sediment (~2.35 km) observed at CDP-2877 on Line 1. Satellite gravity data aided in deciphering the crustal architecture of the study area using gravity modeling. The crust's nature beneath Narcondam remains a subject of debate, whereas below Alcock Rise, some authors suggest either oceanic or island arc crust. Our integrated geophysical approach, encompassing gravity modeling, seismic interpretation, and focal mechanism solutions, pivots in evaluating evidence related to the paleo ANF. This comprehensive method allowed for an in-depth examination of the crustal architecture and upper mantle structure beneath both Narcondam Island and the northern part of Alcock Rise. The interpreted seismic section along with the focal mechanism interpretation in the basin indicates the presence of the Paleo ANF, spanning the basin and extending to the Moho. Its significance lies in facilitating fluid migration and influencing depocenter variation during the basin's evolution.

How to cite: Srivastav, H., Ghosal, D., and Kumar, P.: Evidence of Paleo ANF and crustal architecture beneath the Narcondam: Insights from High-Resolution Reflection Seismic Data and Gravity modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3317, https://doi.org/10.5194/egusphere-egu24-3317, 2024.

Subsurface fault zones play an important role in fluid flow. However, the quantitative research regarding fault damage zones based on conventional seismic attributes is challenging. Therefore enhancing the interpretation of subsurface fault zones using advanced workflows is a priority. We try to highlight these apparent fault zone arrays using 3D seismic data from the M17 prospect. Based on the dip-steering cube computed from the original seismic data, several conditioning approaches were co-used with multiple seismic attribute calculations and a supervised neural network. The computed hybrid attributes based on these methods have enhanced the images of the fault zone arrays. We propose five basic types of fault zone architecture regarding the fault zone arrays based on quantitative analysis via the hybrid attributes and previous research. The fault zone types correspond to different linkage types, representing different evolution stages of fault zone growth. This research has implications for understanding the architecture and growth of related fault zone arrays.

How to cite: cui, L., dong, D., and huang, Y.: Insights into Fault Zone Architecture and Growth Based on Enhanced Image of Fault Zone Arrays Using Hybrid Attributes  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3512, https://doi.org/10.5194/egusphere-egu24-3512, 2024.

EGU24-3916 | ECS | Posters on site | TS5.1

Seismic Attenuation Imaging in the Western Part of the North Anatolian Fault Zone 

Wei-Mou Zhu, Luca De Siena, Lian-Feng Zhao, David G. Cornwell, Xiao-Bi Xie, Simona Gabrielli, Aqeel Abbas, Xi He, Lei Zhang, Panayiota Sketsiou, Stella Lamest, and Zhen-Xing Yao

Colossal and devastating earthquakes are typically associated with the slip and rupture of fault zones. Fault zone imaging is challenging yet crucial to understand fault structure and behavior, and consequently hazard assessment and mitigation. Seismic attenuation imaging provides constraints on the fault zone structure that are independent of seismic velocity imaging. Here, we image the S-wave total attenuation (Qs) structure of the western part of the North Anatolian Fault Zone (NAFZ) using data recorded by the DANA (Dense Array for North Anatolia) array. The area of interest is divided into three distinct regions by the northern and southern segments of the NAFZ, which extends from north to south: the Istanbul Zone to the north, the Armutlu Block in between, and the Sakarya Terrane to the south, respectively. The Armutlu Block exhibits much higher attenuation compared to the other two regions. The anomaly body has an attention value of 0.0008 with a notable 3D distribution pattern: It extends from 30.2°E to 30.6°E and around roughly 40.6°N following the northern strand of the NAF and shows a west-east trend, dipping deeper into the crust to the east from depths of 5 to 15 km. Combining previous geological, geodetic, micro-seismicity, and other geophysical observations, we inferred that the high values are a sign of fluid pathways. Micro-seismicity and strain distributions around the Armutlu Block are in line with the assumption fluids migrate through cracks and increased permeability attributed to the background stress, particularly residual stress after the 1999 M7.4 Izmit earthquake and M7.2 Düzce earthquake.

This research is supported by the National Natural Science Foundation of China (U2139206, 41974061, 41974054) and the Special Fund of China Seismic Experimental Site (2019CSES0103). The first author has also been financially supported by the China Scholarship Council (202204910302).

How to cite: Zhu, W.-M., De Siena, L., Zhao, L.-F., G. Cornwell, D., Xie, X.-B., Gabrielli, S., Abbas, A., He, X., Zhang, L., Sketsiou, P., Lamest, S., and Yao, Z.-X.: Seismic Attenuation Imaging in the Western Part of the North Anatolian Fault Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3916, https://doi.org/10.5194/egusphere-egu24-3916, 2024.

EGU24-4302 | ECS | Posters on site | TS5.1

Imaging of Main Himalayan Thrust in Central Seismic Gap using seismic interferometry   

Saneesh Ali T S, Sandeep Gupta, Sudesh Kumar, Krishnavajjhala Sivaram, and Vishal Rawat

The Main Himalayan Thrust (MHT) demarcates the boundary between the underthrusting Indian Plate and the overriding Himalayan orogeny. Stress accumulation on the MHT due to the underthrusting of the Indian Plate leads to the occurrence of bigger earthquakes in the Himalayas. It is, therefore, imperative to understand the MHT's geometry in different Himalayan segments. Furthermore, how this geometry varies along the Himalayan arc while taking into account the uneven distribution of earthquakes offers a comprehensive insight into earthquake nucleation in the region. The central seismic gap is one of the most significant segments of the Himalayas, which is considered a potential region for the proposed great earthquake in the future. This study focuses on defining the MHT geometry by constructing a 3-D model within the central seismic gap using the seismic interferometry technique.  We analyzed the data sets obtained from 159 broadband stations spread across the area to construct a comprehensive three-dimensional geometry of MHT. The different arc normal cross-sections highlight variations in the MHT's geometry along the arc in the central seismic gap.

Keywords: Main Himalayan Thrust, seismic interferometry, central seismic gap, crustal imaging.

How to cite: Ali T S, S., Gupta, S., Kumar, S., Sivaram, K., and Rawat, V.: Imaging of Main Himalayan Thrust in Central Seismic Gap using seismic interferometry  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4302, https://doi.org/10.5194/egusphere-egu24-4302, 2024.

EGU24-4975 | Posters on site | TS5.1

Deep borehole based subsurface geophysical monitoring network: TELLUS Project 

Yeonguk Jo, Sehyeok Park, and Changhyun Lee

We introduce a comprehensive strategy to monitor subsurface fault behavior and associated geophysical environment (e.g., micro-seismicity, stress, groundwater), using a deep borehole based monitoring system. This study provides an in-depth overview of the TELLUS (The Earth Login Leverage for Underground Signal) project, with its individual monitoring system tracking subsurface fault movements with high precision by deploying borehole seismometers, and gathering important data on various geophysical properties.

This paper details site selection process and characterizations, the operational framework on monitoring system installations, and the potential of deep borehole monitoring approach in advancing subsurface-related geophysical studies. We conducted extensive review of the distributions of major fault systems in the south-eastern part of South Korea. Subsequently, we strategically selected and arranged candidates for monitoring system installations. Total of six TELLUS deep borehole monitoring systems were installed in the vicinity of the major faults (Yangsan and Ulsan fault).

In the TELLUS observatories, preliminary monitoring data is being collected in real time, and this is establishing a foundation for a more precise understanding of the behavior of subsurface faults and the related geophysical environment. It would be expected that the comprehensive analysis of these datasets will further elucidate the intricate subsurface geophysics. This enhanced understanding promises to contribute substantially to our seismic risk assessment capabilities and to the broader field of geoscience research, offering new insights into earthquake prediction and geophysical phenomena.

How to cite: Jo, Y., Park, S., and Lee, C.: Deep borehole based subsurface geophysical monitoring network: TELLUS Project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4975, https://doi.org/10.5194/egusphere-egu24-4975, 2024.

EGU24-6400 | ECS | Posters on site | TS5.1

Accurate seismic phase picking using High-Order Statistics: the case study of the Irpinia Seismic Array in Southern Italy 

Giovanni Messuti, Mauro Palo, Silvia Scarpetta, Ferdinando Napolitano, Francesco Scotto di Uccio, Paolo Capuano, and Ortensia Amoroso

Fault imaging and characterization of crustal structures, along with source parameter estimation, strongly depend on reliable direct seismic wave arrival times. To lower the detection threshold of small earthquakes and improve the quality of fault imaging, dense arrays of seismic stations are being installed more and more frequently in different parts of the world. Given the rising number of new, denser seismic networks and the growing demand for high-quality seismic catalogs, the use of automatic techniques is crucial to efficiently process and analyze the vast amount of seismic data, contributing to the advancement of seismic research and monitoring capabilities.

The Irpinia fault system (Southern Italy) hosted in 1980 the M 6.9 earthquake and is currently monitored by the Irpinia seismic network (ISNet), which is composed of 31 seismic stations covering an area of about 100x70 km2 along the Campania-Lucania Apennine chain. ISNet was integrated by 200 seismic stations grouped in small-aperture arrays of 10 stations during the 1-year DETECT project (DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging). DETECT focused on the acquisition of a unique multiparametric dataset and aimed to monitor and image the fault system during the inter-seismic phase fostering at the same time the collaboration among various institutions.

The use of seismic arrays, in a region characterized by high seismic hazard, presents a unique opportunity to introduce a novel technique that accurately reveals the first arrivals of seismic phases of small earthquakes. We examined 226 micro-earthquakes, with magnitude ranging from -0.27 to 2.28, detected by the seismic arrays during the first six months of the DETECT project (September 2021 - February 2022). We present a novel approach that utilizes high-order statistics (HOS), computed on the vertical components of waveforms, to identify P-wave arrival times and provide reliability measurements for our predictions. The advantage of the arrays’ geometry enabled the integration of the HOS technique with a criterion designed to select the optimal onsets. The proposed methodology incorporated over 3,300 additional P-wave arrival times into the existing catalog. Furthermore, semblance measurements among traces recorded at the same array highlighted the superior quality of the selected picks compared to the existing ones.

This work is partially supported by project TOGETHER - Sustainable geothermal energy for two Southern Italy regions: geophysical resource evaluation and public awareness financed by European Union – Next Generation EU (PRIN-PNRR 2022, CUP D53D23022850001).

How to cite: Messuti, G., Palo, M., Scarpetta, S., Napolitano, F., Scotto di Uccio, F., Capuano, P., and Amoroso, O.: Accurate seismic phase picking using High-Order Statistics: the case study of the Irpinia Seismic Array in Southern Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6400, https://doi.org/10.5194/egusphere-egu24-6400, 2024.

EGU24-6580 | Orals | TS5.1 | Highlight

Seismic imaging of crustal fault systems 

CharLotte Krawczyk

The construction of geodynamic and reservoir models requires - as many other applications - the knowledge of fault signatures and fracture systems.  In general, structural images of the subsurface rely on sampling and experiment design, wavefield components retrieved, as well as coherence and focusing potential of the data recorded in different geological settings.  Nonetheless, direct geophysical images of especially sub-/vertical or inactive faults are still hampered by fracture complexity and associated diffuse wavefields.  Furthermore, back-tracing weak signals to their originating location remains one of the challenges for high-resolution imaging.  While petrophysical and mechanical rock properties characterize the hosting material as such, they can provide at the same time assistance in fault or horizon tracking, respectively, and may allow pattern identification, for instance by machine learning tools.

In the overview presented, we will discuss different examples from recent active and passive seismic surveys covering both sedimentary and hardrock environments using either dense or sparse seismic and fibre-optic arrays.  These experiments are adapted to investigation depths between some km and only few 10s of metres scale, encompassing geodynamic, geothermal, hazard and critical zone investigations.  Thereby, the wide applicability of seismic methods for imaging and characterizing distinct horizons, transitional zones, and fault systems is emphasized.

How to cite: Krawczyk, C.: Seismic imaging of crustal fault systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6580, https://doi.org/10.5194/egusphere-egu24-6580, 2024.

EGU24-7098 | ECS | Posters on site | TS5.1

Shallow velocity structure of the Tainan frontal thrust based on Eikonal tomography 

Tzu-Cheng Yang, Ying-Nien Chen, and Ruey-Juin Rau

    We deployed a dense array of 173 seismometers covering a 30 by 40 km2 area in the Tainan frontal thrust of southwestern Taiwan from February to June 2021. The seismic array with an inter-station distance of about 2 km, spanned from west to east, across four major tectonic regimes: Anping Plain, Tainan Tableland, Dawan Lowland, and Chungchou Tableland. Structurally, the Houchiali Fault separates the Tainan Tableland and Dawan Lowland, while the right-lateral Hsinhua Fault is located 5 kilometers northeast of the Houchiali Fault. For the Eikonal tomography analysis, we included data from ten BATS (Broadband Array in Taiwan for Seismology) stations, five stations from CWASN (Central Weather Administration Seismographic Network), and one station from TSMIP (Taiwan Strong Motion Instrumentation Program). These stations were strategically positioned at distances ranging from 40 to 80 kilometers away from the dense array, with azimuths between 45° to 140° and 270° to 360°. We then calculated the cross-correlation function (CCF) between 173 seismometers and these stations. These results were subsequently used by beamforming to measure the relative surface wave arrival times. To perform Eikonal tomography, we calculated the surface wave propagation of the ambient noise and the shallow velocity structure for each period between 4 and 10 seconds. Our result shows that the velocity on Tainan Tableland is almost uniform, which is probably due to the gently folded character of the underneath Tainan anticline. Meanwhile, a low-velocity zone of approximately 2.5 by 2.5 km2 with a 4s period was revealed northeast of the Houchiali Fault and southwest of the Hsinhua Fault, with a shear-wave velocity of approximately 0.5 km/s. Upon reaching the Hsinhua Fault to the northeast, the velocity increases five times to 2.5 km/s. For the 4s period, the average velocity in this region is approximately 1.5 km/s, however, the velocity distribution does not conform with the regional velocity models. This suggests the presence of potentially unexamined small-scale structures in this area. Furthermore, this area encountered strong shaking from three local or regional moderate earthquakes that occurred in 1946, 2010, and 2016 respectively. Coincidentally, the low-velocity zone aligns roughly with the soil liquefaction sites caused by these three events.

How to cite: Yang, T.-C., Chen, Y.-N., and Rau, R.-J.: Shallow velocity structure of the Tainan frontal thrust based on Eikonal tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7098, https://doi.org/10.5194/egusphere-egu24-7098, 2024.

EGU24-7099 | ECS | Posters on site | TS5.1

Three-dimensional shallow velocity structure beneath the urban agglomerations revealed by methane source and dense array 

Yunpeng Zhang, Liwei Wang, Weitao Wang, Shishuo Liu, Xiuwei Ye, Wei Yang, Shanhui Xu, and Xiaona Ma

The three-dimensional (3D) velocity structure beneath urban agglomerations is an important data for urban construction planning and earthquake hazard risk assessment. Combining a short-period dense array with the active source can enable us to conduct high-resolution imaging of shallow structures, with a short observation time. With the increasing limitations on the usage of explosives, we have developed a new type of active source, the methane source, which has been proven to be environmentally friendly, efficient, safe, and economical. It produces seismic waves by rapidly releasing high-pressure air in borehole by igniting oxygen and methane with the reaction products of carbon dioxide and water, and can be applied to various complex terrains to detect small-scale subsurface structures, particularly in cities and fault zones.

To obtain the high-resolution structure beneath the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), we deployed a dense array consisting of 6,172 short-period stations, and carried out 63 active source excitations using new methane green sources in 2020. Using the manually picked 16,885 first-arrival phases from 63-shots methane sources, we present the first high-resolution 3D shallow P-wave velocity structure (above 1.5 km depth) in the central area of the GBA. The obtained results show that (1) the velocity images have a good correspondence with the regional topography and shallow lithology distribution. The depression area presents a low Vp distribution, while the uplift area with high Vp anomalies, which corresponds to clastic sedimentary rocks, granites, and metamorphic rocks, respectively. (2) The velocities have a strong anomaly on both sides of the Guangcong fault, Shougouling fault, Zhujiangkou fault, and Baini-Shawan fault. Among them, the Shougouling fault has the strongest controlling effect, making the velocity images show obvious differences between the north and south side along the fault at different depths. (3) The cross-fault velocity profiles show that regional faults control the distribution and burial depth of sedimentary layers. Our study shows that combination using of new green methane source and dense short-period array is an effective method to detect the shallow velocity structure and fault system under urban agglomerations.

How to cite: Zhang, Y., Wang, L., Wang, W., Liu, S., Ye, X., Yang, W., Xu, S., and Ma, X.: Three-dimensional shallow velocity structure beneath the urban agglomerations revealed by methane source and dense array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7099, https://doi.org/10.5194/egusphere-egu24-7099, 2024.

EGU24-7510 | ECS | Posters on site | TS5.1

Seismic insights into the structure of the Balmuccia Peridotite within the Ivrea Verbano Zone 

Damian Pasiecznik, Andrew Greenwood, and Florian Bleibinhaus

In the Ivrea Verbano Zone (IVZ) Italy, which is characterized with lower-crustal rocks and fragments of upper mantle rocks, a high-resolution seismic survey is conducted across the Balmuccia Peridotite. This study is in preparation of a proposed deep scientific drilling project which focuses on targeting mantle rocks and understanding the region's complex geology. Specifically, we target characterizing structures within the peridotite body.

The seismic survey employs a fixed spread of 200 vertical geophones and 160 3C-sensors, spaced at ca. 10 m along three sub-parallel receiver lines spaced 40-80 m apart. Vibroseis source points are at 22 m stations along a 2.2 km line utilizing a 12-140 Hz 10 s linear sweep with 3 s listening time. The survey aims to explain the seismic characteristics of the peridotite body and its relation to the surrounding geological structures.

The P-wave traveltime tomography reveals a range of seismic velocities within the peridotite from 6 to 8 km/s, with a mean velocity of ca. 7 km/s. These variations reflect the heterogeneity of the peridotite, influenced by the presence of fractures and faults. Notably, the higher velocities observed are consistent with findings from laboratory studies on small-scale samples from the area. The reflection seismic analysis shows subvertical reflectors that coincide with the peridotite boundaries mapped at the surface. These reflectors come together at a depth of 0.175 km b.s.l., suggesting that the peridotite has a lens-like structure. In addition, several features within the peridotite suggest a highly fractured body. Nevertheless, limitations in the imaging process do not allow for a thorough interpretation of the area below the imaged lens-shaped body. A deep reflector is identified at approximately 1.3 km depth. This feature potentially marks the top of the Ivrea Geophysical Body (IGB), aligning with previous geophysical estimations.

How to cite: Pasiecznik, D., Greenwood, A., and Bleibinhaus, F.: Seismic insights into the structure of the Balmuccia Peridotite within the Ivrea Verbano Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7510, https://doi.org/10.5194/egusphere-egu24-7510, 2024.

EGU24-7896 | ECS | Posters on site | TS5.1

Physics-informed neural networks for 3D seismic travel time tomography 

Shaobo Yang and Haijiang Zhang

Seismic travel time tomography is a widely used technique to image the Earth’s interior. Recently, there have been growing interests in employing deep learning for seismic tomography, and physics-informed neural networks (PINNs) are attractive for their integration of physical information into the networks and their greater stability compared to conventional neural networks. PINNs have been successfully used in 2D tomography, including cross-hole tomography (Waheed et al., 2021) and surface wave phase velocity tomography (Chen et al., 2022). However, 3D seismic tomography based on PINNs has not been developed. Here we propose a novel method for 3D travel time tomography based on PINNs and show its effectiveness using both synthetic and real data. The network consists of two branches, one taking in the 3D coordinates of a pair of source and receiver for fitting observed travel times and another taking in the receiver location for predicting velocities. The loss function also consists of two terms, the data fitting residual term and the Eikonal equation residual term. In this way, the two branches are connected using the Eikonal equation loss function term. After training, the network can simultaneously reconstruct the travel time fields and estimate the subsurface velocities. Our method is tested using synthetic and real travel time data for seismic network in Parkfield, California. Compared to traditional travel time tomography methods, this approach offers many advantages, including meshless modeling, no need for regularization and independent on the initial velocity models.

How to cite: Yang, S. and Zhang, H.: Physics-informed neural networks for 3D seismic travel time tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7896, https://doi.org/10.5194/egusphere-egu24-7896, 2024.

EGU24-8875 | ECS | Posters on site | TS5.1

Body wave seismic attenuation tomography of the crust in the Sichuan-Yunnan Region, China 

Jiachen Wang, Haijiang Zhang, Jing Hu, and Ying Liu

   The Sichuan-Yunnan Region is located at the southeastern margin of the Tibetan plateau in southwest China. Determining the structure of southeaster margin of the Tibetan plateau is very important for understanding the eastward growth of the plateau. At present, most of seismic tomography studies are focused on resolving multiscale velocity anomalies of the crust and mantle. However, seismic attenuation structure of the crust and upper mantle in the Sichuan-Yunnan Region is less studied, which can be used to better understand the temperature regime and the distribution of partial melting. In this study, based on a high-resolution community velocity model of the crust and uppermost mantle in this area (Liu et al., 2021), we determined body wave attenuation structure in the Sichuan-Yunnan region using data from 350 stations and 9837 seismic events observed between 2010 and 2013 (Figure 1).

 

Figure 1. Distribution of seismic events (red circles) and stations (blue triangles) in the Sichuan-Yunnan region.

    Q value is a reduction to a dimensionless form of the more usual measures of attenuation (Knopoff, 1964. Body wave attenuation tomography typically needs to extract a parameter called t* from the displacement or velocity spectrum in the frequency domain to calculate Q using the following equation:

     

    Here the influence of frequency on Q was not considered. Using the measured absolute t* values, the attenuation structure was then determined with the following relationship between t* and Q:

    For the Sichuan-Yunnan region, we constructed three-dimensional Qp and Qs models with a horizontal spatial grid interval of 0.4° × 0.4°. Our attenuation models exhibit a high consistency with large-scale features in previous researches. In the shallow depths (<20 km), inside the Chuan-Dian diamond block, it exhibits high Q anomalies, which may be related to the high density and low porosity characteristics of the Emeishan Large Igneous Province (ELIP). Previous studies suggest the presence of high Vp and Vs anomalies in the same zone (Liu et al., 2021). In comparison, most of the fault zones show low Q anomalies, indicating that fractures and fluids in the crust can increase the attenuation of seismic waves. At deeper depths (20-40 km), the ELIP still maintains a high Q anomaly, and separates two clear stripes of low Q anomalies along the Lijiang-Xiaojinhe Fault and Xiaojiang Fault. This suggests the existence of partial melting along the two fault zones that could be caused by upwelling of hot mantle materials. In addition, high Q values are observed in the Yangtze craton and Sichuan Basin, corresponding to stable tectonic block and weak tectonic activity.

How to cite: Wang, J., Zhang, H., Hu, J., and Liu, Y.: Body wave seismic attenuation tomography of the crust in the Sichuan-Yunnan Region, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8875, https://doi.org/10.5194/egusphere-egu24-8875, 2024.

EGU24-9088 | ECS | Posters on site | TS5.1

Seismogenic structure of the 2021 Ms6.4 Yangbi earthquake by seismic tomography based on the variation of information  

Yuqi Huang, Haijiang Zhang, Jing Hu, ying liu, Ji Gao, and Max Moorkamp

Seismic tomography is a useful tool to obtain the velocity structure of the Earth's interior. Compared with the Vp and Vs models, the Vp/Vs model is of great significance for studying the properties of subsurface structure, such as fluid saturation and porosity.  However, due to different data quality and quantity for P- and S-wave, Vp and Vs models generally have different resolutions and uncertainties, leading to some artifacts in the Vp/Vs model. Tryggvason and Linde (2007) proposed to use the structural similarity in Vp and Vs models to better constrain the Vp/Vs model. However, the clustering relationship between Vp and Vp/Vs models is not optimized, which limits the further geological interpretations based on velocity models. In this study, we aim at developing a new seismic tomography method based on the variation of information for Vp and Vp/Vs models. This method follows joint inversion of magnetotelluric and gravity data based on the variation of information (Moorkamp, 2022), which can improve the clustering relationship between electrical resistivity and density.
 The 2021 Ms6.4 Yangbi earthquake is located at the intersection of the Red river fault and the nearly north-south trending Lijiang-Dali fault system on the southwestern boundary of the Sichuan-Yunnan block. This earthquake has the classic characteristic of a "foreshock-mainshock-aftershock" sequence. In this study, we have developed a new seismic tomography method based on the variation of information to couple the Vp/Vs model with the Vp model to obtain more reliable Vp, Vs, and Vp/Vs models in the source region of the Yangbi earthquake. Our results show that the foreshocks occur in structures with low Vp, high Vs and low Vp/Vs, while the main shock occurs in the area with high Vp, high Vs and low Vp/Vs. Based on the cross-plot analysis and petrophysical experimental data, we suggest that long-term stress accumulation causes shearing in areas with high quartz content at a depth of 10km. 

How to cite: Huang, Y., Zhang, H., Hu, J., liu, Y., Gao, J., and Moorkamp, M.: Seismogenic structure of the 2021 Ms6.4 Yangbi earthquake by seismic tomography based on the variation of information , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9088, https://doi.org/10.5194/egusphere-egu24-9088, 2024.

EGU24-9340 | Orals | TS5.1 | Highlight

Dike-like structures control the unrest in Campi Flegrei 

Anna Tramelli and Marco Calò

The occurrence of seismicity in active calderas causes great concern as it is one of the main precursors for the volcanic eruptions.

Campi Flegrei is one of the largest known active calderas and its historical unrests are characterized by a high number of low to moderate magnitude earthquakes usually associated with soil uplifts reaching several centimeters or even meters within each cycle.

The last unrest started in 2006 and is currently accompanied by a large sequence of events localized beneath the Soflatara-Piscarelli system, together with the increment of gas emission in Piscarelli and strong variations of several geochemical and geophysical parameters.

Here we show two classes of seismic models generated using passive methods that employed both Earthquakes and Ambient Noise recorded from 2005 till March 2022.

These models enabled us to demonstrate, for the first time, the existence of vertically elongated high P-wave velocity bodies beneath Pisciarelli, Pozzuoli, and a resurgent formation situated offshore. The most evident dike-like structures are positioned at the border of the resurgence dome involved in the uplift, indicating that the peripheral structures regulate the upward fluid migration, contributing to the ongoing unrest.   

How to cite: Tramelli, A. and Calò, M.: Dike-like structures control the unrest in Campi Flegrei, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9340, https://doi.org/10.5194/egusphere-egu24-9340, 2024.

In the northern Los Angeles area, the interaction of complex tectonics and sedimentary structures has a significant influence on the attenuation characteristics of the crust. The region is also characterized by partially fluid-saturated crust and seismic sequences that promote intense fracturing. Modelling high-frequency seismic attenuation to image fine-scale crustal features and gain insight into the driving mechanisms of the seismicity is a powerful tool for seismic hazard assessment across this densely populated area.

We develop the first high-resolution 3D seismic attenuation model across the Chino and San Bernardino basins using 5,300 three-component seismograms from local earthquakes (M<3.6). The events were recorded by 410 nodal stations deployed along eight linear arrays during the 2017-2020 Basin Amplification Seismic Investigation experiment and 10 Southern California Seismic Network broadband stations. We present peak delay and coda-attenuation tomography in 6-12 and 12-24 Hz frequency bands (with horizontal and vertical grid spacings of 3 km and 1 km) as proxies of seismic scattering and absorption, respectively.

The attenuation models show distinct scattering contrasts in the uppermost 10 km of the crust across two major faults in the northern edge and in the middle of the Chino basin, suggesting variations in fracture intensity in the basement. Low scattering values characterize the crustal block bounded by these two faults, while high scattering coincides with zones of seismicity indicating highly fractured fault-rocks, such as the areas across the Cucamonga, Fontana, and San Andreas faults. The N-S pattern of high absorption and seismicity migration associated with the 2019 Fontana seismic sequence suggests potential groundwater movement across the fault into a buried intensely fractured zone in the basement that we interpret was once an elevated part of the Perris Block. Low scattering values beneath the Chino basin in the source region of the seismic sequence may confirm the presence of fluid-saturated rocks and increased pore pressure. The attenuation results allow the small-scale characterization of fractured basement rocks and fluid migration pathways, and show a heterogenous pattern of seismic wave amplification beneath the region.

How to cite: Nardoni, C. and Persaud, P.: Imaging Fracture Networks beneath the Los Angeles Metropolitan Area using High-Frequency Seismic Attenuation Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9648, https://doi.org/10.5194/egusphere-egu24-9648, 2024.

EGU24-12789 | Posters on site | TS5.1

Imaging the crustal structure of the Central Pyrenees using Seismic Interferometry 

Ruth Soto, Juvenal Andrés, Anna Gabàs, Fabián Bellmunt, Albert Macau, Pilar Clariana, Carmen Rey-Moral, Félix Rubio, Esther Izquierdo-Llavall, Tania Mochales, Emilio L. Pueyo, and Conxi Ayala

The Pyrenees constitute a natural laboratory where hundreds of geological and geophysical data have been acquired during the last decades. It represents a roughly E-W oriented doubly vergent orogen formed during the Alpine Orogeny. Deep seismic reflection data obtained during the 80s revealed its crustal architecture that resulted from the subduction of the Iberian plate under the European lithosphere at its central part.

In this work we applied seismic interferometry to the same passive dataset through two different techniques aiming to construct two independent images of the Central Pyrenean lithosphere, to enhance the current knowledge of the area. The main objectives are to compare them and correlate the obtained results with previous data. Data were acquired within the IMAGYN project along a NE-SW 70 km-long profile extending from the Southern Pyrenees (Pedraforca and Cadí Units, northern Iberia) to the northern part of the Axial Zone, close to Ax-les-Thermes (France). Data came from three to five months of continuous recording from an almost linear array of 43 seismic stations (being 17 and 26 broadband and short-period stations, respectively). The two applied techniques are (1) the global-phase seismic interferometry (GloPSI), using continuous recordings of teleseismic (30 < epicentral distance < 95⁰) and global earthquakes (> 120⁰ epicentral distance), and (2) the use of continuous ambient seismic noise recordings through autocorrelation. Despite both methods rely on different energy sources, they are complementary and use static receivers. In the first method (GloPSI), we extracted global phases (PKP, PKiKP and PKIKP) and their reverberations within the lithosphere. The selected phases were autocorrelated and stacked to construct a high-resolution pseudo zero-offset reflection image. The second approach provided an approximation to the zero-offset reflection response of a single station. Results reveal features that can be correlated in both reflection images. The crust-mantle boundary is mapped as a relative flat interface at approximately 35-40 km depth. Crustal interfaces detected at 15 and 25 km depth can be related to the Conrad discontinuity and other compositional changes within the crust.

(This work is part of the project “High-resolution imaging of the crustal-scale structure of the Central Pyrenees and role of Variscan inheritance on its geodynamic evolution” (IMAGYN), PID2020-114273GB-C22 funded by MCIN/AEI/10.13039/501100011033)

How to cite: Soto, R., Andrés, J., Gabàs, A., Bellmunt, F., Macau, A., Clariana, P., Rey-Moral, C., Rubio, F., Izquierdo-Llavall, E., Mochales, T., Pueyo, E. L., and Ayala, C.: Imaging the crustal structure of the Central Pyrenees using Seismic Interferometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12789, https://doi.org/10.5194/egusphere-egu24-12789, 2024.

EGU24-13950 | ECS | Posters on site | TS5.1

Retrieving Seismic Reflective Waves from DAS VSP: a Case Study from MiDAS Project 

Zhuo-Kang Guan, Hao Kuo-Chen, Chun-Rong Chen, and Kuo-Fong Ma

The Longitudinal Valley in eastern Taiwan situated at the boundary between the Philippine Sea Plate and the Eurasian Plate, making it one of the significant seismogenic regions in Taiwan. In 2018, a magnitude 6.4 earthquake occurred offshore of Hualien, at the northern end of this valley. More than 4,000 aftershocks received over following two weeks beneath the Longitudinal Valley. Surprisingly, Hualien City and the Milun Fault, situated near the epicenter, did not experience notable aftershocks. However, they did display evident co-seismic deformation during the mainshock. Milun fault Drilling and All-inclusive Sensing (MiDAS) project aims to establish a comprehensive and long-term monitoring system, which involves three boreholes encompassing the fault for both surface and subsurface geoscientific observations. This study utilized a 700-meter DAS (Distributed Acoustic Sensing) setup within the borehole A of the MiDAS project to conduct VSP (Vertical Seismic Profiling) experiments. Additionally, electrical logging and surface reflection seismic data were gathered.  According to the 2D reflection seismic profile, the results depicted a gently sloping stratum on the northwest side arching towards the southwest. Most layers tapered beneath the Milun Terrace, and the fault-induced stratigraphic disturbance was not clearly discernible, making it challenging to determine if the layers were intersected by the fault. However, pronounced folding structures were evident beneath the terrace, correlating with areas of intense co-seismic deformation. From the VSP experiment, the data exhibited pronounced P-waves and Tube waves, suggesting the presence of fluids around the casing rather than rocks or cement. After data processing, the P-wave velocity correlated well with the downhole sonic logging data. Also, reflection signals with two-way travel times ranging from 0.27 to 0.45 seconds were observed in both seismic profiles. This suggests that the VSP effectively resolved reflection signals from depths of 340 to 612 meters. These signals displayed a high resemblance to lithology indicators such as Gamma ray and resistivity, confirming the authenticity of the separated reflection signals obtained from shallow depth, lower signal-to-noise ratio data.

How to cite: Guan, Z.-K., Kuo-Chen, H., Chen, C.-R., and Ma, K.-F.: Retrieving Seismic Reflective Waves from DAS VSP: a Case Study from MiDAS Project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13950, https://doi.org/10.5194/egusphere-egu24-13950, 2024.

Neotectonic movements pose significant hazards and hold crucial scientific and social relevance, notably in seismic hazard assessment and subsurface utilization. In regions like northern Germany, a presumed aseismic region, understanding these processes remains limited because many faults are buried under sediments. Despite confirmed neotectonic activity, the specifics of these processes and associated structures remain largely unknown.

Improving our understanding of neotectonic activity requires investigations of recently-active fault zones, such as the Osning Fault System (OFS) in North Rhine-Westphalia, Germany. Using near-surface geophysics becomes crucial in this endeavour, which so far were not used at the OFS.

The OFS stands out as a site of recent and historical seismic activity, experiencing several large earthquakes over the past four centuries. Notably, major earthquakes in 1612 and 1767 with intensities ranging from VI to VII on the MSK scale, emphasize the seismic significance of the OFS. Unlike other faults in the region, the faults of the OFS reach the basement and the fault zone dips north-eastward. Furthermore, the former iceload from Scandinavia influenced the fault system by facilitating glacial isostatic adjustment, which subsequently enabled fault reactivation. The complex nature of the fault system spans various geological phases, prompting a comprehensive investigation approach to understand its regional neotectonic evolution.

Our geophysical and geological approach integrates high-resolution 2D P- and SH-wave reflection seismics and retrodeformation of previously-published cross-sections. This is complemented by surface geological maps and limited drilling information. Our aim is to identify and interpret fault geometry and kinematics.

While P-wave seismic surveys used for imaging of deep structures often lack high-resolution in the shallow subsurface, the integration of SH-wave reflection seismics compensates for this limitation, offering enhanced resolution, especially at the near-surface. The survey involved three P-wave profiles employing a hydraulically-driven vibrator vehicle and four SH-wave profiles utilizing an electro-dynamic micro-vibrator with varying source point spacing.

These seismic profiles successfully delineate fault structures within the Cretaceous formations, revealing previously unidentified extensions of the OFS. Although the P-wave profiles inadequately image the Quaternary layers, there are indications that the faults extend into this formation. The SH-wave profiles, with their superior resolution in the near-surface due to lower wave velocities, confirm these assumptions, revealing further faulting and deformation features within the Quaternary sediments. Interpretation and fault imaging are further enhanced by full waveform inversion of P- and S-wave data, testing of different migration methods for the S-wave data, and seismic attribute analysis.

Retrodeformation and balancing of existing cross-sections and the interpreted seismic profiles allows the fault geometry and kinematics to be assessed. We determined which adjustments were necessary to make the profiles more geologically plausible. This combined geophysical and geological approach enabled a more comprehensive interpretation and understanding of the local fault geometry and the neotectonic evolution of the OFS.

How to cite: Wadas, S., Tanner, D., and Polom, U.: The structure and neotectonic evolution of the Osning Fault System in Germany derived from near-surface P- and SH-wave reflection seismics and retrodeformation modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15033, https://doi.org/10.5194/egusphere-egu24-15033, 2024.

EGU24-15578 | Posters on site | TS5.1

Scattering and absorption imaging of the Nesjavellir (Iceland) geothermal area 

Paolo Capuano, Ferdinando Napolitano, Luca De Siena, Thorbjorg Ágústsdóttir, Vala Hjörleifsdóttir, Mauro Palo, and Ortensia Amoroso

Detailed imaging of the elastic and anelastic properties of the crustal structures of geothermal regions is crucial from a scientific and industrial standpoint. The Hengill volcano region is the most productive high-temperature geothermal region in Iceland, located in the southwestern region of Iceland (30 km east of Reykjavík). To the north of the Hengill volcano is the Nesjavellir geothermal subfield, which lies within the Hengill fissure swarm trending N30°E.

Scattering and absorption measurements have proven reliable proxies for the spatial extension of faults, thrusts and fluid reservoirs across tectonic, volcanic and hydrothermal settings. Scattering marks tectonic interactions and lithological contrasts due to wave-trapping mechanisms that increase energy across the earthquake coda. Fluid content is, instead, the primary controller of seismic absorption. Rock physics studies and numerical simulations have proven the sensitivity of this parameter to strain rate and pore space topology.

The present work aims to provide the first 3D images of seismic scattering and absorption accross the Nesjavellir geothermal area at different frequency bands, measured through peak delay mapping and coda-attenuation tomography, respectively. Manually picked seismic events that occurred between November 2017 and December 2022, recorded by three permanent and temporary seismic networks, have been used to provide the first attenuation imaging of this geothermal area.

The preliminary results show, firstly, the stability of the peak delay and coda attenuation results as the analysis parameters change. The 3D scattering and absorption imaging show that the well-resolved areas of the Hengill region are characterized by high scattering, coinciding with highly-fragmented fissures at the surface. High absorption anomalies mark the Nesjavellir geothermal sub-field, mainly between 4 and 6 km depth, where seismic tomographies highlight high Vp/Vs.

The work is supported by project TOGETHER - Sustainable geothermal energy for two Southern Italy regions: geophysical resource evaluation and public awareness financed by European Union – Next Generation EU ( PRIN-PNRR 2022, CUP D53D23022850001).

How to cite: Capuano, P., Napolitano, F., De Siena, L., Ágústsdóttir, T., Hjörleifsdóttir, V., Palo, M., and Amoroso, O.: Scattering and absorption imaging of the Nesjavellir (Iceland) geothermal area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15578, https://doi.org/10.5194/egusphere-egu24-15578, 2024.

EGU24-16491 | ECS | Posters on site | TS5.1

The Attenuation and Scattering Signature of Fluid Reservoirs and Tectonic Interactions in the Central-Southern Apennines (Italy)  

Donato Talone, Luca De Siena, Giusy Lavecchia, and Rita de Nardis

The intricate tectonics of Central-Southern Italy, characterized by its complex fault network and sparse seismicity distribution, have posed a significant challenge to understanding the region's seismic hazard, its three-dimensional structural assessment, and the role of fluids in the seismic release. Conventional geophysical techniques, often limited by low seismicity rates, have struggled to provide a comprehensive picture of the crustal structures, and a coherent geophysical model of the area is still absent. Leveraging the last decade’s expanded detection capabilities of the Italian seismic network, we were able to make up for this lack and employed seismic attenuation and scattering tomography methods to produce complete 3D attenuation models of the crust.

By analyzing the energy loss of seismic waves as their propagation through the crust, the study revealed a pervasive pattern of high attenuation zones that extend along the entire Apenninic Chain, particularly concentrated in Southern Italy. The distribution of these anomalies aligns closely with the regional fault structures suggesting a strict relationship with the fracture level due to the tectonic processes. In contrast to the bigger anomalies, the study also identified prominent low attenuation and scattering volumes corresponding to the Fucino and Morrone-Porrara fault systems. These are likely regions of accumulated stress where the locked seismic energy release contributes to the high seismic hazard. Furthermore, the study identified a previously undetected high-attenuation region beneath the Matese extensional system, indicating a potential source of both deep and shallow circulation of fluid. Another anomaly was detected near the L'Aquila 2009 seismogenic area, suggesting a regional distribution of fluid-rich areas.

The findings of this study provide unprecedented insights into the tectonic interactions and fluid sources of Central-Southern Italy, with significant implications for seismic hazard assessment, fluid exploration, and the development of effective mitigation strategies for this geologically active region.

How to cite: Talone, D., De Siena, L., Lavecchia, G., and de Nardis, R.: The Attenuation and Scattering Signature of Fluid Reservoirs and Tectonic Interactions in the Central-Southern Apennines (Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16491, https://doi.org/10.5194/egusphere-egu24-16491, 2024.

EGU24-16588 | ECS | Orals | TS5.1

Ambient noise based seismic imaging of the Tuscan Magmatic Province, Italy 

Konstantinos Michailos, Geneviève Savard, Elliot Amir Jiwani-Brown, Domenico Montanari, Michele d'Ambrosio, Gilberto Saccorotti, Davide Piccinini, Nicola Piana Agostinetti, Riccardo Minetto, Marco Bonini, Chiara Del Ventisette, Francisco Muñoz, Juan Porras, and Matteo Lupi

The Tuscan Magmatic Province (TMP) is the result of several geodynamic events associated with the formation of the Apennines orogen and the Tyrrhenian Basin. Previous studies highlighted different aspects of the TMP, characterised by a complex geology, a thin continental crust, low seismicity rates, and locally high heat flow rates (e.g., Larderello-Travale and Amiata geothermal fields). Despite numerous active and passive seismic investigations in the past, the knowledge of the crustal structure across the broader TMP region is limited, particularly when considering its spatial coverage. To tackle this problem, we use ambient noise tomography and waveform data from the TEMPEST temporary seismic network and permanent seismometers. The TEMPEST network operated from late 2020 to late 2021, comprising 30 broadband seismometers, augmenting the existing permanent seismometer network.

Here we analyse Rayleigh wave group-velocity dispersion data from all seismic stations of our composite seismic network of 62 seismometers and generate 2-D maps of group velocities at different periods. We observe relatively low group velocities that may represent possibly two plutonic bodies in the region (i.e., Larderello and Mt Amiata). To further constrain the volume of the plutonic bodies, we intend to perform a series of inversions to estimate the variation of shear-wave velocity with depth. Our approach showcases the effectiveness of ambient noise tomography in unravelling crustal structures in geologically complex regions such as the Tuscan Magmatic Province, Italy, and its implications for geodynamic and tectonophysics studies.

How to cite: Michailos, K., Savard, G., Jiwani-Brown, E. A., Montanari, D., d'Ambrosio, M., Saccorotti, G., Piccinini, D., Agostinetti, N. P., Minetto, R., Bonini, M., Del Ventisette, C., Muñoz, F., Porras, J., and Lupi, M.: Ambient noise based seismic imaging of the Tuscan Magmatic Province, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16588, https://doi.org/10.5194/egusphere-egu24-16588, 2024.

EGU24-17959 | ECS | Orals | TS5.1

Assessing the geometry and topology of a fault network along the Northern North Sea rift margin: insights from broadband 3D seismic reflection data 

Edoseghe Edwin Osagiede, Casey Nixon, Rob Gawthorpe, Atle Rotevatn, Haakon Fossen, Christopher A-L. Jackson, and Fabian Tillmans

Recent advances in seismic reflection acquisition and processing technologies have led to a general improvement in the resolution of seismic reflection data, allowing for better imaging of subsurface structures, particularly fault networks. Leveraging high-resolution, broadband 3D seismic reflection data from the northern North Sea, we, for the first time, investigate how the geometrical and topological properties of the Late Jurassic normal fault network vary spatially along the rift margins. We also discuss the factors that may have influenced the spatial variability of the rift fault network properties. Our results reveal that normal faults closer to the North Viking Graben exhibit dominant N-S and NE-SW strikes that are sub-parallel to the graben axis and associated step-over zone, whereas those farther from the graben, exhibit an additional NW-SE strike, resulting in a complex fault network. We identify two broad topological domains within the fault network: 1) dominated by isolated (I-) nodes, partially connected (I-C) branches, low fault density, and connectivity, and 2) dominated by abutting (Y-) nodes, fully connected (C-C) branches, moderate to high fault density and connectivity. These topological domains correlate with previous sub-division of the rift margin in the northern North Sea into platform and sub-platform structural domains, respectively. There is also a positive correlation between the spatial variability of the fault orientations, density, and connectivity, highlighting the relationship between normal fault network geometry and topology. We conclude that variation in the amount of relative strain, the presence of pre-existing structures, accommodation zone- and fault damage zone-related deformation are among the main factors that influence the spatial variation of fault network properties both at a regional and local scale. This study provides a new, but complementary way of characterising large-scale structural domains in rift systems. Additionally, our assessment of fault network topology provides important insights into the connectivity of rift-related normal faults, which have implications when considering the integrity of structural traps and subsurface fluid flow related to hydrocarbon and geothermal reservoirs, and CO2 storage.

How to cite: Osagiede, E. E., Nixon, C., Gawthorpe, R., Rotevatn, A., Fossen, H., Jackson, C. A.-L., and Tillmans, F.: Assessing the geometry and topology of a fault network along the Northern North Sea rift margin: insights from broadband 3D seismic reflection data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17959, https://doi.org/10.5194/egusphere-egu24-17959, 2024.

EGU24-18014 | Orals | TS5.1

Passive seismic survey across the fault-zone of Introdacqua, central Italy: the subsurface geological structure role on the site amplification pattern  

Marta Pischiutta, Alessia Mercuri, Federico Fina, Francesco Salvini, Luca Minarelli, Giovanna Cultrera, and Giuseppe Di Giulio

In this work we perform a detailed passive seismic survey in proximity of a shear zone in the Introdacqua area, central Italy, around the permanent seismic station IV.INTR of the Italian seismic network RSN. This station is located on a prominent ridge (width of about 200 m, relative height of about 240 m), and is affected by a clear directional amplification between 1 and 3 Hz, with maximum amplification along N160° azimuth, as shown by HVSRs calculated using both seismic events and ambient noise recordings (CRISP database, www.crisp.ingv.it). This effect was confirmed by 11 ambient noise measurements performed nearby station IV.INTR in the framework of an agreement with the Italian Civil Protection. Since the maximum amplification occurs parallel to the topography elongation, it is not explainable through the topo-resonant model (e.g. Géli et al. 1988).

In this work, to better investigate the anomalous seismic response, as well as the areal extension of the directional effect, we implement an array of further 32 ambient noise measurement points, including a larger area around the topography. We find that the directional effect along N160° azimuth is gathered only at measurement sites close to IV.INTR, disappearing when increasing distances (over 300 m). A detailed structural geological survey suggests the presence of intensely fractured rocks produced by a fault located close to station IV.INTR, fractures strike being concentrated around N70°-80° azimuth, transversally to the directional effect. This is in agreement with several literature papers suggesting that across fault zones directional amplification is transversal to the prevailing fracture strike (e.g. Pischiutta et al., 2023, and references therein).

The Introdacqua study case suggests that anomalous amplification patterns can be found on topography as an effect of the subsurface geological structure, rather than being produced by the sole convex shape. Since topographic irregularities and rock fractures often coexist in tectonically active zones, this is a key point to interpret amplification at sites with pronounced topography. For this reason, Introdacqua was chosen as a test-site in the of the ongoing INGV-GEMME international project, whose aim is the study of the seismic site response in complex 3D geological and morphological settings, and the deep investigation of the wave propagation by using 3D numerical modeling, to provide guidelines for future site characterization.

How to cite: Pischiutta, M., Mercuri, A., Fina, F., Salvini, F., Minarelli, L., Cultrera, G., and Di Giulio, G.: Passive seismic survey across the fault-zone of Introdacqua, central Italy: the subsurface geological structure role on the site amplification pattern , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18014, https://doi.org/10.5194/egusphere-egu24-18014, 2024.

EGU24-18800 | ECS | Orals | TS5.1

 The TEst Site IRpinia fAult (TESIRA) project. Initial Findings from Active-Source Seismic Experiments 

Giuseppe Ferrara, Pier Paolo Gennaro Bruno, Luigi Improta, Stefano Maraio, David Iacopini, Vincenzo Di Fiore, and Paolo Marco De Martini

The scientific project TESIRA (TEst Site IRpinia fAult), funded in 2021 by the University of Naples “Federico II”, aims, through the integration of a multivariate dataset, to achieve a high-resolution 3D geophysical imaging of the shallow structure of the southern branch of the 1980 Ms=6.9 Fault at Pantano San Gregorio Magno (SA). The set of data acquired during the project life-span included: a microgravimetric survey; 3D and 2D Electrical Resistivity measurements; aeromagnetic and GPR surveys by drone; a CO2 surface degassing measurement and a full-waver electric investigation.

Specifically, the active-source seismic dataset acquired at Pantano consists of four high- to very-high resolution seismic profiles spanning a total length of 3150 m and a high-resolution seismic volume covering an area of 12.5 acres. The seismic experiment's location was strategically chosen to illuminate key features of the Pantano basin affected by coseismic surface faulting, such as the rupture during the November 23,1980 Irpinia earthquake and the southern segment of the Pantano-San Gregorio Fault System (PSGM).

We share the early findings obtained through standard Common Depth Point processing and post-stack depth migration. Even at this initial stage, the results offer a clear picture of the intricate 3D structure of the basin, revealing a complex pattern of the carbonatic basement resulting from active faulting. Additionally, the seismic images underscore the evident influence of active faulting on the basin's formation and recent sedimentation. Future analyses, including full-waveform inversion and post-stack depth migration, are planned to enhance the imaging of this critical sector in the southern Apennines. Although seismic data present the highest resolution among the geophysical datasets at Pantano, their integration with the extensive data collected during the TESIRA project will facilitate a reliable interpretation of the complex basin subsurface, useful to improve our understanding of the interplay between active surface faulting and recent basin growth pattern.

How to cite: Ferrara, G., Bruno, P. P. G., Improta, L., Maraio, S., Iacopini, D., Di Fiore, V., and De Martini, P. M.:  The TEst Site IRpinia fAult (TESIRA) project. Initial Findings from Active-Source Seismic Experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18800, https://doi.org/10.5194/egusphere-egu24-18800, 2024.

EGU24-19431 | ECS | Orals | TS5.1 | Highlight

Multi-scale investigation of the InSight landing site, on Mars, using one-station seismology 

Sebastian Carrasco, Brigitte Knapmeyer-Endrun, Ludovic Margerin, Eleonore Stutzmann, Martin Schimmel, Keisuke Onodera, Sabrina Menina, Wanbo Xiao, Zongbo Xu, Cedric Schmelzbach, Manuel Hobiger, and Philippe Lognonné

The internal structure of a planet provides constraints for understanding its evolution and dynamics. In November 2018, the InSight spacecraft landed on Mars and deployed a set of geophysical instruments, including one seismological station. In this work, the subsurface structure at the InSight landing site (ILS) is explored, from the shallow subsurface to crustal depths, by applying single-station seismological techniques (SST) on martian ambient vibrations and seismic events data.

The shallow subsurface at the ILS, in the order of meters, is investigated using the horizontal-to-vertical spectral ratios (HVSR) from the coda of martian seismic events. Assuming a fully diffuse wavefield, a nonlinear inversion using the conditional Neighbourhood Algorithm (NA) allowed to map the shallow subsurface at the ILS. Due to the non-uniqueness problem, different sets of models are retrieved. The 8 Hz HVSR peak can be explained by a Rayleigh wave resonance due to a shallow high-velocity layer, while the 2.4 Hz trough is explained by a P-wave resonance due to a buried low-velocity layer. The kilometer-scale subsurface was constrained by Rayleigh wave ellipticity measurements from large martian seismic events. The ellipticity measurements (0.03-0.07 Hz) were jointly inverted with P-to-s Receiver Functions and P-wave lag times from autocorrelations, to provide a subsurface model for the martian crust at the ILS. The joint inversion allowed the thickness and velocities of a new surface layer, previously proposed only conceptually, to be constrained by multiple seismological data. The HVSR in the 0.06-0.5 Hz frequency range from the coda of S1222a, the largest event ever recorded on Mars, suggests a gradual transition from shallow to crustal depths and consolidates the group of shallow subsurface models with the largest shear-wave velocities as the most compatible with the crustal structure.

A comprehensive multi-scale model of the ILS subsurface is proposed. The ILS is characterized by the emplacement of a low-velocity regolith/coarse ejecta layer over a high-velocity Amazonian fractured lava flow (~2 km/s, ~30 m thick). A buried Late Hesperian-Amazonian sedimentary layer is deposited below (~450 m/s, ~30 m thick), underlain by a heavily weathered Early Hesperian lava flow. The latter overlays a thick, likely Noachian sedimentary layer that extends to a depth of 2-3 km. This shallow structure forms the first crustal layer derived from the joint inversion. Deeper crustal layers are consistent with other reported ILS models, with intracrustal discontinuities at 8-12 km and 18-23 km depth. The Moho depth at the ILS is found at 35-45 km depth. Shear-wave velocities above ~20 km depth are lower than 2.5 km/s, slower than in other regions of Mars, suggesting a higher alteration due to local processes or a different origin of the upper crust at the ILS. The proposed model is consistent with the geologic history of Mars and other independent observations, confirming the great potential of SST for multi-scale investigation of, e.g., other planetary bodies or understudied regions on Earth.

How to cite: Carrasco, S., Knapmeyer-Endrun, B., Margerin, L., Stutzmann, E., Schimmel, M., Onodera, K., Menina, S., Xiao, W., Xu, Z., Schmelzbach, C., Hobiger, M., and Lognonné, P.: Multi-scale investigation of the InSight landing site, on Mars, using one-station seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19431, https://doi.org/10.5194/egusphere-egu24-19431, 2024.

EGU24-20377 | ECS | Posters on site | TS5.1

High-resolution crosshole seismic imaging of glacial sediments by full-waveform inversion 

Sarah Beraus, Daniel Köhn, Thomas Burschil, Hermann Buness, Thomas Bohlen, and Gerald Gabriel

During the Quaternary, glaciers shaped the Alpine region by excavating deep valleys and refilling them with the sediments that they transported. One such overdeepened valley is the Tannwald Basin (ICDP site 5068_1), which was created by the Rhine Glacier in what is thought to have been several glaciations. The sediments found in such valleys thus provide climate archives and tell us about the landscape evolution if we understand the sedimentation processes that took place.

To study these glacial sediments in terms of their small-scale structure and deposition, we acquired P- and S-wave seismic crosshole data using high-frequency borehole sources. While the pressure field was recorded by a 24-station hydrophone array, the S-waves excited by horizontally and vertically polarizing sources, respectively, were recorded by an 8-station 3C geophone string.  

Since the S-wave data is quite complex, we directly apply elastic mono-parameter full-waveform inversion (FWI). This mitigates the phase misidentification problem in deriving an S-wave model from phase picks. In preparation for the inversion, we rotate the data into a ray-based coordinate system so that the SV-wave dominates on the vertical component and the SH- wave dominates the horizontal component. We then invert the vertical component of the SV-dataset and the transverse component of the SH-dataset using the appropriate parameterization. We apply a global correlation norm and preconditioning to ensure proper and fast converge of the inversion. In addition, we use the multistage approach to deal with the non-linearity of the problem. Anisotropic Gaussian filtering of the gradients as a function of the S-wave wavelength at higher frequency stages pushes the vertical resolution of our model below 1 m. This represents a significant improvement over surface seismic and traveltime tomography methods. A comparison with the lithology known for one of the boreholes shows an impressive correlation. Thus, our approach can bridge the gap between traditional surface seismic imaging and borehole methods.

In future research, we will repeat this approach for the SH-dataset. In the case of structural similarity, but a systematic difference in the S-wave velocities, this will provide us with evidence of seismic anisotropy, which will then need to be further characterized and quantified. From this, we will be able to infer the sedimentation processes that will help us to understand the evolution of the Alpine landscape. Eventually, FWI of the P-wave data will provide a more comprehensive, high-resolution image of the subsurface at the drill site.

How to cite: Beraus, S., Köhn, D., Burschil, T., Buness, H., Bohlen, T., and Gabriel, G.: High-resolution crosshole seismic imaging of glacial sediments by full-waveform inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20377, https://doi.org/10.5194/egusphere-egu24-20377, 2024.

EGU24-63 | ECS | PICO | TS5.2

Harmonic Dynamic of the Earth 

Xianwu Xin

The Harmonic Motion Phenomenon of the Earth is introduced through Experiments: Under the Combined Action of Tidal Force and the Earth's Rotation, Continental Unit Body Segments, like Caterpillars, actively crawl westward on the Mantle. Based on the Force Analysis of the Earth Motion Process and the Generalized Hooke's Law, the Harmonic Motion Equation and the Crustal Motion Equation of the Earth are derived, also the Conversion Equation of Continental Drift Datum has been derived. The Velocity Field of Continent Latitudinal Movement is calculated, and compared with the Measured Value of ITRF2000 station. From the Perspective of Kinematics, it is proved that the Harmonic Motion of the Earth is the Basic Dynamic Mechanism of the crust and inside of the Earth Movement. The Degree of Dominance which this Dynamic Process to Continental Drift is 72% to 97.4%. It's Energy comes from the Rotation Energy of the Earth. Using the results of Motion Calculation to was reconstructed the Proto Ancient Continent, that was it moment of started cracked at before 250 million years. In addition, the Driving Force Equation of the Earth’s Harmonic Motion is derived. Discussed the Driving Force accumulation process and the formation mechanism of Earthquake: The Thrust of the Rock Stratum to the Hindered Portion slowly increases with the Creep between stratus and the Successive Compression each time it from Peak Point to Valley Point. Continuously increase the Elevation and Area of the Compression Zone. When the Driving Forces Accumulation reaches the Limit of the Strength of the Hindered Rock Stratum, sudden movement or Fracture Occurs, and an Earthquake formation. Earthquakes are a Process of Concentrated Energy Release. In High-Temperature and High-Pressure Areas within 700km underground, when Earthquakes, some Rocks melt to form Magma, and driven by Harmonic Motion, enriches westward along Rock Fractures and enters the Ocean Ridges Bottoms and the Below of the Volcano. The Magma of Below the Volcano erupts from the Earth's Surface after increasing Pressure. The Magma at the Bottom of the Ocean Ridge is driven by the Footpath Board Effect and moves upwards along the Cracks, and Condensed on the Surface of the Sidewall, when change the Gaps of the Cracks along with the Ocean Floor Undulating, the Ocean Floor on Both sides of the Ocean Ridge is pushed apart from each other. This kind of process of Ocean Floor Fluctuate Spreading leads to Gradual wear and tear of the Ocean Floor, Ultimately Subducting beneath Land or trenches and returning to the Mantle. In Passive Mantle Convection and Ocean Floor Fluctuate Spreading, the Driven Force of Magma flow is provide by the Earth's Rotation through Fluctuate Processes, magma does not output Power. At last, according to the Driving Force Equation of Earth‘s Harmonic Motion, the Energy Conversion Equation is given. The Total Power of Earth‘s Harmonic Motion is calculated, and compared with the Relevant Measured Values. It is further proved from the Perspective of Dynamics and Energy Conversion: The Harmonic Dynamic Proces of the Earth is the Basic Dynamical Proces of Tectonic Movement.

How to cite: Xin, X.: Harmonic Dynamic of the Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-63, https://doi.org/10.5194/egusphere-egu24-63, 2024.

Fold-and-thrust belts (FTBs) evolve over a mechanically weak basal décollement that separates overlying intensely deformed rocks from the underlying less deformed or undeformed rocks. Although fold-and-thrust belts are often considered laterally cylindrical in nature, a closer inspection reveals remarkable variations in structural style (e.g., fold geometry) both along and across the strike of mountain belts. Using crustal scale thin-sheet laboratory experiments, this study focuses on the role of laterally varying coupling strength of the basal décollement on the evolution of structural styles in natural FTBs. In this study, we used a rectangular slab of silicon putty, a linear viscous material, of uniform thickness in all experiments to simulate the crustal section and the models were deformed at a uniform convergence velocity of ~7.649 × 10-5 ms-1. Analyses of experimental results show remarkable changes in the wedge growth with the introduction of along strike variations in décollement strength. The segment of the deforming wedge over weakly coupled décollement propagates at a faster rate towards the frontal direction compared to the laterally continuous segment over a strongly coupled décollement, leading to an overall sinuous geometry of the deformation front. In contrast, an approximately linear deformation front represents a condition of uniform along-strike coupling strength at the basal décollement. Based on our experimental results, we argue that the broad arcuation of the mountain front along the eastern margin of the Zagros fold-thrust belt (i.e., Fars arc region) might have resulted due to along strike variations in the décollement strength, while the occurrence of a linear deformation front from the central to western margin of the fold-and-thrust belt represents a segment of the wedge with a uniform coupling strength at the basal décollement. Our experimental results can be carefully used to explain the cause of strike-wise segmentation of tectonic processes in orogenic belts, variations in topography and earthquake activities.   

How to cite: Roy, S., Willingshofer, E., and Bose, S.: Influence of lateral variations of décollement strength on the structure of orogenic wedges: insights from experimental viscous wedge models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3310, https://doi.org/10.5194/egusphere-egu24-3310, 2024.

With the wide application of high-quality three-dimensional (3-D) seismic volumes in hydrocarbon exploration, it has been found that a special type of fault system, i.e., conjugate strike-slip fault system, is often developed in the Cratonic basins (e.g., Tarim Basin, Sichuan Basin, and Ordos Basin in China). They not only can directly indicate the principal stress direction, but also play a crucial role in controlling the transport and formation of hydrocarbons in the basin. Analysis of 3-D seismic data revealed that the Tarim Basin exhibited typical X-shaped (symmetrical) and asymmetrical (two sets of faults differing greatly in number) conjugate strike-slip fault systems. However, there is a lack of analogue models on the geometries and progressive evolution of conjugate strike-slip faults, as well as a poor understanding of the mechanisms of asymmetric conjugate strike-slip fault systems. Additionally, previous experiments have not been compared with such natural examples.

Based on the structural analysis of strike-slip faults in the Tarim Basin using seismic reflection data, we used three sets of symmetric (rectangular shape) and two sets of asymmetric (parallelogram shape) rubber basement models to investigate the geometries and progressive evolution of conjugate strike-slip faults. In this study, our research successfully modelled the kinematic and geometric evolution of different types of conjugate strike-slip fault systems, and found that they have the same acute angle and that the direction of their angular bisectors is parallel to the direction of contraction. In symmetric models, we observed the development of numerous typical X-shaped conjugate strike-slip faults were developed. Conversely, the development of two sets of faults in the asymmetric models showed an asymmetry, i.e., one set of faults was more obviously developed than the other, and with the degree of asymmetry increased, the asymmetry was even more obvious. Furthermore, we analysed the stress state of the models using the Mohr space and inferred that the stress state of the model changed from the strike-slip in the early stages to the extension in the later stages.

We proposed two synoptic models, namely, the symmetric conjugate strike-slip fault system (SCSFS) model and the asymmetric conjugate strike-slip fault system (ACSFS) model, for conjugate strike-slip fault systems based on the results of the different models. The models and experimental results were compared with natural examples of the two sets of strike-slip fault systems in the Tabei uplift in China’s Tarim Basin, which exhibited many strong similarities in their structural geometries, and they also provided further insight into the mechanisms of strike-slip faults in the Tabei uplift. These synoptic models proposed based on the analogue models may provide useful templates for the seismic interpretation and mechanism of different types of conjugate strike-slip fault systems in nature and for inferring the orientation of the maximum principal stress.

How to cite: Xiao, K. and Tong, H.: Analogue modelling of conjugate strike-slip faults in the Cratonic basin: A case from the Tarim Basin, NW China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3751, https://doi.org/10.5194/egusphere-egu24-3751, 2024.

Fault evolution is influenced by multiple factors, including the reactivation of pre-existing structures, stress transmission within ductile detachment layers, and the growth, interaction, and connection of newly formed fault segments. In the same stress field, displacement vectors of fault strikes, dip-slip vectors, and subtle fractures accommodate strain distributed everywhere. This study employs PIV analysis and model reconstruction to simulate oblique extensional fault systems formed at four different angles. Simulation modelling indicates that oblique extensional reactivation of pre-existing structures controls the linear arrangement of fault segments in the overlying strata. Arcuate faults can be classified into linear master fault segments controlled by pre-existing structures, curved splay faults in termination zones, and normal fault segments responding to regional stress fields. Along-strike displacement is regulated by linear segments within the master strike-slip fault, while progressive bending of splay faults, relay ramps' dislocation, and inclined displacements are regulated by relay ramps within the overlap zone. Small-angle (15°) oblique extension favours the formation of fault segments with distinct step-like features, leading to additional relay ramps. In contrast, high-angle (60°) oblique extension often results in the development of more continuous fault segments. As faults continuously evolve, new fault segments tend to deviate from the control of pre-existing structures, concentrating more on the development of planar and continuous master faults. Finally, we compared the established model with the transtensional fault system within the intraplate rift system in eastern China, demonstrating that the oblique extension angle controls the composite characteristics of the overlying strata faults.

How to cite: Wang, Y. and Yu, F.: The Linkage Evolution of Strike-Slip Faults with Normal Faults—Insights from Analogue Modelling at Various Oblique Extension., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4813, https://doi.org/10.5194/egusphere-egu24-4813, 2024.

EGU24-6667 | ECS | PICO | TS5.2

Decoding the extensional phase of the Atlas system: Unraveling Crustal Stretching during rifting:  

Mouad Ankach, Mohamed Gouiza, and Khalid Amrouch

The Atlas fold and thrust belt extend from the Atlantic rifted margin of Morocco to Tunisia over a distance of 2500km. Before its inversion in the Cenozoic to the present, the Atlas system evolved initially as a rift basin that opened simultaneously with the Atlantic rift in the west and the Tethys in the north, during the upper Triassic-Jurassic period.

The Western High Atlas is believed to be influenced by the Atlantic Ocean (also known as the Atlantic domain), where the Triassic to Early Jurassic strata are considered to be syn-rift, while the Middle Jurassic to Cretaceous deposits are labelled as post-rift. In contrast, the Marrakech High Atlas (MHA), Central High Atlas (CHA), Middle Atlas (MA), and the Eastern High Atlas (EHA) are assumed to be influenced by the Tethys Ocean (also known as Tethyan domain), where the Triassic to Jurassic sediments are considered to be syn-rift. This implies that the Mesozoic rifting along the Atlas was diachronous, making it difficult to determine the exact timing and kinematic of crustal stretching. Constraining the extensional phases in the Atlas system is crucial for understanding how the Atlas crust was stretched and thinned. Our work aims to quantify the magnitude and regional kinematic of stretching in the Atlas system using various methods, namely, thickness variation method, subsidence analysis and palinspatic reconstruction of 2D cross-sections.

Our preliminary results indicate that the maximum stretching factor (beta factor) in the Atlas is β = 1.25; and that crustal thinning did not exceed 20%, based on tectonic subsidence analysis. While the palinspatic restoration suggest that the Moroccan Atlas system underwent approximately a uniform stretching with β = 1.11 in EHA (Midelt-Errachidia area), β = 1.08 in CHA (Imilchil area), and β = 1.12 in the East Marrakech High Atlas (EMHA: Demnat area). These values indicate that the Moroccan Atlas crustal thickness has been thinned by 9% in EHA, 8% in CHA, and 11% in EMHA. In addition, the geological context of the High and Middle Atlas regions, where the estimated shortening is reported to be less than 20%, the stretching factor (β) was calculated based on the crust thickness. The initial crustal thickness (IC) of the Meseta block, which constitutes one of the Atlasic rift shoulders, considered an undeformed area, served as a reference. Accounting for the observed shortening, the final crustal thickness was deduced by subtracting the reported shortening value representing 7.8 km from the observed crustal thickness (39 km), resulting in a β value of 1.25, which is consistent with the result obtained from the subsidence analysis.

Keywords: Atlas system, extension, stretching factor, Thinning factor,

 

 

 

How to cite: Ankach, M., Gouiza, M., and Amrouch, K.: Decoding the extensional phase of the Atlas system: Unraveling Crustal Stretching during rifting: , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6667, https://doi.org/10.5194/egusphere-egu24-6667, 2024.

EGU24-6869 | ECS | PICO | TS5.2 | Highlight

Multiscale, multisensor analysis of scaled seismotectonic models: Bridging the Gap Between Laboratory and Nature through Machine Learning 

Giacomo Mastella, Fabio Corbi, Jonathan Bedford, Elvira Latypova, Federico Pignalberi, Marco Scuderi, and Francesca Funiciello

Despite considerable progress in monitoring natural subduction zones, key aspects of megathrust seismicity remain puzzling, mainly due to the temporally incomplete and spatially fragmented available record. Scaled seismotectonic models yield valuable insights by spontaneously creating multiple stick-slip cycles in controlled, downscaled three-dimensional laboratory replicas. Here we report recent progress in analog modeling of the megathrust seismicity, particularly focusing on a meters-scale elasto-plastic model featuring a frictionally segmented, granular fault that mimics the subduction channel at natural subduction zones. We showcase how by employing analog materials under low-stress conditions, the potentialities of monitoring can be maximized using three diverse techniques: 1)  Precise monitoring of surface spatial deformation over time is achieved through digital image correlation techniques, mirroring a uniformly distributed dense geodetic network spanning land to trench in real subduction zones. 2) A Micro-Electro-Mechanical (MEMS) accelerometric network, emulating a seismic network, captures seismic wave propagation at the model surface. 3) Embedded piezoelectric sensors within the granular analog fault capture near-field acoustic signatures of frictional instabilities. These diverse monitoring techniques allow for investigating the consistency between continuous seismic activity and surface deformation data, offering insight into both micro and macroscopic features of analog seismic cycles. At the macroscopic level, the models' frictional behavior can be numerically reproduced via rate and state numerical simulations, considering earthquake fault slip as a nonlinear dynamical process dominated by a single slip plane. At smaller scales, the model accounts for complexities in fault slip emerging from grain interactions, reflecting nonlinearities that arise when considering faults as distributed three-dimensional volumes. These fundamental attributes, coupled with their capacity to create extensive catalogs of small labquakes, make scaled seismotectonic models exceptional apparati for employing Machine Learning (ML) in comprehending multi-scale spatiotemporal seismic processes. Cutting-edge Deep Learning methods are employed to predict the spatiotemporal evolution of surface deformation, where regression algorithms not only forecast timing but also the propagation and magnitude of analog earthquakes across diverse spatiotemporal scales. Given that one of the monitoring systems used in seismotectonic analog models mimics a geodetic-like network in nature (GNSS data-Global Navigation Satellite Systems), an attempt to generalize the promising outcomes achieved in the laboratory to natural subduction faults is proposed.  Such promising avenues emphasize the potential for ML to bridge the gap between laboratory experiments and real-world seismic events. These initial findings, combined with advancements in the instrumentation of fault laboratories in nature and expanding data reservoirs, reinforce the belief that ML can significantly augment our understanding of the multiscale behaviors of natural faults.

How to cite: Mastella, G., Corbi, F., Bedford, J., Latypova, E., Pignalberi, F., Scuderi, M., and Funiciello, F.: Multiscale, multisensor analysis of scaled seismotectonic models: Bridging the Gap Between Laboratory and Nature through Machine Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6869, https://doi.org/10.5194/egusphere-egu24-6869, 2024.

EGU24-7785 | ECS | PICO | TS5.2

Haromonic Curvature and Bedding Uncertainty Across Scales 

David Nathan, Mario Zelic, Eun-Jung Holden, Daniel Wedge, and Christopher Gonzalez

Observations of geological structures are often made at different scales and often can cross multple orders of magnitude. This attribute of scale though is often not explicitly incorporated into the workflow of geological modeling and is usually treated as data preparation or sampling bias. The spectral properties of the discrete Laplacian operator, when applied to reconstructed surfaces from implicit modeling though offer a potential means of bridging this gap, when also combined with appropriate directional statistical anaysis. We present an example of how bedding orientation measurements from a 1:5000 scale surface map and drillhole bedding orientation picks from borehole televiewer images can be integrated using the manifold harmonics of the Laplacian operator and a mixture of von-Mises Fisher probability distributions. This provides automated insights for sampling for modeling and also possible kinematic and tectonics processes.

How to cite: Nathan, D., Zelic, M., Holden, E.-J., Wedge, D., and Gonzalez, C.: Haromonic Curvature and Bedding Uncertainty Across Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7785, https://doi.org/10.5194/egusphere-egu24-7785, 2024.

This study investigates a fold-and-thrust belt (FTB) beneath the South Yellow Sea Basin, a noteworthy petroleum exploration target, featuring a basement high and a detachment layer. In the central basin, magnetic anomalies reveal the development of the basement high. Seismic reflection data, in conjunction with drilling information, disclose the presence of the Lower Silurian Gaojiabian Formation, exceeding ~500 m, acting as a low-cohesion detachment layer. However, the impact of these features on regional structures and the resulting hydrocarbon preservation conditions remains uncertain. This study explores the kinematic characteristics and deformation localization associated with the basement high and intermediate detachment using four sandbox models and particle velocity analysis within the FTB framework. Model 1, the reference, utilized pure quartz sand without either feature. Model 2 examined the role of the intermediate detachment using glass microbeads, revealing a limited effect in generating typical thin-skinned FTB. Model 3 considered the basement high and found that it strongly influenced the deformation regime of the wedge. Model 4 examined both features and suggested their combined influence on FTB deformation processes. In Model 2, lacking a pre-existing basement high, the intermediate detachment did not contribute to FTB deformation. In Model 3, lacking an intermediate detachment, deformation propagated along the surface of the basement high upon reaching its edge. In Model 4, shortening propagated upward along the edge of the basement high and then into the intermediate detachment, producing comparable structural geometry to the prototype, including both thick- and thin-skinned FTBs in nature. The results indicate that in the central South Yellow Sea Basin, structural layers between the basement high and detachment are likely to experience weak deformation; thus, favorable hydrocarbon preservation conditions can be anticipated in this region. This study holds significant importance in guiding future petroleum exploration efforts in the central South Yellow Sea Basin.

How to cite: Zhang, P., Fu, Y., and Yan, B.:  Influence of Basement High and Detachment on the Kinematics of a Fold-and-Thrust Belt in the Central South Yellow Sea Basin with Implications for Hydrocarbon Preservation: Insights from Analog Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8859, https://doi.org/10.5194/egusphere-egu24-8859, 2024.

EGU24-10540 | ECS | PICO | TS5.2

Proto-ophiolite serpentinization may influence ophiolite emplacement: Insights from numerical models  

Afonso Gomes, Filipe Rosas, Nicolas Riel, João Duarte, Wouter P. Schellart, and Jaime Almeida

Ophiolites are exposed remnants of oceanic lithosphere that are critical to our understanding of the structure, composition, and evolution of oceanic plates.

Some ophiolites (e.g., some Tethyan-type ophiolites) originate in the oceanic forearc of an intra-oceanic subduction system (i.e., in the overriding plate). If the trailing edge of the subducting oceanic lithosphere is connected to a continental passive margin, then that passive margin may also be subducted (beneath the forearc and proto-ophiolite) once all the oceanic lithosphere is “consumed” at the trench. The subduction of the continental passive margin means that a buoyant continental crust will underthrust the oceanic forearc (i.e., proto-ophiolite). This crust goes through a burial-exhumation cycle, and as it exhumes it can drag and detach the tip of the overlaying oceanic forearc, creating an ophiolite klippe. The exhumation-emplacement process is, however, still not fully understood, particularly regarding the constraints imposed by the forearc itself. For example, the detachment of the tip of the forearc (ophiolite) from the remainder of the plate should, at least in part, be controlled by the mechanical properties of the forearc (i.e., presumably the tip of a “weak” forearc will detach more easily than the tip of a “strong” forearc).

Present-day intra-oceanic subduction forearcs (i.e., present-day model-types for Tethyan-type ophiolites) experience significant chemical alteration induced by the circulation of metamorphic fluids originating from the dehydration of the underlying subducting plate. This chemical alteration occurs mostly in the form of serpentinization of forearc peridotites, leading to a substantial weakening of the forearc lithospheric mantle. The circulation of these fluids, and hence the serpentinization process, is thought to occur primarily along preexisting deeply rooted fault systems, further weakening these strain-localizing structures, although some diffuse alteration probably also occurs. It is then reasonable to assume that the paleo forearcs that originated Tethyan-type ophiolites were also subject to these chemical and mechanical alterations, which are then expected to have affected the ophiolite emplacement process.  

Here we present novel 2D and 3D dynamic numerical models that investigate the role of forearc weakening on ophiolite emplacement processes. Specifically, we test different mechanical weakening patterns, i.e., localized (serpentinized faults) vs homogeneous (diffuse serpentinization) weakening.

Preliminary results suggest that prior serpentinization of the forearc has a critical control on ophiolite emplacement. Furthermore, differing degrees of forearc serpentinization, as well as serpentinization distribution patterns, result in different tectonic regimes of ophiolite emplacement.

 

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020) and through scholarship SFRH/BD/146726/2019.

How to cite: Gomes, A., Rosas, F., Riel, N., Duarte, J., P. Schellart, W., and Almeida, J.: Proto-ophiolite serpentinization may influence ophiolite emplacement: Insights from numerical models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10540, https://doi.org/10.5194/egusphere-egu24-10540, 2024.

EGU24-12208 | PICO | TS5.2

Numerical and analogue modelling of boudinage under non-coaxial shear strain 

Filipe Rosas, Afonso Gomes, Jaime Almeida, João Duarte, Nicolas Riel, and Wouter Schellart

The recognition of different boudinage patterns is of key importance to the unravelling of the tectono-metamorphic evolution of different domains in different tectonic contexts and at different considered spatio-temporal scales.

The main reason for this is twofold: (1) Boudins tend to preserve the relic metamorphic conditions that characterize deformation prior to the one recorded by matrix fabrics and associated mineral associations. (2) Specially under shear deformation regimes, quarter-structure geometric patterns comprising rotated boudins and folded matrix planar fabrics, can be used to determine the shear sense of the later (sin-boudinage) deformation.

In the present work, we present preliminary numerical and analogue modelling results of boudinage, under non-coaxial (shear strain) deformation. We specifically investigate the potential influence of three main parameters on the genesis of different (boudins-folds) quarter structures patterns: i) the viscosity contrast between the boudin and the matrix; ii) the original position of the non-equidimensional boudin; and ii) the assumed (bulk) shear strain rate.

We proceed by presenting a preliminary comparison of our results with archetypical natural examples of boudinage, in different tectonic-structural contexts and at different scales, further illustrating the potential value of these type of structures in the unravelling of the deformation history in different situations.

Acknowledgements

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

How to cite: Rosas, F., Gomes, A., Almeida, J., Duarte, J., Riel, N., and Schellart, W.: Numerical and analogue modelling of boudinage under non-coaxial shear strain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12208, https://doi.org/10.5194/egusphere-egu24-12208, 2024.

EGU24-12468 | ECS | PICO | TS5.2

Asthenospheric flow-driven lithospheric deformation in analogue models – a novel methodological approach and implications for natural systems  

Nemanja Krstekanic, Ernst Willingshofer, Antoine Auzemery, Liviu Matenco, and Jasper Smits

In subduction systems, asthenospheric flow, generated by subducting slabs, is considered as one of the key forces contributing to the deformation of the overlying lithosphere. Previous analogue modelling studies predominantly focused on understanding the kinematics and dynamics of subduction roll-back-driven asthenospheric flow, without looking at the influence of that flow on upper-plate deformation due to the modelling setups or methodological limitations. We developed a novel analogue modelling approach where gravity-driven asthenospheric flow represents the main driver for upper plate deformation. Volume-constant flow within the deformation box is achieved by an inlet-outlet system. In the models, we gradually increase the setup complexity from single-layer asthenosphere-only models to 4-layer asthenosphere-lithosphere models to test flow velocity distribution and its sensitivity to the outlet size, model thickness and rheological stratification of the model, as well as the transfer of deformation from the asthenosphere to the overlying lithosphere. Furthermore, we study the effects of the inherited lithospheric structures, such as weak zones representing old sutures, on deformation transfer. The results are compared with the Pannonian-Carpathians system of south-eastern Europe, where the large Pannonian back-arc basin formed during the Miocene retreat of the Carpathians slab.

For the methodological approach, the results show that asthenospheric flow can be fully controlled by the inlet-outlet system by adjusting the outlet size, which provides an efficient mechanism for the deformation of the overlying mechanically stratified lithosphere. The models also demonstrate that the back-arc extension is initiated farther away from the asthenospheric flow origin (i.e., the outlet in the models or slab-roll back in nature). The subsequent deformation propagates in two directions, towards the flow origin, and farther away from it, both directions controlled by the shape of an indenter located laterally to the subduction zone. Most of the back-arc extension and the lithospheric thinning are accommodated in the area farther to the “slab” due to the strain shadow effect of the indenter. The indenter also contributes significantly to the strain partitioning in its closer proximity where a complex pattern of bi-directional extension, transtensional, strike-slip and transpressional deformation forms. The weak zones accommodate the onset of back-arc extension or act as transfer zones between areas with different extension rates, depending on their orientation relative to the asthenospheric flow. These models show several similarities with the Pannonian-Carpathians system, where most of the Pannonian lithospheric thinning is located at a significant distance from the subducting Carpathians slab, bypassing the Transylvanian-Apuseni area. This extension started by reactivation of the Neotethys suture zone, while the Mid-Hungarian Fault zone transferred the deformation between areas of higher extension to the south and lower extension to the north. Furthermore, several triangular-shaped sub-basins within and at the margin of the Pannonian Basin are radially located around the Moesian NW corner, similar to our modelling results. The complex pattern of the bi-directional extension and strike-slip observed in the models were recorded by the Carpathians-Balkanides orocline in the vicinity of the Moesian indenter.

How to cite: Krstekanic, N., Willingshofer, E., Auzemery, A., Matenco, L., and Smits, J.: Asthenospheric flow-driven lithospheric deformation in analogue models – a novel methodological approach and implications for natural systems , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12468, https://doi.org/10.5194/egusphere-egu24-12468, 2024.

EGU24-13464 | ECS | PICO | TS5.2

A new geodynamic model of the Azores archipelago: preliminary results 

Jaime Almeida, João Duarte, Filipe Rosas, Rui Fernandes, Fernando Geraldes, Luis Carvalho, and Ricardo Ramalho

The Azores archipelago is an integral part of the Macaronesian geographic region (which also includes the volcanic archipelagos of Madeira, Selvagens, Canaries and Cape Verde). This region, located in the centre of Atlantic Ocean, has its individual islands spread around a triple junction, which has been suggested to affected by a plume-ridge interaction (Storch et al., 2020; Beier et al., 2022). One of the major questions surrounding its history concern the why/how the Terceira Rift (i.e., the NW-SE oriented connection between the mid-ocean ridge and the Gloria Fault Zone) was formed.

To explore this issue, we have run sets of 3D viscoelastoplastic models for the region using the state-of-the-art modelling code LaMEM (Kaus et al., 2016). As our objective was to evaluate how the geological data and the suggested evolution for the region fit geodynamic constraints. We based our numerical models on previously established evolutionary models for the region, such as the leaky transform model (Madeira and Ribeiro, 1990).

Preliminary results hint that the formation of the Terceira Rift could be formed as the result of a shift in the regional tectonic forcing, which we attribute to the collision between the Iberian and Eurasian plates. Furthermore, our results suggest that a strong rheological contrast in the region was required to ensure the localization of deformation. Models without this feature tended to maintain a simple E-W connection between the Gloria Fault Zone and the southern part of the mid-ocean ridge.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through projects GEMMA (https://doi.org/10.54499/PTDC/CTA-GEO/2083/2021) and national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

 

References

Beier, C. et al. (2022) ‘The submarine Azores Plateau: Evidence for a waning mantle plume?’, Marine Geology, 451, p. 106858. Available at: https://doi.org/10.1016/j.margeo.2022.106858.

Kaus, B.J.P. et al. (2016) ‘Forward and Inverse Modelling of Lithospheric Deformation on Geological Timescales’, NIC Series, 48, pp. 978–3.

Luis, J.F. and Miranda, J.M. (2008) ‘Reevaluation of magnetic chrons in the North Atlantic between 35°N and 47°N: Implications for the formation of the Azores Triple Junction and associated plateau’, Journal of Geophysical Research: Solid Earth, 113(B10). Available at: https://doi.org/10.1029/2007JB005573.

Madeira, J. and Ribeiro, A. (1990) ‘Geodynamic models for the Azores triple junction: A contribution from tectonics’, Tectonophysics, 184(3–4), pp. 405–415. Available at: https://doi.org/10.1016/0040-1951(90)90452-E.

Storch, B. et al. (2020) ‘Rifting of the oceanic Azores Plateau with episodic volcanic activity’, Scientific Reports, 10(1), p. 19718. Available at: https://doi.org/10.1038/s41598-020-76691-1.

How to cite: Almeida, J., Duarte, J., Rosas, F., Fernandes, R., Geraldes, F., Carvalho, L., and Ramalho, R.: A new geodynamic model of the Azores archipelago: preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13464, https://doi.org/10.5194/egusphere-egu24-13464, 2024.

Eastern Sichuan fold belt, a prolific hydrocarbon province in China, shows the similar fold styles to the Swiss Jura Mountain fold belt, which’s therefore called as Jura-type fold by Chinese geologists. However, it’s still a matter of geologist’s debate on the formation mechanism of the eastern Sichuan fold belt.

To unravel how this type of fold trains form, a systematic scaled 2D contractional analogue experiments with composite materials were conducted. Silica-sand represents the overburden with added mica-flakes, and a stiff plasticine interlayer introducing different mechanical anisotropies. Viscous silicone rubber represents the salt detachment. The following 3 main issues have been investigated: 1) what type mechanical stratigraphy can form the fold train during lateral contraction; 2) what are the mutual interaction between faulting and folding during the formation process of detachment fold; 3)what are kinematics and its related strain distribution patterns for a detachment fold system.

The modelling results indicate that the presence of a stiff plasticine layer is the key perquisite for the formation of a concentric fold train for the following reasons: 1) it encourages the shortening to be periodically accommodated by sinusoidal-symmetric buckle folds at the inceptive folding stage; 2) it can keep the break-thrust ramps from being activated with further shorting delaying the development of faulted detachment folds at the later folding stage. As for silicone detachment, it mainly plays a role in the amplification of detachment folds via the redistribution of ductile material between the syncline and anticline domain.

DIC strain data show that the main sections of detachment fold-the limbs, especially in the forelimb, and the hinge are easily strained. More specifically, the normal faults and breakthrusts can form in the anticlinal hinge and limbs, respectively, when the detachment fold cannot be tightened any more. However, the strain is not easily accumulated in the syncline domain.

Our modelling result together with the latest interpretation of seismic reflection suggest that the eastern Sichuan fold belt is a result of faulted detachment folds, mainly controlled by the competence contrast within the overburden and the thickness of both the weak viscous detachment and strong brittle overburden.

Keywords: Eastern Sichuan Basin; Analogue modelling; DIC; Fold-thrust belt; Detachment fold

How to cite: Feng, G., Adam, J., Chen, S., and Wang, X.: Key controlling factors on the formation of Jura-type fold in eastern Sichuan Basin, South China: insights from analogue modelling with optical strain monitoring (Digital Image Correlation), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13637, https://doi.org/10.5194/egusphere-egu24-13637, 2024.

EGU24-13652 | ECS | PICO | TS5.2

Crust-mantle delamination enables continental subduction and flake tectonics: insights from numerical modelling 

Nuno Rodrigues, Filipe Rosas, Nicolas Riel, Jaime Almeida, Afonso Gomes, and João Duarte

Continental collision occurs when two continents are dragged towards each other by the pull of the attached subducting oceanic lithosphere. Previous geodynamic modeling studies of collisional systems focused on first-order processes (such as coupled/decoupled regimes, continental delamination, slab break-off dynamics) and regional or even local scale dynamics (e.g., exhumation of HP/UHP rocks, surface topography). However, continuous subduction of continental lithospheric mantle after the onset of collision and long-term dynamics of continental subduction remains poorly constrained. Long-term continental subduction bears major geodynamic implications for the evolution of past and present collision zones.

To this aim, we use the geodynamic code LaMEM to perform high-resolution (2048 × 512) 2D buoyancy-driven numerical models, coupled with phase diagrams to account for density changes, of continued continental subduction with conditions that favor flake tectonics. We investigate the role of lower crust rheology to assess which rheological scenarios allow continental flaking and, thus, continued subduction of continental lithospheric mantle.

Our preliminary results exhibit long-term continental subduction, due to decoupling of the lower crust from the subducting continental mantle and/or density changes. This separation allows the deformation to be transmitted onto the overriding plate, with the emplacement of the subducting plate crust onto the overriding plate spanning more than 350 km and lasting over 100 Myr.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and through scholarship UI/BD/154679/2023.

How to cite: Rodrigues, N., Rosas, F., Riel, N., Almeida, J., Gomes, A., and Duarte, J.: Crust-mantle delamination enables continental subduction and flake tectonics: insights from numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13652, https://doi.org/10.5194/egusphere-egu24-13652, 2024.

The deformation associated with the evolution of fold-thrust tectonic (FTT) wedge has been in the focus of research due to their association with hydrocarbons resources. Analogue sandbox modelling has been proven to be useful in characterizing FTT wedge. However, it is less convenient to interpret the influence of complex boundary conditions and material rheological parameters and to derive the stress distribution pattern from the analogue models. Nonetheless, these challenges can be accomplished competently by means of an exact numerical equivalence of those analogue models. Therefore, we undertook a numerical replication of the analogue sand-box with an absolute identical set up. This makes the attempt unique from earlier approaches, where lengths, rheology, and/or cohesive strengths were likely varied for converging the solutions in codes. Here, propagation parallel profile of sandbox experiments is numerically modelled in a 2-dimensional (2D) space with a plain strain assumption. For simplicity, the models are devoid of complex geological phenomena such as isostasy, pore fluid pressure and surficial processes. The present model enforces an elastoplastic constitutive relationship having exactly same rheology as our sand-box model. The model comprises cover material resting over a rigid decollement with frictional interaction. The cover material is subjected to asymmetrical push from one end as in physical experiment. With the identical rheology, dimensions, and geometry our numerical model successfully produced comparable results with our physical sandbox models. The measured kinematic attributes of the wedge such as taper angle, wedge width, thrust spacing, displacement along thrust from our numerical model are found in good agreement both qualitatively and quantitively with their analogue counterparts. The dynamics of deformation has also been investigated by extracting the magnitudes of stresses from each node of the numerical mesh of the present models.  From the dynamic analysis, the spatial distribution of stresses revealed that within a deforming wedge all the stress parameters are maxed periodically at a certain distance away from the pushing end boundary. The position of maximum stress is found consistent with the zone localized failure. Monitoring the periodic peaks of stress approximate the location of failure, in return leading to measure the thrust spacing. Furthermore, empirical relationships for stress distribution within a collisional wedge have been successfully developed from the observed stress distribution patterns. With the help of these relationships, mathematical expressions were developed for predicting 2D curvature of a thrust plane within a tectonic wedge. 

How to cite: Behera, A. and Bhattacharjee, D.: The dynamics of fold-thrust tectonic wedge: An insight from impeccable simulation of Physical Sandbox Experiment with Finite Element Model., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14388, https://doi.org/10.5194/egusphere-egu24-14388, 2024.

EGU24-14511 | PICO | TS5.2

Machine learning reveals the width of fault damage zones in northeast Sichuan Basin, China 

Jingbo Zhang, Sixian Chen, and Zonghu Liao

Abstract

Accurate understanding and identification of faults architecture is crucial in seismic data interpretation and earthquake analysis, where fault slip surfaces may interact with damage rocks, forming damage zones with a width larger than hundred meters. We use machine learning (ML) to show 10 kinds of seismic attributes from a seismic survey could be applied in identification and quantification of fault damage zone in northeast Sichuan Basin, China. The results indicate: (1) Six seismic attributes provide highest contribution to the fault characterization, including root mean square amplitude attributes, azimuth angle attributes, reverse attributes, original attributes, chaotic body attributes and ant body attributes; (2) The application of SHAP (SHapley Additive exPlanations) algorithm improves the model's accuracy, as the loss value (Mean Square Error , MSE) of the test data is restored from 17.86% to 16.03%; (3) Width estimation from the kernel density estimation algorithm (KDE) show the fault damage zone ranges from 0.3 to 1.2 km. Our work provides new insights into the interpretation of fault architecture in the subsurface, and we argue the geometrical parameters of the fault damage zone is significant for understanding the evolution of fault and earthquake simulations.

Keywords:  Fault damage zone; Seismic interpretation; Machine learning (ML); Geometrical parameters

Figure1.The seismic attributes of the actual work area entered into the model and the model calculation results: (A) Original attributes of the work area. (B) Variance attribute of the work area. (C) Results calculated by the ML model

Figure2. Thermal diagram presents the structure of the fault damage zone: (A) A vertical line perpendicular to the fault orientation correction; (B) indicates the fault range with a thermal index greater than 1.572; (C) indicates a fault range with a thermal index greater than 2.065; (D) indicates a thermal index greater than 2.401 fault range. The width of the damage zone could be estimated by these figures.

 

Figure3. Descriptive diagram of fault damage zone width. Fault_1 represents the direction of fault width with thermal index greater than 1.572; Fault_2 represents the direction of fault width with thermal index greater than 2.065; Fault_3 represents the fault width trend map with thermal index greater than 2.401

How to cite: Zhang, J., Chen, S., and Liao, Z.: Machine learning reveals the width of fault damage zones in northeast Sichuan Basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14511, https://doi.org/10.5194/egusphere-egu24-14511, 2024.

EGU24-16472 | PICO | TS5.2

How the rigidity of the subducting plate affects the geometry of accretionary prisms? 

Laetitia Le Pourhiet, Alexis Gauthier, Nadaya Cubas, Julie Tugend, and Geoffroy Mohn

Simulations of accretionary prisms are most of the time realized either using a simplified set up that cannot account for the evolution of temperature with the growth of the prism nor deformable basement or using a very large size simulation of the complete subduction zone using a larger resolution locally. The first method is over-simplified and discards the possibility to study crustal scale accretionary prism, the second method is very costly numerically.  

Here, we present simulations of accretionary prisms that use 1/ heatflux as boundary condition allowing the temperature at the base of the model to evolve as the accretionary prism grows and 2/ flexural deformation of the basement in response to the growth of the accretionary prism. This new boundary condition is very cheap to compute as we implemented it by solving analytically the flexure equation using sinus decomposition and image method.  

We then present a set of numerical simulations of crustal scale accretionary prism with particular focus on the geometry of the subducting basement in order to better understand how the alternation between period of subduction erosion and accretion affects the geometry of the accretionary prism and its thermal history as a function of the rigidity of the subducting plate. We compare our simulations with a set of east-west trending seismic profiles located southwest of Taiwan showing along strike structural variations of the accretionary prism.    

How to cite: Le Pourhiet, L., Gauthier, A., Cubas, N., Tugend, J., and Mohn, G.: How the rigidity of the subducting plate affects the geometry of accretionary prisms?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16472, https://doi.org/10.5194/egusphere-egu24-16472, 2024.

EGU24-17730 | ECS | PICO | TS5.2

Numerical simulation of Landscape Evolution using Landlab: A case study of Dibang Basin, North-East India 

Uma Narayan M, Surendra Kumar Sahu, Rishikesh Bharti, and Archana M Nair

The continual modification of the topography due to varied processes results in diverse and dynamic terrain. Landscape evolution studies can link the effect of small-scale topographic quantities on long-term landscape evolution. In this study, the evolutionary pattern of the Dibang basin, located at the limb of the Eastern Himalayan Syntaxis stretch along the active tectonic region of northeast India is analysed using the stream power incision model (SPIM). SPIM is an empirical power law equation linking erosion with channel area and bed slope.  With constant tectonic forcing and homogeneous physical properties, river profiles deviate from linearity and exhibit convexity (indicating uplift) and concavity (indicating erosion) in their longitudinal profiles. These deviations indicate the transient responses of the river profile due to tectonics. Here, the landscape is modelled assuming that the Dibang River lying close to the mountain front shows bedrock properties. The evolved topography is seen to exhibit an erosion-dominated landscape with a rapid decrease in the mean elevation. The profile of the Dibang River exhibits a concave-convex-concave shape, indicating that the river channel is in a state of disequilibrium. The steepness index is observed to be varying across the Dibang basin with higher values in the middle and upper right parts of the basin. The χ plot also reveals the transient nature of the river profile.

How to cite: Narayan M, U., Sahu, S. K., Bharti, R., and Nair, A. M.: Numerical simulation of Landscape Evolution using Landlab: A case study of Dibang Basin, North-East India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17730, https://doi.org/10.5194/egusphere-egu24-17730, 2024.

EGU24-18656 | PICO | TS5.2

Fracture and magma pathways development above sill like magmatic chambers in strike-slip setting 

Martin Staněk, Prokop Závada, and Ondřej Krýza

The Reykjanes Peninsula (RP) in southwestern Iceland represents a zone of oblique rifting where the divergent boundary of the Mid-Atlantic ridge is offset to the eastern Iceland along a left-lateral transform fault - the South Iceland Seismic Zone (SISZ). RP and the SISZ represent regions of the most abundant earthquake activity on Iceland, development of fissure arrays and occasional lava eruptions. A series of earthquake swarms at RP in the 2021-2023 period indicates development of distributed fracture networks along ENE direction of the transform fault and two new fissure arrays trending NE divided by a gap in seismicity. In the last 3 years, the volcanic activity culminated two times in volcanic eruptions, bringing magmas from Moho depth at 15 km.

Inspired by the recent tectonic activity at RP, we conducted a series of analogue experiments consisting of a silicone magma chamber embedded in a photoelastic gelatine crust. The aim of our study is to constrain the links between the depth level of the magma chamber, the crustal scale fracture arrays, faults, magma pathways, superficial fractures and the location of related potential volcanic activity in a transform setting. Inducing strike slip deformation of the system, we explored the influence of shape and orientation of the magmatic chamber on the evolution and pattern of progressively developed fractures along the central shear domain. During the experiment, we captured the stress fringe patterns in the fractured gelatine. The surface deformation was traced by a stereoscopic digital image correlation (DIC) system employing two high-speed LaVision cameras. Analog magma spreading was traced using fluorescent dye mixed to the silicone or into the gelatine interlayer.

Modelling results show that decoupling of the crust above the magma reservoir in strike-slip setting produces a domain with higher vorticity bounded by a conjugate set of tensional fractures. The largest open fractures initiate at and propagate from the intersection of the principal strike-slip fault plane with the vertical contact of the magma chamber and the surrounding crust. Including other open fractures, the orientation of the fracture set is oblique (~ 60°) to the fault plane. With formation approximately coeval to those of the fractures, fine wrinkles at the crust surface are observed with orientation of ~ 120° with respect to the fault plane.

How to cite: Staněk, M., Závada, P., and Krýza, O.: Fracture and magma pathways development above sill like magmatic chambers in strike-slip setting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18656, https://doi.org/10.5194/egusphere-egu24-18656, 2024.

EGU24-2384 | ECS | Orals | EMRP1.6

Frictional slip sequences in homogeneous and bimaterial interfaces 

Songlin Shi, Meng Wang, Yonatan Poles, and Jay Fineberg

Earthquake-like ruptures disrupt the frictional interface between contacting bodies and initiate frictional motion (stick-slip). The interfacial slip (motion) immediately resulting from a rupture during each stick-slip event is usually much smaller than the total slip recorded during the duration of the event. Slip after the onset of friction is generally attributed to the continuous motion of global ‘dynamic friction’. Here, we demonstrate that numerous hitherto invisible secondary ruptures are initiated immediately after each initial rupture by directly measuring the contact area and slip at the frictional interface. Each secondary rupture generates incremental slip that, when not resolved, may appear as steady sliding of the interface. Each slip increment is linked, via fracture mechanics, to corresponding variations of contact area and local strain. Cumulative interfacial slip can only be described if the effects of these secondary ruptures are taken into account. These weaker slip sequences can also be observed in bimaterial interfaces and exhibit strong directional effects. In addition, the seismic moments we estimate based on slip sequences are consistent with the Gutenberg-Richter (G-R) law. These results have important implications for our fundamental understanding of frictional motion and the important role of aftershocks within natural faults in generating earthquake-mediated slip/afterslip.

How to cite: Shi, S., Wang, M., Poles, Y., and Fineberg, J.: Frictional slip sequences in homogeneous and bimaterial interfaces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2384, https://doi.org/10.5194/egusphere-egu24-2384, 2024.

EGU24-3912 | ECS | Orals | EMRP1.6

Back-Propagating Rupture: Nature, Excitation, and Applications 

Xiaotian Ding, Shiqing Xu, Eiichi Fukuyama, and Futoshi Yamashita

In recent years, an intriguing feature of back-propagating rupture (BPR) has been reported during some earthquakes (Ide et al., 2011; Houston et al., 2011; Hicks et al., 2020; Okuwaki et al., 2021; Vallée et al., 2023). The occurrence of BPR challenges the classical interpretation of rupture propagation as a “forward” problem, while remaining less understood by the earthquake science community. Here, using fracture mechanics, we first argue that BPR is nothing but an intrinsic component of rupture propagation; however, its observability is usually masked by the superposition effect of interfering waves behind the primary, forward-propagating rupture front. We then suggest that perturbation to an otherwise smooth rupture process can break the superposition effect and hence can make BPR observable. To test our idea, we report results of mode-II rupture propagation from both numerical simulations and laboratory observations. By introducing a variety of perturbations (lateral variation in bulk or interfacial properties along the fault, singular stress drop, coalescence of two rupture fronts, etc.) during rupture propagation, we show that prominent phases of BPR indeed can be successfully excited. We further classify BPR into two modes: higher-order rupture or interface wave, depending on whether the already-ruptured fault is quickly healed and whether additional stress drop can be produced. Lastly, we propose several application potentials for BPR, such as constraining the velocity structure of fault zones, probing the mechanical state of faults, and studying the stability of perturbed slip along a homogeneous or bimaterial interface. Our study refines the understanding of the nature and complexity of rupture process, and can help improve the assessment of earthquake hazards.

How to cite: Ding, X., Xu, S., Fukuyama, E., and Yamashita, F.: Back-Propagating Rupture: Nature, Excitation, and Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3912, https://doi.org/10.5194/egusphere-egu24-3912, 2024.

EGU24-5187 | Orals | EMRP1.6

The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes  

Fabio Corbi, Giacomo Mastella, Elisa Tinti, Adriano Gualandi, Laura Sandri, Matthias Rosenau, Silvio Pardo, and Francesca Funiciello

Modeling the seismic cycle requires multiple assumptions and parameters. Providing a quantitative assessment of the model behavior is pivotal for determining the degree of similarity between different scales and modeling strategies and for exploring dependencies with respect to selected parameters. Here we compare stick-slip ruptures nucleating spontaneously in scaled seismotectonic models (i.e., laboratory experiments capturing the first-order physics of the seismic cycle of subduction megathrusts) with slow earthquakes in nature. We rely on two non-dimensional parameters, namely the Ruina number (Ru) and system dimension (D) to quantify model behavior. Ru is proportional to the ratio of the asperity size to the critical nucleation size. Within the rate- and state friction framework, for velocity weakening asperities Ru controls the behavior of the system, which can be either periodic or not, and it can exhibit both slow and fast ruptures. D measures how complicated the system evolution is. D reveals how many variables are required to describe the seismic cycle because it tells us the minimum dimension needed to embed the observed dynamics. 

By coupling the Simulated Annealing algorithm and quasi-dynamic numerical simulations, we retrieve rate and state friction parameters characterizing single asperity models with different lateral extent of the velocity weakening patch. Similarly to slow earthquakes, we found optimal rate and state parameters indicative of low (< 4) Ru. We also found a direct proportionality between Ru and the lateral extent of the asperity. 

Next, we implement tools from non-linear time-series analysis and Extreme Value Theory to compute D from models of different sizes, materials, deformation rates and frictional configurations (single or twin asperities along strike). Our analysis supports the existence of a low dimensional attractor (D<5) describing the dynamics of scaled seismotectonic models. In particular, our models display D=3.0-4.2, which is remarkably similar to D=3.2 of slow earthquakes identified along the Cascadia subduction zone. Under the explored conditions, D appears more affected by the material behavior of the analog upper plate (i.e., gelatin vs. foam rubber) than by the lateral frictional segmentation of the megathrust.

Despite the different spatio-temporal scales, our results support a scenario where scaled seismotectonic models and slow earthquakes share similar dynamics.



How to cite: Corbi, F., Mastella, G., Tinti, E., Gualandi, A., Sandri, L., Rosenau, M., Pardo, S., and Funiciello, F.: The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5187, https://doi.org/10.5194/egusphere-egu24-5187, 2024.

EGU24-5767 | ECS | Posters on site | EMRP1.6

Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity  

Pierre Romanet, Marco Scuderi, Stéphanie Chaillat, Jean-Paul Ampuero, and Frédéric Cappa

Numerical modeling of Discrete Fracture Networks (DFNs) is commonly used to assess the behavior and properties of hydraulic diffusion and seismicity in the Earth’s crust within a network of fractures and faults, and to study the hydromechanical evolution of fractured reservoirs stimulated by hydraulic injection and production. The modelling of such fractures is typically carried out under a quasi-static approximation, and occasionally accounting for elasto-dynamics in single-rupture studies that assume a slip-weakening friction law. 

In this work, we develop a 2D DFN model to simulate fluid-induced seismicity that couples hydraulic diffusion and slip governed by rate-and-state friction on multiple interacting faults. The main goal of this numerical model is to establish a connection between laboratory derived friction parameters and field observations, enabling the inference of the long-term evolution of fractured reservoirs and crustal fault systems undergoing multiple earthquakes and (slow) slip events induced by fluid pressure perturbations.

In the model, the elastic interactions are computed with a boundary element method, accelerated by the hierarchical matrix method. We assessed the convergence of the method at fracture junctions and verified it does not create unphysical singularities. The use of rate-and-state friction makes it possible to model several seismic events over the injection duration.

The simulations will be later used to fit measurements of permeability and friction collected in laboratory experiments, in-situ observations of fault slip and opening from fluid injection experiments at decametric scale, and finally, induced seismicity at reservoir scale.

 

How to cite: Romanet, P., Scuderi, M., Chaillat, S., Ampuero, J.-P., and Cappa, F.: Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5767, https://doi.org/10.5194/egusphere-egu24-5767, 2024.

EGU24-6284 | ECS | Posters on site | EMRP1.6

Fault drainage state and frictional stability in response to shearing rate steps in natural gouge 

Raphael Affinito, Derek Elsworth, and Chris Marone

Elevated pore fluid pressures are frequently implicated in governing fault zone seismicity. While substantial evidence from geodetic and geological studies supports this notion, there is a notable scarcity of experimental observations of how fluid pressure influences fault stability during shear. Understanding the precise interplay between porosity, fault slip rate, and frictional stability is pivotal for assessing the significance of processes like dilational strengthening or thermal pressurization in the context of seismic hazards. Here, we prepare fault gouges from the Utah FORGE enhanced geothermal field injection well 16A at depths corresponding to seismic events (between 2050 – 2070m). Experiments were conducted inside a pressure vessel and loaded under a true-triaxial stress state, replicating in-situ stress conditions observed at the Utah FORGE site. The applied fault normal stress and during the experiments were held constant at 44MPa. Pore fluid pressure was varied between successive experiments (13, 20, and 27 MPa) to span a range of effective stresses to examine impacts on fault dilation/compaction and the successive frictional stability. Different fluid pressure boundary conditions: constant volume or pressure were applied to explore how changes in shearing rate influence gouge stability thought the fault drainage state. Our data indicate that the Utah FORGE samples are velocity-neutral and transition to velocity-weakening behavior at elevated pore pressure and shear strains >7. We find dilatancy coefficients e = ∆f/∆ln(v), where f is porosity and v is fault slip velocity, consistent with quartz-feldspathic-rich rocks ranging from 5–12^10-4, indicating a conditionally unstable regime. Furthermore, our results demonstrate that the boundary conditions for pore fluids influence frictional stability viachanges in effective normal stress. For example, when pore volume has zero flux, an expansion in the void volume during slip results in a decrease in pore pressure, transitioning the system towards frictional stability. Our results indicate that the connectivity of pore conduits may be more important than the imposed pore pressure conditions when considering the impact on fault stability. We suggest that the interplay between fault slip and fluid mobility within a fault is a delicate balance for predicting and managing seismic hazards.

How to cite: Affinito, R., Elsworth, D., and Marone, C.: Fault drainage state and frictional stability in response to shearing rate steps in natural gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6284, https://doi.org/10.5194/egusphere-egu24-6284, 2024.

EGU24-7508 | Orals | EMRP1.6

A granular numerical model for the friction and wear of a lab-scale fault asperity 

Guilhem Mollon, Adriane Clerc, Amandine Ferrieux, Lionel Lafarge, and Aurelien Saulot

Seismic faults are often represented using two different and self-excluding conceptual models. In the first representation, seismic faults are seen as the interface between two surfaces of bare rock, with a roughness extending at all scales. These surfaces interact mechanically through a certain number of “asperities” which constitute the “real contact area”. When adopting this view, attention is paid on the statistics of the asperities population in the fault plane. Faults are thus considered as 2D objects, since their thickness is disregarded.

In the second representation, seismic faults are seen as mathematical planes separated by a certain thickness of granular gouge created by abrasive wear of the surfaces during previous slips. This view is analogous to the tribological “third body” theory, and is supported by field observations and experimental evidences of gouge creation in rotary shear and triaxial experiments. It is convenient to adopt this perspective when weakening phenomena within the gouge are to be spatially resolved in the direction orthogonal to the fault plane. Variations along this plane are then ignored, as well as fault roughness, and faults are mostly seen as 1D objects.

Unification of these two representations requires a better understanding of the interactions between geometrical asperities and a layer of gouge, and in particular of the phenomena that lead to the creation of the latter through the wear of the former. In this communication, we present a numerical model which aims at reproducing lab tests of millimetric single-asperity friction and wear. The model is essentially granular in order to represent the progressive degradation of the asperity along sliding, the separation of powdery matter, its successive ejection and reinjection by the contact (thanks to a periodicity in boundary conditions), and the build-up of a gouge layer. It also includes a coupling with continuum mechanics in order to maintain a meaningful stress field in the asperity beyond the region of degradable rock.

Numerical results show that: (i) the rate of wear of the asperity and the counterface are directly linked to the normal load applied to the contact; (ii) an established layer of gouge develops in the interface and controls the friction coefficient; (iii) a constant level of surface roughness is established after a sufficient sliding distance, both for the asperity and the counterface; (iv) an accurate control of the asperity boundary conditions is necessary in order to obtain repeatable friction and wear. These results are a first step towards a better understanding of the wear kinetics as a function of asperity geometry, load, and roughness, before the introduction of thermal aspects (including melting) in a future version of the model.

How to cite: Mollon, G., Clerc, A., Ferrieux, A., Lafarge, L., and Saulot, A.: A granular numerical model for the friction and wear of a lab-scale fault asperity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7508, https://doi.org/10.5194/egusphere-egu24-7508, 2024.

EGU24-7803 | ECS | Posters on site | EMRP1.6

Fluid driven seismic cycle modelling in subduction zones 

Betti Hegyi, Taras Gerya, Luca Dal Zilio, and Whitney Behr

The role of fluid flow in triggering earthquakes in subduction zones is a critical yet complex aspect in seismology. Despite extensive study through geological, geophysical observations, and laboratory experiments, fully understanding and modelling these processes within a coupled solid-fluid interaction framework remain challenging. This study employs a coupled seismo-hydro-mechanical code (i2elvisp) to simulate fluid-driven earthquake sequences in a simplified subduction megathrust environment. We incorporate non-uniform grid resolution, enhancing the resolution of seismic events within the subduction channel. The code integrates solid rock deformation with fluid dynamics, solving mass and momentum conservation equations for both phases, alongside gravity and temperature-dependent viscosity effects. Brittle/plastic deformation is modelled through a rate-dependent strength formulation, with slip instabilities governed by compaction-induced pore fluid pressurisation. Our approach demonstrates the significant impact of fluid pressurisation on deformation localization, achieving slip rates up to metres per second in a fully compressible poro-visco-elasto-plastic medium. By refining the vertical model resolution in the subduction channel to less than or equal to 200 metres, we ensure convergence in terms of event recurrence interval and slip velocity. The models successfully replicate various slip modes observed in nature, ranging from regular earthquakes (including partial and full ruptures) to transient slow slip phenomena and aseismic creep. This research focuses on the parameters influencing the dominant slip mode, their distributions, and interactions along a modelled subduction interface. Our findings indicate that the dominant slip mode and the earthquake sequences are significantly influenced by porosity, permeability, and temperature-dependent viscosity. We explore two distinct viscosity gradients in the subduction channel to represent subduction zones with differing thermal profiles. In 'hot' subduction models, the brittle-ductile transition commences at shallower depths than in 'cold' subduction cases, influencing the nucleation depth of seismic events. These viscosity variations markedly impact model evolution; regular earthquakes exhibit higher velocities and slip rates in 'hot' scenarios, which are also more conducive to hosting aseismic creep or slow slip events. In conclusion, our study elucidates the pivotal role of fluid pressure evolution in seismicity within subduction zones and provides deeper insights into earthquake source processes. Through comprehensive modelling and analysis, we enhance understanding of the complex dynamics governing fluid-induced seismic activity and contribute to the broader field of earthquake source processes. 

How to cite: Hegyi, B., Gerya, T., Dal Zilio, L., and Behr, W.: Fluid driven seismic cycle modelling in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7803, https://doi.org/10.5194/egusphere-egu24-7803, 2024.

EGU24-8381 | Posters on site | EMRP1.6

Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure 

Lei Zhang, Changrong He, and Sylvain Barbot

To investigate the frictional behavior of basalt under hydrothermal conditions, we apply sliding experiments using basalt gouge under the temperature of 100-600ºC, effective normal stress of 150MPa, and fluid pressure of 30MPa and 100MPa, respectively. Experiment results under 30MPa pore pressure show that basalt exhibits velocity-strengthening behavior at 100-200ºC and changes to velocity-weakening behavior at 400-600ºC; meanwhile, at 400ºC, velocity dependence of basalt evolves with slip from initial velocity weakening to velocity-strengthening. Results under 100MPa fluid pressure show a similar transition of velocity dependence at 300ºC; however, at higher temperatures of 400-600ºC, velocity strengthening behavior occurs, accompanied by strong slip weakening behavior at the slowest loading rate (0.04μm/s). During the velocity step, the experiment exhibits a rate-dependent creep without transient evolution with slip. Microstructure observation reveals significant differences between samples sheared under 30MPa and 100MPa fluid pressure. At higher fluid pressure and temperatures of 400-600ºC, the porosity of the basalt gouge layer is significantly reduced, and deformation is characterized by pervasive shear with no apparent localization. Such results suggest that the healing process/plastic deformation is activated at higher fluid pressure, leading to slip stability transition and slip-weakening of frictional strength.

How to cite: Zhang, L., He, C., and Barbot, S.: Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8381, https://doi.org/10.5194/egusphere-egu24-8381, 2024.

EGU24-8887 | ECS | Posters on site | EMRP1.6

High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge 

Jianhua Huang, Bo Zhang, Junjie Zou, Honglin He, Jiaxiang Dang, and Jinjiang Zhang

        Abundant cherts (nodules and bands) were discontinuously hosted by dolostones of the Mesoproterozoic group Strata (∼1.5 Ga) in the Shanxi graben system, North China, where earthquakes are common. Measurements of the shear strength and stability of granular quartz reveal that quartz is a typical tectosilicate which exhibits high frictional strength and velocity-weakening properties. Conversely, dolomite is usually frictionally weak but velocity strengthening. The two minerals also behave differently during coseismic slip. Due to the high temperature generated by frictional heating, the thermal decomposition of dolomite usually results in calcite, periclase nanoparticles and carbon dioxide. However, quartz melts by friction at high temperatures. In order to investigate the role of quartz in dolomite fault rock during the process of coseismic slip, high velocity shear experiments were conducted on the quartz-bearing dolomite fault gouge taken from Yuguang Basin South Margin Fault (YBSMF), northeast of the Shanxi graben system. Also, we carried out high velocity experiments with the synthetic quartz-dolomite gouge with different mass ratio. For a slip velocity ≥ 0.1 m/s and normal stresses from 1.0 to 1.5 MPa, the friction values of the gouge decrease exponentially from a peak value of more than 0.5 to a steady-state value from 0.1 to 0.4. This high-velocity weakening feature was observed in the synthetic quartz-dolomite gouge as well as in the YBSMF gouge. With the increase of quartz content, the slip weakening distance (Dw) increases from 4.27 to 13.24 m, and the steady-state friction coefficient increases from 0.2 to 0.4 at 1.0 MPa normal stress and 1.0 m/s slip velocity. The textures of the gouge are characterized by grain comminution, R shear planes and localized deformation zone in the friction weakening stage. The slip surfaces are characterized by mirror-like smooth surface and nanoparticle aggregates. The theoretical calculation results show that the temperature inside the gauge layer did not exceed 300 °C during the experiments. However, the microstructures present that the dolomite experienced thermal decomposition, indicating that the temperature at the asperity exceeds 550 ℃. We suggest that thermal decomposition together with flash heating may lead to the slip-weakening behavior of quartz-bearing dolomite gauge, and the addition of quartz will increase of the strength of the dolomite gouge.

How to cite: Huang, J., Zhang, B., Zou, J., He, H., Dang, J., and Zhang, J.: High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8887, https://doi.org/10.5194/egusphere-egu24-8887, 2024.

EGU24-9165 | ECS | Posters on site | EMRP1.6

Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland) 

Wei-Hsin Wu, Wei Feng, Rodrigo Gomila, Telemaco Tesei, Marie Violay, Anette K. Mortensen, and Giulio Di Toro

Fault’s frictional strength and particularly its ability to heal during the interseismic period (fault frictional healing Δμ) is critical to understand the seismic cycle, yet the understanding of temperature and phase-dependent healing characteristics of natural geothermal conditions remains limited. Here we examined the frictional healing of both simulated fresh and chlorite-altered basaltic gouge from Krafla geothermal field (Iceland) under realistic geothermal conditions of water temperature Tf = 100-400 ˚C and pressure Pf = 10-30 MPa (water in liquid, vapor and supercritical state) by performing Slide-Hold-Slide (SHS) experiments. All experiments were performed under a constant effective normal stress of 10 MPa and initiated with a 5-mm run-in slip at a loading point slip rate V of 10 mm/s before the SHS sequence. For each SHS sequence, shearing was held from 3 s to 10,000 s, separated by a slip interval of 1mm. Our mechanical results indicate that frictional healing, the difference between peak friction reached upon re-shear and the steady-state friction before the hold, increases with increasing logarithm of hold time in all experiments, as suggested by previous studies. Meanwhile, frictional healing rate (β = Δμ/log(1+ thold/tcutoff)), commonly regarded as the quantification of the rate of healing, increases with increasing temperature for both fresh and altered basalt. For fresh basalt, β increases from 0.007 at Tf = 100 ˚C to 0.060 at Tf = 300 ˚C (liquid) before dropping to 0.036 at Tf = 400 ˚C (vapor) and eventually increases to 0.096 at Tf = 400 ˚C (supercritical). For altered basalt, β  increases continuously from 0.003-0.007 at Tf = 100 ˚C to 0.013-0.022 at Tf = 300 ˚C and reaches its maximum value of β = 0.024-0.035 at Tf = 400 ˚C (vapor) and β = 0.030 at Tf = 400 ˚C (supercritical). Besides this temperature-dependent relationship, the dramatic decrease of β in fresh basalt to values similar to those of altered basalt when water changed from liquid to vapor state also suggests that the physical state of water can control the healing rate. Subsequent microanalytical analyses (XRPD, XRF, SEM-EDS) performed on the deformed gouges from altered basalts suggest an increase in hydrothermal alteration with increasing temperature, as shown by a depletion in K2O at Tf ≥ 300 ˚C. SEM-BSE images of fine platy matrices in shear bands formed at Tf = 400 ˚C point towards a dissolution of quartz, pyroxene and plagioclase. Therefore, we suggest that the healing rate of both fresh and altered basalt not only scales with the ambient temperature but is also affected by the physical state of water, particularly in the case of fresh basalt, potentially related to more intense fluid-rock interactions with increasing temperature.

Keywords: frictional healing, frictional healing rate, hydrothermal fluids, basaltic gouge, Krafla geothermal field

How to cite: Wu, W.-H., Feng, W., Gomila, R., Tesei, T., Violay, M., Mortensen, A. K., and Di Toro, G.: Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9165, https://doi.org/10.5194/egusphere-egu24-9165, 2024.

EGU24-9541 | Posters on site | EMRP1.6

Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures 

Marco Scuderi, Nathalie casas, Giuseppe Volpe, and Cristiano Collettini

Mineralogy, fabric, and frictional properties are fundamental aspects of natural and experimental faults that concur in controlling the fault strength and the fault slip behavior. Mineralogy controls the fabric evolution influencing the micro-mechanisms at play during fault deformation and needs an in-depth investigation to better understand and foresee the frictional response of experimental faults. Classically, this investigation has been conducted by relating the fault frictional behavior to the post-experimental microstructures. However, this “classical” approach provides a direct but static view of the fault deformation where the evolution of fabric with deformation can be only speculated.

To investigate in “real-time” the deformation micro-mechanisms at play during the experiments, the recording and analyses of Acoustic Emissions (AEs) produced by the deforming fault gouge can provide new insights.

In this study, we present a systematic study of microstructural, mineralogical, frictional, and AEs analysis coming from a suite of frictional experiments in a double direct shear configuration (biaxial apparatus, BRAVA2). We conducted experiments on gouges made of bi-disperse and layered mixtures of quartz and phyllosilicate. These experiments were performed at a constant normal stress of 52MPa and under 100% humidity. The friction evolves with the phyllosilicate content from µ ~ 0.6 for 100% quartz to µ ~ 0.4 for 100% phyllosilicates. At the end of the experiments samples were carefully collected and prepared for microstructural analysis. The fabric of the experimental samples show an evolution from localized to distributed and foliated fabric with increasing amount of phyllosilicate content.

We then integrate specific features of AEs, such as amplitude and AE rate, to unveil the micro-mechanisms at play during the experimental fault deformation. Our results show that the overall AE behavior is controlled by mineralogy. Deformation of quartz gouge produces the largest number of AEs whereas phyllosilicates are almost not producing AEs. Furthermore, the AE behavior of bi-disperse mixtures of quartz and phyllosilicates is strongly controlled by the amount of phyllosilicates. In fact, increasing the amount of phyllosilicate, the number, the rate, and the amplitude of AEs decrease. This behavior could be explained by the lubricant role of phyllosilicates which hinder the interaction between quartz grains favoring foliation sliding as main deformation mechanism and thus reducing the frictional strength. These results suggest that for bi-disperse mixtures the AEs reflect the frictional behavior of the mixture. Layered quartz-phyllosilicates mixtures show instead a non-trivial acoustic emission behavior which cannot be directly related to the measured frictional strength of the layered mixture: friction is controlled by the frictionally weaker mineral phase, whereas the AEs are probably dependent by the interplay between the stronger and weaker phase of the layered mixture.

Our results show that fault fabric together with mineralogy strongly control the micro-mechanisms at play during deformation and therefore the frictional response. Our findings support the use of the AE analysis as a new tool for the investigation of the micro-mechanisms at play during deformation, improving our interpretation of the mechanical behavior of fault gouges.

How to cite: Scuderi, M., casas, N., Volpe, G., and Collettini, C.: Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9541, https://doi.org/10.5194/egusphere-egu24-9541, 2024.

EGU24-9941 | ECS | Posters on site | EMRP1.6

Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge 

Michele De Solda, Michele Mauro, Federico Pignalberi, and Marco Scuderi

In the last decades, rock mechanics laboratory experiments have allowed framing earthquake physics as a frictional problem. When the accumulated stress on a fault exceeds the frictional forces holding it in place, a rapid acceleration occurs. This movement can be stable or unstable, involving phases of adhesion (stick) and rapid sliding (slip). In these terms, an earthquake results from the release of mechanical energy during one of these slip phases.

 

Modern friction theories propose that the frictional forces holding the fault in place are controlled by small asperities defining the real contact area (RCA). Therefore, understanding the mechanics of contacts on the fault and their evolution under stress and velocity changes can shed light on the microphysical processes underlying earthquakes.

 

In the laboratory, it is now possible to investigate the dynamics of experimental faults, predicting their instability behavior based on Rate and State Friction theory and its experimentally obtainable parameters (a-b, Dc). However, these parameters lack an explicit relationship with contact mechanics, necessitating additional measurements complementing the system's state information. One of the most widely used techniques for studying RCA during laboratory experiments involves investigating changes in acoustic transmissivity (velocity, amplitude) of generated and recorded ultrasonic waveforms (UW) passing through the sample during the deformation. At a given wavelength, analytical expressions for these quantities depend on the elastic properties and densities of the fault portion crossed by the wave. Simultaneous knowledge of stress conditions and elastic properties allows the formulation of constitutive laws for the evolution of contacts between fault asperities.

 

In double direct shear experiments (DDS) within biaxial apparatuses, the sample dimensions (gouge) impose stringent limits on the spatial and temporal resolution of the signal. These limits highlight the current sensor technology's deviation from the ideal behavior.

 

Here, we present a methodology and a waveform recording and synchronization protocol

implemented on the biaxial apparatus BRAVA2 in the Rock Mechanics and Earthquake Physics laboratory at Sapienza University of Rome. We focus on the types of sensors used and their specifications to provide accurate measurements of the deformation processes occurring within the gouge layers.

 

Several studies have conducted DDS experiments using UW, but they rarely take into account the characterization of the impulse signal, various reflections in the sample assembly, and conversion modes of the generated waveforms. These are all essential components to identify the interaction of the experimental system with the propagation of the ultrasonic waves, to exploit the received signal in its entirety.

We believe that a careful signal characterization is necessary to fully understand the physical processes during deformation within the sample and, consequently, to attempt upscaling to natural earthquakes.

How to cite: De Solda, M., Mauro, M., Pignalberi, F., and Scuderi, M.: Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9941, https://doi.org/10.5194/egusphere-egu24-9941, 2024.

EGU24-10564 | Posters on site | EMRP1.6

An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions 

Yu-Han Wang and Elías Rafn Heimisson

The interactions between fluids and fault structures play a pivotal role in understanding fault slip behavior. Over the years, various numerical methods have been developed to simulate these interactions. Volume-based methods, like the finite difference method (FDM), excel in their capacity to handle the intricacies of real-world fault structures, including material heterogeneity. On the other hand, the spectral boundary integral method (SBIM) is renowned for its computational efficiency. Recently, a hybrid approach has garnered significant attention, offering the benefits of both volume-based and SBI methods. This hybrid method allows for the consideration of fault structures' heterogeneity while maintaining computational efficiency. In this study, we introduce a novel hybrid method that bridges the SBIM and the FDM to model fluid migration in fault structures. Through rigorous model verification, we establish that our hybrid method can achieve a remarkable speedup of up to one thousand times compared to the FDM. Furthermore, we conducted two parametric studies to address open questions in fluid migration modeling within fault structures. First, we investigate the mobility contrast ratio between the host rock and the damage zone to determine the limits under which we can assume a zero-leak-off interface. Second, we explore the role of fault zone width in maintaining the validity of this zero-leak-off assumption. Building upon these foundational investigations, we demonstrate the possibility of extending the numerical framework to describe fault-fluid interactions considering poroelastic coupling.

How to cite: Wang, Y.-H. and Rafn Heimisson, E.: An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10564, https://doi.org/10.5194/egusphere-egu24-10564, 2024.

The slip behavior of crustal faults is known to be controlled by the mineralogic composition of the fault gouge. The exact properties determining the frictional behavior of geologic materials, including diverse remains an important question. Here, we use a geochemical approach considering the role of water-rock interactions. As a mechanism, we suspect that the mineral surface charge allows attractive and repulsive forces (Van Der Waals type), and that those forces may influence the static mechanical behavior of clays (cohesion, static friction).  On the other hand, we suspect that the water bound to the mineral surfaces may play a role during shearing.  To address these ideas, we measured the cation exchange capacity (CEC) of 10 different rock and mineral types, including non-clays and a range of phyllosilicate minerals, using CEC as a proxy for the mineral surface charge and the ability to bind water to the mineral surfaces.  For these materials, we conducted laboratory shearing experiments measuring the pre-shear cohesion, peak friction coefficient, residual friction coefficient, post-shear cohesion, and velocity-dependent friction parameters under 10 MPa effective normal stress.  
Our results show that low CEC materials (< 3 mEq/100g) tend to exhibit high friction, low cohesion, and show velocity-weakening frictional behavior. The phyllosilicate minerals exhibit larger CEC values up to 78 mEq/100g and correspondingly lower friction coefficients, higher cohesion, and velocity-strengthening frictional behavior. Zeolite exhibits a relatively high CEC value typical of phyllosilicates, but its strength and frictional characteristics are that of a non-clay with low CEC. This suggests that grain shape and contact asperity size may be more important for non-phyllosilicates. For phyllosilicates, we suggest that the systematic patterns in strength and frictional behavior as a function of CEC could be explained by water bound to the mineral surfaces, creating bridges of hydrogen or van der Waals bonds when the particles are in contact. Such bonding explains the large cohesion values for high-CEC materials under zero effective stress, whereas surface-bound water trapped between the particles under load explains low friction.  Beyond the results of this study, CEC appears to be a controlling factor for other properties such as permeability and even the amount of bound DNA in sediments.

 

How to cite: Ikari, M. and Conin, M.: Cation Exchange Capacity Quantifies the Link Between Mineral Surface Chemistry and Frictional-Mechanical Behavior of Simulated Fault Gouges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10969, https://doi.org/10.5194/egusphere-egu24-10969, 2024.

During natural and induced seismic activities, pore fluid pressure within fault zones and their surrounding rock may respond differently to stress variations, introducing additional complexities to seismic hazard assessment. While theoretical investigations have recognized the influence of such poroelastic heterogeneity on fault instability, incorporating phenomena like slip-induced dilation or compaction, the chosen poroelastic properties in these studies lack robust constraints from experimental measurements. Addressing this gap, our study focuses on quantifying the heterogeneity of poroelastic properties in the presence of a fresh fault, aiming to elucidate the coupling between poroelasticy and fault dilatancy during fault slip.

In our experimental investigation, we examined the evolving dynamics of pore pressure both on- and off-fault in initially intact Westerly granite samples. Applying confining stress of 100 MPa and a pore pressure of 60 MPa at two sample ends to replicate crustal settings, we induced a sliding fault plane through loading to failure under a constant strain rate. In the faulted samples, we measured the pore pressure response under sudden step loading in the direction of the maximum compression σ1. Each loading step of around 5 MPa was imposed incrementally increasing the differential stress from 5 MPa to approximately 80 MPa (frictional resistance) after achieving pore pressure equilibrium. Detailed measurements, including displacement, bulk deformation, differential stress, local pore pressure and acoustic emissions were recorded throughout these tests. A spring-slider model coupled with 1-D fluid diffusion was used to try to simulate experimental observations.

Our results indicate that both the shear zone and the bulk exhibit a diminishing Δp/Δσ1 with increasing differential stress. Measurements within the fault zone consistently yield positive values, surpassing those off the fault, with the discrepancy more pronounced at lower stress levels. In regions farther away from the shear zone, the off-fault response Δp/Δσ1 presents a smaller value compared to locations proximal to the fault zone and may even exhibit slight negativity. During fault slip, on-fault measurements exhibit an instantaneous increase upon step loading followed by a gradual decrease, as a result of the interplay between poroelasticity and fault dilatancy. These observations were effectively reproduced by the numerical model integrating the poroelastic measurements and rate-and-state fault friction with slip-dependent dilatancy. The implications of this investigation extend to an enriched understanding of the heterogeneity in poroelastic responses between fault zones and host rocks, serving as valuable benchmarks for informing future numerical simulations, particularly in the context of naturally formed fresh faults. 

How to cite: Liu, D. and Brantut, N.: Poroelastic heterogeneity in the presence of a fresh fault: experimental insights and numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10998, https://doi.org/10.5194/egusphere-egu24-10998, 2024.

EGU24-11200 | Orals | EMRP1.6

Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front 

Francois Passelegue, Pierre Dublanchet, Nicolas Brantut, and Hervé Chauris

A growing amount of evidence indicate that aseismic transients driven by overpressure play an important role in the triggering of induced seismicity. Understanding the physical control on aseismic slip development is thus important for seismic hazard assessment. We conducted an investigation into the propagation dynamics of a fluid-driven slip front along a laboratory frictional interface composed of granite. The experiments were carried out under a confining pressure of 90 MPa, with an initial uniform fluid pressure of 10 MPa. Fault reactivation was initiated by injecting fluids through a borehole directly connected to the fault.

Our findings reveal that the peak fluid pressure at the borehole leading to reactivation exhibits an increase proportionate to the injection rate. Employing three fluid pressure sensors and eight strain gauges strategically positioned around the experimental faults, we performed an inversion analysis to image the spatial and temporal evolution of (i) hydraulic diffusivity and (ii) kinematic fault slip during each injection experiment. Our inversion methods integrated both deterministic and Bayesian procedures, facilitating the tracking of the fluid pressure front along the fault interface and the subsequent propagation of the slip front over time.

The migration pattern shares many similarities with natural slow slip events suspected to play a role in the development of natural and induced earthquake swarms or aftershock sequences.  We demonstrate that increasing the fluid injection rate induces a transition from a quasistatic propagation of the slip front correlated with the increase in fluid pressure to a dynamic scenario where the slip front outgrows the fluid pressure front, accelerating during its propagation. Furthermore, we establish that temporarily shutting off fluid pressure during injection induces the propagation of a pore-pressure back-front, which halts the propagation of the slip front, aligning with theoretical expectations.

How to cite: Passelegue, F., Dublanchet, P., Brantut, N., and Chauris, H.: Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11200, https://doi.org/10.5194/egusphere-egu24-11200, 2024.

EGU24-11407 | ECS | Posters on site | EMRP1.6

Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear 

Sofia Michail, Paul Antony Selvadurai, Markus Rast, Antonio Felipe Salazar Vásquez, Patrick Bianchi, Claudio Madonna, and Stefan Wiemer

Faults in nature exhibit complex surface characteristics with patches of the fault (asperities) that may slip dynamically while other sections are more prone to creep (Beeler et al., 2011). Asperities forming in nature may be due to the geometric interactions between surfaces within a fault that contribute to complex stress states that are not well understood. Fault roughness is believed to play an important role in the control of the contact conditions established by asperities, directly affecting its potential to slip unstably. How the asperities are formed and how their seismogenic properties evolve due to wear is an important question with implications to slip budget and earthquake potential.

In this study, we performed a triaxial experiment at sequentially increasing confining pressures (Pc = 60, 80, 100 MPa) on a saw-cut sample of Carrara marble. We analysed the quasi-static frictional response that benefited from novel arrays of distributed strain sensors (DSS) obtained using fiber optics. This sensor offered unique insight into the axial strain with a spatial resolution of 2 mm. The frictional behaviour during the first confining pressure step exhibited a dynamic instability in the form of a stick-slip event (SS) that produced a measurable stress drop. In the subsequent confining pressure stages, where an increase in confining pressure translated to increased normal stress, the fault behaved in a stable manner and no dynamic instabilities were produced. This observation is inconsistent with frictional stability theory (e.g. Rubin and Ampuero, 2005) and required pre- and post-mortem campaigns into the surface characteristics and their evolution to explain this abnormal behaviour. Therefore, we employed experimental techniques (pressure sensitive film (PSF), optical and stylus profilometry) along with finite element (FE) model in ABAQUS to characterize the pressure and roughness.

The DSS array showed extensional axial strain closer to the edges of the fault, while only compression was expected in this triaxial loading test. The pre-experimental profilometry revealed an asperity located at the centre of the fault with a curvature ratio of h/L=0.1% inherited from the hand-lapping preparation, which dominated the initial contact conditions prior to the SS and explained the DSS observations. The DSS results were confirmed using a FE model which justified the effect of the fault geometry (h/L) on the strain response. After the SS, wear and smoothening of the central asperity was seen in roughness measurements. The profilometric measurements showed that gouge was deposed adjacent to the high normal stress asperity center (PSF) and were characterized by increased RMS roughness. These small amounts of gouge on the fault surface were sufficient to suppress the seismic response of the asperity. These findings show that the seismic potential of a carbonate (softer) asperity, may be highly influenced by the debris produced during wear. Its impact on earthquake nucleation could provide insight into large-scale earthquake preparation processes on carbonate faults in nature.

 

References:

  • Beeler, M., Lockner, D. L. and Hickman, S. H. (2001), Bull. Seis. Soc. Am., 91 (6): 1797–1804
  • Ampuero, J.-P. and Rubin, A. M. (2008), J. Geophys. Res., 113, B01302

How to cite: Michail, S., Selvadurai, P. A., Rast, M., Salazar Vásquez, A. F., Bianchi, P., Madonna, C., and Wiemer, S.: Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11407, https://doi.org/10.5194/egusphere-egu24-11407, 2024.

EGU24-11536 | Orals | EMRP1.6 | Highlight

Fault activation from up close 

Men-Andrin Meier, Domenico Giardini, Stefan Wiemer, Massimo Cocco, Florian Amann, Elena Spagnuolo, Paul Selvadurai, Elisa Tinti, Luca Dal Zilio, Alba Zappone, Giacomo Pozzi, Mohammadreza Jalali, and Valentin Gischig and the FEAR science team

Our understanding of earthquake rupture processes is generally limited by the resolution of available observations. In all but exceptional cases, earthquake observations are made at comparatively large distances from the rupture itself, which puts a limit on what spatial scales can be resolved. At the same time, it is clear that small scale processes may play a crucial, if not dominant, role for various seismogenic processes, including rupture nucleation, co-seismic weakening and stress re-distribution.

The Fault Activation and Earthquake Rupture ('FEAR') project aims at collecting and interpreting a multitude of earthquake-relevant observations from directly on and around the process zone of an induced earthquake. To this end, we attempt to activate a natural granitic fault zone in the BedrettoLab, at a depth of ~1km, after instrumenting the fault zone with a multi-domain and multi-scale monitoring system. The goal is to observe and study earthquake rupture phenomena in a natural setting, from unusually close distance.

In this talk, we outline the project status, the science goals, and the plans for the main experiments, which are scheduled for the years 2024 - 2026. Notable milestones we report on include

  • the identification and detailed characterisation of the target fault zone
  • the beginning of niche and tunnel excavations
  • laboratory experiments that characterise the frictional and mechanical behaviour of both gauge material and host rock of the target fault zone
  • development of numerical models for 2D and 3D dynamic rupture propagation
  • development of tailored monitoring methods for seismicity, strain, temperature, pressure, bio-geo-chemistry and other relevant observables
  • development of remote experiment control methods
  • test stimulations in a nearby rock volume of similar geology, with an already existing monitoring system, where we tested the influence of pre-conditioning injection protocols
  • similar test stimulations in the same volume where we aim at triggering a larger event (target Mw~0)
  • active seismic experiments in an underground salt mine, to calibrate the very- to ultra-high frequency (1k Hz - 500k Hz) acoustic emission sensors

Together, these and other efforts constitute the necessary ingredients we need for interpreting the near-source observations that we will collect during the fault activation experiments.

How to cite: Meier, M.-A., Giardini, D., Wiemer, S., Cocco, M., Amann, F., Spagnuolo, E., Selvadurai, P., Tinti, E., Dal Zilio, L., Zappone, A., Pozzi, G., Jalali, M., and Gischig, V. and the FEAR science team: Fault activation from up close, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11536, https://doi.org/10.5194/egusphere-egu24-11536, 2024.

EGU24-12986 | ECS | Posters on site | EMRP1.6

Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations 

Elvira Latypova, Fabio Corbi, Giacomo Mastella, Jonathan Bedford, and Francesca Funiciello

The short seismic record with respect to the return time of large subduction earthquakes and the spatial fragmentation of available geophysical data represent unfavourable conditions for robust hazard assessment. Over the last decade, data from scaled seismotectonic models have become useful in filling the observational gaps of seismic and geodetic networks. Such models allow reproducing hundreds of analogue seismic cycles in a few minutes of experimental time and with the advantage of known and controllable boundary conditions. 

Here we present experimental results from Foamquake – an established 3D seismotectonic model, which simulates megathrust subduction. Recent technical advances in experimental monitoring have allowed us to include into our research a high-frequency camera to record model surface deformation at 50 Hz and a network of 5 accelerometers (located on the model surface) that measure the three components of acceleration at 1 kHz. To analyse the camera data, we used particle image velocimetry (PIV) to derive surface displacements, such as in a dense, homogeneously distributed geodetic network spanning updip to scaled depths that are often offshore and, therefore, typically under-monitored in natural subduction zones.

We performed 33 experiments exploring 10 different geometrical configurations of asperities along the analog megathrust. In particular, we varied the number of asperities, their size, location, and extra normal load. We observed that the rupture pattern of analogue earthquakes predictably changes as the extra normal load varies and the distribution of asperity configurations becomes more complex. Depending on the number and size of the asperities and the size of the barrier between them, we noticed different ratios between full and partial ruptures with different recurrence time (Rt) intervals. In some experiments we detected cascades of ruptures. We used the coefficient of variation (CoV) of recurrence time to quantify analog earthquakes periodicity. Most of our models display quasi-periodic analog earthquakes recurrence with CoV<0.5, but multi-asperity experiments with variable-size and extra normal load lean toward random behaviour as testified by CoV~0.8.

Future investigations include the following steps – exploring this great volume of data using machine learning, looking for spatial and temporal relationships between accelerometer and PIV displacements, and tracking in detail the aseismic processes that may precede and follow earthquake rupture.

How to cite: Latypova, E., Corbi, F., Mastella, G., Bedford, J., and Funiciello, F.: Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12986, https://doi.org/10.5194/egusphere-egu24-12986, 2024.

EGU24-13117 | ECS | Posters on site | EMRP1.6

A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach 

Ludovico Manna, Giovanni Toscani, Matteo Maino, Leonardo Casini, and Marcin Dabrowski

The 2D, plane strain, Finite Element Method-based linear elastic model that I present aims to assess the differential stress response to variations in the geometric configuration of a system of multiple collinear elliptic cracks intercepting a body of rock undergoing elastic deformation. The assumption underlying this simulation is that a collection of thin voids in a continuum medium can replicate the features observed in a system consisting of rough fault profiles in partial contact subjected to shear. The linear elastic model is designed to reproduce the stress and displacement fields around a rough fault, with a specific focus on stress concentration around its contact asperities. The model also allows to record the principal stress field on the domain for a wide range of scales and geometric properties of the system of collinear cracks embedded in the deforming rock. Analyzing the dependence of differential stress on parameters describing the geometry of rough fractures allows for considerations on the primary factors influencing brittle failure. Additionally, the examination of principal stresses around the tips of the cracks helps evaluate the potential orientation of new fracture patterns that may emerge when the yield strength of the deforming material is locally exceeded. The magnitude and orientation of the principal stresses are also crucial for the understanding of fracture coalescence and frictional reactivation of shear cracks in an elastic rock, which in turn is one of the main factors that govern the seismic cycle of natural faults. Furthermore, a comparison of the results of the present model with recent wing crack models of brittle creep suggest that our code may also be useful to obtain estimates of the critical distance between cracks for their interaction to coalesce into larger fractures. The process is assumed to indefinitely continue at greater scales, which offers the chance to propose a model for fault formation and propagation.

How to cite: Manna, L., Toscani, G., Maino, M., Casini, L., and Dabrowski, M.: A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13117, https://doi.org/10.5194/egusphere-egu24-13117, 2024.

EGU24-13433 | Orals | EMRP1.6

The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading 

Michele Fondriest, Fabio Arzilli, Benoit Cordonnier, Michael Carroll, and Mai-Linh Doan

The propagation of earthquake fault ruptures in the crust involve the generation of unloading stress pulses sufficiently large to induce dynamic failure of water-saturated rocks under tensional stresses and hydrofracturing. Similar processes are also activated during underground rock mass excavation activities in mines and tunnels. The current knowledge about rock fracturing via dynamic unloading is mainly limited to empirical records and numerical simulations, while there is a general paucity of experimental studies, due to difficulties in reproducing large instantaneous decompressions on rock samples using standard triaxial rigs. Until now rapid decompression and fracturing of large rock samples in dry conditions was reported only by using an unconventional gas-confined vessel.

Here, we report rock-fracture results for newly conceived rock decompression experiments, completed through the innovative use of a “cold-seal pressure vessel” (CSPV) apparatus which is routinely employed in experimental petrology. We applied instantaneous large decompressions on water-saturated rock samples equilibrated at high confinement (up to 200 MPa) and temperatures (up to 540°C). The tested rock samples were fine-grained Westerly granite, coarse-grained tonalite and micritic limestone. During the decompressions the rock samples hydrofractured due to the confinement dropping faster than the pore pressure within the rock. Porosity measurements, SEM imaging and X-ray µCT acquired before and after the tests suggest that the magnitude of dynamic fracturing not only positively correlates with the pressure drops but it mostly increases when the decompression is associated to a phase change of the pore water (e.g. supercritical fluid to subcritical gas) . Water vaporization or degassing imply an instantaneous volume expansion (up to 70 times) which critically enhances dynamic fracture propagation along rock grain boundaries. The induced fractures span from mm-long transgranular cracks to microcracks with submicrometric aperture. Therefore, synchrotron light high-resolution microtomography (final pixel resolution of 0.3 µm) was employed to fully resolve and quantify the 3D fracture networks of these deformed rock samples. Such unique dataset allowed us to determine at different scales the fracture intensity, aperture and connectivity of the dynamically induced fracture networks and to assess the key contribution of pore-water physical state changes on the initial stages of dynamic fracturing in rocks at crustal conditions. Such results will contribute to close a current knowledge gap in rock mechanics.

How to cite: Fondriest, M., Arzilli, F., Cordonnier, B., Carroll, M., and Doan, M.-L.: The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13433, https://doi.org/10.5194/egusphere-egu24-13433, 2024.

Establishing a constitutive law for fault friction is a crucial objective of earthquake science. However, the complex frictional behavior of natural and synthetic gouges in laboratory experiments eludes explanations. Here, we present a constitutive framework that elucidates the slip-rate, state, temperature, and normal stress dependence of fault friction under the relevant sliding velocities and temperatures of the brittle lithosphere during seismic cycles. The competition between healing mechanisms explains the low-temperature stability transition from steady-state velocity-strengthening to velocity-weakening as a function of slip-rate and temperature. In addition, capturing the transition from cataclastic flow to semi-brittle creep accounts for the stabilization of fault slip at elevated temperatures. The brittle behavior is controlled by the real area of contact, which is a nonlinear function of normal stress, leading to an instantaneous decrease of the effective friction coefficient upon positive normal stress steps. The rate of healing also depends on normal stress, associated with an evolutionary response. If these two effects do not compensate exactly, steady-state friction follows a nonlinear dependence on normal stress. We calibrate the model using extensive laboratory data covering various relevant tectonic settings. The constitutive model consistently explains the evolving frictional response of fault gouge from room temperature to 600º for sliding velocities ranging from nanometers to millimeters per second, and normal stress from atmospheric pressure to gigapascals. The frictional response of faults can be uniquely determined by the in situ lithology and the prevailing hydrothermal conditions.

How to cite: Barbot, S.: Constitutive behavior of rocks during the seismic cycle in non-isothermal, non-isobaric conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14003, https://doi.org/10.5194/egusphere-egu24-14003, 2024.

EGU24-14504 | Posters on site | EMRP1.6

The role of poroelasticity in rupture dynamics across fault stepovers 

Luyuan Huang, Luca Dal Zilio, and Elías Rafn Heimisson

Understanding earthquake rupture propagation across fault stepovers is pivotal for assessing the seismic hazard, offering vital insights into dynamic rupture processes within intricate fault geometries. However, the role of poroelastic effects within strike-slip fault systems featuring stepovers remains unexplored in dynamic models simulating Sequences of Earthquakes and Aseismic Slip (SEAS). Many existing models neglect poroelastic effects, and among those that consider them, a typical standard value of 0.8 is adopted for Skempton's coefficient B. Furthermore, a single dynamic rupture simulation is unable to address the frequency at which ruptures propagate through the stepover. Instead, these simulations only provide a binary status, indicating whether the ruptures jump or arrest. Thus, the investigation into how poroelasticity influences the likelihood of an earthquake jumping through a stepover emerges as a significant area of study. In response, we introduce a quasi-dynamic boundary element model that simulates 2D plane-strain earthquake sequences. This model incorporates undrained pore pressure responses affecting the fault's clamping and unclamping mechanisms and is governed by rate-and-state friction, with state evolution defined by the aging law. We first illustrate that dynamic rupture occurring in either left-lateral or right-lateral fault stepovers leads to a dynamic decrease (unclamping) or increase (clamping) in the effective normal stress. Dynamic variations of the effective normal stress depend on Skempton's coefficient. Consequently, higher Skempton's coefficients can promote rupture jumping across fault segments even for larger stepover distances. We then conduct a thorough parameter space study, evaluating the effects of Skempton's coefficient variations and stepover width on fault interactions within a fluid-filled porous environment. The likelihood of rupture jumping involves a trade-off between Skempton's coefficient and stepover width. We validate the numerical model by comparing it to an analytical solution that involves a plane strain shear dislocation on a leaky plane within a linear poroelastic, fluid-saturated solid. This validation demonstrates that a simple analytical solution, primarily dependent on fault dislocation and Skempton's coefficient, has the potential to effectively predict the pore pressure change. The critical jumping width for 50% chance of rupture jumping predicted by our model explains the threshold dimension of the fault step, above which ruptures do not propagate. This study highlights the significance of incorporating poroelastic effects on- and off-fault in understanding the dynamic variations of the effective normal stress, which could significantly alter the overall length of fault rupture.

How to cite: Huang, L., Dal Zilio, L., and Rafn Heimisson, E.: The role of poroelasticity in rupture dynamics across fault stepovers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14504, https://doi.org/10.5194/egusphere-egu24-14504, 2024.

EGU24-14566 | Posters on site | EMRP1.6

Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions 

Weifeng Qin, Lu Yao, Tongbin Shao, Wei Feng, Jianye Chen, and Shengli Ma

The frictional properties of faults are primarily controlled by their mineral composition, as well as ambient and deformation conditions, such as temperature, pore fluid, normal stress, and slip displacement. While many studies have been conducted to decipher how temperature and pore fluid may affect the frictional behavior of faults, less attention has been paid to the slip displacement effects, especially under hydrothermal conditions. By employing a rotary shear apparatus equipped with an externally-heated hydrothermal pressure vessel, we conducted large-displacement (up to 521 mm) friction experiments on chlorite under temperature (T) of 25 to 400℃ and pore water pressure (Pp) of 30MPa. The imposed effective normal stresses were 200 MPa and the slip rates ranged from 0.4 to 10 μm/s. The experiments unveiled significant slip strengthening in chlorite within the temperature range of 25 to 400 °C. Moreover, with increasing temperatures, there was an overall increasing trend in both the rate of slip strengthening and the ultimate frictional strength. For example, under T = 25 °C, the friction coefficients at displacements of 5, 90, and 521 mm were 0.33, 0.49, and 0.59, respectively, in contrast to 0.46, 0.79, and 0.88, respectively, at the same three displacements under T =400 °C. Under all the temperature and displacement conditions, chlorite exhibited velocity strengthening behavior without discernible temperature dependence, although the velocity-dependence parameter (a-b) increased with slip displacement. Microstructural analysis revealed that, the entire layer of the chlorite gouge experienced pervasive and intense shear deformation after slip of 521 mm, with extremely remarkable grain-size reduction. The thermogravimetrical and FTIR data of the deformed chlorite samples, together with the microstructural data, suggest that the dehydroxylation and the distortion of crystal structure of chlorite might occur during the friction experiments conducted at T ≥ 200 °C. Such changes may explain the more pronounced slip strengthening of chlorite with increasing temperatures towards 400 °C. This explanation can be further demonstrated by a comparative experiment conducted under varying temperatures (400°C for the first 100 mm of slip, followed by 25°C for the rest of 100 mm slip), wherein the friction coefficient at T = 25°C during the latter stage of slip remains as high as that at T = 400°C. These findings highlight the importance of slip displacement in controlling the frictional strength and its variations of chlorite-bearing faults at depths, and have profound implications for understanding the fault slip behaviors and earthquake mechanisms in subduction zones.

How to cite: Qin, W., Yao, L., Shao, T., Feng, W., Chen, J., and Ma, S.: Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14566, https://doi.org/10.5194/egusphere-egu24-14566, 2024.

EGU24-15205 | ECS | Posters on site | EMRP1.6

Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults 

Federica Paglialunga, Francois Passelegue, and Marie Violay

Many aspects of earthquake physics are still not completely understood given its intrinsically complex nature. Among the others, the nucleation process; when and where an earthquake will occur, as well as its magnitude. Seismology is a commonly used method for studying earthquakes, but it faces challenges in accessing precise information about the physical processes taking place on the fault plane.

Here, we show how laboratory seismology can directly shed light on fault plane dynamics. Our approach involves reproducing in the laboratory on a large biaxial apparatus with a fault length of 2.5 m generated by two analog (PMMA) samples brought into contact. The experimental setup allows to impose both a heterogeneous loading distribution through the use of independent pistons loading the fault in the normal direction and specific boundary conditions (i.e. by modifying stopper and puncher dimensions). The stress state is measured through strain gauges at high frequency (40 KHz) along 15 locations along the fault. The experiments provide insights into two crucial aspects of laboratory earthquakes: (i) the nucleation location of ruptures and (ii) the complexity of the seismic cycle.

Our findings reveal that the initial on-fault stress distribution plays a significant role in both aspects. We observe that ruptures consistently nucleate in locations where the stress ratio τ/σn is the highest. Notably, such values change among experiments, challenging the widespread notion that a friction coefficient solely governs the onset of instability. Furthermore, we demonstrate how the heterogeneity of the initial prestress distribution along the fault controls the complexity of the seismic cycle. In certain cases, the seismic cycle manifests as system-size events with complete ruptures occurring regularly in time, devoid of precursors. Conversely, other initial stress distributions generate more complex cycles, characterized by multiple precursors before a main rupture, predominantly occurring in zones of elevated τ/σn (referred to as 'friction asperity'). The complexity of the seismic cycle can be described in terms of the number of precursory events, inter-event time, and the size of finite ruptures.

This study, carried out in a long laboratory fault, highlights the complexities that emerge when heterogeneous, hence more realistic, stress conditions are applied, providing valuable insights into the physics of natural earthquakes.

How to cite: Paglialunga, F., Passelegue, F., and Violay, M.: Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15205, https://doi.org/10.5194/egusphere-egu24-15205, 2024.

EGU24-15273 | ECS | Orals | EMRP1.6

Impact of multiscale heterogeneities on the nucleation of earthquakes 

Mathias Lebihain, Thibault Roch, Marie Violay, and Jean-François Molinari

Earthquake nucleation is traditionally described using cascading or slow pre-slip models. In the latter, nucleation occurs as the sudden transition from quasi-static slip growth to dynamic rupture propagation. This typically occurs when a region of the fault of critical size Lc, often called nucleation length, is sliding. This transition is relatively well-understood in the context of homogeneous faults. Yet, faults exhibit multiple scales of heterogeneities that may emerge from local changes in lithologies or from its self-affine roughness. How these multiscale heterogeneities impact the overall fault stability is still an open question.

Combining the nucleation theory of [Uenishi and Rice, JGR, 2003] and concepts borrowed from statistical physics, we propose a theoretical framework to predict the influence of brittle/ductile asperities on the nucleation length Lc for simple linear slip-dependent friction laws. Model predictions are benchmarked on two-dimensional dynamic simulations of rupture nucleation along planar heterogeneous faults. Our results show that the interplay between frictional properties and the asperity size gives birth to three (in)stability regimes: (i) a local regime, where fault stability is controlled by the local frictional properties, (ii) an extremal regime, where it is governed by the most brittle asperities, and (iii) a homogenized regime, in which the fault behaves at the macroscale as if it was homogeneous and the influence of small-scale asperities can be averaged.  

Using this model, we explore the overall stability of rough faults, featuring multiscale distributions of frictional properties. We also investigate the stability of velocity-neutral faults that features brittle asperities. Overall, our model provides a theoretical basis to discriminate which heterogeneity scales should be explicitly described in a comprehensive modelling of earthquake nucleation, and which scales can be averaged.

How to cite: Lebihain, M., Roch, T., Violay, M., and Molinari, J.-F.: Impact of multiscale heterogeneities on the nucleation of earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15273, https://doi.org/10.5194/egusphere-egu24-15273, 2024.

EGU24-18100 | ECS | Posters on site | EMRP1.6

Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods 

Nico Bigaroni, Julian Mecklenburgh, and Ernest Rutter

During interseismic periods a fault at depth can experience non-constant effective normal stress due to fluctuations in the pore-fluid pressure. Pore-pressure oscillations may influence the healing capability of the fault and ultimately affect its reactivation. Thus, studying the behaviour of faults during interseismic periods is a critical factor in understanding the seismicity. Triaxial tests were conducted using saw-cut (45o) samples of Pennant Sandstone to investigate the influence of pore-pressure oscillations during slide-hold-slide (SHS) tests (th = 900 – 7300s) on its frictional behaviour and fault reactivation. The cylindrical samples were hydrostatically compacted at 30 MPa and pore-pressurized with argon gas at 5, 10 and 18 MPa resulting in effective normal stress (σ’n) 25, 20 and 12 MPa, respectively. Then the saples were deformed at a constant shear displacement rate ≈ 4.5 μm/s. To overcome the displacement hardening tendency of the sample geometry, we servo-controlled the confining pressure so that the resolved normal stress on the sliding surface is kept constant. Experimental observations revealed a significant influence of pore-pressure oscillation on the frictional behaviour resulting in an increase in both frictional healing and creep relaxation. Moreover, this effect was enhanced as the effective normal stress was increased further. To understand better the underling mechanism(s) that influences these time-dependent processes we coupled the frictional results with permeability measured using the oscillating pore pressure method during the SHS tests. Finally, we tested how the pore-pressure oscillation affected the fault reactivation by conducting creep experiments at constant shear stress while the fault was brought to reactivation via progressive increase in fluid pressure. Our results demonstrated how non-constant effective normal stress history during interseismic periods deeply affects the fault behaviour, with important implications for natural and human-induced seismicity.

How to cite: Bigaroni, N., Mecklenburgh, J., and Rutter, E.: Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18100, https://doi.org/10.5194/egusphere-egu24-18100, 2024.

EGU24-19397 | Orals | EMRP1.6

The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model 

Fabian Barras, Einat Aharonov, and François Renard

Observations suggest that large earthquakes often propagate as self-healing slip pulses but the mechanical reason of this ubiquity remains debated. Pulse-like ruptures differ from the classical crack-like dynamics by the fact that the slipping portion of the fault is limited to the immediate vicinity of the propagating tip. In this work, we first propose a minimal model describing the dynamics of large earthquakes. In its simplest form, the model contains only two free parameters: a dimensionless stress parameter characterizing the initial state of stress along the fault and a ratio of elastic moduli. The model illuminates how self-healing slip pulses can be produced by the paucity of elastic strain energy that arises once the rupture dynamics interplays with the finite geometry of fault zones—even in the absence of additional mechanisms such as rate-dependent friction.

Next, we discuss the example of faults surrounded by a damage zone whose reduction in elastic wave velocity restricts the flow of strain energy to the rupture tip and promotes pulse-like rupture. Using the proposed model, we demonstrate how the contrast in wave velocities and the initial stress level in the fault zone mediate the propagation mode of the earthquake.

How to cite: Barras, F., Aharonov, E., and Renard, F.: The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19397, https://doi.org/10.5194/egusphere-egu24-19397, 2024.

EGU24-408 | Posters on site | GMPV7.2

Tracking Crystal-Melt Segregation and Accumulation in the Intermediate Magma Reservoir 

Jianfeng Ma, Xiaolei Wang, Alexandra Yang Yang, and Taiping Zhao

The genesis of intermediate intrusions is highly controversial, and one of the hot topics is whether they represent frozen melts or cumulates in the evolution of magmatic systems. Distinguishing accumulation from crystallization melt differentiated along the liquid line of descent is the key issue. The Paleoproterozoic intermediate intrusions in southern North China Craton provide an excellent case to decipher this issue. Multiple lines of evidence, including mineral textures, geochemistry as well as alphaMELTS modeling, indicate disequilibrium between whole-rock and minerals, with melt extraction occurring at temperatures of 760°–820°C and with 10–40 wt.% of trapped melts. Effective water storage, revealed by amphibole and clinopyroxene hygrometers, plays a crucial role in promoting crystal-melt segregation in pluton-sized reservoirs in the upper crust. This study demonstrates that the accumulation in intermediate magmas can be identified even without evident complementary initial and extracted melts and provides deep insights into the genesis of intermediate continental crust.

How to cite: Ma, J., Wang, X., Yang, A. Y., and Zhao, T.: Tracking Crystal-Melt Segregation and Accumulation in the Intermediate Magma Reservoir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-408, https://doi.org/10.5194/egusphere-egu24-408, 2024.

EGU24-460 | ECS | Orals | GMPV7.2

Source peritectic crystal entrainment to mantle magmas produced Earth’s largest chromite deposit 

Tahnee Otto, Gary Stevens, Jean-Francois Moyen, Matthew Mayne, and John Clemens

The mechanisms responsible for the formation of the mineral deposits and complex layered stratigraphy in layered mafic intrusions from cratonic environments have remained elusive, largely because the nature of the mantle melting processes that generated the parental magmas are poorly understood. The largest chromium deposits reside within the mafic-ultramafic Rustenburg Layered Suite (RLS) of the Bushveld Complex, South Africa, as laterally continuous layers of chromitite. The RLS has complex, small-scale chemical stratigraphy (Mg#, An#, Sr(i), etc.) and has surprisingly evolved Sr-isotopic compositions. Due to the low solubility of chromium in the basaltic melts theorised as parental to the suite, several models attempt to explain the chromium enrichment. Perhaps the most plausible hypothesis yet proposed to account for the origin of the RLS chromitites, as well as the associated ferromagnesian silicate layered package, is that the suite was produced from hybrid magmas that formed though the assimilation of Kaapvaal craton rocks by komatiitic magmas. As komatiites arise by high degrees of mantle melting, they carry high concentrations of all strongly compatible elements that are enriched in the mantle, but have very low abundances in crustal rocks. However, average RLS compatible trace-element ratios are not similar to mantle values, with Cr/Ni and V/Ni indicating massive enrichment of chromium and vanadium over nickel. Using phase-equilibrium modelling techniques, this study investigated the possibility that the layering and chromitite formation in the RLS are a consequence of the entrainment of components of the magma source rocks. Results reveal a wedge-shaped domain in pressure-temperature space in the subcratonic mantle in which chromium-bearing orthopyroxene is produced as a peritectic product of incongruent melting of various fertile mantle source compositions. Given the ease of orthopyroxene nucleation and the high rates of plume-driven melt production apparent in the formation of large igneous provinces, entrainment of this orthopyroxene in the melts, on extraction from their mantle sources, seems unavoidable. During ascent, magmas with entrained peritectic orthopyroxene crystallise peritectic olivine and chromite due to reaction of the orthopyroxene with melt – a double-peritectic mechanism. These chromite- and olivine-bearing magmas intrude the upper continental crust as sills of crystal-melt slurry and can produce chromite and dunite layers by density separation immediately after emplacement, even if no further cooling occurs before melt drainage. If metasomatism of the mantle source by crustally-derived fluids (ideally ancient and of low volume) is accepted as plausible, then the very high ratios of chromium and vanadium to other compatible elements for average RLS is a superior fit with the formation of the suite by broadly basaltic melts that entrained peritectic orthopyroxene, rather than formation by reactive assimilation of crust by komatiitic magmas. Thus, this study presents a novel, chemically and thermodynamically constrained model that is a simple, first order, source-dependent alternative to the complex petrogenetic models of the current paradigm.

How to cite: Otto, T., Stevens, G., Moyen, J.-F., Mayne, M., and Clemens, J.: Source peritectic crystal entrainment to mantle magmas produced Earth’s largest chromite deposit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-460, https://doi.org/10.5194/egusphere-egu24-460, 2024.

EGU24-673 | ECS | Posters on site | GMPV7.2

Geology, petrography and emplacement conditions of the Esenköy Pluton (NW Anatolia) 

Gökçenur Bayram, Esra Tükel, Işıl Nur Güraslan, Alp Ünal, and Şafak Altunkaynak

One of the least studied plutons in NW Anatolia, the Esenköy pluton intruded into the Palaeozoic Armutlu metamorphics. Along its southwestern boundary with the Esenköy pluton, basement rocks are found as "roof pendants". Both the Esenköy pluton and the Armutlu metamorphics are cut by aplite and diorite porphyry dykes. The pluton is mainly granodioritic in composition and is made up of 45-50% plagioclase, 25-30% quartz, 12-15% alkali feldspar, 6-9% hornblende, and 3-5% biotite. It exhibits predominantly holocrystalline porphyritic texture, and graphic-granophyric textures are also widespread throughout the main plutonic body. Diorite porphyry dykes display micro-granular porphyritic texture, while aplite dykes commonly show micro-granular texture.

Chemical analyses of plagioclase and amphibole minerals in granodiorite samples reveal that plagioclases are predominantly andesine (An35-50) in composition. Zoned plagioclases generally show normal zoning with a decrease in calcium ratios from the core to the rims of the crystals. Amphiboles are all calcic in composition and are represented by magnesio-hornblende. Geothermobarometric calculations, using the chemistry of amphiboles and plagioclases from the same samples, yield pressure values ranging from 1.12 to 1.41 kbar and temperature values ranging from 741 to 787 °C. These temperature and pressure conditions suggest that the Esenköy pluton is emplaced at depths of 3.37-4.23 km within the crust. Contact relationships, textural properties and geothermobarometric calculations collectively indicate that the Esenköy pluton is an epizonal pluton that was emplaced into shallow levels of NW Anatolian crust.

How to cite: Bayram, G., Tükel, E., Güraslan, I. N., Ünal, A., and Altunkaynak, Ş.: Geology, petrography and emplacement conditions of the Esenköy Pluton (NW Anatolia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-673, https://doi.org/10.5194/egusphere-egu24-673, 2024.

EGU24-744 | ECS | Posters on site | GMPV7.2

Gel wax and Ultrasound Transmission Gel as upper and lower crustal rheology analogue 

Uddalak Biswas, Atin Kumar Mitra, and Nibir Mandal

The laboratory modelling of upper and lower crustal rocks has been challenging in terms of rheological scaling for geologists. Upper and lower crusts have been considered as coulomb-brittle or elastic and viscous rheological material, respectively, by the analogue modeller in simulating several deformation related phenomena. However, in nature, they are not purely viscous or elastic, or plastic. Rather, they behave visco-elasto-plastically. This work introduces two new materials of complex visco-elastic and visco-elastoplastic rheology i) Gel wax and, ii) Ultrasound Transmission Gel (USTG). Gel wax is a commercial wax which is composed of mineral oil and hydrocarbon-based polymer. It is used for making transparent, long-lasting candles with melting temperatures of 70-80°C. On the other hand, USTG is a gel-like substance made mainly of Carbopol powder and water.

In this present work, we performed amplitude and frequency sweep tests in a rheometer for both the Gel wax and USTG to understand their complex rheology. The results suggest that Gel wax can be an appropriate analogue material to simulate upper crustal experiments. Similarly, visco-elastoplastic rheology of USTG is analogous to lower crustal rocks.

Considering these materials as crustal analogues, we conducted a few dike emplacement experiments following proper geometric, kinematic and dynamic scaling. The experimental results revealed remarkable 3D dike geometry as both the materials are transparent. Finally, we matched these patterns with a few exposed dikes observed in the field, which supports the applicability of Gel wax and USTG as crustal rock analogues.

How to cite: Biswas, U., Mitra, A. K., and Mandal, N.: Gel wax and Ultrasound Transmission Gel as upper and lower crustal rheology analogue, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-744, https://doi.org/10.5194/egusphere-egu24-744, 2024.

EGU24-2048 | ECS | Orals | GMPV7.2

Accretion of the lowermost oceanic crust at fast-spreading ridges: Insights from the East Pacific Rise (Hess Deep, IODP Leg 345) 

Valentin Basch, Alessio Sanfilippo, Jonathan Snow, Matthew Loocke, and Alberto Zanetti

At mid-ocean ridges, melts formed during adiabatic melting of a heterogeneous mantle migrate upwards and ultimately crystallize the oceanic crust. In this context, the lower crustal gabbros represent the first crystallization products of these melts and the processes involved in the accretion of the lowermost crust drive the chemical evolution of the magmas forming two thirds of Earth’s surface. At fast-spreading ridges, elevated melt supply leads to the formation of a ⁓6 km-thick layered oceanic crust. Here, we provide a detailed petrochemical characterization of the lowermost portion of the fast-spread oceanic crust drilled during IODP Leg 345 at the East Pacific Rise (IODP Site U1415), together with the processes involved in crustal accretion. The recovered gabbroic rocks are primitive in composition and range from olivine-rich troctolites to troctolites, olivine gabbros, olivine gabbronorites and gabbros. Although textural evidence of dissolution-precipitation processes is widespread within this gabbroic section, only the most interstitial phases record chemical compositions driven by melt-mush interaction processes during closure of the magmatic system. Yet, the occurrence of primitive orthopyroxene in most of the olivine-bearing samples indicates that reactive processes allowed for its local saturation within the percolating MORB-type melt. Comparing mineral compositions from this lower crustal section with its slow-spreading counterparts, we propose that the impact of reactive processes on the chemical evolution of the parental melts is dampened in the lowermost gabbros from magmatically productive spreading centres. Oceanic accretion thereby seems driven by in situ crystallization in the lowermost gabbroic layers, followed by upward reactive percolation of melts towards shallower sections. In addition, we here furnish a first estimate of the trace element composition of the parental melts that led to the accretion of the lower crust at Hess Deep, Atlantis Massif and Atlantis Bank; we show that the primary melts of the East Pacific Rise are more depleted in incompatible trace elements compared to those formed at slower spreading rates, as a result of higher melting degrees of the underlying mantle.

How to cite: Basch, V., Sanfilippo, A., Snow, J., Loocke, M., and Zanetti, A.: Accretion of the lowermost oceanic crust at fast-spreading ridges: Insights from the East Pacific Rise (Hess Deep, IODP Leg 345), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2048, https://doi.org/10.5194/egusphere-egu24-2048, 2024.

EGU24-2731 | Orals | GMPV7.2

Plutonic Nature of a Transcrustal Magmatic System: Evidence from Ultrahigh Resolution Sr-Disequilibria in Plagioclase Microantecrysts from the Southern Taupo Volcanic Zone, New Zealand 

Georg Zellmer, Daniel Coulthard Jr, Raimundo Brahm, Charline Lormand, Naoya Sakamoto, Yoshiyuki Iizuka, and Hisayoshi Yurimoto

The residence timescales of antecrystic minerals contribute a key piece of information regarding the petrologic evolution of transcrustal magmatic systems and may be inferred using a combination of observations derived from microanalytical chemistry and diffusion modelling. Here, we present state-of-the-art stacked CMOS-type active pixel sensor (SCAPS) isotopographic images of tephra-hosted plagioclase microantecrysts from Tongariro Volcanic Centre in the southern Taupo Volcanic Zone, New Zealand. These crystals exhibit high-frequency Sr and anorthite zonation at sub-micron spatial resolution. We also find that all crystals display high-frequency intracrystalline Sr chemical potential variations, indicating that they have not resided at magmatic temperature for diffusive relaxation to advance significantly. To quantify crystal residence times at the well-constrained magmatic temperatures of these tephras, we first forward-modeled intracrystalline Sr diffusion over time using numerical methods. Results were then analyzed using novel spatial Fourier-transform techniques developed to understand the systematics the diffusive decay of Sr disequilibria in the spatial frequency domain. This ultimately permitted the estimation of Sr concentration profiles at crystal formation, prior to uptake into the carrier melt at the onset of eruption. Our data imply residence times of days to weeks for the studied microantecrysts. This is inconsistent with long antecryst residence times in magmatic mushes at elevated temperatures, pointing instead to a cool plutonic nature of the magmatic plumbing system beneath the southern Taupo Volcanic Zone.

How to cite: Zellmer, G., Coulthard Jr, D., Brahm, R., Lormand, C., Sakamoto, N., Iizuka, Y., and Yurimoto, H.: Plutonic Nature of a Transcrustal Magmatic System: Evidence from Ultrahigh Resolution Sr-Disequilibria in Plagioclase Microantecrysts from the Southern Taupo Volcanic Zone, New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2731, https://doi.org/10.5194/egusphere-egu24-2731, 2024.

Understanding the processes involved in the transformation of juvenile basaltic oceanic arc crust into mature continental crust remains a key challenge in Earth sciences. In this contribution, we present a comprehensive synthesis of in situ zircon U-Pb age and Hf-O isotope data for Paleozoic intrusions within the West Junggar oceanic arc, NW China. Our study reveals four distinct pulses of magmatic activity: Early Cambrian to Early Ordovician (515 to 486 Ma); Late Ordovician to Middle Devonian (445 to 392 Ma); Early Carboniferous (343 to 310 Ma) and Late Carboniferous to Middle Permian (309 to 259 Ma). These pulses have varied spatial and temporal distributions. All magmatic rocks display consistently high zircon Hf and whole-rock Nd isotope values, but substantial variations in zircon O isotopes. There are two groups of intrusions: those with high zircon δ18O (>6.5‰) and those with mantle-like zircon δ18O (ca. 5.5‰). The high zircon δ18O intrusions are predominantly concentrated in the southern West Junggar and their Hf and Nd isotopes indicate the involvement of supracrustal material and juvenile basaltic crust in their petrogenesis. Binary mixing calculations indicate a contribution from the supracrustal rocks ranging from 10% to 50%. The intrusions with mantle-like zircon δ18O are found primarily in northern West Junggar with a small amount occurring in southern West Junggar. The intrusions record a variety of magma sources and processes as demonstrated by Hf-O isotope and geochemical data. These data indicate partial melting of metasomatized depleted mantle, mixing of depleted mantle and juvenile crust, and partial melting of trapped juvenile oceanic crust or mafic lower crust. Hf model ages reveal significant crustal growth in the West Junggar, characterized by three distinct episodes of crust formation occurring at approximately 656-684 Ma, 524-536 Ma, and 441-471 Ma, involving periodic remelting of igneous material derived from a depleted mantle source. This newly-formed crust maintains a mantle-like oxygen isotope composition despite being repeatedly sampled by magmas for up to 0.26 Ga. Since the timing of crustal growth occurred independently of the major magmatic pulses, the latter reflect primarily reworking and remelting processes. Two significant episodes of magmatic activity, the late Silurian to early Devonian and the late Carboniferous to early Permian, preserve a signature of ocean ridge subduction. High-temperature magmatism during these periods promoted extensive melting of the mafic lower crust, oceanic crust, and supracrustal rocks, leading to the compositional transformation from basaltic to felsic continental crust. This comprehensive compilation provides valuable insights into granite petrogenesis, crustal evolution, and the diverse processes involved in the maturation of oceanic arc crust and its contribution to continental crust formation and evolution.

 

How to cite: Yin, J., Wang, T., and Huang, H.: Ocean arc to continental crust: zircon Hf-O isotopes and crustal evolution of West Junggar, NW China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2959, https://doi.org/10.5194/egusphere-egu24-2959, 2024.

Ferro-basaltic liquids intersect a binode during fractionation, splitting into two immiscible silicate liquids, one Si-rich and the other Fe-rich. The two liquids have very different physical properties: the Si-rich liquid is more buoyant and viscous, preferentially wetting plagioclase, whereas the Fe-rich liquid preferentially wets grains of mafic minerals and Fe-Ti oxides. The density difference means that when a crystal-poor magma body intersects the binode, it is likely to undergo compositional stratification, with implications for the compositions of any eruptions. When the interstitial liquid in a crystal mush unmixes, the density difference is compounded by the differences in wetting properties, leading to complex behaviour if capillary forces act in a different direction to that of gravity. The extent and scale of differential migration of unmixed liquids may thus play an important role in the genesis of the Daly Gap, while the preferential partitioning of P, PGE and REE into the Fe-rich conjugate has significant implications for formation of economically important deposits.

The Skaergaard Intrusion of East Greenland records abundant evidence for differential migration of immiscible silicate liquid conjugates. At the intrusion scale, the roof rocks are more silica-rich than the cumulates at the floor, consistent with intersection of the binode by the bulk magma leading to the accumulation of the buoyant Si-rich conjugate in the roof mush. This is supported by the localised presence of reverse modal layering on the floor, interpreted as bodies of dense Fe-rich liquid ponded at the top of thin (<1m) mush. Large-scale lateral migration of Fe-rich liquid along fractures developing in the solidifying wall mush may have been the underlying cause of metasomatism to form localised 100m-scale patches of replacive pyroxenite. Evidence of metre-scale differential migration within the crystal mush on the intrusion floor is provided by paired silicic and mafic late-stage segregations, recording downwards penetration and disruption of the floor mush by dense Fe-rich liquid, coupled with limited upwards flow of viscous Si-rich liquid. Further evidence of metre-scale differential migration is provided by compositional rims developed on the tops and bases of (almost) fully-solidified blocks in the floor cumulates of material solidified at the roof, fragmented and released during contemporaneous seismic activity. The mafic rims at their tops formed by the ponding of downwards-moving Fe-rich liquid while the felsic rims at their bases formed by the ponding of upwards-moving Si-rich liquid against the impermeable autoliths, consistent with the extent of rim development being a function of autolith shape, rather than composition. Differential migration on the cm-scale, driven by capillarity and the differences in wetting properties of the two immiscible conjugates, is suggested as the mechanism by which poorly-defined cm-scale micro-rhythmic layering is superimposed on graded modal layering.

The Skaergaard examples of differential migration provide the opportunity to constrain the length- and time-scales of differential migration of unmixed immiscible silicate conjugates, to quantify the effects of capillarity and emulsion coarsening, and to assess the more general importance of liquid immiscibility on petrogenetic evolution.

How to cite: Holness, M., Nielsen, T., and Namur, O.: Differential migration of immiscible liquids in gabbroic crystal mush: the Skaergaard Intrusion, East Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3983, https://doi.org/10.5194/egusphere-egu24-3983, 2024.

EGU24-4426 | Posters on site | GMPV7.2

A mantle source for water in Appinite complexes: implications for genesis of granitoid batholiths and crustal growth 

J. Brendan Murphy, Christopher J. Spencer, Donnelly B. Archibald, and William J. Collins

Appinite plutonic rocks range from ultramafic to felsic in composition, are characterized by idiomorphic hornblende as the dominant mafic mineral in all lithologies, and by spectacularly diverse textures, including planar and linear magmatic fabrics, multiple comb layers, mafic pegmatites and widespread evidence of mingling between mafic and felsic compositions. These features suggest that they are anomalously water-rich mafic magmas.  

The ca. 607 Ma Greendale Complex in the Antigonish Highlands of Nova Scotia is typical of appinite complexes which commonly occur as small (~2 km diameter) plutons adjacent to major deep crustal faults along the periphery of voluminous granitoid plutons emplaced in the waning stages of regional arc activity. Isotopic data from hornblendes in the Greendale Complex yield δD values ranging from -61 to -72 and δO18 from 3.7 to 7.0, indicating the water in the appinite magma has a strong mantle component. These data suggest the appinites may represent aliquots of hydrous basaltic magma derived from mafic underplates originally emplaced along the base of the crust during protracted subduction. Transfer of heat and fluids to the base of the crust triggered generation of coeval (615-604 Ma) granitoid magmas by partial melting in the overlying MASH zone. The granitoid magmas were emplaced in the shallow crust when transient stresses activated favourably-oriented structures which became conduits for magma transport. The ascent of late mafic magmas within the Antigonish Highlands was impeded by the rheological barriers created by the structurally overlying granitoid magma bodies. Magmas that form the Greendale Complex evaded those rheological barriers because they preferentially exploited the deep crustal Hollow Fault that bounded the plutonic system.

Collectively, these mineralogical, textural and geochemical features suggest a complex magmatic history involving repeated water saturation episodes within the plumbing system as mafic, mantle-derived magmas ascended and differentiated at mid-to-upper crustal levels (ca. 3-5 kbar). More generally, the most mafic components of appinite complexes may provide a window into the composition of the mafic underplate and insights into processes that generate granitoid batholiths and crustal growth in arc systems.

 

How to cite: Murphy, J. B., Spencer, C. J., Archibald, D. B., and Collins, W. J.: A mantle source for water in Appinite complexes: implications for genesis of granitoid batholiths and crustal growth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4426, https://doi.org/10.5194/egusphere-egu24-4426, 2024.

EGU24-5671 | ECS | Posters on site | GMPV7.2

Geochemistry and geochronology of Midyan terrane granitoids, NW Saudi Arabia: Implications for growth of the Arabian-Nubian Shield 

Wafa AL-Hakimi, Sabyasachi Chattopadhyay, Faris Sulistyohariyanto, Scott A. Whattam, Hossein Azizi, Keewook Yi, and Fatemeh Nouri

 The 900–550 Ma Arabian-Nubian Shield (ANS) represents the northern part of the East African Orogen (EAO) and was generated by Neoproterozoic juvenile crust addition and ultimately, collision of eastern and western Gondwana ca. 600 Ma. The ANS  encompasses the greatest volume of Neoproterozoic juvenile crust preserved on Earth and embodies over 610,000 km2 across NE Africa and the western part of the Arabian Peninsula. The ANS comprises stacks of thin-skinned nappes resulting from oblique convergence of bounding plates and resulting amalgamation of intra-oceanic arcs generated within the Mozambique Ocean. As such, the ANS is a classic example of an accretionary orogen. Final accretion and ANS consolidation were accompanied and followed by emplacement of within-plate alkaline plutons c. 640–550 Ma, which represent the largest volume of alkaline granitoids on the planet. Overall, ANS tectonic evolution encompasses an orogenic cycle beginning with the fragmentation of Rodinia (870–800 Ma) and ending with amalgamation of eastern and western Gondwana in the Cambrian.

This study combines field observations, petrography, whole rock major-and-trace element chemistry, along with U-Pb zircon geochronology and Sr-Nd-Pb isotope data of four granitoid suites of the northwestern part of the Midyan terrane (Ifal, Muwylih, Midyan, and Lawaz), that provides an excellent opportunity for further understanding of the factors influencing the shift from A- to I-type granitoids. Samples are mostly granite-granodiorite-diorite with subordinate gabbro and gabbro diorite. Seven samples are A-type, while the remaining 26 are I-type. Petrographically, I-type rocks consist of K-feldspar, quartz, albite, mica, amphiboles, and sodic-pyroxene as major minerals with a variety of accessory minerals, including Fe-oxides and zircon. Major oxide abundances such as CaO, TiO2, and P2O5 manifest a clear decrease with increasing SiO2 content, except for K2O, which indicates fractionation of, for example, plagioclase, Fe-Ti oxides, and apatite. Whole rock data shows clearly distinct characters of the A-type being metaluminous, enrchied in ∑REE with an average of 355 µg/g. In contrast, the I-type is meta-luminous-peraluminous, which only has an average of ∑REE 197 µg/g. The chondrite-normalized patterns of the A-type show lower negative Eu anomalies (Eu/Eu*=0.61) in comparison to the I-types (Eu/Eu*=0.86), depicting the different degrees of plagioclase fractionation. The primitive-mantle normalized patterns show depletions in  Sr and Ti, indicating fractionation of feldspar and Fe-Ti phases in both types. The U-Pb zircon ages indicate two distinct pulses of granitoid magmatism.  The first pulse is attributed to A2 (post collision)-type ca. 634–640 Ma, followed by a second pulse of I-type in nature ca. 618–598 Ma. The A and I-type Sr-Nd isotope data attest to the juvenile nature of the crust from the ANS (εNd =4.88–5.15), while some I-types (εNd =3.91) are derived from partial melting of a pre-existing crust. We conclude that the magmatism in the Midyan terrane area is shown to have shifted from a within-plate setting associated with orogenic collapse and partial melting of the lower crust into volcanic arc affinity with a more depleted source.

 

How to cite: AL-Hakimi, W., Chattopadhyay, S., Sulistyohariyanto, F., Whattam, S. A., Azizi, H., Yi, K., and Nouri, F.: Geochemistry and geochronology of Midyan terrane granitoids, NW Saudi Arabia: Implications for growth of the Arabian-Nubian Shield, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5671, https://doi.org/10.5194/egusphere-egu24-5671, 2024.

EGU24-5812 | Orals | GMPV7.2 | Highlight

Visualising magma plumbing systems in 4D 

Craig Magee

Significant advances have been made in using a wide variety of geophysical techniques to track melt migration, image the structure of active and ancient magma plumbing systems, and constrain emplacement mechanics. In particular, integrating traditional petrological and geochemical results with such geophysical data and modelling has afforded exciting insights into the development of entire magmatic systems. However, divisions between the scales and physical settings over which these methods are applied remain. To characterise these differences and promote the benefits of further combining geophysical, petrological, and geochemical datasets, I discuss how geophysical techniques can be utilised to provide structural context and place physical constraint to the chemical evolution of magma plumbing systems. I am no expert in many geophysical techniques and thus lean on the work of many others, showcasing the importance of collaboration to pushing the boundaries of our science. Here, I will examine on what we can do with some geophysical and geodetic techniques, whilst importantly highlighting what we cannot do with them, and discuss how their application can help us solve some of the key questions within our field. Overall, I hope to show that approaching problems concerning magma plumbing systems from an integrated petrological, geochemical, and geophysical perspective, brought together with various modelling methods, will yield important scientific advances and provide exciting future opportunities for the entire volcanological community.

How to cite: Magee, C.: Visualising magma plumbing systems in 4D, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5812, https://doi.org/10.5194/egusphere-egu24-5812, 2024.

EGU24-5981 | Orals | GMPV7.2

The 3D anatomy of magma transport in fast-spreading oceanic crust of the Oman ophiolite 

Antony Morris, Andrew Parsons, Michelle Harris, Chris MacLeod, Benoit Ildefonse, Charlotte Atton, Simon Allerton, and Derya Gürer

At fast-spreading oceanic ridges such as the East Pacific Rise, divergence between tectonic plates is accommodated almost exclusively by magmatic accretion. A robust understanding of magmatic accretion during seafloor spreading is therefore necessary to model the structure and composition of oceanic lithosphere and exchanges in heat and mass at a global scale over geological time. Whereas most models consider magmatic accretion in 2D, variations in ridge axial morphology and magmatic compositions highlight the occurrence of ridge-parallel variations in magmatic processes along fast-spreading systems. This suggests that magmatic accretion may be a 3D process involving significant ridge-parallel magma transport.

To constrain the process of magmatic accretion at fast-spreading ridges, we present our on-going investigation of magma transport in the Oman ophiolite. The first order structure and composition of the ophiolite, defined by a sheeted dyke complex with an underlying axial melt lens of variable thickness on top of foliated gabbro, is analogous to the East Pacific Rise. This provides a unique opportunity to investigate magmatic accretion processes above and below an axial melt lens system in three dimensions at ridge segment- to grain-scales for the first time.

We present new data constrains the directions of magma transport in the crust of the Oman ophiolite. This includes analyses of foliated gabbros and sheeted dyke complexes from the Fizh, Salahi, and Sarami blocks, which define a complete ridge segment. Using anisotropy of magnetic susceptibility (AMS), we report the orientations of magnetic fabrics that serve as proxies for magmatic flow directions. Combining AMS data with paleomagnetic analyses of magnetic remanence directions allows us to restore magmatic flow directions to their paleo-ridge orientation, prior to obduction. Our results indicate that magmatic flow directions vary along the length of the ridge segment and cannot be explained by simple 2D models. Our data show that ridge-parallel lateral flow is a common phenomenon in both the sheeted dykes and foliated gabbros over the length of a ridge segment. Our results also have important implications for competing models of crustal accretion.

How to cite: Morris, A., Parsons, A., Harris, M., MacLeod, C., Ildefonse, B., Atton, C., Allerton, S., and Gürer, D.: The 3D anatomy of magma transport in fast-spreading oceanic crust of the Oman ophiolite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5981, https://doi.org/10.5194/egusphere-egu24-5981, 2024.

EGU24-6145 | ECS | Orals | GMPV7.2

Geodetic observations of simultaneous rift-scale magma inflow in multiple sills in the Central Afar rift 

Alessandro La Rosa, Carolina Pagli, Hua Wang, Freysteinn Sigmundsson, Virginie Pinel, and Derek Keir

During plate spreading, large volumes of magma can be extracted from the upper mantle and intrude the crust. Geophysical and geochemical studies at active magmatic rifts and passive margins show that crustal intrusions mainly occur in the form of transient sill-like bodies. The sills pond at various crustal levels, potentially feeding shallower plumbing systems, dike intrusions and surface eruptions. Trans-crustal magma migration and intrusion thus have a key role in controlling extension, strain localization and subsidence during rifting. However, a clear understanding of the mechanisms of sill intrusion, their connection to upper mantle processes, as well as the spatial and temporal response of the sills to a new arrival of magma is still limited by the paucity of direct observations. In this study, we provide one of the few direct InSAR observation of rift-scale deformation caused by magma inflow from the upper mantle to multiple crustal sills in the Central Afar (CA) rift.

We used InSAR time-series from 255 ESA Sentinel-1 interferograms during 2014-2021 and combined them with available GNSS measurement to retrieve the 3D velocity field and the temporal evolution of surface deformation in CA. We observed four uplift patterns with rates of ~5 mm/yr, that we inverted using four inflating Okada tensile dislocation sources (sills). Our best-fit model shows four sills elongated in a NW-SE direction, similar to the rift trend, and opening rates ranging between 16 and 44 mm/yr. The sills are located at various crustal depths but mainly in the mid-to-lower crust, following the thinning of the crust imaged seismically in CA. Cross-correlation of time-series also show that the uplift above the four sills starts simultaneously in December 2016 and continue until March 2021.

We interpreted the simultaneous inflation of four distant sills as the result of a shared pressurization event caused by an episodic magma inflow from a common source in the upper mantle. Our results show that magma supply from the mantle beneath continental rifts is episodic, and occurs across large spatial scales but short temporal scales over which deep crustal magma ponding takes place. Such process could explain how the thick intruded crust common at magma-rich rifted margins is created and could help in understanding the long-term dynamics of rifting episodes and volcanism.

How to cite: La Rosa, A., Pagli, C., Wang, H., Sigmundsson, F., Pinel, V., and Keir, D.: Geodetic observations of simultaneous rift-scale magma inflow in multiple sills in the Central Afar rift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6145, https://doi.org/10.5194/egusphere-egu24-6145, 2024.

EGU24-6844 | ECS | Posters on site | GMPV7.2

Quaternary Magmatism in NW Svalbard: Refining the Architecture and Evolution of Sverrefjellet Volcano 

Dmitrii Zastrozhnov, Sverre Planke, John Millett, Rafael Horota, Agnes Kontny, Kim Senger, Sebastian Tappe, Anniken Helland-Hansen, Maria Telmon, Peter Betlem, Alexander Minakov, and Horst Kaempf

Sverrefjellet is the remnant of an extinct alkali basaltic stratovolcano located in NW Svalbard, representing a distinctive phase of Quaternary magmatism in the High Arctic. It is part of the Bockfjorden Volcanic Complex, which consists of several eruption centers within the Woodfjorden-Bockfjorden area. The volcanism occurred during the northern hemisphere’s glaciations and reveals evidence for magma interactions with glaciers. The Quaternary eruption centers are localized along the Breibogen Fault and were probably linked to the evolution of the Knipovich mid-oceanic ridge, yet the exact age of the magmatic activity remains uncertain. Sverrefjellet is renowned for its high abundance of mantle-derived xenoliths, which have become a focal point in most publications on this volcano to date. However, the magmatic architecture and physical volcanology of Sverrefjellet have received only limited attention after the initial mapping by Skjelkvåle et al. (1989).

In July 2023, an international multi-disciplinary geoscientific expedition to Woodfjorden-Bockfjorden was undertaken. One of the primary objectives was to perform detailed mapping and systematic sampling of volcanic-related units within Sverrefjellet volcano, with the aim of exploring and refining magma emplacement processes. To facilitate this, drones were utilized to acquire high-resolution 3D digital textured models over the best-exposed outcrops of the volcano. The in-field sampling of the main volcanic units was accompanied by extensive (∼100) magnetic susceptibility measurements with a hand-held Kappameter (SM-30). In total, 20 rock samples have been prepared for petrographic, SEM and EPMA analyses.

We observed the presence of mantle-derived xenoliths in all volcanic units, which include dyke intrusions, pillow basalts with associated lava tubes, basaltic lava flows, and various volcanogenic sediments. The slopes of the extinct volcano display predominant frost weathering, with the southern slope adorned with olivine sand and gravel sourced from 'bomb-shaped' nodules or clasts that typically contain peridotite xenoliths as their cores. The presence of pillow lavas and associated 1 to 2 meter large lava tubes suggests subglacial magma emplacement. This is supported by their relatively high elevation at 200-300 meters above sea-level, which makes interaction with seawater highly unlikely.

In between lava flows and dykes, texturally distinctive zones characterized by platy tops and bottoms as well as numerous flattened boulder-sized xenolithic nodules were observed. Petrographic and SEM analyses of xenoliths and host basalts revealed no preferred alignment of crystals within the platy zones, suggesting that these schistose textures developed due to rapid magma cooling and subsequent freeze-thaw action rather than tectonic shearing. The basalts display typical ferrimagnetic susceptibilities (average: 3.24 × 10-3 SI), whereas the volcanogenic sediments exhibit low paramagnetic susceptibility (0.38 × 10-3 SI), indicating rapid magma quenching during fragmentation, which is characteristic of subglacial emplacement.

Our preliminary results support a subglacial origin for the Sverrefjellet eruptions. Ongoing detailed mapping and thorough magnetic mineralogy analyses, coupled with geochronological and geomorphological studies, will enhance our understanding of subglacial volcanic processes at the extinct Sverrefjellet volcano and more broadly. Additionally, these findings will contribute to a better understanding of the nature and origin of High Arctic Quaternary magmatism and its paleogeographic setting.

How to cite: Zastrozhnov, D., Planke, S., Millett, J., Horota, R., Kontny, A., Senger, K., Tappe, S., Helland-Hansen, A., Telmon, M., Betlem, P., Minakov, A., and Kaempf, H.: Quaternary Magmatism in NW Svalbard: Refining the Architecture and Evolution of Sverrefjellet Volcano, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6844, https://doi.org/10.5194/egusphere-egu24-6844, 2024.

EGU24-7511 | Orals | GMPV7.2

Imaging the magma plumbing system of Ciomadul volcano and the Perşani Volcanic Field and constraining postcollisional magma dynamics  

Matthew J. Comeau, Graham J. Hill, Svetlana Kovacikova, Jochen Kamm, Réka Lukács, Ioan Seghedi, Alexander Grayver, István Bondár, and Harangi Szabolcs

There are indications that some long-dormant or seemingly inactive volcanoes may have potentially active magma storage systems. One such system is Ciomadul volcano, which is located at the south-eastern terminus of the Carpathian volcanic chain (Romania). With the last eruption occurring at ~30 ka, this is the youngest volcano in eastern-central Europe. Understanding the nature and structure of the magma plumbing system is crucial to elucidating the evolution of the volcano and to assessing its hazard potential. This includes the depth, size, and geometry of the magma storage region, the amount and composition of the melt present, and the link between mantle and crustal processes.  

Ciomadul is situated in a geodynamically active region about 50 km from the Vrancea zone, where deep earthquakes are frequent. These earthquakes may represent the descent of a dense lithospheric slab beneath a continental collision zone and this may imply an asthenospheric upwelling due to return flow of mantle material. To the north-west of Ciomadul lies a chain of older volcanic complexes, the Călimani–Gurghiu-Harghita volcanic complex; about 40 km west of Ciomadul towards the Transylvanian Basin, a monogenetic basaltic volcanic region was developed at 1.2–0.5 Ma (Perşani volcanic field). Seismic tomography has revealed low-velocity columns through the lithosphere beneath both Ciomadul and Perşani. However, high-resolution images of the complex geometry of the system are lacking.  

We report here on a 3-D electrical resistivity model of the region that was generated from 41 magnetotelluric measurements acquired in 2022 that form a 75 km by 75 km array. The data typically had reliable periods from 128 Hz to 4,100+ s. Choosing appropriate locations for measurement was critical, away from sources of cultural electromagnetic noise that can contaminate the signals, as was careful data processing, including applying data pre-selection schemes and manual time windows in addition to standard approaches using robust statistics.  

Phase tensor analysis suggests that the data are 3-D at all scales. The 3-D electrical resistivity model reveals conductive anomalies (<10 ohm-m) in the subvolcanic crust. These are interpreted as melt-bearing magma reservoirs distributed in the mid-lower crust (depths of ~10–25 km) and a quasi-vertical conduit extending to the near surface. The crustal reservoir is oriented north-south, has its western margin beneath the surface vent of Ciomadul, and extends ~20 km eastward. These results are consistent with the quantitative petrological models placing the upper melt-bearing silicic crystal mush reservoir at a depth of 5–20 km beneath Ciomadul, and a magma-generation area in the asthenosphere (85–105 km depth). In contrast, no strong conductive anomaly is observed in the crust below Perşani, which fits the magma evolution model, i.e. small batches of mantle-derived magmas ascend rapidly through the crustal column. Our results suggest that Ciomadul, a seemingly inactive volcano, is still underlain by a melt-bearing magma body and therefore can be regarded as having potential for reactivation and further volcanic eruptions.  

How to cite: Comeau, M. J., Hill, G. J., Kovacikova, S., Kamm, J., Lukács, R., Seghedi, I., Grayver, A., Bondár, I., and Szabolcs, H.: Imaging the magma plumbing system of Ciomadul volcano and the Perşani Volcanic Field and constraining postcollisional magma dynamics , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7511, https://doi.org/10.5194/egusphere-egu24-7511, 2024.

EGU24-7717 | ECS | Orals | GMPV7.2

Plumbing system architecture, magma differentiation, and volatile element evolution in an active rift segment: Constraints from melt inclusions in Asal rift (Djibouti, Afar). 

Juliette Pin, Lydéric France, Gilles Chazot, Etienne Deloule, Yafet Gabrewold Birhane, Raphaël Pik, and Irene Schimmelpfennig

The Asal Rift, situated within the Afar region, presents a unique opportunity to study continental rifting and ongoing break-up mechanisms. Here we present a comprehensive study based on volatile element contents of magmas within the Asal rift's segment. Samples were gathered from various volcanic sub-segments within the active part of the Asal rift, and a subset was collected to document the successive steps of the recent 1978 Ardoukoba eruption. Altogether our new sampling is offering a chronological framework crucial to understanding this magmatic system and the eruptive sequences. Quenched pyroclastic deposits (scoria) were used as they are more likely to preserve the magma's volatile content without significant degassing upon cooling at surface than lava flows. By analyzing over 400 melt inclusions within plagioclase and olivine crystals of 15 new samples, we provide insight into the pre-eruptive volatile content of Asal magmas. The melt inclusions volatile contents (H2O, CO2, Cl, and S) were quantified through SIMS analyses at CRPG. Sample preparation for SIMS measurements was carefully achieved to avoid any contamination or volatile loss. After estimation of the volatile migration through the shrinkage bubbles of the melt inclusions by Raman spectroscopy, and correction from post-entrapment crystallization processes, we reconstructed the initial magmatic volatile content at the reservoir depth. This content, combined with detailed petrographic study, field observations, and new dating, allows us to propose a comprehensive picture of the Asal Rift plumbing system architecture, and to discuss its spatial variability and temporal evolution. The wealth of data allowed us to highlight a relative homogeneity of the reservoir volatile contents over the recent Asal rift segment erupted magmas, and to discern the depth range of the Asal igneous reservoir that spans from approximately 5 km to 25 km (based on solubility models of VESIcal (1)). Furthermore, volatile data, combined with in-situ major and trace element analysis, provides insights into magma differentiation, degassing, and into the volatile content of the mantle source. We investigate 3 potential steps of degassing and their effect on volatile, trace and major element: within the plumbing system (during the differentiation), during magma ascent, and at the surface during the eruption (unlikely given the sampling method). Finally, our study focused on the 1978 Ardoukoba eruption within the Asal rift. With a sampling of the entire eruptive sequence, we were able to highlight the evolution of the volatile content during this eruption, showing that the initial differentiated magma reservoir underwent a recharge event before eruption. In conclusion, this new in-situ high-resolution volatile, trace and major element extended dataset 1/ delineated the extensive depth range of the magmatic reservoir, 2/ allows a better understanding of the dynamics of magma reservoirs that feed continental rift systems, and 3/ provides new constraints on the magma evolution, differentiation, and degassing at depth within such a system.

(1) Iacovino, K., Matthews, S., Wieser, P. E., Moore, G. M., & Bégué, F. (2021). VESIcal Part I: An Open‐Source Thermodynamic Model Engine for Mixed Volatile (H2O‐CO2) Solubility in Silicate Melts. Earth and Space Science, 8(11).

How to cite: Pin, J., France, L., Chazot, G., Deloule, E., Gabrewold Birhane, Y., Pik, R., and Schimmelpfennig, I.: Plumbing system architecture, magma differentiation, and volatile element evolution in an active rift segment: Constraints from melt inclusions in Asal rift (Djibouti, Afar)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7717, https://doi.org/10.5194/egusphere-egu24-7717, 2024.

EGU24-7781 | ECS | Orals | GMPV7.2

What modulates eruptive styles and timescales at Villarrica and Osorno volcanoes (Chile)? 

Sri Budhi Utami, Jacqueline Vander Auwera, Tonin Bechon, Paul Fugmann, and Olivier Namur

Villarrica and Osorno are two active stratovolcanoes in the Central Southern Volcanic Zone (CSVZ) of the Chilean Andes that share several geochemical characteristics: near-primary, tholeiitic parent magmas (50-53 wt. % SiO2), overlapping major/trace element differentiation trends, and comparable storage conditions [1-4]. Yet, their current or recent eruptive styles diverge significantly. Villarrica is a steady-state, open-vent volcano with a lava lake that produced ~100 moderate-intensity, Strombolian eruptions since 1579; Osorno is a closed-vent volcano with 10x less eruptions for the same period. Our initial hypothesis proposed that differences in eruptive style and frequency could be due to a relatively higher degree of crustal permeability under Villarrica than Osorno [5]. Although preliminary data shows that some differences exist in olivine chemistry and textures between Villarrica (Fo72-87) and Osorno (Fo66-82) [4,5,6], both volcanoes have broadly similar compositional ranges and multimodal distributions, with comparable diffusion timescales. This suggests the degree of crustal permeability underneath both volcanoes are likely comparable, prompting us to consider other parameters, such as magma supply rate. In this contribution, we discuss and evaluate the role of magma supply rate and other parameters in modulating eruptive styles at Osorno and Villarrica, based on an updated dataset of magma storage conditions, diffusion timescales, and inferences drawn from published literature. We aim to further current understanding of subduction zone magmatism and geodynamics, with implications on volcanic hazard reduction.

1. Vergara et al. (2004). J. S. Am. Earth Sci. 17: 227-238. 2. Morgado et al. (2015). JVGR, 306: 1-16. 3. Pizarro et al. (2019). JVGR. 384: 48-63. 4. Bechon et al. (2022). Lithos. 106777. 5. Utami et al. (2023) Goldschmidt 2023 Abstract 6. Romero et al. (2022). Bull. Volc. 85 (2).

How to cite: Utami, S. B., Vander Auwera, J., Bechon, T., Fugmann, P., and Namur, O.: What modulates eruptive styles and timescales at Villarrica and Osorno volcanoes (Chile)?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7781, https://doi.org/10.5194/egusphere-egu24-7781, 2024.

EGU24-9055 | ECS | Posters on site | GMPV7.2

Continuous Subsidence of Dallol Volcano (Danakil Depression) as a result of magmatic and hydrothermal interaction: Insights from InSAR Observation 

Birhan Kebede, Carolina Pagli, Derek Keir, Alessandro La Rosa, and Freysteinn Sigmundsson

Axial rift volcanoes characterised by an active magmatic and hydrothermal system offer a unique opportunity to study the interaction between these processes. The Dallol volcanic and hydrothermal area is situated in the Afar rift, on the axis of Erta Ale ridge, in a depressed salt plain. Dallol has been experiencing deformation at least since the first dike intrusion observed by InSAR in 2004. Here, we present the results of a new InSAR analysis of Dallol between 2014 and 2023, and inverse modelling of the observed deformation. We used SAR data from the ESA´s Sentinel 1A/B ascending (014) and descending (079) orbits to produce over 651 interferograms. Then we obtained InSAR average velocity maps revealing the presence of three closely spaced and concentric deformation signals of a range increase, consistent with subsidence, of up to 40 mm/yr in the satellite Line-of-Sight (LOS). The main deformation signal corresponds to the Dallol crater, while the two smaller maxima occur on the bishophite precipitating Black Mountain area south of Dallol and at the location of a circular pool at the edge of the salt plain, west of the crater. Our modelling results indicate that the deformation sources can be explained by contractions of three Okada tensile dislocation sources situated at different shallow depths, ranging between 0.7-1.7 km, with a length of 1-3 km and volume decrease of 1-3x10-4 km3/yr. Time series analysis also shows that the subsidence pattern was about linear while small seasonal fluctuation patterns are identified at the two smaller maximas. We interpret that the main subsidance at the Dallol crater is likely caused by the depressurisation of shallow sills, while a possible contribution to the defomration from the hydrothermal system due to seasonal flooding is envisaged for the other two maximas.

How to cite: Kebede, B., Pagli, C., Keir, D., La Rosa, A., and Sigmundsson, F.: Continuous Subsidence of Dallol Volcano (Danakil Depression) as a result of magmatic and hydrothermal interaction: Insights from InSAR Observation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9055, https://doi.org/10.5194/egusphere-egu24-9055, 2024.

To understand the style, longevity and hazards of volcanic fissure eruptions, we need to understand the magma flow dynamics governing their feeder dykes. Microstructural analysis through optical microscopy and electron backscatter diffraction (EBSD) can be used to observe crystal alignment, shape and size from dyke samples to investigate magmatic fluid flow and deformation processes during the ascent of magma. Plagioclase is a mineral ubiquitously found in volcanic rocks that forms throughout magma crystallisation at a wide range of temperatures (~1300-400°C), and is therefore a mineral commonly used to investigate magma flow dynamics in dykes and sills. In particular, microlites of plagioclase (<0.1 mm) are amongst the last crystals to form at shallow crustal depths so have the potential to record the near surface flow behaviour and deformation processes that can lead to eruption.

Here we examine elongate plagioclase microlites from oriented samples of a basaltic dyke from the Budj Bim Volcanic Complex, the only known fissure-fed eruption in the Newer Volcanics Province, south east Australia. Extensive quarrying of the Little Mount scoria cone has provided excellent exposure of the internal architecture of its feeder dyke. Optical microscopy observations show the dyke is comprised of zoned olivine phenocrysts (20%, <0.5 mm diameter), pyroxenes (20%, <0.1 mm diameter) and a fine-grained plagioclase-rich groundmass with minor oxides (5%, <0.05 mm diameter). EBSD of the plagioclase microlites shows they share a strong shape preferred orientation (SPO) and crystallographic preferred orientation (CPO). Plagioclase microlite orientation can be used as an indicator of magma flow, as elongate crystals may reorient due to flow and/or pure shear within the ascending magma. Using these novel data, we propose a model for plagioclase orientation, and therefore potential magma flow dynamics in the Little Mount dyke. Understanding the physical and chemical processes governing historic fissure eruptions such as the Budj Bim Volcanic Complex enables us to inform hazard mitigations for future fissure eruptions worldwide. 

How to cite: Hrintchuk, J. A., Kavanagh, J. L., and Mariani, E.: Plagioclase preferred orientation provides insights into magma flow dynamics of a basaltic dyke from the Budj Bim Volcanic Complex, Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9775, https://doi.org/10.5194/egusphere-egu24-9775, 2024.

EGU24-10207 | Orals | GMPV7.2

Transcrustal, interconnected, or isolated magma reservoirs, can we tell the difference? 

Fidel Costa and Jean-Philippe Metaxian

The organization of melts below active volcanoes plays a large role on the size, composition, and character of the ensuing eruptions. In principle it should be possible to determine the distribution of melts with geophysical data, such as inversion of seismic velocity, density, and gravity. In practice, it appears that the size and distribution of the melts have a topology that only allows for very approximate information, typically made of “hot big potatoes” where melts are likely to reside. This is specially the case for many calderas and large stratovolcanoes from subduction zones, and unfortunately such view is not good enough to address the likely size of future events. Petrological studies of erupted crystals can, also in principle, provide a view of the depth and possible variety storage areas. However, geothermobarometry data tend to have large errors on pressure, and in a similar manner to most geophysical data many calderas and stratovolcanoes show a very wide distribution of depths (transcrustal systems?). Notwithstanding, many systems show a broad agreement between the petrological and geophysical data, with three or more storage areas, roughly at 30 km (or deeper), 7-10 km, and 1-3 km. Moreover, the configuration of the distribution of the melts may change over time, and crystal-kinetic and some geophysical data suggest that in mafic volcanoes new connections and merging of melts from different environments may occur days prior to eruption, whereas large-scale amalgamation melts from multiple reservoirs to a much larger one can occur in years to decades in silicic eruptions from calderas. Yet, data from geophysical and petrological studies of several recent monogenetic dike-fed eruptions, show simpler magma plumbing configurations, with well-defined areas of isolated magma storage and connections between them near-real time, from which magmas of different compositions are erupted. In this presentation we will review the data on magma plumbing structure and dynamics from different datasets and discuss how could progress be made for their use in mitigation of volcano hazards.

How to cite: Costa, F. and Metaxian, J.-P.: Transcrustal, interconnected, or isolated magma reservoirs, can we tell the difference?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10207, https://doi.org/10.5194/egusphere-egu24-10207, 2024.

The Qinling Orogen, as the most prominent mountain belt in the central part of China, has experienced multiple tectonic-magmatic thermal events. Abundant granitoids were developed in response to the tectonic regime transformation during Mesozoic. These granitoids serve as valuable indicators to reflect the process and dynamic mechanism of the orogeny, as their growth process hold important structural information about the tectonic evolution. Although some geochronological and geochemical data exist from this region, it lacks systematic and sufficient tectonomagmatic information to develop a regionally coherent and viable geodynamic model for the Mesozoic magmatic evolution of the Qinling Orogen.

This study strategically focuses on the Mesozoic Taibai pluton in the Qinling Orogen, aiming to investigate the relationship between tectonics and magmatism and their variation in time and space during Mesozoic. Through multiscale structural analysis and geochronology methods, we have delineated three deformation phases, with representative rock samples reflecting mid-high temperature deformation conditions, evident in both microscopic observations and EBSD analysis, The quartz’s dynamic recrystallization and c-axis fabric analysis revealed that the Houzhenzi Shear Zone (HSZ, south of the Taibai pluton) experienced deformation under green-schist facies conditions at ∼400–550 °C. The results of Anisotropy of Magnetic Susceptibility indicate that the HSZ deformed in response to pure shear-dominated transpression and top-to-NW shear sense, exhibiting two superimposed phases of shear deformation. Together with previously published data, our results concluded the relationship between the Taibai pluton and the structural features of shear zones. The research indicates that the Qinling Orogen was dominated by compressional tectonics during the Late Mesozoic, Taibai pluton was obliquely extruded under the influence of surrounding shear zones. This research contributes to a more comprehensive understanding of the complex processes involved in continental tectonics and magmatic evolution. This work was financially supported by NSFC projects (grants 4217020371, 4180020120).

How to cite: Yan, S., Li, Y., Tao, W., Liu, Y., and Liu, F.: Structural Study of the Taibai Pluton in the Qinling Orogen, Central China: Implications for Relationship between Tectonics and Granite Magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10396, https://doi.org/10.5194/egusphere-egu24-10396, 2024.

EGU24-10782 | ECS | Posters on site | GMPV7.2

Complex magma flow dynamics within fossil dykes: linking multi-method observations across scales from the Reyðarfjörður dyke swarm, eastern Iceland. 

Stefano Urbani, Janine Kavanagh, Tegan Havard, Dawid Rybak, Katharine Gilchrist, Simon Martin, Andrew Biggin, Elisabetta Mariani, and Steffi Burchardt

Since dykes represent the main mechanism for magma movement from the Earth’s crust to the surface, understanding how they generate a path to feed an eruption is crucial for volcanic hazard assessment. To this purpose, key information can be obtained by studying fossil dykes in extinct and eroded volcanic systems where dykes show a variety of shapes, segmentation, and propagation paths due to a suite of pre-, syn- and post-emplacement physical processes (e.g. heat transfer, host rock layering, local stress variations).

To discern the factors that control these complex geometries and reveal how they affect the dynamics of magma transport, we used a multi-method approach on a N-S trending fossil dyke from the Reyðarfjörður dyke swarm (eastern Iceland). We collected meso-scale geometric data from drone photogrammetry, and rock magnetic, petrographic and microstructural laboratory analyses were conducted on oriented rock cores and samples to reveal microscopic magma flow indicators (e.g., magnetic fabrics and crystal alignment). Rock cores were sampled both across the thickness and along the breadth of the dyke segments, also recording the core position relative to different cooling surfaces (i.e. from the dyke margin to its interior).

The studied dyke is exposed for ˜900 m across its breadth in ˜300 m height. It comprises several segments showing different shapes (from straight to curved paths), thickness (spanning from 0.5 to 5 m) and linkage pattern (i.e. connected or not connected segments). The photogrammetry and geological field observations show the curved segments are more frequent in the shallower and thicker portions of the dyke, whereas the amount of offset, overlap and spacing between the segments is higher in the shallower portions of the dyke exposure. Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM) were used to identify magnetic fabrics that may be related to magma flow in the rock cores. These results show that the magnetic data record complex magma flow dynamics spanning from sub-horizontal to subvertical along the dyke path, which is inferred for adjacent connected segments and from the dyke margin to its interior.

We relate the geometrical variability of the dyke segments to the far-field stress (controlled by regional extension) versus the near- field stress (controlled by local magma overpressure), the latter being dominant in the shallower (and thicker) portions of the dyke. This generates a mixed mode fracturing during dyke propagation, reflecting its geometrical variability, that also controls a complex magma flow pattern within the dyke. Microstructure analysis is in progress and it is expected to complement magnetic fabric analysis and fieldwork in the interpretation of magma flow dynamics. Current results already show that a multimethod approach aimed at linking observations from the mesoscale to the microscale is required to better capture small scale and complex propagation paths and magma flow patterns providing more reliable insights on dyke propagation.

How to cite: Urbani, S., Kavanagh, J., Havard, T., Rybak, D., Gilchrist, K., Martin, S., Biggin, A., Mariani, E., and Burchardt, S.: Complex magma flow dynamics within fossil dykes: linking multi-method observations across scales from the Reyðarfjörður dyke swarm, eastern Iceland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10782, https://doi.org/10.5194/egusphere-egu24-10782, 2024.

Dikes supply magma to most volcanic eruptions. Understanding under what conditions propagating dikes reach the surface to erupt or, alternatively, become arrested (stop their propagation) or deflected so as to propagate primarily laterally or change into sills, is thus one of the fundamental tasks of volcanology. Many dike segments injected from magma sources do not reach the surface to feed volcanic eruptions. Instead, the dike segments become arrested, commonly at or close to contacts between mechanically dissimilar layers/units, at various crustal depths. This means that many and perhaps most volcanic unrest periods with dike injections do not result in eruptions. There are several conditions in the crust that make dike arrest likely, but the main one is layering where the layers have contrasting mechanical properties. Such layering means that local stresses are heterogeneous and anisotropic and thus in some layers unfavourable (e.g., because the layers act as stress barriers) for vertical dike propagation, resulting in dike arrest, lateral dike propagation beneath the stress barrier, or dike deflection into a sill. Here I show that once a dike has formed, its very existence tends to make the local stress field along the dike homogeneous (with invariable orientation of principal stresses) and favourable (with dike-parallel orientation of the maximum compressive principal stress) for later dike injections. This means that a later-injected dike may use an earlier-injected dike as a path, either along the margin or the centre of the earlier dike, thereby generating a multiple dike. Because earlier feeder-dikes form potential paths for later-injected dikes to the surface, many volcanic eruptions are fed by multiple dikes. Multiple dikes thus tend to favour dike propagation to the surface, thereby facilitating dike-fed eruptions. Examples of multiple-dike-fed eruptions include recent ones in Etna (Italy) and Kilauea (Hawaii), as well as in the Icelandic volcanoes Krafla and Hekla. Here, however, the focus is on several eruptions in the past few years on the Reykjanes Peninsula, Iceland. In particular, I discuss the eruptions of 2021, 2022, and 2023 in the volcano Fagradalsfjall as well as the 2023 eruption along the volcanic fissure Sundhnukar (close to the town of Grindavik), all the eruptions occurring on the Reykjanes Peninsula.

Gudmundsson, A., 2022. The propagation paths of fluid-driven fractures in layered and faulted rocks. Geological Magazine, 159, 1978-2001.

Gudmundsson, A., 2023. Multiple dikes make eruptions easy. EarthArXiv, https://doi.org/10.31223/X5M67Q

 

How to cite: Gudmundsson, A.: How multiple dikes facilitate volcanic eruptions, with application to recent events on the Reykjanes Peninsula, Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12898, https://doi.org/10.5194/egusphere-egu24-12898, 2024.

EGU24-13447 | Posters on site | GMPV7.2

Advances in Igneous Petrology: Coupled chemical maps & thermodynamic models to tackle mushes crystallization dynamics 

Lydéric France, Aurore Toussaint, and Valentine Charvet

The assemblage and evolution in time through various differentiation processes of igneous reservoirs shapes magmatism expressions at depth and at surface. Our knowledge of those systems largely relies on theoretical or applied thermomechanical and kinetic models, on geophysical data from active systems, and on structural and petrological data from active and fossil systems. Petrological approaches commonly use textures, thermodynamic models, chemical compositions of major and trace elements to decipher on the dynamics of complex igneous processes. Although chemical maps are more and more common, the overwhelming of the published data reposes on punctual measurements.

Here by using the example of a basalt crystallizing from liquidus to solidus in closed system, we present a new petrological approach that couples chemical maps to thermodynamic models to provide the first maps of thermodynamic parameters with a value attributed to each pixel (e.g., temperature or melt fraction maps in plutonic rocks). If the cooling rate is quantified by other means (e.g., diffusion chronometry), then the first of its kind movies of the crystallization evolution can be built from the first crystal to form to the last melt drop crystallization. We will present such results, allowing the igneous petrologist to explore their data in a new perspective. As an example the studied samples could be observed at various stages of the crystallization path highlighting a heterogeneous interstitial melt spatial distribution during magma solidification. This result has potentially important implications on melt segregation at the scale of the igneous reservoir. The presented results highlight that such a heterogeneous melt distribution was already present at the magma/mush transition. Additional simplified numerical crystallization models suggest that this heterogeneous a melt distribution is related to an early heterogeneous nucleation process, and may be common in volcanic and igneous plumbing systems.

Overall, this new approach will eventually help to make progress in our understanding of igneous systems.

How to cite: France, L., Toussaint, A., and Charvet, V.: Advances in Igneous Petrology: Coupled chemical maps & thermodynamic models to tackle mushes crystallization dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13447, https://doi.org/10.5194/egusphere-egu24-13447, 2024.

EGU24-14370 | Orals | GMPV7.2

Magmatic Structure and Melt Storage beneath the Katmai Volcanic Group, Alaska 

Graham Hill, Paul Bedrosian, Bethany Burton, Jade Crosbie, Bennett Hoogenboom, Michael Mitchell, Jared Peacock, and Erin Wallin

The Katmai volcanic group (KVG) within the Alaskan Aleutian arc is an unusually dense group of active volcanic centres (Mounts Martin, Mageik, Trident, Katmai, Griggs, Snowy, and Novarupta). The KVG was the locus of the largest eruption of the 20th century. During the 1912 eruption, rhyolite was erupted from a new vent (Novarupta) contemporaneous with the collapse of nearby Mount Katmai (10 km away). A hydraulic connection has been hypothesized between the two vents based on the above observation and on a small volume of juvenile andesitic magma with the geochemical signature of Mount Katmai that erupted from Novarupta at the onset of the three-day eruption. Unanswered questions about the structure and dynamics of the KVG include the origin and storage zone for the 1912 erupted rhyolite, its connection (if any) to the dense group of andesitic stratovolcanoes surrounding the Novarupta vent, the cause for off-arc centres such as Mount Griggs, and the reason for enhanced magmatic flux beneath the KVG relative to other segments of the arc. Our recent wideband (1 kHz – 1 mHz) magnetotelluric survey of the region encompasses the entire Katmai group of volcanoes (110 sites) and is bisected by an arc-perpendicular profile crossing the Alaska Peninsula (18 sites) and spanning subducting slab depths of 60-200 km. Coast effects are present in the magnetotelluric data; however, qualitative analysis of the data indicates the Jurassic sedimentary section upon which the arc is built, the highly resistive arc itself, and a swath of elevated conductivity beneath the arc axis that likely reflects melt storage. 3D inversion of the data is ongoing.

How to cite: Hill, G., Bedrosian, P., Burton, B., Crosbie, J., Hoogenboom, B., Mitchell, M., Peacock, J., and Wallin, E.: Magmatic Structure and Melt Storage beneath the Katmai Volcanic Group, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14370, https://doi.org/10.5194/egusphere-egu24-14370, 2024.

EGU24-14687 | ECS | Posters on site | GMPV7.2

The geochemical evolution of an extreme rejuvenated lava: A case study on Aitutaki of the Cook-Austral island chain   

Angus Rogers, Oliver Nebel, Hugh O'Neill, Greg Yaxley, Yona Nebel-Jacobsen, and Xueying Wang

Aitutaki is a basaltic Ocean Island in the South-Central Pacific Ocean, a region densely populated with age-progressive islands and seamounts considered to be a result of three or more overlapping mantle plumes. Recent (~1.9 Ma) volcanic activity at Aitutaki is difficult to reconcile with direct melting of a mantle plume, and may instead be an example of rejuvenation, whereby volcanism reappears after an extended hiatus. We have analysed samples of 21 lavas collected from Aitutaki for whole-rock major and trace elements and radiogenic isotopes, with electron probe microanalysis (EPMA) of olivine crystals and xenocrysts. Whole-rock MgO in these samples ranges from 10.3 to 13.9 wt. %. Petrographic examination and EPMA data indicate olivine accumulation is not the cause of these high values. Evidently, very little fractionation occurred during melt ascent through the volcanic plumbing network. Direct eruption of high-MgO (>10 wt.%) primitive magma is unusual in Ocean Island basalts, except among rejuvenated volcanics.

Our radiogenic isotope data closely overlap in Pb-isotope space with the nearby Samoan rejuvenated lavas from Savai’i and Tutuila, and otherwise have an EM1-FOZO signature. The major elements, trace elements and radiogenic isotopes all distinguish two populations of lavas, indicating the lavas are sourced from different regions or source materials in the asthenosphere. By analysing the spatial distribution of these chemical anomalies on the island, we observe the least evolved and most trace-element enriched samples (lowest SiO2, highest Th/Y) concentrate in geographically distinct regions on the island. Without a geochemical continuum between these two populations, we suggest the surface distribution of the enriched and depleted lavas may reflect spatial isolation of the mantle sources. Aitutaki produced multiple pulses of geochemically diverse lavas with extreme compositions throughout a short-lived (~50 ka) rejuvenated eruption cycle, exemplifying the processes responsible for producing rejuvenated lavas and challenging our understanding of the petrogenesis of such volcanism.

How to cite: Rogers, A., Nebel, O., O'Neill, H., Yaxley, G., Nebel-Jacobsen, Y., and Wang, X.: The geochemical evolution of an extreme rejuvenated lava: A case study on Aitutaki of the Cook-Austral island chain  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14687, https://doi.org/10.5194/egusphere-egu24-14687, 2024.

EGU24-15239 | Orals | GMPV7.2

Modelling multi-phase flows in magmatic systems 

Tobias Keller

Magmatic systems in the Earth's mantle and crust range from melt-poor partially molten rock, to mush bodies at intermediate melt fractions, and lenses of melt-rich, eruptible magma suspensions. Previous process-based models, however, have represented magmatic systems as either porous flows at low melt fractions (<20%) or suspension flows at high melt fractions (>60%). A lack of theoretical basis to represent mush flows at intermediate phase fractions has thus far hindered investigations into the dynamics of crustal mush bodies. Previous theories were formulated specifically for two-phase flows of melt-solid mixtures, hence not allowing for the inclusion of a third, volatile or other fluid phase. My contribution addresses this gap by presenting a comprehensive theoretical model [1] of magmatic multi-phase flows across all phase fractions at the system scale, rooted in mixture theory. I substantiate its applicability with a numerical implementation utilising a finite-difference staggered-grid approach [2]. 

 

Numerical experiments replicate expected behaviours for two-phase flows including rank-ordered porosity wave trains in 1D, and porosity wave breakup in 2D in the porous flow regime, as well as particle concentration waves in 1D, and mixture convection in 2D in the suspension flow regime. In the mush regime, numerical experiments show strong melt localisation into lenses and stress-aligned melt-shear bands. A further application to a three-phase flow problem of immiscible melt segregation from a crystallising magma body demonstrates the versatility of the theoretical model and its numerical implementation. The model code is available open source at github.com/kellertobs/pantarhei.

 

References

[1] Keller & Suckale, GJI, 2019. https://doi.org/10.1093/gji/ggz287.

[2] Wong & Keller, GJI, 2022. https://doi.org/10.1093/gji/ggac481.

How to cite: Keller, T.: Modelling multi-phase flows in magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15239, https://doi.org/10.5194/egusphere-egu24-15239, 2024.

EGU24-16269 | Orals | GMPV7.2

Direct coupling of petrological and thermo-kinematic modelling: application to magmatic chambers 

Nicolas Riel, Boris Kaus, Hendrik Ranocha, Pascal Aellig, and Eleanor Green

Understanding how magmatic systems work is of interest to a wide range of Earth Scientists. One of the key components when studying magmatic systems is the ability to predict stable mineral assemblage. These predictions allow retrieving critical information such as mineral stability, fraction and composition of melt.

However, the dynamic evolution of magmatic chambers, including the cycling between magmatic recharge and extraction in and out of the reservoir, imply that compositions of crystals and melts are constantly evolving. Hence, the use of phase equilibrium parameterization or look-up-tables of fixed bulk-rock composition is inappropriate to predict the dynamic chemical evolution of magmatic systems, and we instead need methods that can take the evolving chemistry into account.

Here, we present an updated version of our in-house Gibbs energy minimization package, MAGEMin [1,2]. MAGEMin is ideally suited so simulate the chemical evolution of magmatic systems by incorporating a range of recently developed thermodynamic melting models suitable to simulate both melting of magmatic arcs and of pelitic crustal rocks. Through its Julia wrapper, MAGEMin_C, it is particularly easy to perform (parallel) pointwise computations, and couple it with other thermal or thermomechanical codes.

We have made several additions to MAGEMin which include a) adding more thermodynamic databases, b) developing a new web-based graphical user interface, MAGEMin_app, which simplifies creating publishable phase diagrams and c) coupling MAGEMin with dynamic codes.

The ability to couple MAGEMin with other codes is demonstrated by linking it with the MagmaThermoKinematics.jl Julia package [4,5] that simulates the thermal evolution of magmatic systems following the intrusion of dikes and sills, in 2D, 2D axisymmetric and 3D geometries. For this to be efficient, we develop a new system in which we dynamically create a database of pre-computed points as a function of pressure, temperature and chemistry that is updated on the fly. This allows simulating the evolving chemistry of a crustal-scale mush system.

 

[1] Riel, N., Kaus, B.J.P., Green, E.C.R., Berlie, N., 2022. MAGEMin, an Efficient Gibbs Energy Minimizer: Application to Igneous Systems. Geochem Geophys Geosyst 23. https://doi.org/10.1029/2022GC010427

[2] https://github.com/ComputationalThermodynamics/MAGEMin

[3] https://github.com/ComputationalThermodynamics/MAGEMin_C.jl

[4] Schmitt, A.K., Sliwinski, J., Caricchi, L., Bachmann, O., Riel, N., Kaus, B.J.P., de Léon, A.C., Cornet, J., Friedrichs, B., Lovera, O., Sheldrake, T., Weber, G., n.d. Zircon age spectra to quantify magma evolution. Geosphere 19. https://doi.org/10.1130/GES02563.1

[5] https://github.com/boriskaus/MagmaThermoKinematics.jl

How to cite: Riel, N., Kaus, B., Ranocha, H., Aellig, P., and Green, E.: Direct coupling of petrological and thermo-kinematic modelling: application to magmatic chambers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16269, https://doi.org/10.5194/egusphere-egu24-16269, 2024.

Carbonatite deposits are rare magmas which represent the primary source of Rare Earth Elements (REE) on Earth; those are often associated with alkaline silicate magmas. A unique opportunity to investigate the natural carbonatite system exists through the study of the only active extrusive carbonatite volcano on Earth, the Oldoinyo Lengai (Tanzania). It has been proposed that carbonatites could be produced by low-degree partial melting of upper mantle domains associated with protracted differentiation that eventually form phonolite together with immiscible carbonatite melts. In such a model, the primitive magmas are proposed to be melilitites or Mg-nephelinite. However, a comprehensive study of the crystallization and immiscibility processes related to those parental melts is still missing.

In this study, we performed equilibrium and fractional crystallization experiments in order to understand the differentiation behaviour of carbonatites' parental magmas at high-pressure, and to decipher on the role of both melilitites or Mg-nephelinite in carbonatite genesis. Volatiles were introduced to both melilitite and Mg-nephelinite starting compositions, and the initial volatile contents (1.2 wt.% of H2O and 0.6 wt.% of CO2) were referred to the previous melt inclusion study by Mourey et al. (2023). The conditions of the first fractional crystallization experiments were established to be just below the liquidus temperature of each composition, i.e., for melilitite = 1250 °C and for Mg-nephelinite = 1200 °C and the subsequent experiments are performed by decreasing the temperature by 15 to 30 °C in each step. At each step, the melt composition in equilibrium with crystallized minerals is determined using an electron microprobe and, mass balance calculations for volatiles. All the experiments were performed at a nominal pressure of 1 GPa (relevant for lower crustal conditions in the Oldoinyo Lengai system), using a piston-cylinder apparatus. A double capsule setup made of AuPd was used to avoid iron and volatile losses during the experiments.

Equilibrium crystallization has not been able to produce phonolite magmas, the evolved term that is observed in the natural system in equilibrium with immiscible alkaline carbonatites. The fractional crystallization experiments of Mg-nephelinite composition highlight an evolution towards the alkaline-rich phonolites after 60% of fractionation, while the evolution of melilitite experiments seems to follow chemical trends that are not consistent with the natural liquid line of descent. The alkaline silicate melt remains abundant in all the fractional crystallization experiments (>65%), which facilitates an efficient equilibrium with silicate minerals and oxides, such as olivine, spinel, clinopyroxene, magnetite, perovskite, phlogopite, melilite and garnet. Mineral assemblages present along the liquid line of descent are consistent with the natural record that has been documented at Oldoinyo Lengai by cognate plutonic samples. Experiments are still ongoing to explore the potential occurrence of carbonatite-silicate melt immiscibility at later stages of the crystallization sequence.

How to cite: Abeykoon, S., France, L., Condamine, P., and Dalou, C.: Fractional crystallization of melilitite and Mg-nephelinite at 1 GPa: An experimental study on the petrogenesis of phonolite and related immiscible carbonatite magmas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18599, https://doi.org/10.5194/egusphere-egu24-18599, 2024.

EGU24-20364 | ECS | Posters on site | GMPV7.2

Plutonic formation through sills stacking and amalgamation: The case of Beauvoir rare-metal granite 

Nicolas Esteves, Lyderic France, Pierre Bouilhol, and Michel Cuney

To better constrain the assembly, evolution and magmatic differentiation associated kinematics of granitic intrusions, we took advantage of a 1 km long drilled core of the Echassières-Beauvoir rare metal granite, allowing a high resolution sampling of a fully recovered plutonic body. Structural and textural data, coupled with high-resolution major and trace element composition of the mineral phases (in-situ measurements and chemical map), provide constraints on the differentiation processes and its dynamics. As Li-mica (lepidolite) is a liquidus phase present all along melt evolution, their compositions allow tracking melt batches and their differentiation state. We show that the granite formed through the stacking of deca- to hectometric crystal-poor sills, defining different sub-units within the granite. As each sub-units are compositionally different, the detailed study of mineral composition provides a dynamic record of the pluton assembly: although globally constructed from bottom to top, sill emplacement can also occur through off-sequence intrusion within or beneath partly crystallized sub-units. Those sub-units seem to be the result of the amalgamation of smaller sills; the latter displaying similar mineral composition from one to the other.

Once intruded these sills crystallize an assemblage of quartz-topaz-mica and alkali-feldspar, recording differentiation trends from core to rim. This differentiation leads to the formation of a quartz-rich mush and associated albite-saturated interstitial residual melts enriched in incompatible elements (e.g. Li, F, P). A part of these residual melts has been extracted from the quartz-rich mush under the form of differentiated magma channels. Now fully crystallized, those channels correspond to albite-rich segregates, forming lobate contacts with the surrounding granite. Locally, these albite-rich segregates are accumulated beneath the overlying subsequently intruded sill, indicating a protracted plutonic construction faster than the solidification of a single sill. Ultimately, the protracted differentiation of the last and upper sub-unit (≈130 m thick) has led to the accumulation of weakly-viscous evolved melt in the upper-part of magmatic reservoir. This newly formed liquid-rich lens could then be mobilized as erupted silica-rich magma, potentially corresponding to rhyolitic intruding the surrounding host-rocks.

How to cite: Esteves, N., France, L., Bouilhol, P., and Cuney, M.: Plutonic formation through sills stacking and amalgamation: The case of Beauvoir rare-metal granite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20364, https://doi.org/10.5194/egusphere-egu24-20364, 2024.

Mid-oceanic ridge basalts (MORBs) are frequently grouped as depleted (D-MORBs), normal (N-MORBs), or enriched (E-MORBs) based on the abundances of highly incompatible elements. E-MORBs, characterized by enriched in incompatible elements, were first noted near mantle plumes, so that enrichment of highly incompatible elements was initially understood as a result of infiltration of plume-related melts into the MORB plumbing system. But for E-MORBs far from plumes, it is still controversial of the lithology of enriched components of these E-MORBs. Two major explanations are proposed that the enriched components are generated by the melting of entrained recycled crust (pyroxenite) beneath ridges or by the melting of refertilized peridotites from subducted slabs. The reason for this problem is that melting of the ambient refractory peridotite along with the enriched component will dilute the signals recorded in MORB. Therefore, the in-situ analyses of minerals and/or melt inclusions will shed new light on this question.

Here high-precision in-situ analyses were conducted on olivine and plagioclase in the studied samples. According to the major and minor element contents of olivine phenocrysts, we found they have similar Ni, Mn and Ni/(Mg/Fe) contents with those from N-MORB at a given Fo, indicating a peridotitic source. Furthermore, in-situ Sr isotope in plagioclase phenocrysts and in-situ Pb isotope of plagioclase-hosted melt inclusions are also reported to constrain origin of parental magma. The isotopic results show that unlike the uniform whole-rock 87Sr/ 86Sr and 206Pb/204Pb ratios, the plagioclase phenocrysts record highly Sr and Pb isotopic heterogeneity. Strontium isotopic heterogeneity is observed between crystals even in a single thin section. Based on the high An contents of plagioclase phenocrysts and chemical disequilibrium between plagioclase phenocrysts and groundmass, we propose they crystallized early in the magma chamber and were most likely formed in different batches of mantle-derived melts. The enrichment of LREE and negative correlations between La/Sm and Pb isotopes melt inclusions, suggest that ancient continent lithosphere materials are likely present in the sub-ridge mantle of the east of the Melville FZ, SWIR. Collectively, we proposed that the continent lithosphere materials were slabbed into the upper mantle under MOR as refertilized peridotites.

How to cite: Li, J., Chen, L., and Dong, Y.-H.: Constraints on the mantle lithology of enriched components: evidence from E-MORB of Southwest Indian Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21561, https://doi.org/10.5194/egusphere-egu24-21561, 2024.

EGU24-21736 | ECS | Posters on site | GMPV7.2

Fe-valence in magmatic clinopyroxene and the redox state of oceanic basalts – perspectives from natural samples and experiments 

Alex G Stewart, Margaret E Hartley, Rhian H Jones, Jon W Fellowes, and David A Neave

The redox state of magmatic systems controls important physico-chemical properties and processes on the Earth, such as the composition of volcanic gases, the rheology of magma, and the transport and deposition of critical metals. In natural silicate magma, Fe is the most abundant multivalent element, and the redox state of the system can be determined if the relationship between Fe valence and fO2 is known. Popular oxybarometers (e.g., Fe3+/FeT in glass or Fe-Ti oxide pairs) can accurately determine the redox state of magmatic systems but suffer limitations such as beam damage during analysis or the requirement of specific phases to be present.

Clinopyroxene is a common igneous mineral that plays a key role in chemical cycling on Earth and is found in igneous rocks ranging from near-primary basalts to rhyolites. Clinopyroxene can incorporate both Fe2+ and Fe3+ and may capture a record of magmatic redox state upon crystallisation. However, attempts to quantify how Fe valence varies in clinopyroxene as a function of redox state are limited, partly due to the inability to routinely measure Fe valence using electron probe microanalysis (EPMA).

To remedy this, we are exploring the utility of the “flank method” [1] and conventional stoichiometric estimates for determining Fe valence using EPMA. Using a suite of Mössbauer calibrated clinopyroxene standards, preliminary “flank method” analyses demonstrate that the FeO content of clinopyroxenes ranging from diopside (FeOT = 3 wt%) to aegirine (FeOT = 28 wt%) can be determined with a RMSE of 0.03 wt%. Additional standards with FeOT from 2 – 10 wt% are being collated to improve the performance of this method when applied to augitic clinopyroxene. Furthermore, it is possible to obtain 3σ uncertainties on Fe3+/FeT of 3-7% using conventional stoichiometric estimates if EPMA analyses are sufficiently precise [2].

Using high-precision EPMA and stoichiometric estimates of Fe3+, we demonstrate that clinopyroxene crystals in oceanic basalts from the Reykjanes Ridge, Iceland and the Canary Islands have Fe3+/FeT of 0.1 – 0.7. Olivine-glass and olivine-spinel pairs constrain the redox state of these oceanic basalts to be equivalent to FMQ, FMQ+1.5 and FMQ+2, respectively, in line with independent estimates from the literature. The partitioning of Fe3+ between clinopyroxene and melt (KD Fe3+cpx-melt) ranges from 0.50 – 1.4 in tholeiitic to alkali basalts, and we show that clinopyroxene Fe3+/FeT increases concomitantly with estimates of redox state.

However, there is currently limited experimental data in which Fe3+ has been measured with sufficient accuracy or precision to fully understand the controls on Fe3+ partitioning in basaltic systems, precluding the use of clinopyroxene as a probe for magmatic redox at present. An experimental campaign is currently underway to help refine models of Fe3+ partitioning, ultimately contributing to the development of a clinopyroxene based Fe-oxybarometer, and to shed light on the poorly defined role of Fe3+ in the chemical evolution of basaltic magmatic systems.

 

[1] Hofer & Brey, 2007. Am Min, 92, pp.873-885.

[2] Neave et al., 2024. CMP, 179, 5. doi: 10.1007/s00410-023-02080-2

How to cite: Stewart, A. G., Hartley, M. E., Jones, R. H., Fellowes, J. W., and Neave, D. A.: Fe-valence in magmatic clinopyroxene and the redox state of oceanic basalts – perspectives from natural samples and experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21736, https://doi.org/10.5194/egusphere-egu24-21736, 2024.

TS6 – Geochronology and rates of tectonic processes

EGU24-447 | ECS | Orals | TS6.2

Tectonic and exhumation history of the Albanian Dinarides orogenic belt 

Francesca Rossetti, Maria Giuditta Fellin, Paolo Ballato, Claudio Faccenna, Maria Laura Balestrieri, Bardhyl Muceku, Cercis Durmishi, Silvia Crosetto, and Chiara Bazzucchi

The orogenic belt of the Albanian Dinarides in the central-eastern Mediterranean results from the eastward subduction of the Adriatic microplate beneath Eurasia since the Early Cretaceous. The belt exhibits compression in the west, at the front of the wedge, and extension in the east, in the internal sector, and consist of NW-SE oriented geological domains that record a long and polyphasic evolution. In the Cretaceous, the obduction of Mid Jurassic ophiolite was followed by continental subduction that in the Eocene led to the development of a flexed foreland in the external Meso-Cenozoic platform-basin system. The progressive migration of the deformation is recorded in the westward decrease of the depositional age of syn-orogenic deposits. Tectono-stratigraphic evidence suggests the development of a W-verging fold-and-thrust belt emplaced along an evaporite decollement level, possibly from the Late Cretaceous in the internal domain to Early Miocene in the outermost unit. 
To investigate the evolution of the Albanian Dinarides, such as the timing of deformation and the spatiotemporal pattern of exhumation, structural geological, stratigraphic and thermochronological data have been integrated. Here we present our first apatite (U-Th)/He (AHe) and fission track (AFT) ages. 
Within the eastern, extensional domain, fully reset AHe ages from Permian granites range from 12 to 18 Ma. In the western units, where compressional deformation is dominant, AHe ages from Eocene to Early Miocene syn-orogenic sediments vary in space: to the east, they cluster in the range of 5 to 2.5 Ma, and to the west, they scatter over a large range older than 5 Ma. All AFT ages scatter between the Early Miocene and the Late Cretaceous.
Altogether the cooling ages show a large-scale pattern characterized by a broad zone of young ages with no clear relation to the southwestward propagation of the fold-and-thrust belt, suggesting a mechanism of reactivation of the system during the Late Miocene-Pliocene. These processes contribute to an amount of exhumation that likely does not exceed approximately 3 km. In this framework, future studies will be essential to integrate the available deep seismic information with surface data, in order to develop a model capable of identifying the mechanisms responsible for the exhumation processes of the Albanian Dinarides.

How to cite: Rossetti, F., Fellin, M. G., Ballato, P., Faccenna, C., Balestrieri, M. L., Muceku, B., Durmishi, C., Crosetto, S., and Bazzucchi, C.: Tectonic and exhumation history of the Albanian Dinarides orogenic belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-447, https://doi.org/10.5194/egusphere-egu24-447, 2024.

EGU24-610 | ECS | Orals | TS6.2

Geomorphological evidence for seismic hazard on the southern edge of the Zimbabwe craton: The Kruger-Malale scarp, South Africa.  

Anzani Ramagadane, Khumo Leseane, Beth Kahle, and Alastair Sloan

South Africa and its immediate surroundings are considered a stable continental region (SCR), characterized by minor seismicity and low strain rates on the order of 1x10 -9 yr -1. Such strain rates imply minimum recurrence intervals for major earthquakes of 10  - 100 Ka, or even longer. Consequently, the 50 - 70  year instrumental catalogues do not fully reflect the seismic risk potential of the region. Earthquakes in SCRs and slowly deforming regions can have large magnitudes, for example, the 2017 MW 6.5 Moiyabana earthquake in Botswana and the 2006 MW 7.0 Machaze earthquake in Mozambique, and occur in areas unprepared for large earthquakes. Given that such events occur infrequently, but appear to be widespread in the continents, it is important to understand the location, geological context and timing of such events and to assess where they may occur in the future. This can be addressed by investigating faults which show geomorphological evidence of neotectonic activity. We present an analysis of the Kruger-Malale scarp, located on the Bosbokspoort fault in the eastern Limpopo belt, South Africa. We applied stereophotogrammetry to aerial photographs from the Chief Directorate of the National Geo-Spatial Information (NGI) to generate a Digital Surface Model (DSM). Our results indicate that the Kruger-Malale scarp is a 55 km long composite scarp with an average cumulative throw of 9 m. We tentatively suggest that the most recent event had an average throw of 2 - 3 m. This structure has the potential to generate MW 7.1 - 7.5 earthquakes. In combination with the 2017 MW 6.5 Moiyabana earthquake in the western Limpopo belt, the Makgadikgadi Rifts in the Magondi belt, the Zambezi Rifts in the Zambezi belt, the Urema Rift in the Mozambique belt and the 2006 MW 7.0 Machaze earthquake in the Mozambique belt there is evidence for extensional deformation completely surrounding the Zimbabwe craton, which appears to behave as a rheologically strong block concentrating strain within the actively (albeit slowly) deforming mobile belts that surround it.

 

How to cite: Ramagadane, A., Leseane, K., Kahle, B., and Sloan, A.: Geomorphological evidence for seismic hazard on the southern edge of the Zimbabwe craton: The Kruger-Malale scarp, South Africa. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-610, https://doi.org/10.5194/egusphere-egu24-610, 2024.

EGU24-991 | ECS | Posters on site | TS6.2

Quantifying crustal thickening and surface uplift in the northernmost Central Andes 

Sebastián Marulanda, Mauricio Parra, Santiago Leon, Edward Sobel, and Johannes Glodny

Since its onset in the Late Cretaceous, episodic mountain building in the Central Andes has shaped the landscape, climate, and biota of western South America through a series of synchronous regional pulses of intensified deformation and surface uplift acting at the scale of the entire orogen. However, despite this common Late Mesozoic through Cenozoic tectonic history, the ~4000 km long Central Andes exhibit remarkable latitudinal differences in both height and width, pointing to the potential importance of local heterogeneities in controlling the magnitude of topographic growth associated with each of the regional mountain building episodes. A thorough understanding of the driving mechanisms behind these latitudinal differences requires first determining the times, rates, magnitudes and spatiotemporal patterns of crustal thickening and surface uplift along the orogen. While this has been done extensively in recent years for the southern and central portions of the Central Andes, such processes are still insufficiently constrained in its northernmost part.

In this work, we use new and published whole-rock geochemistry data from the Late Cretaceous to Late Miocene arc-related magmatism recorded in northernmost Peru to quantitatively estimate crustal thickening and surface uplift using empirically calibrated “chemical mohometers” based on the ratios of key trace elements. We compare our results with the tectonostratigraphic evolution and tectonic subsidence history of the adjacent foreland and hinterland basins. Finally, we present new apatite U-Th-Sm/He and apatite fission-track thermochronological data from a transect across the northernmost Central Andes. These data, integrated with structural observations and the reconstructed crustal thickening and surface uplift history, unravel the relative contribution of magmatism and shortening to the observed crustal thickening.

How to cite: Marulanda, S., Parra, M., Leon, S., Sobel, E., and Glodny, J.: Quantifying crustal thickening and surface uplift in the northernmost Central Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-991, https://doi.org/10.5194/egusphere-egu24-991, 2024.

The Kumaon Himalaya is one of the most seismically dynamic regions of the Central Seismic Gap (CSG), falling into Seismic Zone V along the Himalayan arc. The 21 km long NW-SE trending Kaladungi Anticline in Kumaon Himalaya is the topographic manifestation of an actively growing fault-bend fold formed in the hanging wall of the kaladungi fault (KF). It, a splay of the Himalayan Frontal thrust system, provides an excellent model of forward and lateral propagation of fault and associated folding in laterally opposite directions along the strike of the fault. It nucleates and extends in the northwest and southeast direction resulting in the diversion of the Dabka and Baur rivers respectively, leaving behind the signature of paleo-wind gaps through which these rivers streamed earlier during the recent past. The lateral propagation of Kaladungi Anticline resulted in the diversion of the Dabka River for about 10-12 km from east to west and this is justified by the existence of four Dabka River wind gaps DWG1, DWG2, DWG3 and DWG4. Similarly, the Baur River shifted for about 5-6 km from west to east leaving signatures of two Baur wind gaps BWG1 and BWG2. The existence of more than one windgap formed by the same river, however, is a strong validation of lateral propagation of fault and related folding. 

How to cite: Ansari, M. A., N. Malik, J., and Dhali, M.: Growth and Lateral Propagation of Fault-related folds in the Shiwalik of Kumaon Himalaya: Mechanism and Geomorphic signatures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1006, https://doi.org/10.5194/egusphere-egu24-1006, 2024.

EGU24-1177 | ECS | Orals | TS6.2

Detecting signals of active tectonics with geomorphological methods in the slowly deforming Val di Fine Basin, Northern Apennines – limits to the resolution? 

Lauretta Kaerger, Chiara Del Ventisette, Paola Vannucchi, Derek Boswell Keir, Carolina Pagli, Romano Clementucci, and Giancarlo Molli

Tectonic and surface processes leave fingerprints on the modern topography. Deciphering tectonic signals becomes especially challenging when mechanisms at different wavelength overlap (e.g. faulting, deep-seated uplift). Nowadays, classic approaches can be combined with new tools and datasets to explore the morpho-structural evolution along a wide range of tectonic settings.

The Val di Fine basin in the western side of the Tuscan Northern Apennines (Italy) is a slowly deforming area, generally assumed to be only of moderate to low seismic hazard. However, the 1846 ~M6 Orciano Pisano earthquake, responsible for significant destruction at the time, is strongly challenging this assumption. The event is presumed to have nucleated in the Val di Fine, however its source as well as precise location remain unclear and hence its seismological relevance.

To clarify this question, we performed a new geomorphological analysis based on a 10x10 m DSM incorporating qualitative and quantitive methods (e.g. slope map, stream network analysis, knickpoint calculation). We complimented this work by field work, focusing on ground truthing of the geomorphic results and fault mapping, as well as a seismogenic approach relocating the freely available INGV earthquake catalogue.

The results of the remote sensing analysis clearly show signs of several hundred meters uplift at the eastern side of the basin since the Pliocene as well as rather unspecific geomorphic features, raising new questions about the topographic development of the basin. The field data and seismogenic record clearly show signs of recent tectonic activity and uplift (newly mapped faults, seismites and small earthquake swarms) as well as clear indications that the basin likely features a more complex fault system then the N-S trending normal faults predominantly recorded in the region. However, these structures and possibly events seem to have left only very limited distinct detectable marks in the geomorphology. This decorrelation between the geomorphic results and field observations prompts the question why the tectono-geomorphic approach seems to be reaching its limit in this region.

Factors like intense human activity and a dense vegetation in the area surely increase the noise level however these are common factors to be accounted for using remote sensing data. The cumulative results for this region rather point towards a complex morpho-structural evolution, characterized by a large-wavelength uplift component with local faulting activity. This may induce a complex response in the topographic expression leading to an overblending of the transient uplift signals through mid- and long-term developments making them more challenging to be detected with the current geomorphological methods.

How to cite: Kaerger, L., Del Ventisette, C., Vannucchi, P., Boswell Keir, D., Pagli, C., Clementucci, R., and Molli, G.: Detecting signals of active tectonics with geomorphological methods in the slowly deforming Val di Fine Basin, Northern Apennines – limits to the resolution?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1177, https://doi.org/10.5194/egusphere-egu24-1177, 2024.

EGU24-1545 | Orals | TS6.2

Geothermochronological insights into the Sierra Nevada de Santa Marta: provenance and exhumation through U-Pb and Fission Track in zircon 

Airton N C Dias, Mauricio Parra, David Chew, Antonio S W Sales, and Vinicius Q Pereira

New geo-thermochronological data from modern sediments of the Sierra Nevada de Santa Marta (SNSM), a prominent mountain range along the Caribbean-South America plate margin in northern Colombia is presented. We applied U-Pb and Fission Track analyses in detrital zircon to document the provenance, exhumation, the cooling histories across high (900-850 ºC) and intermediate temperatures (320-180 ºC). The Zircon Fission Track (ZFT) results show Cenozoic ages, predominantly between 65-15 Ma. Populations between 55 and 80 Ma come from regions with intermediate elevations of the river basins. In general, this is in agreement with the ancient history of exhumation through the ~300 °C isotherm in SNSM. These same data can be observed in its extension to the south, in the Cordillera Central (CC) in Colombia.  The youngest population, up to 35 Ma that occurs in SNSM, corresponds to sediment collected from elevations lower than 900 m and documents the accentuated exhumation resulting from the dismemberment and translation of the SNSM. This can be associated with transtension by the oblique convergence of the Caribbean plate. U-Pb results include Mesoproterozoic (1000-1500 Ma), Carboniferous (300-350 Ma), Jurassic (200-150 Ma), Triassic (250-200 Ma) and Upper-Cretaceous (100-70 Ma) populations. These results show a correlation with the basement, which is well marked during the Neoproterozoic and Jurassic. A spatial analysis by inverse methods including detrital ages and the spatial distribution of lithostratigraphic units is being developed to understand the spatial distribution of current denudation and its controls.

How to cite: Dias, A. N. C., Parra, M., Chew, D., Sales, A. S. W., and Pereira, V. Q.: Geothermochronological insights into the Sierra Nevada de Santa Marta: provenance and exhumation through U-Pb and Fission Track in zircon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1545, https://doi.org/10.5194/egusphere-egu24-1545, 2024.

The uplift of the Tibetan Plateau is one of the most important geological events in Asia and is a natural laboratory for the study of continental dynamics. The Longxian-Baoji Fault Zone (LBFZ) is at the intersection of the northeast margin of the Tibetan Plateau, the southwest margin of the Ordos Block, and the Qinling Orogen. It is the leading edge of the northeastward extension of the Tibetan Plateau that was formed by the collision between the Indian and Eurasian plates. Since the late Cenozoic, the tectonic deformation of the LBFZ has been intense, and earthquakes have been repeated in history. To evaluate the relative tectonic activity within the LBFZ and discuss the influence of the northeastward expansion of the Tibetan Plateau on the geomorphological evolution of the LBFZ, this paper cambines field surveys, used remote sensing images, and extracted data of the Qianhe, Hengshuihe, and Jinlinghe River Basins based the ASTER GDEM, computed six geomorphic indices, including the hypsometric integral (HI), standardized stream length-gradient index (SL/K) and Hack profile, elongation ratio (Re), the drainage basin asymmetry factor (AF), valley floor width-to-height ratio (VF) and transverse topographic symmetry factor (T), and the index of relative active tectonics (IAT) was obtained. The following understandings are finally drawn: Various geomorphic indices indicate that the geomorphological response to the tectonic activity and relative uplift of the LBFZ include rivers with generally high SL/K values, drainage basins with relatively high HI and low Re (elongated) values, basins with different degrees of asymmetry (AF, T), and leading edges of mountains with low VF values. The LBFZ has experienced relatively high tectonic activity.The calculation results of the AF and T show that the regional tectonic tilt direction presents obvious zoning on both sides of the fault zone. On the TGF and the southwest side of the TGF (Longxi block), the drainage basin tilts to the east and southeast. These indicate that tectonic activity since the Cenozoic has influenced the evolution of the watershed in this area. The results of the IAT show that the tectonic activity of the LQF is the highest in the area, followed by that of the TGF; activity of the GGF is weak, and the activity of the QBF is the lowest. Correlation analysis between the IAT and the frequency and magnitude of earthquakes in the region shows that the frequency and magnitude of earthquakes are also higher . It shows that the IAT has a good correlation with the earthquake frequency and magnitude. At the same time, the areas with strong tectonic activity in the study area were delineated, which shows the distribution characteristics along the LQF and the TGF, and mainly the LQF. This will provide certain reference significance for earthquake risk assessment in Baoji. The northeastward expansion of the Tibetan Plateau affected the LBFZ region, and the stress brought about by it controlled the tectonic deformation in the region and also sculpted the modern landscape. 

Keywords: Geomorphic indices, Longxian–Baoji Fault Zone, Northeastern Tibetan Plateau, Southwest margin of Ordos, Tectonic activity

How to cite: Zhou, X., Huang, Q., Xu, S., and Liu, L.: Assessment of the relative tectonic activity of the Longxian–Baoji Fault Zone in the northeastern Tibetan Plateau based on geomorphic indices, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2551, https://doi.org/10.5194/egusphere-egu24-2551, 2024.

EGU24-3236 | Orals | TS6.2

Fossil earthquakes preserved on fossils: New examples 

Jih-Pai Lin, Chien-Chia Tseng, Chung-Pai Chang, and Chi-Wen Chen

The coastal plain of Miaoli is classified as part of the Outer Foothill of the Western Foothill in Taiwan. Around six million years ago, the initiation of the Penglai Orogeny set off significant tectonic activities in the Miaoli region, resulting in the formation of numerous faults and folds. These geological structures have played a concurrent role in influencing the occurrence and preservation of fossil echinoids in the area.

Unlike the commonly reported deformed fossils found in Mesozoic and older strata, this study documents new instances of deformed fossils from the Pleistocene strata in Taiwan. Through micro-CT tomographic imaging, the 3D geometry of fault planes in deformed sand dollars is revealed. Thin sections expose additional tectonic structures, including pressure solutions, box folds, and monoclines. Some deformations, both ductile and brittle, such as fractures along the taphonomically weak ossicle boundaries, may have originated from sedimentary processes. However, fault features triggered by earthquakes are unmistakably preserved in rare specimens.

Notably, a thorough analysis of earthquake epicenters in Miaoli since 1997 indicates that no earthquakes occurred in proximity to the fossil localities. Consequently, it is deduced that the deformed specimens are a result of ancient or fossilized earthquakes. This study presents novel and distinctive evidence contributing to the comprehension of neotectonics regarding the collision between the Philippine Sea Plate and Eurasia Plate in Taiwan, as inferred from fossils.

How to cite: Lin, J.-P., Tseng, C.-C., Chang, C.-P., and Chen, C.-W.: Fossil earthquakes preserved on fossils: New examples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3236, https://doi.org/10.5194/egusphere-egu24-3236, 2024.

EGU24-3286 | ECS | Posters on site | TS6.2

The role of dip-slip components in creating and maintaining a strike-slip landscape 

Yifei Li, Huiping Zhang, and Xudong Zhao

Stream-channel offsets are widely used for identifying strike-slip faults and estimating fault slip rates. Most strike-slip faults have the component of dip-slip motion. Here, we used a landscape evolution model to investigate the role of dip-slip in creating and maintaining stream-channel offsets in the strike-slip environment. Our results show that the length of stream-channel offsets is primarily controlled by the vertical slip rate difference (VSRD) between the above fault part and the below fault part. The average cumulative offsets of the stream channels are positively associated with VSRD and are negatively related to the strike-slip rates. The positive VSRD leads to underestimates of offsets by promoting stream capture while the negative VSRD may lead to overestimates of offsets by creating pre-existing offsets and shutter ridges which inhibits stream capture. Our results call for careful studies of surface processes when using stream-channel offsets to infer fault slip and estimate slip rates.

How to cite: Li, Y., Zhang, H., and Zhao, X.: The role of dip-slip components in creating and maintaining a strike-slip landscape, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3286, https://doi.org/10.5194/egusphere-egu24-3286, 2024.

EGU24-3416 | ECS | Posters on site | TS6.2

Re-visiting the dip-slip rate of the North Tehran Fault at the northern megacity of Tehran (Iran) using luminescence dating  

Maryam Heydari, Mohammad R. Ghassemi, Christoph Grützner, and Frank Preusser

The North Tehran Fault (NTF) is the most active tectonic structure crossing the northern fringe of the densely populated megacity of Tehran (Iran). It extends over 68 km and juxtaposes the southern piedmonts of the Central Alborz Mountains (volcanic rocks associated with the Karaj Formation) from the Neogene-Quaternary Tehran Alluvium. The NTF is an oblique-slip fault in which the left-lateral strike-slip faulting accompanies the dominant reverse motion.

The geomorphic features affected by the NTF’s activity appear to be limited and concealed during the past few decades due to the rapid northward expansion of the Tehran metropolitan area. Nevertheless, numerous evident fault outcrops, displaying stratigraphic offsets in various locations along the megacity, are still accessible.

This study selects two fault outcrops inside the city in the western segment of the NTF and a third one in the eastern termination of the NTF close to its junction with the Mosha Fault. These sites were already studied in previous works, however, no reliable geochronological data have been available so far for them. In the first two western sites, the Eocene Karaj Formation rocks were thrust over Quaternary alluvial-colluvial deposits. The subsidiary fault is almost parallel to the main NTF in the second site at Kan, which separates the old alluvial-colluvial deposits in the hanging wall from the younger deposits in the footwall. The third site is located close to the termination of the NTF in the Kond region. Here, remnants of Quaternary fluvial terraces are uplifted by the NTF and form elevated landforms identified in its hanging wall.

To estimate the dip-slip rate for the NTF, we applied luminescence dating to the alluvial-colluvial deposits and fluvial terraces to constrain the deposition time. By incorporating the measured vertical offset for each site, the dip-slip rates of the NTF were established at different locations.

How to cite: Heydari, M., Ghassemi, M. R., Grützner, C., and Preusser, F.: Re-visiting the dip-slip rate of the North Tehran Fault at the northern megacity of Tehran (Iran) using luminescence dating , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3416, https://doi.org/10.5194/egusphere-egu24-3416, 2024.

EGU24-6226 | ECS | Posters on site | TS6.2

A 60.000-year tectonic record: speleoseismology insights from a fault zone 

Uroš Novak and Stanka Šebela

Northwestern Dinarides is a region of slow tectonic deformation with rates of 2-4 mm/year. Active deformations are largely accommodated by thrusting and dextral strike-slip faulting. The region exhibits moderate to strong seismicity and swarming events. However, the absence of Quaternary sediments across majority of fault scarps does not allow paleoseismic trenching on active fault segments in order to reconstruct a paleoearthquake record of the area. Even so, Northwestern Dinarides are an analogue for karstic phenomena, such as caves and abundance of speleothem forms in them. Generating the region as an ideal testing ground for speleoseismology. The investigated site of Postojna Cave is a 24 km long cave system, located in SW Slovenia, crosscut by the right-lateral strike slip Dinaric fault system (NW-SE striking). The karstic massif in which the cave evolved is enclosed by two major regional active faults, Idrija, Predjama faults and a smaller, active, Selce fault. Postojna Cave presents a diverse array of speleothem formations, characterized by their various morphologies. Some of these formations exhibit signs of deformation or breakage, with certain instances suggesting possible alteration induced by tectonic and seismic activities.

The investigated speleothems are located in an expansive cave chamber, on a subvertical fault zone with a Dinaric strike. The researched fault had a TM extensometer installed more than 20 years ago, to measure tectonic displacements within the fault. In the years 2009-2010 and in 2014 it exhibited displacements (tectonic transients) coinciding with major regional seismicity. The synchronous displacements and the abundance of deformed speleothems within a singular fault zone is why the location was chosen within the cave for sampling. Speleothems were sampled with a diamond corer in an overall distance of 50 m, along the strike of the fault. Specifically, fractures healed with speleothem in flowstone that is located directly within the fault core zone and on the hanging wall of the fault. Additionally, a few of youngest growth speleothems on fractured columns bridging the hanging wall and the footwall were included.

U-Th geochronology was done on nine sampled deformed speleothems using MC-ICP-MS. The results revealed ages from approximately 55,000 years BP to too recent for analysis (<0.5 ky). Two notable clusters of ages were recognized, 22 and 6.5 ky BP. The majority of the dated speleothems coincide with ages derived from local paleoseismic trenching data, younger than thresholds of 12 ky BP and 8.4 ky BP. Covering the age of youngest deformations on the near Selce fault (12 ky BP) and Predjama fault (8.4 ky BP). The most recent speleothem sample could potential represent deformations attributed to earthquakes that occurred approximately or are younger than 1500 CE. The most plausible interpretation of the dated deformed speleothems suggests that the ages at 22 ky BP and 6.5 ky BP may signify distinct tectonic deformation events, possibly indicative of paleoearthquakes. However, it is important that all speleothems dated as younger than the most recent deformations along the Selce and Predjama faults could potentially represent seismic or aseismic tectonic deformations.

How to cite: Novak, U. and Šebela, S.: A 60.000-year tectonic record: speleoseismology insights from a fault zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6226, https://doi.org/10.5194/egusphere-egu24-6226, 2024.

EGU24-6673 | ECS | Posters on site | TS6.2

Drainage base-level fall history in North-western Apennines and implications on the Alessandria Basin tectonic activity 

Victor Buleo Tebar, Mauro Bonasera, Simone Racano, and Giandomenico Fubelli

Drainage networks are particularly sensitive systems among all the topographic features in terms of their response to perturbations driven by active tectonics. Indeed, fluvial landscapes can record several information about different processes especially in geodynamically active areas, allowing to relate spatial-temporal variation in base-level fall and vertical incision of stream channels with certain morphometric features. This study focuses on the tectonic evolution of the Alessandria Basin, a syn-orogenic tectonic basin located at the junction between the Alps and the Apennines, that experienced progressive subsidence during the overthrusting of the Monferrato Arc (the westernmost outer arc of the Apennine belt) onto the Po Foreland Basin. Different studies carried out in this region have assessed the Neogene tectonic evolution at a regional scale, although Quaternary activity is still poorly understood in terms of both Alps/Apennines uplift and activity of the compressive front of the Monferrato Arc. In this study, we applied river linear inversions to reconstruct the baselevel-fall history of 6 catchments that drain into the Alessandria Basin. We used 9 10Be-derived basin-average denudation rates to calculate the erodibility parameter needed for inferring base-level fall rates from previously chi-transformed river profiles. The results describe the last ~ 3 Ma of tectonic activity, highlighting increases in baselevel-fall rate with an initial peak around 3 Ma, and a second around 2 Ma. While the first peak is coeval with the vertical uplift that affected most of the northern-central Apennine, the second one suggests an acceleration in subsidence of the Alessandria Basin concurrently with the uplift of the Monferrato Arc.

How to cite: Buleo Tebar, V., Bonasera, M., Racano, S., and Fubelli, G.: Drainage base-level fall history in North-western Apennines and implications on the Alessandria Basin tectonic activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6673, https://doi.org/10.5194/egusphere-egu24-6673, 2024.

EGU24-6996 | Posters on site | TS6.2

Exploring Structural Activity Through Gravel Rock Fracture Characteristics: A Case Study of the Milun Fault in Hualien, Taiwan 

Yi-Chun Hsu, Chung-Pai Chang, Shao-Yi Huang, Chun-Chin Wang, and Jiun-Yee Yen

Hualien City in Taiwan is situated in the northernmost segment of the Longitudinal Valley, transitioning from the subduction of the Philippine Sea Plate to a collision environment. It is one of the most seismically active regions in Taiwan. The Milun Fault, a significant active fault, traverses through the urban area of Hualien, causing an uplift of the Milun Terrace and deformation and fracture of Milun gravel rocks in the hanging wall. The Milun Fault was the seismogenic fault for the 1951 Hualien earthquake (ML 7.3) and experienced approximately 70 cm of horizontal displacement triggered by the 2018 earthquake. The proximity of the Milun Fault to several secondary fault systems indicates complex structural activity.

This study focuses on observing the gravel rock layers beneath the Milun Tableland along the northern coast, utilizing a well-cemented beachrock layer as a key bed to assess variations in uplift across different areas.  Based on the investigations, the gravel rock layers beneath the Milun Tableland can be broadly divided into three zones:(a) Southeast Stable Zone: Characterized by a low beachrock layer height of approximately 3 meters. Minimal evidence of fault activity is observed in this area. (b) Damaged Zone (Middle): Marked by a beachrock height reaching up to 4.5 meters. Multiple fault systems are developed within the gravel rock layers, leading to fragmentation and damage. (c) Northwest Stable Zone: With a beachrock height of less than 1 meter, this area shows observable fractures in the underlying gravel rock but lacks clear structural activity. Measurements of slickenside and identification of fracture axes in the gravel rocks provide the maximum stress direction for each zone, indicating stress orientations ranging approximately between 160-170. The inferred trend of the Principal Displacement Zone (PDZ) aligns with a strike of 010, consistent with the surface rupture observed during the 2018 Hualien earthquake.

The field data from this study can offer additional information about the Milun Fault system. By incorporating the analysis results of surface rupture caused by the earthquake in 2018, it can further confirm the flower structural characteristics of the Milun Fault system. Additionally, it allows for observing other motion features associated with lateral fault movements.

How to cite: Hsu, Y.-C., Chang, C.-P., Huang, S.-Y., Wang, C.-C., and Yen, J.-Y.: Exploring Structural Activity Through Gravel Rock Fracture Characteristics: A Case Study of the Milun Fault in Hualien, Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6996, https://doi.org/10.5194/egusphere-egu24-6996, 2024.

EGU24-7399 | ECS | Posters on site | TS6.2

Mechanical Models for East-West Extension within the Pamir Orogen: Insights from of the Holocene slip rate of the Kongur Normal Fault 

Qi Liu, Jie Chen, Tao Li, Jianhong Xu, Ning Di, and Ming Luo

The Pamir orogen, laying at the northwestern syntaxis of the Indo-Asian collision zone and one of the most tectonically active regions of central Asia, experiences significant extension in its interior. Although internal extension is common in mature orogens, the Pamir is special because (i) its extension is primarily concentrated on the Kongur Extensional System (KES) rather than distributed on multiple normal faults; (ii) the KES is localized at the eastern region of the Pamir rather than centralized, suggesting asymmetric extension; and (iii) extension along the KES decreases southward, instead of decreasing from central portion to its northern and southern ends. Because of these unique characteristics, the causes of internal extension of the Pamir and formation of the KES have inspired numerous investigations, which in turn have led to the proposal of various mechanical models. Defining multi-timescale deformation rates along the KES, especially for late Quaternary and modern slip rate, is prerequisite for better understanding the nature of extension in the Pamir.

In this study, we focus on one of the most debated structure within the Pamir: the nearly NNW-trending Kongur Normal Fault (KNF), the most primary and striking part of the KES. This fault is characterized by dramatically increased topography (elevation up to > 7,500 m) which is expressed as lofty Kongur and Muztaghata massif in its footwall. Thermochronology ages suggest that the initiation, largest magnitude of extension and highest long-term exhumation rates along the KES are in the vicinity of the Kongur massif. Although some studies have focused on determining the tectonic activity of the KES since the late Cenozoic, almost no late Quaternary rates estimate yet exists on active fault (KNF) bounding the Kongur massif. Moreover, Glaciers have oscillated considerably throughout the Quaternary at Kongur and Muztaghata massif, offering a unique opportunity to expand our understanding of the role of glaciers in shaping the topography.

At Bulunkou, the KNF is branched into two segment. The surface trace of the both segments of KNF is clearly visible as a straight line feature, and characterized by offsets of different geomorphic surfaces. We determined the Holocene slip rates of both segment of KNF through geomorphic mapping on high-resolution DEMs and cosmogenic 10Be exposure dating of boulders on displaced geomorphic surfaces. Finally, we observed a very high Holocene slip rates (even probably can reach to 10-13 mm/a) of KNF at Bulunkou. Correlating our new observations of KNF with kinematics and slip rates along the whole KES, we clarify the role of the KES in accommodating internal extension of the Pamir.

How to cite: Liu, Q., Chen, J., Li, T., Xu, J., Di, N., and Luo, M.: Mechanical Models for East-West Extension within the Pamir Orogen: Insights from of the Holocene slip rate of the Kongur Normal Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7399, https://doi.org/10.5194/egusphere-egu24-7399, 2024.

EGU24-8986 | ECS | Orals | TS6.2

Tectonic geomorphology and morphostratigraphy applied to the study of the evolution of fault systems at different scales 

Simone Racano, Peter van der Beek, Taylor Schildgen, Victor Buleo Tebar, Mauro Bonasera, Domenico Cosentino, and Marco Tallini

In active tectonic areas, fault systems represent one of the main structural elements in shaping landscapes. Thus, the study and dating of landforms and continental deposits affected by tectonic deformation, such as river profiles and knickpoints, paleosurfaces, strath and alluvial terraces, are crucial to assess the activity state of the faults and how they evolved over time. Some features may provide a time-averaged history of deformation (e.g., deformed geomorphic markers), while others have the potential to record a continuous history of deformation (e.g., rock-uplift histories from inversions of river profiles). In this work, we present three case studies where we reconstruct the history and characteristics of fault systems at different scales through a combination of geomorphological and morphostratigraphical analyses. At a regional scale, we present the case study of the North Anatolian Fault (NAF). We reconstructed a spatio-temporal history of rock-uplift by inverting river profiles from 19 different catchments draining the northern part of the Central Pontides, a mountain belt uplifted by the transpression produced by the NAF. We found that uplift migrated westward over time, and combining our results with other published data, we proposed a model describing the age and propagation rates of the NAF from the nucleation point in the Eastern Pontides to the Marmara Sea. The second case study investigates, at a meso-scale, the Quaternary evolution of the northwestern sector of the Apennine Chain (Italy). By combining the rock-uplift history inferred from the inversion of river profiles from 6 catchments draining the Apennine Belt and the morphostratigraphy of the youngest marine units uplifted during the Pliocene in the Po Plain, we inferred the main activity phases of the thrust-top/compressive arc system of the Alessandria Basin and Monferrato Arc, one of the outermost arcs of the northern Apennines. The third case study is a local investigation into identifying the master faults in the Aterno River Valley, one of the most active tectonic intramontane basins in the Central Apennines (Italy). Because the tectonic complexity of the area makes it unsuitable for reconstructing a continuous deformation history by the inversion of river profiles, we applied a different approach by combining the deformation of dated paleosurfaces and fluvial terraces with the present characteristics of the topography (slope, relief, present elevation of deformed paleosurfaces and terraces) and drainage system (channel steepness index, knickpoints). We identified two opposite fault segments (Monte Marine Fault in the Upper Aterno Valley and Bazzano-Monticchio-Fossa Fault in the Lower Aterno Valley), respectively dipping SW and NE, representing the master faults of two different half-grabens.

How to cite: Racano, S., van der Beek, P., Schildgen, T., Buleo Tebar, V., Bonasera, M., Cosentino, D., and Tallini, M.: Tectonic geomorphology and morphostratigraphy applied to the study of the evolution of fault systems at different scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8986, https://doi.org/10.5194/egusphere-egu24-8986, 2024.

Faulting and folding of basement rocks together accommodate convergence within continental orogens. Here we use the river terraces sequences along the Dongda river as the geomorphic tracer to examine deformation patterns at the northeastern Qilian Shan. Five river terraces, T1 (youngest), T2, T3, T4a and T4b (oldest), were identified and dated as 4.2 ± 0.3 ka, 6.1 ± 0.5 ka, 12.4 ± 2.5 ka, 16.4 ± 0.2 ka and 27.4 ± 2.5 ka, respectively. Three major reverse faults, Minle-Damaying fault, Huangcheng-Ta’erzhuang fault, and Fengle fault, contribute to deformation of the region. Based on displaced terrace treads, we estimated the vertical slip rate along the Minle-Damaying fault as 0.7–1.2 mm/a, along Fengle fault as 0.5–0.7 mm/a. Apart from surface displacement across faults, folding of the Dahuang Shan anticline at the hangingwall of Fengle fault adds to an additional uplift rate of ~ 0.2 mm/a at its crest. Inhomogeneous uplift of the intermontane basins between Minle-Damaying fault and the Dahuang Shan anticline indicates a 0.9 ± 0.2 mm/a uplift rate along the Huangcheng-Ta’erzhuang fault. Kinematic modeling shows that the deformation propagated from North Qilian to the foreland along a south-dipping 10° décollement which rooted Haiyuan fault at the depth of 20–25 km, accommodating 2.7–3.8 mm/a total crustal shortening rate. We suggest that the thrusts formed and high strain rate at eastern Qilian as a results of strain partitioning within the Haiyuan-Qilian systems, might coincided with the restraining bend of Haiyuan fault system, and strain rate within this complex structure may bear high regional seismic hazard.

How to cite: Hu, X. and Wang, Y.: The thrust structure and slip partitioning of Haiyuan-Qilian systems at NE margin of Tibetan plateau, constrained from geomorphic evidence , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9405, https://doi.org/10.5194/egusphere-egu24-9405, 2024.

EGU24-11036 | ECS | Orals | TS6.2

A reappraisal of the Carboneras Fault (SE Spain) from new structural, geochronological and thermal constraints 

Leonardo Del Sole, Gianluca Vignaroli, Vincenzo Moretto, Manuel Curzi, Luca Aldega, Roelant van der Lelij, and Giulio Viola

Fault zones are complex structural features wherein each recorded episode of deformation contributes to their structural intricacy. In particular, the absence of tight constraints on the time dimension of the accommodated deformation history makes the understanding of the progressive evolution of fault zones particularly challenging and may lead to inaccurate reconstructions of faulting histories.

With the aim to further improve our understanding of mature fault zones, we studied key outcrops from the northeasternmost sector of the Carboneras Fault (CF) in the Betics of Spain. The CF is a NE-SW striking, >100 km-long, crustal-scale, left-lateral transpressive fault forming part of the Iberia-Africa diffuse plate boundary. The CF has been active from the early-middle Miocene to the Present and it is described as accommodating up to c. 40 km offset. We adopted a multitechnique and multiscalar approach that builds upon the examination and characterization of brittle structural facies (BSFs) that are used as archives of the fault evolution in time and space as expressed by a multitude of geological features and characteristics (composition, shape, color, geometry and kinematics, relative crosscutting relationships, petrophysical properties, absolute age, etc.).

Field structural analysis shows that the CF deforms Permo-Triassic basement rocks (e.g., phyllite, schist, quartzite) and Neogene sedimentary and volcanic rocks. The CF overall structural architecture reflects the tight juxtaposition of several BSFs that are genetically associated with (i) an E-W striking, high-angle, pervasive foliation associated with (c. upright) folds, and (ii) NNE-SSW to E-W-striking, low-angle reverse faults, where inclined folds and oblique foliations indicate top-to-the S/SE transport. (iii) These BSFs are truncated by a steeply dipping, and rather localized BSF defined by pervasive foliation and minor strike-slip faults, which strike NE-SW and are oriented like the CF’s regional trend. Samples collected from 17 BSFs and respective fault rocks were investigated by means of X-ray diffraction, K-Ar dating of synkinematic clay minerals and microtextural characterization. Illite Age Analysis (IAA) K-Ar geochronology of eight fault gouges suggests three faulting events during the (i) Chattian (26.39 ± 2.95 Ma) along E-W BSFs, (ii) middle-late Miocene (between 12.18 ± 0.71 and 10.02 ± 0.52 Ma) along NE-SW BSFs and (iii) late Pliocene-Early Pleistocene (between 3.35 ± 1.60 and 1.08 ± 0.81 Ma) along E-W BSFs. The analysis of mixed-layer illite-smectite (I-S) and the transformation sequence smectite-random-ordered mixed layer (R0 I-S)-ordered mixed layer (R1 and R3 I-S)-illite-di-octahedral K-mica (muscovite) was used to constrain the maximum temperature of synkinematic clay minerals. The highest temperature (≥ 275°C) is associated with the oldest gouge found in the E-W-striking BSFs. The other two age clusters are associated with intermediate (110-140°C) and lower (70-90°C) temperatures.

Results suggest that the CF underwent a long-lived polyphase faulting history at progressively shallower/colder conditions. The main phase of NE-SW directed strike-slip faulting occurred during the late Serravallian-early Tortonian. Recent fault movement reactivated instead E-W fabrics inherited from a phase of c. NNW-SSE directed, late Oligocene thrust-related shortening. These findings lead to new insights into the spatio-temporal evolution and mechanisms of growth and exhumation of major strike-slip faults.

How to cite: Del Sole, L., Vignaroli, G., Moretto, V., Curzi, M., Aldega, L., van der Lelij, R., and Viola, G.: A reappraisal of the Carboneras Fault (SE Spain) from new structural, geochronological and thermal constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11036, https://doi.org/10.5194/egusphere-egu24-11036, 2024.

The Coastal Cordillera of Central Chile, recognized as the world's longest coastal mountain range, exhibits notable variations in erosion rates, mean precipitation, vegetation cover, and topography along its expanse. Serving as a natural laboratory, this region facilitates an in-depth exploration of the intricate interplay between tectonics and climate, owing to its distinct climate gradient and unique subduction margin features. Moreover, subduction and migration of the aseismic Juan Fernandez Ridge (JFR) from northern latitudes to its current position (~ 33.5°S) establish distinct subduction erosion conditions in the north and accretion conditions in the south of the ridge. This has implications for the tectonic deformation style of the forearc, potentially influencing the style and timing of uplift.

Across the region, numerous high elevation – low relief surfaces, often surrounded by knickpoints resembling flat mountain tops, offer valuable insights into the temporal aspects of knickpoint formation hence uplift processes, which might reflect the history of the ridge subduction.  Using geomorphometric indices such as steepness, chi, and knickpoint zones along rivers, we conduct a comprehensive analysis of these surfaces. Initial morphological assessments reveal no obvious trend in the distribution of these surfaces along the strike, although their size diminishes from north to south. Additionally, we used in situ cosmogenic 10Be nuclides to quantify erosion rates at five different flat mountain tops, thereby determining the knickpoint initiation time. Erosion rates are lower above knickpoint than the ones below knickpoints as expected.  Consistently low erosion rates (0.004 mm/yr – 0.07 mm/yr) prevail across the region. Considering the substantial height of these surfaces (approximately 1.5-2 km), the initiation time of the knickpoints might show the history before arrival of the JFR in the south, whereas in the north they might be comparable with the passage of the JFR. However, by incorporating paleoclimate and geodynamic conditions overtime into the landscape evolution model, we anticipate obtaining more precise results for comparison. In conclusion, the Coastal Cordillera of Central Chile undergoes complex interactions among tectonics, seismology, and climate. A nuanced understanding of these processes contributes significantly to broader insights into convergent plate boundaries and the geological evolution of forearcs.

 

How to cite: Yazici, M., Scherler, D., and Oncken, O.: Unraveling Flat Mountain Tops in the Coastal Cordillera of Central Chile: Based on Erosion Rates, Knickpoints, and Uplift Mechanisms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12360, https://doi.org/10.5194/egusphere-egu24-12360, 2024.

Gilbert-type deltas, built into rift basins, record interactions between fault-driven uplift and subsidence, sediment supply, and drainage network evolution. Typically forming at the junction of progressive fault segments, the syn-rift stratigraphy of uplifted Gilbert deltas offers a preserved record of the dynamic behavior of sedimentary source-to-sink systems through geological time. Of the physical parameters preserved in delta stratigraphy, grain size distributions contain unique information about sedimentary source-to-sink system dynamics over time. Specifically, downstream fining trends in syn-rift deposits reflect interactions between sediment supply to the basin and accommodation space creation driven by active faulting and subsidence. This work aims to understand how grain size distribution can quantify the syn-linkage phase of normal fault segments in the Gulf of Corinth. We examined two Pleistocene geological examples of uplifted Gilbert deltas with distinct tectonic configurations: 1) The Kerinitis Delta, formed by the relatively simple interaction of two same-aged fault segments, the Pirgaki and Mermoussia (P-M) Faults, which experienced a single linkage event; and 2) the more complicated Akrata Delta, formed by multiple linkage events between fault segments of the East Heliki Fault (EHF) and Derveni Fault (DF). We collected gravel grain size distribution data across 62 localities. Additionally, we captured scaled grain-size photographs in inaccessible areas. By tracing stratigraphic units and measuring their thicknesses, we reconstructed hanging-wall subsidence and paleo-fault slip rates. Using a self-similarity-based grain size fining model, we are able to reconstruct sediment supply rates and paleo-catchment erosion rates during the evolution of the fault systems. Further, we reconstructed the catchment averaged erosion rate to be markedly lower than the reconstructed footwall uplift, implying the landscape's transient response to fault growth. Our analysis demonstrates that grain size trends serve as a powerful tool for quantifying the complete growth histories of faults underlying normal fault-driven Gilbert delta systems. We demonstrate the feasibility of converting high-resolution grain size fining patterns preserved in Gilbert delta stratigraphy into reconstructed records of fault slip rates, hanging wall subsidence rates, sediment flux changes, and other key forcing parameters over 105 year timescales. This significantly expands the quantitative toolbox available to translate syn-rift sedimentary architecture into rich chronologies unravelling structural deformation patterns, including fault interactions, segment linkage, and overall progression.

How to cite: Rezwan, N., Whittaker, A. C., Hobley, D., and Zhou, Z.: Quantifying normal fault growth histories from Gilbert Delta stratigraphy using downstream grain size trends: Examples from the Kerinitis and Akrata Delta, Gulf of Corinth. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12627, https://doi.org/10.5194/egusphere-egu24-12627, 2024.

The Island of Rhodes constitutes an exhumed portion of the Eastern Hellenic forearc and, thus, lends itself to investigating upper plate deformation kinematics of oblique subduction. Much of the east coast of the island features prominent marine terraces carved into Cretaceous carbonate rocks and decorated by Pleistocene marine deposits. The terraces are displaced by kilometer-scale faults, which are part of an island-wide pattern of linear morphological discontinuities, the kinematics of which are unknown. The generation of a UAV-based high-resolution digital surface model of a coastal hill slope near the town of Archangelos allowed us to quantify the horizontal and vertical components of fault displacements. The hill slope counts 17 marine terraces, serving as ideal kinematic marker surfaces, that are displaced by a set of three NNE-striking continental margin-parallel faults. Slip vectors inferred from the displacement components indicate oblique normal sense-of-displacement on the faults on the order of tens of meters. Interestingly, displacement magnitudes increase with elevation and age of the terraces, thus, the results point to normal faulting during rock uplift (exhumation) and approximately 400m of rock uplift. Kinematic analysis of nearby small-scale brittle shear faults (slickensides) in Plio-Pleistocene marine deposits indicate an overall NE-SW extension, in agreement with the kinematics of the kilometer-scale faults cutting the marine terraces. Therefore, we conclude that tectonics of the Eastern Hellenic forearc throughout Plio-Pleistocene around the island of Rhodes is characterized by rock uplift during distributed margin-parallel left-lateral shear.

How to cite: Ferreira, M. M. M. and Riller, U.: Pleistocene-Recent deformation regime of the Eastern Hellenic forearc inferred from multiscale fault-kinematic analysis, Island of Rhodes, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13544, https://doi.org/10.5194/egusphere-egu24-13544, 2024.

EGU24-13641 | Orals | TS6.2

Is the crust in intraplate regions critically stressed? 

Maria Beatrice Magnani and Michael Blanpied

The emergence in 2008 of seismicity induced by energy industry practices in the Central United States (CUS) has presented both a challenge and an opportunity to address pressing questions about intraplate deformation. Human activity is reactivating slip on long-dormant faults by perturbing the state of stress of these faults through either wastewater injection or hydrocarbon production stimulation. By illuminating the presence, orientation and dimension of faults that are near failure and favorably oriented to the present stress field, induced seismicity provides a window into the stress conditions of intraplate faults and into the processes that drive seismicity in stable continental interiors. Thus, the emergence of induced seismicity can be viewed as one of the largest intraplate earthquake and tectonic experiments at the continental scale of our history.

Today we understand that subsurface pressure changes resulting from fluid injections can trigger earthquakes over a range ofdistances and times. The resulting earthquake productivity also varies markedly between sedimentary basins. A key observation is that even small fluid pressure perturbations can initiate slip on preexisting faults. This corroborates the concept of a criticallystressed crust, in which faults sit close to frictional failure. This, together with the observation that fluid pressures appear to remain at hydrostatic levels, is proposed to explain the occurrence of fault slip in intraplate regions. The hypothesis implies that faults rupture repeatedly, thereby preserving permeability and dissipating overpressure in the crust. Much of the research on intraplate seismicity is, in fact, framed within this hypothesis.

But there’s the rub: this hypothesis appears to be inconsistent with other key observations emerging from regions affected byinduced seismicity. In this presentation we analyze and compare the long-term fault displacement in regions of the CUS where seismicity is interpreted to be anthropogenic versus of natural origin. In regions of natural seismicity, faults exhibit a long deformation history, in agreement with the hypothesis of a critically stressed crust. But in regions of induced seismicity, we employ high resolution seismic reflection data to show that faults failing today due to wastewater injection had little to no activityfor the past 300 million years. Thus, while these latter faults must have been close to failure, as predicted by the critically stressed crust hypothesis, it does not explain their quiescence over such long time.

As research progresses and data availability improves, this contradiction is becoming more acute. We are learning that the changesin pressure necessary to cause faults to slip are vanishingly small, indicating that faults are precariously close to failure. At the same time, high-quality data show that these faults have been largely inactive for millions of years. Reconciling these observations requires moving from the macro scale of the seismic reflection images to the micro scale of rock mechanics of the faulting process, to understand the conditions that favor slip in the basement of the Central US in particular, and of other regions in the world in general.

How to cite: Magnani, M. B. and Blanpied, M.: Is the crust in intraplate regions critically stressed?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13641, https://doi.org/10.5194/egusphere-egu24-13641, 2024.

EGU24-14293 | ECS | Posters on site | TS6.2

Preliminary study on the characteristics and slip rate of the Quaternary fault in Mogod, Mongolia 

Dong-Eun Kim, Jin-Hyuck Choi, Yann Klinger, Tae-Ho Lee, Hoil Lee, Youngbeom Cheon, and Yire Choi

A comprehensive, interdisciplinary study was carried out to investigate the characteristics of the 1967 magnitude 7.1 earthquake along the right-lateral strike fault in Mogod, Mongolia. This fault consists of three segments—two strike faults and a reverse fault spanning from north to south. Recent research revealed a 25 ka cycle in the movement of the reverse fault segment located in the south (Bollinger et al., 2021).

To understand two remaining faults, four excavation surveys (T1, T2, T3, T4) were conducted along the two northern segments. Optically Stimulated luminescence (OSL) was used to track the deposition period in unconsolidated sedimentary layers where surface ruptures occurred, aiding in estimating the recent earthquake of the fault. An additional excavation survey was conducted near the river crossing the fault (at location T4) to determine the thalweg for evaluating geological displacement over the geological timescale.

The excavation results revealed Quaternary surface ruptures in three trenches with OSL sampling. A total of 51 samples were respectively collected from Trench T2 (24 samples), T3 (18 samples), and T4 (9 samples). The Quaternary sediment layers have been deposited since the Last Glacial Maximum (LGM), around ~20 ka. Excavation sites (3 upstream and 4 downstream) intersecting the fault line (T4) aimed to assess displacement caused by seismic activity.

In summary, seismic movements resulting in surface ruptures were detected in the northern two segments around the 20 ka. Further analysis would provide a more precise earthquake recurrence cycle, potentially revealing the timing of subsequent seismic events. Furthermore, completion of the identifying the thalweg, it is expected to reveal the slip rate over geological time scales.

How to cite: Kim, D.-E., Choi, J.-H., Klinger, Y., Lee, T.-H., Lee, H., Cheon, Y., and Choi, Y.: Preliminary study on the characteristics and slip rate of the Quaternary fault in Mogod, Mongolia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14293, https://doi.org/10.5194/egusphere-egu24-14293, 2024.

Repeated reoccurrence of the low to moderate intensity earthquakes in the Central India region for a long period scruples its acceptability as a stable continental region. In last five years, the National Centre for Seismology INDIA has reported a 27 number of earthquakes of low to moderate intensity around the Tan Shear Zone (TSZ) and Balrampur Fault geofracture in the eastern part of the Central India Tectonic Zone. Moreover, the presence of steep geothermal gradient recorded in the area, only along the aforementioned lineaments, maybe considered as an indirect evidence of frictional heat generation due to seismic/aseismic creep related to tectonic rejuvenation. The kinematics of this reactivation of preexisting structural heterogeneity under the present tectonic configuration is not well understood in this area. The present study has been conducted to address this issue of tectonic reactivation in the area specifically confined between Tan Shear Zone in the north and Balrampur Fault in the south. The Differential Interferometric Synthetic Aperture Radar (DInSAR) technique has been adopted to understand the kinematic of ground movement due to a very recent earthquake event (dated 24 March 2023 with intensity of 3.9) in this zone of interest.   Furthermore, a few numerical experiments have been carried out using finite element method (FEM)  to model the possible influence of preexisting heterogeneity on strain localization in response to current tectonic setup around the study area. In numerical model, we have assumed a hypothetical graben, formed by gravity sag in granitic rheology, filled with layer of sedimentary rheology, equivalent to Gondwana rocks.

Through the DInSAR analysis of SLC image pairs, it has been revealed that the central part spanning ~25 Km length exhibits nearly uniform rate of upliftment due to the earthquake event. The axis of uplift flanked by an undisturbed zone Toward TSZ in the south and the Balrampur Fault in the north, shows a trend parallel to the boundary of Son-Mahanadi graben. For a plausible explanation of the uplift paralleling the preexisting steep graben boundary several hypothetical set-ups were tried with FEM as explained above. Thereby, it has been enumerated that even though the geometric reactivation of the steep graben boundary fault in the reverse-slip mode was not possible, due to stress-buttressing with the preexisting mechanical heterogeneity a hanging wall-cut reverse fault nucleated from the graben collar. Uplift due to this reverse fault resemblance the axial uplift in the study area by its position and orientation with respect to the preexisting structural heterogeneity. This study with multidisciplinary approaches can be considered as a classic example of shallow brittle failure causing seismicity in any Stable Continental Region.

How to cite: Ali, M., Behera, A., and Bhattacharjee, D.: Influence of pre-existing structural weakness on active tectonics in the eastern part of cratonised Peninsular India: An integrated approach of DInSAR and Numerical Modelling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14384, https://doi.org/10.5194/egusphere-egu24-14384, 2024.

EGU24-14396 | Posters on site | TS6.2

Resetting of IRSL and IRPL signals by frictional heating in experimentally sheared Granite rock at seismic slip rates 

Huili Yang, Jie Chen, Furong Cui, and Myungho Kook

Recent studies on natural and experimental seismic faults have revealed that frictional heating plays an important role in earthquake dynamics. We report IRSL and IRPL signals changes in the granite rock after frictional experiments. Our results indicate that high-rate (2.0 m/s) frictional heating during seismic events can reset the 'geologic clocks' of fault rocks. Thus, the IRSL and IRPL signal in granite from natural fault zones has the potential to directly constrain the age of seismic events. Whereas low-rate (2.0 mm/s) frictional slip, even over long times (1000 s), does not reset the IRSL and IRPL signals in granite. The result is similar to the quartz gouge(Hui Li Yang., et al., 2019).

How to cite: Yang, H., Chen, J., Cui, F., and Kook, M.: Resetting of IRSL and IRPL signals by frictional heating in experimentally sheared Granite rock at seismic slip rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14396, https://doi.org/10.5194/egusphere-egu24-14396, 2024.

EGU24-14954 | Posters on site | TS6.2

Onset of compressive exhumation of the northern Santa Bárbara System (NW Argentina). Tectonic implications from low-T thermochronology 

Victor Hugo Garcia, Antonella Galetto, Edward R. Sobel, Patricio Payrola, Carolina Montero, Leonardo Elías, Ahmad Arnous, Johannes Glodny, Fernando Hongn, and Manfred R. Strecker

The Santa Bárbara System (SBS), located at the Central Andes of northwestern Argentina, is a thick-skinned fold-and-thrust belt (FTB) that represents the outermost portion of the orogenic wedge and the western boundary of the undeformed Chaco-Paraná foreland basin. The present-day structural architecture of the SBS is mainly governed by the reactivation of basement anisotropies and the inversion of Cretaceous normal faults imprinting an overall vergence towards the west. Some of the major faults show evidence of active tectonics in the landscape, which also correlates with instrumental seismicity and destructive earthquakes recorded.

Studies based on seismic interpretation of growth strata in synorogenic deposits have shown that the basement ranges of the southern SBS began to be uplifted during the late Miocene, although the magnitude of exhumation has not yet been quantitatively established. On the other hand, thermochronological analyses of basement samples from the neighboring Eastern Cordillera (EC) have highlighted the relevance of a late Miocene (ca. 10 Ma) exhumation event that propagated the orogenic front into the Mojotoro range, west of the northern SBS.

In this contribution, we present the first (U-Th-Sm)/He cooling ages from Paleozoic rocks of the northern SBS and from the Neoproterozoic basement of the Reyes range, in the EC. The integration of these data with previously published cooling ages allows to conclude that the late Miocene compressional event reached the northern SBS, driving the exhumation of the basement-cored ranges by 7-8 Ma, much earlier than previous estimations. In addition, the Reyes range sample yielded a younger cooling age (ca. 4 Ma) which agrees well with the model of hinterland reactivation of faults due to the recovery of a sub-critical orogenic wedge, as proposed by previous publications.

Based on the available structural reconstructions, an average exhumation rate of ca. 0.7 mm/a can be estimated for the western frontal thrusts of the northern SBS. This value agrees with the late Pleistocene-Holocene rates obtained for neotectonic morphostructures of the Lerma Valley, the easternmost intermontane basin of the EC, suggesting the continuation of a similar deformation pattern throughout the Quaternary for this portion of the Andean back-arc. Additionally, our results shed light on the tectonic evolution style of thick-skinned FTB´s and broken foreland basins.

How to cite: Garcia, V. H., Galetto, A., Sobel, E. R., Payrola, P., Montero, C., Elías, L., Arnous, A., Glodny, J., Hongn, F., and Strecker, M. R.: Onset of compressive exhumation of the northern Santa Bárbara System (NW Argentina). Tectonic implications from low-T thermochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14954, https://doi.org/10.5194/egusphere-egu24-14954, 2024.

EGU24-15246 | ECS | Posters on site | TS6.2

Sentinel-1 Insights into interseismic coupling along the plate boundary of the Western Makran Subduction Zone 

Alireza Sobouti, Samie Samiei Esfahany, Mohammad Ali Sharifi, Amir M. Abolghasem, Abbas Bahroudi, and Anke M. Friedrich

The Makran Subduction Zone (MSZ) of Iran and Pakistan, where the oceanic Arabian plate is sinking beneath the overriding continental Eurasian plate, is among the least explored subduction zones. Limited geodetic measurements, especially in the Western MSZ (WMSZ) with lower seismicity, have posed challenges in assessing the potential for future seismic events. The extensive spatial coverage offered by the Interferometric Wide-Swath (IW) mode of Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) allows for measuring tectonic deformation at a scale of millimeters per year across distances spanning hundreds of kilometers. Nevertheless, the presence of other signals and errors­­­­­—with similar spatio-temporal patterns to the signal of interest—poses challenges to accurately estimating the low-amplitude, large-scale subduction-induced deformation from InSAR observations.

In this contribution, we analyze more than eight years of continuous Sentinel-1 InSAR data from both ascending and descending orbits in the WMSZ area of Iran, to capture the Line-Of-Sight (LOS) interseismic crustal deformation rate. Our approach integrates a comprehensive and novel atmospheric mitigation strategy, accompanied by corrections for non-tectonic processes and rigid plate motion, aiming to isolate the tectonic-related signal from other non-tectonic signals and errors. In the following step, we investigate three trench-perpendicular profiles to infer the spatial and along-dip distribution of plate coupling from the Line-Of-Sight (LOS) deformation rates obtained through InSAR.

Due to the limited InSAR coverage near the trench (as located beneath the sea), it is not possible to constraint coupling in that area that extends 150 km far from the trench and reaches a depth of 10 km. Our findings reveal significant variations in interseismic coupling from west to east. We observe regions of weak and strong coupling, located near Jask (the westernmost part of the WMSZ) and Chabahar (the easternmost part of the WMSZ), respectively. The middle profile, located near the epicenter of a 5.9 magnitude earthquake that occurred in 1989 (Mw 5.9), exhibits a moderate coupling of 65 percent. Additionally, the coupling is notably high at depths between 10 and 20 km, gradually decreasing to zero at depths between 30 and 40 km.

In summary, the enhanced spatial resolution of InSAR, along with the high precision of deformation rates provided by the advanced error mitigation on the long time series of Sentinel-1 significantly improves our ability to characterize the locking depth at which the boundaries between two plates are accumulating stress in WMSZ.

How to cite: Sobouti, A., Samiei Esfahany, S., Sharifi, M. A., Abolghasem, A. M., Bahroudi, A., and Friedrich, A. M.: Sentinel-1 Insights into interseismic coupling along the plate boundary of the Western Makran Subduction Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15246, https://doi.org/10.5194/egusphere-egu24-15246, 2024.

EGU24-15504 | Posters on site | TS6.2

Cenozoic clockwise rotation of the northeastern Tibetan Plateau 

Rong Huang and Weitao Wang

Vertical–axis rotations recorded by paleomagnetic results from the northeastern Tibetan Plateau afford new insights into the tectonic processes related to the growth of the Tibetan Plateau. The Qinling Mountain is a special orogenic belt that bridges the crustal shortening of the northeastern margin of the Tibetan Plateau in the west with the extensional North China block in the east. In this study, we focus on the intermountain basins across the West Qinling Mountain. We present geochronological and paleomagnetic results from the basalt and redbed sequences from the Cretaceous–Cenozoic basins within the West Qinling Mountain. Constrained by precise ages, our paleomagnetic results reveal that approximately 10–20◦ clockwise vertical–axis rotation occurred across the West Qinling Mountain during the middle to late Miocene, indicating a significant period of outward growth of the Tibetan Plateau.

How to cite: Huang, R. and Wang, W.: Cenozoic clockwise rotation of the northeastern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15504, https://doi.org/10.5194/egusphere-egu24-15504, 2024.

EGU24-15558 | ECS | Posters on site | TS6.2

Isolating tectonic signals from transient and lithologically heterogeneous landscapes in the Gulf of Corinth, Greece 

Ziqiang Zhou, Alexander Whittaker, Rebecca Bell, and Gary Hampson

Landscape is the integrated product of external forcings (e.g., tectonics and climate) and internal bedrock erodibility. In principle, hard bedrock with low erodibility can steepen rivers in a similar way to tectonic uplift. A key challenge in tectono-geomorphic analysis is thus separating tectonic and lithological effects on landscapes. To address this, we focus on multiple rivers that are transiently incising through contrasting lithologies in the Gulf of Corinth, Greece where tectonic history is broadly well-constrained, and climate is relatively uniform. We first exploit topographic metrics and river long profiles to demonstrate that landscapes are responding to both tectonics and lithology. In particular, the long profiles are divided into knickpoint-bounded segments, and at this scale, channel steepness is shown to be more sensitive to lithology than the entire catchment, possibly due to the relatively uniform uplift rate in the channel segments. We then use segment-scale steepness variations between different lithologies to constrain their relative erodibility (Klime : Kcong. : Ksand-silt. : Kp-con sed = 1 : 2 : 3 : 4), which is further converted into actual lithological erodibility by modelling a well-constrained, ~750ka knickpoint in the Vouraikos. The effectiveness of lithological erodibility is supported by the observation that if lithological erodibility is used to calibrate studied river long profiles in Chi distance, we obtain long profile concavities that fall within the theoretical range. Finally, we use lithology-calibrated metrics to provide new geomorphic constraints on the timing and magnitude of tectonic perturbations. These geomorphic results are interpreted in conjunction with previous studies to shed new light on fault growth and linkage history in the Gulf of Corinth. Our study therefore demonstrates tectonic signals can be isolated from transient and lithologically heterogeneous landscapes by accounting for spatial variability in lithology.

How to cite: Zhou, Z., Whittaker, A., Bell, R., and Hampson, G.: Isolating tectonic signals from transient and lithologically heterogeneous landscapes in the Gulf of Corinth, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15558, https://doi.org/10.5194/egusphere-egu24-15558, 2024.

EGU24-16512 | Posters on site | TS6.2

Separation of exhumation and post-intrusion cooling with thermochronology, Al-in-Hbl geobarometry, and numerical thermal modeling: an example from Central Japan 

Saki Minami, Shigeru Sueoka, Shoma Fukuda, Luca C. Malatesta, Tetsuo Kawakami, Fumiko Higashino, Yuya Kajita, and Takahiro Tagami

Granites are generally emplaced several kilometers deep. Therefore, areas where granites younger than ~5 Ma are exposed must have been uplifted and exhumed rapidly. Young granites are distributed along convergent plate boundaries [1]. The Japanese islands, consisting of active island arcs, have some young granites, such as the world’s youngest Kurobegawa granite of ~0.8 Ma [2] in Hida mountain range, central Japan. The Tanigawa-dake area, in the southern end of the Northeast Japan arc, hosts such granites of late Miocene to Pliocene ages ranging from ~6.0–5.5 Ma, ~4.0 Ma to 3.3–3.2 Ma (zircon U-Pb) [3,4]. Previous studies [4] also reported zircon (U-Th)/He dates (ZHe) of 3.3–1.4 Ma and apatite (U-Th-Sm)/He (AHe) dates of 2.8–1.0 Ma for these young granites and the Cretaceous granites. Exhumation rates of 0.3–1.7 mm/yr were estimated by AHe dates and assumption of constant geothermal gradients of 40–60 °C/km [6]. However, the AHe dates might reflect initial cooling phase of the young plutons as well as cooling derived from exhumation, potentially leading to an overestimation of exhumation rates in the Tanigawa-dake area.

This study aims to constrain a more reliable exhumation history. We applied two methods for the youngest pluton (~3.3 Ma): (1) Al-in-Hbl geobarometry [5] to estimate the emplacement depth and (2) 1D numerical simulation of geothermal structure based on heat advection-diffusion-production equation [7] to explore the best cooling/exhumation histories consistent with the reported zircon U-Pb age, ZHe and AHe dates. As a result of Al-in-Hbl geobarometry, solidification pressures of 0.9–2.6 kbar were estimated. Emplacement depths derived from these pressures are 3.4–9.5 km by assuming the granites density of 2.7 g/cm3. Exhumation rates were calculated to be 1.0–2.9 mm/yr for the youngest pluton, assuming an intrusive age of ~3.3 Ma [3]. In the 1D heat advection-diffusion-generation model, the best exhumation rates are ~1.2 mm/yr and the best emplacement depth is ~4.0 km. Comparing with the exhumation rate estimated from the AHe age of ~1.0 Ma [4] in the same pluton (0.8–1.7 mm/yr), the geobarometry method yielded similar or higher exhumation rates (1.0–2.9 mm/yr). Similarly, the modeled rate (1.2 mm/yr) fits with the exhumation rate estimated using AHe age. This indicates that the initial cooling was finished by the time of the AHe date for ~3 Ma pluton, i.e., the previous geothermal structure in this area had relaxed to the current one. Consequently, the exhumation rates calculated from AHe date and current geothermal gradient were consistent with those obtained from the combination of geobarometry, zircon U-Pb, ZHe and AHe datings and numerical thermal modeling.

 

References [1] Harayama (1992) Geology, 20, 657–660, [2] Ito et al. (2013) Sci. Rep., 3:1306, [3] Minami et al. (2021) EPS., 73:231, [4] Minami et al. (2023) Thermo2023 abstract, p.129, [5] Mutch et al. (2016) Contr. Mineral. and Petrol., 171:85, [6] Tanaka et al. (2010) EPS., 56, 1191–1194, [7] Murray et al. (2018) G-Cubed, 19, 3739–3763.

How to cite: Minami, S., Sueoka, S., Fukuda, S., Malatesta, L. C., Kawakami, T., Higashino, F., Kajita, Y., and Tagami, T.: Separation of exhumation and post-intrusion cooling with thermochronology, Al-in-Hbl geobarometry, and numerical thermal modeling: an example from Central Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16512, https://doi.org/10.5194/egusphere-egu24-16512, 2024.

EGU24-17056 | Posters on site | TS6.2

Deformation at Mefite d’Ansanto area (Italy) through an interdisciplinary approach: GNSS Network and Digital Elevation Model 

Alessandra Esposito, Fawzi Doumaz, Alessandro Galvani, Mirko Iannarelli, Mimmo Palano, Grazia Pietrantonio, Federica Riguzzi, Vincenzo Sepe, Federica Sparacino, and Daniele Trippanera

In the frame of FURTHER project, “The role of FlUids in the pReparaTory pHase of EaRthquakes in Southern Apennines”, (https://progetti.ingv.it/en/further), consisting in a multidisciplinary study based on seismological, geodetic, and geochemical observations to understand the role of fluids in the seismogenic processes in the Southern Apennines, we focus on the geodetic monitoring at Mefite d’Ansanto (AV) deep CO2 degassing area located at the northern tip of the Mw6.9, 1980 Irpinia fault. Mefite d’Ansanto represents the largest low-temperature non-volcanic CO2 emission of the Earth (Chiodini et al. 2010).

To provide an improved picture of the regional crustal deformation and investigate the relationship among deformation, crustal fluids, and physical-hydraulic properties pattern, we installed a new GNSS network and realized a detailed Digital Elevation Model (DEM).

The new local GNSS network, MefiteNet, consists of four stations (one permanent and three survey-style stations) that monitor the degassing area of approximately 1 km2 by April 2022.

Two aerial photogrammetric surveys were performed over Mefite area with a quadcopter drone to obtain a high-resolution Digital Elevation Model (DEM) to estimate the amount and the morphological variations of the Mefite lake level in space and time. The flight technique, that takes into account the topography, was chosen to ensure a constant pixel size on the ground and avoid lack of aerial coverage.

We show the first results of the GNSS data analysis recorded by the MefiteNet and the preliminary results regarding morphological analysis.

How to cite: Esposito, A., Doumaz, F., Galvani, A., Iannarelli, M., Palano, M., Pietrantonio, G., Riguzzi, F., Sepe, V., Sparacino, F., and Trippanera, D.: Deformation at Mefite d’Ansanto area (Italy) through an interdisciplinary approach: GNSS Network and Digital Elevation Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17056, https://doi.org/10.5194/egusphere-egu24-17056, 2024.

EGU24-17123 | ECS | Orals | TS6.2

A new method to restore tectonically beheaded stream networks 

Adrien Moulin, Matthieu Ribot, and Sigurjón Jónsson

Drainage capture and beheading represent extreme cases of divide mobility, during which large parts of drainage areas are suddenly gained or lost. Though these events may occur in any environment, some of them are directly controlled by displacement on dip-slip faults. In such a case, topographic barriers built through vertical tectonic displacements result in breaking across-fault hydrological connections. Beheaded valleys represent the end-product of this process and can theoretically be used as strain markers that record cumulative displacement on the causative fault. In practice, it is however difficult to derive robust displacement estimates from beheaded valleys because the pre-deformation geometry is generally unknown. This difficulty is usually tackled by introducing two main assumptions: (1) the stream profile was at steady-state at the time of beheading, and (2) the beheading event did not significantly modify the upstream profile. These two assumptions allow constraining the pre-deformation profile by propagating the upstream “undeformed” profile in the downstream direction. We here propose a new approach which offers an opportunity to get rid of the latter assumption, provided that the former is true.

We first present theoretical expectations for the topographic encoding of dip-slip-faulting-induced beheading in chi-transformed coordinates (chi = along-stream distance normalized by the drainage area) as a function of drained catchment loss and post-beheading vertical uplift. In chi-elevation plots, we define “co-tectonic lines” that connect pairs of points located at the same distance from the fault but along distinct downward-branching beheaded channels. The orientation of these lines is insensitive to tectonic displacement, and becomes increasingly tangent to the pre-deformation steady-state profile as catchment loss corrections applied to chi approach the actual values. We then define a two-fold strategy to retrieve the initial unstrained geometry: (1) analyze the distribution of co-tectonic lines for a range of catchment loss solutions, and (2) evaluate the consistency of these distributions with respect to steady-state conditions. We employ this strategy on a fossilized beheaded stream network which formed in response to slip on normal faults of the Wadi al-Akhdar Graben (WAG, NW Saudi Arabia). This natural prototype is ideal to test the method because pre-deformation catchment geometries can be readily quantified in the landscape due to the local arid low-erosion conditions. Forward modeling of the beheaded stream profiles of the WAG well predicts the drained catchment loss quantified independently (at the 90% confidence level), and provides pre-deformation profiles that reduce the quantified cumulative uplift by ~30% relative to the standard method. These results show that working on chi-transformed profiles represents a promising way to reduce the uncertainties associated to the restoration of tectonically beheaded valleys.

How to cite: Moulin, A., Ribot, M., and Jónsson, S.: A new method to restore tectonically beheaded stream networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17123, https://doi.org/10.5194/egusphere-egu24-17123, 2024.

EGU24-18030 | ECS | Posters on site | TS6.2

Timing of deformation in the Moravosilesian Foreland Basin – new insights from detrital zircon U-Pb dating 

Yao Xiao, Johannes Rembe, Renata Čopjaková, and Renjie Zhou

The Moravosilesian Foreland Basin preserves information of an important interval of the evolution of the eastern European Variscan Orogen. The basin largely was deposited on the Brunovistulian microplate, which underthrusts east-vergent Moldanubian and Moravosilesian units. It hosts an up to 7.5 km thick suite of siliciclastic marine sediments, recording the unroofing of the adjacent Moldanubian zone and the Moravosilesian nappes. Moreover, the basin records polyphase, late-stage Variscan, foreland-affecting deformation occurring between 330 Ma and 310 Ma. Outcrops of the basin can be found in the Drahany upland, southeast of the Czech town of Olomouc and the Nízký-Jeseník mountains, northeast of Olomouc. We conducted zircon U-Pb dating on four detrital samples of a suite of three marine formations in the Drahany upland (Yao et al., 2024). Maximum depositional ages (MDA) of the allochtonous Protivanov (328.7 ± 1.8 Ma), and the parautochthonous Rozstání (326.1 ± 1.0 Ma) and Myslejovice (335.1 ± 2.4 to 329.8 ± 2.4 Ma) formations are coeval to the depositional age of tuff layers within the shallow marine to continental, synorogenic, coal-rich Ostrava formation of the Nízký-Jeseník mountains, which were deposited between 329.2 ± 0.5 Ma and 324.2 ± 0.5 Ma.
This finding challenges the established stratigraphy of the Protivanov, Rozstání and Myslejovice formations, which were previously based on detrital fossiliferous limestone pebbles. The MDAs of all three formations suggest a Serpukhovian rather than Visean depositional age. This has strong implications on the timing of NE-verging basin folding and thrusting. It constraines late-stage Variscan deformation propagation into the foreland to a timespan between <326 Ma (youngest MDA in the Drahany upland) and 303 Ma (opening of the adjacent Boskovice graben (Nehyba et al., 2012)). This timespan postdates time estimates made for compressive tectonics in the region (e.g. Tomek et al., 2019), which proposed the termination of Brunovistulian underthrusting at ~330 Ma.

Nehyba S, Roetzel R and Maštera L 2012 Geologica Carpathica 63 365–82

Tomek F, Vacek F, Žák J, Petronis M S, Verner K and Foucher M S 2019 Tectonophysics 766 379–97

Xiao Y, Rembe J, Čopjaková R, Aitchison J C, Chen Y and Zhou R 2024 Gondwana Research 128 141–60

How to cite: Xiao, Y., Rembe, J., Čopjaková, R., and Zhou, R.: Timing of deformation in the Moravosilesian Foreland Basin – new insights from detrital zircon U-Pb dating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18030, https://doi.org/10.5194/egusphere-egu24-18030, 2024.

EGU24-19249 | ECS | Orals | TS6.2

Development of half-grabens along the northwestern end of Gediz-Alaşehir Graben: Inferences from morphometric and kinematic analysis 

Taner Tekin, Tamer Dönmezoğulları, Taylan Sançar, and Bora Rojay

Aegean Extensional Province under which evolution was primarily influenced by the interaction of the northward subducting African plate beneath along “Mediterranean Ridge” and the extrusion of the Anatolian continental fragment caused by relative motion along two major continental transform faults, dextral North Anatolian Fault and sinistral East Anatolian Fault. The resultant interaction led to a crustal extension in NW-SE trending direction in Western Anatolia known as the Gediz-Alaşehir Graben (GAG).

The study of dynamic morphology along the graben displayed by mountain front morphology (mountain front sinuosity and symmetry of mountain ridges) is studied. To understand the dynamic effects, a series of profiles was taken from Spildağ Mountain in the west to Gölmarmara Lake in the east.

Secondly, kinematic data are collected from fault planes from NW-SE trending, NE facing four faults developed between Manisa fault to Gölmarmara fault. The Angelier Inversion method was applied to the Win-Tensor program (Delvaux and Sperner, 2003) and used in the analysis of the fault slip data. The result is an NE-SW extensional regime that is overprinted onto NE-SW dextral and sinistral oblique-slip motion.

Mountain front sinuosity (Smf) and sudden changes of slope along topographic profiles (kinks) indicate the activity of the faults but different rates of deformations. Moreover, indicators manifest a series of NE-facing half grabens that exist within the Gediz-Alaşehir graben. The ages from the dating of the calcite samples from either fault scarps and trenches are going to assist in better comprehension of the active tectonics of Gediz-Alaşehir graben.

To sum up, the Gediz-Alaşehir graben which was constructed on four half-grabens developed under the NE-SW extensional regime during the post-Late Miocene manifests the current configuration of the topography.

Keywords: Aegean Extensional Province, Gediz-Alaşehir Graben, morphometric analysis, kinematic analysis.

How to cite: Tekin, T., Dönmezoğulları, T., Sançar, T., and Rojay, B.: Development of half-grabens along the northwestern end of Gediz-Alaşehir Graben: Inferences from morphometric and kinematic analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19249, https://doi.org/10.5194/egusphere-egu24-19249, 2024.

EGU24-20038 | ECS | Orals | TS6.2

Neogene gravity collapse of the eastern and western Niger Delta: Results from 2D forward kinematic structural modelling 

Kelvin Ikenna Chima, Estelle Leroux, Marina Rabineau, Didier Granjeon, Maryline Moulin, Philippe Schnurle, and Daniel Aslanian

The Cenozoic Niger Delta displays a complex gravity collapse system underpinned by overpressured shale that forms a décollement for normal faults, detachment folds and imbricate-fold-thrust structures in a linked extensional-contractional system. To better understand the timing and dynamics of gravity-driven deformation in the eastern Niger Delta (END) and western Niger Delta (WND) since the late Cretaceous, we performed 2D forward kinematic structural restoration and backstripping of regional 2-D seismic sections using KronosFlow software. The restored cross-section, in the END, extends from the present-day onshore (the Oligocene-Tortonian extensional zone) to the abyssal plain, while that of the WND extends from the present-day continental shelf to the abyssal plain. A comparison of restored cross sections shows that the modern continental shelves of the END and WND are dominated by counter-regional and regional normal faults, respectively. Between the late Eocene (ca. 34 Ma) and the late Miocene (9.3 Ma), the END displays gravity-driven deformation, localised in the Oligocene-Tortonian extensional zone with relatively low deformation on the slope and the deep basin. However, a correlation of restored cross sections over the late Eocene-late Miocene, suggests that gravity-driven deformation in the WND was localised within the Oligocene-Tortonian extensional zone with little or no deformation on the slope and the deep basin. Between the late Miocene (ca. 9.3 Ma) and the early Pliocene (ca. 5.7-4.9 Ma), the Oligocene-Tortonian extensional zone prograded to the present-day continental shelf resulting in a coupling of extensional deformation to contractional deformation in the END at least since the late Miocene. In the WND, the Oligocene-Tortonian extensional zone prograded to the present-day continental shelf during the late Miocene (ca. 9.5 Ma) but there was no coupling between extension and contraction until the early Pliocene (ca. 4.9 Ma). While there is a general reduction in gravity-driven deformation in the END over the Pleistocene, there is an overall increase in gravity collapse of sedimentary wedge in the WND. The unique structural configuration of the present-day continental shelf in the END and WND exerted distinct control on the gravity collapse of the regions throughout the Neogene. The dominance of counter-regional normal faults on the END continental shelf facilitated a large-scale increase (x2) in regional subsidence and sediment storage on the shelf over the late Eocene-late Miocene. However, the dominance of regional normal faults on the WND continental shelf facilitates an overall progradation and sediment transfer to the deep basin since the late Miocene/early Pliocene. This study documents the long history of gravity-driven deformation of the eastern and western Niger Delta and could be applied in the reconstruction of other shale tectonic basins.

How to cite: Chima, K. I., Leroux, E., Rabineau, M., Granjeon, D., Moulin, M., Schnurle, P., and Aslanian, D.: Neogene gravity collapse of the eastern and western Niger Delta: Results from 2D forward kinematic structural modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20038, https://doi.org/10.5194/egusphere-egu24-20038, 2024.

TS8 – Global and Planetary Tectonics and the evolution of the Earth

EGU24-415 | ECS | Orals | TS8.1

The South Atlantic Magmatic Province: An Integration of Early Cretaceous LIPs in the West Gondwana 

Antomat Avelino de Macedo Filho, Alisson Oliveira, Valdecir Janasi, and Maria Helena Hollanda

Extensive igneous activity, currently identified from NE Brazil and western Africa to the Falkland Islands and South Africa, preceded the fragmentation of the Western Gondwana supercontinent in the Early Cretaceous. The Paraná-Etendeka Magmatic Province (PEMP) is characterized by continental basaltic flows and igneous plumbing systems in SE South America and its African counterpart. In NE Brazil, dyke swarms and sill complexes compose the Equatorial Atlantic Magmatic Province (EQUAMP). A prominent feature of EQUAMP is the Rio Ceará-Mirim dyke swarm, an arcuate igneous plumbing system approximately 1,100 km in length. Aeromagnetic data suggests that the Rio Ceará-Mirim dykes stretch from the corner of South America to the northwest border of the São Francisco Craton. At this point, the dykes shift orientation to the NNW, extending towards the south, where they appear to connect with the Transminas dyke swarm (northern PEMP). The apparent continuity of dykes as a single entity would constitute a massive transcontinental swarm of about 2,300 km. A similar relationship is observed for the Riacho do Cordeiro (southern EQUAMP) and Vitória-Colatina (northern PEMP) dykes, indicating continuity across the São Francisco Craton of about 1,600 km. This study, supported by new petrological, geochemical, isotopic, and geochronological data, combined with geophysical and geodynamical analyses, demonstrates that the Transminas and Vitória-Colatina dyke swarms share the same composition and age as the Rio Ceará-Mirim and Riacho do Cordeiro dyke swarms, respectively. The set of new evidence supports a genetic connection between the PEMP and EQUAMP. Therefore, they can be collectively referred to as a single large igneous province related to the early stage of the South Atlantic rifting process in the West Gondwana realm: The South Atlantic Magmatic Province.

How to cite: Avelino de Macedo Filho, A., Oliveira, A., Janasi, V., and Hollanda, M. H.: The South Atlantic Magmatic Province: An Integration of Early Cretaceous LIPs in the West Gondwana, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-415, https://doi.org/10.5194/egusphere-egu24-415, 2024.

EGU24-1934 | ECS | Posters on site | TS8.1

The hypothesis of a lost Cenozoic “Himalandia” between India and Asia 

Liang Liu, Lijun Liu, Jason Morgan, Yi-Gang Xu, and Ling Chen

            The type of lithosphere subducted between India and Tibet since the Paleocene remains controversial; it has been suggested to be either entirely continental, oceanic, or a mixture of the two. As the subduction history of this lost lithosphere strongly shaped Tibetan intraplate tectonism, we attempt to further constrain its nature and density structure with numerical models that aim to reproduce the observed history of magmatism and crustal thickening in addition to present-day plateau properties between 83˚E and 88˚E. By matching time-evolving geological patterns, here we show that Tibetan tectonism away from the Himalayan syntaxis is consistent with the initial indentation of a craton-like terrane at 55±5 Ma, followed by a buoyant tectonic plate with a thin crust, e.g., a broad continental margin (Himalandia). This new geodynamic scenario can explain the seemingly contradictory observations that had led to competing hypotheses like the subduction of Greater India versus largely oceanic subduction prior to Indian indentation.

How to cite: Liu, L., Liu, L., Morgan, J., Xu, Y.-G., and Chen, L.: The hypothesis of a lost Cenozoic “Himalandia” between India and Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1934, https://doi.org/10.5194/egusphere-egu24-1934, 2024.

EGU24-2317 | Posters on site | TS8.1

Rayleigh-wave Ambient Noise Investigation for the OHANA Experiment in the NE Pacific 

Gabi Laske, Grace Atkisson, Sujania Talavera Soza, John Collins, and Donna Blackman

The OHANA experiment comprises a 15-month deployment of 25 broadband ocean bottom seismometers (OBSs) in the northeast Pacific Ocean, about halfway between Hawaii and the North American west coast. The primary objective of this project is to explore the crust, lithosphere and asthenosphere in a 600~km wide region west of the Moonless Mountains, covering mainly 40-to-50 Myr old Pacific lithosphere. A fundamental question to be addressed is whether this particular area has the signature of a typical oceanic lithosphere that has a normal plate cooling history. Alternatively, we seek evidence for a previously proposed reheating process, e.g. resulting from small-scale shallow-mantle convection. 

The new data enhance seismic imaging in a regional as well as in a global context. Regionally, short-period ambient noise and long-period earthquake-derived Rayleigh wave dispersion provide the centerpiece for imaging the crust and upper mantle. In  a top-down approach,
we start with the assembly and analysis of ambient-noise cross-correlation functions between 5 and 25 s. We present an initial assessment of high signal-to-noise quality cross-correlation functions. We derive path-averaged dispersion curves for the fundamental mode and present tomographic images from initial inversions. 

Furthermore, our cross-correlation functions contain prominent waveforms from overtones that can help improve resolution as a function of depth.

How to cite: Laske, G., Atkisson, G., Talavera Soza, S., Collins, J., and Blackman, D.: Rayleigh-wave Ambient Noise Investigation for the OHANA Experiment in the NE Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2317, https://doi.org/10.5194/egusphere-egu24-2317, 2024.

EGU24-2624 | ECS | Posters on site | TS8.1

Ridge-dual hotspots interaction and potential hotspot-hotspot interaction in the Southeastern Indian Ocean  

Yiming Luo, Jian Lin, Zhiyuan Zhou, Fan Zhang, Xubo Zhang, and Jinchang Zhang

We investigated the impacts of the Kerguelen and Amsterdam-St. Paul (ASP) hotspots on mantle evolution and crustal accretion of nearby spreading ridges in the Southeastern Indian Ocean. Gravity analysis revealed enhanced magmatism and thickened crust along the ridge caused by the Kerguelen and ASP hotspots. By employing plate motions derived from the GPlates global plate reconstruction model, along with the ASPECT 3-D mantle convection code, we presented a comprehensive depiction of the ridge-dual hotspot system, which has been relatively underexplored in previous research. Model results indicated that the Kerguelen hotspot had a significantly greater influence on mantle temperature and ridge crustal thickness compared to the ASP hotspot. Furthermore, there is evidence suggesting a potential interaction between the dual hotspots, leading to the migration of ASP plume materials towards the Kerguelen plume.

How to cite: Luo, Y., Lin, J., Zhou, Z., Zhang, F., Zhang, X., and Zhang, J.: Ridge-dual hotspots interaction and potential hotspot-hotspot interaction in the Southeastern Indian Ocean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2624, https://doi.org/10.5194/egusphere-egu24-2624, 2024.

EGU24-2711 | ECS | Orals | TS8.1

Links between large volcanic eruptions, basal mantle structures and mantle plumes 

Annalise Cucchiaro, Nicolas Flament, Maëlis Arnould, and Noel Cressie

As part of mantle convection, mantle plumes rise from the deep Earth, leading to volcanic eruptions during which large volumes of mafic magma are emplaced at Earth’s surface over a few million years. In 1971, Jason Morgan showed that seamount chains could be used to calculate the absolute motion of tectonic plates above fixed mantle plumes. This ground-breaking work notably led to the study of the relationship between Earth’s deep interior and its surface. Mantle plumes have been critical to constrain absolute plate motions in Earth’s recent geological past, with the development of both fixed-hotspot and moving-hotspot plate-motion models. Recent studies also revealed a statistical link between large volcanic eruptions and basal mantle structures in space and time, suggesting that large volcanic eruptions, mantle plumes, and hot basal structures are intrinsically connected. In these studies, mantle plumes were considered as the implicit process connecting volcanic eruptions at the surface to hot basal mantle structures. Geodynamic models suggest that mantle plumes are generated by two large antipodal hot basal mantle structures, up to ~1,200 km thick, and shaped by subducted oceanic crust through time. Here, we systematically compare three volcanic-eruption databases, four global tomographic models, and six reconstructions of past global mantle flow, to investigate the spatio-temporal links between volcanic eruptions, hot basal mantle structures, and modelled mantle plumes from 300 million years ago to the present day. We find that large volcanic eruptions are spatially closer to fixed and moving hot basal mantle structures than to modelled mantle plumes, because mantle plumes cover an area that is five orders of magnitude smaller than the area covered by hot basal mantle structures. The strength of the spatial-statistical relationships is largest between volcanic eruptions and modelled mantle plumes and, overall, it is larger between volcanic eruptions and moving basal mantle structures than between volcanic eruptions and fixed basal mantle structures.  This suggests that large volcanic eruptions are preferentially associated with mantle plumes generated from the interior of mobile basal mantle structures, which is in sharp contrast to previous studies that suggested mantle plumes are generated from the edges of fixed basal mantle structures.

How to cite: Cucchiaro, A., Flament, N., Arnould, M., and Cressie, N.: Links between large volcanic eruptions, basal mantle structures and mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2711, https://doi.org/10.5194/egusphere-egu24-2711, 2024.

EGU24-4020 | ECS | Orals | TS8.1

Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction 

Björn Heyn, Grace Shephard, and Clint Conrad

Between about 130 and 75 Ma, the Arctic was impacted by widespread and long-lived volcanism known as the High Arctic Large Igneous Province (HALIP). HALIP is a very unusual large igneous province because it exhibits prolonged melting over more than 50 Myr with pulses of activity, an observation that is difficult to reconcile with the classic view of large igneous provinces and associated melting in plume heads. Hence, the suggested plume-related origin and classification of HALIP as a large igneous province has been questioned, and alternative mechanisms have been invoked to explain at least part of the volcanism. However, the Arctic also exhibits a very complex and time-dependent tectonic history that includes cratons, continental margins and rifting, all of which are expected to interact with the rising plume and affect its melting behaviour.

 

Here, we use 2-D numerical models that include melting and melt migration to investigate a rising plume interacting with a lithosphere of variable thickness, i.e. an extended-basin-to-craton setting. Models reveal significant spatial and temporal variations in melt volumes and pulses of melt production, including protracted melting for at least about 30-40 Myr, but only if feedback between melt and mantle convection is accounted for. In particular, we find that melt migration transports heat upwards and enhances local lithospheric thinning, resulting in a more heterogeneous distribution of melting zones within the plume head underneath the Sverdrup Basin. Once the thicker continental and cratonic lithosphere move over the plume, plume material is deflected from underneath the Greenland craton and can then re-activate melting zones below the previously plume-influenced Sverdrup Basin, even though the plume is already ∼500 km away. Hence, melting zones may not represent the location of the deeper plume stem at a given time. Plume flux pulses associated with mantle processes, rifting of tectonic plates or magmatic processes within the crust may alter the timing and volume of secondary pulses and their surface expression, but are not required to generate pulses in magmatic activity. Hence, we propose that the prolonged period of rejuvenated magmatism of HALIP is consistent with plume impingement on a cratonic edge and subsequent plume-lithosphere interaction. Based on melt fractions, our models suggest that HALIP magmatism should exhibit plume-related trace element signatures through time, but potentially shifting from mostly tholeiitic magmas in the first pulse towards more alkalic compositions for secondary pulses, with regional variations in timing of magma types.

How to cite: Heyn, B., Shephard, G., and Conrad, C.: Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4020, https://doi.org/10.5194/egusphere-egu24-4020, 2024.

The India-Asia convergence has persisted since the onset of collision at ~55 Ma, indicating the driving forces of Indian indentation do not disappear on continental collision in the convergence process. What drives ongoing India-Asia convergence? This puzzle cannot be well resolved by the traditional theory of plate tectonics and the concept of Wilson Cycle. Consequently, questions concerning the primary driving force of the ongoing India-Asia convergence and the magnitude of this force still await an answer. Previous works have proposed multiple candidates for the primary driver of India-Asia convergence, including the continental subduction of the Indian lithosphere under Tibet, oceanic subduction at the Sumatra-Java trench, as well as the basal drag exerted by the mantle flow on the base of Indo-Australia plate. Here we present global geodynamic models to investigate the driving forces behind the India-Asia convergence, which produce good fits to the observed motions, stresses and strains within the Indo-Australia plate. On this basis, we quantitatively calculate the magnitude of effective forces of boundary forces (slab pull and ridge push) and basal drag. We conclude that the Sumatra-Java subduction is the primary driver of the ongoing India-Asia convergence. Indo-Australia plate motion is driven at the Sumatra-Java trench, impeded along the Himalaya, which could increase the shear stress within the plate. Different from the recent emphasis on the basal drag as a dominant driving force for the India-Asia convergence, this study shows that basal drag acts as the resisting force for the northeastward motion of the giant Indo-Australia plate, though it serves as a driver in some local regions.

 

How to cite: Zheng, Q. and Hu, J.: Driving forces for the ongoing India-Asia convergence: insight from global high-resolution numerical modeling of mantle convection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4314, https://doi.org/10.5194/egusphere-egu24-4314, 2024.

EGU24-4754 | Orals | TS8.1

Mantle plumes imaged by seismic full waveform inversion: from the core-mantle-boundary to surface hotspots 

Barbara Romanowicz, Federico Munch, and Utpal Kumar

With recent progress in resolution in global seismic mantle imaging provided by numerical wavefield computations using the Spectral Element Method and full waveform inversion, Jason Morgan’s suggestion from over 50 years ago that mantle plumes may be rooted at the core-mantle boundary (CMB) has been confirmed. Yet the imaged plumes present intriguing features that contrast with the classical thermal plume model and should inform our understanding of mantle dynamics. Among other features, they are broader than purely thermal plumes, and do not extend straight from the CMB to the corresponding hotspot volcanoes, but they are frequently deflected horizontally in the extended transition zone (400-1000 km depth), so that their lower mantle location can be significantly offset (as much as a 1000 km) from their surface expression. They appear to be thinner in the upper mantle. This, together with similar horizontal flattening observed in subduction zones suggests a change in the radial viscosity structure of the mantle that may occur deeper than usually assumed to be related to the 660 km phase change. The fattest plumes have been shown to be anchored within the perimeter of the large low shear velocity provinces (LLSVPs) and an increasing number of them appear to house mega-ultra low velocity zones within their roots.  Moreover, in the upper mantle, they appear to be associated with regularly spaced low velocity channels aligned with absolute plate motion.

We discuss these features in the light of recent regional imaging updates in the south Atlantic and beneath Yellowstone, contrasting the corresponding mantle plumes, and in particular showing mounting evidence that the LLSVPs are not compact “piles” extending high above the CMB, but rather a bundle of thermo-chemical plumes feeding secondary scale convection in the top 1000 km of the mantle.

How to cite: Romanowicz, B., Munch, F., and Kumar, U.: Mantle plumes imaged by seismic full waveform inversion: from the core-mantle-boundary to surface hotspots, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4754, https://doi.org/10.5194/egusphere-egu24-4754, 2024.

EGU24-6247 | ECS | Posters on site | TS8.1

Slab dynamics in the mantle: a back-to-basics approach 

Abigail Plimmer, Huw Davies, and James Panton

Subduction is one of the most fundamental processes on Earth, linking the lithosphere and mantle and is a key driving force in mantle circulation. Despite this, and the advancement of geophysical methods which allow us to better understand mantle dynamics, our understanding of slab behaviour is still limited. The Earth is a very complex system, and so conclusions regarding slab dynamics are also sensitive to the interplay between countless processes acting within the mantle. 

There is much to learn about slab sinking in the mantle from considering a single 'perfect' plate, such that the dynamics can be isolated from any pre-established or distal processes. We present a range of 3D spherical mantle circulation models which evolve from the initial condition, driven by a 'perfect' plate at the surface. Each of these plates comprises a rectangular geometry, bound by a subduction zone on one side, a spreading ridge on the opposite side, and two tranform faults on the adjacent edges. We vary the geometry of the plate, both in terms of the length of the subducting trench, and the distance from the trench to the ridge, and vary the plate velocity.

We will report the slab behaviour in terms of plate geometry, mantle properties, and plate velocity, focussing on the evolution of downwellings, upwellings and other mantle structures in response to mantle circulation models driven solely by a single plate at the surface.

How to cite: Plimmer, A., Davies, H., and Panton, J.: Slab dynamics in the mantle: a back-to-basics approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6247, https://doi.org/10.5194/egusphere-egu24-6247, 2024.

EGU24-6549 | ECS | Posters on site | TS8.1

Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models 

Taiwo Ojo, Joshua Guerrero, Chad Fairservice, Pejvak Javaheri, and Julian Lowman

We implement an innovative method of plate identification for the purpose of evaluating plate motion in numerical mantle convection models. Our method utilizes an existing tool,  Automatic Detection Of Plate Tectonics (ADOPT), which applies a tolerance (threshold) algorithm to elevation maps, to detect candidate plate boundaries at the surface of 3-D spherical mantle convection models. The logarithm of the strain-rate field yields a well-defined elevation map where local maxima lineations indicate spreading centres, zones of convergence, transform faults or diffuse deformation zones. For the plates found by ADOPT’s analysis, we determined rotation (Euler) poles implied by the velocities  within  the plate interiors. Subsequently, we examined the velocity field of each model plate for its agreement with rigid motion about the Euler poles.  We apply our method to snapshots taken from three previously published mantle convection calculations that appear to generate plate-like surface behaviour. Self-consistently generated model plates were obtained by combining a highly temperature-dependent viscosity with a yield stress that adds a strain-rate dependence to the viscosity, thus allowing for both intra-plate low strain-rate and weakening along tightly focussed plate boundaries. We generally identify more (and smaller) rigid plates for low yield stress or low threshold. Strong agreement of the surface velocities with rigid-body rotation around Euler poles is found for many of the plates identified; however, some plates also exhibit internal deformation. Regions that show a departure from rigidity can be decomposed into subsets of rigidly moving plates. Thus, the identification of a mantle convection model's maximally rigid plate surface may require plate boundary detection at both low and high thresholds. We suggest that as global mantle convection models superficially converge on the generation of plate boundary network similar to those observed with plate tectonics (including transform fault generation), testing for plate rigidity through the determination of Euler poles can serve as a quantitative measure of plate-like surface motion.

How to cite: Ojo, T., Guerrero, J., Fairservice, C., Javaheri, P., and Lowman, J.: Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6549, https://doi.org/10.5194/egusphere-egu24-6549, 2024.

EGU24-6630 | Posters on site | TS8.1

Gondwanan Flood Basalts Linked Seismically to Plume-Induced Lithosphere Instability 

Ya-Nan Shi and Jason Morgan

Delamination of continental lithospheric mantle is now well-recorded beneath several continents. However, the fate of delaminated continental lithosphere has been rarely noted, unlike subducted slabs that are reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5  horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500-700 km depths beneath former Gondwana, with the slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2-4×106 km3, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa.

How to cite: Shi, Y.-N. and Morgan, J.: Gondwanan Flood Basalts Linked Seismically to Plume-Induced Lithosphere Instability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6630, https://doi.org/10.5194/egusphere-egu24-6630, 2024.

EGU24-7075 | Orals | TS8.1

Absence of surface volcanism and the indeterminate evidence for continental mantle plumes 

Simone Pilia, Giampiero Iaffaldano, Rhodri Davies, Paolo Sossi, Scott Whattam, and Hao Hu

There are rare occurrences on Earth where mantle plumes intersect with continents, resulting in surface volcanism.Unlike their more common counterparts in oceanic lithosphere, where the ascent of melts is facilitated by a thinner lithosphere, identifying continental plumes is challenging. Surface volcanism, traditionally a key indicator of mantle plumes, may play a diminished role in regions characterized by complex tectonics and variations in lithospheric thickness.

Eastern Oman provides an excellent example where a continental mantle plume has remained undetected due to the absence of current surface volcanism. The region exhibits evidence of intraplate basanites, although with an age of ~35-40 Ma. Given their geochemical signature, these alkaline rocks likely originated from a mixture of melts from a plume-derived source and those from a lithosphere-derived component. Using P- and S-wave arrival-time residuals from distant earthquakes, we image a new mantle plume in eastern Oman, which we name the Salma plume. This continental plume is revealed in our 3-D P- and S-wave tomographic models as a 200 km low-velocity conduit extending to at least the base of the upper mantle, and located below the area of Tertiary intraplate volcanism. Despite experiencing minimal shortening since the Paleogene, the shallow-marine sediments of the Salma Plateau in eastern Oman reach elevations exceeding 2000 meters. Ongoing uplift, indicated by elevated Quaternary marine terraces, suggests that the plateau is still rising. The present uplift rate is modest but maps of residual topography show a positive trend in eastern Oman that can be associated to the presence of a plume.

Incorporating a geodynamic perspective, our analysis of noise-mitigated Indian plate motion relative to Somalia reveals that India underwent a constant-velocity reorientation of approximately 15˚  from 48 to 30 Ma, concurrent with the arrival of the plume head beneath eastern Oman. We quantitatively demonstrate that increased asthenospheric flow induced by the plume flux in eastern Oman, adjacent to the Indian plate in the Eocene, may be responsible for deflecting the Indian plate path, as indicated in kinematic reconstructions.

The consequence of ignoring a plume in Oman is that we were unable to understand many of the enigmatic observations from plume impingement at ~40 Ma. Our study underscores the potential of combining seismology, geology, geochemistry, and geodynamics to be a more effective approach for detecting continental plumes than relying solely on surface volcanism, and has transformed our understanding of the tectonic evolution of the area and beyond.

How to cite: Pilia, S., Iaffaldano, G., Davies, R., Sossi, P., Whattam, S., and Hu, H.: Absence of surface volcanism and the indeterminate evidence for continental mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7075, https://doi.org/10.5194/egusphere-egu24-7075, 2024.

EGU24-7255 | Orals | TS8.1

Short-period (400 kyr) pulsation of the Réunion plume 

Vincent Famin, Xavier Quidelleur, and Laurent Michon

Many hotspots worldwide display evidence of fluctuating magmatic emplacement rates in their history, at periods of 1-20 Myr, indicative of changing melt production within underlying mantle plumes. Here we report unprecedentedly short fluctuations of magmatic activity in the Réunion hotspot, emblematic because it started with the Deccan traps suspected to have caused the Cretaceous-Paleogene mass extinction. Using K-Ar geochronology, field observations, and geomorphology, we reconstructed the volcanic history of La Réunion and Mauritius islands, the two latest manifestations of the Réunion hotspot. Our reconstruction reveals coeval magmatic activity pulses and rest intervals for the two islands over the past 4 Ma. The period of these pulses, of ~400 kyr, is an order of magnitude shorter than any fluctuation found on other hotspots. Given the distance between La Réunion and Mauritius (~230 km), this synchronous short-period pulsation of the Réunion hotspot cannot stem from the lithosphere (≤70 km thick), and must be attributed to deeper plume processes. Moreover, this ~400 kyr periodicity coincides with the recurrence time of magmatic phases in the Deccan traps, suggesting that the pulsation began with the initiation of the hotspot. We propose that the Réunion plume is regularly pulsing with a periodicity of ~400 kyr, possibly since the Cretaceous-Paleogene transition, thus delivering extremely short-period waves of magma to the surface, synchronous over hundreds of kilometers. Understanding the geodynamic causes of this superfast beat of the Réunion plume is the objective of the four-year project “Plum-BeatR”, funded by the Agence Nationale de la Recherche (ANR- 23-CE49-0009), starting in 2024.

How to cite: Famin, V., Quidelleur, X., and Michon, L.: Short-period (400 kyr) pulsation of the Réunion plume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7255, https://doi.org/10.5194/egusphere-egu24-7255, 2024.

Plate tectonics plays a pivotal role in shaping the Earth's surface and is intricately linked to internal processes, including the subduction of cold slabs and the ascent of hot mantle plumes. Statistical analyses have unveiled a strong correlation between the distribution of large igneous provinces (LIPs) over the past 320 Ma and two large low-velocity provinces (LLVPs) beneath Africa and the Pacific Ocean. Consequently, hypotheses have emerged suggesting the long-term stability of these LLVPs. However, numerical modeling challenges this notion, suggesting that these basal mantle structures are mobile. To resolve these debates, we attempt to study these basal mantle structures from the evolution of intermediate-scale thermochemical anomalies. We report such an intermediate-scale thermochemical anomaly beneath the NW Pacific Ocean based on existing tomographic models and use paleogeographically constrained numerical models to study its evolution. Considering different plate configurations in North Pacific, our models consistently show that this anomaly was separated from the Perm anomaly by the subduction of the Izanagi slab in the Cretaceous. After the separation, it generated a mantle plume, inducing an oceanic plateau that got subducted beneath Kamchatka in Eocene. This scenario is consistent with multiple lines of evidence, including the seismic anomaly in the lower mantle, a seismically detected megameter-scale reflector that coincides with the subducted oceanic plateau and changes in Pacific Plate motion that correlated with the Eocene trench-plateau collision. We propose that intermediate-scale low velocity structures constantly undergo segregation and coalescing, and are sources of plumes that lie outside the two major LLVPs. Merging of the reported anomaly with the Pacific LLVP suggests the latter is still under assembly.

How to cite: Zhang, J. and Hu, J.: Segregation of thermochemical anomaly and associated deep mantle plume outside the large low-velocity provinces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8432, https://doi.org/10.5194/egusphere-egu24-8432, 2024.

EGU24-8563 | ECS | Orals | TS8.1

UPFLOW body wave tomography of the whole mantle column beneath the Azores-Madeira-Canaries region 

Maria Tsekhmistrenko, Ana Ferreira, and Miguel Miranda

We present initial tomographic findings from the ERC-funded UPFLOW (Upward mantle flow from novel seismic observations) project, showcasing results from a large-scale passive seismology experiment conducted in the Azores-Madeira-Canaries region between July 2021 and September 2022. Recovering 49 out of 50 ocean bottom seismometers (OBSs) in a ~1,000×2,000 km2 area with an average station spacing of ~150-200 km, we analyze approximately ~8000 multi-frequency (T ~2.7-30 s) body-wave travel time cross-correlation measurements derived from UPFLOW OBS data and over 120 teleseismic events. A preliminary P-wave tomographic model is presented, offering insight into the region's mantle dynamics.

Furthermore, by integrating UPFLOW's OBS data with global seismic data from both temporary and permanent stations, we expand the dataset to around 600,000 multifrequency measurements. This comprehensive dataset is employed to construct a global P-wave model, providing enhanced resolution throughout the entire mantle column beneath the Azores-Madeira-Canaries region. A comparative analysis with existing global tomography models is performed, and we discuss the geodynamical implications of our new, high-resolution model.

How to cite: Tsekhmistrenko, M., Ferreira, A., and Miranda, M.: UPFLOW body wave tomography of the whole mantle column beneath the Azores-Madeira-Canaries region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8563, https://doi.org/10.5194/egusphere-egu24-8563, 2024.

EGU24-8567 | Orals | TS8.1

Iceland plume and its magmatic manifestations: LIP-Dornröschen in the North Atlantic 

Alexander Koptev and Sierd Cloetingh

The North Atlantic region is a prime example of the interaction between plate tectonic movements and thermal instabilities in the Earth’s mantle. The opening of the Labrador Sea/Baffin Bay and the North Atlantic, the widespread volcanism and the localized uplift of the topography in Greenland and the North Atlantic are traditionally attributed to the thermal effect of the Iceland mantle plume. However, several prominent features of the region – the temporal synchrony of magmatism and break-up events, the symmetrical configuration of the Greenland-Iceland-Faroe Ridge, and the diachronous domal uplift of the North Atlantic rifted margins – have inspired alternative, “non-plume” views. According to these, the North Atlantic Igneous Province (NAIP) and Iceland magmatism originate from plate tectonic processes sourced in the shallow upper mantle, at odds with the unequivocal presence of deep-seated low-velocity seismic anomalies beneath Iceland and the isotopic signatures of plume-derived melts in Cenozoic magmatic units.

We resolve apparent contradictions in the observations and reconstructions and reconcile end-member concepts of the Late Mesozoic-Cenozoic evolution of the North Atlantic realm. We show that simultaneous Paleocene (~62-58 Ma) magmatism in Western Greenland/Baffin Island and the British Isles, which together form the NAIP, is driven by two processes accidently coinciding in time: 1) the propagation of the Labrador Sea/Baffin Bay spreading axis has overlapped with the ~100-80 Ma dated segment of the Iceland hotspot track near the West Greenland margin, while 2) the actual tail of the Iceland plume has reached the eastern continental margin of Greenland, allowing a horizontal flow of hot plume material along corridors of relatively thinned lithosphere towards Southern Scandinavia and Scotland/Ireland. In this framework, the subsequent formation of the symmetrical Greenland-Iceland-Faroe Ridge can be coherently explained by the continuous supply of hot plume material through an established channel between Eastern Greenland and the British Isles. In contrast to the Scotland/Ireland region, the South Norway continental lithosphere remains too thick to enable localized uplift of the topography and melting immediately after plume lobe emplacement at ~60 Ma. Therefore, the development of topographic domes in Southern Scandinavia only started ~30 Myr later in the Oligocene as a consequence of increasing ridge-push compression that built up during the opening of the Norwegian-Greenland Sea.

The evolution of the North Atlantic region shows that a thermal anomaly that has been hidden below a thick lithosphere for tens of Myr without signs of excessive magmatism can be re-initialized (or “re-awakened”) by the lateral propagation of spreading ridges or by the tapping of its source beneath thinner segments of the overlying lithosphere due to horizontal plate movements. We dub this type of Large Igneous Province (LIP) as LIP-Dornröschen (LIP-Sleeping Beauty). We hypothesise that the term LIP-Dornröschen may be applicable to a broad family of LIPs, including Precambrian and oceanic LIPs. This means that the interpretation of the timing of LIP formation from the perspective of mantle dynamics should be treated with caution, as there may be delays between the timing of upwelling in the mantle and detectable magmatic manifestations at or near the Earth’s surface.

How to cite: Koptev, A. and Cloetingh, S.: Iceland plume and its magmatic manifestations: LIP-Dornröschen in the North Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8567, https://doi.org/10.5194/egusphere-egu24-8567, 2024.

EGU24-9504 | ECS | Orals | TS8.1

Depth dependence of mantle plume flow beneath mid-ocean ridges 

Sibiao Liu, Fan Zhang, Lei Zhao, Xubo Zhang, and Jian Lin

Hotspot-related anomalies observed in mid-ocean ridge systems are widely interpreted as the result of upwelling mantle plumes interacting with spreading ridges. A key indicator of this interaction is 'waist width', which measures the distance of plume flow along the ridge. Current scaling laws for waist width, premised on a gradual decrease in plume temperature along the ridge, often overlook sub-ridge longitudinal thermal variations, potentially biasing width measurements at various depths. In this study, we refined waist width measurements by tracking the material flow and its thermal diffusion from the plume source in plume-ridge interaction models. These non-Newtonian viscoplastic models integrate ridge spreading, lithospheric cooling with hydrothermal circulation, and mantle dehydration. Model results show that the hot plume initially boosts upwelling from the deep mantle to near the dehydration zone, followed by a slowdown and lateral spread across and along the ridge. In addition to strongly correlating with plume flux and spreading rate, the pattern and distance of plume flow vary with depth. At deeper depths, the plume expands radially in a pancake-like thermal pattern with shorter along-ridge distances, while shallower, it shows an axial pipe-like dispersion over longer distances, forming a concave structure. This is shaped by the cooling of the plume material during the phase of decelerated upwelling and along-ridge dispersion within the dehydration zone and cooling of the oceanic lithosphere associated with plate spreading. Estimates of plume buoyancy flux, derived from both material- and isotherm-tracking waist widths, show significant variations at different depths, suggesting that understanding depth-dependent plume dynamics beneath mid-ocean ridges is crucial for reconciling the observed discrepancies in buoyancy flux estimates.

How to cite: Liu, S., Zhang, F., Zhao, L., Zhang, X., and Lin, J.: Depth dependence of mantle plume flow beneath mid-ocean ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9504, https://doi.org/10.5194/egusphere-egu24-9504, 2024.

EGU24-9647 | Posters virtual | TS8.1

Influence of the Kerguelen hotspot on eastern Indian lithosphere by trans-dimensional Bayesian inversion of Rayleigh wave dispersion data 

Nirjhar Mullick, Vivek Kumar, Gokul Saha, Shyam S. Rai, and Thomas Bodin

Mantle plumes play major role in modifying the continental lithosphere producing rifts and massive amounts of basaltic volcanism as the anomalously hot mantle undergoes decompressive melting. If conditions are favourable the rift may widen and a new ocean is formed. During the break up of Eastern Gondwana at ~ 130 Ma, the Kerguelen mantle plume influenced the separation of India from Antarctic and Australian plates and generation of the Eastern Indian Ocean. Eastern India-Bangladesh region (83-94ºE, 21-26ºN) carries imprints of the plume activity in the form of the Rajmahal and Sylhet traps and their subsurface expression in Bengal basin and extensive lamproytes. Existing geophysical studies of the region are mainly crustal scale and do not explicitly refer to the Kerguelen plume activity providing geophysical evidence for the same. We present here lithospheric shear velocity structure of the region up to a depth of ~ 175 km by trans-dimensional Baysian inversion of Rayleigh group velocity dispersion data (7-100s at 1º X 1º resolution). Using the same, we investigate the influence of the Kerguelen plume on the lithosphere of the Eastern India-Bangladesh region that comprises the Eastern India craton, the Bengal basin, the Bhrahmaputra basin, Bangladesh and the Shillong- Mikir plateau.

How to cite: Mullick, N., Kumar, V., Saha, G., Rai, S. S., and Bodin, T.: Influence of the Kerguelen hotspot on eastern Indian lithosphere by trans-dimensional Bayesian inversion of Rayleigh wave dispersion data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9647, https://doi.org/10.5194/egusphere-egu24-9647, 2024.

EGU24-10288 | Posters on site | TS8.1

Heterogeneous mantle source of Mauna Loa volcano (Hawai’ian plume) revealed by Sr-isotope and trace elements signatures of olivine-hosted melt inclusions 

Adrien Vezinet, Blas Barbera, Alexander V. Sobolev, Valentina G. Batanova, Charbel Kazzy, and Aleksandr V. Chugunov

Melt inclusions hosted in highly magnesian olivine crystals have proven invaluable for probing the composition of the mantle through time since their geochemical signature is reflecting that of parental melt. Additionally, the geochemical study of melt inclusions has shown to be more suited to identify the heterogeneity in the magma from which they crystallized, particularly the chemically depleted domains [1, 2]. Here, we will present new major, minor & trace elements, H2O contents and Sr-isotope signature of more than 300 olivine-hosted naturally quenched melt inclusions from Pu’u Wahi (910 yr-old) and Puʻu Mahana (ca. 50 kyr-old), two ash cones associated with Mauna Loa, the largest shield volcano of the Hawai’ian seamount chain. In order to have a high degree of confidence in the geochemical proxies, Sr-isotope and trace elements analyses were conducted through laser ablation split stream (LASS) protocol on top of EPMA and Raman (for H2O contents) analytical spots. Preliminary results in our new set of inclusions show the presence of high (Sr/Ce)N inclusions, previously interpreted as indicating either gabbro influence in the source of the plume [3] or interactions between plagioclase-rich cumulates and percolating mantle-derived melts [4]. Further, “ultra-depleted melts”, UDM, indicated by K2O contents < 0.1 wt.% identified in [1], have also been re-identified in this new set of inclusions (not analyzed for Sr-isotope yet). 87Sr/86Sr of non-UDM inclusions ranges from 0.70361±0.00025 to 0.70427±0.00025, i.e. analogous to the most recent TIMS values [4, 5]. Additional LASS analyses will be conducted before the meeting. The full set of analyses will be confronted to published results on the same volcano [1, 3-6] and integrated in a larger framework of interactions between mantle plume and consequences for plate tectonic.

References:

  • Sobolev, A.V., et al., Nature, 2011. 476(7361).
  • Stracke, A., et al., Nature Geoscience, 2019. 12(10).
  • Sobolev, A.V., et al., Nature, 2000. 404(6781).
  • Anderson, O.E., et al., Geochemistry, Geophysics, Geosystems, 2021. 22(4).
  • Reinhard, A., et al., Chemical Geology, 2018. 495.
  • Sobolev, A.V., et al., Nature, 2005. 434(7033).

How to cite: Vezinet, A., Barbera, B., Sobolev, A. V., Batanova, V. G., Kazzy, C., and Chugunov, A. V.: Heterogeneous mantle source of Mauna Loa volcano (Hawai’ian plume) revealed by Sr-isotope and trace elements signatures of olivine-hosted melt inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10288, https://doi.org/10.5194/egusphere-egu24-10288, 2024.

EGU24-10507 | ECS | Posters on site | TS8.1

The density and viscosity of a bilithologic plume-fed asthenosphere 

Jia Shao and Jason Morgan

Pyroxenites are generated by the subduction of sediments and oceanic basalts into the deep mantle. These rocks, together with the larger volume fraction of their surrounding mantle peridotites make up a lithologically heterogeneous two-component mantle, sometimes called a ‘marble-cake’ or ‘plum-pudding’ mantle. Geochemical and petrological observations have shown that pyroxenites play a significant role in the genesis of oceanic island basalts (OIB). However, the consequences of preferential pyroxenite melting on bulk mantle properties have yet to be systematically explored. For example, how does the plume melting process modify a plum-pudding mantle’s bulk density and viscosity? This question could be very important, in particular if the asthenosphere is formed by material from upwelling, melting plumes.

To explore the above questions, we use the thermodynamic software Perple_X to determine densities for different degrees of depleted (i.e. partially melted) peridotites and pyroxenites. We then include these relations into a one-dimensional numerical simulation code for the upwelling and pressure-release melting of a potentially wet multi-component mantle. We investigate the density changes associated with the melting of this idealized mantle’s pyroxenites and peridodites, and also the viscosity change by assuming that the reference viscosity of pyroxenite is 10-100 times that of dry peridotite at similar P-T conditions, since the peridotite’s olivines are the weakest large volume-fraction minerals in the upper mantle. We have explored the effects of mantle temperature, initial water contents, initial fractions of pyroxenites and peridotite, peridotite solidi, and the thickness of the overlying lithosphere which will affect the depth-interval of upwelling and melting. Preliminary results show that significant density and viscosity changes should take place during plume upwelling and melting. ~30% partial melting of pyroxenite would lead to a net bulk density reduction of 0.3%, comparable to the thermal buoyancy associated with a ~100° temperature increase. As long as the surrounding peridotites do not melt, the mixture’s aggregate viscosity will remain that of wet peridotitic mantle; after the peridotites have melted a percent or so, the aggregate viscosity will increase 10-100-fold to that of dry peridotite. This could lead to the formation of a 10-100x asthenospheric viscosity restitic hotspot swell root. Eventual peridotitic melting will reduce the density of the more depleted peridotites relative to fertile peridotite as originally noted by Oxburgh and Parmentier (1977), but to a lesser degree than the density reduction associated with the preferential removal of pyroxenites by their partial melting. A dynamical consequence is that the asthenosphere is likely to be strongly stratified by density, with its most pyroxenite-depleted materials likely to rise to form a layer along the base of the overlying oceanic lithosphere. 

How to cite: Shao, J. and Morgan, J.: The density and viscosity of a bilithologic plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10507, https://doi.org/10.5194/egusphere-egu24-10507, 2024.

EGU24-10967 | ECS | Posters on site | TS8.1

From plumes to subduction network formation and supercontinent break-up 

Michaël Pons, Stephan V. Sobolev, Charitra Jain, and Elodie Kendall

The evolution of modern plate tectonics is described by the Wilson cycle, which portrays the dynamics of the supercontinental cycle through the interaction of the oceanic plate with the continental plate over periods of hundreds of millions of years. This cycle is characterized by a phase of supercontinent assembly and enhanced orogenic collision, followed by a phase of supercontinent fragmentation and dispersal, as shown by the geological record. The dynamics of the Wilson cycle is intrinsically linked to mantle convection and subduction dynamics. While the assembly phase appears to follow a degree-2 mantle convection style, the mechanism responsible for supercontinent fragmentation is still debated. We hypothesize that the dispersal phase is mostly governed by trench roll-back from subductions and mantle plumes. To test this hypothesis, we have built a series of 2D and 3D geodynamic models of the Earth on a global scale using the ASPECT code. We have tested different scenarios in which we prescribe the distribution of the supercontinent Rodinia at 1Ga or Pangea at 250 Ma and let the models evolve self-consistently.  In some model variants, the strength of the supercontinent and that of the surrounding oceanic area is changed. We will present our preliminary results and discuss the dynamics of continental dispersal and its link to subduction and mantle dynamics. In particular, 3D models will demonstrate how regional plume-induced retreating subduction zones evolve into a global network of subduction zones and tectonics plate boundaries which ultimately leads to the break-up of the supercontinent.

How to cite: Pons, M., V. Sobolev, S., Jain, C., and Kendall, E.: From plumes to subduction network formation and supercontinent break-up, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10967, https://doi.org/10.5194/egusphere-egu24-10967, 2024.

While the temperature drop across the thermal boundary layer (TBL) at the base of the mantle is likely > 1000 K, the temperature anomaly of plumes, which are believed to rise from that TBL is only up to a few hundred K. Reasons for that discrepancy are still poorly understood. It could be due to a combination of (1) the adiabat inside the plume being steeper than in the ambient mantle, (2) the plume cooling due to heat diffusing into the surrounding mantle as it rises, (3) the hottest plume temperature representing a mix of temperatures in the TBL, and not the temperature at the core-mantle boundary (CMB), (4) plumes not directly rising from the CMB due to chemically distinct material at the base of the mantle, (5) a plume-fed asthenosphere which is on average warmer than the mantle adiabat, reducing the temperature difference between plumes and asthenospheric average. Here we use the ASPECT software to model plumes from the lowermost mantle and study their excess temperatures. We use a mantle viscosity that depends on temperature and depth with a strong viscosity increase from below the lithosphere towards the lower mantle, reaching about 1023 Pas above the basal TBL, consistent with geoid modelling and slow motion of mantle plumes. With a mineral physics-derived pyrolite material model, the difference between a plume adiabat and an ambient mantle adiabat just below the lithosphere is about two thirds of that at the base of the mantle, e.g. 1280 K temperature difference at the CMB reduces to about 835 K at 200 km depth. In 2-D cartesian models, plume temperature drops more strongly and is rather time variable due to pulses rising along plume conduits. In contrast, 3-D models of isolated plumes are more steady and, after about 10-20 Myr after the plume head has reached the surface, their temperatures remain rather constant, with excess temperature drop compared to an adiabat for material directly from the CMB usually less than 100 K. This extra temperature drop is small because plume buoyancy flux is high. Hence the above points (2) and (3) do not contribute much to reduce temperature of isolated 3-D plumes. In our models, the asthenosphere is on average about 200-400 K hotter than the mantle beneath, due to plume material feeding into it. While this appears to reduce the plume temperature anomaly, a resulting cooler mantle adiabat also corresponds to an even stronger temperature drop in the basal TBL, offsetting that effect. In the Earth, plumes are likely triggered by slabs and probably rise preferrably above the margins of chemically distinct piles. This could lead to reduced excess temperatures, if plumes are more sheet-like, as the 2-D models, or temperature at their source depth is less than at the CMB.

How to cite: Steinberger, B. and Roy, P.: Why are plume excess temperatures much less than the temperature drop across the core-mantle boundary?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11566, https://doi.org/10.5194/egusphere-egu24-11566, 2024.

EGU24-11719 | Orals | TS8.1

Prospects of Neutrino Oscillation Tomography of the Earth  

Veronique Van Elewyck, Joao Coelho, Yael Armando Deniz Hernandez, Stephanie Durand, Nobuaki Fuji, Edouard Kaminski, Lukas Maderer, Eric Mittelstaedt, and Rebekah Pestes

Much has been learned about the deep Earth through a combination of geophysical constraints, theories of Earth’s formation, and seismic measurements. However, such methods alone cannot directly resolve the full structure of the inner Earth, e.g. in terms of matter density, composition and temperature distributions.

Complementary information about Earth’s interior can be provided by small, nearly massless elementary particles called neutrinos that propagate through the Earth. Neutrinos exist in different flavours and are known to experience a quantum phenomenon of flavour oscillation as they propagate. With an extremely small chance of interacting with matter, neutrinos can travel long distances through very dense materials (e.g., the Earth’s core). For atmospheric neutrinos of energy ~GeV crossing the Earth, the flavour oscillation patterns are distorted due to coherent forward scattering on electrons along their path. Measuring the flavour, energy and angular distributions of such neutrinos therefore provides sensitivity to a new observable of geophysical interest: the electron number density in the layers of matter traversed.

After a short introduction to the concepts of neutrino oscillation tomography, we will discuss the potential of this method to address open questions concerning inner Earth's structure and composition (such as the amount of light elements in the core and the nature of LLSVPs), the status of sensitivity studies, and the perspectives opened by the next generation of atmospheric neutrino detectors.

How to cite: Van Elewyck, V., Coelho, J., Deniz Hernandez, Y. A., Durand, S., Fuji, N., Kaminski, E., Maderer, L., Mittelstaedt, E., and Pestes, R.: Prospects of Neutrino Oscillation Tomography of the Earth , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11719, https://doi.org/10.5194/egusphere-egu24-11719, 2024.

The Rajmahal Traps is one of the two major Large Igneous Provinces (LIPs) that erupted in the Indian subcontinent in the Mesozoic. The trap was the product of activity at the Kerguelen hotspot, located in the Indian Ocean, that initiated around 117 Ma. Earlier studies on the eruption location of the Rajmahal trap show that its location does not coincide with the present-day location of the Kerguelen Hotspot. This difference in the paleo-locations could be the result of mantle dynamics beneath the Indian Ocean during the Cretaceous and has been explained with concepts such as the multiple diapir-single plume model, the migration pathway of the hotspot beneath the mantle, and the complex plume-ridge interaction.

In this study, we use paleogeographic reconstruction software GPlates to reconstruct the paleogeography of the Rajmahal Traps on the Indian subcontinent plate in an Antarctica fixed reference frame since 117 Ma to pin-point the paleo-location of the Kerguelen hotspot and eruption location of the Rajmahal trap along with the tectonic changes that the Indian Ocean was encountering. The mantle structure below the Indian Ocean was further studied using publicly available P-wave tomography data. The paleogeographic reconstruction linked to the mantle structure hints towards the presence of a tree-like hotspot-plume structure beneath the Kerguelen hotspot where a deep-seated single plume feeds into various fissures at the surface which are active at different points in time.

Our kinematic analysis for the Indian Plate reveals significant changes in the velocity of the plate since the Cretaceous at specific points in time in response to tectonic activities initiated by the plumes present in the Indian Ocean. These activities that link to changes in the velocity include interactions with the Morondova plume (velocity increase at 90 Ma) and Reunion hotspot (velocity increase between 78 – 62 Ma), and other processes like continental collision (velocity decrease at 56 Ma and between 50-43 Ma) and slab pull (velocity increase at 56 Ma). Using this new velocity profile, we have developed a revised velocity model for the drift of the Indian subcontinent since the Cretaceous.

How to cite: Guleriya, S., Beniest, A., and Tiwari, S. K.: Change in eruption location in Kerguelen hotspot and Kinematic Reconstruction of Rajmahal Trap:  Implications for Cretaceous to present day Geodynamics of Indian plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11883, https://doi.org/10.5194/egusphere-egu24-11883, 2024.

EGU24-12584 | Orals | TS8.1

Robust hotspot origin far from LLSVP margins 

John Tarduno

W. Jason Morgan’s seminal development of plate tectonic theory set the foundation for current investigations of mantle convection and the nature of deep mantle plumes. More recently, hotspots have been proposed to occur at the edges of stationary African and Pacific large low shear velocity provinces (LLSVPs) and that this has a special significance in terms of plume/hotspot generation. The basis for this proposed global correlation has in turn been challenged, and whether LLSVPs edges are the sites of initial mantle plume formation debated. A different approach is to consider hotspots with the greatest buoyancy flux because to be successful, any global model should be able to explain their origin. In all analyses of buoyancy flux, the Pacific’s Hawaiian hotspot, which figured prominently in Jason’s early papers, stands out above all others. However, paleomagnetic and age-distance relationships indicate that the Hawaiian hotspot originated >1500 km N of the Pacific LLSVP and subsequently drifted to its edge where it may have become anchored. The hotspot with the highest buoyancy flux in the Atlantic is Iceland, which is far from the African LLSVP. Iceland represents the youngest of three past episodes of extraordinary volcanism affecting the North Atlantic-Arctic region, namely the North Atlantic Tertiary Volcanic Province, the High Arctic Large Igneous Province, and the Siberian Traps. This recurrent volcanism spanning more than 250 million years requires either drift of a single pulsing plume, or separate plumes, generated far from the edge of the proposed stationary African LLSVP. Thus, the nature and histories of these robust hotspots in the Pacific and Atlantic imply an origin distinct from stationary LLSVPs.  

How to cite: Tarduno, J.: Robust hotspot origin far from LLSVP margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12584, https://doi.org/10.5194/egusphere-egu24-12584, 2024.

EGU24-13570 | Orals | TS8.1

Changes in the Rate of Ocean Crust Production Over the Past 19 Myr: Implications for Sea Level, Mantle Heat Loss, and Climate 

Colleen Dalton, Timothy Herbert, Douglas Wilson, and Weimin Si

The rate of ocean-crust production exerts control over mantle heat loss, sea level, seawater chemistry, and climate. Reconstructing ocean-crust production rates back in time relies heavily on the distribution of present-day seafloor age. Different strategies to account for the incomplete preservation of older seafloor have led to differing conclusions about how much production rates have changed since the Cretaceous, if at all. We have constructed a new global synthesis of ocean-crust production rates along 18 mid-ocean ridges for the past 19 Myr at high temporal resolution.  We find that the global ocean-crust production rate decreased by ~37% from its maximum during 19-15 Ma to its minimum during 6-4 Ma. Our ability to resolve these changes at a statistically significant level is due to the availability of many new plate reconstructions at high temporal resolution and our use of an astronomically calibrated magnetic time scale with small uncertainties in reversal ages. We show that the reduction in crust production occurred because spreading rates slowed down along almost all ridge systems. While the total ridge length has varied little since 19 Ma, some fast-spreading ridges have grown shorter and slow-spreading ridges grown longer, amplifying the spreading-rate changes. The change in crust production rate skews the seafloor area-age distribution toward older crust, and we estimate that sea level may have fallen by as much as 32-37 m and oceanic heat flow may have been reduced by 6%. We also show, using a simple model of the carbon cycle, that the inferred changes in tectonic degassing resulting from the crust-production changes can account for the majority of long-term surface-temperature evolution since 19 Ma.

How to cite: Dalton, C., Herbert, T., Wilson, D., and Si, W.: Changes in the Rate of Ocean Crust Production Over the Past 19 Myr: Implications for Sea Level, Mantle Heat Loss, and Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13570, https://doi.org/10.5194/egusphere-egu24-13570, 2024.

EGU24-13786 | ECS | Posters on site | TS8.1

Counterflow and entrainment within a buoyant plume-fed asthenosphere 

Xianyu Li, Jia Shao, Guanzhi Wang, Yanan Shi, and Jason Morgan

Laboratory and numerical experiments and boundary layer analysis of the entrainment of buoyant asthenosphere by subducting oceanic lithosphere (cf. Morgan et al., Terra Nova, 2007) implies that slab entrainment is likely to be relatively inefficient at removing a buoyant and lower viscosity asthenosphere layer. Such asthenosphere would instead be mostly removed by accretion into overlying oceanic lithosphere, both at mid-ocean ridges where a ~60-km compositional lithosphere forms due to the melt-induced dehydration of upwelling peridotitic mantle, and later with the thermal growth of  overlying oceanic lithosphere. When an oceanic plate subducts, the lower (hot) side of a subducting slab entrains a 10– 30 km-thick downdragged layer, whose thickness depends upon the subduction rate and the density contrast and viscosity of the asthenosphere, while the upper (cold) side of the slab may entrain as much by thermal ‘freezing’ onto the slab as by mechanical downdragging.  

Here we use 2-D numerical experiments to investigate the dynamics of entrainment and counterflow at subduction zones. We explore situations with both stable subduction geometries and slab rollback. Due to its low viscosity, a plume-fed asthenosphere is particularly likely to be stratified in its internal density, with variable amounts of plume melt-extraction leading to variable pyroxenite fractions and associated vertical density stratification within a bilithologic ~80-90% peridotite, ~10-20% pyroxenite asthenosphere. While this type of vertical density stratification appears to lead to similar predicted entrainment by subducting slabs, it will generate more complex patterns of asthenospheric counterflow that involve shallower and time-dependent counterflow behind the subducting slab.

How to cite: Li, X., Shao, J., Wang, G., Shi, Y., and Morgan, J.: Counterflow and entrainment within a buoyant plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13786, https://doi.org/10.5194/egusphere-egu24-13786, 2024.

EGU24-13826 | ECS | Posters on site | TS8.1

Understanding Ni-Cu Sulphide Deposits in a Plate Tectonic and Mantle Convection Context 

Isadora Page, Ben R. Mather, Nicole Januszczak, Michele Anthony, and R. Dietmar Muller

Nickel-Copper (Ni-Cu) sulphide deposits are a diverse class of deposits, formed during the cooling and crystallisation of metal-rich mafic to ultramafic magmas. Despite sharing several key ore-forming processes, many of these deposits form in contrasting geologic environments and periods. The objective of this research project is to investigate the spatial and temporal distribution of Ni-Cu sulphide deposits in a mantle convection and plate tectonic context, and to explore the influence of different mantle and tectonic parameters on their origins and occurrence. We first determine the location of these deposits in relation to relevant geologic and tectonic features through time, including subduction zones, large igneous provinces (LIPs), and mantle plumes. Using a 1 billion year plate model we extract key parameters relating to subduction, as well as the spatio-temporal distribution of LIPs through time. Employing an associated geodynamic model, we identify model mantle plumes and quantify their key properties. Preliminary findings indicate that certain mantle plumes associated with deposits exhibit increased plume flux in the upper mantle preceding deposit formation, and that many deposits are spatially associated with LIPs throughout their formation history. For several deposits located in convergent margin settings, we have identified a notable spike in subduction volume and convergence rate during a 50-100 million year period prior to the onset of mineralisation. While the angle of the subducting slab is highly variable throughout the evolution of these deposits, several deposits are associated with a distinct steepening of the subducting plate in the lead-up to deposit formation. The findings of this study aim to contribute new insights into the dynamic processes governing the genesis of magmatic Ni-Cu sulphide deposits. These insights aid in our understanding of the interplay between mantle dynamics, plate tectonics, and deposit formation, and hold implications for future critical mineral exploration.

How to cite: Page, I., Mather, B. R., Januszczak, N., Anthony, M., and Muller, R. D.: Understanding Ni-Cu Sulphide Deposits in a Plate Tectonic and Mantle Convection Context, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13826, https://doi.org/10.5194/egusphere-egu24-13826, 2024.

EGU24-13939 | ECS | Posters on site | TS8.1

Numerical exploration of the dynamics of the subduction plate boundary channel  

Guanzhi Wang, Jason P. Morgan, and Paola Vannucchi

The plate ‘interface’ at subduction zones has often been idealized as a single fault with ‘asperities’, however there is increasing evidence that plate boundary motions typically occur across a ~100-1000m channel or shear zone. Here we investigate the dynamics of slip in a mechanically heterogeneous plate boundary shear zone, and will typically use periodic boundary conditions to model the channel at a ~m-scale.  In contrast to most previous numerical studies, we imagine that this shear zone is embedded within finite strength wall-rock associated with the downgoing and overriding plates that themselves are capable of subduction-related deformation, for example during bend-faulting of the lower-plate or a forearc deformation event. We first look at how stress-concentrations can form by the clogging of strong blocks in a channel with a weaker matrix. We find that the strength of the surrounding wall-rock will play a key role in the channel’s response to a clogging event. In general, a clogging event can be mitigated by failure of surrounding relatively weak wallrock along the edges of a subduction channel in the conceptual process put forward by von Huene et al. (2004) to drive basal erosion of the forearc. We also consider cases where metamorphic transitions have led to the existence of weaker blocks within a stronger matrix. In this case, frequent tremor-like failure of the weak blocks can coexist with rarer earthquake failure of the stronger surrounding matrix.  Finally we explore the mechanical effects of channel widening and narrowing events that will invariably lead to a component of local pressure-driven flow within a subduction shear channel. Numerical snapshots and videos are used to visualize these potential modes of subduction shear zone deformation.

How to cite: Wang, G., P. Morgan, J., and Vannucchi, P.: Numerical exploration of the dynamics of the subduction plate boundary channel , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13939, https://doi.org/10.5194/egusphere-egu24-13939, 2024.

EGU24-14528 | Posters on site | TS8.1

Using Dynamic Topography and Seismic Tomography to explore the compensation of seafloor in oceanic and back-arc basins 

Jialei Qiu, Nadia Padavini, Paola Vannucchi, and Jason Morgan

Both dynamic topography and seismic tomography have played crucial roles in providing invaluable insights into the Earth's interior structure and geological processes. Here we explore to what degree dynamic topography within ocean and back-arc basins can be correlated with the upper mantle seismic structure that has been imaged in recent high-resolution global models.

To explore the global ocean dynamic topography associated with subsurface mantle convection, we need to remove the influences of known contributing factors to seafloor relief such as the cooling of the ocean floor and the thickness of the ocean crust and sediments. We developed a series of scripts in PyGMT and MATLAB to do this, based on seafloor ages in GPLATES and sediment/crust information in CRUST1.0. With these corrections for near-surface structure, we obtained global average residual-depth values that serve as a basis for analyzing global subsurface structures linked to the asthenosphere and upper mantle, which we then compare to the vertically averaged shear-wave seismic structure above the transition zone. Our preliminary study highlights that the significant ~km-difference in dynamic topography between the Philippine back-arc basin and the Lau-Tonga backarc appear to be linked to a major difference in asthenosphere thickness and density beneath these two regions.

How to cite: Qiu, J., Padavini, N., Vannucchi, P., and Morgan, J.: Using Dynamic Topography and Seismic Tomography to explore the compensation of seafloor in oceanic and back-arc basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14528, https://doi.org/10.5194/egusphere-egu24-14528, 2024.

EGU24-16479 | Posters on site | TS8.1

H, He, and seismic evidence for a bilithologic plume-fed asthenosphere  

Jason P. Morgan and W. Jason Morgan

Chemical diffusion in the mantle has typically been viewed to play a negligible role in geodynamic processes.  However, diffusion rates for water (H) and helium (He) are large enough that they lead to observable differences between pyroxenite-rich melting associated with ocean island volcanism (OIB) and more peridotite-rich melting associated with mid-ocean ridge basalts (MORB). Laboratory measurements of diffusion rates of H and He at ambient mantle temperatures in olivine are of order ~10 km/1.7Gyr for He and ~250 km/1.7 Gyr for H. If the mantle is an interlayered mixture of recycled oceanic basalts and sediments surrounded by a much larger volume of residual peridotites, then chemical diffusion can shape the mantle in two important ways.  Hydrogen will tend to migrate from peridotites into adjacent pyroxenites, because clinopyroxene has a much stronger affinity for water than the olivine and orthopyroxene that form the bulk of mantle peridotites. Therefore pyroxenite lithologies will typically have twice or more the water content of their surrounding damp peridotites. This will strongly favor the enhanced melting of pyroxenites that is now mostly agreed to be a common feature of the OIB source. Radiogenic 4He will have the opposite behaviour — it will tend to migrate from where it is produced in recycled incompatible-element-rich (e.g. U and Th-rich) pyroxenites into nearby, larger volume fraction, but U+Th-poorer peridotites, while the radioisotopes of Ar and Ne that are also produced by the decay of the incompatible elements K, U, and Th will diffuse much less, and thus remain within their original pyroxenite source.  This effect leads to lower 4He/21Ne and 4He/40Ar ratios in OIB in comparison to the predicted values based on the mantle’s bulk geochemistry, and complementary higher 4He/21Ne and 4He/40Ar ratios in the MORB source that is formed by the plume-fed asthenospheric residues to OIB melt extraction at plumes.

 The recent observation of a 150-km-deep positive shear velocity gradient (PVG) beneath non-cratonic lithosphere (Hua et al., 2023) is further evidence for the initiation of pyroxenitic melting at this depth within the asthenosphere. It also implies that lateral temperature variations at this depth are quite small, of order +/- 75°C. This near uniformity of temperatures near both mantle plumes and mid-ocean ridges is, in turn, strong evidence in favor of the hypothesis that the asthenosphere is fed by mantle plumes. We propose that two filtering effects occur as plumes feed the asthenosphere, removing both the hottest and coldest parts of upwelling plume material. First, the peridotite fraction in the hottest part of upwelling plume material melts enough for it to dehydrate, thereby transforming this fraction into a more viscous and buoyant hotspot swell root that moves with the overlying plate, not as asthenosphere. Second, since plume material is warmer than average mantle, it is more buoyant, creating a natural density filter that prevents any cooler underlying mantle from upwelling through it. These rheological and density filters make the asthenosphere sampled by melting at mid-ocean ridges have a more uniform temperature than its typical underlying mantle.

How to cite: Morgan, J. P. and Morgan, W. J.: H, He, and seismic evidence for a bilithologic plume-fed asthenosphere , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16479, https://doi.org/10.5194/egusphere-egu24-16479, 2024.

EGU24-17078 | ECS | Orals | TS8.1

Insight into the formation of the Siberian Large Igneous Province: A study of olivine-hosted melt inclusion in meimechite 

Mateo Esteban, Alexander Sobolev, Valentina Batanova, Adrien Vezinet, Evgeny Asafov, and Stepan Krasheninnikov

Meimechite (i.e., rare high MgO and TiO2 ultramafic rocks) concluded the Permo-Triassic Trap magmatism ca. 250 Ma-ago, known as a Siberian Large Igneous Province (SLIP) in the Meimecha-Kotui region, northern Siberia (e.g. [1]). In addition to their elevated MgO contents, meimechite’s melts display almost no crustal contamination, making them ideally suited to investigate the mantle source of the SLIP. Formerly, two opposing models were evoked for the origination of the meimechite: i) the hottest phanerozoic mantle plume [1] or ii) water fluxing of the asthenospheric mantle in a long-lived subduction zone [2]. Based on an extended analytical workflow we will shed new light on the source of these unusual rocks.

Here we present new results for more than 300 olivine-hosted homogenized melt inclusions from Siberian meimechite including major, minor and trace elements, water and Sr-isotopes contents (EPMA, LA-ICP-MS and Raman spectrometry) along with the chemical composition of their host olivine (EPMA, LA-ICP-MS). When encountered, spinel inclusions were analysed by EPMA for major element abundances.

We show that the Siberian meimechite crystallised from a highly magnesian (MgO > 22 wt%) parental melt deficient in H2O compared to Ce and K concentrations, which was degassed of most of its CO2 and likely part of its H2O while rising to shallower depths. Three independent geothermometers (Mg-Fe and Sc-Y olivine melt and Al olivine-spinel) confirm the high crystallisation temperature of the Siberian meimechite, ca. 1400oC. Furthermore, the calculated potential temperatures (over 1500oC) imply a mantle plume origin of the Siberian meimechite and, consequently, of the SLIP.

Initial 87Sr/86Sr values of melt inclusions reveal heterogeneous populations ranging from 0.7022±0.0002 to 0.7039±0.0004 suggesting mixing between at least two depleted mantle components. The less depleted group has an average Bulk Silicate Earth (BSE) model age of 876±88 Ma, whereas the more depleted group is significantly older with an average model age of 1716±76 Ma. All source components display significantly fractionated proxies of continental crust extraction (Nb/U, Th/U and Ce/Pb [3]), indicating major events of continental crustal formation and deep recycling of residual lithosphere before the Proterozoic Eon.

References:

[1] – Sobolev, A.V., et al., Russ. Geol. Geophys., 2009 and references therein. [2] – Ivanov, A.V., et al., Chem. Geol., 2018. [3]- Hofmann, A.W. et al. EPSL, 1986.

How to cite: Esteban, M., Sobolev, A., Batanova, V., Vezinet, A., Asafov, E., and Krasheninnikov, S.: Insight into the formation of the Siberian Large Igneous Province: A study of olivine-hosted melt inclusion in meimechite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17078, https://doi.org/10.5194/egusphere-egu24-17078, 2024.

EGU24-17341 | ECS | Orals | TS8.1

The Influence of Mantle Plumes on Plate Tectonics 

Ingo L. Stotz, Berta Vilacís, Jorge N. Hayek, Sara Carena, Anke Friedrich, and Hans-Peter Bunge

Our understanding of plate tectonics and mantle convection has made significant progress in recent decades, yet the specific impact of mantle plumes on plate tectonics remains a topic of controversy. The motions of the Earth’s lithosphere serves as a powerful lens into the dynamic behavior of the asthenosphere and deeper mantle, helping to untangle such controversies. Surface observations, therefore, provide important constraints on mantle convection patterns through space/time. Among these observations, the record of plate motion changes stands out, as it enables the geographical identification of torque sources. Consequently, surface observations provide essential constraints for theoretical models and numerical simulations.

The analytical Poiseuille flow model applied to upper mantle flux in the asthenosphere offers a robust and testable prediction: Poiseuille flow induced plate motion changes should coincide with regional scale mantle convection induced elevation changes. Mantle plumes can generate such pressure driven flows, along with intraplate magmatism and induce buoyancy-driven uplift that leaves an imprint in the sedimentary record.

Here, I will present a synthesis of geological and geophysical observations, supported by analytical calculations, to illustrate that a significant number of plate motion changes can be attributed primarily to torques originating from mantle plumes.

How to cite: Stotz, I. L., Vilacís, B., Hayek, J. N., Carena, S., Friedrich, A., and Bunge, H.-P.: The Influence of Mantle Plumes on Plate Tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17341, https://doi.org/10.5194/egusphere-egu24-17341, 2024.

Models depicting the plate kinematic development of the Indian Ocean have a range of applications including in paleogeographic studies and in formulating and testing ideas about plume/plate interactions. Until now, these applications have been forced to tolerate egregious model/observation inconsistencies concerning the relative motion history of India and Madagascar. Whilst the Phanerozoic record of these motions begins with ∼90 Ma basalts that erupted along a narrow rift basin, all modern plate kinematic models for the Indian Ocean predict hundreds of kilometres of relative motions, in diverse and conflicting senses, over several tens of millions of years prior to the eruptions. The diversity of these predicted motions suggests they are artefacts that arise from differing approaches taken to modelling the development of the eastern and western parts of the ocean, rather than a reflection of insufficient or absent geological observations. In this contribution, I present a new model for the early plate kinematic development of the Indian Ocean that is constrained by observational evidence for relative plate motion azimuths in the Enderby and western Bay of Bengal basins and by explicitly maintaining a rigid mid- and early Cretaceous Indo-Malagasy body. This approach requires the model to feature two small tectonic plates between the continental margins of eastern India and East Antarctica. The older of the two, Mandara, is an intraoceanic plate in the Enderby Basin that may have formed in relation to delivery of excess melt from the Kerguelen plume to the basin's mid-ocean ridge. The younger plate, Vasuki, in the western Bay of Bengal Basin, also accommodated plume-related melt at its boundaries, in its case from the Marion and possibly also the Crozet plume. The model shows this plate transporting Sri Lanka ∼800 km southwards along the eastern Indian continental margin to its present location. The model also requires the presence of around half a million square kilometres of continental crust beneath the Kerguelen Plateau, which lies within the range of published observation-led estimates of its extent. Neither the absence of evidence for relative motions between India and Madagascar prior to ∼90 Ma, nor the modelled Euler rotation pole's location afterwards, are consistent with suggestions that traction forces related to the ascent of the Marion plume drove the mid-Cretaceous onset of subduction in the western Neotethys.

How to cite: Eagles, G.: A new model of plate kinematics describing the early development of the Indian Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17862, https://doi.org/10.5194/egusphere-egu24-17862, 2024.

EGU24-18017 | Orals | TS8.1

Flexural Pumping and the Origins of Petit-Spot Volcanism 

Paola Vannucchi, Yanan Shi, Ting Yang, Gou Fujie, and Jason P. Morgan

Most volcanic activity on Earth is linked to well-known processes like plate tectonics and mantle plumes, typically through mechanisms such as flux-melting in subduction zones and decompression-melting at ridges and mantle plumes. However, recent discoveries point to a different origin for some intraplate volcanism, a key example being 'Petit-Spots'—small volcanic mounds that erupt on incoming plates near subduction zones. Here we propose that flexural pumping, occurring as the subducting slab unbends, transports fluids released by intra-slab dehydration to the slab's base where these fluids induce flux-melting in the warm slab base and asthenosphere beneath the slab. Counterflow in the buoyant asthenosphere beneath the subducting plate further expands the region of petit-spot volcanism. This mechanism not only explains the origin of petit-spot volcanism but also suggests a broader conceptual model for generating low-degree melts in the oceanic asthenosphere.

How to cite: Vannucchi, P., Shi, Y., Yang, T., Fujie, G., and Morgan, J. P.: Flexural Pumping and the Origins of Petit-Spot Volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18017, https://doi.org/10.5194/egusphere-egu24-18017, 2024.

EGU24-18296 | ECS | Posters on site | TS8.1

How could a single Iceland Plume produce the widely scattered North Atlantic Igneous Province volcanism? New clues from Britain and Ireland. 

Raffaele Bonadio, Sergei Lebedev, David Chew, Yihe Xu, and Javier Fullea

The extensive Paleocene magmatism of the British and Irish Tertiary Igneous Province (BITIP)—a part of the North Atlantic Igneous Province (NAIP)—was accompanied by significant uplift and exhumation, as evidenced by geothermochronological and other data. The enigmatic origins of the volcanism and uplift are debated. The Iceland Hotspot reached the North Atlantic at that time and could probably supply anomalously hot asthenospheric material to the volcanic areas of NAIP, but they were scattered over a broad area thousands of kilometres across. This motivates alternative, non-plume explanations.

Here, we obtain a map of the lithosphere-asthenosphere boundary (LAB) depth in the region using thermodynamic inversion of seismic surface-wave data. Love and Rayleigh phase velocity maps in broad period ranges were computed using optimal resolution tomography with direct model error estimation and supplied the data for the inversion.

Our results reveal a consistently thinner-than-average lithosphere beneath the Irish Sea and surroundings, encompassing northern Ireland and western Scotland and Wales. The Paleocene uplift, BITIP volcanism and crustal underplating are all located in the same regions, which are underlain, consistently, by anomalously thin lithosphere.

The previously unknown lithospheric anomalies we discover yield a new insight into how the Iceland Plume could cause volcanism scattered over the vast NAIP. Plume material is likely to have flowed into pre-existing areas of thin continental lithosphere, whose thickness was then reduced further by the erosion by the hot asthenosphere. The thinning of the lithosphere and the presence of hot asthenosphere beneath it can account for the uplift, volcanism and crustal underplating. The localisation of the plume material in scattered thin-lithosphere areas, such as the circum-Irish-Sea region, can explain the wide scatter of the volcanic fields of NAIP.

How to cite: Bonadio, R., Lebedev, S., Chew, D., Xu, Y., and Fullea, J.: How could a single Iceland Plume produce the widely scattered North Atlantic Igneous Province volcanism? New clues from Britain and Ireland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18296, https://doi.org/10.5194/egusphere-egu24-18296, 2024.

The X-discontinuity at 300 km beneath the Hawaiian hotspot has been hypothesized to require at least 40% basalt, a figure that would far exceed the plume's buoyancy and thus be irreconcilable with initial entrainments.
We had previously explored the potential for large basalt accumulations to form over time by simulating a section of the plume conduit, with known quantities of basaltic material flowing in as discrete heterogeneities. For entrainments of 10-20%, we had estimated average accumulations of 20-25% at ~300 km depth.
While this simplified setting recreated segregation of the denser material, it did not feature a realistic plume. On the other hand, employing mechanical mixture compositions hamper quantitative analyses of the recycled basalt.

I have overcome this issue by developing a novel implementation to the ASPECT code.
My advancement features a mechanical mixture composition (82% harzburgite — 18% basalt) for both the background mantle and the plume. The recycled material is then added to the self-consistent rising plume in the form of compositionally distinct basaltic heterogeneities. By combining these two approaches, I was able to successfully reproduce and quantify material segregation while keeping an accurate plume composition.

Preliminary results, conducted in a 2000 km * 1000 km 2D domain, with entrainments of 10-20%, and a maximum resolution of 0.98 km in the heterogeneities, show average basalt accumulations of 20-22% around 300 km depth. Occasional, transient peaks at 31% and 35% can be observed for plumes incorporating 15% basalt. Over the model time (20 Ma), the denser material tends to sink between 360-660 km depth, generating large average accumulations of 35-40%. 

This new strategy not only opens promising scenarios by overcoming long-standing model limitations, but also reinforces the potential for mantle plumes to accumulate more denser material than classically thought, shedding further light on the controversial link between the X-discontinuity and the Hawaiian plume activity.

How to cite: Monaco, M.: A Novel Implementation to Simulate Basalt Segregation in the Hawaiian Mantle Plume Overcomes Model Limitations and Elucidates the Origin of the X-discontinuity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18845, https://doi.org/10.5194/egusphere-egu24-18845, 2024.

EGU24-19459 | ECS | Posters on site | TS8.1

Influence of small-scale convection on the cooling of oceanic lithosphere at slow and fast spreading ridges 

Raghu Ram Gudipati, Marta Pérez-Gussinyé, and Javier García-Pintado

Classic models of continental rifting predict that after continental break-up, the extended lithosphere returns to its original thermal state (McKenzie, 1978). At this time, the heat-flow should decrease from the proximal margin sectors, where the radiogenic crust is still relatively thick, towards its distal sectors, where the crust has extensively thin and the thermal lithosphere thickness approximates that of the adjacent untinned continental lithosphere. This should occur after approximately ~50 Myr for 120 km thick continental lithosphere (McKenzie, 1978). Although, good quality heat flow data is very scarce along margins, some of them, such as the Voring basin, show instead increasing heat flow towards the distal margin sectors ~60 Myr after break-up (Cunha et al., 2021). Recent numerical models have suggested, instead, that the lithosphere under the hyper-extended continental margins, does actually not return towards its original thermal thickness, instead it acquires a thickness which is similar to that of the adjacent plate, resulting in higher heat-flow towards the distal margins at ~80-100 Myr after break-up (Perez-Gussinye et al., 2023). In those models, the delay in thermal relaxation under the hyper-extended margins is caused by small-scale convections cells, a process which also prevents the oceanic lithosphere to infinitely cool and is responsible for the flattening of the oceanic bathymetry at old ages. Interestingly, the models show that the delay in thermal relaxation under both the hyper-extended rifted margins and the old oceanic crust increases with decreasing rifting and spreading velocity, such that is most obvious in ultra-slow margins and adjacent oceanic basins (Perez-Gussinye et al., 2023). Here we use updated 2D numerical models which include the thermal consequences of serpentinisation, melting and melt emplacement to understand the thermal evolution of oceanic plates and compare the resulting plate structure, heat-flow and bathymetry with the observations from seismic LAB structure, and global heat-flow and bathymetry databases.

 

References

Cunha, T.A., Rasmussen, H., Villinger, H. and Akinwumiju, A.A., 2021. Burial and Heat Flux Modelling along a Southern Vøring Basin Transect: Implications for the Petroleum Systems and Thermal Regimes in the Deep Mid-Norwegian Sea. Geosciences, 11(5), p.190.

McKenzie, D., 1978. Some remarks on the development of sedimentary basins. Earth and Planetary science letters, 40(1), pp.25-32.

Pérez-Gussinyé, M., Xin, Y., Cunha, T., Ram, R., Andrés-Martínez, M., Dong, D. and García-Pintado, J., 2024. Synrift and postrift thermal evolution of rifted margins: a re-evaluation of classic models of extension. Geological Society, London, Special Publications, 547(1), pp.SP547-2023.

How to cite: Gudipati, R. R., Pérez-Gussinyé, M., and García-Pintado, J.: Influence of small-scale convection on the cooling of oceanic lithosphere at slow and fast spreading ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19459, https://doi.org/10.5194/egusphere-egu24-19459, 2024.

EGU24-19570 | ECS | Orals | TS8.1

The tectonic evolution of the western North American margin since the Devonian 

Andres Felipe Rodriguez Corcho, Sabin Zahirovic, Michele Anthony, Dene Tarkyth, Christopher Alfonso, Maria Seton, Dietmar Muller, Bruce Eglington, and Basil Tikoff

The western North American margin records multiple phases of rifting and convergence, resulting from the interaction between western Laurentia, rifted continental fragments, and intra-oceanic terranes originating in the Panthalassa and Pacific oceanic plates. Quantitative plate reconstructions of this margin have prioritised diverging interpretations regarding the subduction polarities of eastern Panthalassa terranes during Jurassic to Cretaceous times. These discrepancies arise from the reliance on either seismic tomography or surface geology as the first-order constraint for determining subduction polarity. We present an updated tectonic reconstruction for western North America from the Devonian to present day. In this new model, we reconcile geological histories based on surface geology, geochronology, paleomagnetism and isotopic data, with interpretations of seismic tomography. The new reconstructions account for the tectonic evolution of the Alaska orocline, western Canada and western United States (US) and south-western (SW) North America, which have not been implemented in detail in previous tectonic models. Our model suggests that most of the terranes of western North America were rifted off Laurentia and Baltica during Devonian to Triassic extension and trench-retreat. Following back-arc rifting and opening, many of the terranes (e.g. Insular, Intermontane, Angayucham) experienced an intra-oceanic phase before accreting to the continental margin of North America at different times, between Early Triassic to Late Cretaceous times. The model illustrates the collision of the Angayucham Terrane, counterclockwise rotation and orocline formation in Alaska during the middle Jurassic. In western US and SW North America, the model showcases Jurassic to Cretaceous extension and rifting. Extension starts first in western US (170-145 Ma) and is then propagated south, causing the opening of the Bisbee Basin (161-105 Ma). The model also captures the Late Cretaceous collision of the Insular Terrane, which triggered transpression, terrane translation for thousands of kilometers and clockwise rotation in western US during Late Cretaceous to Paleogene times. Our updated model highlights the importance of surface geology in constraining the polarity of ancient subduction zones interpreted from seismic tomography.

How to cite: Rodriguez Corcho, A. F., Zahirovic, S., Anthony, M., Tarkyth, D., Alfonso, C., Seton, M., Muller, D., Eglington, B., and Tikoff, B.: The tectonic evolution of the western North American margin since the Devonian, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19570, https://doi.org/10.5194/egusphere-egu24-19570, 2024.

Geodynamicists have long proposed that mantle convection creates dynamic topography — a long-wavelength, low-amplitude signal extending beyond plate tectonics. This predicts transient vertical Earth surface movement of 1–2 km across thousands of horizontal kilometers at any location, including continental interiors. Despite these claims, experts working on local observations, using the multitude of high-resolution geological, sedimentological, and geomorphological data, face challenges in finding clear evidence to unequivocally support dynamic models of whole mantle convection, including the plume mode. Moreover, regional-scale stratigraphic techniques, such as sequence stratigraphy, which enabled hydrocarbon exploration, invoke unconformities on multiple scales but, from their far-field perspective, render correlation to distinct geodynamic events difficult.

To circumvent this scaling and correlation problem, I propose to reverse the stratigraphic perspective to an outwards-directed view. This approach requires a theoretical geodynamic framework and the identification of tectonic events (center, near field), such as magmatic arcs, flood basalts, or uplifted domes, followed by outward-directed geological mapping of regional-scale stratigraphic unconformities —predicted by theory— to distal regions. This approach is analogous to the way in which paleoseismologists examine so-called event horizons, i.e., unconformities in the stratigraphic record adjacent to fault scarps that preserve a record of the Earth's surface at the time of earthquake rupture.

This event-based stratigraphic mapping method (EVENT-STRAT) enables analysis of geological events on geological maps compiled at regional to continental scales. The technique connects local work into a continent-scale framework, allowing identification of transient patterns related to dynamic mantle-derived events. The EVENT-STRAT mapping method is designed to visualize geological effects resulting from both the plate and the plume mode of mantle convection. The toolbox consists of the hiatus mapping method (Friedrich 2019, Geological Magazine) and the event-based stratigraphic framework mapping (e.g., Friedrich et al. 2018, Gondwana Research). The upcoming EVENT-STRAT mapping method involves multiple polygonal stacking to analyze various stratigraphic event horizons, such as hiatus surfaces and unconformities. The most significant current challenge is to add the high-precision stratigraphic data compiled on local chronostratigraphic charts to continent-scale geological maps. This effort requires the attention of geological surveys on international scales seeking to compile theory-based geodynamic-stratigraphic parameters on the next generation of global and continent-scale geological maps.

How to cite: Friedrich, A. M.: Geodynamic Stratigraphy — Defining the Need for Mapping Strategies to link Models of Mantle Dynamics to Surface Processes on Geological Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19837, https://doi.org/10.5194/egusphere-egu24-19837, 2024.

The depleted mantle and the continental crust are largely geochemically and isotopically complementary. However, the question of when the depleted mantle reservoirs developed on Earth remains a topic of considerable debate. In this study, we report the existence of a ca. 3.8 Ga detrital zircon from the quartzite of the Paleoproterozoic Songshan Group in the southern North China Craton. In situ zircon hafnium isotopic characteristics of the 3.8–3.2 Ga detrital zircons indicate the presence of source rocks as old as ca. 4.5 Ga in the southern North China Craton. Together with the global zircon U-Pb-Hf isotope dataset from the North China Craton, Jack Hills, Acasta as well as available μ142Nd values of ancient rocks from Archean craton worldwide, the new results indicate that the silicate Earth has differentiated at 4.5–4.4 Ga almost immediately after accretion, developing continental crust and a complementary depleted mantle reservoir at that same time.

How to cite: Si, B., Diwu, C., and Si, R.: Eoarchean-Paleoarchean crustal material in the southern North China Craton and possible mantle reservoir of early Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-406, https://doi.org/10.5194/egusphere-egu24-406, 2024.

EGU24-1479 | Orals | GD3.1 | Highlight

Recipes for a Hadean Earth 

Stephen J. Mojzsis and Anna Medvegy

Silicate+metal worlds like Earth form hot owing to gravitational heating from accretion and differentiation, and intrinsic radioactive decay. Concurrent cooling sets off a chemical and mechanical cascade wherein siderophile elements (Fe+Ni) form a metallic core, and lithophile elements (Mg, Si, Al, Ca, Na, etc.) partition into mantle and siliceous crust. The outcome is a rocky surface beneath an outgassed fluid envelope composed of atmophile elements and compounds (CO2, H2O, H2, etc.). In its first 500 Myr (q.v. Hadean eon), Earth’s crust co-existed with liquid water; it was molded by volcanism, affected by late accretion bombardments and harbored diverse hydrothermal systems. Volcanism and differential buoyancy of the crust mandates the presence of scattered emergent landmasses. Such Hadean surfaces could host diverse (sub-)aqueous where organic chemical ingredients became concentrated to reactivity beneath a dense atmosphere bathed by the active young Sun. Soon after planet formation, it seems proto-biochemical reactions led to full-fledged living biochemistry. We do not know whether the earliest environments for life were ideally suited for its origin, or merely just good enough to accomplish the task. The inferred complexity for even the minimum biological entity means that operative and persistent biochemistry are the most difficult developmental stages to reach.

How to cite: Mojzsis, S. J. and Medvegy, A.: Recipes for a Hadean Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1479, https://doi.org/10.5194/egusphere-egu24-1479, 2024.

EGU24-1792 | ECS | Orals | GD3.1

Litho-structural framework of the Eoarchean Tussaap supracrustal belt, Itsaq gneiss complex, southwestern Greenland 

Peter Haproff, Alexander Webb, Chit Yan Eunice Leung, Christoph Hauzenberger, Jiawei Zuo, and Anthony Ramírez-Salazar

The Isua and Tussaap supracrustal belts of the Itsaq gneiss complex, southwestern Greenland, form the largest and best-preserved exposure of Eoarchean supracrustal materials on Earth. Previous studies have almost exclusively focused on the ∼35-km-long, arc-shaped Isua supracrustal belt and adjacent ca. 3.8–3.7 Ga meta-tonalite bodies, which are the basis for competing Archean tectonic regime interpretations (i.e., plate versus heat-pipe tectonics). In this study, we performed geologic field mapping of the seldom-explored Tussaap supracrustal belt, located ~11 km south of the Isua supracrustal belt, to better constrain its litho-structural framework and test the predictions of existing Eoarchean tectonic models. Observations from this study and previous works show that the Tussaap supracrustal belt consists of a east-northeast-striking, ~12-km-long and <1-km-wide, mostly continuous belt of greenstone rocks flanked to the north and south by ca. 3.8 Ga meta-tonalite. Lithologies of the Tussaap supracrustal belt consist of interlayered garnet ± staurolite ± sillimanite paragneiss, felsic schist, garnet mafic schist, amphibole-rich garbenschiefer, and minor pegmatite bodies and meta-ultramafic rocks. The northern and southern contacts between the Tussaap supracrustal belt and meta-tonalite are ~100-m-wide transitional zones featuring interlayered and folded meta-tonalite and greenstone rocks that increase in abundance towards each lithologic unit. Both the Tussaap supracrustal belt and adjacent meta-tonalite feature well-developed, southeast-dipping foliation and southeast-plunging stretching lineation (average 162° trend, 40° plunge). Macroscopic sheath and often rootless, disharmonic folds with hinges parallel to stretching lineation occur throughout the study area. In contrast with previous interpretations, no discrete tectonic discontinuities (i.e., brittle faults and ductile shear zones) were observed within the Tussaap supracrustal belt and meta-tonalite. Similarly, no apparent metamorphic field gradient was observed in the study area. This litho-structural framework is consistent with that of the Isua supracrustal belt and meta-tonalite bodies to the north, indicative of spatially-uniform strain and metamorphism. Based on our preliminary observations, the Archean development of the region can be explained by uniform subvertical shearing and folding of an interlayered volcanic-intrusive sequence (i.e., heat-pipe tectonics). Additional structural, geochronologic, and geochemical analyses of the Tussaap supracrustal belt and meta-tonalite are required to further elucidate their emplacement and metamorphic histories and differentiate end-member models of Archean tectonics.

How to cite: Haproff, P., Webb, A., Leung, C. Y. E., Hauzenberger, C., Zuo, J., and Ramírez-Salazar, A.: Litho-structural framework of the Eoarchean Tussaap supracrustal belt, Itsaq gneiss complex, southwestern Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1792, https://doi.org/10.5194/egusphere-egu24-1792, 2024.

An Archean ancestral landmass of Columbia supercontinent is a matter of concern to geologists. A single supercontinent called “Kenorland” or several supercratons have been mainly proposed, but more evidence from geological records and palaeomagnetism argue for the latter supercraton solution, in which two long-lived supercratons Sclavia and Superior were recently reconstructed. Studies has shown that the Northern China blocks, including the North China and Tarim cratons, the Alxa, Quanji blocks, were involved in the reconstruction of Columbia. However, their affinity in Archean supercratons remained little constrained. Owe to the lack of reliable palaeomagnetic data old than 1.8 Ga, the geological piercing points in these blocks could allow us to figure out the question. Then, compilation and comparison of Neoarchean–early Paleoproterozoic magmatism, metamorphism, and sedimentary records, have been conducted among these blocks. As a result, 2.4-2.2 Ga magmatism and khondalite-like sedimentary sequence may be used as indicators of the affinity of these blocks in northern China. Consequently, the Kuruktag Block, Quanji Block, Alxa Block, TNCO, Khondalite Belt have similar evolutionary history during the Neoarchean-Paleoproterozoic, suggesting their close affinity at that period. Besides, the North China craton and Dharwar craton of India shield were proved to be connected during the Archean-Proterozoic. And latest study indicate the Dharwar craton was one of the Sclavia supercraton. Therefore, we speculate that during the Neoarchean–early Paleoproterozoic, the Kuruktag-Quanji-Alxa-TNCO-Khondalite Belt link was close to the Dharwar craton in Sclavia supercraton. The absence of Siderian glacial event (ca. 2.4 Ga) in the Alxa, Quanji, Kuruktag blocks and TNCO, Khondalite Belt of the North China craton rule out the link with Superia, which is common in Superia supercraton. Further geological and paleomagnetic studies are required to constrain the above hypothesis, the relation between these blocks clusters and other cratons, which is crucial to understand the origins of blocks in northern China.

How to cite: Zhang, Q. and Yao, J.: Paleogeographic affinity of Northern China block clusters in Archean-Paleoproterozoic supercraton solution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2507, https://doi.org/10.5194/egusphere-egu24-2507, 2024.

1 Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China.

2Department of Earth Sciences, The University of Hong Kong, Hong Kong, Hong Kong.

3Department of Geology, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China.

* Corresponding author: wuzq10@ustc.edu.cn.

The origins of the Archean cratons were most important events in the early Earth and crucial for understanding how the early Earth worked. The mechanisms for the origins of the Archean cratons remain unclear. It is widely accepted that Archean tonalite-trondhjemite-granodiorite (TTG) plutons were derived from hydrous mafic magmas in the garnet/ amphibole stability field. Although the subduction can bring water to the mantle to produce granitic magma, the island Arc Model for the origin of continents meets fundamental challenges. The growing evidences support the plume-driven oceanic plateau models for the origin of continents. However, the lower parts of the oceanic plateau have been thought to be dry. How to generate the hydrous meta-basalt at the base of the oceanic plateau remain an open question.

Here we show that the Archean cratons resulted from the evolution of the hydrous magma ocean (Wu et al., 2023). The whole-mantle magma ocean created by the moon-forming giant impact likely evolved into an outer magma ocean and a basal magma ocean because the magma ocean would initially crystallize in the mid mantle and the basal magma ocean is denser than the overlying solid mantle. The basal MO at the beginning should contain a certain amount of water since extensive studies suggest substantial accretion of water-rich bodies during core formation. The major lower-mantle minerals have limited water storage capacity. Therefore, with progressive crystallization, the basal magma ocean becomes increasingly enriched in water. The basal magma ocean eventually becomes gravitationally unstable because of the enrichment of water. The triggered massive mantle overturns transported a large amount of water upward to the shallow part of the Earth and resulted in the major pulses of the crust and thick SCLM generations. The model can account for many observations including the source of water needed for generation of the continental crust, the major pulse of crustal growth around the end of the Archean, why the TTG and thick SCLM basically occurred in the Archean, and why only the Earth among inner planets was covered with the continental crust.

 

Wu, Z., Song, J., Zhao, G., & Pan, Z. (2023). Water-induced mantle overturns leading to the origins of Archean continents and subcontinental lithospheric mantle. Geophysical Research Letters, 50, e2023GL105178. https://doi.org/10.1029/2023GL105178

How to cite: Wu1, Z.: Water-induced mantle overturns and the origins of Archean cratons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2870, https://doi.org/10.5194/egusphere-egu24-2870, 2024.

The BIFs in Bundelkhand Craton occurred as a discontinuous unit within the east-west trending Bundelkhand Tectonic Zone (BTZ). The BIFs were associated with amphibolite, calcsilicate rocks, and quartzite. The BIFs were massif in appearance in the Mauranipur (east of Bundelkhand Tectonic Zone, BTZ) that graded to layered variety in the Babina area (west of the BTZ).

The Bundelkhand BIFs were characterized by 45 to 55 wt.% SiO2 and 44 to 55 wt.% Fe2O3 content. The Al2O3 content was usually low and varied between > 1 to 3 wt%. Barring a few samples, the MnO and CaO contents are < 1 wt.%. The higher MnO (~ 3.70 wt.%) and CaO (~ 1 wt.%) implied a different redox condition and involvement of CaCO3 in the early stages of BIF formations. The ΣREE content of Bundelkhand BIFs varied between 10 – 38 ppm, with Eu/Eu*SN values between 1.1 to 1.5. Geochemically, the BIFs were classified as Algoma-type BIFs deposited by low-temperature hydrothermal fluids. Monoclinic amphiboles, quartz and garnet were the dominant silicate phase for Mauranipur BIFs. Hornblende was present with monoclinic amphibole in the garnet-absent BIFs. Isolated grains of magnetite were dispersed throughout the Mauranipur BIFs. In contrast, alternate hematite and SiO2-rich layers with locally developed low-T amphiboles characterized Babina BIFs. The Fe-rich oxides were mostly hematite. Mineral microstructure and P-T pseudo-section modeling implied Minnesotaite and Fe-Ca carbonate phases were the primary minerals in BIFs, deposited at temperature ~ 200°C at 0.05 to 0.1 GPa. The primary minerals experienced dehydration and decarbonization reactions, leading to the stabilization of amphibole and garnet at a temperature of ~450°C and pressure of 0.1—0.2 GPa. When plotted in a P-T diagram, the increase in temperature corresponds to tectonic activity and plutonism, leading to micro-bock accretion and growth of Bundelkhand Craton.

How to cite: Raza, M. B. and Nasipuri, P.: Mineralogy and P-T condition of Algoma type Banded Iron Formation from Bundelkhand Craton, North-Central India and their implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2992, https://doi.org/10.5194/egusphere-egu24-2992, 2024.

Iron Formations (IF) are economically significant sedimentary rocks primarily formed in the Precambrian evolutionary history of the Earth. In the Precambrian period, Iron Formations were deposited within marine sediments on stable continental margins (superior-type) and in association with volcanic rocks and many volcanic Massive Sulphide (VMS) deposits (Algoma-type). Most scientists agree that for BIF to form, photosynthesis and changing ferrous iron from seawater into mixed-valence iron (oxy-hydroxide) oxides and carbonate phases during oxidation are needed.
The present study is based on the Superior-type BIFs from the Girar Supracrustal Belt of Southern Bundelkhand terrane, which mainly consists of Neoarchean K-rich granitoids with a minor volume of a schist complex, TTG, sanukitoids, and mafic-ultramafic layered intrusion. The Girar schist (metasedimentary) belt is mostly made up of two types of rocks: (i) quartzite and (ii) BIFs. There are also some dolomitic marble and chlorite schist lenses close to the quartzite/BIF boundary. The BIFs consist of thick-bedded quartz and hematite with magnetite. The quartzites display low-grade metamorphism of fuchsite- and hematite-bearing quartz arenite with thick meta-argillite (schist) laminae and lesser quartz pebble conglomerates.
P-T pseudosection modelling indicates that Fe-carbonates and iron-oxyhydroxides (minnesotaite) are the primary phases that stabilize at 200 – 250 O C, 0.1–0.15 GPa. Subsequently, the low-temperature phases experienced dehydration and decarbonisation reactions with an increase in temperature, leading to the stabilisation of hematite and magnetite. The absence of orthopyroxene in the BIFs suggests these rocks suffer amphibolite facies
metamorphism, which is uncommon in generally undeformed superior-type BIFs.

How to cite: Bisht, B. P. S.: Mineralogy and P-T conditions of Superior- type Iron Formation fromBundelkhand Craton, North Central India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3109, https://doi.org/10.5194/egusphere-egu24-3109, 2024.

EGU24-3114 | ECS | Orals | GD3.1

Reconstruction of the Tarim craton within Rodinia: constraints from magmatic- orogenic records in the Altyn belt 

Wei Li, Jinlong Yao, Guochun Zhao, and Yigui Han

The position of the Tarim craton within the Rodinia supercontinent has long been the focus of scientific debate, with competing models varying from internal to external positions. The Altyn belt in the southeast Tarim margin records an extensive Neoproterozoic magmatic-sedimentary successions which likely recorded the convergence of Tarim to Rodinia. Thus, we here investigated the granitoids exposed in the Kuoshi-Kalaqiaoka and Tula areas in the eastern and western segment of the South Altyn belt. We present new field geology, zircon U–Pb–Hf–O isotopes and H2O, and whole rock geochemistry data from these granitoids. Zircon U–Pb data yielded ages of 914 ± 3.9 Ma for the Tula granite, 919 ± 5.2 Ma and 932 ± 6.5 Ma for the Kuoshi granite. The Tula and Kalaqiaoka granite samples mostly display high ACNK values that are typical of S-type granitoids, consistent with the presence of Al-rich minerals, such as garnet and muscovite. In addition, the Tula granite have higher zircon δ18O (7.62 to 10.85‰, peaked at 8.9‰) and lower εHf(t) (-4.0 to +0.3) values, along with lower H2O content (medium values at 102 and 251 ppmw), indicating that the primary magmas were generated from recycled ancient crust in a water-deficient syn-collisional setting, with minor juvenile contribution. On the other hand, the Kuoshi granite have high Sr (169–259 ppm), Sr/Y (17.85–19.33) and (La/Yb)N (30–49) ratios that are indicating of adakitic affinity. The Kuoshi granite are also characterized by lower δ18O (4.15 to 9.81‰, peaked at 8.2‰) and εHf(t) values(−2.4 to 0.6), along with higher H2O content (medium values at 255 and 795 ppmw) and MgO. These signatures suggest that the Kuoshi pluton was formed by recycling ancient crust and subducted continental crust. Overall, the granitoids across the South Altyn belt reflect a transformation of tectonic regime from water-enriched subduction setting to water-deficient syn-collisional setting. Moreover, the Hf isotopes evolution tend of the early Neoproterozoic granitoids and Suoerkuli Group across the South Altyn belt also suggest a transformation from slab retreat to syn-collision in the early Neoproterozoic. Therefore, overall data and field relations across the Altyn belt indicate an early Neoproterozoic magmatic-sedimentary successions that are similar to that of the Eastern Ghats Belt in India. Given the available paleomagnetic data and detrital zircon age patterns, we conclude a position of the Tarim craton between Australian and North India block in the periphery of Rodinia, close to East Antarctica as well. This research was supported by NSFC Projects (42322208 and 41972238), National Key Research and Development Programs of China (2022YFF0802700 and 2023YFF0803604) and Hong Kong RGC GRF (17308023).

How to cite: Li, W., Yao, J., Zhao, G., and Han, Y.: Reconstruction of the Tarim craton within Rodinia: constraints from magmatic- orogenic records in the Altyn belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3114, https://doi.org/10.5194/egusphere-egu24-3114, 2024.

EGU24-3303 | ECS | Orals | GD3.1

Redox state of Archean surface environments: Insights from the Banded Iron Formations (BIFs) of the Western Dharwar Craton, Southern India  

Aindrila Mukherjee, Jayananda Mudlappa, Pritam Nasipuri, and Aadhiseshan Krishnasamy Raveendran

The interplay of geological, chemical and biological processes that drive the oxygenation of the oceans-atmosphere of the early earth are spatially linked to the emergence of biosphere. Banded Iron Formations (BIFs) from the Archean greenstone belts form important archives for understanding the redox conditions of Archean surface environments. The Archean Dharwar craton preserves BIFs in the volcano-sedimentary greenstone belts of two distinct stratigraphic units (older Sargur Group and younger Dharwar Supergroup) corresponding to a time span of 3300-2600 Ma.  These BIFs are confined to the highest stratigraphic levels forming summits of greenstone belts.  They show alternate layers of chert and iron oxides, and petrographic data reveal diverse mineralogy including oxides, carbonate, sulphide and silicate facies. The occurrence of riebeckite and stilpnomelane in BIFs of younger Dharwar Supergroup indicates recrystallization under low-grade metamorphism. Slightly higher abundances of CaO and Al2O3 reveal significant influence of crustal source and precipitation of CaCO3 during BIFs formation. Mesoscopic layers of chert and iron oxide with variable thickness suggest fluctuating redox state of surface environments. The higher enrichment of Ni (6-26 ppm) than the Cr content (3-19 ppm) with variable Sr concentrations may be attributed to feldspar breakdown during hydrothermal fluid acceleration. Trace element ratios (Y/Ho, Sm/Yb, Eu/Sm) coupled with positive Eu anomalies of the BIFs from both older Sargur Group and younger Dharwar Supergroup BIFs reveal dominant hydrothermal input in BIFs origin. The PAAS normalized REE data preclude major continental input in the origin of BIFs. The variable negative Ce anomalies imply periodic fluctuating surface environments (oxic to anoxic) at the dawn of the Great Oxidation Event close to 2340 Ma. This is consistent with the published Fe, N, and S isotope data on the BIFs of the Western Dharwar craton.

 

How to cite: Mukherjee, A., Mudlappa, J., Nasipuri, P., and Krishnasamy Raveendran, A.: Redox state of Archean surface environments: Insights from the Banded Iron Formations (BIFs) of the Western Dharwar Craton, Southern India , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3303, https://doi.org/10.5194/egusphere-egu24-3303, 2024.

EGU24-3394 | Orals | GD3.1

Paleoarchean volcanic stratigraphy and geochemistry of the mafic-ultramafic Kromberg Formation type-section, Barberton greenstone belt, South Africa. 

Eugene Grosch, Sibu Ndlela, David Murphy, Nicola McLoughlin, Jakub Trubac, and Jiri Slama

In this study, the c. 3.334 Ga Kromberg Formation of the Onverwacht Group, in the south-eastern limb of the Onverwacht Anticline in the Barberton greenstone belt (South Africa) is investigated. Various geodynamic models have been proposed for the evolution of the Kromberg Formation, but detailed geochemical constraints on the mafic-ultramafic sequence are sparse. The objectives are to constrain the Paleoarchean mantle source characteristics and geodynamic setting for the Kromberg mafic-ultramafic rocks, placed in the context of recent high-resolution field mapping data. To study the protolith volcanic rocks, sampling has been conducted to avoid areas affected by deformation-related alteration. In addition, screening for alteration due to Archean seawater silicification has also been conducted. In conjunction with major, trace and rare earth element data, this study presents the first whole-rock Lu-Hf isotope analyses of mafic-ultramafic rocks of the Paleoarchean Kromberg Formation type-section in the Barberton greenstone belt (Grosch et al., 2022). Three compositionally distinct volcanic rock types are identified namely Group 1 metabasalts, Group 2 metabasalts and komatiitic metabasalts. The geochemistry of these rock types will be presented, and a possible geodynamic setting on the early Earth will be explored.  

Grosch, E.G., Ndlela S., Murphy D., McLoughlin N., Trubac J., Slama J., (2022) Geochemistry of mafic-ultramafic rocks of the 3.33 Ga Kromberg type-section, Barberton greenstone belt, South Africa: Implications for early Earth geodynamic processes. Chemical Geology 605, 120947

How to cite: Grosch, E., Ndlela, S., Murphy, D., McLoughlin, N., Trubac, J., and Slama, J.: Paleoarchean volcanic stratigraphy and geochemistry of the mafic-ultramafic Kromberg Formation type-section, Barberton greenstone belt, South Africa., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3394, https://doi.org/10.5194/egusphere-egu24-3394, 2024.

EGU24-3563 | ECS | Orals | GD3.1

The geological record of H2 production in the Archean 

Renée Tamblyn and Jörg Hermann

The oxidation of iron from rocks during subaqueous alteration is a key source of the molecular hydrogen (H2) used as an energy source by chemosynthetic organisms, which may represent some of the earliest forms of life on Earth. In the Archean, a potential source of ultramafic material available for serpentinisation reactions that release H2 are komatiites. Komatiites are highly magnesian lavas, which contain evidence of extensive serpentinisation and magnetite (Fe2+Fe3+2O4) production close to the Archean seafloor. H2 production in komatiitic compositions has been modelled and experimentally investigated; however, the natural rock record has remained unexplored. Here, we examine the geological evidence of H2 production from the basaltic to komatiitic rock record held in Archean cratons. From the petrological investigation of thirty-eight samples of komatiitic basalt to komatiite, we identify the unique serpentinisation reaction responsible for H2 production from these lithologies. With support from over 1100 bulk rock geochemical analyses, we directly quantify Fe3+ and therefore H2 production of komatiites in the Archean. The chemical (high Mg) and physical (low viscosity flow) characteristics of komatiite flows allowed for extensive hydration and serpentinisation in oceanic plateaus, and therefore high H2 production available to chemosynthetic early life.

How to cite: Tamblyn, R. and Hermann, J.: The geological record of H2 production in the Archean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3563, https://doi.org/10.5194/egusphere-egu24-3563, 2024.

EGU24-4334 | Orals | GD3.1

Earth's evolution over time revealed by the Nb/U, Ce/Pb and Nb/Th ratios in the sources of mantle plumes. 

Alexander Sobolev, Adrien Vezinet, Aleksandr Chugunov, Mateo Esteban, Valentina Batanova, Nicholas Arndt, Charitra Jain, Stephan Sobolev, Evgeny Asafov, and John Valley

Magmas from mantle plumes are potentially the best monitors of Earth's compositional and thermal evolution over time. However, their erupted products are commonly modified by syn- and post-magmatic processes and thus do not fully retain original information about their mantle sources. Such data can be recovered from melt inclusions in olivine phenocrysts in the most primitive magmas from mantle plumes. Such inclusions, shielded by host olivine, retain original isotopic and critical trace element signatures of deep mantle sources even for Archean and Hadean Eons.

We will present the results of a study of chemical and Rb-Sr isotope composition (EPMA, LA-ICP-MS and RAMAN) of melt inclusions and chemical (EPMA, LA-ICP-MS) compositions of host olivines for komatiites and plume-related picrites with eruption age from 3.3 Ga to 1 Ka.

Recent advances in in-situ split stream LA-ICP-MS measurements of 87Sr/86Sr ratios and trace element contents of olivine-hosted melt inclusions revealed significant mantle source heterogeneities of magmas from individual plumes. The results are confirmed by geodynamic modelling (Jain et al., this meeting).

We show that the melt inclusions of most studied mantle plumes display heterogeneous populations in age-corrected 87Sr/86Sr ratios and include groups with model ages more than 1 Ga older than the emplacement age. The oldest inclusion groups found in Archean komatiites correspond to Hadean (4.3±0.2Ga, Vezinet et al., in review) and Eo-Paleoarchean (3.6±0.2 Ga) model ages. These and most inclusions from studied komatiites and picrites display Nb/U, Nb/Th and Ce/Pb significantly higher than in BSE.

Evolution over time of canonical proxies of continental crust generation (Nb/U, Th/U and Ce/Pb, Hofmann et al., 1986) in mantle plumes, combined with geodynamic modelling, suggests:

  • Most of the continental crust was generated in several Hadean and Archean pulses by plume-induced subduction and melting of the hydrated mafic/ultramafic crust or mantle. Hadean continental crust was subducted or/and reworked.
  • Restites left after extraction of continental crust were continuously subducted to the core-mantle boundary from the mid-Hadean and later recycled in Archean mantle plumes.
  • Active formation of both continental and oceanic crust in Hadean was governed by plume-induced subduction, which ceased after cold subducted material hindered the propagation of large plumes at the core-mantle boundary. After heating the recycled lithosphere at the core-mantle boundary, the process repeats, producing oscillating subduction and crustal formation in Hadean-Archean.

How to cite: Sobolev, A., Vezinet, A., Chugunov, A., Esteban, M., Batanova, V., Arndt, N., Jain, C., Sobolev, S., Asafov, E., and Valley, J.: Earth's evolution over time revealed by the Nb/U, Ce/Pb and Nb/Th ratios in the sources of mantle plumes., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4334, https://doi.org/10.5194/egusphere-egu24-4334, 2024.

The results of the U-Pb-Hf-O isotope study of zircon from (meta)igneous rocks sampled in all domains of the Ukrainian Shield allow recognition of the four main stages of continental crust formation:

1. The Eoarchean stage (ca. 4000-3600 Ma). Rocks of this stage occur in the Dniester-Bouh and Azov domains. In the former, they are represented by heavily metamorphosed enderbites and mafic schists reaching an age of 3.8 Ga. In contrast, tonalites with an age of 3.67 Ga were identified in the Azov Domain. The oldest zircon reaching an age of 3970 Ma was found in the Mesoarchean metadacite in the Azov Domain. The Eoarchean rocks are rare, but their presence indicates that crust-forming processes have started already in the Eoarchean, or even in Hadean, time.

2. The second major event took place between c. 3.2 and 2.7 Ma. Rocks, formed during this age interval, compose around half of the Ukrainian Shield. Considering the long duration of this event, it may have consisted of several separate episodes. The whole set of rock associations typical for the Archean continental crust, including TTG series, greenstone belts and sedimentary basins, has been formed. Hafnium isotope composition in zircon reveals the juvenile nature of this event. Some remobilization of the older crust is also recorded from several samples.

3. Nearly half of the rock assemblages were dated at ca. 2.15-1.90 Ga. In contrast to the Archean events that resulted in the formation of apparently more or less equant terranes, the Paleoproterozoic events led to the formation of orogenic belts. These belts comprise metamorphosed in amphibolite or epidote-amphibolite facies supercrustal sequences, and abundant granitic intrusions. According to the existing models, the formation of the orogenic belts was related to the assembly of Baltica as a part of the Columbia/Nuna supercontinent. Hafnium-in-zircon and whole-rock Nd isotopes indicate the predominantly juvenile nature of these rocks, with some contamination by the Archean crust.

4. The last major stage of the Ukrainian Shield evolution was linked to the formation of the Prutivka-Novohol large igneous province, which between 1.8 and 1.72 Ga affected the whole Shield. It resulted in the emplacement of numerous mafic dykes and layered massifs, alkaline intrusions, and huge anorthosite-mangerite-charnockite-granite complexes. All igneous rocks formed during this stage reveal signs of crustal contamination, although input of moderately depleted mantle material is also evident.

Obtained isotope and geochronological data demonstrate that the growth of the continental crust in the Ukrainian Shield was episodic. The mechanisms of the crustal growth were different at different times. During both Archean events, the main mechanism was mafic underplating with further remelting and generation of TTG series, whereas greenstone belts represent the results of mantle plume activity. In the Paleoproterozoic, the main mechanism of crustal growth was the subduction of the oceanic lithosphere that led to the formation of volcanic arcs. Mantle plumes remained an important mechanism of the input of mantle-derived material into the continental crust.

How to cite: Shumlyanskyy, L.: The main stages of the Ukrainian Shield evolution and plate tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4724, https://doi.org/10.5194/egusphere-egu24-4724, 2024.

EGU24-4875 | ECS | Posters on site | GD3.1

Plume-induced continental crust growth rate in Early Earth:Insight from numerical modeling 

Xinyi Zhong, Zhong-Hai Li, and Yang Wang

The origin of Earth’s felsic continental crust is still a mystery. The continental crust requires two-steps partial melting of mantle rocks. There are two proposed hypotheses for the continental crust growth in the Early Earth. One is the subduction-related magmatism, e.g. island arc, that produces intermediate to felsic magma which constitutes the early buoyant continental crust. The other is that the magmatism induced by mantle plume creates the thick basaltic crust, and which partially melts into continental crust. However, both two models have their deficiencies. It is still a controversial topic that when plate tectonics begins, which is an obstacle for applying the subduction-induced model in the Early Earth. On the other hand, the plume-induced model seems to be inefficient to support the continental crust growth. The previous numerical studies haves generally focused on the mechanisms of the continental crust formation, while efficiency of the model remains unknown. Thus, we simulated the melt transport process and integrated petrological model in our numerical model to evaluate the efficiency and the plausibility of continental crust production by mantle plume in the Earth’s history. The comparison between our model results and the reconstruction model of continental crust growth provides a new insight for the problem. The results indicates that the mantle plume is an efficient and possible way to support rapid continental crust growth in the Archean. Other mechanisms, e.g. subduction, may take dominant role since the Proterozoic because of low efficiency of plume-induced continental crust production.

How to cite: Zhong, X., Li, Z.-H., and Wang, Y.: Plume-induced continental crust growth rate in Early Earth:Insight from numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4875, https://doi.org/10.5194/egusphere-egu24-4875, 2024.

EGU24-5245 | Orals | GD3.1

Elemental fluxes into 3.0-billion-year-old marine environments: evidence from trace elements and Nd isotopes in banded iron formations from the Murchison Greenstone Belt, South Africa 

Johanna Krayer, Sebastian Viehmann, Alina Mayer, Toni Schulz, Christian Koeberl, Axel Hofmann, Jaganmoy Jodder, Matthias Willbold, and Stefan Weyer

Banded Iron Formations (BIFs) are authigenic, marine sediments directly reflecting the chemical composition of ancient seawater. BIFs serve as prime geochemical archives for the reconstruction of Precambrian marine environments. However, due to the scarcity of well preserved Archean rocks, atmospheric and hydrospheric environmental conditions within this time frame are still incompletely understood. In particular, elemental fluxes derived from continental weathering and submarine hydrothermal fluxes that affected ancient seawater chemistry are cornerstones for our understanding of the evolution of marine habitats through time. Here we present major- and trace element concentrations in combination with Nd isotopic compositions of 13 samples of Mesoarchean Algoma-type greenschist-facies BIFs from the ca 3.0 Ga old Murchison Greenstone Belt, South Africa. Individual Fe- and Si-rich layers are monitored for sample purity based on their chemical composition. Neodymium isotope compositions, in combination with trace element contents of BIF samples with varying amounts of clastic detritus, are further used to reconstruct the Murchison depositional environment and identify the origin of dissolved and detrital components entering the ancient ocean around 3.0 Ga ago.

Eight samples with low immobile element concentrations display typical shale-normalized Archean seawater-like rare earth and yttrium (REYSN) patterns with positive LaSN, EuCN, and GdSN anomalies, super-chondritic Y/Ho ratios, and an enrichment of heavy REYSN over light REYSN, implying an open marine-dominated depositional setting with contributions from submarine high-temperature, hydrothermal systems. A Sm-Nd regression line yields an age of 2.98 ± 0.19 Ga that overlaps with the proposed depositional age, suggesting negligible post-depositional alteration on the REY composition of the pure BIF layers. In contrast, higher concentrations of immobile elements (e.g., Zr) and/or non-seawater-like REYSN patterns are characteristic for the remaining five BIF samples, indicating elevated detrital input or post-depositional alteration. A regression line of the impure BIF layers yields an age of 2.49 ± 0.15 Ga, reflecting a potential post-depositional overprinting event such as the 2.6 Ga old Limpopo orogeny. The Nd isotopic compositions of pure and impure BIF samples cover a wide range of ca. two epsilon units suggesting a mixture of weathered mafic and felsic sources for the dissolved and suspended fluxes into the Murchison ocean.

How to cite: Krayer, J., Viehmann, S., Mayer, A., Schulz, T., Koeberl, C., Hofmann, A., Jodder, J., Willbold, M., and Weyer, S.: Elemental fluxes into 3.0-billion-year-old marine environments: evidence from trace elements and Nd isotopes in banded iron formations from the Murchison Greenstone Belt, South Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5245, https://doi.org/10.5194/egusphere-egu24-5245, 2024.

EGU24-5391 | ECS | Posters on site | GD3.1

Diverse P-T-t paths within the Neoarchean sagduction regime of North China Craton: insights from field data and numerical modeling 

Chenying Yu, Ting Yang, Jian Zhang*, Guochun Zhao, Peter A. Cawood, Changqing Yin, Jiahui Qian, Peng Gao, and Chen Zhao

The Neoarchean greenstone-granite rock association preserved in the Eastern Block of the North China Craton exhibits distinctive dome-and-keel structures. Although the metamorphic data from these rock assemblages provide valuable insights into the tectonic evolution of this region, the interpretation of the clockwise paths with nearly isothermal decompression (ITD) and the anticlockwise P–T paths involving near-isobaric cooling (IBC) remain inconsistent and controversial. By conducting 2D numerical models with the initial and boundary conditions similar to those of the Neoarchean Eastern Block, we investigated the coexistence of diverse P-T paths and determined their possible geodynamic regime. The model results demonstrate that the combination of crustal density inversion and heat from the high-temperature lower boundary initiates a crustal-scale sagduction process, leading to the formation of dome-and-keel structures. Additionally, we identified four primary types of P-T-t paths. Firstly, an anticlockwise IBC-type P-T-t path reveals the supracrustal rocks gradually subside to a deep crustal level, where they experience a prolonged residence period characterized by ambient mantle cooling without significant exhumation. Secondly, a clockwise ITD-type P-T-t path suggests the supracrustal rocks descend to the deep crust and are partly entrained by upwelling TTG magmas, leading to their rapid ascent to a middle crustal level. Thirdly, a newly identified crescent-type P-T-t path indicates an integrated burial-exhumation cycle, consisting of an initial burial stage with high dT/dP, followed by a rapid exhumation stage and a subsequent cooling stage exhibiting low dT/dP. Lastly, a hairpin-type P-T-t path highlights the slow exhumation rate experienced by deeply buried supracrustal rocks. The dome-and-keel structure and P-T-t paths observed in the numerical model are consistent with the geochronological, metamorphic and structural data of the Eastern Block. Based on these observations, we propose that the crustal-scale sagduction involving a mantle plume could responsible for the geological complexity of eastern China.

This work was financially supported by the National Natural Science Foundation of China (42025204) and National Key Research and Development Program of China (No. 2023YFF0803804).

How to cite: Yu, C., Yang, T., Zhang*, J., Zhao, G., Cawood, P. A., Yin, C., Qian, J., Gao, P., and Zhao, C.: Diverse P-T-t paths within the Neoarchean sagduction regime of North China Craton: insights from field data and numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5391, https://doi.org/10.5194/egusphere-egu24-5391, 2024.

EGU24-6614 | Orals | GD3.1

Evolving Chemistry of Lithospheric Mantle Based on Oxygen Isotope and Trace Element Analyses of Olivines from Mantle Xenoliths across Earth’s History 

Ilya Bindeman, Valentina Batanova, Alexander Sobolev, Dmitri Ionov, and Leonid Danyushevsky

Oxygen is the most abundant element in the terrestrial mantle and crust. We have recently reported on a 0.2‰ δ18O decrease of continental mantle peridotites from the original primary Bulk Silicate Earth-Moon value of 5.57‰ [1] in the mid-Archean to the Phanerozoic explained by the initiation of surface recycling (linked to intensity and style of plate tectonics) sometime in the Archean. Even small variations in the volatile mass balance are critical in explaining phenomena such as the Great Oxidation Event at ~2.4 Ga that may have mantle origin. As low-δ18O subduction fluids are derived by the dehydration (and potentially oxidation) of low-δ18O interiors of subducted slabs, this work further explores this process to observe temporal changes related to the progressive input of volatile elements and potential lithospheric mantle oxidation. This study presents a record of trace elements measured in same olivines (Li, Na, Al, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Ga, Y, Zr) including oxidation-sensitive elemental ratios V/Sc and Zn/Fe for this collection. Prior melt-depletion of mantle peridotites, estimated using bulk Al2O3 content of the xenoliths, increases with age from ~25 to 35%, leading to depletion of Yb, Y, Co, Mn, Ca, P, with smaller effects on the elemental ratios.  We observe significant ranges of V/Sc (0.2-14), Li/Y and other ratios, not related to prior melt depletion that may be linked to subduction-related re-distribution of incompatible elements by subduction [2], and scattered correlation with age and δ18O values. Further trends will be analyzed during the talk after considering craton-specific domains and global trends. This work can potentially contribute to constraining a global mass balance of crustal growth and recycling based on co-variations of isotopes of a major element oxygen and trace elements in the predominant lithospheric reservoir of subcontinental mantle.

[1]Bindeman ea, (2022) Nat Comm 13, 3779; [2] Doucet ea, (2020) NatGeosci 13, 511.

How to cite: Bindeman, I., Batanova, V., Sobolev, A., Ionov, D., and Danyushevsky, L.: Evolving Chemistry of Lithospheric Mantle Based on Oxygen Isotope and Trace Element Analyses of Olivines from Mantle Xenoliths across Earth’s History, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6614, https://doi.org/10.5194/egusphere-egu24-6614, 2024.

EGU24-7106 | ECS | Orals | GD3.1 | Highlight

Fresh water on Earth four billion years ago 

Hamed Gamaleldien, Li-Guang Wu, Hugo K.H. Olierook, Christopher L. Kirkland, Uwe Kirsche, Zheng-Xiang Li, Tim Johnson, Sean Makin, Qiu-Li Li, Qiang Jiang, Simon A. Wilde, and Xian-Hua Li

The operation of a hydrological cycle (i.e., exchange of water between the land, oceans, and atmosphere) has significant implications for the emergence of life. The oldest confirmed single-celled organisms at ~3.48 billion years ago (Ga) (Pilbara Craton, Western Australia) are thought to have formed in the presence of meteoric (fresh) water on emerged (subaerial) land in a hot spring environment. However, when widespread interaction between fresh water and emerged continental crust first began is poorly constrained. In this study, we use >1000 oxygen isotope analyses of Jack Hills detrital zircon to track fluid-rock interactions from the Hadean to the Paleoarchean (~4.4–3.1 Ga). We identify extreme isotopically light O (i.e., δ18O < 4.0 ‰) values older than 3.5 Ga. The data define two periods of magmatism with extreme isotopically-light O as low as 2.0 ‰ and –0.1 ‰ at around 4.0 and 3.4 Ga, respectively. Using Monte Carlo simulations, we demonstrate that such values can only be generated by the interaction of crustal magmatic systems with meteoric water. Our data constrains the earliest emergence of continental crust on Earth, the presence of fresh water, and the start of the hydrological cycle that likely provided the environmental niches required for a life less than 600 million years after Earth’s accretion.

How to cite: Gamaleldien, H., Wu, L.-G., Olierook, H. K. H., Kirkland, C. L., Kirsche, U., Li, Z.-X., Johnson, T., Makin, S., Li, Q.-L., Jiang, Q., Wilde, S. A., and Li, X.-H.: Fresh water on Earth four billion years ago, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7106, https://doi.org/10.5194/egusphere-egu24-7106, 2024.

Several studies have already concluded the presence of 7-8 ocean equivalent water (OCE) in the mantle of earth, structurally occurring as H+/OH. This can affect the seismic anomaly, mechanical strength, ionic diffusion, etc. of the mantle. The upper mantle is primarily composed of olivine, which first transforms to wadsleyite and then to ringwoodite at ~13 and ~18 GPa, respectively. Petrological and mineralogical experiments have demonstrated that H, occurring as point defects can act as a source of water in the upper mantle. Being the abundant mineral in upper mantle, it is very important to investigate the ability of olivine to act as a potential mineral phase to house water. Incorporation of water in mantle minerals has been a burning topic for many theoretical and experimental works. Even a trace amount of water in mineral structure can significantly alter their physical (e.g., elastic behaviour, seismic velocities, etc.) and chemical properties (e.g., ionic diffusion, electrical conductivity, etc.). FT-IR studies suggested that a rapid diffusion of H+ in olivine makes it a better candidate for point defects compared to larger and heavier OH ions. Karato & Jung (2003)  showed that increment of H concentration in olivine decreases its strength. Later, Mao et al. (2008) and Panero et al. (2010) observed qualitatively similar trend in high pressure olivine polymorphs. They observed drastic reduction in selective elastic constants of C11compared to C12 and C44 as H content increases in ringwoodite. Huang et al. (2005) found that temperature and water increases electrical conductivity in both the polymorphs. Yoshino et al. (2009) reported that a hike in temperature switches H-diffusion mechanism in olivine from proton conduction to small polaron conduction. The H diffusion in Fe-bearing olivine is experimentally shown to be dictated by (i) Proton-polaron (PP) mechanism and (ii) Proton-vacancy (PV) mechanism in <1 GPa. The PV is found to be valid for incorporating more water in olivine compared to PP. However, the second method, despite being strongly anisotropic, allows a faster diffusion. Much of the existing studies deals with temperature and water content as the key physical factors in controlling proton diffusivity. The fact that most of these studies have not carried out in the exact pressure (p) and temperature (T) conditions of mantle of Earth demand further studies on the same. Present study involves the study of H diffusion in lattice structure of olivine and wadsleyite; their mechanical stability, physical and chemical properties under mantle p–T conditions. Our results suggest a drop in seismic velocities in both olivine and wadsleyite phases. This can explain few outstanding geological events such as, weakening of upper mantle etc. This study will also provide a water budget in these mantle minerals. Therefore, the proposed research embarks on advancing theoretical understanding of hydrous mineral phases, which have a stability under extreme thermo-mechanical conditions.

How to cite: Das, P. K. and Karangara, A.: First principle investigations on the water budget in olivine phases: Implications towards the behavior of hydrous mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7388, https://doi.org/10.5194/egusphere-egu24-7388, 2024.

EGU24-9476 | Orals | GD3.1

Spatially explicit simulations of the effect of tidal energy dissipation on the climate on early Earth 

Georg Feulner, Benjamin Biewald, J. A. Mattias Green, Matthias Hofmann, and Stefan Petri

The potential impact of the increased rates of tidal energy dissipation on the climate on early Earth is usually assessed in terms of the global contribution to the energy balance which is small compared to the incoming solar radiation. However, tidal energy dissipation depends strongly on the distribution of landmasses, and regional energy input could, in principle, impact the local and global climate state via changes in circulation patterns and feedbacks in the Earth system. Here we investigate these effects by calculating tidal energy dissipation for a randomly generated continental distribution representative of early Earth, and three different rotation rates, and feeding it into a coupled climate model. Despite marginal global impacts, tidal energy dissipation can have significant regional effects caused by changes in ocean circulation and amplified by the ice-albedo feedback. These effects are strongest in climate states and regions where meridional heat transport close to the sea-ice margin is altered. This suggests that tidal heating could have contributed to sustaining regions with no significant ice cover.

How to cite: Feulner, G., Biewald, B., Green, J. A. M., Hofmann, M., and Petri, S.: Spatially explicit simulations of the effect of tidal energy dissipation on the climate on early Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9476, https://doi.org/10.5194/egusphere-egu24-9476, 2024.

EGU24-10677 | Posters on site | GD3.1

Geochemical and Nd isotopic constraints on the evolution of Neoarchean continental crust underlying the central Deccan Traps 

Marc C. Halfar, Bradley J. Peters, James M.D. Day, and Maria Schönbächler

Ancient rocks documenting early silicate Earth processes are only sparsely preserved on its modern surface. Some of the oldest known crustal lithologies (≤3.7 Ga) can be found within the Indian Shield. However, a substantial area of the western and central Indian basement has been covered by the ~66 Ma old Deccan flood basalts. Some Deccan-related mafic dykes in the Nandurbar-Dhule region of the Narmada-Tapi rift zone host xenolithic crustal material, which can be used to study the otherwise inaccessible basement. Textural and mineralogical heterogeneity amongst these xenoliths implies that they derive from different depths of a single column of crust and represent randomly sampled crustal rock types with possibly distinct heritages. Well studied examples of these dykes are the adjacent Rajmane and Talwade dykes south of Duhle, which host Neoarchean-aged [1] crustal xenoliths with highly variable 87Sr/86Sr ratios between 0.70935 and 0.78479 [2]. This led previous researchers to infer a genetic relationship of these xenoliths with rocks from the Dharwar Craton [1, 2].

In this study, xenolith samples are used to investigate the evolution of sub-Deccan continental crust and evaluate whether randomly sampled crustal lithologies share a common Hadean heritage that is similar to published data for Dharwar granitic rocks. Our samples (n = 17) originate from two mafic dykes near Talwade and Ranala in the Nandurbar-Dhule region. We report major and trace element abundances and 142Nd isotopic compositions. The CIPW norms of xenoliths define a nearly continuous petrological evolution trend from tonalites to reworked, orthoclase-rich granites, with subordinate trondhjemitic compositions. The vertical cross-section of crust underlying the dykes therefore provides an opportunity to study the geochemistry of evolving primitive continental crust. Trace element abundance data also conform to a tonalite-trondhjemite-granodiorite-like (TTG) composition for a subset of the xenoliths, whereas others resemble younger granitoids, which might represent reworked TTG equivalents, or younger intrusions.

The short-lived (t1/2 = 103 Ma) 146Sm-142Nd decay system is particularly sensitive to magmatic fractionation processes that occurred within the first ca. 500 Ma of Earth’s history. Heterogeneous 142Nd/144Nd compositions (expressed as μ142Nd = [(142Nd/144Nd)sample/(142Nd/144Nd)JNdi – 1] * 106) are typically restricted to Archean-aged rocks and reveal information about the preservation of mantle heterogeneity over geological timescales. The μ142Nd of dyke host lavas (n = 3) are heterogeneous (μ142Nd = -2.0 ±5.1 to +6.1 ±5.1) but unresolved from the terrestrial standard. Such heterogeneity suggests that the parental magmas to the dykes experienced complex lithospheric and crustal assimilation during their ascent. Felsic xenoliths have homogeneous μ142Nd compositions (μ142Nd = -0.9 ±2.3, 95% c.i., n = 7). Combined with the major and trace element data, this implies an extensively reworked crust underneath the Deccan Traps. The lack of recognizable μ142Nd anomalies is consistent with data of younger Dharwar granitoids [3] and may reflect regional overprinting of mantle μ142Nd heterogeneity at or before the Neoarchean emplacement age of the xenoliths.

 

[1] Upadhyay et al. (2015) J. Geol. 123(3), 295–307.

[2] Ray et al. (2008) Gondwana Res. 13, 375–385.

[3] Ravindran et al. (2022) Goldschmidt Abst. 10986.

How to cite: Halfar, M. C., Peters, B. J., Day, J. M. D., and Schönbächler, M.: Geochemical and Nd isotopic constraints on the evolution of Neoarchean continental crust underlying the central Deccan Traps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10677, https://doi.org/10.5194/egusphere-egu24-10677, 2024.

EGU24-10889 | Orals | GD3.1

Archaean record of the Singhbhum Craton, India: new insights from greenstone belts and cratonic cover sequences.  

Jaganmoy Jodder, Axel Hofmann, Marlina Elburg, and Rebeun Ngobeli

In recent times, the Archaean geological record of the Singhbhum Craton has been scrutinized regarding early Earth crustal processes, tectonics, magmatic-detrital zircon geochronology, early life research, and Fe-Mn mineralization associated with volcano-sedimentary successions. However, many of these studies are hampered by a lack of a basic stratigraphic framework of the various litho-stratigraphic units, complicating our understanding of the overall Archaean geology of the Singhbhum Craton. Here, we share first-hand information on the Palaeoarchaean greenstone belts and Meso-Neoarchaean intracontinental volcano-sedimentary sequence of the Singhbhum Craton.

New magmatic zircon U-Pb ages determined from felsic volcanic rocks of the Badampahar Group are represented by their crystallization age at c. 3.51 Ga. Intrusive granitoids exposed in the Daitari and Gorumahisani greenstone belts yield crystallization ages ranging from 3.38 to 3.29 Ga and having inherited zircons being 3.58, 3.55, and 3.51 Ga old. A granitoid intrusive into iron formation of the Gorumahisani greenstone belt has an age of c. 3.29 Ga.  Detrital zircons recovered from Koira Group sandstone intercalated with iron formation yield a maximum depositional age of 2.63 Ga. 

We demonstrate that Palaeoarchaean greenstones exposed in the northern and southern parts of the Singhbhum Craton consists largely of sub-marine mafic-ultramafic volcanic rocks interlayered with minor felsic volcanic and chemical sedimentary rocks. Importantly, the ca. 3.51 Ga felsic volcanic rocks from the Badampahar Group permit comparison with co-eval felsic volcanic units reported from the lower part of the Onverwacht, Nondweni, Warrawoona groups of the Kaapvaal and Pilbara cratons. Otherwise, new age constraints of the Koira Group allow for better correlations with Meso-Neoarchaean cratonic cover successions elsewhere. 

How to cite: Jodder, J., Hofmann, A., Elburg, M., and Ngobeli, R.: Archaean record of the Singhbhum Craton, India: new insights from greenstone belts and cratonic cover sequences. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10889, https://doi.org/10.5194/egusphere-egu24-10889, 2024.

EGU24-12762 | ECS | Orals | GD3.1

Boron isotopes in global TTGs trace the increase in deep crustal recycling in the Mesoarchean   

Jeroen Goumans, Matthijs Smit, and Kira Musiyachenko

Granitoids of the Tonalite-Trondhjemite-Granodiorite (TTG) group are a prime constituent of Archean cratons. Differences in the composition of these rocks relative to modern-day, more potassic granitoids have been proposed to reflect changes in the conditions and mechanisms of crust generation. By extension, these differences may indicate changes in the tectonic regime through geological time. Despite a continuously growing body of TTG research, consensus on TTG generation and Archean tectonic settings has not yet been reached. A remaining open question regarding TTGs is whether a reworked crustal component is present. Silicon and O isotopes have been previously employed to address this question and both isotope systems suggest that at least some TTGs indeed contain reworked material. Boron provides an alternative isotope system that can trace surface-altered material in magmatic rocks because B isotopes fractionate significantly at Earth’s surface but remain relatively unaltered at high temperatures. On modern-day Earth, the deep recycling of isotopically heavy seawater-derived B through subduction results in a diverse, but on average heavy, B isotope composition in arc granitoids. Conversely, juvenile granitoids formed in settings unrelated to subduction typically have mantle B-isotope values. These systematics are likely uniform and would apply to the Archean as well, given that Archean seawater also appears to exhibit isotopically heavy B. The B isotope system may thus be used to investigate the presence of subducted or otherwise surface-derived material in Archean granitoids. To this end, B isotopes were analyzed for a geographically and temporally spread sample set of pristine TTGs and related granitoids (n=45, from 9 different Archean terranes covering an age range of 3.78 to 2.68 Ga). This is a considerably larger and more geographically spread sample set than a B-isotope pilot study on TTGs (Smit et al., 2019), and may as such provide more globally representative results. The B isotope signature of TTGs seem to diversify over time, diverging more from mantle-derived values starting between 3.3 and 2.9 Ga. TTGs younger than 2.9 Ga exhibit up to δ11B = +10.5 ± 0.2‰, and 48% of the samples have δ11B values heavier than depleted mantle, whereas this is 18% for TTGs older than 3.3 Ga. The B isotope signature additionally diversifies with decreasing K2O/Na2O and La/Sm. Boron isotope compositions do not correlate with geochemical or petrological proxies for (post-)magmatic processes, such as weathering, metamorphism, hydrothermal alteration, or the loss of magmatic fluids, and therefore seem to be at least not significantly altered by these processes. Instead, isotopically heavy B in TTGs may be explained by the addition of a sodic and 11B-rich contaminant into the TTG source. These contaminant characteristics point to seawater-altered oceanic crust, possibly introduced to the TTG source through subduction. If this is correct, the temporal trend observed in the δ11B values in TTGs may reflect a shift from local and episodic to global and systematic subduction of oceanic crust in the Mesoarchean.

Smit, M.A. et al., 2019, Formation of Archean continental crust constrained by boron isotopes: Geochemical Perspectives Letters, doi:10.7185/geochemlet.1930.

How to cite: Goumans, J., Smit, M., and Musiyachenko, K.: Boron isotopes in global TTGs trace the increase in deep crustal recycling in the Mesoarchean  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12762, https://doi.org/10.5194/egusphere-egu24-12762, 2024.

EGU24-12921 | Posters on site | GD3.1 | Highlight

Earth’s early tectonic modes and implications for habitability 

Peter Cawood and Priyadarshi Chowdhury

Tectonic mode manifests how a planet’s interior is cooling, and it encompasses all the geological activities (e.g., magmatism, deformation, metamorphism, sedimentation) that characterize the planetary body. Tectonic processes exert first-order control on factors key to planetary habitability (e.g., Southam et al., 2015). For example, tectonic mode controls the long-term prevalence of surface oceans, the sustenance of physicochemical conditions (e.g., temperature) favourable for metabolic activity, fluxing of elements in and out of the planet’s interior and thereby, the availability of bio-essential nutrients (e.g., C, O, H, N, P, S) (Cockell et al., 2016). However, all tectonic modes do not regulate these processes efficiently. For example, stagnant-lid mode restricts heat and material exchange between a planet’s interior and surficial reservoirs compared to plate tectonics. Further, certain factors determining a planet’s tectonic mode – like internal heat budget, mechanical behaviour of rocks, and volatile content – can vary with time, leading to the prevalence of different tectonic modes during planetary evolution. Thus, a planet’s habitability is critically intertwined with its tectonic evolution.

Modern Earth is the only known planet with plate tectonics, felsic crust, and life. Plate tectonics has resulted in a Goldilocks environment for long-term habitability via chemical cycling across the Earth system, regulating temperature through the carbonate-silicate cycle, sustaining oceans at the surface, and developing bimodal hypsometry with emergent felsic crust releasing bio-essential minerals through weathering and erosion. This has resulted in diverse habitats facilitating life’s complex phylogenetic tree. However, life initiated on Earth in the Hadean or early Archean when non-plate-tectonic modes like the stagnant- or squishy-lid modes are inferred to be prevalent (e.g., Cawood et al., 2022). Their potential to promote habitability is unknown, with few studies suggesting that they may lead to habitable conditions (e.g., Tosi et al., 2017). Nevertheless, our terrestrial planetary neighbours’ records suggest that such modes are unlikely to provide the environmental stability necessary to develop a long-term phylogenetic landscape. The geochemical cycling of elements through these modes may occur (e.g., via magmatism and episodic recycling of lithosphere) but is likely to be spatially and temporally discontinuous and limited, thereby limiting the supply of bio-essential nutrients and longevity of oceans on a planetary surface. As such, these modes inhibit a surficial environment in long-term dynamic equilibrium, leading to inhospitable habitats either through the development of a run-away greenhouse (e.g., Venus) or the loss of early atmosphere and oceans to space (e.g., Mars).

Thus, the tectonic evolution of Earth and its resultant habitability are a predictable consequence of its position, composition, size, and heat energy within the solar system. These conditions may serve as a template to search for exoplanet habitability; however, a degree of unpredictability will remain in knowing whether a similar set of planetary criteria would produce the same outcome.

References:

Cawood et al., 2022. Reviews of Geophysics, 60, e2022RG000789

Cockell et al., 2016. Astrobiology, 16(1), pp.89-117.

Southam et al., 2015. Planets and Moons, 10, pp.473-486.

Tosi et al., 2017. Astronomy & Astrophysics, 605, p.A71.

How to cite: Cawood, P. and Chowdhury, P.: Earth’s early tectonic modes and implications for habitability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12921, https://doi.org/10.5194/egusphere-egu24-12921, 2024.

The Limpopo Belt of southern Africa is a classical Paleoproterozoic orogenic belt that is believed to have resulted from the collision between the Kaapvaal and Zimbabwe Cratons. Previous studies have primarily focused on geochronology, petrology, and geochemistry of different rock assemblages, resulting in a general tectonic framework indicating at least two significant tectonothermal events from Mesoarchean to Paleoproterozoic. However, the spatial and temporal relationships between these events, as well as their overall structural patterns in the field, are poorly understood. The Central Limpopo Belt contains the best lithological exposures of different ages, making it the most promising area for detailed structural mapping and analysis, and for gaining a better understanding of these issues.
Based on the detailed field-based structural analyses, four generations of deformation were identified. The earliest D1 deformation is characterized by the penetrative S1 foliations only preserved within the 3.6-3.4 Ga anorthosites that now occur sporadically as xenoliths or boudins in the highly deformed 2.9-3.3 Ga Sand River gneiss. S2 are penetrative gneissic foliations that were extensively developed in the Sand River gneiss and were intensively superimposed by subsequent deformations into tight to isoclinal folds. After restoration of their attitude, S2 foliations strike NW-SE and dip steeply to SW at high angles, indicating that the D2 deformation experienced a roughly NE-SW-oriented compression between 2.9-2.6 Ga. D3 deformation resulted from significant NW-SE-oriented compression that intensively superimposed the earlier S2 fabrics into vertically inclined isoclinal folds and tectonites S3-L3. Strain measurements on these tectonites indicate that all pre-existing rock assemblages were stretched or sheared along the vertical orientation, resulting in the development of numerous sheath folds in the Sand River gneiss and 2.6-2.7 Grey gneiss. Associated with the zircon ages from anatexis melts, the D3 deformation most likely occurred at 2.1-2.0 Ga. SHRIMP U-Pb zircon age dating recorded these two metamorphic ages of ~2.6 Ga and 2.0 Ga on a single zircon of the foliated Sand River gneiss. A regional large scale inclined open fold F4 gently refolded the D1-D3 fabrics and marked the final deformation of the Central Limpopo Belt, occurring sometime after ~2.0 Ga. 
Detailed structural data of this study, in combination of available geochronological and metamorphic data lead us to propose that the ~2.65 Ga and ~2.0 Ga tectonothermal events occurred under different tectonic environments. The ~2.65 Ga tectonothermal event developed coevally with D2 deformation and high-grade metamorphism during the NE-SW collisional event. In contrast, the ~2.0 Ga tectonothermal event occurred during a NW-SE-oriented collisional event between the Kaapvaal and Zimbabwe Cratons, resulting in the formation of the major Limpopo tectonic linear belt seen today.

Acknowledgement
This work was financially supported by the National Natural Science Foundation of China (42025204) and National Key Research and Development Program of China (No. 2023YFF0803804).

 

How to cite: Zhang, J., Brandl, G., Zhao, G., Liu, J., and Zhao, C.: Deciphering a complex Neoarchean-Paleoproterozoic collisional history between the Kaapvaal and Zimbabwe Cratons: new constraints from polyphase deformation of the Central Limpopo Belt, southern Africa , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14565, https://doi.org/10.5194/egusphere-egu24-14565, 2024.

EGU24-16380 | ECS | Orals | GD3.1

Linking early Earth’s internal and external reservoirs: a change in oxygen fugacity of sub-arc magmas across the Great Oxidation Event 

Hugo Moreira, Craig Storey, Emilie Bruand, James Darling, Mike Fowler, Marine Cotte, Edgar E. Villalobos-Portillo, Fleurice Parat, Luís Seixas, Pascal Philippot, and Bruno Dhuime

Plate tectonics exerts a first-order control on the interaction between Earth’s reservoirs. Atmospherically-altered surface materials are recycled to the mantle via subduction, while volatiles from the mantle are liberated to the atmosphere via volcanism. This cycle regulates much of Earth’s climate, ocean levels and metallogenetic processes within the continental crust. However, the interplay between Earth’s atmospheric changes and the geochemical evolution of mantle-derived magmas has remained obscure for the ancient geological history. This has led to multiple conflicting models for the crustal evolution in the early Earth.

A time-integrated evolution of the mantle-crust-atmosphere-hydrosphere interaction is yet to be fully established. For instance, secular change of the ocean and atmosphere system is evident from several proxies but the feedback of these changes to magmatic and geochemical processes in the lithosphere remain unclear. Moreover, no clear consensus has been reached on the timing of modern-style plate tectonic initiation and the evolution of net growth of the continental crust.

To explain overt and cryptic global trends in the geochemistry of magmatic rocks, a better understanding of mineral reactions and how these control trace element evolution in magmas at the lithosphere-scale is paramount. For example, the elemental and isotopic composition of apatite inclusions hosted by zircon offers a way to better understand the evolution of magmas and, to some extent, the nature of magma sources. These proxies rely on the robust data acquisition of other isotope systems with different geochemical behaviour, such as U-Pb and Lu-Hf analyses in the host zircon crystal.

A combination of methods and proxies including the elemental composition of apatite via EPMA and the oxygen fugacity based on sulphur speciation via μ-XANES of apatite inclusions was applied to ancient sub-arc magmas formed in regions akin to modern subduction zones. These magmas share a common mantle source but crystallised more than 200 million years apart (at 2.35 and 2.13 billion years ago). Importantly, they bracket the Great Oxidation Event, when atmospheric oxygen levels increased by five orders of magnitude, causing a permanent and dramatic change in Earth’s surface chemistry. As such, these sub-arc magmas were investigated as potential tracers of the interaction between Earth’s atmosphere and the mantle.

The information from several inclusions from co-magmatic rocks can then be interpreted in the light of U-Pb, Lu-Hf, trace elements and oxygen isotope analyses of the host zircon grains. Altogether, the results show a shift in oxygen fugacity of sub-arc magmas across the Great Oxidation Event. The change in oxygen fugacity is thought to be caused by recycling into the mantle of sediments that had been geochemically altered at the surface by the increase in atmospheric oxygen levels. This study opens a wide window of opportunities for the time-integrated investigation of the interaction between atmosphere and oceans with the evolving terrestrial mantle.

How to cite: Moreira, H., Storey, C., Bruand, E., Darling, J., Fowler, M., Cotte, M., Villalobos-Portillo, E. E., Parat, F., Seixas, L., Philippot, P., and Dhuime, B.: Linking early Earth’s internal and external reservoirs: a change in oxygen fugacity of sub-arc magmas across the Great Oxidation Event, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16380, https://doi.org/10.5194/egusphere-egu24-16380, 2024.

EGU24-18408 | Orals | GD3.1

Archean continental crust formed by melting mafic cumulates 

Matthijs Smit, Kira Musiyachenko, and Jeroen Goumans

Large swaths of juvenile crust with tonalite-trondhjemite-granodiorite (TTG) composition were added to the continental crust from about 3.5 billion years ago. Although TTG magmatism marked a pivotal step in early crustal growth and cratonisation, the petrogenetic processes, tectonic setting and sources of TTGs are not well known. Part of this issue is the general difficulty in disentangling the chemical effects of fractional crystallization and partial melting, which impedes constraining primitive melt compositions and, by extension, investigating source-rock lithology and composition. To investigate these aspects, we assessed the composition and petrogenesis of Archaean TTGs using high field-strength elements that are fluid immobile, uniformly incompatible, but differently compatible between various residual minerals. The Nb concentrations and Ti anomalies of TTGs show the overwhelming effects of amphibole and plagioclase fractionation and permit constraints on the composition of primary TTGs. The latter are relatively incompatible element-poor and characterised by variably high La/Sm, Sm/Yb and Sr/Y, and positive Eu anomalies. Differences in these parameters do not represent differences in melting depth, but instead indicate differences in the degree of melting and fractional crystallisation. Primary TTGs formed by the melting of rutile- and garnet-bearing plagioclase-cumulate rocks that resided in the roots of mafic proto-continents. The partial melting of these rocks likely was part of a causal chain that linked TTG magmatism to the formation of sanukitoids and K-rich granites. These processes explain the growth and differentiation of the Archean continental crust, without requiring external forcing such as meteorite impact or the start of global plate tectonics.

How to cite: Smit, M., Musiyachenko, K., and Goumans, J.: Archean continental crust formed by melting mafic cumulates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18408, https://doi.org/10.5194/egusphere-egu24-18408, 2024.

EGU24-19222 | ECS | Posters on site | GD3.1

Petrogenetic and Geochemical studies of Sittampundi Anorthosite Complex, Southern Granulite Terrain, India. 

Amandeep Kaur, Rajagopal Krishnamurthi, and Nachiketa Rai

The Sittampundi Anorthosite complex (SAC), in the Southern Granulite terrain of Peninsular India, is a layered Archean anorthosite comprising gabbroic rocks at the base overlain by leucogabbros and anorthosites interlayered with well-developed massive chromitites. The complex has been subjected to high-pressure granulite facies (800-900°C and 11-14 Kbar) metamorphism and later retrogressed to amphibolite-facies metamorphism (550-480°C and 5.5-4.5Kbar) during exhumation (Chatterjee et al., 2022). Detailed petrography, mineral chemistry as well as major and trace element geochemistry have been used to constrain its petrogenesis and geodynamic setting.

The presence of highly calcic plagioclase and igneous amphibole indicates that magma was quite hydrous in nature. Chromites are Fe-Al rich in nature, and on the differentiation diagram, they plot near to podiform chromites and supra-subduction zone setting. Geochemical trends in major and trace elements indicate that the gabbro, leucogabbro and anorthosites were derived from the fractionated magma. However, the mineral assemblage and chromite chemistry in chromitite indicate they formed due to magma mixing.  Based on experimental studies, the composition of plagioclase limits the pressure to 2-3kb and depth of crystallization to approximately 7-11 kilometres. The findings of this study indicate the hydrous magma parental to SAC originated in a subduction zone setting in the Neoarchean.

How to cite: Kaur, A., Krishnamurthi, R., and Rai, N.: Petrogenetic and Geochemical studies of Sittampundi Anorthosite Complex, Southern Granulite Terrain, India., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19222, https://doi.org/10.5194/egusphere-egu24-19222, 2024.

EGU24-19385 | Orals | GD3.1 | Highlight

The conceptual model of the formation of Earth’s habitability 

Yun Liu

The difficulty in direct differentiation of the felsic crustal components from Earth’s mantle peridotite leads to a requirement for the presence of a large amount of hydrated mafic precursor of TTG in Earth’s proto-crust, the origin of which, however, remains elusive. The mafic proto-crust may have formed as early as  4.4 Ga ago as reflected by the Hf and Nd isotopic signals from Earth’s oldest geological records, i.e., zircons. The Archean continents, primarily composed of the felsic tonalite–trondhjemite–granodiorite (TTG) suite, were formed or conserved since  3.8 Ga, with significant growth of the continental crust since  2.7 Ga. Such a significant time lag between the formation of the mafic proto-crust and the occurrence of felsic continental crust is not easily reconciled with a single-stage scenario of Earth’s early differentiation. 
Here, inspired by the volcanism-dominated heat-pipe tectonics witnessed on Jupiter’s moon Io and the resemblances of the intensive internal heating and active magmatism between the early Earth and the present-day Io, we present a conceptual model of Earth’s early crust-mantle differentiation and the formation of habitability, which involves the tremendous heat obtained by the Moon-forming giant impact. It  forces Earth to choose an Io-like tectonics, which can efficiently dissipate heat and extract a mafic proto-crust from the early mantle, then followed by an intrusion-dominating regime that could account for the subsequent formation of the felsic continents as Earth cools. The episodic heat-pipe tectonics destroy most of rocks formed during Hadean era. The cool and hard rock layer formed due to the heat-pipe tectonics is essential for the formation of habitability of the earth. By this way, the required conditions by a habitable Earth, e.g., adequate surface temperature, aqueous sphere, and towering mountains, etc., would be appeared within a surprisingly short time. Therefore, the Moon-forming giant impact is the most important reason to make a habitable Earth. It not only brought tremendous heat into Earth and forced Earth to choose the volcanism-dominated heat-pipe tectonics but also completely destroyed the proto-atmosphere to avoid over-heated situations occurred like that of Venus at present. 

How to cite: Liu, Y.: The conceptual model of the formation of Earth’s habitability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19385, https://doi.org/10.5194/egusphere-egu24-19385, 2024.

EGU24-21184 | Orals | GD3.1

A widespread, short-lived, off-craton subduction source for hidden crustal growth in Earth’s infancy 

Eric Vandenburg, Oliver Nebel, Peter Cawood, Fabio Capitanio, Laura Miller, Marc-Alban Millet, and Hugh Smithies

The scarce geological record of Earth’s infancy, particularly before 3 billion years ago (Ga), is restricted to cratons, many of which likely originated as volcano-plutonic plateaus in a non-mobile lid geodynamic regime. However, this scarcity is at odds with the significant volumes of continental crust at 3 Ga that multi-proxy models of mantle depletion and crustal growth predict. This challenges the notion that plateau-type cratonic nuclei represent the predominant tectonomagmatic settings operating on the early Earth. Reconciling this paradox necessitates a “silent majority” of missing off-craton Archean crust of an uncharacterized affinity.

To investigate a potential rare remnant example of an Archean crust constructed away from cratonic nuclei, we report major and trace-element chemostratigraphic data from the 3.1 Ga Whundo Group of the Pilbara Craton, investigating the petrogenetic processes related to its formation. These data reveal three magmatic cycles of intercalated supracrustal successions comprising six groups: tholeiites, boninites, calc-alkaline BADR (basalt-andesite-dacite-rhyolite), high-magnesium ADR (including a subset of transitionally adakitic affinity), Nb-enriched basalts (NEB), and boninite-calc-alkaline hybrids. Th/Yb-Nb/Yb, Gd/YbN-Al/TiN, and Nd isotope systematics are inconsistent with contamination by felsic basement characteristic of cratonic cores, suggesting eruption onto thin, juvenile lithosphere that was only later incorporated into the Pilbara Craton.

How to cite: Vandenburg, E., Nebel, O., Cawood, P., Capitanio, F., Miller, L., Millet, M.-A., and Smithies, H.: A widespread, short-lived, off-craton subduction source for hidden crustal growth in Earth’s infancy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21184, https://doi.org/10.5194/egusphere-egu24-21184, 2024.

TS9 – General Topics in Tectonics and Structural Geology

EGU24-2270 | ECS | Posters on site | ITS1.8/TS9.1

Geologic formation database for Africa with projections onto plate reconstructions 

Wen Du, James Ogg, Gabriele Ogg, Rebecca Bobick, Jacques LeBlanc, Monica Juvane, Dércio José Levy, Aditya Sivathanu, Suyash Mishra, Yuzheng Qian, and Sabrina Chang

It is a challenge to obtain information about the geologic formations and their succession in Africa due to lack of on-line lexicons for most regions.  Therefore, we established AfricaLex as a free public online database that includes details on the geologic formations in all major basins, onshore and offshore, of Africa.

AfricaLex (https://africalex.geolex.org/) offers search for geologic formations in the database by standard search criteria (name, partial name, age, region, lithology keywords, or any combination), and a map-based graphic user interface with stratigraphic-column navigation. The returned entries can be displayed by-age or in alphabetical order. Each formation is color-coded based on the Geologic Time Scale 2020, and with digitized regional extent in GeoJSON format. These enable plotting of the individual formations or time-slices of all formations across Africa of a user-selected age, with each regional-extent filled with their appropriate lithologic facies pattern, onto any of three proposed plate reconstruction models with a single click.

The aim is to make information on Africa geology and its component geologic formations more to accessible to geologists and the general public from the world and for improving paleogeographic maps.  Users can obtain a view of the sediments and volcanics that were accumulating at any time across the ancient land of Africa.These lexicon systems will be interlinked to other stratigraphic and paleogeographic databases through the lUGS Deep-Time Digital Earth platform.

How to cite: Du, W., Ogg, J., Ogg, G., Bobick, R., LeBlanc, J., Juvane, M., Levy, D. J., Sivathanu, A., Mishra, S., Qian, Y., and Chang, S.: Geologic formation database for Africa with projections onto plate reconstructions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2270, https://doi.org/10.5194/egusphere-egu24-2270, 2024.

EGU24-2425 | ECS | Posters on site | ITS1.8/TS9.1

South East Asia and Middle East Geologic Formation Databases with Visualizations on Plate Reconstructions 

ONeil Mamallapalli, Raju DSN Datla, Hongfei Hou, Bruno Granier, Nallapa Reddy Addula, Jacques LeBlanc, James Ogg, Nusrat Kamal Siddiqui, Cecilia Shafer, Gabriele Ogg, and Wen Du

In a successful collaboration with numerous regional experts on the stratigraphy of Southeast Asia and the Middle East, our international team developed cloud-based stratigraphic lexicons with graphical user-interfaces. These databases consist of the Indian Plate (indplex.geolex.org) of nearly 1000 onshore and offshore sedimentary and volcanic formations across India, Pakistan, Nepal, Bhutan, Sri Lanka, Bangladesh, and Myanmar, of southeast Asian regions (chinalex.geolex.org; thailex.geolex.org; vietlex.geolex.org; japanlex.geolex.org) with ca. 5000 formations as of January 2024), and of Middle East regions (mideastlex.geolex.org; qatarlex.geolex.org). The entries for each formation contain details on the succession of lithology, as well as the fossils present, age range, regional distribution and associated images. APIs enable easy access and integration with other applications. A comprehensive search system allows users to retrieve information on all geologic formations for a specific date or geologic stage from multiple databases. The cloud-based databases and websites can be explored through user-friendly map and stratigraphic-column interfaces generated from TimeScale Creator software.

Regional extents of each formation in GeoJSON format enables visualization as facies-pattern-filled polygons projected onto three proposed plate reconstructions of its corresponding time interval; or as time slices of regional paleogeography. These lexicon systems will be interlinked to other stratigraphic and paleogeographic databases through the lUGS Deep-Time Digital Earth platform. This comprehensive approach allows one better comprehend deep-time dynamics and gain valuable insights into the evolution of the different regions of our planet Earth.

How to cite: Mamallapalli, O., Datla, R. D., Hou, H., Granier, B., Addula, N. R., LeBlanc, J., Ogg, J., Siddiqui, N. K., Shafer, C., Ogg, G., and Du, W.: South East Asia and Middle East Geologic Formation Databases with Visualizations on Plate Reconstructions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2425, https://doi.org/10.5194/egusphere-egu24-2425, 2024.

EGU24-2473 | Orals | ITS1.8/TS9.1

Online databases of the geologic formations of Asia and Africa with display onto plate reconstructions 

James Ogg, Wen Du, Aditya Sivathanu, Sabrina Chang, Suyash Mishra, Sabin Zahirovic, Aaron Ault, O'Neil Mamallapalli, Haipeng Li, Mingcai Hou, and Gabriele Ogg

Building paleogeographic maps that are projected onto different tectonic plate reconstruction models requires team efforts to compile extensive interlinked databases of regional sedimentary and volcanic facies, data sharing standards, and computer projection methods. Two goals of the Deep-Time Digital Earth (DDE) program of the International Union of Geological Sciences (IUGS) Paleogeography Working Group are: (1) to interconnect online national databases for all geologic formations, and to compile these online "lexicons" for countries that currently lack these; (2) to project the combined paleogeographic output of these distributed databases for any time interval onto appropriate plate tectonic reconstructions.

Therefore, we have worked with regional experts to compile and interlink cloud-based lexicons for different regions of the world that are enhanced by graphic user-interfaces. Online lexicons with map-based and stratigraphic-column navigation are currently completed for the Indian Plate (ca. 800 formations), China (ca. 3200), Vietnam-Thailand-Malaysia (ca. 600), and all major basins in Africa (ca. 700) and in the Middle East (ca. 700 formations). These will soon be joined by Japan (ca. 600 formations) and basins in South America (ca. 700 formations). A multi-database search system (age, region, lithology keywords, etc.) enables all returned entries be displayed by-age or in alphabetical order. The genera in the "fossil" field are auto-linked to their entries and images in the online Treatise of Invertebrate Paleontology. With a single click, a user can plot the original extent of the geologic formation (or an array of regional formations of a specified age) onto different plate reconstruction models with the polygon(s) filled with the appropriate lithologic facies pattern(s). Our team collaborated with the Macrostrat team at Univ. Wisconsin (Madison) to interlink with their extensive regional facies-time compilations for North America and the ocean basins to enable a near-global coverage. Following the lead of Macrostrat's ROCKD app, this project is in partnership with UNESCO's Commission for the Geologic Map of the World and other geological surveys to enable linking online geologic map units for direct access to the lexicon details on that geologic formation and its former paleogeographic setting. Essentially, goal is to create a view of the sediments and volcanics that were accumulating onto the Earth's surface at any time in the past.

The main website (https://geolex.org) has links to the growing array of regional lexicons.

How to cite: Ogg, J., Du, W., Sivathanu, A., Chang, S., Mishra, S., Zahirovic, S., Ault, A., Mamallapalli, O., Li, H., Hou, M., and Ogg, G.: Online databases of the geologic formations of Asia and Africa with display onto plate reconstructions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2473, https://doi.org/10.5194/egusphere-egu24-2473, 2024.

EGU24-3558 | ECS | Posters on site | ITS1.8/TS9.1

Semi-Supervised Machine Learning for Predicting Lacustrine Carbonate Facies in theBarra Velha Formation, Santos Basin 

Pedro Vitor Abreu Affonso, Ana Luiza Spadano Albuquerque, and André Luiz Durante Spigolon

There is an increasing availability of geoscientific exploration data for the oil and gas industry. Supporting data-driven tools have become important for the optimization and geoscientific information gain from this kind of data and thus allowing a fastest and more trustable decision making. Nonetheless, the development of this kind of technology depends on the standardization of the data and its descriptive methodologies, that many times diverges between the geoscientists and its many data sources, that recurrently comes from different scales of samples. The complexity of non-conventional reservoir, like the ones from brazilian pre-salt, increases those pre-existing difficulties. In this sense, this work evaluates the results of a semi-supervised Machine-learning methodology that was applied to the aptian carbonates of Barra Velha formation, from the Santos Basin pre-salt. This methodology follows a PU-learning approach with the utilization of the Random-forest algorithm based on public data from geological cores, side samples and geophysical data from the corresponding depths of the Barra Velha carbonates. A team of geoscientists provided a carbonate facies grouping, and this work regrouped it based on quantitative and qualitative descriptions, and in depositional criteria related for those samples, aiming to better utilize this data for Machine-learning. To deal with the fact that the samples belong for different scales and data-sources, the classified samples from geological cores were select as “labeled”, and the rest of it was defined as “unlabeled”, establishing a criteria for description of the samples and that fits the workflow for semi-supervisioned Machine-learning. Model evaluation metric were analyzed and compared to results of a regular supervisioned model approach. The results show that the overall precision of the semi-supervisioned model has increased significantly by 10% in relation to the supersivioned methodology, and critical suggestions were made based on the results for motivation of future researches from this topic.

How to cite: Abreu Affonso, P. V., Spadano Albuquerque, A. L., and Durante Spigolon, A. L.: Semi-Supervised Machine Learning for Predicting Lacustrine Carbonate Facies in theBarra Velha Formation, Santos Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3558, https://doi.org/10.5194/egusphere-egu24-3558, 2024.

EGU24-4485 | ECS | Posters on site | ITS1.8/TS9.1

WebGPlates: A Unity-based Tool For Enhancing Paleogeographic Research 

Haipeng Li, Han Cheng, Sabin Zahirovic, and Yisa Wang
GPlates, an open-source, cross-platform GIS software, has been pivotal in plate tectonics and paleogeography. The recent browser-based implementation of GPlates, facilitated by pyGPlates and Cesium, offers real-time rotation of online datasets. Yet, this approach encounters limitations in data rotation efficiency and integration with diverse datasets. To address this issue, we introduce the Unity-based WebGPlates (https://dplanet.deep-time.org/DPlanet/), which harnesses the capabilities of the Web Assembly and Unity framework for enhanced computing efficiency and browser-based rendering. More importantly, WebGPlates integrates with the Deep-time Digital Earth Platform, ensuring comprehensive data access and services. Our preliminary results highlight the potential of WebGPlates as an indispensable tool in paleogeographic research. We extend an invitation to the whole community to engage and collaborate utilizing this enhanced platform.

How to cite: Li, H., Cheng, H., Zahirovic, S., and Wang, Y.: WebGPlates: A Unity-based Tool For Enhancing Paleogeographic Research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4485, https://doi.org/10.5194/egusphere-egu24-4485, 2024.

EGU24-5551 | Posters on site | ITS1.8/TS9.1

Intercomparison and Definition of Uncertainties of Deep-Time Global Earth Reconstructions: What’s the problem? 

Christian Vérard, Florian Franziskakis, and Grégory Giuliani

Global Earth reconstruction maps are used as baseline information for many studies, with high-level impacts and large implications. Yet, virtually no study fundamentally question the reliability of those reconstructions. In many cases, the model the study uses is not even credited. The reason for the absence of such discussion probably lies in the fact that none of the plate tectonic / palæogeographic modellers themselves have been able so far to assess the reliability of their own maps.

Why? First, because actually, there are ‘palæo-continental’, ‘plate tectonics’, ‘palæo-environmental’, and ‘palæogeographic’-types of reconstruction and it is difficult to compare apples and oranges. Second, because the workflow, definition, standard and vocabulary used to by the modellers can be quite different. And third and overall, because data, which reconstructions are based upon, may be contradictory and modellers must make choices.

If, for example, 4 data suggest a collision at a given time and a fifth does not, can we state that the model should display a collision zone at the 80% confidence level? What geological information is undoubtedly a proof of a collision? If among the 5 data, 2 corresponds to flysch-series, 1 corresponds to S-type granite, the 4th to tectonic unconformities and structural deformation, and the 5th is the definition of a retrograde path of metamorphic P – T conditions, is it sufficient to talk about collision, and do the 5 data have the same weight in terms of uncertainties? What about if the model does not display the collision zone at time the 4 first data suggest collision, but does display collision at the next time slice in agreement with the 5th information?

Contradictory data and debatable choices will always exist, and the existence of numerous global Earth reconstruction models is thus a wealth. However, in order to talk about uncertainties and to allow some intercomparison, the modellers of the Earth reconstruction community must collaborate, form an International Panel for Earth Reconstruction (IPER), and lay the foundation for shared definitions, concepts, vocabulary, and FAIR principles. A quantification of uncertainty on past reconstructions may then possibly be achieved by intercomparison between various models.

How to cite: Vérard, C., Franziskakis, F., and Giuliani, G.: Intercomparison and Definition of Uncertainties of Deep-Time Global Earth Reconstructions: What’s the problem?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5551, https://doi.org/10.5194/egusphere-egu24-5551, 2024.

EGU24-5938 | ECS | Posters on site | ITS1.8/TS9.1

Dynamic interaction between thermal insulation by cratonic keels and asthenospheric convection: insights from numerical experiments 

João Pedro Macedo Silva, Victor Sacek, and Gianreto Manatschal

The conductive heat transport in the lithosphere is less efficient than the convective heat transport in the asthenospheric mantle. Therefore, the lithosphere behaves as a thermal insulation above the asthenospheric mantle. As a consequence, the temperature in the mantle can increase, also affecting the rheological structure of the mantle, both in the asthenosphere and at the base of the lithosphere. As the thickness of the thermal lithosphere can vary laterally from less than 100 km to more than 200 km under cratonic domains, the impact of thermal insulation can vary geographically. Therefore, the variation of lithospheric thickness may affect the efficiency of the heat transport from the asthenosphere to the lithospheric mantle. Using thermo-mechanical numerical models, we investigate how lateral variation of lithospheric thickness affects the heat flow to the surface, the convective pattern inside the asthenospheric mantle and the impacts of thermal evolution of cratonic keel over time scales of hundreds of million years. We test scenarios considering different lateral positions for the cratonic keel, scenarios with relative movement between lithosphere and asthenospheric mantle to emulate lateral movement over geological time. We also test the impacts of assuming different mantle potential temperatures for the asthenosphere. Additionally, yield strength envelopes are calculated in different portions of the lithosphere in the numerical domain to assess the impact of the thermal insulation to the rheological structure of the lithosphere. The preliminary results indicate that rising/hot thermal anomalies tend to concentrate at the base of cratonic keels, which may eventually act as a weakening effect in the lithosphere. In scenarios with relative movement, we observe a systematic shift in the location of hot thermal anomalies in the opposite direction of the relative movement.

How to cite: Macedo Silva, J. P., Sacek, V., and Manatschal, G.: Dynamic interaction between thermal insulation by cratonic keels and asthenospheric convection: insights from numerical experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5938, https://doi.org/10.5194/egusphere-egu24-5938, 2024.

EGU24-6149 | ECS | Orals | ITS1.8/TS9.1

Robust estimation of seismogenic depths and their uncertainties 

Álvaro González

Earthquakes occur in a depth range where the physical conditions allow rocks to behave as brittle and to deform in a stick-slip fashion. This range is limited by the so-called upper and lower seismogenic depths, which are input parameters for bounding seismogenic ruptures in models of seismic hazard assessment.

Usually, such limits are estimated from the observed depth distribution of hypocenters. An exact estimation is not possible, because earthquake locations (and particularly hypocentral depths) are uncertain. Also, the sample of observed earthquakes is finite, and shallower or deeper earthquakes than those so far observed at a site could eventually happen. For these reasons, the extreme values of the distribution (the shallowest and the deepest earthquakes in the sample) are weak estimators, especially if a small sample (with few earthquakes) is used.

A common, more statistically robust, proxy to those limits is a given percentile of the distribution of earthquake depths. For example, the 90%, 95% or 99% percentiles (named D90, D95 or D99, respectively) are frequently used as proxies to the lower seismogenic depth. But the actual uncertainties of such estimates are, so far, not properly assessed.

Here I present a method for calculating such percentiles with an unbiased estimator and quantifying their uncertainties in detail.

Earthquakes are more easily missed (more difficult to detect) the deeper they are. So earthquake catalogues preferentially contain shallow events. To avoid this bias, only those events with magnitude at least equal to the magnitude of completeness of the sample are regarded.

A mapping procedure is used in order to highlight spatial variations of seismogenic depths, considering, for each point in the map, the subsample of its closest earthquakes. Uncertainties arising from the finite sample size are dealt with by using bootstrap.

Each hypocentral location is randomized in space in a Monte Carlo simulation, to take into account the reported location uncertainties. Also, crustal earthquakes can be considered separately from deeper ones, by truncating the hypocentral depth distribution with a Moho model for which the uncertainty can also be taken into account.

This procedure allows calculating statistically robust maps of the seismogenic depths with a realistic treatment of their uncertainties, as exemplified with the analysis of a regional seismic catalogue.

How to cite: González, Á.: Robust estimation of seismogenic depths and their uncertainties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6149, https://doi.org/10.5194/egusphere-egu24-6149, 2024.

EGU24-6992 | ECS | Orals | ITS1.8/TS9.1

Streamlining Multi-Data Geophysical Inference with BayesBridge 

Fabrizio Magrini, Jiawen He, and Malcolm Sambridge

The Earth's interior structure must be inferred from geophysical observations collected at the surface. Compared to just a few decades ago, the amount of geophysical data available today is voluminous and growing exponentially. Dense seismic networks like USArray, AlpArray, and AusArray now enable joint inversions of various geophysical data types to maximise subsurface resolution at scales ranging from local to continental. However, the practical application of joint inversions faces several challenges:

  • Various geophysical techniques typically probe different scales and depths, complicating the choice of an appropriate discretisation for the Earth's interior.
  • Different geophysical observables may respond to physical properties that are not directly related (e.g., density and electrical conductivity), making the construction of self-consistent parameterisations a non-trivial task.
  • Without a comprehensive understanding of noise characteristics, standard methods require assigning weights to different data sets, yet robust choices remain elusive.

Capable of overcoming these recognised challenges and allowing estimates of model uncertainty, probabilistic inversions have grown in popularity in the geosciences over the last few decades, and have been successfully applied to specific modelling problems. Here, we present BayesBridge, a user-friendly Python package for generalised transdimensional and hierarchical Bayesian inference. Computationally optimised through Cython, our software offers multi-processing capabilities and runs smoothly on both standard computers and computer clusters. As opposed to existing software libraries, BayesBridge provides high-level functionalities to define complex parameterisations, with prior probabilities (defined by uniform, Gaussian, or custom density functions) that may or may not be dependent on depth and/or geographic coordinates. By default, BayesBridge employs reversible-jump Markov chain Monte Carlo for sampling the posterior probability, with the option of parallel tempering, but its low-level features enable effortless implementations of arbitrary sampling criteria. Utilising object-oriented programming principles, BayesBridge ensures that each component of the inversion -- such as the discretisation, the physical properties to be inferred, and the data noise -- is a self-contained unit. This design facilitates the seamless integration of various forward solvers and data sets, promoting the use of multiple data types in geophysical inversions.

How to cite: Magrini, F., He, J., and Sambridge, M.: Streamlining Multi-Data Geophysical Inference with BayesBridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6992, https://doi.org/10.5194/egusphere-egu24-6992, 2024.

EGU24-7570 | ECS | Posters on site | ITS1.8/TS9.1

Navigating the Academic Landscape: Intelligent Retrieval Systems for Geoscience Exploration 

Yi Xu, Cheng Deng, Shuchen Cai, Bo Xue, and Xinbing Wang

The surge in academic publications mirrors the evolutionary strides of human civilization, marked by an exponential growth in their numbers. Addressing the lacuna in well-organized academic retrieval systems for geoscientists, the Geo-Literature system emerges as a transformative tool. This system, boasting a vast repository of over seven million papers and information on four million scholars, employs cutting-edge technology to reshape the landscape of academic search, analysis, and visualization within the geoscience domain.

Driven by the necessity to bridge the gap between modeling frameworks and geological constraints, Geo-Literature incorporates geoscience knowledge mining and representation technologies. Through its intelligent update and fusion system, it not only integrates new publications but also analyzes language, space, and time relationships, effectively overcoming challenges posed by knowledge ambiguity. The platform's geoscience knowledge interaction and presentation technology facilitate intelligent retrieval, recommendation systems, and the creation of comprehensive scholarly portraits.

The impact of Geo-Literature transcends conventional academic boundaries. Establishing associations, mapping key attributes, and providing hierarchical visualizations, the system assists researchers in uncovering knowledge and forming a nuanced understanding of the academic space in geosciences. Consequently, Geo-Literature not only enhances the efficiency of paper retrieval but also contributes to broader scientific goals by fostering interdisciplinary collaboration and advancing our comprehension of Earth's deep-time processes.

How to cite: Xu, Y., Deng, C., Cai, S., Xue, B., and Wang, X.: Navigating the Academic Landscape: Intelligent Retrieval Systems for Geoscience Exploration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7570, https://doi.org/10.5194/egusphere-egu24-7570, 2024.

EGU24-7977 | Orals | ITS1.8/TS9.1

Reconstructing the Earth in Deep-Time: A New and Open Framework for the PANALESIS Model 

Florian Franziskakis, Christian Vérard, and Gregory Giuliani

The Panalesis model (Vérard, 2019) was developed in a preliminary version according to concepts, methods and tools that follow the work carried out for more than 20 years at the University of Lausanne (Stampfli & Borel, 2002; Hochard, 2008). Although the techniques are relevant, development under ArcGIS® does not allow visibility and easy accessibility of the model to the scientific community.

A major effort is therefore underway to migrate the entire model to an open source version using a FAIR approach for research software (Chue Hong et al., 2021). This migration concerns both the plate tectonic maps covering all the world over the entire Phanerozoic and part of the Neoproterozoic, but also the creation of paleoDEMs (global quantified topographies).

The Panalesis model and its entire architecture is therefore currently migrated to QGIS (a free and open source geographic information system). TopographyMaker, the software designed to convert polylines from the reconstruction map into a points grid with elevation values is now working as a plugin on QGIS. The output palaeoDEMS will also be published according to the FAIR principles for scientific data management and stewardship (Wilkinson et al., 2016).

The development and future refinements of TopographyMaker will enhance the Earth system modelling, especially coupling between models of different shells of the Earth such as atmospheric circulation, climatic evolution, and mantle dynamics. The topography is, for instance, considered a first order controlling factor for CO2 evolution over geological timescales, through silicate weathering (MacDonald et al., 2019).

How to cite: Franziskakis, F., Vérard, C., and Giuliani, G.: Reconstructing the Earth in Deep-Time: A New and Open Framework for the PANALESIS Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7977, https://doi.org/10.5194/egusphere-egu24-7977, 2024.

EGU24-8215 | ECS | Orals | ITS1.8/TS9.1

Physically Structured Variational Inference for Bayesian Full Waveform Inversion 

Xuebin Zhao and Andrew Curtis

Full waveform inversion (FWI) has become a commonly used tool to obtain high resolution subsurface images from seismic waveform data. Typically, FWI is solved using a local optimisation method which finds one model that best fits observed data. Due to the high non-linearity and non-uniqueness of FWI problems, finding globally best-fitting solutions is not necessarily desirable since they fit noise in the data, and quantifying uncertainties in the solution is challenging. In principle, Bayesian FWI calculates a posterior probability distribution function (pdf), which describes all possible model solutions and their probabilities. However, characterising the posterior pdf by sampling alone is often intractably expensive due to the high dimensionality of FWI problems and the computational expense of their forward functions. Alternatively, variational inference solves Bayesian FWI problems efficiently by minimising the difference between a predefined (variational) family of distributions and the true posterior distribution, requiring optimisation rather than random sampling. We propose a new variational methodology called physically structured variational inference (PSVI), in which a physics-based structure is imposed on the variational family. In a simple example motivated by prior information from past FWI solutions, we include parameter correlations between pairs of spatial locations within a dominant wavelength of each other, and set other correlations to zero. This makes the method far more efficient in terms of both memory requirements and computational cost. We demonstrate the proposed method with a 2D acoustic FWI scenario, and compare the results with those obtained using three other variational methods. This verifies that the method can produce accurate statistical information of the posterior distribution with significantly improved efficiency.

How to cite: Zhao, X. and Curtis, A.: Physically Structured Variational Inference for Bayesian Full Waveform Inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8215, https://doi.org/10.5194/egusphere-egu24-8215, 2024.

EGU24-13715 | ECS | Posters on site | ITS1.8/TS9.1

Accelerating Geoscience Research: An Advanced Platform for Efficient Multimodal Data Integration from Geoscience Literature 

Zhixin Guo, Jianping Zhou, Guanjie Zheng, Xinbing Wang, and Chenghu Zhou

In the era of big data science, geoscience has experienced a significant paradigm shift, moving towards a data-driven approach to scientific discovery. This shift, however, presents a considerable challenge due to the plethora of geoscience data scattered across various sources. These challenges encompass data collection and collation and the intricate database construction process. Addressing this issue, we introduce a comprehensive, publicly accessible platform designed to facilitate extracting multimodal data from geoscience literature, encompassing text, visual, and tabular formats. Furthermore, our platform streamlines the search for targeted data and enables effective knowledge fusion. A distinctive feature of it is its capability to enhance the generalizability of Deep-Time Digital Earth data processing. It achieves this by customizing standardized target data and keyword mapping vocabularies for each specific domain. This innovative approach successfully overcomes the constraints typically imposed by a need for domain-specific knowledge in data processing. The platform has been effectively applied in processing diverse data sets, including mountain disaster data, global orogenic belt isotope data, and environmental pollutant data. This has facilitated substantial academic research, evidenced by developing knowledge graphs based on mountain disaster data, establishing a global Sm-Nd isotope database, and meticulous detection and analysis of environmental pollutants. The utility of our platform is further enhanced by its sophisticated network of models, which offer a cohesive multimodal understanding of text, images, and tabular data. This functionality empowers researchers to curate and regularly update their databases meticulously with enhanced efficiency. To demonstrate the platform's practical application, we highlight a case study involving compiling Sm-Nd isotope data to create a specialized database and subsequent geographic analysis. The compilation process in this scenario is comprehensive, encompassing tasks such as PDF pre-processing, recognition of target elements, human-in-the-loop annotation, and integrating multimodal knowledge. The results obtained consistently mirror patterns found in manually compiled data, thereby reinforcing the reliability and accuracy of our automated data processing tool. As a core component of the Deep-Time Digital Earth (DDE) program, our platform has significantly contributed to the field, supporting forty geoscience research teams in their endeavors and processing over 40,000 documents. This accomplishment underscores the platform's capacity for handling large-scale data and its pivotal role in advancing geoscience research in the age of big data.

How to cite: Guo, Z., Zhou, J., Zheng, G., Wang, X., and Zhou, C.: Accelerating Geoscience Research: An Advanced Platform for Efficient Multimodal Data Integration from Geoscience Literature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13715, https://doi.org/10.5194/egusphere-egu24-13715, 2024.

EGU24-13884 | ECS | Posters virtual | ITS1.8/TS9.1

Bayesian network based evaluation and comparison of the urban flood risk factors for the 2016 flood and a 100-year return period flood event in Baton Rouge, Louisiana  

Fuad Hasan, Sabarethinam Kameshwar, Rubayet Bin Mostafiz, and Carol Friedland

The study focuses on evaluating and comparing different flood risk factors that correlate with each other and affect the probability of flooding. Previous research is limited to identifying these factors’ influence on specific flood events. In contrast, buildings are constructed based on design flood maps, such as the 100/500-year return period flood map in the United States. Therefore, it is important to compare risk factors obtained from historical events and flood maps to identify any missing flood risk factors. To this end, a study was conducted to determine the difference between the probability of flooding and associated factors from a historic 2016 flood event in Baton Rouge, Louisiana, with the 100-year return period Federal Emergency Management Agency (FEMA)  flood map using a Bayesian network. The Bayesian network approach was used for this study due to its transparent forward and backward inference capabilities. The potential flood risk factors (population, household income, land cover, race, rainfall, river, and road proximity, and topography) were identified and corresponding data was preprocessed in ArcGIS to convert them as raster files of the same extent, and coordinate system. The factors were also classified based on different approaches (i.e., equalization, percentile, k-means clustering, etc.) to identify the most suitable classification method. A likelihood maximization-based parameter learning approach was used to obtain the conditional probability tables in the Bayesian network. This approach was used to develop separate Bayesian networks for the 2016 flood and the 100-year flood map. After setting up the Bayesian networks, sensitivity analysis, influential strength, and correlation matrix were generated, which were used to identify the most important flood risk factors. E.g., it was observed that land cover,topography, and river proximity are highly influential to the probability of flooding.

How to cite: Hasan, F., Kameshwar, S., Mostafiz, R. B., and Friedland, C.: Bayesian network based evaluation and comparison of the urban flood risk factors for the 2016 flood and a 100-year return period flood event in Baton Rouge, Louisiana , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13884, https://doi.org/10.5194/egusphere-egu24-13884, 2024.

EGU24-14483 | Posters on site | ITS1.8/TS9.1

CoFI - Linking geoscience inference problems with tools for their solution 

Jiawen He, Juerg Hauser, Malcolm Sambridge, Fabrizio Magrini, Andrew Valentine, and Augustin Marignier

Inference problems within the geosciences vary significantly in size and scope, ranging from the detection of data trends through simple linear regressions, to the construction of complex 3D models representing the Earth’s interior structure. Successfully solving an inverse problem typically requires combining various types of data sets, each associated with its own forward solver. In the absence of established software, many researchers and practitioners resort to developing bespoke inversion and parameter estimation algorithms tailored to their specific needs. However, this practice does not promote reproducibility and necessitates a substantial amount of work that is frequently beyond the primary objectives of the research.

Our aim with CoFI (pronounced: coffee), the Common Framework for Inference, is to capture inherent commonalities present in all types of inverse problems, independent of the specific methods employed to solve them. CoFI is an open-source Python package that provides a link to reliable and sophisticated third-party packages, such as SciPy and PyTorch, to tackle inverse problems of a broad range. The modular and object-oriented design of CoFI, supplemented by our comprehensive suite of tutorials and practical examples, ensures its accessibility to users of all skill levels, from experts to novices. This not only has the potential to streamline research but also to support education and STEM training.

This poster presentation aims to give an overview of CoFI’s main features and usage through practical examples. Moreover, we hope to foster collaboration and invite contributions on inference algorithms and domain-relevant examples.

How to cite: He, J., Hauser, J., Sambridge, M., Magrini, F., Valentine, A., and Marignier, A.: CoFI - Linking geoscience inference problems with tools for their solution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14483, https://doi.org/10.5194/egusphere-egu24-14483, 2024.

EGU24-14517 | Orals | ITS1.8/TS9.1

Multiproxy investigation of secular changes in tectonic regimes and crustal recycling in Earth history 

N. Ryan McKenzie, Hangyu Liu, Cody Colleps, and Adam Nordsvan

Tectonic processes influence numerous biogeochemical cycles. Accordingly, the evolution of the continental curst and changes in tectonic styles are inherently linked with secular chages in Earth’s surface environment. Here we present multiproxy mineralogical and geochronologic data to evaluate compositional changes in the upper crust along with variations in tectonic regimes and crustal recycling.  Our data indicate transitions from dominantly mafic to volumetrically extensive felsic upper crust occurred from the Archean into the Paleoproterozoic, which corresponds with evidence for enhanced crustal reworking. That later Paleoproterozoic through the Mesoproterozoic is characterized by a general reduction in crustal recycling and assimilatory tectonics with relatively limited active crustal thickening. Finally, the Neoproterozoic–Phanerozoic represents an interval with of increased juvenile magmatism and extensional tectonics, corresponding with deep and steep subduction and slab-rollback. This leads to enhanced island arc and back-arc basin formation, and subsequent arc collision.  These major shifts in composition and tectonic regimes that broadly bookended the Proterozoic have profound effects on numerous biogeochemical cycles particularly carbon, oxygen, and phosphorous cycles, and are thus likely linked to changes in the oxidative state and climate of Earth’s surface system observed during these times.

How to cite: McKenzie, N. R., Liu, H., Colleps, C., and Nordsvan, A.: Multiproxy investigation of secular changes in tectonic regimes and crustal recycling in Earth history, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14517, https://doi.org/10.5194/egusphere-egu24-14517, 2024.

EGU24-15087 | ECS | Orals | ITS1.8/TS9.1

A web-based and data-driven approach to paleogeographic reconstructions 

Jovid Aminov, Guillaume Dupont-Nivet, Nozigul Tirandozova, Fernando Poblete, Ibragim Rakhimjanov, Loiq Amonbekov, and Ruslan Rikamov

Paleogeographic maps illustrate the distribution of land and sea, as well as the topography of the Earth’s surface during different geological periods based on the compilation of a wide range of geological and geophysical datasets. These maps provide boundary conditions for various models of the Earth’s systems, including climate, mantle convection, and land surface evolution. A number of software programs and computer algorithms have been developed in the past three decades to reconstruct either the past positions of continents and oceans or their elevation and depth. We recently developed the open-source and user friendly "Terra Antiqua", allowing users to create digital paleogeographic maps in a Geographic Information System (GIS) environment (QGIS), using various tools that are easy to operate in combination with Gplates, a widely used software for plate tectonic reconstructions. The next step is to develop a comprehensive and integrated solution easily accessible on the web that can automate most of the steps involved in reconstructing past plate configurations and topography. We present here a web application ("Terra Antiqua online") that we are developing for the creation of digital paleogeographic maps. The web application has two parts: (1) The front-end uses CesiumJS, an open-source JavaScript library for making 3D globes and maps, to visualize the databases and let the users interact with it.  (2) The back-end uses Python algorithms and libraries such as GDAL and pyGPlates to process the data and perform tectonic and hypsometric reconstructions.  Terra Antiqua online uses pyGplates API to access existing tectonic models and apply them to rotate plate positions and datasets to their past position. New developments are allowing it to estimate the elevation, depth and distribution of the land and sea by automatically processing various geological proxy data (e.g. paleofacies maps, paleo-elevation proxies, fossils databases etc…) according to physically based algorithms. The project further aims to incorporate web-based landscape modeling tools and develop a community around a geological database and paleogeographic reconstruction methods and standards.

How to cite: Aminov, J., Dupont-Nivet, G., Tirandozova, N., Poblete, F., Rakhimjanov, I., Amonbekov, L., and Rikamov, R.: A web-based and data-driven approach to paleogeographic reconstructions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15087, https://doi.org/10.5194/egusphere-egu24-15087, 2024.

EGU24-15385 | ECS | Orals | ITS1.8/TS9.1

Probabilistic Approach toward Seismic Exploration with Autonomous Robotic Swarms 

Kai Nierula, Dmitriy Shutin, Ban-Sok Shin, Heiner Igel, Sabrina Keil, Felix Bernauer, Philipp Reiss, Rok Sesko, and Fabian Lindner

This research introduces a novel approach to seismic exploration on the Moon and Mars, employing autonomous robotic swarms equipped with seismic sensing and processing hardware. By relying on probabilistic inference methods, we aim to survey large surface areas to both autonomously identify and map subsurface features such as lava tubes and ice deposits. These are crucial for future human habitats and potential in-situ resource utilization.

This endeavor presents unique challenges due to the communication limitations and uncertainties inherent in remote, autonomous operations. To address these challenges, we adopt a distributed approach with robotic swarms, where each rover processes seismic data and shares the results with other rovers in its vicinity, contending with imperfect communication links. Thus, the swarm is used as a distributed computing network. The decisions made within the network are based on probabilistic modeling of the underlying seismic inference problem. A key innovation in this respect is the use of factor graphs to integrate uncertainties and manage inter-rover communications. This framework enables each rover to generate a localized subsurface map and autonomously decide on strategic changes in the seismic network topology, either exploring new areas or repositioning to enhance measurement accuracy of targeted underground regions.

The vision is to implement this approach on a distributed factor graph, allowing for a coordinated, probabilistic analysis of seismic data across the swarm. This strategy represents a significant departure from traditional static seismic sensor arrays, offering a dynamic and adaptable solution for planetary exploration. The first step towards realizing this vision involves implementing a Kalman filter for the one-dimensional linear heterogeneous wave equation. This has been achieved by reformulating finite difference schemes for wave propagation simulation into a state-space description. The resulting linear continuous n-th order system can be explicitly solved and rewritten into a discrete state space model that can be used in the standard Kalman filter recursion. However, the standard Kalman filter is limited due to its assumption that both model and process noise are Gaussian. With factor graphs, this limitation can be overcome, enabling a more robust and versatile analysis. Several simulation results will be shown to demonstrate the performance of these approaches.

We intend to extend the approach to higher-dimensional problems, implementing distributed versions of the Kalman filter and factor graph with simulated, non-perfect communication links. Eventually, the seismic inverse problems will be solved in these frameworks. Successfully achieving these objectives could greatly enhance our capabilities in extraterrestrial exploration, paving the way for more informed and efficient future space missions.

How to cite: Nierula, K., Shutin, D., Shin, B.-S., Igel, H., Keil, S., Bernauer, F., Reiss, P., Sesko, R., and Lindner, F.: Probabilistic Approach toward Seismic Exploration with Autonomous Robotic Swarms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15385, https://doi.org/10.5194/egusphere-egu24-15385, 2024.

EGU24-15712 | ECS | Orals | ITS1.8/TS9.1

GeoBUS - A Probabilistic Workflow Combining ERT Inverse Modeling and Implicit Geological Modeling  

Christin Bobe, Jan von Harten, Nils Chudalla, and Florian Wellmann

The interface between different rock units is usually described as a sharp boundary in geological models. Such geological interfaces are often a main target of geological as well as geophysical investigations. In the inverse images derived from electrical resistivity tomography (ERT), geological interfaces are typically represented by a continuous, smooth change in the electrical resistivity. This smoothing of interfaces is often unwanted since it deviates significantly from typical geological features where the exact location of the interface can be precisely determined.

The proposed GeoBUS workflow (Geological modeling by Bayesian Updating of Scalar fields) aims to generate probabilistic geological models which include the information from probabilistic ERT inversion results using Bayesian updates. The GeoBUS workflow consists of three main steps. The method Kalman ensemble generator (KEG), a numerical implementation for computing Bayesian updates, plays an important role in this workflow.

In the first step of the GeoBUS workflow, the KEG is used for inversion of ERT data. The KEG generates probabilistic, yet smooth images of the subsurface in terms of electrical resistivity.

In the second step of the GeoBUS workflow, we perform implicit geological modeling of the subsurface creating an ensemble of scalar fields. For the geological modeling, we use point information, i.e. the location and orientation of present geological units, along with the uncertainty associated to both location and orientation. The resulting ensemble consists of scalar fields that are defined everywhere in space and build the basis of the geological model. Drawing contours into each scalar field for the scalar field values for which geological interfaces are confirmed, we create an ensemble of geological models.

For the third and final step of the GeoBUS workflow, we adopt the subsurface discretization used for the ERT inverse modeling and use the ensemble of geological models from step two to assign a probabilistic scalar field value to each cell of the discretized subsurface. This discrete version of the scalar field is used as the prior for a second KEG application. Based on literature values, we assign a probability density function for electrical resistivity values to each geological unit of the geological model to formulate a corresponding likelihood. Using the KEG, we derive a Bayesian update of the discretized scalar field combining the petrophysical likelihood and the information from the ERT inversion. This results in a posterior scalar field which again can be used to generate an ensemble of geological models that now includes the information from the geophysical measurements.

We demonstrate this novel workflow for simple and synthetic two-dimensional subsurface models, generating both synthetic geological and geophysical data. This way we aim to (1) create simple benchmark examples, and (2) give a first evaluation of the performance of the GeoBUS workflow. 

How to cite: Bobe, C., von Harten, J., Chudalla, N., and Wellmann, F.: GeoBUS - A Probabilistic Workflow Combining ERT Inverse Modeling and Implicit Geological Modeling , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15712, https://doi.org/10.5194/egusphere-egu24-15712, 2024.

EGU24-16036 | Orals | ITS1.8/TS9.1

An Independent State sampler for Trans-dimensional Bayesian Inference 

Malcolm Sambridge, Andrew Valentine, and Juerg Hauser

Over the past twenty years, Trans-dimensional Bayesian Inference has become a popular approach for Bayesian sampling. It has been applied widely in the geosciences when the best class of model representation, e.g. of the subsurface, is not obvious in advance, or the number of free variables undecided. Making arbitrary choices in these areas may result in sub-optimal inferences from data. In trans-D, one typically defines a finite number of model states, with differing numbers of unknowns, over which Bayesian Inference is to be performed using the data.

A key attraction of Trans-D Bayesian Inference is that it is designed to let the data decide which state, as well as which configurations of parameters within each state, are preferred by the data, in a probabilistic manner. Trans-D algorithms may hence be viewed as a combination of fixed dimensional within-state sampling and simultaneous between-state sampling where Markov chains visit each state in proportion to their support from the data.

In theory, each state may be completely independent, involving different classes of model parameterization, with different numbers of unknowns, data noise levels, and even different assumptions about the data-model relationship. Practical considerations, such as convergence of the finite length Markov chains between states, usually mean that each state must be closely related to each other, e.g. differing by a single layer in a 1-D seismic Earth model. In addition, since the form of the necessary Metropolis-Hastings balance condition depends on the mathematical relationship between the unknowns in each state, then implementations are often bespoke to each class of model parameterization and data type. To our knowledge there exists no automatic trans-D sampler where one can define arbitrary independent states, together with a prior and Likelihood, and simply pass to a generalised sampling algorithm, as is common with many fixed dimensional MCMC algorithms and software packages. 

A second limitation in trans-D sampling is that since implementations are bespoke within a class of model parameterizations, within-state sampling is typically performed with simplistic and often dated algorithms, e.g. Metropolis-Hastings or Gibbs samplers, thereby limiting convergence rates. Over the past 30 years fixed dimensional sampling has advanced considerably with numerous efficient algorithms available and many conveniently translated into user friendly software packages, almost all of which have not been used within a trans-D framework due to a lack of a way to conveniently deploy them in a trans-D setting.

In this presentation we will address all of these issues by describing the theory under-pinning an ‘Independent State’ (IS) Trans-D sampler, together with some illustrative examples. In this algorithm class, sampling may be performed across states that are completely independent, containing arbitrary numbers of unknowns and parameter classes. In addition, the IS-sampler can conveniently take advantage of any fixed dimensional sampler without the need to derive and re-code bespoke Markov chain balance conditions, or specify mechanisms for transitions between model parameters within different states. In this sense it represents a general purpose automatic trans-D sampler.

How to cite: Sambridge, M., Valentine, A., and Hauser, J.: An Independent State sampler for Trans-dimensional Bayesian Inference, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16036, https://doi.org/10.5194/egusphere-egu24-16036, 2024.

EGU24-16101 | Posters virtual | ITS1.8/TS9.1

Utilizing Large Language Models for Geoscience Literature Information Extraction 

Peng Yu, Cheng Deng, Huawei Ji, and Ying Wen
Extracting information from unstructured and semi-structured geoscience literature is a crucial step in conducting geological research. The traditional machine learning extraction paradigm requires a substantial amount of high-quality manually annotated data for model training, which is time-consuming, labor-intensive, and not easily transferable to new fields. Recently, large language models (LLMs) (e.g., ChatGPT, GPT-4, and LLaMA), have shown great performance in various natural language processing (NLP) tasks, such as question answering, machine translation, and text generation. A substantial body of work has demonstrated that LLMs possess strong in-context learning (ICL) and even zero-shot learning capabilities to solve downstream tasks without specifically designed supervised fine-tuning.
In this paper, we propose utilizing LLMs for geoscience literature information extraction. Specifically, we design a hierarchical PDF parsing pipeline and an automated knowledge extraction process, which can significantly reduce the need for manual data annotation, assisting geoscientists in literature data mining. For the hierarchical PDF parsing pipeline, firstly, a document layout detection model fine-tuned on geoscience literature is employed for layout detection, obtaining layout detection information for the document. Secondly, based on the document layout information, an optical character content parsing model is used for content parsing, obtaining the text structure and plain text corresponding to the content. Finally, the text structure and plain text are combined and reconstructed to ultimately obtain the parsed structured data. For the automated knowledge extraction process, firstly, the parsed long text is segmented into paragraphs to adapt to the input length limit of LLMs. Subsequently, a few-shot prompting method is employed for structured knowledge extraction, encompassing two tasks: attribute value extraction and triplet extraction. In attribute value extraction, prompts are generated automatically by the LLMs based on the subdomain and attribute names, facilitating the location and extraction of values related to subdomain attribute names in the text. For triplet extraction, the LLMs employ a procedural approach to entity extraction, entity type extraction, and relation extraction, following the knowledge graph structure pattern. Finally, the extracted structured knowledge is stored in the form of knowledge graphs, facilitating further analysis and integration of various types of knowledge from the literature.
Our proposed approach turns out to be simple, flexible, and highly effective in geoscience literature information extraction. Demonstrations of information extraction in subdomains such as radiolarian fossils and fluvial facies have yielded satisfactory results. The extraction efficiency has significantly improved, and feedback from domain experts indicates a relatively high level of accuracy in the extraction process. The extracted results can be used to construct a foundational knowledge graph for geoscience literature, supporting the comprehensive construction and efficient application of a geoscience knowledge graph.

How to cite: Yu, P., Deng, C., Ji, H., and Wen, Y.: Utilizing Large Language Models for Geoscience Literature Information Extraction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16101, https://doi.org/10.5194/egusphere-egu24-16101, 2024.

EGU24-16434 | ECS | Posters on site | ITS1.8/TS9.1

Probabilistic inversion of geoelectric and induced polarization measurements on reduced model spaces using Hamiltonian Monte Carlo 

Joost Hase, Florian M. Wagner, Maximilian Weigand, and Andreas Kemna

The probabilistic formulation of geoelectric and induced polarization inverse problems using Bayes’ theorem inherently accounts for data errors and uncertainties in the prior assumptions, both of which are propagated naturally into the solution. Due to the non-linearity of the physics underlying the geoelectric forward calculation, the inverse problem must be solved numerically. Markov chain Monte Carlo (MCMC) methods provide the capability to create a sample of the corresponding posterior distribution, based on which statistical estimators of interest can be approximated. In a typical geoelectric imaging application, the subsurface is discretized as a 2-D mesh with the model parameters representing the averaged values of the imaged electrical conductivity within the individual cells. The resulting model space is often of high dimensionality and usually insufficiently resolved by the measurements, posing a challenge to the efficient application of MCMC methods. In our work, we use the Hamiltonian Monte Carlo (HMC) method to sample from the posterior distribution and operate on a reduced model space to enhance the efficiency of the inversion. The basis of the reduced model space is constructed via a principal component analysis of the model prior term. We consider different resolution measures to ensure that the information lost by operating in the reduced model space is negligible. In addition to the inversion of electrical resistivity tomography measurements in real variables, we also demonstrate the model space reduction and subsequent application of HMC for the solution of the complex resistivity tomography inverse problem in complex variables, imaging the distribution of the complex electrical conductivity in the subsurface. This study contributes to the needed increase of uncertainty quantification in the inversion of geoelectric and induced polarization measurements, aiming to provide a reliable basis for the processing and interpretation of geophysical imaging results.

How to cite: Hase, J., Wagner, F. M., Weigand, M., and Kemna, A.: Probabilistic inversion of geoelectric and induced polarization measurements on reduced model spaces using Hamiltonian Monte Carlo, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16434, https://doi.org/10.5194/egusphere-egu24-16434, 2024.

EGU24-17157 | ECS | Orals | ITS1.8/TS9.1

Impact modeling with Bayesian inference for crop yield assessment and prediction 

Odysseas Vlachopoulos, Niklas Luther, Andrej Ceglar, Andrea Toreti, and Elena Xoplaki

It is common knowledge that climate variability and change have a profound impact on crop production. From the principle that “it is green and it grows” to the assessment of the actual impacts of major weather drivers and their extremes on crop growth through the adoption of agro-management strategies informed by tailored and effective climate services, there is a well documented scientific and operational gap. This work focuses on the development, implementation and testing of an AI-based methodology that aims to reproduce a crop growth model informing on grain maize yield in the European domain. A surrogate AI model based on Bayesian deep learning and inference is compared for its efficiency against the process-based deterministic ECroPS model developed by the Joint Research Centre of the European Commission. The rationale behind this effort is that such mechanistic crop models rely on multiple input meteorological variables and are relatively costly in terms of computing resources and time, crucial aspects for a scalable and widely adopted solution. Such approaches make it possible to run very large ensembles of simulations based, for instance, on ensembles of climate predictions and projections and/or a perturbed parametrization (e.g. on the atmospheric CO2 concentration effects). Our surrogate crop model relies on three weather input variables: daily minimum and maximum temperatures and daily precipitation, where the training was performed with the ECMWF-ERA5 reanalysis. 

How to cite: Vlachopoulos, O., Luther, N., Ceglar, A., Toreti, A., and Xoplaki, E.: Impact modeling with Bayesian inference for crop yield assessment and prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17157, https://doi.org/10.5194/egusphere-egu24-17157, 2024.

EGU24-17939 | ECS | Posters on site | ITS1.8/TS9.1

Bayesian optimal experimental design for fracture imaging 

Zhi Yuan, Chen Gu, Yichen Zhong, Peng Wu, Zhuoyu Chen, and Borui Kang

Fracture imaging is a pivotal technique in a variety of fields including Carbon Capture, Utilization, and Storage (CCUS), geothermal exploration, and wasterwater disposal, essential for the success of the field operation and seismic hazard mitigation. However, accurate fracture imaging is challenging due to accurate fracture imaging is challenging due to the complex nature of subsurface geology, the presence of multiple overlapping signals, and the variability of fracture sizes and orientations. Additionally, limitations in the resolution of current imaging technologies and the need for high-quality data acquisition further complicate the process.

To address these challenges, we have conducted fracture imaging experiments utilizing acoustic sensors in laboratory-scale specimens with varied fracture geometries.A dynamic acquisition system involving robotic arms have been developed, enabling the flexible positioning of sensors on any part of the specimen's surface.This not only significantly reduces the time and resources required for experiments but also increases the adaptability of the process to different surface topography of specimens and fracture geometries.

In addition, we employ Bayesian optimization algorithms to enhance the efficiency of sensor placement in laboratory-scale specimens, aiming to achieve precise fracture imaging with the least number of measurements necessary. This algorithmic approach optimizes the data collection process, ensuring that we gather the most relevant and accurate information with minimal intrusion. The collected data is then rigorously compared and calibrated against findings from numerical simulations, which helps in refining the algorithm for broader applications.

How to cite: Yuan, Z., Gu, C., Zhong, Y., Wu, P., Chen, Z., and Kang, B.: Bayesian optimal experimental design for fracture imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17939, https://doi.org/10.5194/egusphere-egu24-17939, 2024.

EGU24-18486 | ECS | Orals | ITS1.8/TS9.1 | Highlight

Towards a community platform for paleoclimate data and temperature gradients over the last 540 million years  

Sebastian Steinig, Helen Johnson, Stuart Robinson, Paul J. Valdes, and Daniel J. Lunt

Earth’s climate shows a remarkable variability on geological timescales, ranging from widespread glaciation to ice-free greenhouse conditions over the course of the Phanerozoic, i.e. the last 540 million years. Earth system modelling allows us to better understand and constrain the drivers of these changes and provides valuable reference data for other paleoclimate disciplines (e.g., chemistry, geology, hydrology). However, the sheer volume and complexity of these datasets often prevents direct access and use by non-modellers, limiting their benefits for large parts of our community.

We present the online platform “climatearchive.org” to break down these barriers and provide intuitive access to paleoclimate data for everyone. More than 100 global coupled climate model simulations covering the entire Phanerozoic at the stage level build the backbone of the web application. Key climate variables (e.g. temperature, precipitation, vegetation and circulation) are displayed on a virtual globe in an intuitive three-dimensional environment and on a continuous time axis throughout the Phanerozoic. The software runs in any web browser — including smartphones — and promotes visual data exploration, streamlines model-data comparisons, and supports public outreach efforts. We discuss the current proof of concept and outline the future integration of new sources of model and geochemical proxy data to streamline and advance interdisciplinary paleoclimate research.

We also present ongoing efforts for an integrated model-data synthesis to quantify changes in meridional and zonal temperature gradients throughout the Phanerozoic and to address the relative roles of individual forcings (greenhouse gases, solar, geography). While substantial effort has been made to quantify the evolution of global mean temperatures over the last 540 million years, changes in the large-scale temperature gradients and their causes are comparably less constrained. As a fundamental property of the climate system, changes in the spatial patterns of surface temperature play a critical role in controlling large-scale atmospheric and ocean circulation and influence hydrological, ecological, and land surface processes. The resulting best estimate product of meridional and zonal temperature gradients over the last 540 million years will represent a step change in our understanding of the drivers and consequences of past temperature gradient changes and will provide the community with a valuable resource for future climatological, geological, and ecological research.

How to cite: Steinig, S., Johnson, H., Robinson, S., Valdes, P. J., and Lunt, D. J.: Towards a community platform for paleoclimate data and temperature gradients over the last 540 million years , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18486, https://doi.org/10.5194/egusphere-egu24-18486, 2024.

EGU24-19320 | Posters on site | ITS1.8/TS9.1

Paleogeographic evolution of Asia in the Cenozoic reconstructed with the Terra Antiqua software 

Guillaume Dupont-Nivet, Jovid Aminov, Fernando Poblete, Diego Ruiz, and Haipeng Li

The ability to reconstruct the geologic evolution of the Earth as a system including the geosphere, atmosphere and biosphere interactions, is essential to understand the fate of our environment in the context of the Climate, Life and Energy crises of the new Anthropocene era. Scientists of tomorrow working on environmental changes require ever more detailed databases and maps to access and correlate the overwhelming mass of information stemming from the ongoing surge of environmental data and models. Earth System reconstructions are fundamental assets to assess potential sources and locations of key geo-resources that are now vital for the energy transition (e.g. raw materials, rare earth elements, subsurface storage, geothermal sites). Earth System reconstructions are also the best means to communicate past and future Life and Environmental evolutions, while providing consciousness of our role and situation in the immensity of Time and Nature. They convey these essential lessons in a didactic fashion for teachers and students, museums, or for governments and NGOs to make decisions and promote public awareness. Although Earth System reconstructions have long been recognized as essential, they have yet to deliver their full breakthrough potential combining various booming disciplines. As part of a large project over Asia, we review here the case of the intensely studied, yet still extremely controversial India-Asia collision with major implications on regional environmental, depositional and global climate transitions. Ongoing debates argue for radically different end-member models of the collision timing and its configuration, and of associated topographic growth in the collision zone. We present here new Asian paleogeographic reconstructions at 50 and 30 Ma that complement an existing set at 60, 40 and 20 Ma with updates. These integrate various end-members models of the India-Asia collision and associated topographic patterns and land-sea masks with implications on the locus, source and generation of resources. Results are provided online (https://map.paleoenvironment.eu/) in various model-relevant formats with associated database and discussion forums to comment an contribute to the amelioration of these maps and databases. We also present the latest developments of the user-friendly and open-source Terra Antiqua Q-GIS plugin (https://paleoenvironment.eu/terra-antiqua/) that has been used and specifically developed with new tools including data-driven and web-based applications

How to cite: Dupont-Nivet, G., Aminov, J., Poblete, F., Ruiz, D., and Li, H.: Paleogeographic evolution of Asia in the Cenozoic reconstructed with the Terra Antiqua software, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19320, https://doi.org/10.5194/egusphere-egu24-19320, 2024.

Geological models can be constructed with a variety of mathematical methods. Generally, we can describe the modeling process in a formal way as a functional relationship between input parameters (geological observations, orientations, interpolation parameters) and an output in space (lithology, stratigraphy, rock property, etc.). However, in order to obtain a suitable implementation in geophysical inverse frameworks, we have to consider specific requirements. In recent years, a substantial amount of work focused on low-dimensional parameterizations and efficient automation of geological modeling methods, as well as their combination with suitable geophysical forward simulations. In this contribution, we focus on differential geomodelling approaches, which allow for an integration of geological modeling methods into gradient-based inverse approaches.

In this work, we emphasize differential geomodelling approaches. These approaches seamlessly integrate geological modeling methods into gradient-based inverse approaches. To achieve this integration, we actively employ modern machine learning frameworks, specifically TensorFlow and PyTorch. We then incorporate these geometric geological modeling methods into a Stein Variational Gradient Descent (SVGD) algorithm. SVGD is adept at addressing the challenges of multimodality in probabilistic inversion. Moreover, we demonstrate the implementation of these methods in a Hamiltonian Monte Carlo approach.

Our results are promising, showing that treating geological modeling as a differentiable approach unlocks new possibilities. This method facilitates novel applications in the integration of geological modeling with geophysical inversion, paving the way for advanced research in this field.

How to cite: Wellmann, F., de la Varga, M., and Liang, Z.: Differentiable Geomodeling: towards a tighter implementation of structural geological models into geophysical inverse frameworks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20508, https://doi.org/10.5194/egusphere-egu24-20508, 2024.

EGU24-21753 | ECS | Orals | ITS1.8/TS9.1

Basin evolution and Paleo reconstruction of the Mesoproterozoic South Nicholson Region, NE Australia 

Harikrishnan Nalinakumar and Stuart Raymond Clark

This study explores the geological complexity of the South Nicholson Region, an area spanning the Northern Territory and Queensland in Australia, from the newly drilled NDI Carrara 1 well, thus exposing the burial history of the Carrara sub-basin. Formed before the formation of the Nuna supercontinent, this region is positioned near resource-abundant basins and boasts a complex geological history. It has undergone significant tectonic shifts, orogenic activities, and the development of sedimentary basins over 1.6 billion of years while the world was developing as we see it in present. Despite its potential for mineral and petroleum resources, the South Nicholson Region was previously under-explored, lacking in-depth seismic, well, and geophysical data. Recently acquired data from the region includes five seismic lines and a new well, offering invaluable insights into the region's subsurface geology, including the identification of a new sub-basin, the Carrara Sub-basin. Characterised by a gravity low on its southeast side, the Carrara Sub-basin encompasses thick sequences of Proterozoic rocks from the Northern Lawn Hill Platform, Mount Isa Province and McArthur Basin. The primary objective of this study is to examine the burial history, tectonic subsidence and paleo-reconstruction of the South Nicholson region.

Our results indicate that the South Nicholson Region has undergone multiple cycles of sedimentation, tectonic uplift and erosion. Between ~1640 Ma and 1580 Ma, the region experienced increasing deposition rates. The presence of an unconformity obscures the sedimentation and tectonic history from 1600 to 500 Ma. However, by 500 Ma, significant subsidence had occurred, indicating that subsidence was the predominant geological force during this period. After this interval, an uplift event is evident, exhuming the layers until 400 Ma. From 400 Ma until today, little to no subsidence has been briefly interrupted by minor uplift events. Our calculated tectonic subsidence curve closely aligns with the regional deposition patterns, highlighting the intricate relationship between sediment deposition and tectonic activities, thereby providing valuable insights into the interplay between sedimentary and tectonic processes in the region.

How to cite: Nalinakumar, H. and Clark, S. R.: Basin evolution and Paleo reconstruction of the Mesoproterozoic South Nicholson Region, NE Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21753, https://doi.org/10.5194/egusphere-egu24-21753, 2024.

CC BY 4.0