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Presentation type:
GD – Geodynamics

EGU24-5404 | ECS | Orals | MAL19-GD | GD Division Outstanding Early Career Scientist Award

Geodynamic controls on sediment-hosted lead-zinc deposits in continental rifts 

Anne C. Glerum, Sascha Brune, Joseph M. Magnall, Philipp Weis, and Sarah A. Gleeson

The growing global demand for metal resources requires new high-grade ore deposit discoveries. Known large sediment-hosted clastic-dominated base metal deposits predominantly occur in failed continental rifts and the passive margins of successful rifts. Understanding the large-scale geodynamic controls on rift-related mineralizing processes occurring on much smaller spatial and temporal scales can thus help identify new areas for exploration.

We numerically model 2D rift systems from inception to break-up with the geodynamic code ASPECT (Kronbichler et al., 2012; Heister et al., 2017) coupled to the landscape evolution model FastScape (Braun and Willett, 2013; Neuharth et al., 2022). With ~300-m resolution simulations, we investigate how rift type and the efficiency of sedimentary processes affect the formation of potential metal source and host rock domains, identified by their lithology and temperature. We subsequently analyse the optimal alignment of these domains where metals are respectively leached and deposited  with faulting events providing potential fluid pathways between them (e.g., Rodríguez et al., 2021). For favourable co-occurrences of source, pathway and host, we identify the tectonic conditions that predict the largest clastic-dominated lead-zinc deposits.

We show that the largest potential for metal endowment is expected in narrow asymmetric rifts at a distance of several tens of kilometres to the shore (Glerum et al., 2023). Characterized by rift migration, these rifts generate a wide and a narrow conjugate margin. On the narrow margin, the long-lived border fault accommodates a thick submarine package of sediments, including deep permeable continental sediments and shallower layers of organic-rich sediments. Elevated temperatures from continued thinning could lead to fluids leaching metals from the permeable sediments. Both the border fault and later synthetic faults can provide fluid pathways from the source to the shallow host rock in potential short-lived mineralisation events. In wide rifts with rift migration, these favourable configurations occur less frequently and less potential source rock is produced, limiting potential metal endowment. In simulations of narrow symmetric rifts, the potential for ore formation is low. Based on these insights, exploration programs should prioritize identifying exhumed ancient narrow margins formed in asymmetric rift systems.

 

Braun and Willett 2013. Geomorphology 180–181. 10.1016/j.geomorph.2012.10.008.

Glerum et al. preprint. EGUsphere 1-40. 10.5194/egusphere-2023-2518.

Heister et al. 2017. Geophys. J. Int. 210 (2): 833–51. 10.1093/gji/ggx195.

Kronbichler et al. 2012. Geophys. J. Int. 191: 12–29. 10.1111/j.1365-246X.2012.05609.x.

Neuharth et al. 2022. Tectonics 41 (3): e2021TC007166. 10.1029/2021TC007166.

Rodríguez et al. 2021. Gcubed 22: 10.1029/2020GC009453.

How to cite: Glerum, A. C., Brune, S., Magnall, J. M., Weis, P., and Gleeson, S. A.: Geodynamic controls on sediment-hosted lead-zinc deposits in continental rifts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5404, https://doi.org/10.5194/egusphere-egu24-5404, 2024.

EGU24-8300 | Orals | MAL19-GD | Augustus Love Medal Lecture

New Frontiers in Geodynamics 

Taras Gerya

Geodynamics is an actively expanding young quantitative science, which defined its mission very generally as introducing of physical-mathematical methods into traditionally observations-focused Earth and planetary sciences in order to understand and quantify origin and evolution of Earth and other planets. As such, this young science is not limited by any specific object or subject and widens its scope through time. This is a very natural process (‘instinctive evolution’) since human scales of direct observation are extremely limited in both time and space and since rapid progress of quantitative physical-mathematical and computational methods offers every day new and exceptional possibilities to explore sophisticated physical-mathematical models for understanding intrinsically complex natural processes. As the result of this ‘instinctive evolution’, new frontiers in geodynamics are (and always were) defined by its expansion toward other fields. Initially, Geodynamics mainly expanded towards Structural Geology and Tectonics. Currently, new Geodynamics expansion tendencies are clearly visible toward: Seismology, Geomorphology, Geochemistry, Petrology, Climatology, Planetology/Astronomy and Biology/Astrobiology. In this lecture, I will give some recent examples of this impressive expansion and outline future expectations and challenges.

How to cite: Gerya, T.: New Frontiers in Geodynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8300, https://doi.org/10.5194/egusphere-egu24-8300, 2024.

GD1 – Mantle Dynamics and Plate Tectonics

EGU24-440 | ECS | Posters on site | GD1.1

Spatial and temporal variation in dynamic mantle support of the Antarctic plate: Implications for ice sheet evolution 

Aisling Dunn, Nicky White, Robert Larter, Megan Holdt, Simon Stephenson, and Chia-Yu Tien

Accurately constraining past and future ice sheet evolution requires a quantitative understanding of key boundary conditions in ice sheet models, including topography and heat flux. Both of these conditions are in part moderated by spatially and temporally variable mantle dynamics. This study exploits an interdisciplinary approach to probe the mantle beneath Antarctica to better understand sub-crustal processes. First, observed bathymetry and topography are corrected for isostatic effects to isolate the residual topographic signal, a proxy for dynamic mantle support. In this way, a comprehensive suite of oceanic residual depth (n = 1120) and continental residual elevation (n = 237) spot measurements are calculated. Secondly, basaltic rare earth element concentrations acquired from an augmented database of Neogene volcanic samples (n = 264) are inversely modelled to determine melt fraction as a function of depth. Thus, we constrain mantle potential temperature and depth to the top of the melting column (i.e. lithospheric thickness). Finally, results from these approaches are interpreted alongside other geological and geophysical data, including free air gravity anomalies and mantle tomographic models to understand present day mantle-lithosphere interactions. Sequence stratigraphic analysis along continental margins (e.g. offshore from Dronning Maud Land and the Wilkes and Aurora Subglacial Basins) is also used to constrain temporal changes in mantle-induced vertical plate motion. Robust observations in the oceanic realm evidence dynamic support beneath the central Scotia Sea, the Marie Byrd Seamounts, in the vicinity of the Astrid Ridge, and beneath the Emerald Fracture Zone. Residual topography measurements define the extent to which these dynamic swells continue onto the continent, with 1-2 km of mantle support throughout West Antarctica, the Transantarctic Mountains, and the Gamburtsev Subglacial Mountains. Collectively, these results highlight considerable spatial and temporal variation in dynamic mantle support throughout Antarctica, making it imperative to account for such mantle-lithosphere interactions when modelling the onset and evolution of glaciation.

How to cite: Dunn, A., White, N., Larter, R., Holdt, M., Stephenson, S., and Tien, C.-Y.: Spatial and temporal variation in dynamic mantle support of the Antarctic plate: Implications for ice sheet evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-440, https://doi.org/10.5194/egusphere-egu24-440, 2024.

EGU24-1686 | ECS | Posters on site | GD1.1

Detecting subduction-related metamorphic events during the early Brasiliano Orogeny in southern Borborema Province using detrital rutile  

Rodrigo I. Cerri, Fabricio A. Caxito, Christopher Spencer, George L. Luvizotto, George W.C. Junior, Nayara M. Santos, and Lucas V. Warren

The ubiquity of detrital zircon in clastic sediments and their typical high U and low common Pb contents, resulting in relatively high precision U-Pb age determination, made zircon one of the primary minerals for provenance studies. Yet, its high closure temperature (>900oC), limited growth of new zircon under upper amphibolite-eclogite facies, inherited bias towards zircon-rich sources (e.g., felsic plutonic rocks), and the refractory behavior in sedimentary deposits rarely representing first-cycle sedimentation, can hamper the ability to detect some key tectonomagmatic events. In this sense, other mineral assemblages, like detrital rutile, that is formed in medium- to high-grade metapelite and metabasite mainly during high-pressure and low-temperature subduction metamorphism, can be used to provide a more complete record of orogenesis with polyphase evolution. Herein, we present U-Pb detrital rutile ages from the Cambrian-Ordovician Tacaratu Formation (lowermost unit of the late Jurassic to Cretaceous Tucano-Jatobá Basin, that directly overlies the Borborema Province in its southern region) to track the complete polyphase evolution of southern Borborema Province in the northeastern Brazil. The geodynamic evolution of this structural province is still a matter of debate, with interpretations varying from reworking of Paleoproterozoic continental crust with sedimentation and metamorphism in intracontinental setting, to oceanic closure during a complete Wilson Cycle with or without terrane accretion. Considering the southern Borborema Province Sergipano Belt, subduction started ca. 740 Ma ending with collisional processes (ca. 590-570 Ma) associated with the closure of the Sergipano-Oubanguides oceanic basin. The Neoproterozoic Pernambuco-Alagoas Domain and Sergipano Belt, both formed due to the collision between São Francisco-Congo Craton and the Pernambuco-Alagoas superterrane, are the main source of detritus of the Tacaratu Formation. Coupled U-Pb detrital zircon and rutile analysis revealed that detrital zircon ages lags (i.e., are younger) detrital rutile ages by around 100 Ma. Detrital rutile and zircon present main young peaks at ca. 650 Ma and 545 Ma, respectively. Recently, Neoproterozoic arc-back-arc amphibolite (ca. 743 ± 3 Ma), a rare setting for the early phases of Brasiliano Orogeny, and Cordilleran-type medium- to high-K granites (ca. 645-610 Ma), were recognized in southern Borborema Province, in agreement with our detrital rutile U-Pb ages. Thus, our detrital rutile ages record earlier phases of Brasiliano Orogeny in the southern Borborema Province (subduction-related metamorphism; closure of Sergipano-Oubanguides ocean), since the Brasiliano Orogeny culminated in the collision of blocks that were followed by high-temperature metamorphism (hampering the formation of younger rutile?). Notwithstanding, detrital rutile ages interesting marks around late Tonian to Cryogenian subduction-related metamorphism, perhaps in a magma-poor orogenic phase.

How to cite: Cerri, R. I., Caxito, F. A., Spencer, C., Luvizotto, G. L., Junior, G. W. C., Santos, N. M., and Warren, L. V.: Detecting subduction-related metamorphic events during the early Brasiliano Orogeny in southern Borborema Province using detrital rutile , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1686, https://doi.org/10.5194/egusphere-egu24-1686, 2024.

EGU24-2023 | Orals | GD1.1 | Highlight

Morphology, structure and gravitational instability of the steep caldera walls of Tambora (Indonesia) influenced by hydrothermal alteration. 

Thomas R. Walter, Claire E. Harnett, Valentin R. Troll, and Michael J. Heap

Calderas are steep morphological and collapse basins that continue to reshape long after initial structural collapse. While large landslides are associated with caldera collapse and widen the basin, little is known about the morphological and structural changes that occur long after caldera formation. Here, we investigate the shape and slope of the Tambora caldera in Indonesia, which formed in 1815 during one of the most devastating eruptions of the past  centuries. The release of over 150 cubic kilometers of volcanic ash created a caldera 6 kilometers wide and 1250 meters deep, causing climatic effects worldwide. Here we explore an ultra-high-resolution dataset we generated from Pleiades, a tri-stereo satellite, that now allows us to apply computer vision approaches to study the morphology and geometry of the Tambora caldera. We generated a 12 million pixel point cloud resampled to a 1 m resolution Digital Elevation Model and a 0.5 m orthomosaic. We explore the dimension, slope, and outline of the caldera and find localized open fissures, tension cracks, and morphological scars. We also apply an unsupervised image classification approach to the stereo multispectral data and find locations of fumarole activity and hydrothermal alteration in close proximity to these structural features. Hydrothermal alteration sites are commonly located in the caldera wall below the scars and open fissures. We explore this proximity of alteration, scarring, and faulting using newDistinct Element Method models, emphasizing that caldera morphology and structure is strongly influenced by hydrothermal weakening that causes flank instability, localized shedding of material, and large-scale morphological changes.

How to cite: Walter, T. R., Harnett, C. E., Troll, V. R., and Heap, M. J.: Morphology, structure and gravitational instability of the steep caldera walls of Tambora (Indonesia) influenced by hydrothermal alteration., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2023, https://doi.org/10.5194/egusphere-egu24-2023, 2024.

EGU24-2321 | ECS | Orals | GD1.1

Cenozoic asthenospheric flow history in the Atlantic realm: Insights from Couette/Poiseuille flow models 

Zhirui Ray Wang, Ingo L. Stotz, Hans-Peter Bunge, Berta Vilacís, Jorge N. Hayek, Sia Ghelichkhan, and Sergei Lebedev

Mantle convection is an essential component of the Earth system. Yet its history is not well known , in part, as the strength of tectonic plates conceals the underlying flow. To date, global mantle convection models have reached an impressive level of sophistication due to significant advancement of computational infrastructures and numerical techniques. This ultimately allows geodynamicists to reconstruct past mantle states through using, for instance, inverse geodynamic models based on adjoint equations. However, key input parameters of these models --- such as thermo-chemical flow properties and rheology --- are complex and poorly known. This in turn limits their ability to effectively interpret the reconstructed mantle flow, thus motivating one to pursue an approach that aims to conceptualize paleo-mantle-flow at a simple analytical level.

To this end, the existence of thin, mechanically weak asthenosphere permits one to develop an analytical Couette/Poiseuille model of asthenospheric flow, where flow is associated with moving tectonic plates, and with lateral pressure gradients due to rising plumes and sinking slabs. Here we present estimates of the Cenozoic asthenospheric flow history from such models in the Atlantic realm. We, moreover, link them to azimuthal seismic anisotropy as well as mantle flow retrodiction simulated by inverse geodynamic models. Our analytically derived asthenospheric flow indicates that it is in broad agreement with the orientation of seismic azimuthal anisotropy, and with the large-scale flow patterns from mantle flow retrodictions. In light of these results, our study suggests exploiting a hierarchy of geodynamic models together with growing observational constraints on mantle flow induced surface expressions to gain a better understanding of paleo-mantle-flow.

How to cite: Wang, Z. R., Stotz, I. L., Bunge, H.-P., Vilacís, B., Hayek, J. N., Ghelichkhan, S., and Lebedev, S.: Cenozoic asthenospheric flow history in the Atlantic realm: Insights from Couette/Poiseuille flow models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2321, https://doi.org/10.5194/egusphere-egu24-2321, 2024.

EGU24-2631 | Orals | GD1.1 | Highlight

River incision on hotspot volcanoes: insights from paleotopographic reconstructions and numerical modelling 

Loraine Gourbet, Sean F. Gallen, Vincent Famin, Laurent Michon, Miangaly Olivia Ramanitra, and Eric Gayer

The influence of climate on landscape evolution in natural settings remains debated. Here, we focus on tropical hotspot volcanic islands because they exhibit relatively uniform lithology and experience significant precipitation and climate gradients. Furthermore, intermittent volcanic flows effectively “reset” the landscape that begins to evolve post-eruption. Thus, we can constrain initial conditions by reconstructing the initial geometry of radiometrically dated volcanic flows. We constrain landscape evolution through time in several volcanic islands with strong climate gradients to assess the role of climate on incision. We perform topographic reconstructions to calculate long-term basin-averaged erosion rates in two islands of the Réunion hotspot (Réunion, Mauritius) and compile published erosion rates on Réunion and Kaua’i (Hawaii hotspot). We define the time since incision started as the age of the surface incised lava flow. To calibrate incision parameters on all three islands, we use the stream power model and apply a data-driven Bayesian approach to obtain the erodibility, K, the drainage area exponent, m, and the slope exponent, n. We also calculate a normalized erodibility index, Kn, using n = 1 to directly compare results among the different study sites. Erosion rates of Réunion Island range from 9.9 ± 0.5 mm/yr to 5.2 x 10-3 ± 2 x 10-4 mm/yr and erosion rates in Mauritius Island range from 6.5 x 10-2 ± 8 x 10-3 mm/yr to 5.1 x 10-3 ± 4 x 10-4 mm/yr. Incision efficiency seems to decrease with time since incision started from 63 ka to ~300 ka and then does not vary significantly with time since incision started from ~300 ka to 4300 ka. This is likely due to the covariation between the age of volcanism repaving and precipitation rates on Réunion, which is related to the configuration of the island’s two volcanoes – the active Piton de la Fournaise located on the windward side and the dormant Piton des Neiges on the center and leeward side. Our empirical calibration of the stream power law shows high dispersion in n and Kn on each individual island. m ranges from 0.2 to 2.9, and Kn ranges from 2.3 x 10-7 to 9.8 x 10-4 m1-2m/yr. For Réunion, we identify a positive trend between mean annual precipitation and erosion rates, and between mean annual precipitation and Kn, for low to moderate erosion rates (<1 mm/yr). For all basins of Réunion, there is also a positive trend between mean annual cyclonic precipitation rates and erosion rates, and between mean annual cyclonic precipitation rates and n. In Kaua’i, there is a positive trend between erosion rates and mean annual precipitation, consistent with previous studies. In Réunion, the proportionality coefficient between erosion and mean annual precipitation is three times greater than in Kaua’i. In addition, considering all three islands, a nonlinear relationship exists between channel slope and incision rate: best-fit n values range from 0.5 to 6, with n generally lower than one on Kaua’i. Our results highlight different sensitivities of fluvial relief to incision, and of incision to climate, between Kaua’i and Réunion islands.

 

How to cite: Gourbet, L., Gallen, S. F., Famin, V., Michon, L., Ramanitra, M. O., and Gayer, E.: River incision on hotspot volcanoes: insights from paleotopographic reconstructions and numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2631, https://doi.org/10.5194/egusphere-egu24-2631, 2024.

The basal Cambrian sandstone unit in the North China craton (NCC) is an example of globally widespread siliciclastic succession that resides on the Great Unconformity and deposited on a hypothesized low-lying peneplain during the Cambrian global eustatic sea-level rise. Detrital zircon age signatures from this distinct sequence enable recognition of the ancient drainage system of the NCC in deep time and track its potential linkage with the Gondwana landmass. LA-ICP-MS U–Pb dating of the fossil-calibrated basal Cambrian (Series 2) detrital zircon samples from seven measured sections reveal marked spatial changes in their age signatures that can be divided into three distinct types. The first is generally characterized by the bimodal age populations with broad peaks at ~1.85 Ga and ~2.5 Ga that correlate with the Archean to Paleoproterozoic basement inboard of the NCC. The second is featured by multi-modal distribution with diagnostic Neoproterozoic peaks that correspond to subregional magmatic record. The third also shows multiple-zircon age populations, but yields significant crystallization ages close to the early Cambrian age. Comparing our new data with existing age spectra for the Cambrian strata across the NCC and the northern Gondwana demonstrates that separate drainage systems did exist in the peneplained basement during global Cambrian transgression and the basal Cambrian unit in the NCC was not a part of the far-travelled sand sheet across the northern margin of Gondwana. The most suitable source for Cambrian-aged grains constrained by paleogeographic restoration is the arc terrane developed along the northern margin of the NCC as a result of subduction of the Paleo-Asian oceanic plate. Our new continental-scale detrital zircon provenance signatures in the basal Cambrian unit suggest that the NCC should be considered a discrete continental block separated by the Proto-Tethys Ocean in the Cambrian, rather than an integral part of the northern Gondwana.

How to cite: Wei, R. and Duan, L.: Detrital zircon age signatures of the basal Cambrian sandstone unit in North China: implications for drainage divides during global Sauk transgression and separation from Gondwanaland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2721, https://doi.org/10.5194/egusphere-egu24-2721, 2024.

EGU24-2858 | ECS | Orals | GD1.1

Deriving mantle temperatures from global seismic models: A quantitative analysis in the light of uncertain mineralogy and limited tomographic resolution 

Gabriel Robl, Bernhard Schuberth, Isabel Papanagnou, and Christine Thomas

Mantle convection is driven by buoyancy forces in Earth’s interior. The resulting radial stresses generate vertical deflections of the surface, leaving traces in the geological record. Utilizing new data assimilation techniques, geodynamic inverse models of mantle flow can provide theoretical estimates of these surface processes, which can be tested against geological observations. These inverse models are emerging as powerful tools, providing the potential for tighter constraints on the relevant physical parameters governing mantle flow.

The geodynamic inversions mentioned above require an estimate of the present-day thermal state of the mantle, which can be derived from seismic observations. Using thermodynamically self-consistent models of mantle mineralogy, it is possible to convert the seismic structure imaged by global tomographic models to temperature. However, both seismic and mineralogical models are significantly affected by inherent limitations and different sources of uncertainty. In addition, owing to the complexity of the mineralogical models, the relation between temperature and seismic velocities is highly non-linear and not strictly bijective: In the presence of phase transitions, different temperatures can result in the same seismic velocity, making the conversion from seismic heterogeneity to thermal structure non-unique.

We investigate the theoretical ability to estimate the present-day thermal state of the mantle based on tomographic models in the case of isochemical convection. The temperature distribution from a 3-D mantle circulation model with earth-like convective vigour serves as the “true” temperature field. Using a closed-loop experiment, we aim to recover this initial model after: 1) mineralogical mapping from the “true” temperatures to seismic velocities, 2) application of a tomographic filter to mimic the effect of limited tomographic resolution, and 3) mapping of the “imaged” seismic velocities back to temperatures. We test and quantify the interplay of smoothed seismic structure due to tomographic filtering with different approximations for the conversion from seismic to thermal structure. Additionally, owing to imperfect knowledge of the parameters governing mineral anelasticity, we test the effects of changes to the anelastic correction applied in the mineralogical mapping. The observed mismatch between the recovered and initial temperature field is dominated by the effect of tomographic filtering, with a depth-dependent average error of up to 200 K. Additionally, we observe systematic large errors in the vicinity of phase transitions. Our results highlight that, given the current limitations of tomographic models and the incomplete knowledge of mantle mineralogy, magnitudes and spatial scales of a temperature field obtained from global seismic models will deviate significantly from the true state, even under the assumption of purely thermally driven mantle flow. Strategies to estimate the present-day thermodynamic state of the mantle must be carefully selected to minimize additional uncertainties.

How to cite: Robl, G., Schuberth, B., Papanagnou, I., and Thomas, C.: Deriving mantle temperatures from global seismic models: A quantitative analysis in the light of uncertain mineralogy and limited tomographic resolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2858, https://doi.org/10.5194/egusphere-egu24-2858, 2024.

Global plate reconstructions that constrain the surface plate motions provide crucial boundary conditions for mantle circulation models. Earth-like plate kinematics could reduce the impact of the uncertain mantle initial conditions and generate slab structures in the mantle that are comparable with seismic tomographies. However, due to the subduction of the oceanic plates, uncertainty increases in global plate reconstruction over time. Here, we utilize a novel slab unfolding technique to retrodeform mantle slabs imaged in the MITP08 seismic topography back to the pre-subduction states at Earth’s surface. Such a technique provides additional constraints on plate reconstructions, especially in regions dominated by intra-oceanic subductions, such as Southeast Asia.

Our reconstruction shows a significant trench retreat along Southeast Asia and Northern Australia between 90 and 65 Ma that opened a gigantic, >3,000 km wide backarc basin. This basin, named the East Asian Sea plate, was later consumed by the west-moving Philippine Sea plate and North-moving Australian plate in the Cenozoic. We then embed our reconstruction in a mantle circulation model, TERRA, testing the fidelity of the reconstruction in a closed-loop experiment.

We found that fragmented, sub-horizontal East Asian Sea slabs can be reproduced in the mantle circulation model. These slabs lying underneath the current Philippine Sea plate and northern Australia are similar to the MITP08 tomography on which the reconstruction is built. Moreover, these slabs at 800-1000 km depths result in a more negative dynamic topography on the present Philippine Sea plates comparable with the observed residual topography. On the contrary, the traditional, Andean-style reconstruction can only produce positive dynamic topography. Other Mesozoic, intra-oceanic subductions in NE Asia and western North America embedded in our reconstruction also produce negative, yet smaller magnitude, dynamic topography, possibly due to the older subduction history and deeper slabs. We conclude the negative dynamic topography within the present Pacific plate is the result of ancient intra-oceanic subductions. 

How to cite: Chen, Y.-W., Bunge, H.-P., Stotz, I., and Wu, J.: Testing tomography-based plate reconstructions from a paired, inverse-forward closed-loop experiment in a mantle circulation model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3083, https://doi.org/10.5194/egusphere-egu24-3083, 2024.

EGU24-3473 | Posters on site | GD1.1

The gully system on the NW sector of La Fossa cone (Vulcano Island): 2D evolution and hazard implication 

Alessandro Fornaciai, Massimiliano Favalli, Luca Nannipieri, Agnese Turchi, Rosanna Bonasia, and Federico Di Traglia

The Island of Vulcano is the emerged portion of a composite volcanic edifice within the Aeolian volcanic archipelago, situated in the southern Tyrrhenian Sea. The remobilization, triggered by heavy rainfall, of loose volcaniclastic material from La Fossa cone and the generation of small debris flows are recurrent hazards on Vulcano. Although these debris flows generally transport small volumes of material, in the case of severe events, they can  be channeled along the roads, flood several buildings, inundate the main harbor, and eventually be discharged into the sea. Gravitational and erosive processes, mainly due to rainfall, have formed several gully systems around the La Fossa cone. The presence of gully systems along slopes enhances both runoff and downslope mass wasting, and, above all, the gullies themselves act as a source of mass wasting due to the collapse of their walls and the processes of aggradation and degradation of their beds. Therefore, understanding the behaviour of gullies and their response to rainfall is crucial for predicting the effects of environmental changes, whether climatic or volcanic, on gully dynamics. 

In the frame of "VOlcaniclastic debris flows at La Fossa cone (Volcano  Island): evolution and hazard implication (VOLF)" project funded by the Istituto Nazionale di Geofisica e Vulcanologia, we here analyze aerial photos of the NW sector of La Fossa cone to describe the evolution of its gully system from the 1954 to 2022. First, we create a georeferenced dataset of photos by orthorectifying existing photos and generating new ones through the Structure from Motion (SfM) method applied to Unmanned Aerial System (UAS) photos. Second, we describe the geomorphological features of the gullies in the NW sector of La Fossa cone, identifying features to be parameterized. Finally, we qualitatively and quantitatively describe their evolution over almost 70 years.  

This work aims to investigate the morphological evolution of the NW flanks of La Fossa cone, a crucial aspect for assessing hazards associated with volcaniclastic sediment-charged flows and floods on Vulcano Island. This is especially relevant in a scenario where ongoing climate changes may potentially disturb the current equilibrium, heightening the likelihood of short-term extreme rainfall events.

How to cite: Fornaciai, A., Favalli, M., Nannipieri, L., Turchi, A., Bonasia, R., and Di Traglia, F.: The gully system on the NW sector of La Fossa cone (Vulcano Island): 2D evolution and hazard implication, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3473, https://doi.org/10.5194/egusphere-egu24-3473, 2024.

The Cheakamus basalts are a set of ~31 km long, 1.65 km3 valley-filling olivine basalts which erupted into the glaciated Callaghan-Cheakamus Valley system of the Garibaldi Volcanic Belt (GVB), British Columbia. Combined paleomagnetic and radiometric (40Ar/39Ar) analysis dates the lavas as a short-lived (< 2 ka duration) eruption at 15.95 ± 7.9 ka (2σ); additional field evidence, including well-glaciated lava flow surfaces overlain by till, indicate the eruption coincided with the early stages of the Fraser Glaciation (LGM) at ~20-18 ka. The lavas preserve features indicative of a landscape hosting diverse and dynamic paleoenvironments. Subaerial eruption of basalt lava filled an ice-free Callaghan Creek drainage system before inundating and damming of the paleo-Cheakamus River, creating an upstream rising body of water. Periodic overtopping of the lava dam resulted in syn-eruptive intermittent flooding and overtopping of lavas expressed by discontinuous lenses of interflow sediment and well-developed entablatures in the upper portions of lava flows. Rare instances of enigmatic cooling columns indicate localized ice contact with glaciers that partially filled the Cheakamus Valley. Emplacement features and morphologies in the Cheakamus Valley have been heavily altered by the erosional overprinting of a glacial lake outburst flood (GLOF) that preliminary 10Be analysis dates at the close of the LGM (11-10 ka). Lavas in the Callaghan valley remain untouched by the GLOF. Their aerial extent and distribution, especially at high elevations in tributary valley mouths suggest bottlenecking and backing-up of lavas due to narrowing in valley topography. Current work combines field mapping and analogue modelling and aims to provide insight into the emplacement dynamics of effusive lavas in the steep, confined terrain of the BC Coast Mountains. Despite, and in part because of, their heavily modified morphology, the Cheakamus basalts act as an excellent recorder of both effusive volcanic processes and the paleoenvironments into which they erupted. Their thorough and accurate analysis is especially pertinent temporally, as they erupted during a time of glacial flux and can provide additional evidence for the timing and location of the advancing Cordilleran ice sheet. Spatially, the Cheakamus basalts are proximal to population centers and transport infrastructure and thus have implications for potential volcanic hazards and attendant risks, as any future effusive, valley-filling basaltic eruption from the GVB will likely share similar emplacement characteristics and processes.

How to cite: Borch, A., Russell, J. K., Barendregt, R., and Friele, P.: Emplacement and erosion of valley-filling basalt lavas in shifting Quaternary environments of the Garibaldi Volcanic Belt, British Columbia, Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4176, https://doi.org/10.5194/egusphere-egu24-4176, 2024.

EGU24-4552 | ECS | Orals | GD1.1 | Highlight

Synthetic Hiatus Maps as a Tool for Constraining Global Mantle Circulation Models 

Hamish Brown, Berta Vilacís, Ingo Stotz, Yi-Wei Chen, and Hans-Peter Bunge
The transient uplift and subsidence of the Earth’s surface induced by mantle convection (dynamic topography) leaves an imprint on the stratigraphic record at inter-regional scales. Dynamically uplifted continental regions result in widespread erosional/non-depositional environments (sedimentary hiatus), while subsided regions result in continuous sedimentation. Thus, by mapping hiatus and no-hiatus signals on inter-continental scales, one gains a proxy for the long-wavelength uplift and subsidence associated with dynamic topography. In this contribution, we report on the use of hiatus maps as a constraint on mantle circulation models (MCMs), which make predictions of the history of dynamic topography. In order to make such a comparison, we filter the modelled dynamic topography through the available data points from the real maps to form hiatus/no hiatus signals. The resulting synthetic hiatus maps are then directly comparable to the true maps. By generating synthetic hiatus maps for a variety of high-resolution TERRA MCMs, we show that such maps allow for the falsification or verification of MCMs based on their prediction of dynamic uplift/subsidence events. We additionally find that eustatic sea-level variations are clearly highlighted by geological series in which the global ratio of hiatus/no-hiatus surfaces is significantly over-/under-predicted by the synthetic maps. We stress that, while plume histories in MCMs are constrained only by the surface tectonic history, this form of comparison paves the way for the validation of adjoint geodynamic models in which plume histories are constrained by seismic tomography.

How to cite: Brown, H., Vilacís, B., Stotz, I., Chen, Y.-W., and Bunge, H.-P.: Synthetic Hiatus Maps as a Tool for Constraining Global Mantle Circulation Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4552, https://doi.org/10.5194/egusphere-egu24-4552, 2024.

EGU24-6544 | Orals | GD1.1

The large-scale landscapes in SW Scandinavia and in SW India are the result of two episodes of Neogene uplift 

Peter Japsen, Paul F. Green, Johan M. Bonow, and James A. Chalmers

Peninsula India and Scandinavia are elevated passive continental margins (EPCMs) characterized by asymmetric relief with high mountains in the west and a gentle slope towards lowlands in the east.

New AFTA data from southern India reveal major Phanerozoic episodes of cooling, reflecting exhumation. Here we focus on the early Miocene episode possibly related to the hard India-Asia collision (van Hinsbergen et al. 2012). The Miocene exhumation resulted in a low-relief landscape; e.g. the Karnataka and Mysore plateaus (Gunnel and Fleitout, 1998) with residual regions of higher ground (e.g. Palani Hills). Today, these plateaus reach an elevation of 1 km along the coast of SW India, sloping towards the east. The Miocene peneplains were graded towards the base level of the adjacent ocean (Green et al. 2013), and therefore reached their present elevation after their formation. Thick piles of Pliocene sediments off SW India (Campanile et al. 2008) suggests that this happened during the Pliocene.

Richards et al. (2016) studied river profiles in Peninsula India and concluded that the regional tilt grew since 25 Ma, maintained by sub-lithospheric processes. However, we find that the relief is the result of two episodes: 1) Miocene peneplanation related to far-field stress. 2) Late Neogene, asymmetric uplift driven by sub-lithospheric processes.

We identified a similar development in SW Scandinavia, where two Neogene episodes of uplift and erosion define main features of the relief (Japsen et al. 2018): 1) Early Miocene uplift leading to formation of the Hardangervidda peneplain (possibly related to the hard India-Asia collision). 2) Uplift beginning in the Pliocene, raising Hardangervidda to its present elevation at 1.2 km. Pliocene uplift raised margins around the NE Atlantic with maximum elevations reached close to Iceland. This suggests support from the Iceland Plume due to outward-flowing asthenosphere extending beneath the conjugate margins (Rickers et al. 2013; Japsen et al. 2024). 
Lithospheric as well as sub-lithospheric processes appear to shape main features of EPCMs.

Campanile et al. 2008. Basin Research. Green et al. 2013. GEUS Bull. Gunnell, Fleitout 1998. ESPL. Japsen et al. 2018. JGSL. Japsen et al. 2024. ESR. Richards et al. 2016. G cubed. Rickers et al. 2013. EPSL.

How to cite: Japsen, P., Green, P. F., Bonow, J. M., and Chalmers, J. A.: The large-scale landscapes in SW Scandinavia and in SW India are the result of two episodes of Neogene uplift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6544, https://doi.org/10.5194/egusphere-egu24-6544, 2024.

Deflection of the Earth’s surface supported by mantle flow, known as dynamic topography, is associated with a free-air gravity anomaly because such topography is not isostatically compensated. Consequently, the ratio of the gravity anomaly to the dynamic topography, known as the admittance, has been used to estimate the amplitude of dynamic topography, which can be difficult to measure directly. However, at long wavelengths (e.g., spherical harmonic degrees 2 to 6) both dynamic topography and gravity anomalies, and thus the admittance, are sensitive to the mantle’s viscosity structure. Previous studies [e.g., Colli et al., 2016] demonstrate a reversal in sign of the free-air gravity anomaly resulting from lower mantle structures as the viscosity of the lower mantle is increased. This indicates potential complexity for inferring long-wavelength dynamic topography from observations of gravity anomalies, because the upper-lower mantle viscosity contrast is poorly constrained. We further investigated the relationship between dynamic topography and gravity anomalies by introducing lateral viscosity variations into a finite element model of global mantle flow. We find that the gravity anomaly above lower mantle density heterogeneity can change dramatically as we begin to introduce different models for lateral viscosity variations into the upper and lower mantle viscosity fields. In such models we find that the sign of the admittance varies laterally, with the horizontal gradients in mantle viscosity perturbing mantle flow patterns in ways that produce large changes gravity anomalies and smaller changes in dynamic topography. A spatially-varying admittance will greatly complicate estimation of dynamic topography from observed gravity, and may help to explain mismatches between observations of dynamic topography and predictions made using global mantle flow models. On the other hand, the reconciliation of such mismatches may help to constrain viscosity heterogeneity in the lower mantle.

Colli, L., S. Ghelichkhan, and H. P. Bunge (2016), On the ratio of dynamic topography and gravity anomalies in a dynamic Earth, Geophysical Research Letters, 43(6), 2510-2516, doi:10.1002/2016GL067929.

How to cite: Conrad, C. P. and Ramirez, F.: Sensitivity of Long-Wavelength Dynamic Topography and Free-Air Gravity to Lateral Variations in Lower Mantle Viscosity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6721, https://doi.org/10.5194/egusphere-egu24-6721, 2024.

EGU24-6783 | Orals | GD1.1

Gully incision development on scoria cones: different behaviors in three volcanic fields reflect environmental conditions. 

Maria Cristina Zarazúa-Carbajal, Greg A. Valentine, and Servando De la Cruz-Reyna

A consequence of alluvial processes acting on scoria cones is the development of a drainage network composed of radially distributed rills and gullies parallel to the volcanic edifice's downslope direction. This work focuses on the quantification of the degree of development of the drainage network by applying the Average Erosion Index method to scoria cones from the arid to semi-arid Lunar Crater volcanic field and comparing with previously obtained results from two tropical volcanic fields (Sierra Chichinautzin volcanic field and Paricutin-Tancitaro region, both in central Mexico). The results show that the method helps to determine geomorphic age relations when calibrated separately for each field. Furthermore, the differences in the resultant rates at which AEI varies as a function of time obtained for the three studied fields indicate that the method provides a tool to quantify the effects of different alluvial rates at volcanic fields across various environments.

How to cite: Zarazúa-Carbajal, M. C., Valentine, G. A., and De la Cruz-Reyna, S.: Gully incision development on scoria cones: different behaviors in three volcanic fields reflect environmental conditions., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6783, https://doi.org/10.5194/egusphere-egu24-6783, 2024.

EGU24-6885 | Orals | GD1.1

Cumulative storage of magma in the Paricutin-Tancítaro region, Mexico, revealed by recurrent swarm seismicity and a high spatial density of morpho-chronometrically dated Holocene monogenetic cones. 

Servando De la Cruz-Reyna, María Cristina Zarazúa-Carbajal, Gema Victoria Caballero-Jiménez, and Ana Teresa Mendoza-Rosas

A region located in the SW sector of the Michoacán-Guanajuato monogenetic field, in central Mexico displays a high spatial density of scoria cones, mostly around Tancítaro, a large central volcano active in the middle Pleistocene. This region became well known when in 1943 a new volcano, Paricutin, was formed in a cornfield at 11 km to the NW of the extinct stratovolcano. The birth of Paricutin was preceded by significant swarm-type seismicity. Afterward, new seismic swarms were reported in the area in 1997, 1999, 2000, 2006, 2020, 2021, 2022, and 2023, with a mean recurrence interval of only 4 yr, most of them (not all) showing the characteristics of a magmatic origin.  Aiming to shed some light on the relation between the high density of monogenetic cones and the recurrent seismicity, we have made a morpho-chronometric estimate of the relative ages of 170 scoria cones located in the Paricutin-Tancítaro region (PTR) within latitudes 19°N and 20°N and longitudes -102.0° E and -102.7° using the Average Erosion Index (AEI) which quantifies the degree of alluvial erosion of scoria cones from a Fourier analysis of their level contours. Monogenetic activity began in the PTR at about 1 Ma, and the AEI analysis shows that such activity increased after the end of the Tancítaro activity, around 232 ka, and further increased in the Holocene when about one-third of the scoria cones in the region were formed, with a mean interval between eruptions between 120 and 240 yr. On the other hand, a detailed study of two of the most energetic seismic swarms, recorded in 2020 and 2021 shows that the magma intrusion volume required to produce the measured cumulative seismic moment of both swarms amounts to about 140 million cubic meters, which is seemingly insufficient to produce a Paricutin-size eruption, which ejected about 1.3 cubic km of magma. We thus propose a possible conceptual explanation of the recurrent emplacement of monogenetic volcanoes and the frequent seismic swarm activity in terms of a persistent magma source under the crustal extension of the PTR producing numerous dike and sill forming intrusions. In some cases, such intrusions may have a cumulative effect forming temporary magma reservoirs capable of producing new monogenetic eruptions. Assuming that about 0.5 to 1 cubic kilometer of magma needs to accumulate to begin an eruption, about 7 to 14 sizable (similar to the 2020-2021) swarms may then represent a significant precursor.    

How to cite: De la Cruz-Reyna, S., Zarazúa-Carbajal, M. C., Caballero-Jiménez, G. V., and Mendoza-Rosas, A. T.: Cumulative storage of magma in the Paricutin-Tancítaro region, Mexico, revealed by recurrent swarm seismicity and a high spatial density of morpho-chronometrically dated Holocene monogenetic cones., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6885, https://doi.org/10.5194/egusphere-egu24-6885, 2024.

EGU24-7187 | ECS | Posters on site | GD1.1

Spontaneous Formation of Mantle Wind by Subduction and Its Impacts on Global Subduction Asymmetry 

Youngjun Lee and Changyeol Lee

Various subduction zone characteristics, including the slab dip, plate velocity, seismicity, and back-arc stress regime, show the global asymmetry with respect to the subduction direction. In particular, the east-directed subducting slabs show shallow dips and slow convergences, contrast to the steep dips and fast convergences of the west-directed subducting slabs. To explain the global asymmetry, the westward lithospheric motion or the eastward mantle wind with respect to the underlying mantle and the overlying plate, respectively, have been proposed. However, the causative force for the lithospheric motion, the tidal force between the Earth and Moon, is only acceptable when the asthenospheric viscosity is dramatically low such as 1015 ~ 1016 Pa·s, which could not globally exist in the mantle. The causative force for the mantle wind has left unknown even though the impact of the mantle wind has been verified. Past studies have shown that slabs sinking into the lower mantle can cause global mantle flow. That is, the slabs sinking at the eastern and western trenches around the Pacific ocean can cause the global mantle flow above the low-viscosity liquid outer core, expressed as the mantle wind. Therefore, to verify whether the subducting slabs around the Pacific ocean cause the mantle wind, we conducted a series of 2-D numerical models using an annulus-shape model domain, which simplifies the subduction history in the paleo- and present-Pacific ocean. Along with an allowance of dynamic subduction, both the realistic mantle viscosity and the major phase transition in the mantle were considered. Results show that the global-scale mantle wind is spontaneously formed by the imbalance in lateral mantle stresses owing to the subducting slabs around the Pacific ocean when the slippery core-mantle boundary operates as a lubricant layer, and the direction and magnitude of the mantle wind are periodically changed every tens of million years. When he eastward mantle wind occurs, it induces the relative westward drift of the plate, and as a result, the westward plate velocity becomes greater than the eastward plate velocity with respect to the hotspot reference frame. Simultaneously, the mantle wind pushes the west-directed subducting slab toward the ocean, forming steep slab dips but does the east-directed subducting slab toward the arc, forming shallow slab dips, consistent with the present subduction asymmetry in the Pacific ocean. After that, the negative buoyancy of the shallow slab steepens the slab itself, changing the direction of mantle wind westward; the opponent slab dips and plate velocities occur in the subduction zones. This study reveals that the present subducting asymmetry is a snapshot expression of the evolving global mantle flow, formed by the subducting slabs.

How to cite: Lee, Y. and Lee, C.: Spontaneous Formation of Mantle Wind by Subduction and Its Impacts on Global Subduction Asymmetry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7187, https://doi.org/10.5194/egusphere-egu24-7187, 2024.

EGU24-8475 | ECS | Posters virtual | GD1.1

Patterns of volcanic eruptions in connection to sea-level change 

Margherita Scala, Maria C Neves, and Stéphanie Dumont

Understanding the relationships between the onset of volcanic eruptions and external forcings, such as solid Earth and ocean tides, can help us to understand the underlying dynamics of volcanic processes and have implications for volcanic monitoring and prediction efforts.

Many studies that explored the relationship between tidal forces and volcanic activity have shown that certain phases of tidal cycles are associated with an increased likelihood of eruptions. At longer-time scales of hundreds of thousands of years, pronounced sea level variations related to ice melting or climatic and astronomical periodic variations have also been associated with pulses of volcanic activity.

Oceans participate in significant redistributions of mass that can affect the stress field within the Earth’s crust over different time scales. Considering that most volcanoes lie near, within or beneath the oceans we hypothesize that stresses induced by ocean loading participate in destabilizing volcanic dynamical systems and ultimately contribute to eruption triggering.

In a previous study we analyzed the worldwide number of monthly volcanic eruptions from the Global Volcanism Program and the global mean sea level between 1880 and 2009 using the Singular Spectrum Analysis time-series analysis technique. We found common periodicities and particularly multi-decadal components of similar periodicities of 20, 30 and 50 years present in both time-series.

In this work we further explore the connection between volcanic activity and sea level by mapping the spatial patterns of volcanic eruptions at the previously identified temporal scales of correlation, ranging from the fortnightly tide to cycles of approximately 100 years. Geographical Information System tools are used to create spatial data layers, perform spatial analysis, and provide geographical visualization. The analysis might reveal global conditions and space-time patterns favorable to eruption triggering.

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: Scala, M., Neves, M. C., and Dumont, S.: Patterns of volcanic eruptions in connection to sea-level change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8475, https://doi.org/10.5194/egusphere-egu24-8475, 2024.

EGU24-8609 | ECS | Posters on site | GD1.1

Implications of dynamic topographic measurements along Africa’s passive margins 

Philippa Slay, Megan Holdt, and Nicky White

Earth’s topography is both isostatically and dynamically supported. Sub-crustal density anomalies, caused by convective mantle processes, generate transient vertical motion at Earth's surface, producing the dynamic component of topographic support. Residual depth measurements are a well-established proxy for quantifying dynamic topography on oceanic crust and provide an observation-led approach to probing mantle dynamics. A global database of residual depth anomalies compiled from seismic reflection profiles and wide-angle seismic experiments is augmented with results obtained from interpreting further seismic experiments in the oceans surrounding the African continent. Residual depth anomalies are calculated by isolating and removing isostatic signals arising from sediment loading and crustal heterogeneity. Following these corrections, observed water-loaded depth-to-basement is compared to that predicted by the plate cooling model, with deviation equal to the residual depth anomaly. Coverage surrounding the African continent is improved, particularly in the Gulf of Guinea and Mozambique Channel. Results are consistent with previous observations, showing dynamic support of ± 1 km out to and including spherical harmonic degree l = 40 (i.e. ~ 1000 km). Results are corroborated by independent geologic and geophysical markers of subsidence and uplift. For example, volcanism and slow shear-wave upper mantle velocity anomalies associated with the Cameroon Volcanic Line indicate dynamic support. Improving the spatial sampling of residual depth anomalies provides insight into the influence of convective circulation on Earth’s surface, culminating in a more robust database against which geodynamic models of mantle convection can be benchmarked.

How to cite: Slay, P., Holdt, M., and White, N.: Implications of dynamic topographic measurements along Africa’s passive margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8609, https://doi.org/10.5194/egusphere-egu24-8609, 2024.

It is widely recognized that mantle dynamics and plate flexure both contribute to Earth’s topography and gravity fields at different wavelengths, yet the actual transition wavelength between them is not well quantified, ranging from ~100 km to ~1000 km. Here we use the observed relationship between topography and the free-air gravity anomaly fields (admittance) to infer the relative contribution of plate flexure and mantle dynamics based on mantle flow models which incorporate an essentially elastic plate. Global and regional Pacific Ocean data studies show that plate flexure and mantle convection potentially contribute to the topography and gravity for wavelengths larger than ~600 km. Plate flexure mainly contributes at wavelengths shorter than ~600 km and is consistent with the support of uncompensated topography for wavelengths shorter than ~200 km. To investigate the admittance associated with mantle dynamics at long wavelengths we have constructed mantle flow models based on a number of different seismic tomography models. The finite element software CitcomS was used to calculate mantle flow and related surface dynamic topography and associated free-air gravity anomaly. Admittance analysis in the Pacific Ocean from different mantle flow models show that the dynamic admittance is generally larger than the observed admittance, while the admittance from plate flexure is smaller than the observed admittance, suggesting that both mantle dynamics and plate flexure contribute to Earth’s topography and gravity at long-wavelengths. The difference between the dynamic admittance and the observed admittance is smallest for cases with temperature-dependent viscosity and weak asthenosphere, and the combined admittance in the presence of both flexure and mantle convection for these cases is generally consistent with the observed admittance. We use a new method to separate the effects of plate flexure and mantle convection to the topography and gravity fields at long wavelengths which has been developed from the plate flexure and dynamic admittances. We assume that the topography and gravity at long wavelength are the combination of plate flexure and mantle dynamics and further assume that the topography and gravity are linearly related through the admittance. The final separated dynamic topography in the Pacific Ocean is generally consistent with previously published residual topography studies at long-wavelengths.

How to cite: Yang, A., Watts, A., and Zhong, S.: Long-wavelength gravity and topography of the Pacific Ocean: Relative contribution of mantle dynamics and plate flexure , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9346, https://doi.org/10.5194/egusphere-egu24-9346, 2024.

EGU24-10128 | ECS | Orals | GD1.1

Exploring the potential of normal mode seismology for the assessment of geodynamic hypotheses 

Anna Schneider, Bernhard Schuberth, Paula Koelemeijer, Grace Shephard, and David Al-Attar

Fluid dynamics simulations are a powerful tool for understanding processes in the Earth's deep interior. Mantle circulation models (MCMs), for example, provide important insight into the present-day structure of the mantle and its thermodynamic state when coupled with mineralogical models, which is essential information for other fields in the geosciences. The evolution of the heat flux through the core-mantle boundary, for instance, is a prerequisite for geodynamo simulations that aim to model the reversal frequency pattern of the Earth's magnetic field on geologic time scales. However, geodynamical modelling requires extensive knowledge of deep Earth properties and plate motions over time. Uncertainties in these model inputs propagate into the MCMs, which subsequently have to be evaluated with independent data, such as the seismological or geological record. Although state-of-the-art MCMs typically explain statistical properties of seismological data, they do not consistently reproduce the location of features in the mantle.

In this contribution, we explore the effect of varying the absolute position of mantle structure on seismic data by applying first-order modifications to an initial MCM. Normal mode data are particularly well suited for assessing the resulting changes in the location of mantle structure, as they capture its long-wavelength component throughout the entire mantle. In addition, the global sensitivity of normal modes reduces the drawbacks of uneven data coverage. Specifically, we use two different seismic forward modelling approaches, an iterative direct solution method for computing full-coupling spectra and a splitting function calculation that is based on the self-coupling approximation. Our goal is to quantify the effects of a limited number of large-magnitude earthquakes, the adequacy of the self-coupling approximation, and the resolvability of relevant model differences through a comprehensive data analysis. Our synthetic forward modelling framework is moreover well suited for testing the depth sensitivity associated with specific frequency intervals in the spectrum that generally is inferred from seismic 1-D profiles within the splitting function approximation.

How to cite: Schneider, A., Schuberth, B., Koelemeijer, P., Shephard, G., and Al-Attar, D.: Exploring the potential of normal mode seismology for the assessment of geodynamic hypotheses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10128, https://doi.org/10.5194/egusphere-egu24-10128, 2024.

EGU24-10566 | ECS | Orals | GD1.1

Global assessment of tomographic resolution and uncertainty with the SOLA method 

Roman Freissler, Bernhard S.A. Schuberth, and Christophe Zaroli

Interpretations of seismic tomography and applications of the resulting tomographic images, e.g. for estimating present-day mantle temperatures, require information on their resolution and uncertainty. Assessing these model properties is often difficult due to the large size of tomographic systems on global scales. In consequence, there have been only few attempts to consistently analyse the spatially variable quality of tomographic images of deep mantle structure. For linear problems, both resolution and uncertainty can be quantified with the tools provided by classic Backus–Gilbert (B–G) inversion. In this theory, averaging kernels define the local resolving power at each model parameter, while uncertainties represent the propagation of data errors into the model values. By using a more efficient variant of B–G inversion, the method of 'Subtractive Optimally Localized Averages' (SOLA), global tomography can be performed with complete information for model appraisal.

Based on the SOLA framework, we present a concept for the assessment of the 3-D resolution information contained in a global set of averaging kernels. It is based on the rigorous estimation of resolution lengths from a 3-D Gaussian parametrization of the averaging kernels, together with a test for the robustness of this approximation. This is a necessary step because a perfectly bell-shaped or delta-like behaviour of resolution can not always be guaranteed in global tomography due to the inhomogeneous data coverage. Therefore, we also develop a classification scheme, which enables a basic identification of those averaging kernels that are too complex to be sufficiently described by the chosen definition of resolution length. We note that this approach is more generally applicable, i.e. it can be used with any explicitly available set of averaging kernels or point-spread functions, but also with alternative parametrizations.

In the context of the SOLA method, our resolution analysis can be further used to locally calibrate the inversion parameters. This involves on the one hand the specification of a target (resolution) kernel. On the other hand, a trade-off parameter needs to be selected that regulates the fit of the averaging to the target kernel, and the conversely affected propagation of data errors.

To this end, we apply our concept for robust resolution estimation to different sets of averaging kernels from SOLA inversions with varying parameter combinations. Most notably, we systematically increase the spatial extent of the target kernels (taken as 3-D Gaussian functions here as well). The final maps of global (and classified) resolution and uncertainty can be viewed together for a complete picture of the model quality. They reveal where, and for which target size and amount of error propagation, resolution lengths are meaningful and model values can be interpreted appropriately.

How to cite: Freissler, R., Schuberth, B. S. A., and Zaroli, C.: Global assessment of tomographic resolution and uncertainty with the SOLA method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10566, https://doi.org/10.5194/egusphere-egu24-10566, 2024.

We present a new book aimed at graduate students, and academics, as well as all volcano enthusiasts. We chose to publish on the topic of volcano geomorphology for two main reasons. Firstly, although several geomorphology textbooks have been published, ones focussed on volcano geomorphology are scarce or outdated and out of print (Cotton, 1944, McDonald, 1972; Ollier, 1969 and 1988). Secondly, many volcanology books have been published over the past few decades, but they do not describe landforms and geomorphic processes in sufficient detail (as stated by the late P. Francis in 1993). To our knowledge, only five modern books on volcanology include a chapter on volcanoes as landforms and landscapes (Francis, 1993 and Francis & Oppenheimer, 2004; Chester, 1993; Scarth, 1993; Lockwood and Hazlett, 2010). They are less process-oriented than modern books on geomorphology.

Our book on Volcano Geomorphology is organised into five main themes, and contains 10 chapters. The first theme is an overview of the geodynamic environments in which the Earth's volcanoes are createdThe second is a detailed account of elementary “constructional” landforms, from lava forms to monogenetic volcanoes, both terrestrial and subaqueous, reflecting a variable degree of magma-water interaction. The third deals with polygenetic volcanic edifices including shield volcanoes, composite cones and volcanic clusters. This is followed by landforms and processes that form calderas, caldera complexes, and volcano-tectonic depressions. The fourth is oriented towards the degradation of volcanoes by short- and long-term erosion processes. The fifth and final theme is twofold: first, we deal with geomorphic hazards on active and dormant volcanoes, along with five specific case studies of recent events; and lastly, we conclude with a chapter presenting a wide array of methods (morphometry, simulations of processes, structural geology, age determination, etc.) that are used to unravel processes on active and dormant volcanoes.
            In summary, our textbook aims to: (1) review the most recent research in geomorphology and physical volcanology, e.g. an improved classification and understanding of volcanic landforms, with respect to geodynamic settings, lithology, and climate; (2) update our knowledge of processes and rates of growth and destruction of volcanic landforms and landscapes by integrating recent results from the expanding sector of volcanology both in the field and in the laboratory; (3) consider how volcanic landforms, landscapes, and processes can be studied by reviewing classical and modern methods.  

In this way, we hope that our compilation, which provides a richly referenced and illustrated piece of work on volcano geomorphology, will be of interest to a broad audience. It is expected to be published later this year (2024).  

How to cite: Karátson, D. and Thouret, J.-C.: ‘Volcano Geomorphology: landforms, processes and hazards’  ̶̶ A new book in ‘Advances in Volcanology’ Collection, Springer Verlag , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11744, https://doi.org/10.5194/egusphere-egu24-11744, 2024.

EGU24-11817 | ECS | Orals | GD1.1

River dynamics in an active volcano with tropical humid conditions 

Sebastián Granados, Nicola Surian, and Guillermo E. Alvarado

 Active volcanic catchments within low-latitude tropical humid climates constitute some of the most dynamic and sediment-rich fluvial systems globally. The combination of factors such as active explosive vulcanism, frequent high-magnitude earthquakes, dense biodiverse vegetation, and intense rainfall leads to very high sediment supply and very active channel morphodynamics within such fluvial systems.

Our research focused on channel dynamics in three remote and challenging-to-access reaches of the Sucio River, situated within the Irazú stratovolcanic structure in Costa Rica's central volcanic chain. This unique setting experiences extreme conditions, including rainfall exceeding 8000 mm annually, infrequent but significant volcanic eruptions (occurring over three times per century), high-magnitude earthquakes (>Mw5), and dense pristine vegetation. The mapped river reaches within this active volcano exhibit a distinctive confined multi-thread channel morphology predominantly comprised of coarse sediments, notably boulders, displaying exceptional dynamism. These reaches showcase rapid shifts between braided, island-braided, and anabranching morphologies in relatively short periods (<20 yrs.). Additionally, the primary sediment sources located in crateric areas have undergone rapid and substantial changes, resulting in the emergence of large landslides and drastic alterations in vegetation.

Employing remote sensing techniques, geostatistical analysis, and fieldwork, we investigated the impacts of eruptions, earthquakes, and rainfall on the Sucio River's channel morphology and its primary sediment sources (craters) from 1961 to 2023. Over 65 images were processed to generate various derived raster products, including supervised classification datasets, change detection outputs, and morphometric parameters (such as channel width, braided index, anabranching index, and area of bars and islands). Moreover, we constructed a precipitation database spanning the study period to assess the frequency, magnitude, and duration of extreme rainfall events. Historical seismic data was utilized to compile a database of relevant earthquakes that might have affected the catchment, given the river's proximity to several active faults. Subsequently, exploratory statistical analysis employing linear regression models helped discern the influential factors behind channel dynamics and changes.

Our findings provide a novel understanding of how this specific fluvial volcanic environment responds to external perturbations and adapts its channel morphology over time. Key outcomes include the rarity of the multithread boulder morphologies observed in these reaches, rapid morphological transformations occurring within this multithread system in short intervals, the significant role of dense pristine vegetation in stabilizing banks and islands, and the cyclic stability-instability phases (erosion-deposition) triggered by pivotal events like eruptions, hurricanes, and high-magnitude earthquakes.

 

This study presents novel insights into channel morphology dynamics in one of Central America's most extensively studied active volcanoes, likely having the river transporting the most sediments in Costa Rica's volcanic regions.

How to cite: Granados, S., Surian, N., and Alvarado, G. E.: River dynamics in an active volcano with tropical humid conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11817, https://doi.org/10.5194/egusphere-egu24-11817, 2024.

EGU24-12015 | ECS | Orals | GD1.1

Unraveling Tasmania's Late Paleozoic Ice Age: Carbon Isotopic and Stratigraphic Signatures in Response to Glacial-Deglacial Cycles and Large Igneous Province (LIP) Events 

Wahyuningrum Lestari, Aisha Al Suwaidi, Calum Fox, Vivi Vajda, Andrea Ceriani, Yadong Sun, Joost Frieling, and Tamsin Mather

Late Paleozoic Ice Age (LPIA), which peaked during the mid Permian, resulting in widespread ice centers across Gondwana during its coldest periods. Assessing the climate change across this glaciation and the following deglaciation interval contribute important data not only in terms of understanding the end-Permian extinction event but also present-day global change. Tasmania, located in a high-latitude setting, forming a bridge between the continents Antarctica and Australia provides a valuable record of the environmental and climatic shifts that occurred in areas proximal to glaciation during the acme and waning stages of the LPIA.

At the time of glaciation, Tasmania was a distinct landmass located within the Paleo-Antarctic Circle at a paleo-latitude of ~78°S. Here we present new high-resolution bulk organic carbon isotope analyses (δ13CTOC), mercury, bulk and trace elemental and sedimentological data combined with palynology and conodont biostratigraphy from the late stage (P3 and P4) of the LPIA Glacial-Deglacial Episode III. We base the data on samples from the Bicheno-5 core, from Eastern Tasmania, which contains approximately 83 meters of middle Permian glaciomarine sediments.

Three negative carbon isotope excursions (CIEs) have been identified in the middle Permian (mPN1, mPN2, and mPN3). The latter two are correlated with the deglaciation episodes in Eastern Australia's glacial intervals P3 and P4 phases. Diamictites and dropstones are typically present in the sediments that record the most positive carbon isotope values, which likely correspond to the peak of the glaciation period. Elemental proxies indicate two cycles of increased weathering and terrestrial sediment influx to the marine system. These cycles coincide with the most negative carbon isotope values and are associated with deglacial cycles in Tasmania and within the paleo-Antarctic circle. The first deglacial cycle (mPN1) coincides with elevated mercury (Hg/TOC) which may hint at a link between deglaciation and volcanism, possibly from the Tarim III LIP.

Comparisons with similar records from the marine Pingdingshan (PDS) section in South China confirms that our data from Tasmania reflect global carbon cycle perturbations providing new insights into the significant global climatic shifts that occurred during the middle Permian. The end stage of the LPIA offers a unique comparison to modern environmental and climatic change in Antarctica associated with anthropogenic global warming.

How to cite: Lestari, W., Al Suwaidi, A., Fox, C., Vajda, V., Ceriani, A., Sun, Y., Frieling, J., and Mather, T.: Unraveling Tasmania's Late Paleozoic Ice Age: Carbon Isotopic and Stratigraphic Signatures in Response to Glacial-Deglacial Cycles and Large Igneous Province (LIP) Events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12015, https://doi.org/10.5194/egusphere-egu24-12015, 2024.

EGU24-12118 | ECS | Orals | GD1.1

Global continental hiatus surfaces as a proxy for tracking dynamic topography since the Upper Jurassic 

Berta Vilacís, Hamish Brown, Sara Carena, Hans-Peter Bunge, Jorge N. Hayek, Ingo L. Stotz, and Anke M. Friedrich

Mantle convection is a fundamental process governing the evolution of our planet. Buoyancies in the mantle induce horizontal and vertical motion of the Earth’s lithosphere, which can be mapped using independent geological datasets. Positive surface deflections induced by mantle convection create erosional/non-depositional environments which lead to gaps (hiatuses) in the stratigraphic record, while negative deflections provide accommodation space for sedimentation to occur. We use continental- and country-scale digital geological maps and regional and local stratigraphic studies at the temporal resolution of geological series (ten to tens of millions of years) to map the distribution of hiatus through geological time.

Here we present global continental hiatus surfaces since the Upper Jurassic. We find that they vary inter-regionally at timescales of geological series and that they correlate with known mantle dynamic events. For example, we tend to observe the appearance of a hiatus surface before the arrival of a mantle plume. In Europe, we mapped a large-scale sedimentary hiatus during the Paleocene, prior to the arrival of the Iceland plume. In Africa and South America, we found a widespread absence of the Upper Jurassic prior to the arrival of the Tristan plume. This pattern can be seen as characteristic of plume-induced dynamic uplift. We observe a sea level signal during some geological series, such as in the Oligocene, when there is a global increase of hiatus areas, coinciding with the onset of Antarctic glaciation and associated sea level drop. At other times, we find that the hiatus areas evolve differently for different continents, precluding their interpretation as an eustatic signal. Spectral analysis shows that hiatus surfaces have shorter wavelengths than no hiatus surfaces, requiring higher spherical harmonic degrees to describe the geological series with larger amounts of hiatus. These include the Upper Jurassic, the Paleocene, the Oligocene and the Pleistocene.

Our results imply that a key property of time-dependent geodynamic Earth models must be a difference in timescale between mantle convection itself and resulting dynamic topography. Moreover, they highlight the importance of continental-scale compilations of geological data to map the temporal evolution of mantle flow beneath the lithosphere, which can provide powerful constraints for global geodynamic models.

How to cite: Vilacís, B., Brown, H., Carena, S., Bunge, H.-P., Hayek, J. N., Stotz, I. L., and Friedrich, A. M.: Global continental hiatus surfaces as a proxy for tracking dynamic topography since the Upper Jurassic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12118, https://doi.org/10.5194/egusphere-egu24-12118, 2024.

While the isostatic compensation of crustal thickness and density heterogeneity provides the dominant contribution to Earth’s observed topography, there nonetheless remains a substantial difference (the ‘residual topography’) between these two fields. This difference is a consequence of dynamic processes occurring within the mantle, most notably due to time-dependent vertical surface stresses driven by mantle convection. Mantle convection dynamics also produce differences between the observed geoid and the isostatic geoid generated by crustal heterogeneity: the ‘residual geoid’. The joint consideration of both residual geoid and topography anomalies provides unique and fundamental global constraints on the amplitude and spatial distribution of density anomalies in the convecting mantle.
Despite the crucial role of isostasy in determining residual geoid and residual topography, accurate constraints depend heavily on the quality of the isostasy calculations. The classical theory of isostasy relies on a 1st-order treatment of hydrostatic equilibrium, which is not sufficiently accurate for the calculation of isostatic geoid anomalies on a compressible, self-gravitating mantle. Consequently, we present a geodynamically consistent approach that is based on the surface loading response (via dynamic kernels) calculated with a viscous flow model that incorporates a fully compressible mantle and core (given by the PREM reference model) with self-gravitation.
Another critical issue that remains outstanding is the accuracy inherent in global crustal heterogeneity models. Here we show that the differences between the residual geoid and topography fields predicted using CRUST1.0 (Laske et al. 2012) and the most recent ECM1 (Mooney et al. 2023) crustal heterogeneity models are substantial. We discuss the importance and implications of these differences in the context of determining the most accurate constraints on density anomalies in the convecting mantle.

How to cite: Kamali Lima, S., Forte, A. M., and Greff, M.: A Geodynamically Consistent Approach to Residual Topography and Geoid Anomalies on the Convecting Mantle: Importance of Global Crustal Models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12457, https://doi.org/10.5194/egusphere-egu24-12457, 2024.

EGU24-13012 | ECS | Orals | GD1.1

Modelling volcano degradation through analogue experiments: the impact of volcano slopes and summit craters on erosion patterns 

Roos M. J. van Wees, Engielle Paguican, Daniel O'Hara, Gabor Kereszturi, Pablo Grosse, Pierre Lahitte, and Matthieu Kervyn

Analogue experiments can enhance our understanding of complex natural volcanic landscapes formed by eruptions, intrusions, remobilisation of volcanic material and erosional processes. Experimental setup in a laboratory offers a controlled setting to investigate the development of rainfall-induced radial drainage basins on scaled volcano cones. It allows to simulate surface runoff, a prominent sediment transport process in volcanic landscapes, primarily influenced by climate, lithology, and topography. By controlling the flowrate within the setup, maintaining a uniform lithology, and using initial axisymmetric cones with the same size, this study aims to record the variations in erosion patterns caused by systematic cone slope and shape changes.

Analogue volcanic cones made up of water-saturated 70 μm silica powder were built upon a drainage layer of coarse sand at the VUB volcanology analogue laboratory. The cones were scaled based on the height/basal width ratios of natural pristine composite volcanoes with a scaling factor of 4.5*10-6 for the basal width. Initial cones had basal widths of 33 cm with two sets of cones with heights ranging from 4.2 to 6.9 cm. For the highest cones, the lower flank was 21 degrees and the upper slope 30 degrees, with a break-in-slope at 45% of the cone height. Experiments included cones with and without summit craters, the craters were 5 cm wide and 0.5 cm deep. Rainfall-induced erosion was simulated with two atomizer sprinklers, creating a mist of droplets of circa 30 μm. Experiments were run for 3 to 5 hours, simulating erosion taking place over several millions of years at natural volcanoes. We generated a minimum of ten Digital Elevation Models (DEMs) by photogrammetry with sub-millimetre spatial resolution, enabling the estimation of volume loss and erosion rates. The automated algorithms MorVolc and DrainageVolc were used to extract morphometric and drainage parameters (e.g., height/basal width ratio, drainage density, irregularity index) from the DEM of each timestep.

The analogue models' drainage networks and morphological characteristics replicate those found on natural volcanoes. Having a steeper slope for the upper flank of the cone delayed the forming of erosional features on the lower flank, while the top part of the volcano incised deeper than the cones with one slope gradient. The cones without a summit crater develop a radial drainage network from an initial set of narrow gullies to a more stable pattern with fewer valleys that gradually widen. The introduction of a summit crater substantially modifies the resulting erosional patterns: the incision of the crater rim forms two to four dominant watersheds that widen faster than the basins of cones lacking a crater. Migration of drainage divides ceases when equilibrium in the landscape is attained, with cones featuring a summit crater reaching this equilibrium later than those without. Analogue experiments are a valuable tool for studying erosional processes in a controlled manner and give insight into complex volcanic landscapes, thereby improving our understanding of long-term volcanic landscape evolution.

How to cite: van Wees, R. M. J., Paguican, E., O'Hara, D., Kereszturi, G., Grosse, P., Lahitte, P., and Kervyn, M.: Modelling volcano degradation through analogue experiments: the impact of volcano slopes and summit craters on erosion patterns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13012, https://doi.org/10.5194/egusphere-egu24-13012, 2024.

Understanding the interaction between oceanic plates and the underlying asthenosphere and its impact on plate thickness is essential for explaining plate motions and mantle convection patterns. While sub-lithospheric small-scale convection provides an explanation for why oceanic plates do not continue to thicken after a certain age, many open questions still surround this process. Here, we link dynamic models of mantle flow, grain-scale processes, seismic imaging, and surface observations to gain new insights into the mechanisms of asthenospheric small-scale convection and its surface expressions.

We have performed a series of high-resolution 3D numerical models of the evolution of oceanic plates and the development of thermal instabilities at their base using the open-source geomodeling software ASPECT. These simulations use an Earth-like rheology that includes coupled diffusion and dislocation creep as well as their interplay with an evolving olivine grain size. Our models quantify how the effective asthenospheric viscosity and the balance between diffusion and dislocation creep affect the morphology and temporal stability of small-scale sub-lithospheric convection, including the age of its onset, the average depth and wavelength of the small-scale convection rolls, and the amplitude of the temperature and grain size anomalies within the rolls.

All of these quantities predicted by the dynamic models can be directly related to both geophysical observables and to surface manifestations such as dynamic topography and heat flux. To accurately compare our model outputs to geophysical data, we convert them to seismic velocity and attenuation using laboratory-derived constitutive relations and taking into account variations in temperature, pressure, grain size, water content and calculated stable melt fraction. We then create synthetic seismic tomography models of different dynamic scenarios and analyze their fit to observations from the Pacific OBS Research into Convecting Asthenosphere (ORCA) experiment. Comparison with both seismic imaging and surface expressions allows us to determine the parameter range in which geodynamic models fit these observations, providing new constraints on the convection patterns and the rheology of the oceanic asthenosphere beneath the Pacific Plate.

How to cite: Dannberg, J., Eilon, Z., Russell, J. B., and Gassmoeller, R.: Sub-Lithospheric Small-Scale Convection as a Window into the Asthenosphere: Insights from Integrating Models Of Mantle Convection, Grain Size Evolution and Seismic Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13895, https://doi.org/10.5194/egusphere-egu24-13895, 2024.

EGU24-15103 | Posters on site | GD1.1

Understanding volcanic edifice erosion and morphologic evolution using numerical models 

Daniel O'Hara, Liran Goren, Benjamin Campforts, Roos van Wees, María Cristina Zarazúa-Carbajal, and Matthieu Kervyn

Volcanic edifices are dynamic landforms whose morphology encodes the long-term (thousands to millions of years) interplay between construction and erosion. Short-term, stochastic episodes of volcanic activity cumulatively build topography, competing with stochastic erosive processes associated with climate and mass wasting to degrade edifices over longer timescales, thus generating a variety of morphologies from simple, cone-like edifices to complex, non-axisymmetric volcanoes. Understanding how these processes interact to shape volcano morphologies over the landform’s lifespan is still in its infancy, especially as construction and erosion are often spatially-heterogeneous and temporally-varying. Despite this, disentangling edifice morphologic histories provide new avenues to better discern an edifice’s volcanic record, assess potential hazards, and quantify the role of climate in landscape evolution.

Numerical modeling has been shown to be a useful approach to exploring long-term landscape evolution. Although the majority of studies have applied landscape evolution models to tectonic settings, modeling has also been applied to simulate erosion and drainage development for specific volcanic features (e.g., channel incision on shield volcanoes, soil diffusion on cinder cones). However, thus far no modeling frameworks have been developed to explore evolution over the full spectrum of edifice types

Here, we investigate volcanic edifice erosion and drainage basin formation using a simplified landscape evolution model. Assuming that the various erosive processes that shape a volcano can be simplified to the competition between advection and diffusion, we use common transport laws (stream power law and linear soil diffusion) to conduct a nondimensional parameter analysis. We then test various parameter combinations to demonstrate the range of morphologic evolutions that can occur over different edifice classifications and environments. Afterwards, we compare our results to previously-derived relationships of natural volcano evolutions to test the ability for simplified models to recreate nature. Finally, we explore the effects of edifice size on the competition between incision- and diffusion-based erosion within the framework of our nondimensional parameters by quantifying drainage development of 156 cinder cones from the Springerville Volcanic Field (AZ, U.S.) and comparing these to both edifice age and planform area.

Our results demonstrate that simplified numerical models are able to recreate the trends observed in nature. Furthermore, we show that the combination of model parameters predicts threshold sizes that volcanic edifices must overcome to begin generating fluvial drainage networks and becoming incised by gullies, broadly inferring parametric thresholds that describe the ratios of erosion processes on these landforms. Our results thus establish a new foundation to study edifice morphologies over several volcano types (cinder cones, shield volcanoes, composite volcanoes) and construction styles (intrusion-driven surface uplift, mantling by lava flows and ash deposits), and provides a basis to test how volcanic environments respond to past and future changes in climate and tectonics.

How to cite: O'Hara, D., Goren, L., Campforts, B., van Wees, R., Zarazúa-Carbajal, M. C., and Kervyn, M.: Understanding volcanic edifice erosion and morphologic evolution using numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15103, https://doi.org/10.5194/egusphere-egu24-15103, 2024.

EGU24-15374 | Orals | GD1.1

A Southern Hemisphere Chronostratigraphic Framework for the Pliensbachian–Toarcian Carbon Cycle Perturbations 

Aisha Al-Suwaidi, Micha Ruhl, David Kemp, Marisa Storm, Stephen Hesselbo, Hugh Jenkyns, Tamsin Mather, Lawrence Percival, and Daniel Condon

Lower Jurassic sedimentary successions from the Neuquén Basin, Argentina are unique in the abundance of radiometrically datable material (ash-beds) present, which can be tied to bio- and chemostratigraphic (carbon-isotope) zonations. Here, we present new U-Pb radio isotopic dates, integrated with carbon-isotope and Hg/TOC data, from three localities in Argentina (Arroyo Lapa, Arroyo Serrucho/Las Overas and Chacay Melehue) to generate a biostratigraphically calibrated composite carbon-isotope curve and geochronological framework for the Pliensbachian–Toarcian transition in South America. Using a Bayesian framework we present an age-depth model for this composite record and estimate the age and duration of key intervals extending from the Latest Pliensbachian carbon isotope excursion (CIE) through the Early Toarcian negative CIE. Using a  statistical analysis of all available Karoo and Ferrar Large Igneous Province (LIP ) U-Pb and Ar-Ar radioisotopic ages we create a timeline of the key events and examine the timing of the carbon cycle perturbations specifically looking at potential links to peaks of extrusive emplacement of the Karoo and Ferrar LIP. The geochronological framework is further compared with other available radioisotopic dates from correlative sections, allowing for a more precise constraint and validation of the timing and duration of these Early Jurassic events.

 

How to cite: Al-Suwaidi, A., Ruhl, M., Kemp, D., Storm, M., Hesselbo, S., Jenkyns, H., Mather, T., Percival, L., and Condon, D.: A Southern Hemisphere Chronostratigraphic Framework for the Pliensbachian–Toarcian Carbon Cycle Perturbations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15374, https://doi.org/10.5194/egusphere-egu24-15374, 2024.

EGU24-15516 | Orals | GD1.1

Uplift and erosion of an intraforeland topographic high: implication for the evolution of the Gondwanian Transantarctic foreland 

Valerio Olivetti, Silvia Cattò, Fabrizio Balsamo, Luca Zurli, Matteo Perotti, Gianluca Cornamusini, Marco Fioraso, Federico Rossetti, and Massimiliano Zattin

The Transantarctic Basin is a continental basin system developed for ca 200 Myr, from the Devonian to the Early Jurassic, along the Panthalassa margin of Gondwana and above the peneplained Ross Orogeny rocks. The Beacon Supergroup strata form the clastic sedimentary infill of the Transantarctic Basin.

Geodynamic interpretation of the Transantarctic Basin is not univocal and likely geodynamic conditions accounting for basin subsidence have been changed in space and time. Involvement of the basin into the Gondwanian orogenic deformation is a key question for defining the geodynamic setting and the tectonic environment during the Beacon Supergroup deposition. Nonetheless, involvement of  Beacon Supergroup  in orogenic shortening is  poorly assessed for the limited exposed rocks and because formation of the Cenozoic  Transantarctic rift shoulder modified the Paleozoic geometry of the Beacon strata.

Here we explored the exhumation pattern and thermal evolution of the basement rocks and the immediately overlain Beacon sandstones through low-temperature apatite fission track and (U-Th)/He zircon thermochronology along the Prince Albert Mts, where Beacon deposits are particularly thin to suppose a relevant erosional event during the Paleozoic. Thermochronological data and thermal modelling pointed out that basement rocks and Beacon sandstones of the Prince Albert Mts have preserved evidence of a Late Paleozoic erosional event that allows to infer an actively eroding topographic high that lasted from Early to Late Paleozoic times, as a consequence of the far-field stress transmitted from the active Gondwanian convergent margin.

How to cite: Olivetti, V., Cattò, S., Balsamo, F., Zurli, L., Perotti, M., Cornamusini, G., Fioraso, M., Rossetti, F., and Zattin, M.: Uplift and erosion of an intraforeland topographic high: implication for the evolution of the Gondwanian Transantarctic foreland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15516, https://doi.org/10.5194/egusphere-egu24-15516, 2024.

EGU24-15687 | Posters on site | GD1.1

The EVoLvE toolkit: a set of methods for systematic quantification of volcano morphometry and their temporal evolution 

Matthieu Kervyn, Roos M.J. van Wees, Pablo Grosse, Pierre Lahitte, and Daniel O'hara

Volcanoes display a wide range of morphologies, resulting from the cumulative imprints of deposition from multiple eruptive events and processes, deformation by intrusive and gravitational processes, as well as erosion throughout the active volcanic phase and beyond. Quantitative documentation of the morphometry of volcanoes offers opportunities to compare volcanic edifices across tectonic regions, define evolutionary trends for volcanoes of different ages and/or stage, or compare natural volcanoes with results from analogue or numerical modelling. Although such morphometric studies exist, the comparability of their results faces challenges related to the contrasted approaches used for delineating volcanic edifices, defining morphometric metrics to characterize volcano sizes, shapes, and erosion patterns, and deriving the pre-erosional volcano volume.

Building upon the MORVOLC (Grosse et al. 2012) and ShapeVolc (Lahitte et al. 2012) algorithms, the EVoLvE project has produced a suite of scripts in MatLab to semi-automatically document the morphometry of stratovolcanoes systematically. First, the manual delineation of a volcano’s base is aided by implementing a slope threshold (suggested to be at 3°) after applying a 300m low-pass filter on the volcano’s topography to identify the prominent volcano landform. Morphometric parameters documenting volcano-scale size, plan-shape, profile shape and slope, as well as metrics derived at regular elevation intervals, following the MORVOLC approach of Grosse et al. (2012), are complemented with a new set of parameters (DrainageVolc) that document the erosion pattern of volcanoes, specifically the drainage density and the geometry of drainage basins. Finally, assuming basins’ divides or local quasi planar surfaces represent the least eroded sections of an edifice, a surface fitting algorithm (ShapeVolc, Lahitte et al. 2012) is used to find the best approximate pre-erosional shape of the volcano,  making it possible to compute its erupted and eroded volumes, and dismantling and degradation rates.

In this contribution, we illustrate how the EVoLvE toolkit can be used to systematically document the morphometry of stratovolcanoes across volcanic arcs, and with contrasted ages to highlight morphological evolution through time. The toolkit can as well be used to compare the morphometry of natural volcanoes with those of synthetic volcanic cones whose erosion is simulated through analogue experiments and numerical landscape evolution models. The Matlab codes of the EVoLvE toolkit are open-source: they aim to contribute to homogenizing the morphometric datasets for volcanoes around the world as a first step towards a more comprehensive understanding of the morphological evolution of volcanoes.

 

References:

Grosse, P., van Wyk de Vries, B., Euillades, P. A., Kervyn, M. & Petrinovic, I. A. 2012: Systematic morphometric characterization of volcanic edifices using digital elevation models. Geomorphology 136, 114-131.

Lahitte, P., Samper, A. & Quidelleur, X. 2012: DEM-based reconstruction of southern Basse-Terre volcanoes (Guadeloupe archipelago, FWI): Contribution to the Lesser Antilles Arc construction rates and magma production. Geomorphology, 136, 148-164.

How to cite: Kervyn, M., van Wees, R. M. J., Grosse, P., Lahitte, P., and O'hara, D.: The EVoLvE toolkit: a set of methods for systematic quantification of volcano morphometry and their temporal evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15687, https://doi.org/10.5194/egusphere-egu24-15687, 2024.

EGU24-15825 | Posters on site | GD1.1

Dynamism of the Neogene and Quaternary erosional processes in the Lesser Antilles volcanoes, constrained by morphometric approaches 

Pierre Lahitte, Louise Bergerot, Pablo Grosse, Roos M. J. van Wees, Daniel O’Hara, and Matthieu Kervyn

Understanding the temporal variations in erosion dynamics is crucial when exploring the intricate relationship between climates and the evolution of landforms. Volcanic surfaces constitute an undeniable asset for documenting temporal variations in erosion dynamics, as they readily reveal the onset of erosion. Indeed, the dating of volcanic materials constrains the age of eruptive activity, volcanic surface formation, and the time since erosion occurred. This study quantifies the Neogene and Quaternary erosional processes that shaped the current Lesser Antilles's volcanic reliefs. We apply morphometric approaches on high-resolution digital topographies of very densely dated volcanoes to discern the influence of factors driving erosion, focusing on climatic context and erosion duration.

The detailed analysis of the erosion signature's evolution was carried out on the French volcanic oceanic arc islands of Basse-Terre (Guadeloupe) and Martinique, thanks to the large number of geochronological constraints (around 100 K-Ar datings on each of them) and the high-resolution topography (LIDAR DEM at horizontal 1m resolution). The meticulous examination of erosion signatures is facilitated because magmatic activity, which produced the same kind of volcanic edifices in both islands, has undergone a spatial migration (westward in Martinique, southward in Basse-Terre). It results in outcrops of terrains spanning vastly different ages (0-3 and 0-25 Ma, respectively), providing a unique opportunity to investigate the distinct influences of geological processes on erosion signature. The study focuses on quantitative analysis of river-long profiles by scaling river profile concavity, hypsometric indexes and knickpoints, which are noticeable slope breaks or abrupt changes in the gradient of the river channel. Thanks to the dense geochronological database, metrics computed for each geomorphological feature can be associated with the age of formation of the local volcanic surface. Then, as these ages are relevant to the cumulated erosion process occurring since the end of the volcanic activity, such metrics can be correlated to the time and evolution trends in morphometric parameters can be investigated.

The 25 Ma-long erosion history of Martinique Island reveals two distinct patterns. During the initial 5 million years of erosion, there is a rapid increase in river concavities and a decrease in the intensity and number of heterogeneities along river profiles, resulting in smoother stream patterns. In contrast, over the 5-25 Ma erosion period, every river's morphometric parameters evolve slowly, suggesting a preservation of river concavity. This transition phase in concavity evolution could mark the moment when the rivers’ incision, driven by regressive erosion and carving into the volcano from every side, having finally affected the summit area, also reached a maximum concavity. Erosive processes then reduced the volcano's elevation but maintained a relatively uniform profile shape and, consequently, concavity over time. Despite Basse-Terre Island's shorter erosion history of 3 million years, morphometric parameters testify that this island experienced strictly similar evolution as Martinique Island during the same erosion lifespan, suggesting a comparable evolution of the Basse-Terre reliefs in the future.

How to cite: Lahitte, P., Bergerot, L., Grosse, P., van Wees, R. M. J., O’Hara, D., and Kervyn, M.: Dynamism of the Neogene and Quaternary erosional processes in the Lesser Antilles volcanoes, constrained by morphometric approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15825, https://doi.org/10.5194/egusphere-egu24-15825, 2024.

EGU24-16531 | ECS | Orals | GD1.1

Exploring the structure of the Cascadia Subduction Zone by coupling 3D thermomechanical modeling and CPO evolution with observations. 

Menno Fraters, Magali Billen, John Naliboff, Lydia Staisch, and Janet Watt

The Cascadia Subduction Zone is characterized by young subducting lithosphere, its isolation from other subducting systems, and its ability to produce megathrust earthquakes (M>9.0) and devastating tsunamis. Due to its high potential hazard and risk, it is also a well-studied subduction zone where modern, diverse and detailed observational datasets are available through the USGS and initiatives like GeoPrisms and EarthScope. These datasets include high quality GPS, onshore and offshore geophysical imaging, geochemical and seismic anisotropy data. Integrating these data sets with geodynamic modeling presents an opportunity to gain insight into outstanding questions regarding slab structure, tectonic evolution, seismic hazards, and the physical processes that can self-consistently explain all these observations. For example, geologic and geophysical data suggest that there may be one or two prominent slab gaps or tears, while tomographic data does not fully constrain the depth extent of the slab. Furthermore, the overriding plate is composed of different terranes and contains numerous active and slowly moving faults, complicating efforts to accurately constrain variations in present-day stress and deformation rates.

In this study we test whether comparison of observations to geodynamic model predictions can distinguish between different slab geometries for the Cascadia Subduction Zone. To this end, we have created regional 3D geodynamic models of Cascadia including the slab based on the Slab 2.0 dataset. The model setup is built with the Geodynamic World Builder, and the models are run with the geodynamics code ASPECT. We present results which compare the Juan de Fuca plate velocities against the present day Euler poles. We have found that matching the plate velocity magnitude and direction is sensitive to the rheological model overall, while at the same time being insensitive to certain aspects of the plate boundary rheologies. During the evolution of these models we track the development of the CPO (Crystal Preferred Orientation) with an implementation of the DREX algorithm, so we can compare it against observations of seismic anisotropy in the region. Our presentation will focus on the importance of the geometry of the slab and the strength of different sections of the interface. Furthermore, these models and demonstrate workflows for linking the model results to surface tectonics.

How to cite: Fraters, M., Billen, M., Naliboff, J., Staisch, L., and Watt, J.: Exploring the structure of the Cascadia Subduction Zone by coupling 3D thermomechanical modeling and CPO evolution with observations., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16531, https://doi.org/10.5194/egusphere-egu24-16531, 2024.

EGU24-17475 | ECS | Posters on site | GD1.1

Surface regimes can provide an inherent perspective into interior dynamics 

Oliver Henke-Seemann and Lena Noack

Tectonic processes shape the Earth's lithosphere and surface. Deformation, as a result of tectonic forcings, arises mainly in the regions of plate boundaries. A recurring process is the subduction of oceanic lithosphere, which is widely regarded as the main driver of plate tectonics and the recycling of surface material into the mantle. In geodynamic models, the breaking of the strong crust is facilitated by processes that mimic plastic deformation. Most efforts to include plate tectonics self-consistently into mantle convection models, combine Newtonian diffusion creep with a stress-dependent pseudo-plastic rheology, given in the form of a yield criterion. Studies from seismology and geodynamic modelling indicate that cold lithospheric crust can reach the lowermost mantle regions, even the core-mantle-boundary. Additionally, the agglomeration of continental lithosphere (the most extreme variants of which are called supercontinents) inhibits the escape of heat over large surface areas, resulting in an abnormally heated mantle beneath. Therefore, it can be argued, that surface processes exert control on mantle dynamics as a whole, by introducing thermal and compositional heterogeneities.

An example of the influence of surface tectonics on the interior can be found in the study of the Earth's geodynamo. Theoretical considerations and numerical models indicate, that the heat flux at the core-mantle boundary partly governs the variability of the geodynamo, and therefore the frequency of geomagnetic reversals and excursions. 

We run several numerical mantle convection simulations in a 2D-spherical annulus geometry, with a visco-plastic rheology to facilitate surface mobilisation. The models are evaluated with respect to well-known diagnostic values, used to recognise plate-like surface deformation, as well as the thermal structure of the lower mantle. In this, we aim to connect tectonic regimes or continental configurations that arise dynamically at the surface, to evolutionary trends in the mantles thermal structure.

How to cite: Henke-Seemann, O. and Noack, L.: Surface regimes can provide an inherent perspective into interior dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17475, https://doi.org/10.5194/egusphere-egu24-17475, 2024.

EGU24-18172 | Orals | GD1.1

On the different contributions to the peculiar topography of the Iberian Peninsula 

Ana M. Negredo, Javier Fullea, Olga Ortega-Gelabert, Carlos Clemente, and Julien Babault

The topography of the Iberian Meseta located between the Pyrenees-Cantabrian Mountains and the Betics Chain is moderately high (660 m on average) compared to the high plateaus on Earth (> 1 km) albeit higher than the topography of the surrounding western European plate. The Iberian Meseta encompasses Cenozoic sedimentary basins, active or inactive Alpine mountain ranges, and low-relief erosional surfaces represented by plateaus with elevations between 600 and 1400 m asl. It is commonly accepted that ~600-700 m surface uplift occurred during the Cenozoic, but the underlaying processes and the precise timing of the onset of the plateau growth are strongly debated. The main objective of the present study is to find out to what extent the topography of the Iberian Meseta has a crustal, lithospheric or a sublithospheric origin. We used the results of a recent modelling based on the joint inversion of both the crustal and lithospheric mantle structure. It encompasses an integrated geophysical-lithological multi-data modelling. The inversion is framed within an integrated geophysical-petrological setting where mantle seismic velocities and densities are computed as a function of temperature and composition whereas crustal density, shear and compressional wave velocities are lithologically linked based on empirical relationships from global petrophysical databases.

We computed the relative contribution to topography of crustal and lithospheric mantle thickness variations and density structure. The topography of the Alpine mountain belts in Iberia is largely associated with thickened crust. We find that the elevated topography in the NW Iberian Meseta (elevation > 700 m) is mostly related to the lithospheric mantle thinning. This is in agreement with Inversion of topographic data, landform dates, and erosion rates suggesting a late Cenozoic mantle-related surface uplift of several hundreds of meters in NW Iberia (EGU24-11613) and in the central Iberia (EGU24-16382). Similarly, a thin and warm lithospheric mantle is responsible for the positive elevation of the onshore Mediterranean margins. A negatively buoyant lithospheric mantle causes >1 km subsidence in the Gibraltar Arc and western Pyrenees.  We solved the Stokes flow to evaluate the contribution of temperature-related buoyancy forces at asthenospheric depths. These forces cause a long wavelength topographic response located in the centre of the Iberian Peninsula reaching a maximum value of only 100-150 m, which is much lower than the values reported in previous works assuming an isostatic balance.

How to cite: Negredo, A. M., Fullea, J., Ortega-Gelabert, O., Clemente, C., and Babault, J.: On the different contributions to the peculiar topography of the Iberian Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18172, https://doi.org/10.5194/egusphere-egu24-18172, 2024.

EGU24-18291 | ECS | Posters on site | GD1.1

Lava tubes formation and extensive flow field development during the 1858 eruption of Mount Vesuvius.  

Thomas Lemaire, Daniele Morgavi, Paola Petrosino, Sonia Calvari, Leopoldo Repola, Lorenzo Esposito, Diego Di Martire, and Vincenzo Morra

Lava tubes are an important transport mechanism in active lava flows. Their presence in a lava flow can influence its distance of emplacement due to the insulation of the hot molten lava by a cooled overlying crust. Understanding mechanisms of formation and development of lava tubes is fundamental to comprehend lava flow propagation and improve knowledge to better manage the hazard during a volcanic crisis. Vesuvius is known for its major explosive eruptions; however, in its history it underwent extensive periods of open conduit, with prolonged explosive activity and lava flows. After the 1631 eruption, Vesuvius entered an effusive period that ended with the 1944 eruption. During these 313 years, over one hundred lava flows emplaced on Vesuvius flanks, particularly the 1858 eruption which produced a compound pahoehoe lava flow that emplaced on the western flank of Vesuvius. 

In this study, we conducted: (1) a temporal and spatial reconstruction of the 1858 lava flow using historical documents (geological maps, paintings, descriptions of eruptions), (2) a morphological and surficial analysis of the 1858 lava flow as well as the definition of new contours based on geological maps and digital elevation models and (3) a complete morphological analysis of the lava tube using high-end technologies (time-of-flight terrestrial laser scanner, Lidar equipped drone and optical cameras).  

On the 1858 lava flow field surface we found numerous tumuli and ephemeral vents. We discovered a small lava tube present in a flat area of the lava flow field (<3°) with ropy to slabby pahoehoe surface lavas. The lava tube is oriented north-south, perpendicular to the main flow direction. It is triangularly shaped with a length of 30.05 meters and a width that varies from 1.20 to 17.61 meters from the northern to the southern part. The average height is around 2 meters. The slope along the flow direction is on average 4.48°. We measured a mean roof thickness of 2.4 meters. The roof is fractured and has collapsed in different areas of the lava tube. Inside, we observed features that relate to the temporal evolution of the lava tube. Stalactites are present on the ceiling of the tube suggesting a prolonged flow of lava within the tube. Multiple layers of lava are covering the wall of the lava tube, the last wall lining is five to seven centimeters thick and, in some areas of the lava tube, has detached from the wall and rolled down on itself, testifying to a sudden drainage of the lava tube when the lining was still plastic.  

The results of the study of the 1858 lava flow field and of its lava tube are essential for expanding our knowledge about the processes at the basis of lava flow field emplacement and development on Vesuvius and the first attempt focused on understanding effusive dynamics governed by lava tube formation (i.e., lava emplacement) at Vesuvius.

How to cite: Lemaire, T., Morgavi, D., Petrosino, P., Calvari, S., Repola, L., Esposito, L., Di Martire, D., and Morra, V.: Lava tubes formation and extensive flow field development during the 1858 eruption of Mount Vesuvius. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18291, https://doi.org/10.5194/egusphere-egu24-18291, 2024.

Gondwana Basins of eastern India preserves sediment record from Carboniferous to Triassic, which were possibly sourced partially from Antarctica through a radial drainage system. This study attempts to test the hypothesis regarding source of sediments based on petrographical and mineral chemical analysis of siliciclastic Paleo-Mesozoic sediments of eastern India. We present an integrated provenance and paleodrainage analysis on the sediments of Bokaro and Raniganj basins, outcrops of which occur along E-W trend along eastern part of India. The sedimentation in these Gondwana basins initiates with basal Talchir Formation, consisting of alternation between conglomerate and fine- to medium-grained sandstones, and is succeeded by Barakar-Barren Measures-Raniganj and Panchet Formation with sandstone-mudstone alternation, with or without coal.  Petrographic study of sandstones reveals moderate sorting, with angular to sub-rounded quartz and feldspar and rounded to well-rounded lithic fragments; however, the abundance of lithic fragments drastically reduces from Talchir to Panchet formation. Feldspar grains shows the dominance of K-feldspar over plagioclase.  Most of the sandstones are classified as feldspatho-quartzose arenite. The Qm-F-Lt plot indicates that these sandstones were derived primarily from transitional continental sources. Heavy minerals in sandstones include garnets, tourmaline, epidote, rutile, zircon, monazite in order of decreasing abundance. Mineral chemistry of garnet in sandstones points their source to metasedimentary amphibolite facies rocks and granitoid. The tourmaline mineral chemistry suggests the derivation of sediments from various sources, including Li-poor granitoids associated with pegmatites, aplites and Ca-poor metapelites. Rutile chemistry in sandstones indicates the predominance of metapelitic source over metamafic source. Insights from heavy mineral analysis indicates that the Gondwana sediments were derived from multiple sources, and such variation in sources bears information about paleogeographic and paleotectonic evolution of the depositional basin.  The mineral composition of source rocks and paleocurrent data tracks the source of sediments to Eastern Granulite-Schist belt and the Eastern Ghat mobile belt, situated to the east and southwest parts of the Gondwana succession.  This study when integrated with geochronological data would reveal the extent to which a particular source provided sediments to these basins, evolution of sediment sources from bottom to top and ultimately will lead to a refined understanding of timing and evolution of East Gondwana assembly.

How to cite: Dutta, A. and Banerjee, S.: Facies Analysis, Petrography, heavy mineral analysis of paleo-Mesozoic sediments of Eastern India: Implications on provenance and basin evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18433, https://doi.org/10.5194/egusphere-egu24-18433, 2024.

EGU24-18733 | Orals | GD1.1

The uplift of East Africa-Arabia swell: the signature of the mantle upwelling and spreading 

Andrea Sembroni, Claudio Faccenna, Thorsten W. Becker, and Paola Molin

The East Africa - Arabia topographic swell is an anomalously high-elevation region of ~4000 km long (from southern Ethiopia to Jordan) and ~1500 km wide (from Egypt to Saudi Arabia) extent. The swell is dissected by the Main Ethiopian, Red Sea, and Gulf of Aden rifts, and characterized by widespread basaltic volcanic deposits emplaced from the Eocene to the present. Although most agree that mantle plumes play a role in generating the swell, several issues including the number and locations of plumes and the uplift signatures remain debated. We seek to address these questions and provide a general evolutionary model of the region. To this end, we conduct a quantitative analysis of topography to infer isostatic and dynamic contributions. When interpreted jointly with geological data including volcanic deposits, the constraints imply causation by a single process which shaped the past and present topography of the study area: the upwelling of the Afar superplume. Once hot mantle material reached the base of the lithosphere below the Horn of Africa during the Late Eocene, the plume flowed laterally toward the Levant area guided by pre-existing discontinuities in the Early Miocene. Plume material reached the Anatolian Plateau in the Late Miocene after slab break-off and the consequent formation of a slab window. During plume material advance, buoyancy forces led to the formation of the topographic swell and tilting of the Arabia Peninsula. The persistence of mantle support beneath the study area for tens of million years also affected the formation and evolution of the Nile and Euphrates-Tigris fluvial networks. Subsequently, surface processes, tectonics, and volcanism partly modified the initial topography and shaped the present-day landscape.

How to cite: Sembroni, A., Faccenna, C., Becker, T. W., and Molin, P.: The uplift of East Africa-Arabia swell: the signature of the mantle upwelling and spreading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18733, https://doi.org/10.5194/egusphere-egu24-18733, 2024.

EGU24-20357 | ECS | Posters on site | GD1.1

A newly discovered youngermost (13.07 Ma) “Upper Tuff”, a large-volume phreatomagmatic ignimbrite in the Pannonian Basin, drapes the present, faulted/dissected topography  

Tamás Biró, Pierre Lahitte, Maxim Portnyagin, Emő Márton, Emőke Mohr, Márton Palotai, Sándor Józsa, Levente Iván, Márton Krasznai, Mátyás Hencz, Jean-Louis Paquette, János Hír, Fanni Vörös, and Dávid Karátson

Silicic ignimbrite volcanism played a major role in the Miocene evolution of the Central Paratethys. The most voluminuous ignimbrites identified to date (18.1–14.4 Ma) were emplaced in various paleoenvironments in the North Pannonian Basin, thus they are extremely helpful in regional stratigraphy. Here, we present the discovery of a previously unknown but widespread, youngest member of the “Upper Rhyolite Tuff“, referred to as Dobi Ignimbrite, which shows a distinctive glass geochemistry. High-precision sanidine and plagioclase Ar-Ar dating yielded 13.066±0.019 Ma (earliest Sarmatian stage in Paratethys chronology), significantly shifting the previously claimed termination (i.e. Badenian) of the North Pannonian ignimbrite flare-up. In addition, we demonstrate that, although the Dobi Ignimbrite is underlain by a marine sedimentary succession, it was emplaced on land, as it bears leaves and tree trunk fragments and is rich in charcoal. Despite the highly faulted terrain as well as intense dissection and erosion controlled by the neotectonic evolution of the Pannonian Basin, the observed areal extent (c. 1000 km2) and calculated minimum volume (c. 50 km3) of the ignimbrite may represent a VEI= 6 or 7 eruption, which needs to be further delineated. At the same time, the ignimbrite has a strongly phreatomagmatic character, suggesting an abundant, possibly shallow sea- or residual lake water source that was likely limited to the vent area (e.g. caldera graben). The detected sharp environmental change from submarine to terrestrial, as defined by the timing of ignimbrite emplacement at c. 13 Ma, marks the latest Badenian regressive period, followed by a Sarmatian erosion during the Central Paratethethys evolution.

 

How to cite: Biró, T., Lahitte, P., Portnyagin, M., Márton, E., Mohr, E., Palotai, M., Józsa, S., Iván, L., Krasznai, M., Hencz, M., Paquette, J.-L., Hír, J., Vörös, F., and Karátson, D.: A newly discovered youngermost (13.07 Ma) “Upper Tuff”, a large-volume phreatomagmatic ignimbrite in the Pannonian Basin, drapes the present, faulted/dissected topography , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20357, https://doi.org/10.5194/egusphere-egu24-20357, 2024.

Four monogenetic volcanoes were formed during the last 100 ka (Late Pleistocene), west of the city of Morelia (Mexico), in the central-eastern part of the Michoacán-Guanajuato Volcanic Field, located in the central region of the Trans-Mexican Volcanic Belt. These include four scoria cones (Melón, Mina, Tzinzimacato Grande, and Tzinzimacato Chico) and some lava flow deposits associated with the material emitted during the effusive phase of the volcanoes. From the study of stratigraphic relationships in the field and geological mapping, the eruptive chronology of the monogenetic volcanoes was determined. Subsequently, based on the analysis of the morphological (flow dimensions) and petrographic characteristics, the eruptive parameters (effusion rate and emplacement time) and the rheology of the lavas were estimated. The flow units of the effusive phase of the volcanoes present different morphological and mineralogical characteristics. The flows with greater slopes have average viscosities of 2.7x108 P and a higher volume content of phenocrysts; the value of this property decreases in the flows with lower slopes, 1.7x108 P as respectively. The results indicate that the most voluminous eruption corresponds to that emitted by the Mina volcano, with an effusion rate of 2.3 m3/s and a total duration of 239 days. The Tzinzimacato Chico volcano emitted a smaller volume of lava during its eruption, with an effusion rate of 0.9 m3/s and a total duration of 117 days, which is considered the most recent.

How to cite: Delgado Granados, H. and Hernández Villamizar, D.: Eruptive parameters of volcanoes Melón, Mina, Tzinzimacato Grande, Tzinzimacato Chico (Mexico) from morphology and petrographic studies , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20487, https://doi.org/10.5194/egusphere-egu24-20487, 2024.

EGU24-21095 | Posters on site | GD1.1

Evolution and Growth of Lava Deltas: Insights from the 2021 La Palma Eruption (Canary Islands) 

Lucía Sáez-Gabarrón, David Sanz-Mangas, Inés Galindo-Jiménez, Juana Vegas, Juan Carlos García-Davalillo, Mario Hernández, Raúl Pérez-López, Carlos Camuñas, Gonzalo Lozano, Carlos Lorenzo Carnicero, Miguel Ángel Rodríguez-Pascua, Maria Ángeles Perucha, Julio López Gutiérrez, and Nieves Sánchez

During the 2021 eruption on La Palma Island, the predominant volcanic hazard was lava flows, while tephra fall and gas emission were significant concerns. Consequently, monitoring the expansion of the lava flow perimeter considering the variations in volcanic activity became fundamental. The interaction of lava with the sea water was also a major concern for emergency managers due to its associated hazards like gas emission and explosive activity due to interaction lava-water, leading to a specific focus on the formation and development of lava deltas.

Almost 10 days after the beginning of the eruption, the lava reached the sea, forming a main structure (south delta) that grew in different phases until nearly the end of the eruption, covering an area of approximately 83 ha. The south delta encroached upon the sea and additionally buried the northern part of a pre-existing lava delta from the 1949 San Juan eruption. About 1300 m from the northernmost tip of the south delta, a new lava flow entry to the sea occurred 64 days into the eruption, feeding a second lava delta (north delta) of about 5 ha over a 4-day period.

This study has made significant technical and scientific contributions, not only during the emergency but also in preparation for future recovery efforts on La Palma. Remotely Pilot Aircrafts (RPAs) provided valuable information about the lava-flow development and enhanced a deeper understanding of the formation and evolution of lava deltas and their potential hazards. Moreover, the study highlights the potential impact on new inhabited or economically exploited areas and is imperative its preservation for the geological heritage, including marine zones. Furthermore, it will play a crucial role in forecasting the behaviour of lava deltas and in the development of mitigation measures for potential future eruptions.

How to cite: Sáez-Gabarrón, L., Sanz-Mangas, D., Galindo-Jiménez, I., Vegas, J., García-Davalillo, J. C., Hernández, M., Pérez-López, R., Camuñas, C., Lozano, G., Lorenzo Carnicero, C., Rodríguez-Pascua, M. Á., Perucha, M. Á., López Gutiérrez, J., and Sánchez, N.: Evolution and Growth of Lava Deltas: Insights from the 2021 La Palma Eruption (Canary Islands), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21095, https://doi.org/10.5194/egusphere-egu24-21095, 2024.

EGU24-21597 | ECS | Orals | GD1.1 | Highlight

The Chon Aike magmatic province: an active margin origin?

Joaquin Bastias-Silva, Richard Spikings, Teal Riley, and Jorge Sanhueza

EGU24-21895 | Orals | GD1.1 | Highlight

Closed loop experiments in global geodynamic earth models 

Hans-Peter Bunge, Ingo L. Stotz, Nicolas Hayek, berta vilacis, hamish brown, roman freissler, bernhard schuberth, sara carena, and anke friedrich

Recent advances in computational capabilities make it possible to compute global geodynamic earth models at near earthlike convective vigor. This paves the way to systematically obtain a range of synthetic data from such models in an approach that is known as closed loop experiments. Here we present results from closed loop experiments in geodynamic earth models targeted at three classes of data that are sensitive to the mantle convection process, namely seismic data, global stress patterns as reflected by the world stress map, and continent scale stratigraphy processed for the distribution of conformable and unconformable successions in recently developed so called hiatus maps. Our results reveal effects from spatially variable data collection and quality (as expected), mantle flow geometries (less expected) and (still poorly known) histories of paleo mantle flow. We conclude that the derivation of process based synthetic data from geodynamic earth models provides crucial information for data interpretion, that closed loop experiments are
a powerful tool to link geodynamic earth models to data, and that closed loop experiments could be helpful to guide future data collection efforts.

How to cite: Bunge, H.-P., Stotz, I. L., Hayek, N., vilacis, B., brown, H., freissler, R., schuberth, B., carena, S., and friedrich, A.: Closed loop experiments in global geodynamic earth models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21895, https://doi.org/10.5194/egusphere-egu24-21895, 2024.

EGU24-22053 | ECS | Posters on site | GD1.1

Revisiting tectonic models for the evolution of the Ellsworth Mountains in Antarctica: A key component for understanding the African-Antarctic section of the paleo-Pacific margin

Paula Castillo, Fernando Poblete, Rodrigo Fernández, Joaquín Bastias-Silva, C. Mark Fanning, Teal Riley, Jaime Cataldo Bacho, Ellen Rosemann, Cristóbal Ramírez de Arellano, and Katja Deckart

EGU24-473 | ECS | Orals | GD1.2

Deep plumbing model of the Cenozoic Manzaz / Atakor intraplate volcanic system, Central Hoggar, Northwest Africa, based on electrical resistivity models 

Zakaria Boukhalfa, Matthew J. Comeau, Amel Benhallou, Abderrezak Bouzid, and Abderrahmane Bendaoud

Continental intraplate volcanic systems, with their location far from plate tectonic boundaries, are not well understood: the crustal and lithospheric mantle structure of these systems remain enigmatic and there is no consensus on the mechanisms that cause melt generation and ascent. The Cenozoic saw the development of numerous volcanic provinces on the African plate. This includes the Hoggar volcanic province, located in Northwest Africa, part of the Tuareg shield. It is composed of several massifs with contrasting ages and eruptive styles. The magmatic activity began at around 34 Ma and continued throughout the Neogene-Quaternary. Phonolite and trachyte domes as well as scoria cones and necks are found in the Manzaz and Atakor volcanic districts. In order to image the crustal and lithospheric mantle structure of this region, and to understand the origins and potential mechanisms of the continental intraplate volcanic activity in the Central Hoggar and specifically the Atakor/Manzaz area, we acquired magnetotelluric (MT) measurements from 40 locations and generated a 3-D electrical resistivity model. The model covers an area of about 100 km by 200 km. Images of the subsurface architecture, in terms of electrical resistivity, from the near-surface to the lithospheric mantle, allow us image the deep plumbing system of the volcanic system. Low resistivity features (i.e., conductors) in the crust that are narrow, linear structures trending approximately north-south, are revealed along the two boundaries of the Azrou N’Fad terrane, in the Manzaz area. They likely reflect the Pan-African mega-shear zones, which were reactivated throughout the tectonic evolution of the region. The model reveals that these faults are lithospheric-scale. In addition, the low-resistivity features likely represent the signatures of past fluid flow. The location of the recent Cenozoic volcanic activity was likely influenced by the pre-existing structure. A deep feature of moderate conductivity is located in the upper lithospheric mantle directly beneath the Manzaz and Atakor Volcanic Districts. It may represent the origin of the overlying anomalies and may suggest metasomatism of the sub-continental lithospheric mantle.

Keywords:  intraplate, Hoggar, alkaline volcanism, magnetotelluric, electrical resistivity.

How to cite: Boukhalfa, Z., J. Comeau, M., Benhallou, A., Bouzid, A., and Bendaoud, A.: Deep plumbing model of the Cenozoic Manzaz / Atakor intraplate volcanic system, Central Hoggar, Northwest Africa, based on electrical resistivity models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-473, https://doi.org/10.5194/egusphere-egu24-473, 2024.

EGU24-1021 | ECS | Posters on site | GD1.2

Geochemistry and geochronology of the High Arctic Large Igneous Province on Svalbard 

Anna Marie Rose Sartell, Christoph Beier, Ulf Söderlund, Kim Senger, Grace E. Shephard, Hans Jørgen-Kjøll, and Olivier Galland

Large Igneous Provinces are defined as magmatic provinces with large magma volumes (> 100,000 km3) emplaced and/or erupted in an intraplate tectonic setting over a vast area within a few Myr, thus having the potential for significant impact on the global climate. The High Arctic Large Igneous Province (HALIP) was emplaced during the Cretaceous. The available ages, ranging between ~140 and 80 Ma, suggests that the magmatism was apparently long-lived and multi-phase. Extrusive and intrusive remnants of the HALIP can be found across the circum-Arctic, specifically in Arctic Canada, Russia, Svalbard, Northern Greenland, and the Arctic Ocean. On Svalbard, the HALIP magmatism is regionally called the Diabasodden Suite. Here, the dolerites have mainly been emplaced as sills at shallow depths and occur all over the archipelago. Despite the relative accessibility of outcrops, the HALIP on Svalbard has been mostly unexplored. As such, available U-Pb geochronology of the Diabasodden Suite is limited, but indicates a shorter time span of 125 – 122 Ma.

Yearly field campaigns since 2020 have resulted in over 150 collected samples from Spitsbergen and Nordaustlandet. This has been accomplished through a collaborative effort, and by strategically targeting outcrops to build a good representative dataset of the Diabasodden Suite. Additionally, a large number of samples have also been taken for a detailed case-study in central Spitsbergen. The dolerite samples are used for whole-rock major and trace element geochemical analysis, U-Pb baddeleyite geochronology and petrological studies. Furthermore, during all field campaigns, high-resolution drone images have also been acquired. These data form the basis for digital outcrop models (DOMs), which are used for thickness measurements of the sills and to put the geochemical data into a 3D perspective. The resulting DOMs are made openly available through the geoscientific database of Svalbard, SvalBox.

Here we present a review of the available geochronology of the HALIP in the circum-Arctic, as well as new data from Svalbard. Specifically, new U-Pb baddeleyite ages of one mafic sill in northern Isfjorden, and an extensive dataset of whole-rock geochemical data from the HALIP on Svalbard to better understand the magmatic history of the HALIP as a whole.

How to cite: Sartell, A. M. R., Beier, C., Söderlund, U., Senger, K., Shephard, G. E., Jørgen-Kjøll, H., and Galland, O.: Geochemistry and geochronology of the High Arctic Large Igneous Province on Svalbard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1021, https://doi.org/10.5194/egusphere-egu24-1021, 2024.

The origin of intraplate magmatism is debated, with two main hypotheses having been proposed. These are deep-seated high-temperature sources (plumes), and  intraplate extension driven ultimately by plate tectonics. A test region in this debate is the 'Jurassic Corridor,' a geological feature proposed to span North America, which contains igneous rocks including kimberlites that are attributed to the Great Meteor Hotspot (GMH). Despite longstanding assumption of this model, close inspection using modern, much-expanded geological information sets shows that the existence of a Jurassic Corridor and GMH lacks support. In this paper we reassess the distribution of kimberlites in North America and on neighboring landmasses. We demonstrate the lack of a clear Jurassic Corridor and show instead that the kimberlites and related rocks are more likely linked to the breakup of the Pangaean Supercontinent and controlled by lithospheric structures. Furthermore, by comparing these findings with global plate models for the last 300 Myr we identify three prominent age peaks in North American kimberlite occurrence that broadly align with periods of heightened plate velocity with respect to Africa. Additionally, the analysis reveals in Africa two peaks in kimberlite abundance and two velocity peaks with respect to North America. Here, however, the velocity peaks occurred approximately 20-30 Myr before the kimberlite abundance peaks. These observations underscore the significance of plate kinematics in controlling kimberlite magmatism and add to a growing body of work linking periods of tectonic upheaval to kimberlite production. The implications of this extend to our broader understanding of intraplate magmatism and warrant a global revaluation of similar phenomena.

How to cite: Peace, A. and Foulger, G.: Beyond the Jurassic Corridor: Exploring North American Kimberlites and their relationship to plate tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1799, https://doi.org/10.5194/egusphere-egu24-1799, 2024.

EGU24-3168 | ECS | Orals | GD1.2

Oceanic remnants in the mantle of the Parana Basin, Central South Atlantic: supporting the large-scale geochemical anomaly in the Northern Parana-Etendeka LIP 

Luizemara Szameitat, Monica Heilbron, Alessandra Bongiolo, Otavio Licht, Maria Alice Aragão, and Francisco Ferreira

The Parana Basin is one of the larger continental Paleozoic basin in Central South America. Although several studies investigated the flooring mantle of the Parana Basin, mantle-scale oceanic relicts have not been interpreted by previous regional geophysical studies. For this work, we used the global-scale tomographic model of P-wave velocity perturbation UU-P07 for mapping slab-like anomalies, and qualitative gravity and magnetic anomalies for indicating orogenic trends. Positive P-wave anomalies were mapped along fifty-two profiles, and revealed slab-like anomalies (long and segmented tabular mantle bodies), and four top slab surfaces (S1, S2, S3 and S4). The biggest anomalous mantle body (top surface S1) is transversal to the central-southern Brasilia Belt trending, and therefore it can be directly linked to the Southern São Francisco craton. However, the other three slab-like tabular bodies cannot be linked to outcropping orogenic trends, due to the extensive and thick sedimentary cover of the Parana Basin. Southwestern São Francisco Craton, elongated bodies coincide with Brazilian/Pan-African island arc collisions (top surface S2), but other possible slabs (top surfaces S3 and S4) are underneath Paraná Basin. Positive anomalies in the residual geoid anomalies (XGM2019e_2159 model) and transformed total magnetic field (vertical integration) follow the possible accretionary trend formed by S2, S3 and S4. Although the assumptions about the origin of these slab-like anomalies need to be investigated further, all these observations have shown the high complexity of the upper mantle beneath Parana floods. Facing the geophysical anomalies, we realize that the mapped slab-like bodies are mostly located under the Central-Northern Parana Basin, where several studies interpreted the existence of remnants of Proterozoic subductions in the mantle. Previous geochemical analysis had linked the high-Ti domain in the Central-Northern Parana floods with the partial melting of oceanic subduction relics. Nonetheless, the abundance of other incompatible elements (e.g., P, F and B) in the early phase of Central-Northern basaltic floods can be inherited from subduction remnants in the mantle. The remarkable early enrichment contrasts with the primitive mantle affinity in tholeiitic magmas of the relative late northern floods of the Parana Basin, the southern floods of the Parana Basin, the Etendeka counterpart, and the continental margins. In agreement with the previous understanding of the chemical evolution, we consider that the early magmatic phase was highly influenced by subcontinental subduction relicts. On the other hand, the advancing lithospheric embrittlement, due to the Atlantic opening process, intensified the rise of primitive fluids. Therefore, geophysical observations support the hypothesis of the existence of oceanic remnants from oceanic closure southern São Francisco Craton, due to the Western Gondwana’s assembly. The location of highly preserved oceanic-like mantle bodies supports the occurrence of enriched magmas in the early magmatic phase of the Northern Parana-Etendeka LIP.

How to cite: Szameitat, L., Heilbron, M., Bongiolo, A., Licht, O., Aragão, M. A., and Ferreira, F.: Oceanic remnants in the mantle of the Parana Basin, Central South Atlantic: supporting the large-scale geochemical anomaly in the Northern Parana-Etendeka LIP, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3168, https://doi.org/10.5194/egusphere-egu24-3168, 2024.

EGU24-4616 | Orals | GD1.2

Understanding Seamount Genesis: Utilizing Gaussian Process Regression and Clustering for Morphological Analysis 

Yanghui Zhao, Bryan Riel, Hanghang Ding, and Dazhen Deng

Seamounts are theorized to originate from deep mantle plumes or shallow, plate-related activities. The mantle plume hypothesis suggests that abnormally hot materials rise from the lowermost mantle and produce large volumes of volcanism on the surface. However, the accuracy of morphological analysis and volume estimation is highly influenced by the representation accuracy of irregularly shaped seamounts and the extent to which thick sediment coverage obscures their bases. As a result, the precise contribution of magma from mantle plumes to surface volcanism remains unclear.

Our study introduces a novel approach using Gaussian Process Regression to reconstruct the complex topography of seamounts, both above and beneath sedimentary covers. This approach advances previous analyses by (1) taking account of irregular seamount topography and (2) correcting for the varying sediment thicknesses that obscure seamount bases. Our investigation yields two principal findings.

1. Refined Volcanism Distribution Mapping

Analysis in the Pacific Ocean indicates that only 18% of total intraplate volcanic activity is attributable to plume-related volcanism. In addition, the volume statistics of plume-related seamounts and those along the Large Low-Shear-Velocity Province margins show no significant distinction from those of other intraplate seamounts. These results suggest that proposed plumes account for only a minority of the volume of intraplate volcanism in the Pacific plate, and that shallow rather than deep processes are dominant.

Along the volcanic Kyushu-Palau Ridge, high seamount volumes are observed near lithospheric weak zones, implying that tectonic inheritance significantly influences magma distribution during volcanic arc formation.

2. Comprehensive Morphological Analysis

Employing machine learning clustering analysis on high-resolution multibeam bathymetry data, we categorize seamounts in the South China Sea basin into three distinct morphological types: Type I, large seamounts with steep slopes and rounded bases, predominantly located along extinct ridges; Type II, linear seamounts characterized by gentler slopes, situated along ridges; and Type III, smaller, elliptically-based seamounts found along transform faults or off-ridge areas. This morphological classification provides a novel quantitative framework correlating seamount shapes with their tectonic environments during volcanic activity.

Overall, this research advances our understanding of seamount genesis, highlighting the importance of shallow tectonic processes in shaping submarine volcanic landscapes.

How to cite: Zhao, Y., Riel, B., Ding, H., and Deng, D.: Understanding Seamount Genesis: Utilizing Gaussian Process Regression and Clustering for Morphological Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4616, https://doi.org/10.5194/egusphere-egu24-4616, 2024.

EGU24-6451 | ECS | Posters on site | GD1.2

Modeling seismic wave propagation across complex volcanic structures of the Hawaii-Emperor Ridge 

Megumi Fujimoto, Robert Dunn, and Chong Xu

Volcanic seamount chains are widespread throughout ocean basins, but their formation and structure are not well understood. Active-source refraction seismology can provide images of the interiors of these volcanoes via P wave travel time tomography, but that requires proper identification of seismic phases that are generated by and propagate across complex volcanic structures. Unfortunately, the current limitation on the number of seismic phases that can be included in tomographic analyses leads to less detailed images and a limited geological understanding of the structures being imaged. The primary objective of this study is to compare recorded seismic wavefields from recent surveys across the Hawaiian-Emperor Seamount Chain with synthetic wavefields generated through waveform modeling. We use simplified yet realistic models of volcanic edifices, the underlying oceanic crust, and the mantle to better understand observed seismic phases and their origins. In previous studies (Dunn et al., 2019; Watts et al., 2021; Xu et al., 2022; MacGregor et al., 2023), several seismic phases were identified in recorded sections along the Hawaiian-Emperor Chain. However, interpreting the origins of some of these phases remains challenging. In this study, we developed an idealized seamount model based on the seismic structure of Jimmu Guyot in the Emperor Ridge (Xu et al., 2022). We calculated the seismic P-SV wavefield for various source and receiver positions using a finite difference wavefield modeling code (Levander, 1988; Lata and Dunn, 2020). Our goal is to model the observed seismograms and identify additional phases, including P-to-S converted waves. Additionally, we aim to verify recent tomographic images of the Hawaiian-Emperor Seamount Chain created by P wave travel time inversion via wavefield comparison. By resolving ambiguities and pinpointing new seismic phases, our aim is to improve seismic images of the Hawaiian-Emperor Chain. This contribution will enhance our understanding of specific structures, such as volcanic cores (a high-density and high-wave-speed interior core of the seamount), the hypothesized magmatic underplating of the oceanic crust by mantle melts rising beneath the volcanic chain, and the nature of the Moho and upper oceanic crust beneath these volcanic edifices.

How to cite: Fujimoto, M., Dunn, R., and Xu, C.: Modeling seismic wave propagation across complex volcanic structures of the Hawaii-Emperor Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6451, https://doi.org/10.5194/egusphere-egu24-6451, 2024.

EGU24-7314 | Posters on site | GD1.2

An ongoing lithospheric dripping process beneath Northeast China and its impact on intraplate volcanism 

Feiyu Lin, Liang Qi, Nan Zhang, and Zhen Guo

Unique intraplate volcano eruptions and westward volcano migration since the Oligocene are observed in NE China, an overriding continental zone tectonically controlled by the subduction of the northwestern Pacific plate and the opening of Japan Sea. Interestingly, these intraplate magmatic events occur around a subsiding basin (the Songliao Basin), but no volcanic activities have been observed within the Songliao Basin. The geodynamic mechanism responsible for these volcanoes remains unclear. To address the geodynamic process beneath NE China, numerical experiments are conducted constrained by datasets from regional reconstruction, seismic and volcanic studies. Vertical velocity field of mantle convection and lithospheric partial melting structures yielded from our numerical model show mantle upwelling and melting center migrates from the east to the west of NE China with the westward propagation of the stagnant slab, leading to the volcano migration. Also, with the subduction retreat of NW Pacific plate and the opening of the Japan Sea, significant lithospheric thickness differences between Changbaishan-Mudanjiang Region and the Songliao Basin develop, leading to lithospheric unstable dripping. This dripping structure prevents the partial melting of the lithosphere but facilitates the subsidence of the Songliao Basin in central NE China. Moreover,  the lithospheric dripping model successfully predicts upper mantle structures consistent with the proposed tomography model, the observed Moho depth, and surface topography variations. Thus, the lithospheric dripping induced by lithospheric thickness difference and the subduction of the Pacific slab provides a robust mechanism for the unique geodynamic process in NE China.

How to cite: Lin, F., Qi, L., Zhang, N., and Guo, Z.: An ongoing lithospheric dripping process beneath Northeast China and its impact on intraplate volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7314, https://doi.org/10.5194/egusphere-egu24-7314, 2024.

The Great Meteor Seamount is a guyot and the largest seamount in the North Atlantic Ocean with an estimated volume of some 24,000 km3. Located ~1280 km west of Africa and ~720 km south of the Azores, the seamount forms part of a group of seamounts which include Hyeres, Irving, Cruiser, Plato, Atlantis, and Tyro. Previous dredged rock, magnetic anomaly lineation, and predicted hotspot track studies suggest the seamount is ~17 Myr in age, was emplaced on oceanic crust and lithosphere with a thermal age of ~68 Ma and is linked to the New England Seamount Chain. However, bathymetric, free-air gravity anomaly and geochemical data are inconsistent with these ages and such a tectonic setting: bathymetric data suggest a guyot depth of ~400 m which is deeper than expected (~187 m), gravity data suggest an effective elastic thickness, Te, of ~20 km which is lower than expected (~26 km) and geochemical data suggest a link, not to the New England Seamount Chain, but to the Azores Islands instead. To address these inconsistencies, we used legacy Ocean Bottom Hydrophone, free-air gravity anomaly and bathymetry data to reassess the seismic structure, Te, and tectonic evolution of Great Meteor Seamount and its neighbouring seamounts. We show the uppermost crustal structure of Great Meteor Seamount is characterised by a relatively low velocity volcano-clastic sediments (2.0-4.5 km/s) and extrusive lava (5.0-6.0 km/s) drape which overlies a relatively high P-wave velocity intrusive ‘core’ of 6.0-6.5 km/s. The lowermost crust, in contrast, is characterized by a 4-km-thick body of P-wave velocity 7.00-7.75 km/s intermediate in velocity between the crust and mantle, the base of which is at depths at ~16 km. This seismic structure has been verified by gravity modelling assuming a Gardner and Nafe-Drake relationship between P-wave velocity and density, but 3-D flexure modelling reveals that a Moho depth at ~16 km requires a low elastic thickness (Te ~10 km) which is inconsistent with the amplitude and wavelength of the free-air gravity anomaly and the relatively flat depth to the top of the oceanic crust beneath the flexural moats flanking the guyot ‘core’. We found that gravity and seismic data are consistent if the Te of flexed oceanic crust at Great Meteor Seamount is ~20 km and is underlain by a ~4-km-thick magmatic underplated body. In contrast, we found that the Irving, Cruiser, Plato, Atlantis, and Tyro seamounts are characterised by a best fit Te of ~10 km and no evidence of underplating. We discuss these findings here with respect to the guyot depth at Great Meteor, terrace depths at Plato, and the tectonic setting of Great Meteor and its neighbouring seamounts.

How to cite: Watts, A. and Grevemeyer, I.: Legacy seismic refraction and gravity anomaly data in the vicinity of Great Meteor Seamount and its implications for plate flexure , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11610, https://doi.org/10.5194/egusphere-egu24-11610, 2024.

EGU24-11775 | Posters on site | GD1.2

TRANSCAUCASUS: Record of 200 My plume activity 

Nino Sadradze, Shota Adamia, Sierd Cloetingh, Alexander Koptev, and Guga Sadradze

Transcaucasus - the westernmost part of the southern Caucasus, represents an area where the Tethys Ocean was closed in the Late Cenozoic because of Eurasian and Africa-Arabian plate convergence. The lithosphere of the region represents a collage of Tethyan, Eurasian, and Gondwanan terranes. During the Late Proterozoic–Early Cenozoic a system of island arc and back-arc basins existed within the convergence zone. Geological and palaeogeographical data supported by paleomagnetic studies indicate the presence of several tectonic units in the regions that have distinctive geological histories.

The region comprises a 30-55 km thick continental crust with significant lateral variations in thickness of the overlying sediments (0-25 km). The travel times velocity anomalies of the P- and S-waves are interpreted as high-velocity bodies down to about 100 km depth, where the mantle lithosphere is thin or even missing.

The Mesozoic-Cenozoic magmatic assemblages reflect a diversity of paleogeographic -paleotectonic environments. They are indicative of a west Pacific-type oceanic basin setting under which the mature continental North Transcaucasian arc developed with zones of rifting and alkaline basaltic volcanism on the active margins of the oceanic domain.

Within-plate magmatic activity in the North Transcaucasus is represented by volcanic and plutonic complexes, including Late Triassic to Early Jurassic subaerial alkali basalts and alkali gabbro; the Late Bathonian-Late Jurassic high titanium alkali basalts and minor trachytes with coal-bearing shales and evaporites intercalations; Albian alkali basalts alternating with redeposited volcaniclastics and shallow marine carbonates.

The Late Cretaceous volcanics are associated with intraplate-type titanium rich alkali basalts and basanites with minor trachytes and phonolites, while the Eocene volcanics are associated with highly potassic to ultrapotassic basalts and basanites. The Late Miocene-Pleistocene volcanism is represented by alkaline basalt-trachytes as well.

The Great Caucasus, a NW–SE-directed mountain range, extends westwards along the pre-Caucasian strip of the Eastern Black Sea and is bounded to the south by the Transcaucasian Massif. The shoreline of the Eastern Black Sea Basin cuts off the Colchis intermontane trough formed over the rigid Georgian Block, the Achara–Trialeti trough and the Artvin–Bolnisi rigid block.

Onshore and offshore data confirm that the subaerial structures have immediate submarine prolongations. Deep drilling conducted within the onshore zone of the Transcaucasus, in the immediate vicinity of the shoreline, revealed that the volcanic formations below the modern sea level extend further into the Eastern Black Sea basin.

Recent data on structure and evolution of the Transcaucasus and adjacent area provide new constraints on the geological history of the lithosphere of the region, particularly on the Eastern Black Sea basin located in the collision zone between Eurasian and Africa-Arabian lithosphere plates, proximal to ancient sutures.

How to cite: Sadradze, N., Adamia, S., Cloetingh, S., Koptev, A., and Sadradze, G.: TRANSCAUCASUS: Record of 200 My plume activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11775, https://doi.org/10.5194/egusphere-egu24-11775, 2024.

EGU24-12578 | Posters on site | GD1.2

The influence of the lithosphere on deep-origin volcanism 

Lara M Kalnins, Amelia K Douglas, Benjamin E Cohen, J Godfrey Fitton, and Darren F Mark

Eastern Australia and the neighbouring Tasman and Coral Seas are home to extensive age-progressive volcanism spanning from ~55 Ma in the north to ~6 Ma in the south. This volcanism forms two offshore seamount trails, the Lord Howe and the Tasmantid Chains, as well as the onshore central volcanoes and leucitites of the East Australian Chain. The three volcanic chains are an average of just 500 km apart, erupted contemporaneously from 35-6 Ma, and share a common age-distance relationship, strongly suggesting a common source, most likely a deep-origin plume. However, they have erupted through lithosphere ranging from oceanic with well-developed seafloor spreading to drowned continental fragments to mainland Australia. How do these diverse settings influence the chemical and physical properties of the resulting mafic volcanism? The East Australian Chain has more fractionated mafic samples, reflecting more complex magmatic plumbing and longer magma residence times in the thick continental lithosphere. However, the most striking result is that the trace element and isotopic ratios remain remarkably similar across the three suites, showing little evidence of crustal or lithospheric assimilation affecting the mafic magmas. 

How to cite: Kalnins, L. M., Douglas, A. K., Cohen, B. E., Fitton, J. G., and Mark, D. F.: The influence of the lithosphere on deep-origin volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12578, https://doi.org/10.5194/egusphere-egu24-12578, 2024.

EGU24-12916 | ECS | Posters on site | GD1.2

First insights into the geochemical and petrological features of the Eger Rift’s plumbing system (Czech Republic) 

Kyriaki Daskalopoulou, Samuel Niedermann, Franziska D.H. Wilke, Martin Martin, and Heiko Woith

The western Eger Rift (Czech Republic) is a non-volcanic rift setting of intraplate seismicity that is characterized by abundant degassing of mantle-derived fluids. Since 2019, gases obtained from the free gas phase and volcanic rock samples of Quaternary age have been collected in order to determine the origin and evolution of volatiles in the system and define the magma chamber p-T conditions. Results of the CO2-dominated gas discharges of the Bublák and Hartoušov mofette fields yield an ~93 % mantle input (considering a subcontinental lithospheric mantle) for He. Ne isotopic ratios range from 9.8 to 11.0 for 20Ne/22Ne and from 0.0282 to 0.0480 for 21Ne/22Ne. Notwithstanding the samples enriched in 20Ne likely due to mass fractionation, many samples show a mixed atmospheric-mantle type source for Ne. However, an additional crustal input cannot be excluded. 40Ar/36Ar ratios also cover a wide spectrum of values (between 300 and 4680). Overall, gas samples typically present a higher-than-atmospheric value with 40Ar likely deriving from the mixing of an atmospheric and deep source. The 4He/40Ar* ratio is moderately constant and falls within the MORB range, suggesting an unfractionated magma that originates from mantle sources.. Results obtained from mineral quantitative analyses and by using thermobarometry of orthopyroxene and clinopyroxene rim pairs of matrix grains yield predominantly temperature and pressure conditions of 700 ±100 °C and 1.1 ±0.5 GPa, respectively, indicating a lithospheric depth that ranges between 40 - 45 km for 1.5 GPa and 20-25km for 0.5 GPa. In addition, pairing cores of mm-sized pyroxenes point to a temperature of 1100 ±100 °C and a pressure of 2.5 ±0.5 GPa that correspond to a lithospheric depth of ~75 km. Those minerals that indicate greater depths are likely the oldest ones as they were able to grow for longer times during their ascent. On the other hand, secondary overgrowths or smaller matrix grains represent younger grains that have grown during magma evolution. Therefore, their diverse chemistry and the wide range of p-T conditions reveal rising (and cooling) of magma.

This research is a part of the “MoRe-Mofette Research” and MoCa - “Monitoring Carbon” projects, which were funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 419880416, 461419881.

How to cite: Daskalopoulou, K., Niedermann, S., Wilke, F. D. H., Martin, M., and Woith, H.: First insights into the geochemical and petrological features of the Eger Rift’s plumbing system (Czech Republic), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12916, https://doi.org/10.5194/egusphere-egu24-12916, 2024.

EGU24-13068 | ECS | Orals | GD1.2

Intraplate magmatism, serpentinization and hydrothermal venting in the ultra-slow spreading setting of the Eurasia Basin, Arctic Ocean 

Juan Camilo Meza, Jan Inge Faleide, Alexander Minakov, and Carmen Gaina

The Eurasia Basin, one of two major oceanic basins of the Arctic Ocean, is composed of the Amundsen and Nansen basins, which were created due to the slow and ultra-slow seafloor spreading at the mid-oceanic Gakkel Ridge initiated during the Paleocene-Eocene transition (53-56 Ma). Since the beginning of the current millennia the Gakkel Ridge and the Eurasia Basin have been subject of marine geological and geophysical studies leading to the collection of diverse datasets including rock samples, seismic, and potential-field datasets. New marine seismic data has become available in the western Eurasia Basin in the very last years, including data acquired by the Norwegian Petroleum Directorate in the context of the UN Law of the Sea, together with seismic lines gathered by Norwegian research institutions and partners. During October-November 2022 the first High Arctic GoNorth marine expedition collected new seismic reflection and refraction, as well as gravity and magnetic datasets. It is considered that this polar region may hold important clues for the understanding of global processes such as passive margin formation, and the complex links between plate tectonics and climate. Volcanic additions have been suggested within the flanks of the Eurasia Basin during different stages in the Cenozoic. Existing hypotheses further postulate corridors of exhumed mantle formed across the western Eurasia Basin because of the magmatic segmentation imposed by the Gakkel Ridge. Consequently, the oceanic basement of this area should be prone to deformation, hydrothermal alteration and serpentinization. However, little is known about the relationships between such processes with the sedimentary units above, or whether such processes occur away from the ridge and to what extent.

The new compilation of multi-channel seismic reflection profiles provides an image of the sedimentary structure and the upper crust, within the oceanic crust and the continent-ocean transition (COT) between northern Svalbard margin and Eurasia Basin. The preliminary analysis of these datasets indicates that the sediments and basement structures within the southwestern corner of the Eurasia Basin have been modified in a unique manner due to an underlying geothermal anomaly beneath the lithosphere. This is expressed as focused late Miocene (< 20 Ma) to recent sill intrusion events resulting in basement and sediment deformation, and intense hydrothermal and sediment evacuation features. We present unique examples of hydrothermal venting on seismic reflection data and discuss implications of the post-rift NE Atlantic and Arctic setting, including the role of breakup magmatism, post-breakup intraplate volcanism, and sheared/passive margin development during the Cenozoic.

How to cite: Meza, J. C., Faleide, J. I., Minakov, A., and Gaina, C.: Intraplate magmatism, serpentinization and hydrothermal venting in the ultra-slow spreading setting of the Eurasia Basin, Arctic Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13068, https://doi.org/10.5194/egusphere-egu24-13068, 2024.

EGU24-13901 | Posters on site | GD1.2

Seismic Silence Speaks Loud: No extensive magmatic underplating found in recent seismic studies of the Hawaiian Ridge 

Robert Dunn, Megumi Fujimoto, Chong Xu, Anthony Watts, Brian Boston, and Donna Shillington

Some prior active-source seismic studies beneath oceanic seamount chains indicate a sub-crustal layer of what is considered to be underplated magmatic material. The classic example is the Hawaiian Ridge, where a seismic study in the early 1980s first proposed the existence of such a layer. Since then, Hawaii has been considered one end-member in a range of possible scenarios, extending from underplating to no underplating, but with possible magmatic intrusion into the lower oceanic crust. Magmatic underplating affects mass flux and lithospheric loading calculations. All else being equal, underplating would be expected to lower the amplitude of the gravity anomaly over the crest of the edifice and provide a positive buoyancy force that makes the plate appear more rigid than it actually is. One hypothesis put forward to explain variations in the style of magmatic emplacement at intraplate volcanoes hinges on the age of the lithosphere at the time of volcano formation. In this model, shallow intrusion into the oceanic crust and overlying edifice is favored for seamounts growing on younger lithosphere, while magmatic underplating is favored for seamounts growing on older lithosphere such as Hawaii. However, recent seismic, gravity, and plate flexure studies conducted along the Hawaiian-Emperor Seamount Chain collectively provide clear evidence for shallow magmatic emplacement and contradict the notion of significant magmatic underplating for ages at the time of loading of ~57 Ma (Emperor Seamounts) and ~90 Ma (Hawaiian Ridge). Additionally, reprocessed legacy seismic data has not revealed evidence for underplating beneath the Hawaiian Ridge. In this presentation, results from these recent studies will be shown, compared, and the evidence for a simple mantle structure without underplating will be presented along with seismic synthetic tests that explore the degree of underplating that may be 'hidden' in the data.

How to cite: Dunn, R., Fujimoto, M., Xu, C., Watts, A., Boston, B., and Shillington, D.: Seismic Silence Speaks Loud: No extensive magmatic underplating found in recent seismic studies of the Hawaiian Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13901, https://doi.org/10.5194/egusphere-egu24-13901, 2024.

EGU24-13934 | ECS | Orals | GD1.2

Bulldoze and rebuild: Modifying cratonic lithosphere via removal and replacement induced by continental subduction 

Lingtong Meng, Chu Yang, Wei Lin, Ross N. Mitchell, and Liang Zhao

Establishing the mechanisms for craton modification is critical for understanding cratonic stability and architecture. Cratons are intrinsically strong with long-term stability, but plate tectonics or mantle plumes cause craton weakening, mechanical decoupling, and lithospheric removal. By comparison, craton modification—craton destruction accompanied or followed by rejuvenation—has received less attention. Oceanic plate subduction dominantly destroys the craton, with a lesser degree of rebuilding. Mantle plumes can facilitate decratonization, by weakening and peeling off the lithospheric mantle, or recratonization, by healing the craton with refractory mantle residues. Compared with the effects of oceanic plate subduction and mantle plumes, the role of continental subduction in craton modification remains an open question. The North China Craton (NCC), a previously stable continent with a lithospheric thickness of >200 km since the Paleoproterozoic, was reworked and partially destroyed due to lithospheric delamination triggered by Early Cretaceous Paleo-Pacific oceanic subduction. In eastern NCC, lithospheric thickness decreased from 200 km to 35 km in the Early Cretaceous in only 10 m.y. The NCC experienced an early Mesozoic continent–continent collision (as the overriding plate) with the South China Block (SCB). The collision provides an opportunity to understand the potential for craton modification due to deep continental subduction induced by continental collision.

In the NCC, combined structural geology, magnetic fabrics, zircon U-Pb dating, and Hf-O isotopes, we report the presence of martial derived from a partially melted SCB’s crust. We proposed a three-stage model to interpret the material sourced from the subducted plate into the overriding carton: (1) SCB bulldozed and rebuilt NCC during 250–220 Ma; (2) during 220-200 Ma, the subducted SCB exhumed along the exhumation channel to underplate beneath the NCC, associated with partial melting; (3) finally, Late Jurassic granite derived partial melting of the SCB entrained Latest Triassic reworked SCB’s crust to emplace.

Combining our new results with previous geophysical observations, we estimate the extent of the bulldozing and rebuilding. We argue that a 200-km-long tract of the NCC lithosphere was bulldozed and rebuilt by the subducted SCB, resulting in a lithospheric suture far from the suture zone at the surface. This lithospheric removal occurred at middle-lower crustal levels (16–20 km depth)—much shallower than previously thought possible. The bulldozed NCC lithosphere was replenished by the subducted SCB continental lithosphere rather than the asthenosphere, thus terminating the lithosphere modification. With essentially no net loss of lithosphere during deep continental subduction, the NCC maintained its stability until Early Cretaceous paleo-Pacific oceanic subduction. This “bulldoze and rebuild” model can thus account for how a craton maintains its stability during a collision with another continental plate.

How to cite: Meng, L., Yang, C., Lin, W., Mitchell, R. N., and Zhao, L.: Bulldoze and rebuild: Modifying cratonic lithosphere via removal and replacement induced by continental subduction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13934, https://doi.org/10.5194/egusphere-egu24-13934, 2024.

Mesozoic intraplate igneous activity is abundant on the Canadian shield and includes multiple kimberlite fields, a province of alkaline magmatism, and individual bodies of kimberlites and ultramafic lamprophyres. Models have variously attributed the emplacement of these intrusions to the influence of Farallon plate subduction, opening of the Atlantic Ocean, or one or several Atlantic hotspots which North American plate is postulated to have drifted over during the Mesozoic. The latter hypothesis relies of the attribution of spatially, temporally and compositionally distributed and diverse magmatic rocks into a poorly defined, age-progressive, ‘corridor’ which may be derived from a common geochemical reservoir. In this study, we aim to test the spatiotemporal association between intraplate igneous activity along this postulated Triassic-Jurassic corridor and several elements of fixed mantle reference frame, such as the Atlantic hotspots and the hypothesised plume-generating zone (PGZ) of the African Large Low Shear Velocity province (LLSVP).

We use published geochronological databases containing locations and isotopic ages of the Mesozoic intrusions of North America and published global plate reconstructions to dynamically calculate distances between the loci of intraplate magmatism and features of the upper and lower mantle assuming the latter remained fixed in the mantle reference frame throughout their history. We use GPlates 2.3.0 software package and pygplates 0.36.0 Python library to build the reconstructions and implement our calculations.

Results demonstrate that none of the examined mantle features show a consistent association with all instances of intraplate magmatism across the Canadian shield during the Triassic-Jurassic. The coeval kimberlitic magmatism in the western Slave province (Jericho kimberlite field) and Baffin Island (Chidliak kimberlite field) appears to be completely spatially unrelated to any of the examined mantle features. The kimberlite fields of the Superior province (Attawapiskat, Kirkland Lake, Timiskaming) experience emplacements long before and after their passage over the PGZ, but their frequency increases in the PGZ’s vicinity, i.e. 76% of emplacement events in these provinces occur within 200 km of the PGZ’s surface projection.

Our results show that intraplate magmatism across many Triassic-Jurassic fields of North America could be initiated independently of the influence of deep mantle structures. Thereby, a geodynamic mechanism nested in the asthenosphere or lithospheric mantle suffices for melt generation in an intraplate setting. However, it cannot be ruled out whether proximity to deep mantle structures is capable of facilitating “shallow” melt generation and emplacement and that deep-seated mantle structures could provide an influx of fluids or thermal energy, increasing melting intensity and volume.

How to cite: Koptev, E. and Peace, A.: The Triassic-Jurassic corridor of North America: are deep mantle structures a sufficient explanation for intracontinental magmatism?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14228, https://doi.org/10.5194/egusphere-egu24-14228, 2024.

EGU24-14365 | ECS | Orals | GD1.2

Intraplate Volcanism by Spontaneous Shallow Upper Mantle Melt Focusing 

Jung-Hun Song, Seongryong Kim, Junkee Rhie, and Tae-Seob Kang

Intraplate volcanism signifies persistent magmatic activity within plate interiors far from active plate boundaries. However, due to limited assessment of the detailed physical conditions of the intraplate upper mantle, the fundamental mechanism behind the genesis of mantle magma remains poorly understood. We analyzed the temperature conditions of the upper mantle beneath global intraplate volcanic regions estimated from seismic velocity and geochemical data. We revealed that excluding volcanoes near major plumes, large proportions (> 70%) of the volcanoes are situated above the upper mantle with moderate temperatures comparable to or colder than those found at mid-oceanic ridges (potential temperature (Tp) ~1250–1350°C). These volcanoes also overlie regions of low vertical and horizontal asthenospheric shear estimated by global mantle convection simulations. Without peculiarities in thermal and large-scale mantle dynamics, we inferred that these volcanic activities are likely driven by a small-scale local convective process confined to the shallow upper mantle. To constrain a more detailed process of intraplate volcanism, we focus on analyzing the upper mantle rheology and melt distribution beneath intraplate volcanoes in NE Asia. Thermodynamic properties, conservatively constrained by high-frequency seismic attenuation and velocities, revealed the common presence of low-viscosity zones concentrated beneath the volcanoes at shallow asthenospheric depths (< 200 km). These regions contain a small fraction of melt (~0.05–0.8%) at cold-to-moderate temperatures (Tp ~1300–1350°C) compared to the average mantle aligning with global analyses. A series of evidence potentially suggests the existence of localized mantle upflux focused beneath intraplate volcanoes. Considering the amount and extent of the estimated mantle melts and numerical mantle convection simulations with lithospheric structures, we propose that undulations in the lithosphere and asthenosphere boundary could play a primary role in controlling the small-scale mantle convection and the location of intraplate mantle melting. Our estimation supports the possibility of the ubiquitous occurrence of intraplate volcanoes independent of dynamic forces for deriving active mantle upwellings (e.g., thermal or chemical buoyancy).

How to cite: Song, J.-H., Kim, S., Rhie, J., and Kang, T.-S.: Intraplate Volcanism by Spontaneous Shallow Upper Mantle Melt Focusing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14365, https://doi.org/10.5194/egusphere-egu24-14365, 2024.

EGU24-14871 | Orals | GD1.2

Santiago Island, Cape Verde: Evidence for island-scale collapse from paleotopography onshore and bathymetry offshore 

Fernando Ornelas Marques, Cristina Catita, Anthony Watts, Anthony Hildenbrand, and Sónia Victória

A volcanic edifice much larger than the current one must have existed in Santiago Island, Cape Verde, because the granular rocks and dyke-in-dyke complex representing magma chambers and deep feeders currently outcrop up to 700 m altitude. Therefore, we must find an explanation for the massive destruction of the original edifice. We developed a new tool for the quantitative reconstruction of ancient topographies in a volcanic ocean island to address this problem, because it allows us to estimate the shape and volume of volcanic rock removed at a certain time. The reconstruction of the topography of the basement complex at ca. 6 Ma ago, before the unconformable deposition of the submarine complex, shows a concave depression coincident with the asymmetric distribution of volcanic complexes east and west of the main divide of the island. This concave depression is here interpreted as the remnant of an island-scale, summit collapse. Instituto do Mar de Cabo Verde bathymetry and RRS Charles Darwin (8/85) seismic reflection profile data suggest that the west side of Santiago is characterised by a narrow insular shelf, a major debris avalanche deposit with scattered blocks and at least one lateral sector collapse structure. Data, however, east of Santiago are limited and so the full extent of mass wasting on the east side of the island is not known. Maio Island, which is similar in age to Santiago, would have acted as a buttress in the east, and it is possible that any eastward collapse might have rotated and travelled to the northeast. Irrespective, one or more mass wasting events west or east of Santiago are consistent with a major destruction of the original volcano edifice which removed the summit, exposed the basement complex of the island, and redistributed volcano-clastic material over a large area of the adjacent seafloor. 

How to cite: Ornelas Marques, F., Catita, C., Watts, A., Hildenbrand, A., and Victória, S.: Santiago Island, Cape Verde: Evidence for island-scale collapse from paleotopography onshore and bathymetry offshore, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14871, https://doi.org/10.5194/egusphere-egu24-14871, 2024.

The Eifel volcanic area in western Germany has been active for tens of million years. Geodetic observations, geochemical analysis and seismological studies all indicate that the source of these long-term volcanic activities is a mantle plume. However, it still remains controversial whether the Eifel plume has a deep origin. This is because the tomography images do not consistently show a continuous plume conduit between the surface and the core-mantle boundary. The Eifel plume is also not associated with any flood basalt province or a clearly age-progressive hotspot track, which is regarded as a key surface feature indicating a deep plume origin. In addition, it has been proposed that the Alpine subduction zone, south-east of the volcanic area, has created a stagnant slab in the mantle transition zone, which might be interacting with the Eifel plume.

Based on the previous studies and observations, our two contrasting hypotheses are as follows: (1) The Eifel plume is not rooted in the lower mantle. In this case, subduction beneath the Alps might trigger a return asthenospheric flow and the ascent of an upper-mantle plume, leading to the formation of intraplate volcanism beneath the European plate. (2) The Eifel plume is assisted from an upwelling in the lower mantle. In this case, the subducting plate might tilt the plume conduit and influence the position where volcanism takes place.

In this study, we apply the Finite-Element-Method geodynamic modeling code ASPECT to model the ascent of the Eifel plume and its interaction with the subducting slab. We design both slab advancing and slab retreating model set-ups, with and without a plume from the lower mantle beneath the subducting plate. We check whether and under what conditions the Eifel plume will be triggered behind the slab due to slab overturn. Preliminary results show that the return flow induced by subduction can help generate an upper-mantle plume and lead to the formation of volcanism. A series of models are also performed to investigate the effects of mantle viscosity and plume temperature on the plume-slab interaction.

How to cite: Li, Y., Steinberger, B., Brune, S., and Le Breton, E.: Intra-plate volcanism generated by slab-plume interaction: Insights from geodynamic modeling of the Eifel plume and its interaction with the European subducting lithosphere beneath the Alpine subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15020, https://doi.org/10.5194/egusphere-egu24-15020, 2024.

EGU24-15229 | ECS | Posters on site | GD1.2

3-D Modelling of Plume-Lithosphere Interaction: The Cosgrove Track, Eastern Australia 

Thomas Duvernay and D. Rhodri Davies

Compared to oceanic hotspot tracks, volcanic provinces within Earth's continents generally exhibit more intricate surface characteristics, such as spatio-temporal distribution and geochemical signatures of erupted lavas. These complex surface patterns relate to dynamic interactions in the uppermost convective layer of the mantle, where decompression melting occurs. The Cosgrove Track of Eastern Australia constitutes a compelling example of such continental volcanic activity. Recent studies support a mantle plume having sustained the volcanism and discuss several notable features, such as lithosphere-modulated volcanic activity, plume waning, separate volcanic tracks, and plate-motion change.

Here, we simulate the proposed interaction between the Cosgrove plume and eastern Australia during the past 35 Myr. We design a 3-D analogue of the Australian continent using available lithospheric architecture determined through seismic tomography and impose the inferred plate motion associated with this region. Our models incorporate updated peridotite melting and melt chemistry parameterisations that provide quantitative estimates of generated melt volume and composition. We find that plume-driven and shallow edge-driven melting processes, modulated by the lithospheric thickness of the Australian continent, combine to explain the observed volcanic record. Our preliminary results agree well with surface observations and provide further insight into the geodynamics of eastern Australia.

How to cite: Duvernay, T. and Davies, D. R.: 3-D Modelling of Plume-Lithosphere Interaction: The Cosgrove Track, Eastern Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15229, https://doi.org/10.5194/egusphere-egu24-15229, 2024.

EGU24-17719 | ECS | Posters on site | GD1.2

Petrology and geochemistry of alkaline Circular Complexes from Sal Island, Cape Verde archipelago. 

María García-Rodríguez, Cristina de Ignacio, David Orejana, Carlos Villaseca, João Mata, and Rita Caldeira

Sal is the oldest island of the Cape Verde archipelago, with magmatic activity starting around 25 Ma (Torres et al., 2010). Located to the northeast of the archipelago, it forms part of a north-south islands alignment and features intrusive bodies potentially representing the subvolcanic roots of exposed volcanic rocks. These intrusions, dated from ≈ 14 to 17 Ma (Torres et al., 2010) are intrusive into the Old Eruptive Complex, located in the central-western part of the island and mostly comprised by gabbro bodies, dyke swarms and several circular gabbro to monzonite complexes.

There are no previous detailed studies concerning mineral chemistry and crystallization conditions of these intrusions, which are a first step, together with precise geochronology, to correlate them with any of the different volcanic series occurring in Sal. In this work we present preliminary mineral chemistry, whole-rock geochemistry and radiogenic (Sr, Nd, Pb) isotope data of the circular complexes aiming to characterize their main features, magmatic evolution and mantle source composition.

The studied rocks range from gabbros to monzonites, sometimes displaying cumulate textures. The main mafic minerals present variable compositions: olivine chemistry ranges from Fo61-81 in gabbros to Fo39-49 in monzogabbros; clinopyroxene is classified as augite-diopside in all samples; amphibole is mainly kaersutite-pargasite-Mg-hastingsite and biotite-phlogopite Mg# is in the range 0.4-0.7. Plagioclase is bytownite-andesine (An30-86) in gabbros, whereas it is more sodic in monzogabbros and monzonites (An16-66), while nepheline (Ne70-86) turns more potassic from gabbros to monzonites. Alkali feldspar (Or20-98) only appears in monzogabros and monzonites. The main accessory phases are ilmenite/Ti-magnetite, chromite, ulvospinel, titanite and apatite.

Major and trace element chemistry points to a progressive evolution from mafic to intermediate types characterized by a linear decrease of MgO, TiO2, FeOT, CaO, Ni and Cr, and a gradual increase of SiO2, Al2O3, K2O, Na2O, Rb, Ba, Zr and Nb. These patterns suggest initial crystallization of mafic phases (olivine, clinopyroxene, ilmenite-magnetite) and calcic plagioclase. The intra-complexes positive correlation between strongly incompatible element pairs: U-Th, La-Ce and Nb-Ta, suggests the predominance of fractional crystallization within each circular complex.

The studied rocks display 87Sr/86Sr and 143Nd/144Nd initial ratios typical of some OIB having more Sr-radiogenic and Nd-unradiogenic compositions than the N-MORB. These signatures and the Pb isotope ratios are close to the FOZO composition, in an intermediate position between the HIMU and N-MORB mantle components. Small εNd and 206Pb/204Pb differences between the several circular complexes define two compositional groups, which implies slight heterogeneities in the mantle sources. These isotopic results support the association of Sal intrusive with the Cape Verde northern islands as no low Nd isotopic ratios have been found that could imply EM-1 enriched components, as those described by Torres et al. (2010) for some lavas.

Torres, P., Silva, L.C., Munhá, J., Caldeira, R., Mata, J., Tassinari, C. (2010): Petrology and geochemistry of lavas from Sal Island: Implications for the variability of the Cape Verde magmatism. Comunicaçoes Geológicas, 97: 35-62.

How to cite: García-Rodríguez, M., de Ignacio, C., Orejana, D., Villaseca, C., Mata, J., and Caldeira, R.: Petrology and geochemistry of alkaline Circular Complexes from Sal Island, Cape Verde archipelago., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17719, https://doi.org/10.5194/egusphere-egu24-17719, 2024.

EGU24-18227 | ECS | Posters on site | GD1.2

A geodynamic perspective on the formation of intraplate volcanism in Central East Asia 

Alexander Rutson, Tiffany Barry, Stewart Fishwick, and Victoria Lane

Central East Asia has experienced intraplate volcanism over the past ~110 Myrs. The mechanism for this volcanism is enigmatic, with several potential causes put forward for the origin, including a mantle plume, edge convection, and lithospheric delamination. One of the big questions for the region is the role played by the long-term subducting systems of the Pacific/Izanagi and the Tethys Ocean(s). And secondarily, how much the volcanism is influenced by the lithospheric conditions and its changing thicknesses across the region.  

To recreate the conditions of mantle circulation and flow beneath Central East Asia, a mantle circulation model has been created using the fluid dynamics code ASPECT; the mantle circulation model is coupled with the plate reconstruction of Muller et al. (2019) for the surface conditions of the past 200 Myrs. To better understand the patterns of mantle flow, particles are emplaced into the model to track flow beneath the region, particularly around the subducted slabs. The mantle flow is compared to localities of intraplate volcanism across Central East Asia to assess whether any upwelling regions correlate with the spatial and temporal origins of the volcanism. Initial results show colder downwelling mantle from the surface boundary beneath Central East Asia at ~120-110 Ma, with warmer mantle upwelling into the region to replace it. The timing of this upwelling mantle coincides with the initiation of intraplate volcanism in the region; however, whether this results in the onset of intraplate volcanism in the region and the following 110 Myrs of intraplate volcanism is still being investigated. The mantle flow from the global models will then be used to inform the boundary conditions of a localised box model for Central East Asia. This model will be used to examine any potential effect of delamination beneath Central East Asia, and whether this model can explain any of the timings of intraplate volcanism formation. 

How to cite: Rutson, A., Barry, T., Fishwick, S., and Lane, V.: A geodynamic perspective on the formation of intraplate volcanism in Central East Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18227, https://doi.org/10.5194/egusphere-egu24-18227, 2024.

EGU24-18822 | ECS | Orals | GD1.2

Plate flexure and tectonic tilt along the Emperor Seamount Chain  

Chong Xu, Paul Wessel, Anthony Watts, Brian Boston, Robert Dunn, and Donna Shillington

The Hawaii-Emperor seamount chain stretches westward from the “Big Island” of Hawaii for over 6000 km until the oldest part of the chain are subducted at the Kuril and Aleutian trenches. Still regarded as the iconic hotspot-generated seamount chain it has been sampled, mapped, and studied to give insights into numerous oceanic phenomena, including seamount and volcano formation and associated intraplate magma budgets, the past absolute motions of the Pacific plate, the drift of the Hawaiian plume, and the thermal and mechanical properties of oceanic lithosphere. Previous work (Wessel et al., EGU 2023 abstract) used a high-resolution free-air gravity anomaly and high-resolution bathymetry data set, together with fully 3-dimensional flexural models with variable volcano load and infill densities, to estimate the optimal effective elastic thickness, Te, and load and infill densities along the Emperor Seamount chain. Here, we use these parameters to calculate the tectonic tilt of a pre-existing volcano that occurs as each new volcano in a seamount chain is progressively added by flexure to the Pacific oceanic plate. We found tilts in the range 0.1-2.1 degrees which are modest compared to other cases of progressive flexure, for example, at seaward dipping reflector sequences in volcanic rifted margins (~5-15 degrees) but may be significant enough to modify the morphology of volcano summits and the stratigraphy of the sequences that accumulate in their flanking moats. They may also modify the physical properties of the edifice such as their magnetisation vectors.

Wessel, P., A. B. Watts, B. Boston, C. Xu, R. Dunn, and D. J. Shillington “Variation in Elastic Thickness along the Emperor Seamount Chain”, EGU 2023 Abstract

How to cite: Xu, C., Wessel, P., Watts, A., Boston, B., Dunn, R., and Shillington, D.: Plate flexure and tectonic tilt along the Emperor Seamount Chain , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18822, https://doi.org/10.5194/egusphere-egu24-18822, 2024.

EGU24-19827 | Posters on site | GD1.2

Seamounts and giant carbonate mounds drive bio-physical connections in the deep-sea: Two case studies from the North Atlantic. 

Christian Mohn, Vibe Schourup-Kristensen, Janus Larsen, Franziska Schwarzkopf, Arne Biastoch, Inês Tojera, Miguel Souto, Manfred Kaufmann, Anna-Selma van der Kaaden, Karline Soetaert, and Dick van Oevelen

Seamounts and carbonate mounds are ubiquitous features of the global deep seascape. They often provide habitat for unique benthic species communities and support increased production and aggregation of phytoplankton, zooplankton, micronekton, and fish. Seamounts and carbonate mounds interact with the surrounding currents generating flow phenomena over a wide range of spatial and temporal scales including stable Taylor caps, energetic internal waves and turbulent mixing, all with the potential to enhance productivity, biomass, and biodiversity in an often food-limited deep-sea environment. We present hydrodynamic and ecological framework conditions at two contrasting topographic features in the North Atlantic, Great Meteor Seamount and Haas Mound. Great Meteor Seamount is of volcanic origin and one of the largest seamounts in the subtropical North Atlantic rising from 4200 m depth at the seafloor to a summit depth of 270 m. Great Meteor Seamount shows remarkable endemism in meiofaunal groups of copepods and nematodes. Haas Mound is one of the largest biogenic carbonate mounds of the Logachev mound province along the Southeast Rockall Bank in the Northeast Atlantic with a species rich benthic fauna dominated by the cold-water coral Desmophyllum pertusum (Lophelia pertusa). We used results from hydrodynamic models to identify the physical processes, which potentially support seamount and carbonate mound biodiversity. The models employ high-resolution local bathymetry, basin-scale lateral forcing and tidal forcing. Our model simulations provide a detailed three-dimensional picture of the fine-scale motions and physical processes, which potentially drive bio-physical connections such as particle retention and continuous or episodic food supply to benthic communities. 

How to cite: Mohn, C., Schourup-Kristensen, V., Larsen, J., Schwarzkopf, F., Biastoch, A., Tojera, I., Souto, M., Kaufmann, M., van der Kaaden, A.-S., Soetaert, K., and van Oevelen, D.: Seamounts and giant carbonate mounds drive bio-physical connections in the deep-sea: Two case studies from the North Atlantic., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19827, https://doi.org/10.5194/egusphere-egu24-19827, 2024.

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.

GD2 – Melts, Volatiles and Chemistry of the Mantle

EGU24-103 | ECS | PICO | GD2.1

 Oxygen-fugacity evolution of magmatic Ni-Cu sulfide deposits in East Kunlun: Insights from Cr-spinel composition  

Lihui Jia, Yi Chen, Bin Su, Qian Mao, and Di Zhang

Redox state of parental magma would have undergone significant changes from partial melting in the mantle to emplacement in the shallow crust, which might play a critical role in the genesis of magmatic Ni-Cu sulfide deposits in convergent tectonic settings. In this study, we present mineralogy, petrology, and fO2 calculations of the Xiarihamu Ni-Cu deposit and the Shitoukengde non-mineralized intrusion in the East Kunlun orogenic belt. Olivine-spinel pairs in different magmatic stages were chosen to estimate the magma fO2 (olivine-spinel oxybarometer), track the changes in oxygen fugacity during magmatic evolution, and reveal its influence on the metallogenic mechanism of the Ni-Cu sulfide deposit. Spinel Fe3+/ΣFe ratios determined by a secondary standard calibration method using electron microprobe. Those ratios of the Xiarihamu Ni-Cu deposit vary from 0.32±0.09 to 0.12±0.01, corresponding to magma fO2 values ranging from ΔQFM+2.2±1.0 to ΔQFM-0.6±0.2. By contrast, those of the Shitoukengde mafic-ultramafic intrusion increase from 0.07±0.02 to 0.23±0.04, corresponding to magma fO2 varying from ΔQFM-1.3±0.3 to ΔQFM+1.0±0.5. A positive correlation between fO2 and Cr-spinel Fe3+/ΣFe ratios suggests that the Cr-spinel Fe3+/ΣFe ratios can be used as an indicator for magma fO2. The high fO2 (QFM+2.2) of the harzburgite in the Xiarihamu Ni-Cu deposit suggests that the most primitive magma was characterized by relatively oxidized conditions, and then became reduced during magmatic evolution, causing S saturation and sulfide segregation to form the Xiarihamu Ni-Cu deposit. The evolution trend of the magma fO2 can be reasonably explained by metasomatism in mantle source by subduction-related fluid and addition of external reduced sulfur from country gneisses (1.08–1.14 wt.% S) during crustal processes. Conversely, the primitive magma of the Shitoukengde intrusion was reduced and gradually became oxidized (from QFM-1.3 to QFM+1.0) during crystallization. Fractional crystallization of large amounts of Cr-spinel can reasonably explain the increasing magma fO2 during magmatic evolution, which would hamper sulfide precipitation in the Shitoukengde intrusion. We propose that the temporal evolution of oxygen fugacity of the mantle-derived magma can be used as one of the indicators for evaluating metallogenic potential of Ni-Cu sulfide deposits, and reduction processes from mantle source to shallow crust play an important role in the genesis of magmatic Ni-Cu sulfide deposits.

How to cite: Jia, L., Chen, Y., Su, B., Mao, Q., and Zhang, D.:  Oxygen-fugacity evolution of magmatic Ni-Cu sulfide deposits in East Kunlun: Insights from Cr-spinel composition , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-103, https://doi.org/10.5194/egusphere-egu24-103, 2024.

EGU24-616 | ECS | PICO | GD2.1 | Highlight

The Namuaiv picrite-melanephelinite pipe, Kola alkaline province, Russia: petrography and evolution of late alkaline melts during forming large alkaline province with carbonatites. 

Darina Shaikhutdinova, Alexey Kargin, Liudmilla Sazonova, Natalia Lebedeva, Anna Nosova, and Yapaskurt Vasiliy

Petrological investigations of large alkaline provinces with carbonatites are very important to understanding the generation and evolution of alkaline melts, as well as processes provided generation of related ore deposits. Most often, generation of large alkaline massifs with carbonatites accompanied by intrusion of related ultramafic alkaline and related alkaline-ultramafic melts as dykes swarms and explosive pipes. These melts could be generated on the initial stages of magmatic activities of alkaline province magmatism, or fix the final stages of alkaline magmatism, after the formation of large alkaline massifs with carbonatites. Studying of these melts could provide insights into the composition of primary melts for large alkaline province, as well as understanding their evolution during magmatic activities. Moreover, the latest melts forming dykes and explosive pipes could provide information about the evolution of the mantle source of these rocks including of processes of lithospheric mantle transformations (enrichment, depleting, mantle metasomatism etc.).

The Kola alkaline province (KAP) with carbonatites is a good natural laboratory for investigation petrology of alkaline melts and their evolutions. KAP includes large alkaline massifs with carbonatites, the early dyke swarms of ultramafic and alkaline lamprophyres and late explosive pipes of the alkaline rocks (Arzamastsev et al., 2005). To investigate the composition of alkaline melts at the late stages of the province's magmatic activity, we have studied the petrography and mineralogy (olivine composition) of the Namuaiv pipe rocks.

The Namuaiv pipe (363 ± 3 Ma; Arzamastsev et al., 2005) erupted the alkaline rocks of the north part Khibiny massif (377± 3 Ma). The detailed petrographical studied suggested, that the pipe breccia was formed during mixing of two portions of alkaline melts close in composition to alkaline picrite and melanephelinite.

The Namuaiv rocks contain several types of olivine grains: (1) picritic melt phenocrysts; (2) antecrysts of ultramafic lamprophyres of the Kandalaksha Bay (Vozniak et al., 2023) that traced the first stages of the province magmatism; and (3) disintegrated fragments of the lithospheric mantle peridotites (mantle xenocrysts). The composition of olivine phenocrysts suggests that in the final stage of KAP activity, the alkaline melts have not fractionated in deep magmatic chambers and their composition is close to primary melts. That is in contrast to the first stages of KAP magmatism, where lamprophyre dikes were formed as fractionated melts (Vozniak et al., 2023). The present of the olivine antecrysts assumes that the Namuaiv melts ascent trough magmatic channels modified by previous portions of alkaline melts, that consistent with the presence metasomatic clinopyroxene-phlogopite xenoliths within the pipe.

The study was supported by the Russian Science Foundation under Grant No 23-77-01052.

Arzamastsev A.A., Belyatsky B.V., Travin A.V. et al. 2005. Dyke rocks in the Khibiny massif: relation to plutonic series, age, and characterization of mantle sources // Petrology. V.42. N3. P.1-23.

Vozniak A.A., Kopylova M.G., Peresetskaya E.V. et al. 2023. Olivine in lamprophyres of the Kola Alkaline Province and the magmatic evolution of olivine in carbonate melts // Lithos 448–449, 107149. doi:10.1016/j.lithos.2023.107149

How to cite: Shaikhutdinova, D., Kargin, A., Sazonova, L., Lebedeva, N., Nosova, A., and Vasiliy, Y.: The Namuaiv picrite-melanephelinite pipe, Kola alkaline province, Russia: petrography and evolution of late alkaline melts during forming large alkaline province with carbonatites., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-616, https://doi.org/10.5194/egusphere-egu24-616, 2024.

EGU24-1231 | PICO | GD2.1

Thermal state and nature of the low crust in the Baikal Rift zone according to the lower crust xenoliths of Cenozoic volcanics and Paleozoic magmas.  

Igor Ashchepkov, Andrey Tsygankov, Galina Burmakina, Sergei Rasskazov, Yusef Ailow, and Nikolai Karmanov

The lower crust and Moho pyroxenites and xenocrysts from Cenozoic volcanoes studied with the EPMA, SEM and LA ICP MS for trace elements evidence about the structure and composition of the transitional zone from the crust to mantle in Cenozoic volcanic regions In Vitim (picrite basalts), Dzhida, (Bartoy volcanoes) and Tunka valley (Karierny volcano). For the comparisons the lower crust xenocrysts from the Angara Vitim batholite were studied. The calculated PT conditions show the PT estimates are localizing within the Moho –and just beneath giving the vast range of temperatures. Lower they trace 90 mw/m2 geotherm. Within the crust the variation of temperature regime are varying from the conductive to advective. Xenocrysts and pyroxenite xenoliths mainly trace 90 mw/m2  SEA plume geotherm the area of the intrusions is over heated to 1350oC.

Fig.1 PT diagram for the xenoliths from Vitim Miocene  Picrite basalts

Fig.2 PT diagram for the xenoliths from Bartoy Pleistocene basalts

Fig.3 PT diagram for the xenoliths from Tunka Pliocene basalts

Fig.4 PT diagram for the xenocrysts from  Magmas of Angara-Vitim batholite

The granulites are typically represent the more colder conditions than SEA geotherm.  Xenocrysts from Angara Vitim batholith magmas reveal more depleted material of lower crust than those found in Cenozoic lavas and possibly are skialites. The xenocrysts and granulate xenoliths in Cenozoic lavas are mainly basic cumulates. The lower crust became more acid to the upper part. The lateral variations in the lower crust sampled material show enrichment in K2O at the boundary with the Siberian craton in Tunka, more metasomatic and hydrous nature in Dzhida zone and more basic and CaO rich characteristic in Vitim area.  These data give the evidence for the conditions of the creation of magmas of Angara-Vitim Batholiths.  It was created by the hot spot created kimberlites and basalts in north and Center of Yakutia in Silurian- Devonian time and Ingashi lamproites,  than it turned in Transbaikalia and after returned to central and Northern Siberia.   

 Supported by Ministry of Science and Higher Education of the Russian Federation. Supported by Russian Science Foundation (23-17-00030). Work is done on state assignment of IGM SB RAS, Geological institute SB RAS Ulan Ude and Institute of Earth crust SB RAS, Irkutsk

How to cite: Ashchepkov, I., Tsygankov, A., Burmakina, G., Rasskazov, S., Ailow, Y., and Karmanov, N.: Thermal state and nature of the low crust in the Baikal Rift zone according to the lower crust xenoliths of Cenozoic volcanics and Paleozoic magmas. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1231, https://doi.org/10.5194/egusphere-egu24-1231, 2024.

Finding of the giant diamond in Ebelyakh of CLIPPIR type of IIa type (Moor, 2014) suggest that similar diamonds should be found in the source kimberlites in Anabar basing and nearest Northern fields located within collision Khapchan terrain. To predict the finding authors are using the method of 5E diagrams based on the principle of analogy of the compositions Fe/(Fe+Mg) – Cr/(Cr+Al) – (Mn,Na) (Mitchell, 1986) for satellite minerals (Gar, Cpx, Chr and Ilmenites) of diamond (DSM) comparing with the etalon diagram for Karowe pipe (reference) and any other pipe. The forecast is quantified by the probability of convergence of these compositions using the division to the cluster groups. It was shown that the convergence of the DSM compositions of the Karowe and Grib pipes is 74%, which can be regarded as an indicator of the possible presence of diamonds in the predicted CLIPPIR pipe (Zinchenko et al., 2021).

 The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO2 diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

 

A.

 

B.

Fig.1.  Mitchels’s diagram for minerals from Leningrad  and Malokuhamskay (B) pipes in comporisond with the Karowe pipe (contur lines) Cr- pyropes, Cr-diopsides, Ilmenites, Cr -spinels together. B. Triangle Na-Mn-Ti and C. Triangle Na-Al-Cr for Cr-diopsides and pyropes. D. distributions of the cluster groups for different minerals. E. Correltions of diamond grade with TiO2 in garnest, Cr-diopsides and Cr-spinels and Fe2O3 in ilmenites

The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO2 diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

A.

B.

 

C.

Fig.2. PTXFO2 diagram for all xenocrysts from Leningrad (A), Malokuonamskaya (B) and Karowe AK-6 pipes. Symboles see legend

Russian Science Foundation grant 23-17-00030

How to cite: Ivanov, A., Zinchenko, V., Ashchepkov, I., Babushkina, S., Oleinikov, O., and Shelkov, P.: The perspectives of finding of giant CLIPPIR-type diamonds in weakly diamondiferous kimberlites of the north of Yakutia (Western Anabar region) using method of 5E Mitchells’s diagrams and cluster analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3574, https://doi.org/10.5194/egusphere-egu24-3574, 2024.

EGU24-3630 | PICO | GD2.1

The influence of the Siberian plume to the formation of Angaro-Vitim batholiths 

Andrey Tsygankov, Igor Ashchepkov, and Burmakina Galina

The influence of the hot spot for the AVB was assumed by (Kuzmin and Yarmolyuk, 2011). It may be the same hot spot that cause the creation of the kimberlites at 420 Ma at the north of Siberian craton (Sun et al,, 2014; 2018) than in the central part of Yakutian kimberlite province 350- 370 Ma. and transferred to the Prisayanie forming kimberlite fields covered by Carboni ferrous Permian sedimentary sequences in the basins of Tumanshet, Biryusa and Chuna rivers. Than it produced the Ingashi kimberlites - lamproites 310 -300 Ma (Kostrovitsly et al., 2022).

Granites of Angara-Vitim batholith were caused and influenced by this huge thermal event. The A-type granitoid magmatism and acid and mafic magmatism accompanied by mingling between these magmas suggest influence of the mantle plume (Litvinovsky et al., 2002; Tsygankov et al., 2019). This explains the K-nature of the granitoid magmatism, corresponding to the selective melting of the K-feldspars (Litvinovsky et al., 2000). This is the reason of the alkaline magmatism widely distributed among the  AVB magmas (Tsygankov et al., 2010-2021).

The huge amount of the volatiles that accompany plumes are responsible for melting in the mantle and crust (White and McKenzie, 1995). But essential parts of plume volatiles are CO2 and CH gases (Marty and Tolstikhin, 1998).. The H2O fluxes correspond to the starting and final stages of plume impulses (Ivanov et al., 2013). The periods of such pulses are nearly close to 30- Ma what is regulated by the Cosmic forces (Abbott, and Isley, 2002). Boundaries of the geological periods correspond to plume events In Transbaikalia, the H2O-rich flux was designated by transition to more acid magmas at 270 Ma. The CO2-rich flux at the maximum was manifested by the generation of the Burpala alkali-carbonatite massif (Vladykin et al., 2017).

Further, numerous already granitic and associated magmas and massifs were found in Eastern Sayan and Southern Pribaikalie. In Svyatoi Nos in Baikal 310 Ma (Kruk et al., 2023). 

The simultaneously and later the hot spot  created the main massifs of the AVB at the time span 275 -320 Ma (Khubanov et al., 2016; 2021).  The further continuation could be found in Khangai  batholith (270-240 Ma) (Yarmolyuk et al., 2013).

Than at the eastern margin, the plume turned to the NNW again and created the Siberian large igneous province- Permo-Triassic traps (Kuzmin and Yarmolyuk, 2011) 260-240 Ma.  the development of the plume magmatism in Early Triassic and later  in Jurassic time probably was transformed to the Island hot spot (Kuzmin and Yarmolyuk, 2010).

RNF grant 23-17-00030

Kostrovitsky  S.I. ea  2021.  Special Publications 513, 45 - 70.

Khubanov V.B ea 2021.   Russian Geology  Geophysics. 62, 1331-1349.

Kuzmin, M.I. , Yarmolyuk,   2014.   Russian Geology and Geophysics, 55, 120-143.

Kuzmin M.I. ea 2010.   Earth-Science Reviews, 102, 29-59.

Yarmolyuk V.V ea 2013,   Petrologiya , 21/2, 115–142.

How to cite: Tsygankov, A., Ashchepkov, I., and Galina, B.: The influence of the Siberian plume to the formation of Angaro-Vitim batholiths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3630, https://doi.org/10.5194/egusphere-egu24-3630, 2024.

EGU24-4048 | PICO | GD2.1

Analyze of the structural conditions of heat and mass transfer under volcanoes of the northwestern sector of the Pacific ocean- Eurasian continent transition 

Viktor Sharapov, Yury Perepechko, Anna Mikheeva, Alexander Vasilevsky, Konstantin Sorokin, Igor Ashchepkov, and Grigory Kuznetsov

Based on the analysis of the tectonophysical characteristics of the actual seismofocal zone (SFZ) in the lithosphere of the Kuril-Kamchatka region and adjacent Oceanic areas,  we estimated the boundary conditions necessary for constructing the quantitative models of heat and mass transfer dynamics in compacted heterophase media under active volcanoes located over the mantle and crustal magmatic   sources of the ocean–continent transition regions of the northwestern sector of the Pacific Ocean.

The methodology of obtaining the information  used for developing of the mathematical models of magmatogenic processes includes: 1) the study of individual porphyry deposits associated with active fluid volcanogenic systems; 2) the study of morphological structures using cosmic satellite images (Sharapov et al., 1980); 3) the study of mantle and crust xenoliths of volcanics (Kutyev, Sharapov, 1979; Sharapov et al., 2009, 2017, 2020); 4) parametric tectono-physical analysis of the modern SFZ of the studied region (Sharapov et al., 1984, 1992); 5) experimental modeling of the  processes of deformation   Earth's crust and lithospheric mantle rocks of modern SFZ (Sharapov et al., 1984, 1992); 6) construction of mathematical models of the petrogenesis under volcanoes (Sharapov et al., 2007, 2020)

According to data on the structure of the Earth's crust under the Avacha volcano; (Koulakov et al., 2014), permeable zones are linear fractures 2-4 km wide, which are conductors of melts and magmatogenic fluids coming from magmatic systems (Koloskov et al., 2014).

An analysis of the time characteristics of formation porphyric deposits in the active margins of the Pacific Ocean (Sharapov et al., 2013) showed that more than 70% of the described deposits are formed during the evolution of fluid mantle-crustal ore-magmatic systems. This study analyzes the data on the structure of the modern SFZ of Kamchatka and the Kuril Island arc, used in constructing a model of heat and mass transfer under volcanoes.

Based on the analysis of the tectonophysical characteristics of the actual seismofocal zone (SFZ) in the lithosphere of the Kuril-Kamchatka region and adjacent Oceanic areas,  we estimated the boundary conditions necessary for constructing the quantitative models of heat and mass transfer dynamics in compacted heterophase media under active volcanoes located over the mantle and crustal magmatic   sources of the ocean–continent transition regions of the northwestern sector of the Pacific Ocean.

T

An analysis of the time characteristics of formation porphyric deposits in the active margins of the Pacific Ocean (Sharapov et al., 2013) showed that more than 70% of the described deposits are formed during the evolution of fluid mantle-crustal ore-magmatic systems. This study analyzes the data on the structure of the modern SFZ of Kamchatka and the Kuril Island arc, used in constructing a model of heat and mass transfer under volcanoes.

RNF grant  24-27-00411

How to cite: Sharapov, V., Perepechko, Y., Mikheeva, A., Vasilevsky, A., Sorokin, K., Ashchepkov, I., and Kuznetsov, G.: Analyze of the structural conditions of heat and mass transfer under volcanoes of the northwestern sector of the Pacific ocean- Eurasian continent transition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4048, https://doi.org/10.5194/egusphere-egu24-4048, 2024.

Small-volume alkaline magmatism has now garnered due attention in geosciences, wherein these rocks provide essential information about deep mantle processes, geochemical composition, and the prevailing geodynamics. The continental alkaline magmatism of deep-seated ultramafic lamprophyres (UML) is spatially and temporally linked with continental breakup and rifting. Additionally, they have gained significant attention in terms of mineralization.

Deccan hosts one of the most extensive and peculiar suites of lamprophyre complexes in India, and this magmatism holds valuable geological information to unveil the geodynamic processes and provide significant implications on the enrichment/depletion processes of SCLM during Deccan times. The present research delves into the mineral and whole-rock geochemical compositions and paleomag dating of lamprophyres from the West Coast Alkaline Complex (WCAC) of the Deccan Large Igneous Province. The study has implications for the relation of lamprophyre magmatism with the Réunion mantle plume, the associated main phase of Deccan tholeiite magmatism, the initiation of rifting in the western Indian subcontinental margin, the separation of Seychelles from the Indian subcontinent, as well as the role of lithosphere thinning in triggering lamprophyre magmatism. WCAC lamprophyres are principally composed of olivine and phlogopite phenocrysts/ macrocryst embedded in a mesostasis of carbonate, clinopyroxene, olivine, nepheline, spinel, and melilite groundmass. The presence of titanian aluminous phlogopite, clinopyroxene, and Al-enriched spinels with high Fe2+/(Fe+Mg) ratios are the characteristic features of WCAC lamprophyres. They are primitive, undersaturated in silica (SiO2: 38.43 – 38.99), and rich in MgO (up to 10 wt. %), TiO2 (up to 4.2 wt. %), and light rare earth elements. Mineral genetic classification schemes and geochemical compositions demonstrate a resemblance with ultramafic lamprophyres. 

High LREE/HREE (La/Yb= 75-82) ratios, similar to UMLs reported globally, and low Ba/Rb and Rb/Sr ratios exhibit the predominance of phlogopite and amphibole in the mantle source. Geochemical investigations inarguably trace their genesis back to the enriched garnet lherzolite mantle, metasomatised by silicate and carbonate veins. They show compositional similarity with global damtjernites and derivation from moderate pressure depth (3-4 GPa) corresponding to 90-100 km thick lithospheric mantle. Paleomagnetic studies support the intrusion of lamprophyres, predominantly during the chron C29n, thereby substantiating their radiometric eruption age at ~65 Ma. Seismic tomography models reveal a current lithospheric thickness of approximately 50 km beneath the WCAC, suggesting delamination of the lithosphere after the intrusion of lamprophyres at 65 Ma. UML magmatism in WCAC resulted from the initiation of a rift, which ultimately led to the separation of the Indian subcontinent and the Seychelles. The impetus behind the emplacement of UML dykes is intricately tied to passive rifting and external plate boundary forces, surpassing the influence of the Reunion mantle plume. The lithospheric thinning presumably occurred after the emplacement of lamprophyres and other alkaline rocks and continued with continental rifting in response to greater plate-tectonic stresses in the region of persistent lithospheric weakness.

How to cite: Singh, A. and Dongre, A.: Post-tholeiite rifting and genesis of ultramafic lamprophyres at ~65 Ma in the Deccan Large Igneous Province, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4288, https://doi.org/10.5194/egusphere-egu24-4288, 2024.

EGU24-4498 | PICO | GD2.1

Role of sediment-derived melts in Mo cycling of subduction zone 

Feng Huang, Jie Li, Jifeng Xu, and Yunchuan Zeng

While heavy molybdenum (Mo) isotope compositions in arc-related rocks have been linked to slab-derived fluids, the origins of arc lavas with light isotopic Mo compositions remain enigmatic. The two potential sources for the origin of light Mo isotopes in arc rocks are (1) dehydrated oceanic crust 1, 2 and (2) subducting sediments 3, 4. Although the former has been extensively recognized, the latter still poses an enigma. We present the Mo-Sr-Nd-Hf isotope compositions and elemental data of a suite of Jiang Tso andesites to elucidate the chemical compositions of sediment-derived melts in the central Tibetan Plateau. The andesites from the Jiang Tso area show elevated Mg# values, along with trace element characteristics reminiscent of melts derived from sediments. Their Sr-Nd-Hf isotope compositions (87Sr/86Sri = 0.710260–0.710671, εNd(t) = –10.63 to –8.97, and εHf(t) = –9.38 to –8.02) closely resemble those of contemporaneous sediments in the central Tibetan Plateau. In addition, these andesites exhibit higher Ce/Mo ratios (396–587) and extremely lighter δ98/95Mo values (−1.62‰ to −0.69‰) compared to the depleted mantle (δ98/95Mo = –0.21‰ ± 0.02‰) 5, 6 and the majority of arc lavas (δ98/95Mo = –0.07‰ ± 0.04‰) 3, suggesting a more plausible explanation lies in the involvement of subducting sediments rather than dehydrated oceanic crust in the source. Our latest findings, integrated with previous studies, indicate that the arc-related rocks exhibiting light Mo isotopes may not solely originate from the rutile-breakdown oceanic crust source but could also result from sediment melting at various sub-arc depths. Consequently, sediment-derived melts play a crucial role in Mo isotope cycling and the formation of arc magmas in subduction zones.

 

1 Chen, S., et al., Nat. Comm. 10, 4773 (2019). 2 Freymuth, H., et al., EPSL 432, 176-186 (2015). 3 Huang, F., et al., GCA 341, 75-89 (2023). 4 König, S., et al., EPSL 447, 95-102 (2016). 5 McCoy-West, A.J., et al., Nat. Geos.12, 946-951 (2019). 6 Willbold, M. & Elliott T., CG 449, 253-268 (2017).

How to cite: Huang, F., Li, J., Xu, J., and Zeng, Y.: Role of sediment-derived melts in Mo cycling of subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4498, https://doi.org/10.5194/egusphere-egu24-4498, 2024.

EGU24-4770 | ECS | PICO | GD2.1

Geochronological, petrological and tectonic implications of the Proterozoic massif-type anorthosite intrusions and related rocks from the northern Oaxacan Complex, southern Mexico 

Luis Alejandro Elizondo Pacheco, Luigi Solari, Hailong He, Juan Alonso Ramírez Fernández, and Roberto Maldonado

Massif-type anorthosite intrusions are enigmatic and significant crustal components widespread worldwide. They occur either as individual massifs or accompanied by mangerite, charnockite, and granite (AMCG suite). This Proterozoic phenomenon has been studied in numerous complexes, generating long-lasting discussions regarding the magmatic source and the tectonic setting where these rocks form. This controversy is still a matter of debate after decades of scientific research. In this sense, Mexico represents a unique and new opportunity to explore such petrological issues because its exposures of massive anorthosite and associated lithologies are mainly unstudied. These rocks are better exposed in the Oaxacan Complex, the most extensive Mexican inlier of Grenvillian rocks. This work is focused on its northern portion. This area is characterized by 1.4-1.1 Ga metamorphic rocks from the El Catrín and El Marquez units that were later intruded by anorthosite, gabbro, leucogabbro, oxide-apatite gabbronorites (OAGN), and granite bodies from the Huitzo suite. New LA-ICP-MS U-Pb zircon data revealed similar crystallization age ranges in the gabbro-anorthositic (1013-960 Ma) and granitic (1012-964 Ma) rocks. Their zircon Hf-O isotopic composition was compared with previous and new data from the older units of the area to assess the possible interaction between mantle- and crustal-derived melts during their generation. The intrusions of massive anorthosite and gabbro exhibit εHf(t) values of -2.54-4.79 and δ18O = 6.84-8.03‰. The granitic rocks have εHf(t) values of -0.79-2.87 and δ18O = 7.80-8.42‰. The lack of mantle-like εHf(t) and δ18O values suggests the participation of high-δ18O supracrustal material with more radiogenic Hf signatures during their generation. Simple binary mixing modeling indicates that the gabbro-anorthositic intrusions incorporated ~20-30% of metasedimentary country rocks, supporting a mantle-dominated origin. A slightly higher crustal component is recognized in the studied granitic intrusion. We also propose that these rocks permit an alternative model where Oaxaquia is paleogeographical relocated close to the eastern margin of Laurentia during the final stages of Rodinia amalgamation due to the resemblance in age to the late- to post-Grenvillian AMCG rocks (1016-956 Ma) outcropping there (e.g., Roseland, Mattawa, Labrieville, and Vieux Fort). This new tectonic view challenges the classical Amazonia-Oaxaquia-Baltica connection.

How to cite: Elizondo Pacheco, L. A., Solari, L., He, H., Ramírez Fernández, J. A., and Maldonado, R.: Geochronological, petrological and tectonic implications of the Proterozoic massif-type anorthosite intrusions and related rocks from the northern Oaxacan Complex, southern Mexico, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4770, https://doi.org/10.5194/egusphere-egu24-4770, 2024.

The geodynamic regime driving formation of Archean felsic continent crust is still an ongoing debated and unsolved fundamental issue. The episodic Archean TTGs and associated granitoids, with emplacement ages of ca. 2.9, 2.7 and 2.5 Ga, occurred in the Jiaobei Terrane, North China Craton (NCC), provide prolonged continuous records of formation processes of Meso-Neoarchean felsic continental crust. To track patterns of crust-mantle differentiation, crustal reworking and recycling, and accordingly, constrain underlying geodynamic regimes associated with formation of the Meso-Neoarchean felsic continental crust, we present comprehensive zircon U-Pb dating, Hf-O isotopes and whole-rock major- and trace-element geochemical data for the episodic Archean TTGs and associated granitoids. The comprehensive dataset decodes the generation of the episodic Archean TTGs over wide-range pressure conditions from amphibolite to eclogite facies and Meso-Neoarchean coupled crust-mantle differentiation, which was likely driven by episodic hot mantle (plume) upwelling. In addition, the ca. 2.9 and 2.7 Ga TTGs shared identical Mesoarchean juvenile crust source and exhibit consistent mantle-like zircon δ18O values, whereas the ca. 2.5 Ga TTGs mainly derived from distinctly younger Neoarchean juvenile crust, implying removal and replacement of the Mesoarchean juvenile lower crust. Importantly, some ca. 2.5 Ga TTGs, granitic gneisses and sanukitoids exhibit significantly higher zircon δ18O values than mantle δ18O values, demonstrating occurrence of Neoarchean supracrustal recycling. Consequently, the combined geochemical dataset with geological evidence allow us to track the geodynamic processes for the formation of the Meso-Neoarchean felsic continent crust in the Jiaobei Terrane, NCC: Episodic hot upwelling mantle (plume)-lithosphere interactions at ca. 2.9, 2.7 and 2.5 Ga resulted in the coupled crust-mantle differentiation over different depths to produce the spatial-temporally coexisted various-pressure-type TTGs, juvenile crust and voluminous dense lower crustal restite, respectively. Subsequently, dense lithospheric delamination triggered by gravitational instability occurred, followed by continental uplifting, subduction of altered oceanic crust, and asthenosphere and mantle-derived mafic melts upwelling, resulting in extensive occurrences of anatexis and metamorphism with anticlockwise P-T paths in the medium-lower crust at ca. 2.5 Ga. Along with large-scale melting and cooling of mantle, thick stable craton lithosphere with strong rigidity and viscosity had likely developed by the end of Neoarchean. The geodynamic processes in Meso-Neoarchean were likely diverse, especially episodic hot upwelling mantle (plume) -lithosphere interaction could be a favored geodynamic regime responsible for formation of Archean felsic continental crust in the Jiaobei Terrane, NCC.

How to cite: Liu, J.: Meso-Neoarchean coupled crust-mantle differentiation followed by gravity-driven lithospheric delamination and subduction initiation in the North China Craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4864, https://doi.org/10.5194/egusphere-egu24-4864, 2024.

EGU24-5761 | PICO | GD2.1

Can Venus and Mars Inform Us About Intraplate Magmatism on Earth? 

Scott King, Megan Duncan, Grant Euen, Joshua Murphy, Savaria Parrish, and Matt Weller

Venus and Mars have operated as one-plate planets for some or all of their history and intraplate magmatic activity on Earth has been suggested as an analogue for the observed volcanic activity on these bodies. Flipping the question around, what can we learn about intraplate magmatism on Earth from other planets?

Volcanic features, including extensive lava flows and vast lava plains, cover large portions of the Martian surface. Mars has two large volcanic provinces: Tharsis and Elysium. While the continent-sized region of elevated terrain called the Tharsis rise receives most of the attention, Elysium—the second largest volcanic province on Mars—is larger than the Ontong-Java plateau—the largest LIP on Earth. Activity detected by the InSight seismometer near Cerberus Fossae (located in Elysium Planitia, southeast of the Elysium volcanic province) is consistent with fluid flow at depth. Cerberus Fossae is among the youngest tectonic structures on Mars and large discharges of water and lava have been proposed to explain the geomorphic structures observed at Cerberus Fossae. The regional gravity and topography, volcanic history, and seismic activity at Cerberus Fossae are consistent with a present-day 2,000-km-radius plume head beneath Elysium Planitia. The characteristics of the Elysium Planitia plume are comparable to terrestrial plumes proposed to explain the formation of terrestrial LIPs. Plumes on Mars appear to be spatially stable for long periods of time, reflecting the stabilizing influence of a thick stagnant lid and sluggish mantle convection.

While Venus is nearly the same size as Earth, there is no evidence supporting Earth-like plate tectonics for the past 250-750 Myrs. The similarity in size invites comparison of present-day volcanic activity between the two planets. This is complicated by the presence of plate tectonics where volcanic activity at ridges and subduction zones has no clear analogue on Venus. Expanding intraplate volcanism on Earth suggests as many as 100 active volcanic events per year on Venus. While detecting surface changes is one goal of the upcoming NASA and ESA Venus missions, surface change associated with volcanic activity has already been found in the Magellan image archive. Herrick and Hemsley identified a 2 km2 volcanic vent that changed shape in the eight months between two Magellan radar images. While sulfuric acid clouds obscure our view of the surface, those same clouds provide the best evidence for ongoing volcanic activity. Assuming the primary mechanism removing atmospheric SO2 is a reaction between calcium minerals on the surface and SO2, an SO2 residence time of ~2 Myrs is required. This requires an outgassing rate of ~6x1010 kg SO2/year—about the same yearly SO2 outgassing rate measured on Earth over the past decade. Converting this outgassing rate to erupted lava, an eruption rate on Venus of ~1 km3/yr is obtained.

How to cite: King, S., Duncan, M., Euen, G., Murphy, J., Parrish, S., and Weller, M.: Can Venus and Mars Inform Us About Intraplate Magmatism on Earth?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5761, https://doi.org/10.5194/egusphere-egu24-5761, 2024.

This study presents the first comprehensive investigation into the petrography, major and trace element mineral chemistry of a mantle-derived eclogite xenolith suite from the Balmoral kimberlite. Most of the eclogite xenoliths from the Balmoral kimberlite pipe are bimineralic (garnet and clinopyroxene) rocks with a substantial number of corundum-bearing xenoliths also recognised. The bimineralic eclogites are classified into low MgO (<15 wt% MgO) and high MgO (<15 wt% MgO) varieties. Mica with average modal abundances ≤10 vol% is observed as an accessory phase in bimineralic xenoliths. Modal abundances of corundum in corundum-bearing samples range between 1 and 6 vol%. Textures are ambiguous in Balmoral eclogites, while the chemical criteria of McCandless and Gurney (1989) place all of them into Group II. The temperature range of Balmoral eclogites (at an assumed pressure of 50 kbar; Ellis and Green, 1979) is between 1046 and 1311 °C. The low-MgO bimineralic eclogites are characterised by relatively higher temperatures than the high-MgO variety. Corundum-bearing eclogites have the highest equilibration temperatures. Based on calculated temperatures, corundum-bearing eclogites have the highest inferred pressures of equilibration with the high-MgO eclogite variety having the lowest. The reconstructed Balmoral major element bulk compositions are characterised by variations in MgO, CaO and Al2O3 contents, with less variation in FeO contents. Reconstructed major element bulk compositions from bimineralic eclogites coincide with those of tholeiitic basalts, and to a lesser extent, basalts from mid-ocean ridges and oceanic gabbros. Corundum-bearing eclogites are similar to oceanic gabbros in general. The REE pattern of bulk eclogite commonly show humped-shaped REEN patterns. High MgO eclogites have a slight enrichment in the LREEN pattern while low MgO eclogites have enrichment in HREEN patterns. These REEN patterns are broadly comparable to those of oceanic gabbro and MORB. The protolith for these Balmoral eclogite xenoliths is thought to be a once composite oceanic crustal section which underwent partial melting during subduction and/or dehydration and, subsequent metasomatic re-enrichment in incompatible trace elements.

How to cite: Pattnaik, J. and Viljoen, F.: Petrology and geochemistry of a Cratonic mantle-derived Eclogite Xenolith Suite from the Balmoral Kimberlite, Kimberley Region, South Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6583, https://doi.org/10.5194/egusphere-egu24-6583, 2024.

EGU24-7403 | ECS | PICO | GD2.1 | Highlight

Quaternary volcanism in southeastern Tibetan Plateau: A record of stagnant oceanic slab in the mantle transitional zone 

Huan Kang, Yongwei Zhao, Xiaoran Zhang, Liyun Zhang, Huiping Zhang, and Haibo Zou

The Tibetan lateral mantle flow bears considerable significance in deciphering the material movement mechanisms within global plate convergence zones. However, the front edge of this mantle flow is unclear. Here we conduct petrological, geochronological, mineralogical, geochemical and Sr-Nd-Pb isotopic investigations on Quaternary intracontinental alkali basalts from the southwestern Yunnan (the south of 27°N), to determine the source characteristics and geodynamic mechanisms of the Quaternary alkali basalts in southeastern Tibetan Plateau and to trace the recent Tibetan mantle flow. Alkali basalts in the region are mainly basanite and trachybasalt with eruptions during the Pleistocene epoch. They possess a highly incompatible elemental and radiogenic Sr-Nd-Pb isotopic composition similar to those of the Ocean Island Basalts, consistent with melts derived from asthenospheric mantle with low-degree partial melting. Calculated magma-water contents of regional alkali basalts range from 1.32 ± 0.48 wt.% to 2.23 ± 0.18 wt.%, corresponding to 269 ppm to 3591 ppm water contents of their mantle source, which are significantly higher than that of the normal upper mantle (i.e., 50–250 ppm). Quantitative trace-element modelling and dramatic variations in oceanic crust-sensitive indicators such as Eu/Eu*, Sr/Sr*, Ce/Pb, (Nb/Th)N-PM and (Ta/U)N-PM indicate variable contributions of upper and lower oceanic crust to magma sources. Systematic examinations of petrological, geochemical, and geophysical evidence reveal that the temporary small-volume Quaternary volcanism in southeastern Tibetan Plateau is not related to Tibetan southeastward mantle flow but is primarily attributed to stagnant Neo-Tethyan slab in the mantle transition zone.

How to cite: Kang, H., Zhao, Y., Zhang, X., Zhang, L., Zhang, H., and Zou, H.: Quaternary volcanism in southeastern Tibetan Plateau: A record of stagnant oceanic slab in the mantle transitional zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7403, https://doi.org/10.5194/egusphere-egu24-7403, 2024.

A low-velocity layer atop the mantle transition zone has been extensively observed worldwide, which may play an important role in mantle dynamics and Earth habitability. In subduction zones, this layer is widely explained as partial melting triggered by slab subduction on a regional or global scale. However, direct observational evidence is still absent, and the response of the layer to slab subduction is not well known. Here, we image the seismic velocity around the mantle transition zone by matching synthetic and observed triplicated seismic P and sP waveforms in the Indian–Eurasian continental subduction zone. Our observations reveal a laterally varied low-velocity layer atop the mantle transition zone beneath the Hindu Kush, where a subducted slab extends to the mantle transition zone. It is characterized by thickness of 56-94 km and P-wave velocity drop of -2.8~-4.7%. The geometric morphology of the low-velocity layer indicates that it is a partially molten layer induced by the subducted slab on a regional scale. Interestingly, our observations also support that the layer has a low viscosity. The decreased viscosity possibly facilitates slab motion in the deep domain; however, the buoyant continental crust in the shallow domain likely resists downwards movement of the slab. This differential movement is more likely to cause slab stretching, tearing and break-off in the middle region, which may contribute to explaining rare recurring large intermediate-depth earthquakes in an intracontinental setting.

How to cite: Li, G.: Seismic evidence of upper mantle melt caused by a subducted slab in the Indian-Eurasian continental subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7577, https://doi.org/10.5194/egusphere-egu24-7577, 2024.

EGU24-8338 | ECS | PICO | GD2.1

The alkaline rocks olivine variety: a case study of Namuaive Pipe, Kola alkaline province, Russia 

Natalia Lebedeva, Anna Nosova, Lyudmila Sazonova, Alexey Kargin, Darina Shaikhutdinova, Vasiliy Yapaskurt, and Vasily Shcherbakov

An alkaline magma undergoes significant modification during its ascent to the surface due to assimilation of mantle and crustal material, exsolution of volatiles, trapping of crystals from earlier crystallized melt batches, fractional differentiation and explosive processes, making a thorough understanding of the petrogenesis of the magma and the nature of its mantle source in large igneous provinces difficult. The dikes and pipes of ultramafic lamprophyres, picrites and nephelinites are characterised by rapid rise of melt batches that could provide a high chance of preserving unworked mantle and crustal material. A study of olivine from these rocks may help to resolve some issues of their mantle sources and melt evolution.

The Namuaive pipe located in the northern part of the nepheline syenite Khibina Massif, Kola alkaline province. The pipe is filled by pyroclastic alkaline picrite (melanephelenite). The rock is texturally heterogeneous, consisting of 30-40 vol % magmaclasts and lapilli, phenocrysts and macrocrysts (up to 40 vol %) of phlogopite, olivine and clinopyroxene, xenoliths of Khibina Massif rocks, and fine grained matrix composed of phlogopite, apatite, perovskite, spinel, Ti-magnetite, nepheline, sodalite, high-Ti garnet.

Olivine is one of the most abundant macrocrysts in alkaline picrite, ranging up to 30 vol %; it is fresh or slightly replaced by serpentine or clinopyroxene-phlogopite intergrowth. Three groups of olivine based on core-to-rim zonation were observed:

  • Euhedral-to-subhedral olivine grains up to 5 mm are phenocrysts. Some grains have spinel inclusions. Phenocrysts show normal Mg#-zonation. They consist of a more magnesian core (Mg# = 0.90-0.89) with Ni content from 1595 to 3058 ppm and a thin marginal ferruginous zone (Mg# = 0.89-0.83) with Ni content from 363 to 2663 ppm.
  • Antecrysts have rounded and often corroded edges. Their size ranges from the first few hundred µm to 1 mm. They are characterised by Fe-rich cores (Mg# = 0.84-0.87) with a wide range of Ni contents from 1200 to 3200 ppm, surrounded by a transitional zone with a gradual increase in magnesium (Mg# = 0.86-0.89) and Fe-rich rind (Mg# = 0.89-0.86) with Ni contents from 1500 to 605 ppm. They have a small clinopyroxene-phlogopite rim and spinel along cracks.
  • The xenocrysts have been divided into two subgroups according to their Mg# and Ni contents. The cores of the first subgroup have Mg# 0.90-0.91 and Ni contents from 2800 to 3200 ppm, the cores of the second subgroup have Mg# 0.91-0.93 and Ni content about 2000 ppm. The rims of both subgroups have Mg# 0.83-0.85 and Ni contents from 1236 to 433 ppm. Some olivine grains are intergrown with high-Cr clinopyroxene and high Mg phlogopite.

The antecrysts reflect mixing of the evolved lamprophyric melts during previous pulses with the partial melt batch that formed the Namuaive pipe. Phenocrysts and other olivine rims formed during fractional crystallization. Antecrysts and phenocrysts equilibrated to melts from wehrlite sources.

The study was supported by the Russian Science Foundation under Grant No 23-77-01052

How to cite: Lebedeva, N., Nosova, A., Sazonova, L., Kargin, A., Shaikhutdinova, D., Yapaskurt, V., and Shcherbakov, V.: The alkaline rocks olivine variety: a case study of Namuaive Pipe, Kola alkaline province, Russia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8338, https://doi.org/10.5194/egusphere-egu24-8338, 2024.

The modal metasomatic alteration for lithosphere mantle may be investigated using mantle xenoliths from kimberlite pipes. The pyroxenite xenoliths from diamondiferous upper-Devonian Udachnaya kimberlite pipe (Daldyn field, Yakutia) were studied, mineral chemical composition was researched. The several stages of metasomatic processes were observed in the lithospheric mantle under the Udachnaya kimberlite pipe.

The most garnets from studied xenoliths demonstrated so-called “normal” trace element distribution that closed to the element coefficients the basalt - silicate melt. All garnets are characterized by a maximum in Ta, a minimum in La-Ce, and a minimum in Ti. Eclogites (especially with a mosaic texture) are characterized by a small minimum in Eu, which may indicate the presence of Pl in the initial rock. The presence of eclogitic xenoliths (with Eu-minimum in garnet) indicates the influence of the subduction component. The pyroxenite xenoliths with narrow variations in the composition of minerals indicates their crystallization from melts, accompanied later by metamorphic recrystallization. The 10% studied xenoliths are observed the secondary metasomatic amphibole (pargasite - taramite) - the evidence of modal Amph metasomatism. The Ti/Eu – La/Yb distribution for clinopyroxene and amphibole demonstrate the influence of silicate (not carbonatite) melts.The increasing concentrations of HFSE and REE group elements can also be traced by the Cpx and Grt chemical composition, it may be indicating the asthenospheric melts. Several garnet samples from high-Zr (80–100 ppm) eclogites demonstrated the features of fluid metasomatism (fluid-produced, accompanied by phlogopite crystallization). Another sign of the alkaline melts influence is secondary Na silicates crystallization (according reaction Grt + Omphacite + K - Fluid = Amph + Сpx2 ± Cal ± Sodalite).

Thus, several stages of metasomatic processes were observed in the lithospheric mantle under the Udachnaya kimberlite pipe. The presence of eclogite xenoliths (with a Eu minimum) indicates the influence of a subduction component. The presence of pyroxenite xenoliths with narrow variations in mineral composition indicates their crystallization from melts - the second stage of metasomatic processes, subsequently be accompanied by metamorphic recrystallization. The content of trace elements in garnets indicates the asthenospheric nature of the melts. Such melts brought elements of the HFSE and REE groups, as well as Pt, Pd and Re. The last stage is most clearly traced using modal Amph metasomatism. The presence of secondary amphibole indicates widespread occurrence of silicate pre-kimberlite metasomatism in the lithospheric mantle beneath the center of the Siberian craton.

The research was supported by Russian Science Foundation grant № 22-77-10073.

How to cite: Kalashnikova, T. and Kostrovitsky, S.: The silicate and carbonatite metasomatic alterations in lithospheric mantle under Siberian craton (the evidence of mantle xenoliths from Udachnaya pipe), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11448, https://doi.org/10.5194/egusphere-egu24-11448, 2024.

EGU24-14538 | PICO | GD2.1

Features of the introduction of magmatic melts in permeable zones of the platform cover 

Yury Perepechko, Konstantin Sorokin, and Sherzad Imomnazarov

The problem of the introduction of heterophase magmatic melts into the conducting channels of the lithospheric mantle under the cratons of the Siberian platform has been studied numerically. The analysis of the features of the introduction of melts was carried out on the basis of a hydrodynamic model of the evolution of magmatic and fluid-magmatic systems. The mathematical model describes the two-speed dynamics of the redistribution of hot heterophase melts and magmatogenic fluids in the flow during their movement from the generation zones to the platform cover, as well as the processes of heat and mass transfer between melts and rocks in permeable zones of the lithosphere. The nature of the flow of mixtures of liquid fractions of aluminosilicate, sulfide, native and oxide liquids, in which a sub-liquid solid phase appears during movement and decompression boiling occurs, the features of heat and mass transfer processes determine the type of magmatic and magmatogenic deposits of the trap formation of the Siberian platform. The flow of magmatic melts in a wide temperature range of 300-1200 °C, the viscosity of the melt phases of 101-106 N, as well as the rate of penetration and the degree of stratification of the heterophase magmatic flow were studied.

The figure shows an example of the randomization of an intrusive flow. (a) (b) An example of the development of heterogeneity in the distribution of the concentration of particles of the dispersed phase (a, m-3) and temperature (b, °C) in an initially stratified magmatic flow embedded in the host rocks. The temperature of the introduced flow is 500 °C, in the channel at the initial moment standard thermodynamic conditions; the dynamic viscosity of the melt is 102 P. The work was carried out with the financial support of the Russian Science Foundation, grant No. 24-27-00411.

How to cite: Perepechko, Y., Sorokin, K., and Imomnazarov, S.: Features of the introduction of magmatic melts in permeable zones of the platform cover, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14538, https://doi.org/10.5194/egusphere-egu24-14538, 2024.

EGU24-14806 | PICO | GD2.1

Reconstructions of mantle structure beneath kimberlites of Anabar shield and surroundings – similarities and differences. 

Sergey Kostrovitsky, Igor Ashchepkov, Svetlana Babushkina, and Nikolai Mdevedev

Comparative study of the mantle xenocrysts from Anabar region (Ary-Mastakh, Dyuken, Orto-Yargyn fields) and Boomerang kimberlites and pipe show essential differences with the mantle in surrounding area from Olenek (Chomurdakh field)

The PTX diagram show presence of the rare lherzolitic pyrope and abundant eclogitic almandines to 6 GPa. In suture zone of Daldyn and Magan terranes (Boomerang pipe) eclogitic omphacites and Cr less pyroxenites and Cr diopsides occurs mainly in the middle mantle part the pyroxenite layer possibly formed after eclogites due to plume melt interaction. Long ilmenite fractionation trend extends from the lithosphere base to the GPa 2.5, which is typical. Geochemistry of minerals vary from most depleted pyropes with V-U shaped REE patterns typical of arc mantle and Ba, U peaks and HFSE minima of subduction type. The fertilization produced the increase of the incompatible elements and sometimes LILE and The marginal parts of the SCLM of Anabar shield are extremely enriched in eclogitic deep-seated material located in lower SCLM part and demonstrating similar thermobarometric trends and features to the diamond inclusions from the Ebelyakh (Mayat) placers. Mantle column beneath several pipes (Losi, Universitetskaya, Kuranakh) contain Cr amphiboles distributes from lithosphere base to Moho. Comparison of reconstructed SCLM beneath Anabar and Chomurdakh field reveal more fertile compositions of the mantle rocks and simpler structure for later field. Abundance of eclogites in Kuranakh and Orto-Yargyn kimberlite in the lower mantle lithosphere part and their PTX trends are similar to the eclogitic diamond inclusions from the Ebelyakh placers. This increase the possibility of finding of diamonds deposits in Anabar shield kimberlites.

RNF grant No. 24-27-00411

How to cite: Kostrovitsky, S., Ashchepkov, I., Babushkina, S., and Mdevedev, N.: Reconstructions of mantle structure beneath kimberlites of Anabar shield and surroundings – similarities and differences., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14806, https://doi.org/10.5194/egusphere-egu24-14806, 2024.

EGU24-16571 | PICO | GD2.1 | Highlight

The origin of melilitites: preliminary results on melting of a carbonated wehrlite 

Stefano Poli and Leone Melluso

Melilitites are ultramafic magmas characterized by normative Ca2SiO4, larnite, high FeO* and TiO2. Liquids compositionally close to melilitites were experimentally reproduced from carbonated lherzolites in alkali, Fe and Ti-free model systems at 3.2-3.3 GPa, approx.  1500 °C (Gudfinnsson & Presnall, 2005), at relatively high melt proportions. In complex compositions, MORB-eclogite derived, carbonated, partial melts reacted with a fertile peridotite were proposed at the origin of melilitites (Mallik & Dasgupta, 2013, 2014). The experimental reconstruction of phase relationships along a join olivine melilitite - carbonate revealed that at 3 GPa, clinopyroxene and olivine or garnet are stable on the liquidus (Brey & Ryabchikov, 1994), suggesting that carbonated wehrlites are potential sources for the genesis of melilitites.

Here, we explore phase relationships on the high pressure melting of a model wehrlite, initially composed of a mechanical mixture of San Carlos olivine, diopside, aegirine, dolomite, rutile and kyanite. Starting materials were loaded in graphite capsules, inserted in sealed platinum capsules. Vitreous carbon spheres and synthetic diamond grains were adopted for liquid traps. 

Preliminary experimental results show that at 3 GPa the solidus is located at temperatures lower than 1200 °C. A thick, orthopyroxene-rich layer, with polygonal microstructure, forms at contact with aggregates resulting from quenched liquids, both at 1200 °C and 1400 °C. Estimates of liquid composition are melilititic, with TiO2 approx. 2.5 wt.% on a volatile free basis.

Currently available experiments suggest that the solidus is controlled by the reaction dolomite + olivine + clinopyroxene = orthopyroxene + liquid, as suggested in Eggler (1976). This is feasible only if the liquid composition is located on the CaO-rich side of the plane diopside-forsterite-dolomite in the model system CaO-MgO-SiO2-CO2, i.e. on the normative larnite (akermanite) portion of the tetrahedron.

 

Brey G.P. & Ryabchikov I.D. (1994). Carbon-dioxide in strongly silica undersaturated melts and origin of kimberlite magmas. Neues Jahrbuch Fur Mineralogie-Monatshefte, (10), 449-463.

Eggler D.H. (1976). Does CO2 cause partial melting in the low-velocity layer of the mantle?. Geology4(2), 69-72

Gudfinnsson G.H. & Presnall D.C. (2005). Continuous gradations among primary carbonatitic, kimberlitic, melilititic, basaltic, picritic, and komatiitic melts in equilibrium with garnet lherzolite at 3–8 GPa. Journal of Petrology46(8), 1645-1659.

Mallik A. & Dasgupta R. (2013). Reactive infiltration of MORB-eclogite-derived carbonated silicate melt into fertile peridotite at 3 GPa and genesis of alkalic magmas. Journal of Petrology54(11), 2267-2300

How to cite: Poli, S. and Melluso, L.: The origin of melilitites: preliminary results on melting of a carbonated wehrlite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16571, https://doi.org/10.5194/egusphere-egu24-16571, 2024.

EGU24-20570 | PICO | GD2.1

On a tectonics, magmatism and hydrocarbons (HC, oil-gas) of the South Caspian - West Baluchestan, Middle East: some problems and constraints 

Alexander Romanko, Nazim Imamvderdiyev, Ilya Vikentiev, Bahman Rashidi, Mehrdad Heidari, and Anton Poleshchuk

Joint analysis of tectonics, magmatism, metallogeny, and hydrocarbons (HC – oil-gas) for the South Caspian - west Baluchestan, Middle East (Alpine time mainly) was made. Different anomalies and degassing here are of interest too.  Specific anomalous deep regime and degassing of CH4, H2 etc. due to a giant African superPlume activity are noted too. Such points discussed as follows:

1.      Alpine North-Eastern (NE) tectonic zoning exists in this region up to Present (Q4). Anomalous long-lived African superPlume activity influences on regional tectonics, related magmatism and fluid regime (Fig.). There are different anomalies in this region on gravity, hydrocarbons (HC), degassing etc.

2. Miocene – Recent (N1-Q) intraplate magmatism with: different subalkaline- alkaline rocks directly relates to superPlume mentioned. There are data about Sr, Ca etc. input in upper younger Caspian Sea sediments from the lower older magmatites. Such magmatic trend exists as: Quaternary carbonatites, Hanneshin, Helmand block (Afghanistan) - Ca-rich volcanites with CaO up to 34.8% -  trachyandesites with CaO = 7.2%.  

  • Oligocene-Recent (Pg3-Q) calk-alkaline subduction-related rocks are as antipodes to mentioned intraplate rocks (intrusive, extrusive and volcaniclastic ones). Relation with African superplume is not formally necessary, but there are our data about warmer calk-alkaline rocks here, ex., warm melt inclusions in them with T crystallization as 1180oC.
  • Decreasing of earthquakes activity from South to the Middle Caspian Sea, at

least (Khain, Bogdanov, 2003 etc.). HC resources decreasing from Persian Gulf to North Caspian Sea

  • Lesser order HC zoning (west to east: oil - gas) in the S-M Caspian Sea exists. Is Great Caucasus a barrier for HC in lesser order?
  • A regional tectonic - HC correlation in Iraq - South Caspian- Turkmenistan exists: more compression and oil in west of region versus less compression and gas in the east of region up to the east Turkmenistan with, however, non-deep sea conditions (transitional facies) in the latter. Moreover, unusual several times repeating of oil - gas - gas-condensate in a stratigraphic section is revealed in west Turkmenistan. Is it a result of deep fluids input too? HC behavior and zoning is not quite clear in this unique economic and geological region.
  • Other HC north-south (N-S) zoning is as follows: HC in the old rocks - since Devonian up to Paleogene (D-Pg) – North Caspian Sea vs. HC in Triassic-Jurassic, Paleogene rocks in the Middle Caspian Sea, and in Low Pliocene (N2) rocks - South Caspian Sea. It could be in agreement with northeastern (NE) superplume activity decreasing. Giant HC resources in Saudi Arabia – Caspian region could be related with this hot regime. HC localizations are in agreement with a regional general geology. Surely, the oil genesis is traditional – organic one.

There is a good correlation as detailed HC structural map - HC maximum. It is in agreement with a young concrete HC localization despite the different age of host rocks.  Mud volcanoes (Kholodov, 2012 etc.) – HC – Salt – magmatism - tectonics in this region studied is the one system.    

This work was made due to the State program of the Geological Institute RAS.

How to cite: Romanko, A., Imamvderdiyev, N., Vikentiev, I., Rashidi, B., Heidari, M., and Poleshchuk, A.: On a tectonics, magmatism and hydrocarbons (HC, oil-gas) of the South Caspian - West Baluchestan, Middle East: some problems and constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20570, https://doi.org/10.5194/egusphere-egu24-20570, 2024.

GD3 – Dynamics and Evolution of Earth and Terrestrial Planets

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.

EGU24-2138 | ECS | PICO | GD3.2

Modelling magma-induced surface uplift and dynamic fracturing around laccoliths on the Moon, Mars, and Earth 

Sam Poppe, Alexandra Morand, Claire E. Harnett, Anne Cornillon, Marek Awdankiewicz, Michael Heap, and Daniel Mège

Dome-shaped uplifted and fractured terrain observed at the surface of the Moon and Mars includes floor-fractured impact craters. Such deformation features are inferred to form by the emplacement and inflation of sill- and laccolith-shaped magma bodies in the shallowest 1-2 km of a planetary body’s rocky crust. Only the final surface deformation features can be observed from space, modelling helps to understand the emplacement dynamics and the deformation of the overlying rock. A mismatch exists, however, between the complex mechanical response of host rocks to magma-induced stresses observed on Earth in exposed volcanic plumbing systems and the linearly elastic deformation assumed by most of the often-used numerical models.

We have implemented simulations of the inflation of a laccolith intrusion in a particle-based host medium in the two-dimensional (2D) Discrete Element Method (DEM). Our approach allows us to investigate magma-induced, highly discontinuous, deformation and dynamic fracturing and visualizes the localization of subsurface strain. We systematically varied a range of numerical model parameters that govern host rock strength (bond cohesion, bond tensile strength, bond elastic modulus), and specific gravity known for the Moon, Mars and Earth. For equal rock stiffness and amounts of intruded magma, our model results show that we can expect more vertical surface displacement on the Moon due to the lower gravity there compared to Mars, and Earth. Rock toughness and rock stiffness control the amount of fracturing more than gravity does.

We also tested how host rock strengths in our 2D DEM model could be upscaled from intact strengths of rock samples collected at Earth analogue sites, or by implementing a digital crack network that simulates the highly fractured conditions of the intensively impacted Lunar and Martian crusts. Our results show that laccolith inflation in pre-cracked host rocks results in higher surface displacements and a higher amount of magma-induced cracking in broader fractured zones. We expect that our model results will induce a better understanding of the emplacement and architecture of shallow magmatic intrusions below magma-induced uplifted terrain and floor-fractured craters on the Moon and Mars.

How to cite: Poppe, S., Morand, A., Harnett, C. E., Cornillon, A., Awdankiewicz, M., Heap, M., and Mège, D.: Modelling magma-induced surface uplift and dynamic fracturing around laccoliths on the Moon, Mars, and Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2138, https://doi.org/10.5194/egusphere-egu24-2138, 2024.

The rock and rock-ice mixtures of the core-enveloping spherical shells comprising terrestrial body interiors have thermally determined viscosities well described by an Arrhenius dependence. Accordingly, the implied viscosity contrasts determined from the activation energies (E) characterizing such bodies can reach values exceeding 1040, for a temperature range that spans the conditions found from the lower mantle to the surface. In this study, we first explore the impact of implementing a cut-off to limit viscosity magnitude in cold regions. Using a spherical annulus geometry, we investigate the influence of core radius, surface temperature, and convective vigour on stagnant lid formation resulting from the extreme thermally induced viscosity contrasts. We demonstrate that the cut-off viscosity must be increased with decreasing curvature factor, ƒ (=rin/rout, where rin and rout are the inner and outer radii of the annulus, respectively), in order to obtain physically valid solutions. We find that for statistically-steady systems, the mean temperature decreases with core size, and that a viscosity contrast of at least 107 is required for stagnant lid formation as ƒ decreases below 0.5. Inverting the results from over 80 calculations featuring stagnant lids (from a total of approximately 180 calculations), we apply an energy balance model for heat flow across the thermal boundary layers and find that the non-dimensionalized temperature in the Approximately Isothermal Layer (AIL) in the convecting layer under a stagnant lid is well predicted by T'AIL=½{ -(2T'out+γ) + √[γ2 + 4γ(1+T'out)] } where γ is a function of E and ƒ, and T'out is the non-dimensionalized surface temperature. Moreover, the normalized (i.e., non-dimensional) thickness of the stagnant lid, L', can be obtained from a measurement of the non-dimensional surface heat flux once T'AIL is determined. Stagnant-lid thicknesses increase from 10 to 30 percent of the shell thickness as ƒ is decreased, and thick lids can overlie vigorously convecting underlying layers in small core bodies, potentially delaying secular cooling and suggesting that small objects with small cores may have developed thick elastic outer shells early in the solar system's history while maintaining vigorously convecting interiors. However, we also find that for the small number of 3-D calculations that we examined, parametrizations based on 2-D calculations overestimate the temperature of the convecting layer and the thickness of the conductive lid when ƒ is small (less than 0.4).

How to cite: Javaheri, P., Lowman, J., and Tackley, P.: Spherical geometry convection in a fluid with an Arrhenius thermal viscosity dependence: the impact of core size and surface temperature on the scaling of stagnant-lid thickness and internal temperature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3226, https://doi.org/10.5194/egusphere-egu24-3226, 2024.

Nearly three decades of investigation has made steady progress towards self-consistently generating multiple features of plate tectonics from global mantle convection models.  Accordingly, the modelling of dynamic plates with migrating boundaries and evolving areas has become commonplace in both 2-D and 3-D geometries. Investigating the properties required for obtaining durable deep mantle formations similar to the Large Low Shear-wave Velocity Provinces (LLSVPs) has received similar attention. In this study, we model LLSVPs by assuming their composition is persistent  (i.e, we assume steady-state chemistry). To this end, we incorporate a Compositionally Anomalous Intrinsically Dense (CAID) mantle component comprising 2–3.5 per cent of the total mantle volume. We explore the impact of both an intrinsic contrast in density and viscosity for the CAID component, in an effort to stimulate the formation of a pair of LLSVP-like structures and a surface that exhibits the principle features of terrestrial plate tectonics; including recognizable and narrowly focused divergent, convergent and (in 3-D) transform plate boundaries that separate 8–16 distinct plate interiors. Although we find that a pair of CAID material provinces can be readily obtained in 2-D calculations while maintaining a surface exhibiting plate-like behaviour, specifying the same system parameters in 3-D calculations does not yield a pair of enduring provinces for any values of the parameters investigated.  In addition, CAID component inclusion in the calculations can affect global geotherms, so that in comparison to the surface behaviour obtained for the initial condition isochemical model, the cases incorporating the dense component do not yield surfaces that simulate plate tectonics. In general, CAID material components that are 3.75–5 percent denser than the surrounding mantle (at surface temperatures), and up to a factor of 100 times greater in intrinsic viscosity, form layers populated by voids, or nodes connected by ridges that reach across the core–mantle boundary (CMB), rather than distinct piles resembling the morphology of the LLSVPs. However, due to their temperature, we find the CAID material forms masses on the CMB that are relatively less dense (0.625–1.5 per cent) and viscous than the adjacent mantle material, in comparison to the percentage differences obtained at common temperatures. By adjusting our yield stress model to account for the influence of the CAID material on the geotherm, we find a highly satisfactory plate-like surface can be re-attained. Nevertheless, the formation of a pair of LLSVP-shaped masses remains elusive in 3-D calculations with plate-like surface behaviour and we suggest that caution is required if inferring the physical properties of the LLSVPs from 2-D models.

How to cite: Lowman, J., Langemeyer, S., and Tackley, P.: Model geometry determined contrast in the feedback between compositionally originating LLSVPs and dynamically generated plates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4709, https://doi.org/10.5194/egusphere-egu24-4709, 2024.

EGU24-6343 | ECS | PICO | GD3.2

Large impacts and their contribution to the water budget of the Early Moon. 

Tristan Engels, Julien Monteux, Maud Boyet, and Ali Bouhifd

The Earth/Moon system likely results from a giant impact between a Mars-size object and the proto-Earth 70 to 110 Myrs after the formation of the first solids of the Solar System. This high-energy context leads to extreme conditions under which volatile elements would not normally be preserved in the protolunar disk. However, recent measurements of lunar samples highlight the presence of a significant amount of water in the Moon's interior (1.2 to 74 ppm). The aim of the present work is to quantify the water contribution of the late accretion on the early Moon. Here, we use a 2D axisymmetric model with the hydrocode iSALE-Dellen to study the fate of a large impactor on a target body similar to the early Moon with a crust, a magma ocean, and a mantle. For this purpose, we compute different models to monitor the depth to which the impacted material is buried at the end of the impact event and the degree of devolatilisation of the impactor. Three parameters are explored: the crustal thickness (ranging from 10 to 80 km), the impactor radius (ranging from 25 to 200 km) and the impactor velocity (ranging from 1 to 4 times the target escape velocity). Our models show that impactors with a radius greater than 50 km impacting a partially molten lunar body with a crust thinner than 40 km could significantly contribute to the water content of the lunar mantle even for impact velocities of less than 5 km s-1. For larger impact velocities (≥ 10 km s-1) the impactor material is significantly molten and its water content is devolatilised within the lunar atmosphere. Depending on the water content of the impactor material and the ability of the lunar magma ocean to maintain chemical heterogeneities, the late lunar accretion following the Moon-forming giant impact could explain the differences in water content between the lunar samples.

How to cite: Engels, T., Monteux, J., Boyet, M., and Bouhifd, A.: Large impacts and their contribution to the water budget of the Early Moon., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6343, https://doi.org/10.5194/egusphere-egu24-6343, 2024.

EGU24-6814 | ECS | PICO | GD3.2

Magnitude estimation of Paleo-moonquakes from boulder tracks in Finsen crater 

Sha Tao, Yaolin Shi, and Bojing Zhu

High-resolution images taken by the Lunar Reconnaissance Orbiter show the existence of many boulder tracks within the Finsen crater. Current research suggests that shallow moonquakes and meteorite impacts are likely to be the cause of boulder falls. Based on a simplified model, we simulate the rolling process of the boulder along the slope when the lunar surface shakes and provide the critical PGA (peak ground acceleration) required for the boulder to start rolling under different conditions. The results show that boulders may roll down slopes within one or more cycles under strong ground shaking. The critical PGA of seismic waves required for a boulder to conduct slope rolling is related to the size of the boulder, the slope at the initial location, the dominant period of the seismic wave, and the ratio of horizontal and vertical peak ground accelerations. Except for rolling against the slope, in some cases, boulders may jump and roll downhill. Using the high-resolution images taken by the LRO to determine how the boulders rolled downhill, we can then estimate the lower limit of the magnitude of moonquakes in the region under different conditions. Finally, we provide a preliminary estimation of the lower limit of the paleo-moonquakes magnitude in the Finsen Crater.

How to cite: Tao, S., Shi, Y., and Zhu, B.: Magnitude estimation of Paleo-moonquakes from boulder tracks in Finsen crater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6814, https://doi.org/10.5194/egusphere-egu24-6814, 2024.

The Large Low-Velocity Provinces (LLVPs) beneath West Africa and the Southern Pacific are characterized by low seismic wave velocities and are associated with plate-unrelated magmatism such as hotspots, large igneous provinces, and kimberlite. Despite their significance, the structure, origin, and feeding processes of LLVPs remain elusive.

Previous studies have suggested that the LLVPs have remained stationary for over 300 million years, but their morphology appears to have changed. While geodynamic simulations favor denser LLVPs, a recent free-oscillation analysis has suggested lighter ones. The High-Velocity Region (HVR), which surrounds the LLVPs, is located beneath present and past subduction zones. Plumes of varying morphology are imaged between hotspots and LLVP margins, with intensive plumes revealing ultra-low velocity zones (ULVZs) at their roots. Ocean island basalts (OIBs) from hotspots are geochemically enriched and originate from multiple reservoirs. Interestingly, OIB chemistry does not correlate with seismic plume imaging and differs between the two LLVPs. OIB near the African LLVP is influenced by fluid-related subducted materials.

In the light of these results, I propose the following new model for the LLVPs. The LLVPs are at higher temperatures than the HVR and the surrounding mantle. They are composed of Fe-enriched mono-mineral bridgmanite rock, called bridgmanitite. The large grain size of bridgmanitite results in high viscosity despite the high temperatures, thereby stabilizing the LLVPs. The LLVPs are block-structured and the relative movement of the blocks changes the LLVP morphology. Bridgmanitite was formed by the solidification of a primordial magma ocean. Its deposition at the core-mantle boundary forms LLVP precursors in the early mantle. These LLVP precursor blocks can be moved by the thrust and sweep of subducted slabs to form the present-day LLVPs. Erosion and plume formation have reduced the volume of the LLVPs and resulted in different LLVP heights. The HVR consists of harzburgite brought from the surface by subduction. It contains only a limited amount of basaltic rock because the basaltic rock was detached from slabs in the mid-mantle due to suppressed grain growth. As a result, the HVR material is high-density due to the low temperature but is intrinsically low-density due to its chemistry. The HVR material has been heated using the LLVP heat to form plumes. Plumes are geochemically depleted when they have formed in the deep mantle. However, they are enriched in incompatible elements and volatiles in the shallow mantle. This enrichment results from melt migration due to the temperature gradient around the plume. Thus, although LLVP heat drives plume formation, the plate-unrelated magmas such as OIB are not directly derived from the LLVPs.

How to cite: Katsura, T.: Large Low-Velocity Provinces (LLVPs): a new model for their structure, origin, and evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8054, https://doi.org/10.5194/egusphere-egu24-8054, 2024.

EGU24-8194 | ECS | PICO | GD3.2

High pressure phase of Magnesiowustite: Implications to the mineralogy of super-Earths 

Anjitha Karangara and Pratik Kumar Das

Recent years have seen the discovery of a huge number of exoplanets, including several planets with very high densities suggesting that they also have rocky interiors which may be 9 – 10 times more massive than Earth. Mineralogy of these so called ‘super-Earth’ planets have been an interesting topic, as it gives implications on the planetary processes (Plate tectonics, geodynamo, etc.) and their habitability. Many studies concluded that such planets may contain ultra-high-pressure analogues of Earth’s lower mantle minerals. (Mg,Fe)O, a binary solid solution of MgO-FeO system is the second most abundant mineral of Earth’s lower mantle. If these super-Earth’s interior can have high pressure analogue of perovskite which is another most abundant phase of lower mantle of Earth as shown by some recent studies then there is a possibility of finding high pressure phase of (Mg,Fe)O also in the lower mantle of those super-Earths. MgO is stable in a NaCl structure (B1) in lower mantle condition of earth. It transforms to CsCl2 (B2) at high pressure (p) and Temperature (T) conditions. However, FeO is stable in B1 structure which transforms to a rhombohedral phase first and then to NiAs-type structure (B8) with increasing p. Finally, above 240 GPa and 4000 K, FeO transforms directly from B1 to B2. Along with structural phase transitions, FeO also undergoes a spin transition from high spin (HS) to low spin (LS) state with increasing pressure. In this study, we performed first principles DFT calculations on the structural phase transitions of MgxFe1-xO (x % = 0, 25, 50, 75 & 100) from B1 to B2 coupled with spin transition. Their mechanical and thermal properties under pressures ranging from 0 – 500 GPa relevant to super-earth planets have also been estimated. Our investigations have confirmed the presence of B1 phase of (Mg,Fe)O in lower mantle of earth with a spin transition from HS -LS which is thought to be responsible for the seismic anomalies of lower mantle of Earth. Spin transition of magnesiowustite and its effect on mechanical and thermal properties have been the topic for several experimental studies for many years. Most of them tried to explain the shear anisotropy of lower mantle with the help of (Mg,Fe)O with various Fe concentrations. Present study attempts to explore the stable phases of MgxFe1-xO relevant to super-Earth conditions. Both mechanical and dynamical behaviour have been investigated in the entire pressure range. Results show a new tetragonal phase of Mg0.25Fe0.75O above 125 GPa, which is found to be both mechanically and dynamically stable. These findings will also attempt to predict the mineralogy and seismicity of those giant planets.

How to cite: Karangara, A. and Das, P. K.: High pressure phase of Magnesiowustite: Implications to the mineralogy of super-Earths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8194, https://doi.org/10.5194/egusphere-egu24-8194, 2024.

EGU24-9734 | ECS | PICO | GD3.2

Thermochemical models of early Earth evolution constrained by geochemical data 

Charitra Jain, Stephan Sobolev, Alexander Sobolev, and Adrien Vezinet

Isotopic systems and trace elements are ideal proxies to constrain the production and recycling of crust (both mafic and felsic) over time. Within the Rubidium-Strontium (Rb-Sr) system, Rb-87 decays to Sr-87 and due to the preferential partitioning of Rb into the crust (relative to Sr) during partial melting, 87Sr/86Sr ratio of the crust is higher than that of the mantle over time. Trace elements such as Niobium (Nb) and Uranium (U) do not fractionate when mantle melts to form mafic magma (oceanic crust) but they do fractionate when oceanic crust is recycled and undergoes fluid-present melting, i.e., during the production of felsic magmas (continental crust) [Hofmann et al., 1986], thereby resulting in a lower Nb/U of the felsic crust compared to the mantle. In this work, we couple the evolution of the above-mentioned geochemical proxies with the melting processes in global convection models using the code StagYY [Tackley, 2008]. Results from these geodynamic models are then compared with geochemical data obtained from olivine-hosted melt inclusions extracted from komatiites of 3.27 Ga Weltevreden formation (Barberton Greenstone Belt, South Africa).

These models self-consistently generate oceanic and continental crust while considering both plutonic and volcanic magmatism [Jain et al., 2019] and incorporate a composite rheology for the upper mantle. Pressure-, temperature-, and composition-dependent water solubility maps calculated with Perple_X [Connolly, 2009] control the ingassing and outgassing of water between the mantle and surface [Jain et al., 2022]. These models show intense production and recycling of continental crust during the Hadean and the early Archean, which is in agreement with new geochemical data [Vezinet et al., in review] and previous geochemical box models [Rosas & Korenaga, 2018; Guo & Korenaga, 2020]. The thermal evolution is also consistent with cooling history of the Earth inferred from petrological observations [Herzberg et al., 2010].

As the estimates of total amount of water (at the surface and in the deep interior) vary from 5-15 ocean masses (OMs) based on magma ocean solidification models to 1.2-3.3 OMs based on petrological models [Nakagawa et al., 2018], different initial values of water are also tested, which show a strong influence on the amount of felsic melts produced. Ongoing work includes incorporating the effect of water on the density and viscosity of mantle minerals and adapting the lithospheric strength with surface topography.

How to cite: Jain, C., Sobolev, S., Sobolev, A., and Vezinet, A.: Thermochemical models of early Earth evolution constrained by geochemical data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9734, https://doi.org/10.5194/egusphere-egu24-9734, 2024.

EGU24-9939 | PICO | GD3.2

Compressible convection in large rocky planets 

Yanick Ricard, Thierry Alboussière, and Stéphane Labrosse

The radial density of planets increases with depth due to compressibility, leading to impacts on their convective dynamics. To account for these effects, including the presence of a quasi-adiabatic temperature profile and entropy sources due to dissipation, the compressibility is expressed through a dissipation number proportional to the planet's radius and gravity. In Earth's mantle, compressibility effects are moderate, but in large rocky or liquid exoplanets (super-earths), the dissipation number can become very large. We explore the properties of compressible convection when the dissipation number is significant. We start by selecting a simple Murnaghan equation of state that embodies the fundamental properties of condensed matter at planetary conditions. Next, we analyze the characteristics of adiabatic profiles and demonstrate that the ratio between the bottom and top adiabatic temperatures is relatively small and probably less than 2. We examine the marginal stability of compressible mantles and reveal that they can undergo convection with either positive or negative superadiabatic Rayleigh numbers. Lastly, we delve into simulations of convection in 2D Cartesian geometry performed using the exact equations of mechanics, neglecting inertia (infinite Prandtl number case), and examine their consequences for super-earth dynamics.

How to cite: Ricard, Y., Alboussière, T., and Labrosse, S.: Compressible convection in large rocky planets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9939, https://doi.org/10.5194/egusphere-egu24-9939, 2024.

Plate tectonics is a fundamental framework for understanding the geodynamic processes shaping our planet, including seismicity, volcanism, mountain building, and even the long-term climate system and habitability of our planet. However, how plate tectonics evolved over 4.5 billion years remains a major unanswered question. In this study, we employ dynamically self-consistent three-dimensional thermochemical geodynamic models to simulate plate tectonics evolution with physically realistic parameters. Our results demonstrate that plate tectonics undergoes three main stages due to differing dominant mantle cooling modes. Initially, magmatism dominates surface heat transport, with extrusive volcanism leading to a mobile heat-pipe mode, characterised by a high level of volcanism, large surface heat flux, and highly mobile plates in the first 1.5 billion years. This differs from the "heat-pipe" mode occurring on Jupiter's satellite Io by additionally having plate-like behaviour as well as crustal delamination and lithospheric dripping. As the mantle cools, it transitions to a stable mode where mantle convection patterns and their surface expressions become stable for around 1-2 billion years, followed by a smooth evolution to present-day plate tectonics. Our model matches key observations of the surface heat flux, strain rate, plate velocity, and plate distribution patterns, indicating that the early mobile heat pipe mode plays a crucial role in efficiently extracting heat from the mantle. Magmatic intrusion is also expected to have important effects, which we will examine. This study may provide insights into the Earth's dynamic processes and mantle-atmosphere feedback related to plate tectonics and the dynamic evolution of other terrestrial planets, which ultimately affect the long-term climate system and habitability of our planet.

How to cite: Yan, J. and Tackley, P.: How did plate tectonics evolve? Insights from 3-D spherical thermochemical convection simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11554, https://doi.org/10.5194/egusphere-egu24-11554, 2024.

EGU24-12766 | PICO | GD3.2

Why does Earth have plate tectonics and what was before? 

Stephan Sobolev, Charitra Jain, and Michael Pons

The Earth is the only planet in our Solar System with active plate tectonics. Answering questions such as why plate tectonics started on Earth and which tectonic regime came before are fundamentally important for understanding the evolution of the early Earth. Currently, the most popular answers are (i) before plate tectonics on Earth, there was stagnant lid or plutonic-squishy-lid tectonic regime with no or minor contribution of subduction; (ii) plate tectonics took over when the initially high mantle temperature on Earth dropped by 100-200K due to secular cooling. In this work, we challenge both these statements based on published and new data and models.

Plenty of observations suggest that plate tectonics started on Earth during mid-Archean. At the same time, the numerical models and petrological data on the thermal evolution of the Earth show that mid-Archean was likely the time of the highest temperature of the Earth’s mantle and that significant secular cooling took place later in the Proterozoic. Moreover, previously published and our new thermochemical models also suggest that among all proposed tectonic regimes, only mobile-lid regime (i.e. plate tectonics) can lead to significant cooling of the Earth. Therefore, we conclude that plate tectonics in mid- or early Archean was unlikely to be initiated due to the significant secular cooling of the Earth’s mantle. The existence of no-subduction regimes, such as stagnant-lid or plutonic-squishy-lid, prior to plate tectonics are challenged by the new geochemical data which suggest extensive subduction and continental crust production already in the Hadean and early Archean.

Here we present global geodynamic models of Earth’s evolution computed using StagYY and ASPECT codes in 2D spherical annulus and 3D geometries respectively. StagYY models suggest that during the Hadean and the early Archean, the tectonic regime was oscillating between plume-induced subduction and plutonic-squishy-lid. The mantle temperature remains high during this time, but significant amount of continental crust is produced in these models, which is in agreement with the new geochemical data (melt inclusions from Weltevreden komatiites). After the emergence of continents in the mid- to late Archean, we decrease the effective friction of the oceanic lithosphere in the models to mimic the lubricating effect of continental sediments in subduction channels. This leads to a transition of the tectonic regime from oscillatory to continuous mobile-lid and to an efficient secular cooling of Earth, which is consistent with petrological observations. Being 2D, all plume-induced subduction zones in StagYY models are global. With the preliminary 3D ASPECT models, we show how a number of plume-induced regional subduction zones in early Earth evolve into a global network of plate boundaries and result in plate tectonics.

How to cite: Sobolev, S., Jain, C., and Pons, M.: Why does Earth have plate tectonics and what was before?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12766, https://doi.org/10.5194/egusphere-egu24-12766, 2024.

Constraining the heat flow across the core-mantle boundary (CMB) is crucial for understanding the thermal history of Earth’s mantle and the core. The primary mechanism governing heat transfer at the CMB is conduction, with lattice vibration (lattice thermal conductivity) commonly considered to be the dominant mechanism of thermal conduction in the lower mantle. However, there are large uncertainties in current estimates of lattice thermal conductivity of mantle material under CMB condition, due to the influence from mineral composition and the post-perovskite phase transition (e.g., Hsieh et al., 2018 PNAS; Ohta et al., 2017 EPSL). On the other hand, the role of radiative contribution (radiative thermal conductivity) remains less well understood. Several recent studies have attempted to measure the radiative thermal conductivity of bridgmanite and pyrolitic materials under lower mantle conditions, but the resulting experimental data have yielded divergent estimations for the radiative thermal conductivity of average mantle material at CMB conditions, ranging from 0.35 W/(m K) to 4.2 W/(m K) (Lobanov et al., 2020 EPSL; Murakami et al., 2022 EPSL). Adopting the highest estimate could result in an approximate 50% increase in the estimated bulk thermal conductivity compared to conventionally assumed values.  

To address the implications of these thermal conductivity uncertainties on mantle convection, we have incorporated variable thermal conductivities into a global thermochemical geodynamic model, StagYY. The simulations use a 2D spherical annulus geometry and extend over a 4.5 Gyr timespan. The geodynamic model includes parameterized core cooling, heat-producing elements partitioning, and crust formation, but it does not include an initial primordial reservoir at CMB. Preliminary findings from our study reveal that the relationship between thermal conductivity and CMB heat flux is not always straightforward. For models with stagnant-lid tectonics, higher thermal conductivity leads to higher CMB heat flux in the initial 1 Gyr and lower CMB heat flux at 4.5 Gyr. However, in models with mobile-lid tectonics, the CMB heat flux also increases with higher thermal conductivity in the first 1 Gyr, but CMB heat flux varies more and becomes unrelated to thermal conductivity at 4.5 Gyr. In summary, deep mantle thermal conductivity has little effect on the present-day CMB heat flux due to plate tectonics on Earth. Varying thermal conductivity mainly influences the amount of core cooling, particularly in early planetary evolution. 

How to cite: Tian, J. and Tackley, P.: The influence of deep mantle thermal conductivity on the long-term thermal evolution of Earth's mantle and core, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12993, https://doi.org/10.5194/egusphere-egu24-12993, 2024.

Outgassing from the interior is a key process influencing the evolution of the atmospheres of rocky planets. For planets with a stagnant lid tectonic mode, previous models have indicated that increasing planet size very strongly reduces the amount of outgassing, even to zero above a certain planet mass (Dorn et al., A&A 2018). This is because melt is buoyant only above a certain depth, which becomes shallower with increasing planet size (hence "g"); for large enough planets this depth may even lie within the lithosphere, preventing eruption and outgassing.

            However, uncertainties in rheology strongly influence the temperature structure of planets, hence (i) the depth at which melt is generated and (ii) the thickness of the lithosphere. One major uncertainty is the rheology of post-perovskite, which constitutes a large fraction of the mantle in large super-Earths. Ammann et al. (Nature 2010) find that diffusion is anisotropic; it is not clear whether the "upper bound" or "lower bound" is relevant to large-scale deformation, but both result in high viscosity at very high pressures, strongly influencing the radial temperature profile (Tackley et al., Icarus 2013). In contrast, Karato (2011, Icarus) argues that a different mechanism - interstitial diffusion - acts to make viscosity almost independent of pressure and relatively low in the post-perovskite regime.

            Another uncertainty is the reference viscosity (the viscosity at a reference temperature, pressure and stress), as this depends on bulk composition, water content, grain size and other properties. Lower reference viscosity results in thinner lithosphere and crust (e.g., Armann & Tackley, JGR 2012).

            Thus, numerical simulations are performed of the long-term (10 Gyr) thermo-chemical evolution of stagnant-lid planets (coupled mantle and core) with masses between 1 to 10 Earth masses, varying the reference viscosity and the rheology of post-perovskite. The simulations are based on the setup of Tackley et al. (2013 Icarus) with the addition of partial melting and basaltic crustal production, and outgassing of a passive tracer that partitions into the melt and outgasses 100% upon eruption.

            Results indicate that:

  • the previously-found trend of lower percentage outgassing with larger planet size is reproduced, but
  • outgassing does not fall to zero even in a 10 Earth mass planet. Outgassing of between 15% and 70% is found for 10 Earth mass planets (up to ~100% for Earth mass planets).
  • Post-perovskite rheology (interstitial, lower-bound or upper-bound) makes only a minor difference to long-term outgassing, but does influence the timing of outgassing.
  • Reference viscosity makes a large difference to outgassing, with lower viscosities leading to substantially larger outgassing percentages.
  • Internal heating plays a major role: stagnant-lid planets initially heat up due to low heat transfer efficiency, thinning the lithosphere and producing widespread melting.

How to cite: Tackley, P.: Outgassing on Stagnant-Lid Planets: Influence of Rheology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13059, https://doi.org/10.5194/egusphere-egu24-13059, 2024.

EGU24-13510 | ECS | PICO | GD3.2

Investigating the stability and composition of LLSVP-like material in mantle convection models 

Nicolas Récalde, J. Huw Davies, James Panton, Donald Porcelli, and Morten Andersen

The Large Low Shear Velocity Provinces (LLSVPs) are basal mantle structures, located beneath the Pacific and Africa, which are defined by their negative anomaly in δVs. Since the first detection of LLSVPs, the reason for their seismic signature has been questioned, whether it is purely thermal, chemical or thermo-chemical in nature. The origin and age of LLSVPs have also been interrogated in the context of mantle dynamics as plumes seem to be associated with these structures and correlate with intraplate volcanism locations. The LLSVPs are often invoked as a potential reservoir to store primitive mantle in order to explain primitive He ratios observed in oceanic island basalts. Such a scenario would suggest that at least some part of the LLSVPs are long-lived, quasi-stable structures. Previous 3D geodynamic experiments suggest that LLSVP longevity is achieved through replenishment of the constituent material [1], potentially disqualifying them as a reservoir of primordial material. However, 2D experiments have shown that remnants of a primordial layer may become trapped within accumulations of recycled, dense oceanic crust for extended periods of time [2]. It remains to be seen if a similar process may occur in 3D simulations.

Using the 3D spherical mantle convection code TERRA [3] and seismic conversion tables [1], we investigate the ability of geodynamic models to generate such seismic structures and the preservation of primordial material within them. We explore various mantle viscosities, densities of material (buoyancy of primitive and enriched material) and concentrations of heat-producing elements. We track the core-mantle boundary coverage and volume of the detected structures to evaluate their stability as a function of time and geodynamical context. Results focus on the composition of these structures, the amount of primitive and early enriched material stored within them and how they evolve with time.

[1]  James Panton, J. Huw Davies, and Robert Myhill. “The Stability of Dense Oceanic Crust Near the Core-Mantle Boundary”. In: Journal of Geophysical Research: Solid Earth 128.2 (2023).

[2]  T. D Jones, N Sime, and P. E van Keken. “Burying Earth’s Primitive Mantle in the Slab Graveyard”. In: Geochemistry, geophysics, geosystems : G3 22.3 (2021).

[3]  John R. Baumgardner. “A Three-Dimensional Finite Element Model for Mantle Convection”. PhD thesis (1983).

How to cite: Récalde, N., Davies, J. H., Panton, J., Porcelli, D., and Andersen, M.: Investigating the stability and composition of LLSVP-like material in mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13510, https://doi.org/10.5194/egusphere-egu24-13510, 2024.

Plate tectonics is the most prominent surface manifestation of mantle convection in Earth. Current observational results suggest that Earth is the only planet displaying plate tectonics. However, whether plate tectonics has accompanied the entire evolutionary history of Earth is a key question. If not, questions such as when plate tectonics began and what kind of tectonic mode prevailed before plate tectonics, have always been at the forefront and hot topics in the field of Earth science.

In this study, we employed three-dimensional spherical mantle convection numerical simulations to explore various mantle convection modes. Results indicate that, under different parameter frameworks, mantle convection modes can be categorized into five types: I) non-plate active lid convection mode, where the surface exhibits multiple concentrated weak zones, resulting in relatively fragmented plates; II) plate-like mobile lid convection mode, characterized by a higher number of subduction zones and mid-ocean ridges on the surface, which spontaneously form, develop and disappear over time, dividing the surface into about 10 plates; III) episodic plate-like mobile lid convection mode, where the surface experiences plate-like mobile lid mode for most of the time, interspersed with transient surface stagnation; IV) episodic stagnant lid convection mode, characterized by long periods of surface stagnation interspersed with short periods of surface movement with the surface mostly featuring only one subduction zone. V) stagnant lid convection mode, where the surface appears as a single rigid layer.

We mainly analyze the influence of lithospheric strength, i.e., yielding stress, Rayleigh number and internal heat rate on these five mantle convection modes. We can better explain the plate tectonics of the present Earth using mode Ⅱ. Because of the higher internal heat rate, higher mantle temperature and lower mantle viscosity, resulting in a larger Rayleigh number, our research suggests that the early Earth was in mode III or IV. Our results suggest that even if there was some type of plate tectonics in the early Earth, it is different from present plate tectonics. Before the onset of plate tectonics, the Earth might have experienced episodic lid convection. The results hold important scientific significance for understanding the evolution of the Earth's plate tectonics.

How to cite: Xiang, S. and Huang, J.: Mantle convection modes in 3D mantle convection simulations and its implications for the evolution of Earth’s plate tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13588, https://doi.org/10.5194/egusphere-egu24-13588, 2024.

EGU24-15952 | ECS | PICO | GD3.2

Constraining Venus's interior with gravity and topography predictions from geodynamic models 

Julia Maia, Ana-Catalina Plesa, Nicola Tosi, and Mark Wieczorek

One of the most informative ways of studying the interior structure and geodynamics of terrestrial planets is the joint investigation of gravity and topography data. In the case of Venus, this is in fact one of the only sources of information about the planet's interior, along with estimations of the tidal Love number [1], moment of inertia factor [2], and the absence of an internally generated magnetic field [3].

Early gravity and topography studies that made use of Pioneer Venus and later Magellan data revealed unique properties of Venus's interior. They showed that Venus has a notably higher gravity-topography correlation for long wavelengths compared to Earth and a globally large apparent depth of compensation [4]. Considering these characteristics and analyzing the wavelength-dependent ratio between gravity and topography, the so-called spectral admittance, [5] concluded that the long-wavelength topography of the planet was supported dynamically, i.e., through convection in the mantle.

Since then, several studies have investigated the gravity and topography signature of Venus with the goal of understanding the planet’s interior by constraining geophysical properties of the mantle, such as the mantle viscosity. Some estimated the dynamic geoid contribution from three-dimensional geodynamic simulations [6,7]. Others adopted the analytical viscous flow model by [11] to study the viscosity structure of Venus's mantle [8,9,10]. The main advantage of the latter method is that it is computationally inexpensive, allowing for the performance of inversions. However, it is a simplified model which neglects lateral viscosity variations.

In this study, we estimate the dynamic topography and geoid signatures from the geodynamical models by [12], which include a strongly temperature-dependent viscosity, hence lateral viscosity variations, to evaluate the influence of different parameters such as the increase of viscosity with depth, the presence of viscosity jumps, and the ratio between intrusive and extrusive magmatism. In a second step, we plan to systematically evaluate the influence of lateral viscosity variations on the geoid and topography and thus to quantify the importance of the simplifications adopted in the analytical model.

Our first results show that the increase of viscosity with depth should be no more than 2 orders of magnitude, since larger values strongly decrease the spectral correlation and admittance at long wavelengths which is inconsistent with the observations. In addition, scenarios where extrusive magmatism dominates tend to overestimate the admittance due to the generation of thick thermal lithospheres in excess of 300 km thickness. These results underscore the importance of gravity and topography analyses for deciphering the geodynamical evolution and tectonic style of Venus.

[1] Konopliv and Yoder (1996) GRL, 23; [2] Margot et al. (2021) Nat Astron; [3] Phillips and Russel (1987) JGR, 92; [4] Sjogren et al. (1980) JGR, 85;  [5] Kiefer et al. (1986) GRL, 13; [6] Huang et al. (2013) EPSL, 362; [7] Rolf et al. (2018) Icarus, 313; [8] Pauer et al. (2006) JGR, 111; [9] Steinberger et al. (2010) Icarus, 207; [10] Maia et al. (2023) GRL, 50; [11] Hager & Clayton (1989) Mantle Convection; [12] Plesa et al. (2023) EGU.

How to cite: Maia, J., Plesa, A.-C., Tosi, N., and Wieczorek, M.: Constraining Venus's interior with gravity and topography predictions from geodynamic models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15952, https://doi.org/10.5194/egusphere-egu24-15952, 2024.

EGU24-16140 | ECS | PICO | GD3.2

Mantle hydration and implications for Earth and exoplanetary research 

Nickolas Moccetti Bardi, Paul J. Tackley, and Marla A. Metternich

So far, most numerical models focused on understanding different aspects of the Earth’s system, such as mantle convection, tectonics, or atmospheric dynamics, have typically adopted a limited perspective constrained to the specific region of interest. Recently, efforts have been made to couple these simulations, enabling them to interact seamlessly with one another. Abstaining from doing so may lead to results that don't accurately represent how the various systems interact.

Achieving the successful integration of the deep carbon cycle and water transport into our mantle dynamics code (StagYY) represents a crucial step towards this goal - a comprehensive, large-scale model of our planet, encompassing phenomena from the Earth's core to the uppermost layers of the atmosphere resulting from a collaborative effort between different research groups. We adopt a thermodynamic approach to quantify the H2O solubility of important water-carrying minerals within the mantle, with the goal of faithfully coupling geodynamic models and realistic transport/incorporation of water across the silicate part of our planet. The details of the numerical implementation are yet the subject of ongoing discussion; however, several crucial considerations must be thoroughly evaluated. These include the assessment of density variations resulting from water integration into nominally anhydrous minerals, the complex multi-stage degassing process of subducting slabs, and the inclusion of exotic phases that are currently absent from the thermodynamic databases being utilized.

The anticipated effects of a water-bearing mantle on the overarching dynamics are still under investigation. Nevertheless in-gassing, degassing, and the internal transport of water within the mantle exert a direct influence on various aspects. These include the governing viscosity field, the extent of H2O-induced melting, and atmospheric CO2 concentrations, among others. If water can, in fact, permeate deep into the mantle, it has the potential to introduce significant deviations in the dynamics of lower mantle convection compared to what current models predict. Furthermore, recent considerations of the stability regime of hydrous phases also point towards interesting implications in the study of water-rich exoplanets as stronger gravity profiles should result in colder geotherms, significantly expanding the thermodynamical stability of water-transporting phases across the P-T parameter space.

Quantifying this process will provide valuable insights for the geodynamic modeling community and help advance our understanding of the deep-Earth system. Furthermore, the distinct chemical exchange dynamics arising from our applications can be investigated further and prove advantageous for the study of exoplanetary atmospheres, especially those around bodies characterized by abundant water, such as water worlds and hycean planets.

How to cite: Moccetti Bardi, N., Tackley, P. J., and Metternich, M. A.: Mantle hydration and implications for Earth and exoplanetary research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16140, https://doi.org/10.5194/egusphere-egu24-16140, 2024.

Crystallization processes, a partial or complete overturn of the early mantle and other processes can lead to a compositionally stably stratified mantle which may hinder of even prevent convective currents. In the classical view, the layer will be stable if the restoring force, generated by the compositional stratification will exceed the driving force as provided by heating the layer from the core. The situation resembles the diffusive scenario of double diffusive convection, characterized by the fast diffusing component (heat) being the driving force, while the slowly diffusing component (composition) acts as the restoring force. If perturbed, subcritical convection can eventually take plain ce.  While in  pure thermal convection , subcritical flow only develops as localized patterns, in the double diffusive case, a perturbation can lead to a global destabilization (blue sky bifurcation) of the system, due to a sufficient finite  amplitude perturbation. . In this study we have investigated the influence of a finite amplitude perturbation of varying magnitudes , namely realze by an impact on a stably stratified mantle. Numerical experiments in 2- and 3D, cartesian and spherical simulations, based on a Finite Volume scheme  have been conducted to study the evolution of such a system. Key parameters  which characterize the evolution are the (1) initial stratification and the structure f the perturbation. The viscosity structure is a further influencing factor.

The experiments show that an impact into a stably stratified mantle can lead to a global destabilization, giving rise to complex flow patterns, including local and transient layering of the mantle flow. An evolutionary path of a planet from a stably stratified state to a complex layered period and/or to a full convection mode seems sensitive.

How to cite: Hansen, U. and Dude, S.: Spontaneous destabilization of a compositionally stably stratified mantle in the Early Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16401, https://doi.org/10.5194/egusphere-egu24-16401, 2024.

EGU24-16653 | PICO | GD3.2

Early formation of a water ocean as a function of initial CO2 and H2O contents in a solidifying rocky planet 

Helene Massol, Anne Davaille, Philippe Sarda, and Guillaume Delpech

We present a numerical model of a cooling magma ocean (MO) and the atmosphere degassing from it. The solidification of the MO leads to the enrichment of the silicate melt in volatiles, thus favoring degassing. Both reservoirs interact via heat and volatile exchange, where the volatiles are H2O and CO2. The aim of this model is to explore the influence of the atmosphere on the surface conditions after the MO stage, and especially the conditions required for the condensation of a water ocean to occur. For example, for an early Earth at 1 AU initially containing 1 Earth's water ocean mass, a water ocean could form for initial CO2 content as large as 1,000 bars. Moreover, a tenth of the actual Earth's water ocean mass would be sufficient to generate a water ocean on early Venus. Liquid water could also be present on the surface of the two exoplanets Trappist-1e and 1f. Comparing our results with other recent models, we discuss the relative influence of the model hypotheses, such as mantle composition, the treatment of the heat transfer in the atmosphere, and the treatment of the last stages of the MO solidification.

How to cite: Massol, H., Davaille, A., Sarda, P., and Delpech, G.: Early formation of a water ocean as a function of initial CO2 and H2O contents in a solidifying rocky planet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16653, https://doi.org/10.5194/egusphere-egu24-16653, 2024.

 New high-pressure, high-temperature layered partial melting experiments have been performed to simulate the interaction between the last stage, dense Fe-Ti-rich cumulate layer that remained after about 99.5% crystallization of the lunar magma ocean (LMO), and the underlying solidified Mg-rich mantle. For this, a synthetic assemblage of an upper Fe-Ti-rich cumulate layer (6.1 wt.% TiO2 and 39.7 wt.% FeO) and a lower forsteritic olivine layer (Mg# = 92.8) has been taken in 1:4 weight ratio, respectively, and subjected to experiments at pressures ranging between 1 to 3 GPa and temperatures varying between 1100 ⁰C and 1525 ⁰C using a piston cylinder apparatus. In the top cumulate layer, phases such as Fe-rich clinopyroxene, Fe-poor clinopyroxene, pigeonite, orthopyroxene, rutile, ilmenite, quartz and melt were formed, depending upon different P-T conditions. The Fe-Ti-rich basaltic melts (5-18.5 wt.% TiO2, 13-28.6 wt.% FeO, and 35-59 wt.% SiO2) produced in this cumulate layer at different degrees of partial melting approach the lunar mare basalts in their compositions and can be used to explain the huge variation in TiO2 enrichment that is observed in lunar basalts (between 0 to ~17 wt. %). Following LMO crystallization, the last stage dense mineral-melt cumulate layer is expected to undergo a gravitational overturn due to density instability. This work aims to simulate the partial melting of the cumulates in this layer as a result of the overturn. The consequent compositional heterogeneity of the lunar mantle is used to justify the observed variation in Ti-rich basalt compositions on the lunar surface. The basaltic melts produced in these experiments are mostly Al, Mg-poor compared to available lunar basalt samples. However, this deficiency may be addressed by assimilation of these melts into low-Ti, Mg-rich basalt magmas that would have subsequently erupted from the underlying mantle. Simulations of such assimilation using thermodynamic modelling have also been done and the results support this theory. The possible fate of the last stage melt of the LMO has thus been studied and used to understand the variable compositions of lunar basalts.

How to cite: Moitra, H., Ghosh, S., Mukherjee, T., and Gupta, S.: Understanding the variability in the titanium contents of lunar basalts using high-pressure, high-temperature layered partial melting experiments and thermodynamic modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17525, https://doi.org/10.5194/egusphere-egu24-17525, 2024.

EGU24-17640 | PICO | GD3.2

Small-scale Structure of the Martian Mantle 

Constantinos Charalambous, Tom Pike, Benjamin Fernando, Henri Samuel, Carys Bill, Philippe Lognonné, and Bruce Banerdt

The InSight mission's SEIS instrument has provided a unique opportunity to probe the deep interior of Mars. This seismic exploration of the Martian interior has emerged as a promising avenue for revealing the enigmatic geophysical properties and dynamic processes within the planet's mantle.

In this study, we present an analysis of the seismic signature of marsquakes which transit deep into the mantle, providing crucial information on the seismic velocity profile and potential heterogeneities. The quakes show a characteristic late emergence of the first energy at higher frequencies which can be analysed as due to the scattering of seismic energy as it transits the mantle. From this we are able to quantify the size distribution of the mantle's small-scale heterogeneity as well as to constrain the rheological properties and convective vigor of the Martian mantle.

As unlike Earth, Mars has sealed its mantle contents under a stagnant lid, we use our observations to provide evidence about the early stages of planetary formation and differentiation on Mars. Our findings contribute to the better understanding of the Martian mantle's geodynamics and allow a comparative assessment of the evolution of planetary interiors that likely apply to other planets that lack plate tectonics.

How to cite: Charalambous, C., Pike, T., Fernando, B., Samuel, H., Bill, C., Lognonné, P., and Banerdt, B.: Small-scale Structure of the Martian Mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17640, https://doi.org/10.5194/egusphere-egu24-17640, 2024.

EGU24-19267 | PICO | GD3.2

Melting and Remelting in a Crystallizing Magma Ocean 

Antonio Manjon Cabeza Cordoba, Maxim D. Ballmer, and Oliver Shorttle

Geodynamic modelling is increasingly dependent on the initial conditions. Non-steady-state planetary evolution models are complex enough that several solutions can be achieved with small variations in the initial temperature, composition, etc. Models of magma ocean evolution predict an overturn of a layer enriched in iron and incompatible elements. The absence of this layer in any tomographic inversion of the Earth suggests that our models of magma ocean evolution are missing key phenomena. Since these models are the basis for the initial conditions of Earth-applied geodynamic planetary models, there is an urgency to find the origin of the discrepancies between our idea of magma ocean crystallization and the current state of the Earth.

To advance our understanding of the consequences of magma ocean crystallization, we carry out high resolution models of mantle flow coupled with (1D) magma ocean evolution (including melting and crystallization processes). We allow two different forms of topography to arise with a sticky air (sticky magma ocean) approximation: dynamic topography and thermodynamic topography. We explore how different equilibration times affect melt segregation and magma ocean composition, as well as how crystal settling influences solid state convection and differentiation. We calculate, as well, chemical exchange between the solid and liquid parts of our model by expanding on previous work, studying different equilibrium constants and allowing the system to self-regulate.

Preliminary results suggest a competition effect between the two forms of topography mentioned above. This competition implies that the equilibrium constant of chemical exchange, as well as melting segregation speed and crystal growth and settling, will have an essential role in the equilibration between the solid mantle and the liquid magma ocean. This and other results have implications for Earth, but also for other discovered magma oceans such as those on the Moon, Mars or even exoplanets.

How to cite: Manjon Cabeza Cordoba, A., Ballmer, M. D., and Shorttle, O.: Melting and Remelting in a Crystallizing Magma Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19267, https://doi.org/10.5194/egusphere-egu24-19267, 2024.

EGU24-22090 | ECS | PICO | GD3.2

Combined impact and interior evolution models in three dimensions indicate a southern impact origin of the Martian Dichotomy 

Kar Wai Cheng, Harry Ballantyne, Gregor Golabek, Martin Jutzi, Antoine Rozel, and Paul Tackley

The origin of the martian crustal dichotomy is a long-standing mystery since its discovery in the Mariner 9 era. Among various proposed hypotheses, a single giant impact origin (i.e. the Borealis impact) is the most well known, and the most studied. However, studies that include realistic impact models often adapt a simplified geological and geophysical model for predicting the final crustal distribution, while long-term mantle convection studies have mostly employed an over-simplified parametrization of the impact. Here we use a coupled SPH-thermochemical approach to first simulate an impact event, and then use the result of this realistic model as the initial condition for the long-term mantle convection model. We demonstrate that a giant impact collision results in a mantle-deep magma pond, which upon crystallisation leads to a thicker crust production on the impacted hemisphere. In other words, an impact-origin of Mars's southern highlands requires the giant impact to occur in the southern hemisphere. We find that both the impact scenario and the mantle properties affect the geometry of the impact-induced crust ("highlands'') and the subsequent state of the interior, and that the formation of "highlands'' extends beyond the initial magma pond.  We show that a near head-on (15o from the normal) impact event with impactor radius of 750 km, together with a mantle viscosity of 1020 Pa s, can best reproduce the southern highlands of Mars with a geometry similar to that of present-day observations.

How to cite: Cheng, K. W., Ballantyne, H., Golabek, G., Jutzi, M., Rozel, A., and Tackley, P.: Combined impact and interior evolution models in three dimensions indicate a southern impact origin of the Martian Dichotomy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22090, https://doi.org/10.5194/egusphere-egu24-22090, 2024.

EGU24-3129 | ECS | Orals | PS1.3

 Viscosity of Venus' mantle as inferred from its rotational state 

Yann Musseau, Caroline Dumoulin, Gabriel Tobie, Cédric Gillmann, Alexandre Revol, and Emeline Bolmont

Venus' rotation is the slowest of all planetary objects in the solar system and the only one in the retrograde direction. It is commonly admitted that such a rotation state is the result of the balance between the torques created by the gravitational and atmospheric thermal tides1. The internal viscous friction associated with gravitational tides drive the planet into synchronization (deceleration) while the bulge due to atmospheric thermal tides tend to accelerate the planet out of this synchronization1,6. Other torque components (related to the two first one) also affect the rotation2. This work first provide an estimate of the viscosity of Venus' mantle explaining the current balance with thermal atmospheric forcing. Second, this study quantify the impact of the internal structure and its past evolution on the gravitational tides and thus on the rotation history of Venus. Using atmospheric pressure simulations from the Venus climate database4,5,7, we first estimated the atmospheric thermal torque and showed that topography and interior response to atmospheric loading, usually ignored in previous studies, have a strong influence on the amplitude of thermal atmospheric torque. Computing the viscoelastic response of the interior to gravitational tides and atmospheric loading3, we showed that the current viscosity of Venus' mantle must range between 2.3x1020 Pa.s and 2.4x1021 Pa.s to explain the current rotation rate as an equilibrium between torques. We then evaluated the possible past evolution of the viscosity profile of the mantle considering different simple thermal evolution scenarios.  We showed that in absence of additional dissipation processes, viscous friction in the mantle cannot slowdown the rotation to its current state for an initial period shorter than 2-3 days, even for an initially very hot mantle. Beyond Venus, these results has implications for Earth-size exoplanets indicating that their current rotation state could provide key insights on their atmosphere-interior coupling.

1Correia, A. C. M. and J. Laskar (2001), Nature.
2Correia, A. C. M. (2003), Journal of Geophysical Research.
3Dumoulin, C., G. Tobie, O. Verhoeven, P. Rosenblatt and N. Rambaux (2017), Journal of Geophysical Research.
4Lebonnois, S., F. Hourdin, V. Eymet, A. Crespin, R. Fournier and F. Forget (2010),  Journal of Geophysical Research.
5Lebonnois, S., N. Sugimoto and G. Gilli (2016), Icarus.
6Leconte, J., H. Wu, K. Menou and N. Murray (2015), Science.
7Martinez, A., S. Lebonnois, E. Millour, T. Pierron, E. Moisan, G. Gilli and F. Lefèvre (2023), Icarus.

How to cite: Musseau, Y., Dumoulin, C., Tobie, G., Gillmann, C., Revol, A., and Bolmont, E.:  Viscosity of Venus' mantle as inferred from its rotational state, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3129, https://doi.org/10.5194/egusphere-egu24-3129, 2024.

EGU24-4022 | Posters on site | PS1.3

Ground-based thermal mapping of Venus:  HDO and SO2 monitoring and upper limits of NH3, PH3 and HCN at the cloud top 

Therese Encrenaz, Thomas Greathouse, Rohini Giles, Thomas Widemann, Bruno Bezard, Franck Lefevre, Maxence Lefevre, Wencheng Shao, Hideo Sagawa, Emmanuel Marcq, and Anicia Arredondo

As part of a long-term monitoring program, full disk thermal maps of HDO (near 7 microns) and SO2 (near 7 and 19 microns) have been obtained at the cloud top of Venus in 2023, using the TEXES(Texas Echelon Cross-Echelle Spectrograph)  imaging spectrometer at the Infrared Telescope Facility (IRTF) at Mauna Kea Observatory. Assuming a constant D/H isotopic ratio, the water abundance has been more or less constant since 2018, at about half its value in 2012-2016. In contrast, the SO2 abundance, which was very high in 2018-2019 and very low between July 2021 and March 2023, has increased by a factor of about 5 between February and July 2023 (close to its maximum level of 2018-2019), and has remained at its high level in September 2023. The origin of these long-term variations is still unclear. In addition, stringent upper limits of NH3 (at 927-931 cm-1), PH3 (at 1161-1164 cm-1) and HCN at 744-748 cm-1) at the cloud top have been obtained in July 2023. These results will be presented and discussed.

How to cite: Encrenaz, T., Greathouse, T., Giles, R., Widemann, T., Bezard, B., Lefevre, F., Lefevre, M., Shao, W., Sagawa, H., Marcq, E., and Arredondo, A.: Ground-based thermal mapping of Venus:  HDO and SO2 monitoring and upper limits of NH3, PH3 and HCN at the cloud top, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4022, https://doi.org/10.5194/egusphere-egu24-4022, 2024.

Coronae are crown-like, tectono-volcanic features found on Venus that typically range in diameter from 100-700 km. Diapirs of warm upwelling material impinging on the lithosphere are often invoked to explain coronae formation. With more than 500 coronae identified on the surface of Venus, if these diapirs are individually linked to a mantle plume, Venus must have a very different mantle structure than Earth. I consider three cases designed to assess the potential relationship between large-scale, long-wavelength lower mantle structure and smaller-scale upper mantle structure that could potentially form diapirs consistent with those that are envisioned to interact with the lithosphere and form coronae. I use the geoid and topography to identify the large-scale pattern of convection because the geoid contains and integral of the temperature anomalies over the depth of the mantle. Plume tails—narrow vertical conduits—integrate to give a positive geoid anomaly while small-scale, time-dependent drips or upwellings are minimized in the depth integration. The first case—the reference case—has a small, stepwise decreases in viscosity between the lower mantle (1022 Pa s), transition zone (1021 Pa s), and upper mantle (5x1020 Pa s) with no phase transformations. This led to 20 ~1000-km diameter mantle plumes that remained stationary for more than 1.5 Gyr. This calculation is consistent with a number of geophysical observations it does not support the formation of coronae by plume-lithosphere interaction. To decouple the lower and upper mantle, I further decrease both the upper mantle and transition zone viscosities to 1020 Pa s while leaving all other parameters unchanged. In this calculation the same 20 ~1000-km diameter mantle plumes formed and remained stationary for more than 1.5 Gyr. The geoid and topography are anti-correlated, inconsistent with the observed values on Venus and, the spatial scale, number, and topographic evolution of the plumes are not consistent with coronae. This calculation does not support the formation of coronae by plume-lithosphere interaction. In an attempt to further decouple the upper and lower mantle I add an endothermic phase transformation at the ringwoodite-bridgmanite boundary in addition to the decreased upper mantle and transition zone viscosities while leaving all other parameters unchanged. Unique to this calculation, a very large number of ~100-km diameter small topographic upwellings form some associated with the large-scale geoid high but never associated with the large-scale geoid low. The inclusion of a phase transformation decoupling the upper and lower mantle has the potential to create diapir-like structures in the upper mantle consistent with coronae formation.

How to cite: King, S.: Linking global-scale mantle flow with diapir-like coronae formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5857, https://doi.org/10.5194/egusphere-egu24-5857, 2024.

EGU24-5946 | ECS | Posters on site | PS1.3

Thermal evolution and magmatic history of Venus 

Carianna Herrera, Ana-Catalina Plesa, Julia Maia, Stephan Klemme, and Lauren Jennings

The recent analysis of radar data from NASA’s Magellan mission suggests that volcanic activity is ongoing on Venus [1], providing unprecedented evidence that Venus’s evolution and present day state has been dominated by volcanic processes. Venus’s geodynamics and tectonics seem to be well characterized by the so-called “plutonic squishy lid” regime, where part of the melt that is formed in the interior rises to the surface but a significant part remains trapped in the crust and lithosphere forming intrusions [2]. These intrusions strongly influence the mantle’s thermal evolution, heat flow, and the present-day thermal state of the subsurface.

This study focuses on the effects of intrusive magmatism on the lithosphere thickness and thermal gradient. The latter is used to evaluate our models by comparing our results to estimates based on studies of the elastic lithosphere thickness [3,4,5]. We use the geodynamic code Gaia in a 2D spherical annulus geometry [6]. Our models vary the intrusive to extrusive ratio from a fully intrusive case to a fully extrusive one and the intrusive melt depth from 10 km to 90 km.

Our models show that depending on the percentage of extrusive melt and the depth of magmatic intrusions, the maximum thermal gradient varies from a few K/km up to almost 40 K/km at present day, with higher values obtained for higher percentages of intrusive melt and shallower the magmatic intrusions. Moreover, our results show that the thermal gradients have remained similar during the last 750 Myr. Models in which the extrusive magmatism is higher than 60% and the depth of magmatic intrusions lies deeper than 50 km cannot explain high local thermal gradients as suggested by studies of elastic lithosphere thickness [3,4,5].

In a recent study [7], the presence of a low viscosity layer (LVL) in the shallow Venusian mantle has been suggested to be related to the presence of partial melt. The LVL starts beneath the lithosphere at depths shallower than 200 km. This places constraints on the depth of melting that we can use to select successful models. Models that are compatible with partial melting starting at depth of 200 km or less beneath the surface require less than 40% extrusive magmatism and an intrusive melt depth strictly higher than 10 km.

We use our models to estimate ranges for melting conditions in the interior at present day. The range of melt temperatures lies between 2000 and 2250 K and the depth of melting between ~200 and 360 km. These estimations serve as a starting point for and will be compared with high-pressure-high-temperature laboratory experiments that will be performed at the University of Münster to select the most likely mantle compositions of Venus that can explain the Venera and Vega data.

References:

[1] Herrick & Hensley, Science, 2023. [2] Rolf et al., SSR, 2023. [3] Smrekar et al., Nature Geoscience, 2023. [4] Borelli et al., JGR, 2021. [5] Maia et al., JGR, 2022. [6] Hüttig et al., PEPI, 2013. [7] Maia et al., GRL, 2023.

How to cite: Herrera, C., Plesa, A.-C., Maia, J., Klemme, S., and Jennings, L.: Thermal evolution and magmatic history of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5946, https://doi.org/10.5194/egusphere-egu24-5946, 2024.

EGU24-7533 | ECS | Orals | PS1.3

Breaking New Ground in Venusian Atmospheric Sulfur Chemistry 

Benjamin Frandsen and Robert Skog

The Venusian atmosphere has rich and diverse chemistry and much of it remains to be explored. Here I present our recent work in identifying new reactions and quantifying their rate constants, along with UV-Vis spectral simulation using quantum chemistry calculations. The research focuses on elemental sulfur allotropes and sulfur oxides. Our UV-Vis spectral simulations are used to narrow the search of the unknown UV absorber by excluding molecules/isomers/conformers without the appropriate absorption and similarly include those with absorption profiles that fit the unknown absorber. Furthermore, we present a mechanism for how substituted sulfuric acid molecules can be formed in the Venusian atmosphere which can impact aerosol formation.

How to cite: Frandsen, B. and Skog, R.: Breaking New Ground in Venusian Atmospheric Sulfur Chemistry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7533, https://doi.org/10.5194/egusphere-egu24-7533, 2024.

EGU24-8135 | ECS | Posters on site | PS1.3

Investigating the volcanic activity on Venus with Magellan data 

Davide Sulcanese, Giuseppe Mitri, and Marco Mastrogiuseppe

Previous studies have inferred volcanic activity on Venus from indirect evidence, including variations in atmospheric composition and thermal emissivity data [1, 2, 3]. More recently, a study hypothesized ongoing volcanic activity on Venus, evidenced by a volcanic vent that collapsed between two different Magellan observing cycles [4]. Expanding upon this premise, we are investigating the surface geology of Venus using the extensive radar and altimetric data acquired by the Magellan spacecraft.

In particular, by properly processing the SAR images, we are conducting a detailed geomorphological analysis of Venus' surface, in order to identify and characterize various surface morphologies. Additionally, the altimetric data provided valuable insights into the topographical variations across Venus, further contributing to the geomorphological assessment.

Our research not only enhances the understanding of the geology of Venus but also underscores the significance of radar imaging in the study of planetary surfaces, where no other imaging techniques are available. The findings highlight the crucial role of continued exploration of Venus, which could be greatly advanced by upcoming missions such as VERITAS and EnVision [5, 6]. Equipped with superior radar technology, these missions are expected to provide images of Venus's surface at an unprecedented resolution and signal-to-noise ratio, far surpassing that of the Magellan SAR, thus enabling a more detailed characterization of Venus's surface morphology.

 

References

1. Truong, N. & Lunine, J. Volcanically extruded phosphides as an abiotic source of Venusian phosphine. Proceedings of the National Academy of Sciences 118, e2021689118 (2021).

2. Esposito, L. W. Sulfur dioxide: Episodic injection shows evidence for active Venus volcanism. Science 223, 1072-1074 (1984).

3. Smrekar, S. E. et al. Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science 328, 605-608 (2010).

4. Herrick, R. R. & Hensley, S. Surface changes observed on a Venusian volcano during the Magellan mission. Science, eabm7735 (2023).

5. Hensley, S. et al. VISAR: Bringing Radar Interferometry to Venus. In Proceedings of International EnVision Venus science workshop, Berlin, Germany (2023).

6. Ghail, R. C. et al. VenSAR on EnVision: Taking earth observation radar to Venus. International journal of applied earth observation and geoinformation 64, 365-376 (2018).

Acknowledgments

G.M., D.S., and M.M. acknowledge support from the Italian Space Agency (2022-15-HH.0).

How to cite: Sulcanese, D., Mitri, G., and Mastrogiuseppe, M.: Investigating the volcanic activity on Venus with Magellan data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8135, https://doi.org/10.5194/egusphere-egu24-8135, 2024.

EGU24-8798 | ECS | Posters on site | PS1.3

Simulating UV-VIS Spectra for Polysulfur Species in the Venusian Atmosphere 

Robert Skog, Benjamin Frandsen, and Theo Kurtén

The Venusian atmosphere has everything to be an exciting natural sulfur laboratory. In addition to relatively high concentrations of sulfur dioxide, suitable conditions in the atmosphere make both thermo- and photochemical reactions possible, allowing for complex chemical reactions and the formation of new sulfur containing compounds. These compounds could explain or contribute to the enigmatic 320-400 nm absorption feature in the atmosphere. One of the proposed absorbers is polysulfur compounds. While some experimentally obtained UV-VIS spectra have been published, studying the different polysulfur species individually is extremely difficult due to the reactive nature of sulfur. In this work UV-VIS spectra for polysulfur species S2 to S8 were simulated using the nuclear ensemble approach to determine if they fit the absorption profile of the unknown absorber.

Geometries were optimized at the ωB97X-D/aug-cc-pV(T+d)Z level of theory, with the S2, S3, and S4 structures also being optimized at the CCSD(T)/aug-cc-pV(T+d)Z level of theory. For the lowest energy isomers UV-VIS spectra were simulated using a nuclear ensemble of 2000 geometries, with vertical excitations calculated at the EOM-CCSD/def2-TZVPD or the ωB97X-D/def2-TZVPD levels of theory.

The simulated UV-VIS spectra for the smaller species were in quite good agreement with experimental results. Two different molecules were identified with substantial absorption cross sections in the range of the unknown absorber: The open chain isomer of S3, and the trigonal isomer of S4 However, the mixing ratios of these species in the Venusian atmosphere are also needed to make a more conclusive statement. Other polysulfur compounds have insignificant absorption cross sections in the 320-400 nm range and can therefore be excluded.

The calculated absorption cross sections can be used to calculate photolysis rates, which can be straight away added to atmospheric models of Venus. In addition, this work will help future space missions to Venus, for example by focusing their search for the unknown absorber.

How to cite: Skog, R., Frandsen, B., and Kurtén, T.: Simulating UV-VIS Spectra for Polysulfur Species in the Venusian Atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8798, https://doi.org/10.5194/egusphere-egu24-8798, 2024.

EGU24-9470 | ECS | Orals | PS1.3

Influence of Possible Bulk Compositions on the Long-Term Evolution and Outgassing of Venus 

Diogo Louro Lourenço, Paul Tackley, Tobias Rolf, Maria Grünenfelder, Oliver Shah, and Ravit Helled

Venus’ mass and radius are similar to those of Earth. However, Venus’ interior structure and chemical composition are poorly constrained. Seemingly small deviations from the Earth might have important impacts in the long-term evolution and dynamics of Venus when compared to our planet and could help to explain the different present-day surface and atmospheric conditions and geophysical activity between these two planets. Shah et al. (ApJ 2022) presented a range of possible bulk compositions and internal structures for Venus. Their models, designed to fit Venus’ moment of inertia and total mass, predict core radii ranging from 2930-4350 km and include substantial variations in mantle and core composition. In this study, we pick ten different Venus models from Shah et al. (ApJ 2022) that range from a small to a big, and from a S-free to a S-rich core. We run mantle convection evolution models for the different scenarios using the code StagYY (Tackley, PEPI 2008; Armann and Tackley, JGR 2012) and explore how different interior structures and chemical compositions affect the long-term evolution and dynamics of Venus. In our models, the bulk composition of the mantle affects the basalt fraction and the solidus and liquidus temperature profiles. We investigate how the composition and size of the core affects magmatism hence outgassing of water and other volatiles to the atmosphere, the basalt distribution, heat flow, temperature of the mantle and lithosphere, and observables such as the moment of inertia and Love numbers. Since the tectonic regime active on Venus is still unknown, we test different evolution scenarios for a planet covered by a stagnant lid, an episodic lid, and a plutonic-squishy lid. The models produce a range of predictions that can be compared to observations by planned missions to Venus, including EnVision measurements by the VenSpec spectrometers, comprising outgassing of water and other volatiles and surface composition. These can be used to constrain Venus’ interior composition and structure, and reveal key information on the differences between Earth and Venus.

How to cite: Louro Lourenço, D., Tackley, P., Rolf, T., Grünenfelder, M., Shah, O., and Helled, R.: Influence of Possible Bulk Compositions on the Long-Term Evolution and Outgassing of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9470, https://doi.org/10.5194/egusphere-egu24-9470, 2024.

EGU24-10478 | ECS | Orals | PS1.3

Cloud radiative feedback on the Venus climate simulated by a General-Circulation Model 

Wencheng Shao, Joao Mendonca, and Longkang Dai

Venus has regained great interest from planetary scientists in recent years because of the multiple upcoming Venus missions (e.g., EnVision, DAVINCI+ and VERITAS). Studying Venus is crucial for understanding the evolution of terrestrial planets as well as projecting the Earth’s future. One important component of the Venus climate system, the sulfuric acid clouds, has exhibited spatial and temporal variabilities. These variabilities are closely connected with the interactions between dynamics, photochemistry, radiative transfer and cloud physics. Current modeling studies of the Venus atmosphere have shed light on the underlying physics of the cloud variabilities. However, none of them has resolved the cloud radiative feedback. As an essential step to fully understanding the complex interactions, we develop a state-of-the-art General-Circulation Model (GCM), with cloud condensation/evaporation and radiative feedback processes included. In this talk, I will quantify the radiative forcing caused by the acidic clouds and provide indications of how the radiative forcing can influence the Venus climate evolution.

How to cite: Shao, W., Mendonca, J., and Dai, L.: Cloud radiative feedback on the Venus climate simulated by a General-Circulation Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10478, https://doi.org/10.5194/egusphere-egu24-10478, 2024.

EGU24-10655 | ECS | Posters on site | PS1.3

Unraveling Venus's Atmospheric Composition: Insights into CO, H2O, and OCS Abundances through Observations and Modeling 

Ting-Juan Liao, Eliot Young, Mark Bullock, dave crisp, and Yuk Yung

The investigation into Venus's atmosphere has highlighted deficiencies in photochemical models when it comes to explaining the distribution of trace gas species, particularly crucial elements like CO and OCS, which play a vital role in Venus's sulfur cycle and cloud formation.

To gain a comprehensive understanding of the abundance and variability of these trace gases ahead of the DaVinci probe's descent, we initiated an observational study using NASA's IRTF telescope equipped with the high-resolution ISHELL spectrometer. Conducted from June 11 to June 30, 2023, our study involved capturing K, H, and J-band spectra of Venus's night side. We employed the SMART software to calculate synthetic spectra, considering various gas abundances and emission angles.

With our high-resolution spectral data (R=λ/Δλ~25,000), we successfully mapped the abundances of CO, H2O, and OCS in the equatorial region, revealing both daily and latitudinal variations. Our focus was on examining the delicate balance between chemistry and transport, evident in the observed anti-correlation between OCS and CO abundance with cloud opacity.

Through near-infrared observations, this study aims to unravel the intricate interplay between atmospheric dynamics and chemical reactions in Venus's cloud formation. By providing insights into observed cloud patterns and elucidating the relationship between atmospheric chemistry, dynamics, and cloud creation on Venus, we contribute crucial parameters to refine existing photochemical models.

How to cite: Liao, T.-J., Young, E., Bullock, M., crisp, D., and Yung, Y.: Unraveling Venus's Atmospheric Composition: Insights into CO, H2O, and OCS Abundances through Observations and Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10655, https://doi.org/10.5194/egusphere-egu24-10655, 2024.

EGU24-12316 | ECS | Posters on site | PS1.3

The link between internal and rotational dynamics of Venus: The amplitude of mantle convection-driven wobble 

Vojtěch Patočka, Julia Maia, and Ana-Catalina Plesa

The spin period of Venus is anomalously large. With one Venusian day being 243 Earth days, the rotational bulge of
Venus has the amplitude of only tens of centimetres, making the Earth’s hotter twin the least rotationally stable planet in
the Solar System. Being a slow-rotator creates a unique link between internal and rotational dynamics. This is because,
on a slow-rotator, convection driven redistribution of mass may produce perturbations of the body’s inertia tensor that
are comparable in amplitude with the inertia of the rotational bulge. Venus thus may respond to mantle convection by
wobbling (Spada et al., 1996), and wobbling is detectable when both the rotational and the figure axes are measured
accurately. The present-day estimate of the angle between the two axes is 0.5°, but it is based on gravity models with a
limited resolution (Konopliv et al., 1999). Future missions to Venus, namely VERITAS and EnVision, are likely to provide
a more robust measurement.

The geodynamic regime of Venus’ mantle remains enigmatic. Observational data does not support the existence of
continuous plate tectonics on its surface, but some recent evidence of ongoing tectonic and volcanic activity (e.g. Herrick
and Hensley, 2023) and crater statistics analyses (e.g. O'Rourke et al., 2014) indicate that the planet is unlikely to be in a
stagnant lid regime (see also Rolf et al., 2022). Here we perform 3D spherical mantle convection simulations of the different
possible tectonic scenarios and compute the resulting reorientation of Venus. The reorientation is accompanied by a wobble
whose average amplitude we evaluate and compare to the present day estimate of 0.5° (Konopliv et al., 1999). Since the
different convective regimes predict vastly different rotational dynamics, the comparison provides a useful constraint on
the interior dynamics of Venus. This work was supported by the Czech Science Foundation through project No. 22-20388S.

References
Herrick, R., Hensley, S., 2023. Surface changes observed on a venusian volcano during the magellan mission. Science
doi:10.1126/science.abm7735.

Konopliv, A., Banerdt, W., Sjogren, W., 1999. Venus gravity: 180th degree and order model. Icarus 139, 3–18.
doi:10.1006/icar.1999.6086.

O'Rourke, J.G., Wolf, A.S., Ehlmann, B.L., 2014. Venus: Interpreting the spatial distribution of volcanically modified
craters. Geophys. Res. Lett. 41, 8252–8260. doi:10.1002/2014gl062121.

Rolf, T., Weller, M., Gulcher, A., Byrne, P., O’Rourke, J.G., Herrick, R., Bjonnes, E., Davaille, A., Ghail, R., Gillmann,
C., Plesa, A.C., Smrekar, S., 2022. Dynamics and evolution of venus’ mantle through time. Space Science Reviews 218,
70. doi:10.1007/s11214-022-00937-9.

Spada, G., Sabadini, R., Boschi, E., 1996. Long-term rotation and mantle dynamics of the Earth, Mars, and Venus.
J. Geophys. Res. Planets 101, 2253–2266. doi:10.1029/95JE03222.

How to cite: Patočka, V., Maia, J., and Plesa, A.-C.: The link between internal and rotational dynamics of Venus: The amplitude of mantle convection-driven wobble, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12316, https://doi.org/10.5194/egusphere-egu24-12316, 2024.

EGU24-12790 | ECS | Posters on site | PS1.3

Seismicity on Venus: optimal detection methods and target regions 

Iris van Zelst, Barbara De Toffoli, Raphaël F. Garcia, Richard Ghail, Anna J. P. Gülcher, Anna Horleston, Taichi Kawamura, Sara Klaasen, Maxence Lefevre, Philippe Lognonné, Julia Maia, Sven Peter Näsholm, Mark Panning, Ana-Catalina Plesa, Leah Sabbeth, Krystyna Smolinski, Celine Solberg, and Simon Stähler

With the selection of multiple missions to Venus by NASA and ESA that are planned to launch in the coming decade, we will greatly improve our understanding of Venus. However, none of these missions have determining the seismicity of the planet as one of their primary objectives. Nevertheless, constraints on the seismicity remain crucial to understand the tectonic activity and geodynamic regime of the planet and its interior structure. 

Funded by the International Space Science Institute (ISSI) in Bern, Switzerland, we have gathered an interdisciplinary team of experts in seismology, geology, and geodynamics to assess the potential seismicity of Venus, specific regions that could be seismically active at present, and the methods to detect them.

Here, we present the findings from our second ISSI team meeting (January 29 - February 2, 2024), aiming to review knowledge on Venus's seismicity and interior and identify the best approaches for future missions. We present the feasibility, advantages, and disadvantages of different seismic observation techniques on the surface (e.g., broadband seismometers, distributed acoustic sensing methods), from a balloon (acoustic sensors), and from orbit (airglow imagers). We make a recommendation for the instrumentation of a future seismology-focused mission to Venus. 

We also suggest target regions with a high likelihood of significant surface deformation and/or seismicity. These targets are useful for the upcoming VERITAS (Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy) and EnVision missions and would specifically benefit from the repeat pass interferometry of VERITAS, which detects surface deformation and can therefore in principle constrain the maximum displacement of surface faulting at locations that are visited twice during the mission. 

How to cite: van Zelst, I., De Toffoli, B., Garcia, R. F., Ghail, R., Gülcher, A. J. P., Horleston, A., Kawamura, T., Klaasen, S., Lefevre, M., Lognonné, P., Maia, J., Näsholm, S. P., Panning, M., Plesa, A.-C., Sabbeth, L., Smolinski, K., Solberg, C., and Stähler, S.: Seismicity on Venus: optimal detection methods and target regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12790, https://doi.org/10.5194/egusphere-egu24-12790, 2024.

EGU24-13314 | ECS | Posters on site | PS1.3

Estimation of Venus' atmospheric density through EnVision precise orbit determination 

Anna Maria Gargiulo, Antonio Genova, Flavio Petricca, Edoardo Del Vecchio, Simone Andolfo, Tommaso Torrini, Pascal Rosenblatt, Sébastien Lebonnois, Jean-Charles Marty, and Caroline Dumoulin

EnVision radio science investigation will deepen our understanding of Venus’ gravity, interior structure and atmospheric properties. To address these scientific questions, a two-way link communication (configuration X/X/Ka-band) is established with the ESA ESTRACK ground stations enabling precise orbit determination (POD) during the science phase. An accurate modeling of the spacecraft’s dynamics, including the atmospheric drag acceleration, is key for retrieving EnVision’s trajectory and constraining Venus’ gravity field, tides and orientation parameters.

Dedicated radio occultation campaigns are designed to characterize electron density profiles in the ionosphere and atmospheric density, pressure and temperature in the mesosphere and upper troposphere of Venus. Furthermore, an accurate POD of the spacecraft also provides complementary information on the atmospheric density at the altitudes crossed by the probe, extending the science return of the EnVision mission.

The atmospheric drag perturbation strongly affects spacecraft trajectories that are characterized by a pericenter altitude above Venus’ surface of less than 220 km. By accounting for different Venus’ atmospheric models, e.g., the Venus Climate Database (VCD) and the Venus Global Reference Atmospheric Model (Venus-GRAM), we investigate the impact of potential errors and uncertainties in the predicted atmospheric properties on the orbit evolution of the spacecraft. We note significant inconsistencies between Venus’ atmospheric models at the spacecraft altitudes including atmospheric density differences of more than 200%. These discrepancies may be representative of the current knowledge of Venus’ upper atmosphere and thermosphere. Thus, we carried out a perturbative analysis of the dynamical forces by introducing a mismodeling in the atmospheric density profiles. We assumed the VCD for the simulation of the radio tracking measurements and we included as a priori model in the estimation process the Venus-GRAM. By developing a batch sequential filter that adjusts a set of atmospheric density scale factors, we compensated for the mismodeling and improved the quality of the dynamical model and of the orbit determination. The proposed approach enables an estimation of the atmospheric density at the spacecraft altitudes with an accuracy of 25% and accuracies in the orbit reconstruction of 1-2 m, 30-40 m and 20-30 m in the radial, transverse and normal directions.

How to cite: Gargiulo, A. M., Genova, A., Petricca, F., Del Vecchio, E., Andolfo, S., Torrini, T., Rosenblatt, P., Lebonnois, S., Marty, J.-C., and Dumoulin, C.: Estimation of Venus' atmospheric density through EnVision precise orbit determination, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13314, https://doi.org/10.5194/egusphere-egu24-13314, 2024.

EGU24-13391 | ECS | Posters virtual | PS1.3

New Evidence for a Global Atmospheric Electric Circuit on Venus 

Blair McGinness, Giles Harrison, Karen Aplin, Martin Airey, and Keri Nicoll

The electrical environment of Venus has been investigated through extensive considerations of whether lightning has been detected in the atmosphere [1]. Although an important process, the presence or absence of lightning does not completely describe Venus’ electrical environment. Little consideration has been made of other related aspects, such as the possible presence of a global atmospheric electric circuit, as is present on Earth. In this context, lightning would be regarded as the source in a possible global circuit, which distributes charge across a planet. New arguments for and against a global electric circuit in Venus’ atmosphere are presented here which arise from re-analysis of data from the Venera 13 & 14 landers.

On Earth, the global atmospheric electric circuit connects regions of disturbed weather to distant regions of fair weather, by current flow between the conducting ionosphere and surface. Disturbed weather regions produce the potential difference between these conducting layers, which drives the current flow. The presence of a similar global circuit on other planets has been proposed, but their existence remains an open question, which motivates further work [2].

The Venera 13 & 14 landers descended through Venus’ atmosphere carrying a wealth of instrumentation. Each lander carried a point discharge sensor, which recorded electrical discharges between the spacecraft and the atmosphere [3]. The discharges recorded were difficult to explain using existing models of Venus’ environment, so it was previously proposed that low atmosphere haze layers could have caused them [4]. Further evidence for these haze layers has been provided by spectroscopic data from the Venera landers, which showed significant atmospheric extinction in the same region [5]. We have attempted to investigate whether it would be plausible for haze layers to cause both the electrical and extinction effects, and whether this favours a global electric circuit in Venus’ atmosphere.

To investigate this, a model describing electrical interactions in Venus’ atmosphere has been produced. The effects of different haze layers on Venus’ electrical environment were able to be studied, via different inputs to the model. The haze layer properties have been constrained by the spectroscopic observations. Results from the electrical modeling were compared with the electrical discharges recorded by the landers, allowing us to determine the conditions which best recreate these observations. Our investigations show that similar results to the observed Venera data can be produced by the electrical model when the effects of a global atmospheric electric circuit are included, but not when they are neglected. These findings are not definitive, but they do provide supporting evidence for the presence of a global electric circuit in Venus’ atmosphere.

References:
[1] R.D. Lorenz (2018). Progress in Earth and Planetary Science, 5. [2] K.L. Aplin (2006). Surveys in Geophysics 27. 63-108. [3] L. Ksanfomality et al. (1982). Soviet Astronomy Letters, 8. 230–232. [4] R.D. Lorenz (2018). Icarus, 307. 146-149. [5] B. Grieger (2003). Proceedings of the International Workshop Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science. 63–70.

How to cite: McGinness, B., Harrison, G., Aplin, K., Airey, M., and Nicoll, K.: New Evidence for a Global Atmospheric Electric Circuit on Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13391, https://doi.org/10.5194/egusphere-egu24-13391, 2024.

EGU24-14161 | ECS | Orals | PS1.3

Exploring origin of life chemistry and exoplanet biosignatures with GCMs 

Stephanie Olson, Jonathan Jernigan, Emilie Lafleche, and Haleigh Brown

Studies of exoplanet habitability involving GCMs typically consider the potential for long-lived surface liquid water—or, in other words, climates that Earth-life may find survivable. However, the presence of life and remotely detectable biosignatures on an exoplanet additionally requires an independent origin of life and that life subsequently thrives rather than simply survives. The origin and proliferation of life are both strongly influenced by climate, and both can therefore be informed by GCM studies in parallel with traditional habitability metrics. 

Wet-dry cycles are thought to be an essential ingredient for the origin of life. Cyclic wetting and drying may arise from either diurnal or seasonal cycles, and thus the likelihood of an origin of life may differ between worlds with very different rotation rates, obliquities, or eccentricities. At the same time, seasonal mixing in aqueous environments can trigger highly productive blooms and amplify biosignatures relative to scenarios lacking temporal variability.  

We used ExoPlaSim (an atmospheric GCM) and cGENIE-PlaSim (a 3D model for ocean dynamics and marine biogeochemistry coupled to a 3D atmospheric GCM) to explore diurnal and seasonal cycles on other worlds—with an eye towards origin of life chemistry and biosignatures. This presentation will ultimately identify the planetary scenarios most conducive to exoplanet life detection. 

How to cite: Olson, S., Jernigan, J., Lafleche, E., and Brown, H.: Exploring origin of life chemistry and exoplanet biosignatures with GCMs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14161, https://doi.org/10.5194/egusphere-egu24-14161, 2024.

EGU24-14443 | Posters on site | PS1.3

Henie Quadrangle (V-58, Southern Venus); Large Igneous Province Features 

Katherine Boggs, Jordan Shackman, Jerry Demorcy, Christine Pendleton, Jess Hall, Mahdi Chowdhury, Holly Bley, Ember Varga, Julia Shustova, Bridgette Dear, Parke Fontaine, Lovleen Dhami, Shane Herrington, Richard Ernst, Hafida El Balil, Erin Bethell, and Simon Hamner

The NASA Magellan Mission (1990 to 1994) produced a valuable resource that planetary geologists continue to use three decades later to unravel the geological characteristics of Venusian Large Igneous Provinces. The ability to be the first to map the surface of Venus is a powerful engagement tool to inspire the next generation of planetary geologists, as illustrated by the size of the Mount Royal University (MRU) Venus geological mapping team (now 25, nearly ¼ of the MRU Geology Major program). MRU is a public undergraduate university. Students are recruited out of 1st and 2nd year courses. In year one (Y1) of the research program students learn how to use the ArcGIS software while being introduced to the geological features of Venus as they map their quadrant, in Y2 or Y3 the students present a poster at an internal research day. The goal by Y4 is for these students to publish a peer-reviewed journal article. Currently one student who ran into pandemic roadblocks through high school could be published while she upgrades her marks, before she is in the MRU Geology Major Program. Such opportunities could prove to be incentives to guide other students past similar roadblocks (we will start working with local junior and high school students in the near future). Collectively we are working towards completing the geological map of the Henie Quadrangle (V-58, south Venus). Detailed mapping (at 1:500,000) revealed that lava canali extend across the entire quadrangle, with evidence for at least three generations of canali. Three canali originate from corona features (e.g. the circumferential dykes around Fotla Corona) suggesting that some canali may be linked to corona formation. The orientation of compressional wrinkle ridges (WR) in northern Henie suggest that these WRs were formed due to strain associated with the formation of the Artemis tectonomagmatic feature which is directly north of Henie. Artemis is possibly the largest such feature in the Solar System. The extent of the Artemis influence is being constrained across the Henie Quadrangle. The source of strain that formed a differently oriented WR swarm to the south of Henie is unknown. There is no evidence for the strain localization into master faults that we see on Earth. More work is needed to develop a model for the formation of the paired Latmikaik-Xacau Coronae and the associated Tellervo Chasma, Sunna-Laverna Dorsae and the Sonmunde-Mdeb-Arubani Flucti. A fissure eruption out of the Sunna Dorsa is proposed as the origin for the surrounding Arubani Fluctus.      

How to cite: Boggs, K., Shackman, J., Demorcy, J., Pendleton, C., Hall, J., Chowdhury, M., Bley, H., Varga, E., Shustova, J., Dear, B., Fontaine, P., Dhami, L., Herrington, S., Ernst, R., El Balil, H., Bethell, E., and Hamner, S.: Henie Quadrangle (V-58, Southern Venus); Large Igneous Province Features, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14443, https://doi.org/10.5194/egusphere-egu24-14443, 2024.

EGU24-14638 | ECS | Orals | PS1.3

Constraining the interior structure and thermal state of Venus 

Michaela Walterová, Ana-Catalina Plesa, Philipp Baumeister, Tina Rückriemen-Bez, Frank W. Wagner, and Doris Breuer

Often termed the twin sister of the Earth, Venus represents an alternative outcome of the evolutionary path taken by large terrestrial planets. Given its extreme surface conditions, lack of surface water, and the absence of plate tectonics, the present-day thermal state of its mantle is likely very different from the Earth. Venus also remains the most enigmatic of terrestrial worlds in terms of interior structure. Both its tidal Love number k2 and the moment of inertia factor, the main sources of information on the core size and interior structure, are known with a large uncertainty of about 10% [1, 2], and the magnitude of tidal dissipation, sensitive to the planet’s thermal state, has only been determined indirectly [e.g., 3]. Yet, the set of observables acquired by the Magellan and Pioneer Venus Orbiter missions can still be used to put constraints on the interior structure.

In this study, we perform a Bayesian inversion of several observational and theoretical constraints (such as the tidal Love number, maximum elastic thickness, or absence of intrinsic magnetic field) to gain insight into the present-day interior structure and thermal state of Venus. This is done by combining the calculation of a global tidal deformation with a 1d parameterised model of mantle convection in the stagnant-lid regime [4,5]. The convection model is based on the thermal boundary layer theory and incorporates partial melting, crustal growth, and inner core crystallization. The elastic structure of the mantle for three selected mineralogical models is obtained from the software Perple_X, based on the minimisation of Gibbs free energy [6]. Finally, to find the tidal parameters, we calculate the deformation of a layered compressible viscoelastic sphere [7]. The mantle is described by the Andrade rheological model, which has proven essential for distinguishing between a fully solid and a fully or partially liquid Venusian core [8]. We vary a large set of rheological, structural, and thermodynamic parameters and predict a range of mantle temperatures consistent with previous stagnant-lid models, average mantle viscosities between 1020-1022 Pa.s, and a tidal quality factor of Q=50+74-24, corresponding to a phase lag of 1.12+1.06-0.67 degrees. Additionally, we discuss how the future measurements of the tidal deformation and the moment of inertia of Venus from EnVision [9] and VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) [10] can improve our understanding of the planet's interior.

[1] Konopliv & Yoder (1995), doi:10.1029/96GL01589.

[2] Margot et al. (2021), doi:10.1038/s41550-021-01339-7.

[3] Correia & Laskar (2003), doi:10.1016/S0019-1035(03)00043-5.

[4] Morschhauser et al. (2011), doi:10.1016/j.icarus.2010.12.028.

[5] Baumeister et al. (2023), doi:10.1051/0004-6361/202245791.

[6] Connolly (2009), doi:10.1029/2009GC002540.

[7] Takeuchi & Saito (1972), doi:10.1016/B978-0-12-460811-5.50010-6.

[8] Dumoulin et al. (2017), doi:10.1002/2016JE005249.

[9] Rosenblatt et al. (2021), doi:10.3390/rs13091624.

[10] Cascioli et al. (2023), doi:10.3847/PSJ/acc73c.

How to cite: Walterová, M., Plesa, A.-C., Baumeister, P., Rückriemen-Bez, T., Wagner, F. W., and Breuer, D.: Constraining the interior structure and thermal state of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14638, https://doi.org/10.5194/egusphere-egu24-14638, 2024.

EGU24-14689 | Orals | PS1.3

Venus atmosphere dynamics: digging into the Venus Express observations 

Dmitrij Titov, Igor Khatuntsev, and Marina Patsaeva

Dynamics of the Venus atmosphere is still an unsolved fundamental problem in the planetary physics. ESA’s Venus Express collected long imaging time series in several wavelengths from UV to near-IR. It was later complemented by JAXA’s Akatsuki observations, thus providing the longest almost uninterrupted monitoring of the Venus atmosphere dynamics for about 26 Venus years. Tracking of cloud features allowed determination of wind speed at different levels within the cloud deck thus enabling significant progress in characterization of the mean atmospheric circulation. The analysis revealed wind variability including changes with altitude, latitude, local solar time as well as influence of the surface topography and long term 12.5 years periodicity.

The images also provided morphological evidences of dynamical processes at the cloud level. UV dark low latitudes were found to be dominated by convective mixing that brings UV absorbers from depth, while bright uniform clouds at middle-to-high latitudes are typical for the regions with suppresses vertical mixing. The latter feature correlates with drastic increase of the total cloud opacity poleward from ~60° latitude that likely indicates presence of a dynamical mixing barrier here. Similarity of the global UV cloud morphology at the cloud top (~70 km) and that in the deep cloud (50-55 km) observed in the near-IR on the night side suggested similar morphology shaping processes throughout the cloud deck. Venus Express observed gravity waves poleward of 65°N concentrated at the edges of Ishtar Terra likely indicating their generation by wind interaction with the surface. 

Venus Express performed about 800 radio occultations providing precise measurements of the atmospheric temperature structure and static stability parameter in the altitude range 40-90 km. The Richardson number latitude-altitude field derived from the wind and temperature measurements suggests presence of convection in the cloud deck and stable mesosphere above it with the convective layer extending to greater depth at high latitudes. The talk will present recent results on the atmospheric circulation, supplemented by a summary of the Venus Express observations related to the atmospheric dynamics and an outlook for further analysis of these data.  

How to cite: Titov, D., Khatuntsev, I., and Patsaeva, M.: Venus atmosphere dynamics: digging into the Venus Express observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14689, https://doi.org/10.5194/egusphere-egu24-14689, 2024.

The dynamic regime prevailing in the mantle of present-day Venus is still unknown. The surface of Venus seems uniformly quite young; it has  been proposed that it was due to a catastrophic resurfacing 150-700 Ma, and that the planet was in a stagnant lid regime since. Indeed, Magellan observations have failed to reveal a continuous set of accretion ridges and subduction zones, signatures of plate tectonics. But subduction features (trench, elastic bulge) are present in a number of localized spots, for exemple around two of the largest coronae, Artemis and Quetzelpetlal. There, subduction would be mainly by roll-back and could have been induced by the impingement of a mantle plume under the lithosphere, as predicted by our recent fluid dynamics laboratory experiments. Further analysis of our experiments suggest that subduction would be facilitated by the presence of a few % of a liquid phase in the asthenosphere. Melt would be most likely for the Venusian case, as anyway hinted by the amount of volcanic features on the surface of the planet. The experimental scaling laws further suggest that roll-back and subduction could be quite fast (10 cm/yr) because of the old age of the subducting lithosphere and the transformation to eclogite of the basaltic crust. This is turn would generate the rapid opening of a back-arc basin. Laboratory experiments show that for Venus temperature conditions, the produced crust and lithosphere could be quite disorganized with a contorted spreading center, large transforms and microplates. Moreover, the buoyancy of the newly created plate would cause it to remain quite elevated compared to the surrounding plains. Hence, inspection of the topography of Venus suggests several new plates created by subduction: beside the interior of Artemis coronae, Enyo Fossae and Asthik Planum could be plausible candidates. 

How to cite: Davaille, A.: Signatures of a regime of episodic localized subduction: from laboratory experiments to Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16255, https://doi.org/10.5194/egusphere-egu24-16255, 2024.

EGU24-16442 | ECS | Posters on site | PS1.3

Sensitivity studies for the VeSUV/VenSpec-U instrument onboard ESA’s EnVision mission 

Lucile Conan, Emmanuel Marcq, Benjamin Lustrement, Nicolas Rouanet, Ann Carine Vandaele, and Jörn Helbert

The next ESA mission to Venus, EnVision, aims to study the planet as a whole, including its various constituting parts as well as their interactions and coupling processes. Several instruments will therefore compose the payload: a synthetic aperture radar (VenSAR, NASA), a subsurface radar sounder and a suite of three spectrometers (VenSpec) will be embedded, and a radioscience experiment will be implemented. Among them, the UV channel of the spectrometer suite, VenSpec-U, will observe the atmosphere above the clouds and will focus on the characterisation of the sulphured gases SO2 and SO, the monitoring of the unknown UV absorber and dynamical processes. These four topics have been identified as the main science objectives of the instrument and have driven the elaboration of a preliminary design based on the requirements (e.g. spectral range, spectral and spatial resolution) that were formulated with respect to these goals.

The compliance of the current design with respect to these requirements, regarding in particular the precision of the retrieved science data, can then be assessed. Sensitivity studies are therefore performed using the Radiative Transfer Model (RTM), updated from the one used for SPICAV-UV/Venus Express retrievals (Marcq et al., 2020), that allows to link atmospheric features and UV reflectance spectra. Two types of perturbations are considered : errors of random nature arising from the presence of noise on the signal, or systematic errors caused by various effects that induce biases on the measurements. The first ones can be characterised through the influence of the Signal-to-Noise Ratio (SNR) on the uncertainties associated to each retrieved parameter through the fitting algorithm. Limits in terms of SNR can then be defined in order to ensure the compliance with the specifications. The second ones are referring to the impact of biases on the retrievals’ accuracy, and evaluate more specifically the effects of the similarities between the spectral characteristics of these biases and those of the atmospheric components aiming to be detected. The implemented method is based on the Effective Spectral Radiometric Accuracy (ESRA) requirement, previously defined within the framework of the ESA Sentinel missions. It allows to study biases independently as well as potential compensations, so that allowable envelopes of residual errors can then be estimated for each of the considered biases.

How to cite: Conan, L., Marcq, E., Lustrement, B., Rouanet, N., Vandaele, A. C., and Helbert, J.: Sensitivity studies for the VeSUV/VenSpec-U instrument onboard ESA’s EnVision mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16442, https://doi.org/10.5194/egusphere-egu24-16442, 2024.

EGU24-16505 | ECS | Posters on site | PS1.3

Influence of the UV absorber distribution on the temperature and circulation ofthe Venusian cloud region 

Peng Han and Sébastien Lebonnois

Until now, the Venus PCM (Planetary Climate Model) was using precomputed tables for the distribution of the solar heating rates in the atmosphere of Venus. A new scheme is now implemented to compute online the radiative transfer of the solar flux, which allows more flexibility to study sensitivity to opacity sources. We have investigated the sensitivity of the temperature and circulation of the Venusian cloud region to the distribution of the UV absorber. Different vertical distributions of the UV absorber, as well as variations of this along latitudes, have been tested, and comparison is discussed of the vertical profile of computed solar heating rates, temperature distribution in the cold collar region, as well as the resulting mean zonal wind field.

How to cite: Han, P. and Lebonnois, S.: Influence of the UV absorber distribution on the temperature and circulation ofthe Venusian cloud region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16505, https://doi.org/10.5194/egusphere-egu24-16505, 2024.

EGU24-16898 | ECS | Posters on site | PS1.3

Laboratory studies and modelling of ferric chloride as the cause of the anomalous UV absorption in the Venusian atmosphere 

Joanna Egan, Wuhu Feng, Alexander James, James Manners, Daniel R. Marsh, and John M. C. Plane

The cause of the inhomogeneous near-ultraviolet absorption observed in the upper clouds of Venus remains a key question in Venusian research. One possible candidate in the literature is ferric chloride. The absorption spectrum of ferric chloride currently in use by models uses ethyl acetate as a solvent and does not reproduce the absorption features observed on Venus. The study of the optical properties and chemistry of ferric chloride in the sulphuric acid cloud droplets is required to draw valid conclusions regarding its suitability as a candidate for the near-UV absorption.

In this study, we measure the absorption spectrum of ferric chloride in sulphuric acid from 200 – 600 nm at a range of temperatures and measure the rate of conversion of the ferric chloride ions into ferric sulphate ions. We then use the resulting ferric chloride absorption coefficients in a 1D radiative transfer model and estimate the required concentration of ferric chloride in the clouds to be 0.6 – 0.9 wt% in the mode 1 (~0.3 µm radius) cloud droplets to match observations. We also predict the atmospheric concentrations of ferric chloride formed from the reaction of iron ablating from cosmic dust entering Venus’ atmosphere around 120 km with hydrogen chloride emitted by volcanic activity, and estimate the accumulation timescale of ferric chloride to produce the required concentrations in the clouds.

How to cite: Egan, J., Feng, W., James, A., Manners, J., Marsh, D. R., and Plane, J. M. C.: Laboratory studies and modelling of ferric chloride as the cause of the anomalous UV absorption in the Venusian atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16898, https://doi.org/10.5194/egusphere-egu24-16898, 2024.

EGU24-17524 | Posters on site | PS1.3

Planetary-scale wave study in Venus cloud layer, simulated by the Venus PCM 

Dexin Lai, Sebastien Lebonnois, and Tao Li

High-resolution runs of the Venus PCM (1.25° in longitude and latitude) successfully simulated Venus atmospheric superrotation. The results show a clear spectrum and structure of atmospheric waves, primarily with periods of 5.65 days and 8.5 days. The simulation successfully reproduces long-term quasi-periodic oscillation of the zonal wind and primary planetary-scale wave seen in observations. These oscillations are obtained with a period of about 163-222 days close to the observations. The Rossby waves show robustness in wave characteristics and angular momentum transport due to Rossby-Kelvin instability by comparing the 5.65-day wave with the 5.8-day wave simulated by another Venus GCM, AFES-Venus. Similarities are also evident between the 8.5-day wave in our simulation and the 7-day wave obtained in AFES-Venus. Furthermore, the long-term variations in angular momentum transport indicate that the 5.65-day wave is the dominant factor of the oscillation on the superrotation, and the 8.5-day wave is the secondary. When the 5.65-day wave grows, its angular momentum transport is enhanced and accelerates (decelerates) the lower-cloud equatorial jet (cloud-top mid-latitude jets). Meanwhile, the 8.5-day wave weakens, reducing its deceleration effect on the lower-cloud equator region. Consequently, this flattens the background wind and weakens instability, leading to the decay of the 5.65-day wave. And vice versa when the 5.65-day wave is weak.

How to cite: Lai, D., Lebonnois, S., and Li, T.: Planetary-scale wave study in Venus cloud layer, simulated by the Venus PCM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17524, https://doi.org/10.5194/egusphere-egu24-17524, 2024.

EGU24-18247 | Orals | PS1.3

Science objective and status of the EnVision Mission to Venus 

Anne Grete Straume-Lindner, Mitch Schulte, Anne Pacros, Thomas Voirin, Lorenzo Bruzzone, Paul Byrne, Lynn Carter, Caroline Dumoulin, Gabriella Gilli, Joern Helbert, Scott Hensley, Kandis Lea Jessup, Walter Kiefer, Emmanuel Marcq, Philippa Mason, Alberto Moreira, Ann Carine Vandaele, and Thomas Widemann

EnVision is ESA’s next mission to Venus, in partnership with NASA, where NASA provides the Synthetic Aperture Radar payload and mission support. The ESA mission adoption is scheduled for January 2024, and the launch for 2031. The start of the science operations at Venus is early 2035 following the mission cruise, and aerobraking phase around Venus to achieve a low Venus polar orbit. The scientific objective of EnVision is to provide a holistic view of the planet from its inner core to its upper atmosphere, studying the planets history, activity and climate. EnVision aims to establish the nature and current state of Venus’ geological evolution and its relationship with the atmosphere. EnVision’s overall science objectives are to: (i) characterize the sequence of events that formed the regional and global surface features of Venus, as well as the geodynamic framework that has controlled the release of internal heat over Venus history; (ii) determine how geologically active the planet is today; (iii) establish the interactions between the planet and its atmosphere at present and through time. Furthermore, EnVision will look for evidence of past liquid water on its surface.

The nominal science phase of the mission will last six Venus cycles (~four Earth years), and ~210 Tbits of science data will be downlinked using a Ka-/X-band communication system. The science objectives will be addressed by five instruments and one experiment, provided by ESA memberstates and NASA. The VenSAR S-band radar will perform targeted surface imaging as well as polarimetric and stereo imaging, radiometry, and altimetry. The high-frequency Subsurface Radar Sounder (SRS) will sound the upper crust in search of material boundaries. Three spectrometers, VenSpec-U, VenSpec-H and VenSpec-M, operating in the UV and Near- and Short Wave-IR, respectively, will map trace gases, search for volcanic gas plumes above and below the clouds, and map surface emissivity and composition. A Radio Science Experiment (RSE) investigation will exploit the spacecraft Telemetry Tracking and Command (TT&C in Ka-/X bands) system to determine the planet’s gravity field and to sound the structure and composition of the middle atmosphere and the cloud layer in radio occultation. All instruments have substantial heritage and robust margins relative to the requirements, with designs suitable for operation in the Venus environment, and were chosen to meet the broad range of measurement requirements needed to support the EnVision scientific objectives. The EnVision science teams will adopt an open data policy, with public release of the scientific data after verification and validation. Public calibrated data availability is <6 months after data downlink.

The mission phase B1 was concluded in December 2023 following the successful Mission Adoption Review and positive science review and recommendations by the ESA Solar System and Exploration Working Group (SSEWG) and Space Science Advisory Committee (SSAC). The mission adoption is scheduled for 25 January 2024. The scientific objectives and status of the EnVision mission preparations will be presented, including an overview of the scientific topics being studied and the next steps in the mission preparation.

How to cite: Straume-Lindner, A. G., Schulte, M., Pacros, A., Voirin, T., Bruzzone, L., Byrne, P., Carter, L., Dumoulin, C., Gilli, G., Helbert, J., Hensley, S., Jessup, K. L., Kiefer, W., Marcq, E., Mason, P., Moreira, A., Vandaele, A. C., and Widemann, T.: Science objective and status of the EnVision Mission to Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18247, https://doi.org/10.5194/egusphere-egu24-18247, 2024.

EGU24-18366 | Posters on site | PS1.3

Zonal winds in Venus mesosphere from VIRTIS/VEx temperature retrievals 

Arianna Piccialli, Davide Grassi, Alessandra Migliorini, Romolo Politi, Giuseppe Piccioni, and Pierre Drossart

Venus is a natural laboratory to study the atmospheric circulation on a slowly rotating planet. The dynamics of its upper atmosphere (60-120 km) is a combination of retrograde zonal wind found in the lower mesosphere and solar-to-antisolar winds that characterize the thermosphere, and it is subject to a strong turbulence and a dramatic variability both on day-to-day as well as longer timescales. Moreover, several wavelike motions with different length scales have been detected at these altitudes within and above the clouds and they are supposed to play an important role in the maintenance of the atmospheric circulation. The basic processes maintaining the super-rotation (an atmospheric circulation located at the clouds level and being 80 times faster than the rotation of the planet itself) and other dynamical features of Venus circulation are still poorly understood [1].

Different techniques have been used to obtain direct observations of wind at various altitudes: tracking of clouds in ultraviolet (UV) and near infrared (NIR) images give information on wind speed at cloud top (~70 km altitude) [2] and within the clouds (~61 km, ~66 km) [3], while ground-based measurements of doppler-shift in CO2 band at 10 μm [4] and in several CO (sub-)millimeter lines [5,6] sound thermospheric and upper mesospheric winds, showing a strong variability.

In the mesosphere, at altitudes where direct observations of wind are not possible, zonal wind fields can be derived from the vertical temperature structure using the thermal wind equation. Previous studies [7,8,9] showed that on slowly rotating planets, like Venus and Titan, the strong zonal winds at cloud top can be successfully described by an approximation of the Navier–Stokes equation, the cyclostrophic balance in which equatorward component of centrifugal force is balanced by meridional pressure gradient.

We will present zonal thermal winds derived by applying the cyclostrophic approximation from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) temperature retrievals. VIRTIS was one of the experiments on board the European mission Venus Express [10]. For this study, we will analyze the complete VIRTIS dataset acquired between December 2006 and January 2010 [11,12].

References

[1] Sanchez-Lavega, A. et al. (2017) Space Science Reviews, Volume 212, Issue 3-4, pp. 1541-1616.

[2] Goncalves R. et al. Atmosphere, 12:2., 2021. doi: 10.3390/atmos12010002.

[3] Hueso, R. et al. (2012) Icarus, Volume 217, Issue 2, p. 585-598.

[4] Sornig, M. et al. (2013) Icarus 225, 828–839.

[5] Rengel, M. et al. (2008) PSS, 56, 10, 1368-1384.

[6] Piccialli, A. et al. A&A, 606, A53 (2017) DOI: 10.1051/0004-6361/201730923

[7] Newman, M. et al. (1984) J. Atmos. Sci., 41, 1901-1913.

[8] Piccialli A. et al. (2008) JGR, 113,2, E00B11.

[9] Piccialli A. et al. (2012) Icarus, 217, 669–681

[10] Drossart, P. et al. (2007) PSS, 55:1653–1672

[11] Grassi D. et al. (2008) JGR., 113, 2, E00B09.

[12] Migliorini, A. et al. (2012) Icarus 217, 640–647.

How to cite: Piccialli, A., Grassi, D., Migliorini, A., Politi, R., Piccioni, G., and Drossart, P.: Zonal winds in Venus mesosphere from VIRTIS/VEx temperature retrievals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18366, https://doi.org/10.5194/egusphere-egu24-18366, 2024.

EGU24-19372 | ECS | Posters on site | PS1.3

Water and the tectonic regime of Venus 

Marla Metternich, Paul J. Tackley, Nickolas Moccetti Bardi, and Diogo L. Lourenço

Observations of Venus imply ongoing tectonic and volcanic activity, suggesting the planet is dynamically active[1,2]. Tectonically altered regions, such as ridges or tesserae, indicate surface mobility. However, unlike Earth, no evidence of active plate tectonics has been identified. The tectonics and volcanism of terrestrial planets are closely tied to active mantle convection modes. Rheology, a crucial element in tectonics, is influenced by the presence of water[3]. Despite this, the impact of water has largely been overlooked in Venus studies, as its interior is typically assumed to be dry. This assumption is being challenged by indications of significant hydrodynamic escape into space, requiring volcanic replenishment. Consequently, water is likely still present in Venus' interior, even if the concentrations are unknown. Importantly, the potential effects of water on Venus' dynamics and evolution remain poorly understood. The interplay between water, mantle dynamics, and volcanic activity would likely contribute to a more comprehensive understanding of Venus' evolution.  This underlines the need to consider complex dynamic thermo-magmatic models that account for water, including composition-dependent finite water solubilities.

 

In this study, we use the numerical code StagYY to perform state-of-the-art 2D models in a spherical annulus geometry to assess the effects of water on the tectono-magmatic evolution of Venus[4,5]. Particular attention will be given to the way water influences mantle convection and tectonics. Indeed, results show that the presence of water can dramatically change the geodynamic regime through the rheology, melting and outgassing. With the introduction of composition-dependent water solubility maps, dehydration processes will redistribute water throughout the mantle[6]. Since water content is directly related to the viscosity structure, the convective regime is expected to change as well. The main question we want to address is how dehydration processes and water distribution influence the convective and tectonic regimes of Venus. Studying the impact of water on Venus's interior may not only unveil insights into its tectonic evolution but also sets the stage for crucial future research, advancing our broader understanding of planetary processes and habitability.

 

[1] Smrekar, S. E., Stofan, E. R., Mueller, N., Treiman, A., Elkins-Tanton, L., Helbert, J., ... & Drossart, P. (2010). Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science, 328(5978), 605-608.

[2]Gülcher, A. J., Gerya, T. V., Montési, L. G., & Munch, J. (2020). Corona structures driven by plume–lithosphere interactions and evidence for ongoing plume activity on Venus. Nature Geoscience13(8), 547-554.

[3]Karato, S. I. (2015). Water in the evolution of the Earth and other terrestrial planets. Treatise on Geophysics, 9, 105-144.

[4] Tackley, P. J. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid. Physics of the Earth and Planetary Interiors, 171(1-4), 7-18.

[5]Tian, J., Tackley, P. J., & Lourenço, D. L. (2023). The tectonics and volcanism of Venus: New modes facilitated by realistic crustal rheology and intrusive magmatism. Icarus, 399, 115539.

[6]Nakagawa, T. (2017). On the numerical modeling of the deep mantle water cycle in global-scale mantle dynamics: The effects of the water solubility limit of lower mantle minerals. Journal of Earth Science, 28(4), Article 4. https://doi.org/10.1007/s12583-017-0755-3

How to cite: Metternich, M., Tackley, P. J., Moccetti Bardi, N., and Lourenço, D. L.: Water and the tectonic regime of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19372, https://doi.org/10.5194/egusphere-egu24-19372, 2024.

EGU24-22187 | Orals | PS1.3

Steam atmospheres and the implications for Venus and Venus-like planets  

Franck Selsis, Jérémy Leconte, Martin Turbet, Guillaume Chaverot, and Emeline Bolmont

A planet with a significant water content can give rise to a steam atmosphere (dominated by water vapor) when the incoming stellar flux exceeds the so-called runaway limit or after large impacts or accretion. All steam-atmosphere current models predict that the greenhouse effect of an ocean worth of water vapor is sufficient to generate a surface magma ocean. This has far reaching consequences for the early evolution of warm rocky planets and the coupling of their interior with the atmosphere. In this paradigm, the solidification of the mantle of Venus is believed to have happened only after the escape of its steam atmosphere to space, leaving the mantle desiccated.

However, these conclusions rely on the assumption that atmospheres are fully convective below their photosphere. This hypothesis was introduced in the 80s and is used in a large part of the literature on the subject. Its validity had however not been assessed thoroughly. We will present the results of a climate model that has been specifically designed to model the radiative-convective equilibrium of steam atmospheres without any a priori hypothesis on their convective nature. These results show that steam atmospheres are generally not fully convective, which yields much cooler surfaces than previous models. A runaway greenhouse does not systematically melt the surface. This changes completely our view of the early evolution of Venus', with even more drastic changes for planets around stars redder than the Sun.

The equilibrium thermal structure of a steam atmosphere, which affects observable signatures and mass-radius relationships of warm Earth-like to water-rich planets, becomes strongly dependent on the stellar spectrum and internal heat flow. Our current constraints on the water content of the internal Trappist-1 planets should for example be revisited. For ultracool dwarfs, these results even question the nature of the inner edge of the sometimes called habitable zone.

How to cite: Selsis, F., Leconte, J., Turbet, M., Chaverot, G., and Bolmont, E.: Steam atmospheres and the implications for Venus and Venus-like planets , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22187, https://doi.org/10.5194/egusphere-egu24-22187, 2024.

EGU24-547 | ECS | Posters on site | BG5.3

Revisiting depositional models for the Ediacara Member of the Rawnsley Quartzite in South Australia 

Karol Faehnrich, Diego C. García-Bellido, Mary L. Droser, and Robert R. Gaines

The Ediacara Member of the Rawnsley Quartzite hosts one of the best preserved and most diverse assemblages of the Ediacara Biota. In it, soft-bodied organisms are preserved across various depositional environments, with a proposed connection between sedimentary facies and fossil assemblages. Recent studies have questioned previously-established facies models, undermining links between paleoenvironment, paleoecology, and taphonomy. Here, we revisit these models using field observations from across the central Flinders Ranges, supplemented by two new cores drilled through the Ediacara Member at the Nilpena fossil site. The two drill sites are 2 km apart and span strata from the top of the underlying Chace Member through the overlying fossiliferous facies of the Ediacara Member. These two cores are easily correlated to surface outcrops and provide the most complete record of the deposition of the Ediacara Member thus far. The core drilled at “One Tree Hill” (OTH-1) reaches a depth of 65 m and records characteristic “petee laminations” below the erosional contact with the Ediacara Member, which is marked by a breccia horizon. The basal breccia of the Ediacara Member gradationally passes into thinly laminated planar to slightly wavy siltstone that then transitions into alternating thin beds of siltstone and thick beds of massive sandstone often affected by soft-sediment deformation. These beds grade into wavy-laminated siltstone interbedded with thin beds of arenite. Forming the top of the core are thick beds of massive arenite. The second drill core (MR-1) spanning 75.8 m records analogous facies with changing thickness and siltstone/sandstone ratio but lacks a breccia horizon at the base of the Ediacara Member. Both cores highlight repeated cycles of alternating deposition of sandstone and siltstone often obscured in the surface exposure. We investigate an array of sedimentary structures observed in the cores and surface exposures in thin sections, exploring the role of microbial matgrounds and silica cementation in sediment binding and transport. Both are critical for any depositional model developed for the Ediacara Member across the Nilpena site and central Flinders Ranges, its accumulation rate, sediment sources and potential triggers for repeated channelized flows observed throughout the unit. A unified depositional model built across this basin will be critical to further untangle the complex interplay between time, changing taxonomic diversity, water depth, and paleoenvironment at the dawn of animal life.

How to cite: Faehnrich, K., García-Bellido, D. C., Droser, M. L., and Gaines, R. R.: Revisiting depositional models for the Ediacara Member of the Rawnsley Quartzite in South Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-547, https://doi.org/10.5194/egusphere-egu24-547, 2024.

EGU24-620 | ECS | Orals | BG5.3

Numerical modelling of magmatic CO2 emissions from the Neo-Tethyan margin during the Early Cenozoic 

Bram Vaes, Pietro Sternai, Léa Ostorero, Luca Castrogiovanni, Christopher Gonzalez, and Yannick Donnadieu

Identifying the geological drivers of long-term climate change is key to improve our understanding of the interactions between the deep Earth and the Earth’s surface. Long-term Cenozoic climate cooling has been largely attributed to an increase in atmospheric carbon consumption by enhanced silicate weathering linked to the uplift of the Tethyan orogenic belt. Alternatively, this cooling trend has been explained by decreasing magmatic CO2 outgassing during the progressive closure of Neo-Tethys Ocean. However, the outgassing rates associated with Neo-Tethyan magmatism remain poorly constrained, making it difficult to assess its contribution to Cenozoic climate change. Here, we present the first results of numerical geodynamic experiments aimed at obtaining improved quantitative estimates of the magmatic CO2 outflux along the Neo-Tethyan margins. To this end, we use 2D numerical petrological-thermomechanical models of oceanic subduction and continental collision that account for partial melting and slab decarbonation. Calibrating these numerical experiments on available geological constraints from the Neo-Tethyan margin, we estimate the Neo-Tethyan magma production volumes through the Early Cenozoic. We discuss how these results are sensitive to changes in model setup and input parameters such as convergence rates, rheology, and crustal composition. To quantify the time-dependent magmatic CO2 emissions, we combine the magma production histories with both modelling- and observation-based quantifications of the volatile contents of pre- and post-eruptive igneous rocks. Finally, we discuss the potential Neo-Tethyan magmatic forcing of Early Cenozoic climate change in light of our new results and its implications for the global carbon cycle and surface-deep Earth feedbacks.

How to cite: Vaes, B., Sternai, P., Ostorero, L., Castrogiovanni, L., Gonzalez, C., and Donnadieu, Y.: Numerical modelling of magmatic CO2 emissions from the Neo-Tethyan margin during the Early Cenozoic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-620, https://doi.org/10.5194/egusphere-egu24-620, 2024.

The Permian section of the Paraná-Etendeka basin is represented by the Palermo and Irati formations, comprising a shallow sea that occupied ca. 5 million km2 of southern Gondwana before completely drying out around 277 million years ago (Irati-Whitehill ocean). This is broadly coincident with the uprising of the Cape Fold Belt of southern Africa and the San Rafael orogeny of the paleo-Pacific margin of South America, leading to the interpretation that basin restriction and the major ecosystem changes that followed were ultimately caused by uprising of mountainous domains surrounding the shallow sea. We combine new iron speciation, organic carbon isotope and trace element data with previous biomarker, organic carbon and nitrogen isotope data to unravel the biogeochemical and redox changes during this transition from an open marine realm to a restricted setting, and to test the hypothesis of external controls on the biogeochemical cycles of southern Gondwana. Mudstones and shales of the Palermo Formation yielded FeHR/FeT around or below 0.2, suggesting oxic bottom water conditions, reinforced by muted redox-sensitive element (RSE) concentrations and overall low Total Organic Carbon (TOC) contents, with δ13Corg around -25‰. Black shales of the overlying Irati Formation, on the other hand, record an abrupt shift to anoxic conditions, with FeHR/FeT between 0.3 and 0.9, representing mostly ferruginous conditions with sporadic euxinic incursions (FePy/FeHR > 0.8), higher concentrations of RSE such as Mo, higher TOC contents and d13Corg rapidly oscillating from ca. -29 up to ca. -19‰. The euxinic intervals are associated with the Assistência Member, containing tephra layers dated at 277 Ma and thus coeval to the Cape and San Rafael orogenies. Our results reinforce the hypothesis of mountain belt formation as the main external driver of biogeochemical changes, leading to toxic conditions for complex life forms in the Permian internal basins and to the accumulation of important organic-rich source rocks in the shallow seas of southern Gondwana.

How to cite: Caxito, F., Sperling, E., Bastos, L., and Pereira, E.: Anoxia in the Permian Irati-Whitehill Ocean of southern Gondwana: A possible link with uprising of the Cape and San Rafael mountain belts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1345, https://doi.org/10.5194/egusphere-egu24-1345, 2024.

EGU24-1446 | Orals | BG5.3

Plant diversification is associated with habitat disruption in the transient Hengduan Mountains 

Yaquan Chang, Wenna Ding, Junqing He, Sean Willett, Katrina Gelwick, Niklaus Zimmermann, and Loic Pellissier

Mountain regions harbor disproportionally high biodiversity levels on Earth, which can hardly be explained solely by contemporary climate and heterogeneity. The complex interactions between the geological and climate dynamics in the mountain system could provide a unique substrate for species to diversify, leading both to higher diversity and higher endemism in the mountains. The Hengduan Mountains region is a unique biodiversity hotspot outside of the tropics. It is characterized by complex geological and climate histories associated with the Indian-Eurasia plate collision and monsoon intensification shaping intense geomorphic processes. These unique and complex histories are expected to have shaped landscapes across millions of years, fostering the emergence of lineages. Using the clade level of phylogenies and species range maps, we generated the spatial pattern of diversification rate for 33 highly diversified clades in the Hengduan Mountains. These spatial clade diversification rate patterns are spatially associated with active deformation history in the past 15 Ma. In this talk, I will present hotspots of diversification rate and potential linkage to geological and climate processes. I will demonstrate that the diversification rate hotspots are concentrated in the Three Rivers Region, Dadu River, and Shangri-La Plateau in the Hengduan Mountains. Then I will show the elevational gradient of the diversification rate within these hotspots and link them to specific geological processes. Specifically, long-term erosion from low-temperature thermochronology indicates the deformation process in the recent 15 Ma associated with new habitat and high diversification speciation process in the Three Rivers region and Dadu River in the Hengduan Mountains. Moreover, the landscape transience characterized by divides migration and low relief surface formation may create habitat disruption and range fragmentation to increase allopatric speciation. Taken together, the high plant diversity of Hengduan Mountain may be caused by intense focalized geological processes generating new species from habitat disruption.

How to cite: Chang, Y., Ding, W., He, J., Willett, S., Gelwick, K., Zimmermann, N., and Pellissier, L.: Plant diversification is associated with habitat disruption in the transient Hengduan Mountains, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1446, https://doi.org/10.5194/egusphere-egu24-1446, 2024.

EGU24-3508 | ECS | Posters on site | BG5.3

Geogenomics and biogeodynamics in the Northern Apennines and Ligurian Alps (Italy)  

Gabrielle Vance, Dominik Kirschner, Sean D. Willett, and Loïc Pellissier

Complex interactions between tectonics and surface processes influence the evolution of aquatic species across orogens. These processes are likely to be important in tectonically active areas where faulting and uplift lead to drainage reorganization. The Northern Apennines are an active orogenic wedge, where horizontal shortening and topographic advection lead to river capture and drainage divide migration, which can separate or connect ecological domains and thus isolate or mix aquatic populations. In contrast, the adjacent Ligurian Alps are a remnant of the Alpine orogen with little modern deformation. In this study, we combine geomorphic analysis with environmental DNA (eDNA) collected from rivers in the Northern Apennines and Ligurian Alps to assess the influence of tectonic advection and subsequent drainage reorganization on the genetic diversity of native freshwater fish. Geomorphic metrics are asymmetric across the main drainage divide (MDD) in both orogens, and divide asymmetry indices based on these metrics suggest an MDD migration direction from Ligurian (coast) to Adriatic (Po Plain), accompanied by river captures. In the Northern Apennines, this suggested drainage divide migration direction is towards the NE, opposite that of the tectonic advection of topography. Geomorphic metrics show greater contrast across the MDD in the Northern Apennines than in the Ligurian Alps. Five native freshwater fish species show statistically significant correlations between genetic distance and divide asymmetry indices across the MDD. Genetic distance is greater across the MDD in the Northern Apennines than in the Ligurian Alps. Endemic species such as Telestes muticellus exhibit greater amplicon sequence variant (ASV) richness on the Ligurian than the Adriatic side of the MDD in both orogens; greater ASV richness in the Northern Apennines than in the Ligurian Alps; and greater ASV richness on the retrowedge of the Northern Apennines than on the prowedge.  Tectonically driven drainage reorganization may promote greater genetic diversity in coastal basins, although we can not rule out anthropogenic population transfer in some cases.

How to cite: Vance, G., Kirschner, D., Willett, S. D., and Pellissier, L.: Geogenomics and biogeodynamics in the Northern Apennines and Ligurian Alps (Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3508, https://doi.org/10.5194/egusphere-egu24-3508, 2024.

EGU24-4614 | Orals | BG5.3

Greenalite provides a snapshot of metal availability in an Archean shelf environment. 

Rosalie Tostevin, Ansahmbom Y. Nke, Harilaos Tsikos, Xolane Mhlanga, and Paul R. D. Mason

Thermodynamic models predict that marine metal availability has changed over geological time, particularly in the Archean Eon (4.0 – 2.5 billion years ago), when seawater was anoxic and Fe2+-rich. Since metals are essential micronutrients required to build metalloproteins, changes in metal availability in seawater would have influenced evolving microbial ecosystems. Recent work on Archean rocks has highlighted the role of greenalite as an abundant, primary precipitate in Archean seawater, and its potential as a faithful geochemical archive. Greenalite can be exceptionally well preserved in early diagenetic chert, providing protection from diagenesis and metamorphic alteration. Furthermore, experimental work has demonstrated that several key metals enter the greenalite precursor phase during precipitation, and the associated partition coefficients are consistent under a range of conditions. Furthermore, most metals are retained in the structure during heating and crystallisation, suggesting that greenalite could represent a robust archive of the metal content of early oceans. Here, we present mineral-specific laser ablation ICP-MS data for natural greenalite from the ~2.5 Ga Transvaal Supergroup, South Africa. Petrographic relationships and rare earth element patterns suggest this greenalite precipitated from seawater in a shelf environment. We place metal abundance into a quantitative framework to predict metal availability in Archean seawater. Our calculations suggest that V and Zn were depleted, Ni was similar, Co was enriched, and Mn was super-enriched in this setting compared to modern marine environments. These results are consistent with predictions based on marine chemistry and proteomics, as well as some bulk geochemical records.

How to cite: Tostevin, R., Nke, A. Y., Tsikos, H., Mhlanga, X., and Mason, P. R. D.: Greenalite provides a snapshot of metal availability in an Archean shelf environment., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4614, https://doi.org/10.5194/egusphere-egu24-4614, 2024.

Evidence for the co-evolution of Earth and life is abundantly preserved in the minerals, which are the oldest objects you can hold in your hand. Each information-rich specimen is a time capsule waiting to be opened and to tell the stories of Earth and other worlds. The emerging field of “mineral evolution” considers changes in the diversity and distribution of minerals through billions of years of planetary history [1-5], and reveals dramatic episodes of the co-evolution of minerals and life, including stages of life's origins, microbial biomineralization, influences of global oxygenation, and the rise of the terrestrial biosphere. 

Traditional approaches to classifying minerals ignore this history. The International Mineralogical Association (IMA) has catalogued >6000 mineral species, each with a unique combination of idealized chemical composition and crystal structure. This essential scheme allows the confident identification of different condensed crystalline building blocks of planets and moons. However, lacking perspectives of time and process, this system is limited in its ability to address the evolution of planets, much less the co-evolution of the geosphere and biosphere.

We have introduced, and are now completing, a new complementary approach to mineral classification called the “evolutionary system of mineralogy.” Our system differs from IMA's in three ways. First, it splits IMA species that form in more than one way; for example, pyrite forms by both abiotic and microbial processes. Second, it lumps IMA species that form continuous solid solutions through the same process; i.e., we lump many different species of the tourmaline group into a single kind. Third, we include varied amorphous or poorly crystalline solids, such as obsidian, kerogen, and limonite, which are important in crustal processes and were included in mineral inventories before the application of x-ray diffraction.

The resulting evolutionary system of mineralogy is being released in 12 parts, 8 of which are now published or in press [6-13]. These works underscore the close connections between mineral and biological evolution. We find that while minerals played key roles in life’s origins and evolution, life changed near-surface environments in ways that led to the formation of approximately half of all known mineral species, most of which are only known to form through biological mediation.

References: 1. Hazen R.M. et al. (2008) Am.Min., 93, 1693-1720; 2. Hazen R. & Morrison S. (2022) Am.Min., 107, 1262-1287; 3. Hazen, R. et al. (2023) In: Bindi and Cruciani [Eds.], Celebrating the International Year of Mineralogy. NY: Springer, pp.15-37; 4. Hazen R. et al. (2023) JGR Planets, 128, e2023JE007865; 5. Hazen R. et al. (2022) Am.Min., 107, 1288-1301; 6. Hazen R. (2019) Am.Min., 104, 468-470; 7. Hazen R. & Morrison S. (2020) Min., 105, 627-651; 8. Morrison S. & Hazen R. (2020) Am.Min., 105, 1508-1535; 9. Hazen R. et al. (2021) Am.Min., 106, 325-350; 10. Morrison S. & Hazen R. (2021) Am.Min., 106, 730-761; 11. Hazen R. & Morrison S. (2021) Am.Min., 106, 1388-1419; 12. Morison S. et al. (2023) Am.Min., 108, 42-58; 13. Hazen R. et al. (2023) Am.Min., 108, 1620-1641; 14. Morrison et al. (2024) Am.Min., 109, in press.

How to cite: Hazen, R.: Documenting the Co-Evolution of Earth and Life: A Mineral Evolution Approach , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4723, https://doi.org/10.5194/egusphere-egu24-4723, 2024.

EGU24-5478 | ECS | Posters on site | BG5.3

Towards integrated models of mantle convection, surface dynamics and climate evolution  

Niklas Werner, Christian Verard, Maura Brunetti, Paul Tackley, and Taras Gerya

The long-term evolution of the biosphere on Earth is tightly coupled to changes in the geosphere and climate. Investigating the evolution of Earth’s climate over the course of the Phanerozoic and beyond requires extensive numerical modelling efforts. Classically, this has been done using Earth System Models of varying complexity. While these models are well-suited to simulate a majority of processes in the ocean, the atmosphere and on the land surface, they lack a key component of the Earth system ―  the interior. Processes in the mantle drive plate tectonics on Earth and by means of degassing are a key factor in determining the atmospheric CO2 concentration, influencing biological evolution. Both, the position of continents as dictated by plate tectonics as well as the concentration of greenhouse gases in the atmosphere are known to be crucial in shaping Earth’s climate. An important suite of mechanisms that influences both climate and mantle can be found in silicate weathering, the erosion of weathered material and its transport and sedimentation in subduction zones. The influx of sediments into subduction zones has been shown to alter the rheology of the subduction slab, influencing the speed of subduction and chemistry of the slab and thereby impacting mantle convection processes (e.g. Bello et al., 2015). Here, we present a framework for coupling the new PANALESIS paleogeographic reconstruction (Vérard, 2019) to an Earth System Model of Intermediate Complexity (EMIC) and the mantle convection model with plate tectonics based on StagYY code. This is done using climate output from the EMIC to force a landscape evolution model that is used to compute sediment influx into subduction zones. Degassing rates obtained from the mantle convection simulations are then used to assess atmospheric CO2 levels and create climate lookup tables for different degassing scenarios. These data can then be used to force a temporally continuous carbon cycle model to update previous pCO2 curves for the Phanerozoic and beyond. Given the new paleogeographic reconstruction and the more sophisticated modelling framework, this approach may give new insights into the long-term interactions between mantle and climate and the consequences for biological evolution.

References

Bello, L., Coltice, N., Tackley, P. J., Müller, R. D., & Cannon, J. (2015). Assessing the role of slab rheology in coupled plate-mantle convection models. Earth and Planetary Science Letters, 430, 191-201.

Vérard, C. (2019). PANALESIS: Towards global synthetic palaeogeographies using integration and coupling of manifold models. Geological Magazine, 156(2), 320-330.

How to cite: Werner, N., Verard, C., Brunetti, M., Tackley, P., and Gerya, T.: Towards integrated models of mantle convection, surface dynamics and climate evolution , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5478, https://doi.org/10.5194/egusphere-egu24-5478, 2024.

EGU24-5524 | ECS | Posters on site | BG5.3

Whence the demise and fall of the RNA World? 

Anna Medvegy and Stephen Mojzsis

A widely promulgated concept for the fundamental ancestor-descendent relationship at life’s origin, and thus the onset of Darwinian evolution, is the RNA World hypothesis. If Darwinian evolution on Earth began with a simple RNA molecule which had the ability to replicate itself, in the long run this must have given way to DNA perhaps via an intermediate RNA(±Peptide) World. This could happen once DNA appeared and became the preferred informational molecule for all extant biology. Yet, making sense of this transition is confounded both by the intervening 4 billion years of biological evolution, and a scarce ancient (pre-3.2 Gyr) geologic record. Here, we explore whether the relative instability of RNA to thermal stresses, salt content, pH, variable UV sensitivity and an overall narrow available suite of metabolic styles, strictly limited the range of suitable habitats for RNA World organisms; they were susceptible to marginalization, assimilation and effective extinction. We propose that main factors responsible for the transition from the RNA±Peptide to DNA+Peptide World included (i) overall changes in the geosphere (e.g. heat flow, crustal type, nutrient availability); (ii) transient global heating of the hydrosphere by late accretion bombardment viz. “thermal bottlenecks”; and, (iii) competition from, and perhaps predation by, metabolically diverse and genomically nimble emergent DNA+Peptide organisms. 

How to cite: Medvegy, A. and Mojzsis, S.: Whence the demise and fall of the RNA World?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5524, https://doi.org/10.5194/egusphere-egu24-5524, 2024.

Plants have been a key interface in the global carbon and water cycles for nearly 475 million years. The magnitude of vegetational effects has waxed and waned dynamically because plant abundance and community composition have changed over time. Unravelling how plant communities have shaped, and been shaped by, global biogeochemical cycles relies upon reconstructing the paleoecology and paleoecophysiology of plants, and this process can be challenging in deep time, when plant communities contained organisms with traits that are rare in—or absent from—present-day ecosystems. Fortunately, the archive of how plants have shaped and responded to environmental change is preserved in the fossil record, because the traits and properties of extinct plants can be interpreted from fossilized anatomy in a qualitative, semi-quantitative, and quantitative way. Traits related to water transport in plants. including drought resistance and hydraulic supply to leaves, are particularly useful and important because these traits link individual plant performance to the water and carbon cycles.

The collapse of tropical everwet rainforests end of the Carboniferous Period (~300 Ma) provides an illustration of how plant water transport traits influenced, and were shaped by, the water and carbon cycles. These traits are quantified by combining mathematical models of stem hydraulic conductivity and drought resistance with anatomical measurements from scanning electron and light microscopy images of fossilized plant water transport cells, called xylem. Analysis of stem hydraulic traits in five lineages of extinct Carboniferous plants—arborescent lycophytes, stem group seed plants, stem group tree ferns, coniferophytes, and sphenophytes—reveals differential hydraulic capacity and drought resistance among these plants, despite their simultaneous presence in tropical everwet ecosystems. Significant differences in these two traits are not only present between these five lineages, but can also be observed within several of these plant groups: for example, key parameters may vary by more than an order of magnitude in related plants. High hydraulic capacity and low drought resistance traits were associated with a decline in relative abundance toward the close of the Carboniferous Period, whereas plants with lower hydraulic capacity and higher drought resistance traits increased in relative abundance and survived this floral transition. This change in relative abundance within these communities shaped the hydrologic and carbon cycles which, in turn, amplified environmental stress that, consequently, further altered plant community composition. Implementing this analysis in trait-aware paleoecosystem models illustrates the effect of plant traits on global environments, and vice versa, yielding insight into plant performance during extreme environmental change that is analogous to anthropogenic impacts predicted for the late 21st century and beyond.

How to cite: Wilson, J.: Plant paleoecophysiology traits in deep time: hydraulic conductivity and drought resistance in late Carboniferous Period plants, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6891, https://doi.org/10.5194/egusphere-egu24-6891, 2024.

EGU24-7442 | Orals | BG5.3

Functional traits and trait diversity of leaves: palaeoecological perspectives 

Anita Roth-Nebelsick and Christopher Traiser

Functional traits were originally defined as any characteristic of an organism that contributes to fitness. From this autecological perspective, trait-based research has considerably expanded into approaches of ecosystem analysis that also have high potential for palaeoecological research. In the ecosystem context, the meaning of “trait” has become much broader, encompassing all sorts of measurable quantities carrying ecological information that are themselves categorized into different “trait classes”. For instance, “response traits” are organismal traits responding to environmental parameters whereas “effect traits” act upon the environment.

As primary producers, plants represent a crucial part of ecosystem functioning. Basic ecophysiological processes of plants, particularly gas exchange and photosynthesis, are key elements in the carbon and water cycle and can thereby be understood as “effect traits”. Fossil anatomical traits, such as from fossil leaves, allow for deriving basic ecophysiological parameters from physical laws (such as calculating leaf gas conductance from the diffusion equation). Biochemical parameters, however, are not provided by fossil material and require therefore estimation based on extant plants (such as kinetic properties of the enzyme apparatus of photosynthesis) which adds a certain error margin to the results. Nevertheless, these “mixed” approaches to fossil plant ecophysiology allow for obtaining crucial benchmark data on various ecosystem characteristics, such as primary productivity or evapotranspiration.

            Another branch of trait-based ecosystem research is the study of functional diversity which can be roughly described as the richness and distribution of functions expressed by organisms coexisting within a habitat. Functional diversity is less frequently considered for fossil vegetation compared to the study of autecological effect traits. One reason may be that various approaches for studying extant functional diversity are difficult or even impossible to apply to fossil plants, requiring the development of novel methods suitable for fossil remains.

As a recent example, the Shannon Diversity of leaf architecture based on functional leaf traits identifiable from fossil leaf material was shown to be related to environmental parameters for extant as well as fossil angiosperms.  Devising trait-based approaches to functional diversity suitable for fossil organisms can offer additional fruitful research perspectives for studying environments of the past.

How to cite: Roth-Nebelsick, A. and Traiser, C.: Functional traits and trait diversity of leaves: palaeoecological perspectives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7442, https://doi.org/10.5194/egusphere-egu24-7442, 2024.

EGU24-8733 | Orals | BG5.3

Biogeodynamics of narrow orogenic arcs and their biodiversity hotspots 

Guillermo Booth Rea, Paloma Mas Peinado, Jorge Pedro Galve, Octavio Jiménez Robles, and Jose Miguel Azañón

Narrow Orogenic Arcs (NOA) on Earth are oftenly biodiversity hotspots, where biogeographic evolution is influenced by tectonic forcing. However, the relationships between tectonic mechanisms intrinsic to NOA, landscape evolution and speciation forming biodiversity hotspots have not been dwelt with. Different mechanisms inherent to NOA, such as slab roll back, slab tearing, edge delamination, mantle upwelling and flow around subducted slabs, basin and archipelago migration and volcanic arc growth drive a dynamic landscape evolution that fosters processes of dispersal and allopatric-speciation. Here, we show this with examples from the Western Mediterranean and Caribbean. Slab tearing drives migrating waves of tectonic uplift and subsidence at the edges of orogenic arcs, coupled with crustal thickening followed by heterogeneous extension, forming endorheic basins and marine gateways among high-elevation ranges. Furthermore, vicariant events by isolation in high-elevation mountain ranges, internal drainage basins, stranded back-arc and volcanic arc archipelagos- seem to have driven the distribution and diversification of many taxa. Dispersal events would have been promoted by- drifting forearc archipelagos, changes of river courses (captures) and land bridges between continents, where ancient lineage dispersal followed by allopatric speciation-multiple diversification resulted in the current complex biological assemblages. The characteristic time and space migration of NOA, fosters recurrent processes of dispersal and vicariance, including in situ diversification through time. In this setting, long-time emerged parts of both drifting-forearc or stranded-backarc archipelagos represent both refuge and diversification centers where insular fauna may relate to distant, previously- attached land masses or islands. This is the case of drifting islands like the late Miocene Alboran archipelago in the Gibraltar arc or the Present Margarita island in the Caribbean, bearing biota with most common recent ancestors in the Balearic islands or the Central Coastal Range of Venezuela, respectively. Insular lineages may disperse by the closure of marine gateways between the mainland continents and drifting archipelagos, a process that may also drive the isolation of confined seaways, like the Mediterranean during the Messinian Salinity Crisis. Topographic uplift closing marine gateways or restricting seaways may occur by lithospheric rejuvenation, following delamination or detachment of subducted subcontinental mantle slabs and also by the growth of a volcanic arc. The emergence of new land and islands in the forearc domain, results in speciation and less species-rich communities in the direction of slab retreat. 

How to cite: Booth Rea, G., Mas Peinado, P., Galve, J. P., Jiménez Robles, O., and Azañón, J. M.: Biogeodynamics of narrow orogenic arcs and their biodiversity hotspots, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8733, https://doi.org/10.5194/egusphere-egu24-8733, 2024.

EGU24-9713 | Orals | BG5.3

Primary producers during the early Earth  

Patricia Sanchez-Baracaldo

Primary producers convert light energy from the sun into chemical energy in the form of sugars, a fundamental process that has enabled life on Earth. Once ancestral cyanobacteria evolved, they played a crucial role in Earth's history by facilitating the rise of atmospheric oxygen, paving the way for the development of complex life forms. Despite its significance, the origins of photosynthesis are still not fully understood. During the talk, I will highlight key evolutionary events in the history of Cyanobacteria: 1) the Archean origin of PSII,  photochemical reaction centre that catalyses the light-driven oxidation of water to molecular oxygen; 2) the emergence of the crown group of Cyanobacteria; 3) the appearance of filamentous forms around the Great Oxidation Event at 2.32 Ga; and 4) the late emergence of marine planktonic groups between 800-600 Mya. Molecular evolution analyses reveal a significant time gap between the Archean origin of oxygenic photosynthesis and the appearance of planktonic forms at the end of the Precambrian era. By studying the 'genomic record,' we can now unravel how oxygenic phototrophs co-evolved with the Earth's biosphere, contributing to the habitability of our planet.

How to cite: Sanchez-Baracaldo, P.: Primary producers during the early Earth , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9713, https://doi.org/10.5194/egusphere-egu24-9713, 2024.

EGU24-10412 | ECS | Orals | BG5.3

Escarpment Retreat Drives Diversification of Eastern Madagascar through Allopatric Speciation 

Yanyan Wang, Sean Willett, Yi Liu, Loïc Pellissier, and Niklaus Zimmerman

Madagascar, as a biodiversity hotspot on Earth, exhibits a high level of endemism as observed from the prevalent vicariant speciation of terrestrial mammals, amphibians, and flora. Species richness of the island is uneven, with the highest species richness and endemism found on the steep great escarpment of the eastern margin. The unevenness is further observed within the escarpment region in that phylogenic turnover shows both latitudinal and altitudinal variations. Madagascar has remained almost tectonically inactive since the last rifting with Seychelles-India in the late Cretaceous. The high diversity and endemism of Madagascar challenge the conventional notion of uplift-driven speciation, which argues that speciation is driven by the formation of diverse habitat types from tectonic uplift.

Although the fundamental topographic framework of Madagascar has been in place since the late Cretaceous, it is modified in the Cenozoic by multiple processes including island-wide mantle-driven dynamic uplift, erosion-driven landward retreat of the escarpment at the eastern margin, localized volcanic and faulting activities. Our topographic reconstruction reveals that the dominant correlation is between the escarpment and species richness. To investigate the causal mechanisms of the diversity at the eastern escarpment, we constructed landscape evolution models, tracing the dynamics of habitable land surface patches throughout model simulations.

We investigated two distinct landscape scenarios: an escarpment retreat model simulating river incision into a pre-existing plateau with negligible tectonic uplift, and a tectonic uplift model featuring spatially and temporally constant uplift with river incision into the resulting mountain range. The steady-state topographic height of the tectonic uplift model is calibrated to match the plateau elevation of the escarpment model to ensure the same number of habitat types between models. The landscape of a great escarpment is highly dynamic and the heterogenous retreat of the escarpment and the water divide makes the geographically isolated drainage basins expand landward at different rates during the retreat process. Within the escarpment region, habitat patches dynamically appear, disappear, fragment, or merge at a frequency that scales with the retreat rate. In contrast, the tectonic uplift model only exhibits similar dynamic landscape change during the transient phase with habitat patches stabilizing spatially and temporally once a steady state topography was achieved.

The models predict that escarpment retreat fosters habitat patch dynamics such that patches isolate, or reconnect with a frequency on the order of a million years, appropriate for allopatric speciation. The habitat patch dynamics are a consequence of processes of catchment expansion, river captures, isolation of highland remnants, and formation of topographic barriers during the retreat. We conclude that the spatially heterogeneous but temporally steady retreat of the Madagascar escarpment since rifting has sustained allopatric speciation over evolutionary timescales resulting in the observed high diversity and its spatial pattern of eastern Madagascar.

How to cite: Wang, Y., Willett, S., Liu, Y., Pellissier, L., and Zimmerman, N.: Escarpment Retreat Drives Diversification of Eastern Madagascar through Allopatric Speciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10412, https://doi.org/10.5194/egusphere-egu24-10412, 2024.

EGU24-10608 | Orals | BG5.3

On the time and space scales of geological, climatic, and biological changes 

Laurent Husson, Manon Lorcery, and Tristan Salles


It is commonplace to claim that the geo-, atmo-, and bio- spheres of the Earth are coupled, or that biodiversity depends on their interplays, but the implicit hypothesis on the time and space scales at which coupling holds are seldom envisioned. For instance, "deep time" is a convenient shortcut that loosely conveys the ideas of steady state and large spatial scales, but what are the limits? Observations often fall short because the geological record is fragmentary, but also because it is uncommon to access crucial informations such as rates of speciation, extinction, or migration. Recent advances in numerical landscape evolution models permit to explore the dynamic equilibrium between the spheres of the Earth. Based on a few examples at different time and space scales, we will browse settings where steady state holds (where biodiversity depends on the instantaneous states of the geology and climate, as for instance set by the Wilson cycle), where transient state prevails (where considering the time derivative of their states is needed, as for instance when the pace of landscape reshaping promotes biodiversification), and where dynamic equilibrium breaks down in some sort of metastable situations (as in the press-pulse theory that well applies to the mass extinction events). 

How to cite: Husson, L., Lorcery, M., and Salles, T.: On the time and space scales of geological, climatic, and biological changes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10608, https://doi.org/10.5194/egusphere-egu24-10608, 2024.

EGU24-12430 | Posters on site | BG5.3

Tectonic “quakes”, scaling and the turbulence of solids 

Shaun Lovejoy, Andrej Spiridonov, and Lauras Balakauskas

Over thirty years ago, Y. Kagan proposed that seismicity is “the turbulence of solids”.  Indeed, fluid turbulence and seismicity have many common features: they are both highly nonlinear with huge numbers of degrees of freedom.  Beyond that, Kagan recognized that they are both riddled with scaling laws in space and in time as well as displaying power law extreme variability and – we could add – multifractal statistics.

Kagan was referring to seismicity as usually conceived, as a sudden rupture process  occurring over very short time periods.  We argue that even at million year time scales, that the movement of tectonic plates is “quake-like” and is quantitatively close to seismicity, yet caused by relatively smooth mantle convection fluid. 

To demonstrate this, we analyse the GPlates data base of 1000 point trajectories over the last 200 Myrs, analyzing the statistics of the dynamically important vector velocity differences where Dr is the great circle distance between two points and Dt is the corresponding time lag.  The longitudinal and transverse velocity components are analysed separately.  The longitudinal scaling of the mean longitudinal difference follows the scaling law <Dv(Dr)> ≈ Dr^H with H close to the theoretically predicted value  H = 1.  This high value implies that  mean fluctuations vary relatively smoothly with distance.  Yet at the same time,  the intermittency exponent C1 is extremely high (C1 ≈ 0.5) implying that from time to time there are enormous “jumps” in velocity. For comparison, laminar (nonturbulent) flow has H = 1 and is not intermittent (C1 = 0), fully developed isotropic fluid turbulence has the (less smooth) value H = 1/3 (Kolmolgorov) but with non-negligible intermittency C1 ≈ 0.07 and seismicity has very large C1 ≈ 1.3.  Our study thus quantitatively shows how smooth fluid-like behaviour can co-exist with highly intermittent quake-like behaviour.

We find that the outer spatial scale is near the size of the Earth (≈15000km) whereas the outer time scale is ≈60Myrs.  We show that the statistics are multifractal with a very large intermittency parameter that is close to that of seismicity determined at sub-decadal time scales.  The transverse scale function is the 2/3 power of the longitudinal scale function,  the transverse intermittency exponent (C1 ) is reduced by this factor.  The temporal scaling of the mean fluctuations of both the longitudinal and transverse components is close to a ½ power of the time lag: Dr≈Dt^(1/2).  However since the spatial scaling of the longitudinal and transverse components are different, we obtain two somewhat different space-time diagrams.  We link the parameter estimates to fundamental mantle convection parameters, and we make corresponding multifractal simulations.

Finally, we discuss the implications for the megaclimate regime, including macro-evolution. Both megaclimate and macroevolution of global diversity are scaling processes with H>0 characterized by intermittent — climate “events”, such as P-Tr hyperthermal, in the case of former, and mass extinctions and originations in the case of latter. The tectonic scaling, and the extreme multifractal behavior grounds both—the long-term climate, and the biological evolution on the first principles of scaling in macroscopic physical systems.

How to cite: Lovejoy, S., Spiridonov, A., and Balakauskas, L.: Tectonic “quakes”, scaling and the turbulence of solids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12430, https://doi.org/10.5194/egusphere-egu24-12430, 2024.

EGU24-12706 | Orals | BG5.3

Ediacaran ultra-weak geomagnetic field, oxygen rise, and the diversification of macroscopic animals 

Rory Cottrell, John Tarduno, Wentao Huang, Shuhai Xiao, Eric Blackman, Tinghong Zhou, Jack Schneider, Richard Bono, and Mauricio Ibañez-Mejia

A major discovery in the last 5 years has been the recognition that the geomagnetic field was at ultralow field strengths, some ten times weaker than the present-day, during the Ediacaran Period. These ultralow values were first reported from single crystal paleointensity analyses of 565 Ma rocks of the Sept Îles Mafic Intrusion Suite (Bono et al., Nature Geosci., 2019), and were later confirmed by studies of dikes and lavas from other sites in Ukraine and Canada (e.g., Thallner et al., EPSL, 2021). The ultralow values are followed by a rapid increase in field strength in the early Cambrian (Zhou et al., Nature Commun., 2022) and together these signals are consistent with initial nucleation of Earth’s inner core, as predicted by thermal models and geodynamo simulations (Davies et al., GJI, 2022). An updated timeline incorporating new paleointensity data from several localities in North America, South America and Africa highlights a striking temporal correspondence between the ultralow field, the Ediacaran diversification of macroscopic animals, and some geochemical indicators for the rise of oxygenation. The onset of inner core growth and unusual state of the geomagnetic field should not correspond with animal evolution or oxygenation unless changes in the Ediacaran magnetosphere attendant with the ultralow field somehow affected the atmosphere, oceans and/or biosphere. We will consider these possibilities. 

How to cite: Cottrell, R., Tarduno, J., Huang, W., Xiao, S., Blackman, E., Zhou, T., Schneider, J., Bono, R., and Ibañez-Mejia, M.: Ediacaran ultra-weak geomagnetic field, oxygen rise, and the diversification of macroscopic animals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12706, https://doi.org/10.5194/egusphere-egu24-12706, 2024.

EGU24-13629 | ECS | Orals | BG5.3

Ecosystem engineers impact marine biodiversity during the Phanerozoic 

Alison Cribb, Simon Darroch, and Thomas Ezard

Ecosystem engineers are keystone taxa whose behaviours alter the habitability of their environments for themselves and other organisms by directly influencing the availability of resources in their ecosystems. From a deep time perspective, ecosystem engineers are hypothesized to have played a major role in the co-evolution of life and the Earth systems, as many major ecosystem engineering activities directly modulate the cycling of key nutrients. Moreover, ecosystem engineers are thought to have impacted diversity by increasing environmental heterogeneity, and so their evolution may drive some of the biodiversity dynamics observed in the fossil record. Here, we investigate the impact of two groups of marine ecosystem engineers – bioturbators and reef-builders – on biodiversity through the Phanerozoic. Using fossil occurrence data from the Paleobiology Database, we calculate the effect size of bioturbating and reef-building ecosystem engineers on various biodiversity metrics for each stage through the Phanerozoic. Most broadly, we find that ecosystem engineers had a positive impact on biodiversity within the environments where they live during the Phanerozoic. We also find clear taxonomic differences between environments with and without ecosystem engineers, suggesting ecosystem engineers create a unique set of environmental characteristics to which taxa of specific ecological characteristics become adapted. These results emphasize the important role of ecosystem engineers in influencing key aspects of the Earth systems on a variety of scales that manifest in changes in biodiversity.

How to cite: Cribb, A., Darroch, S., and Ezard, T.: Ecosystem engineers impact marine biodiversity during the Phanerozoic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13629, https://doi.org/10.5194/egusphere-egu24-13629, 2024.

EGU24-13765 | Posters on site | BG5.3

Antifeedant biomarkers in Cretaceous sediments from the North Sudetic Basin, Poland 

Magdalena Goryl, Leszek Marynowski, and Bernd R.T. Simoneit

The Late Cretaceous succession of siliciclastic sediment from the Czerna Formation in the North Sudetic Basin (SW Poland) consists of sandstones, dark grey mudstones and shales with coal intercalations. Samples of dark grey mudstone with lignite fragments from the inoperative sandstone quarry in Rakowice Małe, and samples of coals and siltstones from the sandstone quarry in Wartowice, were selected for gas chromatography-mass spectrometry analyses. All samples were thermally immature (the mean vitrinite reflectance (Rr) values did not exceed 0.45%).

The samples contained phenolic abietans, including ferruginol and chamaecidin, which act as a defence mechanism against insect and microbial attack in coniferous trees (e.g., Gonzalez, 2015). Therefore, these compounds are widespread in extant coniferous trees (Simoneit et al., 2021) and can be identified in the geological record through their primary and diagenetic products. For instance, ferruginol (natural product), along with its derivatives: simonellite and retene, are present in the Cretaceous sedimentary rocks of the North Sudetic Basin. Another compound identified in the investigated samples is bergamotan. Perry et al. (2003) found that two derivatives of this compound were responsible for the insect antifeedant activity. Moreover, some of the identified compounds, such as chamazulene, are known in medical science for their anti-inflammatory properties (Safayhi et al., 1994).

The presence of natural products with antifeedant activity against insects in Cretaceous samples suggests that plants had developed host defence mechanisms tens of millions of years ago.

 

Acknowledgements

The authors acknowledge financial support from the Polish National Science Centre (grant 2018/31/N/ST10/01646 to MG).

 

References

Gonzalez, M.A., 2015. Aromatic abietane diterpenoids: Their biological activity and synthesis. Natural Product Reports 32, 684–704.

Perry, N. B., Burgess, E. J., Foster, L. M., Gerard, P. J. (2003). Insect antifeedant sesquiterpene acetals from the liverwort Lepidolaena clavigera. Tetrahedron Letters 44(8), 1651–1653.

Safayhi, H., Sabieraj, J., Sailer, E. R., Ammon, H. P. (1994). Chamazulene: An antioxidant-type inhibitor of leukotriene B4 formation. Planta Medica. 60 (5), 410–3. 

Simoneit, B. R. T., Rybicki, M., Goryl, M., Bucha, M., Otto, A., Marynowski, L. (2021). Monoterpenylabietenoids, novel biomarkers from extant and fossil Taxodioideae and rocks. Organic Geochemistry, 154, 104172.

How to cite: Goryl, M., Marynowski, L., and Simoneit, B. R. T.: Antifeedant biomarkers in Cretaceous sediments from the North Sudetic Basin, Poland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13765, https://doi.org/10.5194/egusphere-egu24-13765, 2024.

Mercenaria stimpsoni is a new paleoclimatic archive in the mid- to high-latitude western Pacific coastal area. This species is a cold-water bivalve with a long life span (>100 years old), and shell growth patterns and oxygen isotope ratios are useful tools as paleoenvironmental proxies. So far it is known that the shells of M. stimpsoni have distinct annual lines with microincrements between each annual line. However, the relationship between microgrowth patterns and marine environment is not understood. Fossil shells of this species are often found in interglacial marine sediments in Central Japan. Thus, understanding the relationship between microgrowth patterns and marine environment is key to reconstruct paleoclimate with high temporal resolution in this region.

The purpose of this study was to evaluate the usefulness of the microgrowth patterns in this species as a paleoenvironmental proxy. Sample shells were collected from the coasts of Hokkaido and Iwate Prefecture, Japan. Shells were then cut into thick sections along the maximum growth axis. The surfaces of the thick sections were polished. Photographs were taken with a Keyence VHX2000 at 300x to 1000x magnification. Photomosaics were created with Adobe Photoshop CC. Then, the number of microincrements and microincrement widths were measured with ImageJ. Then, 120 to 150 μg of carbonate powder was collected from the outer outer layer along the growth direction and provided for oxygen isotope analysis. Finally, we compared microgrowth patterns with marine environmental data. Growth line observations confirmed that approximately 100 microgrowth lines were formed per year in the shells, and that the micorogrowth patterns might reflect mainly seawater temperatures and planktonic blooms. In the poster presentation, we will report the relationship between microgrowth patterns and marine environment. By clarifying the relationship between them, the temporal resolution of paleoclimate reconstruction using this species can be improved to less than the annual scale.

How to cite: Miki, S. and Shirai, K.: Evaluation of the microgrowth patterns of shells of long-lived bivalve, Mercenaria stimpsoni as a paleoenvironmental proxy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14316, https://doi.org/10.5194/egusphere-egu24-14316, 2024.

EGU24-15098 | ECS | Orals | BG5.3

Climatic controls on dinosaur evolution, diversity and biogeography 

Emma Dunne, Lisa Schnetz, Alexander Farnsworth, Stephan Lautenschlager, Pedro Godoy, Eren Tasimov, Richard Butler, and Sarah Greene

Dinosaurs were dominant members of terrestrial ecosystems throughout the Mesozoic, yet only recently are studies beginning to illuminate the key role of global climate variation in controlling dinosaur biodiversity, global distribution, and macroevolution. Our work uses statistical, biogeographic, and phylogenetic comparative approaches with comprehensive fossil occurrence data and paleoclimate data from general circulation models to quantitatively examine key hypotheses connecting patterns of dinosaur diversity and evolution with climatic conditions. We examined the impact of climate change in driving early dinosaur evolution across the end-Triassic mass extinction (ETME). Our results demonstrate that the geographic distribution of early sauropodomorphs was constrained by climate and following the ETME, the expansion of climate zones facilitated the geographic expansion of sauropodomorphs and other dinosaurs. Evolutionary model-fitting analyses provide evidence for an important evolutionary shift from cooler to warmer climatic niches during the origin of Sauropoda. This same approach is also revealing the relationship between climatic conditions and dinosaur diversity in the Jurassic to Cretaceous, with implications for our understanding of the origins of sauropod gigantism and the evolution of herbivory. Our results suggest that primary productivity was a key climatic factor in driving sauropod evolution and promoting the evolution of larger body sizes, supporting the hypothesis that gigantism was facilitated by the increasing availability of high quality vegetation. Analyses of dinosaur paleoclimatic niche space show evidence of niche partitioning between herbivorous theropods and ‘traditional’ herbivorous dinosaurs (e.g. sauropods), indicating that climatic changes may have influenced evolutionary innovations related to dinosaur diet. Further work examining the relationship between dinosaur diversity and changes in vegetation using state-of-the-art vegetation models will illuminate the key role played by environmental change in controlling dinosaur diversity and evolution throughout the Mesozoic.

How to cite: Dunne, E., Schnetz, L., Farnsworth, A., Lautenschlager, S., Godoy, P., Tasimov, E., Butler, R., and Greene, S.: Climatic controls on dinosaur evolution, diversity and biogeography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15098, https://doi.org/10.5194/egusphere-egu24-15098, 2024.

EGU24-15732 | ECS | Posters on site | BG5.3

Deciphering the dynamics of the Mulde Event—Bayesian ultra-high-resolution ostracod paleocommunity analysis  

Liudas Daumantas, Simona Rinkevičiūtė, Sigitas Radzevičius, and Andrej Spiridonov

Silurian period witnessed a series of global extinction events, such as the Mulde/lundgreni Event during of the late Wenlock epoch.  These events triggered complex and abrupt changes in Earth's biota. The brief nature of these events requires a high sampling resolution for paleontological studies, a feat seldom achieved. By integrating published data with new samples from the Gėluva-118 core, we have attained resolution of ≈ 10 Ka in examining ostracod paleocommunities during the Mulde/lundgreni Event.

Our approach involved a custom-made binary recursive segmentation algorithm for the hierarchical subdivision of stratigraphically contiguous segments. This algorithm was applied to the ostracod taxonomic compositional time series data from the Gėluva-118 core (Lithuania). The results revealed significant changes in ostracod community composition, enabling us to delineate the event's stages. We employed a Bayesian Age-Depth model to assess the timing of these changes. The median and 95% Highest Density Interval (HDI) durations for each stage, as well as for the entire event, are as follows: Collapse – 50 Ka (11 – 171 Ka), Maximal Stress – 120 Ka (31 – 601 Ka), Recovery – 80 Ka (21 – 576 Ka), and the entire Mulde/lundgreni Event – 260 Ka (100 – 1,136 Ka). Our analysis of bootstrapped sample averages of diversity indices revealed that the Maximal Stress stage, marked by a severe scarcity of ostracods, signified a distinct shift in community diversity state. Prior to this stage, ostracod communities were less diverse, yet exhibited higher increases in evenness with growing diversity, indicating distinct community assembly and community structure patterns. Ostracod communities from the Collapse and Recovery stages resembled those adjacent to the Mulde/lundgreni Event interval but showed significantly reduced abundances, lower inverse Simpson index, and higher evenness. Furthermore, our findings suggest a nonlinear recovery stage, punctuated by setbacks and stabilization phases.

These insights demonstrate the potential of high-resolution paleontological studies in deciphering the chronology and pace of intermittent global events.

This research was supported by S-MIP-21- 9 “The role of spatial structuring in major transitions in macroevolution”.

How to cite: Daumantas, L., Rinkevičiūtė, S., Radzevičius, S., and Spiridonov, A.: Deciphering the dynamics of the Mulde Event—Bayesian ultra-high-resolution ostracod paleocommunity analysis , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15732, https://doi.org/10.5194/egusphere-egu24-15732, 2024.

EGU24-15917 | ECS | Orals | BG5.3

Stress, strain and crustal flow patterns in a corner collision: insights from coupled 3D numerical models 

Luuk van Agtmaal, Attila Balazs, Dave May, and Taras Gerya

Large and fast collisional systems such as the Eastern Tibetan-Himalayan orogenic system can have distinct corner structures. Away from the corners, plate convergence is accommodated primarily by convergence-parallel processes such as (continental) subduction, crustal thickening and buckling. Around the corners, oblique and convergence-perpendicular processes become more important, such as strike-slip, transpressional and transtensional faults. The strike of the subduction front itself can also vary in space, as tomographic images show for the case of the Indian slab beneath Tibet and Burma. At the corners themselves, a peculiar syntaxis structure may form which is characterised by effective strain localisation and high rates of exhumation and erosion. However, our understanding of the temporal evolution of orogenic syntaxis formation is still elusive. 

Here, we use high-resolution, three-dimensional thermomechanical models to investigate principal stress orientations, strain rate patterns and upper versus lower crustal flow patterns within a continental corner collision setting loosely resembling the Eastern Tibetan-Himalayan orogenic system. We use a 1000 x 200 x 1000 (x * y * z) model domain with a permeable lower boundary and a 2 km grid resolution in each dimension. Each grid cell has 8 markers. The models are carried out using I3ELVIS (Gerya and Yuen, 2007) coupled to the surface process model FDSPM (Munch et al., 2022). Our numerical experiments highlight that i) significant lateral variability occurs despite prescribing orthogonal kinematic boundary conditions; ii) a high variability of stress states and deformation styles occur within the modelled orogen and plateau; iii) Lower crust beneath the plateau escapes later than upper crust, but around 3-4 times faster. Lastly, we examine the sensitivity of the model evolution to different degrees of strain weakening, intracrustal layering, and the diffusion coefficient of the surface process model.

Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1), 83–105. https://doi.org/10.1016/j.pepi.2007.04.015

Munch, J., Ueda, K., Schnydrig, S., May, D. A., & Gerya, T. V. (2022). Contrasting influence of sediments vs surface processes on retreating subduction zones dynamics. Tectonophysics, 836, 229410. https://doi.org/10.1016/j.tecto.2022.229410

How to cite: van Agtmaal, L., Balazs, A., May, D., and Gerya, T.: Stress, strain and crustal flow patterns in a corner collision: insights from coupled 3D numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15917, https://doi.org/10.5194/egusphere-egu24-15917, 2024.

EGU24-17160 | Orals | BG5.3

Uncovering life and planetary co-evolution through the genomic record 

Cara Magnabosco, Paula Rodriguez, Fatima Husain, Maddie Paoletti, Chris Parsons, Jack Payette, Sarah Swartz, Erik Tamre, and Greg Fournier

The maintenance of Earth’s habitability over geologic timescales is largely driven by the metabolisms and ecologies of bacteria and archaea. In this context, the role that microorganisms have played throughout major environmental transitions during the Archean and Proterozoic Eons are especially noteworthy. The “genomic record” represents the accumulated adaptations to planetary change maintained within the collective genetic pool of life. In this presentation, we will describe how the genomic record can be used to improve our understanding of microbial natural history and present six broadly applicable principles to aid in the investigation these complex questions. This framework will then be used to guide a a meta-analysis of microbial genomes derived from collections large metagenomic databases across diverse environments to illustrate how specific environmental variables drive the microbial diversity patterns we see today.

How to cite: Magnabosco, C., Rodriguez, P., Husain, F., Paoletti, M., Parsons, C., Payette, J., Swartz, S., Tamre, E., and Fournier, G.: Uncovering life and planetary co-evolution through the genomic record, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17160, https://doi.org/10.5194/egusphere-egu24-17160, 2024.

EGU24-17379 | ECS | Orals | BG5.3

125 Ma of physiographic changes and mammal macroevolution 

Manon Lorcery, Laurent Husson, Tristan Salles, Oskar Hagen, Alexander Skeels, and Sébastien Lavergne

Changes in the physical environment, whether geological or climatic, are known to be major drivers of biodiversity. At the interface between the solid Earth and the climate lies the physiography, and landscape complexity and variety may control biodiversity mechanisms at a finer scale that the large scale patterns of plate tectonics and global climate. To test whether variation of physiography through time and space can explain the current richness pattern of biodiversity and understand the impact of landscape complexity evolution on specific mechanistic processes, we simulated the diversification of terrestrial mammals at global scale, over 125 Ma of geological and climatic changes, using a spatially explicit eco-evolutionary simulation model (genesis). We designed four evolutionary scenarios in which evolution was only dependent on climate and plate tectonics (M0), and scenarios where physiographic diversity was implemented in speciation (M1), dispersion (M2) and niche ecology (M3). To assess whether model predictions are consistent with the empirical distribution of terrestrial mammals, we statistically identify general emergent patterns of biodiversity within and across spatial and temporal scales. 

How to cite: Lorcery, M., Husson, L., Salles, T., Hagen, O., Skeels, A., and Lavergne, S.: 125 Ma of physiographic changes and mammal macroevolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17379, https://doi.org/10.5194/egusphere-egu24-17379, 2024.

EGU24-18509 | Orals | BG5.3

Exploring the Links between Testate Amoeba Traits and Eutrophication in Lakes 

Helen Roe, Andrew Macumber, Stephen Prentice, Timothy Patterson, Carl Sayer, and David Emson

There is considerable potential to apply traits-based approaches to the subfossil remains of shell-forming micro-organisms which preserve well in sediments and whose short generation times make it possible to achieve high-temporal resolution in palaeoecological studies.  In this paper we review progress in applying traits-based approaches to freshwater testate amoebae (Arcellinida), a diverse group of protists which are abundant in lakes and are valuable palaeoecological indicators.  Drawing on published studies from the last ~10 years, we describe the methodologies which have been applied to delimit testate amoeba (TA) traits and review the challenges associated with their measurement and interpretation.  We also showcase the results of ongoing work in seven lakes (UK, Canada) which aims to (i) examine the character and causes of trait-based variability in palaeolimnological settings; (ii) apply novel biometric approaches to aid in trait delimitation; and (iii) explore the potential for combining phylogenetic with advanced morphometric approaches to better understand the ecological and evolutionary significance of TA traits.

            We applied geometric morphometric analysis to define test size and shape indices and summarise testate amoeba community dynamics along a temporal gradient of eutrophication in a large shallow lake in Scotland, UK.  Cluster analysis of test size and shape indices yielded three assemblages, each dominated by a single shape: elongate, spherical and ovoid. When plotted stratigraphically, we observed increases in spherical tests, decreases in elongate tests and shrinking of test size coeval with eutrophication. Decreases in the elongate cluster may reflect benthic conditions with reduced oxygen levels, while increases in the spherical cluster are likely associated with an expanding macrophyte community that promoted pelagic and epibiotic life habits.  Shrinking of test size may be a stress response to eutrophication and/or warming temperatures. Tracking community dynamics using test size and shape indices was found to be as effective as using traditional species-based approaches to summarize key palaeolimnological changes, with the added benefit of being free of taxonomic bias.  The approach thus shows significant potential for future studies of aquatic community change in nutrient-impacted lakes.

            To further investigate the functional significance of the Arcellinida shape groups, we examined the phylogenetic signal of morphological traits in elongate Difflugia species which occur in eutrophic and mesotrophic lakes.  Previous phylogenetic work has shown that whilst overall test morphology (e.g., spherical or elongate) is generally conserved in Arcellinida lineages, the taxonomic significance of other traits (e.g., size, ornamentation, mixotrophy/heterotrophy metabolism type) is not well understood.  Our analyses revealed two clades which could be reliably separated by test size and the presence/absence of mixotrophy.  This suggests that test size may reflect trophic level, with smaller taxa occupying lower trophic levels.  In addition to having larger tests, elongate mixotrophic Difflugia are characterised by wide, flat bases and inflation of the lower part of the test.  These morphological traits may provide additional space for endosymbionts and/or increased surface area to aid light transmission.  Continued research into the ecological and evolutionary significance of morphological traits will serve to strengthen palaeoecological inferences, increasing the importance of lacustrine testate Arcellinida as environmental proxies.

How to cite: Roe, H., Macumber, A., Prentice, S., Patterson, T., Sayer, C., and Emson, D.: Exploring the Links between Testate Amoeba Traits and Eutrophication in Lakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18509, https://doi.org/10.5194/egusphere-egu24-18509, 2024.

EGU24-18542 | Posters on site | BG5.3

Continuous 3D modelling over deep time – the SCION Earth Evolution Model 

Benjamin Mills, Dongyu Zheng, Khushboo Gurung, Andrew Merdith, Alexander Krause, Zhen Xu, Fred Bowyer, and Stephen Hunter

Earth system models for deep time have typically been unable to represent geological timespans in 3D because climate and ocean circulation plays a key role in global biogeochemistry and generating a 3D physical climate simulation is extremely computationally expensive. This means that Earth System Modelling for periods of over 1 Myr has been exclusively carried out in nondimensional box models, which leads to oversimplification of spatially heterogeneous processes like continental weathering and marine carbon burial. This simplification may be a key reason why so many climate questions over deep time remain unresolved. The SCION (Spatial Continuous IntegratiON) project aims to produce a 3D and self-consistent climate and biogeochemical system that can be run over billion-year timeframes. To do this, it employs a physical climate emulator which is developed using a Deep Learning method trained on hundreds of General Circulation Model runs over different paleogeographies and CO2 levels. The SCION development project – SIM-EARTH – also includes a new process-based reconstruction of paleotopography using the GPlates kinematic plate model, development of a long-term dynamic global vegetation module and ocean biogeochemical module, and databasing projects to establish 3D datasets for marine and terrestrial palaeontology and geochemistry that can be compared to model outputs at the local scale to test hypotheses. We hope that new model frameworks like this can help us better understand the evolution of Earth’s surface conditions over time, assess the contribution of the biosphere to global environmental change, and help determine what fundamental characteristics are required for a planet to be habitable for complex life.

How to cite: Mills, B., Zheng, D., Gurung, K., Merdith, A., Krause, A., Xu, Z., Bowyer, F., and Hunter, S.: Continuous 3D modelling over deep time – the SCION Earth Evolution Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18542, https://doi.org/10.5194/egusphere-egu24-18542, 2024.

EGU24-18738 | ECS | Orals | BG5.3

How did the Permian-Triassic hot house climate shape the vegetation landscape and how did the land plant fight back? 

Zhen Xu, Jianxin Yu, Jason Hilton, Barry H. Lomax, Paul B. Wignall, and Benjamin Mills

During the Permian-Triassic Mass Extinction (PTME) ~252Ma, diverse lowland forests were replaced by low diversity pioneer herbaceous lycopod communities that proceeded to dominate the Early and Middle Triassic landscape. The flourishing of Early-Middle Triassic herbaceous lycopods was coincident with data that suggests lethally warm surface temperatures (>40ºC) occurred across large regions of the planet. To explore how these plants were able to thrive during this interval of enhanced climatic stress, we collected data from over 400 fossil plant specimens from South China, supplemented by additional data from literature reviews from other regions and geological ages. Our studies on their morphology indicate that among all Phanerozoic lycopods the transitional Permian-Triassic genus Tomiostrobus (=Annalepis) has the closest morphological relationship with the recent lycopod Isoetes.

Extant Isoetes are renowned for their flexibility with regard to the photosynthetic pathway they use and their capacity to absorb CO2 through their roots. To evaluate whether this photosynthetic flexibility was linked to their Early-Middle Triassic ecosystem dominance, we undertook carbon isotope and sedimentary facies analysis including plant taphonomy to test for the presence of the Crassulacean Acid Metabolism (CAM) photosynthetic pathway. Plants capable of CAM pathway growing in stressful environment typically have heavier isotopic signatures while show typical C3 plant signatures in hospitable environment. Our carbon isotope data shows that Permian Triassic Transition Tomiostrobus isotopic signature is on average ~2‰ less negative when compared to contemporary non lycophyte vegetation. Furthermore, the carbon isotope of the Middle Triassic lycopods ~1.07‰ heavier than the other plants, while Late Permian Lepidodendron exhibits a similar δ13C value with other contemporary plants. These findings suggest that CAM photosynthesis may have played a role in the dominance of the Triassic herbaceous lycopods. The dominance of CAM plants following the PTME has implications from an Earth Systems standpoint due to their diminished productivity and a lower capacity for biotic weathering, features that likely suppressed negative feedback loops important in driving climate stabilization during the ~5Ma PTME recovery phase.

How to cite: Xu, Z., Yu, J., Hilton, J., Lomax, B. H., Wignall, P. B., and Mills, B.: How did the Permian-Triassic hot house climate shape the vegetation landscape and how did the land plant fight back?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18738, https://doi.org/10.5194/egusphere-egu24-18738, 2024.

EGU24-19816 | ECS | Posters on site | BG5.3

Modelling the life-environment interface in ancient shelf seas 

Sara Sjosten, Stuart Daines, and Tim Lenton

The co-evolution of life and environment is a dynamic system of feedbacks. Much of the evolution of life took place in localized shelf sea environments where evolving biota and redox conditions created feedbacks which are hypothesized to have increased the ecospace for life to radiate - and sometimes perhaps brought about its own demise. Models can suggest hypotheses to test ecosystem dynamics and the effects of changes to life or the environment on the other. A particular modelling challenge is to connect these localized environments to global Earth system dynamics over long timescales. A hierarchy of models is needed to separate spatial and temporal scales and allow for the construction of models specific enough to be supported by limited geological data. We introduce a 1D column model of an ocean shelf sea in the PALEO framework to represent the ecological dynamics of important early life forms such as plankton, sponges and early burrowers and their effects on redox conditions, sediment burial and diagenesis. This model demonstrates that ecological dynamics and nutrient cycling can be modelled at the finest scales, while remaining computationally viable over geological timescales. Ongoing work integrating this model with data from critical time intervals in the Ediacaran and Cambrian can provide specific hypotheses for the local behavior of the life-environment interface and can be connected to broader models for global investigations.

How to cite: Sjosten, S., Daines, S., and Lenton, T.: Modelling the life-environment interface in ancient shelf seas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19816, https://doi.org/10.5194/egusphere-egu24-19816, 2024.

EGU24-19830 | ECS | Posters on site | BG5.3

Exploring the role of weathering dynamics, nutrient input and palaeoredox conditions on the origin of biomineralization and ecosystem habitability in the late Ediacaran Nama Group, Namibia   

Fred Bowyer, Gustavo Paula-Santos, Collen-Issia Uahengo, Kavevaza Kaputuaza, Junias Ndeunyema, Mariana Yilales, Ruaridh Alexander, Andrew Curtis, Simon Poulton, Simone Kasemann, and Rachel Wood

     The first animals (metazoans) with skeletons belong to the tubular ‘cloudinid’ morphogroup, the lowest occurrence of which marks the base of the Nama biotic assemblage (ca. 551–550 Million years ago, Ma). This evolutionary first appearance coincided with, or immediately post-dated, a major faunal turnover event associated with the loss of many soft-bodied White Sea assemblage taxa that dominated the preceding ca. 6–10 Myrs. At present, there is no evidence that the majority of cloudinid skeletons were biomineralized under strong biological control. Instead, these early biomineralizing metazoans may have acquired their skeletons with relative ease in response to ambient seawater chemistry in carbonate settings. The trigger for the origin of metazoan biomineralization remains unknown, but may have been linked to changes in seawater Mg/Ca and/or environmental oxygen concentration.  

     Weathering-derived nutrient input can fuel marine productivity and regional deoxygenation on short-medium timescales, leading to organic carbon and pyrite burial and atmospheric oxygenation on longer timescales. Changes to the intensity and style of weathering on the global scale can also alter the flux of dissolved cations (e.g., Ca and Mg) and alkalinity to the oceans. Despite their importance, global weathering dynamics at the dawn of animal biomineralization remain poorly understood. Carbonate-hosted Sr and Li isotopes have the potential to track the degree and style of weathering, and temporal trends in both datasets may therefore provide meaningful insights into the dynamics of associated elemental fluxes to regional palaeoenvironments. 

     Late Ediacaran sedimentary rocks of the Nama Group (ca. 551–538 Ma) host a rich fossil assemblage that includes impressions of both soft-bodied organisms and the lowest known occurrence of the skeletal cloudinid, Cloudina. Here we present new Sr and Li isotope data from carbonates in four outcrop sections, and new data of carbonate carbon isotopes, major and trace element concentrations, and Fe speciation from two cores drilled as part of the ICDP GRIND-ECT project, which together span the entire Ediacaran portion of the Nama Group succession. The combination of these data, when considered within a sequence stratigraphic framework, clearly reveals the influence of changes in regional weathering intensity/style on marine palaeoredox dynamics. Furthermore, calibration of these new data within a global chronostratigraphic age model reveals cyclicity in weathering proxies from multiple cratons that respond directly to changes in eustatic sea level. The implications of these new time-calibrated geochemical and stratigraphic data are considered relative to the timing of the earliest metazoan biomineralization, and major faunal turnover events that preceded and coincided with deposition of the Nama Group succession. 

How to cite: Bowyer, F., Paula-Santos, G., Uahengo, C.-I., Kaputuaza, K., Ndeunyema, J., Yilales, M., Alexander, R., Curtis, A., Poulton, S., Kasemann, S., and Wood, R.: Exploring the role of weathering dynamics, nutrient input and palaeoredox conditions on the origin of biomineralization and ecosystem habitability in the late Ediacaran Nama Group, Namibia  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19830, https://doi.org/10.5194/egusphere-egu24-19830, 2024.

EGU24-21627 | ECS | Orals | BG5.3

Regional tectonics shaped plant biodiversity in Colombian Andes 

Yi Liu, Richard Ott, Loïc Pellissier, and Niklaus Zimmermann

Northern South America, particularly the geologically dynamic Colombian Andes, stands as a region of highest plant biodiversity. While the influence of mountain uplift in the tropical Andes on biodiversity patterns is well-recognized, the repercussions of these landscape changes on the evolutionary dynamics of the local flora have been understudied. Here, we aim to fill this gap by investigating the role of uplift history and landscape evolution in driving the assembly and maintenance of plant biodiversity in the Colombian Andes. We integrate a comprehensive reconstruction of individual geological blocks with plant phylogenies, distribution patterns, and the resulting biogeographic structuring of the endemic flora. Our comparative analysis reveals a substantial agreement between the geological blocks and biogeographic realms instead of climate, indicating the fundamental role of regional tectonics shapes the observed pattern of biodiversity. Notably, the northern segments of the Western and Central Cordillera and Eastern Cordillera, representing the two most-recent fast uplift blocks, exhibit a higher prevalence of endemic species and a significant accumulation of in situ speciation events over the last 10 million years. Our findings provide a detailed perspective on how landscape changes have driven the diversification of flora in the Colombian Andes and contribute to a broader understanding of the intricate interplay between geological processes and plant evolution, emphasizing the importance of considering regional tectonic dynamics in unraveling the heterogeneous biodiversity patterns on Earth.

How to cite: Liu, Y., Ott, R., Pellissier, L., and Zimmermann, N.: Regional tectonics shaped plant biodiversity in Colombian Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21627, https://doi.org/10.5194/egusphere-egu24-21627, 2024.

GD4 – Subduction and Orogeny

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.

GD5 – Rifting and Mid Ocean Ridges

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.

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.

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.

GD6 – Crust, Lithosphere and Asthenosphere

EGU24-649 | ECS | Posters on site | GD6.1

A lower crust shear zone favors delamination and continental subduction in the Apennines 

Irene Menichelli, Irene Bianchi, and Claudio Chiarabba

Understanding the physical characteristics and structure of the lithosphere is crucial in unraveling the evolution of mountain belts. In this study, we present detailed Vs profiles of the Apennine lithosphere that shed light on a controversial aspect of continental subduction: the intricate process of crustal delamination from the descending plate. Through an accurate analysis of a dense teleseismic Receiver function data set (comprising over 15,000 teleseismic events), we find that the delamination of continental lithosphere is facilitated by the development of a low Vs shear weak zone within the mid-lower crust.

Utilizing a Reversible-jump Markov chain Monte Carlo (RjMcMC) approach for computing 1D Vs models across the central Apennines, we mitigate the reliance on a-priori information, thus enhancing the robustness of the final solution.
We observe a double Moho beneath the outer regions of the current mountain range, indicating the gradual development of a shallow interface. This incipient formation of the double Moho finds a mature-stage equivalent in the backarc, where crustal thinning and magmatism ensued following the re-establishment of the shallow Tyrrhenian Moho.

Proposing a novel scenario for Apennine subduction, we hypothesize that the onset of delamination occurs in the forearc, necessitating a longer thermal rebalancing. This hypothesis suggests that sustained continental subduction can persist if it develops at mid-lower crustal depths within weak rheology inhibiting the slab break-off process.
Our findings present a new perspective on continental subduction and offer prognostic insights into the long-term evolution of the Apennines over the next 7-10 million years.

How to cite: Menichelli, I., Bianchi, I., and Chiarabba, C.: A lower crust shear zone favors delamination and continental subduction in the Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-649, https://doi.org/10.5194/egusphere-egu24-649, 2024.

EGU24-1098 | ECS | Posters on site | GD6.1

Crustal Structure across the Northern Scandinavian margin along the Senja OBS Profile  

Rafet Ender Alemdar, Metin Kahraman, Alexey Shulgin, Asbjorn Breivik, Irina Artemieva, and Hans Thybo

The Senja onshore-offshore seismic profile is located in the northwestern part of Fennoscandia, extending from onshore Norway into the North Atlantic Ocean. The Fennoscandian lithosphere has been formed by the amalgamation of terranes and microcontinents to an Archean core, primarily during the Palaeoproterozoic. The later Sveconorwegian (Grenvillian) and Caledonian orogenies had strong effect on the western part of Fennoscandia. The Scandia Mountain range extends along the west coast with elevation up to 2500 m, mainly coinciding with the surface outcrops of Caledonian deformed crust. Its location far from any active plate boundary makes this mountain range enigmatic. The offshore continental part of Fennoscandia experienced a long post-Caledonian extensional period for more than 200 My, and it now forms a continental shelf below sea level extending to the continent to ocean transition.

We present a crustal-scale seismic profile along the NW-SE striking Senja OBS Profile in northern Scandinavia between 12°E and 20°E. This profile covers both offshore and onshore domains over a total distance of ~300 km across the Norwegian shelf in the North Atlantic Ocean, Senja Island, and mainland Norway. Airgun shots from the vessel Hakon Mosby were used as sourced for the refraction/wide-angle reflection survey. The dataset includes recordings on 5 ocean bottom seismometers (OBS) on the shelf, slope, and oceanic environment, complemented by 68 onshore stations at 1.3-kilometre intervals. We present a seismic p-wave velocity model derived by ray-tracing modelling of P-wave arrivals along the profile.

The model includes a deep sedimentary basin extending to ~10 kilometres depth with velocities between ca. 2 km/s and 5.10 km/s, which gradually thickens from the coast to its maximum thickness of 10 km about 25 km from the coast. This deep sedimentary basin is very wide (approximately 8 km). Further offshore the sedimentary cover of the shelf and oceanic environment is relatively thin. The upper crustal velocity below the sedimentary sequence has velocities of ~ 6.0 km/s.

 

How to cite: Alemdar, R. E., Kahraman, M., Shulgin, A., Breivik, A., Artemieva, I., and Thybo, H.: Crustal Structure across the Northern Scandinavian margin along the Senja OBS Profile , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1098, https://doi.org/10.5194/egusphere-egu24-1098, 2024.

EGU24-2015 | ECS | Orals | GD6.1

Craton Formation by Underplating and Development of the MLD: Evidence from Bayesian Surface Wave Inversion  

Alistair Boyce, Thomas Bodin, Stephanie Durand, Dorian Soergel, and Eric Debayle

Craton formation and evolution remains enigmatic because observations from long and short period seismic waves and geochemical data are inconsistent. For example, both internal layering and radial anisotropy are poorly constrained. By inverting cratonic Rayleigh and Love surface wave dispersion curves for shear-wave velocity and radial anisotropy using a flexible Bayesian scheme, we show that these inconsistencies can be reconciled. Our methodology does not require any vertical smoothing and only includes anisotropic layers where necessary to fit the data. Results show all cratons possess a positively radially anisotropic upper lithospheric layer that is best explained by Archean underplating. An isotropic layer lies beneath, likely indicative of two-stage craton formation. We find a variable amplitude low velocity zone (LVZ) may exist within the upper anisotropic layer of up to 9 of 12 cratons studied. This LVZ is well correlated to observed Mid-Lithospheric Discontinuities (MLDs). Our results suggest the MLD is best explained by post formation modification within cratons.

How to cite: Boyce, A., Bodin, T., Durand, S., Soergel, D., and Debayle, E.: Craton Formation by Underplating and Development of the MLD: Evidence from Bayesian Surface Wave Inversion , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2015, https://doi.org/10.5194/egusphere-egu24-2015, 2024.

Since the Early Mesozoic, extensive Cretaceous intraplate volcanism, cratonic lithospheric thinning, and widespread crustal deformation have been documented in Northeast (NE) Asia. Global plate reconstruction models and paleo-magnetic data suggest a highly complex subduction system under NE Asia since the early Mesozoic, with proposed Mesozoic models including continuous subduction of the Izanagi plate and possible subduction of intra-oceanic arcs and early Cenozoic subduction of an active spreading ridge. Although subduction is a critical factor impacting continental deformation, the interactions between deep dynamic processes and surface tectonic responses remain debated. Based on a systematic investigation of seismic tomography, plate reconstruction, and igneous rock data, we present a new model of continental co-deformation with a multistage subduction history involving the Proto-ocean, Izanagi, and Pacific plates in Northeast Asia. The high-resolution mantle seismic structures were ascertained using a novel global tomographic inversion based on adaptive inversion mesh refinement and regional velocity perturbation constraints from 298,725 hand-picked and > 16 million arrival times of multiple P-wave phases (e.g., P, pP (pwP), PP, PcP, Pdiff, PKP, PKiKP) which were recorded by the 4,107 temporary and permanent stations in Northeast Asia. The unprecedented data reveal new integrative views on the geometry and behavior of mantle high-velocity anomalies associated with a sequence of oceanic lithosphere subduction events. The extensive compilation of dated volcanic samples provides strong constraints on past subduction events. Positions of remanent slabs derived from a multistage subduction history were reconstructed using the ages of initial subduction and slab sinking rates, where the geographical distribution of remnant slabs observed in our tomographic model helps to define the plate reconstruction history since the Early Mesozoic. The inferred multi-plate subduction configuration with slab advance, rollback, stagnation, break-off, and foundering, together with implied slab dehydration, should have resulted in various degrees of fluid-rock interactions among the slabs, the asthenosphere, and the continental lithosphere. We argued that fluid intrusions and mantle flow have played crucial roles in episodic intraplate volcanism and craton lithosphere thinning in different subduction stages. The Early Cretaceous intraplate volcanism, the ancient cratonic lithospheric thinning, and the crustal deformation have been caused mainly by a successive effect of the Proto oceanic plate and Izanagi slab subduction, but less by the Pacific plate subduction. These findings provide a systematical framework for understanding the co-evolution of the continental lithosphere with deep mantle dynamics in NE Asia and also serve as an excellent illustration of how the Earth's interior works.

How to cite: Wang, Z., Liu, L., Fu, Y., and Zhao, L.: Tomographic evidence on multistage plate subduction in Northeast Asia: Implications for lithospheric deformation and intraplate volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2673, https://doi.org/10.5194/egusphere-egu24-2673, 2024.

EGU24-3139 | ECS | Orals | GD6.1

A rock density model for geodynamic and tectonic studies of the Southern Benue Trough in Nigeria from a tailored gravity data 

Ojima Apeh, Robert Tenzer, Luan Pham, Elochukwu Moka, Emmanuel Onah, Victus Uzodinma, and Elijah Ebinne

The application of gravity data in mapping of the Earth’s subsurface has steadily been on the increase globally. Gravity information is more often used to understand mechanisms associated with rock formations, interpret underground faulting and fracturing zones as well as estimating depths of underlying geological structures. A rock density mapping could be used to estimate mineral deposits, differentiate lithofacies, understand the general dynamics of heat flow, interpret geomorphologies, and determine the size and characteristics of different types of rocks in the Earth’s crust. Recently, there is a growing trend of applying an apparent density mapping technique for the estimation of rock densities from gravity data. In this study, we compute a high-resolution tailored Bouguer gravity data over the Southern Benue Trough of Nigeria and use approximate rock density ranges of some common rock types and existing geological/geophysical information to understand geodynamic processes and tectonic events predominant within the study area. We further apply the inverse density deconvolution filter (i.e., the apparent density mapping technique) to a computed short-wavelength gravity component (realized from a gravity separation approach) in order to estimate rock densities. According to our estimates, the rock densities within the study area vary between 2.50 and 2.74 g/cm3, with minimum density values attributed to volcano-sedimentary deposits along the Cameroon Volcanic Line and maximum density values at the eastern and southern parts associated with mafic igneous rocks. A comparison of estimated rock densities with available in-situ rock density data showed slightly higher rock density estimates in most cases than the in-situ rock density values at 50 sample locations. However, estimated rock densities are within the range of density variations of sedimentary and basement rocks predominant in the study area. Our gravity and density maps reveal the geometry of main geological structures dominated by sedimentary basins, igneous intrusions, uplifts, volcanoes, and diapirs occurring within the study area. Folds, faults, and fractures forming ridges and troughs in different directions (mostly NE-SW) are also manifested in those maps. The compiled maps could identify these subsurface geological structures as well as reveal different erosion patterns and landforms characteristic of the study area. The revealed patterns of crustal deformations within the study area demonstrate compressional and extensional tectonic events which may have possibly led to the faulting and fracturing systems with thermal and chemical variations among ores and gangue minerals in the area. These findings confirm the different geomorphic processes and structural deformations well-known about the study area. In conclusion, we point out that a rock density model could be an essential tool for studying geodynamic processes and tectonic events in a region since it can demonstrate mechanisms of tectonic events, patterns of deformation regimes, and mineral prospectivity of such an area.

 

Keywords: gravity; rock densities; tectonics; geodynamics; density inversion; mineral deposits

How to cite: Apeh, O., Tenzer, R., Pham, L., Moka, E., Onah, E., Uzodinma, V., and Ebinne, E.: A rock density model for geodynamic and tectonic studies of the Southern Benue Trough in Nigeria from a tailored gravity data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3139, https://doi.org/10.5194/egusphere-egu24-3139, 2024.

Since last 1960’s, the plate tectonics has been played a main role for the study on the Earth’s evolution and global tectonics, but mostly focused on the global divergence and convergence, and focused on the continental margin—subduction and collision. However, the plate tectonics cannot resolve all of the tectonic evolution and reconstruction of the global evolution, like non-rigid blocks and continental lithospheric deformation; and mountain building within the continent; large scales deformation and tectonics in the continental interiors and so on. Thus, “Intracontinental Tectonics and Orogeny” has been studied. 

Globally, there are lots of tectonics or deformation types have been found and the intracontinental mountain building and the orogeneses have been classified, like types of the Alice Spring in Australia, the Tianshan in Asia and the Pyrenees in Europe. They are with different orogenic frameworks including deformation, magmatism, sedimentation and metamorphism. Also, they have formed in different tectonic backgrounds, such as on the reworking orogenic belt, intracontinental rift-basin deformation, and multiple-stage orogeny between the continental blocks, and linkages to plate tectonics and non-plate tectonics in mechanism and dynamics.  

How to cite: Wang, Y., Liu, S., and Gong, M.: Classification of intracontinental (intraplate) orogeny based on tectonics and its evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3525, https://doi.org/10.5194/egusphere-egu24-3525, 2024.

EGU24-4613 | ECS | Posters on site | GD6.1

Mantle discontinuities beneath Arctic ocean and Aleutian-Alaska subduction zone 

Ye Yuan, John Keith Magali, and Christine Thomas

We investigate the properties of mantle discontinuities beneath the Arctic ocean and the Aleutian-Alaska subduction zone with underside reflections of PP and SS waves. The depth distributions of the 410-km and 520-km discontinuities suggest a relatively normal mantle transition zone beneath the Arctic ocean and a cold mantle transition zone with the subducted Pacific plate beneath Aleutian-Alaska subduction. The depth of the 660 km discontinuity shows normal behavior beneath the Arctic Ocean. However, the detection of deep reflectors with opposite polarities in depth range of 720~770 km beneath the eastern Aleutians introduces additional complexity for explaining the slab morphology.  We test several plausible compositions using mineralogical modeling along a subduction geotherm. The deep reflectors are interpreted as mid-ocean ridge basalt (MORB) crust associated with the Pacific slab that may deform or buckle at the bottom of the mantle transition zone beneath the eastern Aleutians.  Meanwhile, an uplifted 660-km discontinuity observed in the adjacent Alaska region suggests a different subduction depth, where the slab may penetrate the 410-km discontinuity but does not reach the 660-km discontinuity,  consistent with previous regional studies. Our observations thus depict a complex slab geometry along the Aleutian-Alaska trench, that is, the slab  may reach the top of the lower mantle beneath eastern Aleutian but remains at the base of the transition zone underneath central Alaska.

How to cite: Yuan, Y., Keith Magali, J., and Thomas, C.: Mantle discontinuities beneath Arctic ocean and Aleutian-Alaska subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4613, https://doi.org/10.5194/egusphere-egu24-4613, 2024.

EGU24-4710 | Posters on site | GD6.1

The Lithosphere Structure Of Bohai Bay Basin: Combining Gravity, Geoid, And Topography Data 

Jing Ma, Wanyin Wang, Hermann Zeyen, and Zhongsheng Li

The Bohai Bay Basin, located in northeast China, is a Meso-Cenozoic strike-slip extensional basin. A lot of research work carried out in Bohai Bay Basin, has shown that there is a huge potential of oil and gas resources. However, the proportion of known oil and gas reserves to the total estimated resources is not high, which means that this area still has broad exploration prospects. Although oil and gas resources are mainly distributed in sedimentary basins, their enrichment degree is largely influenced by the structure and development of the lithosphere. Based on lithospheric local isostasy theory and thermal conduction principle linked to temperature dependence of rock densities, the three-dimensional deep structure of the lithosphere under the Bohai Bay Basin is calculated by using geoid and gravity anomalies, topographic and existing geological-geophysical data. The results show that the lithosphere-asthenosphere boundary of Bohai Bay Basin gradually rises from the western onshore to the eastern offshore area from 90 to 110 km. The thinnest lithosphere is found under the Bozhong Depression in the southeast of the Bohai Bay Basin. It is concluded that the thinning of the lithosphere in the Bohai Bay Basin is closely related to the subduction of the Meso-Cenozoic Pacific plate, which led first to thickening followed by delamination of the North China Craton lithosphere, and then the magma upwelling led to slow uplift of the Earth’s surface and continuous stretching of the lithosphere. At the same time, favorable conditions of temperature, pressure, chemistry and structure were provided for the formation of oil and gas. In this wqy, the Bohai Bay basin developed into the present oil-rich basin. This study provides a new perspective for understanding the deep structure and hydrocarbon resource control mechanisms of Bohai Bay Basin.

How to cite: Ma, J., Wang, W., Zeyen, H., and Li, Z.: The Lithosphere Structure Of Bohai Bay Basin: Combining Gravity, Geoid, And Topography Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4710, https://doi.org/10.5194/egusphere-egu24-4710, 2024.

Despite numerous geophysical observations on Hindu Kush, fine structures of mantle discontinuities remain less explored. By stacking near-source SdP phases from large datasets, we conducted systematic imaging of mantle discontinuities beneath Hindu Kush. Compared with the IASP91 model, we find an abrupt topographic transition of the 410-km discontinuity (410) from uplifts of up to 41 km within the subducting slab to depressions of less than 20 km near the slab edge, as well as a slightly depressed 660-km discontinuity (660) with depths of 660-668 km, and a fluctuant 300-km discontinuity (300) with depths of 264-337 km. We suggest that the sinking Indian slab elevates the 410 due to its cold interior, and deepens it near the slab edge by the hot mantle upwelling of slab-entrained mantle escaping below the slab, but has almost no impacts on the 660. Moreover, the fluctuant 300 can be explained by the coesite to stishovite phase transition in the eclogite-rich mantle within the subduction zone. When considered alongside other studies, our seismic results offer new insights into subduction dynamics of the Indian slab.

How to cite: Cui, Q., Zhou, Y., Gao, Y., and Liu, L.: Deep dynamics of subducting Indian slab revealed by mantle discontinuity structures beneath Hindu Kush from SdP observation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4912, https://doi.org/10.5194/egusphere-egu24-4912, 2024.

Olivine and its polymorphs are the dominant minerals in the upper mantle and transition zone. The olivine phase transitions, determined primarily by pressure and temperature, control mantle discontinuities and influence mantle dynamics. Pressure is a first-order control on olivine phase transition and relates primarily to depth; therefore, it is commonly used to interpret the depths of mantle discontinuities. However, mantle dynamic models predicted stress levels of 100-300 MPa or as high as 1 GPa. Previous work has provided a complete picture of how such stresses would affect the positions where mineral reactions occur (and hence large-scale mantle structure). In this work, we plan to focus on the feedback between pressure and stress on the olivine phase transition at grain scale, and then the results can be extrapolated and upscaled to mantle scale deformation.

 

We use the Open Phase Studio software based on the phase field model to simulate olivine phase transitions. The phase field model uses order parameters to distinguish different phases and describe their evolution. The parameter value of 1 indicates the bulk of the phase, and a value of 0 indicates the absence of this phase and is a smooth function of position. The smooth transition of a phase parameter indicates a diffuse interface between phases. The total free energies, interface properties, and microstructure control the phase field evolution. Open Phase Studio considers the Helmholtz free energies of each phase and uses their elastic energies to account for the pressure and stress effects on phase evolution. This software currently focuses on models of alloys, but appropriate values for silicates can be input. As a foundation, we first consider an Al-Li alloy to understand the behaviour of models. Then, we input olivine thermodynamic data via temperature-composition (T-x) phase diagrams for olivine composition and their elastic moduli to test the phase transition under different stress boundary conditions. We present our preliminary results here.

How to cite: Lu, L. and Wheeler, J.: Grain-scale simulation of olivine phase transition under stress: implications for mantle discontinuities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5239, https://doi.org/10.5194/egusphere-egu24-5239, 2024.

The La Réunion hotspot is one of the best examples of a primary plume, manifested as intraplate volcanism, a linear chain of volcanos with age progression, a large igneous province and geochemical anomaly. In this study, we investigate the mantle transition zone structure in and around the La Réunion Island using 3D migration of P-Receiver functions to decipher the effect of the plume on the Mantle Transition Zone(MTZ) and its architecture. Results indicate a thin MTZ beneath Madagascar, its western side, the eastern and south-eastern side of La Réunion sampling the oceanic region, in terms of a depressed 410 km and elevated 660 km discontinuity. A thin MTZ suggests high-temperature anomalies within, caused by the plume. Interestingly, we detect a depressed 410 km discontinuity exactly beneath the La Réunion hotspot and a broader depression of the 660 km discontinuity in and around it. These maiden results shed light on the high-temperature anomalies in the mid mantle, probably sourced from the La Réunion plume and provide evidence for Majorite-garnet (Mj) to Perovskite (Pv) phase transformation at the 660 km discontinuity. We postulate that the conduit of the La Réunion plume has initially hit the 660 km discontinuity and got horizontally spread at this depth and further progressed to the 410 km discontinuity as a columnar structure.

How to cite: Bommoju, Dr. P. R.: Inference of a plume conduit in and around the LaRéunion Island from 3D Migration of Ps conversionsfrom the Mantle Transition Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5520, https://doi.org/10.5194/egusphere-egu24-5520, 2024.

EGU24-6651 | ECS | Orals | GD6.1

A Global View of Upper Mantle Stratification: CRISP-RF 

Sayan Swar, Tolulope Olugboji, Ziqi Zhang, Steve Carr, Jean-Joel Legre, Canberk Eckmecki, and Mujdat Cetin

Abstract:

Our planet’s mantle is the largest rock-layer by volume. Across its old and stable Archean and Proterozoic terranes, seismological evidence suggests ubiquitous, spatially variable, and puzzling discontinuities, within, across and beneath the upper mantle lithosphere (~50- 350 km). A variety of explanations have been proposed, including phase transformations, melting and compositional anomalies, anisotropy, and elastically accommodated grain. To evaluate these, and other models, it is crucial to improve our threshold for detecting such discontinuities especially in reverberant and noisy environments. Here, we present a new method for sifting through the echoes and reverberations: CRISP-RF (Clean Receiver function Imaging with Sparse Radon Filters). With a global dataset of Ps converted waves, we use CRISP-RF to isolate hard-to-detect wave conversions buried in reverberations and noise. This refined, high-resolution, global view of upper mantle stratification will ensure robust evaluation of proposed models of upper mantle structure, evolution, and dynamics.

How to cite: Swar, S., Olugboji, T., Zhang, Z., Carr, S., Legre, J.-J., Eckmecki, C., and Cetin, M.: A Global View of Upper Mantle Stratification: CRISP-RF, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6651, https://doi.org/10.5194/egusphere-egu24-6651, 2024.

The continental mid-lithospheric discontinuity (MLD) has been widely detected within most cratons, with the dominant depth of 70-100 km and a significant drop of shear-wave velocity of 2-12%. However, the formation mechanism and corresponding strength of the MLD are widely debated, which may strongly affect the roles of MLD on craton evolution. In this study, we have conducted systematic numerical models with hydrated blocks generation routine to simulate the formation of MLD. Model results indicate that the MLD may be induced by the accumulation of hydrous minerals within cratonic lithosphere, and acts as a water collector during craton evolution. Further on, we focus on the roles of MLD in craton evolution. Based on the comparison among variable mechanisms, the viscosity of MLD may vary from the relatively high viscosity induced by wet olivine to the rather low viscosity induced by antigorite. Thus, systematic numerical modeling has been conducted with the MLD of contrasting strengths, i.e. the wet olivine-induced MLD or antigorite-induced MLD, to investigate the effects of MLD on the craton instability under variable tectonic regimes (stable, extension, compression, mantle flow traction, or mantle plume). Model results indicate that the wet olivine-induced MLD could not lead to lithospheric delamination under all the tested tectonic regime. In contrast, the weak antigorite-induced MLD could localize large strain and decouple the overlying and underlying lithosphere significantly; despite this, the lithospheric delamination requires additional conditions. Craton destruction only occurs with the connection of the weak antigorite-induced MLD and the sub-plate asthenosphere during craton extension or mantle plume activity. The partial melting process during large amount of extension or upwelling of mantle plume with high temperature anomaly and large size is a key condition. In addition, the depleted cratonic lithospheric mantle with low density would increase the intrinsic buoyancy of lithosphere, and inhibit the lithospheric delamination and craton destruction. Therefore, the effect of MLD on the craton destruction is not as significant as previously considered in the models, which requires additional strict conditions that are not widely satisfied on the Earth. This may explain the general stability of most cratons with widespread MLDs.

How to cite: Fu, H.-Y. and Li, Z.-H.: Formation mechanism of continental mid-lithosphere discontinuity and its effects on craton instability under variable tectonic regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7017, https://doi.org/10.5194/egusphere-egu24-7017, 2024.

EGU24-7153 | ECS | Posters on site | GD6.1

A new method for constraining crustal Vp/Vs ratio using P and S wave multiples 

Fanchang Meng, Chunquan Yu, and Xianwei Zeng

The ratio between compressional and shear wave speeds (Vp/Vs) in the Earth's crust is crucial for gaining a better understanding of its chemical composition and geological evolution history. Many studies employed H-κ stacking of receiver functions to estimate the crustal Vp/Vs ratio. However, the Vp/Vs ratio obtained from H-κ stacking can be biased due to lateral variations in crustal structures and/or incorrect absolute wave speed assumption. In this study, we propose a novel method to estimate the crustal Vp/Vs ratio using P and S wave multiples near receivers, that is the PpPmp (where m represents the Moho) and SsSms phases. The absolute arrival times of PpPmp and SsSms are sensitive to crustal thickness and wavespeeds, but the ratio of their arrival times is most sensitive to the crustal Vp/Vs ratio. We first verify the new method using synthetic tests on various crustal models. Synthetic results show that in the presence of lateral variation in crustal structure, the new method gives more accurate Vp/Vs ratios than the conventional H-κ stacking of receiver functions. We further validate the new method using field data recorded by the broadband station HYB in the eastern Dharwar Craton. Our data analysis involved preprocessing and manual selection of teleseismic events. Ultimately, the observed PpPmp and SsSms phases from 351 teleseismic events were used to calculate the Vp/Vs ratio beneath the HYB station, resulting in a value of 1.737±0.016. We find that this value is comparable to research results obtained by previous researchers using receiver function inversion (Zhou et al., 2000). Our new method for estimating crustal Vp/Vs ratio can potentially to applied to many other regions of tectonic importance.
This study is supported by National Natural Science Foundation of China (43/K22431006).

How to cite: Meng, F., Yu, C., and Zeng, X.: A new method for constraining crustal Vp/Vs ratio using P and S wave multiples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7153, https://doi.org/10.5194/egusphere-egu24-7153, 2024.

Knowledge of elastic properties of the Earth's crust provide important constraints on its chemical composition, isostasy and tectonic evolution. However, accurate determination of crustal properties beneath sedimentary basins is challenging. This challenge mainly arises from interference caused by sedimentary reverberations, which may either mask desired signals or cause significant bias in parameter estimates. Some studies attempted to remove the sediment effect by applying wavefield downward continuation or resonance filters to conventional receiver functions, but successful applications were limited. Recently, a novel method utilizing Pn and its multiples, named as PnPn, has been developed and proven effective in imaging the Moho beneath sedimentary basins. Arrival times of Pn multiples are sensitive to crustal thickness (H) and P wave speed (Vp). In contrast, arrival times of converted phases in receiver functions are most sensitive to crustal thickness and Vp/Vs ratio. In this study, we apply a joint analysis of the newly developed Pn multiple method and conventional receiver functions to investigate the sedimentary and crustal structures of the northern Ordos basin along a west-east trending profile. We first apply a multi-frequency receiver function waveform fitting technique to constrain the shallow sediment structure. Then, we combine receiver functions and Pn multiples to determine the thickness, Vp and Vp/Vs ratio of the crystalline crust. Our results show that the interior of the Ordos basin is characterized by thick sediments, with the maximum thickness reaching 4.6 km. The sediment thickness shoals toward the eastern margin of the Ordos basin. The sediment structure in general is consistent with previous findings from active source studies and is of higher resolution than previous passive source studies. For the crystalline crust beneath the northern Ordos basin, the absolute Vp ranges from 6.45 to 6.57 km/s and the Vp/Vs ratio ranges from 1.73 to 1.78. These values suggest an overall intermediate crustal composition beneath the northern Ordos basin, in contrast to felsic crustal composition beneath the eastern North China Craton. The crustal thickness in the interior of the northern Ordos basin is remarkably flat, approximately 40 km, closely aligning with the Airy model. However, a deviation from Airy isostasy of approximately 5 km in crustal thickness is observed at the eastern margin of the Ordos basin, which could be due to increased bulk density of the crust accompanying the thinning of low-density sedimentary layer.

How to cite: Yin, W. and Yu, C.: Sedimentary and crustal structures beneath the northern Ordos basin constrained by receiver functions and Pn multiples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7369, https://doi.org/10.5194/egusphere-egu24-7369, 2024.

EGU24-7989 | Posters on site | GD6.1

Mantle Transition Zone structure beneath the Central and Eastern European region based on P-to-S Receiver Function analysis 

Dániel Kalmár, Konstantinos Michailos, Laura Petrescu, György Hetényi, Götz Bokelmann, and AlpArray and PACASE Working Groups

The depths of mineralogical phase transitions in the mantle (at ~410 and ~660 km depth) offer crucial insights into the thermal conditions of the mantle transition zone and, by extension, the upper mantle's state and circulation. Our approach involves conducting P-to-S receiver function analysis to determine the mantle transition zone's thickness and the absolute depths of the ~410 km and ~660 km discontinuities in the Central and Eastern European region.

Our workflow meticulously attends to each step, starting from data download, quality control, and culminating in the calculation of P-to-S receiver functions. We use data from multiple sources, including the AlpArray and AdriaArray Seismic Networks, the PACASE, Carpathian Basin, and South Carpathian Project temporary seismic networks, as well as the permanent stations of the Hungarian National Seismological network and of the neighboring countries. This analysis covers the time period from 2002 to 2023, involving over 860 seismological stations. Our extensive dataset, consisting of approximately 2 million three-component waveforms and over 120,000 high-quality P-to-S radial receiver functions, coupled with dense piercing-point coverage, allows us to achieve unprecedented resolution.

We present Common Conversion Point cross-sections migrated with a 3D tomographic velocity model underneath the Alps, Carpathians, and the Pannonian Basin. Additionally, we aim to offer new insights into the mantle transition zone's thickness beneath intriguing regions (e.g., Vrancea zone, Alpine Tethys Ocean zone, Eastern Alps–Pannonian Basin transition zone). For a precise understanding of geodynamic processes such as slabs, mantle plumes, and volcanism, it is imperative to accurately map these boundaries.

How to cite: Kalmár, D., Michailos, K., Petrescu, L., Hetényi, G., Bokelmann, G., and Working Groups, A. A. P.: Mantle Transition Zone structure beneath the Central and Eastern European region based on P-to-S Receiver Function analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7989, https://doi.org/10.5194/egusphere-egu24-7989, 2024.

EGU24-8696 | Posters on site | GD6.1

Mapping the Moho in the Bohemian Massif and the Western Carpathians with P-receiver functions 

Hana Kampfová Exnerová, Jaroslava Plomerová, Luděk Vecsey, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

We present the Moho depths in the Bohemian Massif and Western Carpathians derived from P-to-S receiver functions calculated from broad-band P-coda waveforms from teleseismic events recorded at temporary and permanent stations operated in a region within 10–23º E and 47.5–52º N during last two decades. By the Zhu and Kanamori method (2000) and the Ps time delays (Kvapil et al., 2021), we process data collected from running AdriaArray Seismic Network (since 2022), PACASE experiment (2019 – 2022), AlpArray Seismic Network (2015 – 2019) and its complementary experiment AlpArray-EASI (2014 – 2015), as well as from previous passive seismic experiments in the region – BOHEMA I-IV (2001 – 2014), PASSEQ (2006 – 2008) and EgerRift (2007 – 2013). By applying different methods, we aim at upgrading the current knowledge of the crust in the broader surroundings of the European Alps (Michailos et al., 2023), the Pannonian Basin (Kalmar et al., 2019), and the Carpathians. Locally, differences between Moho depth from individual methods could highly exceed 5 km, thus reflecting various sensitivities of individual methods to the local complex structure. An extended amount of data and regionally combined evaluation provide a homogeneous estimate of Moho depths, particularly for the usage in deep Earth studies, e.g., in applying crustal corrections in the upper mantle tomography of Central Europe.

How to cite: Kampfová Exnerová, H., Plomerová, J., Vecsey, L., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: Mapping the Moho in the Bohemian Massif and the Western Carpathians with P-receiver functions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8696, https://doi.org/10.5194/egusphere-egu24-8696, 2024.

EGU24-9487 | ECS | Orals | GD6.1

A new global crust model: ECM24 

Biao Lu, Mark van der Meijde, Islam Fadel, Mirko Reguzzoni, Lorenzo Rossi, Daniele Sampietro, Fabio Cammarano, and Jordi Julia

Despite 160 years of probing the world crust, due to lack of seismic and ground gravity observations, there are still white spots in the worlds' crustal thickness map. The crustal structure in those regions is among the least understood of the Earth's continental areas, and variations in basic but fundamental parameters - such as crustal thickness - are still poorly constrained over large areas. Recent research has shown that satellite gravity-based crustal modeling in regions with limited seismological coverage can provide unique insights in crustal thickness and underlying geodynamical processes.

In almost all of these cases the gravity signal related to crustal structure is isolated by applying 3 different corrections: topography, sediments, and upper mantle structure. Of these three, the upper mantle correction is least well addressed. It doesn’t account for any lateral inhomogeneity upper mantle composition close to the crust-mantle boundary. As a result, satellite gravity data reductions for upper mantle structure are a source of uncertainty.

Our new model includes a new state-of-the-art upper mantle correction. By combining satellite gravity and seismic tomography, we have formulated a new methodology to integrate potential field data inversions, tomographic modelling, and petrolophysics into a single inversion scheme. Our crustal thickness model ECM24 has therefore more accurate crustal thickness values, is seismically fitting better than previous models, and is also very consistent with gravity observations.

How to cite: Lu, B., van der Meijde, M., Fadel, I., Reguzzoni, M., Rossi, L., Sampietro, D., Cammarano, F., and Julia, J.: A new global crust model: ECM24, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9487, https://doi.org/10.5194/egusphere-egu24-9487, 2024.

EGU24-9631 | Posters on site | GD6.1

European and Siberian lithospheric thermo-chemical heterogeneity and density structure. 

Alexey Shulgin and Irina Artemieva

We present a new combined model for the density structure of the lithospheric upper mantle beneath Europe and Siberia, based on a 3D tesseroid gravity modeling. Our results are based on the EuNaRho model (Shulgin & Artemieva, 2019) complimented by similar modeling approach for Siberia. For Siberia modeling is preformed based on a detailed crustal structural database SibCrust (Cherepanova et al., 2013) constrained by regional seismic data. The presented residual lithospheric mantle gravity anomalies are derived by removing the 3D gravitational effect of the crust. Later, these anomalies are converted to lithosphere mantle in situ densities. To evaluate chemical heterogeneities of the lithospheric mantle, thermal effects are removed based on the global continental thermal model TC1 (Artemieva, 2006). The resulting density model at SPT conditions shows a highly heterogeneous structure of the cratonic lithospheric mantle, and distinct change at the transition between different tectonic units. We speculate on the origin of these anomalies.

How to cite: Shulgin, A. and Artemieva, I.: European and Siberian lithospheric thermo-chemical heterogeneity and density structure., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9631, https://doi.org/10.5194/egusphere-egu24-9631, 2024.

EGU24-9813 | Orals | GD6.1

Seismic evidence favoring depletion of Precambrian lithosphere and partial melt at the base of tectonic plates 

Eric Debayle, Yanick Ricard, Durand Stéphanie, and Thomas Bodin

Most global tomographic studies of the upper mantle and their thermochemical interpretations have focused on shear velocity (Vs). Shear attenuation has a different sensitivity to temperature, composition and melt content and therefore provides complementary constraints on the origin of seismic heterogeneities. In the upper mantle, shear attenuation is negligibly dependent on major element chemistry and exponentially dependent on temperature.

Here, we first simultaneously interpret two recent global Vs and Qs models, which are obtained from the same Rayleigh-wave dataset, at the same resolution and using the same modelling approach. Comparison with mineralogical data suggests that partial melt occurs within the LVZ and down to 150–200 km beneath mid-ocean ridges, major hotspots and back-arc regions. A small part of this melt (less than 0.3%) remains trapped within the oceanic LVZ.

Melt is mostly absent under continental regions. In these regions, we observe high seismic velocity keels extending to depths that often exceed 200 km. The thermochemical interpretation of our global shear velocity models requires mineralogical depletion and a decrease of compositional density beneath Precambrian cratons. These conditions ensure their preservation for billions of years in a convective mantle, in agreement with mantle xenoliths suggesting that high viscous keels formed early in the history of cratons.

 

How to cite: Debayle, E., Ricard, Y., Stéphanie, D., and Bodin, T.: Seismic evidence favoring depletion of Precambrian lithosphere and partial melt at the base of tectonic plates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9813, https://doi.org/10.5194/egusphere-egu24-9813, 2024.

EGU24-9864 | Orals | GD6.1

Effects of variations in density and effective viscosity of the mantle lithosphere on the distribution of intraplate earthquakes in western and central Europe  

Judith Bott, Magdalena Scheck-Wenderoth, Ajay Kumar, Mauro Cacace, Sebastian Noe, and Jan Inge Faleide

The distribution of seismicity in intracontinental western and central Europe is not well understood despite evidence for tectonic forces and glacial isostatic adjustments to partially affect local stress and strain relationships. Our region of interest, located between the northern Alpine Deformation Front and the southwestern margin of Fennoscandia, is well differentiated into seismically quiet domains (e.g., most of Ireland, the southern North Sea and the Paris Basin region) and elongated zones of increased seismicity, such as across mainland Britain and the European Cenozoic Rift System. Some inherited zones of crustal weakness have been suggested to control the observed clustering of active deformation, but the majority of earthquakes in the region cannot unequivocally be mapped to specific crustal discontinuities. To investigate potential effects of upper mantle heterogeneities on the lateral distribution of earthquakes across stable western and central Europe, we have derived thermal field variations from a continent-scale tomographic shear-wave velocity model by using a Gibbs's free energy minimization approach. This way we find that seismicity in this intraplate region is largely limited to areas that exhibit a temperature-controlled low-density layer in the uppermost lithospheric mantle and preferentially clustered above large lateral gradients in upper mantle effective viscosity. We propose that the spatial correlations between mantle low-density bodies and crustal seismicity reflect gravitational instabilities due to buoyancy forces within the mantle lithosphere. In addition, lateral contrasts in temperature and related effective viscosity seem to foster localized deformation within the shallow mantle which imposes differential loading of the overlying crust and earthquake clustering.

How to cite: Bott, J., Scheck-Wenderoth, M., Kumar, A., Cacace, M., Noe, S., and Faleide, J. I.: Effects of variations in density and effective viscosity of the mantle lithosphere on the distribution of intraplate earthquakes in western and central Europe , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9864, https://doi.org/10.5194/egusphere-egu24-9864, 2024.

EGU24-11165 | Posters on site | GD6.1

Cratons are not all that stable! 

Hans Thybo

Cratons are usually considered ‘old and stable’ geological units and, therefore, the do not receive as much consideration by geophysical data acquisition as active tectonic regions. However, abundant evidence shows that ‘stable’ cratons are modified substantially during their existence as demonstrated by geophysical data imaging cratonic lithosphere in several cases:

(1) The Baltic Shield formed during the Svecofennian orogeny c. 1.7 Ga and its western parts were reworked by the Sveconorwegian/Grenvillian orogeny. Recent geophysical interpretations image a large body of crustal material in eclogite facies beneath the present Moho in the central shield. This body probably formed after the initial cratonization (Buntin et al., 2021).

(2) The isopycnicity hypothesis proposes that a trade-off between composition and temperature of the lithospheric mantle maintains constant topography in cratons (Jordan, 1978) based on kimberlite data from South Africa. However, gravity data from Siberia shows that kimberlite pipes solely modify cratons in isostatic equilibrium (Artemieva et al., 2019). Therefore, kimberlite sampling is nonrepresentative, and the real composition of most cratonic mantle lithosphere is unknown.

(3) Strong seismic anisotropy is observed in many cratons and is commonly attributed to the mantle due to frozen-in lithospheric features or asthenospheric flow. Recently it was demonstrated that a major part of the anisotropy resides in the crust of the Kalahara craton and that the fast axes are parallel to the strike of major dyke swarms and orogenic fabric (Thybo et al., 2019). This finding indicates significant craton modification by magmatic intrusion.

(4) Modification by external stresses and induced magmatism may even split existing cratons.  Integrated interpretation of existing data and geodynamic modelling show that a linear sequence of volcanic harrats in the Arabian craton potentially represents the formation of a new plate boundary (Artemieva et al., 2022). It is probable that the extension in the northern Red Sea rift will jump to the volcanic lineament, which eventually will develop into new ocean spreading and effectively split the existing craton.

References

Artemieva, I.M.., Thybo, H. & Cherepanova, Y, 2019. Isopycnicity of cratonic mantle restricted to kimberlite provinces. Earth Plan. Sci. Lett. 505, 13-19, doi:10.1016/j.epsl.2018.09.034 (2019).

Artemieva, I.M., Yang, H., Thybo, H. Incipient ocean spreading beneath the Arabian shield, Earth-Science Reviews, 226, 103955 (2022)

Buntin, S., Artemieva, I.M., Malehmir, A., Thybo, H. et al. Long-lived Paleoproterozoic eclogitic lower crust. Nat Commun 12, 6553 (2021).

Jordan, T. Composition and development of the continental tectosphere. Nature 274, 544–548 (1978)

Thybo, H., Youssof, M. & Artemieva, I.M. Southern Africa crustal anisotropy reveals coupled crust-mantle evolution for over 2 billion years. Nat Commun. 10, 5445 (2019)

How to cite: Thybo, H.: Cratons are not all that stable!, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11165, https://doi.org/10.5194/egusphere-egu24-11165, 2024.

Sedimentary and crustal thickness constraints are important for a wide range of geological and geophysical applications, including: a) measuring dynamic topography; b) calculating heat flow; c) generating seismic tomographic models; d) improving predictions of resource distribution; and e) accurately assessing seismic hazards. In this contribution, we present the methodology and preliminary results of an ongoing study to improve sedimentary and crustal thickness constraints in the continental realm. Active-source seismic experiments and well data provide high-accuracy constraints for total sedimentary thickness. Interpolation between sedimentary thickness measurements is undertaken using a minimum curvature gridding algorithm. We investigate the impact of varying the grid resolution across a range of sedimentary basins, and demonstrate that a high-resolution grid (e.g., ~ 0.03 degrees) is crucial in order to capture lateral heterogeneity. We define crustal thickness as the vertical distance between the base of the sediment (i.e. top basement) and the Moho. Our new sedimentary thickness estimates constrain the top basement while measurements from a new publication of active- and passive-source seismic data are used to constrain Moho depth. Resulting crustal thickness estimates show relatively thin crust beneath a number of continental sedimentary basins. We investigate whether our new estimates of sedimentary and crustal thickness can improve predictions of surface heat flow. Our results demonstrate that constraints of the outermost layers of the Earth are important for understanding the interaction between crust, lithosphere and asthenospheric mantle.

How to cite: Holdt, M. and White, N.: Global Sedimentary and Crustal Thickness Constraints: Implications for Lithosphere-Asthenosphere Dynamics., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11624, https://doi.org/10.5194/egusphere-egu24-11624, 2024.

EGU24-12307 | Orals | GD6.1 | Highlight

Broad variability in craton reworking 

Irina M. Artemieva

Cratons are commonly considered as stable parts of continents that can survive a long-term interaction with mantle convective instabilities, basal drag and plate tectonic processes. However, geochemical evidence, geophysical observations and numerical modeling question their long-term stability and suggest heterogeneous modification with possible partial destruction of cratonic lithosphere. Cratonic modification may be identified either from a significant reduction in lithospheric thickness or from densification of cratonic lithospheric mantle e.g. through melt-metasomatism. Both characteristics can be identified through geophysical modeling, such as joint interpretation of thermal and gravity data. The examples from the cratons of Eurasia, South Africa, Greenland and Antarctica demonstrate various degrees of lithosphere reworking by mantle convection and plate tectonics processes. Sharp lithosphere thinning across Greenland possibly marks the Iceland plume passage (10.1016/j.earscirev.2018.10.015) which can hardly be identified from seismic observations (10.1029/2018JB017025). In contrast, the cratonic Siberian LIP region preserves a thick lithosphere, but with a fertile mantle (10.1016/j.epsl.2018.09.034). Similarly thick but fertile lithosphere is present below the southern Africa cratons (10.1016/j.gr.2016.03.002, 10.1016/j.gr.2016.05.002) and in parts of the North China craton (10.1029/2020JB020296), where spatially limited geochemical data have earlier been interpreted as lithosphere destruction by the Mesozoic Pacific plate subduction. Indeed, the lithosphere of West Antarctica has been essentially destroyed by the Mesozoic Phoenix plate subduction, most likely in the back-arc settings (10.1016/j.earscirev.2020.103106). In contrast, the India plate subduction produced heterogeneous pattern in lithosphere thinning below Tibet (10.1029/2022JB026213). Continental regions, typically considered to be stable cratons, may have also essentially lost their cratonic signature, such as cratonic East Antarctica (10.1016/j.earscirev.2022.103954) and the East European craton with strong variations in both lithosphere thickness (10.1016/j.earscirev.2018.11.004) and mantle density (10.1029/2018JB017025). The observed broad variability in the present-day cratonic lithosphere structure precludes unique interpretations of past interactions of the cratons with mantle convection and plate tectonics processes, and indicates the existence of various types and multiple phases of such interactions, controlled by lithosphere rheology.

How to cite: Artemieva, I. M.: Broad variability in craton reworking, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12307, https://doi.org/10.5194/egusphere-egu24-12307, 2024.

EGU24-12342 | Orals | GD6.1

Deformation of Western Anatolia under the effect of the Hellenic Trench and the North Anatolian Fault 

Tülay Kaya-Eken, Akinori Hashima, and Haluk Özener

The Anatolian Plate, surrounded by the Eurasian, African and Arabian plates, represents a great laboratory for geoscientists with its all complicated tectonic settings. The region is located at a widely spread active tectonic deformation zone that has primarily been controlled by the African plate subduction beneath the Hellenic Trench and the movement of the North Anatolian Fault Zone (NAFZ). The effect of crustal thinning due to the extensional regime gave rise to the formations of horst and graben systems leading to large earthquakes (e.g. The Mw7.0 2020 Samos earthquake) with normal faulting mechanisms in western Türkiye. A precise evaluation of tectonic deformation process and the potential seismic risk in this area requires a comprehensive understanding of the quantitative impact of both the Hellenic subduction and the NAFZ to the surface movement. To distinguish these individual contributions, we examine the published regional GPS data along Greece-Türkiye region. Considering a basic elastic-viscoelastic layered earth model, our first step is to estimate the contribution of the NAFZ to the GPS velocity at each station under various average slip rare conditions. We then perform an inversion on the residual velocities obtained by subtracting the calculated velocity from the observed data. This inversion allows us to derive the subduction rate along the Hellenic Trench. Our modelling indicates an optimal slip rate of <35 mm/yr that identifies the NAF zone and an average subduction rate of about 40 mm/yr for the the Hellenic Trench. These results suggest the significance of both the Hellenic Trench slab rollback and the NAFZ movement highlighting their essential roles in the observed deformation beneath this region.

How to cite: Kaya-Eken, T., Hashima, A., and Özener, H.: Deformation of Western Anatolia under the effect of the Hellenic Trench and the North Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12342, https://doi.org/10.5194/egusphere-egu24-12342, 2024.

EGU24-13677 | Posters on site | GD6.1

Lithospheric Structure beneath Northeastern Tibet Plateau and Sichuan Basin revealed by S-Receiver Function Imaging  

Yaoyang Zhang, Ling Chen, Yinshuang Ai, Hui Fang, and Gang Wang

    Based on the seismic data of 60 portable stations and 90 permanent CEA stations in the northeastern Tibet Plateau and adjacent regions, we utilized the wave equation post-stack migration method of S-receiver function to image the lithospheric structure of northeastern Tibet Plateau and the Sichuan Basin.

Fig. 1 Distribution of the seismic stations and imaging profile

    The imaging results show that the Moho in the northeastern Tibet Plateau is deeper than 50 km, and it gradually becomes shallow along the profile to the southeast until reaches about 45 km below the Sichuan Basin. The negative anomaly signals corresponding to the Lithosphere and Austhenosphee Boundry (LAB) are obvious in most areas, but under the Sichuan Basin, there are many strong negative anomaly signals in the migration images of different frequencies. In general, the LAB along the profile is undulating and discontinuous: The lithosphere is deeper in the southern Qilian Orogenic Belt, up to ~200 km, with no significant change at the boundary between the Qilian Orogenic Belt and the western Qinling Orogenic Belt. The lithosphere gradually thinned to ~150 km beneath the western Qinling Orogenic Belt, with a step of ~100 km at the tectonic boundary between the Qinling Orogenic Belt and the Songpan-Garze block, and the signal intensity is obviously weakened. LAB was maintained at this depth level until near the Longmenshan Fault, and the lithosphere thickened again to ~190 km after entering the Sichuan Basin. Moreover, there are two discontinuities within the lithosphere of the Sichuan Basin, with depths of ~100 km and ~140 km, respectively, and the latter becomes shallower to ~110 km in the western margin of the Sichuan Basin. Our observations of mid-lithospherci discontinuity (MLD) beneath the Sichuan Basin provide further evidence that the cratonic lithospheric mantle is generally stratified.

Fig. 2 The migration results of the profile

    It is proposed that the lithospheric thinning along the eastern margin of the Songpan-Garze Block may be related to the eastward flow of hot mantle materials beneath the eastern Tibet Plateau. Blocked by the Ordos block and the Sichuan Basin, which have preserved the ancient and rigid craton roots, the eastward flow of mantle materials from the Tibet Plateau will turn to the west of the two blocks. A small part of the blocked mantle material migrates eastward to the Qinling Orogenic Belt, while most of it migrates southward clockwise along the mantle flow path to the west of the Sichuan Basin. The lithosphere in the eastern margin of the Songpan-Garze block, heated by the mantle flow, will be subjected to thermochemical erosion and destruction in the process of collision with the Yangtze craton, and is more likely to be delaminated, resulting in significant thinning and destruction under long-term action.

How to cite: Zhang, Y., Chen, L., Ai, Y., Fang, H., and Wang, G.: Lithospheric Structure beneath Northeastern Tibet Plateau and Sichuan Basin revealed by S-Receiver Function Imaging , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13677, https://doi.org/10.5194/egusphere-egu24-13677, 2024.

EGU24-14107 | ECS | Orals | GD6.1

Deformation of the northeastern Tibetan Plateau and adjacent areas: Evidence from MT array data 

Haoxiang Yin, Sheng Jin, and Gaofeng Ye*

The uplift and growth of the Tibetan Plateau is an essential geologic issue. The closure of the Neo-Tethys Ocean and northward subduction of the Indian Plate formed the Tibetan Plateau and influenced the strain on its northeastern margin. We obtained the lithospheric electrical structure by inversion of MT array data collected at the Alxa and Ordos blocks neighboring the northeastern Tibetan Plateau. It shows the Ordos Block has noticeable electrical differences between the north and south parts. The northern lower crust to the upper mantle characterized large-scale low-resistivity anomaly, while the south is a stable craton block. The retreat of the Paleo-Pacific Plate caused the North China Craton to be in a tensional environment. With the northward subduction of the Indian lithosphere, the Tibetan Plateau continues to grow in a northeastern direction, resulting in an intensification of the subduction of the Alxa Block to the Ordos Block, and the north Ordos Block was pried up and in a weak state. The Asian asthenosphere became active under the influence of Indian lithospheric subduction. It jumped over the rigid Alxa and southern Ordos blocks to deform the northern part of the Ordos Block and form the large-scale partial melting. Since partial melt is more viscous than rigid blocks, it better equilibrates crustal deformation, resulting in flatter topography.

How to cite: Yin, H., Jin, S., and Ye*, G.: Deformation of the northeastern Tibetan Plateau and adjacent areas: Evidence from MT array data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14107, https://doi.org/10.5194/egusphere-egu24-14107, 2024.

The thermal state of the Earth’s interior is a key factor in controlling various geological processes. However, our knowledge of the geotherm and its temporal and spatial variability is usually poorly constrained, as it is typically based on point-wise data. Specifically, for the lower continental crust (LCC), data on rock’s thermal properties are scarce, and therefore temperature estimates are uncertain.

 

We collect new data and provide new insights in this domain, realized in the frame of project DIVE (Drilling the Ivrea-Verbano zonE; www.dive2ivrea.org), which aims at a better understanding of the physical and chemical evolution and formation of the LCC. The first borehole in Ornavasso (DT-1B) has been successfully completed and reached a depth of 578.5 m with 100% core recovery; it provides continuous drill cores of mainly felsic metasedimentary and metamafic lithologies. The second borehole in Megolo di Mezzo (DT-1A) is ongoing and planned to be completed in Spring 2024.

 

The first results on the thermal characterization of lower crustal rocks are based on 17 fresh cores from DT-1B, sampling all the lithologies present in the borehole. We performed continuous, high-resolution (2 mm) thermal conductivity (TC) measurements using an Optical TC Scanner (Popov et al., 1999), profiling over 10 metres of rock cores in total. Our results show that TC can exhibit large variations even within a given lithology, as a result of mineralogical variability, indicating that this approach provides more representative results compared to conventional methods (e.g. needle-probe technique). We also measured the concentrations of heat producing elements (U, Th, K) using powder-based gamma spectrometry, and use (spectral) gamma borehole logs to evaluate the variability of heat production (A) in the borehole. The correlation of both TC and A with other petrophysical properties is analyzed.

 

Based on the new measurements, we investigate the consequences on LCC geotherms. The small-scale TC variations affect heat flow calculations and have implications for their uncertainty. These are quantified through model calculations as part of an upscaling procedure employing harmonic averaging. We aim to quantify the effect of continuous TC profiling and how our approach influences the level of uncertainties by applying many realizations of heat flow calculations. The probability distribution of heat flow can be determined by using Bullard’s approach (Bullard 1939; Beardsmore & Cull, 2001) and by randomly selecting rock’s thermal property data while calculating the geotherm. Further samples from DT-1B and a new set of samples from DT-1A will provide a representative dataset for the LCC.

 

 

References

 

Beardsmore, G. R. (Graeme R., & Cull, J. P. (James P. (2001). Crustal heat flow: a guide to measurement and modelling. Cambridge University Press.

 

Bullard, R. (1939). Heat flow in South Africa. Mon. Not. R. Astr. Soc., Geophys, 173, 229–248.

 

Popov, Y. A., Pribnow, D. C., Sass, J. H., Williams, C. F., & Burkhardt, H. (1999). Characterization of rock thermal conductivity by high-resolution optical scanning. Geothermics, 28(2), 253–276.

How to cite: Lemke, K. and Hetényi, G.: Thermal characterization of the lower continental crust: first results from the DT-1B borehole of project DIVE (Ivrea-Verbano zone, Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14356, https://doi.org/10.5194/egusphere-egu24-14356, 2024.

EGU24-14363 | Posters on site | GD6.1

Crustal S-wave 3D azimuthal anisotropy beneath the southern Sichuan-Yunnan block of SW China from multiple seismic arrays 

Yuan Gao, Ying Li, Huajian Yao, Jianhui Tian, Yuanyuan V Fu, and Qiong Wang

The southern Sichuan-Yunnan block (SYB) is intersected by the NW-striking Honghe faults (HHF) and the nearly NS-trending Xiaojiang faults (XJF), providing an excellent zone for exploring severe crustal deformation and complicated tectonic movement. However, the crustal-mantle deformation mechanisms are still controversial, partially due to the lack of detailed information. With ambient noise data from several temporary seismic arrays and regional permanent seismic stations, we applied the direct surface wave tomography to obtain S-wave velocity and azimuthal anisotropy simultaneously. The crustal S-wave structures show complex heterogeneity both horizontally and vertically, relating to geologic settings and large faults. In the mid-lower crust, there are two significant low-velocity anomalies with strong azimuthal anisotropy, with the NNW-SSE direction near the northwest end of HHF and the NE-SW direction around the mid-south segment of XJF, respectively. The fast axis within the SYB shows approximately in the N-S direction, which differs from those in the low-velocity zones on its east and west sides. Therefore, we consider the ductile deformation in the mid-lower crust is more likely restricted by large faults. At the end of the wedged intersection, the southward mid-lower crustal flow could be blocked by the HHF, resulting in the weak materials distributed along the faults rather than crossing over at large-scale. Combining other independent studies, we conclude that there may be different deformation between the crust and the lithospheric mantle. This 3-D model provides important constraints for the regional deformations and plate tectonics of the large boundary faults [supported by NSFC Projects 42074065 & 41730212].

How to cite: Gao, Y., Li, Y., Yao, H., Tian, J., Fu, Y. V., and Wang, Q.: Crustal S-wave 3D azimuthal anisotropy beneath the southern Sichuan-Yunnan block of SW China from multiple seismic arrays, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14363, https://doi.org/10.5194/egusphere-egu24-14363, 2024.

EGU24-15642 | Posters on site | GD6.1

Tectono-metamorphic interaction between the upper mantle and lower crust during continental rifting in the western Betic Cordillera 

Károly Hidas, Juan Díaz-Alvarado, Luis González-Menéndez, Antonio Azor, and Antonio Pedrera

Recent geological mapping in the Ronda peridotites (Betic Cordillera, S Spain) has unveiled a consistent field correlation between lower crustal metamorphic units and specific tectono-metamorphic domains of the ultramafic massif. Mylonitic and highly tectonized spinel ±garnet peridotites (i.e., Grt-Spl mylonite and Spl tectonite domains) –that are considered to originate from a thick continental lithosphere– are in contact with garnet-bearing gneisses (i.e., kinzigites of the Jubrique unit) along a narrow but continuous mylonitic shear zone. Phase equilibrium calculations indicate that these metamorphic rocks align with an initial continental setting characterized by normal crustal thicknesses, which underwent two melting events. The first melting occurred at the base of the lower crust, while the second one took place at shallower crustal conditions and led to a more restricted melt production. By contrast, the spinel ±plagioclase peridotites (i.e., Pl-tectonite domain) –that are stable only at shallowest mantle levels within a highly extended continental lithosphere– are consistently found exposed in contact with heterogeneous granites and migmatites that form part of the Guadaiza crustal unit. According to new thermodynamic modeling, this migmatitic series record a single melting event characterized by a moderate melt production at the base of an extremely thin continental crust. The systematic correlation observed between the crustal metamorphic units and specific ultramafic domains of the Ronda peridotites –consistently overlaying the mantle rocks– indicates that their juxtaposition primarily resulted from the severe extension of the continental lithosphere.

Previous and new U-Pb radiometric dating of zircons from gneisses, migmatites, and heterogeneous granites show that extensional processes, crustal anatexis, and melt stagnation occurred at around 280 Ma. Considering the structural position and correlation between mantle and crustal rocks, these radiometric ages suggest that a Permian high-temperature / low- to medium-pressure event uniformly affected the crustal units over the Ronda peridotites. This event coincided with the formation of characteristic ultramafic mineral assemblages in the Ronda massif, providing evidence for the interaction between upper mantle rocks and lower- to mid-crustal metamorphic rocks during that period.

This research received funding from the Agencia Estatal de Investigación of the Ministerio de Ciencia e Innovación (AEI, MICINN, Spain) under the grant no. PID2020-119651RB-I00/AEI/10.13039/501100011033.

How to cite: Hidas, K., Díaz-Alvarado, J., González-Menéndez, L., Azor, A., and Pedrera, A.: Tectono-metamorphic interaction between the upper mantle and lower crust during continental rifting in the western Betic Cordillera, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15642, https://doi.org/10.5194/egusphere-egu24-15642, 2024.

EGU24-17843 | Orals | GD6.1

Detached Tonga slab in the mantle transition zone imaged by stress variations of deep-focus earthquakes 

Pavla Hrubcová, Ghazaal Rastjoo, and Václav Vavryčuk

Tonga is a part of Tonga-Kermadec, the 2,550 km long subduction system in SW Pacific. It represents a convergent plate boundary and the outcome of the Pacific plate submerging underneath the Australian plate. The Tonga slab subducts steeply into the mantle and is the fastest converging and the most seismically active deep subduction system in the world. In the mantle transition zone, especially at depths greater than 500 km, the geometry of the slab becomes complex, forming separated slab segments. Moreover, it undergoes strong deformation and sharp bending in the north, which results in significantly different course of the southern and northern Tonga slab.

We focused on the mantle transition zone in the southern part of Tonga (south of latitude 22°S). We performed stress analysis by inverting focal mechanisms of deep earthquakes available in the Global Centroid Moment Tensor catalog. We focused on depths ranging from 400 to 680 km, where seismic activity forms two subparallel bands of events, in the west and east. We revealed two distinct stress regimes that characterize this deep Tonga double seismic zone and distinguish two slab segments. The stress orientation in the eastern slab segment matches the down-dip compressional stress regime of the subducting slab. However, the stress orientation of the western slab segment is different, with the maximum compression in the vertical direction. This suggests that the western slab segment is no longer connected to the subducting slab. Such findings are also supported by the horizontal westward detachment of the western slab segment at 520 km depth and by substantially different fault orientations in both slab segments. This points not only to the retention of the southern Tonga slab in the mantle transition zone but also to its detachment at the base of the upper mantle with a remnant slab no longer connected to the younger actively subducting slab.

How to cite: Hrubcová, P., Rastjoo, G., and Vavryčuk, V.: Detached Tonga slab in the mantle transition zone imaged by stress variations of deep-focus earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17843, https://doi.org/10.5194/egusphere-egu24-17843, 2024.

EGU24-17947 | ECS | Posters on site | GD6.1

Multi-scale Potential Field Modelling to Delineate the Lithosphere Structure below the Eastern Indian Shield and its Tectonic Implications   

Sumanta Kumar Sathapathy, Munukutla Radhakrishna, and Yellalacheruvu Giri

The Precambrian terrains of the Eastern Indian Shield (EIS) comprise of Bundelkhand, Singhbhum, and Bastar cratons with intervening Proterozoic mobile belts such as Central Indian Tectonic Zone, Eastern Ghat Mobile Belt, Singhbhum Mobile Belt and Chotanagpur Granite Gneissic Complex. This region is also characterised by the presence of Proterozoic Mahanadi Rift, Chhattisgarh and Vindhyan Basins with significant coverage of Indo-Gangetic Plain sediments in northern part. In this study, we present the results of a seismically well-constrained 2-D multi-scale geopotential modelling to delineate lithosphere structure across different Precambrian terrains of the EIS. The joint interpretation of the potential field data reveals that i) mobile belts are bounded by the deep crustal faults with denser crust, ii) presence of thick underplated crust below Singhbhum craton, Singhbhum Mobile Belt, Chotanagpur Granite Gneissic Complex and the surrounding rift basin, iii) localised Moho upwarp at a depth of ~36-37 km below the Proterozoic basins, iv) the Lithosphere-Asthenosphere Boundary (LAB) varying between 90-200 km below the EIS region. The distinct crustal structure along with relatively deeper LAB (130-200 km) below the mobile belts suggests the Proterozoic amalgamation and lithosphere reworking. Below the Singhbhum craton, LAB is observed at a depth of ~145-155 km, which is comparatively thinner with respect to other cratonic areas elsewhere. The observed crustal underplating and thinner LAB below the Singhbhum craton indicate the lithosphere erosion and magmatic upwelling caused by the major Paleo-Mesoproterozoic and early- Cretaceous Large Igneous Province (LIP) events.  

How to cite: Sathapathy, S. K., Radhakrishna, M., and Giri, Y.: Multi-scale Potential Field Modelling to Delineate the Lithosphere Structure below the Eastern Indian Shield and its Tectonic Implications  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17947, https://doi.org/10.5194/egusphere-egu24-17947, 2024.

EGU24-18927 | Orals | GD6.1

Crustal Structure of the Lofoten Shelf, NE North Atlantic,along the Silver-Road refraction profile 

Metin Kahraman, Hans Thybo, Irina Artemieva, Alexey Shulgin, Peter Hedin, and Rolf Mjelde

The Lofoten continental shelf is located at the edge of the Baltic Shield in the northeastern North Atlantic Ocean. It was formed during continental break up in early Eocene associated with intense magmatism, leading to large intrusions and basaltic volcanic rocks now hidden below Cenozoic sediments. The Lofoten shelf is relatively narrow.

We present results of ray tracing model of seismic refraction/wide-angle reflection data along the offshore Silver Road profile across the Lofoten Shelf at the northeastern Baltic Shield. The ~300km long WNW/ESE trending offshore section between 63oN and 71oN profile is perpendicular to the coastline and extends a ~300km onshore section. Wide-angle seismic data obtained from air gun shots from the vessel Hakon Mosby along the whole offshore profile were recorded by 16 ocean bottom seismometers on the shelf, slope and oceanic environment as well as by 270 onshore seismic stations.

The new offshore crustal velocity - depth model covers the anomalous and heterogeneous transition from shelf to oceanic lithosphere around the North Atlantic Ocean. The results will test existence of crustal root and magmatic intrusions along the offshore profile.

How to cite: Kahraman, M., Thybo, H., Artemieva, I., Shulgin, A., Hedin, P., and Mjelde, R.: Crustal Structure of the Lofoten Shelf, NE North Atlantic,along the Silver-Road refraction profile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18927, https://doi.org/10.5194/egusphere-egu24-18927, 2024.

This study employs gravity modelling to investigate the subsurface geometry of a pull-apart basin located in Elazığ, Turkey. The study area is situated along the East Anatolian Fault Zone—a major active system that recently produced two devastating M7.0+ earthquakes at Kahramanmaraş in February 6, 2023.

Recently collected gravity data, comprising approximately 600 data points from Sivrice and Gezin provinces, form the basis of our investigation. Preliminary examinations show that the gravity anomalies in Gezin are notably lower than those in Sivrice, suggesting a deeper basement for the former. We aimed to estimate the subsurface model using a proprietary computer program. Given the known different geological units with constant density contrasts, the program was employed to deduce their geometry up to a maximum depth of 350 meters in 2D. A total of 16 sections were modeled—8 each for Sivrice and Gezin provinces—yielding RMS values consistently below 0.1 mGals. Next, quasi-3D and 3D models were prepared for Talwani models at Sivrice and Gezin. We assumed the geometry beneath Lake Hazar to be similar to the bathymetry of the lake, assigning sediment thickness to estimate the basement in this part. The individual models were then integrated into a full 3D representation of the geometry of the basin.

Our findings suggest that the pull-apart basin situated here is in its extinction phase, with pull-apart tectonics no longer active, and only strike-slip movement along main East Anatolian Fault is observed. Notably, slips along the main fault have impacted the basement geometry. This study contributes valuable insights into the current state of the basin, emphasizing the importance of 3D modelling in unraveling the complexities of pull-apart basins.

How to cite: Aydın, N. G. and İşseven, T.: Gravity Modelling of a Pull-Apart Basin in Elazığ, Turkey: Unraveling the 3D Basement Geometry (Preliminary Results), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-397, https://doi.org/10.5194/egusphere-egu24-397, 2024.

EGU24-1294 | Posters on site | G4.3

Voxel-based Density Models for Accurate Gravitational Field Computation 

Benjamin Haser, Thomas Andert, and Roger Förstner

Asteroids and moons are promising targets for physical space exploration. The use of physically-based simulations within a virtual environment for (deep) space missions can significantly benefit the testing and validation of guidance, navigation, and control algorithms. This approach offers advantages in terms of cost and time efficiency. Especially for orbit propagation and landing maneuvers, information about the gravitational field is crucial. However, several factors contribute to the complexity of this task, such as limited information available about the inner structure of celestial bodies. The lack of detailed knowledge about their shapes further adds to the challenge.

This study presents a voxel-based mass concentration (MASCON) method to model detailed and realistic density distributions, enabling accurate gravity field determinations. We chose a cube with constant density as first case due to the perfect shape reconstruction and the availability of an analytical solution for its gravity field. To validate our results, we calculated the surface gravity and compared it with the analytical solution, ensuring the accuracy of our calculations. Furthermore, the surface gravity is derived for different resolutions and compared against other state-of-the-art methods like the polyhedral method that provides a closed-form analytical solution of the gravity field for homogeneous density. The other two methods for validation also use a MASCON approach, one utilizing polydisperse sphere packing and another with MASCON represented in spherical coordinates. The relative errors of the gravitational acceleration between the four methods will be evaluated for a cube and sphere, with homogeneous density.

The second aspect of this study was to create a tool that generates realistic density distributions. We are able to successfully reproduce natural environments by placing body-specific restrictions on three-dimensional Perlin noise with additional normalization. The simulator can add the following structural features to the density distribution: an arbitrary number of centralized or decentralized shells, with varying thickness and densities, anomalies of arbitrary size and shape, only restricted by its maximum permille of the body's volume. Furthermore, we implemented different normalization techniques to keep the mass of all generated bodies fixed. Our results show that the tool can generate realistic density distributions and calculate the corresponding gravitational field correctly. The data generated here is used to train Machine Learning and Deep Learning algorithms for gravity inversion.

 

How to cite: Haser, B., Andert, T., and Förstner, R.: Voxel-based Density Models for Accurate Gravitational Field Computation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1294, https://doi.org/10.5194/egusphere-egu24-1294, 2024.

Precise determination of Moho topography holds paramount importance in advancing our comprehension of Earth's structural characteristics, geodynamic phenomena, and the exploration of resources. This study introduces an innovative methodology employing conditional Generative Adversarial Networks (cGAN) to unveil Moho topographies from observed gravity anomalies. To address the scarcity of real Moho datasets for training the cGAN model, we meticulously generated a comprehensive set of quasi-realistic synthetic training data using the FFT filtering technique. The forward estimation of gravity anomalies, arising from synthetic Moho topographies, was assessed through spherical prism-based gravity modeling. These estimated anomalies served as input data for the training of the cGAN model. For evaluating the efficacy of our developed cGAN algorithm in deriving Moho architecture, we conducted a comparative analysis against a conventional inversion scheme. This assessment utilized various synthetic datasets and a real case study in Southern Peninsular India, renowned for its geological diversity and ancient continental tectonic blocks. The established Bott's inversion scheme was employed as a benchmark to validate the Moho surface estimation obtained through the Deep Learning approach. To mitigate the impact of diverse factors such as topography, bathymetry, sediments, crustal and mantle heterogeneities, observed gravity anomalies underwent meticulous corrections using spherical prism-based forward gravity modeling for real case studies. The gravity contribution exclusively associated with the pure Moho was subsequently inverted using both the cGAN and traditional Bott's inversion schemes. Crucial hyperparameters, including the mean Moho depth and density contrast between the crust and mantle, were determined by utilizing seismic constraints. Our results underscore the potential of the cGAN and spherical prism-based gravity modeling approach in accurately predicting Moho topography. This study provides valuable insights into high-resolution Earth's Moho architecture and contributes to advancing our understanding of geodynamic processes, facilitating resource exploration endeavours with reduced computational demands.

How to cite: Roy, A., Sharma, R. K., Jash, D., and Kallukalam, T. J.: Innovative Insights into Earth's Interior: Moho Topography Estimation using Conditional Generative Adversarial Networks from Observed Gravity Anomalies , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1405, https://doi.org/10.5194/egusphere-egu24-1405, 2024.

EGU24-2837 | ECS | Orals | G4.3

Joint inversion of airborne gravity and magnetic data for the crustal structure in central Dronning Maud Land 

Mikhail Ginga, Jörg Ebbing, Antonia Stefanie Ruppel, Andreas Läufer, and Graeme Eagles

Topography and physical conditions at the base of the Antarctic ice sheet are critical inputs for studies of its present and future ice discharge, and of subglacial geology and hydrology. Airborne gravity and magnetic data, especially when interpreted jointly can help us to link the geology from outcrops towards the coastal areas to unknown subglacial regions further inland. Here we use airborne geophysical data obtained during the joint AWI-BGR campaign WEGAS/GEA between 2015 and 2017 in central Dronning Maud Land (DML) as input for a novel joint inversion scheme. With regard to Gondwana reconstruction, this region is critical because it hosts the ice-covered Forster Magnetic Anomaly, a prominent lineament crossing central DML for some 100s of kilometers south of the main mountain chain. This lineament, originally interpreted as the main pan-African suture of East and West Gondwana, likely represents the eastern margin of Kalahari and its boundary to the Tonian Oceanic Arc Super Terrane (TOAST). In the inversion using the software jif3D, sources of the gravity and magnetic field are combined through a coupling method which decreases the variation of information (VI), so data misfit and model dissimilarity are minimized simultaneously. The model results can be classified in geologically meaningful provinces by applying cluster analysis based on machine learning. Our joint inversion approach improves previous interpretations and sheds light on the crustal architecture of the study area, contributing to further studies on the interaction between the ice sheet and the underlying solid earth.

How to cite: Ginga, M., Ebbing, J., Ruppel, A. S., Läufer, A., and Eagles, G.: Joint inversion of airborne gravity and magnetic data for the crustal structure in central Dronning Maud Land, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2837, https://doi.org/10.5194/egusphere-egu24-2837, 2024.

In Western Europe, the Variscan belt contacts Avalonia along the Rhenohercynian Suture, a result of Early Carboniferous continental collision. Moving east of the Harz Mts., the Rhenohercynian suture disappears beneath a thick sedimentary sequence of the Permian-Mesozoic basin. Its extension is either truncated by major NW-SE strike-slip faults like the Elbe, Odra, or Dolsk faults or bends under the cover of a thick sedimentary succession. The extension of Avalonia into Poland is challenging to determine, with the thinned margin of Baltica considered the substratum of the Permian-Mesozoic basin. Deep seismic soundings show that the thinned margin of Baltica reaches the NW-SE oriented Dolsk or Odra fault, potentially bringing the crust of Baltica into direct contact with the crust of the Variscan internides of the Bohemian Massif. Along the Dolsk fault, there is the two-layered, low-velocity Variscan crust in the SW that contacts the three-layered Baltica crust. The geometry of this contact remains unknown, but the lower, high-velocity crust of Baltica may extend southwest to the Odra fault. In the basement of the sedimentary sequence between the Dolsk and Odra faults, low-grade metamorphosed phyllites with a metamorphic age of approximately 360 Ma are found. They apparently represent a fragment of Variscan metamorphic nappes.

The Variscan front is oriented NE-SW in Western Europe, but in Poland, it bends by 90° to the NW-SE direction, continuing to the border of Ukraine. In southeastern Poland, the front enters the slope of the East European Platform, constituting an undisputed example of a direct contact between the Variscan belt and Baltica. If the geometry of the Variscan front reflects the structure of the orogen, the edge of Baltica must have initially played the role of a transform margin with a right-lateral displacement. NW-SE strike-slip faults, parallel to this margin, truncated the Rhenohercynian and other Variscan sutures from the NE. The following accretion event resulted in NE-SW shortening, either thin-skinned, leading to folding of the external fold-and-thrust belt, or thick-skinned, resulting in the emplacement of the Variscan nappe stack on the Baltica margin.

The last folding of external Variscides in Poland occurred around 305 Ma and was immediately followed by the emplacement of a large igneous province at the Carboniferous to Permian transition. The centre of magmatism was in NE Germany, the area of greatest crustal thinning. The origin of the igneous province was linked to plate boundary forces leading to extension and continental rifting. The latter produced the Mid-Polish trough, an elongated continental rift running NW-SE parallel to the Teisseyre-Tornquist zone. Permian rifting further attenuated the Baltica margin and, jointly with coeval magmatism, reshaped the margin of Baltica masking its contact with the Variscan belt. Toward the east, the continuity of the Variscan internides was disrupted by early Mesozoic rifting in the area of the present-day Carpathians.

How to cite: Mazur, S.: From Carboniferous convergence to Permian continental rifting – the interaction of Baltica with the Variscan belt of Europe at the time of the Pangaea assembly, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4560, https://doi.org/10.5194/egusphere-egu24-4560, 2024.

The South China Sea, situated at the convergence of the Tethys and Pacific tectonic domains, holds immense geological significance due to its interaction with multiple tectonic plates (Hall 2002; Hayes and Nissen 2005; Metcalfe 2011). With its abundant sedimentary basins, the region is of paramount importance for geological and structural studies, particularly in relation to its potential for oil and gas resources. In this study, we propose the utilization of satellite gravity data to analyze the tectonic structure of the South China Sea, focusing on three key areas:

1. High-resolution construction of gravity gradient anomalies and fault identification: By integrating Fast Fourier Transform algorithms with satellite gravity anomalies and high-resolution terrain elevation data, we obtaina comprehensive dataset of full tensor gravity gradient information. Through spatial analysis of this data, we successfully identify 17 significant and deep faults, as well as partition the study area into 9 distinct tectonic units characterized by well-defined geological structures.

2. Moho Depth Determination and Interpretation: Employing an improved regularization Bott's method, we determine the Moho depth using information obtained from sonar-buoy detection and submarine seismograph detection profiles. Regularization parameters are introduced to ensure the smoothness of the inversion results. By analyzing the distribution characteristics of the Moho and its relationship with tectonic units, we conduct a comprehensive analysis to comprehend the coupling between shallow and deep structures. The resultsreveal distinct regional characteristics in the depth distribution of the Moho surface in the South China Sea, shedding light on the distribution of continental crust, oceanic crust, and the ocean-continent transition zone.

3. Comprehensive Geophysical Analysis: We employ a combination of seismically constrained Moho undulation, gravity data, gravity gradient anomalies, and unconstrained 3D correlation imaging to investigate the crustal structure of the South China Sea. Integrating various geophysical datasets, we gain a deeper understanding of the distribution of continental crust, oceanic crust, and transitional crust within the region. Notably, the results shows that the trench-island arc-back arc basin systemplays a pivotal role in the active continental margin of the Western Pacific. This comprehensive analysis provides valuable insights into the tectonic dynamics and geological processes occurring in the South China Sea region.

*This study was supported by y the Basic Frontier Science Research Program of the Chinese Academy of Sciences (No. ZDBS-LY-DQC028).

Reference:

Hall, R. (2002). Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations, J. Asian Earth Sci. 20:353–431.

Hayes, D.E., Nissen, S.S. (2005). The South China Sea margins: implications for rifting contrasts, Earth Planet Sci. Lett., 237: 601–616.

Metcalfe, I. (2011). Tectonic framework and phanerozoic evolution of Sundaland, Gondwana Res., 19 (1): 3–21.

How to cite: Guo, D.: Constrained Gravity Inversion for the Moho Depth and Tectonic Patterns in South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4845, https://doi.org/10.5194/egusphere-egu24-4845, 2024.

EGU24-6228 | Posters on site | G4.3

Harnessing Modern 3D Gravity Analysis Techniques: A Study of the Ligurian Offshore Area 

Hans-Jürgen Götze, Ronja Strehlau, Denis Anikiev, Anke Dannowski, and Magdalena Scheck-Wenderoth

This interdisciplinary study describes the integration of gravity field analysis, curvature techniques and various spatial applications. The data are based on land-based Free Air and Bouguer gravity data from the AlpArray Gravity Research Group, complemented by recent satellite missions. New seismic and seismological data from the AlpArray initiative and the German MB-4D Priority Program were used as independent boundary conditions for the 3D modeling and inversion of the gravity data. Prior to this modeling, Euler deconvolution, terracing/clustering techniques, and advanced filtering methods were employed to reveal intricate details of the region's gravitational signatures. For example, a distinct zoning of gravity is observed in the central part of the Ligurian Sea, pointing to traces of past rifting processes. Analysis of various curvature parameters (e.g., dip-, min-, max- and shape-curvature) of the processed gravity fields, in particular gradients and residual fields support the identified zonation of the gravity fields, which reflect the geological structures in the crust. The final 3D modeling of the Ligurian Sea area is based on a previous density model of the entire Alpine region and includes density distribution of the upper mantle. These densities were derived from tomographic velocity models, accounting for petrology, temperature, and pressure. Additional information of the upper crust was obtained from the refraction seismic results of the LOBSTER project, offering a comprehensive understanding of spatial phenomena. Calculations of the gravitational potential energy (GPE) provide additional information on local stresses, facilitating a deeper understanding of the flexural rigidity in the area. By elucidating the relationship between processing techniques and 3D modeling, this work advances interdisciplinary interpretation crucial for geological studies in the Ligurian offshore area.

How to cite: Götze, H.-J., Strehlau, R., Anikiev, D., Dannowski, A., and Scheck-Wenderoth, M.: Harnessing Modern 3D Gravity Analysis Techniques: A Study of the Ligurian Offshore Area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6228, https://doi.org/10.5194/egusphere-egu24-6228, 2024.

EGU24-6402 | Posters on site | G4.3

Participative gravity-modelling challenge to constrain the Balmuccia peridotite body (Ivrea-Verbano Zone, Italy) 

György Hetényi, Ludovic Baron, Matteo Scarponi, Shiba Subedi, Konstantinos Michailos, Fergus Dal, Anna Gerle, Benoît Petri, Jodok Zwahlen, Antonio Langone, Andrew Greenwood, Luca Ziberna, Mattia Pistone, Alberto Zanetti, and Othmar Müntener

The Balmuccia peridotite exposes relatively fresh mantle rocks at the Earth’s surface, and as such it is of interest for geologists and geophysicists. The outcrop is a kilometre-scale feature, yet its extent at depth is insufficiently imaged. Our aim is to provide new constraints on the shape of the density anomaly this body represents, through 3D gravity modelling. In an effort to avoid personal or methodology bias, we hereby launch an invitation and call for participative modelling. We openly provide all the necessary input data: pre-processed gravity data, geological map, in situ rock densities, and digital elevation model. The expected inversion results will be compared and jointly analysed with all participants. This approach should allow us to conclude on the shape of the Balmuccia peridotite body and the associated uncertainty. This crowd effort will contribute to the site surveys preparing a scientific borehole in the area in frame of project DIVE. The full description, the dataset, as well as the tentative timeline can be found at https://zenodo.org/records/10390437

How to cite: Hetényi, G., Baron, L., Scarponi, M., Subedi, S., Michailos, K., Dal, F., Gerle, A., Petri, B., Zwahlen, J., Langone, A., Greenwood, A., Ziberna, L., Pistone, M., Zanetti, A., and Müntener, O.: Participative gravity-modelling challenge to constrain the Balmuccia peridotite body (Ivrea-Verbano Zone, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6402, https://doi.org/10.5194/egusphere-egu24-6402, 2024.

Coseismic gravity changes provide significant information for the study of the mechanisms of large earthquakes and for developing fault models (Sun, 2012). In this research,  coseismic gravity changes of the 2008 Ms8.0 Wenchuan earthquake in China were studied by using gravity observation data and simulation based on a fault model.

Firstly, a fine processing of relative and absolute gravity data from the Longmenshan Gravimetric Network was carried out and observed gravity change of 22 stations near this earthquake were obtained; Secondly ,simulation of coseismic gravity changes was conducted based on half-space dislocation theory using the fault model obtained by Wang et al(2008) through inversion with multiple types of geodetic survey data, including GPS, INSAR, and leveling, and the results were compared with the observations..

It was found that the observed and simulated results are basically consistent, showing that the significant changes are mainly concentrated in the near-rupture zone in the hanging wall of the Yingxiu–Beichuan fault and that the changes decrease rapidly away from the rupture zone. The changes exhibit a positive to negative trend from east to west in the footwall of the Yingxiu–Beichuan fault and have a distribution characterized by alternate positive and negative changes in the hanging wall of the fault. This demonstrates the reliability of the observed results and the reasonableness of the fault model used in this paper.

In the near-rupture zone on the west and east sides of the Yingxiu–Beichuan fault, there are still some differences between the observed and simulated results. The trends in the spatial distribution of these differences exhibit a deviation similar to “phase delay”; in other words, an observed result deviates from the corresponding simulated result in terms of spatial position, which is speculated to be caused by errors in the geometric parameters and in the slip distribution of the fault model. After the slip distribution of  the Pengguan fault model was modified based on the actual surface rupture distribution, the simulated result at the Hongjiawan station near the eastern boundary of the fault model showed greater consistency with the observed result. This indicates that the observed gravity change results in this paper can provide an important reference for further detailed study of the fault model.         

            Fig1.Schematic of the Chengdu Gravimetric Network                        Fig2.Spatial distribution of observed gravity changes and simulated results

 

 

How to cite: Hao, H. and Hu, M.: Coseismic gravity changes of the 2008 Wenchuan earthquake in China observed by surface gravimetric data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7561, https://doi.org/10.5194/egusphere-egu24-7561, 2024.

EGU24-8059 | Posters on site | G4.3

Enhancing sub-ice geology in East Antarctica with Self-Organizing maps based on gravity, magnetic and radar data 

Jörg Ebbing, Jonas Liebsch, and Kenichi Matsuoka

Sub-ice geology significantly influences the dynamics and future evolution of the Antarctic Ice Sheet, but largely inaccessible for direct sampling. Here, we present an approach, where we use a Self-Organizing Map (SOM) to describe sub-glacial properties. Based on attributes derived from gravity, magnetics and radar data from the NASA Operation Ice Bridge dataset in East Antarctica, we train a SOM, where attributes are selected to best represent sub-glacial conditions. Therefore, we study the trade-offs between these data sets helping to identify for which properties these are most sensitive.
The trained SOM identifies the outlines of the main geological structures beneath the ice and supplements models based on inverse and forward modelling. In contrast to such often regional interpretations, the SOM captures small-scale structures at the ice bed, as we illustrate with case examples, and highlights areas with inconsistencies in existing geological interpretations. The SOM can furthermore be used as input for inverse modelling of the physical properties of the sub-glacial geology in Antarctica.

How to cite: Ebbing, J., Liebsch, J., and Matsuoka, K.: Enhancing sub-ice geology in East Antarctica with Self-Organizing maps based on gravity, magnetic and radar data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8059, https://doi.org/10.5194/egusphere-egu24-8059, 2024.

EGU24-8934 | Posters on site | G4.3

What can we learn from magnetic surveys at different scales? Geological insight from mineral to airborne surveys in the Bjerkreim-Sokndal Layer Intrusion, Norway 

Suzanne McEnroe, Madeline Lee, Yuleika Madriz, Richard Gloaguen, Zeudia Pastore, Peter Lelièvre, and Nathan Church

Multiple magnetic surveys, including fixed-wing, helicopter-borne, uncrewed aerial vehicle (UAV), and ground magnetics have been acquired over parts of the Bjerkreim-Sokndal layered intrusion (BKS) in Rogaland, Norway. The Proterozoic 230 km2 Bjerkreim-Sokndal layered complex intrudes into anorthosites and hosts recurrent megacyclic units (MCU) with varying cumulus and critical minerals. Some MCUs are associated with strong magnetic remanence, resulting in Koenignsberger ratios (Q ratio) over 5 and anomalies of 12 000 nT below background.  A comparative analysis of these surveys over the Bjerkreim Lobe provide insights into what features can be mapped at different scales. Here we focus on new geological details provided by UAV, ground, and mineral scale surveys.  A UAV can typically operate at a maximum altitude of 150 m above terrain to a minimum of tens- of centimeters in ideal conditions. Thus, UAV magnetic surveys are optimal for understanding the change of a magnetic anomaly with varying source-separation through multiple flight altitudes. Survey altitudes by UAVs overlap with the source-sensor separation of ground and low-altitude crewed flights, therefore allowing a comparative analysis.

In 2023, the Norwegian University of Science and Technology and Helmholtz Institute Freiberg acquired coincident magnetic survey grids by UAV and ground magnetometer over key sites in the Bjerkreim lobe. Here we compare results of crewed-, uncrewed-, and ground-based data collected over the eastern margin of the Bjerkreim lobe and assess how these impact subsequent geologic interpretations. The petrophysical database for the survey area also contains > 1500 previously collected samples in combination with surface geometry information. This database in combination with the extensive lateral magnetic survey data at various sensor heights and other available complementary geophysics, including gravity, provide excellent parameters and constraints for forward modelling and inversions.

In the Bjerkreim lobe two MCU have significant magnetic remanence where anomalies are several thousand nT below background due to natural remanent magnetizations that are typically > 15 A/m. Therefore, an additional focus is on understanding the nature of the magnetic mineralogy using high-resolution scanning magnetic microscopy. These large amplitude magnetic anomalies may also cause logistical challenges for both airborne- and ground magnetic surveying. UAVs employ onboard magnetometer for navigation and attitude corrections which can be impacted by these large magnetic gradients. Similarly, significant noise or sensor drop-outs when the sensor’s dead zone is aligned with these large, often steep, magnetic gradients.

How to cite: McEnroe, S., Lee, M., Madriz, Y., Gloaguen, R., Pastore, Z., Lelièvre, P., and Church, N.: What can we learn from magnetic surveys at different scales? Geological insight from mineral to airborne surveys in the Bjerkreim-Sokndal Layer Intrusion, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8934, https://doi.org/10.5194/egusphere-egu24-8934, 2024.

EGU24-9258 | ECS | Orals | G4.3

Moho Depth Model and Structural Characteristics of China and Adjacent Regions 

Zhixin Xue, Dongmei Guo, Jian Fang, and Huiyou He

The Moho interface is an important parameter for describing the structure and morphology of the Earth's crust, and it is of significant importance in the study of the formation and evolution of the crust and mantle, as well as deep-seated dynamic processes (Stern et al., 2018). Existing Moho models derived from seismic data often suffer from inaccuracies due to irregular distribution and regional imbalances of seismic data. However, with the development of gravity satellite technology, high-precision satellite gravity data has injected new vitality into the study of lithospheric tectonic features and crustal evolution. In this study, constrained by seismic data (Li et al., 2013; Zhang et al., 2021), we utilized an improved regularized Bott method (Uieda et al., 2017) to invert high-precision satellite gravity data and obtained a high-precision unified Moho depth model for the East Asian region, encompassing both land and sea areas. The research results show that the Moho depth model exhibits a continuous increase in depth from east to west, and its overall distribution in the horizontal direction is non-uniform, displaying distinct regional block features. This paper provides a high-resolution and high-precision Moho model for studying the evolution of the East Asian continental tectonics and plate interactions, and further discusses the macrostructural framework and geological implications of East Asia.

References

Li Y Gao M, Wu Q. Crustal Thickness Map of the Chinese Mainland from Teleseismic Receiver Functions [J]. Tectonophysics, 2013, 611.

Stern, Robert, J, et al. Continental crust of China: A brief guide for the perplexed [J]. Earth Science Reviews the International Geological Journal Bridging the Gap Between Research Articles & Textbooks, 2018.

Uieda L, Barbosa V. Fast nonlinear gravity inversion in spherical coordinates with application to the South American Moho [J]. Geophysical Journal International, 2016.

Zhang J , Yang G , Tan H , et al. Mapping the Moho depth and ocean-continent transition in the South China Sea using gravity inversion [J]. Journal of Asian Earth Sciences, 2021, 218(3–4):104864.

How to cite: Xue, Z., Guo, D., Fang, J., and He, H.: Moho Depth Model and Structural Characteristics of China and Adjacent Regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9258, https://doi.org/10.5194/egusphere-egu24-9258, 2024.

EGU24-10299 | ECS | Orals | G4.3

Satellite gravity validation by new airborne gravimetry in coastal regions of Antarctica and Norway 

Bjørnar Dale, Sebastian Bjerregaard Simonsen, Ove Christian Dahl Omang, Tim Enzlberger Jensen, and René Forsberg

Airborne gravimetry provides gravity observations of higher spatial resolution than what can be obtained from satellite gravity field measurements, and together with terrestrial measurements they augment the satellite observations to determine high-resolution geoid models. Satellite altimetry in coastal and ice-covered regions is known to have significant errors. We use modern strapdown gravimetry for the surveys and compare the indirect method, using Kalman filtering, and the direct filtering method for the processing. We present the result of strapdown gravimetry for two airborne campaigns conducted in Antarctica 2022 and Norway 2023. During both campaigns the sensors used were an iMAR navigation-grade inertial measurement unit together with a geodetic GNSS receiver.

The 2022 campaign covered part of the sea-ice covered Weddell Sea and was surveyed as a piggyback activity as part of the ESA CRYO2ICE and NERC DEFIANT 2022 Antractica campaign. The 2023 airborne campaign was carried out in the coastal region of Norway near Trondheim. In both areas the data were compared to satellite altimetry and other gravity data from ship or airborne surveys. Both campaigns show improvements in spatial resolution and accuracy of the new mGal-level airborne gravimetry data when compared to satellite altimetry and older marine gravity observations.

How to cite: Dale, B., Bjerregaard Simonsen, S., Christian Dahl Omang, O., Enzlberger Jensen, T., and Forsberg, R.: Satellite gravity validation by new airborne gravimetry in coastal regions of Antarctica and Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10299, https://doi.org/10.5194/egusphere-egu24-10299, 2024.

EGU24-11380 | ECS | Orals | G4.3

Gravity inversion of sub-ice shelf bathymetry in West Antarctica using a geostatistical Markov Chain Monte Carlo approach 

Michael Field, Emma MacKie, Lijing Wang, and Atsuhiro Muto

Sub-ice-shelf bathymetry controls the delivery of warm water to the ice-shelf bottom in West Antarctica, making the bathymetry beneath ice shelves in the Amundsen Sea critical inputs to ice-sheet and ocean models. Previous estimates of the bathymetry have often used deterministic inversion frameworks or do not account for the non-uniqueness of the inverse problem, and ultimately lack robust uncertainty quantification. To provide more robust and reproducible bathymetry models, we implement a random walk Metropolis-Hastings Markov Chain Monte Carlo (MCMC) inversion approach, which iteratively generates model perturbations using random Gaussian fields and forward models the gravity disturbance of proposed bathymetry models. After convergence, our approach samples the posterior distribution allowing for estimation of the mean and variance of the bathymetry while providing realistic models of the sub-ice-shelf bathymetry. An ensemble of bathymetry models can then be used in ice-sheet and ocean simulations to propagate the uncertainty in bathymetry to dynamic ice processes, resulting in better uncertainty quantification of future sea-level rise. In addition to providing more robust bathymetry models, this work provides a step forward in the reproducibility of geophysical inversions by leveraging the growing open-access geoscientific computing ecosystem of Python.

How to cite: Field, M., MacKie, E., Wang, L., and Muto, A.: Gravity inversion of sub-ice shelf bathymetry in West Antarctica using a geostatistical Markov Chain Monte Carlo approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11380, https://doi.org/10.5194/egusphere-egu24-11380, 2024.

EGU24-12072 | Posters on site | G4.3

3D joint inversion of regional magnetotelluric, seismic, gravity and magnetic datasets to image lithospheric structure of Ireland 

Dmitry Molodtsov, Duygu Kiyan, and Christopher Bean

Regional gravity and magnetic surveys are essential sources of information about the structure and geodynamics of the lithosphere. However, geologically meaningful inversion of gravity and magnetic data usually requires integration with other geophysical methods. We have developed a 3-D joint inversion framework that has the flexibility of using independent inversion codes and model discretizations for each of the included methods, is easily expandable and supports a wide range of the coupling constraints. Here we show its application to the regional geophysical datasets available in Ireland. We present the results of joint inversion of long-period magnetotelluric data, seismic traveltimes, and land gravity – a multiparameter geophysical model of the crust and uppermost mantle of the whole Ireland. On a smaller scale, we present the results of joint inversion of gravity, airborne magnetic and magnetotelluric data for the Limerick Basin, focusing on imaging of a Carboniferous volcanic structure.  The main aim is to better understand the Pb-Zn mineral systems which are controlled by the tectonics of the basement and lower crust. Exploration-scale geophysical surveys and geothermal exploration will also benefit from the regional 3-D geophysical models.

How to cite: Molodtsov, D., Kiyan, D., and Bean, C.: 3D joint inversion of regional magnetotelluric, seismic, gravity and magnetic datasets to image lithospheric structure of Ireland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12072, https://doi.org/10.5194/egusphere-egu24-12072, 2024.

EGU24-12510 | ECS | Orals | G4.3 | Highlight

Are there thick sediments within South Pole Basin? Investigating the lithology of SPB using COLDEX airborne geophysics  

Megan Kerr, Duncan Young, Weisen Shen, Gregory Ng, Shivangini Singh, Dillon Buhl, Jamin Greenbaum, Shuai Yan, and Donald Blankenship

Because sedimentary basins may exert considerable control over ice sheet dynamics and basal heat flow, it is vital to constrain the extent, thickness, and level of consolidation of sediments throughout the continent and at local scales. Until recently, the South Pole Basin (SPB), situated between the Gamburtsev Subglacial Mountains, the Transantarctic Mountains, and Recovery Subglacial Highlands, has been one of Antarctica's least-explored regions. Previous studies based on seismic and machine learning models, including those by Baranov & Morelli (2023) and Li et al. (2022), have characterized SPB as a sedimentary basin with sediment thicknesses exceeding 1 km. Conversely, a seismic study conducted by Zhou et al. (2022) identifies SPB as a region with little to no sedimentary rock. A lack of dense geophysical data as well as the inherent difficulty of studying geology beneath the Antarctic Ice Sheet introduced a large amount of uncertainty into these assessments. Recent airborne radar, gravity, and magnetics data collected by the Center for Oldest Ice Exploration (COLDEX) has revealed two distinct geomorphological provinces within South Pole Basin: the southern portion of SPB which exhibits relatively smooth, reflective bedrock, while the northern SBP manifests as much rougher terrain. The abrupt boundary between Inner and Outer SPB is associated with the onset of subglacial melting, inferred from a rapid thinning of the basal layer, decreased ice sheet surface slope, and presence of subglacial lake-like features. In addition to surficial differences, these provinces are marked by distinct free-air, Bouguer, and isostatic gravity signatures. A large, arc-shaped magnetic high parallel to Recovery Subglacial Highlands cuts across SBP, facilitating a robust depth to basement analysis and providing constraints for gravity inversions. By integrating COLDEX data with previous airborne surveys and newly collected seismic data, we offer a revised geological interpretation of the South Pole Basin and discuss its tectonic history, potential for groundwater storage, and the preservation of ancient ice in this region.

How to cite: Kerr, M., Young, D., Shen, W., Ng, G., Singh, S., Buhl, D., Greenbaum, J., Yan, S., and Blankenship, D.: Are there thick sediments within South Pole Basin? Investigating the lithology of SPB using COLDEX airborne geophysics , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12510, https://doi.org/10.5194/egusphere-egu24-12510, 2024.

Joint inversion can utilize multiple geophysical datasets to supplement or enhance the information on subsurface structures, improve the resolution and certainty of recovered subsurface structures, and provide broad prospects for various geophysical application scenarios. Model coupling is crucial in joint inversion, and there are two main coupling methods based on structural similarity and petrophysical information. These two coupling methods have their own advantages and disadvantages. The structural similarity-based coupling method can obtain structurally similar models without prior information, but the assumption of structural similarity between models is not always valid. The petrophysics-based coupling method provides finer constraints on physical property values, and its difficulty lies in acquiring petrophysical information, which is usually imprecise and incomplete in the inversion region. Joint inversion using a single model coupling approach is insufficient to face complex joint inversion situations. Combining the two coupling methods can complement the structural similarity of the model in the inversion of incomplete petrophysical information.

We develop a novel joint inversion method based on the extended alternating direction method of multipliers (eADMM), which is compatible with multiple model coupling methods and reduces non-uniqueness and uncertainty more effectively. Multiple model coupling methods are contained in an indicator function, which requires the model to satisfy specific mathematical sets, allowing the various models to satisfy arbitrary relationships and ranges. The inequality constraints and linear and nonlinear relational equations extracted from the petrophysical information are expressed directly in mathematical sets, and the structural similarity coupling is implemented by a constraint set that requires a cross-gradient of zero between models. The solution of the indicator function in the eADMM framework is converted into a projection function, and we develop corresponding projection algorithms for multiple constraint sets of both model coupling strategies. The constraint sets are also spatially flexible. Regions with complete petrophysical information and regions requiring increased structural similarity can be constrained by the corresponding sets, respectively.

We apply the method to gravity and magnetic data to test its performance. We compare the performance of our method with that of the joint inversion using a single coupling method for incomplete petrophysical information, including petrophysical information for partial regions and partial geologic units. Synthetic examples show that regions and geologic units with known petrophysical information are recovered with accurate geometric boundaries and physical property values closer to the true values, and structural similarity coupling provides structural information for unknown regions or geologic units, recovers more accurate geometric structures and reduces model uncertainty. The new joint inversion method provides higher resolution models than the traditional joint inversion method, and the inversion results are closer to the true model.

How to cite: Wang, K. and Yang, D.: joint inversion of gravity and magnetic data with petrophysical and structural coupling constraints using indicator functions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14351, https://doi.org/10.5194/egusphere-egu24-14351, 2024.

EGU24-14771 | ECS | Orals | G4.3

Joint inversion of potential field data to unmask sub-ice geology, from a case study in Scandinavia to application in NE Greenland 

Agnes Dakota Wansing, Jörg Ebbing, Max Moorkamp, and Björn Heincke

The surface geology of Greenland is only known along the ice-free coast. The remaining 80% of Earth's largest island are covered by ice that masks the surface geology and makes direct observation nearly impossible. Interpolation of the known coastal geology over the inland ice, combined with expert knowledge, can provide a first, but not well-constrained picture. In contrast, the surface geology in Scandinavia is well-studied. The formerly adjacent northeastern part of Greenland belongs to the same Caledonian orogeny and is expected to be somewhat similar to Scandinavia. Therefore, we use Scandinavia as a case study to set up a workflow of joint inversion of potential field data to find physical relations for the known geological structure and apply this workflow to NE Greenland.

Results from individual inversion of potential field data are non-unique and have limited depth resolution. Combining gravity and magnetic data in a joint inversion can minimise the non-uniqueness and improve the depth resolution. The coupling furthermore creates comparable anomaly patterns for both inverted parameters. As coupling method, a variation of information (VI) constraint is used in the inversion. The VI creates representative parameter relationships where different branches reflect the numerous combinations of density and susceptibility for various rock types. Thus, the inverted parameter relationship can be used to map the surface geology.

Crucial parts in the workflow setup are how deeper sources are handled for the gravity data and at which resolution and height the magnetic data are required.  The simultaneous analysis of the well-studied surface geology in Scandinavia helps to verify the analysis, providing higher confidence in the resulting sub-ice geology for NE Greenland.

How to cite: Wansing, A. D., Ebbing, J., Moorkamp, M., and Heincke, B.: Joint inversion of potential field data to unmask sub-ice geology, from a case study in Scandinavia to application in NE Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14771, https://doi.org/10.5194/egusphere-egu24-14771, 2024.

EGU24-15133 | ECS | Posters on site | G4.3

Investigating the feasibility of resolving hydrological processes with a Differential Quantum Gravimeter by hydrological scenario modeling 

Marvin Reich, Camille Janvier, and Andreas Güntner

Quantum sensors have gained increased attention in the last years, both from the applied but also from the manufacturer perspective. Most instruments are still limited to operation within a dedicated lab. With the Absolute Quantum Gravimeter (AQG), one device has already proven mobile capabilities and was used in several research studies. This application perspective is an important topic for new instruments, in order to meet scientific requirements in terms of usability and usefulness for various research interests.

One of these research interests is hydrology. From the monitoring perspective, hydrological observations in the field traditionally rely on point measurements, often in form of invasive sensor installations. These spatially-limited observations sometimes complicate natural hydrological process investigations. An advantage is provided when using the hydrogravimetric method, with its integral nature of monitoring water mass changes as a whole.

In this contribution, we address the above-mentioned important topics for a first feasibility study of an emerging instrument: the Differential Quantum Gravimeter (DQG). Developed by Exail Quantum Sensors, the DQG measures the acceleration due to gravity and the vertical gravity gradient simultaneously. It is an industry-grade demonstrator that has been operational for three years now and has achieved state-of-the-art sensitivity on the gradient of about 60E/sqrt(tau) and a long-term stability on the gradient around 1E. For gravity measurements the performances are on par or better than the AQG with a sensitivity of 600nm/s²/sqrt(tau) and a stability down to 5nm/s².

In preparation for first field measurements, we were interested in its performance for resolving hydrological dynamics and processes. We set up different hydrological modeling scenarios to forward model gravity responses and their DQG-related gravity gradients from water mass changes. Scenarios for obtaining these water mass changes consisted of vertical 1D models using the software Hydrus. Developing scenarios from very simple to more complex soil layer setups, we tested different forcing types (precipitation, evapotranspiration) with varying magnitudes and durations. The overall objective was to simulate resulting gravity gradients at different locations as the DQG would monitor them. Varying the theoretical placement of the DQG within the model domain enabled us to investigate its sensitivity to the simulated hydrological processes with respect to its location and distance to different magnitudes of water mass changes. Forward modeled data was averaged at different time periods and combined with realistically expected noise of the instrument. The study helps to evaluate the capabilities of the instrument as a tool to observe water fluxes in the soil, as well as optimal implementation of the DQG for planning first field measurements.

How to cite: Reich, M., Janvier, C., and Güntner, A.: Investigating the feasibility of resolving hydrological processes with a Differential Quantum Gravimeter by hydrological scenario modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15133, https://doi.org/10.5194/egusphere-egu24-15133, 2024.

EGU24-16919 | ECS | Posters on site | G4.3

Unravelling Deep Aquifer Communication in the Coastal Sahel Region: Insights from Geophysical Methods in the Tunisian Oriental Atlas 

Khaoula Charrek, Kristine Walraevens, Thomas Hermans, and Hakim Gabtni

Understanding the communication pathways of deep aquifers in the Tunisian Oriental Atlas along the southern Mediterranean margin, particularly within the coastal Sahel region, is of utmost importance for designing effective well drilling strategies and reducing risks for groundwater drilling.

In this study, we employed Gravity, Time Domain Electromagnetic (TDEM) methods and the variation of the piezometric level to investigate the structural setting and aquifer characteristic. Gravity and TDEM are two geophysical methods that provide insights into the density variation of underground bodies and reveal resistivity distribution at different depths, respectively. By integrating these methods, we aim to unravel the intricate hydrogeological system in the study area.

Our findings highlight a major fault line with a significant water level discrepancy, which is crucial information for groundwater exploration and exploitation. This study provides insights into the hydrogeological dynamics of the coastal Sahel region, facilitating the design of new drilling strategies. The gained knowledge supports informed decision-making in selecting optimal target production zones, ultimately minimizing drilling risks and promoting sustainable groundwater management in the Tunisian Oriental Atlas.

How to cite: Charrek, K., Walraevens, K., Hermans, T., and Gabtni, H.: Unravelling Deep Aquifer Communication in the Coastal Sahel Region: Insights from Geophysical Methods in the Tunisian Oriental Atlas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16919, https://doi.org/10.5194/egusphere-egu24-16919, 2024.

EGU24-17112 | ECS | Posters on site | G4.3

Application of numerical integration and CUDA parallel in the calculation of ocean gravity gradient 

Zhourun Ye, Jingyu Bu, and Nico Sneeuw

Through Stokes kernel function and gravity anomaly, it is possible to calculate the gravity gradient disturbance on the geoid and its external space. For this Stokes’ integral expression, we apply Laguerre wavelet numerical integration to improve the accuracy of its computational results. Meanwhile, compute unified device architecture (CUDA) is used to implement parallel computing on the Graphic Processing Unit (GPU) for speeding up. The full tensors of gravity gradient in the experimental ocean area with 3°×2°are computed. Compared to serial computing, its computing acceleration ratio can be more than 10 times faster. The results of the vertical gravity gradient are compared and validated from the public model from the University of California San Diego.

How to cite: Ye, Z., Bu, J., and Sneeuw, N.: Application of numerical integration and CUDA parallel in the calculation of ocean gravity gradient, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17112, https://doi.org/10.5194/egusphere-egu24-17112, 2024.

EGU24-17176 | ECS | Posters on site | G4.3

Bayesian Joint Inversion of Bouguer Gravity and Surface Wave data: application to the Western Alps 

Matteo Scarponi and Thomas Bodin

The Western Alps constitute a complex and heterogeneous orogenic system, generated by the continental collision between the European and Adriatic tectonic plates. Three main tectonic domains can be identified across local to regional scales, based on geophysical and geological observations: the European and Adriatic domains, and the high-density, high-velocity anomaly known as Ivrea geophysical body (IGB). Despite being one of the best-studied collisional systems in the world, the 3D Western Alpine lithosphere and its along-arc compositional and structural variations are still subjects of investigations.

 

In this framework, we exploit the inherently-3D information provided by gravity data. In particular, we set up a 3D Bayesian joint inversion of Bouguer gravity anomaly and surface wave dispersion data, to obtain a new 3D ρ-vS model of the Western Alpine lithosphere. We benefit from the Bouguer anomaly map by Zahorec et al. (2021), obtained by homogeneous processing of gravity data across the Alpine domain, and from seismic data recorded by permanent and temporary seismic networks: e.g. IvreaArray, AlpArray (Hetényi et al. 2017, 2018), CIFALPS I and II (e.g. Paul et al. 2022).

 

We perform 3D forward gravity modeling by discretizing the study area in unitary volumes of constant density (voxels), accounting for spherical Earth structure and surface topography. The gravity effect of each voxel is pre-computed, and then only needs to be scaled with density during the inversion. This significantly decreases the computational cost of the forward model, and thus allows us to explore the parameter space with Monte Carlo sampling. We use a Bayesian framework and implement a Markov chain Monte Carlo (McMC) algorithm. We test different types of  parameterizations to reduce the non-uniqueness of gravity inversion. We plan to jointly invert gravity with surface wave dispersion data, providing complementary information on vS. Finally, existing receiver function studies (e.g. Monna et al. 2022, Paul et al. 2022, Michailos et al. 2023) provide prior information on crustal and lithospheric geometry.


We expect to obtain a new 3D ρ-vS model for the Western Alpine crust and lithosphere. This will provide new information on the European-Adriatic collision boundary, together with the IGB structure, and their three-dimensional variation along the orogen. The new model will be also useful to constrain rock composition, upon comparison with the geological observations at the surface.

How to cite: Scarponi, M. and Bodin, T.: Bayesian Joint Inversion of Bouguer Gravity and Surface Wave data: application to the Western Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17176, https://doi.org/10.5194/egusphere-egu24-17176, 2024.

EGU24-17476 | Posters on site | G4.3

A year-long gravity record at Astroni, Campi Flegrei (Southern Italy): some considerations on data processing for volcano monitoring and precise gravity tides 

Alessandro Fedele, Umberto Riccardi, Tommaso Pivetta, Stefano Carlino, and Giuseppe Ricciardi

High-precision observations of gravity plays a central role in modern approaches for active volcano monitoring. Time-lapse observations over a network of benchmarks are frequently used to detect underground mass redistribution in the plumbing system of active volcanoes. Such approach however does not allow to retrieve small mass variations occurring over short terms (i.e. few hours or days). To fill this gap, continuous gravity monitoring at a fixed station may be employed. In January 2023 the relative gravimeter gPhoneX#116 was installed at the WWF Nature Reserve of Astroni volcano, in the Campi Flegrei caldera, to further complement time-lapse observations periodically performed over a network of benchmarks. During the 1-year of recordings, the gPhone has continuously recorded the relative gravity changes, only shortly interrupted by a few technical issues. The purpose of the observations is to monitor continuously the short-term gravity signals in one of the world's highest-risk volcanoes; to pursue this objective targeted and meticulous corrections need to be applied to remove the effect of several other geophysical effects, such as tides and atmospheric effects, which may superpose on the signals of interest. Special effort was devoted to the study of instrumental drift, which can mask actual gravity changes due to mass variations occurring in the volcanic and geothermal systems. In this contribution we report the various processing steps and analysis performed to obtain reliable parameters of the Earth tides, non-tidal corrections and gravity residuals. The retrieved Earth tide model is then used to properly reduce tidal effects in high-precision relative and absolute gravity measurements.

How to cite: Fedele, A., Riccardi, U., Pivetta, T., Carlino, S., and Ricciardi, G.: A year-long gravity record at Astroni, Campi Flegrei (Southern Italy): some considerations on data processing for volcano monitoring and precise gravity tides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17476, https://doi.org/10.5194/egusphere-egu24-17476, 2024.

EGU24-18969 | ECS | Posters on site | G4.3

GRAVHEDRAL: a novel gravity inversion method to unravel planets’ interior 

Alessandro Ghirotto, Andrea Zunino, Egidio Armadillo, Anna Mittelholz, and Andreas Fichtner

Suitable modelling capabilities paired with planetary-scale datasets provide fundamental information to unravel planets’ interior and evolution. Despite the key role and tremendous effort of decades of scientific missions in advancing the understanding of planets’ subsurface, knowledge about their crustal structures and processes shaping them is still limited. This is mainly due to a sparse record of return samples or meteorites, in addition to the scarcity of surface geophysical measurements. Planets’ crust is however a recorder of ancient geological events leading to nonhomogeneous 3D density distributions, expressed in the form of gravity anomalies. While on Earth combined geophysical data can inform on subsurface properties, for other planets such datasets are sparser, and orbiter-based gravity data is one of few or even the only global-scale source of information related to their interior. Developing an innovative modelling methodology suitable to exploit such orbiter-based data can help infer the 3D density distribution in planets’ crusts, providing key insights to reconstruct their geological history. Here we present GRAVHEDRAL, a fully non-linear 3D inversion methodology of gravity anomaly data suitable for both local- and planetary-scale studies and capable of addressing limitations of existing modelling strategies. Such limitations are related to the challenge of i) characterizing complex 3D density distributions, which are expected in actual geological scenarios, and ii) mitigating the non-uniqueness of the solution. Using GRAVHEDRAL, planets’ interiors (e.g., crust, mantle, etc.) are parameterized in terms of polyhedra with density contrasts expressed as high-order polynomial functions, whose gravity responses can be computed thanks to recently derived analytical formulae. The inversion scheme relies on the Hamiltonian Monte Carlo (HMC) method, a probabilistic approach that is currently gaining momentum in the geophysical community. Compared to other probabilistic approaches, the HMC strategy allows the model space to be explored more efficiently thanks to the gradient calculation of the posterior probability density of the model parameters (i.e., polyhedra node positions and/or density contrasts). Statistical analysis and uncertainty estimation on the model parameters can be performed from the collection of posterior models, enabling the appraisal of different probable geological scenarios to address the non-uniqueness of the solution. GRAVHEDRAL aims to provide the space science community with a flexible tool to help image the still poorly known 3D crustal density distribution of other celestial bodies of our solar system, allowing researchers to test the occurrence of Earth-like geological structures on other terrestrial planets and thus to decipher the reasons behind their different geological evolution.

How to cite: Ghirotto, A., Zunino, A., Armadillo, E., Mittelholz, A., and Fichtner, A.: GRAVHEDRAL: a novel gravity inversion method to unravel planets’ interior, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18969, https://doi.org/10.5194/egusphere-egu24-18969, 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
  • Delunel R, Schlunegger F, Valla PG, Dixon J, Glotzbach C et al. (2020) Earth-Sci. Rev. 211:103407.
  • 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.
  • Wölfler A, Wolff R, Hampel A, Hetzel R, Dunkl I (2023) Tectonics 42:e2022TC007698.

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.

GD7 – Rheology and Multiscale Mineralogy in Geodynamics

The faceting behaviour of olivine controls many properties on the grain surface such as diffusion and storage.  This behaviour and its effects are poorly understood due to the difficulty of examining them and the many controls that are on this paper.  In this talk I shall present a thermodynamic model of olivine faceting and how it is controlled by temperature, pressure, iron, grain size and water content.  In turn I shall discuss how this faceting then controls other important properties such as storage of water on the grain boundaries and how these are perhaps an overlooked sink in the Earth’s mantle.

How to cite: Muir, J.: Olivine faceting and water storage: A complex dynamic anisotropic sink, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2395, https://doi.org/10.5194/egusphere-egu24-2395, 2024.

A connected set of singularity points is called the singularity line. Along this line, the slowness surfaces (or phase velocity surfaces) of different wave modes coincide. For anisotropic models, the singularity lines are mostly known in transversely isotropic media (Crampin and Yedlin, 1981). Recently, it was shown that they also can be defined in the special types of orthorhombic media: degenerate (Stovas et al, 2023b) and pathological (Stovas et al, 2023a). Singularity line can also exist in the low symmetry anisotropic models, monoclinic and triclinic (Khatkevich, 1963; Vavrycuk, 2005; Roganov et al, 2019).

In this paper, we focus on singularity lines in monoclinic media with a horizontal symmetry plane. We define the singularity lines in all coordinate planes, and in vertical planes of arbitrary azimuthal orientation. Since the monoclinic anisotropic model can be considered as the transversely isotropic medium with a vertical symmetry axis being perturbed with the multiple azimuthally non-invariant fracture sets, identification of singularity lines can give additional constraints in inversion of seismic data for fracture prediction. The singularity lines being converted into the group velocity domain results in continuous bands in the group velocity surface (traveltime surface) shaping the lacunas for S1 wave and internal refraction cones for S2 wave associated with strong anomalies in wave amplitudes.

The singularity directions satisfy the following polynomial equations (Alshits, 2004; Roganov et al., 2019), , where  are the third-order polynomials given by the elements of the Christoffel matrix. Resolving this system of equations, we define the conditions (in terms of stiffness coefficients) for existence of singularity lines in vertical planes. The Sylvester criterion is applied to control the physical realizable model. Mostly, the obtained models have singularity lines formed by S1 and S2 waves, while one model has singularity line composed of S1S2 and PS1 legs connected by the triple PS1S2 singularity point.

 

 

References

Alshits, V.I., 2004, On the role of anisotropy in crystalloacoustics, In: Goldstein R.V., Maugin G.A. (eds) Surface Waves in Anisotropic and Laminated Bodies and Defects Detection. NATO Science Series II: Mathematics, Physics and Chemistry, vol 163. Springer, Dordrecht.

Crampin, S., and M. Yedlin, 1981, Shear-wave singularities of wave propagation in anisotropic media, J. Geophys., 49, 43–46.

Khatkevich, A.G., 1963 Acoustic axes in crystals, Sov. Phys. Crystallogr. 7, 601–604.

Stovas, A., Roganov, Yu., and V. Roganov, 2023a, On pathological orthorhombic models, Geophysical Prospecting, 71(8), 1523- 1539.                                                                    

Stovas, A., Roganov, Yu., and V. Roganov, 2023b, Degenerate orthorhombic models, Geophysical Journal International, accepted for publication.                  Roganov, Yu., Stovas, A., and V. Roganov, 2019, Properties of acoustic axes in triclinic media, Geophysical Journal, 41(3), 3-17.                                                    Vavrycuk, V., 2005, Acoustic axes in triclinic anisotropy, The Journal of the Acoustical Society of America 118, 647-653.

How to cite: Stovas, A.: Singularity lines for monoclinic media with a horizontal symmetry plane, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2468, https://doi.org/10.5194/egusphere-egu24-2468, 2024.

How continental plate boundary faults develop with depth has been under debate. We inverted SKS shear wave splitting data along the San Andreas Fault (SAF) into two layers of anisotropy using a Bayesian inversion. While the two layers are statistically required, the fast polarization directions of the upper layer do not match the strike of the SAF as previously reported. To capture the lithospheric shear zone, we progressively decrease the upper limit of the delay time of the upper layer. In northern California where SAF strikes 140-150, the upper layer fast directions get close to these azimuths when the delay time is reduced to ~0.5 s. In southern California where the SAF strikes 120-130, the upper layer fast directions capture the SAF with delay times of a similar magnitude. For olivine LPO with vertical shear plane, these delay times translate to a anisotropy layer of 40 km thickness, or a depth of 70 km from the surface, assuming the seismogenic zone in the crust is too localized to influence the SKS splitting. This depth coincides with the depth of lithosphere-asthenosphere boundary independently estimated. The lower-layer fast directions are in between the absolute plate motion directions of the American and the Pacific plates, or at least agree with that predicted from surface wave study in northern California. We picture a vertical continental shear zone widening to at least 200 km at the bottom of the lithosphere, transitioning to a horizontal shear regime in the asthenosphere driven by plate motions. This architecture of continental shear zone is consistent with our understanding of the rheology of crust and mantle.

How to cite: Kuo, B.-Y., Peng, C.-C., and Wang, P.-C.: Structures of the continental shear zone beneath the San Andreas Fault inferred from two-layer modeling of SKS splitting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3339, https://doi.org/10.5194/egusphere-egu24-3339, 2024.

The seismic moment tensor, which represents the equivalent body-force system of the seismic source (Backus and Mulcahy, 1973), may exhibit non-double couple components (NDCs) when the earthquake occurs on a planer fault if the source medium is anisotropic (Aki and Richards, 1981; Kawasaki and Tanimoto, 1981). Kawakatsu (1991, GRL) reported that the NDCs of the moment tensors for shallow earthquakes from the Harvard CMT catalog (Dziewonski et al.,1981; predecessor of GCMT) exhibit a systematic characteristic dependent on faulting types. Specifically, the sign of NDC on average systematically switches between normal-faulting and reverse-faulting. The average NDC parameter ε (Giardini, 1983) is negative for thrust faulting and positive for normal faulting. This behavior can be explained if the source region is transversely isotropic with a vertical symmetry axis (radially anisotropic). In fact, the transverse isotropy model of PREM at a depth of 24.4 km predicts the observed systematic NDC pattern, although the magnitude is slightly underestimated, indicating the potential to enhance our understanding of the lithospheric transverse isotropy using the NDC of the moment tensors.

To investigate the lithospheric transverse isotropy structure utilizing the NDCs of the moment tensors, we propose a novel inversion scheme, building upon the approaches employed by Vavrycuk (2004) and Li, Zheng, et al. (2018) for deep and intermediate-depth earthquakes, but with necessary modifications to address shallow sources (Kawakatsu, 1996, GJI). Synthetic tests conducted under conditions of random faulting indicate the potential to constrain the S-wave anisotropy (ξ) and the fifth parameter (ηκ; Kawakatsu, 2016, GJI). However, in realistic scenarios where a predominant stress regime influences earthquake occurrence to limit the diversity of faulting types, a significant correlation between these two parameters is anticipated, especially in regional-scale cases. Preliminary application of this method to real data sourced from the GCMT catalog suggests that the lithospheric transverse isotropy of PREM serves as a suitable initial model. However, some adjustments may be necessary, particularly regarding the fifth parameter, to enhance the model's fidelity in representing observed NDCs of the moment tensors.

How to cite: Kawakatsu, H.: Characterizing Lithospheric Transverse Isotropy via Non-double Couple Components of Moment Tensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3697, https://doi.org/10.5194/egusphere-egu24-3697, 2024.

The continental lithosphere of the Iranian plateau is complicated by a multitude of tectonic processes resulting from the convergence between the Arabian and Eurasian plates. In order to investigate the deformation mechanisms of the uppermost mantle, this study presents a radial anisotropy model beneath the Iranian Plateau constructed by long period (10-100 s) Rayleigh and Love waves from ambient noise data. The broadband Rayleigh and Love signals are extracted from continuous data recorded by 88 seismic stations using a double-beamforming algorithm. Due to utilizing long period surface waves, we apply finite-frequency ambient noise tomography to generate two-dimensional dispersion maps. These phase velocity maps are consistent with those obtained from conventional methods. Finally, we invert Rayleigh and Love local phase velocity dispersion curves using a Bayesian Markov chain Monte Carlo inversion method. The obtained radial anisotropy model shows negative values in Central Iran suggesting a horizontal character of the minerals likely due to a channelized asthenospheric flow in the upper mantle.

How to cite: Movaghari, R. and Yang, Y.: Uppermost mantle radial anisotropy based on double-beamforming of ambient noise cross correlation beneath Iranian plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3769, https://doi.org/10.5194/egusphere-egu24-3769, 2024.

Complex tectonics and significant crustal anisotropy are observed at the intersection of the Red River Fault (RRF) and the Xiaojiang Fault (XJF) in the southern Sichuan-Yunnan block, in the SE Tibetan Plateau. The fast S polarization of upper crustal anisotropy varies from NW-SE in the west to NE-SW in the east near the Yimen region. However, small-scale anisotropic structures remain challenging due to limited measurements. Using two years of seismic data from the temporary linear HX Array and permanent stations, this study employed machine learning to construct a high-precision earthquake catalog for S-wave splitting, revealing the upper crustal anisotropy. The new catalog has nearly twice as many earthquakes as the China Earthquake Networks Center. The seismicity is concentrated in the Yimen region with various strike-slip faults, which has a strong correlation with high- and low-velocity boundaries, especially near the edge of the low-velocity zone. Spatial variations in upper crustal anisotropy along the HX Array correspond to geological structures and regional stress. Despite a dominant NE-SW PFS (i.e., fast S-wave polarization) in the Yimen region, stations show dual dominant directions with high values of DTS (i.e., delay times between split S-waves), indicating intricate tectonic and stress interactions. The middle segment of the RRF shows significantly lower DTS values than either side, along with a vertically distributed earthquake swarm, possibly indicating locked structures with high seismic hazard. A comparison between the upper and whole crustal anisotropy reveals consistent deformation within blocks and nearly orthogonal deformation near the RRF and the XJF. The boundary faults likely play a crucial role in influencing the crustal anisotropy both horizontally and vertically. The faults like the Shiping-Jianshui and the Puduhe, running parallel to the RRF and the XJF, are believed to affect the crustal structure. This study highlights that microseismic detection enhances earthquake catalog completeness, providing insights into detailed structures [supported by NSFC Projects 42074065 & 41730212].

How to cite: Li, Y., Gao, Y., and Tian, J.: Microseismic records based on machine-learning reveal the crustal anisotropy beneath the southern Sichuan-Yunnan block in the SE Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4528, https://doi.org/10.5194/egusphere-egu24-4528, 2024.

EGU24-7126 | ECS | Posters on site | GD7.1

Seismic anisotropy of the crust and upper mantle beneath eastern Pamir 

Changhui Ju, Junmeng Zhao, Qiang Xu, and Guohui Li

The East Pamir seismic experiment (8H) was conducted in the eastern Pamir and the adjacent Tarim Basin from August 2015 to May 2017. Utilizing seismograms from the 8H network and nine permanent seismic stations operated by the China Earthquake Administration, we computed shear wave splitting parameters through cluster analysis of the minimum energy method. A total of 452 high-quality individual SKS-splitting measurements were obtained at 39 seismic stations. Given the predominant availability of events with a back-azimuth (BAZ) around ~110° and the absence of a broad range of BAZ values, we opted for a single-layer anisotropic model to interpret the measurements.

The upper mantle seismic anisotropy structure in the Western Himalayan Syntaxis (WHS) exhibits distinctive regional characteristics in various regions. Group A comprises 15 stations situated near the Alai Valley and the Tien Shan with a northeast-oriented Fast Polarization Direction (FPD), aligned with the strike of the orogen and the Absolute Plate Motion (APM) azimuthal direction (~80°) of the Eurasian plate. This group exhibits relatively larger Delay Time (DT) and may be originated from the oriented arrangement of olivine crystals in the mantle lithosphere of the Eurasian continent during the northward subduction of the Indian continent. Group B consists of 21 stations located in the eastern Pamir and adjoining Tarim Basin, demonstrating a curved orientation. While this orientation contradicts the APM direction, it approximately parallels the trend of large-scale surface structures. Combining these observations with previous imaging results, we propose that during the northward advancement of the Indian continent, mantle material flow (escape) in the Pamir-Hindu Kush region formed seismic anisotropy structures similar to those in the Western Himalayan Syntaxis (WHS).

How to cite: Ju, C., Zhao, J., Xu, Q., and Li, G.: Seismic anisotropy of the crust and upper mantle beneath eastern Pamir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7126, https://doi.org/10.5194/egusphere-egu24-7126, 2024.

EGU24-8306 | ECS | Posters on site | GD7.1

Modulation of crustal and mantle flow systems by a heterogeneous cratonic root: Evidence from seismic azimuthal anisotropy analysis 

Lin Liu, Stephen Gao, Kelly Liu, Sanzhong Li, and Youqiang Yu

In contrast to many prior studies that relied on station-averaged shear-wave splitting (SWS) measurements and sparsely distributed stations, this study takes advantage of the recent deployment of broadband seismic stations at intervals of less than 50 km to explore the intricate seismic azimuthal anisotropy between the dynamic Tibetan Plateau and the stable North China Craton. Our analysis encompasses 6,409 high-quality individual SWS measurements from 465 closely spaced stations located along the boundary of the northeastern Tibetan Plateau and the western North China Craton. Notably, twenty of these stations show splitting parameters with a π/2 periodicity based on azimuthal variations, indicating a complex double-layer horizontal anisotropy structure. The anisotropy of the upper layer is linked to ductile flow in the middle-to-lower crust originating from the Tibetan Plateau. This flow encounters the rigid lithosphere of the Alxa Block, leading to a bifurcation into northeastward and southeastward directions. The anisotropy in the lower layer, exhibiting fast orientations in an NW-SE direction, is consistent with the observed one-layered anisotropy and aligns with the absolute plate motion (APM) of the Eurasian plate. The coherence in the spatial distribution of splitting parameters indicates that the predominant source of observed anisotropy is asthenospheric flow. This mantle flow exhibits a southeastward orientation beneath the Alxa block, transitioning to an almost eastward direction along the thinner lithospheric passage between the Ordos and Sichuan cratonic keels. This pattern unveils the influence of cratonic edges in modulating localized mantle flow systems.

How to cite: Liu, L., Gao, S., Liu, K., Li, S., and Yu, Y.: Modulation of crustal and mantle flow systems by a heterogeneous cratonic root: Evidence from seismic azimuthal anisotropy analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8306, https://doi.org/10.5194/egusphere-egu24-8306, 2024.

EGU24-8694 | Orals | GD7.1

A new method to measure seismic anisotropy of the upper mantle directly from the width and orientation of the particle motion of shear waves  

Luděk Vecsey, Jaroslava Plomerová, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

Splitting of shear waves proves their propagation within an anisotropic medium. Frequently used methods of evaluating of upper mantle anisotropy search for two parameters - the delay time of the slow split shear wave and the polarization direction of the fast split shear wave. The parameters retrieved by the standard methods such as energy minimization on the transverse component of the shear waveforms or eigenvalue of cross-correlation matrix suffer from e.g., ubiquitous noise, errors in sensor orientation and numerous so-called ‘null splits’ or unrealistically large values. However, well-resolved splitting parameters from core-mantle refracted shear SK(K)S phases are limited to relatively narrow fans of back azimuths. Such incomplete back-azimuth coverage prevents modelling anisotropic structures with symmetry axes oriented generally in 3D, i.e., with tilted axes, to be compatible with 3D anisotropic models from independent observables.  Generally used averages of time delays and polarization pairs lead to simplified models of the upper mantle, which concentrate on modelling the present-day flow in the sub-lithospheric mantle.

Therefore, we propose a new method directly exploiting variations in width and orientation of particle motion (PM) of split shear waves, which allows measuring anisotropic characteristics for a larger amount of waveforms and improves azimuthal coverage in a region. We characterize the PM by two parameters, the PM width and the PM orientation. At each station, we plot the normalized width of the PM as a ratio of lengths of the minor to major axes in dependence on back-azimuths. Variations of the PM width with back-azimuth exhibit oscillations with several extremes of different amplitudes. Such behaviour results from wave propagation through the anisotropic upper mantle. One of the advantages of the method is that the width of the PM is invariant of potential mis-orientation of sensors.

We test the PM method on a set of SKS waveforms recorded at a subset of stations included in several recent or running passive seismic experiments (EASI, AlpArray, PACASE, AdriaArray). The stations form a band of about 200km broad running from the western Bohemian Massif through the Eastern Alps to the Adriatic Sea. Stations characterized by similar variations of the PM parameters group into sub-regions, which are compatible with the main tectonic features of the whole region. The formation of such lithospheric blocks of similar anisotropic signals is in agreement with 3D self-compatible anisotropic models of the mantle lithosphere domains derived from independent observables. We present complementary studies of the anisotropic structure of the mantle lithosphere in contributions by Zlebcikova et al. (GD7.1, EGU 2024), which shows anisotropic model of the upper mantle derived from 3D coupled anisotropic-isotropic teleseismic tomography (code anitomo), and in contribution by Kvapil et al. (GD7.1, EGU 2024), in which anisotropic structure of the lower crust is modelled from ambient noise.

How to cite: Vecsey, L., Plomerová, J., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: A new method to measure seismic anisotropy of the upper mantle directly from the width and orientation of the particle motion of shear waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8694, https://doi.org/10.5194/egusphere-egu24-8694, 2024.

EGU24-8851 | Orals | GD7.1

Constraining D" seismic anisotropy with reflections and splitting 

Christine Thomas and Angelo Pisconti

Detection of D" anisotropy is usually carried-out with shear wave splitting analysis. To constrain azimuthal anisotropy and infer mineralogy and deformation style, a number of crossing paths is necessary. Here we use an approach that utilises the polarity of P- and S- wave reflections from the D" discontinuity, compared with the main phases P and S, and combines these measurements with ScS splitting results. Using deformation scenarios for a number of lower(most) mantle candidate materials, we calculate the reflection coefficient for P and S-wave reflections and ScS splitting predictions. From our modelling, a clear distinction between different anisotropic media is possible by using both types of observations together. Furthermore, the approach allows to use only a single direction to distinguish between different scenarios. We apply the method to the Central/South Atlantic and South Africa, across the border of the large-low seismic velocity province (LLSVP). Shear wave splitting observations suggest that anisotropy is present in this region of the mantle, in agreement with previous studies that partially sampled this region. Modelling the observations with lattice preferred orientation and shape preferred orientation of materials expected in the D" region, we find two domains of mineralogy and deformation: sub-horizontally aligned post-perovskite outside the LLSVP, beneath the South and Central Atlantic, which is replaced by up-tilted aligned bridgmanite within the LLSVP beneath South Africa.

How to cite: Thomas, C. and Pisconti, A.: Constraining D" seismic anisotropy with reflections and splitting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8851, https://doi.org/10.5194/egusphere-egu24-8851, 2024.

EGU24-8905 | Posters on site | GD7.1

Anisotropic structure of the central European lower crust from ambient noise inversion 

Jiří Kvapil, Jaroslava Plomerová, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

Previous research of the Bohemian Massif (BM) crust with the use of ambient noise tomography (ANT) indicates a transversely isotropic structure of the lower crust (Kvapil et al. 2021). In this study, we have developed a new approach for evaluations of localised seismic anisotropy by travel time integration method.

The method calculates synthetic Rayleigh (vertical ZZ correlation) and Love (transverse TT correlation) velocities and derives the vSH/vSV from the initial 3D isotropic vSV model. The higher ratio of measured vSH/vSV to synthetic vSH/vSV indicates the existence of velocity anisotropy in the lower crust of the BM in the reference ANT model (Kvapil et al., 2021). The new method evaluates azimuthal variations of the synthetic parameters due to heterogeneities reflecting local geology effects and corrects the observed velocity ratios. Then the 1D stochastic joint (ZZ, TT) inversion is applied to retrieve the depth dependence of the velocity ratio. We use cross-correlation of ambient noise and earthquake data from seismic stations included in the AlpArray, PACASE, and Adria Array passive seismic experiments and data from the PASSEQ experiment, which complement the sparse coverage in the northern part of the BM.

Seismic anisotropy records the stress/strain conditions of each originally independent tectonic microplates during the formation of the BM crust. We demonstrate that synthetic modelling over the reference isotropic velocity model is an efficient tool for extracting radial and azimuthal shear velocity anisotropy in the lower crust directly from Rayleigh and Love wave dispersion curves. Regions with consistent parameters of seismic anisotropy correlate well with the major tectonic units of the BM. We show that variations in azimuthal and radial anisotropy of the lower crust on a regional scale can provide constraints for the reconstruction of geodynamic processes during the formation of the BM. We present complementary studies of the anisotropic structure of the mantle lithosphere in contributions by Zlebcikova et al. (GD7.1, EGU 2024), which shows an anisotropic model of the upper mantle derived from a 3D coupled anisotropic-isotropic teleseismic tomography (code anitomo), and in contributions by Vecsey et al. (GD7.1, EGU 2024), suggesting a new method for evaluation of anisotropy from shear waves.

How to cite: Kvapil, J., Plomerová, J., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: Anisotropic structure of the central European lower crust from ambient noise inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8905, https://doi.org/10.5194/egusphere-egu24-8905, 2024.

EGU24-8928 | Posters on site | GD7.1

Anisotropic tomography of the upper mantle beneath the Eastern Alps and the Bohemian Massif 

Helena Žlebčíková, Jaroslava Plomerová, Luděk Vecsey, and AlpArray Working Groups

Teleseismic body waves recorded during passive seismic experiments allow us to investigate isotropic velocities of the Earth’s upper mantle in a great detail, on scales of tens of kilometres. However, most of the tomography studies neglect the body-wave anisotropy completely or limit it either to azimuthal or radial anisotropy. We have developed a code called AniTomo for coupled anisotropic-isotropic travel-time tomography of the upper mantle (Munzarová et al., Geophys. J. Int. 2018) which allows for inversion of relative travel-time residuals of teleseismic P waves simultaneously for 3D distribution of P-wave isotropic-velocity perturbations and anisotropy of the upper mantle. We assume weak anisotropy of hexagonal symmetry with either ‘high-velocity’ axis a (lineation) and low velocity (b,c) plane or ‘low-velocity’ axis b and high velocity plane (a,c) (foliation) that is oriented generally in 3D. Such an approach of searching for orientation of the symmetry axes freely in any direction is unique and more general in comparison with the published methods that usually assume only horizontal or vertical orientation of the high-velocity symmetry axis. The code represents a step further from modelling homogeneously anisotropic blocks of the mantle lithosphere (e.g., Vecsey et al., Tectonophysics 2007; Plomerová et al., Solid Earth 2011) towards modelling anisotropy arbitrarily varying in 3D. We present complementary studies of anisotropic structure of the mantle lithosphere in contributions by Vecsey et al. (GD7.1, EGU 2024), suggesting a new method for evaluation of anisotropy from shear waves and in contribution by Kvapil et al. (GD7.1, EGU 2024), in which anisotropic structure of the lower crust is modelled from ambient noise. 

We have applied the AniTomo code on P-wave travel time deviations recorded during passive seismic experiments AlpArray-EASI (2014-2015) and AlpArray Seismic Network (2016-2019) to image the upper mantle large-scale anisotropy beneath the western part of the Bohemian Massif and the Eastern Alps. We interpret the P-wave tomography results along with results of splitting parameters from core-mantle refracted shear waves at 240 broad-band stations in about 200 km broad and 540 km long band along 13.3° E longitude. The code allows to control the depth variations and an extent of the fabric. The joint inversion/interpretation allows for distinguishing which type of the models (a-axes model or b-axis model) approximates better the anisotropic structure.

The derived anisotropic-velocity models of the mantle lithosphere cluster into domains with boundaries coinciding with boundaries of the main tectonic sub-regions. These domains are compatible with domains inferred from a joint interpretation of directional variations of P-wave travel-time residuals and SKS-wave splitting parameters. The coincidence of boundaries of the anisotropic models of the mantle lithosphere domains with main tectonic features, correlation of the anisotropy depth extent with the LAB models as well as a decrease of anisotropy strength in the sub-lithospheric mantle support fossil origin of the directionally varying component of the detected anisotropic fabrics of the continental mantle lithosphere.

How to cite: Žlebčíková, H., Plomerová, J., Vecsey, L., and Working Groups, A.: Anisotropic tomography of the upper mantle beneath the Eastern Alps and the Bohemian Massif, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8928, https://doi.org/10.5194/egusphere-egu24-8928, 2024.

EGU24-9012 | ECS | Posters on site | GD7.1

Seismic Anisotropy in Northwest Himalaya from core refracted shear (SKS) and direct S waves  

Rupak Banerjee, Frederik Tilmann, Supriyo Mitra, Tuna Eken, Keith Priestley, and Sunil Wanchoo

Recent enhancement in instrumentation in the northwest (NW) Himalaya provides an unprecedented dataset to study the deformation due to the Indo-Eurasia convergence. The NW Himalaya is unique in terms of hosting a seismic gap and a flat-ramp geometry at its decollement. We determine azimuthal  seismic anisotropy using core refracted shear waves (SKS) and interpret the results to develop insight about the prevailing geodynamics. Here, 459 raypaths with moment magnitude (Mw) >= 5.5, recorded at 15 seismographs of the J&K Seismological NETwork (JAKSNET), operational between 2013 and 2022, are used. To avoid contamination from direct S and SKiKS phases, we analyze the data within the epicentral distance range of 90°-125°, filtered at 0.04-0.2 Hz. We perform a 2-D grid search over the splitting parameters (delay time and fast axis azimuth) and compute their optimum values, for which the energy of the transverse component is minimum (MTE) after correcting for the inferred splitting. Simultaneously, the Rotation Correlation (RC) method is employed to calculate the delay time and fast axis azimuth corresponding to the maximum correlation coefficient between the splitting-corrected horizontal components. We use selection criteria based on the quality factor and the signal-to-noise ratio (SNR) to determine the measurements to be used for station averaging. The quality factor depends on the similarity of results obtained from the RC and MTE methods, hence helps in avoiding subjective interpretation about the quality of the measurement. The non-null splitting measurements passing these selection criteria are then used for station averaging applying the circular mean method and the energy map stacking method. We observe mostly N-S to NE-SW trending fast axes azimuths (13 of 15 stations); this direction corresponds to the absolute plate motion of India in a no-net rotation frame. The two remaining stations show average NW-SE fast directions, which are parallel to the mountain front, but also these stations show somewhat contradictory single splitting measurements, and one of those two anomalous stations is located very close to stations with NE-SW fast measurements, so we will not interpret these. The mean delay times range from 1.5-3.3 s, with the majority of the stations exhibiting > 2s split time being situated on the foreland basin deposits of the Sub-Himalaya. The high absolute Indian plate motion of 51 mm/yr appears to align the upper mantle olivine beneath the orogeny and NE oriented fast axes track the mantle flow manifested by the basal shear of the plate motion. To complement the SKS data, which are dominated by results with eastern backazimuths and corresponding initial polarisation, we further measured splitting for direct S-wave with the reference station method. Here, the correlation between the horizontal traces of the target and reference stations is maximised after correcting the target trace with trial splitting parameters and differences in gain; the reference station trace has previously been corrected for SKS splitting. We will present direct S splitting measurements from 370 events with Mw>=5.5 and distance within 40°-80° with an interstation spacing of <120 km.

How to cite: Banerjee, R., Tilmann, F., Mitra, S., Eken, T., Priestley, K., and Wanchoo, S.: Seismic Anisotropy in Northwest Himalaya from core refracted shear (SKS) and direct S waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9012, https://doi.org/10.5194/egusphere-egu24-9012, 2024.

EGU24-12689 | Orals | GD7.1

Full waveform anisotropic tomography of the transition zone beneath the south west Pacific 

Dorian Soergel, Utpal Kumar, Nicolas Valencia, and Barbara Romanowicz

The presence of ponding slabs at the base of the mantle transition zone (600-700 km) has been well known for a long time and can be explained by the changes in material properties related to phase changes around this depth. However, recent tomographic studies have shown the presence of slabs stagnating at larger depths of around 1000 km. While geodynamic simulations and experiments provide different insights, seismic tomography is crucial to constrain these geodynamic models. More specifically, seismic anisotropy is of particular interest to understand the dynamics of the mantle because of its sensitivity to the flow of mantle material.

The south-west pacific zone is an area with a very complex tectonic setting, with several subduction zones in a relatively small area, illuminated by a very high level of seismicity. It is thus of particular interest to understand the dynamics of the extended transition zone. As such, it has been the object of numerous tomographic studies, including high-resolution full-waveform tomography. In most cases, these studies only invert for radial anisotropy, as azimuthal anisotropy is generally more difficult to measure. However, azimuthal anisotropy is equally important as radial anisotropy and a proper interpretation in terms of mantle flow requires both. We present updated results of a full-waveform inversion of the region including azimuthal anisotropy recovered from body and surface waveforms and XKS-splitting data.

How to cite: Soergel, D., Kumar, U., Valencia, N., and Romanowicz, B.: Full waveform anisotropic tomography of the transition zone beneath the south west Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12689, https://doi.org/10.5194/egusphere-egu24-12689, 2024.

EGU24-12788 | ECS | Posters on site | GD7.1

P-wave anisotropic tomography unveils the crustal structure of Etna volcano (Italy) 

Rosalia Lo Bue, Francesco Rappisi, Marco Firetto Carlino, Elisabetta Giampiccolo, Ornella Cocina, Brandon Vanderbeek, and Manuele Faccenda

Mount Etna (Italy), renowned for its persistent eruptive activity, is a hazardous volcano shaped by the intricate interplay between magma uprising and a complex tectonic and geodynamic context. Despite extensive monitoring, seismic tomography encounters challenges in accurately depicting the shallow-intermediate P-wave velocity structures, primarily due to the common assumption of isotropy. This study discards such simplification, employing a novel methodology (Vanderbeek and Faccenda, 2021) to simultaneously invert for perturbations to P-wave isotropic velocity and three additional anisotropic parameters (i.e., magnitude of hexagonal anisotropy, azimuth, and dip of the symmetry axis).

By analysing the seismicity recorded in the Mt. Etna area from 2006 to 2016, we constructed 3D anisotropic P-wave tomography models to better constrain the crustal structure of Etna volcano within the framework of its local tectonic setting. The revealed anisotropy patterns are consistent with the structural trends of Etna, unveiling the depth extent of fault segments. We identify a high-velocity volume, deepening towards northwest, recognized as the collision-related subducting foreland units (i.e. Hyblean foreland carbonate slab; Firetto Carlino et al., 2022) that appear to confine a low velocity anomaly, hypothesized to be the expression of a deep magmatic reservoir. A likely tectonic-origin discontinuity affects the subducting units, facilitating the transfer of magma from depth to the surface. This geological setting may explain the presence of such a very active basaltic strato-volcano within an atypical collisional geodynamic context. 

This research improves our understanding of the dynamics governing magma and fluid ascent beneath the volcanic edifice and emphasises the importance of considering anisotropy in seismic investigations. It contributes to our framework for understanding volcanic processes and mitigating associated risks.

 

VanderBeek, B. P., & Faccenda, M. (2021). Imaging upper mantle anisotropy with teleseismic P-wave delays: insights from tomographic reconstructions of subduction simulations. Geophysical Journal International, 225(3), 2097-2119.

Firetto Carlino, M., Scarfì, L., Cannavò, F., Barberi, G., Patanè, D., & Coltelli, M. (2022). Frequency-magnitude distribution of earthquakes at Etna volcano unravels critical stress changes along magma pathways. Communications Earth & Environment, 3(1), 68.

How to cite: Lo Bue, R., Rappisi, F., Firetto Carlino, M., Giampiccolo, E., Cocina, O., Vanderbeek, B., and Faccenda, M.: P-wave anisotropic tomography unveils the crustal structure of Etna volcano (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12788, https://doi.org/10.5194/egusphere-egu24-12788, 2024.

EGU24-13005 | Orals | GD7.1

Azimuthal and radial anisotropy in the upper mantle from global adjoint tomography 

Ebru Bozdag, Ridvan Orsvuran, Lijun Liu, and Daniel Peter

Earth’s upper mantle and lithosphere show significant evidence for anisotropy related to deformation and composition. First-generation GLAD (GLobal ADjoint) models (GLAD-M15 (Bozdag et al. 2016), GLAD-M25 (Lei et al. 2020), GLAD-M35 (Cui et al. submitted)) are radially anisotropic in the upper mantle. Starting from GLAD-M25, we performed 25 conjugate gradient iterations and constructed model GLAD-M50-AZI by including azimuthal anisotropy in the parameterization of the inverse problem. We inverted azimuthally anisotropic normalized parameters Gc’ and Gs’ simultaneously with vertically and horizontally polarized shear waves beta_v and beta_h, respectively. Due to our parameterization, our data set consists of only minor- and major-arc Rayleigh and Love waves from 300 globally distributed earthquakes. GLAD-M50-AZI captures plate motions globally well, which are also supported by the transverse isotropy, specifically at the subducted slabs and mid-ocean ridges. Furthermore, it approaches continental-scale resolution in regions with good data coverage depicting smaller-scale tectonic and flow patterns, giving us a chance to have a more detailed and unified view of the anisotropy globally. In the next step, we explore how anisotropy derived from seismic tomography compares to geodynamical modeling observations to have better insight into mantle dynamics. We perform numerical simulations to compute synthetic seismograms and full-waveform inversion on Texas Advanced Computing Center’s Frontera system. 

How to cite: Bozdag, E., Orsvuran, R., Liu, L., and Peter, D.: Azimuthal and radial anisotropy in the upper mantle from global adjoint tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13005, https://doi.org/10.5194/egusphere-egu24-13005, 2024.

EGU24-13585 | ECS | Orals | GD7.1

Exploring the Development of Shear Wave Radial Anisotropy in the Lower Mantle due to Slab-induced Plume Generation from LLSVPs 

Poulami Roy, Bernhard Steinberger, Manuele Faccenda, and Juliane Dannberg

Seismic anisotropy, which involves directionally dependent wave propagation, is likely to occur in the lowermost few hundreds km of the mantle, especially at the edges of Large Low Shear Velocity Provinces (LLSVPs). This anisotropy may be indicative of significant deformation, potentially due to mantle flow interacting with the sides of these provinces or the generation of mantle plumes. In this study, we investigate subducted slab induced plume generation from an LLSVP boundary and the flow behaviour of the lower mantle using compressible 2-D and 3-D mantle convection models in the geodynamic modeling software ASPECT combined with mantle fabric simulation in ECOMAN. In our geodynamic simulation, we assume that the LLSVPs are chemically distinct piles with intrinsically high viscosity. We use the Clapeyron slope of the phase transition from Bridgmanite to post-Perovskite from the previous mineralogical study by Oganov & Ono (2004) in the mantle fabric calculation. Modeling lattice preferred orientation of Bridgmanite and post-Perovskite in the lower mantle reveals that the lower mantle is overall isotropic except the regions of plume conduits and the surroundings of the subducted slab where vertically polarized shear wave (Vsv ) is faster. The generation of anisotropy are caused by the accumulation of high finite strain in these regions. The bottom 300 km of the lower mantle is characterized by fast horizontally polarized shear wave (Vsh ) beneath the subducted slab which deflects to fast Vsv at the margins of the LLSVPs due to the rheological contrast between the highly viscous LLSVP and less viscous ambient mantle. Our result shows that six possible slip systems [100](010), [100](001), [010](100), [001](100), [110](-110) and [-110](110) of Bridgmanite and the slip system [100](001) of post-Perovskite can produce a fast Vsv in the plume generation zones where post-Perovskite transforms to Bridgmanite and fast Vsh at the base of the subducted slab where post-Perovskite is preserved in the D”. However, our models do not show anisotropy inside of the LLSVPs and the subducted slab, possibly because of their high viscosity. Our findings are comparable with the previous seismic observations beneath the Iceland plume where Vsv > Vsh and the slab-driven flow at the base of the mantle beneath the northeastern Pacific Ocean where Vsh > Vsv .

How to cite: Roy, P., Steinberger, B., Faccenda, M., and Dannberg, J.: Exploring the Development of Shear Wave Radial Anisotropy in the Lower Mantle due to Slab-induced Plume Generation from LLSVPs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13585, https://doi.org/10.5194/egusphere-egu24-13585, 2024.

EGU24-14416 | Orals | GD7.1

Examining Depth Origin of Anisotropy in an Active Orogenic Belt of Taiwan Using Shear Wave Splitting Results from the Formosa Array. 

Ratna Mani Gupta, Hsin-Hua Huang, Po-Fei Chen, Cheng-Horng Lin, and Cheng-Chien Peng

The Taiwan orogenic belt originates from the collision between the Philippine Sea Plate (PSP) and the Eurasian Plate (EU) with a subduction polarity reversal. The reversal around northern Taiwan creates a complex geodynamic process from subduction waning to post-collision extension. We study the deformation fabric with the shear wave splitting (SWS) method to unravel this tectonic complexity using multiple core phases (PKS, SKS, and SKKS, hereafter XKS). Prevailing SWS research acknowledged the presence of orogen-parallel anisotropy. However, recent studies with numerical modeling and coherency analysis suggested that the anisotropy source is in the asthenosphere. A recent dense seismic array (Formosa Array) of 148 seismic stations in northern Taiwan enables us to revisit this debate with improved spatial and back azimuthal coverage of the SWS measurements. The results show distinct variations in fast direction (Φ) from different back-azimuths and a much larger average delay time (dt) of ~2 sec compared to that derived from local subduction events (at 100-250 km depth). Application of the Fresnel zone and spatial coherency analysis also support an asthenospheric source for the observed anisotropy. The findings emphasize the need for depth-source analysis of anisotropy to better elucidate the responsible mechanisms of complex tectonic settings.

How to cite: Gupta, R. M., Huang, H.-H., Chen, P.-F., Lin, C.-H., and Peng, C.-C.: Examining Depth Origin of Anisotropy in an Active Orogenic Belt of Taiwan Using Shear Wave Splitting Results from the Formosa Array., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14416, https://doi.org/10.5194/egusphere-egu24-14416, 2024.

EGU24-14883 | ECS | Posters on site | GD7.1

Modeling pressure-dependent seismic anisotropy in the lower mantle reveals anisotropic discontinuity at 1000 km 

John Keith Magali, Christine Thomas, Jeffrey Gay, Angelo Pisconti, and Sebastien Merkel

There is growing evidence, both from a modelling perspective and seismic observations, that seismic anisotropy in the lower mantle is localized around penetrating slabs where large straining is anticipated. It is believed that the high stresses experienced near the slab activate dislocation creep mechanisms that drive the crystallographic preferred orientation (CPO) of bridgmanite aggregates. Still, deformation mechanisms in bridgmanite remain enigmatic. In recent years, deformation experiments in bridgmanite subjected to mantle temperatures and pressures suggest that its microstructures evolve with pressure, providing another perspective on the debated structure and deformation in the lower mantle. Using this information, we develop a numerical technique that calculates pressure-dependent large-scale seismic anisotropy in a pyrolitic mantle with variable velocity gradients. As a first test, we use the method to predict seismic anisotropy by calculating anisotropic reflection coefficients of underside reflections off a depth corresponding to 50 GPa where pressure-induced slip transitions in bridgmanite are expected. For this, we consider two simple deformation styles: (1) uni-axial compression, akin to vertically penetrating slabs, and (2) simple shear associated with corner-type flows. Finally, we demonstrate a multiscale approach that calculates large-scale seismic anisotropy from a fully time-dependent thermo-chemical model of free subduction with latent heating and phase transitions. The result is a long-wavelength equivalent azimuthal and radial anisotropy maps that are actually comparable to a seismic tomography model. We demonstrate how such an approach can create discontinuities in anisotropy at ~1000 km and provide insights as to how it relates to the heterogeneous distribution of the 1000-km discontinuity.

How to cite: Magali, J. K., Thomas, C., Gay, J., Pisconti, A., and Merkel, S.: Modeling pressure-dependent seismic anisotropy in the lower mantle reveals anisotropic discontinuity at 1000 km, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14883, https://doi.org/10.5194/egusphere-egu24-14883, 2024.

EGU24-15225 | ECS | Orals | GD7.1

Exploring Mantle Dynamics of the Cascadia Subduction System through Anisotropic Tomography with Transdimensional Inference Methods 

Brandon VanderBeek, Gianmarco Del Piccolo, and Manuele Faccenda

The Cascadia subduction system is an ideal location to investigate the nature of mantle flow and associated driving forces at a convergent margin owing to the dense network of on- and off-shore seismic instrumentation. While numerous shear wave splitting and tomography studies have been performed with these data, they have produced conflicting views of mantle dynamics collectively referred to as the Cascadia Paradox. On the overriding plate, splitting observations are consistent with large-scale 3D toroidal flow while off-shore splitting patterns are more easily explained by 2D plate-driven flow. Either geometry is difficult to reconcile with seismic tomographic models that image a fragmented Juan de Fuca slab descending beneath the Western USA. However, these observations offer only an incomplete image of Cascadia mantle structure. Shear wave splitting provides a depth integrated view of anisotropic fabrics making inferences regarding the 3D nature of mantle deformation difficult. Prior high-resolution body wave tomography typically neglects anisotropic effects which can in turn yield significant isotropic imaging artefacts that complicate model interpretation. To overcome these limitations, we invert P-wave delay times for a 3D hexagonally anisotropic model with arbitrarily oriented symmetry axes using the reversible jump Markov chain Monte Carlo algorithm. This stochastic imaging approach is particularly well-suited to the highly non-linear and under-determined nature of the anisotropic seismic tomography problem. The resulting ensemble of solutions allows us to rigorously assess model parameter uncertainties and trade-off between isotropic and anisotropic heterogeneity. We investigate whether the fragmented nature of the subducted Juan de Fuca slab is a well-resolved feature and to what extent its geometry trades off with anisotropic parameters. In light of our new 3D anisotropic model, we re-evaluate the Cascadia Paradox and attempt to reconcile disparate views of Western USA mantle dynamics.

How to cite: VanderBeek, B., Del Piccolo, G., and Faccenda, M.: Exploring Mantle Dynamics of the Cascadia Subduction System through Anisotropic Tomography with Transdimensional Inference Methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15225, https://doi.org/10.5194/egusphere-egu24-15225, 2024.

EGU24-16887 | ECS | Posters on site | GD7.1

The effect of centimeter-scale folding and crenulation on anisotropy homogenization of schists and phyllites from the NW-Tauern Window (Eastern Alps, Austria) 

Dustin Lang, Rebecca Kühn, Rüdiger Kilian, Hannah Pomella, and Michael Stipp

The interpretation of seismic data in orogens is usually difficult to decipher as structural information is limited to surface and borehole data. Seismic interpretations very much depend on the elastic wave velocity model, which in the simplest case is a function of rock composition. Seismic velocities can also be anisotropic, i.e. depend on the wave propagation direction inside the rock. Seismic anisotropy can be subdivided into intrinsic (crystallographic preferred orientation (CPO)) and extrinsic (shape preferred orientation, compositional layering or fractures) anisotropy. Microstructures in thin section scale have an impact not only on millimeter-scale but also on larger anisotropies in the field such as meter- to kilometer-scale folds. Here we explore the effect of microstructure (mainly folding and crenulation) on the homogenization of seismic anisotropy from samples of millimeter to thin section scale.

The investigated samples are phyllosilicate- and graphite-rich samples (Innsbruck quartzphyllite and Bündner schist) from the N-S running Brenner Base Tunnel Project (NW-Tauern Window). Phyllosilicate-rich sections with layers of different composition and structure were selected from drill core samples of the exploration tunnel. The CPO of phyllosilicates and graphite from 1.5 – 3.5 mm thick cylinders was measured using high energy X-ray diffraction at DESY (Hamburg, Germany) and the ESRF (Grenoble, France). Pole figure data was directly extracted using single peak fitting. The CPO of quartz was determined by using EBSD. Seismic velocities for each sample were computed using µXRF-based modal composition and single crystal stiffness tensors. We measured the smallest representative volume element which we consider to be undisturbed by microstructural effects. Therefore, we estimate an upper bound of expected intrinsic velocity anisotropies. Thin section-scale anisotropies were modeled from the upper bound anisotropy and the observed microstructure, i.e., small-scale folding. Computed velocities were compared to Vp-anisotropy measurements on the drill cores.

The velocity anisotropy is primarily governed by the content and distribution of phyllosilicates and graphite. Given the crystal symmetry and the low single crystal elastic anisotropy, phases such as feldspar, quartz or calcite can be considered as irrelevant with respect to seismic anisotropies. The simulation of a crenulation cleavage has a stronger impact than centimeter-size folding: The crenulation cleavage reduces the anisotropy for example from 14 % to 12 %. Centimeter-size folding with observed interlimb angles of 140° in contrast is negligible.

The effect of microstructures like centimeter-scale folds and crenulation has only a limited impact on anisotropies of foliated rocks during homogenization from millimeter to thin section-scale. We assume that during homogenization to a larger scale, the effect of folding with small interlimb angles or different fold axes within the homogenized volume will have a stronger influence on seismic anisotropy.

How to cite: Lang, D., Kühn, R., Kilian, R., Pomella, H., and Stipp, M.: The effect of centimeter-scale folding and crenulation on anisotropy homogenization of schists and phyllites from the NW-Tauern Window (Eastern Alps, Austria), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16887, https://doi.org/10.5194/egusphere-egu24-16887, 2024.

EGU24-17055 | ECS | Orals | GD7.1

Deformation of the Indian Lithosphere from radial anisotropy: Signatures of laterally varying plate geometry beneath Tibet and hotspot volcanism beneath the Deccan Plateau.  

Arijit Chakraborty, Monumoy Ghosh, Siddharth Dey, Shubham Sharma, Sankar N. Bhattacharya, and Supriyo Mitra

The Indian Lithosphere has been shaped by multiple tectonic processes, which include break-up from the Gondwana Supercontinent, traversing over the Reunion and Kerguelen hotspots, collision with Eurasia, and underthrusting beneath the Himalaya and Tibetan Plateau. Seismic velocity structure and radial anisotropy of the lithosphere preserves imprints of these  tectonic processes and related deformation. We perform joint-modeling of fundamental-mode Rayleigh (LR) and Love (LQ) wave group-velocity dispersion, for periods between 10 and 120s, to obtain radially anisotropic shear-wave velocity structure across India, Himalaya and Tibet. 1D path-average dispersion curves, computed for ~14700 regional earthquake-receiver raypaths, has been passed through systematic quality control of signal-to-noise ratio (>3), elimination of multipathed energy using polarization analysis, and removal of overtone interference, by synthetic tests. These 1D dispersion data are combined through a tomographic formulation to obtain 2D maps. The tomographic parametrization is done using  4906 nodes as apex of triangular elements of side 1°. LR and LQ fundamental-mode group-velocity dispersion data at these nodes are the observation input to the joint inversion. The inversion is done in 2-steps, first by parameterizing the model as isotropic layers and using an isotropic inversion scheme to obtain the best fitting Vs model; second using this output Vs model into an anisotropic inversion scheme, implemented using Genetic Algorithms (GA). GA exhaustively searches the model-space composed of Vsh, Vph and Xi[Vsh^2/Vsv^2] as free parameters. The fit to both LR and LQ datasets significantly improve in the anisotropic inversion. 

 

Results are presented as 2D depth-slice maps and cross-sections constructed using bilinear interpolation. The main findings from our models are lateral variation in the voigt-average Vs beneath the Tibetan Plateau at depth between 80-140 km. Western Tibet has high Vs and positive Xi, while Central-Eastern TIbet has Low Vs and negative Xi. From cross-sections across both regions, we infer that the dip and underthrusting of the Indian Plate beneath Tibet has lateral variation. The high Vs and positive anisotropy in Western Tibet indicates a shallow underthrusting of the Indian lithosphere up to the Tarim Basin, with simple-shear deformation. Where as, the lower Vs and negative anisotropy in Central-Eastern Tibet is a result of partial-underthrusting of India at a steeper-angle up to the Bangong-Nujiang Suture, and pure-shear deformation of thickened Tibet Lithosphere beneath North-Central Tibet. A negative anisotropy signature along the Reunion volcanic track is observed between 100 and 160 km depth. We infer this to be the signature of  Reunion hotspot volcanism in the Indian lithosphere caused by the vertical ascent of a huge volume of melt arising from the plume-head. Similar observations are also made beneath the track of the Kergulean hotspot. 

How to cite: Chakraborty, A., Ghosh, M., Dey, S., Sharma, S., Bhattacharya, S. N., and Mitra, S.: Deformation of the Indian Lithosphere from radial anisotropy: Signatures of laterally varying plate geometry beneath Tibet and hotspot volcanism beneath the Deccan Plateau. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17055, https://doi.org/10.5194/egusphere-egu24-17055, 2024.

EGU24-17743 | Orals | GD7.1

Predicting seismic anisotropy in the upper mantle using supervised deep-learning 

Andrea Tommasi, Nestor Cerpa, Fernando Carazo, and Javier Signorell

Both elastic and viscoplastic behaviors of the Earth’s upper mantle are highly anisotropic, because olivine, which composes 60-80% of the mantle, has a strong intrinsic anisotropy and develops strong crystal preferred orientations (CPO). Predicting the evolution of anisotropy with strain is essential to: (1) probe indirectly the deformation in the mantle based on seismic measurements and (2) accounting for the deformation history when simulating the long-term dynamics of the Earth. However, traditional micro-mechanical approaches to model the evolution of CPO-induced elastic and viscous anisotropies are too memory-costly and time-consuming for coupling into geodynamical simulations. To speed up the prediction of seismic anisotropy in the mantle, we developed deep-learning (DL) surrogates trained on a synthetic database built with viscoplastic self-consistent simulations of texture evolution of olivine polycrystals in typical 2D geodynamical flows. A first challenge was the choice of memory-saving representations of the CPO. Training the DL models on the evolution of the elastic tensor components avoided the need of storing the CPOs. However, the major challenge has been to prevent error compounding in a recursive-prediction scheme – where a model prediction at a given time step becomes the input for the next one - to evaluate the anisotropy evolution along a flow line. We implemented multilayer feed-forward (FFNN), ensemble, and transformer neural networks, obtaining the best efficiency/accuracy ratio for the FFNN. The results highlight the importance of (1) the standardization of the outputs in the training stage to avoid overfitting in predictions, (2) the statistical characteristics of the strain histories in the training database, and (3) the influence of non-monotonic strain histories on error propagation. Predictions for complex unseen strain histories are accurate, much more time-efficient and memory-costly than the traditional micro-mechanical models. Our work opens thus new avenues for modeling the strain-controlled evolution of mechanical anisotropy in the Earth’s mantle. This work was supported by the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation programme [grant agreement No 882450 – ERC RhEoVOLUTION.

How to cite: Tommasi, A., Cerpa, N., Carazo, F., and Signorell, J.: Predicting seismic anisotropy in the upper mantle using supervised deep-learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17743, https://doi.org/10.5194/egusphere-egu24-17743, 2024.

EGU24-18148 | ECS | Orals | GD7.1

Trans-dimensional Mt. Etna P-wave anisotropic seismic imaging 

Gianmarco Del Piccolo, Rosalia Lo Bue, Brandon Paul VanderBeek, Manuele Faccenda, Ornella Cocina, Marco Firetto Carlino, Elisabetta Giampiccolo, Andrea Morelli, and Joseph Byrnes

Trans-dimensional inference identifies a class of methods for inverse problems where the number of free parameters is not fixed. In seismic imaging these methods are applied to let the data, and any prior information, decide the complexity of the models and how the inferred fields partition the inversion domains. Monte Carlo trans-dimensional inference is performed implementing the reversible-jump Markov chain Monte Carlo (rjMcMC) algorithm; the nature of Monte Carlo exploration allows the algorithm to be completely non-linear, to explore multiple possibilities among models with different dimensions and meshes and to extensively investigate the under-determined nature of the tomographic problems, showing quantitative evidence for the limitations in the data-sets used. Implementations of this method overcome the main limitations of traditional linearized solvers: the arbitrariness in the selection of the regularization parameters, the linearized iterative approach and in general the collapse of the information behind the solution into a unique inferred model.

We present applications of the rjMcMC algorithm to anisotropic seismic imaging of Mt. Etna with P-waves. Mt. Etna is one of the most active and monitored volcanoes in the world, typically investigated under the assumption of isotropic seismic speeds. However, since body waves manifest strong sensitivity to seismic anisotropy, we parametrize a multi-fields inversion to account for the directional dependence in the seismic velocities. Anisotropy increases the ill-condition of the tomographic problem and the consequences of the under-determination become more relevant. When multiple seismic fields are investigated, such as seismic speeds and anisotropy, the data-sets used may not be able to independently resolve them, resulting in non-independent estimates and corresponding trade-offs. Monte Carlo exploration allows for the evaluation of the robustness of seismic anomalies and anisotropic patterns, as well as the trade-offs between isotropic and anisotropic perturbations, key features for the interpretation of tomographic models in volcanic environments. The approach is completely non-linear, free of any explicit regularization and it keeps the computational time feasible, even for large data-sets.

How to cite: Del Piccolo, G., Lo Bue, R., VanderBeek, B. P., Faccenda, M., Cocina, O., Firetto Carlino, M., Giampiccolo, E., Morelli, A., and Byrnes, J.: Trans-dimensional Mt. Etna P-wave anisotropic seismic imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18148, https://doi.org/10.5194/egusphere-egu24-18148, 2024.

EGU24-21240 | Posters on site | GD7.1

Anisotropy and XKS-splitting from geodynamic models of double subduction: Testing the limits of interpretation 

Jan Philipp Kruse, Georg Rümpker, Frederik Link, Thibault Duretz, and Harro Schmeling

We utilize three-dimensional geodynamic models to predict XKS-splitting in double subduction scenarios characterized by two outward-dipping slabs. These models are highly applicable in various realistic settings, such as the central Mediterranean. Our primary focus is on the analysis of XKS-splitting, a key geophysical observable used for inferring seismic anisotropy and mantle flow patterns.Our models simulate the concurrent subduction of two identical oceanic plates separated by a continental plate. The variation in the strength of the separating plate causes a transition from a retreating to a stationary trench. The models offer detailed insights into the temporal evolution of mantle flow patterns, particularly the amount of trench-parallel flow induced by this specific type of subduction.In the subsequent step, we employ the well-known D-Rex model to estimate Crystallographic Preferred Orientation (CPO) development in response to plastic deformation resulting from mantle flow. Based on the D-Rex model results, which incorporate the full elastic tensor of a deformed multiphase polycrystalline mantle aggregate, we derive synthetic apparent splitting parameters and splitting intensities at virtual receivers placed at the surface using multiple-layer anisotropic waveform modeling. To identify regions with pronounced depth-dependent variations of anisotropic properties, particularly the fast polarization directions, we define a complex anisotropy factor dependent on the apparent splitting parameters and splitting intensities.Finally, using the apparent splitting parameters, we conduct two-layer model inversions at selected locations characterized by a large complex anisotropy factor. The two-layer model provides apparent splitting parameters as a result of analytical waveform modeling for two anisotropic layers. We observe that while several models can effectively explain the apparent splitting parameters, only a subset can accurately reproduce the depth-dependent anisotropic properties. Our findings unequivocally demonstrate that a classical XKS-splitting analysis can effectively identify areas characterized by complex anisotropy and provide accurate approximations of the depth-dependent variations of anisotropic properties within these regions. However, caution is warranted when interpreting results obtained through inversion based on a two-layer analysis.

How to cite: Kruse, J. P., Rümpker, G., Link, F., Duretz, T., and Schmeling, H.: Anisotropy and XKS-splitting from geodynamic models of double subduction: Testing the limits of interpretation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21240, https://doi.org/10.5194/egusphere-egu24-21240, 2024.

EGU24-1660 | ECS | Orals | GD7.2

Structural softening in poro-elasto-plastic media 

Yury Alkhimenkov and Ruben Juanes

Structural softening is a well-known phenomenon in single-phase materials. If we consider a single-phase material, assume an elastoplastic rheology, and perform a strain-driven loading under pure shear boundary conditions, the evolution of the integrated stress will exhibit a softening beyond its peak. This is true for non-associated flow rules considering an ideal plasticity model with, for example, Mohr-Coulomb or Drucker-Prager yield criteria. The post-peak softening is usually associated with the development of the localized shear zones. However, this phenomenon hasn’t been properly analyzed for the case of porous rocks modeled with the quasi-static Biot’s poroelastic equations.

In this contribution, we present numerical results considering the poro-elasto-plastic rheology with a focus on structural softening. We show that the post-peak structural softening might be significant and exhibit large stress drops. The most important outcome is that even a little fluid overpressure leads to much larger stress drops compared to scenarios without any kind of fluid overpressure. This result may shed some light on the phenomenon of large earthquakes associated with small injection rates in geothermal or CO2 sequestration fields.

 

References:

Vermeer, P. A. (1990). The orientation of shear bands in biaxial tests. Géotechnique40(2), 223-236.

How to cite: Alkhimenkov, Y. and Juanes, R.: Structural softening in poro-elasto-plastic media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1660, https://doi.org/10.5194/egusphere-egu24-1660, 2024.

EGU24-4132 | ECS | Orals | GD7.2

On the link between subduction and lithospheric texture : insights from convection in colloidal dispersions 

Manon Pépin, Gianluca Gerardi, Hugo Remise-Charlot, Christiane Alba-Simionesco, and Anne Davaille

Strain-localization along plate boundaries and subduction of the lithosphere are key-features of Earth’s mantle plate tectonics and convective dynamics. Numerous mechanisms, operating on various time and length-scales, are able to produce strain localization. But the exact process(es) that control lithospheric subduction from convection in a viscous mantle remain debated. Laboratory experiments, where one can 1) characterize and control the fluid rheology, and 2) determine the structure/texture of the resulting lithosphere, can give valuable constraints to the ongoing discussion. To date, we have found only one fluid able to produce in the laboratory self-consistent subduction during convection: colloidal dispersions of silica nanoparticles (‘NP’). These fluids encompass a large diversity of rheological behavior, from viscous to elasto-visco-plastic to brittle, depending on the nanoparticles volume fraction. But we can now go one step further, and investigate the links between the rheological properties and the nanoparticles’organization.

 

So we studied Ludox® dispersions with NP of two different diameters (16 and 28 nm) and vary the water concentration, while keeping the ionic content constant. The rheology is characterized using shear rate and oscillatory tests. The organization of the nanoparticles is probed with Small-Angle Neutron Scattering (SANS) and Small-Angle X-ray Scattering (SAXS) measurements, and the solvent (water) state thanks to thermal analysis (ThermoGravimetric Analysis, TGA, and Differential Scanning Calorimetry, DSC). These measurements allow us to identify three types of water, (i) water adsorbed at the surface of the particles, (ii) water confined in nano-cavities and (iii) free water, and to determine the evolution of their amounts with increasing particle volume fraction. Rheology seems mainly controlled by the amount of free water. As the fraction of the latter decreases, the material becomes more heterogeneous at the meso-scale, with the formation of particle aggregates and free water channels. The rheology becomes more non-newtonian with the apparition of a yield stress, which value increases with decreasing free water. In convection-evaporation experiments, this results in the formation of a lithospheric « skin » floating on a less concentrated solution, and strong localization of deformation on this heterogeneous skin that can induce its break-up and subduction. Interestingly enough, subduction is observed for skins still containing a little amount of free water (0.2-1%). On a rocky planet, this suggests that the existence of partial melt in the asthenosphere and the lithosphere could be important to allow subduction. This could explain why localized subduction may exist on present-day Venus: eventhough there is no liquid water ocean on the surface of Venus today, there is plenty of evidence of active volcanism, which indicate the existence of a sizable amount of partial melt.  

How to cite: Pépin, M., Gerardi, G., Remise-Charlot, H., Alba-Simionesco, C., and Davaille, A.: On the link between subduction and lithospheric texture : insights from convection in colloidal dispersions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4132, https://doi.org/10.5194/egusphere-egu24-4132, 2024.

Ophiolites are remnants of oceanic crust and mantle, now typically found within continental mountain ranges. Particularly in areas once part of the Tethys Ocean, ophiolites are often accompanied by narrow strips of metamorphic rocks, commonly referred to as metamorphic soles. These rocks exhibit peak metamorphic conditions characteristic of either granulite or amphibolite facies. Geochronological studies of Tethyan ophiolites indicate that the development of these metamorphic soles occurred almost simultaneously with the crystallization of the ophiolite's crustal sequence. Geological evidence also suggests that the metamorphism of the sole rocks took place concurrently with deformation, likely at the same time as the ophiolite's obduction. In our research, we explore the metamorphic effects of shearing in an ophiolite sequence overlying a crustal sequence. Our findings reveal that a strong crustal lithology can produce additional heat through the dissipation of mechanical energy, which can explain the high temperatures found in metamorphic-sole rocks. In addition, heating of the footwall rocks eventually leads to the migration of the active shear zone from the mantle sequence into the upper crustal domain. This migration is responsible for the metamorphic sole incorporation at the base of the ophiolite. Finally, we demonstrate that stopping the shearing process rapidly cools these rocks, corresponding with the findings from thermochronological studies from Oman ophiolite.

How to cite: Ibragimov, I. and Moulas, E.: A thermo-mechanical model of the thermal evolution and incorporation of the metamorphic sole in the Oman ophiolite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5497, https://doi.org/10.5194/egusphere-egu24-5497, 2024.

EGU24-8478 | Orals | GD7.2

Reaction-driven mineral expansion and its impact on fluid flow 

Viktoriya Yarushina, Johannes C. Vrijmoed, and Lawrence H. Wang

Addressing climate change necessitates shifting from fossil fuels to renewables and implementing carbon capture and storage (CCS). Storing CO2 in mafic and ultramafic rocks is appealing due to the potential for mineral conversion. Recent pilot studies showed the feasibility of mineral CO2 storage in basalts. However, combating climate change requires increasing injection volumes by several orders of magnitude. Discussion continues on whether mineralization processes will still be as efficient at larger scales. One foreseen issue is the potential pore clogging due to mineral precipitation, eventually impeding the reaction. While reactive transport models based on dissolution-precipitation mechanism predict pore clogging and thus the limited extent of reaction, there is clear field evidence for complete reactions in natural analog systems. Besides, developing new injection sites requires pre-injection feasibility studies based on numerical simulations. These simulations aim to provide an initial evaluation of the potential success and challenges associated with the proposed CO2 injection project. They require large-scale, high-resolution simulations, which are challenging for commercially available codes. Recent success in using GPUs for scientific computing combined with matrix-free numerical methods stimulates the development of new numerical models and the revisiting of underlying theoretical approaches. CCS in depleted reservoirs, especially with old plugged-and-abandoned wells, also presents challenges. CO2 interacting with old cement compositions may compromise well integrity, leading to potential CO2 leakage along wellbores. Chemical reactions, fluid flow, and deformation are intricately coupled processes. Studies highlight the dependence of reaction progress both on assumed kinetics and constitutive hydro-mechano-chemical models. While conventional knowledge suggests transport-dominated reactions leading to pore clogging, recent observations challenge this, indicating that reaction-induced alterations occur in the solid phase without changing pore volume. A novel model addressing reaction-driven mineral expansion is presented, preserving porosity while allowing solid volume change. Examining fluid-rock interaction at the pore scale, we derive effective rheology for reacting porous media. The micromechanical model assumes rocks or cement as assemblies of solid reactive grains, accommodating externally applied and reaction-induced stresses through elastic, viscous, and plastic deformation mechanisms. Depending on the level of reaction-induced stresses, the model predicts either pore clogging or porosity-preserving solid volume increase as dominant mechanisms, with the latter facilitating complete reactions. Macroscopic stress-strain constitute laws account for chemical alteration and viscoelastic deformation, elucidating the dependence of mechanical rock properties on fluid chemistry [1]. We use a two-phase continuum medium approach and local equilibrium thermodynamic models [2] to investigate the coupling between reaction, deformation, and fluid flow on a larger scale. We consider two simple examples of the carbonation of portlandite and the hydration of mantle rocks. Both reactions are associated with a change in solid volume. We show how reaction-driven mineral expansion affects the porosity evolution and reaction progress.

References:

1. Yarushina, V.M., Y.Y. Podladchikov, and H.L. Wang, On the Constitutive Equations for Coupled Flow, Chemical Reaction, and Deformation of Porous Media. Journal of Geophysical Research-Solid Earth, 2023. 128(12).

2. Vrijmoed, J.C. and Y.Y. Podladchikov, Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems. Geochemistry Geophysics Geosystems, 2022. 23(4).

How to cite: Yarushina, V., Vrijmoed, J. C., and Wang, L. H.: Reaction-driven mineral expansion and its impact on fluid flow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8478, https://doi.org/10.5194/egusphere-egu24-8478, 2024.

EGU24-8862 | Posters on site | GD7.2

Multicomponent Fluid Flow in Deforming and Reacting Porous Rock in the Earth’s crust: hydro-mechanical-chemical model 

Andrey Frendak, Lyudmila Khakimova, Leonid Aranovich, and Yury Podladchikov

We propose a coupled hydro-mechanical-chemical model and its 1D numerical implementation. We demonstrate its application to the model filtration of a multicomponent fluid in deforming and reacting host rocks, considering changes in the densities, phase proportions, and the chemical compositions of the coexisting phases.

The numerical results show the propagation of a porosity wave by means of a viscous (de)compaction mechanism accompanied by the formation of an elongated zone with higher filtration properties. After the formation of such a channel, the formation and propagation of the reaction fronts occurs and are associated with the transformation of the mineral composition of the original rock.

How to cite: Frendak, A., Khakimova, L., Aranovich, L., and Podladchikov, Y.: Multicomponent Fluid Flow in Deforming and Reacting Porous Rock in the Earth’s crust: hydro-mechanical-chemical model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8862, https://doi.org/10.5194/egusphere-egu24-8862, 2024.

EGU24-10501 | Orals | GD7.2 | Highlight

Modelling focused fluid flow in the subsurface: its controlling factors and the formation of seismic chimney  

Lawrence Hongliang Wang and Viktoriya Yarushina

Seismic chimneys, prevalent along continental margins, intricately contribute to Earth's degassing processes, facilitating fluid migration from the deep Earth to the surface. This phenomenon carries significant implications for subsurface storage utilization. Among the principal mechanisms driving seismic chimney formation is the fluid flow instability within porous subsurface rocks. While numerical studies of geodynamical two-phase flow have successfully replicated vertical fluid flow structures, many of these models overlook elastic compaction, advection of solid and poro-space, and geological heterogeneity, thereby limiting their applicability in subsurface scenarios. In addressing these limitations, this study incorporates a viscoelastic rheology into the geodynamical two-phase flow model to explore the controlling factors influencing the formation of focused fluid flow, accounting for various rock properties, including geological heterogeneity. Initial investigations into the impact of elastic compaction by varying Deborah numbers reveal a limited influence on fluid flow compared to viscous compaction. Through a comparative analysis of models with and without advection, we observe the potential importance of solid advection in fluid migration, particularly under conditions of high background porosity (≥0.1) and relatively low permeability. This effect is accentuated when the solid matrix undergoes significant deformation. Channel widths range from 2-3 compaction lengths to a maximum of 5-10 compaction lengths, primarily contingent on the viscosity ratio between shear and bulk viscosity and the fluid supply. Further simulations involving fluid flow encountering a horizontal block with rock heterogeneity and geological heterogeneity demonstrate the potential for fluid penetration through the structure or deflection to the side, contingent upon rock properties and block size. Finally, we apply our model to a specific seismic chimney at Loyal Field in Scotland, UK, successfully reproducing the observed upward-bending structure in the seismic image with a consistent width-height ratio. This comprehensive investigation sheds light on the complex interplay of various factors influencing focused fluid flow, including geological heterogeneity, thereby contributing valuable insights to the understanding of seismic chimney formation in real-world geological settings.

 

How to cite: Wang, L. H. and Yarushina, V.: Modelling focused fluid flow in the subsurface: its controlling factors and the formation of seismic chimney , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10501, https://doi.org/10.5194/egusphere-egu24-10501, 2024.

Seeking to better investigate the mechanism of transformational faulting (i.e. dynamic olivine phase transition considered as the main earthquake mechanism in the deep Upper Mantle), experiments were carried out in a 1-atm rig using synthetic samples of peridotite analogues. The samples consisted of Mg2GeO4 with minor MgGeO3. In brief, using Ge instead of Si allows studying deep processes without increasing the confining pressure. At 1 atm, γ-Mg2GeO4 (high-pressure olivine polymorph) transitions to α-Mg2GeO4 (olivine) at 810 °C. The hope was to generate and document strain localization features due to local phase transition and/or locally nucleate the phase transition due to strain localization. Working with this material in this apparatus between 760 and 860 °C could have appeared clever.

The experimental setup allowed runs lasting a few hours up to a full day. However, after one day at 800 °C and an axial stress > 300 MPa, the synthetic samples, characterized by a small grain size and a high homogeneity, remained perfectly elastic. Runs were too cold and dry for any nucleation of the high-pressure phase γ-Mg2GeO4. Due to both kinetic and rheological issues, beginning to observe strain localization would have taken months, which would most probably have killed the apparatus in only one run due to the corrosion of the external furnace. 

This failed experimental journey turned into an opportunity to study something else: the temperature window was shifted to 950-1250°C. Some experiments revieled a significant viscosity reduction in a narrow temperature window (1000-1150°C), which we propose to interpret as an analogue of the lithosphere-Asthenosphere boundary (LAB). Until recently, melting was the only “transformation” considered in the interrogations about the reduced viscosity of the LAB. In this study, based on our unexpected experimental results, we document a solid-state viscosity reduction that seems to be associated with grain-boundary instability in the context of a competition between diffusive and displacive processes (i.e. premelting). We propose to broaden the discussion including solid-state transformations and potential metastable phases that are not yet fully understood. Although the most studied mineral, olivine has not revealed all its secrets. Additional experiments are required to fully understand what happened.

How to cite: Ferrand, T. P. and Deldicque, D.: Unexpected softening of a synthetic peridotite analogue (magnesium germanate) in a narrow temperature window: the Lithosphere-Asthenosphere Boundary accidentally reproduced?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10931, https://doi.org/10.5194/egusphere-egu24-10931, 2024.

EGU24-14329 | Orals | GD7.2 | Highlight

Generation of Felsic Crust: A Fluid Transport Perspective 

Leonid Aranovich, Lyudmila Khakimova, Andrey Frendak, and Yury Podladchikov

Continental crust consists mainly of felsic rocks rich in silicon and aluminum, and is formed in subduction zones via processes linked to plate tectonics. Most recent models of the felsic crust formation rely on differentiation of basaltic magma generated via partial melting of mantle wedge peridotite under influence of a fluid phase liberated from subducting hydrated oceanic crust. Here we present an alternative model that invokes metasomatic alteration of mantle peridotite due to interaction with a water-rich fluid phase. The model is based on calculations of solid phase assemblages in equilibrium with a fluid saturated in major elements at varying pressure-temperature conditions. Calculations employed THERMOLAB software [1] along with thermodynamic properties of solids (both the standard state and mixing) according to [2,3] and aqueous solution models [4]. The calculations reveal that the SiO2 content in the fluid exerts major control on the solid phase assemblage. On decompression path from 2.5 to 0.2 GPa at 700oC in the model system NCMASH it changes from a six-mineral assemblage olivine (Ol) + orthopyroxene (Opx) + pargasite(Parg) + diopside + biotite + clinochlore to a three-phase Ol+Opx+Parg. The system Si/O ratio along the path increases from 0.26 (close to that of Ol, Si/O=0.25) to 0.28, thus pre-conditioning mantle protolith for subsequent melting that would generate diorite-granodiorite-granite melts.

How to cite: Aranovich, L., Khakimova, L., Frendak, A., and Podladchikov, Y.: Generation of Felsic Crust: A Fluid Transport Perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14329, https://doi.org/10.5194/egusphere-egu24-14329, 2024.

We present undated results of a numerical model of pressure increase in a quasi-isochoric magma system due to the flotation of bubble-crystal clusters (vesicular mafic enclaves), that are common in silicic rocks that experience magma chamber refill by water and CO2-saturated basaltic magma. The model accounts for water solubility and diffusion and utilizes measured size distributions of mafic enclaves in volcanic and plutonic rocks around the world. These mafic enclaves have sizes ranging from (~1 to >30 cm), lognormal size distribution that we explain by flotation. They have lower densities (density difference =10-30%) than silicic hosts due to bubbles. The principal results of the model are: 1) enclaves are capable of rapid (days-months) flotation leading to pressurization of shallow magma chambers over cracking limit (100 MPa) using fluid rise mechanisms below; 2) The dynamics of pressure increase is strongly non-linear and is determined by the initial size distribution of enclaves, and other parameters; 3) Diffusion of water out of enclaves is slower than the rise time for most realistic viscosities of the silicic host melt. We consider cases when overpressuring causes density reversal due to solubility increase, and consider the role of convection. We present examples of high concentrations of enclaves within silicic domes that we explain by pre-eruption accumulation by flotation to the roof 

Bindeman I.N., Podladchikov Y.Y., Inclusions in volcanic rocks and a mechanism for triggering volcanic eruptions, Modern Geology, 19, 1-11, 1993.
Steinberg, G.S., Steinberg, A.S., Merzhanov A.G., Fluid mechanism of pressure growth in volcanic (magmatic) systems, Modern Geology, 13, 257-265, 1989a.
Steinberg, G.S., Steinberg, A.S., Merzhanov A.G., Fluid mechanism of pressure growth and the seismic regime of volcanous prior to eruption, Modern Geology, 13, 267-274, 1989b.
Steinberg, G.S., Steinberg, A.S., Merzhanov A.G., Fluid mechanism of pressure rise in volcanic (magmatic) systems with mass exchange, Modern Geology, 13, 275-281, 1989c.

How to cite: Podladchikov, Y. and Bindeman, I.: Vesiculated basaltic enclave flotation as a mechanism of fluid pressure increase in magma chambers during silicic-basaltic magma mixing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14561, https://doi.org/10.5194/egusphere-egu24-14561, 2024.

EGU24-14845 | ECS | Posters on site | GD7.2

Multicomponent Pore Fluid Transport by Hydration Porosity Waves in the Litosphere: A Model for Continental Crust Formation 

Lyudmila Khakimova, Andrey Frendak, Leonid Aranovich, and Yury Podladchikov

Revealing of continental crust formation mechanism is a fundamental problem. There are metamorphic based theories and leading magmatic ones. Most recent models rely on differentiation of basaltic magma generated by partial melting of peridotite under influence of a fluid escape from subducting hydrated oceanic crust.

Here we present hypothesis of alternative mechanism of continental crust formation which invokes the multicomponent pore fluid transport by reactive porosity waves through the base of the Lithosphere. It includes partial hydration of mantle peridotite due to interaction with aqueous solutions transported through fluid-rich channels-like structures in rocks undergoing visco-elastic deformation coupled with reactions, phase transformations, volume and density changes.

To support the hypothesis, we propose a coupled hydro-mechanical-chemical model for simulating the filtration of multicomponent fluid through deforming mineral matrix treating zero porosity limit. Along with a number of constitutive relations, this model is closed by tabulated thermodynamic data, which are to be preliminarily calculated using linprog minimization in ThermoLab. We present 2D numerical implementation utilizing accelerated pseudo-transient numerical scheme. Results illustrate hydration porosity wave propagation witj peridotite alteration and the visco-elastic deformation of the zero porosity mineral matrix, with reference to the system up to 12 components including the corresponding solid and aqueous solutions.

How to cite: Khakimova, L., Frendak, A., Aranovich, L., and Podladchikov, Y.: Multicomponent Pore Fluid Transport by Hydration Porosity Waves in the Litosphere: A Model for Continental Crust Formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14845, https://doi.org/10.5194/egusphere-egu24-14845, 2024.

EGU24-15095 | ECS | Posters on site | GD7.2

Control of buoyancy forces and thermal softening on the emplacement of low-angle thrust sheets during continental collision 

Olga Dubina, Stefan Schmalholz, and Yury Podladchikov

A characteristic feature of some collisional orogens, such as the Alps, are low-angle thrust sheets. The most prominent thrust sheet in the Alps is likely the Glarus nappe that has been displaced at least 30 to 40 km. The Glarus thrust has been studied for more than 150 years and these studies created much knowledge of, for example, rock deformation, strain localization, and softening mechanisms. However, the type of forces and the mechanisms that drive the tens of kilometers displacement at a low angle during continental collision remain unclear. Furthermore, the relative importance of softening mechanisms at the base of the thrust sheet is still disputed and proposed mechanisms include fluid overpressure, grain size reduction, or fluid release caused by shear heating.

In this study, we investigate the formation of low-angle thrust sheets and nappes with two-dimensional thermo-mechanical numerical models. We consider a lithosphere-mantle system with a continental crust that exhibits initially a horizontal variation in crustal thickness. The lithosphere is shortened by far-field convergence velocities. For simplicity, we apply thermal softening due to shear heating as the only softening mechanism since this mechanism requires the least assumptions in our thermo-mechanical model. The applied numerical algorithm is based on a staggered finite difference discretization and a matrix-free iterative pseudo-transient solver.

Preliminary numerical results indicate that buoyancy forces due to lateral crustal thickness variations can trigger the formation of sub-horizontal thrusting and a switch from a locally pure shear-dominated to a simple shear-dominated deformation. Without lateral thickness variations and associated buoyancy forces, thermal softening causes thrusting with 45-degree angles and, hence, no low-angle thrusting. We perform systematic numerical simulations and dimensional analysis to evaluate the conditions that are required to generate low-angle thrusting during lithospheric shortening.

How to cite: Dubina, O., Schmalholz, S., and Podladchikov, Y.: Control of buoyancy forces and thermal softening on the emplacement of low-angle thrust sheets during continental collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15095, https://doi.org/10.5194/egusphere-egu24-15095, 2024.

EGU24-15242 | ECS | Posters on site | GD7.2

Numerical modelling and classification of thermo-hydro-mechanical convective regimes 

Boris Antonenko, Lyudmila Khakimova, and Yury Podladchikov

The simulation and visualization of geodynamical processes poses a major challenge for due to spatial and time scales spanning many orders of magnitude and highly nonlinear phenomena. Modeling and solving such processes are necessary in order to accurately predict changes in natural systems. Two-phase models of fluid flow in deformable porous media are widely used to explain the various processes that occur in the Earth’s interior and subsurface. However, thermal processes, especially volume changes caused by thermal expansion, are typically ignored.

In this study, numerical simulation methods were used to describe a mathematical model of heat transfer processes in a porous media. The purpose of these studies is to determine the influence of nondimensional parameters (Rayleigh numbers) on the convection regimes (free and porous convections). To study these problems, numerical modeling of a nonlinear thermo-hydro-mechanical processes in porous materials filled with a fluid under gravity. The finite difference staggered grid discretization and a graphics processing unit based pseudo-transient solver are utilized in the numerical simulation.

We perform systematic numerical simulations and dimensional analysis to classify the regimes of convection.

How to cite: Antonenko, B., Khakimova, L., and Podladchikov, Y.: Numerical modelling and classification of thermo-hydro-mechanical convective regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15242, https://doi.org/10.5194/egusphere-egu24-15242, 2024.

EGU24-15390 | ECS | Posters on site | GD7.2

Numerical modelling of antigorite dehydration at 3 GPa: reaction-induced stress variations and effects of tectonic forcing 

Kristóf Porkoláb, Evangelos Moulas, and Stefan Schmalholz

Dehydration reactions at high pressures are considered as sources of stress perturbations potentially leading to the nucleation of intermediate-depth earthquakes. Dehydration reactions entail the release of water and significant solid volume changes, while solid deformation, fluid flow, and the migration of the reaction front interact with each other. Observation-based quantification of such complex interactions is challenging; hence, the exact mechanisms of dehydration-induced seismicity remain unclear. One of the most prominent dehydration reactions in subducted slabs, that may contribute to intermediate-depth seismicity, is the breakdown of antigorite at high pressures. To improve the understanding of this process, we quantify interactions between the metamorphic reaction, solid deformation, and fluid flow for the phase transformation of antigorite --> enstatite + forsterite + water. We present a two-phase, hydro-mechanical-chemical model that is based on the coupled solution of rock deformation, Darcy-flow of pore fluids, and equilibrium thermodynamics of the dehydration reaction (assuming isothermal conditions). We consider total and non-volatile mass conservation, while solid and fluid densities are based on thermodynamic lookup tables. We investigate the magnitude of reaction-induced stresses and test the effects of kinematic boundary conditions and rheological heterogeneities via a broad parameter study. We relate our findings to natural examples of antigorite dehydration and discuss implications for dehydration-induced earthquakes.

Acknowledgements

The reported investigation was financially supported by the National Research, Development and Innovation Fund, Hungary (PD143377).

How to cite: Porkoláb, K., Moulas, E., and Schmalholz, S.: Numerical modelling of antigorite dehydration at 3 GPa: reaction-induced stress variations and effects of tectonic forcing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15390, https://doi.org/10.5194/egusphere-egu24-15390, 2024.

EGU24-15613 | Posters on site | GD7.2

Numerical simulation of multicomponent multiphase reactive fluid flow in porous media 

Anna Isaeva, Lyudmila Khakimova, and Yury Podladchikov

Multicomponent multiphase reactive transport in porous media controls various phenomena in geological formations such as carbonization, fluid flow in a petroleum reservoir, mobility of radioactive waste in repositories, etc. Despite the obvious differences between these geological processes, they have much in common from a numerical simulation point of view.

We draw parallels between mathematical models of processes from two different areas of research. Firstly, we study the process of carbonization. Secondly, we consider the process of retrograde condensation, which is known to occur when natural gas flows in reservoir rock (during isothermal pressure reduction). Retrograde condensation is a property of multicomponent mixtures, such as natural gas. 

Both systems considered exhibit complex behavior and phase  transitions. But both systems can be described by the same generalized equations. We discuss the differences and similarities between these mathematical models.

How to cite: Isaeva, A., Khakimova, L., and Podladchikov, Y.: Numerical simulation of multicomponent multiphase reactive fluid flow in porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15613, https://doi.org/10.5194/egusphere-egu24-15613, 2024.

EGU24-15739 | Posters on site | GD7.2

Occurrence of eclogite in felsic continental rocks as a natural consequence of burial 

Johannes C. Vrijmoed, Yury Y. Podladchikov, Marcin Dabrowski, and Lyudmila Khakimova

The occurrence of eclogite enclosed in felsic continental rocks have been subject of intense discussion over several decades. The eclogite facies mineralogy preserves the only evidence that the rocks were buried to great depth and therefore this has significant consequences for the understanding of geodynamic processes in continental collision zones. However, often the enclosing felsic gneiss lacks evidence of this high-pressure metamorphism.

This apparent conflict in metamorphic pressure is founded on experimental phase equilibria studies in which pyroxene and plagioclase in igneous mafic rocks transform at high pressure to the characteristic garnet and omphacite assemblage of eclogite. In contrast, the felsic rocks preserve a mineral assemblage expected to equilibrate at lower pressure. A common explanation is that the enclosing felsic gneiss was retrogressed on the exhumation path, whereas eclogite has been preserved due to slower reaction kinetics in mafic rocks. The preservation of original igneous structures of various mafic rocks and incomplete reactions in metagabbro may also be attributed to metastability. Subsequently, it has been shown that large areas of the enclosing felsic gneiss have retained their original low-pressure mineral assemblage (e.g. Peterman et al., 2009). Consequently, large areas of felsic gneiss were never metamorphosed in the eclogite facies. It is firmly established that fluids play an important role in metamorphic reactions. In contrast, the role of mechanics and the heterogeneity of rock mechanical properties during metamorphism has received less attention.

Mechanical properties of mafic rocks can be different from the surrounding felsic lithologies. Therefore, a mechanical model was proposed for a mafic inclusion in felsic continental rock in which the entire domain was subjected to burial (Podladchikov & Dabrowski, 2017). The model predicted a much higher pressure in the mafic inclusion than in the felsic matrix. The overpressure in the mafic inclusion resulted from difference in compressibility between the mafic and felsic lithologies. This may explain the contrast in high pressure eclogite compared to the enclosing lower pressure felsic continental rocks.

In this study, we combine the mechanical model with thermodynamic calculations using Thermolab (Vrijmoed & Podladchikov, 2022) and apply it to ultra-high-pressure rocks in western Norway. We retrieve density, compressibility, and thermal expansivity for observed rocks from phase equilibria calculations as input into the mechanical models. With Thermolab, complex fluids including more than 40 aqueous species, and multi-component melt and solid solution models, can be conveniently coupled to reactive transport and mechanical models to quantify the effect of burial overpressure.

References:

Podladchikov, Y. Y., Dabrowski, M., (2017), Overpressure by burial, Geophysical Research Abstracts, Vol. 19, EGU2017-18976, 2017, EGU General Assembly 2017.

Vrijmoed, J.C. and Y.Y. Podladchikov, (2022), Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems. Geochemistry Geophysics Geosystems, 2022. 23(4).

Peterman, E. M., Hacker, B.R., Baxter, E. F. (2009), Phase transformations of continental crust during subduction and exhumation:Western Gneiss Region, Norway, Eur. J. Mineral. 2009, 21, pp. 1097-1118

How to cite: Vrijmoed, J. C., Podladchikov, Y. Y., Dabrowski, M., and Khakimova, L.: Occurrence of eclogite in felsic continental rocks as a natural consequence of burial, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15739, https://doi.org/10.5194/egusphere-egu24-15739, 2024.

EGU24-16643 | ECS | Posters on site | GD7.2

Multistep Numerical THMC Reactive Porosity Waves Transport Model to Explain Intraplate Volcanism and Mantle Metasomatism. 

Marko Repac, Lyudmila Khakimova, Yury Podladchikov, Kurt Panter, Stefan Schmalholz, and Sebastien Pilet

Ongoing debates persist regarding the role of the lithospheric mantle in the generation of intraplate volcanoes. Most geochemical models propose that these volcanoes originate from magmas formed in the asthenosphere. Intraplate basalt composition, particularly their high content of trace elements, implies that these magmas are produced at low degree of partial melting. However, the melt migration through the lithospheric mantle remains largely unexplored. As these small quantities of magma traverse the lithosphere, their limited heat transport results in rapid cooling due to the lithosphere's strong geotherm (McKenzie, 1989), casting doubt on their ability to directly reach the surface. In contrast, this process induces a chemical effect characterized by the metasomatic enrichment of the lithospheric mantle, observed across oceanic, continental, and cratonic environments.

Here, we developed a numerical finite difference model, incorporating thermo-hydro-chemical-thermal (THMC) processes, to investigate melt migration across the lithosphere. The model includes conservation equations for mass, fluid, and solid momentum, featuring a non-linear porosity-permeability relation for decompaction weakening and reactive porosity waves essential for flow channelization. Thermodynamic calculations employed Thermolab (Vrijmoed & Podladchikov, 2022), a versatile Gibbs energy minimizer. Amphiboles and phlogopites are crucial phases for mantle metasomatism and alkaline magma generation. We successfully model these phases within expected PT ranges. Using both solution models and fixed composition phases.

The model progresses through multiple steps, initiating at the asthenosphere-lithosphere boundary. Initial melt, present there if volatile content is sufficient, migrates upward with a decreasing volume but increasing volatile content as the pressure and temperature decrease. At a given point, the freezing effect of volatiles on mantle melting temperature is no longer sufficient to stabilize melt in equilibrium with the surrounding mantle. Melt migration concludes with the formation of hydrous phases like pargasite or phlogopite depending on the pressure. The second step, addressing excess volatiles after hydrous phases crystallization, involves their further upward transport as fluid, metasomatizing the overlying mantle until depletion of fluid. This process explains several aspects of metasomatism, such as hydrated phase formation and cryptic metasomatism associated with fluid migration. On the other hand, our model confirms that magma does not seem capable of crossing the lithosphere without reacting with the surrounding mantle and crystallizing. To take this further, we consider the hypothesis that the process of melt transport in the lithosphere occurs through the repeated migration of several pulses of magma from the asthenosphere. The emplacement of the first porosity wave is fundamental in establishing a pathway through which all successive pulses will traverse. Following this intricate process, a more extensive segment of the lithosphere undergoes metasomatism. Additionally, the recurrent influx of melt/fluid gradually elevates temperatures in the metasomatized area, potentially leading to the subsequent re-melting of hydrous phases, thereby engendering alkaline melts observed at the surface.

  • McKenzie, D. (1989). Some remarks on the movement of small melt fractions in the mantle. Earth and Planetary Science Letters, 53-72.
  • Vrijmoed & Podladchikov. (2022). Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems .G3, 23, e2021GC010303

How to cite: Repac, M., Khakimova, L., Podladchikov, Y., Panter, K., Schmalholz, S., and Pilet, S.: Multistep Numerical THMC Reactive Porosity Waves Transport Model to Explain Intraplate Volcanism and Mantle Metasomatism., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16643, https://doi.org/10.5194/egusphere-egu24-16643, 2024.

EGU24-16982 | ECS | Posters on site | GD7.2

Microstructural relationships from locally equilibrated domains in UHP eclogites (Snieznik Massif, NE Bohemian Massif) 

Malgorzata Nowak, Lucie Tajcmanova, Jacek Szczepanski, and Marcin Dabrowski

The Snieznik eclogites experienced peak ultrahigh-pressure (UHP) metamorphism in around ~770°C at ~3.2 GPa followed by isothermal decompression and amphibolite-facies retrogression during Variscan Orogeny. The well-preserved peak metamorphic assemblage of these UHP eclogites comprises garnet + omphacite + kyanite + phengite + rutile + coesite. The mineral assemblage connected with the isothermal decompression episode is present in the form of diopside-amphibole-plagioclase symplectites that are locally disintegrating the main foliation.

Here, we investigate plagioclase rims developed around kyanite at the interface with quartz and diopside-plagioclase symplectite. They are present only around kyanite occurring in the vicinity of zones developed during the isothermal decompression event. In some parts, the plagioclase rims are locally replaced by the diopside-plagioclase symplectite. The monomineralic plagioclase rims, having max. 20 µm radial thickness, are polycrystalline. They consist of individual plagioclase grains (each 2-15 µm in diameter) with different crystallographic orientations. The rims as a whole exhibit zoning with the highest Ca content observed at the contact with the kyanite grains. The measured CaO content increases from ~2% near quartz and diopside-plagioclase symplectite to ~6% at the kyanite boundary.

In this contribution we investigate the chemical and mechanical effects, that might have contributed to the preservation of the observed zoning and the microstructural heterogeneity of the rims.

How to cite: Nowak, M., Tajcmanova, L., Szczepanski, J., and Dabrowski, M.: Microstructural relationships from locally equilibrated domains in UHP eclogites (Snieznik Massif, NE Bohemian Massif), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16982, https://doi.org/10.5194/egusphere-egu24-16982, 2024.

EGU24-17074 | ECS | Posters on site | GD7.2

Thermal porosity waves 

Ludovic Räss, Ivan Utkin, and Yuri Podladchikov

Fast vertical fluid transfers in the crust play a crucial role in transporting elements and energy from deep environments into the shallow subsurface. These fluid transfers also impact magmatic processes, metamorphism, and heat distribution. Heat distribution in the subsurface is key for temperature-dependent geological processes, geothermal energy, and reservoir operations. Therefore, assessing the efficiency of heat transport by localised fluid flow is important.

Nonlinear porosity waves, resulting from hydro-mechanical interactions, provide a mechanism for fast vertical fluid transfers in the subsurface. However, their ability to transport heat has not been fully explored yet.

In this study, we investigate the coupling of hydro-mechanical processes with thermal processes to assess the efficiency of heat transport by porosity waves in a porous subsurface environment. We use numerical simulations to solve the coupled thermo-hydro-mechanical equations and present high-resolution modeling results. We also evaluate the role of a consistent and conservative formulation. Our preliminary findings suggest that porosity waves do not significantly enhance heat transfer in the subsurface. Additionally, we discuss the influence of parameters such as porosity, permeability, and fluid properties on the efficiency of heat transport.

How to cite: Räss, L., Utkin, I., and Podladchikov, Y.: Thermal porosity waves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17074, https://doi.org/10.5194/egusphere-egu24-17074, 2024.

Numerous studies emphasize the significance of thermal softening induced by shear heating and the concurrent generation of ductile shear zones in geological processes spanning various spatial and temporal scales. Thermal softening is proposed as a primary mechanism in the formation of tectonic plate boundaries and as a potential mechanism of intermediate-depth and deep-focused earthquakes, where large confining pressure inhibits brittle fracture. In the latter scenario, seismic velocities during shearing are achieved through the spontaneous viscous dissipation of stored elastic energy, a phenomenon known as self-localizing thermal runaway (SLTR) [1].

Resolving SLTR poses a formidable numerical challenge due to the multiscale nature of the process. The slow initial stage of differential stress buildup and strain localization is succeeded by the rapid development of a thin shear zone, necessitating high spatial and temporal resolution. Prior numerical studies of self-localizing thermal runaway were confined to 1D, restricting applications to less realistic geometries and simpler model setups.

In this study, we explore the viscoelastic effects of spontaneous flow localization through numerical modeling in 2D. We develop a fully coupled thermo-mechanical solver utilizing a novel conservative energy formulation. Our work demonstrates the potential for SLTR instability in various 2D model setups. Through systematic numerical experiments, we compare the onset of localization with 1D predictions. Additionally, we investigate the role of heterogeneities in the distribution of material properties on the development of a ductile shear zone.

[1] Braeck, S., & Podladchikov, Y. Y. (2007). Spontaneous thermal runaway as an ultimate failure mechanism of materials. Physical Review Letters98(9), 095504.

How to cite: Utkin, I.: Spontaneous strain localisation in a viscoelastic material owing to thermal softening , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17292, https://doi.org/10.5194/egusphere-egu24-17292, 2024.

EGU24-19341 | Posters on site | GD7.2 | Highlight

Reactive porosity waves in a dehydrating and deforming slab: a scale invariant fluid release process 

Timm John, Liudmila Khakimova, Konstantin Huber, Johannes Vrijmoed, Yuri Podladchikov, and Marco Scambelluri

Subduction of hydrated lithosphere slabs into the mantle leads to the release of hydrous fluids, which contribute to a wide range of subduction zone phenomena, such as arc volcanism and seismicity. The efficiency of slab devolatilization is crucial for maintaining the overall stability of the Earth's chemical reservoirs over geological timescales. The formation of channelized fluid flow structures during dehydration, such as olivine veins observed in the Erro Tobbio meta-serpentinites (Italy), enhances the efficiency of fluid release from the subducting slab and might be crucial for devolatilization to keep up with the rate of plate subduction.

Observed olivine-rich vein assemblages and the presence of mineral-bound H2O in the matrix is indicative of high temperatures and partial dehydration. Porosity structures develop into vein-like structures at the onset of dehydration due to intrinsic chemical heterogeneities [1], with connectivity being already reached at low porosities [2]. As dehydration progresses, the fluid pressure in the porous network rises, and buoyancy forces lead to an upward fluid flow in the rock. Porosity waves are a potential mechanism to explain fluid flow focusing structures in rocks undergoing viscous deformation.

This work presents a 2D hydro-mechanical-chemical model for reactive porosity waves in a dehydrating and deforming serpentinite that is part of a subducting slab. Based on [3], we chose SiO2 as the metasomatic agent in a MgO-FeO-SiO2 system with H2O in excess. As model input, we use chemical data of serpentinites from the Mirdita ophiolite (Albania) that has not entered a subduction zone. The 2D chemical mapping of the sample from outcrop down to µm-scale shows scale-invariant heterogeneities of SiO2 and FeO. Similar heterogeneities occur on the km-scale where they manifest as lithological differences between serpentinized harzburgites and dunites. This dataset of chemical maps ranging continuously from the µm- to dm-scale represents a scale-independent pattern of chemical heterogeneities in a dehydrating slab.

Numerical results using this data as input show spontaneous formation of fluid-rich high-permeable channels in deforming and dehydrating serpentinite associated with further olivine formation during the reactive flow of Н2О−SiО2 fluid carrying low SiO2 concentration. The numerical simulations show similar pattern to field observations from Erro Tobbio. We conclude that the formation of a fluid channeling network takes place from the µm- up to km-scale and provides the main fluid escape mechanism in subduction zones.

 

[1] Plümper, O. et al. Fluid escape from subduction zones controlled by channel-forming reactive porosity. Nat Geosci 10, 150–156 (2017).

[2] Bloch, W. et al. Watching dehydration: Seismic Indication for Transient Fluid Pathways in the Oceanic Mantle of the Subducting Nazca Slab. Geochem Geophy Geosy 19, doi:10.1029/2018gc007703 (2018)

[3] Huber, K. et al. Formation of olivine veins by reactive fluid flow in a dehydrating serpentinite. Geochem Geophy Geosy, 23, e2021GC010267 (2022).

How to cite: John, T., Khakimova, L., Huber, K., Vrijmoed, J., Podladchikov, Y., and Scambelluri, M.: Reactive porosity waves in a dehydrating and deforming slab: a scale invariant fluid release process, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19341, https://doi.org/10.5194/egusphere-egu24-19341, 2024.

EGU24-19434 | Posters on site | GD7.2

Numerical assessment of effective bulk moduli of porous rocks using high-performance computing on GPUs 

Maxim Yakovlev and Victoriya Yarushina

The coupled process models incorporate fluid flow, chemical transport, and mechanical deformation equations. These equations adhere to the thermodynamic principles ensuring the preservation of mass and energy within the system. However, for accurate predictions, it is crucial to establish closure equations that provide additional information and ensure the model's completeness. Closure equations are derived either from extrapolating experimental data or from micromechanical models that consider processes at the scale of individual grains or particles. Microscale models are often based on simplified analytical solutions obtained for idealized conditions, which may not fully capture the complexity of real-world situations. For instance, these models may assume a dilute concentration of voids or pores, neglecting interactions between the pores. While this assumption may be suitable for very small porosities below 1%, it may not accurately reflect interactions at porosities around 10%, influencing the compaction process. One approach to address this challenge is to derive more sophisticated analytical solutions, which may sometimes be impractical. Alternatively, a common strategy is to retain simplified solutions and validate them against numerical simulations that include multiple interacting voids. Effective bulk modulus, frequently employed to describe compaction-driven fluid flow in porous rocks, relies on effective media models. We propose a new effective media model based on a Representative Volume Element consisting of multiple interacting pores. To address stress and strain field interactions caused by multiple pores in an elastoplastic matrix, we utilize the numerical simulator CAE Fidesys, implementing classical associated plastic flow laws with von Mises and Tresca yield criteria. For viscoplastic rocks, the correspondence principle is applied. We derive 2D effective stress-strain relations for porous viscoelastoplastic rocks under a general non-hydrostatic stress field and compare the results with existing and novel analytical solutions.

How to cite: Yakovlev, M. and Yarushina, V.: Numerical assessment of effective bulk moduli of porous rocks using high-performance computing on GPUs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19434, https://doi.org/10.5194/egusphere-egu24-19434, 2024.

EGU24-19660 | ECS | Posters virtual | GD7.2

Role of pore fluids in time-dependent deformation and microcracking of rock under high deviatoric stress 

Nikita Bondarenko, Roman Makhnenko, and Yury Podladchikov

Rock underground may be exposed to elevated deviatoric stress over prolonged time period resulting in time-dependent deformation and microcracking. This process of subcritical time-dependent deformation is sensitive to environmental conditions, such as applied state of stress, presence and chemical composition of pore fluids, and drainage conditions. To improve the understanding of processes occurring at subcritical stress, the laboratory brittle creep experiments are conducted on Berea sandstone specimens under various conditions. Strong correlation between time-dependent deformation and microcracking activity is observed in all conducted tests. Significant variation of magnitude-frequency relation of the acoustic emission signals occurs during macroscopic failure preparation, which can serve as a potential prognostic feature. The collected data on time-dependent deformation is interpreted by introducing viscosity as a coefficient of proportionality between deviatoric strain rate and applied deviatoric stress. It appears that viscosity is exponentially decreasing when the state of stress is approaching critical conditions associated with macroscopic failure. Empirically-based relationship is established describing the impact of mean and deviatoric stress on viscosity in wide range of applied stress. The presence of non-aqueous fluids (oil or CO2) appears to have significantly weaker impact on the creep deformation compared to aqueous fluids (deionized water and water with dissolved CO2). Finally, the drainage condition appears to be essential. If the mass of pore fluid inside the specimen remains constant throughout the experiment (undrained condition), the microcracking results in phenomena similar to dilatant hardening of the material observed at constant applied state of stress. This effect might be qualitatively similar to the ones occurring in the off-fault plasticity zones and provide the fault stabilization mechanism.

How to cite: Bondarenko, N., Makhnenko, R., and Podladchikov, Y.: Role of pore fluids in time-dependent deformation and microcracking of rock under high deviatoric stress, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19660, https://doi.org/10.5194/egusphere-egu24-19660, 2024.

EGU24-22551 | Orals | GD7.2 | Highlight

Thermal softening in the ductile and brittle lithosphere 

Dániel Kiss

Plate tectonics on Earth is characterized by a largely localized distribution of lithospheric strain, both in the ductile and in the brittle regimes. While deformation in brittle or elastic materials is generally localized, in homogenous ductile or viscous materials some strain localization requires a softening mechanism. Here we will focus on thermal softening, a consequence of the conversion of mechanical work into heat (i.e. shear heating) and the temperature dependence of rock viscosities.
First, I briefly list the fundamental features of ductile shear zone evolution due to thermal softening driven by steady-state background deformation. (1) After an initial transient period, the maximum temperature and stress in the shear zone converges to a (quasi-)constant value (temperature increase and stress drop). (2) The steady-state maximum temperature can be estimated using a scaling law. (3) With ongoing deformation, the high-temperature zone and consequently the shear zone widen, which indicates that shear zone width is controlled by conduction time scales.
Second, I demonstrate that thermal softening is a feasible mechanism of lithospheric scale ductile strain localization by comparing geological observations and model results of subduction initiation, ophiolite emplacement, and high-temperature metamorphic nappes.
Finally, I will investigate the possible occurrence and importance of thermal softening in the brittle, elastoplastic domain, often associated with much shorter time scales such as slow slip events and earthquakes. Data from rock deformation experiments indicate that steady-state friction angle becomes primarily velocity-dependent at high slip rates, which is consistent with thermal softening. Numerical models of Maxwell visco-elastic deformation show that thermal softening can be an efficient mechanism of limiting elastic stress build-up, often resulting in a rapid stress release, often referred to as thermal runaway.  

How to cite: Kiss, D.: Thermal softening in the ductile and brittle lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22551, https://doi.org/10.5194/egusphere-egu24-22551, 2024.

EGU24-22558 | ECS | Posters on site | GD7.2 | Highlight

Influence of intracrystalline deformation on chemical diffusion in garnet around coesite inclusions 

Cindy Luisier, Lucie Tajcmanova, Thibault Duretz, Larissa Lenz Lenz, and Liudmila Khakimova

Coesite inclusions in garnets are emblematic observations, typical of Ultra-High-Pressure (UHP) rocks.  While small inclusions may fully preserve coesite, sufficiently large inclusions undergo partial transition of coesite to quartz. Here, we focus on samples from UHP rocks from Dora Maira Massif (Western Alps). Classical petrographic analysis indeed reveals the coexistence of quartz and coesite as well as deformation of the surrounding garnet (radial fractures). In addition, microprobe analysis further shows chemical zoning in garnet around partially transformed inclusions. This observation suggests a link between chemical zoning and deformation related to the phase transition. Such an observation provides a unique opportunity to investigate the relation between multi-component diffusion and garnet deformation using both microprobe analysis and quantitative modelling.

How to cite: Luisier, C., Tajcmanova, L., Duretz, T., Lenz, L. L., and Khakimova, L.: Influence of intracrystalline deformation on chemical diffusion in garnet around coesite inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22558, https://doi.org/10.5194/egusphere-egu24-22558, 2024.

EGU24-22560 | ECS | Orals | GD7.2 | Highlight

Application of reaction front propagation modelling to amphibolite-facies plagioclase hydration: an example from the Bergen arcs, Norway 

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

Fluid inflitration along brittle presursors is commonly with associated with hydration and deformation of the host rock. In many cases the relative timing of fracturing, fluid infiltration, reaction, and deformation is unclear, making it difficult to disentangle the relative importance of processes that facilitate advancement of the hydration front. 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 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 petrography, quantitative mineral chemistry and bulk rock analyses have been applied to investigate compositional variations and assemblage microstructure across both interfaces. Here, we produce hydro-chemical numerical models based on local equilibrium thermodynamics in an attempt to reproduce the characteristics of the hydration and deformation interfaces. Here, we present a comparison between the observed characteristics of the hydration front and those produced by modelling of the reaction front propagation.

How to cite: Moore, J., Piazolo, S., Beinlich, A., Austrheim, H., and Putnis, A.: Application of reaction front propagation modelling to amphibolite-facies plagioclase hydration: an example from the Bergen arcs, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22560, https://doi.org/10.5194/egusphere-egu24-22560, 2024.

EGU24-425 | ECS | Posters on site | ITS5.14/GD7.3

Dynamic recrystallization of olivine during simple shear: evolution of microstructure and crystallographic preferred orientation from full-field numerical simulations 

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

The deformation of the upper mantle is predominantly governed by the mechanical behavior of olivine (Karato et al., 1989). During mantle flow, olivine undergoes crystal-plastic deformation, leading to the development of crystallographic preferred orientations (CPOs). In this process, the a-axes of olivine polycrystalline aggregates align with the flow direction (Hansen et al., 2012). Consequently, the observed CPOs in olivine-rich rocks serves as an indicator of the mantle flow direction. While the influence of plastic deformation is well understood, the role of dynamic recrystallization during deformation remains not fully comprehended, hindering our ability to interpret the deformation history of naturally-deformed rocks.

This contribution employs microdynamic numerical simulations of olivine polycrystalline aggregates with varying iron content (fayalite content) to explore the CPO and grain size response to dynamic recrystallization. Utilizing a full-field approach with explicit simulation of viscoplastic deformation (http://www.elle.ws; Bons et al., 2008; Piazolo et al., 2019) and dynamic recrystallization processes under simple shear boundary conditions up to high strain, this study indicates that simulations with only dislocation glide and also those including recrystallization successfully reproduce such steady state conditions, without requiring other potential mechanisms. The model establishes a framework for understanding the development of olivine CPOs in mantle rocks, highlighting the interplay between plastic deformation and dynamic recrystallization processes, including grain boundary migration, intracrystalline recovery, and new grain nucleation.

Acknowledgements: Yuanchao Yu acknowledges funding by the China Scholarship Council for a PhD scholarship (CSC-202008130104). This work has been developed using the facilities of the Laboratory of Geodynamic Modelling of GEO3BCN-CSIC.

How to cite: Yu, Y., Llorens, M.-G., Griera, A., Gomez-Rivas, E., Bons, P. D., Garcia-Castellanos, D., Hao, B., and Lebensohn, R. A.: Dynamic recrystallization of olivine during simple shear: evolution of microstructure and crystallographic preferred orientation from full-field numerical simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-425, https://doi.org/10.5194/egusphere-egu24-425, 2024.

EGU24-2189 | ECS | Orals | ITS5.14/GD7.3

Modeling ice and olivine CPO evolution and its affect on large-scale flow in two-way coupled simulations 

Nicholas Rathmann, David Lilien, Christine Hvidberg, Aslak Grinsted, Dorthe Dahl-Jensen, Klaus Mosegaard, Ivanka Bekkevold, and David Prior

We present a spectral-space CPO model that allows for efficient and seamless simulation of anisotropic polycrystalline flows at large scale, relevant for ice sheets and Earth’s upper mantle. The CPO model is two-way coupled with a bulk orthotropic power-law rheology using a linear grain homogenization scheme, making analytical and frame-independent calculations of CPO-induced viscous anisotropy possible and computationally cheap. The effect of two-way coupling flow and CPO evolution is explored in idealized finite element simulations of ice stream flow and mantle thermal convection. In both cases, we find that strain-rate fields are non-trivially affected, and we briefly discuss the consequences for ice-stream self-reinforcement and the coupling between plate motions and the sublithospheric mantle.

This contribution is mainly focused on introducing our modeling framework “specfab” to the wider community.

How to cite: Rathmann, N., Lilien, D., Hvidberg, C., Grinsted, A., Dahl-Jensen, D., Mosegaard, K., Bekkevold, I., and Prior, D.: Modeling ice and olivine CPO evolution and its affect on large-scale flow in two-way coupled simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2189, https://doi.org/10.5194/egusphere-egu24-2189, 2024.

EGU24-4569 | Orals | ITS5.14/GD7.3 | Highlight

A structural geologist's view on the Northeast Greenland Ice Stream 

Paul D. Bons, Steven Franke, Daniela Jansen, Yu Zhang, and Ilka Weikusat

The Northeast Greenland Ice Stream (NEGIS) is a fascinating, over 500 km long structure in the Greenland Ice Sheet. The ice stream shows many features, such as folds and shear zones, that are also common in other ductile rocks. Geological methods and expertise may contribute to a better understanding of NEGIS and similar deformation structures in ice sheets. It is standard practice in oil and gas exploration to create 3D-structural models from parallel seismic lines. This approach, applied to radar profiles, is relatively new in glaciology (Bons et al., Nat. Comm. 2016, DOI: 10.1038/ncomms11427) but provides far more insight into the structural architecture and evolution of ice sheets than single radar sections. A 3D-structural model of upstream NEGIS reveals how pre-existing folds are offset within the ice stream. With that, classical strain analysis methods can be applied to quantify the deformation of these folds in the shear margins. This reveals that the total offset at the level of the EGRIP drilling project is in the order of up to 75 km and that the finite shear strain in the shear margins is around 18. With present-day shear-strain rates in the shear margins, such a finite offset and shear strain are achieved in ≤2000 yrs. This strain analysis also proves that ice does not flow through shear margins, but that the shear margins instead advect with the ice. This means that 'flow lines' (which should better be called 'streamlines') are not the same as 'path lines', as is now often assumed. The two are only the same in a time-invariant velocity field, which does not apply to NEGIS. Shear zones in other ductile rocks show that rocks never flow through shear zones, but shear zones can shift or 'jump' to new locations, as is actually observed in NEGIS. Geological principles to analyse and date the formation and activity of salt diapirs and syn-sedimentary faults can also be applied to folds observed in and around NEGIS. This reveals that fold amplification inside the shear margins ceased about 2000 yrs ago, which can be explained by the formation of the shear margins and concomitant reorientation of the CPO. A combination of several structural geological methods thus enables constraining the age of NEGIS as we now know it to about 2000 yrs, which is much less than previously assumed. The surprisingly late appearance of NEGIS, as well as the demise of ice streams in the Holocene (based on 3D-analyses of folded stratigraphy; Franke et al., Nature Geosci. 2022, Doi: 10.1038/s41561-022-01082-2) indicates that ice sheets are very dynamic, mostly due to the highly non-linear (n=4) and anisotropic rheology of ice.

How to cite: Bons, P. D., Franke, S., Jansen, D., Zhang, Y., and Weikusat, I.: A structural geologist's view on the Northeast Greenland Ice Stream, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4569, https://doi.org/10.5194/egusphere-egu24-4569, 2024.

EGU24-5872 | ECS | Orals | ITS5.14/GD7.3

How ice anisotropy contributes to fold and ice stream in large-scale ice-sheet models 

Yu Zhang, Paul D. Bons, Till Sachau, and Steven Franke

Satellite and airborne sensors have provided detailed data on ice surface flow velocities, englacial structures of ice sheets and bedrock elevations. These data give insight into the flow behaviour of ice sheets and glaciers. One significant phenomenon observed is large-scale folds (over 100 m in amplitude) in the englacial stratigraphy in the Greenland ice sheet. A large population of folds is located at ice streams, where the flow is distinctly faster than in the surroundings, such as the North-East Greenland Ice Stream (NEGIS). While there is no consensus regarding the formation of large-scale folds, unraveling the underlying mechanisms presents significant potential for enhancing our understanding of the formation and dynamics of ice streams.

Ice in ice sheets is a ductile material, i.e., it can flow as a thick viscous fluid with a power-law rheology. Furthermore, ice is significantly anisotropic in its flow properties due to its crystallographic preferred orientation (CPO). Here, we use the Full-Stokes code Underworld2 (Mansour et al.,2022) for 3D modelling of the power-law and transversely isotropic ice flow, also in comparison with the isotropic ice models.

Our simulated folds with anisotropic ice show complex patterns on a bumpy bedrock, and are classified into three types: large-scale folds (fold amplitudes >100 m), small-scale folds (fold amplitudes <<100 m, wavelength <<km) and recumbent basal-shear folds. Our results indicate that bedrock topography contributes to perturbations in ice layers, and that ice anisotropy due to the CPO amplifies these into large-scale folds in convergent flow by horizontal shortening. As for our ice stream model, we simulate convergent flow as initial condition, which subsequently initiates the development of shear margins due to the rotation of the ice crystal basal planes. As soon as the shear margins develop, the ice stream starts to propagate upstream in a short time and narrows in the upstream part. Our modeling shows that the anisotropic rheology of ice and CPO change play a significant role for large-scale folding and for the initiation of ice streams with distinct shear margins. Hence, we promote the implementation of ice anisotropy in large-scale ice-sheet evolution models as it holds the potential to introduce novel perspectives to the glaciological community on the dynamics of ice flow.

 

References

John Mansour, Julian Giordani, Louis Moresi, Romain Beucher, Owen Kaluza, Mirko Velic, Rebecca Farrington, Steve Quenette, & Adam Beall. (2022). Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud (v2.12.0b). Zenodo. https://doi.org/10.5281/zenodo.5935717

How to cite: Zhang, Y., Bons, P. D., Sachau, T., and Franke, S.: How ice anisotropy contributes to fold and ice stream in large-scale ice-sheet models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5872, https://doi.org/10.5194/egusphere-egu24-5872, 2024.

EGU24-7333 | Orals | ITS5.14/GD7.3

A physically-based formulation for texture evolution during dynamic recrystallization. A case study for ice 

Maurine Montagnat, Thomas Chauve, Véronique Dansereau, Pierre Saramito, Kevin Fourteau, and Andréa Tommasi

Dynamic recrystallization can have a strong impact on texture development during the deformation of polycrystalline materials at high temperature, in particular for those with strong viscoplastic anisotropy such as ice. Owing to this anisotropy, recrystallization is essential for ensuring strain compatibility. The development of recrystallization textures leads to significant mechanical softening, both in laboratory or natural conditions (glaciers, ice sheets). Accurately predicting ice texture evolution due to recrystallization during tertiary creep remains a challenge, yet is crucial to account adequately for texture-induced anisotropy in large-scale models of glacial ice flow. We propose a new formulation for texture evolution due to dynamic recrystallization. This formulation is physically-based on an orientation attractor which maximizes the Resolved Shear Stress (RSS) on the easiest slip system in the crystal (basal slip for ice). The attractor is implemented in an equation of evolution of the crystal orientation with deformation, which is coupled to an anisotropic viscoplastic law (Continuous Transverse Isotropic - CTI) that provides the mechanical response of the ice crystal. The set of equations, which is the core of the R3iCe open source model is solved using finite elements method with a semi implicit scheme coded using the Rheolef library. R3iCe is validated by comparison with laboratory creep data for ice polycrystals under simple shear, uniaxial compression and tension. It correctly reproduces the texture evolution and the mechanical softening observed during tertiary creep. R3iCe therefore allows predicting enhancement factors that may be implemented in large-scale flow models. Although the validation was performed for ice, the R3iCe implementation is generic and applies for any material adequately described using a CTI law.

How to cite: Montagnat, M., Chauve, T., Dansereau, V., Saramito, P., Fourteau, K., and Tommasi, A.: A physically-based formulation for texture evolution during dynamic recrystallization. A case study for ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7333, https://doi.org/10.5194/egusphere-egu24-7333, 2024.

EGU24-8169 | ECS | Posters on site | ITS5.14/GD7.3

The coupled evolution of crystal orientation fabric and ice flow in ice streams 

Laura Rysager, Nicholas Rathmann, Christine Hvidberg, and Aslak Grinsted

The evolution of grain orientations as a function of flow in polycrystalline glacier ice can greatly affect the bulk viscous anisotropy of ice, and hence mass loss from Earth’s large ice sheets through fast-flowing ice streams where such effects are thought to be important. In this study, we model the strain-induced evolution of grain orientation (fabric) of Lagrangian parcels of ice propagating into, and through, the North-East Greenland Ice Stream (NEGIS) given the local deformation as observed from satellite-derived surface strain rate fields. This allows us to estimate the local flow enhancement factors to be better at understanding the relevance of viscous anisotropy of ice in the ice streams. As the parcels move into and through the ice stream, very different strain-rate regimes are encountered (outside, in the shear margin, and inside the ice stream) which change the fabric over short spatial/temporal scales. To test the model predictions, we compare the modeled fabric eigenvalues with horizontal eigenvalue differences inferred from radar measurements made near the EGRIP drill site.

How to cite: Rysager, L., Rathmann, N., Hvidberg, C., and Grinsted, A.: The coupled evolution of crystal orientation fabric and ice flow in ice streams, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8169, https://doi.org/10.5194/egusphere-egu24-8169, 2024.

Rocks from the Earth mantle and polar ices have in common a nonlinear rheology and low crystal symmetries leading often to a limited number of independent slip systems for the glide or climb of dislocations. Both deform at elevated homologous temperatures, mostly under creep. Very large plastic deformation occurs during large scale geophysical flows, leading to pronounced crystallographic texture and an associated anisotropic rheology. Polar ice is a pure material, whereas several mineral phases are present simultaneously the mantle. The mantle deforms at extremely slow strain-rates, 10 orders of magnitude smaller than standard laboratory strain-rates, and thus the estimation of the mantle behaviour requires a drastic extrapolation from lab data. A consequence of the features outlined above is that deformation of mantle rocks or polar ices leads to a strong heterogeneity of the stress and strain-rate fields inside the polycrystalline aggregates, at the intragranular (micron) scale. This field heterogeneity has strong implication in terms of texture evolution, recrystallization, but also on the effective flow stress. Another consequence is that simple or ad-hoc micromechanical models are often inaccurate when the goal is to estimate the in situ nonlinear and anisotropic rheology, and the microstructure evolution at large strain, as the activation of slip systems is highly sensitive to stress fluctuations. In this presentation, we will review existing mean-field models for polycrystalline aggregates, show their capabilities / limitations with respect to reference full-field solutions, and show the benefit of the fully-optimized second order self-consistent scheme recently proposed by Song and Ponte Castañeda [2018]. Examples for ice and few mantle minerals will be given for illustrative purpose.

 

D. Song and P. Ponte Castañeda, Fully optimized second-order homogenization estimates for the macroscopic response and texture evolution of low-symmetry viscoplastic polycrystals, Int. J. plasticity 110 (2018), 272–293

How to cite: Castelnau, O. and Ponte Castañeda, P.: Accurate mean-field micromechanical modelling of the nonlinear anisotropic response of polycrystalline aggregates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8435, https://doi.org/10.5194/egusphere-egu24-8435, 2024.

EGU24-10371 | ECS | Posters on site | ITS5.14/GD7.3

Eggs and sausages: wireless instrumentation for measuring ice anisotropy and kinematics 

Lisa Craw, Michael Prior-Jones, Nicolas Rathmann, Jonathan Hawkins, Christine Dow, and Elizabeth Bagshaw

Field observations of ice flow properties on large temporal and spatial scales are vital to improve our understanding of ice sheet and glacier dynamics. However, we are currently limited in what we can observe, and on what timescales, with wired instrumentation and remote sensing. We present preliminary tests of wireless instrumentation to measure the kinematics and anisotropy of flowing ice.

We used a spherical probe ("cryoegg") emitting VHF radio waves to measure birefringence in 19 azimuthal directions around a borehole in the Northeast Greenland Ice Stream (NEGIS). From these data we are able to infer information about crystal anisotropy in the ice in three dimensions, and compare with a transfer matrix radio propagation model. This is a significant improvement on previous monostatic radar methods, which are limited to observations of crystal orientations in the horizontal plane.

Additionally, we present initial observations of borehole tilt, temperature, pressure and conductivity from Donjek Glacier, Canada, collected using wireless borehole instruments ("cryowursts''). These data were transmitted through up to 170m of ice, and received at a solar-powered and satellite-enabled receiving station on the glacier surface. There is potential for these instruments to transmit data continuously from surging glaciers over multiple years.

These preliminary studies demonstrate new possibilities for collecting exciting long-term datasets for glaciology.

How to cite: Craw, L., Prior-Jones, M., Rathmann, N., Hawkins, J., Dow, C., and Bagshaw, E.: Eggs and sausages: wireless instrumentation for measuring ice anisotropy and kinematics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10371, https://doi.org/10.5194/egusphere-egu24-10371, 2024.

EGU24-11119 | ECS | Posters on site | ITS5.14/GD7.3

Direct estimation of anisotropic viscosity parameters using texture scores of olivine polycrystals 

Ágnes Király, Clinton P. Conrad, Lars N. Hansen, Yijun Wang, and Ben Mather

Earth’s various layers – from the inner core to the cryosphere – exhibit mechanical anisotropy, meaning their properties depend on the direction in which forces are applied. In the upper mantle, the primary source of anisotropy is the crystallographic preferred orientation (CPO) of olivine that is a result of sub-grain rotation during plastic deformation. The alignment of olivine grains allows the anisotropic behavior of single olivine crystals to add up leading to a macroscopic scale anisotropic viscosity (AV) linked to the CPO.

The role of anisotropic viscosity has been examined in various geodynamic scenarios. However, due to the computational complexity of the problem, there has not been a comprehensive integration of olivine CPO development with the linked anisotropic viscous behavior into geodynamic models. Here, we present an approach that directly derives anisotropic viscosity parameters from the orientation distribution (texture) of olivine grains.

Olivine polycrystals exhibit an orthotropic symmetry within the CPO’s reference frame, i.e., when the models' reference frame is aligned with the mean orientation of the olivine symmetry axes. In this case, AV can be characterized by six independent parameters, which are related to the Hill plastic yield criteria (Hill, 1948; Signorelli et al., 2021).  To determine these independent parameters, existing micromechanical models are employed, enabling the calculation of the stress required to achieve a specific strain rate on an aggregate. By applying the micromechanical model to a given texture, we can evaluate different strain rates and use the anisotropic constitutive equation (e.g. Signorelli et al., 2021) to fit the calculated strain rates with those employed in the micromechanical model, thereby identifying the best-fitting anisotropic parameters. However, simply applying this method inside a geodynamic model is too computationally costly. Thus, we built a large database (>10 000 entries) of textures occurring in geodynamic simulations, describing each texture with a set of scores derived from the orientation matrices of the three olivine symmetry axes. For each texture we applied the micromechanical model by Hansen et al., (2016), and used a minimum search function to find the best fitting AV parameters. Finally, linear regression models were utilized to establish a straightforward mapping of anisotropic parameters directly from a combination of textures scores. To determine which combination of texture scores provides the best outcome, we tested the results against both laboratory data and on a simple shear (numerical) experiment.

The approach presented here is advantageous for integrating anisotropic viscosity into 4D geodynamic models because it allows for a direct determination of the viscosity tensor from the evolving rock texture, saving a large amount of computational time.

 

Hansen, L.N., Conrad, C.P., Boneh, Y., Skemer, P., Warren, J.M., and Kohlstedt, D.L., 2016a, Viscous anisotropy of textured olivine aggregates: 2. Micromechanical model: Journal of Geophysical Research: Solid Earth

Hill, R., 1948, A theory of the yielding and plastic flow of anisotropic metals: Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences

Signorelli, J., Hassani, R., Tommasi, A., and Mameri, L., 2021, An effective parameterization of texture-induced viscous anisotropy in orthotropic materials with application for modeling geodynamical flows

How to cite: Király, Á., Conrad, C. P., Hansen, L. N., Wang, Y., and Mather, B.: Direct estimation of anisotropic viscosity parameters using texture scores of olivine polycrystals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11119, https://doi.org/10.5194/egusphere-egu24-11119, 2024.

EGU24-11580 | ECS | Orals | ITS5.14/GD7.3

Deformation and recrystallization inside the Northeast Greenland Ice Stream – findings from microstructural analysis of the EastGRIP ice core 

Kyra Streng, Johanna Kerch, Paul Bons, Nicolas Stoll, Daniela Jansen, and Ilka Weikusat

Solid ice discharge from land-based ice masses into the ocean raises the global sea level and accelerates due to anthropogenic climate change. Modelling ice flow dynamics aims to provide better projections of future sea level rise. The Antarctic and Greenland ice sheets are predominantly drained through ice streams, which are regions of higher ice flow velocity than their surroundings, and thus play an important role in ice sheet dynamics. However, little is known about their rheology. Therefore, they may introduce large uncertainties in ice sheet models.

In order to study the main deformation and recrystallization mechanisms dominant in an ice stream, we conducted microstructural analyses on samples from the EastGRIP ice core that was drilled in the largest Greenlandic ice stream, the Northeast Greenland Ice Stream (NEGIS).

The data set contains 1064 samples, oriented vertically and horizontally to the ice core axis, from depths between 111 and 2121 m. Analyses of the deepest 550 m of the ice core are pending. All samples were scanned with 5 µm resolution under bright-field illumination with a Large Area Scanning Macroscope (LASM). The obtained microstructure, i.e. grain shape, size, and elongation, was extracted using digitalised grain boundary networks by means of a machine-learning based image analysis software. We determined six different rheological regimes through the ice column. Most microstructural changes were interpreted as changes in recrystallization mechanisms, whereas the dominant deformation mode, horizontal extension, appears to remain fairly constant below 500 m of depth. Previous numerical high-strain ice deformation simulations showed strain localisation with the development of visible shear bands. A similar setting was expected inside ice streams, but at the investigated depths of the EastGRIP ice core, no clear shear bands could be discerned so far for the applied sampling resolution.

These results indicate that NEGIS has no strong high-strain localisation down to 2121 m depth but probably deforms as a block with extension along flow. The high ice flow velocities, therefore, might have to be compensated either in the lowest 500 m or below the ice.

How to cite: Streng, K., Kerch, J., Bons, P., Stoll, N., Jansen, D., and Weikusat, I.: Deformation and recrystallization inside the Northeast Greenland Ice Stream – findings from microstructural analysis of the EastGRIP ice core, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11580, https://doi.org/10.5194/egusphere-egu24-11580, 2024.

EGU24-12319 | ECS | Posters on site | ITS5.14/GD7.3

Refractive Index Matched (RIM) PIV in Free Surface Flows of Particle-Laden Yield Stress Fluids 

Kasra Amini, Yanan Chen, Christophe Ancey, Outi Tammisola, and Fredrik Lundell

Flow of lava, avalanches, mudslides, and many geophysical and planetary flow systems are examples of free-surface flows of Yield Stress Fluids (YSFs). This category of fluids is known for its dual behavior below- and above a yielding threshold for the applied shear stress on each fluid element. The material behaves as an amorphous elastic solid below the yielding threshold and fluidizes above it. This will lead to the presence of unyielded plug regions translating and rotating as solid-like segments within the yielded surrounding fluids. The existence of macroscopic particles in the fluid adds to the complexity of the flow setting. Transport of debris in the riverbeds and avalanches, dispersion of the cooled-down agglomerates of lava in the molten medium, and migration of solid material such as icy rocks in high pressure YSF-like, sub-terranean oceans of Europa (Jupiter’s moon) are among numerous natural examples of particle-laden flows of YSFs. To replicate the conditions experimentally, aqueous solutions of Carbopol with yield stress  are used in combination with hydrogel particles. The elastic hydrogel particles have been used in volume fractions φ = 0, 10, 20, and 30 % as mono- and duodispersed suspensions. The excellent refractive index matching of these elastic particles with Carbopol permits accurate recording of the illuminated flow field seeded with tracer particles for PIV measurements, without optical blockage of the macro particles in the optical path. Measurements are performed with channel inclinations ranging from zero to 18°, with controlled deployment of gate opening ranging from 3 cm (i.e. 50 % of the channel width) to a full open dam-break situation. Stream-wise PIV recordings of the transient and semi-steady field are complemented with span-wise recordings targeting statistical results on the particle migration and sedimentation. The results are put in context with the experiments on Newtonian and YSFs in free surface flumes containing rigid particles [1,2], as well as duct flow experiments on Carbopol with the same elastic particles [3].      

References

 [1] Christophe Ancey, Nicolas Andreini, Gaël Epely-Chauvin, The dam-break problem for concentrated suspensions of neutrally buoyant particles, J. Fluid Mech. (2013), vol. 724, pp. 95–122.

[2] G Rousseau, C Ancey, An experimental investigation of turbulent free-surface flows over a steep permeable bed, J. Fluid Mech. (2022), vol. 941, A51.

[3] Sagar Zade, Tafadzwa John Shamu, Fredrik Lundell, Luca Brandt, Finite-size spherical particles in a square duct flow of an elastoviscoplastic fluid: an experimental study, J. Fluid Mech. (2020), vol. 883, A6

How to cite: Amini, K., Chen, Y., Ancey, C., Tammisola, O., and Lundell, F.: Refractive Index Matched (RIM) PIV in Free Surface Flows of Particle-Laden Yield Stress Fluids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12319, https://doi.org/10.5194/egusphere-egu24-12319, 2024.

EGU24-14098 | ECS | Orals | ITS5.14/GD7.3

Nonlinear Viscoelastic Model for Ice and Olivine, Constrained by Experimental Data using MCMC 

Ron Maor, Lars Hansen, and David Goldsby

Mechanisms of energy dissipation in ice and olivine have been studied experimentally in the past, with an observed strain-amplitude dependence that indicates nonlinear viscoelastic behavior resulting from the presence and motion of dislocations. In a range of low to moderate stress amplitudes, dislocations can ”bow out” between pinning points. If the resolved shear stress is sufficiently large, dislocations may escape their pinning points and elastically interact with each other. The transition from pinned to unpinned motion, along with the subsequent interactions and recovery processes, are associated with the shift from anelastic to steady-state viscous behavior. This transition forms the basis of a viscoelastic model. Despite the experimental evidence of nonlinear mechanisms, the availability of comprehensive nonlinear viscoelastic models for geological materials is limited. In this work, we propose a nonlinear viscoelastic model that captures the effect of dislocation dynamics on energy dissipation. The model is based on the well-known linear Burgers model, modified to incorporate non-linear steady-state viscous flow, and enhanced by the integration of fabric and grain-size evolution dynamics. The proposed model is tested against data from constant strain-rate and forced oscillation experiments, and the parameters are constrained using Markov Chain Monte Carlo (MCMC) methods. The model successfully reproduces data from deformation experiments in the dislocation creep regime and can be extended to experiments involving other deformation mechanisms as well.

How to cite: Maor, R., Hansen, L., and Goldsby, D.: Nonlinear Viscoelastic Model for Ice and Olivine, Constrained by Experimental Data using MCMC, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14098, https://doi.org/10.5194/egusphere-egu24-14098, 2024.

The rheology and deformation mechanisms of mafic blueschists play a key role in the mechanical behavior of subducting oceanic crust in subduction zones. While mafic blueschists are often ubiquitous along the plate interface from the base of the seismogenic zone (~35 km) to the sub-arc depths (~100 km), the strength of this lithology still remains poorly constrained. Observations of blueschists from exhumed subduction terranes suggests that blueschist can accommodate significant strain, largely partitioned into the sodic amphibole glaucophane. However, it remains an open question whether the observed deformation is accommodated by dislocation or diffusion deformation processes.

We present microstructural and textural analyses to investigate the glaucophane fabric and deformation mechanisms in three naturally deformed blueschists exhumed from variable P-T conditions: (1) a lawsonite blueschist from the Catalina Schist (Santa Catalina Island, CA, USA), (2) higher-grade epidote blueschist from the Bandon blueschist (Bandon, OR, USA) and (3) an epidote-blueschist from the Cycladic Blueschist Unit (Tinos, GR). We used electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to interpret the textural and geochemical record of deformation mechanisms that were active during the subduction history of these exhumed blueschists. All three blueschists display well-developed foliations and lineations which are defined by interconnected layers of glaucophane. EBSD microstructural analysis of glaucophane in the samples reveals evidence of dislocation accommodated deformation including: (1) strong crystallographic preferred orientation (CPO) development, (2) intragranular orientation gradients, (3) activity of dislocation motion on multiple slip systems, and (4) subgrain boundary formation. Core-mantle structures in which the daughter grains display evidence of a weakened CPO inherited from the mother (core) grains imply the activity of subgrain boundary recrystallization in the samples. Taken together, this microstructural evidence implies that dislocation creep accommodated deformation was active in all three blueschists during their deformation history. SEM images and EDS maps of glaucophane reveal evidence of chemical zoning in grains with higher Ca and Al concentrations in the rims and along the walls of  (micro)fractures within the grains (Bandon, OR Sample). The Catalina lawsonite blueschist displays interspersed evidence of microfractures with higher concentrations of Fe and lower Al and Mg concentrations. This chemical zoning and microfractures suggest micro-boudinage and/or coupled dissolution-precipitation occurred in these samples, and that potential fluid-mediated diffusion accommodated deformation processes may be preserved in these two mafic blueschists. We leverage the relationships between the textural and chemical evidence in concert with P-T estimates for their host terranes to interpret the deformation histories of these samples during subduction and exhumation. Crosscutting relationships between the chemical zoning and intragranular orientation gradients in the samples suggests that dislocation-related deformation was prograde and predates diffusion-related processes which became active in the Catalina and Bandon samples at or near peak conditions and during retrogression. Together, these results suggest that glaucophane can readily deform by dislocation creep, and also record fluid-mediated processes during deformation.

How to cite: Ott, J., Condit, C., Pec, M., and Journaux, B.: Microstructural evidence of dislocation creep and diffusion accommodated deformation of glaucophane in naturally deformed lawsonite and epidote blueschists, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14104, https://doi.org/10.5194/egusphere-egu24-14104, 2024.

EGU24-19147 | ECS | Orals | ITS5.14/GD7.3

Multi-scale anisotropy development in viscous flow due to fabric evolution: Numerical modelling, upscaling, and application for strain localization 

William R. Halter, Roman Kulakov, Thibault Duretz, and Stefan M. Schmalholz

Viscous flow controls large parts of tectonic deformation. Viscous strain localization and associated softening mechanisms are important for subduction initiation and the generation of tectonic nappes. However, viscous flow of geologic materials can have a complex behaviour due to their evolving microstructure, such as an evolving anisotropy due to fabric development or a crystallographic preferred orientation, or due to other evolving microstructure, like, e.g., grain size or dynamic recrystallization.

In this contribution, we focus on strain localization in viscous rock due to the generation of anisotropy resulting from fabric evolution. Particularly, we focus on multi-scale anisotropy evolution in shear zones with many strong or weak inclusions, representing for example porphyroclasts. The shape change and relative alignment of the inclusions during shearing generates an anisotropy on the scale of the inclusions, termed here macroscale. We spatially resolve this macroscale anisotropy in the numerical simulations. Additionally, we consider the evolution of a microscale anisotropy in the shear zone matrix, representing the formation of a mylonitic foliation. We do not spatially resolve this microscale anisotropy but model it with an anisotropic flow law that involves different normal and tangential viscosities. We calculate the finite strain ellipse during shearing and use its aspect ratio as proxy for the anisotropy that governs the ratio of normal to tangential viscosity. To track the orientation of the anisotropy during deformation we apply a director method.

We perform numerical simulations with the two-dimensional state-of-the-art thermo-mechanical code MDoodz (Duretz et al. 2021). We evaluate the impact of micro- and macroscale anisotropy on strain softening and localization in shear zone up to shear strains in the order of ten. We further discuss the quantification of effective anisotropies that can be used for upscaling, for example for lithospheric scale numerical models. Moreover, we compare the numerical results to the analytical solution and the numerical results of Dabrowski et al. (2012). A particular feature of some simulations is the formation of buckle folds in regions with highly stretched weak inclusions.

 

Bibliography

Duretz T., R. de Borst and P. Yamato (2021), Modeling Lithospheric Deformation Using a Compressible Visco-Elasto-Viscoplastic Rheology and the Effective Viscosity Approach, Geochemistry, Geophysics, Geosystems, Vol. 22 (8), e2021GC009675

Dabrowski, M., D. W. Schmid, and Y. Y. Podladchikov (2012), A two-phase composite in simple shear: Effective mechanical anisotropy development and localization potential, J. Geophys. Res., 117, B08406, doi:10.1029/2012JB009183

How to cite: Halter, W. R., Kulakov, R., Duretz, T., and Schmalholz, S. M.: Multi-scale anisotropy development in viscous flow due to fabric evolution: Numerical modelling, upscaling, and application for strain localization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19147, https://doi.org/10.5194/egusphere-egu24-19147, 2024.

EGU24-25 | Orals | G3.4

Enabling Subglacial Geodesy Through High-Precision Radar Sounding and GNSS Time Series Observations 

Dustin Schroeder, Jasmin Falconer, and Matthew Siegfried

Our capacity to estimate vertical motion of the solid Earth with high precision has transformed our understanding of a variety of Earth processes, including mantle dynamics, plate tectonics, volcanic hazards, earthquake rupture, and surface-water balance. Geodetic observations of solid Earth deformation were first achieved on land with conventional surveying techniques, global navigation satellite system (GNSS) deployment, and satellite remote sensing, then expanded to the global ocean with seafloor geodesy techniques like GNSS-Acoustic (GNSS-A) experiments and fiber-optic sensing. Although we can now assess solid Earth deformation nearly everywhere on Earth, we still have not achieved subglacial geodesy: directly observing uplift or subsidence beneath glaciers and ice sheets. Due to decreasing ice mass, we expect high rates of uplift beneath Earth’s ice masses (i.e., glacial isostatic adjustment, or GIA), but available GNSS observations from exposed rock on the periphery of the Greenland and Antarctic ice sheets suggest uplift rates can be highly variable on 10s of km length scales. Recent observational and modeling studies have suggested that GIA could provide a critical stabilizing feedback for ice-sheet mass loss on decadal and centennial timescales, therefore developing and deploying the technology needed for subglacial geodesy is critical for accurate projections of sea level change, particularly in Antarctica where areas of exposed bedrock are rare. To address this challenge, we present a suite of combined radar sounding / GNSS experiments and systems under development to constrain uplift rates beneath both slow-flowing (< 10 m/yr) and fast-flowing ( > 10 m/yr) ice. We also discuss a range of related systems and experiments under development to constrain and correct for potentially confounding firn compaction signals.

How to cite: Schroeder, D., Falconer, J., and Siegfried, M.: Enabling Subglacial Geodesy Through High-Precision Radar Sounding and GNSS Time Series Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-25, https://doi.org/10.5194/egusphere-egu24-25, 2024.

EGU24-2515 | ECS | Posters on site | G3.4

Towards exact free oscillation spectra through generalised normal mode coupling 

Alex Myhill and David Al-Attar

Long period free oscillation spectra provide one of the main constraints on large-scale lateral structures within the Earth’s mantle. These observations are particularly noteworthy for their direct sensitivity to density variations, which gives them the potential to resolve long-standing questions relating to the nature of the two Large Low Shear Velocity Provinces. However, due to both computational expediency and incomplete theory, there are inaccuracies within existing codes for forward modelling of free oscillation spectra. This has limited the ability of previous studies to reliably infer Earth structure using such observations.

This poster outlines work on a new open-source code for modelling free oscillation spectra within laterally heterogeneous Earth models. We apply a generalised normal mode coupling method that overcomes various limitations with the traditional mode coupling approach. We account fully for the non-linear dependence of the matrix elements on density and boundary topography, and exactly solve the equations of motion. Computational costs have been minimised by using high-performance libraries, and efficient numerical linear algebra, in addition to parallelisation. Our code is also suitable for calculation of sensitivity kernels using the adjoint method. Benchmarks against current codes as well as performance benchmarks are shown to demonstrate the accuracy and efficiency of our new method.

How to cite: Myhill, A. and Al-Attar, D.: Towards exact free oscillation spectra through generalised normal mode coupling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2515, https://doi.org/10.5194/egusphere-egu24-2515, 2024.

EGU24-3467 | ECS | Posters on site | G3.4

A comparison of linear and non-linear theories for modelling solid Earth dynamics 

Ziheng Yu, Matthew Maitra, and David Al-Attar

To date, most computational work in solid Earth geophysics has been based on linearised continuum mechanics. This is justified so long as deformation from the reference state remains sufficiently small. The dependence on linearisation also reflects computational limitations of the past: most tractable problems relied on geometric symmetries along with linearity to reduce the calculation to the solution of decoupled systems of ordinary differential equations.

Increases in computational power have allowed for increasingly routine applications of fully numerical techniques such as finite-difference, finite-element, and finite-volume methods. This has allowed geophysical problems to be solved in increasingly realistic Earth models. Although for the most part, the equations being solved are the same as linearised ones used previously, keeping nonlinear terms significantly increases the complexity of solution schemes. Within the context of fully numerical methods, non-linear problems are solved using iterative schemes that involve repeated solution of the corresponding linearised equations. This implies that solving non-linear equations should only be appreciably more expensive if non-linear effects are physically important.

Within this presentation, we compare the use of linearised and non-linear equations of motion, focusing on quasi-static elastic and viscoelastic loading problems of relevance to studies of glacial isostatic adjustment. This is achieved using the open-source finite-element package FeniCSx which facilitates rapid development and testing. Starting from simple representative examples, we quantify the errors associated with linearisation along with the added cost of solving non-linear problems.

How to cite: Yu, Z., Maitra, M., and Al-Attar, D.: A comparison of linear and non-linear theories for modelling solid Earth dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3467, https://doi.org/10.5194/egusphere-egu24-3467, 2024.

EGU24-4786 | Posters on site | G3.4

Towards closing the Australian vertical land movement budget 

Matt King, Carsten Ankjær Ludwigsen, and Christopher Watson

GPS analysis of Australian vertical land motion (VLM) consistently suggests widespread subsidence of Australia of about 1-1.5mm/yr since ~2000, in contrast to most models of Glacial Isostatic Adjustment which predict motion closer to zero or slightly positive. These GPS findings have been corroborated by estimates from altimeter-minus-tide gauge measurements, suggesting they are robust within their terrestrial reference frame. Here we revisit the potential causes for this misfit, exploring a new reconstruction of global ice-loading changes and its impact on vertical land motion. We show this likely produces a subsidence of Australia of about 0.5mm/yr. We explore this in combination with estimates of hydrological, atmospheric and non-tidal ocean loading displacements. The residual signal is discussed within the context of different GIA model predictions, reference frame errors, and the possible impact of far-field postseismic signal.

How to cite: King, M., Ludwigsen, C. A., and Watson, C.: Towards closing the Australian vertical land movement budget, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4786, https://doi.org/10.5194/egusphere-egu24-4786, 2024.

EGU24-5259 | ECS | Orals | G3.4

The lateral heterogeneity of Glacial Isostatic Adjustment modelling across the Arctic 

Tanghua Li, Timothy Shaw, Nicole Khan, F. Chantel Nixon, W. Richard Peltier, and Benjamin Horton

The Arctic has been key area for glacial isostatic adjustment (GIA) studies because it was covered by large ice sheets at the Last Glacial Maximum. Previous GIA studies applied mainly 1D Earth models. The few studies that did include 3D Earth structures have not considered the lateral heterogeneity differences across different regions of the Arctic. Here, using the latest standardized deglacial relative sea-level (RSL) databases from Norway and Russian Arctic, we investigate the effects of 3D structure on GIA predictions and explore the magnitudes of the lateral heterogeneity in both regions.

The 3D Earth structure consists of 1D background viscosity model (ηo) and lateral viscosity variation, the latter is derived from the shear velocity anomaly from seismic tomography model and controlled by scaling factor (ß) denoting the magnitude of lateral heterogeneity.

The Norway RSL database includes 413 sea-level index points (SLIPs), 175 marine limiting data and 433 terrestrial limiting data, while the Russian Arctic database includes 353 SLIPs, 78 marine limiting data and 92 terrestrial limiting data.

We find 3D Earth structures have significant influences on RSL predictions and the optimal 3D model notably improves the fit with RSL data. However, we realize RSL data from Norway and Russian Arctic prefer different 3D structures to provide the best fits. The Russian Arctic database prefers a softer background viscosity model (ηo), but larger scaling factors (ß) than those preferred by Norway database. We further test the extent to which the 3D structure can be eliminated by refinement of ice model.

How to cite: Li, T., Shaw, T., Khan, N., Nixon, F. C., Peltier, W. R., and Horton, B.: The lateral heterogeneity of Glacial Isostatic Adjustment modelling across the Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5259, https://doi.org/10.5194/egusphere-egu24-5259, 2024.

EGU24-5642 | Orals | G3.4

Polar motion of a 3D viscoelastic earth model: Consequences for GIA signals in GRACE-FO 

Volker Klemann, Meike Bagge, Robert Dill, Jan M. Hagedoorn, Zdeněk Martinec, and Henryk Dobslaw

Surface deformations due to changes in the rotation of the Earth are significantly impacted by glacial isostatic adjustment (GIA). The long-term trend of polar motion contributes to global observations like that of the current satellite gravity mission GRACE-FO. The theory and how to apply this contribution to correct GRACE observational data is well understood and goes back to the concise studies of Mitrovica et al. (2005) and Wahr et al. (2015), respectively. According to the International Earth Rotation Service (IERS), a standard correction method is suggested, where the observed long-term trend of the polar motion is considered to originate from GIA. Recent studies show that the modelled GIA contribution to polar motion strongly depends on structural features of the Earth's interior as well as on the glacial history. Other processes like mantle convection or more recent climatic processes are attributed to contribute as well (Adhikari et al. 2018).

In this presentation we focus on the impact of the Earth's viscosity structure on the modelled polar motion. In addition to its radial stratification, we discuss the influence of lateral variability. We apply the numerical 3D viscoelastic lithosphere and mantle model VILMA, which solves the gravitationally self-consistent field equations in a spherical geometry, and which considers the rotational feedback and the sea-level equation. The theory of Martinec and Hagedoorn (2014) applied here is not based on the normal mode theory, but solves the field equations in the time domain. We show the consistency of the chosen approach and rate the influence of lateral changes in viscosity against the impact of radial viscosity stratification. The study was motivated by the ESA Third Party Mission 'GRACE-FO' and contributes to the German Climate Modelling Initiative 'PalMod'.

Lit:
Adhikari, S, Caron L, Steinberger, B, ..., Ivins, ER (2018). What drives 20th century polar motion? Earth Planet. Sci. Lett. doi:10.1016/j.epsl.2018.08.059
Martinec, Z, Hagedoorn, JM (2014). The rotational feedback on linear-momentum balance in glacial isostatic adjustment. Geophys. J. Int. doi:10.1093/gji/ggu369
Mitrovica, JX, Wahr, J, Matsuyama, I, Paulson, A (2005). The rotational stability of an ice-age earth. Geophys. J. Int. doi:10.1111/j.1365-246X.2005.02609.x
Wahr, J, Nerem, RS, Bettadpur, SV (2015). The pole tide and its effect on GRACE time-variable gravity measurements: Implications for estimates of surface mass variations. J. Geophys. Res. Solid Earth. doi:10.1002/2015JB011986

How to cite: Klemann, V., Bagge, M., Dill, R., Hagedoorn, J. M., Martinec, Z., and Dobslaw, H.: Polar motion of a 3D viscoelastic earth model: Consequences for GIA signals in GRACE-FO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5642, https://doi.org/10.5194/egusphere-egu24-5642, 2024.

EGU24-5655 | Posters on site | G3.4 | Highlight

Causes of Global Elastic Vertical Land Movement from 1900 to 2022 

Per Knudsen, Carsten Bjerre Ludwigsen, Ole Baltazar Andersen, Matt King, and Christopher Watson

Elastic vertical land movement (eVLM) is the lithosphere's immediate elastic response to the loading and unloading of the Earth's surface mass. Understanding eVLM is crucial for interpreting relative sea level changes, particularly in coastal regions where subsidence or uplift can significantly alter the impacts of sea level changes recorded by tide gauges. Here we present a comprehensive global eVLM model, offering valuable insights for geodesy and related fields, especially in assessing observations from tide gauges and GNSS.

Our eVLM model spans from 1900 to 2022, featuring a 0.5-degree spatial resolution. It provides annual data from 1900 to 1990 and monthly data from 1991 to 2022, enabling both long-term and seasonal assessment. The dataset is available in three different reference frames: Centre of Mass (CM), Centre of Figure (CF), and ITRF2020, and thus suitable for many geodetic applications.

This study incorporates mass change estimations from Greenland, Antarctica, global glaciers, and land water storage (LWS), divided into natural LWS variations and anthropogenic water management like groundwater depletion and dam retention. Thus, we can explain regional VLM patterns that cannot be solely attributed to Glacial Isostatic Adjustment (GIA) models, for example, subsidence across Australia or uplift in Scandinavia that is larger than modeled GIA.

Methodology: We employed a composite loading model, integrating ice models from Greenland (Mankoff et al., 2021) and Antarctica (Otosaka et al, 2022; Nilsson et al, 2022) and glacier models (Hugonnet et al., 2022), GRACE observations, and a land water storage model (Müller-Schmied et al, 2023). Each of the aforementioned five causes of eVLM was perturbed with its uncertainty a thousand times, and the sea level equation was resolved for each variant using the ISSM-SEESAW framework (Adhikari et al., 2016). To align the results with observations in the ITRF2020 reference frame, which mirrors CM on secular timescales and CF on non-secular timescales (Dong et al, 2003). To accommodate this, we applied CM and CF Love loading numbers (Blewitt, 2003) in our calculations, enabling analysis in all three reference frames.

How to cite: Knudsen, P., Ludwigsen, C. B., Andersen, O. B., King, M., and Watson, C.: Causes of Global Elastic Vertical Land Movement from 1900 to 2022, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5655, https://doi.org/10.5194/egusphere-egu24-5655, 2024.

EGU24-5748 | ECS | Orals | G3.4

Rapid Earth uplift in southeast Greenland driven by recent ice melt above low-viscosity upper mantle 

Maaike F. M. Weerdesteijn and Clinton P. Conrad

Along the periphery of the Greenland ice sheet, Global Navigation Satellite System (GNSS) stations observe uplift of a few mm/yr, reflecting Earth’s response to past and contemporary changes in Greenland’s ice mass. On the coast of southeast Greenland, near the Kangerlussuaq glacier, GNSS stations show abnormally rapid ground uplift, faster than 10 mm/yr. Current earth deformation models, which employ a layered Earth structure, cannot explain such rapid uplift. Here we develop 3D regional models of uplift in response to deglaciation occurring over timescales corresponding to the last glacial cycle (past 1000s of years), the last millennium (past 100s of years), and recent rapid deglaciation (past 10s of years). These 3D models incorporate a track of low-viscosity upper mantle and thin lithosphere, consistent with the passage of Greenland over the Iceland plume during the past ~50 Myr. We find that the fastest ground uplift occurs where rapid deglaciation occurs above the low-viscosity plume track of the Iceland plume. This uplift reflects viscous deformation of the upper mantle, and is much larger than the (instantaneous) elastic deformation that also results from this deglaciation. Above the low-viscosity plume track, the uplift contribution is greatest for the most recent deglaciation (past decades), followed by the contribution from deglaciation during the last millennium. The combination of these viscous contributions can explain uplift observations of more than 10 mm/yr near the rapidly deglaciating Kangerlussuaq glacier, which lies above the Iceland plume track, and slower uplift in the surrounding areas. Rapid uplift observed to the south of the Kangerlussuaq glacier can be explained if the low-viscosity plume track extends farther southward beneath the Helheim glacier, which is also rapidly deglaciating. Such rapid viscous uplift from recent and local ice melt is not usually considered in glacial isostatic adjustment (GIA) models, but likely happened in the past in response to previous deglaciation. It will also become increasingly important in the future as deglaciation accelerates.

How to cite: Weerdesteijn, M. F. M. and Conrad, C. P.: Rapid Earth uplift in southeast Greenland driven by recent ice melt above low-viscosity upper mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5748, https://doi.org/10.5194/egusphere-egu24-5748, 2024.

EGU24-6043 | ECS | Posters virtual | G3.4

A parametric study of sea level and grounding line projections in the Amundsen Sea sector for coupled solid Earth - ice sheet models. 

Luc Houriez, Eric Larour, Lambert Caron, Nicole-Jeanne Schlegel, Tyler Pelle, and Hélène Seroussi

The evolution of the Antarctic Ice Sheet (AIS) represents one of the most important and uncertain contributions to sea level rise in the upcoming centuries. Thwaites glacier and the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) have been identified as the continent's most critical areas. The retreat of Thwaites' glacier grounding line - the transition area where ice is no longer grounded and becomes afloat - is the subject of considerable study for modelers as it governs the collapse of the glacier.

 

Recent advances towards coupling of dynamical ice models with Glacial Isostatic Adjustment (GIA) models has provided the means to improve grounding line projections by considering solid-Earth processes and their interactions with the cryosphere and hydrosphere. However, the spatial and temporal model resolution necessary to fully capture these interactions, and its sensitivity to model parametrization, remains elusive.

 

We investigate the grounding line retreat of Thwaites Glacier through 2350 using the parallelized coupled physics capabilities of the Ice-sheet and Sea-level System Model (ISSM) which capture the complex interactions between solid-Earth, ice-sheets, and ocean. We incorporate realistic climatology, ocean melt rates, and GIA models and we discuss the impact of spatial and temporal model resolution, and solid-Earth parametrization, on the grounding line retreat and sea level change.

 

© 2024 California Institute of Technology. Government sponsorship acknowledged.

How to cite: Houriez, L., Larour, E., Caron, L., Schlegel, N.-J., Pelle, T., and Seroussi, H.: A parametric study of sea level and grounding line projections in the Amundsen Sea sector for coupled solid Earth - ice sheet models., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6043, https://doi.org/10.5194/egusphere-egu24-6043, 2024.

EGU24-6485 | Posters on site | G3.4

Body tides and elastic stresses in the Earth’s crust 

Marianne Greff-Lefftz and Laurent Métivier

Solid tides, predominantly diurnal and semi-diurnal, are commonly observed on Earth's surface through horizontal and vertical movements (a few tens of centimeters), along with gravity measurements (~100 microgal). This study focuses specifically on tidal effects within the elastic stress field at the surface, which is approximately 1000 Pascals.

We initially established a correlation between tidal elastic pressure and natural hydrogen emission. Hydrogen, in its gaseous form, escaping from Proterozoic basins, represents a potential source of carbon-free energy, leading to extensive research on vents. A notable characteristic of these emissions is the consistent daily cycle observed in specific regions. While atmospheric pressure effects have been shown to account for this cycle, solid tides could serve as an alternative explanation. Considering that tidal waves do not have a uniform spatial distribution on the Earth's surface, we computed time series of elastic pressure at two locations where natural hydrogen emissions are observed: one near the equator in the Sao Francisco basin (Brazil) and another near the North Pole in the Lovozero deposits (Kola Peninsula).

We then explored the maximum shear stress generated by tidal potential in areas experiencing tectonic stresses. We demonstrated that in expansive regions, the maximum shear stress correlates with the peak of the tidal potential, while in compressive regions, it is associated with the minimum tidal peak.

How to cite: Greff-Lefftz, M. and Métivier, L.: Body tides and elastic stresses in the Earth’s crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6485, https://doi.org/10.5194/egusphere-egu24-6485, 2024.

EGU24-6863 | ECS | Orals | G3.4

Modelling Glacial Isostatic Adjustment in Firedrake  

William Scott, Mark Hoggard, Sia Ghelichkhan, Angus Gibson, Stephan Kramer, and Rhodri Davies

Melting ice sheets transfer water from land into ocean basins. The resulting sea-level rise is, however, highly spatially non uniform and time dependent due to complex feedbacks between viscoelastic deformation of the solid Earth in response to these evolving surface loads and coupled perturbations in the gravitational field and rotation axis. Together, these processes are referred to as Glacial Isostatic Adjustment (GIA) and accurate models of GIA are crucial for robust interpretation of both modern and paleo measurements of sea-level change and ice-mass balance. 

A limitation with many existing GIA modelling codes is their inability to incorporate lateral variations in Earth structure. Nevertheless, there is mounting evidence for the presence of significant lateral changes in mantle viscosity, for example beneath West Antarctica, that give rise to complex interactions between rates of surface rebound, sea-level change and ice retreat. Understanding these processes requires development of a new generation of GIA codes capable of handling such variations in rheology at increasingly fine spatial and temporal evolution. 

In this presentation, we will introduce a new project to model GIA using the Firedrake finite element framework and present results for several community benchmarks. Firedrake leverages automatic code generation to create a separation of concerns between employing the finite-element method and implementing it. This approach maximises the potential for collaboration between computer scientists, mathematicians, scientists and engineers and enables sophisticated high performance simulations. A key advantage of Firedrake is the automatic availability of sensitivity information through the adjoint method, allowing us to investigate inverse problems. We are developing an open-source tool highly suited to the challenge of modelling complex Earth structure in GIA, building on the Firedrake-based G-ADOPT project for mantle convection. We envision that future applications might include, but are not limited to, investigating non-linear and transient rheologies, feedbacks between sea-level and glacier dynamics, and reducing uncertainty on sea-level projections into the future. 

How to cite: Scott, W., Hoggard, M., Ghelichkhan, S., Gibson, A., Kramer, S., and Davies, R.: Modelling Glacial Isostatic Adjustment in Firedrake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6863, https://doi.org/10.5194/egusphere-egu24-6863, 2024.

EGU24-6898 | Posters on site | G3.4

Mid-Holocene ice history inferred from GIA-induced crustal motion around Lützow-Holm Bay, East Antarctica 

Jun'ichi Okuno, Akihisa Hattori, Koichiro Doi, Yoshiya Irie, and Yuichi Aoyama

The history of ice melting and the viscoelastic properties of the mantle heavily influence Antarctic crustal deformation caused by Glacial Isostatic Adjustment (GIA). The interaction between ice history and mantle viscosity further complicates the complex Antarctic GIA. Nonetheless, geodetic observations, such as GNSS, are crucial for constraints on the GIA model parameters.

For over two decades, the Japanese Antarctic Research Expedition (JARE) has been using GNSS and absolute gravity measurements to obtain data along the coast of Lützow-Holm Bay, primarily at Syowa Station. This study examines the geodetic signals associated with GIA from observations along the Lützow-Holm Bay coastline in East Antarctica, and we also conduct GIA simulations based on the recent report of rapid ice thinning in the target region during the mid-Holocene.

Based on geomorphological surveys and surface exposure ages, Kawamata et al. (2020: QSR) showed that the region experienced rapid ice thinning of over 400 m from about 9 to 6 ka. Representative deglaciation models, such as ICE-6G, do not account for this rapid thinning process. Therefore, we investigate the variability of the geodetic signals using the ice history, including this rapid thinning. Our predictions demonstrate that incorporating the modified ice history results in consistent outcomes with the observations. This finding supports the notion that rapid ice melting occurred in the Holocene and suggests that geodetic observations can help constrain this region's ice sheet melting process. Additionally, we will present a possibility of the readvance following the rapid retreat based on the precise GIA modelling.

How to cite: Okuno, J., Hattori, A., Doi, K., Irie, Y., and Aoyama, Y.: Mid-Holocene ice history inferred from GIA-induced crustal motion around Lützow-Holm Bay, East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6898, https://doi.org/10.5194/egusphere-egu24-6898, 2024.

EGU24-7839 | ECS | Posters on site | G3.4

Holocene water-level indicator database for the Dutch coastal plain 

Kim de Wit, Roderik S.W. van de Wal, and Kim M. Cohen

The evolution of the Holocene coastal plain in the Netherlands is strongly influenced by global sea-level rise and regional subsidence patterns. Added up these components are known as relative sea-level rise (RSLR), and explain the coastal plain build-up and accommodation space. Due to RSLR, geological indicators of gradual-drowning formed, such as basal peat layers. These indicators have been sampled and dated from different depths and locations across the coastal plain and are used to document rising coastal sea levels and inland groundwater levels. Databasing and spatial-temporal analysis of the large set of indicators (N=~720) serves to assess local and regional variabilities in RSLR.

Collection of geological water level indicators in the Netherlands started as early as the 1950ies. It was carried out for various purposes: RSLR reconstruction, geological mapping of the coastal-deltaic plain, wetland paleoenvironmental reconstructions. Full formal overview of this data did not exist, as past reviews and data compilations (N=50-300) were subregion restricted and usage specific. Regional differences within the Netherlands, e.g. greater RSLR in the north than in the SW, are also long noticed, and mostly attributed to  differential subsidence as caused by glacial isostatic adjustment (GIA: Scandinavian forebulge collapse, at non-linear rate) and longer-term North Sea Basin tectono-sedimentary subsidence (at a linear rate).

Here, we present a uniform database of Holocene coastal plain water level indicators for the Netherlands, using the HOLSEA workbook format. By compiling a database of geological water level indicators, with an explicit and consistent  standardized treatment of dealing with vertical uncertainties, age uncertainties, and indicative meaning of each indicator (e.g. does it resemble former inland  groundwater level, or former sea-level), we enable more accurate break down of differential subsidence and its source components.

Database compilation included documentation of all vertical corrections applied, such as for water depth, (paleo-)tides, long-term background land motion and for compaction, as well as the propagation of uncertainties associated with these corrections.  The ~720 indicators are further categorized into sea level index points (SLIPs), sea-level upper limiting data (ULD) and sea-level lower limiting data (LLD). ULD data is further categorized to separate tidally, river gradient and local-hydrology influenced indicators. Vertically corrected relative sea-level positions and relative groundwater-level positions are reported separately.

Spatial-temporal analysis of the Holocene water level data allowed for an interpolated reconstruction of Holocene RSLR, resulting in map-output that has continuous coverage of the Dutch coastal plain. Furthermore, this data-driven RSLR reconstruction is used to further disentangle components of RSLR: the Holocene water level rise part versus the two main land subsidence parts, independently from global sea-level analysis, basin-geological subsidence reconstructions and geophysical GIA-modelling  output.  We  compare our reconstructed sea level plains to the RSLR output of glacio-isostatic adjustment modelling, which incorporate ice sheet deglaciation history and Earth-rheological models. This enhances our ability to quantify the contributions of GIA and basin subsidence to past and ongoing RSLR and subsidence in the Netherlands.

How to cite: de Wit, K., van de Wal, R. S. W., and Cohen, K. M.: Holocene water-level indicator database for the Dutch coastal plain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7839, https://doi.org/10.5194/egusphere-egu24-7839, 2024.

EGU24-8753 | ECS | Posters on site | G3.4

Internal Mass-Induced Elastic Deformation: A Semi-Analytic Approach     

He Tang, Wenke Sun, and Yuting Ji

This research presents an innovative semi-analytical method to study the deformation of a viscoelastic, spherical, layered Earth model under periodic loading. We explore the effects of surface mass changes on deformation over various timescales, including annual and interannual, using a linear rheology profile. Our approach leverages a novel set of formulas in the spectral domain, linking mass, geoid, and displacement through complex Love numbers and Stokes coefficients. This technique bypasses the traditional reliance on viscoelastic Green’s functions.

In our analysis, we particularly focus on the impact of annual cyclic mass loading on viscoelastic loading deformation. We consider both steady-state creep and additional transient creep across a broad spectrum of viscosities. Our findings reveal that while steady-state viscosity values, constrained by Glacial Isostatic Adjustment (GIA) data, show minimal viscoelastic impact on annual load deformation, the inclusion of transient creep, primarily informed by post-seismic data and modeled through the Burgers model, significantly alters the deformation's amplitude and phase. This underscores the importance of rheological properties in understanding Earth's deformation.

Furthermore, our results demonstrate a notable difference in how the horizontal displacement, as opposed to geoid and vertical displacement, responds to viscosity changes. This disparity is observed regardless of the rheological model applied, indicating a greater sensitivity of horizontal displacement to viscosity variations in periodic load deformation. Our study provides new insights into the complexities of Earth's viscoelastic response to cyclic loading, contributing to a deeper understanding of geophysical processes.

How to cite: Tang, H., Sun, W., and Ji, Y.: Internal Mass-Induced Elastic Deformation: A Semi-Analytic Approach    , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8753, https://doi.org/10.5194/egusphere-egu24-8753, 2024.

EGU24-10534 | ECS | Posters on site | G3.4

Reduction of temporal variations in tidal parameters by application of the local response models at globally distributed SG stations 

Adam Ciesielski, Thomas Forbriger, Walter Zürn, Andreas Rietbrock, and Przemysław Dykowski

The already 100 years old harmonic analysis of tides is based on the assumption of separable and non-separable contributions depending on the time series length (Rayleigh criterion in tidal analysis). A priori wave groups had to be composed of different harmonics, which leads to an inaccurate (biased) estimate of tidal parameters. An alternative Regularization Approach to Tidal Analysis, RATA, constrains the solution to be close to a reference model what stabilises the linear regression, making wave grouping obsolete. In this way, the resolution power of the harmonic analysis is exploited to a much larger extent, since the risk of over-fitting is strongly reduced.

We used RATA method to analyse data from globally distributed superconducting gravimeters (SGs) and we are able to achieve super resolution that even highly violates the Rayleigh criterion. The results from double-sphere SG instruments give an indication of the minimum error for the accuracy. We estimated local response models for over 10 stations in Europe, which confirms the consistency of the method. The small differences in phases and amplitudes are most likely caused by ocean loading with varying distance to the ocean. The investigation of stations on other continents reveals significant disparities between the observed tidal response (which accounts for the loading signals as well) and the Earth body model assumptions (like Wahr-Dehant-Zschau elastic analysis model).

Temporal variations of tidal parameters, seen in the moving window analysis (MWA), are known for all tidal wave groups at different SG stations around the globe. The amplitude of variations usually is greater than the standard deviation by a factor of 2 (minimum) to 32 (maximum). In our investigation, we approximated the effect of the time-invariant ocean loading and radiation tides in the data by application of the local response models, already estimated with RATA. We repeated the MWA of 12 wave groups composed from summed harmonics. We found that the periodic variations of groups M2, K1, µ2, N2, L2, and S2 are reduced by up to a factor of 9 compared to earlier studies. Some long-period variations previously seen in the M1, O1, Q1, and J1 groups are captured as well. The previously neglected influence of radiation tides, degree 3 tides, and significant satellite constituents were the main causes of apparent modulations in previous studies. Hence, with the local model correction, a proper investigation of the remaining temporal variations to study instrument stability or time-varying contributions of ocean loading is more applicable.

How to cite: Ciesielski, A., Forbriger, T., Zürn, W., Rietbrock, A., and Dykowski, P.: Reduction of temporal variations in tidal parameters by application of the local response models at globally distributed SG stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10534, https://doi.org/10.5194/egusphere-egu24-10534, 2024.

EGU24-10834 | ECS | Orals | G3.4

Towards imaging 3D crust and mantle structure by means of ocean tidal loading tomography 

Andrei Dmitrovskii, Federico Munch, Christian Boehm, Hilary Martens, and Amir Khan

Ocean tide loading (OTL) brings about recurring deformation of the Earth’s surface. Some of the OTL harmonics, e.g. M2, O1, Mf, cause sufficiently large surface displacement to be registered by the Global Navigation Satellite Systems (GNSS). These displacements are sensitive to the interior structure of the planet in a broad range of temporal and spatial scales making them a potentially unique source of information about the planet’s response at low frequencies. Comparison between observations and predictions for 1D elastic Earth models result in discrepancies of up to 3 mm (Bos et al., 2015, Martens et al., 2016). Spatial coherency of these discrepancies hints to 3D interior structure as one of the main sources of such residuals.
In this context, we present a framework to invert OTL observations for 3D crustal and mantle structure based on a trust-region Newton-type iterative algorithm. Furthermore, we resort to the adjoint approach as an efficient means of computing the gradient for the high-dimensional model space. Focusing on the design of the inverse algorithm, we constrain ourselves to deformations of an isotropic elastic planet, which are governed by a self-adjoint forward operator. In order to assess the robustness of the method, we perform a suite of 3D synthetic inversions that mimic the distribution of the GNSS stations in South America. Preliminary results indicate enhanced sensitivities to the crustal and upper mantle density and elastic properties in the vicinity of the coastlines.

How to cite: Dmitrovskii, A., Munch, F., Boehm, C., Martens, H., and Khan, A.: Towards imaging 3D crust and mantle structure by means of ocean tidal loading tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10834, https://doi.org/10.5194/egusphere-egu24-10834, 2024.

We compute daily GPS solutions for about 200 permanent stations in Greenland, Scandinavia and Canada for the 2000 – 2023 period, using the CNES/GINS software in precise point positioning with integer ambiguity resolution (IPPP) mode. The observed vertical displacements are caused by both past- and present-day ice mass (PDIM) changes. The glacial isostatic adjustement (GIA) is the visco-elastic Earth’s response to the Pleistocene glaciation and deglaciation, whereas the PDIM is often estimated assuming an elastic Earth’s response.

We revisit the problem of the separation of GIA and PDIM using state-of-the-art ice models (for example, ICE-6G and ICE-7G) and observations from space gravimetry (GRACE and GRACE Follow On) and altimetry (CryoSat-2 and ICESat-2).

In particular, we investigate different rheology models, including the classical Maxwell model used in GIA modeling, but also the Burgers model allowing transient anelastic deformation at timescales of 10 to 20 years.

We found that the Burgers model with a transient viscosity of about 1018 Pa.s in the upper mantle, combined with the VM5a or VM7 viscosity profiles (Maxwell component) is in better agreement with the observed GPS vertical displacements.

 

How to cite: Boy, J.-P. and Taghiyev, V.: Vertical deformation in Greenland: separation of past and present-day ice mass loss contributions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12953, https://doi.org/10.5194/egusphere-egu24-12953, 2024.

EGU24-13658 | Orals | G3.4

GIA constraints for Greenland from combined GRACE and GNSS observations 

Valentina R. Barletta, Andrea Bordoni, and Shfaqat Abbas Khan

Currently, many different glacial isostatic adjustment (GIA) models have been proposed for Greenland, as a consequence of a still largely unknown deglaciation there. GNSS trends are often used to constrain GIA models regionally. However, the GNSS uplift rates contain a large contribution from present-day mass changes (mostly due to ice melting) that must be removed to extract the GIA uplift rates. The elastic uplift rates estimates are potentially affected by uncertainties. They depend on the Earth model chosen (usually PREM-based models) and on high-resolution mass changes estimates, usually obtained from volume changes measured with altimetry. The volume changes need to be converted into mass variations, mostly using models (surface mass balance and firn compaction models) that can introduce biases. Since the elastic uplift rates are proportional to the mass changes, any uncertainty in the mass variations directly affects the elastic uplift rates eventually, as well as the GIA GNSS residuals uplift rates obtained from them. And in turn, these biases reflect directly in the GIA models constrained with those GNSS.

Here we propose a novel additional GIA constraint based on both GRACE and GNSS observations. We start from a very simple model, based on three basic and general assumptions: 1) Elastic uplift rates at a given distance from a mass distribution (e.g. a disk changing height) are proportional to the mass variation. 2) The GIA induced uplift rates can be considered proportional to the apparent mass changes produced by GIA gravity changes (e.g. Wahr et al 2000 and Riva et al. 2009). 3) The total uplift rate measured by a GNSS is the sum of the elastic uplift rate caused by any surface mass changes and the GIA induced uplift rate (assuming that uplifts rates due to plate tectonics are negligible in Greenland). We then show that this simple model can be applied to Greenland, and still retain most of its validity. The three points above become three equations in four unknowns, namely the surface mass changes and the related elastic uplift rate, the GIA uplift rate and its related apparent mass change.  Using the average uplift rate measured by the whole GNET (Greenland GNSS Network) and the total GMB (Greenland Mass Balance) measured with GRACE, from the three equations we derive a global consistency relation between the average GIA uplift rate and its related apparent mass change for the whole Greenland.

In this way, the combined analysis of the GMB from GRACE and GNET provides a very solid constraint for Greenland-wide GIA models. GIA models constrained only regionally might provide estimates that are not consistent in other Greenland regions. The four GIA models that we tested do not respect the consistency relation we found. This relation does not allow to determine the GIA uplift rate uniquely, but we show that together with some basic considerations about the plausible deglaciation scenarios, it allows to identify a reasonable range for the GIA component in the average GNSS uplift rate.

How to cite: Barletta, V. R., Bordoni, A., and Khan, S. A.: GIA constraints for Greenland from combined GRACE and GNSS observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13658, https://doi.org/10.5194/egusphere-egu24-13658, 2024.

EGU24-13928 | ECS | Orals | G3.4

The impact of regional-scale variability in upper mantle viscosity on GIA in West Antarctica 

Erica Lucas, Natalya Gomez, Konstantin Latychev, and Maryam Yousefi

West Antarctica is underlain by a laterally heterogenous upper mantle, with localized regions of mantle viscosity reaching several orders of magnitude below the global average. Accounting for 3-D variability in upper mantle structure in glacial isostatic adjustment (GIA) simulations has been shown to significantly impact the predicted spatial rates and patterns of crustal deformation, geoid and sea-level changes. Uncertainty in constraining the viscoelastic structure of the solid Earth remains a major limitation in GIA modeling. To date, investigations of the impact of 3-D Earth structure on GIA have adopted solid Earth viscoelastic models based on global- and continental-scale seismic imaging with variability at spatial scales >150 km. However, regional body-wave tomography shows mantle structure variability at smaller spatial scales (~50-100 km) in central West Antarctica (Lucas et al., 2020). Here, we investigate the effects of incorporating this smaller-scale lateral variability in upper mantle viscosity into 3-D GIA simulations. Lateral variability in upper mantle structure at the glacial basin scale is found to have a significant impact on GIA model predictions, especially in coastal regions undergoing rapid ice mass loss. For example, incorporating a transition from lower viscosity at the mouth of Thwaites Glacier to higher viscosity further upstream impacts the predicted rate and pattern of solid Earth deformation and sea-level change in response to ongoing and projected ice mass loss, with possible implications for the evolution of the overlying ice and the interpretation of geophysical observables.

How to cite: Lucas, E., Gomez, N., Latychev, K., and Yousefi, M.: The impact of regional-scale variability in upper mantle viscosity on GIA in West Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13928, https://doi.org/10.5194/egusphere-egu24-13928, 2024.

EGU24-15498 | Posters on site | G3.4 | Highlight

Earth’s hypsometry and what it tells us about global sea level 

Vivi Kathrine Pedersen, Natalya Gomez, Jerry X. Mitrovica, Gustav Jungdal-Olesen, Jane Lund Andersen, Julius Garbe, Andy Aschwanden, and Ricarda Winkelmann

Over geological time scales, the combination of solid-Earth deformation and climate-dependent surface processes have resulted in a distinct hypsometry (distribution of surface area with elevation), with the highest concentration of surface area focused near the present-day sea surface. However, this distinctive signature of Earth’s hypsometry does not constitute a single well-defined maximum at the present-day sea surface (0 m). Earth’s hypsometry also shows a prominent maximum ~5 m above the present-day sea surface. Here we explore the nature of this 5-m maximum and examine how it evolved over the last glacial cycle and may evolve moving towards a near-ice-free future. We find that the current elevation of this 5-m hypsometric maximum cannot be explained by ongoing sea-level adjustments following the last glacial cycle. Instead, we suggest that global sea level must have been higher for a significant portion of Earth’s recent multi-million-year history. Indeed, global sea level must have been higher by as much as ~9.5 m to bring this hypsometric maximum in accordance with the sea surface, to account for glacial isostatic adjustments such as ocean syphoning. This signifies that our current polar ice-sheet and sea-level state (and our global reference level) should be considered an anomaly in a geological perspective.

How to cite: Pedersen, V. K., Gomez, N., Mitrovica, J. X., Jungdal-Olesen, G., Andersen, J. L., Garbe, J., Aschwanden, A., and Winkelmann, R.: Earth’s hypsometry and what it tells us about global sea level, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15498, https://doi.org/10.5194/egusphere-egu24-15498, 2024.

EGU24-15975 | ECS | Posters on site | G3.4

A rapid numerical routine for viscoelastic earthquake cycle simulations.  

Sharadha Sathiakumar and Rishav Mallick

Earth’s largest quakes and trans-oceanic tsunamis emanate from subduction zones around the world. Following such large earthquakes, viscoelastic processes and on-fault aseismic fault slip play a crucial role in dissipating the stresses induced by the earthquake, facilitating the solid Earth's return to equilibrium.  The rheological properties of lithospheric rocks govern these postseismic processes and influence time-dependent deformation during the earthquake cycle. Geodetic observations offer an opportunity to constrain these rheological properties, providing valuable insights into the regional lithospheric structure, and potentially improving our understanding of earthquake-related hazards.   

To build intuition for geodetically recorded postseismic deformation, we develop a robust and efficient two-dimensional quasi-static periodic earthquake cycle simulator exploiting the boundary element method and semi-analytical solutions to systems of coupled ordinary differential equations. We investigate the impact of lateral and depth-dependent variations in the viscosity structure of the mantle wedge and the oceanic mantle, to discern their respective contributions and roles in surface deformation observations. We account for the long-term viscous flow rate in the mantle and show that neglecting this term in the earthquake cycle introduces biases in the effective viscosity structure of the lithosphere-asthenosphere system, particularly in the context of power-law rheologies. The low computational cost of our numerical routine makes it ideal for incorporating into future inverse modelling frameworks to estimate regional rheological structure from geodetic observations of subduction zone earthquake cycles.  

How to cite: Sathiakumar, S. and Mallick, R.: A rapid numerical routine for viscoelastic earthquake cycle simulations. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15975, https://doi.org/10.5194/egusphere-egu24-15975, 2024.

EGU24-16655 | ECS | Orals | G3.4

Does thicker ice cover cause stronger glacially triggered earthquakes? - A case study from the southwestern Baltic Sea 

Elisabeth Seidel, Holger Steffen, Rebekka Steffen, Niklas Ahlrichs, and Christian Hübscher

Increasing and decreasing ice masses cause an isostatic adjustment of the crust, which can trigger fault reactivation. It could be assumed that the higher the ice load, the stronger the glacially induced fault reactivation, leading to stronger earthquakes. Here we focus on glacially triggered fault reactivation in the southern Baltic Sea over the past 200,000 years (since the Upper Saalian). Our study area comprises the Caledonian Suture Zone between the East European Craton and the West European Platform as well as the trans-regional Tornquist Zone. Consequently, it reflects a polyphase tectonic history. The fault zones and systems in this geoarchive have been mapped and studied through several reflection seismic investigations. They display variations in their characters, strike and dip directions, age, and depths, documenting the complex evolution.

We focus on faults indicating reactivation during the Quaternary, determined by the seismic sections. After documenting their fault properties, we calculated the glacially induced Coulomb Failure Stress changes (∆CFS) at the faults over the past 200,000 years using finite-element simulations of various glacial isostatic adjustment models. The results show significant local and temporal differences in fault reactivation. We observe that shorter ice advances and lower ice loads correlate with higher ∆CFS, suggesting a higher potential for fault reactivation, which could potentially lead to stronger earthquakes if released in one event. Moreover, we will discuss if the lateral ice thickness gradient or the steepness of the flanks of the ice sheet might play a major role.

How to cite: Seidel, E., Steffen, H., Steffen, R., Ahlrichs, N., and Hübscher, C.: Does thicker ice cover cause stronger glacially triggered earthquakes? - A case study from the southwestern Baltic Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16655, https://doi.org/10.5194/egusphere-egu24-16655, 2024.

EGU24-18171 | ECS | Posters on site | G3.4

Impact of the Earth's mantle transient rheology on surface deformation induced by decades of hydrological mass redistribution 

Maxime Rousselet, Alexandre Couhert, Kristel Chanard, and Pierre Exertier

Over the past decades, modern geodetic observations have provided crucial constraints on the Earth's rheological properties over a wide range of time scales. Whole mantle steady-state viscosity has been inferred from geodetic observations related to glacial isostatic adjustment. More recently, geodesy has helped probing Earth’s upper mantle transient response to stresses induced by rapid regional changes in hydrology, including recent ice melting, during which viscosity rapidly increases from an elastic to a viscous regime. Here we investigate the potential of using decades of global hydrological mass redistributions, mainly driven by recent ice melting, to constrain the Earth's mantle transient rheology. We quantify the sensitivity of the Earth surface deformation and gravity field to mass redistribution at very large spatial scales to variations in the Earth’s mantle rheology using a spherically layered model and considering Maxwell and Burgers behaviors. Mass redistribution is estimated using low-degree spherical harmonics of the Earth’s gravity field inferred from over 30 years of Satellite Laser Ranging (SLR) observations. We discuss the importance of accounting for the Earth's lower mantle transient rheology at timescales of a few decades and evaluate to what extent it can be constrained by combining long geodetic time series of the Earth’s gravity field and surface deformation.

How to cite: Rousselet, M., Couhert, A., Chanard, K., and Exertier, P.: Impact of the Earth's mantle transient rheology on surface deformation induced by decades of hydrological mass redistribution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18171, https://doi.org/10.5194/egusphere-egu24-18171, 2024.

EGU24-18865 | ECS | Posters on site | G3.4

Towards constraining Venus structure by means of atmospheric loading displacement response  

Federico Daniel Munch, Amir Khan, Hilary Martens, and Christian Boehm

Surface mass loads produce a wide spectrum of deformation responses in planetary bodies that can be exploited to probe material properties in planetary interiors. In particular, the redistribution of fluid mass associated with Venus’s atmospheric dynamics leads to periodic changes in the Venusian surface displacements and thus gravitational field. These periodic variations could potentially be detected by upcoming Venus missions, e.g., VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) and EnVision, which are expected to greatly  improve our knowledge of Venus’s gravity field. 

By combining a state-of-the-art general circulation model of Venus’s atmosphere with a novel approach to the solution of the quasi-static momentum equations in the coupled gravito-elastic problem, we explore the sensitivity of the atmospheric loading response to mantle structure. In addition, we investigate the effect of 3-D crustal and lithospheric variations on Venus’s gravity field and the tidal and load Love numbers. Preliminary results suggest that an accurate estimation of the time-varying gravity field and surface displacements can provide important constraints on the interior structure of Venus through the measurement of the load Love numbers.

How to cite: Munch, F. D., Khan, A., Martens, H., and Boehm, C.: Towards constraining Venus structure by means of atmospheric loading displacement response , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18865, https://doi.org/10.5194/egusphere-egu24-18865, 2024.

GD8 – Core Dynamics

EGU24-255 | PICO | GD8.1

Iron hydride FeHx in the Earth's inner core and its geophysical implications 

Feiwu Zhang, Hua Yang, and Joshua Muir

The Earth's inner core, formed as a result of cooling and crystallization of the outer core iron alloys, plays a fundamental role in the evolution of our planet. There is still much uncertainty on the phases of iron at high pressures and temperatures. Furthermore, the chemical composition of the Earth's core has attracted growing attention in the last several decades. The presence of small amounts of light alloying elements such as Si, O, S, C, and H in the core has been proposed to explain the seismic and density anomalies in the Earth's core. Among these light elements, hydrogen has the highest abundance in the solar system, and therefore, it is potentially one of the main light elements in the Earth's core.

In order to explore the possibility, structure, mobility, and concentration of H in the Earth's inner core, especially under high temperatures, we have employed evolutionary crystal structure prediction methods and density functional theory (DFT) calculations to examine the structural models of Fe-H binary at core pressure and temperature conditions[1]. The influence of temperature on the stabilities of the Fe-H binary has been simulated within the quasi-harmonic approximation (QHA) framework. Molecular dynamics calculations are also performed to detect the state and mobility of H under core conditions. The ionic conductivity of Fe-H alloy, as well as the H concentration in the Earth's inner core, was determined, and its implications on the composition and evolution of the Earth's core are discussed [2,3].

Our study suggests that the Fe-H binary adopts numerous possible structures under core-like conditions, while the fcc structure is concluded to be a strong candidate for the H-bearing phase in the Earth's inner core. The high mobility of H in the solid Fe lattice at high temperatures indicates that H is transferred to a superionic state, where the H superionic state transfer temperature in Fe fcc lattice is ∼500 K higher than that in the hcp Fe system. H is a key light element for reducing the density and elastic modulus of Fe, but the wave velocities of the Fe-H binary still remain too high to account for the seismological observations of the inner core. Other light elements are, therefore, also required to match all the geophysical models.

References:

[1] Yang H et al (2022) Geochemistry, Geophysics, Geosystems, 23 (12), e2022GC010620

[2] Yang H et al (2023) American Mineralogist, 108 (4), 667-674

[3] ] Yang H et al (2023) Geophysical Research Letters, 50 (22), 2023GL104493

How to cite: Zhang, F., Yang, H., and Muir, J.: Iron hydride FeHx in the Earth's inner core and its geophysical implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-255, https://doi.org/10.5194/egusphere-egu24-255, 2024.

EGU24-289 | ECS | PICO | GD8.1

Top-heavy double-diffusive convection with core-mantle boundary heat flux variations 

Souvik Naskar, Jonathan Mound, Christopher Davies, and Andrew Clarke

The geomagnetic field is sustained by thermochemical convection in Earth’s outer core. Crystallization of the solid inner core releases latent heat and light elements, providing both thermal and chemical buoyancy sources. Most geodynamo simulations use the codensity approach, ignoring the vastly different diffusivities and different boundary conditions for the thermal and chemical fields and thus cannot capture double-diffusive effects. In this study, we consider a numerical convection model of a Boussinesq mixture of light elements in a heavy fluid confined within a rotating spherical shell. The governing parameters are the Ekman number (𝐸 = 2 × 10−5), a non-dimensional measure of the rotation rate, the thermal and chemical flux Rayleigh numbers (𝑅𝑎𝑇 = 9 × 106 − 1.2 × 108 and 𝑅𝑎𝜉 = 3 × 106 − 5 × 1010), representing the non-dimensional thermal and chemical forcing, and the thermal and chemical Prandtl numbers (𝑃𝑟𝑇 = 1 and 𝑃𝑟𝜉 = 10), that are fluid properties. We have performed a detailed analysis of the force balance that emerges within these simulations. We find a transition from a thermal wind to a chemical wind balance with increasing chemical forcing in the azimuthally averaged ”mean” forces in the radial direction. The transition is found to occur at buoyancy ratio, Λ = (𝑅𝑎𝑇 /𝑃𝑟𝑇 )/(𝑅𝑎𝜉 /𝑃𝑟𝜉 ) ≃ 1. However, the corresponding ”fluctuating” balance is quasi-geostrophic in all directions. The analysis lets us locate the geophysically relevant ”rapidly rotating” regime in this parameter space.

We proceed by imposing a laterally heterogeneous thermal flux at the core-mantle boundary (CMB) in our rapidly rotating double-diffusive simulations. Recent thermally-driven simulations with lateral variations in CMB heat flux produce local regions with a subadiabatic thermal gradient near the CMB (Mound et al., 2019), termed as regional inversion lenses (RILs). This may reconcile the conflicting inferences about the possibility of a globally stratified layer at the top of the core (Kaneshima 2018; Gastine et al. 2020), by accommodating the possibility of both stable and unstable regions. Our goal is to assess the effect of chemical buoyancy on the RILs. The parameter space now also includes the pattern and amplitude of lateral variation in the CMB heat flux. A standard ’tomographic’ pattern, as suggested by seismic measurements (Masters et al., 1996), has been used in these simulations. The amplitude is characterized as 𝑞 = (𝑞𝑚𝑎𝑥 − 𝑞𝑚𝑖𝑛)/𝑞𝑎𝑣𝑔 where 𝑞𝑚𝑎𝑥, 𝑞𝑚𝑖𝑛, and 𝑞𝑎𝑣𝑔 are the maximum, minimum and horizontally averaged heat flux through the CMB. We study the RILs by varying the lateral heterogeneity with 𝑞∗ = {1, 2.3, 5} and buoyancy ratios with Λ = 400-0.01. These RILs are characterized by their strength, measured by a characteristic Brunt-Väisälä frequency (𝑁). Their thickness (𝐿) is measured as the distance of the point of neutral stability from CMB, and the chemical anomaly (𝛿𝜉 ) represents the difference in chemical composition across the lenses. The scaling dependence of these quantities (Mound & Davies, 2020) on the chemical forcing has been explored to extrapolate their values for Earth-like parameters.

 

How to cite: Naskar, S., Mound, J., Davies, C., and Clarke, A.: Top-heavy double-diffusive convection with core-mantle boundary heat flux variations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-289, https://doi.org/10.5194/egusphere-egu24-289, 2024.

Near the equatorial region of the Earth’s core, secular variation in the geomagnetic field consists of short period fluctuations. Such fluctuations in the magnetic field are believed to be the result of equatorially trapped waves close to the core-mantle boundary. The balance between the magnetic, Coriolis and buoyancy forces can sustain waves if a stably stratified layer exists in the outermost regions of the core. In this study, a shallow water model with additional magnetic field effects has been used to investigate the characteristics of such equatorially trapped waves. A two-layer model is studied analytically to investigate the effects of radially varying background magnetic fields on the equatorially confined MAC waves. Dispersion relations obtained are significantly influenced by the dependency of the second layer pressure gradient on that of the first layer.  Moreover, the reduced gravity effects in the second layer also modifies the second layer dynamics. Additional parameters, formulated in terms of density, magnetic field strength and buoyancy frequency of both layers characterize the system. The modified properties of a two layer model compared to a single layer is investigated for various regimes of such control parameters. It is found that the alteration in the second layer’s buoyancy frequency significantly influences the dynamics of the MAC (Magnetic-Archimedes-Gravity) wave.

How to cite: Sharma, D. K. and Sahoo, S.: Equatorially trapped waves in a stratified region in the Earth’s outer core modeled using 2-layer shallow water equations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2692, https://doi.org/10.5194/egusphere-egu24-2692, 2024.

EGU24-3475 | ECS | PICO | GD8.1

Back reaction of magnetic field on rotating penetrative convection 

Tirtharaj Barman, Arpan Das, and Swarandeep Sahoo

The origin of the Earth's and planetary magnetic field is thought to arise from the convective flow of conducting liquid metal, particularly iron, in the deep interior of planetary systems through dynamo action. In numerical simulations, the nature of the resulting magnetic field depends on the imposition of buoyancy profiles that drive convection. Additional influence of imposed magnetic field on convective flows have been studied to understand the back reaction of dynamo action on fluid flow. In the present study, onset of  magnetoconvection is investigated to understand the physical effects in polar regions of the Earth's core where buoyancy forces exhibit a substantial component along the rotation axis. A simplified plane layer convection setup has been used to investigate the fundamental physical mechanisms. Various strengths of uniform magnetic fields in both horizontal and vertical directions have been incorporated. The novel aspect of the study is the incorporation of thermally stable layers with weak and strong stratification. Imposition of thermally stable stratification reduces the threshold of convective instability. It also restricts heat transport to unstable regions only. However, rapid rotation favors penetration of axial velocity into the thermally stable region, although critical thermal forcing for initiating convection also increases. The spectral characteristics of the flow is significantly modified due to the imposition of a stable stratified layer with background uniform magnetic field.

How to cite: Barman, T., Das, A., and Sahoo, S.: Back reaction of magnetic field on rotating penetrative convection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3475, https://doi.org/10.5194/egusphere-egu24-3475, 2024.

EGU24-3539 | PICO | GD8.1

Probing the deep Earth interior by a synergistic use of magnetic and gravity fields, and Earth's rotation   

Mioara Mandea, Veronique Dehant, and Anny Cazenave

In order to understand the processes involved in the deep interior of the Earth and explaining its evolution, in particular the dynamics of the Earth’s fluid iron-rich outer core, only indirect satellite and ground observations are available. They each provide invaluable information about the core flow but are incomplete on their own. This is the case of (1) the magnetic field, which can be used to infer the motions of the fluid at the top of the core on decadal and sub-decadal time scales, (2) the gravity field variations, which reflect changes in the mass distribution within the Earth, and (3) the Earth's rotation changes (or variations in the length of the day). These variations are occurring at multi-annual timescales and largely related to the core fluid motions. Earth's rotation variations are induced through exchange of angular momentum between the core and the mantle at the core-mantle boundary. We are particularly interested by the 6 and 8-year variations. They are presented together with the main activities proposed in the frame of the GRACEFUL ERC project, which aims at combining all information from observation as well as modelling the core flow in a completely coupled core and mantle system.

 

How to cite: Mandea, M., Dehant, V., and Cazenave, A.: Probing the deep Earth interior by a synergistic use of magnetic and gravity fields, and Earth's rotation  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3539, https://doi.org/10.5194/egusphere-egu24-3539, 2024.

EGU24-3649 | ECS | PICO | GD8.1

Estimating core dynamics via the assimilation of magnetic field models into numerical dynamos 

Kyle Gwirtz, Weijia Kuang, and Terence Sabaka

A significant portion of the Earth’s observed magnetic field is sustained by fluid motion in the planet’s outer core (geodynamo) and varies over time. Records of the past magnetic field come from a variety of sources including, paleo- and archaeomagnetic data. In the modern era, satellite-based observations from missions such as SWARM, have led to a new level of spatial and temporal resolution in our knowledge of the magnetic field. Such observations of the field’s secular variation (SV) can provide a unique window into the deep interior of the Earth. However, understanding the origins and implications of observed SV calls for connecting data to models of Earth’s core dynamics.

Over the last 10-15 years, there has been increasing interest in using data assimilation (DA) to connect numerical dynamo simulations with magnetic field observations. DA is a general term for methods by which one can produce a “weighted combination” of numerical models and observations, to estimate a system’s overall state. This approach is widely used in applications such as numerical weather prediction, where DA is used to, for example, determine initial conditions for forecasts.

We present recent work in the development of DA as a tool for understanding the Earth’s deep interior, using NASA’s Geomagnetic Ensemble Modeling System (GEMS). In simple terms, we “nudge” an ensemble of numerical geodynamo model runs toward observed magnetic field variations according to an Ensemble Kalman Filter (EnKF) framework. This process has the potential to recover information about dynamics which cannot be directly observed, such as the fluid flow and magnetic field deep within the interior. We highlight recently improved capabilities of GEMS, investigate its ability to constrain the core state, and discuss the impact of SWARM data on this work.

How to cite: Gwirtz, K., Kuang, W., and Sabaka, T.: Estimating core dynamics via the assimilation of magnetic field models into numerical dynamos, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3649, https://doi.org/10.5194/egusphere-egu24-3649, 2024.

EGU24-4505 | PICO | GD8.1

Non-negligible Oxygen in the Earth's Inner Core: The importance of high temperatures 

Qianxi Chen, Joshua Muir, and Feiwu Zhang

The core of the Earth must have some light elements which are small in concentration but could have dramatic effects on the behavior of the core. Oxygen is one such element. It has long been concluded based on experiments and theoretical calculations (Alfè, Gillan, and Price 2002) that the inner core partitions negligible amounts of O from an enriched outer core and thus its possible effects can be ignored. An oxygen-rich outer and oxygen-poor inner cores has also been proposed as a way to explain various seismic data (Badro, Côté, and Brodholt 2014). The discovery of Fe-O superionic alloys (He et al. 2022) calls these conclusions into questions as the state of O is substantially different at high vs low temperatures which could affect extrapolations of experimental results to high temperatures.

Focusing on the most thermally stable superionic alloys in the inner core, our study systematically investigates the partitioning behaviour of oxygen between solid inner and liquid outer core by an advanced combination of ab initio molecular dynamics (AIMD) simulations and the two-phase thermodynamics (2PT) model (Lin, Blanco, and Goddard 2003). We conclude that while O remains favoured in the liquid state under core conditions non-negligible amounts of O enter the inner core and thus its possible presence cannot be ignored. With realistic concentrations of O in the outer core we produce a density contrast between liquid and solid oxygen that is in the range of that observed at the inner core boundary (ICB) thus showing the importance of obtaining accurate partitioning values and their effect on seismic structure.

This study provides a new and reliable approach to the thermodynamic properties of the superionic state and a new theoretical basis for understanding the internal structure of the Earth's core, contributing to understanding of the complexity of the Earth's interior and providing useful insights into future directions of research in the field of Earth sciences. It also shows the stark difference between high and low temperature structures and how accurate temperatures need to be considered when looking at core structures.

 

Alfè, D., M. J. Gillan, and G. D. Price. 2002. 'Ab initio chemical potentials of solid and liquid solutions and the chemistry of the Earth’s core', The Journal of Chemical Physics, 116: 7127-36.

Badro, James, Alexander S. Côté, and John P. Brodholt. 2014. 'A seismologically consistent compositional model of Earth’s core', Proceedings of the National Academy of Sciences, 111: 7542-45.

He, Yu, Shichuan Sun, Duck Young Kim, Bo Gyu Jang, Heping Li, and Ho-kwang Mao. 2022. 'Superionic iron alloys and their seismic velocities in Earth’s inner core', Nature, 602: 258-62.

Lin, Shiang-Tai, Mario Blanco, and William A. Goddard. 2003. 'The two-phase model for calculating thermodynamic properties of liquids from molecular dynamics: Validation for the phase diagram of Lennard-Jones fluids', The Journal of Chemical Physics, 119: 11792-805.

How to cite: Chen, Q., Muir, J., and Zhang, F.: Non-negligible Oxygen in the Earth's Inner Core: The importance of high temperatures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4505, https://doi.org/10.5194/egusphere-egu24-4505, 2024.

EGU24-7843 | ECS | PICO | GD8.1

Numerical and experimental investigation on the effect of topography on the hydrodynamics of planetary fluid envelops. 

Vadim Giraud, Jérôme Noir, Fabian Burmann, and David Cébron
The majority of investigations into planetary core and subsurface ocean dynamics have traditionally assumed a perfectly smooth interface. However, geodynamical models and seismic observations on Earth suggest the presence of topography. This study addresses the role of topography in the simplified but fundamental case of differential rotation between the topography and the fluid within a cylinder.
We conducted numerical and experimental analyses, exploring various ranges of Rossby numbers (from 10-1 to 10-4 ) and different wavelengths and heights of topography, always greater than the Ekman boundary layer. Numerical simulations were performed using the spectral elements code Nek5000, while experiments were conducted with water on a rotating table employing particle imagery velocimetry (PIV).
Our observations reveal that the topography emits inertial waves into the fluid, and their patterns are correlated with the derivatives of the topography's height, rather than directly with its height. The controlling parameters influence the frequencies and amplitudes of the inertial waves, leading to the derivation of scaling laws in Rossby number, wavelength, and topography height. From these scaling laws, we propose a model for the dynamics of the fluid, including energy transfers.
 
 

How to cite: Giraud, V., Noir, J., Burmann, F., and Cébron, D.: Numerical and experimental investigation on the effect of topography on the hydrodynamics of planetary fluid envelops., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7843, https://doi.org/10.5194/egusphere-egu24-7843, 2024.

EGU24-9031 | ECS | PICO | GD8.1

A criterion for the existence of polar vortices in the Earth’s core 

Debarshi Majumder and Binod Sreenivasan

Observations of the Earth’s magnetic field indicate that there are anticyclonic polar vortices in the core. In the presence of the self-generated magnetic field, the polar azimuthal flow is believed to be produced by one or more coherent upwellings within the tangent cylinder, offset from the rotation axis. In this study, convection within the tangent cylinder in rapidly rotating dynamos is understood through the analysis of forced magnetic waves in an unstably stratified fluid. In the dipole-dominated dynamo regime, the isolated upwellings within the tangent cylinder are produced by the localized excitation of slow Magnetic-Archimedean-Coriolis (MAC) waves. If the forcing is so strong as to cause the collapse of the axial dipole, the convection takes the form of an ensemble of plumes supported entirely by fast waves whose frequency is of the same order as that of linear inertial waves. The resulting weak polar circulation is comparable to that in nonmagnetic convection. The observed peak azimuthal motions of 0.6 to 0.9° yr-1 are obtained only in the dipolar dynamo regime, where the Rayleigh number must be of ~103 times the Rayleigh number for the onset of nonmagnetic convection.

How to cite: Majumder, D. and Sreenivasan, B.: A criterion for the existence of polar vortices in the Earth’s core, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9031, https://doi.org/10.5194/egusphere-egu24-9031, 2024.

EGU24-11249 | ECS | PICO | GD8.1

The Adiabatic Heat Flux through the Top of the Core of Ancient Vesta from High-P,T Resistivity Experiments 

Eric Lenhart, Wenjun Yong, and Secco Richard

Heat flow mechanisms in terrestrial planetary cores contribute to geophysical processes with broader significance such as the generation of a magnetic field. Thermal convective flow in a planetary core may be found with the combination of adiabatic heat flow estimates—which this study seeks to estimate—and thermal evolution models of total heat flow across the core-mantle boundary. Experimental data constraining the effects of light elements on these processes is still needed. In the case of asteroid Vesta, the core is expected to be composed of Fe alloyed with 13-16wt% S (Steenstra et al., 2019) and 1-2wt% Si (Pringle et al., 2013).

To simulate the conditions of the early Vestan core, the resistivity of Fe alloyed with 16wt% S and 2wt% Si (Fe-16S-2Si) was measured at high pressures and into the liquid state. A 1000-ton cubic anvil press applied a static pressure of 2, 3, 4, or 5 GPa on the sample. The resistivity of Fe-16S-2Si was then calculated from the voltage drop and constant current across the sample at 300-2000 K along with post-experimental geometry measurements.

With the electrical resistivity data, the thermal conductivity of Fe-16S-2Si is estimated using the Wiedemann-Franz Law. For 2-4 GPa, a thermal conductivity of 11+1.5 W/m/K is found. For the top of the core of ancient Vesta, an adiabatic heat flux of 0.3-0.4 mW/m2 is derived. These results indicate that the light elements expected in the Vestan core have a large effect on the thermodynamic properties, including more than halving the expected adiabatic heat flow. Since the total heat flux across the early Vestan core-mantle boundary has been previously estimated as >10 mW/m2 (Weiss et al., 2010), thermal convection alone may account for the magnetic dynamo in early Vesta with the presence of light alloying elements.

References:

Pringle, E.A., Savage, P.S., Badro, J., Barrat, J.-A., Moynier, F., 2013. Redox state during core formation on asteroid 4-Vesta, Earth and Planetary Science Letters, v. 373, p. 75-82.

Steenstra, E.S., Dankers, D., Berndt, J., Klemme, S., Matveev, S., van Westrenen, W., 2019. Significant depletion of volatile elements in the mantle of asteroid Vesta due to core formation, Icarus, v. 317, p. 669-681.

Weiss, B.P., Gattacceca, J., Stanley, S., Rochette, P., Christensen, U.R., 2010. Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation, Space Science Reviews, v. 152, p. 341-390.

How to cite: Lenhart, E., Yong, W., and Richard, S.: The Adiabatic Heat Flux through the Top of the Core of Ancient Vesta from High-P,T Resistivity Experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11249, https://doi.org/10.5194/egusphere-egu24-11249, 2024.

The thermal and electrical conductivities of materials in planetary mantles and cores are crucial for understanding planetary evolution and dynamics. The experimental determination of conductivities at mantle and core pressure-temperature conditions in the diamond anvil cell requires that the sample thickness is precisely known. The standard approach has been to estimate sample thickness from the equations of state of the sample, assuming isotropic contraction (upon compression) or expansion (upon decompression). Recently, however, it has been shown [1] that common pressure media used in diamond anvil cell experiments thin in a strongly non-isotropic manner. If samples embedded in pressure media also deform non-isotropically, then the extant experimental estimates of mantle and core conductivity may contain systematic errors of approximately 30-50% [1]. In situ measurements of sample thickness are needed to verify this inference.

 

We will report on the first in situ interferometric measurements of Fe foil thickness in a diamond anvil cell with sample configurations resembling that of previous experiments to measure the conductivity of Fe. Our preliminary data show that the contraction and expansion of Fe is strongly non-isotropic, potentially explaining the discrepancies in the reported iron conductivity at core-mantle boundary conditions [2, 3]. We will also discuss practical aspects of future measurements of thermal and electrical conductivity of mantle and core materials in a diamond anvil cell.

 

[1] Lobanov, S. S., & Geballe, Z. M. (2022). Non-isotropic contraction and expansion of samples in diamond anvil cells: Implications for thermal conductivity at the core-mantle boundary. Geophysical Research Letters, 49, e2022GL100379. [2] Zhang Y., Hou M., Liu G., Zhang C., Prakapenka V.B., Greenberg E., Fei Y., Cohen R. E., and Lin J.-F (2020) Reconciliation of Experiments and Theory on Transport Properties of Iron and the Geodynamo. Phys. Rev. Lett. 125, 078501. [3] Ohta, K., Kuwayama, Y., Hirose, K. et al. (2016). Experimental determination of the electrical resistivity of iron at Earth’s core conditions. Nature 534, 95–98.

 

How to cite: Breton, H. and Lobanov, S.: In Situ Measurements of Sample Thickness in Diamond Anvil Cells Suggest Large Systematic Errors in High-Pressure Conductivities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14702, https://doi.org/10.5194/egusphere-egu24-14702, 2024.

EGU24-18333 | ECS | PICO | GD8.1

Possible Observations of PKJKP in the AlpArray Seismic Dataset 

On Ki Angel Ling, Simon C. Stähler, and Domenico Giardini

Understanding the elastic properties of Earth's inner core is crucial for unraveling its role in the planet’s evolution and dynamics. Seismic shear waves provide a direct means to constrain the shear modulus of the solid inner core at high frequencies. However, their detection has been challenging due to their extremely weak amplitude and interference from other seismic arrivals (Doornbos, 1974). This study aims to provide direct observations of inner-core shear waves through a systematic search using the AlpArray Seismic Network (AASN), a large European seismic array. The approach combines 3-C polarization filtering and slant-stacking techniques. The inspection focuses on events between 2015 and early 2022 within the epicentral distance range of  ~110-150° from the AASN. This source-receiver geometry is close to that of previous PKJKP observation reported using the Gräfenberg array (Cao et al., 2005).

Our systematic search and classification reveal multiple potential observations of PKJKP at frequencies > 0.1 Hz, consistent in both time and slowness with the 1-D Earth model ak135, as well as previous body-wave-based observations, particularly Wookey and Helffrich (2008). The new evidence of PKJKP demonstrates a path forward for formalizing a method for the repeatable detection of inner-core shear waves for different source-receiver geometries. Additional PKJKP observations and comprehensive modeling are essential for gaining insights into the intricate inner-core structure and phenomena, such as anisotropy and focusing effects, which could explain the limited number of observations to date.

How to cite: Ling, O. K. A., Stähler, S. C., and Giardini, D.: Possible Observations of PKJKP in the AlpArray Seismic Dataset, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18333, https://doi.org/10.5194/egusphere-egu24-18333, 2024.

EGU24-20444 | PICO | GD8.1

Effects of mantle structure on models of seismic anisotropy in the inner core 

Daniel Frost, Barbara Romanowicz, and Prajna Paramita Das

Mapping inner core (IC) seismic anisotropy at high resolution provides important insight on the growth of the inner core through time, its internal dynamics, and its role in the production of the geodynamo. Since the discovery of IC anisotropy (ICA) in 1986, numerous studies have suggested the presence of significant lateral and depth variations in its character and strength. In particular, there is controversial evidence for the presence of a distinct region, spanning the central third of the IC in radius, referred to as the “innermost inner core”. Yet, obtaining robust constraints on the 3D structure of ICA is hampered by the uneven sampling by seismic waves passing through the inner core, and the possible contamination of measurements by unmodelled 3D mantle structure, to which all seismic core phases are sensitive.

Typical ICA models rely on differential travel time measurements between the inner core traversing wave PKPdf (PKIKP) and a reference phase that has a similar path in the mantle, but does not enter the IC (PKPab, PKPbc, PKPcd and related phases). This kind of measurement is thought to minimize mantle contamination, but the global dataset is limited by the distribution of earthquake sources and stations.

Recently, Pham and Tkalcič (2023) devised a clever method to augment the available dataset by including measurements from exotic pairs of core phases that reflect several times at the earth’s surface and repeatedly sample the central part of the inner core, referred to as PKPn. They proposed a new model for ICA and in particular a distinct model for the innermost inner core.

However, we found that their model does not fit the travel time data measured using conventional PKPdf. We investigated the possible cause of this discrepancy by selecting PKPdf measurements on paths sampling similar portions of the mantle as the 16 measurements by Pham and Tkalcič (2023). While some measurements agree, the discrepant data correspond to paths that repeatedly interact with subducted slabs in the mantle.  We thus proceeded to analyse the effects of mantle structure, particularly subducting slabs, on differential travel times of core-sensitive phases. We assessed observed PKPdf and PKPdfn differential times for systematic bias. We find that the higher the “n”, i.e. the greater the number of passages through the mantle, the greater the effect of mantle structure on the PKPdfn measurements, suggesting that the discrepancies between the proposed ICA model constrained by these measurements compared with traditional direct PKP observations are likely due to mantle heterogeneity.

How to cite: Frost, D., Romanowicz, B., and Das, P. P.: Effects of mantle structure on models of seismic anisotropy in the inner core, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20444, https://doi.org/10.5194/egusphere-egu24-20444, 2024.

EGU24-20584 | PICO | GD8.1

New facilities for high pressure / high temperature experiments on iron alloys at planetary core conditions on the European XFEL 

Sébastien Merkel and Hélène Ginestet and the EuXFEL 3063 and 2740 community proposals

The European XFEL is a new X-ray facility installed near Hamburg, Germany, that provides extremely intense X-ray flashes of less than 50 fs (10-12 s) that can be repeated every 220 ns (10-9 s). The facility, coupled with the High Energy Density (HED) instrument, opens new avenues for experiments on iron alloys under planetary core conditions.

The instrument can be coupled with diamond anvil cell experiments. In this case, the X-ray flashes of the XFEL are not only used to measure diffraction images in less that 50 fs, but also to heat the samples and gradually increase sample temperatures every 220 ns, reaching several thousands of degrees at pressures well over a megabar in microseconds. During the 3063 community proposal, we hence tested a new method to explore the phase diagrams of iron alloys at planetary core conditions, inducing phase transformations, melting and microstructural changes in conditions and timeframes that could not be reached in previous experimental systems.

The instrument is also compatible with laser-driven shock experiments. DiPOLE 100-X is a world-class laser that can deliver up to 100 J (in 1-omega) and 50 J (in 2-omega) over up to 15 ns pulses, with a repetition rate up to 10 Hz. It is now installed at the High-Energy Density (HED) beamline of the European XFEL. By shining DIPOLE pulses into polymers in the back of our samples, we can generate pressure and temperature conditions well over 100 GPa and several thousands of K and using the European XFEL, we can get in-situ X-ray diffraction! The facility was tested in May 2023 during the 2740 community proposal, involving over 100 scientists from over 40 world-wide institutions.

In this presentation, I will hence present these new experiments at the European XFEL and preliminary results that can be obtained. These new measurements will require a lot of development and metrology, however, which are actively pursuing at present.

Our work is supported by the ERC HotCores (Grant No 101054994) at the université de Lille.

How to cite: Merkel, S. and Ginestet, H. and the EuXFEL 3063 and 2740 community proposals: New facilities for high pressure / high temperature experiments on iron alloys at planetary core conditions on the European XFEL, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20584, https://doi.org/10.5194/egusphere-egu24-20584, 2024.

EGU24-20752 | PICO | GD8.1

Top-down crystallization in small planetary bodies: The effect of non-equilibrium and core composition 

Attilio Rivoldini, Tina Rückriemen-Bez, Sten Anders, Chris Davies, Sven Eckert, Ludovic Huguet, and Anne Pommier

Understanding the crystallization of metallic cores is necessary to constrain the structure and thermal evolution of terrestrial bodies in our solar system and beyond. Core cooling is also closely related to the generation and sustainability of a magnetic field. The core crystallization regime depends primarily on the depth of intersection of the core temperature with the liquidus ([1], and refs therein). Core composition, pressure, and thermal profile are the major parameters controlling the depth of intersection. If the temperature gradient across the core is steeper than that of the liquidus, solidification starts at the top, the “top-down” crystallization regime. At low pressure (≤10 GPa) relevant to small terrestrial planets, moons, and possibly some asteroids, the eutectic temperature decreases with increasing pressure (e.g., [2] for the Fe-S system),  favoring  an  onset  of  crystallization  at  the  top  of  the  core. Top-down crystallization has been proposed to exist in several planets and moons in the Solar System, such as Mercury [2], [3], Mars ([4], [5]), and Ganymede [6], [7], [8], [9].

In this study, which was performed by the International Space Science Institute (ISSI) Team “A new non-equilibrium model of iron snow in planetary cores”, we investigate the effect of non-equilibrium as well as the effect of the core composition on top-down crystallization. We find that the time scale of phase relaxation is significantly shorter than the time scales usually employed in one-dimensional evolution models. Consequently, the assumption of equilibrium in these models remains valid. Nevertheless, the time scales associated with crystallization, melting, and crystal settling may be similar to the phase relaxation time scale, which warrants a closer investigation. Additionally, if the amount of supercooling required to initiate nucleation is large [11], non equilibrium could play a much larger role. In terms of core chemistry we studied two different core alloys (Fe-S and Fe-C) motivated by silicate-metal partitioning experiments (reviewed by [12]) at various concentrations in the framework of the equilibrium top-down crystallization model. We find that the time scales of growing either the snow zone (iron-rich compositions) or the flotation crust (iron-poor compositions) can vary significantly between the Fe-S and Fe-C system. Furthermore, the exact concentration of sulfur or carbon has an impact on the thermodynamic parameters, subsequently affecting the entropy available to the dynamo.

References:

[1] Breuer et al., 2015. [2] Chen et  al., 2008. [3] Dumberry & Rivoldini, 2015. [4] Stewart et al., 2007. [5]  Davies & Pommier, 2018. [6] Hauck et al., 2006. [7] Christensen, 2015. [8] Rückriemen et al., 2015. [9] Rückriemen et al., 2018. [10] Loper, 1992. [11] Huguet et al., 2018. [12] Pommier et al., 2022.

How to cite: Rivoldini, A., Rückriemen-Bez, T., Anders, S., Davies, C., Eckert, S., Huguet, L., and Pommier, A.: Top-down crystallization in small planetary bodies: The effect of non-equilibrium and core composition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20752, https://doi.org/10.5194/egusphere-egu24-20752, 2024.

GD9 – Geodynamics of Specific Regions

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.

We performed (U-Th-Sm)/He apatite and zircon thermochronology (AHe and ZHe, respectively) on basement rocks from the Central Taurides, southern Turkiye to constrain its Tertiary >2000m surface uplift history. The samples were collected from the Alanya and Antalya units exposing in the southern part of the Central Taurides. The Alanya Massif represent a Late Cretaceous HP/LT eclogite to blueschist facies metamorphic pile whereas the Antalya Unit shows a relatively coherent stratigraphy consisting mainly of Triassic sandstones together with Permian and Jurassic limestones that are exposed as tectonic windows below the Alanya Massif. The AHe ages from the Alanya Massif cluster in with Early Oligocene (ca. 30 Ma), Early Miocene (ca. 20 Ma) and Late Miocene (ca. 8 Ma) ages. Apatites from one of the sandstone samples from the Antalya Unit gave also a Late Miocene age (ca. 9 Ma), consistent with the cooling ages of the tectonically overlying metamorphic rocks. In contrast, apatites from a sandstone sample exposed in the north show old, dispersed ages suggesting that they escaped from tectonic burial during the Eocene nappe stacking. ZHe ages from one of the metamorphic samples gave a ca. 30 Ma age; indistinguishable from its apatite ages. Our new AHe and ZHe age data indicate that, during Late Eocene nappe tectonics, the Alanya Massif and the underlying Antalya Unit was buried enough to reset the AHe and ZHe ages. Following the compressional regime, during the Early Oligocene, the Alanya Massif was subjected to a fast exhumation, possibly through an extensional detachment. This post-contractile-tectonic exhumation continued episodically during the Early Miocene until just prior to the Miocene transgression. The final Late Miocene exhumation ages are noteworthy and overlaps well with the beginning of the surface uplift of the southern margin of the Anatolian plateau. The new thermochronological data from the Central Taurides suggest that the extension of the southern margin of the Anatolian Plateau had already started in the Early Oligocene, predating the Arabia-Anatolia collision. The extension could have been triggered by the roll-back of the until then intact Bitlis-Cyprus-Hellenic slab, which created a widespread Oligo-Miocene extensional regime on the overriding Anatolian margin.

How to cite: Aygül, M., Uysal, I. T., Sobel, E. R., Okay, A. I., and Glodny, J.: New (U-Th-Sm)/He low-temperature apatite and zircon thermochronology ages reveal episodic Tertiary exhumation and uplift of the Central Taurides, southern Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1527, https://doi.org/10.5194/egusphere-egu24-1527, 2024.

The Oligocene-to-present tectonic history of the western Mediterranean region is characterized by the ESE-ward roll-back of isolated Alpine and Neo Tethys oceanic slab fragments that determined the spreading of two diachronous back-arc basins: the Liguro-Provencal Basin between 30 and 15 Ma and the Tyrrhenian Sea between 10 and 2 Ma. Such geodynamic events induced the fragmentation and dispersal of the Alpine chain through the formation and migration of microplates and terranes, making the debate on the nature, origin, and evolution of such crustal blocks vivid since the 1970s. For instance, it is commonly accepted that the Corsica-Sardinia microplate rotated counterclockwise (CCW) by at least 50° during Oligo-Miocene and that the Calabro-Peloritan, Kabylies and Alboran blocks drifted hundreds of kms on top of nappe piles ESE-ward, SE-ward and SW-ward, respectively. These blocks, know all together as AlKaPeCa, presently form isolated and enigmatic igneous/metamorphic terranes stacked over the Meso-Cenozoic sedimentary successions of the Apennines and Maghrebides. Besides back-arc basins widths and ages, no other kinds of geologic/geophysical data from Corsica-Sardinia microplate or AlKaPeCa terranes constraining their drift magnitudes exist. On the other hand, drift timing may be properly documented by paleomagnetic vertical-axis rotations obtained from different age rocks, and such data usefully complement ages derived from back-arc basins.

We paleomagnetically sampled the Meso-Cenozoic sedimentary cover of the Calabrian (Longobucco sequence) and Peloritan (Longi-Taormina sequence) terranes and the mid-late Eocene continental Cixerri Formation of SW Sardinia. In addition, we re-evaluated previous paleomagnetic results from the whole Corsica-Sardinia microplate and considered the robust Serravallian-Pleistocene dataset from the Calabrian block. Such data indicate a novel rotation and drift history in the western Mediterranean region (Siravo et al., 2021; 2022). The South Sardinia, Peloritan and Calabrian blocks belonged to the “Greater Iberia plate” before mid-Oligocene (<30 Ma) dispersal, as they all show its characteristic paleomagnetic fingerprint (middle Cretaceous 30°-40° CCW rotation). Rifting of the Liguro-Provencal between 30 and 21 Ma induced 30° CCW rotation of both South Sardinia and Calabria blocks, whereas the Peloritan block, located further south, was passively drifted SE ward at the non-rotation apex of a Paleo Appennine-Maghrebides orogenic salient. South Sardinia plus the adjacent Calabrian block and North Sardinia-Corsica blocks assembled in the early Miocene and rotated 60° CCW as a whole between 21 and 15 Ma. After 10 Ma ago the Calabrian block detached from south Sardinia following the opening of the Tyrrhenian Sea and rotated 20° clockwise (CW), at the apex of a Neo Appennine-Maghrebides Arc. On the other hand, the Peloritan terrane rotated 130° CW on top of the Sicilian Maghrebides, along the southern limb of the orogenic salient.

 

REFERENCES

Siravo, G., Speranza, F., & Macrì, P. (2022). First Pre‐Miocene Paleomagnetic Data From the Calabrian Block Document a 160 Post‐Late Jurassic CCW Rotation as a Consequence of Left‐Lateral Shear Along Alpine Tethys. Tectonics, 41(7), e2021TC007156.

Siravo, G., Speranza, F., & Mattei, M. (2023). Paleomagnetic evidence for pre‐21 Ma independent drift of South Sardinia from North Sardinia‐Corsica:“Greater Iberia” vs. Europe. Tectonics, e2022TC007705.

How to cite: Siravo, G. and Speranza, F.: Paleomagnetism of the Peloritan, Calabrian and South Sardinia blocks unveils a Greater Iberia plate and its mid Oligocene-early Miocene breakup    , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1733, https://doi.org/10.5194/egusphere-egu24-1733, 2024.

EGU24-2454 | Orals | GD9.2

Multiengine-driving Tethyan evolution 

Zhong-Hai Li

Tethys tectonic system has experienced a long-term evolution history, including multiple Wilson cycles; thus, it is an ideal target for analyzing plate tectonics and geodynamics. Tethyan evolution is typically characterized by a series of continental blocks that separated from the Gondwana in the Southern Hemisphere, drifted northward, and collided and accreted with Laurasia in the Northern Hemisphere. During this process, the successive opening and closing of multistage Tethys oceans (e.g., Proto-Tethys, Paleo-Tethys, and Neo-Tethys) are considered core parts of the Tethyan evolution. Herein, focusing on the life cycle of an oceanic plate, four key geodynamic processes during the Tethyan evolution, namely, continental margin breakup, subduction initiation (SI), Mid-Ocean Ridge (MOR) subduction, and continental collision, were highlighted and dynamically analyzed to gather the following insights. (1) Breakup of the narrow continental margin terranes from the northern Gondwana is probably controlled by plate subduction, particularly the subduction-induced far-field stretching. The breakup of the Indian continent and the subsequent spreading of the Indian Ocean can be attributed to the interactions between multiple mantle plumes and slab drag-induced far-field stretching. (2) Continental margin terrane collision-induced subduction transference/jump is a key factor in progressive Tethyan evolution, which is driven by the combined forces of collision-induced reverse push, far-field ridge push, and mantle flow traction. Moreover, lithospheric weakening plays an important role in the occurrence of SI. (3) MOR subduction is generally accompanied by slab break-off. In case of the considerably reduced or temporary absence of slab pull, mantle flow traction may contribute to the progression of plate subduction. MOR subduction can dynamically influence the overriding and downgoing plates by producing important and diagnostic geological records. (4) The large gravitational potential energy of the Tibetan Plateau indicates that the long-lasting India-Asia continental collision requires other driving forces beyond the far-field ridge push. Further, the mantle flow traction is a good candidate that may considerably contribute to the continuous collision. The possible future SI in the northern Indian Ocean will release the sustained convergent force and cause the collapse of the Tibetan Plateau. Based on the integration of these four key geodynamic processes and their driving forces, a “multiengine-driving” model is proposed for the dynamics of Tethyan evolution, indicating that the multiple stages of Tethys oceanic subduction provide the main driving force for the northward drifting of continental margin terranes. However, the subducting slab pull may be considerably reduced or even lost during tectonic transitional processes, such as terrane collision or MOR subduction. In such stages, the far-field ridge push and mantle flow traction will induce the initiation of new subduction zones, driving the continuous northward convergence of the Tethys tectonic system.

How to cite: Li, Z.-H.: Multiengine-driving Tethyan evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2454, https://doi.org/10.5194/egusphere-egu24-2454, 2024.

EGU24-3712 | Orals | GD9.2

Quantitative Sn-wave Attenuation Beneath the Tibetan Plateau and Lithospheric Rheology 

Lian-Feng Zhao, Xiao-Bi Xie, Xi He, and Zhen-Xing Yao

Sn wave, a regional seismic phase, propagates horizontally in the uppermost mantle and is sensitive to lateral variations in mantle lid thickness, temperature, and melt. The physical properties of the lithosphere can be indicated by Sn propagation efficiency or attenuation. The inefficient Sn propagation has been typically used to describe the regions with high-temperature anomalies in the uppermost mantle and infer the subduction front of the Indian lithosphere in the north Tibetan plateau. Here we collect 122,481 tangential-component digital seismograms, isolate the geometric spreading and attenuation for SH-type Sn wave, and construct a broadband uppermost mantle shear wave attenuation model in the Tibetan region. Beneath the central and north parts of the Tibetan plateau the Sn waves are strongly attenuated, while relatively weaker attenuation can be observed in the perimeter of the plateau, i.e., the Himalaya mountains in the south, Tarim and Qaidam basins and Eastern Kunlunshan terrain in the north, and Sichuan basin in the east. These weak attenuation regions are likely where the old crustal fragments were deposited during the collision between the Indian and Asian plates. In contrast, strong Sn attenuation likely indicates local lithospheric delamination in central and eastern Tibet. Furthermore, the correlation between strong Sn and Lg attenuation zones reveals the potential mantle upwelling with deep heat sources invading the crust.

How to cite: Zhao, L.-F., Xie, X.-B., He, X., and Yao, Z.-X.: Quantitative Sn-wave Attenuation Beneath the Tibetan Plateau and Lithospheric Rheology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3712, https://doi.org/10.5194/egusphere-egu24-3712, 2024.

     The collision between the Indian and Eurasian plates in the Cenozoic eras resulted in the formation of the world's largest and highest plateau. The intensive collision, subduction, and related deep dynamic processes led to significant crustal shortening, uplifting, and expansion of the Plateau, accompanied by eastward extrusion of plateau materials. The southeastern Tibetan Plateau (SETP) is one of the most important channels for escaping plateau materials. The widespread existence of crustal weak material flow in the SETP has become widely accepted. However, previous research has mostly been limited to two-dimensional profiles or spaced data measurement points. Therefore, obtaining reliable and high-resolution geophysical models of the lithosphere is crucial for understanding the deformation mechanisms of the plateau.

    Our three-dimensional resistivity model shows unprecedented resolution of the Simao Block of the Indochina Block, offering new insights into the material transport and deformation mechanisms of the SETP. Two consecutive large-scale high-conductivity anomalies observed in the middle-lower crust are speculated to be partial melting associated with crustal flow. The rigid lithosphere separated by significant strike-slip faults on the SETP may be pulled by ductile materials flow, where plastic flows in the middle-lower crust drive the rigid blocks to extrude and escape along the boundary faults, thus dominating the deformation of the lithosphere. The large-scale delamination of the continental lithosphere leads to upwelling of the asthenosphere along mechanically weak areas. Upwelling hot materials continue to heat the entire crust, and the expanding and diffusing lower crust further accelerates partial melting and plastic flow in the middle-lower crust.

How to cite: Ye, G., Sang, W., Wei, W., Jin, S., Lei, Q., and Dong, H.: Preliminary Results of Material Transport Model of Rigid Block Extrusion Driven by Crustal Flow Beneath the SE Tibetan Plateau: insights from high-resolution 3-D Magnetotelluric Imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4844, https://doi.org/10.5194/egusphere-egu24-4844, 2024.

The Lhasa Terrane in southern Tibet is widely recognized as having separated from the northern margin of Gondwana with a Precambrian basement and undergoing a protracted and intricate evolution. Abundant Early Cretaceous volcanic rocks are present in the central Lhasa subterrane, Tibet, playing an essential role in models aimed at comprehending the tectonic-magmatic evolution and mantle-crust interaction of this terrane. In this study, we present a well-preserved section of Zenong Group volcano-sedimentary sequence in Eyang, Xainza area within the central Lhasa subterrane. Our new data combined with existing literature data indicate that there was an extensive period of magmatism (approximately 140 Ma to 102 Ma) throughout the Early Cretaceous in the central Lhasa subterrane, reaching its peak around 113 Ma with remarkable compositional diversity.

However, the composition of Early Cretaceous volcanic rocks in the central Lhasa subterrane underwent a temporal transition from high-silica rhyolites to dacites and andesites, exhibiting a reverse cyclicity. Moreover, the intermediate rocks from the upper section display elevated whole rock εNd(t) and zircon εHf(t) values, as well as decreased 87Sr/86Sr ratios compared to the high-silica rocks from the lower section. These observations collectively suggest: (a) involvement of open-system processes encompassing mantle-derived magmas and ancient crustal-derived materials; (b) an increasing contribution of mantle sources in the magma genesis; (c) variable magma origins with distinct petrogenetic histories rather than a uniform source involving assimilation-fractional crystallization processes.

The high-silica rhyolites from the bottom of the Eyang section display characteristics of fractional crystallization and exhibit varying zircon εHf(t) values (−16.7 to −7.8), negative εNd(t) values (−13.7 to −13.1), highly variable initial Sr isotopic compositions, and radiogenic Pb isotopic signatures, indicating that a combined process of magma mixing (involving crustal-derived felsic melts and mantle-derived mafic melts) followed by fractional crystallization was primarily responsible for their formation. The dacitics from the upper part of the Eyang section show higher εHf(t) values (−9.9 ~ +0.5) and εNd(t) values (−10.6 to −9.5) than the high-silica rhyolites, suggesting that these dacitic rocks were also largely derived from anatexis of ancient crustal material with more involvement of mantle-derived magmas. The andesites exhibit more enriched Sr-Nd-Hf isotopic compositions compared to the contemporaneous dacitics, as well as less radiogenic Pb isotopic compositions, suggesting their likely derivation from partial melting of an enriched mantle wedge previously metasomatized by melts derived from subducted sediments.

We propose that the high-silica rhyolites in the lower section of the Xainza area (≥ ca. 120 Ma) are associated with slab roll-back, while the dacites and andesites in the upper section (≤ca. 120 Ma) are linked to slab break-off during southward subduction of Bangong-Nujiang Ocean lithosphere. Furthermore, it is evident that the ancient basement of the central Lhasa subterrane underwent localized reworking by mantle-derived melts.

How to cite: Huang, Y., Zhao, Z., and Zhu, D.-C.: Compositional and tectonomagmatic evolution of Early Cretaceous magmatism in the central Lhasa suberrane, Tibet: Implications from the Zenong Group volcanic rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4877, https://doi.org/10.5194/egusphere-egu24-4877, 2024.

EGU24-5416 | ECS | Posters on site | GD9.2

Mantle transition zone anomalies beneath Iberia and NW Maghreb 

Joan Antoni Parera Portell, Flor de Lis Mancilla, José Morales, and Jordi Díaz

The 410 and 660 discontinuities are predicted to be the result of isochemical phase changes in olivine. The differing Clapeyron slope of the reactions, though, leads to opposite 410 and 660 behaviour for a same temperature variation, with cold and hot mantle anomalies resulting in a thicker or thinner transition zone (MTZ), respectively. Here we use more than 56500 high-quality P-wave receiver functions obtained from 881 broadband seismic stations to locate anomalies in the MTZ beneath Iberia and NW Maghreb. We obtained robust maps of the 410 and 660 discontinuity depth thanks to the combined measurements of several 3D depth migrations using regional and global P-wave tomography models, and used these maps to calculate the MTZ thickness. Our results reveal several large-scale anomalies in the region mostly linked to the thermal effects of cold subducted slabs, but we also found evidence for significant chemical heterogeneity in the MTZ. The Gibraltar-Alboran and Alpine-Tethys slabs cause a continuous MTZ thickening along the Mediterranean coasts. Accompanying the slab anomalies are up to three areas with a low-velocity layer (LVL) located at the top of the 410 discontinuity, which provide evidence for partial melting coinciding with an MTZ enriched in water due to slab dehydration reactions. A similar LVL is also found at the top of the lower mantle where the Alpine-Tethys slab pushes the 660 discontinuity downwards. Mantle upwelling occurs at the back of the Gibraltar-Alboran slab, where we find the thinnest MTZ in the region. Upwelling hot materials seem to travel SW following a toroidal flow along the southern boundary of the slab and cause the 410 discontinuity to deepen significantly. Even though the MTZ thickness remains near-standard, the 410 also deepens in a more discontinuous manner beneath the Atlas Mountains. The active anorogenic volcanism in the Western Mediterranean correlates remarkably well with the LVL on top of regions with sunken 410, possibly pointing at a MTZ source for the melts.

How to cite: Parera Portell, J. A., Mancilla, F. D. L., Morales, J., and Díaz, J.: Mantle transition zone anomalies beneath Iberia and NW Maghreb, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5416, https://doi.org/10.5194/egusphere-egu24-5416, 2024.

The Central Asian Orogenic Belt (CAOB) is one of the largest orogenic collages in the world, and preserves important records of accretionary orogeny and Phanerozoic continental growth. The Yili Block is one microcontinent in southwest of CAOB, with Precambrain basement rocks exposed in the northern and southern margin. The Middle to Late Ordovician arc-type magmatic rocks were identified in the northern margin of the Yili Block with a subduction-related calc-alkaline affinity conclude that the southward subduction of the Junggar Ocran beneath the Yili Block, but the Silurian magmatism is rarely reported.

Mafic dikes preserve a considerable amount of geological information about geodynamics, crustal evolution and transformation of the regional stress field. Multi-period basic dikes, including Neoproterozoic and Carboniferous, are exposed in the northern margin of the Yili Block, which record important information about the transformation process of regional tectonic system. Recently, we have identified early Silurian diabase dikes in the Precambrian metamorphic rocks in the Wustu area, Wenquan County, northern margin of Yili Block. This paper reports zircon U-Pb age and Lu-Hf isotopic compositions, whole-rock geochemistry and Sr-Nd isotopic compositions for the Wustu diabase dikes and its surrounding rocks. One diabase sample yielded a zircon U-Pb age of 442±7 Ma with positive εHf(t) values (+3.0~+9.1), and its surrounding rock sample (leucogranite) yielded a zircon U-Pb age of 901±3 Ma. The diabase samples have high TFe2O3 contents (8.34%~9.81%) and K2O+Na2O contents (5.72%~6.86%), low MgO contents (3.69%~4.38%) and TiO2 contents (1.69%~2.00%) and belong to the high-K calc-alkaline series. The samples are enriched in the large ion lithophile elements (LILEs, such as Rb, Th, U and K) and have negative anomalies in the high-field-strength elements (HFSEs, e,g. Nb, Ta and Ti), with low Nb/Th ratios (0.13~1.16), Nb/La ratios (0.42~0.45) and high Zr/Hf ratios (39.6~42.2). They also have high initial 87Sr/86Sr ratios (0.707369~0.708637) and positive εNd(t) values (+1.9~+3.6). Our results indicate that they were sourced from a metasomatic sub-continental lithospheric mantle, which mainly composed of spinel iherzolite and garnet iherzolite. The trace element contents and its ratios, such as Zr (212×10-6~242×10-6), Hf (5.16×10-6~6.02×10-6), Nb (6.69×10-6~9.24×10-6), Ta (0.60×10-6~0.81×10-6), Zr/Y (5.21~6.82) and Hf/Th (0.69~0.91), indicate that the diabase dikes formed in an extensional setting during the early Silurian. Finally, we propose that the extensional tectonic setting maybe relate to the change of the subducted slabs angle or tectonic regime transition induced by the collage of the Aktau-Wenquan continental domain to the Yili Block in the end of Ordovician.

How to cite: Chen, Y., Wang, M., Zhu, S., and Cao, M.: The Early Silurian diabase dikes in the northern margin of the Yili Block, southwestern CAOB: insight into rift-related magmtism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6914, https://doi.org/10.5194/egusphere-egu24-6914, 2024.

Although the arc magmatism before collision has been considered as the main mechanism to the continental crustal growth and vertical geochemical fractionation for many years, the syn-collision magmatism related to the melting of accumulation in the base of arc could be an important contribution to crustal net growth and fractionation. Hence, the syn-collision magmatism could be an ideal object to research the continental crustal maturation and stratification. The arc magmatism could be controlled by the connecting magmatic reservoir in different depth and the experimental data show that the arc magma could be polybaric fractionation. However, the detail fractional phase in different level is not clear. Therefore, we selected the Early Eocene mafic rock series in the Tengchong Block, southwestern extension of Tibet, to reveal the detail magmatic evolution process. The rocks include hornblendite, hornblende (Hb) gabbro and diorite with different mineral assemblages, which is the syn-collision magmatism related to the Indian-Asian continental collision. These rocks have zircon ages of ca. 54Ma, and similar whole rock Sr-Nd and zircon Hf isotopes, indicating they are coeval and congenetic. In contrast to the isotopic composition, the major elements of the suits are variable, such as SiO2 contents of 48.72-61.49 wt.%, MgO contents of 12.02-2.69wt.%. The clinopyroxene (cpx) is mainly enclosed in the hornblende in the samples and part of the Hb could be the products of the replace reaction associated with cpx and others could be direct crystallization from the magma. The crystallization parameters calculation results show that the clinopyroxenes have high pressures of 2.4-10.7kbar with average of 7.6kbar and temperatures of 1006-1208°C with average of 1154°C. The hornblende crystallized at the pressures of 2.2-7.8kbar with average of 3.8kbar, and temperatures of 776-875°C with average of 827°C. In addition, the plagioclases in the all samples have three types, including high An core, low An rim with overgrowth rim as type I, low An core, high An mantle low An rim with overgrowth rim as type II, low core with overgrowth rim as type III. The homogeneous in-situ Sr isotopes show the compositions variation from the core to rim could be resulted from the process of dissolution and reprecipitation during the batches recharging of homogeneous magma. Therefore it could conclude that the primary magma of the Eocene mafic rocks could be fractionated in the lowermost crust, and the major crystallization phase dominated by clinopyroxene and forming the pyroxenite as the base of the arc. Then the evolution mafic magma emplace and form a mafic reservoir in the middle crust according to the assembly of batches of magma and finally occurring the further fractionation that the hornblende-dominated accumulation forming the hornblendite and the hornblende and plagioclase accumulation forming the Hb-gabbro and diorite. This polybaric fractionation within the continental crust during syn-collision could lead to the melt transition from mafic to granitic and further strengthen the crustal maturation and stratification.

Supported by National Natural Science Foundation of China [Grant Nos. 42272052 and 41902046], Fundamental Research Funds [Grant No. 300102273102]

How to cite: Zhao, S., Wen, T., and Fang, X.: Polybaric and multistage fractionation of syn-collision mafic magma in continental arc: constraints from the Eocene mafic rocks in the Tengchong Block, southeastern extension of Tibet , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6939, https://doi.org/10.5194/egusphere-egu24-6939, 2024.

EGU24-6941 | ECS | Orals | GD9.2

Machine Learning unravels the protracted role of India-Eurasia collision in the uplift of the Tibetan plateau 

Zhikang Luan, Jia Liu, Johnny ZhangZhou, Qunke Xia, and Eero Hanski

The Tibetan Plateau, Earth's largest and highest plateau, boasts an extraordinarily thick continental crust (60-80 kilometers) and an average elevation exceeding 4000 meters. Unraveling the plateau's uplift history, vital for comprehending Earth's Cenozoic history and its environmental impacts, has long been a subject of debate. While prior studies predominantly attribute the plateau's formation to the India-Asia collision, 45-59 million years ago, its timing and underlying mechanisms remain contentious. Airy isostasy as a response to crustal thickening during the Indian-Asian collision was considered the main factor for the uplift of the Gangdese terrain, the important portion of the Tibetan. Trace elemental ratios, e.g. Sr/Y and (La/Yb)n ratios, of the bulk magmatic rocks were the main geochemical indexes to recover the thickening history. However, the resultant crustal thickness and the consequent geodynamics recovered by different indexes remain controversial. Here, we compile the geochemical data for the volcanic rocks from global young arcs and continental orogens and built a supervised Machine Learning model to estimate crustal thickness. The reliability of this new model was tested, and the crustal thickening history of Gangdese terrain was recovered with it. The results reveal that the Gangdese terrane maintained a global-average thickness during the early stage of the India-Asia collision, which was not sufficient to support the uplift to >3000 m, as revealed by the recent paleoaltimeter data, through Airy isostasy.  This challenges the conventional belief of rapid uplift due to crustal thickening upon the Indian-Asian collision. Instead, our results suggest a protracted uplift process that parallels crustal thickening, reshaping our understanding of this iconic geological feature.

 

How to cite: Luan, Z., Liu, J., ZhangZhou, J., Xia, Q., and Hanski, E.: Machine Learning unravels the protracted role of India-Eurasia collision in the uplift of the Tibetan plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6941, https://doi.org/10.5194/egusphere-egu24-6941, 2024.

EGU24-8570 | ECS | Orals | GD9.2

Temporal and chemical changes during the Late Cretaceous arc magmatism in the Western Pontides (Turkey)  

Ezgi Sağlam, Turgut Duzman, Cemre Ay, Aral Okay, Gültekin Topuz, Gürsel Sunal, Ercan Özcan, Demir Altıner, Aynur Hakyemez, Jia-Min Wang, and Andrew RC Kylander-Clark

During the Late Cretaceous, a 2700 km long magmatic arc extended from the Lesser Caucasus through the Pontides into Srednogorie, Timok, Banat, and Apuseni (ABTS) in the Balkans. We studied the arc volcanic rocks in three regions of the Western Pontides, and compared them to the other arc magmatic rocks from the Lesser Caucasus, Eastern Pontides and Balkans. Prior to the onset of the arc magmatism, the region underwent uplift and erosion. New and published geochronologic and biostratigraphic data indicate that magmatism in the Lesser Caucasus, Pontides and Balkans started during the Turonian (ca. 93 Ma), peaked in the middle Campanian (80–78 Ma), and subsequently became rare and sporadic after the late Campanian (ca. 75 Ma). The arc magmatism, characterized by typical subduction signatures, was mainly of middle to high-K calc-alkaline affinity. Late Cretaceous volcanism occurred in a submarine and extensional environment. Along the whole belt, the arc volcanic rocks are overlain by Maastrichtian to Paleocene marine limestones and sandstones, marking the end of the main phase of arc magmatism. However, in the Western Pontides, Maastrichtian limestone sequence includes a volcanic horizon with a U-Pb zircon age of ca. 71 Ma. The geochemistry of the Maastrichtian volcanic rocks is more diverse compared to the older arc volcanic rocks, including alkaline and calc-alkaline basalts, as well as adakitic dacites. The coeval initiation of arc magmatism along the 2700-km-long magmatic arc is associated with the acceleration of Africa-Eurasia convergence at ca. 96 Ma, which is also independently indicated by the beginning of intra-oceanic subduction, inferred from the ages of suprasubduction-zone ophiolites and sub-ophiolite metamorphic rocks in Anatolia. The end of the magmatic activity in the arc is associated with a marked decrease in the convergence rate during the Campanian.     

How to cite: Sağlam, E., Duzman, T., Ay, C., Okay, A., Topuz, G., Sunal, G., Özcan, E., Altıner, D., Hakyemez, A., Wang, J.-M., and Kylander-Clark, A. R.: Temporal and chemical changes during the Late Cretaceous arc magmatism in the Western Pontides (Turkey) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8570, https://doi.org/10.5194/egusphere-egu24-8570, 2024.

EGU24-8893 | ECS | Orals | GD9.2

A missing Cretaceous magmatic arc of Neo-Tethys in Iran 

Yiyang Lei, Yang Chu, Bo Wan, Wei Lin, Ling Chen, Guangyao Xin, and Morteza Talebian

Magmatic arcs are generally considered to be the direct record of subduction zone. Magmatic activity can start with subduction initiation until the end of oceanic subduction. In the Neo-Tethys tectonic domain, arc magma gaps in Alps and Iran prove that arc magmatism and oceanic subduction are not always coupled.

Unlike the Alps, where arc magmatism is absent, or the Gangdese, where arc magmatism is continuous, Iran exhibits an intermittent arc magma record. Since the subduction of the Neo-Tethys Ocean in the Jurassic, Iran has recorded two phases of magmatic activities: the Middle Jurassic (200-140 Ma, with a peak at ~170 Ma) and the Eocene (55-25 Ma, with a peak at ~40 Ma), which are attested by the age peaks of detrital zircons from Mesozoic-Cenozoic clastic rocks. The Cretaceous magma record is sparse, but Cretaceous detrital zircons are abundant (120-65 Ma, with a peak at ~90 Ma). Regarding this mismatched age record of detrital zircons and magmatic rocks, we choose the Makran forearc basin deposits as the target because it receives thick detritus from Eurasia to form a tens of kilometer thick sedimentary sequence. We conducted a detrital zircon study from the Makran to explore the magmatic evolution of the Iranian Tethys zone.

Euhedral zircon grains, obvious oscillatory zoning, low zircon Th/U>0.1, and trace element geochemistry indicate Cretaceous magmatic zircons sourced from the continental magmatic arcs rather than ophiolites. Positive zircon Hf isotopes excludes the source region of the Gangdese arc which is more depleted. We further used machine learning to confirm our provenance results, that reveal Cretaceous (120-65 Ma) magmatism by the Neo-Tethys Ocean subduction in Iran.

The decreasing trend of Cretaceous zircons U-Pb in Late Cretaceous to Pliocene strata indicates gradual denudation of the Cretaceous magmatic arc from deep to shallow. Cretaceous zircon peaks disappears abruptly in the Pliocene rocks, implying that the Cretaceous magmatic arc was completely denuded. Thus, we confirm that since the subduction initiation, magmatic activity was continuous in Iran but the “missing” was due to the denudation process. This works also highlights the importance of comprehensive analysis before discussing subduction geodynamics based on the record of magmatic outcrops.

How to cite: Lei, Y., Chu, Y., Wan, B., Lin, W., Chen, L., Xin, G., and Talebian, M.: A missing Cretaceous magmatic arc of Neo-Tethys in Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8893, https://doi.org/10.5194/egusphere-egu24-8893, 2024.

The Ediacaran to Cambrian in the northwest Yangtze Block, has long been considered to be formed in a passive margin. Wells and seismic data, however, show that a Lower Cambrian thick siliciclastic rock succession occurs in the northwest Sichuan Basin, the provenance of which has not received attention from previous workers. In this study, we first propose that an Early Cambrian foreland basin was formed in the northwest Yangtze Block. Stratigraphic correlation shows a distinct stratigraphic absence from the Lower Cambrian to Devonian in the Bikou terrane, implying an orogeny might take place from NW to SE. A regional seismic profile shows a wedge stratigraphic geometry of the Lower Cambrian from NW to SE, further indicating a typical structure of a foreland basin. Field outcrops show an overall coarsening-upwards siliciclastic succession of the Lower Cambrian. The petrological analysis of siliciclastic rocks presents an immature feature implying a proximal source. Paleocurrent measurements of siliciclastic rocks point to dominant SE-vergent orientations. The age spectra of detrital zircon U-Pb dating of the Canglangpu Formation show a dominant Early Cambrian age of ca. 530 Ma, together with some positive ɛHf(t) values, indicating that the detrital zircon grains from the Lower Cambrian were derived from a northwest proximal juvenile continental arc and older crust. Therefore, the northwest Yangtze Block experienced a tectonic transition from an Ediacaran passive margin to an Early Cambrian foreland basin. The formation of the Early Cambrian foreland basin appears to have been strongly influenced by an orogenic loading northwestward. Here, this previously-overlooked orogenic event is named as the Motianling orogeny. The origin of the Early Cambrian orogeny may be related to subduction of the Proto-Tethys ocean beneath the northwest Yangtze Block, resulted in continental collision and uplift of northwest microterranes that provided siliciclastic sediments to fill the foreland basin southeastward.

How to cite: Gu, Z., Jian, X., and Watts, A.: Tectonic evolution of an Early Cambrian foreland basin in the northwest Yangtze Block, South China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9027, https://doi.org/10.5194/egusphere-egu24-9027, 2024.

EGU24-9628 | ECS | Orals | GD9.2

Kinematics of Intra-Plate Strike-Slip Earthquakes in an Oblique Convergent Setting  : Insights from the Eastern Himalayan and Indo-Burman Plate Boundary Systems 

Dibyajyoti Chaudhuri, Rupak Banerjee, Sankha Subhra Mahanti, Ajay Kumar, and Supriyo Mitra

North-East India comprises a part of the eastern extremity of the Alpine-Himalayan Belt and is one of the most rapidly deforming regions owing to its unique geological setup. The tectonics of this region is dominated by oblique convergence between two nearly perpendicular plates and results in a zone of distributed deformation. This region is associated with a large number of intra-plate strike-slip and oblique-slip (thrust) earthquakes which are not related to any of the plate boundaries. In this study we model the source mechanisms of five recent strong-to-moderate earthquakes (5.5≥Mw≤6.0) using teleseismic P and SH waveforms inversion and use source directivity and back-projection of the high-frequency energy from multiple teleseismic arrays for the largest event, to isolate the fault plane from the auxiliary plane. We then combine these mechanisms with results from previous studies of earthquake source and GPS geodetic velocity vectors and the GPS-derived strain field to build a kinematic model for this region. The depth distribution of the earthquakes reveals that they occur in the lower crust of the underthrusting Indian Plate. The oblique-thrust and thrust events are the result of compressive stresses in the inner arc of the flexed Indian Plate. The oblique convergence of the Indian Plate with respect to Tibet and the slab pull force from the subduction of the Indian Plate beneath Burma combined together are responsible for the strike-slip earthquakes. The region north of the Dauki Fault in the vicinity of the Kopili Fault Zone deforms through dextral strike-slip faulting and anti-clockwise rotation of blocks along NW-SE trending transverse structures. The transitional crust of the Bengal Basin has several NE-SW trending paleorifts which manifest sinistral strike-slip motion and clockwise rotation. The GPS velocity vectors and the strain field indicate that throughout most of the region north of the Dauki Fault there is a strong coupling between the surface deformation and the earthquake faulting whereas towards the south in some areas the coupling is weaker. The strike-slip events in the Indo-Burman Ranges probably occur due to a complex interplay between the trench-normal slab pull forces and lateral shear forces set up by the strike parallel components of the interplate coupling resistance and the mantle drag forces.

How to cite: Chaudhuri, D., Banerjee, R., Mahanti, S. S., Kumar, A., and Mitra, S.: Kinematics of Intra-Plate Strike-Slip Earthquakes in an Oblique Convergent Setting  : Insights from the Eastern Himalayan and Indo-Burman Plate Boundary Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9628, https://doi.org/10.5194/egusphere-egu24-9628, 2024.

EGU24-11578 | Orals | GD9.2 | Highlight

Crustal Structure in the Central Tethys Realm 

Vahid Teknik, Hans Thybo, and Irina Artemieva

The central Tethys realm including Anatolia, Caucasus and Iran is one of the most complex geodynamic settings within the Alpine-Himalayan belt. We calculate the depth to magnetic basement and the average crustal magnetic susceptibility, which is sensitive to the presence of iron-rich minerals, to interpret its present structure and the tecto-magmatic evolution. The data demonstrates that the structural complexity increases from the Iranian plateau into Anatolia.

In Iran, our data reveals the presence of hitherto unknown sedimentary basins and we identify two unknown parallel Magmatic-Ophiolite Arcs hidden by the sedimentary cover in eastern Iran. Based on the width of the magmatic anomalies we find that the paleo-subduction zone at the Urmia-Dokhtar Magmatic Arc (Neo-Tethys subduction structure at Zagros) was steeply dipping (> 60°) in the SE and, in contrast, it had shallow dip(< 20°) in the NW part.

Our results for Anatolia demonstrate exceptional variability of crustal magnetization with smooth, small-amplitude anomalies in the Gondwana realm and short-wavelength high-amplitude variations in the Laurentia realm. Poor correlation between known ophiolites and magnetization anomalies indicates that Tethyan ophiolites are relatively poorly magnetized, which we explain by demagnetization during recent magmatism. We analyze regional magnetic characteristics for mapping previously unknown oceanic fragments and mafic intrusions, hidden beneath sedimentary sequences or overprinted by tectono-magmatic events. By the style of crustal magnetization, we distinguish three types of basins and demonstrate that many small-size basins host large volumes of magmatic rocks within or below the sedimentary cover. We map the width of magmatic arcs to estimate paleo-subduction dip angle and find no systematic variation between the Neo-Tethys and Paleo-Tethys subduction systems, while the Pontides magmatic arc has shallow (∼15°) dip in the east and steep (∼50°–55°) dip in the west. We recognize an unknown, buried 450 km-long magmatic arc along the western margin of the Kırşehir massif formed above steep (55°) subduction. We propose that lithosphere fragmentation associated with Neo-Tethys subduction systems may explain high-amplitude, high-gradient crustal magnetization in the Caucasus Large Igneous Province. Our results challenge conventional regional geological models, such as Neo-Tethyan subduction below the Greater Caucasus, and call for reevaluation of the regional paleotectonics.

References:

Teknik V., Thybo H., Artemieva I.M., Ghods A., 2020, Crustal density structure of NW Iranian Plateau. Tectonophysics, 792, 228588, doi: 10.1016/j.tecto.2020.228588.

Teknik, V., Artemieva, I. M., & Thybo, H. 2023. Geodynamics of the central Tethyan belt revisited: Inferences from crustal magnetization in the Anatolia-Caucasus-Black Sea region. Tectonics, 42, https://doi.org/10.1029/2022TC007282.

How to cite: Teknik, V., Thybo, H., and Artemieva, I.: Crustal Structure in the Central Tethys Realm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11578, https://doi.org/10.5194/egusphere-egu24-11578, 2024.

EGU24-12661 | ECS | Posters on site | GD9.2

Interpretation of crustal structure and hydrocarbon potential of the South Caspian and Kura basins, Azerbaijan  

Nazim Abdullayev, Fakhraddin Kadirov, Ibrahim Guliyev, Shalala Huseynova, Arzu Javadova, Bakir Maharramov, and Abdulvahab Mukhtarov

The South Caspian Basin and Kura basin have had a complex tectonic and stratigraphic history and characterized by different thermal regimes. The basins are a genetically linked system created in a Mesozoic extensional setting with a complex Cenozoic sedimentary filling.

The study presents a new interpretation of the regional geodynamic history and crustal structure based on the new geological and geophysical data. New insights at the South Caspian Basin and Kura basin formation, evolution, and hydrocarbon potential were achieved by integrating published structural maps into the tectonostratigraphic framework delineating these basins and geothermal data, including onshore and offshore borehole temperature measurements, geothermal gradients, and heat flow data. The gravity and magnetic data were used to understand the regional geological model.

For the first time geological evolution of the offshore the South Caspian Basin and onshore Kura Basin were linked within a single map set. Delineating and linking these basins allow novel understanding the geodynamic history of the Black Sea and Caspian regions. The study reveals several specific regions including “cold” South Caspian basin with a 20 km thick sedimentary succession and less than 10 km crustal thickness, “intermediate” Lower Kura basin, and “warm” Kura basin (including Yevlakh Agjabadi depression) with less than 10 km thick sedimentary succession and the crustal thickness of 20 to 25 km. According to the proposed evolution history the basins adjacent to the South Caspian basin involves Mesozoic island arc extension origin followed by subsequent development in Jurassic, with possible additional rifting in Eocene and flexural overprint in Tertiary.

The South Caspian basin contains the dynamic petroleum systems with the prolific Oligocene-Miocene source rocks characterized with proved hydrocarbon potential increasing basinwards.

Inherited tectonic boundaries between the South Caspian and Kura Basins such as the West Caspian Fault zone serve as markers for hydrocarbon prospectivity. The crustal parameters control the distribution of temperature gradients within the basins and hence hydrocarbon generation. Isothermal surfaces are displaced: depth of the surfaces changes across the boundary between the continental crust of the onshore Kura Basin and the different “oceanic-type” crust of the South Caspian basin. This boundary is located at around 500 km where isothermal values are abruptly displaced downwards by about 4 km. A sharp increase in depth of the 120°C isotherm along the boundary has significant implications for the thermal maturity of the source rocks. Rapid burial rates of the offshore South Caspian basin together with the low geothermal gradient have delayed the maturation of organic matter in the source rocks, making the South Caspian basin the location of one of the world’s deepest active petroleum systems. Thus, in deep and prospective offshore South Caspian hydrocarbon generation occurs at greater depth compared to onshore areas, characterized by a more limited hydrocarbon potential. The difference in maturity of onshore and offshore source rocks could play a role in segregating hydrocarbon prospective areas.

How to cite: Abdullayev, N., Kadirov, F., Guliyev, I., Huseynova, S., Javadova, A., Maharramov, B., and Mukhtarov, A.: Interpretation of crustal structure and hydrocarbon potential of the South Caspian and Kura basins, Azerbaijan , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12661, https://doi.org/10.5194/egusphere-egu24-12661, 2024.

EGU24-14740 | ECS | Orals | GD9.2 | Highlight

Strong Variability in the Thermal Structure of Tibetan Lithosphere 

Bing Xia

We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temperature of 1300°C) and surface heat flow in Tibet and adjacent regions based on a new thermal-isostasy method. The method accounts for crustal density heterogeneity, is free from any assumption of a steady-state lithosphere thermal regime, and assumes that deviations from crustal Airy-type isostasy are caused by lithosphere thermal heterogeneity. We observe a highly variable lithospheric thermal structure which we interpret as representing longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo-slabs. Cratonic-type cold and thick lithosphere (200–240 km) with a predicted surface heat flow of 40–50 mW/m2 typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphere. We identify a “North Tibet anomaly” with thin (<80 km) lithosphere and high surface heat flow (>80–100 mW/m2). We interpret this anomaly as the result of removal of lithospheric mantle and asthenospheric upwelling at the junction of the Indian and Asian slabs with opposite subduction polarities. Other parts of Tibet typically have intermediate lithosphere thickness of 120–160 km and a surface heat flow of 45–60 mW/m2, with patchy anomalies in eastern Tibet. While different uplift mechanisms for Tibet predict different lithospheric thermal regimes, our results in terms of a highly variable thermal structure beneath Tibet suggest that topographic uplift is caused by an interplay of several mechanisms.

How to cite: Xia, B.: Strong Variability in the Thermal Structure of Tibetan Lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14740, https://doi.org/10.5194/egusphere-egu24-14740, 2024.

EGU24-15423 | ECS | Posters on site | GD9.2 | Highlight

Relocated Earthquakes Confined to the Upper Crust in the Southern Tibet 

Gaochun Wang, Hans Thybo, and Irina M. Artemieva

We have located a total of 202 local earthquakes, based on the data recorded by the Hi-CLIMB seismic stations from 2002-2005, in the southern Tibet. The focal depths of all relocated earthquakes, in the Lhasa terrane, are shallow than 30km, however, the depths can extend to 50km under Himalaya, although there are many earthquakes deeper than 80 km according to the catalogue.  The absence of the earthquakes of the lower crust, in Lhasa terrane, implying a brittle upper crust lying on a soft felsic lower crust. Moreover, the focal depths, in Himalaya, show a low angle (~12°) of subducted Indian lower crust. The focal mechanisms show that the normal faults are the main type of the crustal deformation, which indicate the dominant direction of the extension is approximately east-west, in Lhasa terrane. The strike-slip faults played a regulatory role between normal faults. The thrust faults are only occurred in the south of STDS. The calculated mechanisms correlate well with the surface geology features. Our new results suggest that the whole crust of the Himalaya is brittle and prone to triggering earthquakes under the northward convergence of the Indian plate. However, the lower crust of the Lhasa terrane may be soft, felsic and stable floating above the mantle, under a brittle upper crust which is easier to collapse.

How to cite: Wang, G., Thybo, H., and Artemieva, I. M.: Relocated Earthquakes Confined to the Upper Crust in the Southern Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15423, https://doi.org/10.5194/egusphere-egu24-15423, 2024.

EGU24-15623 | ECS | Orals | GD9.2

Locked Frontal and Lateral Ramps on the Main Himalayan Thrust beneath NW Himalaya illuminated by precisely located seismicity 

Sk Shamim, Ayon Ghosh, Supriyo Mitra, Keith Priestley, Swati Sharma, and Sunil Kumar Wanchoo

The Kashmir ‘seismic gap’ in NW Himalaya, between the 1905 Kangra and 2005 Muzaffarabad earthquake rupture zones, has been replete with moderate-to-small earthquakes. GPS geodetic measurements across the Himalayan-arc reveal arc-normal convergence of ~11 mm/yr, which reduces towards the foreland in the India-fixed reference frame. In 2013 the Jammu And Kashmir Seismological NETwork (JAKSNET), and later the Himachal Pradesh Seismological NETwork (HiPSNET) was established to study the seismological characteristics of this ‘seismic gap’. Using continuous waveform data from these networks an earthquake catalog has been created using the Regressive ESTimator (REST) algorithm. Following this, seismic phases were manually picked from ~1100 earthquake records to determine the accurate arrival-times. A subset of these events based on the quality of picked phases are relocated using a probabilistic Non-Linear Location (NLL) method. These earthquakes have magnitudes between 0.5 and 4.5, and are distributed throughout the crust, with the majority concentrating at shallow (<25 km) depth. These shallow earthquakes are concentrated beneath the Higher Himalaya with lateral variations south of the Kishtwar window and to a region to its east. In arc-normal cross-section, the hypocenters lie on and above the MHT and the depth increases hinterlandward. Two distinct clusters of seismicity with increasing depth coincides with the mid-crustal frontal ramp observed in Vs structure beneath the Kishtwar window. The arc-parallel cross-section shows two eastward dipping hypocenter-clusters on and above the MHT. The one west of the Kishtwar window coincides with the lateral ramp observed in the Vs model. We conjecture that the one to the east also illuminates a similar transverse structure within the Himalayan wedge. Comparison of our hypocentral distribution with GPS velocities across this region reveal a frictionally locked shallow segment of the MHT, with the down-dip unlocking-zone highlighted by the across-arc clustering of seismicity beneath the Higher Himalaya. The locked-to-creep transition occurs immediately north of the mid-crustal frontal-ramp. We compute strain-rate from the sparse GPS data which reveals a predominant NE-SW compression and high strain-rates in regions of clustered shallow-seismicity. We are in the process of further refining the hypocentral locations using a double-difference relocation method, results of which will be presented. 

How to cite: Shamim, S., Ghosh, A., Mitra, S., Priestley, K., Sharma, S., and Wanchoo, S. K.: Locked Frontal and Lateral Ramps on the Main Himalayan Thrust beneath NW Himalaya illuminated by precisely located seismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15623, https://doi.org/10.5194/egusphere-egu24-15623, 2024.

EGU24-18337 | ECS | Posters on site | GD9.2

New scenario for structural segmentation and subduction modeling in Makran (Iran and Pakistan) 

Peyman Namdarsehat and Wojciech Milczarek

The Makran subduction zone is located in southeastern Iran and southern Pakistan. It was formed by the subduction of part of the oceanic crust of the Arabian Plate beneath the Eurasian Plate. In the eastern part of this zone, the convergence rate, coastal uplift and seismicity are higher than in the western part of this zone. In addition, there are a larger number of Quaternary volcanoes in the western part due to a subduction arc of the oceanic lithosphere. The study of the velocity vectors shows that the asymmetric pressure impressed the Makran and in addition a number of tectonic evidences were attributed to different dip angles of subduction. The results indicate that the segmentation of the Makran is influenced by two key factors: asymmetric pressure, resulting in varying convergence rates, and different subduction dip angles. These factors are identified as the origin parameters that contribute to the formation of two distinct blocks with contrasting structures. Based on the considerations made in this study, subduction in the Makran was modeled. And a new structural segmentation was presented in this zone. The results indicate a propagation of the eastern boundary of the Lut block in Makran. The model presented in this paper was able to show the tectonic problems of the Makran and furthermore demonstrate the discrepancy between the tectonic features of the western and eastern blocks of the Makran.

How to cite: Namdarsehat, P. and Milczarek, W.: New scenario for structural segmentation and subduction modeling in Makran (Iran and Pakistan), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18337, https://doi.org/10.5194/egusphere-egu24-18337, 2024.

EGU24-19538 | Posters on site | GD9.2

Crustal structure of the Dinarides: new insights from the receiver functions and ambient noise tomography  

Josip Stipčević, Tena Belinić Topić, Stéphane Rondenay, and Petr Kolínský

The Dinarides, located at the eastern edge of the Adriatic Sea, are the focus of ongoing geophysical research due to their complex tectonic characteristics and distinctive structural transition zones. Prior investigations have identified a two-layered crust with variable thickness, featuring a transitional zone between Dinaric and Pannonian crust. Recent studies have introduced the concept of a deep-seated Dinaric crustal root, marked by a discernible transition to shallower crust along the northern edge.

This study includes two complementary research approaches to advance our understanding of the Dinarides' crustal structure: receiver function analysis and ambient noise tomography. The P receiver function method was applied to 123 seismic stations across the broader Dinaric area, involving 1234 teleseismic earthquakes recorded from 2016 to 2023. Results are presented through cross-sectional CCP stacking images, offering a comprehensive visualization of the converted Ps phase crucial for mapping significant crustal discontinuities. Additionally, seven years of continuous data, recorded from 2016 to the end of 2022 at 121 seismic stations, were utilized to calculate phase velocities of surface waves. Eikonal tomography was applied to both Rayleigh and Love waves, with local dispersion curves independently inverted for each surface wave type. The outcomes provide distributions of vertically and horizontally polarized shear-wave velocities, presented as maps at various depths and cross-sectional profiles, contributing to an in-depth exploration of shear-wave velocities across the entire region.

The results reveal intriguing insights: a pronounced high-velocity anomaly beneath the Dinarides at shallower depths, a significant low-velocity anomaly in the mid-crust beneath the Dinarides for vertically polarized shear waves, and a distinct, localized thick low-velocity anomaly beneath the NW Dinarides for horizontally polarized shear waves. These findings collectively suggest complex variations in crustal thickness and seismic properties, particularly thickening crust toward the Southern and Inner Dinarides.



How to cite: Stipčević, J., Belinić Topić, T., Rondenay, S., and Kolínský, P.: Crustal structure of the Dinarides: new insights from the receiver functions and ambient noise tomography , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19538, https://doi.org/10.5194/egusphere-egu24-19538, 2024.

EGU24-21398 | Orals | GD9.2

Fault rupture mapping of the February 6, 2023 earthquake sequence, eastern Türkiye 

Jiannan Meng, Timothy Kusky, Walter D. Mooney, Erdin Bozkurt, Mehmet Nuri Bodur, and Lu Wang

The powerful earthquake that struck eastern Türkiye on February 6th 2023 is the most devastating earthquake of the past century in the region. Here we present our first-hand field measurements of the ground offsets and the high resolution (centimeter level) drone-mapped surface ruptures 10 days after the first shock. It is clear that the initial rupture was on the Dead Sea fault zone (DSFZ), yet maximum displacements and energy release (Mw 7.8) occurred 24 sec later when rupture transferred to the East Anatolian fault zone (EAFZ). Seven hours later, a Mw 4.5 aftershock at the junction of the EAFZ with the east-west striking Çardak-Sürgü fault (Ç-SF) triggered the second large (Mw 7.5) earthquake, causing another round of the damage in the region. The maximum ground offsets are around 47.5 kilometers away from the epicenter in this event on the EAFZ. The surface ruptures directly cut young basins and mountains, as well as activating some pre-existing surfaces. Our observation provides important data on surface deformation during large continental strike-slip earthquakes, rupture propagation mechanisms, and how slip may be transferred between complex fault systems. We also provide insight into how slip along linked fault systems accommodates global plate motions.

How to cite: Meng, J., Kusky, T., Mooney, W. D., Bozkurt, E., Bodur, M. N., and Wang, L.: Fault rupture mapping of the February 6, 2023 earthquake sequence, eastern Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21398, https://doi.org/10.5194/egusphere-egu24-21398, 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.

GD10 – Modelling, Data collection and Inversion

Traditional geomechanical modelling involves a lot of a priori knowledge regarding, among others, the distribution of material properties and boundary conditions to apply to a model. Setting those parameters is usually time-consuming, starting with extensive literature reviews to get initial estimates, which are then refined by trial and error by calibrating the numerical simulations against observations. In particular, the boundary conditions typically remain poorly constrained since precise data is rarely available.

In this contribution, we present a physics-based machine learning approach to infer the current displacements and full stress tensor distribution of an effective 2D linear elastic model, based on stress orientation and Global Navigation Satellite System (GNSS) data. This allows for automatic retrieval of a reasonable approximation of the model's elastic material properties, consistent displacement, and stress values over the whole physical domain, including at the boundaries, which could be used for instance in following forward simulations.

We show an application to the Australian continent, for which a rich dataset of stress orientation is available from the World Stress Map project and the GNSS measurements are particularly steady. This allows us to compare various options to account for stress orientation and displacement information as input data. Interestingly, we recover the smoothest stress field compatible with the (very accurate) GNSS observations and consequently identify areas where the resulting stress orientation differs from current estimates.

How to cite: Poulet, T. and Behnoudfar, P.: Retrieving stress and elastic properties distributions from stress orientation and satellite data using physics-informed machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1400, https://doi.org/10.5194/egusphere-egu24-1400, 2024.

EGU24-3547 | Posters on site | GD10.1

ECOMAN 2.0: an open-source software package for coupling geodynamic and seismological modelling. 

Manuele Faccenda, Brandon VanderBeek, Albert de Montserrat, and Jianfeng Yang

In this contribution we introduce ECOMAN 2.0, an open-source software package for (1) modelling the strain-/stress-induced rock fabrics and related mechanical anisotropy, and (2) performing isotropic and anisotropic inversions using real/synthetic P- and S-wave travel-times and S-wave splitting parameters.  

The strain-induced intrinsic mantle fabrics are modelled inputting the velocity, pressure, temperature and dominant creep mechanism fields from large-scale mantle flow simulations into D-Rex (Kaminski et al., 2004). This open-source software has been parallelized using a hybrid MPI and OpenMP scheme and modified to account for combined diffusion-dislocation creep mechanisms, LPO of transition zone and lower mantle polycrystalline aggregates (Wadsleyite, Bridgmanite, post-Perovskite), P-T dependence of single crystal elastic tensors, advection and non-steady-state deformation of crystal aggregates in 2D/3D cartesian/spherical grids (Faccenda, 2014; Faccenda and Capitanio, 2013). The new version of D-Rex can solve for the LPO evolution of 100.000s polycrystalline aggregates of the whole mantle in a few hours, outputting the full elastic tensor of poly-crystalline aggregates as a function of each single crystal orientation, volume fraction and elastic moduli scaled by the local P-T conditions.

Extrinsic elastic anisotropy due to grain- or rock-scale fabrics or fluid-filled cracks can also be estimated with the Differential Effective Medium (DEM) (Faccenda et al., 2019). Similarly, extrinsic viscous anisotropy can be modelled yielding viscous tensors to be used in large-scale mantle flow simulations (de Montserrat et al., 2021). 

The elastic tensors can then be interpolated in a tomographic grid for (i) visual inspection of the mantle elastic properties (such as Vp and Vs isotropic anomalies; radial, azimuthal, Vp and Vs anisotropies), (ii) generating input files for large-scale synthetic waveform modelling (e.g., SPECFEM3D format), or (iii) P- and S-wave isotropic and anisotropic inversions (e.g., Faccenda and VanderBeek, 2023). The latter can be performed with the new PSI (Platform for Seismic Imaging) module, which includes recently developed techniques for seismic anisotropic inversions of body waves (VanderBeek and Faccenda, 2021; VanderBeek et al., 2023).

How to cite: Faccenda, M., VanderBeek, B., de Montserrat, A., and Yang, J.: ECOMAN 2.0: an open-source software package for coupling geodynamic and seismological modelling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3547, https://doi.org/10.5194/egusphere-egu24-3547, 2024.

EGU24-5381 | Orals | GD10.1

Structure and numerical solution of a thermal problem with internal Dirichlet conditions 

Sergio Zlotnik, Mariano Tomás Fernández, and Pedro Díez

Inverse problems in geophysics seeking to understand the current state of planet Earth use data from multiple observables and involve a variety of physical principles. One of the key fields to determine is the temperature, affecting almost all the other physical quantities involved (e.g. densities, viscosities, wave propagation velocities, among others).

The Lithosphere-Asthenosphere Boundary (LAB) is a boundary layer that affects most of the processes and properties in the Earth structure. Determining its location is one of the goals of inversions. It is usual within numerical studies to define the LAB as an isotherm. The need of determining the thermal field in accordance with a given LAB location leads to a mathematical problem with imposed interior Dirichlet conditions. In particular, the isotherm defining the LAB has to be located in the position tested by the inverse solver. Several approaches are sucessfully used to solve this kind of problem, but usually they lack of a sound physical model at least in some parts of the domain.

Here we analyze the mathematical structure of a thermal problem with known interior conditions and then propose several numerical procedures to solve it. The proposed methods are tailored to the geophysical case and are based on the certainty of the different boundary conditions that are imposed in the model.

Moreover, because this thermal solver is expected to be used many times within an inverse scheme, we want the numerical mesh to be fixed. The LAB, therefore, will not fit the mesh.

How to cite: Zlotnik, S., Fernández, M. T., and Díez, P.: Structure and numerical solution of a thermal problem with internal Dirichlet conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5381, https://doi.org/10.5194/egusphere-egu24-5381, 2024.

EGU24-6508 | ECS | Posters on site | GD10.1

TerraNeo: Development of a scalable mantle convection code for exascale computing 

Eugenio D'Ascoli, Andreas Burkhart, Nils Kohl, Hans-Peter Bunge, and Marcus Mohr

Simulating the Earth’s mantle convection at full convective vigor on planetary scales is a fundamental challenge in Geodynamics even for state of the art high-performance computing (HPC) systems. Realistic Earth mantle convection simulations can contribute a decisive link between uncertain input parameters, such as the mantle viscosity structure, and testable preconditions, such as dynamic topography. The vertical deflections predicted by such models may then be tested against history of dynamic topography from stratigraphic observations. Considering realistic Earth like Rayleigh numbers (∼ 108 ) a resolution of the thermal boundary layer of 10 − 50 km is necessary considering the volume of the Earth’s mantle.

Simulating Earth’s mantle convection at this level of resolution requires solving sparse indefinite systems with more than 1012 degrees of freedom, computationally feasible only on exascale HPC systems. This is achievable only by mantle convection codes providing high degrees of parallelism and scalability. Earlier approaches with prototype frameworks using hierarchical hybrid grids (HHG) as solvers for such systems demonstrated the scalability of the underlying concept for future generations of exascale computing systems.

Building up on the TerraNeo project here we report on the progress of utilizing the improved framework HyTeG (Hybrid Tetrahedral Grids) based on matrix-free multigrid solvers in combination with highly efficient parallelisation and scalability. This will allow to solve systems with more than a trillion degrees of freedom on present and future generations of exascale computing systems. We also report on the advances in developing the scalable mantle convection code TerraNeo using the HyTeG framework to realise extreme-scale mantle convection simulations with realistic, Earth like parametrisation and a resolution in the order of ∼ 1km.

How to cite: D'Ascoli, E., Burkhart, A., Kohl, N., Bunge, H.-P., and Mohr, M.: TerraNeo: Development of a scalable mantle convection code for exascale computing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6508, https://doi.org/10.5194/egusphere-egu24-6508, 2024.

EGU24-6715 | Orals | GD10.1

Hydro-mechanical-chemical modelling of dehydration during serpentinite deformation: Comparing laboratory and numerical experiments 

Stefan Markus Schmalholz, Mattia Luca Mazzucchelli, Lisa Eberhard, and Oliver Plümper

Dehydration reactions play a pivotal role in the dynamics and seismicity at subduction zones and in the deep water cycle. These reactions often occur during rock deformation. The dehydration of antigorite serpentinite is particularly important at subduction zones. This dehydration has been investigated with laboratory experiments of serpentinite deformation. Yet, the reproduction of such laboratory deformation experiments of serpentinite dehydration with mathematical models is still a major challenge. Here, we test a two-dimensional (2D) hydro-mechanical-chemical (HMC) numerical model for serpentinite dehydration by comparing the numerical results with the results of laboratory experiments.

The laboratory experiments are performed with a Griggs apparatus. Natural antigorite serpentinites with and without preferred orientation are deformed by vertical compression for a confining pressure of 1.5 GPa and maximum differential stresses between 350 and 700 MPa. For comparison, also experiments with hydrostatic stress are performed. The experimental temperature is between 620 and 650 °C. The applied confining pressure and temperature are in the olivine stability field according to the measured chemical composition of the serpentinite and thermodynamic Perple_X calculations. However, olivine only forms locally in the serpentinite if the serpentinite is deformed under differential stress. Olivine does not form in serpentinite under hydrostatic stress. Hence, we hypothesize that olivine formation is controlled by reaction kinetics and that the kinetics are locally faster in serpentinite that deforms under differential stress.

We elaborate a 2D HMC numerical algorithm that can simulate dehydration and olivine generation in a deforming serpentinite [Schmalholz et al., 2023]. The algorithm is based on a staggered finite difference discretization and employs a matrix-free, pseudo-transient iterative solver. Furthermore, the algorithm is programmed in the Julia language, employs the ParallelStencil package, and runs on GPUs. We discuss three major numerical challenges: First, the treatment of large changes in solid density during the generation of olivine by serpentinite dehydration. Second, the treatment of large temporal and spatial gradients in the unknowns, such as porosity and fluid pressure. Third, the treatment of strongly nonlinear relations between unknowns and parameters, such as the relations between density and fluid pressure, porosity and permeability, and porosity and rock viscosity. We implement several mathematical formulations for the reaction kinetics and discuss which formulation can explain the laboratory results best. We further discuss potential numerical benchmarks of such HMC algorithms for modelling the coupling of chemical reactions, fluid flow and rock deformation.       

References

Schmalholz, S. M., E. Moulas, L. Räss, and O. Müntener (2023), Serpentinite Dehydration and Olivine Vein Formation During Ductile Shearing: Insights From 2D Numerical Modeling on Porosity Generation, Density Variations, and Transient Weakening, Journal of Geophysical Research: Solid Earth, 128(11), e2023JB026985, doi:https://doi.org/10.1029/2023JB026985.

How to cite: Schmalholz, S. M., Mazzucchelli, M. L., Eberhard, L., and Plümper, O.: Hydro-mechanical-chemical modelling of dehydration during serpentinite deformation: Comparing laboratory and numerical experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6715, https://doi.org/10.5194/egusphere-egu24-6715, 2024.

EGU24-8080 | Posters on site | GD10.1

One dimensional models of frictional plastic strain localisation 

Thibault Duretz and Laetitia Le Pourhiet
Frictional plasticity governs the state of stress and the deformation style of the Earth’s upper crust. Frictional models depend on both deviatoric stress and pressure and include coupling between shear and volumetric stress via dilatancy and compaction. Elastic-plastic strains can takes the form of shear bands that can further be compared to geological observations. The study of frictional shear banding is non trivial because (1) this process is highly non-linear and (2) the models may require enrichment/regularisation to yield successful integration. 2D or 3D models may be used to model shear banding, they are however computationally expensive, which hinders systematic exploration of shear banding processes. We here present a 1D dimensional model of frictional plastic strain deformation. These models allow for exploring the process of strain localisation and the coupled effects of fluid flow and material microstructure.  

How to cite: Duretz, T. and Le Pourhiet, L.: One dimensional models of frictional plastic strain localisation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8080, https://doi.org/10.5194/egusphere-egu24-8080, 2024.

EGU24-10708 | Orals | GD10.1

Synergistic Approach to Robustly Reconstruct Eruption Plume Dynamics: Application to Campi Flegrei, Italy 

Beatriz Martinez Montesinos, Yujiro J Suzuki, Leonardo Mingari, and Antonio Costa

Explosive volcanic eruptions can inject high quantities of magmatic materials into the atmosphere representing a risk to life and society. To quantify the potential impacts of a future eruption or to forecast what will happen in the next few hours when a volcano is erupting, atmospheric dispersion models are commonly used providing important information for civil protection and other stakeholders. Spatiotemporal distributions of volcanic ash in volcanic plumes are used as an input by a numerical simulation of tephra dispersal and are called eruption source parameters (ESPs). They have been poorly constrained and therefore their variation between models affects volcanic tephra hazard assessment. Since the goodness of ESPs increases with knowledge of the dynamics of eruptive columns, reconstruction of volcanic columns from past eruptions will improve the assessment of volcanic hazards for future eruptions.

In this work we take advantage of recent advances in computational capabilities and modeling in order to robustly reconstruct the dynamics of eruption columns from past eruptions. We do that by applying a synergistic approach between atmospheric dispersion models capable of reproducing the transport of volcanic ash due to atmospheric wind, eruption cloud dynamics models that resolve the ascending and the horizontal spreading of umbrella cloud, and inversion methods able to estimate ESPs using geological data information of tephra deposits.

Specifically, we use the latest version of the ash dispersal model FALL3D that allows us to determine EPSs by inverting field data using the novel GNC (Gaussian with non-negative constants) ensemble-based inversion method, and the eruption cloud dynamics model SK-3D that accurately resolves the turbulence of the volcanic plumes.

As an application, we focus on Campi Flegrei (CF) caldera, in Italy. CF is currently a densely populated area under busy air traffic routes where the monitoring system of the Vesuvius Observatory highlights some variations in the state of the volcanic activity. CF has generated several explosive eruptions in recent geological times, including the ~39 ka Campanian Ignimbrite (CI) super-eruption that is the largest explosive eruption in Europe in the last 200 ka. To reconstruct the CI super-eruption and assess such a huge eruption in CF, we apply our methodology to the geological data associated with this eruption.

How to cite: Martinez Montesinos, B., Suzuki, Y. J., Mingari, L., and Costa, A.: Synergistic Approach to Robustly Reconstruct Eruption Plume Dynamics: Application to Campi Flegrei, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10708, https://doi.org/10.5194/egusphere-egu24-10708, 2024.

EGU24-11777 | ECS | Posters on site | GD10.1

ShellSetHPC – Parallel dynamic neotectonic modelling 

Jon Bryan May, Peter Bird, and Michele Matteo Cosimo Carafa

Geodynamic forward models are typically computationally expensive, they generally draw on a large set of input and testing data and will normally have quite large model domains in order to ensure that the results are practical and applicable. To reduce simulation time many programs will use some form of parallel computing in their calculations, e.g., programs may use the message passing interface (MPI) communication protocol or OpenMP API to partition the domain into reasonable chunks divided between multiple processes, this can improve performance by having multiple processes solve smaller parts of a large problem in parallel.

Geodynamic inverse modelling involves using known phenomena to constrain a model, or set of models, to improve knowledge of unknowable or unmeasurable parameters involved within a dynamic system. For example, one could use measured GPS velocities and seafloor spreading rates to infer changes to mantle convection or combine GPS velocities with near-surface temperatures to monitor the growth of magma chambers.

Since geodynamic inversion involves running multiple constrained forward models it naturally suffers from the performance issues linked to the forward models themselves, briefly: a poorly performing forward model will mean a poorly performing inverse model. More than that, the inverse model must perform multiple (the more the better) forward models with updated parameters. These requirements, a good enough forward model, and an efficient method of performing multiple models in parallel while optimizing the desired parameters, leads to an obvious conclusion: to perform forward models in parallel while searching for an optimal model.

To this end we present a geodynamic inversion model, which we call ShellSetHPC, which uses a combination of existing, well known, and robust software to model the neotectonics of planetary lithosphere. This is further combined with an efficient, de-centralised random search algorithm able to generate testable models within a user defined N-dimensional space. This algorithm is also able to launch multiple models in parallel thanks to an MPI framework. The forward model makes use of Intel’s thread safe math kernel library (MKL) to solve the linear system in parallel. This hybrid approach lends itself to use on high performance computing (HPC) machines which would allow a more complete utilisation of these features.

In this work we will present scaling results on an HPC cluster and compare these with results obtained from more typical search algorithms. All tests are performed within a realistic geological setting, the results of which will be used to gather insight into the performance of the driving model generators and their settings.

How to cite: May, J. B., Bird, P., and Carafa, M. M. C.: ShellSetHPC – Parallel dynamic neotectonic modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11777, https://doi.org/10.5194/egusphere-egu24-11777, 2024.

EGU24-12283 | Posters on site | GD10.1

Modeling fluid-induced dyke propagation in elasto-visco-plastic rocks 

Anton A. Popov, Nicolas Berlie, and Boris J.P. Kaus

Developing a deep understanding of magmatic processes, such as the ascent of magmatic melts through the lithosphere, is a notoriously complex interdisciplinary task that involves contributions from various branches of geosciences. Here, we focus on the implementation of mode-1 plasticity, which is highly relevant for the modeling of dyke propagation through the brittle crust under an excess of fluid (melt) pressure, as part of a nonlinear elasto-visco-plastic rheology that is also appropriate for modeling the ductile-brittle transition in the upper mantle.

For this, we adopt a coupled poro-elasto-visco-plastic description of the strain localization process to capture the onset and advance of vertical dykes originating from magma reservoirs located at various depth. We mostly aim to investigate the hydro-mechanical interactions of such a system (e.g. permeability increase and elastic modulii degradation with increasing plastic strain, and influence of fluid pressure on both total stresses and on the yield surface). Thermal effects are essentially ignored, apart from the background geothermal gradient. The reservoir is represented as a cavity subjected to an increased fluid pressure.

We describe the brittle deformation using multi-surface plasticity models in the framework of the flow plasticity theory. A number of challenging problems are usually encountered in this case from an algorithmic viewpoint, including a lack of convexity and continuity of both the yield surface and flow potential, spurious elastic domains, singularity points and loss of convergence. We address these issues by using a relatively simple Perzyna-type visco-plastic model that consists of a linear Drucker-Prager shear failure envelop, and a circular tensile cap. Both surfaces are combined with each other in a way that enforces dimensional consistency, convexity, and continuity throughout the entire stress space.

Finally, we discuss the algorithmic details of the model which is incorporated in an implicit finite element code and demonstrate the  application results.

How to cite: Popov, A. A., Berlie, N., and Kaus, B. J. P.: Modeling fluid-induced dyke propagation in elasto-visco-plastic rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12283, https://doi.org/10.5194/egusphere-egu24-12283, 2024.

EGU24-14391 | Posters on site | GD10.1

Progress and perspectives on using the Lattice Boltzmann Method for geodynamics simulation research 

Peter Mora, Gabriele Morra, Leila Honarbakhsh, Christian Huttig, and Nicola Tosi

The Thermal Lattice Boltzmann Method (TLBM) for geodynamical simulation research offers an alternative to classical PDE based methods for 2D and 3D geodynamics simulation research. It is based on modelling the Boltzmann equation on a discrete lattice which involves the movement of number densities carrying mass and energy density on a discrete lattice and their relaxation to equilibrium which model collisions. We present examples in 2D and 3D to illustrate the capabilities, performance, and accuracy of this method for geodynamics research, namely: (1) ability to handle highly nonlinear rheology, ultra-high Rayleigh numbers, a wide range of Prandtl numbers, and multiphase flow, (2) linear scaling up to 300K cores on HPC CPU clusters, and (3) ability to closely match the Blankenbach benchmarks demonstrating the LBMs accuracy. Examples in 2D include high Rayleigh number simulations to Ra = 1015, highly nonlinear rheology leading to the emergence of plate-tectonic like behaviour, and planetary accretion. Examples in 3D include modelling of a mantle with an aspect ratio of 25x25x1 representing a case from a recent nature paper, and modelling a case of an aspect ratio of 14.4x14.4x1 which is similar that of the Earth for Ra = 106 and Pr = 100. Potential benefits of the TLBM include an ability for higher resolution simulations than can be achieved using classical methods, and faster simulations which may allow phase space studies to determine which parameter combinations lead to which class of behaviour. As the TLBM is a new method for geodynamical simulation, it will take some time to determine the limits of this method. For example, a simulation can be made to run faster by increasing the physical time step, but eventually, if the time step is too large, the Mach numbers on the lattice become too high leading to lower accuracy and eventually instability due to non-convergence of the collision step which involves a relaxation of the number densities to equilibrium. We believe that over time, these limitations will become well understood and that the outstanding parallel scaling performance on HPC CPU clusters of the TLBM - which makes possible 3D models up to 50003 - will  open up exascale computing to geodynamics research and will lead to fundamental advances in geodynamics research. As such, the TLBM may become a valuable tool to advance geodynamics research into the future through large to exascale simulations that may lead to new insights into the dynamics and evolution of the earth and exoplanets from the early lava world stage through to plate tectonics or other regimes.

How to cite: Mora, P., Morra, G., Honarbakhsh, L., Huttig, C., and Tosi, N.: Progress and perspectives on using the Lattice Boltzmann Method for geodynamics simulation research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14391, https://doi.org/10.5194/egusphere-egu24-14391, 2024.

EGU24-14445 | Posters on site | GD10.1

Sequence: A coupled sequence-stratigraphic model built using Landlab 

Eric Hutton, Michael Steckler, and Gregory Tucker

Landlab is an open-source Python package that streamlines the creation, combination, and reuse of 2D numerical models and is a key element of the Community Surface Dynamics Modeling System (CSDMS) Workbench. The Landlab Toolkit provides building blocks for model development such as grid data structures, input/output functions, and a library of several dozen components that each model a separate physical process. Additionally, it provides a framework for assembling integrated models from component parts. We've found that Landlab significantly accelerates model development, encourages user-developers to adopt standard practices and contribute new components to the library. It serves as a platform that nurtures a community of model developers, assisting them in creating coupled models to investigate non-linear interactions between geologic processes.

Using the Landlab toolkit, we developed a new model, Sequence, which is a modular 2D (i.e., profile) sequence stratigraphic model that incorporates key geophysical processes influencing accommodation space in both terrestrial and marine environments. These factors include tectonics and faulting, eustatic sea level changes, flexural isostatic compensation of sediment and water, sediment compaction, and hypopycnal sediment plumes. Each process is encapsulated as an individual, standalone Landlab component, providing flexibility in the construction of new models. Sequence serves not only as a distinct model, but also as a scaffold for the development of new models.

Sequence simulates the evolution of stratigraphy on a continental margin over time scales ranging from thousands to millions of years. Sediment transport and deposition primarily occur during infrequent, high-energy events like storms and floods. For these extended time frames, Sequence employs a scale-integral approach. This method utilizes differential equations to summarize the cumulative effect of sediment transport and deposition across different depositional environments over longer periods (e.g., on the order of a hundred years). The model features a moving-boundary formulation to track shoreline changes and partitions the domain into distinct areas: coastal plain, continental shelf, and upper and lower slope/rise. Submarine sediment transport and deposition are modeled through nonlinear diffusion, with a diffusion coefficient that varies inversely with water depth. The model tracks evolving stratigraphic layers and sediment lithology that is a mixtuer of two grain sizes (sand and mud) each with separate transport functions.

How to cite: Hutton, E., Steckler, M., and Tucker, G.: Sequence: A coupled sequence-stratigraphic model built using Landlab, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14445, https://doi.org/10.5194/egusphere-egu24-14445, 2024.

EGU24-15096 | Posters on site | GD10.1

Multi-GPU Material Point Method Solver for Landslide Simulation 

Zenan Huo, Michel Jaboyedoff, Yury Podladchikov, Ludovic Räss, and Emmanuel Wyser

We present a high-performance Material Point Method (MPM) numerical solver for simulating the landslide run-out process with high resolution. The solver has been adapted to run on multi-GPU platforms. The current version is backend-agnostic, operating efficiently across various CPU and GPU hardware from different vendors, utilizing the same codebase. We evaluate multiple performance metrics and ensure minimal data synchronization between different devices at each iteration. We validate the solver's accuracy by comparing the simulation results of an aluminum-bar collapse with the corresponding experimental outcomes. Consistency is observed between numerical and experimental results for the free and failure surfaces. The results also indicate favorable performance scalability in high-resolution models, significantly enhancing computational efficiency. Further, we simulate the slumping mechanic problem with a simplified landslide geometry. The results show that the shear band develops within the high plastic strain area. The failure surface is in good agreement with the solution reported by Huang[1] et al., demonstrating that MPM can accurately handle failure and large deformation problems as they occur in landslides. Our multi-GPU implementation using MPI makes it possible to perform large-scale simulations that enable to tackle research in the field of geotechnical engineering.

References:
[1]. Huang, Peng, Shun-li Li, Hu Guo, and Zhi-ming Hao. “Large Deformation Failure Analysis of the Soil Slope Based on the Material Point Method.” Computational Geosciences 19, no. 4 (August 2015): 951–63. https://doi.org/10.1007/s10596-015-9512-9.

How to cite: Huo, Z., Jaboyedoff, M., Podladchikov, Y., Räss, L., and Wyser, E.: Multi-GPU Material Point Method Solver for Landslide Simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15096, https://doi.org/10.5194/egusphere-egu24-15096, 2024.

EGU24-15998 | Posters on site | GD10.1

The Geophysical Model Generator: a tool to unify and interpret geophysical datasets 

Marcel Thielmann, Boris J.P. Kaus, Arne Spang, Christian Schuler, and Pascal Aellig

Geophysical datasets and their interpretations form the basis of geodynamic simulations of the Earth’s mantle and lithosphere. Yet, creating geodynamic models from these datasets is often non-trivial, particularly in complex regions such as active orogens. Creating self-consistent three-dimensional models from these datasets poses a challenge due to technical issues such as different data set formats and different spatial resolutions, but also due to discrepancies in the data itself. At the same time, the different datasets obtained through initiatives such as AlpArray contain a wealth of data that can help to constrain subsurface models to an unprecedented extent. Yet interpreting these different data still involves subjective steps and ideally different datasets are combined in the process.

To facilitate the joint interpretation of these datasets and the generation of geodynamic model setups, we therefore developed an open-source package - the Geophysical Model Generator (GMG) - to assist with unifying these datasets in a common data format that can then be further used to visualize, compare and interpret data. Within this package, we provide a set of routines to import different datasets, convert them to a common data format and to process them further (e.g., to create vote maps from different tomographies). These unified datasets can then be exported as vtk-files for further 3D visualization (e.g., Paraview). Moreover, with the Geophysical Model Generator it is also possible to create model setups for numerical models (such as the 3D geodynamic code LaMEM). This package thus covers the entire workflow from data import to numerical model generation. Key features of the Geophysical Model Generator include 1) the creation of 3D volumes from seismic tomography models, 2) the import of 2D data (e.g., surface or Moho topography or screenshots from published papers) and 3) the incorporation of point data such as earthquake locations or GPS measurements. Both scalar and vector data can be handled. With these tools, one can then create a consistent overview of the entire data available for a given region.

The package is written in Julia and hosted as a public open-source repository on GitHub (https://github.com/JuliaGeodynamics/GeophysicalModelGenerator.jl). To assist the joint interpretation of different geophysical datasets, we furthermore provide a graphical user interface that allows to view and compare them (https://github.com/JuliaGeodynamics/GeoDataPicker.jl). The GUI provides an interactive interface, allows loading different datasets and facilitates the manual interpretation of different structures (such as subducting slabs) along profiles and visualize them in 3D while taking different data into account. 

How to cite: Thielmann, M., Kaus, B. J. P., Spang, A., Schuler, C., and Aellig, P.: The Geophysical Model Generator: a tool to unify and interpret geophysical datasets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15998, https://doi.org/10.5194/egusphere-egu24-15998, 2024.

Quantifying surface manifestations of deep mantle dynamics represents an ultimate goal of Earth science. This task has remained challenging due to uncertain initial and boundary conditions of the 4D nature of Earth evolution. A promising solution is through data assimilation, which substantiates a large number of model parameters with available data, thus greatly reducing model uncertainties. During the past decade, our group has developed both forward-in-time and backward-in-time data assimilation techniques that have greatly improved the quantitative expressions on the linkage between deep mantle dynamics and surface tectonics. Here, I will demonstrate how these data-assimilation models work in practice, and how oceanic subduction and the resulting mantle flow influence the Earth surface through generating 3D lithospheric deformation, intraplate volcanism, and earthquakes. Specific examples include the circum-Pacific plates subduction below continents, and evolution of the cratonic lithosphere.

How to cite: Liu, L.: Linking surface tectonics with mantle dynamics using numerical models with data assimilation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16051, https://doi.org/10.5194/egusphere-egu24-16051, 2024.

EGU24-16070 | ECS | Orals | GD10.1

Thermo-Hydromechanical modelling of poro-(visco-)elasto-plastic reservoir processes using GPUs in Julia     

Dániel Kiss, Viktoriya Yarushina, Boris Kaus, and Alexander Minakov

One of the continuing trends in geodynamics is to develop codes that are suitable to model thermo-hydromechanical processes with an increasing level of self-consistency. Developing such models is particularly challenging as some coupling terms can introduce strong non-linearities. We demonstrate that a finite difference discretization combined with pseudo transient solvers are well suited for such problems. Moreover, due to the inherent parallelism of the algorithm and thanks to the novel Julia language and the ParallelStencil.jl package, GPU implementation is not only feasible but also straightforward.

Here, we consider fluid flow in a deformable porous medium coupled to thermo-mechanical processes. We present a thermodynamically self-consistent set of governing equations, describing such processes. The governing equations consist of the conservation of mass, momentum, and energy in two phases. One phase represents the solid skeleton, which deforms in a poro-(visco-)elasto-plastic manner. The second phase represents a low viscosity fluid (water, CH, melt), percolating through the solid skeleton, that is described by Darcy’s law. A special process we will investigate is brittle failure of the matrix due to high fluid pressure (hydro-fracturing, fault reactivation, diking).

The system of equations is solved numerically, using the pseudo transient method, that is well suited to solve highly non-linear problems, as solving the global equations and iterating the non-linearities can be done at the same time. Moreover, the algorithm requires large number of local and cheap operations, which is ideal for GPU implementation. We will describe the governing equations, their numerical implementation, and show examples of numerical simulations that include mode-1 and mode-2 fractures. We apply the numerical model to study the effects of pore pressure in a siliciclastic reservoir on fault reactivation and associated integrity of cap rocks, and to provide a continuum analogue to magmatic dike emplacement.

How to cite: Kiss, D., Yarushina, V., Kaus, B., and Minakov, A.: Thermo-Hydromechanical modelling of poro-(visco-)elasto-plastic reservoir processes using GPUs in Julia    , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16070, https://doi.org/10.5194/egusphere-egu24-16070, 2024.

EGU24-16244 | ECS | Orals | GD10.1

Building an ecosystem of computational geosciences software: why Julia? 

Albert de Montserrat Navarro, Ludovic Räss, Boris Kaus, Ivan Utkin, and Pascal Aellig

Traditionally, the Earth science community has relied on statically compiled and explicitly typed, long-lived programming languages, namely C/C++ and Fortran, for computationally intensive production runs. In contrast, dynamic languages such as Python and MATLAB have served as alternatives for less computationally demanding tasks, prototyping, visualisation and teaching. The lower entry-level of the latter is often used as a “glue language” where the performance-critical code is written in a static language. In the recent decades other modern languages (C#, Nim, Go, Rust…) have been developed, but so far none of them have had a significant impact on the general scientific community.  Among the new modern programming languages there is Julia -with the 1.0 version being released just in 2018- which was designed with the computational scientific community as the main target user base. 
Julia’s main appeal for computational science are (i) performance, it produces compiled machine code with performance potentially similar to other statically compiled languages; (ii) interactivity,  it is a dynamic language, and most of the development and prototyping can be done in interactive sessions using its built-in REPL (read-eval-print loop); and (iii) readability, code is often easier to read than e.g. C++ or Rust. Julia also natively supports linear algebra operations (e.g. it ships its own wrappers for   libraries such as OpenBlas, SuiteSparse or LAPACK), multi-threading and distributed parallelism, which are crucial for a vast number of scientific applications. 


Additionally, Julia offers a series of features that are not intrinsic to the language itself which can ease and improve the user experience compared to traditional C/C++/Fortran: (i) Julia has a well-built package manager where one can easily add and install any version of any registered third-party package by typing two words in the REPL;  (ii) Julia itself is open source, as well as all the registered packages (hosted in Git repositories), and discourages black-box software; (iii) reproducibility is easy thanks to .toml files containing what exact version packages are needed to be installed.

Here we will discuss how the combination of the previous points, along with other important features of the language (multiple dispatch, metaprogramming,…), and existing scientific libraries (GPU support, auto-differentiation,…) make Julia an excellent platform for the geoscientific community to build an ecosystem of open-source  and highly modular software, opposite to the classic lone-wolf large monolithic code. Finally, we will present an overview of the current status of the JuliaGeodynamics and related organisations, as well as the general Earth sciences ecosystem.

How to cite: de Montserrat Navarro, A., Räss, L., Kaus, B., Utkin, I., and Aellig, P.: Building an ecosystem of computational geosciences software: why Julia?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16244, https://doi.org/10.5194/egusphere-egu24-16244, 2024.

EGU24-16725 | Posters on site | GD10.1 | Highlight

Using Julia for teaching and research in the Geosciences 

Boris Kaus, Albert de Montserrat, Nicolas Riel, and Pascal Aellig

Julia is a relatively new scientific computing language with which you can write code that is nearly as fast as Fortran or C, but being a dynamic language, it remains very compact. Since the language is newer than say Python, many of the shortcomings of earlier languages have been fixed. Installing and updating packages with external dependencies is straightforward, for example, and exact reproducibility of computational results can be done by uploading a single additional file.

Here we will discuss our recent experiences with using Julia for teaching and research:

  • The binarybuilder package simplifies the precompilation of non-Julia open-source packages (C, C++, Fortran), allowing cross-compilation for Apple, Linux, and Windows. Uploaded centrally, these precompiled binaries can be effortlessly installed via the Julia package manager. This expedites the setup of complex research code in teaching, reducing the time spent on package installation during the initial lecture to just a matter of minutes. Examples where this was recently implemented was GMT.jl (the Julia interface to the Generic Mapping Tools) which now comes with precompiled version of GMT. Likewise, we provide precompiled packages for LaMEM (a parallel 3D geodynamic code) and MAGEMin (a new thermodynamic code).
  • It is quite easy to call such binary packages, either by calling the executable itself or by automatically creating wrapper (using Clang.jl) and calling the functions within dynamic libraries directly from julia.
  • There is a large and ever-growing ecosystem of existing packages that are useful for computational geosciences. Whereas it is still not as mature as in Python or MATLAB, much of what is required in our daily life is already there, including plotting, machine learning, data I/O.
  • It is easy to develop additional packages, and testing is build-in the language (and CI/CD is free on GitHub for open-source packages). That encourages users to implement tests and helps maintaining packages.
  • Packages can talk to each other in a straightforward manner, which facilitates building composable software stacks.
  • There is great support for GPU computing.
  • It is possible to create GUI’s that run in a webbrowser (for example by using Dash.jl). Recent examples where we used that is in InteractiveGeodynamics.jl (which provides user interfaces to simulate typical geodynamic problems such as convection), GeoDataPicker.jl (a 2D/3D tool to analyze and visualize geodynamic data) and MAGEMin_app (a web-based tool to compute phase diagrams).
  • It can directly be used in Jupyter notebooks (as the “Ju” in its name stands for Julia).
  • It is easy for students to start writing simple codes without having to think about definition of types or having to load packages to create vectors or matrixes, which makes it well-suited for teaching quantitative classes. In many cases, these simple codes already run very fast, as the Julia compiler does an excellent job in optimisations. With a few additional tricks (ensuring type stability and reducing allocations) the simple examples can be turned into a high-performance code that runs at nearly the speed of the more classical languages, while having the advantage to still be very compact and readable.

We will highlight these aspects including with interactive demos.

How to cite: Kaus, B., de Montserrat, A., Riel, N., and Aellig, P.: Using Julia for teaching and research in the Geosciences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16725, https://doi.org/10.5194/egusphere-egu24-16725, 2024.

EGU24-16931 | Orals | GD10.1

Continuum models of dykes: a comparison to discrete fracture models 

Yuan Li, Timothy Davis, Adina Pusok, and Richard Katz

Dykes are fluid-filled fractures that transport melt within the lithosphere. Their presence impacts lithospheric stresses and hence the forces of plate tectonics. Accurate representation of dykes in geodynamic models is crucial for modelling the dynamics of rifting. Li et al. (2023) approximated dyking as plastic tensile failure in a two-phase continuum with a poro-viscoelastic—viscoplastic (poro-VEVP) rheology. Li et al. only partially validated this model approach, and hence the extent to which it approximates a natural fracture remains unclear. In this study, we extend the comparison between our continuum formulation and the widely accepted theory of Linear Elastic Fracture Mechanics (LEFM) to the case of a buoyancy-driven dyke (Roper and Lister, 2007). We achieve this through detailed consideration of the dynamics and energetics.

 

Comparing the dynamics of the continuum and LEFM models is challenging due to their differing assumptions and the limitations of finite-difference numerical solutions. The continuum model treats the liquid phase as porous flow, while the LEFM model assumes a lubricated channel flow inside of an open fracture. A drawback of numerical computations is that the grid size can exceed the dyke width. In fact, one shortcoming of the previous computational framework is that the dyke width can grow to several grid cells, which further complicates the comparison. To overcome these challenges, we adjust both models to have the same geometry and mechanics: (1) we incorporate in the continuum model an anisotropic permeability treatment based on plastic strain components; (2) we introduce an intermediate 'poro-fracture' model that is a modified LEFM model for porous channel flow.

 

Our results show that the poro-VEVP model converges to the LEFM poro-fracture model at a toughness value that is large relative to natural rock and at a propagation speed that is slow relative to the standard LEFM formulation. Firstly, we attribute the slow propagation speed in the continuum model to the high Darcy’s drag force, which can be improved by augmenting the permeability. Secondly, we show that plasticity in the continuum model relates quantitatively to the toughness in the fracture model. It is evidenced by the good agreement between the two models in stress field prediction and also the dyke porosity profiles when a specific toughness value is applied to the fracture model. Intriguingly, this toughness is derived from equating the total energy dissipation rate in the continuum model to the energy required to open a fracture, thereby establishing an energy-based connection between the two models.



References

Li, Y., Pusok, A., Davis, T., May, D., and Katz, R., (2023). Continuum approximation of dyking with a theory for poro-viscoelastic–viscoplastic deformation, Geophysical Journal International.

Roper, S.M. and Lister, J.R., (2007). Buoyancy-driven crack propagation:the limit of large fracture toughness. Journal of Fluid Mechanics.

How to cite: Li, Y., Davis, T., Pusok, A., and Katz, R.: Continuum models of dykes: a comparison to discrete fracture models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16931, https://doi.org/10.5194/egusphere-egu24-16931, 2024.

EGU24-18423 | ECS | Posters on site | GD10.1

Free surface methods applied to global scale numerical geodynamic models 

Timothy Gray, Taras Gerya, and Paul Tackley

The study of coupled Earth systems, and in particular the coupled interactions between the lithosphere, atmosphere, and biosphere, have received greater attention in recent years (Gerya et al. 2020). Interactions between these systems occur primarily at the surface, and are driven on the large scale by topographic and bathymetric evolution controlled by deep mantle processes. However, due to the large difference in length scales between the mantle and the surface, it is difficult to capture topographic evolution to a high degree of accuracy in existing global mantle convection models including a free surface boundary condition.

Global mantle convection models incorporating a free surface often employ a marker-in-cell technique with a layer of “sticky air” (i.e. material with the density of the air and sufficiently low viscosity, which is still much higher than that of real air) to characterise the surface. However, accurate topographic evolution using this method requires a high density of markers near the surface. This need for additional computational resources motivates alternative methods of tracking the interface between the air and rock layers, as is done frequently in existing multiphase fluid flow codes. We demonstrate the implementation of two such methods of modelling the surface. The first is a Lagrangian marker chain (or mesh in 3D models) which, when combined with an appropriate remeshing procedure, directly tracks the rock-air interface. The second is a volume of fluid approach adapted from the open source code gVOF using the unsplit volume of fluid library gVOF (López & Hernández, 2022).

We demonstrate toy models and benchmarks (based on those in Crameri, 2012) comparing the Lagrangian marker method and the volume of fluid methods as implemented in the global scale mantle convection code StagYY (Tackley, 2008). Models of global scale topography and evolution produced using StagYY may then be used as a tool for further studies on the coupling of mantle dynamics with modelling of the landscape, and the evolution of the atmosphere and biosphere. Initial applications include modelling hypsometric curves from global scale numerical models, and the tracking of sea level changes over time.

How to cite: Gray, T., Gerya, T., and Tackley, P.: Free surface methods applied to global scale numerical geodynamic models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18423, https://doi.org/10.5194/egusphere-egu24-18423, 2024.

EGU24-18807 | ECS | Orals | GD10.1

Thermal runaway and the challenges of rapid localization 

Arne Spang, Marcel Thielmann, Daniel Kiss, and Casper Pranger

Thermal runaway is a ductile weakening mechanism that describes the feedback loop of shear heating, temperature-dependent viscosity and localization. It has been linked to deep-focus earthquakes which are unlikely to be caused by brittle failure due to the large lithostatic pressure.

We present one- and two-dimensional (1D and 2D) numerical, thermomechanical models that investigate the occurrence, nucleation and temporal evolution of thermal runaway in a simple shear setting. The models are characterized by a visco-elastic rheology where viscous creep is accommodated with a composite rheology of diffusion and dislocation creep as well as low-temperature plasticity. We implement the model in the Julia programming language and utilize the pseudo-transient iterative method to solve this nonlinear system of equations. Graphical processing unit (GPU) computing (by making use of the package ParallelStencil.jl) allows us to achieve high resolution models in 2D.

Like brittle plasticity, thermal runaway presents the challenge of modeling a very thin shear band in a continuum mechanics approach with finite resolution. To address this issue, we tested two different regularization techniques to provide stable solutions and introduce a grid-independent shear zone width. A viscosity regularization and a second-order gradient regularization achieve similar results. Loading and heating time scales of thousands of years in combination with relaxation time scales on the order of seconds also require an adaptive time stepping scheme that can span 12 orders of magnitude. We achieve this by adjusting time steps to the maximum gradients in temperature and stress, and by dynamically rescaling variables during computation to minimize rounding errors. Combining the aforementioned techniques allows us to cover loading and heating on geological time scales as well as near-instantaneous stress drop and local temperature surge in one model framework.

2D experiments show that thermal runaway allows highly localized ductile ruptures to nucleate at small heterogeneities and propagate like brittle fractures. The ruptures accelerate during propagation and reach the highest velocities when two tips link up. Rupture trajectories are usually parallel to the direction of background deformation but bend in the vicinity of other ruptures to allow for a link up.

How to cite: Spang, A., Thielmann, M., Kiss, D., and Pranger, C.: Thermal runaway and the challenges of rapid localization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18807, https://doi.org/10.5194/egusphere-egu24-18807, 2024.

EGU24-19212 | ECS | Posters on site | GD10.1

3D Modelling of pegmatites migration at the onset of partial melting 

Mathis Bergogne, Laetitia Le Pourhiet, Ludovic Räss, Yury Podladchikov, Ivan Utkin, and Alexis Plunder

Pegmatites (and rare metal granites) are igneous rocks with a granitic composition, characterised by crystal growth dominated texture. They are often enriched in rare elements (such as Li, Cs, Be, Nb, Ta…) and offer valuable deposit of economic interest that belong to the list of critical raw material defined by the European commission. The aim is to use modeling to understand the formation of pegmatite, and especially the parameters that control the migration distance between their sources (granite, migmatites) and their level of emplacement.

We use a two phase flow finite difference code, in Julia, based on the porosity waves with compressible fluid in compressible medium, where the porosity is interpreted as melt [1,2], to model the magma migration inside migmatitics domes. To improve the yet existing codes, we implement temperature in our two phase flow formulation, it will be calculated from energy conservation to take into account the latent heat of the partial melting and the crystallisation. It will allow the to stop the experiments upon magma crystallisation. It will also be use to increase the viscosity of the melt while it cools down.

We here present the results of a preliminary 1D version of our model (without temperature). It shows that an increase in the ratio of matrix permeability over the fluid viscosity results in a greater distance travelled by the melt, for a constant number of time step. For a fluid viscosity of 104 Pa.s the increase of matrix (dynamic) permeability from 10-13 to 10-11 m-2 fasten the migration of the melt of a factor 2 and the travelled distance by a factor 1. When the energy will be implemented, we will compare the impact of matrix permeability, the fluid viscosity and the geothermal gradient on the height of the magmatic migration.

 

References:

[1] L. Räss, T. Duretz & Y.Y. Podladchikov (2020). https://doi.org/10.1093/gji/ggz239

[2] A. Plunder & al. (2022). https://doi.org/10.1016/j.lithos.2022.106652

How to cite: Bergogne, M., Le Pourhiet, L., Räss, L., Podladchikov, Y., Utkin, I., and Plunder, A.: 3D Modelling of pegmatites migration at the onset of partial melting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19212, https://doi.org/10.5194/egusphere-egu24-19212, 2024.

EGU24-19607 | ECS | Posters on site | GD10.1

Accelerating Geocomputing with Julia at Scale 

Samuel Omlin, Ludovic Räss, and Ivan Utkin

The ongoing digitalisation in geosciences, along with higher resolution data and more powerful computers, necessitates efficient workflows and tools for processing large amounts of data, modelling processes, and addressing new problems and challenges.

The Julia language offers an great basis for this by combining the benefits of a high-level language, such as ease of use and interactivity, with the features of a low-level language, including speed, efficiency, scalability, and native GPU support.

We will present recent efforts to accelerate geocomputing using Julia at scale. These efforts are supported by the PASC-funded GPU4GEO project, in collaboration with the Swiss National Supercomputing Centre. We will showcase the current HPC building blocks that we have developed, which enables geoscientists to write high-performance stencil codes that can scale from their laptops to the largest supercomputers. Additionally, we will demonstrate preliminary results on using automatic differentiation to perform inverse modelling. This allows us to efficiently constrain models with data.

Additionally, we discuss how these recent developments, along with future ones, will accelerate geocomputing and enable the education of the next generation of geoscientists.

How to cite: Omlin, S., Räss, L., and Utkin, I.: Accelerating Geocomputing with Julia at Scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19607, https://doi.org/10.5194/egusphere-egu24-19607, 2024.

EGU24-322 | ECS | Posters virtual | GD10.2

Joint long-period P and S velocity inversion for Earth's mantle based on deep learning 

Jun Su, Christine Houser, and John Hernlund

Many large-scale structures in the mantle have been proposed to explain seismic observations and constrain geodynamic models. While the geophysical community cannot agree on the morphology and nature(s) of large low shear velocity provinces (LLSVPs) due to the difference in approaches, decorrelated P and S velocity anomaly (dVno longer proportional to dVS), inherently associated with changes in composition and/or phase, can help examine geodynamic models and imply the thermal/chemical evolution of the mantle. To further apply the inference to finer structures and to improve the precision for quantitative mineral physical implications, it is necessary to build a new seismic dataset for P and S waves measured in a self-consistent manner.

In this study, we trained a phase-picking model using code modified from EQTransformer (Mousavi et al., 2020). Our training dataset includes 65,298 traces, where teleseismic P and S arrivals are manually picked at the long-period (~20 sec) onset. Based on the machine-learning architecture proven useful for seismicity at local to regional distances, we managed to reproduce the manual picking results by machine and extend the picking catalog for seismic data to the present. We also conduct tomographic inversion for the global mantle to obtain a three-dimensional velocity model for both P and S waves. The new model has a higher resolution, allowing interpretations to understand geodynamics better.

How to cite: Su, J., Houser, C., and Hernlund, J.: Joint long-period P and S velocity inversion for Earth's mantle based on deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-322, https://doi.org/10.5194/egusphere-egu24-322, 2024.

EGU24-557 | ECS | Orals | GD10.2

Temporal Record of Plume-Ridge Interaction in the North Atlantic: Interdisciplinary Insights from IODP Expedition 395C 

Callum Pearman, Nicky White, John Maclennan, and Chia-Yu Tien and the IODP Expedition 395 science party

The Icelandic mantle plume is regarded as one of the most significant mantle upwellings on Earth, however the dynamics of its interaction with the surrounding asthenosphere and mid-oceanic ridge systems in the North Atlantic are poorly understood. The clearest manifestation of this plume-ridge interaction are the Reykjanes V-shaped ridges and V-shaped troughs (VSRs and VSTs) that straddle the Reykjanes Ridge axis south of Iceland. These time-transgressive linear features are particularly well exposed by short-wavelength gravity data and are thought to represent the progressive sampling of thermal asthenospheric pulses that horizontally advect away from the Icelandic mantle plume conduit. The Reykjanes Ridge therefore acts as a ‘window-sampler’ into the temporal and spatial dynamics of plume outflow. International Ocean Discovery Program (IODP) Expedition 395C drilled into two VSR and VST pairs along a plate-spreading flow line approximately 600 km south of Iceland in summer 2021. Over 400 m of basalt was recovered, which represents a magmatic record over 15 Ma of plate spreading at a fixed distance from the mantle plume conduit. We present Nd isotopic analysis of recovered whole-rock that reveals a linear isotopic evolution from ƐNd of 7.5 to 10.5 over 14 Ma (n = 50), which implies that the ‘plume-like’ enriched component of the mantle source has been progressively diluted by mixing with depleted upper mantle material. This evolution occurred synchronously with the entire timeframe of VSR formation as defined by free-air gravity anomalies, and a long-wavelength increase in crustal thickness implied by wide-angle seismic experiments. It is therefore apparent that the dynamics of plume-ridge interaction are directly interlinked with changes in magmatism, structural tectonics and crustal production. Furthermore, major and trace elements of both whole-rock and glass samples have been measured, by multiple analytical techniques, revealing distinct compositions between and within boreholes. These observations can be understood in terms of temporal changes in the depth and degree of melting. In summary, petrological, petrophysical and geochemical analysis of this rock core in conjunction with consideration and modelling of wide-angle seismic surveys, gravity and bathymetric data can be used to develop a quantitative understanding of the dynamics of plume-ridge interaction, test hypotheses for the formation of VSRs, and constrain the temporal evolution of the North Atlantic mantle domain.

How to cite: Pearman, C., White, N., Maclennan, J., and Tien, C.-Y. and the IODP Expedition 395 science party: Temporal Record of Plume-Ridge Interaction in the North Atlantic: Interdisciplinary Insights from IODP Expedition 395C, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-557, https://doi.org/10.5194/egusphere-egu24-557, 2024.

EGU24-1275 | ECS | Posters on site | GD10.2

Enhanced subduction flux during the assembly of Pangea recorded by global intracontinental magmatism 

Qian Chen, He Liu, Andrea Giuliani, Tim Johnson, Luc Doucet, Lipeng Zhang, and Weidong Sun

Plate tectonics drives the compositional diversity of Earth’s convecting mantle through subduction of lithosphere. In this context, the role of evolving global geodynamics and plate (re)organisation on the spatial and temporal distribution of compositional heterogeneities in the convecting mantle is poorly understood. We test the hypothesis that an increase in the cumulative length of subduction zones associated with supercontinent assembly triggered geochemical enrichment of the convective mantle globally, in particular since the emergence of protracted, cold, deep subduction in the late Neoproterozoic. We compiled the trace element and Nd isotopic compositions of intracontinental basalts formed over the last billion years (1000 Myr).  After careful filtering to eliminate samples with evidence for crustal contamination, the data show that intracontinental basalts formed before 300 Ma exhibit supra-chondritic initial 144Nd/143Nd values. Those with sub-chondritic initial 144Nd/143Nd values become common only after 300 Ma, broadly coeval with the global appearance of kimberlites with geochemically enriched isotopic signatures. We attribute these step-changes in the sources of intraplate magmatism to a rapid increase in the supply of deeply subducted lithosphere due to increased peri-continental subduction during the assembly of Pangea.

How to cite: Chen, Q., Liu, H., Giuliani, A., Johnson, T., Doucet, L., Zhang, L., and Sun, W.: Enhanced subduction flux during the assembly of Pangea recorded by global intracontinental magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1275, https://doi.org/10.5194/egusphere-egu24-1275, 2024.

EGU24-2139 | ECS | Orals | GD10.2

Geodynamic-mineralogical predictions of mantle transition zone seismic structure 

Isabel Papanagnou, Bernhard S. A. Schuberth, Christine Thomas, and Hans-Peter Bunge

A main objective in geodynamics is to create models that provide quantitative information to other Earth science disciplines. In order to assess the validity of the underlying assumptions and chosen input parameters related to different geodynamic hypotheses, it is crucial to test these models against observations. In this, thermodynamic models of mantle mineralogy represent an essential tool. On the one hand, they enable the linking of temperature fields from mantle circulation models (MCMs) to seismic observations. On the other hand, they provide critical information on material behaviour in response to changing temperature and pressure conditions that occur over time within such mantle convection simulations. Some of the most interesting aspects in this context relate to mineral phase transitions and associated dynamic effects on mantle flow.

The mantle transition zone (TZ) in particular is expected to influence vertical mass flow between upper and lower mantle as it hosts a complex set of mineral phase transitions as well as an increase in viscosity with depth. Still, neither its seismic structure nor the associated dynamic effects have conclusively been constrained. The seismic discontinuities at around 410 and 660 km depth (‘410’ and ‘660’) have classically been related to phase transitions between olivine polymorphs, the pressure of which is modulated by lateral temperature variations. The resulting topography of these discontinuities is seismically visible and can thus potentially provide insight on temperature and phase composition at depth. Besides the olivine phase changes, the disassociation of garnet may additionally impact the 660 at higher temperatures. However, the volume of material affected by this garnet transition and its dynamic implications have not yet been quantified.

Here, we present hypothetical realizations of TZ seismic structure and major discontinuities based on the 3-D temperature field of a published MCM for a range of relevant mineralogies, including pyrolite and mechanical mixtures (MM). Systematic analysis of these models provides a framework for dynamically informed interpretations of seismic observations and gives insights into the potential dynamic behaviour of the TZ. Using our geodynamic-mineralogical approach we can identify which phase transitions induce specific topographic features of 410 and 660 and quantify their relative impact. Areal proportions of the garnet transition at the 660 are ∼3 and ∼1 per cent for pyrolite and MM, respectively. This proportion could be significantly higher (up to ∼39 per cent) in a hotter mantle for pyrolite, but remains low (< 2 per cent) for MM. In pyrolite, both slabs and plumes are found to depress the 660 —with average deflections of 14 and 6 km, respectively— due to the influence of garnet at high temperatures indicating its complex dynamic effects on mantle upwellings. Pronounced differences in model characteristics for pyrolite and MM, particularly their relative garnet proportions and associated topography features, could serve to discriminate between the two scenarios in Earth.

How to cite: Papanagnou, I., Schuberth, B. S. A., Thomas, C., and Bunge, H.-P.: Geodynamic-mineralogical predictions of mantle transition zone seismic structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2139, https://doi.org/10.5194/egusphere-egu24-2139, 2024.

The temperature at Earth’s core-mantle boundary (CMB) is a key parameter to understand the dynamics of our planet’s interior. However, it remains poorly known, with current estimate ranging from about 3000 K to 4500 K and more. Here, I introduce a new approach based on joint measurements of shear-wave velocity, VS, and quality factor, QS, in the lowermost mantle.  Lateral changes in both VS and QS above the CMB provide constraints on lateral temperature anomalies with respect to a reference temperature, Tref, defined as the average temperature in the layer immediately above the CMB. The request that, at a given location, temperature anomalies inferred independently from VS and QS should be equal gives a constraint on Tref. Correcting Tref for radial adiabatic and super-adiabatic increases in temperature gives an estimate of the CMB temperature, TCMB. This approach further relies on the presence of post-perovskite (pPv) phase in the deep mantle and on the fact that VS-anomalies are affected by the geographical distribution of phis phase. As a result, the inferred Tref is linked to the temperature TpPv at which the transition from bridgmanite to pPv occurs close to the CMB. A preliminary application to VS and QS measured beneath Central America and the Northern Pacific suggest that for TpPv = 3500 K, TCMB lies in the range 3470-3880 K with a 95 % likelihood. Additional measurements in various regions, together with a better knowledge of TpPv, are needed to determine a precise value of TCMB with this method.

How to cite: Deschamps, F.: Estimating the temperature at the core-mantle boundary from measurements of shear-wave velocity and seismic attenuation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2497, https://doi.org/10.5194/egusphere-egu24-2497, 2024.

The study of the Earth’s interior has been traditionally based on seismological and geodynamic modelling, the first one providing important information about its present-day structure, composition and state, while the second about its dynamics and compositional evolution. Seismological and geodynamical modelling are very often conducted independently, which creates mechanical and geometrical inconsistencies across the models, hampers the interpretation of seismic observations in terms of geodynamic processes and enhances the non-uniqueness of geodynamic model predictions.

An alternative approach is combining computational seismology and geodynamics with mineral physics, which provides a comprehensive understanding of the Earth's interior processes, seismic behavior, and material properties. In this multidisciplinary methodology, the geodynamic flow calculations are used to compute the rock elastic properties as a function of strain-induced mantle fabrics through micro-mechanical models of crystal aggregate deformation, and of the local P-T conditions with thermodynamically self-consistent models of mantle mineralogy. The obtained seismic mantle structure is then used for seismological synthetics, such that specific hypotheses on mantle dynamics can be tested directly against seismic data. Examples from the South American, North American, and the Central Mediterranean convergent margins will be discussed.

Finally, I will introduce ECOMAN, a recently developed, open-source software package that is intended to overcome the computationally intensive nature of this approach and the lack of a dedicated and comprehensive computational framework for modelling strain-/stress-induced rock fabrics and testing the effects of the resulting mechanical (elastic and viscous) anisotropy on seismic imaging and mantle convection.

How to cite: Faccenda, M.: Constraining Mantle Convection Patterns by Joint Geodynamic and Seismological Modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5439, https://doi.org/10.5194/egusphere-egu24-5439, 2024.

Mantle convection causes the most important contribution to the geoid and dynamic topography. With high resolution tomography models and numerical simulation methods solving the governing equations of mantle convection, the model geoid can fit well compared to observation. However, if wave speed variations are converted to density variations assuming both are due to temperature variation in the entire mantle, there is still a large discrepancy between the present dynamic topography predicted by mantle flow and that induced from observations: Especially large negative topography is predicted in cratons, contrary to observations. In order to improve the fit of model dynamic topography compared to observations, chemical density anomaly in earth’s lithosphere need to be included. In this study, we will combine these with lateral viscosity structure and study the effect on model dynamic topography and geoid, and investigate which density models would yield a good fit. In the sublithospheric mantle, under the assumption that the density anomalies are thermally induced from temperature variation in the mantle, we use temperature-dependent viscosity. We also include thermo-chemical density anomalies in the Large low-shear-velocity provinces (LLSVPs) in the lowermost mantle to compute their effect on the model geoid and dynamic topography. Our overall objective is a better constraint on the Earth’s interior structure, by achieving good fits of both dynamic topography and geoid to their observations, to provide as a good reference for the Earth’s study.

How to cite: Cui, R., Steinberger, B., and Fang, J.: Modeling geoid and dynamic topography from tomography-based thermo-chemical mantle convection with temperature- and depth-dependent viscosity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5452, https://doi.org/10.5194/egusphere-egu24-5452, 2024.

The effects of pressure and temperature on the phase transformation of olivine to wadsleyite and then ringwoodite within the mantle is well understood. However, the extent to which stress affects this phase transformation is not clear. Understanding how stress influences the kinetics of the olivine to spinel phase transformation and the mechanism in which it does so at grain scale, will have broader implications for mantle dynamics. Deformation experiments using Mg2GeO4 have been used as an approximate analogue for fayalite as it transforms from olivine to ringwoodite at lower pressures and temperatures rather than the conditions found at d410 (Vaughan, 1981). This enables the use of larger samples than possible for the silicate system, and allows for extensive microstructural investigations. This session aims to discuss high pressure deformation experiments on Mg2GeO4 (olivine) during the transformation to ringwoodite using a Griggs-type, solid medium, deformation apparatus. These experiments expand on (Vaughan 1984) which linked kinetics of the reaction in a model that matches other stressed reactions in the mantle (Wheeler, 2020). Experiments were conducted at a range of confining pressures 0.8 - 1.2 GPa at a fixed temperature of 900 °C and a strain rate of 10-6 /s. The four samples were deformed to finite strains ranging from 10 to 45 %. The aim of the conditions chosen was to apply varying amounts of differential stress and therefore differing the σ1 stress on the sample as a whole. Samples were characterised down to the level of individual interfaces using Electron Backscatter Diffraction (EBSD) to understand the physical mechanism of the reaction and the kinetics that govern it.

How to cite: Akhtar-Lewis, S.: Effects of Stress on the Olivine–Spinel Phase Transformation in the Mantle: Griggs-Type Deformation Experiments Using Mg2GeO4 as an Analogue., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6130, https://doi.org/10.5194/egusphere-egu24-6130, 2024.

EGU24-6325 | ECS | Posters on site | GD10.2

Assessment of geodynamic predictions with surface-wave tomography in the Pacific upper mantle accounting for full 3D resolution and robust uncertainties. 

Franck Latallerie, Paula Koelemeijer, Andrew Walker, James Panton, and Huw Davies

Surface-waves carry important information about upper mantle structure, especially in poorly sampled areas such as oceanic regions. Surface-wave tomography models can be used to assess geodynamic simulations by comparing observed and predicted structures. However, surface-wave data are noisy and sparse resulting in tomography models being noisy and blurred pictures of the Earth's structure. As a result, tomography models can hardly be compared directly to geodynamic predictions which aim to predict the true structure of the Earth. Although challenging, assessing geodynamic simulations with surface-wave tomography requires accounting for full 3D resolution and robust uncertainties.

In this study, we present a workflow to quantitatively assess geodynamic model predictions using surface-wave tomography. Specifically, we measure dispersion data for paths crossing the Pacific ocean and estimate data uncertainties including measurement and theoretical errors. We use a finite-frequency forward theory to linearly relate data to the three-dimensional Vsv structure in the upper mantle. Subsequently, we apply the SOLA (Backus-Gilbert-style) method in 3D to control and produce the full three-dimensional resolution and robust model uncertainties together with the Vsv tomography model. Equipped with this, we assess predictions for the Pacific upper mantle from a set of geodynamic simulations based on different input parameters.

Preliminary results highlight physical parameters of mantle convection influencing significantly the misfit between observed and predicted structure in the Pacific upper mantle; and, for quantitative parameters, inform us on values that provide the best fits.

How to cite: Latallerie, F., Koelemeijer, P., Walker, A., Panton, J., and Davies, H.: Assessment of geodynamic predictions with surface-wave tomography in the Pacific upper mantle accounting for full 3D resolution and robust uncertainties., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6325, https://doi.org/10.5194/egusphere-egu24-6325, 2024.

EGU24-6554 | ECS | Posters virtual | GD10.2

Mid-mantle imaging through a reverberant transition zone: A CRISP-RF approach 

Steve Carr and Tolulope Olugboji

On a planet that dissipates heat through whole mantle convection, no sharp changes in elastic properties are expected in the mid-mantle: ~750-1300 km. Yet, a growing number of seismic studies continue to document evidence of discontinuities across these depths. Compared to the upper mantle, the global prevalence and causal origins of such features remain relatively enigmatic. Here, we investigate mid-mantle layering beneath two large seismic arrays (US and Alaska) using high-resolution Ps-converted waves. The challenge is that top-side reflections (reverberations) from the mantle transition zone interfere with and contaminate desired mid-mantle conversions and make their interpretation difficult. In the past, the slowness slant stack (vespagram) approach has been used. We extend the resolution of this stacking scheme using a newly developed sparsity-promoting, non-linear, CRISP-RF technique (Clean Receiver function Imaging with Sparse Radon Filters). Preliminary results suggest that CRISP-RF can isolate high-frequency (0.5Hz) mid-mantle body wave conversions buried within transition zone reverberations. With our filtered Ps-RFs and machine learning, we will present tighter constraints on mid-mantle layering (depth, sharpness, spatial variation)  exploring important implications for its origin.  

How to cite: Carr, S. and Olugboji, T.: Mid-mantle imaging through a reverberant transition zone: A CRISP-RF approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6554, https://doi.org/10.5194/egusphere-egu24-6554, 2024.

EGU24-7341 | Orals | GD10.2 | Highlight

Chocolate in the marble cake: the fate of eclogite and pyroxenite during mantle convection and melting 

Romain Tilhac, Carlos Garrido, Stephan König, and María Isabel Varas-Reus

The presence of lithologies derived from recycled oceanic lithosphere in the convective mantle is an expected consequence of subduction. Geochemical studies have provided compelling evidence of the contribution of recycled eclogite and pyroxenite in the mantle source of oceanic basalts, particularly ocean island basalts (OIB). However, identifying their signatures in mid-ocean ridge basalts (MORB) is challenging due to more intricate melting and mixing processes. Furthermore, the use of elemental and isotopic proxies of different geochemical affinities provides contrasting pictures on their source heterogeneity. Understanding the role of pyroxenite and eclogite during partial melting bears critical information regarding the fate of recycled lithospheric material, the dynamics and timescales of mantle convection and the thermal regime of mid-ocean ridges.

We present a numerical approach based on the thermodynamically constrained Mixed-Source Melting model (MSM3), enabling a coherent assessment of the role of recycled lithologies. Within a comprehensive plate tectonic cycle, the MSM3 model simulates the two-stage recycling of eclogites derived from subducted oceanic crust in a marble-cake mantle.

  • Stage 1 corresponds to the formation of secondary pyroxenite from the hybridization of high-degree eclogite-derived melts interacting at high pressure with peridotite in the convective mantle.
  • Stage 2 corresponds to the formation of MORB in a triangular melting regime from the adiabatic decompression melting of a 3-lithology source of peridotite, pyroxenite and residual eclogite obtained from stage 1.

To tackle the diversity of geochemical proxies applied to oceanic basalts, MSM3 recovers melt and residual compositions in terms of major elements and sulfur, as well as any lithophile and chalcophile trace elements and isotope systems. This is achieved thanks to the integration of melting models with pMELTS calculations constrained by a thermodynamic parametrization specific to pyroxene-rich lithologies (Melt-PX), calculations of sulfur concentration at sulfide saturation (SCSS), and composition-dependent partition coefficients. To take into account the inherent variability of most parameters (e.g., potential temperature, source proportions, sulfur contents) and avoid arbitrary choices, we use a stochastic approach by running the MSM3 model as an inversion based on adaptative Monte Carlo simulations.

We here demonstrate the flexibility of this approach, even for systems controlled by sulfides. We show that, over potential temperatures ranging between 1280 and 1420 ºC, the generation of 0-10% of pyroxenitic heterogeneities from subducted eclogite, and the contribution of both eclogite and pyroxenite in the melting regime of MORB produce 20-95 % of the melts aggregated at the ridge. Such proportions correspond to up to 30 times the proportion of these lithologies in the mantle. This over-contribution is controlled by the melting regime properties and is enhanced or attenuated by the mass balance specific to the elements and isotope systems considered (concentrations, partitioning behavior, modal evolution of the main host minerals in the different lithologies). In other words, the more-fusible pyroxenite and eclogite act as chocolate in the marble-cake mantle, giving the dominant flavor to its melting products, although different geochemical proxies may "taste" it differently.

How to cite: Tilhac, R., Garrido, C., König, S., and Varas-Reus, M. I.: Chocolate in the marble cake: the fate of eclogite and pyroxenite during mantle convection and melting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7341, https://doi.org/10.5194/egusphere-egu24-7341, 2024.

EGU24-8992 | Posters on site | GD10.2

Imaging deep subducted lithosphere beneath the Indian Ocean with seismic source array recordings 

Christine Thomas and Björn Holger Heyn

The D" region, located just above the core-mantle boundary (CMB), is a geologically interesting region that has been imaged using both tomographic and reflection techniques. However, reflection studies often rely on array analysis techniques, and the lack of suitable seismic arrays in the oceans has left large areas of D" unmapped. One notable area, that is currently sparsely sampled, is beneath the Indian Ocean, where ancient subducted lithosphere has been imaged near the CMB in global tomography studies. We take advantage of the long-running history of five GEOSCOPE stations located in the western Indian Ocean and Antarctica, to investigate the possibility of using source arrays to detect P-wave reflections from the discontinuity above the D" layer. Despite restricting the selected earthquakes around Indonesia to a 120 km depth range and implementing several source normalization techniques, source-array stacks (i.e., source vespagrams) were difficult to interpret. We infer that this complication arises from differing earthquake depths, violating the plane wave assumption made when constructing these stacks. Therefore, we extend our method to a source-array scatter imaging method, which we call source migration, that does not rely on travel-times calculated for a plane wave. Using this technique in conjunction with source normalization, we found clear evidence for a D" P-wave reflector at four of the six GEOSCOPE stations considered in the study. The depth of the reflector for our imaged region varies between 190 km above the CMB beneath the Great Australian Bight and 220 to 270 km beneath the Indian Ocean west of Australia. Our determined depth in the northern portion of our study area is consistent with previous studies of D" depths using S-waves. We suggest that our D" reflections are the result of the previously imaged subducted lithosphere in the region and find that this lithosphere likely thins to the southeast. Additionally, our work more broadly indicates that the long-running history of single global seismic stations combined with source array techniques may be utilized to compliment and extend previous work imaging D" using conventional receiver-array techniques.

How to cite: Thomas, C. and Heyn, B. H.: Imaging deep subducted lithosphere beneath the Indian Ocean with seismic source array recordings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8992, https://doi.org/10.5194/egusphere-egu24-8992, 2024.

EGU24-10944 | ECS | Orals | GD10.2

Constraining global mantle circulation models with global seismic observations 

William Sturgeon, Ana M.G. Ferreira, James Panton, and J. Huw Davies

In order to improve our understanding of mantle flow, we require a joint collaboration between all fields of Earth Sciences. Seismic tomography provides key information on the current state of the mantle and therefore can constrain mantle circulation models. We present high-resolution (degree-60) global models of frequency-dependent phase and group velocity measurements from huge a huge dataset of ~47 million Rayleigh and Love waves. These include fundamental mode measurements, which are sensitive to the uppermost mantle and up to 6th overtone, adding sensitivity to the transition zone, covering a period range of 16-375 s. We also present global models of mantle attenuation (degree-20), made from ~10 million Rayleigh wave amplitude measurements, including fundamental and up to 4th overtone measurements (35-275 s). All seismic maps presented also have associated uncertainty maps, which are essential for robust interpretation but also for multidisciplinary interpretations of mantle circulation models.

We constrain 3D mantle circulation models, known as TERRA models, at the present day. In order to do this, we construct 1D profiles of velocities and density from a suite of TERRA models on a 2x2 degree grid. Forward modelling of each 1D profile using MINEOS provides global predictions of seismic observables at all seismic wave periods, including phase velocity and group velocity. A misfit can then be calculated between the seismic models and predictions from the suite of TERRA models. This provides constraints on which TERRA models are most Earth-like, which will improve our understanding of mantle flow.

How to cite: Sturgeon, W., Ferreira, A. M. G., Panton, J., and Davies, J. H.: Constraining global mantle circulation models with global seismic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10944, https://doi.org/10.5194/egusphere-egu24-10944, 2024.

EGU24-11588 | ECS | Posters on site | GD10.2

Modelling the global geodynamic and seismological consequences of different phase boundary morphologies.  

Gwynfor Morgan, J. Huw Davies, Bob Myhill, James Wookey, and James Panton

Throughout Earth’s mantle, several significant phase transitions occur, with the Ol→Wd and Rw→Brm+Pc reactions (exothermic and endothermic respectively) producing large discontinuities in Earth’s seismic velocity structure at 410 and 660km depth respectively (‘410’ & ‘660’). The equilibrium depth of these reactions is sensitive to temperature, and the resulting topography has been observed with various seismic phases. Numerical modelling from the 1980s onwards has suggested that the topography on endothermic phase transitions can stagnate downwellings and even layer mantle convection for extreme Clapeyron slopes or density changes. The thermodynamic properties of the post-spinel reaction make it unlikely that slabs would stagnate due to effects associated with phase transitions. At cooler temperatures the post-spinel reaction splits into two reactions (Rw + Ak → Ak + Pc → Brm + Pc) which seems to explain well aspects of the observed topography of the ‘660’ discontinuity. It has been suggested that this second reaction (which has a more extreme Clapeyron slope than the post-spinel reaction) could stagnate downwellings. Recently, Ishii et al (2023) suggested that the post-garnet reaction (Gt → Brm + Cor [+ St]) is in fact univariant, producing a sharp reaction that is endothermic for cooler temperatures and exothermic at higher temperatures – and that this may contribute to slab stagnation. Here, we test these slab stagnation mechanisms using realistic mineral physics and whole-mantle convection models (MCMs).

The lack of anti-correlation between the topography of the ‘410’ and ‘660’ discontinuities does not match simple theory if they are controlled solely by temperature variations across the post-olivine and post-spinel reactions respectively. Previous work has shown that the calculated topography on the discontinuities can be markedly different for various single-composition mantles generated from MCMs (Papanagnou et al, 2022). Here we will explore the impact of laterally varying chemistry generated in thermochemical MCMs on global discontinuity topography.

How to cite: Morgan, G., Davies, J. H., Myhill, B., Wookey, J., and Panton, J.: Modelling the global geodynamic and seismological consequences of different phase boundary morphologies. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11588, https://doi.org/10.5194/egusphere-egu24-11588, 2024.

EGU24-11790 | Orals | GD10.2

Thermo-compositional model of the South African cratonic mantle obtained from seismic and gravity data 

Magdala Tesauro, Mikhail Kaban, and Mohammad Youssof

Xenolith data reveal lateral and vertical compositional variations of the upper mantle of the Precambrian cratons, indicating a different degree of refertilization with respect to the most depleted mantle in iron components, characterizing the oldest Archean cratons. The South African cratonic region is composed of the Kaapvaal and Zimbabwe craton, both of Archean age, having deep and fast lithospheric roots, which are likely depleted in heavy constituents. In contrast, there exist regions, such as the Limpopo belt, a terrane that was trapped between the Kaapvaal and Zimbabwe cratons during their collision (2.6–2.7 Ga), and Bushveld Complex, an area characterized by intraplate magmatism occurred 2.05 Ga, whose negative velocity anomalies in the upper mantle, indicate a more fertile composition due to metasomatism. To unravel the origin of these anomalies and link them to the tectonic history of the area, we apply an integrative technique based on a joint interpretation of the seismic tomography and gravity data, which can discern temperature and compositional variations. To this aim, we combine the global surface seismic tomography model [1] with the embedded regional model [2], derived from teleseismic tomographic inversion of the S-body wave dataset recorded by the Southern African Seismic Experiment. The combined seismic model is inverted for temperature, assuming an initial composition, representative of a refertilized upper mantle [3], using a mineral physics approach [4]. The composition and temperature of the upper mantle are iteratively changed, increasing progressively the amount of iron depletion, to fit the residual density, obtained from the joint inversion of the residual gravity and residual topography. The great advantage of using both the gravity field and residual topography lies in their different dependence on the distribution of density heterogeneities (depth and size). In a second type of inversion we included the GOCE gravity gradient [5]. The obtained results show that the most depleted lithosphere is confined at depth lower than 100 km, generating a temperature higher than ~200, with respect to that of a refertilized lithosphere. The Southeastern Terrane of the Kaapval craton are characterized by thicker and more depleted cratonic roots than the Zimbawe craton. The presence of a depleted mantle below the cratonic crust may indicate that the crust and mantle have been connected since the craton formation. These results, related to the different structures and properties of the upper mantle, improve our understanding of the evolution of the South African cratonic lithosphere.

References

[1] Schaeffer and Lebedev, 2013. https://doi.org/10.1093/gji/ggt095

[2] Youssof et al., 2015. http://dx.doi.org/10.1016/j.epsl.2015.01.034

[3] Griffin et al., 2004. doi:10.1016/j.chemgeo.2004.04.007

[4] Conolly, 2005. doi:10.1016/j.epsl.2005.04.033

[5] Kaban et al., 2022. doi.org/10.1007/s00024-021-02925-6

How to cite: Tesauro, M., Kaban, M., and Youssof, M.: Thermo-compositional model of the South African cratonic mantle obtained from seismic and gravity data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11790, https://doi.org/10.5194/egusphere-egu24-11790, 2024.

EGU24-12417 | Posters on site | GD10.2

Quantifying mantle mixing through configurational Entropy 

Cedric Thieulot, Erik van der Wiel, and Douwe van Hinsbergen

Geodynamic models of mantle convection provide a powerful tool to obtain insights into the structure and composition of the Earth’s mantle that resulted from a long history of differentiating and mixing. Comparing such models with geophysical and geochemical observations is challenging as these datasets often sample entirely different temporal and spatial scales. Here, we explore the use of configurational entropy, based on tracer and compositional distribution on a global and local scale. We show means to calculate configurational entropy in a 2D annulus and find that these calculations may be used to quantitatively compare long-term geodynamic models with each other. The entropy may be used to analyze, with a single measure, the mixed state of the mantle as a whole and may also be useful to validate numerical models against local anomalies in the mantle that may be inferred from seismological or geochemical observations.

How to cite: Thieulot, C., van der Wiel, E., and van Hinsbergen, D.: Quantifying mantle mixing through configurational Entropy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12417, https://doi.org/10.5194/egusphere-egu24-12417, 2024.

EGU24-14060 | ECS | Orals | GD10.2 | Highlight

Constraining LLSVPs initial conditions and heating scenarios from simulations of mantle convection with heterogeneous thermal conductivity 

Joshua Guerrero, Frédéric Deschamps, Wen-Pin Hsieh, and Paul Tackley

New insights from models of thermo-chemical mantle convection featuring heterogeneous thermal conductivity indicate that heat-producing element (HPE) enrichment in large low shear velocity provinces (LLSVPs) significantly impacts the long-term stability of these regions. Because the internal heating rate was more significant in the past, thermal conductivity's influence on thermal buoyancy (and bulk erosion) must have also been more substantial. As a consequence, the initial volume of the LLSVPs may have been significantly larger than their present-day volume. In numerical models, the evolution and stability of LLSVPs are often initiated by considering a dense and uniformly distributed layer on top of the core-mantle boundary. From energy balance calculations, a thin layer of LLSVP material (small mantle volume fraction) supports more HPE enrichment than a thicker layer (larger mantle volume fraction) to maintain the mantle's heat budget. For example, an initial layer thickness of 160km (~3% mantle volume) implies present-day HPE enrichment factors up to ~70 times the ambient mantle heating rate. This should be compared with more conservative factors of 10 to 20 for similar dense layer thicknesses employed in previous studies of thermochemical pile stability. Thus, HPE enrichment may have been significantly underestimated in earlier models of LLSVP evolution. Conversely, and assuming that LLSVPs formed from a much larger reservoir, HPE enrichment may be overestimated based on the present-day LLSVP volume. Our study considers LLSVPs with a primordial geochemical reservoir composition (consistent with an undegassed 4He/3He signature and HPE enrichment). We examine models of thermo-chemical mantle convection models with time-dependent internal heating rates and HPE enrichment (implied by the initial dense layer thicknesses). In this new context, we re-examine, in particular, the impact of a fully heterogeneous lattice thermal conductivity (derived from conductivity measurements of upper and lower mantle minerals). Furthermore, in light of recent developments with radiative conductivity, we also examine the added effect of a strongly temperature-dependent radiative conductivity component on the stability of LLSVPs. Using LLSVPs' present-day volume and core-mantle boundary coverage as a constraint, we recover potential initial conditions, heating scenarios, and thermal conductivity for an Earth-like model.

How to cite: Guerrero, J., Deschamps, F., Hsieh, W.-P., and Tackley, P.: Constraining LLSVPs initial conditions and heating scenarios from simulations of mantle convection with heterogeneous thermal conductivity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14060, https://doi.org/10.5194/egusphere-egu24-14060, 2024.

EGU24-14786 | ECS | Orals | GD10.2

Global full-waveform inversion reveals previously undetected positive wave speed anomalies beneath the Pacific Ocean 

Thomas Schouten, Lars Gebraad, Sebastian Noe, Anna Gülcher, Sölvi Thrastarson, Dirk-Philip van Herwaarden, and Andreas Fichtner

Seismic tomography, a critical tool for studying Earth's interior structure and dynamics, has revealed positive seismic wave speed anomalies in the mantle that are commonly interpreted as slabs, the remnants of subducted lithosphere. However, classical travel-time tomography relies on the inversion of travel times of a few easily identifiable body wave phases along ray paths or volumetric sensitivity kernels, which is strongly dependent on the geometry of seismic sources and receivers. Since both of these are primarily clustered on modern convergent plate boundaries, the resulting tomographic resolution is highly variable across the mantle. Full-waveform inversion (FWI) attempts to reduce this dependence by fitting whole seismograms, thereby including many reflected and refracted body wave phases to enhance the volumetric sensitivity of the inversion.

Here, we analyse a new global tomographic model constructed using FWI. The mantle structure imaged in this model reveals significantly more positive seismic wave speed anomalies in the mantle when compared to travel-time tomography, particularly in regions with low seismic activity and limited station coverage. Notably, FWI detects positive wave speed anomalies with slab-like morphologies at ~1000 km depth beneath the Pacific Ocean that fall outside the coverage of classical travel-time tomography. We demonstrate the sensitivity of FWI to wave speed anomalies below the western Pacific using forward wavefield modelling. Importantly, we find that these newly imaged positive wave speed anomalies do not correspond to reconstructed subduction zones in existing global plate reconstructions.

Our work challenges the widespread assumption that positive wave speed anomalies (exclusively) represent subducted slabs, highlighting potential gaps in either global plate reconstructions or the current understanding of the nature of seismic anomalies in the mantle.

How to cite: Schouten, T., Gebraad, L., Noe, S., Gülcher, A., Thrastarson, S., van Herwaarden, D.-P., and Fichtner, A.: Global full-waveform inversion reveals previously undetected positive wave speed anomalies beneath the Pacific Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14786, https://doi.org/10.5194/egusphere-egu24-14786, 2024.

Subducted slabs provide the primary driving force for mantle convection, and the slab strength directly controls the transfer of the forces between the slab and the lithospheric plates at the surface. The analysis of subducted slab viscosity structure has been one of the main concerns in geodynamics over the past few decades. Previous studies, using the topography, gravity or geoid as crucial observations, have provided some constraints on the viscosity of subduction plates (Bessat et al., 2020; Hager, 1984; Moresi & Gurnis, 1996). However, slab viscosity constrained by surface topography and gravity data is significantly lower than that suggested by mineral physics laboratory experiments. It is unclear whether the free-slip top boundary condition used in many previous studies affects the inverted slab viscosity with gravity or geoid data.

In this study, we develop 2-D free-surface subduction models that can generate realistic topography by a modified "sticky-air" method using Underworld2 software (Moresi et al., 2019), and we compare the computed topography and gravity in our free-surface subduction models with observations to constrain the subducting slab viscosity. We investigate the influence of slab viscosity at the bending region and below the bending region on the topography and the gravity, respectively. Our model results support relatively weak slabs (20-120 times more viscous than the upper mantle) at the bending region, consistent with previous studies with a free-slip top boundary. The viscosity of the slab below the bending region barely affects the surface topography and gravity field, and both strong and weak slabs fit the observed topography and gravity field, suggesting that extra independent observations are needed to constrain the deep slab viscosity. Besides, in this study, we also find the comprehensive relations between subduction interface viscosity, surface topography and gravity anomaly, and trench motion. Models with trench advance have significantly low topography and gravity above the volcanic arc, contradicting subduction zone observations. Together with present trench motion observations and previous studies, we support the idea that the trench retreats under normal single-slab subduction conditions.

 

Bessat, A., Duretz, T., Hetényi, G., Pilet, S., & Schmalholz, S. M. (2020). Stress and deformation mechanisms at a subduction zone: insights from 2-D thermomechanical numerical modelling. Geophysical Journal International, 221(3), 1605–1625. https://doi.org/10.1093/gji/ggaa092

Hager, B. H. (1984). Subducted slabs and the geoid: Constraints on mantle rheology and flow. Journal of Geophysical Research: Solid Earth, 89(B7), 6003–6015. https://doi.org/10.1029/JB089iB07p06003

Moresi, L., & Gurnis, M. (1996). Constraints on the lateral strength of slabs from three-dimensional dynamic flow models. Earth and Planetary Science Letters, 138(1–4), 15–28. https://doi.org/10.1016/0012-821X(95)00221-W

Moresi, L., Giordani, J., Mansour, J., Kaluza, O., Beucher, R., Farrington, R., et al. (2019, February 18). underworldcode/underworld2: v2.7.1b (Version v2.7.1b). Zenodo. https://doi.org/10.5281/ZENODO.2572036

How to cite: Deng, L. and Yang, T.: Constraining subducting slab viscosity with topography and gravity fields in free-surface mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16119, https://doi.org/10.5194/egusphere-egu24-16119, 2024.

EGU24-16771 | ECS | Posters on site | GD10.2

Trace element and bulk chemistry of plumes and ridges in geodynamic simulations 

James Panton, Huw Davies, and Paul Beguelin

Volumetrically, the most important magmatic source on Earth is beneath mid-ocean ridges, from which mid-ocean ridge basalts (MORBs) are sourced. Second to this is plume related magmatism, the source for ocean-island basalts (OIBs). Decades of geochemical analysis have discerned that MORBs exhibit low isotopic variation, which is interpreted to mean that their source is globally homogeneous at an ocean basin (and possibly global) scale. OIBs, however, exhibit strong isotopic variation not just spatially, but even temporally, indicating a compositionally heterogenous source region. Global scale numerical geodynamic models, driven by reconstructed plate motions, generate both plume and ridge structures at which melting occurs, similar to Earth, however it is not known how well dynamic models can re-create the first-order observation that ridge lavas are typically homogenous compared to plume lavas.

Using the 3D spherical mantle convection code, TERRA, constrained by plate motion reconstructions spanning 1Gyr of Earth’s history, ridge and plume structures are simultaneously generated. The location of ridges is known from the input plate reconstruction model, while plumes are identified using the simulated temperature and radial velocity fields and a combination of K-means and density-based clustering. Using our approach, we can not only compare the properties of ridges and plumes, but can also compare the properties of ridges across different ocean basins and of individual simulated mantle plumes. Analysis of the bulk composition and melting age of tracer particles associated with ridges and plumes allows us to better interpret the history of material found in these regions. We analyse the U ratio to see if recent (~600 Ma) changes in the subducted U flux are evident in differences in the U composition of plume and ridge material.

How to cite: Panton, J., Davies, H., and Beguelin, P.: Trace element and bulk chemistry of plumes and ridges in geodynamic simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16771, https://doi.org/10.5194/egusphere-egu24-16771, 2024.

EGU24-17413 | ECS | Orals | GD10.2 | Highlight

Neutrino oscillations investigation of the base-of-the-mantle structure: simulation tools and preliminary results 

Rebekah Pestes, Joao Coelho, Yael Deniz Hernandez, Stéphanie Durand, Nobuaki Fuji, Eric Mittelstaedt, and Véronique Van Elewyck

The origin of Large Low-Velocity Provinces (LLVPs) at the base of mantle remains a mystery, but particle physics may be able to provide another piece of the puzzle. Using a phenomenon known as neutrino oscillation, atmospheric neutrino experiments are sensitive to the electron number density inside the Earth, which is complementary to the information seismology can provide. In order to reveal lateral heterogeneities in density and chemical composition such as those expected for LLSVPs across the Earth’s lower mantle, we have developed a numerical method that allows us to compute the sensitivity of neutrino oscillation data to 3D Earth structure. Based on this approach, we will present some preliminary assessment of the potential resolving power of ongoing and future neutrino experiments.

How to cite: Pestes, R., Coelho, J., Deniz Hernandez, Y., Durand, S., Fuji, N., Mittelstaedt, E., and Van Elewyck, V.: Neutrino oscillations investigation of the base-of-the-mantle structure: simulation tools and preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17413, https://doi.org/10.5194/egusphere-egu24-17413, 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).

 

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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.

GD11 – Geodynamics and society: Short Courses, EDI, and General Interest

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