Presentation type:
GMPV – Geochemistry, Mineralogy, Petrology & Volcanology

EGU23-17120 | Orals | MAL26 | Robert Wilhelm Bunsen Medal Lecture

Mineral-fluid reactivity: The action is at the interface 

Susan Stipp

For more than 30,000 years, humans have been able to characterise materials, so they could choose the best for making tools, jewellery, shelter and clothing. For more than 300 years, scientists and craftsmen have known enough about fluids to characterise them and use them, even if they never succeeded in precipitating gold from solutions of lead. However, it has only been the last 30 years that we have been able to characterise the composition and structure of the mineral-fluid interface with techniques that can "see" at the nanometre scale and to simulate interactions from first principals. Once one can understand the mechanisms that control the solid-fluid interface, one can control the material’s properties and its behaviour. This is the key to designer materials and solving challenges in nature.

My journey into the nanometre scale world of interfaces began with demonstrating that the surface of a calcite crystal is not simply a termination of the bulk structure. Instead, it is a defect, where the atoms at the interface are restructured. In response to fracture in a vacuum or in contact with gas, water or organic compounds, the atoms of the mineral surface rearrange and the molecules in the fluid in contact organise themselves to delocalise charge differences between each other and with the surface. This plays a role in the behaviour of adsorbates. In turn, ion and organic compound adsorbates can modify surface properties, dramatically changing behaviour, even at tiny fractions of a monolayer. Understanding mineral-fluid-organic compound interactions gives us a powerful tool, the ability to predict behaviour and to control reactions.

Work in my group shows that the character of simple organic compounds, i.e. their functional group(s), size and branching, determine their adsorption energy on calcite. Density functional theory simulations match very well with adsorption energy determined with X-ray photoelectron spectroscopy. If we can define such relationships for other mineral systems, it could lead to a whole new conceptual framework for describing and predicting mineral-water-organic compound reactivity.

How to cite: Stipp, S.: Mineral-fluid reactivity: The action is at the interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17120, https://doi.org/10.5194/egusphere-egu23-17120, 2023.

EGU23-9133 | ECS | Orals | GMPV4.1 | GMPV Division Outstanding Early Career Scientist Award Lecture

The generation, dissipation and geological implication of grain-scale stress variation in metamorphic rock 

Xin Zhong

Metamorphic rocks are composed of minerals formed within a wide range of pressure-temperature (P-T) conditions. These minerals possess distinct physical properties with respect to their thermo-elasticity, viscosity and plasticity etc. When far-field nonhydrostatic stress was present during tectonic deformation or the P-T conditions were changed during burial or exhumation processes, grain-scale stress variation can be developed to maintain mechanical equilibrium. The induced stress variations can also be released over geological time. The magnitude, effect and geological implications of the preserved stress variations have been investigated and better understood in recent years, but a lot remains to be explored. It is important because it may as well open an opportunity to decipher the overseen information stored in the rock that is difficult to be detected or achieved with conventional methods.

The geological implication of grain-scale stress variation is directly manifested by a simple mineral inclusion-host system, such as quartz or zircon inclusion in garnet. The different thermal-elastic response between the inclusion and host upon P-T changes will result in a residual stress stored in an entrapped mineral inclusion. The inclusion stress (strain) can be directly measured with e.g. Raman spectroscopy. Combined with an elastic model, it is possible to obtain constraints on the entrapment P-T conditions. This elastic thermobarometry technique has been applied in many recent petrological studies because no global or local chemical equilibrium assumption is needed. However, it relies on the inclusion-host system being elastic and neglects the non-elastic behavior of minerals. As an example, I will present an integrated observational, experimental and numerical modelling work that highlights the importance of considering non-elastic behaviour of the mineral. The heating experiment shows that under conditions at which free fluid is present, a garnet host will be drastically weakened and partially release the inclusion pressure. This is further correlated with a nappe-scale study in the Adula nappe, Alps. A smooth T gradient is found increasing from the north (500-550 oC) to the south (700 oC) using the Zr-in-rutile thermometer. However, the entrapment P calculated with the quartz inclusion in garnet barometer demonstrate a GPa level steep drop in the middle-south, where the rocks have been hydrated during retrograde metamorphism and abundant micro-hydrous inclusions (e.g. chlorite, amphibole) are found in the garnet. It is interpreted that a combined effect of temperature and water fugacity will drastically speed up the inclusion pressure relaxation on a regional metamorphic scale. In the end, it is highlighted that mechanics with non-elastic stress-strain (rate) relationships are potentially needed when dealing with the generation and dissipation of the stress variations in metamorphic rocks that underwent retrograde hydration or very high T conditions to better extract geological information.

How to cite: Zhong, X.: The generation, dissipation and geological implication of grain-scale stress variation in metamorphic rock, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9133, https://doi.org/10.5194/egusphere-egu23-9133, 2023.

GMPV1 – Developments in approaches and techniques with interdisciplinary applications

The erosion of mountain landscapes is the greatest source of terrestrial sediment to global ocean basins and a critical part of the global carbon cycle regulating Earth’s climate over geologically relevant timescales. In particular, the expansion of mountain glaciers may accelerate bedrock erosion and rapidly increase the flux of terrestrial sediment from source areas. However, the mechanisms by which glaciation augments sediment flux are complex, and understanding them requires further research. Our research adopts a novel approach to determine the source of sediment in rivers exiting a glaciated landscape, combining detrital zircon fission-track “tracer” thermochronology and Raman spectroscopy of carbonaceous material (RSCM). Our research focuses on the Southern Alps of New Zealand as a model landscape with well-constrained lithology and a predictable exhumation gradient. In 5 west-draining transverse river catchments, we test the hypothesis that modern sediment is preferentially derived from glaciated, high-elevation areas of the catchment. Our 5 rivers span a range of glacial coverage, allowing us to further test the hypothesis that glacially-sourced sediment increases with the degree of glaciation in the catchment. Our preliminary results suggest that sediment is not exclusively derived from glaciated areas of the catchment, but may instead reflect additional deglaciated source areas affected by landsliding, possibly induced by seismicity along the Alpine Fault. Our research demonstrates a powerful and novel approach to tracing sediment sources within an individual catchment area and highlights complex interrelationships between mountain glaciation and changes in the magnitude and sources of sediment fluxes.

How to cite: Harris, D.-A., Lang, K., Roda Boluda, D., and Kurth, M.: Tracing sediment source within a glaciated landscape: new observations from detrital thermochronology and Raman spectroscopy in the Southern Alps of New Zealand, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-581, https://doi.org/10.5194/egusphere-egu23-581, 2023.

EGU23-1082 | ECS | Orals | GMPV1.2

Shocker: xenotime can date impacts 

Cilva Joseph, Denis Fougerouse, Aaron J. Cavosie, Hugo K. H. Olierook, Steven M. Reddy, Raiza R. Quintero, Allen Kennedy, David W. Saxey, and William D.A. Rickard

Constraining precise ages for impact events is crucial in establishing Earth’s history, and several geochronometers have been developed to date impacts. We present electron backscatter diffraction (EBSD), sensitive high-resolution ion microprobe (SHRIMP) and atom probe tomography (APT) data from shocked xenotime [(Y,HREE)PO4] collected from two impact sites to investigate the potential of xenotime as an impact geochronometer. A detrital xenotime grain from the Vredefort dome (South Africa) contains planar fractures, planar deformation bands and {112} twinning, the latter of which are diagnostic shock microstructures. However, APT analysis from the twin domains and also from the host yielded no evidence of Pb mobility at the nanometer scale during the impact. SHRIMP analysis (n=24) on the grain yielded a discordia with an upper intercept of 3136 ± 110 Ma and an imprecise lower intercept of 1793 ± 280 Ma. These correspond, respectively, to the bedrock age and a post-impact, cryptic terrane-wide fluid infiltration event. Three neoblastic grains from the Araguainha dome (Brazil) experienced partial to complete recrystallisation. The least recrystallised grain yields the oldest 238U/206Pb age of 479 ± 26 Ma, whereas a completely recrystallised neoblastic grain gave an age of 257 ± 11 Ma.  APT analysis on the latter grain showed different nanoscale features that shed light on Pb mobility during shock deformation and recrystallisation.  Based on observations of nanoscale Pb mobility and the correlation between recrystallisation and isotopic resetting, and prior published ages, we interpret 257 ± 11 Ma to date the impact event. These data confirm that recrystallised neoblastic xenotime is a useful impact geochronometer. 

How to cite: Joseph, C., Fougerouse, D., J. Cavosie, A., K. H. Olierook, H., M. Reddy, S., R. Quintero, R., Kennedy, A., W. Saxey, D., and D.A. Rickard, W.: Shocker: xenotime can date impacts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1082, https://doi.org/10.5194/egusphere-egu23-1082, 2023.

EGU23-1147 | ECS | Orals | GMPV1.2

A detective duo; an apatite–zircon case study of the Johnston Complex, Wales 

Anthony Clarke, Chris Kirkland, and Stijn Glorie

Determining the crystallization of S-type granitic material can be challenging due to a lack of neoblastic zircon growth (e.g. thin overgrowths) and the potential of large inherited zircon cargos. Coupled apatite–zircon geochronology can help address such complexities and also clarify post-magmatic thermal history, given the disparate Pb closure temperatures in these minerals. Here we present a case study on the Johnston Complex, a rare outcrop of the Precambrian basement in southern Britain, representing a window into the tectonic regime of Avalonia. Zircon and apatite yield identical U-Pb ages, within uncertainty, of 569 ± 2 Ma and 576 ± 11 Ma, respectively. A minor antecrystic zircon core component is identified at 615 ± 11 Ma. Given the previously reported zircon U-Pb age of 643 Ma, these results demonstrate that the Complex represents a composite suite of plutons along its ca. 20 km length. Zircon Lu-Hf data imply a broadly chondritic source, with model ages consistent with crustal extraction during Rodinia formation. Zircon trace elements are consistent with a calc-alkaline continental magmatic arc setting. Whilst, apatite trace elements demonstrate a sedimentary component within the melt. Combined, these results support arc granite production within the peri-Gondwanan realm during amalgamation of Eastern Avalonia and associates the Johnston Complex to the Cymru subterrane. Importantly, congruent zircon–apatite ages imply rapid cooling after crystallisation, and that subsequent thermal heating did not exceed the apatite Pb closure temperature.

How to cite: Clarke, A., Kirkland, C., and Glorie, S.: A detective duo; an apatite–zircon case study of the Johnston Complex, Wales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1147, https://doi.org/10.5194/egusphere-egu23-1147, 2023.

EGU23-1262 | ECS | Orals | GMPV1.2

Revealing the hidden Mesozoic exhumation history of the Qinling orogenic belt, Central China: insights from multiple geochronological and geochemical data of the molasse granitic gravels 

Heng Peng, Jianqiang Wang, Chiyang Liu, Jiaoli Li, Xiaoqin Jiao, Liying Zhang, and Massimiliano Zattin

Qinling Orogenic Belt with its Meso-Cenozoic intracontinental orogeny and uplift, is a key physiographic element that characterized the differential evolution of the geology, geography and climate in continental China (Dong et al., 2022). However, numerous thermochronological dates of the Qinling bedrocks (Dong et al., 2011; Yang et al., 2017) show that there is a wide cooling gap between Triassic and Early Cretaceous. In this study, we studied this gap by multiple geochronology and geochemistry on Lower Cretaceous molasse granitic gravel samples, with the aim to recover the hidden Mesozoic exhumation history. We report the first detailed zircon U-Pb ages, whole-rock major and trace elements and Sr-Nd-Pb isotopic data, which suggest that these clasts derive from Late Triassic I-type granites which were emplaced in a syn-collisional setting during a subduction phase. Their provenances were also determined by comparison with the geochemical fingerprint of Qinling granitic bedrocks. New zircon and apatite U-Pb, (U-Th)/He and fission-track data, as well as biotite 40Ar-39Ar, were performed on the granitic gravels dated between ca. 222 Ma to 110 Ma. Thermal history modeling, based on the multiple geochronological data, shows rapid cooling from ca. 700 °C to 200 °C during Late Triassic-Early Jurassic, then followed by a period of slow cooling from Middle Jurassic to Early Cretaceous.

As a whole, our new multiple geochronological and geochemical data and the related thermal history modeling results provide new insights on the prolonged pre-Cenozoic cooling history as well as the intracontinental deformation of the Qinling, which were mostly related to Paleo-Tethyan subduction and Late Triassic North China-South China Block collision.

Reference:

Dong, Y., Genser, J., Neubauer, F., Zhang, G., Liu, X., Yang, Z. and Heberer, B., 2011. U-Pb and 40Ar/39Ar geochronological constraints on the exhumation history of the North Qinling terrane, China. Gondwana Research, 19(4): 881-893.

Dong, Y., Sun, S., Santosh, M., Hui, B., Sun, J., Zhang, F., Cheng, B., Yang, Z., Shi, X., He, D., Yang, L., Cheng, C., Liu, X., Zhou, X., Wang, W. and Qi, N., 2022. Cross Orogenic Belts in Central China: Implications for the tectonic and paleogeographic evolution of the East Asian continental collage. Gondwana Research, 109: 18-88.

Yang, Z., Shen, C., Ratschbacher, L., Enkelmann, E., Jonckheere, R., Wauschkuhn, B. and Dong, Y., 2017. Sichuan Basin and beyond: Eastward foreland growth of the Tibetan Plateau from an integration of Late Cretaceous-Cenozoic fission track and (U-Th)/He ages of the eastern Tibetan Plateau, Qinling, and Daba Shan. Journal of Geophysical Research: Solid Earth, 122(6): 4712-4740.

How to cite: Peng, H., Wang, J., Liu, C., Li, J., Jiao, X., Zhang, L., and Zattin, M.: Revealing the hidden Mesozoic exhumation history of the Qinling orogenic belt, Central China: insights from multiple geochronological and geochemical data of the molasse granitic gravels, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1262, https://doi.org/10.5194/egusphere-egu23-1262, 2023.

EGU23-1407 | Posters on site | GMPV1.2

Rift propagation in south Tibet controlled by under-thrusting of India: A case study at the Tangra Yumco graben (south Tibet) 

Ralf Hetzel, Reinhard Wolff, Kyra Hölzer, István Dunkl, Qiang Xu, Aneta Anczkiewicz, and Zhenyu Li

Active graben systems in south Tibet and the Himalaya are the expression of ongoing E-W extension, however, the cause and spatio-temporal evolution of normal faulting remain debated. We reconstruct the history of normal faulting at the southern Tangra Yumco graben by using new thermochronological data and thermo-kinematic modelling (Wolff et al., 2022). The Miocene cooling history of the footwall of the main graben-bounding fault is constrained by zircon (U-Th)/He ages between 16.7±1.0 and 13.3±0.6 Ma, apatite fission track ages (15.9±2.1 to 13.0±2.1 Ma), and apatite (U-Th)/He ages (7.9±0.4 to 5.3±0.3 Ma). Thermo-kinematic modelling of the data indicates that normal faulting began 19.0±1.1 Ma ago at a rate of ~0.2 km/Myr and accelerated to ~0.4 km/Myr at ~5 Ma. In the northern Tangra Yumco rift, re-modelling of published thermochronological data (Wolff et al., 2019) shows that faulting started ~5 Ma later at 13.9±0.8 Ma. The age difference and the distance of 130 km between the two sites indicates that rifting and normal faulting propagated northward at an average rate of ~25 km/Myr. As this rate is similar to the Miocene convergence rate between India and south Tibet, we argue that the under-thrusting of India beneath Tibet has exerted an important control on the propagation of rifts in south Tibet.

References

Wolff, R., Hetzel, R., Hölzer, K., Dunkl, I., Xu, Q., Anczkiewicz, A.A., Li, Z. (2022). Rift propagation in south Tibet controlled by underthrusting of India: A case study at the Tangra Yumco graben (south Tibet). J. Geol. Soc. Lond., https://doi.org/10.1144/jgs2022-090.

Wolff, R., Hetzel, R., Dunkl, I., Xu, Q., Bröcker, M. & Anczkiewicz, A.A. (2019). High-angle normal faulting at the Tangra Yumco graben (southern Tibet) since ~15 Ma. J. Geology, 127, 15–36, http://doi.org/10.1086/700406.

 

How to cite: Hetzel, R., Wolff, R., Hölzer, K., Dunkl, I., Xu, Q., Anczkiewicz, A., and Li, Z.: Rift propagation in south Tibet controlled by under-thrusting of India: A case study at the Tangra Yumco graben (south Tibet), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1407, https://doi.org/10.5194/egusphere-egu23-1407, 2023.

Silicic magma flare-up episodes are characterized by the addition of large volumes of evolved magma (>65 wt% SiO2) to the continental crust in geologically short time intervals (106-107 years). Flare-up events are often associated with (trans-)extensional tectonics and contribute to crustal differentiation and critical metal mineralization. Related volcanic aerosol dispersion in the atmosphere can also trigger global environmental changes. During flare-up episodes, long-lived caldera complexes are thought to be primary eruptive sources at the Earth’s surface. However, a substantial proportion of the overall mobile magma can be trapped in extra-caldera dikes, fissures and monogenetic edifices controlled by the extensional stress regime.

In the Southern Alps of Northern Italy, a post-Variscan magmatic flare-up is recorded in a ca. 400 km long array of largely undeformed magmatic bodies of Early Permian age (285-275 Ma; [1]), then located along the northern margin of Gondwana. In the Southern Alps this flare-up produced more than 5*104 km3 of rhyolitic volcanic and cogenetic intrusive rocks. Two major caldera complexes (Sesia Caldera; Ora Caldera) were capable of ejecting volumes >103 km3 of magma during individual catastrophic eruptive events. However, magmatic activity also resulted in numerous scattered volcanic centers with relatively small eruptions (0.1 – 1 km3 each) and punctuated by quiescent intervals.

In this study we focus on two Early Permian fault-bounded basins, ca. 40 km apart, in the central Southern Alps: the Orobic Basin (Bergamo) and the Collio Basin (Brescia). The stratigraphic records of both basins preserve proximal and distal volcanic products and both successions terminate with erosional unconformities of Middle- to Late Permian age. New zircon LA-ICP-MS U-Pb ages indicate that the onset of explosive, rhyolitic magmatism was essentially coeval at ~284 Ma. The Collio Basin contains just a few ignimbrite sheets dispersed in an essentially (fluvio)-lacustrine sedimentary fill and recording a pulsated volcanic activity of nearly 5 Myr (youngest ignimbrite ~280 Ma). After an initial phase (1-2 Myr) of a similar pulsed nature, the Orobic Basin became the locus of extrusion of much larger volumes of rhyolitic magma (probably in excess of 100 km3) in less than 1 Myr (283-282 Ma). This was followed by a depositional style similar to the Collio but with a scarcer pyroclastic contribution.

The contrasting volcanic record in these two basins, which share size and tectonic environment but not magmatic evolution, provides a striking example of magmatic architecture diversity in the midst of a silicic flare-up event. Further investigation into the timing (CA-ID-TIMS U-Pb geochronology) and compositional evolution (e.g., zircon d18O, eHf) of volcanic products in the Collio and Orobic basins is expected to provide a much better resolved comparison and open a window into the combined tectono-magmatic processes that ultimately regulate the size and frequency of catastrophic, caldera-forming eruptions in silicic flare-up provinces.

[1] Schaltegger, U., & Brack, P. (2007). International Journal of Earth Sciences, 96(6), 1131-1151.

How to cite: Tavazzani, L., Szymanowski, D., Forni, F., Cadel, G., and Brack, P.: Magmatic architecture and basin evolution in the midst of a silicic flare-up: U-Pb zircon geochronology of volcanic deposits from two Early Permian, Collio-type basins of Southern Alps (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1426, https://doi.org/10.5194/egusphere-egu23-1426, 2023.

EGU23-1931 | Orals | GMPV1.2

Ultra-slow cooling of ultra-hot orogens 

Chris Clark, Michael Brown, Tim Johnson, Ruairidh Mitchell, and Saibal Gupta

The rate of cooling of metamorphic rocks provides a first-order constraint on the tectonic processes controlling heat flow and exhumation. For example, for small crustal terranes that were subducted to ultrahigh pressure conditions during the early stages of collisional orogenesis, exhumation is generally fast with rates similar to plate velocities, such that cooling is also rapid. Similarly, rates of cooling are commonly fast (generally ~20–30°C/Myr) during exhumation of metamorphic core complexes or due to transpression. By contrast, cooling in some granulite terranes can be slow and close-to-isobaric, leading to time-integrated cooling rates of <5°C/Myr. The implication of such slow rates of cooling is that these granulite terranes were close to isostatic equilibrium as a result of sustained high mantle heat flow that limited exhumation by erosion. However, constraining initial cooling rates in granulite terranes can be difficult, particularly where the rocks reached ultrahigh temperatures (>900 °C) that exceed the closure temperature of many geochronometers. In order to overcome this difficulty, we combine U–Pb zircon geochronology with Ti-in-zircon thermometry to investigate the thermal history of metapelitic rocks from the Eastern Ghats Province of eastern India. For the combined dataset of metamorphic zircon from the samples, concordant dates decrease continuously within 2σ uncertainty from around 950 Ma to 800 Ma, consistent with c. 150 Ma of zircon crystallization. Ti-in-zircon temperatures for each dated spot during this period decrease with age, corresponding to linear cooling rates ranging from 0.26 to 0.90°C/Myr. We propose that retention of heat producing elements in the lower crust of the Eastern Ghats Province and a low net erosion rate were responsible for c. 150 Myr of ultra-slow cooling. The location of the Eastern Ghats Province on the margin of the supercontinent Rodinia may have been a contributing factor enabling the region to remain relatively undisturbed until it was exhumed during the formation of Gondwana.

How to cite: Clark, C., Brown, M., Johnson, T., Mitchell, R., and Gupta, S.: Ultra-slow cooling of ultra-hot orogens, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1931, https://doi.org/10.5194/egusphere-egu23-1931, 2023.

EGU23-1954 | Orals | GMPV1.2

Statistical analysis of Europium anomalies in detrital zircons record major transitions in Earth geodynamics at 2.5 Ga and 0.9 Ga 

Antoine Triantafyllou, Mihai Ducea, Gilby Jepson, Alex Bisch, and Jerome Ganne

Trace elements in zircon are a promising proxy to quantitatively study long-term Earth’s lithospheric processes and its geodynamic regimes. The zircon Eu anomaly reflects the crystallization environment of its felsic or intermediate parental magma. It specifically provides insight into the water content, magmatic redox conditions, and the extent of pla­gioclase fractionation in the source rock or its occurrence as a cogenetic crystallizing phase from the magma. We performed a statistical analysis of Eu anomaly from a global compilation of detrital zircons and display it as a timeseries and found a major decrease in Eu anomaly ca. 2.5 Ga and an important increase ca. 0.9 Ga. Combining these trends with thermodynamic modelling, we suggest that these variations could be due to long-term change in the chemical system of the mafic source from which the intermediate to felsic melt and derived zircons are produced. The 2.5 Ga drop was likely associated with an enrichment in incompatible elements in the mafic source, which extended the pressure-temperature field of plagioclase stability as a cogenetic melt phase. We interpret the 0.9 Ga rise to record increasing hydration of magmagenetic sites due to the general development of cold subduction systems, which would delay and/or suppress the saturation of plagioclase in hydrous magmagenetic sites.

How to cite: Triantafyllou, A., Ducea, M., Jepson, G., Bisch, A., and Ganne, J.: Statistical analysis of Europium anomalies in detrital zircons record major transitions in Earth geodynamics at 2.5 Ga and 0.9 Ga, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1954, https://doi.org/10.5194/egusphere-egu23-1954, 2023.

EGU23-2154 | ECS | Orals | GMPV1.2

Multiple dates in millimetres; diffusion as an explanation for Rb-Sr age discrepancies in biotite 

Riley Rohrer, Chris Clark, Chris Kirkland, and Tim Johnson

In situ analysis of the Rb–Sr isotopic composition of biotite via triple quadropole LA–ICPMS is an increasingly popular method for constraining the time through the Sr closure temperature in rocks. Although interpreting the radiogenic product can be complicated by various factors that can affect diffusion of Rb and Sr, the role of the different minerals that may be in contact with biotite in regard to local diffusion gradients is poorly understood. In this study, we show the importance of analysing Rb–Sr isotopic data in the context of detailed petrographic observations, which reveals that the ratios obtained are affected by various diffusion pathways between like material and minerals that preferentially incorporate Sr. The studied samples are metapelites from the Fraser Zone (Western Australia) that have peak metamorphic conditions of about 850 °C and 9 kbar and a history of cryptic biotite Ar-Ar ages of ~1205 Ma, which on face value could imply exhumation rates that are some of the fastest recorded in Earth’s history. However, new biotite data from in-situ Rb-Sr analysis highlights differences in Sr retentivity. While calculated isochrons may at first yield large errors, sorting based on the location of the grains in terms of surrounding minerals yields a possible solution for varying Sr values skewing the ages in the sample. This results in an average age of 1205 Ma for biotite and sillimanite surrounded grains and 1107 Ma, from biotite and sillimanite surrounded grains and quartz and K-feldspar surrounded grains. This shows that the diffusive properties of Sr between biotite and the surrounding minerals creating variable re-equilibration between the different domains surrounding biotite. The complexities of Sr diffusion within between the various phases are still unknown, but the apparent effect between the surrounding material on the biotite and the measured initial Sr values does play a key factor in the final calculated ages and the interpretations they represent.

How to cite: Rohrer, R., Clark, C., Kirkland, C., and Johnson, T.: Multiple dates in millimetres; diffusion as an explanation for Rb-Sr age discrepancies in biotite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2154, https://doi.org/10.5194/egusphere-egu23-2154, 2023.

The Austroalpine nappes in the Eastern European Alps have preserved the record of two orogenic phases in the Cretaceous and Tertiary but their cooling and exhumation history remains poorly constrained. Here we use new low-temperature thermochronological data and thermokinematic modeling to unravel the exhumation history of the Austroalpine nappes in the Nock Mountains east of the Tauern Window (Wölfler et al., submitted). Our data show that the central Nock Mountains (Ötztal-Bundschuh and Drauzug-Gurktal nappes) cooled through the zircon fission track closure temperature (~240 °C) already in the Late Cretaceous. Apatite fission track ages cluster around 35-30 Ma, indicating that the rocks have been at depths of ≤5-6 km since the Eocene-Oligocene boundary. In contrast, the Radenthein and Millstatt Complexes, which are located south of the Hochstuhl Fault, cooled below 240 °C during the Eocene and show apatite fission track ages of ~15 Ma. Thermokinematic modeling of an age-elevation profile in the central Nock Mountains (near Innerkrems) revealed a phase of enhanced exhumation (~0.62 km/Ma) between ~100 and ~85 Ma, which we relate to syn- to late-orogenic Late Cretaceous extension. After a period of slow exhumation (~0.03 km/Ma), the exhumation rate increased to ~0.16 km/Ma at ~32 Ma. In contrast, thermokinematic modeling of an age-elevation profile near Millstatt shows that rocks of the Radenthein and Millstatt Complexes were rapidly exhumed (~0.78 km/Ma) from ~44 Ma to ~38 Ma during the initial Europe-Adria collision. After a phase of slow exhumation (~0.07 km/Ma) between ~38 and ~19 Ma, the exhumation rate increased to ~0.3 km/Ma with the onset of Miocene lateral extrusion in the Eastern Alps. Altogether, ~16 km of rock have been removed since ~100 Ma in the Innerkrems region, whereas ~11 km of rock have been removed in the last ~44 Ma in the Millstatt area. These findings are consistent with pressure-temperature estimates for the Ötztal-Bundschuh nappe and the Radenthein/Millstatt Complexes, respectively (Koroknai et al., 1999; Schuster, 2003; Krenn et al., 2003, 2011). The distinct differences in the cooling histories north and south of the Hochstuhl Fault further suggest that this fault, which has hitherto been considered as a dextral strike-slip fault during Miocene lateral extrusion (Polinski & Eisbacher, 1992; Linzer et al., 2002), also accommodated a considerable amount of thrust movement. The difference between the amount of exhumation north and south of the Hochstuhl Fault indicates ca. 5 km of vertical offset between ~44 and ~38 Ma.

How to cite: Wölfler, A., Hampel, A., Wolff, R., Hetzel, R., and Dunkl, I.: Phases of enhanced exhumation during the Cretaceous and Tertiary orogenies in the Eastern European Alps: new insights from thermochronological data and thermokinematic modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2925, https://doi.org/10.5194/egusphere-egu23-2925, 2023.

EGU23-3132 | ECS | Orals | GMPV1.2

A new calibration of radiation damage control on He diffusivity in apatite: implications for (U-Th)/He thermochronology 

Alexis Derycke, Kerry Gallagher, and Cécile Gautheron

In low temperature thermochronology, reliable interpretation of (U-Th)/He data is controlled by our understanding of helium diffusion in a crystal. The diffusion kinetics can be simulated through the classic Arrhenius-type equation, with parameters frequency factor Do and activation energy Ea (Farley, 2000). For apatite, it has been demonstrated that accumulated radiation damage perturbed the Arrhenius-type equation and exerts a strong control on He diffusion. Two models have been developed to parameterise the evolution of diffusion kinetics in apatite in terms of accumulated radiation damage: one based on the physical phenomenon (Gautheron et al., 2009) and the other calibrated on empirical observations (Flowers et al., 2009). As the amount of radiation damage depends on both time (U and Th decay producing damage) and temperature (annealing of radiation damage), both of these models are routinely used to interpret apatite (U-Th)/He data in terms of thermal histories. However, results obtained from inverse thermal history modelling with these two models can differ and be inconsistent with other low thermochronological data (e.g., apatite fission tracks). In this contribution we present a new radiation damage-based diffusion model that combines the approaches of both the Gautheron et al. and Flowers et al. models.

Our new model is based on the theoretical diffusion model proposed by Gerin et al. (2017) but incorporates a new calibration from the available He diffusion experiment results. The Gerin et al. model is built on a theoretical understanding of the fundamental physical processes and predicts diffusion parameters for different levels of crystal lattice damage, using quantum calculus. We recalibrated this model through an empirical law based on real crystal mesh damage calculated from available experimental data. To test the reliability of the revised model and to compare it to the existing models, it was implemented in the modelling software, QTQt (Gallagher, 2012). Here we present results of both forward and inverse modelling to highlight the benefits of the new model. The results are assessed in terms of the impact for “deep time” (>500 Ma) thermochronology, in which accumulated radiation damage can have a significant control on the inferred thermal history models.

 

Farley, K.A., 2000. Helium diffusion from apatite: General behavior as illustrated by Durango fluorapatite. J. Geophys. Res. 105, 2903–2914. https://doi.org/10.1029/1999JB900348

Flowers, R.M., Ketcham, R.A., Shuster, D.L., Farley, K.A., 2009. Apatite (U–Th)/He thermochronometry using a radiation damage accumulation and annealing model. Geochimica et Cosmochimica Acta 73, 2347–2365. https://doi.org/10.1016/j.gca.2009.01.015

Gallagher, K., 2012. Transdimensional inverse thermal history modeling for quantitative thermochronology. Journal of Geophysical Research: Solid Earth 117, n/a-n/a. https://doi.org/10.1029/2011JB008825

Gautheron, C., Tassan-Got, L., Barbarand, J., Pagel, M., 2009. Effect of alpha-damage annealing on apatite (U–Th)/He thermochronology. Chemical Geology 266, 157–170. https://doi.org/10.1016/j.chemgeo.2009.06.001

Gerin, C., Gautheron, C., Oliviero, E., Bachelet, C., Mbongo Djimbi, D., Seydoux-Guillaume, A.-M., Tassan-Got, L., Sarda, P., Roques, J., Garrido, F., 2017. Influence of vacancy damage on He diffusion in apatite, investigated at atomic to mineralogical scales. Geochimica et Cosmochimica Acta 197, 87–103. https://doi.org/10.1016/j.gca.2016.10.018

How to cite: Derycke, A., Gallagher, K., and Gautheron, C.: A new calibration of radiation damage control on He diffusivity in apatite: implications for (U-Th)/He thermochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3132, https://doi.org/10.5194/egusphere-egu23-3132, 2023.

EGU23-3705 | ECS | Orals | GMPV1.2

Finding Quaternary Seismogenic Activity Along the Eastern Periadriatic Fault System: Dating of Fault Gouges via Trapped Charge Methods 

Erick Prince, Tsukamoto Sumiko, Grützner Christoph, Vrabec Marko, and Ustaszewski Kamil

The Periadriatic Fault System (PAF) is among the largest and most important post-collisional structures of the Alps; it accommodated between 150-300 km of right-lateral strike-slip motion between the European and Adriatic plates from about 35 until 15 Ma. Recent GPS data suggest that Adria-Europe convergence is still being accommodated in the Eastern Alps. However, according to instrumental and historical seismicity records, seismotectonic deformation is mostly concentrated in the adjacent Southern Alps. In this contribution, we present our first results for dating earthquakes along the PAF during the Quaternary by applying two trapped charge dating methods. Both Electron Spin Resonance (ESR) and Optically Stimulated Luminescence (OSL) are especially useful as ultra-low temperature thermochronometers due to their dating range (a few decades to ~1 Ma) and low closing temperature (below 100°C). We aim to show which segments of the PAF system accommodated seismotectonic deformation by directly dating quartz and feldspar from fault gouges. For ESR, we measure the signals from the Al center in quartz following the single aliquot additive (SAAD) and single aliquot regenerative (SAR) protocols, focusing on the 100-150 µm grain size fraction. For OSL, we measure the IRSL signal at 50°C (IR50) and the post-IR IRSL signal at 225°C (pIRIR225) on potassium feldspar aliquots of the 100-150 µm grain size fraction. Our ESR results indicate the PAF system accommodated seismotectonic deformation during the last 1 Ma, while the OSL signals for all samples were in saturation. The minimum ages obtained from OSL suggest that the events are likely not younger than 0.4 Ma. We also studied a segment of the nearby Lavanttal Fault, for which our ESR results suggest that the last earthquakes strong enough to produce sufficient shear heating to produce a partial reset on the geochronometer probably happened before 4 Ma.

How to cite: Prince, E., Sumiko, T., Christoph, G., Marko, V., and Kamil, U.: Finding Quaternary Seismogenic Activity Along the Eastern Periadriatic Fault System: Dating of Fault Gouges via Trapped Charge Methods, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3705, https://doi.org/10.5194/egusphere-egu23-3705, 2023.

The Paricutin-Tancítaro region (PTR), located in the SW sector of the Michoacán-Guanajuato monogenetic field, in central Mexico, is characterized by a high spatial density of monogenetic scoria cones around Tancítaro, a stratovolcano active in the middle Pleistocene. The PTR area has been active for around one million years, and the latest eruption, beginning in 1943, formed the Paricutin volcano. We use the Average Erosion Index (AEI) to estimate the relative ages of 170 PTR scoria cones located within latitudes 19°N and 20°N and longitudes -102.0° E and -102.7° E. The AEI quantifies the erosional state of scoria cones from a morphological analysis of their level contours extracted from a high-resolution DEM (the 12-m TanDEM-X in this case). The analysis provides a metric for the undulations along the level contour curves at different altitudes, reflecting the width and amplitude of erosional rills and gullies on the cone’s surface. We compute a functional relationship between AEI and age by correlating 10 published radiometric ages with the measured AEIs of those cones. Then, using that function, we assign an age to each of the 170 cones, assuming that all the monogenetic volcanoes in the analysis have been exposed to similar erosive conditions. Finally, we tessellate the study area with a 0.1° x 0.1° grid and identify the number of events per grid module to compute the probability of at least one eruption occurring in the module in a specific time, using a Poisson process distribution obtained from the count of the number of events per 20 ky time intervals. Our results suggest that the dispersed volcanic activity in the PTR started to increase after the last eruption of Tancitaro (~237 ka), with a further activity increase during the Holocene, mainly concentrated on the NE sector of Tancítaro, where Paricutin is located. Holocene vents align to the NE, parallel to the Tepalcatepec-Tangancícuaro normal fault system. Furthermore, our results suggest a spatial coincidence between the regions with a higher probability of an eruption, based on the obtained eruption history, and the location of the recent seismic swarms in the PTR, the last two in 2020-2021, suggesting an increase in volcanic and seismic hazards in that area. To what extent? It is the subject of our forthcoming research.

How to cite: De la Cruz-Reyna, S.: Temporal and Spatial distribution of scoria cones in the Paricutin-Tancítaro volcanic region, Mexico: A morpho-chronometric approach to monogenetic hazard evaluation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4567, https://doi.org/10.5194/egusphere-egu23-4567, 2023.

40Ar/39Ar dating has been a valuable and widely used method for dating orogenic processes such as prograde and retrograde metamorphism and brittle and ductile deformation, through the analysis of K-bearing rock-forming minerals such as white mica. The in situ 40Ar/39Ar method, in which a short wavelength laser is used to ablate an analyte and deliver the liberated Ar to a noble gas spectrometer, is particularly valuable as an approach to dating deformation or metamorphism because it allows for targeting of specific chemical and structural domains, and the mapping of intragrain age distributions. Rb-Sr dating can also be applied to K-bearing minerals because of Rb’s propensity to substitute for K. The Rb-Sr method has been under-used in recent decades because the isobaric interference between parent 87Rb and daughter 87Sr has necessitated the chemical separation of Rb from Sr via ion exchange chromatography prior to mass spectrometric analysis, and hence bulk sampling of the target analyte. New tandem mass spectrometers, in which two quadrupoles are separated by an intervening reaction chamber into which a reactive gas can be introduced, have opened up the opportunity of applying laser-based in situ sampling approaches to beta decay geochronometers, including Rb-Sr (Zack and Hogmalm, 2016).

We have collected new in situ Rb/Sr data for white mica from three different tectono-metamorphic settings previously dated using the in situ 40Ar/39Ar method: recrystallization of white mica in a Paleozoic low-temperature ductile shear zone; development of multiple cleavage domains in low-temperature metamorphic rocks deformed in the Paleozoic, and; slow cooling of rocks following regional amphibolite-facies metamorphism in a Paleoproterozoic orogeny. , This allows a direct comparison between these two approaches, with the goal of exploring the functionality and utility of in situ Rb-Sr data, and testing geological interpretations based upon the in situ 40Ar/39Ar method. Our results show that the in situ Rb-Sr method is a highly complementary approach to the 40Ar/39Ar method for white mica, particularly in cases for which the target mica population has a large internal spread in Rb/Sr. allowing for the rigorous testing of assumptions and hypotheses about timing and conditions of rock cooling, deformation, and fluid events developed using 40Ar/39Ar datasets.

 

Zack, T. and Hogmalm, K.J., 2016. Laser ablation Rb/Sr dating by online chemical separation of Rb and Sr in an oxygen-filled reaction cell. Chemical Geology, 437, pp.120-133.

How to cite: Kellett, D., Larson, K., and Skipton, D.: Integration of in situ Rb-Sr and in situ 40Ar/39Ar dates under diverse tectono-metamorphic scenarios, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5290, https://doi.org/10.5194/egusphere-egu23-5290, 2023.

EGU23-6766 | ECS | Posters on site | GMPV1.2

New high-resolution step heating experiments using a coupled Diode laser and thermocouple for thermochronology applications 

Julien Amalberti, Peter van der Beek, Cody Colleps, Maxime Bernard, and Isabel Wapenhans

Step-heating experiments constitute a key technique to study the release of volatile elements from geological materials as a function of temperature. In the case of noble gases (He, Ne, Ar, Kr, and Xe), step-heating is particularly useful to determine diffusion kinetics, structural defects, or spatial homogeneity within the material. These parameters are critical in the application of diffusion-based thermochronology such as the apatite (U-Th)/He system, where mapping out the spatial distribution of natural 4He provides crucial information on the thermal history of apatite crystals. Characterizing the diffusion and distribution of 4He via step-heating additionally has the potential to detect anomalously behaved grains and to directly constrain grain-to-grain variability in diffusivities within samples with significant radiation damage-induced age dispersion.

Within the ERC-funded COOLER project, we aim to further the development of high-resolution, ultra-low temperature 4He/3He thermochronology. To this end, we developed a new technique for precise step-heating experiments coupled with a diode laser including an inline single-wavelength pyrometer. The new protocol uses an all-alumina ceramic crucible fitted with a K-thermocouple ~0.1 mm below the center of the crucible pit. The head of the thermocouple is located directly below the sample within the ceramic matrix, allowing precise temperature measurements of the sample. The crucible is mounted on an alumina rod connected to a noble-gas preparation line. Gas released from the sample is purified and analyzed by a Thermo Scientific Helix SFT™ multi-collector mass spectrometer. The sample is wrapped in Pt foil and indirectly illuminated with a diode laser. Laser and PID temperature controls are carried out by a custom LabVIEW program. Temperature calibration is performed by comparing measured and theoretical melting points of well-known materials loaded in the alumina crucible pit.

Our initial results show very short response times for the thermocouple (a few seconds) and excellent agreement with the melting point of Indium (Tmelt = 157°C). Although the current design is limited to hold only a single sample, it enables precise calibration of the emissivity value for a specific capsule assembly, which is a key parameter for pyrometer control of the temperature. Consequently, by calibrating the Pt capsule emissivity prior to the step-heating experiment, they can then be mounted in a multiple laser sample holder (up to 36 samples per chamber). The single-wavelength pyrometer of our system enables temperature measurements for large sample batches. Temperature is also cross-calibrated between the pyrometer and the thermocouple to ensure its correct reading.  This new approach, coupled with analytical automation, will lead to significant improvement in the accessibility and efficiency of routine 4He/3He analyses for geologic applications.

How to cite: Amalberti, J., van der Beek, P., Colleps, C., Bernard, M., and Wapenhans, I.: New high-resolution step heating experiments using a coupled Diode laser and thermocouple for thermochronology applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6766, https://doi.org/10.5194/egusphere-egu23-6766, 2023.

EGU23-6959 | Orals | GMPV1.2

Timescale of pervasive melt migration in the continental crust 

Pavlina Hasalová, Karel Schulmann, Urs Schaltegger, Pavla Štípská, Andrew Kylander-Clark, Robert Holder, Roberto Weinberg, and Petra Maierová

Movement of a large volume of granitic melt is an important factor in the compositional differentiation of the continental crust and the presence of melt in rocks profoundly influences their rheology. Different mechanisms controlling melt migration through crust were proposed. We suggest that pervasive melt flow, analogous to reactive porous melt flow in mantle, could be possibly one of them. It is generally accepted that migration of felsic melts in continental crust starts with short distance pervasive microscopic flow into segregation veins which extract melt. However, we show that pervasive melt flow may be a regional mode of melt migration in continental crust. In such scenario, melt driven by deformation passes pervasively along grain boundaries through the whole rock volume. And the term pervasive melt flow is used for grain-scale, diffuse, porous and reactive flow of felsic silicate melt through rocks. This is effectively an open-system process that thoroughly reworks the resident rock mass. Through-flow of melt destroys pre-existing fabrics and the original chemical and isotopic nature of the protolith. Melt segregation is inefficient and protolith become isotropic granite-like, with partly preserved relics of the original, without ever containing more than a few melt percent at any time. The fabric and geochemical nature of these granites encapsulates the complex history of hybridization.

In order to decipher duration of pervasive melt migration we used precise U-Pb monazite ID-TIMS (isotope dilution thermal ionization mass spectrometry) and U-Pb monazite Laser Ablation Split Stream (LASS) geochronology in combination with monazite chemistry as well as U-Pb zircon SHRIMP geochronology. Monazite reveal continuous chemical equilibration with passing melt. They are getting progressively enriched in HREE and depleted in Eu. Monazites in the least affected rock preserve original magmatic zoning in Th and U, in contrast to more with melt equilibrated rock types, where this zoning is lost. Data for each migmatite type reveal  similar date spread for both cores and the Y-rich well defined rims of single monazite grains, indicating a disconnect between U-Pb dates and chemical zoning. There is also no correlation between U-Pb ages and Yb/Gd ratio. This suggest perturbance of the isotopic system. We interpret these random distribution within-grain date variations as a result of dissolution-reprecipitation reactions between monazite grains and melt. During the coupled dissolution-reprecipitation radiogenic Pb was redistributed within the grain. This is supported by dissolution of apatite into silicate melts that stabilizes monazite during migmatitization, preventing their dissolution but not reaction with passing melt. Redistribution of radiogenic Pb resulted in meaningless individual ages from different migmatite types, but gave overall duration of the thermal event – pervasive melt flow. Duration of pervasive melt flow was dated 8-10myr. This suggest that porous flow of silicate melts in continental crust is a process which can operate over a long time and impacts on the rheology of the crust during orogeny.

How to cite: Hasalová, P., Schulmann, K., Schaltegger, U., Štípská, P., Kylander-Clark, A., Holder, R., Weinberg, R., and Maierová, P.: Timescale of pervasive melt migration in the continental crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6959, https://doi.org/10.5194/egusphere-egu23-6959, 2023.

EGU23-7367 | ECS | Orals | GMPV1.2

40Ar/39Ar dating of pseudotachylytes: a case study on post-metamorphic brittle fault in the NW Alps 

Zeno G. Lugoboni, Gloria Arienti, Valentina Barberini, Andrea Bistacchi, Christian Cannella, Simona Caprarulo, and Igor M. Villa

Pseudotachylytes are solidified frictional melts produced by seismic fault slip. Being melts that solidified in seconds or minutes after the seismic slip event, they have always been considered a very favourable tool to date brittle deformation. However, since all pseudotachylytes are composed of inherited clasts, melt-derived matrix and (quite often) also alteration products, it is necessary to discriminate the Ar contribution of these three reservoirs to obtain meaningful ages. This can be done by analyzing Ca/K and Cl/K signatures provided by Ar systematics. Furthermore, microstructural analysis and microCT allow quantifying the clast-to-pseudotachylyte matrix ratios for each sample, and XRPD allows detecting potential alteration phases. Here we present the results of step-heating 40Ar/39Ar analyses performed on pseudotachylytes of the Trois Villes Fault and the Quart Fault, which crop out in a region of the Western Alps (Aosta Valley) affected by three different post-metamorphic brittle deformation phases: D1 characterized by NW-SW extension, D2 with NE-SW extension, and D3 showing N-S extension. The relative chronology of these deformation phases is based on consistent cross-cutting relationships. D1 ages of 29–32 Ma have been inferred from syn-kinematic magmatic dikes and hydrothermal veins. However, no absolute ages were so far available for D2 and D3, as direct radiometric dating of fault rocks has never been performed before in the area. Our results are consistent with the relative chronology and greatly improve our understanding of the tectonics of this area.

How to cite: Lugoboni, Z. G., Arienti, G., Barberini, V., Bistacchi, A., Cannella, C., Caprarulo, S., and Villa, I. M.: 40Ar/39Ar dating of pseudotachylytes: a case study on post-metamorphic brittle fault in the NW Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7367, https://doi.org/10.5194/egusphere-egu23-7367, 2023.

EGU23-7959 | ECS | Posters on site | GMPV1.2

Developing techniques and reference materials for LA-ICP-MS U-Pb geochronology of Sn-W minerals 

Dawid Szymanowski, Lorenzo Tavazzani, Yannick Buret, Marcel Guillong, Alejandro Cortes Calderon, and Cyril Chelle-Michou

Tin-tungsten magmatic-hydrothermal deposits are sources of critical raw materials (Sn, W, Nb, Ta, Li), key to the development of technologies involved in the green transition. However, the current and projected supply of many of these mineral commodities is often dominated by entities whose practices or geopolitical setting may raise issues from a social, political, or environmental standpoint. To meet a steadily increasing demand, new responsible mineral extraction projects must therefore be developed. Successful exploration and economic appraisal of newly identified mineral deposits require (1) an understanding of the ore-forming processes to build an exploration model, and (2) an early estimate of the deposit size to facilitate well-targeted investments. One key parameter that helps to achieve both goals is the knowledge of absolute timing and duration of the mineralisation process.

We present new analytical developments in U-Pb dating of strategic Sn-W ore minerals (cassiterite, wolframite, scheelite) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We used a suite of Sn-W mineral specimens to characterise U/Pb downhole fractionation behaviour and polyatomic interference patterns for these three matrices, allowing the optimisation of ablation and ICP-MS settings. In parallel with technical developments, we compiled a large library of potential primary and secondary cassiterite, wolframite, and scheelite reference materials (RMs) which we characterised for major and trace elements. To further our understanding of geochemistry of Sn-W phases, we also performed high-resolution compositional mapping of key trace elements (e.g. U, Pb, REE) with an ultra-fast washout laser ablation system.

Promising RM candidates will be developed into primary RMs with a careful characterisation of compositional homogeneity and precise age determination by isotope dilution-thermal ionisation mass spectrometry (ID-TIMS). Thus characterised RMs and a set of analytical best practices will be made available to laboratories wishing to test and further develop such methods. The ultimate goal of this effort is to build a set of community shared materials and techniques that will allow precise and accurate temporal characterisation of Sn-W mineralisation.

How to cite: Szymanowski, D., Tavazzani, L., Buret, Y., Guillong, M., Cortes Calderon, A., and Chelle-Michou, C.: Developing techniques and reference materials for LA-ICP-MS U-Pb geochronology of Sn-W minerals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7959, https://doi.org/10.5194/egusphere-egu23-7959, 2023.

EGU23-8495 | Posters on site | GMPV1.2

From sedimentation to multiple tectono-thermal events: U/Pb zircon and allanite dating in the Eastern Alps 

Sebastian Stumpf, Etienne Skrzypek, Kurt Stüwe, and Christoph Iglseder

The affiliation of the Ennstal Phyllite Zone (EPZ) to either the micaschist units of the Koralpe-Wölz nappe system (KW-NS) to its south or to nappes of the “Greywacke Zone” to its north and east is still debated. Due to similarities with phyllites of the “Greywacke Zone” in the north and phyllonitic micaschists in the south, no clear lithological boundary between these units is observable. Petrographic observations suggest a continuous eoalpine metamorphic gradient with no metamorphic gap between the KW-NS and the EPZ. In order to clear this debate and further constrain the tectonic and temporal evolution of these units, we present new LA-MC-ICP-MS U/Pb age dating results for metapelite samples from the EPZ as well as for the adjacent units of the KW-NS.

Two samples (EA09 and SP02) from the central EPZ and one sample (SP62) from the northernmost part of the Wölz-Complex of the KW-NS were selected for detrital zircon age dating. The distribution of approximately 150 dates per sample reveals major peaks at the Ediacaran-Cryogenian boundary (624 – 646 Ma), a smaller peak at the Neoproterozoic-Mesoproterozoic boundary (~1000 Ma) followed by a hiatus and a smaller peak in the mid-Paleoproterozoic (~2000 Ma). All samples show similar mid-Paleoproterozoic and Neoproterozoic-Mesoproterozoic peaks. Sample SP62 contains one grain of Cambrian age (523 Ma) and one grain of mid-Ordovician age (460 Ma) whereas the youngest zircons from the EPZ samples yield Ediacaran ages of 629 Ma and 625 Ma. The lack of zircons of Ordovician age in samples EA09 and SP02 indicate an affiliation of the EPZ with the basal units of the “Greywacke Zone”.

We also dated metamorphic allanite and REE-bearing epidote rims which are interpreted to form at low pressure and temperature conditions in metapelites. Allanites from the EPZ yield metamorphic ages of 105 ± 3.5 Ma in the northern part of the unit and 279 ± 6 Ma in the southern part. Allanite cores from two micaschist samples from the northern and central Wölz-Complex yield ages of 316 ± 21 Ma and 286 ± 11 Ma. Their respective epidote rims yield eoalpine ages of 98 ± 2 Ma and 96 ± 2 Ma. One micaschist sample from the Rappold-Complex yields ages of 326 ± 9 Ma for the allanite cores and 101 ± 1 Ma for the epidote rims. These ages are interpreted as prograde crystallization of allanite and epidote and give us petrochronological information about three distinct metamorphic events: Variscan, Permian and Eoalpine. By gathering three distinct eoalpine ages within the EPZ and the KW-NS, we can further constrain the metamorphic evolution of the eoalpine lower plate.

How to cite: Stumpf, S., Skrzypek, E., Stüwe, K., and Iglseder, C.: From sedimentation to multiple tectono-thermal events: U/Pb zircon and allanite dating in the Eastern Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8495, https://doi.org/10.5194/egusphere-egu23-8495, 2023.

Interpreting cooling ages from multiple thermochronometric systems and/or from steep elevation transects with the help of a thermal model can provide unique insights into the spatial and temporal patterns of rock exhumation. Several well-established thermal models allow for a detailed exploration of how cooling or exhumation rates evolved in a limited area or along a transect. However, integrating large, regional datasets in such models remains challenging due to the difficulty of extracting exhumation rates from ages that are affected by variable effective cooling temperatures, sampling elevations, and surface temperatures. Here we present a thermal model that can be used to rapidly provide a synoptic overview of exhumation rates from thermochronologic data spread over wide regions. The model incorporates surface temperature based on a defined lapse rate and sample elevation relative to a mean relief value that is dependent on the thermochronometric system of interest. Other inputs include sample age, thermochronometric system, and an initial (unperturbed) geothermal gradient. The model is simplified in that it assumes steady, vertical rock-uplift when calculating exhumation rates. For this reason, it does not replace more powerful and versatile thermal-kinematic models like PECUBE, but it has the advantage of simple implementation and rapidly calculated results. In our example dataset, we show the results of exhumation rates calculated from 1785 thermochronologic ages from the Himalaya associated with five different thermochronometric systems; results were calculated in under a second on a standard laptop. Despite the synoptic nature of the results, we show how they illustrate several fundamental features of the mountain belt, including strong regional differences that reflect known segmentation patterns and changing exhumation rates in areas of newly developed ramp structures. The results can also be correlated with geomorphic metrics to probe potential controls on surface morphology.

How to cite: van der Beek, P. and Schildgen, T.: Age2exhume: A Matlab/Python script to calculate steady-state vertical exhumation rates from thermochronologic ages in regional datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8741, https://doi.org/10.5194/egusphere-egu23-8741, 2023.

EGU23-8976 | Orals | GMPV1.2

How useful is the initial Pb composition of magmatic allanite ? 

Etienne Skrzypek, Daniela Gallhofer, Christoph Hauzenberger, and Isabella Haas

Allanite-group minerals are known to incorporate not only U and Th but also initial, non-radiogenic Pb. Allanite can therefore be analyzed in order to assess its crystallization age as well as the ambient Pb composition at the time of crystallization. Whereas allanite age dating has been the focus of many studies, constraining its initial Pb composition has received much less attention. We collected a series of Phanerozoic, allanite-bearing magmatic rock samples (volcanic, plutonic, pegmatite) and measured both the age and initial Pb composition of allanite by laser ablation-multi collector-inductively coupled plasma-mass spectrometry. We show that allanite data can be corrected for mass bias and fractionation using zircon (for U/Pb and Th/Pb ratios) and glass (for Pb/Pb ratios) as reference material as long as allanite is not metamict. A lower intercept age and y-axis intercept Pb composition can be determined by linearly regressing U-Pb data in a Tera-Wasserburg diagram, and a 230Th disequilibrium correction is highly recommended. We find a good agreement between our allanite U-Pb dates and published U-Pb zircon ages for the same localities. Our initial Pb compositions are validated by a fair agreement with Pb isotopic data measured on co-genetic feldspars from the same samples. The initial Pb composition of samples ranging from ca. 530 to 18 Ma reveals fluctuations in initial 207Pb/206Pb ratio, which points to different degrees of crustal (elevated μ=238U/204Pb) contribution. These variations could be due to post-magmatic deformation, weathering or metamorphism, but we believe that they rather reflect differences in initial magma composition. We thus emphasize the usefulness of allanite initial Pb compositions to discuss the source of igneous rocks.

How to cite: Skrzypek, E., Gallhofer, D., Hauzenberger, C., and Haas, I.: How useful is the initial Pb composition of magmatic allanite ?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8976, https://doi.org/10.5194/egusphere-egu23-8976, 2023.

EGU23-9864 | Orals | GMPV1.2

Luminescence chronology and thermometry studies of plant opal phytoliths 

Joel Spencer and David Sanderson

In this work we have been investigating the luminescence properties of plant opal phytoliths to assess their suitability for determination of age and/or thermometric information from soil and sediment sequences. Opal phytoliths, or bio-opal, form when monosilicic acid from soil-waters is taken up by plants and chemically altered to silica, producing intra- or extra- cellular structures that give grasses and stems their strength. Opal phytoliths are usually considered to be non-crystalline and referred to as silica mineraloid structures, with ~4-9% water, <5% other elements, and specific gravity ranging from ~1.5-2.3. They are known to be resistant to degradation and hence preserved in soil or sediment even after decomposition of organic matter. Our earlier work examined a <2.37 g/cm3 density fraction in parallel with quartz grains from samples collected from fluvial terraces and soil pits on Konza Prairie Biological Station native tall grass prairie a few km from Kansas State University. We observed generally similar luminescence characteristics from the phytolith fractions to quartz, with bright blue optically stimulated luminescence (OSL) signals and good single-aliquot regenerative-dose characteristics. In two hours the OSL signal is ~90% bleached by white light, whereas red fluorescence lab lighting has a negligible effect over the same exposure time. Thermoluminescence (TL) data suggested the presence of feldspatic-like minerals or perhaps thermal degradation of the phytoliths during TL measurement; the phytolith fractions were also stimulated by low-temperature infrared stimulated luminescence (IRSL50) perhaps also indicating presence of contaminant minerals. Initial SEM analyses identify what appear to be weathered silica grains, but also highly weathered, pitted concretions with silicate-like structures according to element mapping but actual mineral identification is presently unclear.

Most recently we have begun analyzing samples collected from a suite of stratified paleosols from the mid-continent stream type-site of Claussen, Mill Creek, Wabaunsee County, Kansas. This site has documented phytolith examples and a radiocarbon framework. We are continuing luminescence characterization studies, incorporating screening of prepared fractions with SEM and IRSL50 evaluation, and pulsed time domain analysis measurements are being explored.

We think luminescence from opal phytoliths shows great promise as an alternative target to quartz or feldspar, but moreover as a sensitive recorder of climatic change or fire exposure on plant communities. This presentation will review our earlier work on phytoliths and discuss most recent findings from the Claussen site.

How to cite: Spencer, J. and Sanderson, D.: Luminescence chronology and thermometry studies of plant opal phytoliths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9864, https://doi.org/10.5194/egusphere-egu23-9864, 2023.

EGU23-11638 | Posters on site | GMPV1.2

Using detrital thermochronology on moraine deposits to infer glacial erosion patterns and rock thermal history : insights from the Arve and Maurienne valleys (Western European Alps) 

Benjamin Guillaume, Nathan Cogné, Kerry Gallagher, Pierre G. Valla, and Christian Crouzet

This study tests the application of combined detrital apatite fission track (AFT) and U-Pb dating to infer both glacial erosion spatial patterns and long-term rock cooling histories in Alpine mountainous settings. We have dated 716 detrital apatite grains from glacial sediments collected in the Maurienne and Arve valleys (Western European Alps, France) from moraine deposits corresponding to different stages of glacial retreat since the Last Glacial Maximum (LGM, ca. 24-21 ka).
The Maurienne valley crosses the internal and external Alps, which exhibit contrasting in-situ AFT and U-Pb ages. Here, we present the measured distribution of both detrital AFT and U-Pb ages at 6 locations along the valley, with catchment elevations ranging from 390 to 1740 m. We show that during glacial retreat, erosion is mainly concentrated in the downstream part of the glacier, near the sampled moraine deposits. This inference suggests that during glacial retreat, glacial erosion is more effective below the ELA (Equilibrium Line Altitude) and specifically close to the glacier front, in areas where ice flow velocity is high and subglacial water is abundant, as predicted by ice-dynamics reconstructions in the European Alps over the last 20 ka.
In the Arve valley, previous studies showed that in situ AFT ages are systematically younger than 7 Ma for the Mont-Blanc massif. We compare the thermal history obtained from these literature bedrock-derived data to that derived from the new detrital AFT data collected in the Little Ice Age (LIA) moraine, just at the front of the Bossons glacier (~1300 m elevation). We also compare our results with 5 other samples down the valley at catchment elevations between 460 and 1050 m to evaluate potential changes in the detrital AFT signal as well as the consistency in the retrieved long-term cooling history.
Based on these first results, we plan to extend our study to other areas (e.g., Patagonia) to investigate both (1) spatial patterns of glacial erosion for older glacial periods (pre-LGM), and (2) long-term rock cooling histories from moraine deposits where modern bedrock is inaccessible (e.g. under modern glaciers or ice fields).

How to cite: Guillaume, B., Cogné, N., Gallagher, K., Valla, P. G., and Crouzet, C.: Using detrital thermochronology on moraine deposits to infer glacial erosion patterns and rock thermal history : insights from the Arve and Maurienne valleys (Western European Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11638, https://doi.org/10.5194/egusphere-egu23-11638, 2023.

Low temperature thermochronology is a field of research in which the thermally controlled retention of radioactive decay products in geological materials is measured to reconstruct mineral and rock temperature-time histories, especially in regard to their passage through the upper crust (i.e., <350 °C). Such temperature-time histories are most often constructed by inverting low temperature thermochronological data using geological constraints in order to identify envelopes of plausible rock thermal histories. While such inversions are highly informative models of the thermal history of rocks, the ultimate goal of most low temperature thermochronological studies is to relate thermal histories to geological processes in order to reconstruct upper crustal tectonic activity and/or landscape evolution. To do this, the (evolving) depths of thermochronometer effective closure temperatures must be estimated, as both heat transfer processes and crustal rock composition/thermal properties will affect the crustal thermal field. 

Here we present an exploration of the relationships between low temperature thermochronometers, temperature-time histories, and geological processes produced using the software Tc1D (https://doi.org/10.5281/zenodo.7124271). Tc1D is a new, open-source thermal and thermochronometer age prediction model for simulating the competing effects of tectonic and surface processes on thermochronometer ages. The Tc1D software is written in Python and uses the finite difference method to solve the heat transfer equation in 1D including the effects of heat conduction, advection (e.g., erosion, sedimentation), and radiogenic heat production on the thermal profile of the lithosphere. The flexibility of the software means that it can be used to explore the effects of a variety of geological processes, including magmatic intrusion and lithospheric delamination, for example. Thermochronometer ages (U-Th/He and fission track ages for apatite and zircon) are predicted by tracking the thermal history of rock particles in the model as they travel from depth to the surface during their exhumation history, both for samples at the modern-day surface and those reaching the surface at past times. The thermal histories are input to age prediction algorithms, including those that account for the effects of radiation damage in minerals (e.g., Flowers et al., 2009; Guenthner et al., 2013), making the software applicable to thermochronometer age interpretation in a wide variety of geological scenarios.  

In this contribution, we present a selection of results using Tc1D, demonstrating potential applications and providing some examples of unintuitive temperature and age relationships. These examples include cases where sample depth does not correlate with temperature, where variations in predicted effective closure temperatures produce unexpected age relationships, and where the thickness of the layer of exhumed rocks can significantly affect predicted ages. We hope that these illustrative examples demonstrate the role for Tc1D in the thermochronologist’s interpretational toolbox. 

How to cite: Whipp, D. M. and Kellett, D. A.: Exploring the relationships between low-temperature thermochronometers, temperature-time histories, and geological processes using Tc1D, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12472, https://doi.org/10.5194/egusphere-egu23-12472, 2023.

EGU23-12637 | Posters on site | GMPV1.2

Erosion patterns in the European Alps from zircon fission-track tracer thermochronology 

Christoph Glotzbach and Sarah Falkowski

Applications of tracer thermochronology exploit a known or assumed surface thermochronometric age map (based on either interpolated observed or modelled bedrock ages) to determine the provenance of detrital grains within fluvial or glacial catchments. The goal is to interpret the erosion pattern and processes within the sampled catchment. So far, most studies focused on modern sediments and glacial deposits.

We extend this approach to several time slices (between 28 and 12 Ma) of well-dated stratigraphic sections of pro- and retro-foreland basins of the European Alps. Foreland basin deposits represent a rich archive of erosional processes that were controlled by tectonics, climate, and lithology. However, importantly, before we reconstruct and interpret past erosion patterns and exhumation from detrital zircon fission-track (ZFT) age distributions and modelled bedrock ZFT ages back in time, we produce a frame of reference of today's situation. We do this by investigating signals from modern river samples and the present-day erosion pattern and mineral fertility in the Alps.

Here, we focus on 26 modern river samples (21 previous samples from the Western and Central Alps, and 5 new samples from the Eastern Alps) and discuss observed and predicted (based on possible erosion scenarios) ZFT age distributions, as well as potential pitfalls of the method (such as poor bedrock control in some areas of the Alps). We also show preliminary results from stratigraphic sections.

How to cite: Glotzbach, C. and Falkowski, S.: Erosion patterns in the European Alps from zircon fission-track tracer thermochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12637, https://doi.org/10.5194/egusphere-egu23-12637, 2023.

EGU23-12969 | Posters on site | GMPV1.2

Characterization of zircon megacrysts from an atypical occurrence of carbonatite at Kawisigamuwa, Sri Lanka 

Daniela Gallhofer, Etienne Skrzypek, Christoph Hauzenberger, Andreas Möller, Joseph Andrew, Luis A. Parra-Avila, Laure Martin, Anthony Kemp, Rohan Fernando, and He Dengfeng

Zircon megacrysts are unusually large crystals (> 5 mm) that are commonly associated with mantle-derived kimberlites, carbonatites, alkali basalts and syenitic pegmatites (e.g., Hoskin and Schaltegger 2003). Such zircons form during relatively short timespans and therefore, are often used as reference material for U-Pb geochronology. Here, we determine the geochemical and isotopic (U-Pb, Hf, O) characteristics of a little-known occurrence of zircon megacrysts at Kawisigamuwa, Sri Lanka.

The dark brown megacrysts are euhedral, commonly elongate crystals with double pyramidal terminations and have faintly corroded crystal surfaces. The zircons consist of oscillatory zoned and nearly featureless cathodoluminescence-bright patches, some of which appear to follow sealed cracks. All zircon domains show a low to moderate FWHM of the ν3 (SiO4) Raman band (2.5 to 7.3 cm-1), have a low to moderate radiation damage (total α-dose mainly <0.5 x 1018 events/g) and therefore are intermediate to well crystalline. Contents of most trace element (U, Th, REE, P) are elevated in the oscillatory zoned domains, while Hf content is elevated in the CL-bright domains and seems to be grain-dependant. The oscillatory zoned domains yielded a TIMS weighted mean 206Pb/238U age of 532.39 ± 0.66 Ma (2sd). The206Pb/238U dates within the CL-bright domains are partially reset by a single event of recrystallisation at ~518 Ma. The mean Hafnium isotopic compositions of the tested grains show a narrow range of 176Hf/177Hf from 0.281969 to 0.282003. Oxygen isotopes determined on two oscillatory zoned zircon megacrysts are homogeneous (mean δ18O of 12.1 and 12.2).    

While some of the trace and major element characteristics (Th/U, Zr/Hf, Hf content) of the Kawisigamuwa megacrysts resemble those of carbonatite zircons, their hafnium and oxygen isotope ratios are clearly different from mantle values. The isotopic values indicate that a significant amount of a crustal component must be involved in the formation of the zircons. Recently, several studies have found evidence for melting of carbonate rocks under high grade metamorphic conditions in Sri Lanka (e.g., Wang et al. 2021). It might be feasible that zircons grow from interaction of crustal derived carbonate melts and silicate melts or wall rocks under high grade metamorphic conditions.

Hoskin P.W.O. and Schaltegger U. (2003). The Composition of Zircon and Igneous and Metamorphic Petrogenesis. Reviews in Mineralogy and Geochemistry, 53 (1), 27–62.

Wang J., Su B.-X., Chen C., Ferrero S., Malaviarachchi S.P.K., Sakyi P.A., Yang Y.-H. and Dharmapriya P.L. (2021). Crustal derivation of the ca. 475-Ma Eppawala carbonatites in Sri Lanka. Journal of Petrology, 62 (11), 1-18.

How to cite: Gallhofer, D., Skrzypek, E., Hauzenberger, C., Möller, A., Andrew, J., Parra-Avila, L. A., Martin, L., Kemp, A., Fernando, R., and Dengfeng, H.: Characterization of zircon megacrysts from an atypical occurrence of carbonatite at Kawisigamuwa, Sri Lanka, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12969, https://doi.org/10.5194/egusphere-egu23-12969, 2023.

EGU23-13440 | ECS | Orals | GMPV1.2

Partially decoupled magmatic and hydrothermal events in porphyry copper systems? 

Adrianna Virmond, David Selby, Jörn-Frederik Wotzlaw, and Cyril Chelle-Michou

Porphyry Copper Systems (PCS) represent a significant source of metals, and will continue to play a key role in future with the development of green technology. Despite being one the most studied mineral systems, the primary controls on the ore tonnage of deposits (that varies up to 5 orders of magnitude in nature) remain poorly constrained. The Eocene Chuquicamata Intrusive Complex (CIC) in northern Chile hosts one of the world’s largest porphyry copper deposits and represent a perfect natural laboratory to explore the influence of timescales in controlling the formation and size of PCS.

Here we investigate the tempo of multiple magmatic-hydrothermal events in the CIC applying molybdenite geochronology (Re-Os ID-NTIMS) and high precision zircon petrochronology (U-Pb CA-ID-TIMS geochronology in tandem with LA-ICPMS trace element composition). Preliminary geochronological results may suggest a partial decoupling of the magmatic and hydrothermal events. Zircon U-Pb geochronology results point to a multi-million-year protracted magmatic history with at least two discrete pulses separated by 500 kyrs. The hydrothermal event appears slightly younger than the youngest magmatic pulse and lasted for ca. 1 Myrs.

The extensive duration of the mineralization scales with the behemothian size of the Chuquicamata deposit (more than 110 Mt of contained copper) and corresponds to predictions from numerical modelling of magma degassing. Interestingly, the apparent temporal decoupling between magmatism and hydrothermal activity at Chuquicamata suggests that syn-mineralization ore-forming magmas might not always intrude as dyke or stock at mineralization depth and can remain hidden at upper to mid-crustal depth. In the absence of high-precision geochronological data, this may bear consequences when assuming a direct genetic link between spatially associated porphyritic rocks and the mineralization.

How to cite: Virmond, A., Selby, D., Wotzlaw, J.-F., and Chelle-Michou, C.: Partially decoupled magmatic and hydrothermal events in porphyry copper systems?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13440, https://doi.org/10.5194/egusphere-egu23-13440, 2023.

EGU23-14643 | ECS | Orals | GMPV1.2

Out-of-sequence fault activity in the High Himalaya revealed by luminescence thermochronometry 

Chloé Bouscary, Georgina King, Jérôme Lavé, Djordje Grujic, György Hetényi, Rafael Almeida, Ananta Gajurel, and Frédéric Herman

Two end-member competing models have been proposed to describe the kinematics of the central Nepal Himalayas in the last few Myr. They differ in their interpretations of which surface breaking faults accommodate current shortening and the kinematics responsible for driving rapid exhumation in the topographic transition zone around the Main Central Thrust (MCT). These locally higher uplift and erosion rates in the High Himalaya could reflect (1) thrusting over a midcrustal ramp with the growth of a Lesser Himalaya duplex at midcrustal depth causing underplating along the Main Himalayan Thrust ramp, or (2) out‐of-sequence thrusting along the front of the High Himalaya, possibly driven by climatically controlled localized exhumation.

To decipher between the two tectonic models, we compare existing low and medium-temperature thermochronometric data (40Ar/39Ar on muscovite, apatite (U-Th)/He - AHe, zircon (U-Th)/He - ZHe, apatite fission track - AFT, and zircon fission track - ZFT), extracted from the world thermochronometric data file of Herman et al. (2013), to luminescence thermochronometry data from 61 newly collected rock samples along transhimalayan rivers between the Kali Gandaki and the Trisuli. The luminescence thermochronometry data provide a new perspective on Late Pleistocene exhumation rates (timescales of 104 to 105 years) of the Nepalese Himalayas, by offering quantitative high-resolution constraints of rock cooling histories within the upper kilometres of the Earth’s crust.

All of the thermochronometric data show younger ages and higher exhumation rates around the topographic transition and the MCT zone through central Nepal. For the higher temperature thermochronometers, there is a continuous trend towards younger ages from the Lesser Himalaya through the topographic transition and the MCT zone. These data suggest that the in-sequence model, with exhumation rates linked to increased erosion and the formation of a duplex below the Higher Himalayas, coincident with the MCT location in some areas, is the model that best describes the thermochronometric ages of this study area on Myr timescales. However, the luminescence thermochronometry data reveal a spatial and temporal variability of the higher exhumation rates at different timescales, suggesting an intermittency of exhumation signal due to geomorphological processes. The luminescence thermochronometry data also highlight a systematic sharp transition at the MCT, pointing to out-of-sequence activity at this tectonic boundary on 100-kyr timescales. Whether this difference in tectonic model between the two timescales is due to low resolution of the higher temperature thermochronometers, shallow isotherms deflected by fluid circulation and hot spring activity near the MCT, or to a change in tectonic regime during the last 200 kyr, out-of-sequence activity of the MCT needs to be considered in seismic hazard models as it could put the local population at risk.

How to cite: Bouscary, C., King, G., Lavé, J., Grujic, D., Hetényi, G., Almeida, R., Gajurel, A., and Herman, F.: Out-of-sequence fault activity in the High Himalaya revealed by luminescence thermochronometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14643, https://doi.org/10.5194/egusphere-egu23-14643, 2023.

EGU23-16555 | Orals | GMPV1.2

In-situ, U-Pb dating of titanite in phonolitic dykes from the Dolomites area (Southern Alps, Italy): new insights on the timing of the Middle Triassic magmatism 

Massimo Coltorti, Nicolò Nardini, Federico Casetta, Lorenzo Tavazzani, Stefano Peres, Theodoros Ntaflos, and Elio Dellantonio

Due to the complex geodynamic framework and the excellent state of preservation of the stratigraphic relationships towards the host metamorphic and sedimentary rocks, the Permo-Triassic magmatic sequences of the Southern Alps (Italy) are intensely studied. Throughout the Southalpine domain, the main peaks of the volcano-plutonic activity are both pre- and post-dated by the emplacement of small volume of magmas with variable chemical affinity. These magmas, preserved as dykes and veins intruded into the plutonic bodies and/or the overlying volcanites, are powerful tools for tracing the evolution of the magma source and reconstructing the temporal evolution of the magmatic episode. Here, we present a detailed geochemical and geochronological study of phonolitic dykes (SiO2 from 56.8 to 57.8 wt.%; Na2O + K2O from 11.1 to 15.3 wt.%) cropping out near Predazzo (Southern Alps; Italy) and intruded into the basaltic to trachyandesitic Middle Triassic lavas. The phonolites are mostly aphyric with a porphyricity index <10%. The main mineral phases are concentric-zoned clinopyroxene, ranging in composition from diopside-hedenbergite, to aegirine (Wo13-51; En2-29; Fs20-85), K-feldspar and rare sodalite. Accessory phases are titanite, apatite and magnetite embedded in a aphyric matrix. Titanite has a highly variable U-Th concentration (U from 24 to 478 ppm and Th from 170 to 4328 ppm) and is characterized by a chondrite-normalized REE pattern with a convex-upward shape (La/YbN from 18.9 to 41.5) with enrichment in LREE and depletion in HREE. Thermometry through Zr-in-Titanite calculations (Hayden et al., 2008) indicate crystallisation temperatures between 860.3 and 942.8 ± 57 °C. In-situ, U-Pb dating on titanite phenocrysts performed by laser ablation-inductively coupled-mass spectrometry (LA-ICP-MS) shows that the age of phonolite dykes is comprised between 240.4 ± 3.2 Ma and 242.0 ± 3.6 Ma, partially overlapping with the emplacement of the Middle-Triassic plutonic bodies of the Dolomites (238.190 ± 0.050 - 238.075 ± 0.087; Storck et al. 2019).

These results provide new insights into the timing of the Middle Triassic magmatic event in the Southern Alps, fostering the debates about the temporal and chemical evolution of the magmatism in between the Variscan orogeny and the opening of the Alpine Tethys.

References:

Hayden, L. A., Watson, E. B., & Wark, D. A. (2008). A thermobarometer for sphene (titanite). Contributions to Mineralogy and Petrology, 155(4), 529-540.

Storck, J. C., Brack, P., Wotzlaw, J. F., & Ulmer, P. (2019). Timing and evolution of Middle Triassic magmatism in the Southern Alps (northern Italy). Journal of the Geological Society, 176(2), 253-268.

How to cite: Coltorti, M., Nardini, N., Casetta, F., Tavazzani, L., Peres, S., Ntaflos, T., and Dellantonio, E.: In-situ, U-Pb dating of titanite in phonolitic dykes from the Dolomites area (Southern Alps, Italy): new insights on the timing of the Middle Triassic magmatism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16555, https://doi.org/10.5194/egusphere-egu23-16555, 2023.

EGU23-123 * | Orals | GMPV1.3 | Highlight

Dating a world-unique Pacific ruin: Nan Madol 

Chuuan-Chou (River) Shen, Felicia Beardsley, Shou-Yeh Gong, Osamu Kataoka, Minoru Yoneda, Yusuke Yokoyama, Leilei Jiang, Albert Yu-Min Lin, James Fox, Jason Barnabas, Gus Kohler, Zoe T. Richards, and Jean-Paul A. Hobbs

Great Holocene civilizations on Pacific islands were created by Homo sapiens. However, most of the construction histories remain uncertain due to the lack of developed writing system and the limitation of dating techniques. Nan Madol (0.7 km in width and 1.5 km in length), an abandoned city called the “Venice of the Pacific” with over 100 artificial islets, is located on the southeastern coast of island Pohnpei in Micronesia. This world-unique ruin, inscribed onto UNESCO’s World Heritage List in 2016, was built with basalt megaliths and scleractinian coral cobbles. Oral histories and previous charcoal 14C ages suggested that the main construction of Nan Madol of Pohnpei could begin in the 13th or 14th century and ceased at the 16th or 17th century, associated with the rise and fall of the Saudeleur Dynasty. However, after 150 years or more of studies, the timing of construction and the dynasty, and the probable influence of environmental factors, remain unresolved. High-precision U-Th dating techniques, developed at the High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, were used to date the selected pristine coral infills and reveal the construction time of the two ruins. With over 150 coral ages determined, results show a peak of construction activity during the middle 11th century could be related to the rise of the Saudeleur Dynasty. In the early 15th century, construction activities ceased, associated with the dynasty’s downfall. Our study shows that Nan Madol construction and the rise and fall of the dynasty occurred 2-3 centuries earlier than previously estimated. Moreover, the entire development was dominated by El Niño-Southern Oscillation variability and tectonic-related sea level rise.

How to cite: Shen, C.-C. (., Beardsley, F., Gong, S.-Y., Kataoka, O., Yoneda, M., Yokoyama, Y., Jiang, L., Lin, A. Y.-M., Fox, J., Barnabas, J., Kohler, G., Richards, Z. T., and Hobbs, J.-P. A.: Dating a world-unique Pacific ruin: Nan Madol, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-123, https://doi.org/10.5194/egusphere-egu23-123, 2023.

EGU23-265 | Orals | GMPV1.3

Mineral/Fluid interaction as a potential bias in calcite U-Pb dating 

Riccardo Lanari, Anda Buzenchi, Alessandro Bragagni, Bruno Dhuime, Mauro Brilli, Chiara Del Ventisette, Massimo Mattei, Sandro Conticelli, and Riccardo Avanzinelli

The application of U-Pb dating method performed on calcite has exponentially increased over the last years, since constraining the age of the crystallization for such syn-kinematic minerals, would provide a specific timing of faults movement. The potential gain of this approach is evident but the robustness of the U-Pb method performed on calcites has been not yet systematically tested.  Here, we firstly demonstrated that a mineral/fluid interaction indeed affects the regression of the 238U/206Pb and 207Pb/206Pb data-points and therefore the age; and secondly, we propose an innovative application of U-Pb dating method and a new strategy to identify and reject analytically robust isochrons.

We explore 36 samples, combining U-Pb dating performed with different methods along with carbon and oxygen stable isotopes compositions measured on the same fibres of calcite. The extremely high precision 207Pb/206Pb measured by Thermal Ionisation Mass Spectrometry  revealed that every sample experienced a certain degree of fluid interaction. We find no correlation between 238U/206Pb and the spread in δ18O. The higher spread in δ18O is instead coupled with a remarkable scattered data-points that yield U-Pb ages calculated with the different methods on the same samples with a large variability. In conclusion, our study demonstrates that great care must be taken when considering radiometric ages made on calcite since LA-ICP-MS large uncertainties might obscure the isotopic reorganization.

How to cite: Lanari, R., Buzenchi, A., Bragagni, A., Dhuime, B., Brilli, M., Del Ventisette, C., Mattei, M., Conticelli, S., and Avanzinelli, R.: Mineral/Fluid interaction as a potential bias in calcite U-Pb dating, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-265, https://doi.org/10.5194/egusphere-egu23-265, 2023.

EGU23-4234 | Orals | GMPV1.3

Application of carbonate U-Pb geochronology in dating of diagenesis and hydrothermal activity 

Zhongwu Lan, Nick M W Roberts, Shitou Wu, Fangyue Wang, Hao Wang, Rong Cao, Zhensheng Li, Ying Zhou, Kaibo Shi, and Bo Liu

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of calcite has been an emerging research direction in recent years that has been widely applied to various disciplines, such as dating of brittle deformation, biological biomineralization, oceanic crust alteration, and hydrocarbon migration. The method has the advantage of quickly locating regions of relatively high uranium content and radiogenic lead that avoids the time-consuming procedures traditionally required for isotope dilution methods. Herein, we show how this method is successfully applied to dating of diagenesis and hydrothermal activity in Precambrian-Phanerozoic sedimentary rocks, but with a note of caution that the susceptibility of the calcite U-Pb isotope system to fluid activities means interpretation of calcite U-Pb data and selection of calcite standard should be cautioned. We demonstrate the following case studies: LA-ICP-MS calcite U-Pb geochronology has aided in defining the Mesoproterozoic-Neoproterozoic boundary (ca. 1010 Ma) in North China Craton. It also constrains the timing of calcite infillings in the Ediacaran cap carbonate to be ca. 636 Ma, indicating an early diagenetic origin and thus confirming a methane seepage hypothesis. Two episodes of hydrothermal activity (ca. 290 Ma and ca. 250 Ma) have been recognized from the Cambrian carbonate in the Tarim region, which was induced by the Permian Tarim Large Igneous Province (LIP) and Indosinian orogeny, respectively.

How to cite: Lan, Z., M W Roberts, N., Wu, S., Wang, F., Wang, H., Cao, R., Li, Z., Zhou, Y., Shi, K., and Liu, B.: Application of carbonate U-Pb geochronology in dating of diagenesis and hydrothermal activity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4234, https://doi.org/10.5194/egusphere-egu23-4234, 2023.

The global-scale glacial events recorded by diamictite and cap carbonate couplets occurred in the late Neoproterozoic and has been recognized on at least 15 paleo-continents. Diamictite and cap carbonate couplets play a pivotal role in establishing regional stratigraphic correlations and understanding the extreme climatic conditions and glacial-interglacial cycles of the Neoproterozoic glaciation. Here we report newly discovered Neoproterozoic glaciogenic diamictite and cap carbonate couplet in the Longshoushan area at the southwestern margin of the Alxa Block, NW China. Based on detailed stratigraphic and sedimentologic studies, we identified massive and stratified diamictites at the bottom of the Hanmushan Group, both with poorly sorted and rounded gravels. The presence of glacial striations and ice-rafted dropstones in stratified diamictites supports a glaciogenic origin. The upward transition from massive diamictites to stratified diamictites indicates the process of glacier retreat. The occurrence of thin-bedded phyllites in the stratified diamictites suggests a short-term deglaciation during the glaciation. The 2- to 2.6-m-thick cap carbonates cover the stratified diamictites and consist of thinly laminated microcrystalline dolomites. The basal cap carbonates contain closely linked sheet cracks, cemented breccias, tepee-like structures and cavities. The cap carbonates show high-resolution 13CPDB chemostratigraphy and negative δ13C values (ca. −2.9 to −4.1‰), typical of the Marinoan cap carbonates. Regional sedimentary characteristics and the C-O isotope values suggest that the diamictites and cap carbonate couplet in the Alxa Block likely correspond to the Marinoan glaciation and subsequent deglaciation (ca. 635 Ma), not the previously assumed Ediacaran glaciation. Thus, the diamictite and cap carbonate sequence marks the Cryogenian-Ediacaran boundary in the Alxa Block and provides evidence for further stratigraphic correlation and investigation. This work was financially supported by NSFC projects (grants 42072264, 41730213, 41902229, 41972237) and Hong Kong RGC GRF (17307918).

How to cite: Shao, D., Han, Y., Li, M., Lu, L., Cao, X., and Ju, P.: Discovery of Neoproterozoic glaciogenic diamictites and cap carbonate couplet in the Alxa Block, NW China: Evidence from stratigraphic, sedimentologic and geochemical studies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4758, https://doi.org/10.5194/egusphere-egu23-4758, 2023.

There has been considerable debate as to whether the Korean peninsula has evolved as part of the Sino-Korean Craton since Neoarchean or whether it is a product of the amalgamation of several continental fragments in the early Mesozoic Era. The relationship between the Neoproterozoic Okcheon Metamorphic Belt (OMB) and the Early Paleozoic Tabaeksan Basin (TB) in the central region of the Korean Peninsula has the potential to provide an answer to this question. Various carbonate rocks appear in OMB, showing unique carbon isotope values ​​according to their geologic age.

The Hyangsanni Dolomite is distributed around the Gyemyeongsan Formation with metavolcanics of about 860 Ma. The Hyangsanni Dolomite has δ13C values between +2.9 ‰ and +6.2 ‰, markedly higher than the Cambro-Ordovician values, and are consistent with the Neoproterozoic values. Considering the low values ​​of 86Sr/87Sr, the deposition period of the Hyangsanni Dolomite is judged to be Tonian before the Sturtian Glaciation.

The Geumgang Limestone has a maximum thickness of several tens of meters adjacent to the diamictite layer proposed as a glacial deposit but shows a very extensible distribution. The δ13C values ​​of the Geumgang Limestone range from -12.25 to -7.88 ‰, suggesting that they may be cap carbonates. However, whether their deposition was related to the Sturtian Glaciation or the Marinoan Glaciation is not yet known.

Between the Cryogenian Seochangri Formation of OMB and the Cambrian Jangsan Formation of TB are carbonate rocks previously considered Ordovician. However, carbon and oxygen isotope values analyzed in this study require different interpretations. Zones with δ13C values ​​ranging from -3.4 to +1.3 ‰ agree with Ordovician seawater values. However, over a larger area, δ13C values ​​show mostly positive values ​​from +1.9 to +7.8 ‰. Also, a significant negative excursion of δ13C values ​​down to -6.9 ‰ occurs near the highest values ​​measured. These values correlate with Ediacaran or Early Cambrian carbonates better than Ordovician seawater. It is the first to discover the possible carbonate rocks of Ediacaran or Early Cambrian in South Korea, supporting that the Neoproterozoic OMB and Early Paleozoic TB have a tectonic evolutionary history of continuous deposition rather than an assembly of different continental fragments.

How to cite: Park, K.-H. and Ha, Y.: Carbon Isotopic Composition of Carbonates of the Okcheon Metamorphic Belt in South Korea from Neoproterozoic to Early Cambrian Potential: Geological and Tectonic Significance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5196, https://doi.org/10.5194/egusphere-egu23-5196, 2023.

EGU23-5345 | ECS | Posters virtual | GMPV1.3

Calcite TLM and LSJ07: two natural reference materials for micro-beam U-Pb geochronology and C, O isotope ratio measurements 

Shitou Wu, Yueheng Yang, Rolf Romer, Nick M W Roberts, and Zhongwu Lan

U-Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method, with potential applications to a vast array of geological issues. Accurate LA-ICP-MS calcite U-Pb dating requires matrix-matched RMs for the correction of instrumental mass bias of Pb/U ratios. Several materials are currently being used as RMs, including WC-1, Duff Brown Tank, ASH-15, JT, and AHX-1A. In this study, we will give a brief introduction of LA-ICP-MS lab at IGGCAS for carbonate U-Pb dating. Meanwhile we further characterized two calcite reference materials for micro-beam U-Pb geochronology and and C, O isotope ratio measurements. LA-ICP-MS multiple spot analyses (> 400) at different regions of materials reveal that calcite TLM and LSJ07 are homogeneous for the U-Pb age with 220.72 +/-0.98 Ma and 26.54+/-0.41 Ma respectively. SIMS multiple spot analyses (> 100) reveals calcite TLM is homogeneous for the O isotope ratio at mm special resolution. MAT 253 gives a bulk result of δ18O =-14.20 ‰. LA-MC-ICP-MS multiple spot analyses (> 200) reveals calcite TLM and LSJ07 are homogeneous for the C and O isotope ratio at mm special resolution. MAT 253 gives bulk results of δ13C =-1.53 ‰ andδ13C =-0.33 ‰ for TLM and LSJ07 respectively. These two materials represent a useful addition to the currently distributed WC-1, Duff Brown Tank, ASH-15, JT, and AHX-1A for micro-analytical techniques of U-Pb geochronology and C, O isotope ratio measurements.

How to cite: Wu, S., Yang, Y., Romer, R., Roberts, N. M. W., and Lan, Z.: Calcite TLM and LSJ07: two natural reference materials for micro-beam U-Pb geochronology and C, O isotope ratio measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5345, https://doi.org/10.5194/egusphere-egu23-5345, 2023.

EGU23-5865 | ECS | Posters virtual | GMPV1.3

Dating and characterizing carbonate rocks in Upper Permian reef-dolostone reservoir systems in Sichuan Basin, southwest China: implications for porosity evolution 

Binsong Zheng, Renjie Zhou, Chuanlong Mou, Jianxin Zhao, and Daryl Howard

Large gas fields are hosted in Upper Permian reef-dolostone bodies in Sichuan Basin, southwest China, among which the Puguang gasfield is the largest marine-carbonate gas system in China. The reservoir rocks are mainly composed of intensively dolomitized sponge-reefs constructed within platform margin reef facies in northern Sichuan Basin. Although major reservoir spaces consist of intercrystal pores, dissolved pores and vugs, the knowledge regarding the evolution of porosities is still limited. Using multiple methods, this study focuses on characterising different phases of carbonates (calcite and dolomite) to understand the dolomitization model and porosity evolution of the Upper Permian Panlongdong reef cropped out in northeastern Sichuan Basin. Two-dimensional high-resolution visualization of element contents in reef dolostones was provided by synchrotron-radiation Micro X-ray fluorescence elemental mapping. O and Sr isotope analysis was carried out to trace the nature of fluids during dolomitization. Laser ablation ICP-MS U-Pb dating was performed on dolomite minerals and secondary calcite cements. Our results suggest that: (1) dolomitization of the reef occurred in the early Middle Triassic (~245 Ma) due to the downward reflux of hypersaline seawater rich in Mg2+, accompanied by a significant increase in porosity because of the selective dissolution of low-Mg calcites; (2) in the Late Triassic, continental collision between South and North China plates induced uplifting and formation of a large quantity of (micro)fractures in northern South China, followed by Sr-depleted freshwater passing through the reef, leading to precipitation of secondary calcite cements (~206 Ma).

How to cite: Zheng, B., Zhou, R., Mou, C., Zhao, J., and Howard, D.: Dating and characterizing carbonate rocks in Upper Permian reef-dolostone reservoir systems in Sichuan Basin, southwest China: implications for porosity evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5865, https://doi.org/10.5194/egusphere-egu23-5865, 2023.

EGU23-7797 | ECS | Orals | GMPV1.3

H2O-present melting curve of magnesite and trace element distribution during melting of (dry) magnesite and calcite in the upper mantle 

Melanie J. Sieber, HansJosef Reichmann, Robert Farla, Oona Appelt, Marcus Oelze, Christian Lathe, and Monika Koch-Müller

The presence of magnesite (MgCO3) in the Earth’s mantle plays a fundamental role in reducing the melting point of the mantle [1] and forming carbonate‑rich melts such as kimberlites and carbonatites [2]. The melting curve of (dry) magnesite is well constrained [3, 4], but melting of magnesite in the presence of H2O, providing the basis for more complex (natural) systems, is poorly understood from some quenched experiments [5]. Also, the distribution of trace elements such as Li, Sr, Pb, and rare earth elements during melting of magnesite is poorly considered in models that evaluate the trace element budget of carbonate‑rich melts parental to kimberlites [6].

Here we report, first, the H2O‑present melting curve of magnesite between 2 and 12 GPa. The melting curve of magnesite mixed with 16 wt% brucite was established by in ‑ situ X‑ray diffraction measurements using the large volume press at P61B at PETRA III (DESY). Second, we report trace element partitioning data for congruent melting of calcite and incongruent melting of magnesite producing carbonate melt and periclase between 6 and 9 GPa. Those results were obtained from quenched experiments using a rocking multi‑anvil press at the GFZ overcoming equilibrium and quenching problems in previous studies [7].

 

1          Dasgupta and Hirschmann, The deep carbon cycle and melting in Earth's interior. Earth and Planetary Science Letters, 2010. 298(1-2): p. 1-13.

2          Jones, Genge, and Carmody, Carbonate Melts and Carbonatites. Reviews in Mineralogy and Geochemistry, 2013. 75(1): p. 289-322.

3          Solopova, Dubrovinsky, Spivak, Litvin, and Dubrovinskaia, Melting and decomposition of MgCO3 at pressures up to 84 GPa. Physics and Chemistry of Minerals, 2014. 42(1): p. 73-81.

4          Müller, Koch-Müller, Rhede, Wilke, and Wirth, Melting relations in the system CaCO3-MgCO3 at 6 GPa. American Mineralogist, 2017. 102(12): p. 2440-2449.

5          Ellis and Wyllie, Carbonation, hydration, and melting relations in the system MgO-H2O-CO2 at pressures up to 100 kbar. American Mineralogist, 1979. 64(1-2): p. 32-40.

6          Girnis, Bulatov, Brey, Gerdes, and Höfer, Trace element partitioning between mantle minerals and silico-carbonate melts at 6–12GPa and applications to mantle metasomatism and kimberlite genesis. Lithos, 2013. 160-161: p. 183-200.

7          Buob, Experiments on CaCO3-MgCO3 solid solutions at high pressure and temperature. American Mineralogist, 2006. 91(2-3): p. 435-440.

How to cite: Sieber, M. J., Reichmann, H., Farla, R., Appelt, O., Oelze, M., Lathe, C., and Koch-Müller, M.: H2O-present melting curve of magnesite and trace element distribution during melting of (dry) magnesite and calcite in the upper mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7797, https://doi.org/10.5194/egusphere-egu23-7797, 2023.

EGU23-9499 | Orals | GMPV1.3

TILDAS measurement of multiple clumped isotope ratios in carbonates: progress and new horizons 

David Nelson, Scott Herndon, Zhennan Wang, Jay Quade, and David Dettman

Isotopic analysis using high resolution Isotope Ratio Laser Spectroscopy (IRLS) has been shown to be advantageous to multiple geochemical applications during the last decade.  These advances include isotopic analysis of the bulk isotopic compositions of water, carbon dioxide, methane and nitrous oxide.  More recently, laser spectroscopy has been used by several groups to examine the isotopic compositions of methane, carbon dioxide and nitrous oxide when carrying two rare isotopes (so called clumped isotopes).   Our recent work using Tunable Infrared Laser Direct Absorption Spectroscopy (TILDAS) has demonstrated highly accurate (~0.01 ‰) measurements of the clumped (16O13C18O or 638 in HITRAN isotope notation) isotopic composition of carbon dioxide derived from carbonate samples with spectroscopic measurement times of ~30 minutes using a dual laser spectrometer.  That spectrometer is optimized for the measurement of the four isotopologues required to calculate Δ638 (or Δ47).  We present here our parallel project to develop a novel dual laser isotope analyzer capable of measuring multiple carbon dioxide isotopic signatures simultaneously.   Specifically, we simultaneously measure the isotopic abundances of the three most abundant clumped isotopologues (Δ638, Δ637 and Δ828) as well as 17O oxygen excess or Δ17O.  Δ638 and Δ828 correspond to the quantities Δ47 and Δ48 when measured by isotope ratio mass spectroscopy (IRMS).   Δ17O is very difficult to measure with IRMS and Δ637 has not been previously measured with any technique to the best of our knowledge.  The new instrument utilizes carefully chosen spectral windows, operates at low sample pressure and exploits automated laser frequency hopping.  This prototype instrument simultaneously measures seven isotopologues of carbon dioxide: 626, 636, 628, 627, 638, 637 and 828.  Our preliminary results for Δ828 (or Δ48) are displayed as an Allan-Werle plot which shows that the precision in the measurement of Δ828 is ~0.09‰ for a single 3 minute sample measurement referenced to a working reference gas.  The plot shows that instrumental drift is very small over periods of several hours and that the precision can be improved to 0.03‰ by processing 10 sub-samples or to 0.01‰ by processing 100 sub-samples.  These measurements are preliminary and somewhat idealized but show promise for this new technique.

How to cite: Nelson, D., Herndon, S., Wang, Z., Quade, J., and Dettman, D.: TILDAS measurement of multiple clumped isotope ratios in carbonates: progress and new horizons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9499, https://doi.org/10.5194/egusphere-egu23-9499, 2023.

For fundamental thermodynamic reasons, 13C-18O bonds in carbonate minerals formed under isotopic equilibrium conditions are more abundant than predicted for a random distribution of isotopes, yielding positive Δ47 clumped-isotope signatures which decrease as a function of formation temperature [1]. Although most Earth-surface carbonates are unlikely to achieve complete isotopic equilibrium, Δ47 values of many biogenic and abiotic calcites formed under very different crystallization conditions (and with irreconcilable water-calcite oxygen-18 fractionation laws) appear to follow indistinguishable temperature calibrations, as independently documented by various groups over the years [e.g., 2-4]. That is not to say that all groups agree on a single calibration linking Δ47 and temperature, and a recent comparison of 14 reprocessed calibration studies still found evidence for statistically significant inter-laboratory discrepancies [3]. Rigorous statistical tests aiming to prove or disprove consistency between Δ47 calibrations are particularly challenging because of potentially large and non-independent analytical errors associated with standardization procedures [5], and even in some cases by large correlations in the uncertainties of estimated formation temperatures, making classical least-squares regression approaches ill suited to model these calibration data sets.

Here I propose a new formulation for least-squares regression of data with an arbitrarily complex covariance structure linking all predictor and response observations, generally applicable to all sorts of geochemical data. I use this “Omnivariant Generalized Least-Squares” (OGLS) approach to compare 7 published Δ47 calibration data sets which have been (re)processed according to the newly established InterCarb Carbon Dioxide Equilibrium Scale (I-CDES), supposedly allowing robust comparisons between Δ47 measurements across laboratories [6]. None of these reprocessed calibration data sets are found to deviate significantly from a single, unified regression line, with an overall reduced chi-squared statistic (adjusted for data covariance according to OGLS) of 0.8 consistent with slightly overestimated uncertainties on temperature constraints. This finding marks another milestone in the 17-year-long progress of Δ47 thermometry, which has now solved most of the methodological challenges standing in the way of its widespread application to many scientific issues. In short: carbonate clumped-isotope thermometry is all grown up now.

[1] Schauble et al. (2006) 10.1016/j.gca.2006.02.011
[2] Kele et al. (2015) 10.1016/j.gca.2015.06.032
[3] Petersen et al. (2019) 10.1029/2018GC008127
[4] Anderson et al. (2021) 10.1029/2020GL092069
[5] Daëron (2021) 10.1029/2020GC009592
[6] Bernasconi et al. (2021) 10.1029/2020GC009588

How to cite: Daëron, M.: Making the Case for Reconciled Δ47 Calibrations Using Omnivariant Generalized Least-Squares Regression, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10066, https://doi.org/10.5194/egusphere-egu23-10066, 2023.

EGU23-10706 | ECS | Posters virtual | GMPV1.3

Geochemical and geochronologic investigations into carbonate veins from historical drill cores in undercover Mt Isa, NW Queensland 

Xingyu Chen, Renjie Zhou, David Wood, Daniel Stirling, Kamalendra Jhala, Ira Friedman, Matt Valetich, and Lizzy Philippa

This study investigates carbonate veins in five drill cores archived at Geological Survey of Queensland from NW Queensland, ~100 km south of Mt Isa, with geochemical and geochronologic approaches in order to characterise origins of fluids and their mineralisation potentials. Carbonate veins are mostly hosted in Proterozoic age (approximately 1800-1650 Ma) supra-crustal rocks, which are inferred from geophysics to be covered by 350 to 2,000 m of younger sedimentary rocks of the Eromanga and Georgina basins. Data regarding the nature of fluid activities is important for comparison between the undercover southern Mt Isa and outcropped Mt Isa mineral district, which is a world-class mineral province.

Multiple-phase carbonate veins (mostly calcite and dolomite) are identified, including late formed brittle veins, pyrite/chalcopyrite mineralisation-bearing carbonate veins, and calcite hosted in crackle breccias. Samples are prepared into one-inch polished mounts and studied with SEM-EDS, and in situ laser ablation ICP-MS for geochemical and U-Pb geochronological studies. Relatively pure calcite phases are also prepared with microdrill for stable isotope C and O analysis. Trace element datasets suggest enrichments in rare earth elements and ytterbium (REE+Y) with distinct negative Eu anomalies. Stable isotopes range ~-5 to – 15 (δ13CVPDB‰) and ~10 to 25 (δ18OVSMOW‰). Trace element data, Yb/La and Yb/Ca ratios, and stable isotope signatures imply that these carbonate veins have hydrothermal origins. 206Pb/238U geochronology data has indicated multi-phase calcite formation ranging from the late Neoproterozoic to Cretaceous. Our results provide a novel dataset to demonstrate the use of carbonate veins in revealing fluid activities in a mineral district and help the future exploration of critical mineral deposits in undercover southern Mt Isa when interpreted against regional structural data and well-documented mineralisation events in the northern Mt Isa district.

 

How to cite: Chen, X., Zhou, R., Wood, D., Stirling, D., Jhala, K., Friedman, I., Valetich, M., and Philippa, L.: Geochemical and geochronologic investigations into carbonate veins from historical drill cores in undercover Mt Isa, NW Queensland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10706, https://doi.org/10.5194/egusphere-egu23-10706, 2023.

EGU23-12216 | ECS | Orals | GMPV1.3

Triple oxygen isotope analyses of carbon dioxide, water and carbonates by VCOF-CRDS technique 

Justin Chaillot, Mathieu Daeron, Mathieu Casado, Amaelle Landais, Marie Pesnin, and Samir Kassi

Oxygen-17 excess (Δ17O) in carbonate minerals can provide valuable insights into past continental and marine environments, long-term trends in the temperature and oxygen-isotope composition of ancient oceans, isotopic disequilibrium effects in biogenic and abiotic carbonates, and cryptic diagenesis. Triple oxygen isotope analyses of carbonates and/or CO2 using isotope-ratio mass spectrometers (IRMS) remain challenging, however, because of isobaric interference between 16O13C16O and 16O12C17O. Using spectroscopic methods, the abundance of each CO2 isotopologue may be directly quantified, potentially providing simple, non-destructive measurements of δ13C, δ18O and Δ17O on small samples of CO2.

Here we report new data characterizing the application of VCOF-CRDS (V-shaped Cavity Optical Feedback - Cavity Ring Down Spectroscopy [1]) to the analysis of small samples (<40 μmol) of pure CO2, as typically produced by phosphoric acid digestion of carbonate minerals.

Instrumental drifts from various sources are observed to bias apparent isotopic abundances by a few tens of ppm, but these drifts are slow enough that they may be precisely monitored and corrected for by repeated analyses of a working gas interspersed between other analyses, requiring only ~8 mn per aliquot and 30 mn between consecutive “unkown” analyses. This approach was tested by analyzing repeated aliquots of another CO2 tank with a different isotopic composition, yielding instrumental repeatabilities of 12 ppm, 13 ppm and 7.4 ppm for δ13C, δ18O and Δ17O, respectively (95 % CL, Nf = 66).

The accuracy of our measurements was tested over a wide range of Δ17O values spanning 130 ppm, by analyzing CO2 equilibrated at 25 °C with different waters whose triple oxygen compositions were independently constrained in the SMOW-SLAP scale by IRMS measurements and by simple nonlinear mixing predictions. We find that our Δ17O measurements are well within analytical uncertainties of predicted values (RMSE = 1.2 ppm), with analytical repeatabilities (including isotopic equilibration and gas manipulation) of 8.6 ppm (95 % CL, Nf = 27).

We will also report the results of our ongoing investigation regarding the isotopic fractionation and analytical noise associated with different acid digestion protocols at different reaction temperatures, and the triple oxygen composition of various international reference materials already used for δ13C, δ18O, and clumped-isotope measurements.

Based on these results, we conclude that VCOF-CRDS offers excellent accuracy, along with state-of-the-art levels of analytical precision/linearity, for straightforward analyses of 17O excess in CO2, water, and carbonate minerals.

[1] Stoltmann et al. (2017) 10.1021/acs.analchem.7b02853

How to cite: Chaillot, J., Daeron, M., Casado, M., Landais, A., Pesnin, M., and Kassi, S.: Triple oxygen isotope analyses of carbon dioxide, water and carbonates by VCOF-CRDS technique, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12216, https://doi.org/10.5194/egusphere-egu23-12216, 2023.

EGU23-12645 | Posters on site | GMPV1.3

The onset of the Ediacaran Nama Group sedimentation in Namibia? 

Inigo Andreas Müller, Fabio Messori, Marcel Guillong, Giovan Peyrotti, Michael Schirra, Elias Samankassou, Ulf Linnemann, Mandy Hofmann, Johannes Zieger, Agathe Martignier, Anne-Sophie Bouvier, Torsten Venneman, Kalin Kouzmanov, and Maria Ovtcharova

The final stage of the Proterozoic, the Ediacaran, shields fascinating insights on the development and dispersal of complex metazoans related to dramatic compositional changes in the atmosphere and hydrosphere.  Alternating sequences of siliciclastic and carbonate rocks of the Namibian Nama basin record the final stage of the Ediacaran and contain a vast amount of soft-bodied fauna, as well as some of the first biocalcifying organisms. However, the sparsity of ash beds at the base of the Nama group, preclude accurate and precise constraints on the onset of the Ediacaran biota in Nama group and correlation with chemo stratigraphic records worldwide.  

Due to the scarcity of ash layers, we apply U-Pb dating to carbonate rocks especially from the lower stratigraphic sections of the Nama Group combining the spatial resolution of LA-ICP-MS and the high-precision ID-TIMS U-Pb dating. The combination with mineralogical and geochemical techniques (d13C, d18O, XRD, SEM, EPMA, CL imaging, LA trace element transects, Raman spectroscopy, clumped isotope thermometry, QEMSCAN, SIMS) enables us to better understand the nature of the analyzed carbonates to distinguish between more pristine and diagenetic phases.

This study elaborates on the potential and limitations of carbonate U-Pb dating for improved stratigraphic correlation on these ancient pre-Cambrian marine carbonates from the Nama Group.

How to cite: Müller, I. A., Messori, F., Guillong, M., Peyrotti, G., Schirra, M., Samankassou, E., Linnemann, U., Hofmann, M., Zieger, J., Martignier, A., Bouvier, A.-S., Venneman, T., Kouzmanov, K., and Ovtcharova, M.: The onset of the Ediacaran Nama Group sedimentation in Namibia?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12645, https://doi.org/10.5194/egusphere-egu23-12645, 2023.

Carbonate veins are ubiquitous in many ore deposits and are often interpreted as a late stage or cross cutting fluid flow events in the ore deposit history. Faults accommodate rock displacement and the resulting zones of weakness act as conduits for magma and localised magmatic-hydrothermal fluid flow, leading to the formation of ore deposits. Dating of both low temperature veins and brittle fault material has been notoriously difficult because of a lack of ‘datable’ material. Using innovative techniques, it is now possible to date carbonate with the U-Pb isotopic system.

Here we use in-situ U-Pb carbonate geochronology to date a variety of fault material and mineralised and unmineralised veins within a major fault-controlled Cu-Au-Mo porphyry system in the central Yukon, Canadian Cordillera. Over 50 samples have been dated, revealing a long history of faulting and fluid flow in the deposit spreading over 10s of millions of years between ~75 Ma and <20 Ma. We combine petrography, U-Pb carbonate geochronology, trace element geochemistry, and clumped isotope analysis to interpret the full temperature-time evolution of the fluids within the deposit. Our results show the carbonate veins crystallised during the main ore-forming event at ~75 Ma. Subsequently, there was a prolonged period of fault-controlled fluid pulsing that likely concentrated metallic minerals in the deposit. The findings show that carbonate veins are not always late features within ore deposits and are an underutilised resource for understanding the full temporal and fluid evolution of a system. Carbonate U-Pb geochronology is therefore potentially incredibly useful for telling the previously untold and long history of fluid flow in a variety of deposit types.

How to cite: Mottram, C., Kellett, D., Dennis, P., and Clog, M.: Longevity of fault-controlled fluid flow within a Cu-Au-Mo porphyry (Yukon, Canada) revealed by coupled U-Pb carbonate geochronology and clumped isotope analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13236, https://doi.org/10.5194/egusphere-egu23-13236, 2023.

EGU23-13798 | ECS | Posters virtual | GMPV1.3

Evolution of the hydrothermal fluids of the Yolindi Fe-Cu skarn deposit, Biga peninsula, NW Turkiye: Evidence from carbon-oxygen isotopic variations of calcite minerals 

Mustafa Kaya, Mustafa Kumral, Amr Abdelnasser, Cihan Yalçın, Sercan Öztürk, Hatice Nur Bayram, and Beril Tanç-Kaya

This work deals recently with the carbon (δ13C) and oxygen (δ18O) isotopic variations in the calcite associated with the hydrothermal mineralization to comprehend the nature of the ore fluid and its source and the evolution of the Yolindi Fe-Cu skarn deposit at North of Biga peninsula (NW Turkiye). The Yolindi area is made up of Torasan Formation (marble, hornfels, phyllite, and schist) which was intruded by Oligocene Hallaçlar volcanic rocks and later early Miocene Şaroluk plutonic rocks. The Yolindi Fe-Cu skarn deposit has been formed along the eastern contact of Şaroluk pluton with the Torasan Formation having widespread prograde and/or retrograde skarn, silicic, and carbonate (calcite) alteration. The prograde skarn is less observed and characterized by formation of garnet with subordinate magnetite. While, the retrograde skarn is highly extensive having epidote, actinolite, chlorite, and carbonate including pyrite, magnetite, chalcopyrite, and specular hematite with subordinate sphalerite and galena. Malachite, azurite, goethite, hemimorphite, and cerussite represent the supergene minerals which locally replaced Fe-oxide and Fe-Cu±Zn±Pb sulfide minerals. At the Yolindi Fe-Cu skarn deposit, carbon and oxygen isotope ratios of calcite minerals from the exoskarn zone are -15.5 to -2.0 ‰ relative to PDB and 0.9 to 17.9 ‰relative to V-SMOW, respectively. Furthermore, it was inferred from the calculated carbon isotopic composition of an ore-forming fluid (δ13CCO2 = -12.7 to +0.8 ‰) that the carbon in the fluid is identical to the reduced carbon in sedimentary and metamorphic rocks. However, the calculated fluid's δ18OH2O values—which vary from 0.9 to 17.2 ‰VSMOW—indicate a mixture of metamorphic and magmatic origins for the hydrothermal fluid. This fluid mixing which has high range of C-O isotopic compositions has been due to a temperature effect along with either CO2 outgassing or fluid/rock interactions. Additionally, the mineralizing fluid is most likely derived from the metamorphic dehydration of carbonate rocks in the Torrasan Formation during Yolindi skarn formation.

Keywords: carbon (δ13C) and oxygen (δ18O) isotope; Fe-Cu Yolindi skarn deposit; Biga peninsula; NW Turkiye

How to cite: Kaya, M., Kumral, M., Abdelnasser, A., Yalçın, C., Öztürk, S., Bayram, H. N., and Tanç-Kaya, B.: Evolution of the hydrothermal fluids of the Yolindi Fe-Cu skarn deposit, Biga peninsula, NW Turkiye: Evidence from carbon-oxygen isotopic variations of calcite minerals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13798, https://doi.org/10.5194/egusphere-egu23-13798, 2023.

EGU23-15731 | ECS | Posters on site | GMPV1.3

Variability of (234U/238U) in surface water and tufa deposits: A study in the Mono Basin, California, USA 

Ke Lin, Sidney R. Hemming, Guleed Ali, In-Tian Lin, Chih-Chieh Su, Scott W. Stine, N. Gary Hemming, and Xianfeng Wang

Uranium concentrations and 234U/238U activity ratios (δ234U) of Earth’s surface waters can provide independent and complementary information on changes in weathering regime and hydroclimate. The response of δ234U variation in surface waters in US Great Basin to climate change however remains unclear, which brings ambiguities in interpreting δ234U in aquatic carbonate deposits. Here, we analysed U concentration and δ234U in a suite of surface waters (creeks, springs and lake) as well as tufa deposits from the last glacial lake highstands in the Mono Basin, California, USA to assess the modern uranium budget in the lake water and the controlling factors on its δ234U. We find that U concentrations in groundwater springs are about one order of magnitude higher than those of creek waters. Hence, even though springs only deliver about 15% of annual inflow to the lake, they contribute 70% of U in the lake water. The residence time of U in lake water is calculated to be approximately 15,000 years, on the same order as those of Li, Na, and Cl, but significantly longer than those of alkaline earth elements. The δ234U in Mono Lake water is 180‰, same as in modern-day tufa deposits. The δ234U in lake highstand tufas is ~ 220‰, suggesting much more enhanced physical weathering associated with mountain glacial activities in the basin, even though chemical weathering was also stronger due to increased precipitation. On the other hand, the higher δ234U values (~ 250‰) in modern creeks and springs is consistent with the overall dry environment and stronger physical weathering in the basin. The 40‰ decrease in δ234U of lake water however cannot be explained by radiative decay. We hypothesis that lake water was more frequently stratified in the past, during the last glacial in particular, and the resulted anoxic environment in deep lake water has probably facilitated precipitations more enriched in 234U. 

How to cite: Lin, K., Hemming, S. R., Ali, G., Lin, I.-T., Su, C.-C., Stine, S. W., Hemming, N. G., and Wang, X.: Variability of (234U/238U) in surface water and tufa deposits: A study in the Mono Basin, California, USA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15731, https://doi.org/10.5194/egusphere-egu23-15731, 2023.

EGU23-15952 | ECS | Posters on site | GMPV1.3

Crack-seal veins: records of 600-million-year complex tectonic and fluid flow evolution in Saudi Arabia 

Adhipa Herlambang, Ardiansyah Koeshidayatullah, Chaojin Lu, Abduljamiu Amao, Abdulwahab Bello, Faisal Al-Ghamdi, Muhammad Malik, and Khalid Al-Ramadan

The Ediacaran Period (635-538 Ma) was marked by considerable tectonic activity, including the end of the Pan-African episode – a long interval of mountain building, rifting, and reorganization spanning most of the Neoproterozoic Era. In Saudi Arabia, the Ediacaran outcrops were developed and preserved in several isolated half-grabens linked to the Ediacaran to early Cambrian Najd strike-slip fault system. This fault system manifested, particularly in the study area, as intensive fractures with a distinctive crack-seal veins morphology. Understanding the mechanism and origin of such fractures could provide unique insights into the structural evolution and paleo fluid flow throughout the history of the Arabian Plate. However, no studies have focused on different structural-controlled diagenetic processes in the Neoproterozoic sequences across the Arabian Plate. Here, we examined precipitated veins along a well-exposed 300 m thick Ediacaran host rock exposure by integrating high-resolution geochemical analyses, carbonate clumped isotopes, fluid inclusions, advanced petrography analysis of Cathodoluminescence microscopy to unravel the structural diagenesis of these Ediacaran strata. The δ18O and δ13C of the carbonate host rocks vary from -11.79 to -7.83‰, and -0.58‰ to 1.1‰, respectively. The estimated paleotemperature of the host rock derived from the clumped isotope is 47-60°C. Furthermore, the current results show that the calcite veins appear in different stages, orientations, geometries, and mineralogy. The δ18O and δ13C of the crack-seal veins vary between -11.2 to -7.8 ‰ and -2.9 to 1.9‰, respectively. The estimated clumped-derived paleotemperature of this vein is 95°C, even higher up to 136°C by utilizing the fluid inclusions. On the other hand, the Mn-rich later phase veins, which cross-cut the crack-seal veins, indicate an isotopic composition of -10.9 to -10.6‰ for δ18O and -18.2 to -15‰ for δ13C, with the estimated paleotemperature of 74-84°C. Hence, we argue that the structural diagenesis history in the study area comprises several distinct tectonic events and fluid circulation members along the fractures associated with different stages of basin evolution. Our findings, for the first time, offer a new understanding of paleo fluid circulation and also highlight the multi-proxy’s potential for investigating the structural diagenesis of calcite veins in the Ediacaran host rock in Arabia.

How to cite: Herlambang, A., Koeshidayatullah, A., Lu, C., Amao, A., Bello, A., Al-Ghamdi, F., Malik, M., and Al-Ramadan, K.: Crack-seal veins: records of 600-million-year complex tectonic and fluid flow evolution in Saudi Arabia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15952, https://doi.org/10.5194/egusphere-egu23-15952, 2023.

EGU23-15974 | ECS | Orals | GMPV1.3 | Highlight

LA-ICP-MS U-Pb carbonate geochronology and its geological applications 

Shitou Wu, Nick Roberts, and Zhongwu Lan

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb geochronology for carbonate minerals, calcite in particular, is rapidly gaining popularity as an absolute dating method. In this study, we review the latest technical progress in LA-ICP-MS carbonate geochronology, including the pre-screening strategies (on-line spot selection with a threshold, image-guided approach, and image-based approach), preferred instrumentation (Q-ICP-MS, SF-ICP-MS and MC-ICP-MS), calibration methods, common Pb corrections and the development of reference materials, with the aim of further improving the precision and accuracy of this technique. We emphasized the characterization of two calcite reference materials (TLM and LSJ07) for micro-beam U-Pb geochronology and C, O isotope ratio measurements. The latest geological applications of LA-ICP-MS U-Pb carbonate geochronology in dating of diagenesis and hydrothermal activity were reviewed.

How to cite: Wu, S., Roberts, N., and Lan, Z.: LA-ICP-MS U-Pb carbonate geochronology and its geological applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15974, https://doi.org/10.5194/egusphere-egu23-15974, 2023.

EGU23-16279 | ECS | Posters on site | GMPV1.3

Interpreting hydrothermal clumped isotope temperatures in the Irish Zn-Pb ore field 

Aileen Doran, Steven Hollis, Julian Menuge, Alina Marca, Paul Dennis, and David van Acken

With the introduction of climate action plans by many countries globally, the development of green technologies like electric vehicles and renewable infrastructure is expected to increase. These technologies are resource intensive, meaning we will require increased production of metals to meet the growing demands of society. However, discovery and exploration rates are not increasing at the same rate as demand. Improving understanding of ore system formation and evolution is a crucial step in aiding future exploration, to help supply these critical resources.

In hydrothermal systems, carbonate minerals (e.g., calcite and dolomite) are often associated with all stages of ore formation, with fluid inclusion thermometry and carbon-oxygen (C-O) isotope ratios traditionally used to study fluid temperature and composition. However, there are several challenges still remaining with these techniques, with fluid inclusions often too small, ruptured or deformed for adequate study. In carbonate minerals, the rare, heavy isotopes 13C and 18O bond or clump more frequently at lower temperatures, with the magnitude of clumping inversely temperature-dependent. Measurement of clumped C-O isotope ratios, using gas source isotope spectrometry, simultaneously yields carbonate δ13C and δ18O values and generates mineral precipitation temperatures, allowing fluid δ18O to be directly calculated. While traditionally applied to low temperate environments, recent applications have included hydrothermal ore systems to study fluid temperature and mixing. When combined with other techniques, such as strontium isotopes, new understanding of the sources, movement and compositional evolution of fluids can be deciphered.

Recent clumped C-O and strontium isotope analyses of ore-related carbonates from the Lisheen and Galmoy deposits, southern Irish Zn-Pb ore field, have facilitated the study of fluid sources, temperatures, mixing, and modification. Lisheen and Galmoy are  hosted in a belt of regionally dolomitized Lower Carboniferous (Mississippian) marine limestones, cut by a series of NE-SW-trending ramp-relay normal faults. Study of these deposits reveals that early dolomitizing and later hydrothermal fluids are part of a complex multistage continuum, with phases of fluid mixing, compositional buffering due to dissolution, and isotope resetting. Consequently, studies of carbonates in other deposits may yield new insights into ore formation, ultimately helping exploration for crucial resources.  

How to cite: Doran, A., Hollis, S., Menuge, J., Marca, A., Dennis, P., and van Acken, D.: Interpreting hydrothermal clumped isotope temperatures in the Irish Zn-Pb ore field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16279, https://doi.org/10.5194/egusphere-egu23-16279, 2023.

Coastal Fars is the main gas-bearing region in Iran, where the reservoir units are dedicated to the Paleozoic hydrocarbon system. Geochemical explorations in this region indicate that natural gas is commonly associated with elevated non-hydrocarbon components, especially hydrogen sulfide and carbon dioxide. Previously it was shown that the Thermochemical Sulfate Reduction (TSR) is the most probable mechanism, accounting for H2S occurrence in Permo-Triassic reservoirs in this region; however, its effect on the accumulated gas’s chemistry transformation has not been studied thoroughly. In this study, the molecular and isotopic composition of 12 gas samples in addition to the previously-published results of integrated analyses on rock and condensate, were utilized to trace potential alterations caused by the given phenomenon exhaustively. A slight increase in aromatic to saturate hydrocarbon components ratio with the extent of TSR and the presence of reported sulfur-rich pyrobitumen (Saberi, et al., 2014) indicate liquid hydrocarbon involvement in the primary stage of the sulfate reduction process. Further, the differential increase of δ13C of gas components, decrease of δ13C (methane) - δ13C (ethane) (from -4.3 to -13.1‰), and increase in carbon-dioxide concentration with the increase of hydrogen sulfide along with gas dryness (from 91 to 96%) show the dominancy of C2-C4 hydrocarbon gas components in the second stage of TSR. Comparative low reservoir temperature (~90°C) does not correspond to the contribution of methane into the given phenomenon; however, a noticeable increase in δ13C (methane) (from -41.7 to -34.7‰) with the increase of hydrogen sulfide was seen. Thermochemical Sulfate Reduction impact on studied parameters is analogous to thermal maturation, but the process from heavy-hydrocarbon-dominated TSR to methane-dominated TSR presents different trends of δ13C (methane) - δ13C (ethane), ln(C1/C2) from those of maturation (Hao, et al., 2008). Simultaneous carbon-dioxide content increase and decrease in its isotopic composition with the extent of TSR indicate its presence relevancy to the given phenomenon; however, carbon isotope values of CO2 (from -5.92 to -13.93‰) are too heavy to verify this idea. According to Dai et.al (Dai, et al., 1996) it can be concluded that carbonate's dissolution has contributed to carbon-dioxide gas. Hence, a series of TSR corresponding to condensate, wet gas, and dry gas stages, respectively, has led to higher aromatic/saturate ratios, heavier hydrocarbon components, lighter carbon dioxide molecules, and relative gas dryness in the studied fields.

 Bibliography

  • Dai, J. X., Song, Y., Dai, C. S. & Wang, D. R., 1996. Geochemistry and Accumulation of Carbon Dioxide Gases in China. AAPG Bulletin, 80(10), pp. 1615-1626.
  • Hao, F. et al., 2008. Evidence for multiple stages of oil cracking and thermochemical sulfate reduction in the Puguang gas field, Sichuan Basin, China. AAPG Bulletin, 92(5), pp. 611-637.
  • Saberi, M. H., Rabbani, A. & Ahmadabadi, K. A., 2014. The Age and Facies Characteristics of Persian Gulf Source Rocks. Petroleum Science and Technology, Volume 32, pp. 371-378.

 

How to cite: Gholizadeh, H., Krasnova, E., and Rabbani, A.: Assessment of natural gas chemistry alteration by extent of H2S production and evidences for multiple stages of TSR in two gas fields in Gavbandi-High, Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-782, https://doi.org/10.5194/egusphere-egu23-782, 2023.

A key task in the analysis of exploration geochemical data is the selection and application of efficient classification models to discriminate mineralization-related signals from other processes affecting variation in element concentrations. Similarly in environmental or urban geochemistry one objective is to separate geochemical patterns associated with anthropogenic contamination from geogenic processes. To classify geochemical maps into background or anomalous samples or regions, a variety of mathematical and statistical models have been developed. In this study various fractal modelling has been applied to centered logratio transformed Cu, Ba, Mn, Pb, Zn, In, As, Au, and Ag contents of soil samples from the Geochemical Atlas of Cyprus. Areas with contamination have previously been shown not to display normal fractal behavior for values exceeding lithology-dependent background populations. Therefore, two new fractal methods – concentration-concentration (C-C) and concentration-distance from centroid-points (C-DC) – were applied to discriminate anthropogenic from geogenic anomalies. One of the strongest indicators of proximity to major Cu mineralization is In. The C-C model displays broad similarity between the Cu-In pairing and the raw Cu, and between its reverse in the In-Cu pairing and raw In. Of the five populations that emerge from the Cu-In fractal model, the first two (regional background and weakly anomalous) are largely restricted to the Circum-Troodos Sedimentary Succession units. The moderately anomalous population extends across all the basalts and north from the Troodos Ophiolite (TO) across the fanglomerates and more recent alluvium-colluvium that contains material shedding north off the TO. It is noted that the strongest anomalies are at the boundary between the sheeted dyke complex and basalts and on one of the major NE-trending structures that cut across the TO, but where there are only a small number of minor Cu mineralization occurrences. In the C-DC model, the centroids used to model the spatial variation of the soil geochemistry were the known mineral deposits. The Cu C-DC model delivers just two populations that are lithologically-controlled. The first spans the ultramafic TO core and the Pakhna Formation carbonates (the two extremes in the raw data geochemical compositions), and all other units, including the TO mafics, Mamonia Terrain, and the fanglomerates and alluvium-colluvium areas in the second population. The In C-DC model is somewhat similar to the In-Cu C-C model, but the second major population is more restricted to the sections of the basalts containing known Cu mineralization as well as a restricted zone in the sheeted dykes in western TO. Applying the C-DC model to the transformed scores, there are three main populations evident. The highest one contains all the known Cu mines and mineral deposits, as well as a number of NE-trending zones that cut across the sheeted dykes on the western and the eastern sides of the TO, and which also appear to follow the major sinistral faults that transect the TO.

How to cite: Sadeghi, B. and Cohen, D.: Discrimination of anthropogenic contamination and the effects of mineralization in soils from background patterns using multifractal modelling: Cyprus case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1585, https://doi.org/10.5194/egusphere-egu23-1585, 2023.

EGU23-2189 | ECS | Orals | GMPV1.4 | Highlight

SelfMin: Self-Supervised Deep Learning for Advanced Mineralogical Analysis 

Ardiansyah Koeshidayatullah and Ivan Ferreira

Mineralogical analysis is critical for understanding the origins and properties of various rock types. Recent advancements in artificial intelligence technologies, particularly supervised deep learning, have transformed qualitative and quantitative mineral analysis. However, current deep-learning approaches require high-quality annotated datasets to acquire and identify different mineralogical characteristics and properties. This is exacerbated by the time-consuming and error-prone labeling processes for the datasets. With self-supervised architectures matching supervised approaches in many computer vision tasks, it is timely to investigate the potential of Self-Supervised Learning (SSL) models in the geosciences. As a result, we use a self-supervised semantic segmentation model to identify and characterize minerals in thin sections, with the model attempting to obtain categories of interest from images without the need for human intervention in annotating the minerals. In this study, we adopted a Self-Supervised Transformer architecture and proposed SelfMin to automatically segment out pyrite minerals from other background gangue minerals in the thin section. Our proposed method achieved 80% in the mean Intersection over Union (mIoU) metric, indicating the model's ability to accurately segment minerals that were not labeled during the annotation process. This work describes the first use of self-supervised deep learning in mineralogical analysis. Further application of this proposed method would allow a robust and efficient advanced qualitative and quantitative mineralogical analysis. It also demonstrates how this technique can be implemented to avoid the need for a large volume of high-quality labeled datasets in other image-based deep learning geosciences analyses.

How to cite: Koeshidayatullah, A. and Ferreira, I.: SelfMin: Self-Supervised Deep Learning for Advanced Mineralogical Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2189, https://doi.org/10.5194/egusphere-egu23-2189, 2023.

EGU23-2439 | ECS | Posters on site | GMPV1.4

Soil Parameters Prediction from Hyperspectral Images via Multitask Learning 

Xiangyu Zhao, Zhitong Xiong, and Xiaoxiang Zhu

Soil parameters are relevant and valuable for various applications such as agriculture production, scientific research, and policy making. Since acquiring such physical or chemical information could be cost-consuming by traditional methods, remote sensing and data analysis have become exciting research fields for soil parameter prediction tasks.   Many papers show that minerals and chemical materials correlate with the corresponding spectral reflectance. Based on this characteristic, there are many works using different data analysis methods such as machine learning and deep learning to predict soil properties, especially from multi- and hyper-spectral images. However, limited by the small data size, many models suffer from the overfitting problem and could not extrapolate to unseen data. Moreover, the currently existing methods only generate predictions with no consideration of the correlation among different target parameters. In this work, we propose and implement a deep learning based multitask method to predict multiple chemical properties simultaneously from hyperspectral images. To initialize the model, we use the pre-trained weights from ImageNet. To make better use of the correlation among different parameters, our model consists of shared layers and task-specific branches where each customized branch generates the prediction for one target property. Our method is implemented on the dataset from the Hyperview challenge organized by KP Labs and ESA. In this dataset, 1732 hyperspectral patches are available now and each patch has 4 soil parameters including K, P205, Mg, and pH. After comprehensive experiments, our method achieves the highest score of 0.87, which shows superior performance in this regression task.

How to cite: Zhao, X., Xiong, Z., and Zhu, X.: Soil Parameters Prediction from Hyperspectral Images via Multitask Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2439, https://doi.org/10.5194/egusphere-egu23-2439, 2023.

EGU23-3925 | Posters on site | GMPV1.4

Designing an API for a mineralogical database 

Liubomyr Gavryliv, Vitaliy Ponomar, and Marián Putiš

An Application Programming Interface (API) is a secured, documented and accessible web service and an entry point to any database—both relational and non-relational. As a rule, it exposes the data in different formats and allows filtering of the data by utilizing the query parameters. Accordingly, it allows the developers and data scientists to retrieve and query data through HTTP or WebSocket protocols using command-line HTTP clients or language-specific ones (e.g., axios, requests). The most complicated and essential aspects of developing an API are choosing the stack, structuring the codebase and optimizing the application's performance. 

A general rule of thumb is to develop an API to be (1) platform-independent and (2) support the versioning and evolution of the service by adding new functionalities while supporting the previous versions. Other features of a robust and reliable API are documentation according to OpenAPI Specification (OAS), scalability, caching, development and production environments portability, concurrency and more.

mineralogy.rocks API for mineralogical and related data is currently a work in progress with open-source code. It follows RESTful architectural concepts, best practices of clean codebase development and the twelve-factor methodology. The application is developed in Django—a Python web framework and utilizes PostgreSQL 13 database under the hood. The APIs' design is organized around the resources, e.g. the endpoints' naming conventions are predictable, standard and follow the same patterns. 

The codebase structure deviates from the standard out-of-the-box structure provided by the Django framework to isolate database-, server- and application-specific utilities. The local environment of the application is set up using Docker and docker-compose containerization technology for the efficiency of the development. 

The CI/CD integration has zero downtime—it is organized around GitHub Actions that allow for building the application, deploying the isolated container to a cloud, and updating the Kubernetes cluster application accordingly. 

The mineralogy.rocks API supports open science and promotes the innovation, quality, and public impact of mineralogy. Our open science activities are implemented to make the results produced and used in research publicly available and their metadata quickly and widely available for reuse.

This project, No. 3007/01/01, has received funding from the European Union’s Horizon 2020 research and innovation Programme based on a grant agreement under the Marie Skłodowska-Curie scheme No. 945478 and was supported by the Slovak Research and Development Agency (contract APVV-19-0065).

How to cite: Gavryliv, L., Ponomar, V., and Putiš, M.: Designing an API for a mineralogical database, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3925, https://doi.org/10.5194/egusphere-egu23-3925, 2023.

EGU23-4648 | ECS | Orals | GMPV1.4

The emergence of Continental Crust Revealed by Machine Learning 

Chuntao Liu, C. Brenhin Keller, Xiaoming Liu, and Zhou Zhang

Reconstructing the emergence of the modern continental crust is crucial to understand the evolution of the crust, the onset of plate tectonics, elemental cycling, and long-term climate. However, it remains highly contentious about when and how the major subaerial continental crust emerged over time. Here, we used a machine learning (ML) model (XGBoost) to reveal the exposed history of continental crust over the last 3.8 billion years ago (Ga). First, we compiled ~10,000 modern subaerial or submarine basalts with major and trace elements to train the ML model. Then, the trained ML model (with resampling) was utilized to predict and calculate the mean proportions of subaerially erupted continental basaltic rocks since 3.8 Ga. The result suggested that the subaerial proportion only reached about 50% at ~2.5 Ga, indicating the exposure of the continental crust was far from the present-day level at the end of the Archean era. On the other hand, since ~1.8 Ga, the subaerial proportion of the continental crust exhibited a dynamic balance between ~60% and 80%, reaching the present-day level.

How to cite: Liu, C., Keller, C. B., Liu, X., and Zhang, Z.: The emergence of Continental Crust Revealed by Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4648, https://doi.org/10.5194/egusphere-egu23-4648, 2023.

The diverse suite of trace elements incorporated into apatite in ore-forming systems has important applications in petrogenesis studies of mineral deposits. Trace element variations in apatite can be used to distinguish between different types of rocks as well as discriminating between deposit types, and thus have potential as mineral exploration tools. Such classification approaches commonly employ two-variable scatterplots of apatite trace element compositional data. While such diagrams offer easy and convenient visualization of compositional trends, they often struggle to effectively distinguish deposit types because they do not employ all the high-dimensional (i.e. multi-element) information accessible from high-quality apatite trace element analysis. To address this issue, we employ, for the first time, a supervised machine learning-based approach (eXtreme Gradient Boosting, XGBoost) to correlate apatite compositions with ore deposit type, utilizing high-dimensional information. We evaluated 8629 apatite trace element data from five deposit types (porphyry, skarn, orogenic Au, iron oxide copper gold, and iron oxide-apatite) along with unmineralized apatite to discriminate between apatite in mineralized vs unmineralized systems. We could show that the XGBoost classifier efficiently and accurately classifies high-dimensional apatite trace element data according to the ore deposit type (overall accuracy: 94% and F1 score: 89%). Interpretation of the model using the SHAPley Additive exPlanations tool (SHAP) shows that Th, U, Eu and Nd are the most indicative elements for classifying deposit types using apatite trace element chemistry. Our approach has broad implications for the understanding of the sources, chemistry and evolution of melts and hydrothermal fluids resulting in ore deposit formation.

Keywords: Machine learning; apatite; Trace elements; Ore deposit type; XGBoost

How to cite: Zhou, T., Qiu, K., and Wang, Y.: From Trace Elements to Petrogenesis: A Machine Learning Approach to Determine Ore Deposit Type from Trace Elements Analysis of Apatite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4857, https://doi.org/10.5194/egusphere-egu23-4857, 2023.

EGU23-5095 | ECS | Posters virtual | GMPV1.4

Metal mineral classification under microscope images using deep learning 

Yiwei Cai, Kunfeng Qiu, and Zhaoliang Hou

Analysis of optical microscopic image data is crucial for identifications of mineral phases, and thus directly relevant to the subsequent methodology selections of the further detailed petrological exploration. So far, large-dimensional image analyses are dominantly based on digital image datasets, and the automatic identification of the optical microscopic data is still poorly examined. Here, by testing the Swin Transformer, a deep learning algorithm on different metal mineral phases, we proposed a well-behaved mineral recognizer with high accuracy of 92.8% and strong global ability. In addition, we apply Class Activation Mapping (CAM) is introduced for the first time in mineral identification tasks and reveals the interpretability of the models, allowing us to more intuitively observe that mineral edges are the most effective model identification features. The results demonstrated that optical microscope data can not only rely on pixel information, and machine learning can accurately extract all available attributes, which reveals the potential to assist in data exploration and provides an opportunity to carry out spatial quantization at a large scale (cm-mm).

Keywords: Metal mineral; Microscope images; Deep learning; Swin Transformer; Class Activation Mapping

How to cite: Cai, Y., Qiu, K., and Hou, Z.: Metal mineral classification under microscope images using deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5095, https://doi.org/10.5194/egusphere-egu23-5095, 2023.

The standard absolute entropies of many minerals and mineral-based inorganic materials are unknown, thereby precluding a complete insight into their thermodynamic stability. This includes many apatites. The Apatite supergroup is one of the largest groups of minerals. Consequently, they are an incomparable testing ground for finding regularities in the variation of their thermodynamic function of state, e.g., standard entropy (S°). In the early 2000’s Jenkins and Glasser [1] showed that the formula unit volume alone, Vm, can be used to estimate the standard entropy for any inorganic compound.

It was recently indicated that in terms of their thermodynamic properties, the apatite supergroup splits into distinct subgroups (populations) [2]. These subgroups are formed by Me10(AO4)6X2 with the same Me2+ cations (e.g., Pb2+, Cd2+, Ca2+, Ba2+, Sr2+) and tetrahedral AO43- anions (e.g., A=P, As, V), but with different anions at the X position (e.g., F-, Cl-, Br-, I-, OH-). We found strong linear relationships between of apatites and their Vm observed within these subgroups. A system of linear relationships (calibrated with existing experimental data) indicating high positive correlations within selected subgroups of apatites is presented in Fig. 1.

Fig. 1 Standard entropy (S°) vs. formula unit volume (Vm)for selected apatite subgroups. Errors bars are within the marker.

Table 1. Selected estimated standard entropies (S°) and calculated formation entropies (ΔS°f, el)of iodine apatites.

Apatite

Estimated S° (J/mol·K)

ΔS°f, el (J/mol·K)

Ca10(PO4)6I2

840.7

-2412.8

Sr10(PO4)6I2

1117.2

-2264.2

Pb10(PO4)6I2

1201.1

-2271.4

Ca10(AsO4)6I2

1016.1

-2205.0

Pb10(AsO4)6I2

1364.5

-2075.5

Pb10(VO4)6I2

1359.6

-2040.0

 

Using the new estimated with high accuracy values, it is possible to calculate the Gibbs energy of formation and plot stability fields for apatites for which this has not been possible so far. Financial support for the research was provided to B.P. by the Polish National Science Centre (NCN) grant No. 2017/27/N/ST10/00776.

References:

[1] Jenkins, H. D. B., & Glasser, L. (2003). Standard absolute entropy, values from volume or density. 1. inorganic materials. Inorganic Chemistry42(26), 8702-8708.

[2] Puzio, B., & Manecki, M. (2022). The prediction method for standard enthalpies of apatites using the molar volume, lattice energy, and linear correlations from existing experimental data. Contributions to Mineralogy and Petrology177(11), 1-34.

[3] Wang, J. (2015). Incorporation of iodine into apatite structure: a crystal chemistry approach using Artificial Neural Network. Frontiers in Earth Science3, 20.

 

How to cite: Puzio, B. and Manecki, M.: Estimation of missing third-law standard entropy of apatites using the optimized Volume-based Thermodynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5863, https://doi.org/10.5194/egusphere-egu23-5863, 2023.

EGU23-6284 | ECS | Posters virtual | GMPV1.4

Machine learning based approach for zircon classification and origin 

Ziyi Zhu, Kunfeng Qiu, Fei Zhou, Yu Wang, and Tong Zhou

Zircon, a stable paragenetic mineral in various geological environments, has been recognized as a great tool to study the ages of primary rocks. Trace elements of zircons thus can record the geological evolution processes. Zircon-associated trace elements have been long studied for zircon classification and formation traditionally using binary diagram technique, classical examples including Th-U and LaN-(Sm/La)N diagrams. However, with the massive increase of zircon research, the traditional binary diagrams currently cannot precisely classify zircon types because the binary plot cannot demonstrate the higher dimensional information. It therefore significantly restricts a clear understanding of zircon formation. To address the research gap, we performed the machine-learning-based approaches on 3498 zircon trace-element data of different zircon genetic types, producing high-dimensional zircon-classification diagram plots. We applied and tested four machine learning methods (random forest, support vector machine, artificial neural network, and k-nearest neighbor) and proposed that support vector machine can best contribute to zircon genetic classification study, with an 86.8% accuracy in the prediction of zircon type and formation. In addition to the high-dimensional zircon classification diagram, this work massively improves the accuracy of zircon formation analyses by trace elements, which benefit future studies in zircons. Using the machine learning approach on zircon trace element big data is an effective multidisciplinary exploration of the modern data science technique in the geochemistry study.

How to cite: Zhu, Z., Qiu, K., Zhou, F., Wang, Y., and Zhou, T.: Machine learning based approach for zircon classification and origin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6284, https://doi.org/10.5194/egusphere-egu23-6284, 2023.

EGU23-8924 | ECS | Orals | GMPV1.4 | Highlight

Symmetry statistics of mineral – paragenetic mode pairs 

Marko Bermanec, Noa Vidović, Liubomyr Gavryliv, Robert M. Hazen, Daniel R. Hummer, Shaunna M. Morrison, Anirudh Prabhu, and Jason R. Williams

Characterizing the types of crystalline structures that form in different environments helps us to better interpret the geologic record and deepens our understanding of mineral stability. To this end, the Dolivo – Dobrovol’sky symmetry index provides a convenient way to quantify the statistical trends in the symmetry of minerals over time (Bermanec et al. 2022). Behavior of the Dolivo - Dobrovol’sky symmetry index was investigated for different paragenetic modes of minerals (Hazen and Morrison 2022). Two datasets were used and compared (code and datasets are available on https://github.com/NoaVidovic/pgm-mineral-pairs-pg). The first one used only minerals, and each mineral was considered just once. In contrast, in the mineral–paragenetic mode pair dataset, minerals were counted once for each of the paragenetic modes in which they occurred.

The paragenetic mode dataset incorporates a number of properties associated with each of more than 60 modes of formation, including relative age and order of that mode’s first appearance, estimated minimum and maximum temperature and pressure of formation, and duration. Paragenetic mode order does not substantially affect the symmetry index of minerals. However, some trends are evident when inspecting the properties of given paragenetic modes. The symmetry indices show a strong correlation with the maximum temperature, maximum pressure, and minimum pressure of paragenetic modes they belong to (Hazen et al. 2022) with correlation coefficients of 69%, 84% and 95%, respectively when using the mineral dataset. These trends show that minerals formed at higher temperature display higher overall symmetry. Trends for pressure are enigmatic: correlations show that minerals formed at higher minimum pressure tend to favor lower symmetry, whereas minerals formed at higher maximum pressure tend to favor higher symmetry.

When using the mineral–paragenetic mode dataset, the correlation coefficients are significantly lower at 42%, 30% and 89% for maximum temperature, maximum pressure, and minimum pressure, respectively. The lower correlation coefficients obtained using the mineral–paragenetic mode pairs might indicate that the paragenetic mode is not as important in terms of trends in symmetry as initially thought. On the other hand, considering a much higher correlation coefficient for the mineral dataset, perhaps there is a more dominant effect where certain P-T conditions tend to favor certain types of symmetry at equilibrium.

How to cite: Bermanec, M., Vidović, N., Gavryliv, L., M. Hazen, R., R. Hummer, D., M. Morrison, S., Prabhu, A., and R. Williams, J.: Symmetry statistics of mineral – paragenetic mode pairs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8924, https://doi.org/10.5194/egusphere-egu23-8924, 2023.

EGU23-10228 | ECS | Orals | GMPV1.4 | Highlight

Interpreting Machine Learning Models for Geochemistry Data Classification using Decision Boundary Maps 

Yu Wang, Kunfeng Qiu, Alexandru Telea, Zhaoliang Hou, and Haocheng Yu

Machine learning has been shown to be a highly effective method for classifying geochemistry data, such as mineral forming environments and rock tectonics. However, it can be difficult to understand the decision-making processes of these models. To address this issue, we propose the use of Decision Boundary Maps (DBMs) as a visualization tool for interpreting machine learning models. These maps project high-dimensional geochemistry data onto a 2D plane and depict the decision boundaries in the projected space, providing a visual representation of the algorithm's decision-making processes. In addition, DBMs can reveal trends, correlations, and outliers in the data, helping to interpret the results obtained from machine learning-based geochemistry data classification. Seeing the positions of data points, rather than just class labels, is especially valuable because samples in geological categories often follow a sequence, such as a magmatic to hydrothermal transition. Observing the positions of data points allows for the identification of trends from one class to an adjacent class.

How to cite: Wang, Y., Qiu, K., Telea, A., Hou, Z., and Yu, H.: Interpreting Machine Learning Models for Geochemistry Data Classification using Decision Boundary Maps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10228, https://doi.org/10.5194/egusphere-egu23-10228, 2023.

EGU23-14683 | Orals | GMPV1.4

Unsupervised Clustering applied on Raman spectra of dispersed carbonaceous material: a case history from the Paris Basin (France) 

Andrea Schito, Natalia Amanda Vergara Sassarini, Marta Gasparrini, Pauline Michel, and Sveva Corrado

In the last decades, the use of Raman spectroscopy on dispersed carbonaceous material in rocks has become a promising tool for geothermometry and thermal maturity assessment. In diagenesis the main problem is linked to organofacies composition and the need of time-consuming optical classification (Henry et al., 2019, Sanders et al., 2022). In this work, three different methods of clustering analysis on Raman spectra were tested as a potential approach to recognize the three main organofacies (amorphous organic matter, translucid and opaque phytoclasts) that characterize a set of 27 organic-rich samples from the Lower Toarcian source rock interval (Schistes Carton) of the Paris Basin (France).

Raman analyses were performed on concentrated organic matter obtained by acid attacks, with around 60 counts for each sample. Principal Component Analysis (PCA) was applied to reduce the dimensionality of each dataset on a 2-D score-plot. Unsupervised clustering was then performed by using three different clustering algorithms: k-means, Gaussian Mixture Models (GMM), and Density-Based Spatial Clustering for Applications with Noise (DBSCAN). The main task of these algorithms is to correctly assign the number of clusters, their size, orientation, and distribution in the score-plot that related to the heterogeneities in organofacies composition.

Results show the best performances are achieved through the application of GMM clustering that can successfully determine cluster’s geometry and optimal numbers with an accuracy mostly higher than 80% for the translucid phytoclasts group, that is the target for thermal maturity assessment.  This is a preliminary attempt showing promising application for unsupervised learning techniques coupled with Raman spectroscopy that could be applied in industrial routinely organic matter characterization or in the analysis of big dataset in both Earth and planetary sciences.

 

Henry, D. G., Jarvis, I., Gillmore, G., & Stephenson, M., 2019. Raman spectroscopy as a tool to determine the thermal maturity of organic matter: Application to sedimentary, metamorphic and structural geology. Earth-Science Reviews 198, 102936.

Sanders, M. M., Jubb, A. M., Hackley, P. C., & Peters, K. E., 2022. Molecular mechanisms of solid bitumen and vitrinite reflectance suppression explored using hydrous pyrolysis of artificial source rock. Organic Geochemistry 165, 104371.

How to cite: Schito, A., Vergara Sassarini, N. A., Gasparrini, M., Michel, P., and Corrado, S.: Unsupervised Clustering applied on Raman spectra of dispersed carbonaceous material: a case history from the Paris Basin (France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14683, https://doi.org/10.5194/egusphere-egu23-14683, 2023.

EGU23-15241 | ECS | Orals | GMPV1.4

3-D Reconstructions of Porous Media from 2-D input via Generative Adversarial Networks (GANs) 

Hannah Vogel, Hamed Amiri, Austin Arias, Oliver Plümper, and Markus Ohl

Many macroscopic transport properties and physical processes, such as the flow of fluids through a porous medium, are directly controlled by its microstructure, specifically the presence and connectivity of individual pore spaces at micron and submicron scales. Reconstructing and evaluating the material properties of porous media plays a key role across many engineering disciplines from subsurface storage (e.g., CO2 and hydrogen) to geothermal energy and reservoir characterization. As such, the rapid and reliable characterization, evaluation, and simulation of complex pore microstructures is required not only to enhance our understanding of the fundamental processes occurring at the pore scale, but to also better estimate their material behavior on a larger scale.

These material behaviors are inherently volumetric and therefore cannot be accurately modelled using two-dimensional (2D) data alone. As a result, the accuracy of reconstruction techniques used to extract these morphological properties and spatial distributions is in part determined by the quality of available three-dimensional (3D) microstructural datasets. However, in comparison to their 3D counterparts, 2D imaging techniques are typically more cost efficient, easier to collect, and higher resolution. Our goal of generating statistically accurate 3D reconstructions of complex pore microstructural distributions based on high resolution 2D datasets is essential to bridging this dimensionality gap.

Newly explored 2D-to-3D reconstruction techniques based on deep-learning (DL) algorithms offer an alternative means of generating robust and statistically representative digital 3D rock reconstructions by measuring some spatial morphological properties and statistical microstructural descriptors (SMDs) of porous media samples from high-resolution 2D datasets. These DL models are highly flexible and capable of capturing a variety of complex microstructural features given representative 2D training datasets. In this paper, we implement a newly developed deep Generative Adversarial Network (GAN), known as SliceGAN, to synthesize novel binary digital 3D reconstructions using high-resolution 2D back-scattered electron (BSE) images obtained from thin-sections oriented in the x-, y- & z-direction.

Our trained model is capable of accurately reconstructing complex 3D microstructural features of porous media through capturing the underlying (micro-)structural and morphological properties contained in the original sample (2D) thin-sections. To demonstrate the effectiveness of our trained model, we conducted a comparative analysis between the generated 3D reconstructions and real sample datasets by evaluating morphological properties (volume fraction, surface area, equivalent diameter, pore orientations, etc.) as well as the widely popular SMD the two-point correlation function (S2 (r) ). The resulting reconstructions are virtually indistinguishable, both visually and statistically, from the real sample. Our research paves the way for quickly and accurately describing complex heterogenous media for the prediction of transport processes, for example, carbon and hydrogen storage and extraction.

How to cite: Vogel, H., Amiri, H., Arias, A., Plümper, O., and Ohl, M.: 3-D Reconstructions of Porous Media from 2-D input via Generative Adversarial Networks (GANs), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15241, https://doi.org/10.5194/egusphere-egu23-15241, 2023.

Recent technological advances allow geoscientists to generate high-resolution (HR) imagery using a variety of different beam-forming mechanisms (e.g. visible light, X-Rays, or charged particles such as electrons and ions). One of the main limitations in producing HR data is the required acquisition time at high magnifications. For example, back-scattered electron (BSE) mapping of a standard petrographic thin section at a resolution of 50nm/pixel takes approximately 60 days and is associated with a storage requirement in the order of 700 GB. Deep-learning methods have proven effective for resolution enhancement in regular photographic images, and in this work we present an integrated image registration and upscaling workflow to enhance image resolution, using real-world BSE datasets.

The proposed workflow requires the acquisition of one, or multiple, HR regions within a region that is imaged at low-resolution (LR). Next, close to pixel-accurate image registration is performed by using the successive implementation of two concepts: i) first the precise location of the HR region within the LR region is determined by using a Fast Fourier Transform algorithm (Lewis, 2005), and ii) final image registration is achieved by iteratively calculating a deformation matrix that, using Newton’s method of optimization, is aiming to minimize an error function describing the differences between both images (Tudisco et al., 2017).

Subsequently, matching HR and LR image pairs are fed into a Generative Adversarial Network (GAN) that learns to produce HR images from the LR counterparts. A GAN consists of two neural networks, a generator and a discriminator. The generator produces synthetic HR data based on LR input, and the discriminator attempts to classify the data as either real HR or synthetic HR. The two networks are trained together in an adversarial process, with the goal of the generator producing synthetic data that the discriminator cannot distinguish from real data.

We demonstrate our method on a variety of large real-world datasets and show that it effectively increases the resolution of full-size BSE maps up to a factor of four, while being able to resolve important features. The upscaling of BSE data, with a factor of four, is associated with a 90% reduction in beamtime and a factor 16 reduction in storage requirements. Image registration, preprocessing, and model training on a high-performance workstation takes 12-24 hours. Having a trained model, inference can be done using a regular laptop.

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

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

How to cite: van Melick, H. and Plümper, O.: Resolution enhancement using deep learning methods: an integrated workflow applied to real-world Back-Scattered Electron (BSE) data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15285, https://doi.org/10.5194/egusphere-egu23-15285, 2023.

EGU23-16338 | ECS | Orals | GMPV1.4 | Highlight

The OneGeochemistry initiative as a CODATA Working Group; bringing together international geochemical data systems for easy data discovery 

Alexander Prent, Lesley Wyborn, Marthe Klöcking, Kerstin Lehnert, Kirsten Elger, Dominik Hezel, Lucia Profeta, Geertje ter Maat, Rebecca Farrington, and Tim Rawling

As geochemical data enable understanding of the Earth system and help to address critical societal issues the organisation thereof is important. Questions asked about processes affecting our environment and geological past become more complex and interdisciplinary in nature as well as multidimensional. To help answer these questions within the geochemistry research capabilities and data compilations are required to be comprehensive and both human and machine readable. Various international organisations are building infrastructure to capture and distribute geochemical data in a consistent manner adhering to the FAIR principles. 

Since May 2021 the OneGeochemistry initiative has officially started efforts towards aligning these organisations’ data frameworks in order to standardise how geochemical data is reported around the globe. In November 2022 the OneGeochemistry initiative applied and was granted to become the OneGeochemistry CODATA Working Group as part of the International Science Councils Committee on Data. The initiative has now also been endorsed by the Geochemical Society, the European Association of Geochemistry and the Working Group has been endorsed by the IUGS Commission on Global Geochemical Baselines. Coordination of the OneGeochemistry initiative is funded through the WorldFAIR project where it is one of the work packages in the larger ‘WorldFAIR: Global cooperation on FAIR data policy and practice’ project. A FAIR Implementation Profile analyses of the geochemistry communities of Australia (AusGeochem), USA (EarthChem, AstroMat) and Europe (GEOROC-DIGIS, EPOS-MSL, NFDI4EARTH) resulted in recognition of the need for common vocabularies for geochemistry data reporting as one of the most important actions to undertake towards international geochemistry data interoperability. A task adopted by EarthChem-DIGIS(GEOROC)-GFZ(DataSystems) collaboration and Research Vocabularies Australia.

Here we will present an overview of the current OneGeochemistry initiative and its preliminary outcomes with regards to FAIR Implementation Profiles and processes that will help enable geochemical data interoperability between various stakeholders.

How to cite: Prent, A., Wyborn, L., Klöcking, M., Lehnert, K., Elger, K., Hezel, D., Profeta, L., ter Maat, G., Farrington, R., and Rawling, T.: The OneGeochemistry initiative as a CODATA Working Group; bringing together international geochemical data systems for easy data discovery, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16338, https://doi.org/10.5194/egusphere-egu23-16338, 2023.

EGU23-16683 | Orals | GMPV1.4

Overcoming Fragmentation of Geochemical Data Resources: Collaboration between EarthChem, Astromat, GEOROC, and MetBase 

Kerstin Lehnert, Marthe Klöcking, Dominik Hezel, Lucia Profeta, Peng Ji, and Adrian Sturm

Global geochemical datasets are increasingly valuable for solving research questions in geochemistry, volcanology and beyond. To support new research, open sharing and access of geochemical data needs to be easy for researchers so they can take full advantage of the rapidly growing volume of data generated in laboratories across the globe, and to comply with the principles of Open Science. Instead, the fragmented landscape of geochemical data systems makes it difficult for researchers to find, access, and contribute their data: Geochemical data are curated and published in a range of thematic, institutional, and programmatic data systems that differ in architecture, metadata schemas, terminology, and data output formats. Researchers have to figure out where to obtain the data they need; learn to use different search applications; retrieve data from multiple databases and painstakingly reformat the datasets they obtained from different systems to integrate them. They need to select an appropriate repository for their data, and potentially work with different submission systems and templates. Collaboration among geochemical data systems is a critical step to overcome this fragmentation and facilitate geochemical data management and access for the research community by coordinating, aligning, and integrating their systems. Through collaboration, data repositories and databases can also leverage each other’s expertise and resources to operate their services more effectively and efficiently.

We here report about new collaborative efforts among four geochemical data systems that aim to harmonize and integrate their data holdings and software ecosystem for the benefit of the research community and to improve their sustainability: EarthChem (https://earthchem.org/), GEOROC (https://georoc.eu/), MetBase (https://metbase.org/), and the Astromaterials Data System (https://www.astromat.org/).  Building on the long-term collaboration between EarthChem and GEOROC, this collaboration leverages the new development of the Astromaterials Data System with modern technology and two new projects funded to overhaul the infrastructure of the GEOROC and MetBase databases as an opportunity to jointly develop a more resilient, sustainable platform for data exchange. Results of the collaboration so far include: a) alignment of the Astronaut and MetBase data models b) migration of the MetBase data holdings into the Astromat synthesis database; c) alignment of the EarthChem and GEOROC data models; d) new automated synchronization process of GEOROC data to the ECP; e) harmonized vocabularies for chemical variables, analytical methods (Others are in development in alignment with emerging efforts of the OneGeochemstry initiative); f) design of the future shared architecture of EarthChem and GEOROC that includes plans for a joint data entry tool for curators and a single data submission platform for researchers to contribute their data to the affiliated domain repositories. 

The ultimate goal of this harmonization between EarthChem, Astromat, GEOROC and MetBase is to make it easier for researchers to access and contribute data. We hope to integrate further systems in the future, building on ongoing collaborations with the Australian Geochemistry Network, the US Geological Survey, SAMIS (Sample Analysis Microinformation System), the GFZ Data Services, and the Sparrow software.

How to cite: Lehnert, K., Klöcking, M., Hezel, D., Profeta, L., Ji, P., and Sturm, A.: Overcoming Fragmentation of Geochemical Data Resources: Collaboration between EarthChem, Astromat, GEOROC, and MetBase, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16683, https://doi.org/10.5194/egusphere-egu23-16683, 2023.

EGU23-440 | ECS | Posters on site | GMPV1.5

Development of oxy-symplectites in the oceanic lower crust at Atlantis Bank Oceanic Core Complex, Southwest Indian Ridge- manifestation of fluctuating oxidation state 

Archisman Dhar, Biswajit Ghosh, Debaditya Bandyopadhyay, Tomoaki Morishita, Akihiro Tamura, Manojit Koley, and Sankhadeep Roy

Symplectitic intergrowth of orthopyroxene (host) with magnetite and minor ilmenite (lamellae) are recorded from Atlantis Bank, an Oceanic Core Complex on Southwest Indian Ridge. The texture is typically developed in oxide-rich gabbros recovered from the lower crustal section in this region and formed at the expense of olivine. Usually, the intergrowth primarily occurs where the olivine is in contact with magmatic magnetite and/or ilmenite. The maximum length and width of the lamellae in thin section go up to 350 µm and 20 µm respectively. The vermicular lamellae commonly maintain orthogonal relationship to the olivine grain boundary. A significant characteristic feature of this symplectitic intergrowth is the presence of domain structure, where each domain is characterized by the different orientation of vermicular lamellae. Locally, occurrences of amphibole rim abutting the intergrowth are noted. Development of orthopyroxene + Fe-Ti oxide symplectite is linked to the olivine oxidation endorsed by the interstitial Fe-Ti oxides during the progressive evolution of the lower oceanic crust at Atlantis Bank. Consequently, the occurrence of this texture dominantly from the oxide-rich lithologies bears significance. A phase equilibria modelling adopted to better comprehend the relationship between the state of oxidation and symplectite formation at Atlantis Bank indicates that this texture can be developed at relatively lower oxidation state at lower temperature for the observed range in olivine compositions. The formation temperature of the oxy-symplectites estimated from ilmenite-magnetite pairs ranges from ~730° to 450°C over an oxygen fugacity range of -0.86 to +3.83 (FMQ buffer). We suggest that, the development of this intergrowth took place under the influence of late-stage Fe-Ti oxides at subsolidus condition, which fostered the olivine oxidation. Temperature and oxygen fugacity ranges estimated from majority of the discrete ilmenite and magnetite pairs away from the symplectites however suggest relatively higher temperature and lower oxidation state (temperature ranges from 720° to 550°C, and oxygen fugacity ranges from -1.91 to +2.77 (FMQ buffer)). Higher oxygen fugacity values recorded from the symplectites further validate the effect of oxidation.

How to cite: Dhar, A., Ghosh, B., Bandyopadhyay, D., Morishita, T., Tamura, A., Koley, M., and Roy, S.: Development of oxy-symplectites in the oceanic lower crust at Atlantis Bank Oceanic Core Complex, Southwest Indian Ridge- manifestation of fluctuating oxidation state, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-440, https://doi.org/10.5194/egusphere-egu23-440, 2023.

EGU23-1895 | ECS | Posters on site | GMPV1.5

Collection, processing, storage and sharing of petrological and microstructural data using QGis as a database. 

Tim-Julian Albrecht, Friedrich Hawemann, and Virginia Toy

In the course of a typical geoscientific research project, observational and analytical data from different scales and sources, of many different types and formats, are collected, and interpreted. While the number of observational and analytical methods and sizes of resultant datasets have dramatically increased in recent times, only a few tools exist to collect, process, store, share and compare various data in simple ways.  

QGis – an open-source geographic information system, originally developed to handle data from Earth’s surface – offers a wide range of tools that can also be employed at the microscale in studies of petrology and/or deformation history. 

We herein present a case study based on a gabbroic sample from the Central Cordillera in western Colombia, showing four generations of fractures, around and within which alteration assemblages attest to fluid inflow and metamorphism. We integrate data from scans of polished surfaces, polarized light microscopy, backscattered, forescattered, and scanning electron microscope images (BSE, FSE, SE), electron probe (EPMA) spot and map microanalyses, and electron backscatter diffraction (EBSD). The use of QGis allowed us to easily relate data from these different sources and consider them in the context of petrological computations made with XMapTools software (Lanari et al., 2014).

In the future, we hope to automatically integrate collected electron microscopic data into QGis and external control via Python interfaces, as is currently permitted by some manufacturers of SEMs. We also plan to integrate computational petrology via plugins. 

We think that this software tool is one of the most multi-functional currently available for harmonized, integrated data collection, processing, storing and sharing, and would like to share our experience with our colleagues so they can also employ it in thorough analysis of samples, and thus also acquire datasets that can be used for comparative studies by collaborating researchers.

How to cite: Albrecht, T.-J., Hawemann, F., and Toy, V.: Collection, processing, storage and sharing of petrological and microstructural data using QGis as a database., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1895, https://doi.org/10.5194/egusphere-egu23-1895, 2023.

EGU23-2383 | Orals | GMPV1.5

Modeling lunar magmas in the Artemis Era 

Kayla Iacovino and Kelsey Prissel

As the planetary science community sets its sights on the Moon, the existence of an open-source, up-to-date, and user-friendly modeling tool for lunar rocks is critical to maximizing the scientific return of ongoing and upcoming lunar missions (e.g., Artemis, PRISM, CLPS). While the creation of new code from the ground up is an important aspect of modern computational petrology, here we advocate for the modernization of legacy code, the results of which dominate the literature and shape our current understanding of geologic processes across multiple scales. Modernization of legacy code is critical as it enables the community to put new model results in the context of modern consensus gentium. Here we discuss how modern best practices for code development, publishing, and maintenance should be applied to upgrading legacy code, using lunar petrologic models as an example. We highlight critical gaps in our ability to model lunar processes that could be filled simply with updated modeling tools (i.e., where underlying experimental and analytical data already exist but are not incorporated into existing modeling tools).

Current modeling tools developed specifically for lunar compositions are sparse and can contain outdated parameterizations. One critical knowledge gap is our ability to model silicic lunar magmas, which are evidenced in nature by felsic fragments in returned Apollo samples and silica-rich volcanic domes identified on the borders of lunar mare by remote sensing. The most popular tool for modeling lunar magmas is MAGPOX, born from a series of FORTRAN scripts and ported to MATLAB, which is underpinned by an exclusively basaltic database. MAGPOX requires the crystallization of olivine on the liquidus, and thus has limited application to the full compositional diversity of lunar magmas. rhyolite-MELTS has been used to model silicic magmatism on the Moon, but its use typically requires additional experimental work given that the MELTS database is biased towards terrestrial rocks with lower FeO, higher alkalis, and higher fO2 than lunar rocks. Notably, the MELTS database includes the same published basaltic lunar rocks used in MAGPOX regressions and so should be trustworthy for silica-poor lunar magmas. Still, the adoption of MELTS by the lunar community requires extensive testing against MAGPOX, PERPLE_X, and large lunar experimental databases.

Before we can even begin to update the parameterizations underpinning MAGPOX or efficiently compare MAGPOX to other models, a modern code library is required to perform adequate testing and benchmarking. In this talk we will explore the state of lunar petrologic modeling, what can be done now, and how we can best bring it into the 21st century.

How to cite: Iacovino, K. and Prissel, K.: Modeling lunar magmas in the Artemis Era, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2383, https://doi.org/10.5194/egusphere-egu23-2383, 2023.

EGU23-3926 | ECS | Orals | GMPV1.5

Open-source Python3 tools for Thermobarometry: Revealing the good, the bad and the ugly of determining P-T-X conditions in igneous systems 

Penny Wieser, Adam Kent, Christy Till, Maurizio Petrelli, Eric Wieser, Jordan Lubbers, David Neave, Sinan Ozaydin, John Donovan, Dawnika Blatter, and Mike Krawczynski

The chemistry of erupted minerals and melts are commonly used to determine the pressures, temperatures and H2O contents of magma storage regions beneath volcanic centres. In turn, these estimates are vital for hazard assessment, to understand the formation of critical metal deposits, and to inform models of continental crust formation. In the last few decades, more than 100 empirical and thermodynamic expressions have been calibrated using measurements of phases in experimental studies where these intensive parameters are known. By collating these different models into a computationally-efficient, open-source Python3 package, Thermobar, we can critically assess the performance of thermobarometers in igneous systems, and propagate analytical errors. When we apply published models for different mineral equilibrium to a new experimental dataset not used in model calibration, we find that stated errors vastly underestimate the true uncertainty when these workflows are applied to natural systems.

Specifically, we find that realistic calculation workflows involving Clinopyroxene (Cpx) equilibrium (e.g., iterating pressure and temperature) have uncertainties spanning the entire crust in most tectonic settings. Using Thermobar functions to propagate analytical error using Monte Carlo simulations, we suggest that these large errors result from imprecise analyses of minor elements such as Na in experimental (and natural) Cpx. Common analytical conditions used for Cpx yield highly correlated pressure-temperature arrays spanning the entire crust, which have been incorrectly interpreted as trancrustal storage in natural systems. Insuffucient analyses of each phase in experimental products means that this analytical error is not sufficiently mediated by averaging, so reported mineral compositions deviate from the true phase composition. This impacts thermobarometer calibration, as well as assessment of these methods using test experimental datasets.

Overall, we demonstrate that the development of Python3 infrastructure for common quantitative workflows in volcanology is vital to allow rigorous error assessment and model intercomparison; such assessments simply aren’t feasible using traditional tools (e.g., Excel workbooks). Specific changes to analytical, experimental and model calibration workflows (e.g., higher beam currents and count times in Na) will be essential to produce a more robust dataset to calibrate and test the next generation of more precise and accurate Cpx-based barometers. In turn, this will enable more rigorous investigation of magma storage geometries in a variety of tectonic settings (e.g., distinguishing true transcrustal storage vs. storage in discrete reservoirs).

 

How to cite: Wieser, P., Kent, A., Till, C., Petrelli, M., Wieser, E., Lubbers, J., Neave, D., Ozaydin, S., Donovan, J., Blatter, D., and Krawczynski, M.: Open-source Python3 tools for Thermobarometry: Revealing the good, the bad and the ugly of determining P-T-X conditions in igneous systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3926, https://doi.org/10.5194/egusphere-egu23-3926, 2023.

EGU23-4954 | Orals | GMPV1.5

From Fieldwork to Publication with AusGeochem: An Open end-to-end Solution for managing FAIR Sample Based Geoscience Data 

Moritz Theile, Wayne Noble, Romain Beucher, Alejandra Bedoya-Mejia, Samuel Boone, and Fabian Kohlmann

Here we introduce the AusGeochem platform enabling geoscientists to manage and publish sample based geoscience data in a consistent and FAIR way. 

The AusGeochem data platform has been built by the AuScope Geochemistry Network (AGN) and Lithodat Pty Ltd as part of a national digital infrastructure project to facilitate the sharing of data produced by geochemistry laboratories across Australia. 

In order to improve national geochemical facility data management, the AusGeochem platform uses detailed structured and standardized method specific data models for collating, preserving, and disseminating geochronology and isotopic data. 

AusGeochem provides researchers with a solution to record and utilize all of this information, while streamlining their workflow from collection to publication. Here we will give an overview of a typical sample workflow. 

The demonstrated workflow contains the following steps: Storing all sample details on-the-fly during sample collection with the field app. Managing the data by logging into the AusGeochem website. Adding subsequent geochemical analyses to the sample. Visualizing the data using analytic dashboards and graphs. Sharing the data with a team of collaborators. And finally, making the data referenceable by minting DOIs and IGSNs.

Manifold data is produced and captured along this process of collecting, analyzing and publishing. This is not confined to just the analytical results, but also a lot of meta information, such as involved people, instruments, funding sources, grant numbers, laboratories and institutions. Being rich in such metadata opens up the path to interesting new functionality, e.g. in the space of structured quantification and quality assessment of research projects.

The AusGeochem platform is of great help for a single researcher or a team of researchers by providing them with the means and tools to make their work more efficient and productive. However, the real benefit comes by having an access control layer, so data from multiple institutions can be  stored on one single platform. Since the data is now all stored in one detailed model, it gives researchers the possibility to apply analysis across data from all contributing institutions on the fly.  This means, no downloading of data from multiple sources required. And most importantly, no difficult and often impossible data preprocessing required.



How to cite: Theile, M., Noble, W., Beucher, R., McMillan, M., Boone, S., and Kohlmann, F.: From Field Application to Publication: An end-to-end Solution for FAIR Geoscience Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11980, https://doi.org/10.5194/egusphere-egu22-11980, 2022.

How to cite: Theile, M., Noble, W., Beucher, R., Bedoya-Mejia, A., Boone, S., and Kohlmann, F.: From Fieldwork to Publication with AusGeochem: An Open end-to-end Solution for managing FAIR Sample Based Geoscience Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4954, https://doi.org/10.5194/egusphere-egu23-4954, 2023.

The phrase “automated mineralogy” has been synonymous with electron microscopy in the geosciences for decades. The use of energy dispersive spectroscopy (EDS) to rapidly map samples and identify phases of interest has gradually seen a shift out of its original industry applications and into the academic research environment. A major issue for academics wishing to take advantage of this powerful tool is the original platforms are rigid in terms of their industry designed outputs, and there has been a lack of development in both the software and hardware capable of providing automated outputs.

However, rather than just looking backwards at what automated mineralogy was originally designed for, there is a more forward looking and important conversation as geoscience projects increase in scope. To think about geoscience in the context of topics such as big data, statistical relevance, and the use of increasingly prevalent machine learning techniques, we need to think about how we collect and store data. This naturally requires a greater integration of the problems geoscientists are trying to address with the solutions that microscopy and microanalysis equipment suppliers provide. Greater access to the data acquired on scientific equipment not only provides greater research flexibility but opens much smarter routes towards a future of correlated datasets with minimal user input.

Using quantitative chemistry as the basis for automated mineralogy provides unique capabilities for large area analysis such as thin sections. Quantitative textural information can be extracted from the sample such as grain sizes, shapes, and mineral associations, alongside quantitative geochemical data providing mineral classification, including mineral and whole rock/sample compositions. This provides a wealth of information for the petrologist to understand their sample and a one-stop-shop for many geoscience workflows. This is a ready made mechanism to generate large datasets across multiple samples in a consistent fashion – the key to big data.

Here we show one example of greater integration of data acquisition with user generated computational software showing the power of large area quantitative EDS mapping with geoscience-oriented functions of XMapTools. By importing calibrated, quantitative EDS maps XMapTools can be used to rapidly perform a variety of petrological calculations without the need for a separate, long-winded calibration step using microprobe data. Here we use quantitative EDS from high grade metamorphic rocks to obtain mineral and bulk compositions alongside textural information such as modal abundances. These mapped data are imported directly into XMapTools and can be used to generate oxide values, cation per formula unit (cpfu), end member proportions, and perform thermodynamic calculations.

How to cite: Taylor, R.: Reimagining automated mineralogy for the 21st century, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7485, https://doi.org/10.5194/egusphere-egu23-7485, 2023.

In contrast to thermodynamic models for metamorphic mineral solutions, which often concern quartz-saturated assemblages, the phase equilibria of feldspars, feldspathoids and melilite in the K2O-Na2O-CaO-Al2O3-SiO2-H2O space are much less established. They provide basis for classification and interpretation of alkaline silica-undersaturated rocks and essential constraints for developing normative calculation and classification algorithms. The existing normative schemes (CIPW, Müller, Le Bas, Rittmann and Curie norms) do not provide satisfactory treatment of nepheline, leucite, clinopyroxene and melilite stabilities and equilibria. In many conventional schemes (1) anorthite persists to very low silica activities despite of its instability and incompatibility with melilite; (2) normative larnite is a principal indicator of melilite presence but provides a poor chemical proxy; (3) compatibilities between alkali feldspar, leucite and nepheline solid solutions are incorrectly predicted (e.g., leucite-albite, feldspar-melilite); (4) desilication steps do not uniquely follow decreasing activity of silica. As a consequence, the norms applied to alkaline silica-undersaturated igneous rocks do not provide unique or correct view of mineral assemblages and their chemographic relations. In this contribution we explore phase equilibria and compatibility relations in the system SiO2-CaAl2O4-NaAlSiO4-KAlSiO4-H2O. We have adopted the thermodynamic models for nepheline, leucite and kalsilite solutions (Sack & Ghiorso 1998). The order-disorder models have been converted to the relevant sets of linearly independent end-members including ordered or anti-ordered intermediate members with macroscopic Margules parameters. These models were designed as transferable between Berman, Holland-Powell or other end-member datasets. In the composition space SiO2-NaAlSiO4-KAlSiO4 at P = 1 bar and T = 1000 oC, alkali feldspar is compatible with nepheline or leucite, separated by an invariant composition Or51Ab49. Consequently, sodic rocks, with molar Na/(Na+K) > 0.75, contain the anorthoclase + nepheline assemblage, whereas with increasingly potassic character, the rocks contain leucite + nepheline, leucite + tetrakalsilite or leucite + kalsilite; the SiO2-richer assemblages consist of leucite + sanidine. With decreasing temperature, tetrakalsilite becomes unstable and is replaced by K-bearing nepheline + kalsilite. Furthermore, the invariant feldspar composition separating the nepheline vs. leucite assemblages rapidly migrates towards sanidine (Or90Ab10 at 800 oC and 1 bar). As a consequence, decreasing crystallization temperature favors the assemblage of alkali feldspar and nepheline (over leucite) for a wide range of bulk Na/(Na+K) ratios. This explains the rarity of sodic feldspar + leucite assemblages in nature. At feldspar subsolvus temperatures, both albite and orthoclase coexist with nepheline, and leucite becomes Na-poor and eventually breaks down to kalsilite and orthoclase. This is consistent with frequent replacement in nature of leucite by secondary products, in particular analcime. The compatibility relations in the SiO2-NaAlSiO4-KAlSiO4 system are conveniently delineated by several intermediate members, e.g., Or75Ab25 or Ne60Ks40, which are used in a new algorithm for normative classification and interpretation of alkaline undersaturated rocks.

 

References

Sack R.O., Ghiorso M.S., 1998. Contrib. Mineral. Petrol. 130, 256-274.

How to cite: Dolejš, D.: Magmatic equilibria between feldspathoids and feldspars: Implementation of thermodynamic models and implications for norm calculation and petrographic interpretation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9700, https://doi.org/10.5194/egusphere-egu23-9700, 2023.

EGU23-12522 | ECS | Posters on site | GMPV1.5

ThermotopesC_DEW, a Python GUI application to automate thermodynamic computations for fluid-rock interactions 

Guillaume Siron, Alberto Vitale-Brovarone, and Simon Matthews

Fluid-rock interactions are one of the most important processes on Earth and play an important role in many metamorphic systems, especially during fluid migration. Research during the past three decades have provided many new software and thermodynamic databases for both mineral and fluids. Yet, in the metamorphic community, the fluid phase is usually modelled using molecular fluids such as pure H2O or  H2O-CO2 mixtures. This may be a limiting factor since aqueous fluids containing dissolved ionic species are involved leading to metasomatic reactions. The Deep Earth Water (DEW) model allows modeling complex fluid-rock interactions involving ionic species at pressure and temperature conditions up to 6 GPa and 1200 °C 1. However, its use through software packages such as EQ3/6 2 may be time-consuming.

 

ThermotopesC_DEW is a Python application with a user-friendly graphical user interface (GUI) that allows automation of thermodynamic computations with the EQ3/6-DEW software package. The application uses the capability of the EQ3 and EQ6 to compute the chemical speciation of a fluid in equilibrium with a user-defined mineral assemblage, and the reaction of this fluid with a new rock, respectively. ThermotopesC_DEW allows the user to compute batches of EQ6 calculations with different fluid-rock ratios set by the user, or to batch process EQ6 computations with different proportions for 3 minerals within a ternary diagram, for a given fluid-rock ratio. The application then allows the user to create customized plots of the computation results in 2D and 3D, for each option and for each variable.

 

In this contribution, we explore the capabilities of ThermotopesC_DEW to investigate fluid-peridotite interactions at subduction zone pressure and temperature conditions, for over 30 000 individual EQ6 runs. Different fluid compositions, reacting assemblages, and fluid-rock ratios were considered.

 

Over the wide range of conditions of these runs, modes of hydrous phases, relative proportions of the different phases, pH and log fO2 vary widely, highlighting the complexity of fluid-rock interaction processes in the subduction zone and warrant the use of simple fluid formulation to model such processes. We believe that user-friendly applications such as the one presented here will allow more petrologists to introduce fluid speciation into their metamorphic projects.

 

1. Sverjensky, D. A., Harrison, B. & Azzolini, D. Water in the deep Earth: The dielectric constant and the solubilities of quartz and corundum to 60kb and 1200°C. Geochim Cosmochim Ac 129, 125–145 (2014).

2. Wolery, T. J. EQ3/6, a software package for geochemical modeling of aqueous systems: Package overview and installation guide (Version 7.0). doi:10.2172/138894.

This work is part of project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 864045).  

How to cite: Siron, G., Vitale-Brovarone, A., and Matthews, S.: ThermotopesC_DEW, a Python GUI application to automate thermodynamic computations for fluid-rock interactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12522, https://doi.org/10.5194/egusphere-egu23-12522, 2023.

Stream sediment geochemistry is a useful tool to derive geochemical insights into local geological units within stream sediment source areas. This has significant applicability within the field of mineral exploration where understanding regional geochemistry is fundamental to successful prospection and can facilitate the identification of critical metal deposits. This can help diversify the supply chain of critical metals, as well as tackle the deficit, especially for cobalt (Co). Cobalt is a growing component in many industrial processes but is mostly required for powering Li-Co batteries in Plug-in Hybrid Electric Vehicles (PHEV)1. Demand for Co is growing exponentially in order to meet future carbon-neutral technological demand as part of joint UK-European initiatives towards a more environmentally sustainable society. 

 

The UK Geochemical Baseline Survey of the Environment (G-BASE) dataset is used to demonstrate that this technique provides a useful tool for isolating potential ‘Critical Minerals’2 in host rocks across the UK Lake District, with priority targeting towards Co-bearing ores. We reduced the dimensionality of the G-BASE stream sediment data to create geochemical maps that identify a combination of volcanic, sedimentary, and plutonic lithologies lining up geological boundaries from established 50k scale geological maps of the area. This was conducted through a combined statistical and mapping approach within QGIS and ioGAS. The resultant lithogeochemical map of the region highlights the average geochemistry for each major lithological group with varying degrees of resolution.

 

This technique also allows for the identification of average ore metal concentrations (Ag, As, Bi, Co, Cu, Mo, Ni, Sn, Zn) for the Skiddaw Group and the Borrowdale Volcanic Group, two established host groups for As-Co-Cu-Ni mineralisation. Average concentrations of Co in the Skiddaw have been modelled to be 63.26 ppm, and in the Borrowdale volcanics to be 26.86 ppm. These values, combined with As, Cu, and Ni modelled concentrations, and other publicly available exploration-related data (structural maps, underlying batholith topography, mining history, mineral occurrences etc.) allowed us to identify 10 prospective areas of interest for possible As-Co-Cu-Ni mineralisation across these two lithological groups. Fieldwork was then undertaken to investigate several of these identified areas in order to establish the success of the model targeting tools. Ore metal-bearing minerals, mostly Cu-Fe-As phases, were identified both disseminated in local shales and andesites, and in hydrothermal quartz-chlorite veins at six sites investigated thus far. Characterisation of these minerals and host rocks is still in progress, making use of SEM-EDS and XRF analytics.

 

We demonstrate this workflow has strong applicability within critical metal exploration and should be applied in other, more prospective regions across the globe. The only pre-requisite to the mapping is the availability of stream sediment databases with sufficient resolution across target areas.

 

1 Dehaine et al. 2021. BATCircle Project Report 04.
2 Resilience for the Future: The UK’s critical minerals strategy, policy paper, 22nd July 2022.

How to cite: Eskdale, A., Gough, A., and Johnson, S.: The applicability of stream sediment geochemistry as a combined geological mapping, and prospective exploration tool for As-Co-Cu-Ni mineralisation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13447, https://doi.org/10.5194/egusphere-egu23-13447, 2023.

EGU23-13612 | ECS | Orals | GMPV1.5

MIN-ML: A Machine Learning Framework for Exploring Mineral Relations and Classifying Common Igneous Minerals 

Sarah Shi, Penny Wieser, Kerstin Lehnert, and Lucia Profeta

Explorations of mineral compositions aiming to reveal complex magmatic processes in melts have proliferated with the growing accessibility of geochemical datasets through databases including PetDB, LEPR/TraceDs, and GEOROC and of computational methods. The generation and continuous quality assurance of mineral data in these databases requires significant human intervention and individual post-processing. One major problem is that minerals may be misclassified (i.e., a compiled dataset of clinopyroxenes may contain some amphiboles), and compilations may contain poor-quality electron microprobe (EPMA) analyses (with low totals, low cation sums, or poor correspondence to the theoretical stoichiometry of a mineral phase). At the moment, individual studies compiling geochemical datasets for specific tectonic settings [1] or calibrating thermobarometers based on mineral-melt equilibrium [2] tend to apply their own filters. With a push for a more consistent approach, we create a new open-source Python package called MIN-ML (MINeral classification using Machine Learning) for classifying common igneous minerals based on oxide data collected by EPMA, with functions for calculating stoichiometries and crystallographic sites based on this classification. Utilizing this package allows for the identification of misclassified mineral phases and poor-quality data. We streamline data processing and cleaning to allow for the rapid transition to usable data, improving the utility of data curated in these databases and furthering computing and modeling capabilities. 

While mineral identification and classification are obviously critical to the success of computational methodologies and machine learning (ML) applied to these large datasets, the question of how to best classify minerals from EPMA analyses comes to the fore. We approach this question by exploring and developing ML workflows, both supervised (classification algorithms) and unsupervised (dimensionality reduction and clustering). Unsupervised methods including autoencoders, a type of artificial neural network, present the opportunity to classify minerals with little a priori information. Autoencoders pair two neural networks with an encoder, compressing input data to a dimensionality-reduced latent representation, and a decoder, expanding latent representations to reconstruct the input and minimize loss. We present a novel autoencoder model aimed at meaningfully representing EPMA analyses of minerals in latent space, investigating the relationships between mineral phases, and performing classifications of these minerals. The model is trained with newly compiled datasets of twelve igneous mineral phases on thousands to tens of thousands of analyses per phase – across tectonic settings to train these ML models. The autoencoder is applied to datasets of mineral analyses from PetDB, LEPR, and GEOROC to evaluate model performance and show significant improvements in mineral phase segregation and classification, critical to rigorous dataset quality control and future integration into data processing routines. 

 

[1] Gale, A., et al., The mean composition of ocean ridge basalts. Geochemistry, Geophysics, Geosystems 14, 489-518 (2013).

[2] Petrelli, M., et al., Machine learning thermobarometry: Application to clinopyroxene-bearing magmas. JGR: Solid Earth 125, e2020JB020130 (2020).

[3] Lehnert, K. A., et al., 2022, IEDA2: Evolving EarthChem, LEPR/TraceDs, and SESAR into a Next Generation Data Infrastructure for Data-Driven Research Paradigms in Geochemistry, Petrology, and Volcanology, in 2022 Goldschmidt Conference.

How to cite: Shi, S., Wieser, P., Lehnert, K., and Profeta, L.: MIN-ML: A Machine Learning Framework for Exploring Mineral Relations and Classifying Common Igneous Minerals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13612, https://doi.org/10.5194/egusphere-egu23-13612, 2023.

EGU23-14346 | Orals | GMPV1.5

Ab initio-assisted computational thermodynamics: a modern approach to phase diagram calculation at planetary conditions 

Donato Belmonte, Mattia La Fortezza, and Francesca Menescardi

Despite the outstanding progress in computer technology and experimental facilities, understanding melting processes and solid-melt phase equilibria at planetary conditions is still an open challenge. In this work a modern computational approach to predict melting phase relations at HP-HT by a combination of first principles DFT and MD calculations, polymer chemistry and equilibrium thermodynamics is presented and discussed. The adopted theoretical framework is physically-consistent and allows to compute multi-component phase diagrams relevant to planetary interiors in a broad range of P-T conditions by a convex-hull algorithm based on the simplex method for Gibbs free energy minimisation. The calculated phase diagrams are in turn used as a source of information to gain new insights on both present-day and early Earth melting processes. Some examples of application of the above method to the CaO-MgO-Al2O3-SiO2 system (CMAS) and relevant ternary and binary subsystems highlights as pressure effects are not only able to change the nature of melting of some minerals (like olivine and pyroxene) from eutectic to peritectic (and vice versa), but also simplify melting relations by drastically reducing the number of phases with a primary phase field at HP-HT conditions. Since the volume-pressure integral contribution to Gibbs free energy become relevant at planetary interior conditions, special attention must be paid to the choice of the P-V-T EoS formalism in order to avoid physical unsoundness or spurious effects in thermodynamic properties (e.g. negative thermal expansion). Ab initio-assisted computational thermodynamics is thus outlined as the main route towards the future development of physically-consistent (besides internally-consistent) thermodynamic databases for global-scale planetary investigations.

Financial support by the Italian Ministry of University and Research (MIUR PRIN 2017, Project 2017KY5ZX8 and MIUR PRIN 2020, Project 202037YPCZ) is warmly acknowledged.   

How to cite: Belmonte, D., La Fortezza, M., and Menescardi, F.: Ab initio-assisted computational thermodynamics: a modern approach to phase diagram calculation at planetary conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14346, https://doi.org/10.5194/egusphere-egu23-14346, 2023.

EGU23-14500 | ECS | Orals | GMPV1.5

Serpentinite dehydration as a multiscale process 

Konstantin Huber, Johannes C. Vrijmoed, and Timm John

Fluid release from hydrated oceanic lithosphere in subduction zones is a key process in the deep earth water cycle. During prograde metamorphism a channelized vein network forms in the dehydrating rock that allows efficient fluid release from the slab into the mantle wedge. The formation of such a vein network is a multiscale process that occurs over a wide range of time and length scales. Previous studies as well as field observations of exhumed meta-serpentinites suggest that the processes governing rock dehydration shift from chemical to mechanical processes going from small to large scales.

To investigate the behavior of a dehydrating slab over this wide range of scales we present a multiscale dataset that includes field-based observations from m to sub-µm scale of a representative serpentinite from the Mirdita ophiolite (Albania). This ophiolite has experienced seafloor alteration, but has not been metamorphosed at conditions that would cause any dehydration. We use these data as input for thermodynamic equilibrium calculations to investigate the effect of chemical heterogeneities in the bulk rock composition while the PT-conditions will be increased following a typical subduction zone geothermal gradient.

For upscaling we perform the calculations at various effective thermodynamic domain sizes (20-100 µm), showing that anisotropic chemical heterogeneities lead to heterogeneous porosity formation on all scales. Bloch et al. (2018) found that for vein-like porosity structures the percolation threshold of an effective bulk media may be reached at a porosity as low as 10-3. Therefore, the anisotropic porosity structure formed by chemical heterogeneities leads to a high connectivity even at low porosities and thus allows efficient fluid flow. Accordingly, going to even larger scales we can use these findings to describe the lithologies found in the field as effective bulk media with an effective fluid flow. This allows us to investigate fluid release from the dehydrating slab on the km-scale by reactive porosity waves using a numerical model.

Bloch, W., John, T., Kummerow, J., Salazar, P., Krüger, O. S., & Shapiro, S. A. (2018). Watching Dehydration: Seismic Indication for Transient Fluid Pathways in the Oceanic Mantle of the Subducting Nazca Slab. Geochemistry, Geophysics, Geosystems, 19(9), 3189–3207. https://doi.org/10.1029/2018GC007703

How to cite: Huber, K., Vrijmoed, J. C., and John, T.: Serpentinite dehydration as a multiscale process, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14500, https://doi.org/10.5194/egusphere-egu23-14500, 2023.

EGU23-15470 | ECS | Posters on site | GMPV1.5

Access to EXCITE: A European infrastructure to promote electron and X-ray microscopy of earth materials 

Geertje ter Maat, Sylvia Walter, Veerle Cnudde, Richard Wessels, and Oliver Plümper

Understanding earth materials is essential for the creation of a sustainable, carbon-neutral society. Earth materials control the feasibility of subsurface energy storage, geothermal energy extraction, and are a source of critical elements for future-proof battery technologies. To tackle the current, pressing scientific questions related to sustainable development for a circular economy, there is an urgent need to make multi-scale, multi-dimensional characterisations of earth materials available to a broad spectrum of earth-science disciplines. Besides society-relevant topics, the properties of earth materials determine how the Earth works on the most fundamental level.
To overcome this challenge, 15 European institutes joined forces to establish EXCITE, providing free-of-charge access to 24 state-of-the art microscopy and x-ray tomography facilities in Europe. EXCITE can help you gain insight into the processes governing the behavior of the Earth crust through microchemical analyses and 2D- to 4D imaging, and down to nanometer resolution. 
In particular, the EXCITE strategy integrates joint research programs with networking, training, and trans-national access activities, thereby enabling both academia and industry to answer critical questions in earth-materials science and technology. 
EXCITE is building a community of highly qualified earth scientists, develops correlative imaging technologies providing access to world-class facilities to particularly new and non-expert users that are often hindered from engaging in problem-solving microscopy of earth-materials.

EXCITE is building a community of highly qualified earth scientists, develops correlative imaging technologies providing access to world-class facilities to particularly new and non-expert users that are often hindered from engaging in problem-solving microscopy of earth-materials.

Access to EXCITE can be requested by applying to our bi-annual call. Interested? Have a look on the EXCITE website (https://excite-network.eu) – and apply!

How to cite: ter Maat, G., Walter, S., Cnudde, V., Wessels, R., and Plümper, O.: Access to EXCITE: A European infrastructure to promote electron and X-ray microscopy of earth materials, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15470, https://doi.org/10.5194/egusphere-egu23-15470, 2023.

EGU23-16579 | Orals | GMPV1.5

Mineral texture classification using deep convolutional neural networks: an application to zircons from porphyry copper deposits 

Chetan Nathwani, Jamie Wilkinson, William Brownscombe, and Cedric John

The texture and morphology of igneous zircon indicates magmatic conditions during zircon crystallisation and can be used to constrain provenance. Zircons from porphyry copper deposits are typically prismatic, euhedral and strongly oscillatory zoned which may differentiate them from zircons associated with unmineralised igneous systems. Here, cathodoluminesence images of zircons from the Quellaveco porphyry copper district, Southern Peru, were collected to compare zircon textures between the unmineralised Yarabamba Batholith and the Quellaveco porphyry copper deposit. Quellaveco porphyry zircons are prismatic, euhedral and strongly oscillatory zoned, whereas the batholith zircons contain more variable morphologies and zoning patterns. We adopt a deep convolutional neural networks (CNNs) approach to demonstrate that a machine can classify porphyry zircons with a high success rate. We trial several existing CNN architectures to classify zircon images: LeNet-5, AlexNet and VGG, including a transfer learning approach where we used the weights of a VGG model pre-trained on the ImageNet dataset. The VGG model with transfer learning is the most effective approach, with accuracy and ROC-AUC scores of 0.86 and 0.93, indicating that a Quellaveco porphyry zircon CL image can be ranked higher than a batholith zircon with 93% probability. Visualising model layer outputs demonstrates that the CNN models can recognise crystal edges, zoning and mineral inclusions. We trial implementing trained CNN models as unsupervised feature extractors, which can empirically quantify crystal textures and morphology. Therefore, deep learning provides a powerful tool for the extraction of petrographic information from minerals which can be applied to constrain provenance in detrital studies.

How to cite: Nathwani, C., Wilkinson, J., Brownscombe, W., and John, C.: Mineral texture classification using deep convolutional neural networks: an application to zircons from porphyry copper deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16579, https://doi.org/10.5194/egusphere-egu23-16579, 2023.

EGU23-17556 | Posters on site | GMPV1.5

Nd-Hf isotopic mapping based on a large archive of age data reveals voluminous continental growth of the Altaids and its control on metallogeny 

Tao Wang, He Huang, Jianjun Zhang, Chaoyang Wang, Guangyue Cao, Wenjiao Xiao, Lingling Yuan, Ying Tong, and Lei Guo

The Altaids, or the Central Asian Orogenic Belts, is generally considered to be the largest Phanerozoic accretionary orogen on Earth, but it is unclear if it was associated with extensive continental crustal growth and whether there is a link between the crustal growth and ore mineralization. This study, based on 5507 whole-rock Nd and 39514 (2443 samples) zircon Hf isotope data of felsic-intermediate-mafic igneous rocks as well as associated 1830 ore deposit data for the Altaids, presents Nd + Hf isotopic contour maps for this region. The maps highlight the three-dimensional (3D) lithospheric compositional architecture of the Altaids and make it possible to quantitatively evaluate the crustal growth and its relationship to ore deposits. The Altaids hosts ~4,107,350 km2 and ~184,830,750 km3 (assuming a crustal thickness of 40-50 km) juvenile crust (εNd(t) > 0), accounting for 58% by isotope-mapped area (~7,010,375 km2) of almost all outcrops of the Altaids (~8,745,000 km2) and formed during 1000–150 Ma (mainly 600–150 Ma). Therefore, the Altaids can be viewed as the largest storage area and most typical "fossils" of the juvenile crust in orogens worldwide. Our results are applicable to other types of orogens, particularly to the final continental collision and its control on mineralization. The juvenile crustal, slightly juvenile-reworked crustal, and slightly reworked crustal provinces controlled the Cu-Au, the Pb-Zn-Ag, and the Li-Be, Nb-Ta, and W-Sn ore deposits. According to the crustal architecture and background of deep compositions, we propose that the ore deposits can be grouped into three types: juvenile crust-related, mixed source (or slightly juvenile crust)-related, and reworked crust-related. This highlights the close relationship between accretion, continental growth, and mineralization and will facilitate exploration for specific ore deposit types in the Altaids.

How to cite: Wang, T., Huang, H., Zhang, J., Wang, C., Cao, G., Xiao, W., Yuan, L., Tong, Y., and Guo, L.: Nd-Hf isotopic mapping based on a large archive of age data reveals voluminous continental growth of the Altaids and its control on metallogeny, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17556, https://doi.org/10.5194/egusphere-egu23-17556, 2023.

Geomorphological mapping is one of the primary research methods used to collect data on glacial landforms and reconstruct glaciological processes. The most common approach is a combination of field-based and remote mapping using data obtained from various sensors. However, one of the crucial methodical problems is collecting remote sensing data in the appropriate spatial resolution for the analyzed landform, which directly affects the data collection time and costs. This study aims to find the optimal resolution of digital elevation models (DEMs) to map subtle glacial landforms: kame terraces, eskers, flutes, and push moraine. Such landforms contain valuable information about the glacial process–form relationships, however, are often too subtle to be recognized on satellite data, and therefore more detailed data (e.g., UAV-based) are required. By “optimal”, we mean the resolution high enough to enable recognition of the landforms mentioned above, and at the same time, as low as possible to minimize the time spent on data collection during the fieldwork.

To find out the optimal resolution, we used detailed (0.02 – 0.04 m ground sampling distance [GSD]) DEMs of the glacier forelands in Iceland (Kvíárjökull, Fjallsjökull and Svinafellsjökull), created based high-resolution images from an unmanned aerial vehicle (UAV). The DEMs were resampled to 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 1.00 and 2.00 m GSD and selected glacial landforms were mapped independently by two operators and cross-checked. The results indicate that 2.0 m resolution is insufficient to properly recognize landforms such as pushed moraines or flutes; however, it can be sufficient to detect kame terraces and major glacifluvial channels. For general mapping of locations of forms such as annual pushed moraines or fluting, the 0.5 m resolution is required. However, to obtain geomorphometric characteristics of the landforms (e.g., height, width, volume) resolution between 0.1 and 0.2 m is necessary. Finer resolution (better than 0.05 m GSD) does not increase the ability to detect landforms or better characterize their geometric properties; however, in some cases might be useful to obtain information about clast characteristics. The experiment proved that decimeter-scale spatial resolution is sufficient for mapping of some geomorphological forms (annual pushed moraines, flutes), which allows for planning UAV missions at a higher elevation above the ground and, therefore, minmizing the duration of field surveys. Moreover, some of the more prominent landforms (e.g., kame terraces, larger moraines) can be successfully detected from aerial or satellite-based DEMs (e.g. freely available ArcticDEM) with a resolution of 2.00 m, the use of which reduces the costs of field research to a minimum.

This research was funded by the National Science Centre, Poland, Grant Number 2019/35/B/ST10/03928.

How to cite: Śledź, S. and Ewertowski, M.: Optimal resolution of UAV-based digital elevation models (DEMs) for mapping of selected subtle glacial landforms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-151, https://doi.org/10.5194/egusphere-egu23-151, 2023.

EGU23-3292 | Posters on site | GI6.1

CO2 concentration and stable isotope surveys in the ambient air of populated areas of La Palma (Canary Islands) by means of mobile Delta Ray measurements using an electrical car 

Nemesio M. Pérez, María Asensio-Ramos, José Barrancos, Eleazar Padrón, Gladys V. Melián, Fátima Rodríguez, Germán D. Padilla, Violeta T. Albertos, Pedro A. Hernández, Antonio J. Álvarez Díaz, Héctor de los Ríos Díaz, David Afonso Falcón, and Juan Cutillas

Anomalous CO2 degassing of volcanic origin was observed by the end of November 2021 in the neighborhoods of La Bombilla and Puerto Naos, located in the western flank of La Palma, about 5 km distance southwestern of the 2021 Tajogaite eruption vents (Hernández et al., 2021). In this study zone, continuous monitoring of CO2 concentration in the outdoors ambient air at 200 cm from the surface has reached a daily average of maximum and mean values about 28,000 and 10,000 ppm, respectively. We started recently to perform CO2 concentration and stable isotope surveys in the outdoors ambient air of Puerto Naos at 140 cm from the surface by means of a Delta Ray analyzer installed in an electrical car which was driving through the streets of Puerto Naos. This instrument is a high performance, mid-infrared laser-based, isotope ratio infrared spectrometer (IRIS) which offers the possibility of performing simultaneous determination of δ13C and δ18O in CO2 at ambient concentrations with a precision as low as 0.05‰. One major advantage of IRIS techniques with respect to more traditional ones (e.g., isotopic ratio mass spectrometry -IRMS-) is the possibility to perform (semi)continuous measurements at high temporal resolution. Since October 2022, seven surveys have been performed at Puerto Naos making up a total of about 600 measurements. The observed CO2 concentrations and the δ13C-CO2 values in the outdoors ambient air ranged from 420 to 3,500 ppm and from -9.0 to -3.2 ‰ vs. VPDB, respectively. Survey data analysis showed a good spatial correlation between relatively high CO2 concentrations with δ13C-CO2 values less 13C-depleted (i.e., volcanic CO2). These observations highlight that stable isotope surveys allow to evaluate the impact of volcanic degassing on the air CO2 concentration and provide valuable results to identify the volcanic CO2 gas hazard zones.

Hernández, P. A., Padrón, E., Melián, G. V., Pérez, N. M., Padilla, G., Asensio-Ramos, M., Di Nardo, D., Barrancos, J., Pacheco, J. M., and Smit, M.: Gas hazard assessment at Puerto Naos and La Bombilla inhabited areas, Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.

How to cite: Pérez, N. M., Asensio-Ramos, M., Barrancos, J., Padrón, E., Melián, G. V., Rodríguez, F., Padilla, G. D., Albertos, V. T., Hernández, P. A., Álvarez Díaz, A. J., de los Ríos Díaz, H., Afonso Falcón, D., and Cutillas, J.: CO2 concentration and stable isotope surveys in the ambient air of populated areas of La Palma (Canary Islands) by means of mobile Delta Ray measurements using an electrical car, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3292, https://doi.org/10.5194/egusphere-egu23-3292, 2023.

EGU23-3620 | ECS | Posters on site | GI6.1

SO2 emissions during the post-eruptive phase of the Tajogaite eruption (La Palma, Canary Islands) by means of ground-based miniDOAS measurements in transverse mode using a car and UAV 

Oscar Rodríguez, José Barrancos, Juan Cutillas, Victor Ortega, Pedro A. Hernández, Iván Cabrera, and Nemesio M. Pérez

Throughout the 85 days that lasted the Tajogaite eruption at Cumbre Vieja volcano (La Palma, Canary Islands, Spain), observations of SO2 emissions were made using ground-based instruments, in transverse mode, static scanners and on-board drones, as well as by numerous satellite instruments. The initial estimates of the total SO2 emission from the eruption were 2.4 Mt from TROPOMI and 1.2 Mt from the traverse data. These measurements formed part of the official monitoring effort, providing insights into the eruption’s evolution and informing the civil defence response throughout the eruption (Hayer C. et al., 2022; Albertos V. T. et al., 2022). Once the Tajogaite eruption was over, we continued performing a SO2 monitoring release to the atmosphere by the Tajogaite volcanic vent since the low ambient concentrations of SO2 make it an ideal volcanic gas monitoring candidate even during the post-eruptive phase. SO2 measurements had been carried out a using a car-mounted and UAV-mounted ground-based miniDOAS measurements throughout this post-eruptive phase. About 80 measurements of SO2 emission rates were performed from December 15, 2021 to December 17, 2022. The standard deviation of the estimated values obtained daily was ~ 20%. The range of estimated SO2 emission values has been from 670 to 17 tons per day, observing a clear decreasing trend of SO2 emissions during the post-eruptive phase. During the first month of the post-eruptive phase, it was observed that the average value of the estimated SO2 emission was about 219 tons/day, while it dropped to 107 tons/day during the second and third month after the end of the Tajogaite eruption. This average value continued decreasing during the fourth month of the post-eruptive phase, about 67 tons/day, and recently measurements provide an average SO2 emission value of 13 tons/day. These relatively low observed SO2 emissions during the post eruptive of the Tajogaite eruption phase seems to be clearly related to shallow magma cooling processes within the Tajogaite volcanic edificie.

Hayer, C., Barrancos, J., Burton, M., Rodríguez, F., Esse, B., Hernández, P., Melián, G., Padrón, E., Asensio-Ramos, M., and Pérez, N.: From up above to down below: Comparison of satellite- and ground-based observations of SO2 emissions from the 2021 eruption of Cumbre Vieja, La Palma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12201, https://doi.org/10.5194/egusphere-egu22-12201, 2022.

Albertos, V. T., Recio, G., Alonso, M., Amonte, C., Rodríguez, F., Rodríguez, C., Pitti, L., Leal, V., Cervigón, G., González, J., Przeor, M., Santana-León, J. M., Barrancos, J., Hernández, P. A., Padilla, G. D., Melián, G. V., Padrón, E., Asensio-Ramos, M., and Pérez, N. M.: Sulphur dioxide (SO2) emissions by means of miniDOAS measurements during the 2021 eruption of Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5603, https://doi.org/10.5194/egusphere-egu22-5603, 2022.

How to cite: Rodríguez, O., Barrancos, J., Cutillas, J., Ortega, V., Hernández, P. A., Cabrera, I., and Pérez, N. M.: SO2 emissions during the post-eruptive phase of the Tajogaite eruption (La Palma, Canary Islands) by means of ground-based miniDOAS measurements in transverse mode using a car and UAV, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3620, https://doi.org/10.5194/egusphere-egu23-3620, 2023.

EGU23-3819 | Posters virtual | GI6.1

Using tunable diode laser (TDL) system in urban environments to measure anomalous CO2 concentrations: the case of Puerto Naos, La Palma, Canary Islands 

José Barrancos, Germán D. Padilla, Gladys V. Melián, Fátima Rodríguez, María Asensio-Ramos, Eleazar Padrón, Pedro A. Hernández, Jon Vilches Sarasate, and Nemesio M. Pérez

Carbon dioxide (CO2) is a colourless and odourless gas. It is non-flammable, chemically non-reactive and 1.5 times as heavy as air; therefore, may accumulate at low elevations. CO2 is a toxic gas at high concentration, as well as an asphyxiant gas (due to reduction in oxygen). Irritation of the eyes, nose and throat occurs only at high concentrations. Since the Tajogaite eruption ended on December 13, 2021, high concentrations of CO2 up to 20% (200.000 ppmv) have been observed inside of buildings of the neighborhoods of La Bombilla and Puerto Naos (La Palma, Canary Islands), which are located about 5 km distance from the Tajogaite eruption vent. Anomalous concentrations of CO2 are manily detected in the ground-floor and basement of the buildings in Puerto Naos, and the distribution of relatively high CO2 concentrations  is not homogeneous or uniform throughout the Puerto Naos area (Hernández P.A. et al, 2022).

The purpose of this study was to use the Tunable Laser Diode (TDL) absorption spectroscopy method to monitor the indoor CO2 concentration of the ground-floor of one of the buildings of Puerto Naos. A CO2-TDL was installed on 9 January 2022 and continues measuring the CO2 concentration along an optical path of about 6 meters. During the period January-March 2022, daily averages of CO2 concentrations from fifteen-minute data ranged from 5000 to 25000 ppmv reaching values up to 40000 ppmv (4%). Over time, a clear decreasing trend of the indoor CO2 concentration has been observed at this observation site and the daily CO2 averages from fifteen-minute data during the last 3 months (October-December 2022) ranged from 1000 to 2500 ppmv. This clear decreasing trend over time has not been observed at other observation sites where the concentration of CO2 inside buildings is being monitored. This observation indicates the complexity of the problem and the need to install a dense network of sensors to monitor CO2 for civil protection purposes.

 

Hernández, P. A., Padrón, E., Melián, G. V., Pérez, N. M., Padilla, G., Asensio-Ramos, M., Di Nardo, D., Barrancos, J., Pacheco, J. M., and Smit, M.: Gas hazard assessment at Puerto Naos and La Bombilla inhabited areas, Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.

How to cite: Barrancos, J., Padilla, G. D., Melián, G. V., Rodríguez, F., Asensio-Ramos, M., Padrón, E., Hernández, P. A., Vilches Sarasate, J., and Pérez, N. M.: Using tunable diode laser (TDL) system in urban environments to measure anomalous CO2 concentrations: the case of Puerto Naos, La Palma, Canary Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3819, https://doi.org/10.5194/egusphere-egu23-3819, 2023.

EGU23-3834 | Posters on site | GI6.1

Modeling outdoor dispersion of CO2 at Puerto Naos (La Palma, Canary Islands) 

Luca D Auria, Alba Santos, Pedro A. Hernández, Gladys V. Melián, Antonio J. Álvarez Díaz, María Asensio-Ramos, Alexis M. González Pérez, and Nemesio M. Pérez

The 2021 Tajogaite eruption in Cumbre Vieja volcano (La Palma, Canary Islands), which started on Sep. 19, 2021, and lasted 85 days, caused extensive damages because of the lava flows and ash fall. However, since the middle of Nov. 2021, some areas located about 5 km SW of the eruptive center started to be affected by intense diffuse CO2 emission. Among them are the urban centers of La Bombilla and Puerto Naos (Hernández et al., 2022). These emissions prevented the population of these two centers from returning to their houses because of high  concentrations of CO2 in indoor and outdoor environments.

In this work, we model the CO2 dispersion process in Puerto Naos to obtain hazard maps with the maximum CO2 concentrations which can be reached in the town in the outdoor environment. To achieve these results, we combined field observations with numerical modelling. Field surveys were realized in low wind conditions, measuring the CO2 concentration with portable sensors  at 15 and 150 cm from the ground at measurement points spaced approximately 10 m from each other along the streets of Puerto Naos.

We realized numerical modelling using the software TWODEE-2, a code for modeling the dispersion of heavy gases based on the solution of shallow water equations (Folch et al., 2009). For this purpose, we used a detailed digital topographic model, including the edifices of Puerto Naos. Using a trial-and-error approach, we determined the gas emission rates from a set of discrete source points in no-wind conditions. Subsequently, we repeated the numerical modelling, keeping the same sources and simulating all the realistic wind conditions in terms of direction and intensity. For each simulation, we determined the maximum CO2 concentration at different elevations from the ground. This allowed obtaining a hazard map with the maximum CO2 outdoor concentrations for each part of the town

The main results highlight that the outdoor environment is affected by a dense layer of CO2, whose flow is strongly conditioned by the urban infrastructures. Furthermore, we evidenced how even light winds can change the gas concentration pattern radically in a few minutes, evidencing the possibility of sudden changes in the CO2 concentration outdoors with no warning.

Folch A., Costa A., Hankin R.K.S., 2009. TWODEE-2: A shallow layer model for dense gas dispersion on complex topography, Comput. Geosci., doi:10.1016/j.cageo.2007.12.017

Hernández, P. A., Padrón, E., Melián, G. V., Pérez, N. M., Padilla, G., Asensio-Ramos, M., Di Nardo, D., Barrancos, J., Pacheco, J. M., and Smit, M.: Gas hazard assessment at Puerto Naos and La Bombilla inhabited areas, Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.

How to cite: D Auria, L., Santos, A., Hernández, P. A., Melián, G. V., Álvarez Díaz, A. J., Asensio-Ramos, M., González Pérez, A. M., and Pérez, N. M.: Modeling outdoor dispersion of CO2 at Puerto Naos (La Palma, Canary Islands), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3834, https://doi.org/10.5194/egusphere-egu23-3834, 2023.

EGU23-5223 | Orals | GI6.1

Event-oriented observation across scales and environmental systems: MOSES started operation. 

Ute Weber and Claudia Schuetze and the MOSES-Team

The novel observing system „Modular Observation Solutions for Earth Systems (MOSES)“, is an initiative of the Helmholtz Association of German Research Centers that aims at investigating the interactions of short-term events and long-term trends across environmental systems. MOSES is a mobile and modular infrastructure and its component measuring systems are managed by the participating research centers. By quantifying energy, water, nutrient and greenhouse gas states and fluxes during events such as heat waves, droughts, heavy precipitation, floods, rapid thaw of permafrost or of ocean eddies, and subsequently along the related event chains, the system delivers data to examine potential long-term impacts of these events and to gain a better understanding of extreme events that are expected to increase in frequency and intensity in a changing climate. In order to obtain comprehensive data sets, a cross-system approach is followed, covering the atmosphere, land surface and hydrosphere. These event-related data sets complement long-term and/or large scale data sets of established national and international monitoring programs and satellite data such as TERENO, ICOS, eLTER, SENTINEL, etc. After a 5-year setup period, MOSES was successfully put into operation in 2022 (Weber et al., 2022, https://doi.org/10.1175/BAMS-D-20-0158.1).

While long-term trends are typically assessed with stationary observation networks and platforms specifically designed for long-term monitoring, proven event-oriented observation systems and strategies are still missing. Event-oriented observation campaigns require a combination of a) measuring systems that can be rapidly deployed at “hot spots” and in “hot moments”, b) mobile equipment to monitor spatial dynamics in high-resolution, c) in situ measuring systems to record temporal dynamics in high-resolution, and d) interoperable measuring systems to monitor the interactions between atmosphere, land surface and hydrosphere. We will present the observation system and the observing strategy on examples from two past test campaigns: 1) The “Swabian MOSES campaign” of 2021 that captured the formation and evolution of supercells, hail and heavy precipitation and the resulting local flash floods (Kunz et al., 2022, https://doi.org/10.3389/feart.2022.999593). 2) The MOSES campaign of 2019 that captured the historical low flow situation along the Elbe River and into the German Bight (e.g., Kamjunke et al., 2021, https://doi.org/10.1002/lno.11778). As an outlook, upcoming national and international campaigns and potential future deployments will be presented.

How to cite: Weber, U. and Schuetze, C. and the MOSES-Team: Event-oriented observation across scales and environmental systems: MOSES started operation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5223, https://doi.org/10.5194/egusphere-egu23-5223, 2023.

EGU23-5684 | ECS | Posters on site | GI6.1

Random Forest Classification of Proterozoic and Paleozoic rock types of Tsagaan-uul area, Mongolia 

Munkhsuren Badrakh, Narantsetseg Tserendash, Erdenejargal Choindonjamts, and Gáspár Albert

The Tsagaan-uul area of the Khatanbulag ancient massif in the Central Asian Orogenic Belt is located in the southern part of Mongolia, which belongs to the Gobi Desert. It has a low vegetation cover, and because of this, remotely sensed data can be used without difficulty for geological investigations. Factors such as sparse population and underdeveloped infrastructure in the region further create a need for combining traditional geological mapping with remote sensing technologies. In existing geology maps of the area, the formations are lithologically very diverse and their boundaries were mapped variously, so a need for a more precise lithology-based map arouse.

This study investigated combinations of fieldwork, multispectral data, and petrography for the rock type classification. A random forest classification method using multispectral Sentinel-2A data was employed in order to distinguish different rocks within Proterozoic Khulstai (NP1hl) metamorphic complex, which is dominated by gneiss, andesite, sandstone, limestone, amphibolite, as well as the Silurian terrigenous-carbonate Khukh morit (S1hm) formation, Tsagaan-uul area. Based on the ground samples collected from field surveys, ten kinds of rock units plus Quaternary sediments were chosen as training areas. In addition, morphometric parameters derived from SRTM data and band ratios used for iron-bearing minerals from Sentinel 2 bands are selected as variables in the accuracy of classification. The result showed that gneisses were recognized with the highest accuracy in the Khulstai complex, and limestones and Quaternary sediments were also well predicted. Moreover, the tectonic pattern was also well recognized from the results and compared to the existing maps provided a more detailed geological image of the area. This study emphasized the need for samples as baseline data to improve the machine learning methods, and the method provides an appropriate basis for fieldwork.

 

How to cite: Badrakh, M., Tserendash, N., Choindonjamts, E., and Albert, G.: Random Forest Classification of Proterozoic and Paleozoic rock types of Tsagaan-uul area, Mongolia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5684, https://doi.org/10.5194/egusphere-egu23-5684, 2023.

EGU23-5689 | Posters on site | GI6.1

Post-earthquake geoenvironmental changes in landslide-affected watersheds in Atsuma, Hokkaido (Japan) 

Yuichi S. Hayakawa, Tennyson Lo, Azim Zulhilmi, Xinyue Yu, and Xiaoxiao Wang

Following drastic changes in geoenvironmental components by coseismic landslides in mountainous watersheds, more gradual changes can be observed in the elements, including bare-land surface conditions, sediment connectivity, and vegetation recovery on sloping terrains. Such geoenvironmental changes may continue for years to decades, with complex interrelationships among various geomorphological and ecological factors. Their assessments are also crucial for local to regional environmental management. After the occurrence of numerous coseismic landslides triggered by the 2018 Hokkaido Eastern Iburi Earthquake in northern Japan, geomorphological and geoecological changes were explored using optical and laser sensors on uncrewed aerial systems. Morphological characteristics of the landslide-affected slopes in the watersheds were assessed with structure-from-motion multi-view stereo photogrammetry and light detection and ranging topographic datasets, while vegetation recovery on the slopes was examined with visible-light and near-infrared images. Although spatial relationships among morphological developments, sediment mobility, and vegetation recovery were not clearly observed, their general temporal trends may be correspondent. Dominant processes affecting the morphological developments are supposed to be frost heave in the cold climate and non-frequent high-intensity rainfalls, and these can be conditioning vegetation growth. Such local changes will be further examined on a wider, regional scale. 

How to cite: Hayakawa, Y. S., Lo, T., Zulhilmi, A., Yu, X., and Wang, X.: Post-earthquake geoenvironmental changes in landslide-affected watersheds in Atsuma, Hokkaido (Japan), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5689, https://doi.org/10.5194/egusphere-egu23-5689, 2023.

EGU23-5750 | Posters on site | GI6.1

Aseismic creep and coseismic dislocation at an active fault in volcanic area: the case of Ischia Island 

Stefano Carlino, Nicola Alessandro Pino, Lisa Beccaro, and Prospero De Martino

Understanding the fault dynamics in volcanic areas is not a simple task, mainly due to both the heterogeneity of volcanic structures and the local stress distribution. The presence of high temperature-high pressure geothermal fluids and relative high strain rates, and the occurrence of viscous processes in the deeper part of the volcano further contribute to generate complex patterns of strain load and release, possibly with aseismic creep and differential movements along the faults.

We present the case of an active fault located Casamicciola Terme town – in northern area of the volcanic caldera of Ischia Island (Southern Italy) – where repeated destructive earthquakes occurred at least since 1769, even causing thousands of victims in a single event, with the last one striking in 2017. To assess a possible mechanism leading to the activation of the Ischia main seismogenic fault, its cyclic nature and the related hazard, we performed a joined analysis of the ground vertical movements, obtained from cGPS (2001-present), DInSAR (2015-2018) time-series, and levelling data of the island (1987-2010). The geodetic data indicate that Casamicciola seismogenic fault is characterized by a complex dynamic, with some pre- and post-seismic aseismic dislocation, along sectors that move differentially, in response to the long-term subsidence of the island. Based on the ground deformation rate and on the distribution of degassing areas, we speculate that fluid pressure variations may have a major role in modulating the apparent non-stationarity of the Ischia stronger earthquakes. Furthermore, we suggest that a punctual monitoring of the distribution in space and time of the aseismic creep could provide clues on the state of strain of the seismogenic fault.

How to cite: Carlino, S., Pino, N. A., Beccaro, L., and De Martino, P.: Aseismic creep and coseismic dislocation at an active fault in volcanic area: the case of Ischia Island, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5750, https://doi.org/10.5194/egusphere-egu23-5750, 2023.

EGU23-6832 | ECS | Orals | GI6.1

Quantifying karstic geomorphologies using Minkowski tensors and graph theory: Applications to SLAM Lidar data from carbonate caves in Northern Bavaria (Germany) 

Rahul Prabhakaran, Ruaridh Smith, Daniel Koehn, Pierre-Olivier Bruna, and Giovanni Bertotti

Karstification is a ubiquitous feature in carbonate rocks. The origins can be hypogenic or epigenic based on the source of the reacting fluids. The presence of karstified lithologies and their spatial heterogeneity poses a major risk in subsurface energy utilization goals (hydrocarbons, geothermal etc). Such dissolution features tend to organize as spatial networks, with their evolution controlled by a complex interplay of several factors, including natural mineralogical variations in host rocks, effects of pre-existing structures, directional history of palaeo-flow paths, and competition between convective transport and dissolution. Accurate quantification of the spatial distribution of karst is difficult owing to resolution issues in 3D data such as seismic and ground penetrating radar. Recent advances in Simultaneous Location and Mapping (SLAM) Lidar technology have made possible to acquire karst cave passage geometries at very high-resolution with relative ease compared to conventional terrestrial lidar. In this contribution, we present a unique dataset of more than 80 caves, scanned using SLAM lidar, in Jurassic carbonates from northern Bavaria, Germany. We introduce a methodology for robustly deriving morphometrics of karstic caves using Minkowski tensors and spatial graph theory. The method is based on a combination representation of cave passage skeletons as spatial graphs and 2D passage cross-sections using Minkowski functionals. The enriched topological representation enables detailed analysis of internal spatial variation within a single cave and also comparison with cave geometries from other caves. We derive a typology of cave systems based on the degree of structural control on karstification using the database.

How to cite: Prabhakaran, R., Smith, R., Koehn, D., Bruna, P.-O., and Bertotti, G.: Quantifying karstic geomorphologies using Minkowski tensors and graph theory: Applications to SLAM Lidar data from carbonate caves in Northern Bavaria (Germany), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6832, https://doi.org/10.5194/egusphere-egu23-6832, 2023.

EGU23-7265 | Posters on site | GI6.1

Low Power, Rugged Edge Computing provides a low cost, powerful solution for on the ground remote sensing in extreme environments 

Nicholas Frearson, Terry Plank, Einat Lev, LingLing Dong, and Conor Bacon

Ground based remote sensing devices increasingly incorporate low cost single board computers such as a Raspberry Pi to capture and analyze images and data from the environment. Useful and cheap as these devices are, they are not designed for use in extreme conditions and as a consequence often suffer from early failure. Here we describe a system that incorporates a commercially available rugged Edge Computer running embedded Linux that is designed to operate in remote and extreme environments. The AVERT system  (Anticipating Volcanic Eruptions in  Real Time) developed at Columbia University in New York and funded by the Moore Foundation uses solar and wind powered Sensor nodes configured in a spoke and hub architecture currently operating on two volcanoes overseen by the Alaska Volcano Observatory in the Aleutian Islands, Alaska. Multiple Nodes distributed around the volcanoes are each controlled by an Edge Computer which manages and monitors local sensors, processes and parses their data via radio link to a central Hub and schedules system components to wake and sleep to conserve power. The Hub Edge Computer collects and assembles data from multiple Nodes and passes it via satellite, cellular modem or radio links to servers located elsewhere in the world or cloud for near real-time analysis. The local computer enables us to minimize local power demand to just a few watts in part due to the extremely low power sleep modes that are incorporated into these devices. For instance, a Node incorporating a webcam, IRCam, weather station, Edge Computer, network switch, communications radio and power management relays draws only 4.5W on average. In addition, this level of local computing power and a mature Linux operating environment enables us to run AI algorithms at source that process image and other data to flag precursory indicators of an impending eruption. This also helps to reduce data volume passed across the network at times of low network connectivity. We can also remotely interrogate any part of the system and implement new data schemes to best monitor and react to ongoing events. Future work on the AI algorithm development will incorporate local multisensor data analytics to enhance our anticipatory capability.

How to cite: Frearson, N., Plank, T., Lev, E., Dong, L., and Bacon, C.: Low Power, Rugged Edge Computing provides a low cost, powerful solution for on the ground remote sensing in extreme environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7265, https://doi.org/10.5194/egusphere-egu23-7265, 2023.

EGU23-8673 | Orals | GI6.1

Are they radon or random signals? Analysis of time series of 222Rn activity concentrations in populated areas of La Palma (Canary Islands, Spain) 

Antonio Eff-Darwich, Germán D. Padilla, José Barrancos, José A. Rodríguez-Losada, Pedro A. Hernández, Nemesio M. Pérez, Antonio J. Álvarez Díaz, Alexis M. González Pérez, Jesús García, José M. Santana, and Eleazar Padrón

Radon, 222Rn, is a radioactive constituent of the surface layer of the atmosphere. The analysis of the temporal and spatial variations in the flux of radon across the soil–air interface is a promising tool to study geo-dynamical processes. However, many of these variations are induced by external variables, such as temperature, barometric pressure, rainfall, or the location of the instrumentation, among others.

Anomalous CO2 degassing has been observed since the end of November 2021 in the neighborhoods of La Bombilla and Puerto Naos, located in the western flank of La Palma, about 5 km distance southwestern of the 2021 Tajogaite eruption vents (Hernández et al. 2022). In order to complement these observations with other independent parameters, a set of radon monitoring stations have been deployed in that area. In an attempt to filter out non-endogenous variations in the radon signal, we have implemented time-series numerical filtering techniques based on multi-variate and frequency domain analysis. A background level for radon emissions at various locations could therefore be defined, by which correlations between radon concentration, gaseous emissions and dynamical processes could be carried out. Some preliminary results corresponding to the first 3 months of data (october-december 2022) are presented.

Hernández, P. A., Padrón, E., Melián, G. V., Pérez, N. M., Padilla, G., Asensio-Ramos, M., Di Nardo, D., Barrancos, J., Pacheco, J. M., and Smit, M.: Gas hazard assessment at Puerto Naos and La Bombilla inhabited areas, Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.

How to cite: Eff-Darwich, A., Padilla, G. D., Barrancos, J., Rodríguez-Losada, J. A., Hernández, P. A., Pérez, N. M., Álvarez Díaz, A. J., González Pérez, A. M., García, J., Santana, J. M., and Padrón, E.: Are they radon or random signals? Analysis of time series of 222Rn activity concentrations in populated areas of La Palma (Canary Islands, Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8673, https://doi.org/10.5194/egusphere-egu23-8673, 2023.

EGU23-8795 | ECS | Orals | GI6.1

Integration of Seismic and Quasi-Static Signals for Improved Volcanic Monitoring 

Joe Carthy, Alejandra Vásquez Castillo, Manuel Titos, Luciano Zuccarello, Flavio Cannavò, and M. Carmen Benitez

The time scale of ground displacement at volcanoes varies between short, sub second seismic events, to days, months or even years. This study is focused on data from seismic and GNSS stations located around Mount Etna. The GNSS and seismic stations operate at different time scales. Data from these different time scales is extracted and combined in order to better understand the subsurface dynamics. The overall aim of this research is to improve volcanic forecasting and monitoring. It does this in a novel way by applying signal processing and machine learning techniques to the rich dataset.

Mount Etna offers an interesting case study as it is a widely monitored volcano with a variety of sensors and with a rich pool of data to analyse. Additionally the volcanic dynamics at Mount Etna are complex. This is a volcano where there is a variety of different sub-surface dynamics due to the movement of both deep and shallow magma. This allows for rich insights to be drawn through the combination of different signal types.

This study looks at combining the information obtained from the seismic array at Mount Etna, with the information obtained from various GNSS stations on the volcano. The seismic array has been able to capture ground velocity data in the frequency range 0.025 Hz to 50 Hz from a range of stations at different locations across the volcano. The GNSS stations measure ground displacement with a sampling frequency of 1 Hz, and they allow for longer term ground dynamic analysis.

We analyse different seismic events, and relate the type and number of the seismic events to the long term ground deformation that we see in the recorded GNSS data. Where links between the two signal types have been identified, research is ongoing to establish a direct connection with known volcanic activity on Mount Etna. This will help establish what the relationship that we are seeing signifies. This integration of data from different types of sensors is a significant step into bridging the gap between seismic and quasi-static ground displacement at active volcanoes and should open the path toward more in depth volcanic monitoring and forecasting.

How to cite: Carthy, J., Vásquez Castillo, A., Titos, M., Zuccarello, L., Cannavò, F., and Benitez, M. C.: Integration of Seismic and Quasi-Static Signals for Improved Volcanic Monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8795, https://doi.org/10.5194/egusphere-egu23-8795, 2023.

EGU23-10069 | ECS | Orals | GI6.1

Vredefort impact site modelling through inhomogeneous depth weighted inversion. 

Andrea Vitale and Maurizio Fedi

We are showing an application of the 3D self-constrained depth weighted inversion of the inhomogeneous gravity field (Vitale and Fedi, 2020) of the Vredefort impact site.

This method is based on two steps, the first being the search in the 3D domain of the homogenous degree of the field, and the second being the inversion of the data using a power-law weighting function with a 3D variable exponent. It does not involve directly data at different altitudes, but it is heavily conditioned by a multiscale search of the homogeneity degree.

The main difference between this inversion approach and the one proposed by Li and Oldenburg algorithm (1996) and Cella and Fedi (2012) is therefore about the depth weighting function, whose exponent is a constant through the whole space in the original Li and Oldenburg and Cella and Fedi approaches, while it is a 3D function in the method which we will discuss here.

The model volume of the area reaches 20 km in depth, while along x and y its extension is respectively 41 by 63 km. The trend at low and middle altitudes of the estimated β related to the main structures is fitting the expectations because the results relate to two main structures, which are geometrically different: the core is like a spheroid body (β ≈ 3) and the distal rings are like horizontal pipes or dykes (1 < β < 2).

With a homogeneous depth weighting function, we recover a smooth solution and both the main sources, the main core and the rings of the impact, are still visible at the bottom of the model (20 km). This is not in agreement with the result by Henkel and Reimold (1996, 1998), which, based on gravity and magnetic inversion supported by seismic data, proposed a model where the bottom of the rings is around 10 km and the density contrast effect due to the core structure loses its effectiveness around 15 km.

Instead, using an inhomogeneous depth weighting function (figure 28) we can retrieve information regarding the position at depth of both core and distal ring structures that better fits the above model. In fact, the bottom of the distal ring structure, that should be around 10 km according to Henkel and Reimold (1996, 1998), is recovered very well using an inhomogeneous depth weighting function, while in the homogeneous case we saw that the interpreted structure was still visible at large depths.

In addition, also the core structure is shallower compared to the homogeneous approach and seems more reliable if we compare it with the model of Henkel and Reimold (1996, 1998).

Instead, the inhomogeneous approach presented in this paper leads naturally us to a better solution because it takes into account during the same inversion process of the inhomogeneous nature of the structural index within the entire domain.

How to cite: Vitale, A. and Fedi, M.: Vredefort impact site modelling through inhomogeneous depth weighted inversion., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10069, https://doi.org/10.5194/egusphere-egu23-10069, 2023.

EGU23-11065 | ECS | Posters on site | GI6.1

The Dynamics of Climate Change Science and Policy in Panama: A Review 

Gustavo Cárdenas-Castillero, Steve Paton, Rodrigo Noriega, and Adriana Calderón

The local studies and reports indicate that the temperature of Panama has increased by approximately 1°C since the 1970s. More evidence shows a constantly rising sea level in the Guna Yala archipelago, coral bleaching on both coasts, and increasingly more frequent and extreme precipitation events throughout Panama. This study includes an analysis of over 400 scientific publications made by researchers from multiple centres and more than 20 Panamanian official reports due to Panama's mandate and duties under the international climate accords. To summarise the results, the studies were gathered according to the climate change effects by Panamanian locations and analysed posteriorly using Rstudio and ArcMAP. The results indicate a significant increase in climate change research beginning in 2007.

This study identified and examined the essential findings per hydroclimatic region, showing the trends, limitations, collaborations, and international contributions. Climate change research in Panama includes some of the longest-term meteorological, hydrological, oceanographic, and biological studies in the neotropics. The most significant number of identified climate change-related studies were conducted, at least in part, in the Barro Colorado Natural Monument located in central Panama. Other frequently used sites include Metropolitan Natural Park, Soberania Park, the Panama Canal Watershed and the Caribbean coast of Colón and Bocas del Toro, primarily due to research conducted by Smithsonian Tropical Research-affiliated investigators. The tropical forests of Panama are some of the bests studied in the world; however, research has been concentrated in a relatively small number of locations and should be expanded to include additional areas to achieve a more complete and comprehensive understanding of climate change will impact Panama in the future.

How to cite: Cárdenas-Castillero, G., Paton, S., Noriega, R., and Calderón, A.: The Dynamics of Climate Change Science and Policy in Panama: A Review, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11065, https://doi.org/10.5194/egusphere-egu23-11065, 2023.

EGU23-12050 | Orals | GI6.1

Stress field analysis from induced earthquakes caused by deep fluid injection: the 2013 St. Gallen (Switzerland) seismic sequence. 

Bruno Massa, Guido Maria Adinolfi, Vincenzo Convertito, and Raffaella De Matteis

The city of St. Gallen is located in the Molasse Basin of northeast Switzerland. Mesozoic units of the substratum are affected by a fault system hosting a hydrothermal reservoir. In 2013 a deep geothermal drilling project started in an area close to the city. During a phase of reservoir stimulation, a sequence of more than 340 earthquakes was induced with a maximum magnitude ML 3.5. Stress inversion of seismological datasets became an essential tool to retrieve the stress field of active tectonics areas. With this aim, a dataset of the best constrained Fault Plane Solutions (FPSs) was processed in order to qualitatively retrieve stress-fields active in the investigated volume. FPSs were obtained by jointly inverting the long-period spectral-level P/S ratios and the P-wave polarities following a Bayesian approach (BISTROP). Data were preliminarily processed by the Multiple Inverse Method to evaluate the possible dataset heterogeneity and separate homogeneous FPS populations. The resulting dataset was then processed using the Bayesian Right Trihedra Method (BRTM). Considering that hypocentral depths range between 4.1 and 4.6 km b.s.l., in order to emphasize depth-related stresses, we performed a first step of raw stress inversion procedure splitting the data into five subsets, grouping events located inside 100-m depth ranges. Once the presence of stress variations with depth has been excluded, the second step of fine stress inversion procedure was performed on the entire dataset. The stress-inversion procedure highlights an active stress field dominated by a well-constrained NE low-plunging σ3 and a corresponding NW low-plunging σ1. The corresponding Bishop ratio confirms the stability of the retrieved attitudes. Results are in good accordance with the regional stress field derived from regional natural seismicity. Additionally, the retrieved, dominant, stress field is coherent with the regional tectonic setting.

This research has been supported by PRIN-2017 MATISSE project (No. 20177EPPN2).

How to cite: Massa, B., Adinolfi, G. M., Convertito, V., and De Matteis, R.: Stress field analysis from induced earthquakes caused by deep fluid injection: the 2013 St. Gallen (Switzerland) seismic sequence., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12050, https://doi.org/10.5194/egusphere-egu23-12050, 2023.

EGU23-13693 | ECS | Orals | GI6.1

Assessing the transfer factors (TFs) of contaminants from soil to plants: the case study of Campania region (Southern Italy) 

Lucia Rita Pacifico, Annalise Guarino, Gianfranco Brambilla, Antonio Pizzolante, and Stefano Albanese

The presence of potentially toxic elements (PTEs) derived from anthropogenic sources in soil represents a serious issue for animal and human health. These elements can easily move from the geological compartment to the biological compartment through to the food chain. (Jarup, 2003).

The geochemical knowledge of a territory allows to assess the degree of contamination of the environment, to locate the sources of environmental hazard and, possibly, to manage the anomalous concentrations of the PTEs in environmental matrices with the purpose of eliminating or minimizing their negative impact on the health of living beings. (Reimann et al. 2005).

Several studies have been already carried out to determine the distribution patterns of PTEs in the soil of Campania region (Southern Italy) (De Vivo et al., 2022) but little is known about the transfer processes of contaminants from soils to agricultural products.

In light of above, we present the results of a new study whose purpose was to determine the Transfer Factors (TFs) of PTEs from soil to a series of agricultural products commonly grown in Campania.

Considering the complex geological and geomorphological settings of the region and the diffuse presence of an historical anthropization related to the industry, agriculture, and urbanization, TFs were calculated for a relevant number of fruit and vegetable samples (3731 specimens). They were collected across the whole regional territory to detect differences between analysed species and to highlight the spatial changes in TFs occurring for individual species.

The TFs were calculated starting from the quasi-total (based on Aqua Regia leaching) and bioavailable (based on Ammonium Nitrate leaching) concentrations of PTEs in 7000 and 1500 soil samples, respectively.

Preliminary results show that TFs determined for the various agricultural species vary in space and in amount independently from the original elemental concentrations in soils. High values of TFs are found in areas where PTE concentrations in soil are low and vice versa, thus suggesting that multiple regression and multivariate analyses could be performed to investigate if some additional chemical and physical characteristics of soil (pH, grainsize, OM, etc.) could have a relevant weight on the transfer processes of contaminant from the soil to the plant life.

 

References

Järup L. 2003. Hazards of heavy metal contamination. Br. Med. Bull. 68, 167–182.

Reimann C., de Caritat P. 2005. Distinguishing between natural and anthropogenic sources for elements in the environment: regional geochemical surveys versus enrichment factors. Science of The Total Environment, Volume 337, Issues 1–3, pages 91-107.

De Vivo B. et al. 2022. Monitoraggio geochimico-ambientale dei suoli e dell'aria della Regione Campania. Piano Campania trasparente. Volume 4. Aracne Editore, Genzano di Roma.

How to cite: Pacifico, L. R., Guarino, A., Brambilla, G., Pizzolante, A., and Albanese, S.: Assessing the transfer factors (TFs) of contaminants from soil to plants: the case study of Campania region (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13693, https://doi.org/10.5194/egusphere-egu23-13693, 2023.

EGU23-13853 | Posters on site | GI6.1

Analysis and Modelling of 2009-2013 vs. 2019-2022 Unrest Episodes at Campi Flegrei Caldera 

Raffaele Castaldo, Andrea Barone, De Novellis Vincenzo, Pepe Antonio, Pepe Susi, Solaro Giuseppe, Tizzani Pietro, and Tramelli Anna

Geodetic modelling is a significant procedure for detecting and characterizing unrest and eruption episodes and it represents a valuable tool to infer volume and geometry of volcanic source system.

In this study, we analyse the 2009–2013 and the ongoing 2019-2022 uplift phenomena at Campi Flegrei (CF) caldera in terms of spatial and temporal variations of the stress/strain field. In particular, we investigate the characteristics of the inflating sources responsible of these main deformation unrests occurred in the last twenty years. We separately perform for the two considered periods a 3D stationary Finite Element (FE) modelling of geodetic datasets to retrieve the geometry and location of the deformation sources. The geometry of FE domain takes into account both the topography and the bathymetry of the whole caldera. For what concern the definition of domain elastic parameters, we take into account the Vp/Vs distribution from seismic tomography. In order to optimize the nine model parameters (center coordinates, sferoid axes, dip, strike and over-pressure), we use the statistical random sampling Monte Carlo method by exploiting both geodetic datasets: the DInSAR measurements obtained from the processing of COSMO-SkyMed and Sentinel-1 satellite images. The modelling results for the two analysed period are compared revealing that the best-fit source is a three-axis oblate spheroid ~3.5 km deep, similar to a sill-like body. Furthermore, in order to verify the reliability of the geometry model results, we calculate the Total Horizontal Derivative (THD) of the vertical velocity component and compare it with those performed directly on the two DInSAR dataset.

Finally, we compare the modelled shear stress with the natural seismicity recorded during the 2000-2022 period, highlighting high values of modelled shear stress at depths of about 3.5 km, where high-magnitude earthquakes nucleate.

How to cite: Castaldo, R., Barone, A., Vincenzo, D. N., Antonio, P., Susi, P., Giuseppe, S., Pietro, T., and Anna, T.: Analysis and Modelling of 2009-2013 vs. 2019-2022 Unrest Episodes at Campi Flegrei Caldera, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13853, https://doi.org/10.5194/egusphere-egu23-13853, 2023.

EGU23-15127 | ECS | Orals | GI6.1

Multiscale magnetic modelling in the ancient abbey of San Pietro in Crapolla 

Luigi Bianco, Maurizio Fedi, and Mauro La Manna

We present a multiscale analysis of magnetic data in the archaeological site of San Pietro in Crapolla (Massa Lubrense, near Naples, Italy). The site consists of the ruins of an ancient abbey. We computed the Wavelet Transform of the Gradiometric measurements and decomposed the data at different scales and positions by a multiresolution analysis, allowing an effective extraction of local anomalies. Modelling of the filtered anomalies was performed by multiscale methods known as “Multiridge analysis” and “DEpth from eXtreme Points (DEXP)”.  The first method analyses a multiscale dataset at the zeroes of the first horizontal and vertical derivatives besides the potential field data themselves (ridges).  The Wavelet Transform Modulus Maxima  lines converged to buried remains. The field, scaled by a power law of the altitude (DEXP transformation) allowed estimates of source depths at its extreme points. The depth estimations for the buried structures obtained from the two methods are very close each other and fairly agree with those from the modelling of GPR anomalies. On the basis of these results, an archaeological excavation followed our indications and brought to light ancient walls.

How to cite: Bianco, L., Fedi, M., and La Manna, M.: Multiscale magnetic modelling in the ancient abbey of San Pietro in Crapolla, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15127, https://doi.org/10.5194/egusphere-egu23-15127, 2023.

EGU23-15190 | Orals | GI6.1

Synthetic aperture radar burst overlapped interferometry for the analysis of large ground instabilities: Experiments in volcanic regions. 

Antonio Pepe, Andrea Barone, Pietro Mastro, Pietro Tizzani, and Raffaele Castaldo

This work presents an overview of some applications of synthetic aperture radar (SAR) interferometry technology for the detection and analysis of large ground displacements occurring in volcanic areas, with the aim to retrieve the three-dimensional (3-D) ground displacement field (up-down, east-west, north-south). Specifically, the work summarizes and investigates the potential of Bursted Overlapped Interferometry (BOI) that properly combined can allow the retrieval, at different scales of resolution and accuracies, of the north-south components of the ground deformations, which are usually not available considering conventional SAR interferometry techniques. In this context, the almost global coverage and the weekly revisit times of the European Copernicus Sentinel-1 SAR sensors permit nowadays to perform extensive analyses with the aim to assess the accuracy of the BOI techniques. More recently, Spectral Diversity (SD) methods have been exploited for the fine co-registration of SAR data acquired with the Terrain Observation with Progressive Scans (TOPS) mode. In this case, considering that TOPS acquires images in a burst mode, there is an overlap region between consecutive bursts where the Doppler frequency variations is large enough to allow estimating and compensating for, with great accuracy, potential bursts co-registration errors. Additionally, and more importantly, in the case of non-stationary scenarios, it allows detecting the ground displacements occurring along the azimuthal directions (almost aligned along north-south) with centimeter accuracy. This is done by computing the difference between the right and left interferograms, i.e., the burst overlapped interferogram, and relating it to the ongoing deformation signals.

This work aims to apply the BOI technique in selected volcanic and seismic areas to evaluate the impact of this novel technology for the analysis of quantifying, over small, covered regions, the accumulated ground displacements in volcanic areas. In such regions, the interest is on quantifying the accuracy of integrated BOI systems for the retrieval of 3-D displacements. To this aim, we selected as a test site the Galapagos Island and we analyze with BOI the north-south ground displacements. At the next EGU symposium, the results of the BOI analyses will be presented, thus also providing comparative analyses with the results obtained from the use of potential field method applied on the ground displacements in volcanic areas. More specifically, by adopting this technique, we are able to estimate independently the north-south components of the ground displacement by exploiting the harmonic properties of the elasticity field.

How to cite: Pepe, A., Barone, A., Mastro, P., Tizzani, P., and Castaldo, R.: Synthetic aperture radar burst overlapped interferometry for the analysis of large ground instabilities: Experiments in volcanic regions., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15190, https://doi.org/10.5194/egusphere-egu23-15190, 2023.

EGU23-16132 | ECS | Orals | GI6.1

Multiscale imaging of low-enthalpy geothermal reservoir of the Phlegraean Fields caldera from gravity and resistivity data. 

Maurizio Milano, Giuseppe Cavuoto, Alfonso Corniello, Vincenzo Di Fiore, Maurizio Fedi, Nicola Massarotti, Nicola Pelosi, Michele Punzo, Daniela Tarallo, Gian Paolo Donnarumma, and Marina Iorio

The central‐eastern sector of the Phlegraean Fields caldera, southern Italy, is one of the most intensely studied and monitored volcanic active area of the word. This area reveals typical characters of a high‐ enthalpy geothermal systems. However, recently the presence of two different geothermal reservoirs has been outlined: one located in the central sector dominated by highly active vapours generated by episodic arrival of CO2‐rich magmatic fluids and the other one located in the eastern sector (Agnano zone) characterized by a shallow (400-500 m b.s.l.) still hot reservoir, heated by the upward circulation of deep no magmatic hot vapor.

In this study we present preliminary results deriving from the integration of different geophysical surveys carried out in the Agnano plain area, in the frame of the GEOGRID research project. We acquired high-resolution gravity data along two parallel profiles and we investigated the depth, shape and density contrast of the subsurface structures by the CompactDEXP (CDEXP) method, a multiscale iterative imaging technique based on the DEXP method. The resulting density models, together with DC resistivity and stratigraphic data, outlines the presence of a complex morphology of the Agnano subsoil characterized by a horst-graben structure. The importance of the structural lines identified by geophysical data, is also confirmed by the alignment of correlate outcropping thermal waters.

How to cite: Milano, M., Cavuoto, G., Corniello, A., Di Fiore, V., Fedi, M., Massarotti, N., Pelosi, N., Punzo, M., Tarallo, D., Donnarumma, G. P., and Iorio, M.: Multiscale imaging of low-enthalpy geothermal reservoir of the Phlegraean Fields caldera from gravity and resistivity data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16132, https://doi.org/10.5194/egusphere-egu23-16132, 2023.

EGU23-1225 | Posters on site | GI5.7

Experiments of arsenic (V) adsorption on birnessite: implications on arsenic cycling 

Hao Wei Huang, Huai-Jen Yang, Li-Yun Huang, and Chia-Ju Chieh

Birnessite occurs as a major manganese oxide in sediments. It is characterized by a high adsorption capacity for trace elements, including arsenic. However, the effects of birnessite on arsenic cycling were less intensively investigated than that of goethite, a commonly recognized arsenic host. Therefore, this study utilizes arsenic-bearing solutions containing 0.1–50 ppm arsenic to synthesize birnessite and uses arsenic sequential extraction procedure (SEP) analysis to quantify its arsenic co-precipitation and adsorption capacity.
    SEPs showed that adsorbed/structural arsenic ratio grew from 0:100 to 60:40, with arsenic concentration increasing from 0.1–50 ppm, implying saturation of structural arsenic. SEPs quantify the adsorbed and structural As of birnessite being 0.831 and 1.308 mg/g, respectively. However, the low arsenic concentrations of < 1% in residual solutions indicate nonattainment of the maximum adsorption capacity. Subsequent adsorption experiments using higher initial arsenic concentrations reaching 250 ppm determined the maximum arsenic adsorption capacity to be 19.81 mg/g at pH 7, comparable to the values of 15.3–22.5 mg/g at pH 6.5 (Manning et al., 2002; Singh et al., 2010) and that of 3.79–15.73 mg/g for goethite. It then appears that birnessite adsorption/desorption is more effective than precipitation/dissolution in controlling arsenic cycling. However, the consideration based on the maximum adsorption capacity might overrate the controls of adsorption/desorption relative to precipitation/dissolution because the natural water generally contains less arsenic than that used for the adsorption experiments. Therefore, we conducted adsorption experiments with low arsenic concentrations of 0.5 ppm and a solid/liquid ratio of 0.01 to 0.001. The results showed that adsorption capacity rose abruptly to 1.416 mg/g in two weeks and then slowly increased to 1.523 mg/g after three months. This feature indicated incomplete filling of the adsorption sites on the surface of birnessite at low As concentration despite its large specific surface area. Another controlling factor was the abundance of birnessite in sediments. If 10% of MnO (0.05–0.15%) in the Chianan sediments in southern Taiwan occurred as birnessite, the adsorbed arsenic was calculated to be 0.0005–0.022 mg, corresponding to < 2 % of adsorbed arsenic in 1 g sediments, based on the SEP data of Yang et al. (2016). In the extreme case that all the Mn occurred as birnessite, birnessite could account for up to 25% of the adsorbed arsenic. Apparently, birnessite is not a major contributor to surface arsenic cycling. However, this inference must be evaluated by considering the adsorption and co-precipitation data from goethite and goethite proportions in sediments.

How to cite: Huang, H. W., Yang, H.-J., Huang, L.-Y., and Chieh, C.-J.: Experiments of arsenic (V) adsorption on birnessite: implications on arsenic cycling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1225, https://doi.org/10.5194/egusphere-egu23-1225, 2023.

EGU23-4067 | Orals | GI5.7

Application of ion-exchange resin sachets and XRF-CS in heavy metal pollution sources monitoring 

Yu-Chen Jian, Ludvig Löwemark, and Alice Chien-Yi Liao

For the past decades, scientists have endeavored to develop efficient and suitable approaches to monitor heavy-metal pollution through technological development. Conventional monitoring methods for heavy metals are still complicated, relatively expensive, and time-consuming. This research aims to develop an innovative heavy-metal monitor, the novel approach of ion-exchange resin sachets combined with X-ray fluorescence core scanner (XRF-CS), to achieve an efficient way to effectively monitor vast areas for contamination. The resin sachets, which have a large capacity to quickly take up heavy metals, were deployed in the river weekly to capture heavy metals and then analyzed using the non-destructive, fast, and cost-efficient Itrax XRF core scanner. Two four-week sampling sessions, performed during the dry and wet periods, respectively, were conducted in northeastern Taiwan, where the environment was contaminated by a copper smelter and coal mine activities in the late twentieth century. The results suggest that ion-exchange resins are useful as long-term monitors of heavy metals in a low pollution-level settings (metal concentration <1 mg/L), and that XRF core scanner data truly reflect metal pollution concentrations as measured by inductively coupled plasma-optical emission spectrometry (ICP-OES). This approach allows us to pinpoint pollution sources along the studied river. Especially, Zn, Ni, Mn, Fe, Cu, Ca, and Sr could be detected near pollution sources, where cps values were 1.8 to 3430.6 times higher than in unpolluted areas. Zn shows the largest difference between polluted and non-polluted areas, with the cps values of the samples in polluted areas 3528 times higher than their non-polluted counterparts. Ni, Mn, Fe, Cu, Ca, and Sr’s cps values were 1.8, 29.2, 46.1, 2.4, 6.2, and 5.9 times higher, respectively, than the corresponding counts measured in non-polluted areas. In addition, our results demonstrate that the intensity of precipitation influences the amount of metal adsorption in the resins; resins showed less adsorption in the dry period, and cps values slightly dropped to 81 to 84 percent of the wet period. In summary, ion-exchange resins are a sensitive tool that can be applied in pollution monitoring at various pollution levels due to their high performance in adsorbing heavy metals. Consequently, ion-exchange resin sachets in combination with XRF core scanner analysis is a cost-effective way to monitor large areas of potentially polluted aquatic systems quickly.

How to cite: Jian, Y.-C., Löwemark, L., and Liao, A. C.-Y.: Application of ion-exchange resin sachets and XRF-CS in heavy metal pollution sources monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4067, https://doi.org/10.5194/egusphere-egu23-4067, 2023.

EGU23-6351 | ECS | Orals | GI5.7

Geochemical baseline values of chalcophile and siderophile elements in soils around the former mining area of Abbadia San Salvatore (Mt. Amiata, Southern Tuscany, Italy). 

Federica Meloni, Barbara Nisi, Caterina Gozzi, Jacopo Cabassi, Giordano Montegrossi, Valentina Rimondi, Daniele Rappuoli, and Orlando Vaselli

Determining the background values of chemical components in environmental matrices is a difficult task. This is particularly true in regions where the human impact due to industrial, mining, agricultural and urban activities coexists with a geological (geogenic) anomaly, which influences the concentration of certain elements in soils, waters and air. In these cases, the term geochemical baseline (GB) is preferable, since it considers the actual content of that element in the superficial environment at a given point in time, including both geogenic and anthropogenic contribution. In this study, a total of 102 top- and sub-soil (collected at 10-50 cm and 50-154 cm depth, respectively) samples and seven rocks, onto which the soils developed, were collected for the determination of GBs for selected chalcophile (As, Cu, Hg and Sb) and siderophile (Co, Cr, Ni, and V) elements in 25.6 km2 around the former mining area of Abbadia San Salvatore (Mt. Amiata, Southern Tuscany, Italy). For about one century, cinnabar (HgS) ore deposits have been exploited to produce liquid mercury from the Mt. Amiata volcanic system and its surroundings, which represents a world-class mercury district. The < 2 mm (as required by the national regulamentation) fraction of the samples was pulverized and analysed by ICP-MS (As, Hg and Sb) and ICP-AES (Co, Cr, Ni, and V) after aqua regia digestion. The compositional data analysis of multivariate compositional vectors, based on the log-ratio approach was used to assess the nature of the geochemical . According to our findings, the centred log-ratio (clr) opposed to that of raw/log transformation, enhances the spatial mapping. This also allowed to obtain better-separated variables in the robust Principal Component Analysis (rPCA). Log-ratio geographical maps evidenced that the underlying bedrock geology (parent lithologies), rather than anthropogenic causes, controls the distribution of the  great majority of the elements in the top- and sub-soils. The resulting clr-PCA approach, associated with the geological features, indicates that the geochemical pattern of Hg-As is to be related to the volcanic rocks and ore-deposits, although an anthropogenic influence due to the past mining activity in the topsoils cannot be ruled out. Sb, Co, Cr, Ni, and V distribution patterns are in most cases attributed to calcareous and clay lithologies. The anomalous content of Sb found within the volcanic rocks was likely due to the presence of previously undetected old mining dump. The two data populations (volcanic and calcareus-clay lithologis) were separated into two different databases and the outliers were removed when necessary. By processing the two datasets, the US-EPA’s ProUCL software was used for calculating the GBs for the selected suite of elements. The obtained values are paramount for establishing specific guidelines and quality standards in environmental legislation and policy-making to be applied by the Municipality of Abbadia San Salvatore

How to cite: Meloni, F., Nisi, B., Gozzi, C., Cabassi, J., Montegrossi, G., Rimondi, V., Rappuoli, D., and Vaselli, O.: Geochemical baseline values of chalcophile and siderophile elements in soils around the former mining area of Abbadia San Salvatore (Mt. Amiata, Southern Tuscany, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6351, https://doi.org/10.5194/egusphere-egu23-6351, 2023.

EGU23-7980 | ECS | Posters on site | GI5.7

A transect of mercury concentrations in fish (Black bass, Micropterus salmoides) from the Valdeazogues river, Almadén Hg mining district, South Central Spain. 

José Ignacio Barquero, Pablo Higueras, Jesus J. Hidalgo, Jose M. Esbri, Saturnino Lorenzo, and Efren Garcia-Ordiales

The Almadén district has been the World’s largest producer of mercury (Hg), for more than 2000 years. The mining activity in the district ceased some 10 years ago; however, the generalized pollution of soils and stream sediments, as well as the atmospheric emissions from these and other sources, still represent possibilities to toxify the human food chain. The Valdeazogues river crosses completely the district, with some 150 km2 extension, and including a huge mine, three mines of median importance, and up to 60 points where cinnabar (HgS) has been recognized.

Largemouth bass (Micropterus salmoides) is a carnivorous freshwater gamefish, very common along the Valdeazogues river. For years it was fished to complement the diet of the local inhabitants, although nowadays is not so common to consume it. We obtained 28 specimens, with sizes between 69 and 335 mm and weight between 11 and 552 gr, in a transect from the El Entredicho open pit to downstream the district (some 36,3 km). The specimens were analyzed using atomic absorption spectrometry with Zeeman effect.

Results show important variations throughout the transect; the largest fish in terms of weight and length had the highest Hg concentration (5246 ng/g), much higher than the fish with the lowest concentration (473.2 ng/g), which was not the specimen with the lowest size. Besides, as we go downstream the Valdeazogues River, moving away from the Entredicho Mine (considered to be the main source of contamination), Hg concentrations drops considerably until stabilizing at approximately 1200 - 1500 ng/g.

How to cite: Barquero, J. I., Higueras, P., Hidalgo, J. J., Esbri, J. M., Lorenzo, S., and Garcia-Ordiales, E.: A transect of mercury concentrations in fish (Black bass, Micropterus salmoides) from the Valdeazogues river, Almadén Hg mining district, South Central Spain., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7980, https://doi.org/10.5194/egusphere-egu23-7980, 2023.

EGU23-8217 | ECS | Orals | GI5.7

Assessing the impact of both a forest and a waste fire on the soil chemistry of two areas in Campania region 

Lucia Rita Pacifico, Annalise Guarino, Antonio Pizzolante, and Stefano Albanese

In the last decades, intentional illegal burnings increased in the numbers and became a problem of a global interest. As a consequence, human beings can be exposed to potentially toxic elements (PTEs) released during the combustion, dispersed by the wind, and accumulated in the fire’s ashes (Dimitrios, 2020).

Several studies highlighted that PTEs content in the deposited ashes can modify the chemical and the physical characteristics of the soil and, therefore, it can influence the development and growth of local microorganisms and vegetation (Raison, 1979). The geochemical characteristics of ashes depend on the nature of burned material (Dermibas et al. 2003) and on many other variables such as the intensity of combustion, the composition of the underlying soil, the bedrock type, etc.

The aim of the study was to verify at two different sites the environmental impact related with the on-set of two fire events occurred in Campania region (Southern Italy) during the 2017 summer season. One of the fires involved a forest (on the slopes of Mt. Somma-Vesuvius) and one affected a waste disposal site, known as Ilside (close to the city of Caserta). The variation occurred to concentration of PTEs in topsoil was used for the purpose.

Specifically, at both locations, 30 topsoil samples were collected before and right after the fire events. In total 60 samples were collected at the surroundings of Mt. Somma-Vesuvius slopes and 60 at the surroundings of Ilside. The post-fire samples were collected in correspondence of pre-existing sampling sites along the main wind directions recorded at the time of the fires.

To explore the potential elemental contamination occurred in soils due to the fire events, the Enrichment Factor (EFs) of a selection of PTEs was determined and mapped for individual samples. A predominant enrichment of Hg was identified for both areas.

Further, a combined application of multivariate statistics and geospatial analysis was also performed on the calculated EFs.

For the Ilside site (where special waste and e-waste were involved in burning) the association of Hg, Tl, Cu and Co was identified as the main responsible of data variability; for the Vesuvian area, the association of Hg, Cu and Cr was found to be quite strong and possibly associated with forest biomass burning.

This study highlighted how different can be the chemical evidence left by fires occurring in the environment depending on the nature of the burnt materials. At same time, result showed that even the burning of biomasses proceeding from a natural area can input in the environment PTEs which can potentially generate an increase of the pre-existing degree of environmental hazard.

References

Dermibas, A., 2003. Toxic Air Emissions from Biomass Combustion, Energy Sources, 25:5, 419-427.

Dimitrios E. A., 2020. Suburban areas in flames: Dispersion of potentially toxic elements from burned vegetation and buildings. Estimation of the associated ecological and human health risk. Environmental Research, Volume 183, ISSN 0013-9351.

Raison, R.J., 1979. Modification of the soil environment by vegetation fires, with particular reference to nitrogen transformations: a review. Plant Soil 51, 73–108.

How to cite: Pacifico, L. R., Guarino, A., Pizzolante, A., and Albanese, S.: Assessing the impact of both a forest and a waste fire on the soil chemistry of two areas in Campania region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8217, https://doi.org/10.5194/egusphere-egu23-8217, 2023.

EGU23-8374 | Orals | GI5.7

Geochemical transport through the critical zone: Statistics and reconstruction 

Karl Fabian, Clemens Reimann, and Belinda Flem


Detecting and quantifying geochemical transport through the critical zone at the continental to regional scale requires reliable  statistical procedures that can be uniquely interpreted. We present methods that provide different views on the same data sets and  formulate rules for their application and interpretation. The statistical analysis of cumulative distribution functions (CDFs) uses cumulative probability (CP) plots for spatially representative multi-element and multi-media data sets, preferably containing >1000 sites.
Mathematical models demonstrate how contamination can influence elemental CDFs of different  sample media. For example large-scale diffuse soil contamination leads to a distinctive shift of the low-concentration end of the distribution of the studied element in its top-soil CP plot, whereas high local contamination influences the high-concentration end. But also bio-geochemical processes can generate recognizable changes in elemental CDFs.
A related and partly unsolved problem is the correct interpretation of compositional data in terms of their transport through  the critical zone. 

 

How to cite: Fabian, K., Reimann, C., and Flem, B.: Geochemical transport through the critical zone: Statistics and reconstruction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8374, https://doi.org/10.5194/egusphere-egu23-8374, 2023.

In 2015, an environmental monitoring plan (http://www.campaniatrasparente.it) was launched with the aim of assessing the conditions of all environmental compartments (air, water, top and bottom soils, vegetables, biological samples) of the Campania region. A total of 5,333 topsoil samples were collected and analysed to determine the concentration of 52 chemical elements by means of Aqua Regia followed by ICP-MS. The main aim of prospecting campaign was to establish the ranges of the natural geochemical background for a few potentially toxic elements (PTEs) to be used as reference to define the degree of contamination of anthropized areas.

In the study area (about 13,600 km2) four volcanic areas are present and their pyroclastic products are spread across the regional territory due to a common (Plinian) explosive behaviour.

Due to the natural enrichment in some PTEs of soil developed on pyroclastic products, to discriminate the anthropic signals from the natural ones using geochemical data it is not a simple task when dealing with Campania soils. Therefore, as a preparatory work, to precisely identify regional areas mantled by “volcanic” soils we trained five machine learning algorithms (MLAs) to recognize when soil geochemistry is linked with the presence of volcanic products. All MLAs were implemented on centered log-ratio transformed data to reduce the closure and scaling effect commonly affecting geochemical data. In total, 1277 volcanic soils (VS) and 353 non-volcanic soils (NVS), respectively, were selected for the training phase. Data related with VS were selected based on the proximity of the samples with the volcanic centres, excluding highly anthropized areas. Data related with NVS were selected by consulting available detailed geological maps of those areas located faraway from volcanic areas where pyroclastic covers are completely absent. During the training phase, a cross-validation procedure was applied for parameters optimization. In the test phase all the MLAs showed an accuracy greater than 98% and the Random Forest algorithm proved to be the most accurate for the prediction of the remaining 3903 unlabelled soils. Therefore, a total of 1739 samples were classified as NVS and 2164 as VS. A subsequent comparison of the results with the existing distribution models of volcanic products has shown that samples classified as VS mainly fall in areas characterized by a high thickness of the pyroclastic fall deposits normally related to i) eruptions occurred in the last 10 Ky; ii) Campanian Ignimbrite eruption (ca. 39 ky BP); iii) Codola eruption (ca. 25 ky BP).

The MLAs results suggested that the most important chemical variables for the specific classification purpose were Ni, Cs, Ca, Co, Rb, Sc, Mn, U, Na. It is also evident that a first classification could be made by using few of these elements, as well. Our findings could be used as a valuable tool to better discriminate soil nature and geochemical characteristic aiming at a more effective assessment of natural background ranges for those elements sourced by both natural processes and human activities.

How to cite: Ambrosino, M., Albanese, S., Lucadamo, A., and Cicchella, D.: Combining compositional data analysis and machine learning to recognize where soil geochemistry is influenced by the presence of pyroclastic covers in Campania region (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8484, https://doi.org/10.5194/egusphere-egu23-8484, 2023.

The contamination of groundwater by geogenic sources is a major problem in many nations, especially those in the developing world. Fluoride (F) is one of the most pervasive and well-documented geogenic contaminants because of the severe health risks it poses due to its toxicity. F contamination in groundwater in India has been the subject of intense research over the past many decades. In this article, we describe the underlying geochemical process liable for F contamination as well as the factors controlling its spatiotemporal distribution in the Sedimentary Alluvial Plain (SAP) of Bankura District, West Bengal, India. To achieve the desired objective, representative groundwater samples were collected from tube wells and hand pumps at different locations of the study region during pre- and post-monsoon seasons. Collected samples were subjected to F and other hydrochemical analysis following standard test methods. Analysis shows that 37% of all groundwater samples collected during the pre-monsoon period have fluoride levels over 1.5 ppm (the limit specified by the World Health Organization, Geneva, 2004); however, the contamination level dropped to 30% during the post-monsoon period. The investigation of groundwater level changes indicates that, as water levels rise during the post-monsoon, F concentrations decrease due to the dilution effect. Piper trilinear diagram suggested Na-Ca-HCO3 type of groundwater for both seasons. According to Gibbs diagrams, rock-water interactions (mineral dissolution) are responsible for major ion chemistry in groundwater samples. Factor analysis (FA) of hydrochemical parameters revealed that the occurrence of F in groundwater was due to the weathering and dissolution of fluoride-containing minerals. X-ray diffraction (XRD) analysis of SAP sediments further confirmed the presence of fluoride-bearing minerals (muscovite and fluorite) in the subsurface lithology of the region. A substantial positive loading (> 0.75) of F with pH and bicarbonate for FA demonstrates that F is being leached from the host material by an alkaline-dominated environment. To account for the spatial variability and seasonality to the spatial change of F concentration in groundwater of the SAP, geographical information systems tools and inverse distance weighting interpolation method were used. The results revealed that significant spatiotemporal variability of F contamination was mainly influenced by the recharging rainwater and the average recharge altitude of groundwater in the area under study. The contamination level is significant in the elevated region where replenishing rainwater is more likely to come into contact with fluoride-bearing minerals when it infiltrates and percolates through the vadose zone. This phenomenon increases the F leaching through chemical weathering along groundwater flow pathways. The findings of this study can serve as a scientific foundation for the efficient management of F-contaminated groundwater in the SAP.

 

How to cite: Ghosh, A., Gogoi, N., Kartha, S. A., and Mondal, S.: Geochemical Evaluation and Spatiotemporal Distribution of Fluoride in Groundwater of the Sedimentary Alluvial Plain of Bankura District, West Bengal, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9327, https://doi.org/10.5194/egusphere-egu23-9327, 2023.

Dichlorodiphenyltrichloroethane (DDT) and its metabolites are highly toxic and pose chronic effects to the biosphere. As a natural storage pool, forests have great potential to capture them from the atmosphere and migrate them to the forest soil, which, in turn, influences the safety of the forest ecological environment. In this study, a systematical survey of DDT and its metabolites has been carried out to measure their spatial variations in Chinese forest soils. The main objectives of this study were to (1) investigate the levels, distribution and sources of DDT and its metabolites, and further estimate their mass inventories in Chinese forest soils, (2) explore the impact of soil properties on their distribution, and (III) assess the ecological and health risks of DDT and its metabolites. The research results were as follows. The average concentration of ΣDDTs reached up to 9.75 ng/g, and p,p’-DDT is the main component. Significant difference in the concentration of ΣDDTs was observed between the southeast and northwest regions (p<0.01), which may be related to multiple factors such as pesticide use, rainfall and altitude. The forest soil quality inventory is about 0.58×103 tons, which is lighter than that of domestic farmland soil. 56.1% of soil samples were less than the low value of risk assessment (ERL). The concentration of ΣDDTs in the East and middle is higher than that in the West, and the high value is mainly distributed in the coastal areas. DDTs were mainly from the input of the mixed source composed of industrial DDT and dicofol, of which at least 97% came from industrial DDT and up to 4% from dicofol. ΣDDTs was only positively correlated with precipitation and population density (p<0.05). The degradation of DDT in soil occured from primary stage to high stage. The possible degradation pathways involved in DDTs entering forest soil were preliminarily deduced. Firstly, the surrounding pollution sources volatilize DDTs from soils to the atmosphere through secondary emission. In this process, DDT was continuously transformed into DDE through photodecomposition. The atmosphere rich in DDTs were transported to the forest area and then into the forest surface soil through atmospheric dry and wet deposition. Then, DDT transported continuously accumulated and degraded in forest soil. In the alternation of anaerobic and aerobic process, the main degradation pathways are DDT→DDD→DDMU, DDT→dicofol+DBP, DDT→DDE→DDMU, DDMU→DDNU.

How to cite: Qu, C., Wang, R., and Sun, W.: The occurrence of dichlorodiphenyltrichloroethanes (DDT) and its metabolites in Chinese forest soils: Implications for sources and environmental processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13317, https://doi.org/10.5194/egusphere-egu23-13317, 2023.

EGU23-15671 | ECS | Posters virtual | GI5.7

Spatio-temporal variations of phosphorus (P) fractions in surface sediments of the southern Caspian Sea 

Pooria Ebrahimi, Mohammad Javad Nematollahi, Hassan Nasrollahzadeh Saravi, Rolf David Vogt, Fariba Vahedi, and Mahdie Baloei

Sediments act as a sink and a secondary source of contaminants, accounting for a central part of coastal and marine biogeochemical cycles. Phosphorus (P) is a macronutrient that governs primary productivity and phytoplankton growth, but excess P influx results in algae bloom and deteriorates aquatic ecosystems. This study assesses seasonal fluctuations, spatial distribution and fractions of P in the sediments of the southern Caspian Sea. In this study, at eight sampling points, composite samples of the surface (from 0 to 10 cm) seabed sediments were collected at 10 and 30 m water depths. The sampling campaigns were carried out in the four seasons and a total of 64 sediment samples were obtained. Total organic matter (TOM), total P (TP) concentration and particle size distribution were determined. Then, P was fractionated using a four-step sequential procedure to quantify the loosely bound P (LP), the reductant soluble P (FeP), the metallic oxide-bound P (AlP) and the calcium carbonate (CaCO3) bound P (CaP). The inorganic P (IP) pool refers to the sum of LP, FeP, AlP and CaP, while the organic P (OP) was calculated by subtracting IP from TP.

The results show that seasonal fluctuations of mean TP were statistically insignificant (p-value > 0.05). Still, the highest levels were recorded in autumn (1555 mg kg-1), followed by winter (1405 mg kg-1), spring (1378 mg kg-1) and summer (1130 mg kg-1). These minor temporal variations in P levels are associated with the seasonal differences in the amount of runoff and the intensity of rivers discharging into the Caspian Sea, and thereby their sediment load and the physicochemical characteristics. The large riverine influx resulted in TP contamination hotspots in the river deltas of Anzali wetland, Babolrood and Sefidrud (northern Iran), where high loadings of suspended particles are discharged into the sea. The spatial TP distribution is thus site-specific and uneven. The main P fraction was CaP, reflecting the phosphate (PO43-) strong affinity for, and association with, calcium-bearing minerals. Only a minor fraction of P was determined as LP. The fraction of the mud-size particles was the main explanatory factor for the spatial distribution of overall low levels of non-residual (or bioavailable) P forms (i.e., LP, FeP and AlP) during spring and summer, while the sand fraction had the greatest explanatory value for the distribution of residual (non-bioavailable) P form (CaP) during autumn and winter. This study demonstrates that P bioavailability in sediments is mostly controlled by the physicochemical characteristics of the sediment material, which again is steered by seawater chemistry. A low content of bioavailable P fractions could therefore be related to the relatively low content of fine-grained (i.e. below 63 µm) particles in sediments of the southern Caspian Sea.

How to cite: Ebrahimi, P., Nematollahi, M. J., Nasrollahzadeh Saravi, H., Vogt, R. D., Vahedi, F., and Baloei, M.: Spatio-temporal variations of phosphorus (P) fractions in surface sediments of the southern Caspian Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15671, https://doi.org/10.5194/egusphere-egu23-15671, 2023.

This study reports on the unique results of the recently concluded Sediment-quality Information, Monitoring and Assessment System to Support Transnational Cooperation for Joint Danube Basin Water Management (SIMONA) project, the largest of its kind in Europe, which was carried out in 2018-2022 as a project of the EU DTP aiming at delivering a ready-to-deploy sediment-quality monitoring system for the effective and comparable measurements and assessment of sediment quality in surface waters in the Danube River Basin in accordance with the EU Water Framework Directive (WFD). The project has developed, tested, demonstrated an innovative environmental geochemical monitoring platform of fluvial (suspended, river bottom and floodplain) sediments using state-of-the-art automated and passive sampling technology for the contamination risk assessment according to the EU WFD in the Danube Basin. Time series analysis and signal processing of one year multi-variate and multi-matrice monitoring data could be used to identify the geochemical background, temporal trends, periodicities and contamination events in the studied EU-defined Hazardous Substances. Since the applied technology, methods and data interpretation is fully consistent with EU legislation risk assessment, results may provide a ‘best solution’ for the spatial and temporal discrimination of contamination. Results of biological contamination assessment of sediments using microbial tests are also presented.

Keywords: data analysis, geochemistry, mobility, speciation, enrichment, time series analysis

How to cite: Kovács, Z., Jordán, G., Szabó, P., and Bálint, M. and the SIMONA Project Team: Development, data modelling of environmental geochemical monitoring of fluvial (suspended, river bottom, floodplain) sediments using unique automated and passive sampling for the contamination risk assessment according to the EU WFD in the Danube Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15997, https://doi.org/10.5194/egusphere-egu23-15997, 2023.

EGU23-16075 | ECS | Orals | GI5.7

Assessing the soil baseline values of a geologically complex territory: the case study of Basilicata region. 

Annalise Guarino, Lucia Rita Pacifico, Antonio Iannone, Andrea Gramazio, and Stefano Albanese

The middle and lower reaches of the Basento river and the whole basin of the Cavone river, in Basilicata region (Italy), underwent to a geochemical prospecting involving soil and stream sediments. Specifically, 190 topsoils were collected within a depth range between 10-15 cm from the ground level and 10 bottom soils were sampled within the depth range between 80-100 cm. 

Samples were analysed at the Life Analytics laboratory (Battipaglia, Italy), by ICP-MS following an aqua regia digestion, to determine the concentrations of 16 potentially toxic inorganic substances (As, Be, Cd, Co, Cr, CrIV, Cu, Hg, Ni, Pb, Sb, Se, Tl, V, Zn, SO4).  

The purpose of the study has been the definition of the upper background limits (UBLs) for the investigation area. An exploratory data analysis (EDA) was conducted on the dataset to outline the main data structural characteristics. Due to the huge number of samples below detection limits (BDL) for Cd, CrIV, Hg, Se, Tl, only As, Be, Co, Cr, Ni, Pb, Cu, V, Zn and SO4 were considered for the UBLs definition. 

The estimate of the above-mentioned values has been conducted following a series of rigorous statistical tests in line with the "Guidelines for the determination of background values for soils and groundwater" released by the Italian National System for Environmental Protection (SNPA).  

In detail, after imputing the few BDL values found in the selected variables by means of K-nearest neighbors (k-NN) algorithm, topsoil and bottom soils data were considered as a whole. Indeed, the dataset was subdivided into 7 subsets according the geopedological units identified based on the local pedological and geological features. 

The BoxCox algorithm was applied to the single subsets to normalize data distribution before any statistical treatment. Outliers were identified by mean of the Dixon’s or Rosner’s Outlier tests depending on the sample size, the observation of boxplots and Q-Q plots and the spatial location of some samples considered as hotspots.  

For each variable and for each subset, two statical indices (i.e.:  95th upper tolerance limit with 95% coverage (95UTL95) and the 95th upper prediction limit (UPL95)) were calculated. The more conservative among them was chosen as representative for the UBLs.

Results showed that the UBLs found are much lower than the guideline values set by the Italian Environmental Law (Legislative Decree 152/2006). Our findings emphasized how the use of guideline values established at a national level is often inadequate to administrate a geologically and pedologically complex territory such as Italy, favoring the chance of running into a wrong identification of local environmental hazards.  

How to cite: Guarino, A., Pacifico, L. R., Iannone, A., Gramazio, A., and Albanese, S.: Assessing the soil baseline values of a geologically complex territory: the case study of Basilicata region., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16075, https://doi.org/10.5194/egusphere-egu23-16075, 2023.

EGU23-16151 | Posters on site | GI5.7

Potentially toxic elements (PTEs) in the soils of a densely populated active volcanic area: the Campi Flegrei case study in Italy. 

Stefano Albanese, Pooria Ebrahimi, Antonio Aruta, Domenico Cicchella, Fabio Matano, Benedetto De Vivo, and Annamaria Lima

The line of research on potentially toxic elements (PTEs) is of growing interest to the scientific community for protecting society against adverse health issues. The Campi Flegrei caldera in southern Italy is an active volcanic area where above two million people live, making it an ideal study area for investigating PTEs of natural and anthropogenic origin through the latest advances in geochemical data analysis. Therefore, a total of 394 topsoil samples (0 to 15 cm) were collected for determining the “pseudo-total” concentrations of elements in the <2 mm fraction using a combination of inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS), following aqua regia digestion.

The median values show that concentrations of Zn, Cu, Pb, V and As are greater (>10 mg/kg) than Cr, Co, Ni, Tl, Sb, Se, Cd and Hg. The geochemical maps generated by the Empirical Bayesian Kriging interpolation technique indicate that the higher concentrations of Pb, Zn, Cd, Cr, Hg, Ni and Sb are related to the greater population density (>6500 persons per Km2) in the urban area, but the elevated levels of As, Tl, Co, Cu, Se and V are observed in the other parts. In the context of compositional data analysis, the correlation diagram and robust principal component analysis detected: (1) the Pb–Zn–Hg–Cd–Sb–Cr–Ni association that likely shows anthropogenic activities such as heavy traffic load and fossil fuel combustion in the urban area; (2) the Al–Fe–Mn–Ti–Tl–V–Co–As–U–Th association that mostly represents the contribution of pyroclastic deposits; and (3) the Na–K–B association that probably reveals the weathering degree.

To choose the PTEs with potential health risks for the local inhabitants, the PTE quantities in soil are compared with the corresponding contamination thresholds established by the Italian legislation for residential land use. The Tl, Pb and Zn contents exceed the threshold in more than 15% of the collected samples, but Tl which derives from a natural source (e.g., leucite) is culled before evaluation. Then, children (0-6 years old) are considered for health risk assessment because: (1) Pb has significant adverse health effects in children; and (2) the more frequent hand-to-mouth behavior in children under 6 years old is linked to the higher chance of exposure. The probabilistic health risk modeling for the children <6 years old highlights negligible (hazard quotient below 1) Pb and Zn non-carcinogenic risk and unexpected (cancer risk ≤1E-06) Pb carcinogenic risk for exposure through soil ingestion. However, for the inhalation pathway, the children aged <1 year old have the highest chance (90%) of acceptable (i.e. from 1E-6 to 1E-4) Pb carcinogenic health risk. This should not be overlooked because Naples is under high environmental pressure and previous studies reported increased Pb and Zn quantities in soil between 1974 and 1999. Overall, the results of geostatistical interpolation, compositional data analysis and probabilistic health risk modeling potentially uncover the link between soil geochemistry and human health in densely populated active volcanic areas.

How to cite: Albanese, S., Ebrahimi, P., Aruta, A., Cicchella, D., Matano, F., De Vivo, B., and Lima, A.: Potentially toxic elements (PTEs) in the soils of a densely populated active volcanic area: the Campi Flegrei case study in Italy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16151, https://doi.org/10.5194/egusphere-egu23-16151, 2023.

EGU23-16341 | ECS | Orals | GI5.7

87Sr/86Sr as an efficient tool to investigate environmental processes in winemaking: a Campania (Italy) case study. 

Piergiorgio Tranfa, Mariano Mercurio, Massimo D'Antonio, Valeria Di Renzo, Carmine Guarino, Rosaria Sciarrillo, Daniela Zuzolo, Francesco Izzo, Alessio Langella, and Piergiulio Cappelletti

In the last few years Sr isotope geochemistry has contributed substantially to environmental and food traceability research. This is achievable because soils, plants and waters all have a peculiar Sr isotopic signature (87Sr/86Sr) inherited from the local geological substratum and affected by geological processes as well as the age and initial rubidium concentration of the rocks. Strontium ions released from the bedrock by weathering processes deriving by the interaction of circulating fluids with rocks, enter the environment and accumulates in water and soils. This reservoir of bioavailable Sr may represent a reliable tracer useful to determine the geographical origin of wines as it is known that strontium is taken first by plant roots, then by grapes, and lastly by wine, with no isotope fractionation when compared to the original 87Sr/86Sr ratio in the soil and rocks. As a result, the study of the Sr isotope ratio in the final product (wine) links directly to its geological origin thus representing a specific geofingerprint for any selected wine. Based on these premises this work aims at confirming the strong link between the product (wine) and its territory, with the final purpose to make it recognizable and distinguishable from similar products and protecting it from possible fraud and adulteration. In this work the 87Sr/86Sr systematics has been used to analyze a total of 39 samples (37 soil samples and 2 wine samples) from Campania (Italy). For a better understanding, both total Sr fraction and bioavailable Sr fraction were analyzed in soil samples (rhizospheric soils, bulk soils and samples collected from different horizons) in order to better investigate the environmental processes involved during the wine production cycle.

How to cite: Tranfa, P., Mercurio, M., D'Antonio, M., Di Renzo, V., Guarino, C., Sciarrillo, R., Zuzolo, D., Izzo, F., Langella, A., and Cappelletti, P.: 87Sr/86Sr as an efficient tool to investigate environmental processes in winemaking: a Campania (Italy) case study., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16341, https://doi.org/10.5194/egusphere-egu23-16341, 2023.

EGU23-1093 | Orals | BG2.1

Lithium isotopes potential in (paleo)ecology 

Fanny Thibon, Jean Goedert, Nicolas Séon, Lucas Weppe, Jeremy E. Martin, Romain Amiot, Sylvain Adnet, Olivier Lambert, Paco Bustamante, Philippe Telouk, Christophe Lécuyer, and Nathalie Vigier

Life evolution has been shaped by marine and continental environmental dichotomy. Particularly, the ecological history of vertebrates is divided into several aquatic and terrestrial phases. Even today, some species spend time in both marine and continental environments during their lifetime. Nevertheless, the timing and location of past ecological transitions, as well as the monitoring of current migration, are still challenging to trace.

To reconstruct the aquatic environments of vertebrates (i.e. seawater vs freshwater), stable (δ13C, δ18O, δ34S) and radiogenic (87Sr/86Sr) isotope systems applied to mineralized tissues have been commonly used in the past decades1–6. Nevertheless, these methods hold some limitations as they cannot be applied universally.

Here, we measured the lithium stable isotope composition of mineralized tissues (δ7Li) from extant vertebrates living in various aquatic environments (seawater, freshwater/terrestrial, and "transitional environments”). We highlight the potential of δ7Li to decipher vertebrates that live in these different environments, in contrast to δ34S and δ18O that cannot distinguish – in some cases – species living in intermediate waters from those living in seawater. Furthermore, we measured the δ7Li values of fossil apatites from extinct vertebrates and obtained values that fall within the range of aquatic environment of their extant relatives7. This new proxy may therefore profit studies in ecology, archaeology and palaeontology.

 

1 M. T. Clementz, A. Goswami, P. D. Gingerich and P. L. Koch, Journal of Vertebrate Paleontology, 2006, 26, 355–370.

2  J. Fischer, S. Voigt, M. Franz, J. W. Schneider, M. M. Joachimski, M. Tichomirowa, J. Götze and H. Furrer, Palaeogeography, Palaeoclimatology, Palaeoecology, 2012, 353–355, 60–72.

3 J. Goedert, C. Lécuyer, R. Amiot, F. Arnaud-Godet, X. Wang, L. Cui, G. Cuny, G. Douay, F. Fourel, G. Panczer, L. Simon, J.-S. Steyer and M. Zhu, Nature, 2018, 558, 68–72.

4 J. Goedert, R. Amiot, D. Berthet, F. Fourel, L. Simon and C. Lécuyer, Sci Nat, 2020, 107, 10.

5 L. Kocsis, A. Ősi, T. Vennemann, C. N. Trueman and M. R. Palmer, Palaeogeography, Palaeoclimatology, Palaeoecology, 2009, 280, 532–542.

6 B. Schmitz, S. L. Ingram, D. T. Dockery and G. Åberg, Chemical Geology, 1997, 140, 275–287.

7 F. Thibon, J. Goedert, N. Séon, L. Weppe, J. E. Martin, R. Amiot, S. Adnet, O. Lambert, P. Bustamante, C. Lécuyer and N. Vigier, Earth and Planetary Science Letters, 2022, 599, 117840.

How to cite: Thibon, F., Goedert, J., Séon, N., Weppe, L., Martin, J. E., Amiot, R., Adnet, S., Lambert, O., Bustamante, P., Telouk, P., Lécuyer, C., and Vigier, N.: Lithium isotopes potential in (paleo)ecology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1093, https://doi.org/10.5194/egusphere-egu23-1093, 2023.

EGU23-2055 | Posters on site | BG2.1

Silver stable isotopic ratios determined in contaminated soils 

Ales Vaněk, Maria Vaňková, Martin Mihaljevič, and Vojtěch Ettler

Silver isotopic fractionation(s) during metallurgical processes (or other high-T processes) and its fate in mining- and smelter-affected environments, Ag-contaminated soils/sediments remain entirely unknown. Regarding the Ag-ore processing (roasting/smelting technologies), it can be assumed that, similarly to other isotopic systems (e.g., Tl and Cu), the isotopically lighter Ag (enriched in 107Ag) enters the smelter emissions (fly ash), and isotopically heavier Ag (enriched in 109Ag) remains in the residual metal phase. Our preliminary data from the Ag-contaminated soils around a former primary Ag-smelter at Příbram (Czech Rep.) indicate an apparent variability of ε109Ag within soil profiles. The identified ε109Ag values presented for the forest soil profile (Fig. 1) recorded ~0 in the organic horizon (O), ~0-+1 in the organo-mineral horizons (A1 and A2), and up to +7 in the mineral horizon (B). This finding suggests both the isotopically-lighter Ag fraction present in the topsoil (Fig. 1), as well as enhanced 107Ag release during high-T smelting operations, i.e., relative to geogenic Ag (local ore). However, the question that clearly remains to date is to which degree the alteration/chemical processes in soil could have produced the Ag isotopic fractionation and which type of mechanisms (e.g. Ag(I)→Ag0) could represent the key geochemical controls.

Fig. 1 An example of vertical evolution of Ag isotopic signatures (ε109Ag, relative to the NIST SRM 978a Ag standard) and Ag concentrations in a forest soil profile, ~1 km away from a former primary Ag-smelter (Příbram, Czech Rep.). The Ag isotopic data are assigned an estimated error of ±0.7 ε109Ag (2sigma), which is based on our long-term reproducibility of multiple separate analyses (n = 6) of NIST SRM 2782 (Industrial Sludge) (Vaněk et al., unpublished data).

How to cite: Vaněk, A., Vaňková, M., Mihaljevič, M., and Ettler, V.: Silver stable isotopic ratios determined in contaminated soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2055, https://doi.org/10.5194/egusphere-egu23-2055, 2023.

EGU23-4677 | ECS | Orals | BG2.1

Equilibrium and kinetic controls contribute to nitrogen and oxygen isotope effects during anammox in a wastewater treatment system 

Paul Magyar, Damian Hausherr, Robert Niederdorfer, Kun Huang, Joachim Mohn, Helmut Bürgmann, Adriano Joss, and Moritz Lehmann

Anammox plays a pivotal role in both natural and engineered systems as a process that simultaneously converts fixed nitrogen to N2 and regenerates NO3. In aquatic and terrestrial ecosystems, isotopic measurements, especially of the NO3pool, provide an essential constraint on the processes that regulate the supply and elimination of fixed nitrogen, but the isotope effects of anammox remain poorly constrained.

We present measurements of the δ15N and δ18O of NO3, NO2, and NH4+ as processed by anammox in a mixed microbial community enriched for N removal from wastewater. We find that oxygen isotope effects expressed in NO2include a substantial contribution from equilibration reactions with water superimposed on kinetic isotope effects. Equilibrium between water and NO2during processing by anammoxis greatly accelerated above rates observed under abiotic conditions even during growth phases when NO2 is rapidly being consumed. In turn, δ18O of NO3 nearly completely reflects the incorporation of O atoms derived from water with little additional isotopic fractionation. The δ15N values of NO3 and NO2 also show evidence for an equilibrium isotope exchange reaction between these molecules, which raises the possibility that nitrite oxidation is partially reversible, while introducing a high degree of variability into the δ15N of NO3 generated by anammox. Finally, variation observed in the δ15N of NH4+ consumed by anammox can be connected to physiological limitations within the anammox cell.

Despite this complexity, we were able to use NO2 and NO3isotope measurements to diagnose changes in the activity of anammox and related processes within the wastewater treatment system during a low-temperature perturbation experiment. These results provide new constraints for interpreting the variability in δ15N and δ18O of NO3in natural systems, with implications for estimating relative rates of fixed N turnover processes.

How to cite: Magyar, P., Hausherr, D., Niederdorfer, R., Huang, K., Mohn, J., Bürgmann, H., Joss, A., and Lehmann, M.: Equilibrium and kinetic controls contribute to nitrogen and oxygen isotope effects during anammox in a wastewater treatment system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4677, https://doi.org/10.5194/egusphere-egu23-4677, 2023.

EGU23-5210 | ECS | Posters on site | BG2.1

Fractionation of nitrogen and oxygen isotopic composition in N2O produced by bacterial denitrification 

Noémy Chénier, Paul M. Magyar, Lukas Emmenegger, Moritz F. Lehmann, and Joachim Mohn

The isotopic composition of nitrous oxide (N2O) reveals valuable information on the biological production sources that contribute to N2O accumulation in the atmosphere, i.e. denitrification, nitrifier-denitrification and nitrification1. Isotopic fingerprints for each of these microbial pathways have been identified in past work, however, overlapping signatures of co-occurring N2O production processes2, and limitations in the robustness of associated fractionation factors under varying growth/environmental conditions3 still pose significant challenges.

We will present data from the initial phase of our project, where we study N2O production and associated N and O isotopic fractionation by the denitrifier Pseudomonas aureofaciens, grown in the laboratory under different growth conditions and thus different reaction kinetics. N2O production was quantified on-line by Fourier-Transformation IR-spectroscopy (FTIR), and the isotopic composition of produced N2O was determined by quantum cascade-laser-absorption spectroscopy (QCLAS). The combination of N2O production and isotope data (continuously measured) allowed us to elucidate changes in N and O isotope fractionation in response to changing reaction kinetics.

In a later phase of the project, we will expand our isotope-analytical capability by including also the doubly-substituted molecules of N2O, 15N15N16O (556), 14N15N18O (458) and 15N14N18O (548). More specifically, we will interrogate the symmetry of N – N bond formation, verify combinatorial effects during N2O production, and we will test whether Δ556, Δ458, and Δ548 (and the preference for 15N substitution in the central/terminal N-position) can be applied as proxies for reaction kinetics4, 5.  

1 Yu, L., Harris, E., Lewicka Szczebak, D., Barthel, M., Blomberg, M.R., Harris, S.J., Johnson, M.S., Lehmann, M.F., Liisberg, J., Müller, C. and Ostrom, N.E., 2020. What can we learn from N2O isotope data?–Analytics, processes and modelling. Rapid Communications in Mass Spectrometry, 34(20), p.e8858.

2 Kantnerová, K., Tuzson, B., Emmenegger, L., Bernasconi, S.M. and Mohn, J., 2019. Quantifying isotopic signatures of N2O using quantum cascade laser absorption spectroscopy. Chimia, 73(4), pp.232-232.

3 Haslun, J.A., Ostrom, N.E., Hegg, E.L. and Ostrom, P.H., 2018. Estimation of isotope variation of N2O during denitrification by Pseudomonas aureofaciens and Pseudomonas chlororaphis: implications for N2O source apportionment. Biogeosciences, 15(12), pp.3873-3882.

4 Yeung, L.Y., 2016. Combinatorial effects on clumped isotopes and their significance in biogeochemistry. Geochimica et Cosmochimica Acta, 172, pp.22-38.

5 Kantnerová, K., Hattori, S., Toyoda, S., Yoshida, N., Emmenegger, L., Bernasconi, S.M. and Mohn, J., 2022. Clumped isotope signatures of nitrous oxide formed by bacterial denitrification. Geochimica et Cosmochimica Acta, 328, pp.120-129.

How to cite: Chénier, N., Magyar, P. M., Emmenegger, L., Lehmann, M. F., and Mohn, J.: Fractionation of nitrogen and oxygen isotopic composition in N2O produced by bacterial denitrification, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5210, https://doi.org/10.5194/egusphere-egu23-5210, 2023.

EGU23-6603 | ECS | Orals | BG2.1

Uniquely low stable iron isotopic signatures in deep marine sediments caused by Rayleigh distillation 

Male Köster, Michael Staubwasser, Anette Meixner, Simone A. Kasemann, Hayley R. Manners, Yuki Morono, Fumio Inagaki, Verena B. Heuer, Sabine Kasten, and Susann Henkel

Microbially mediated iron (Fe) reduction is suggested to be one of the earliest metabolic pathways on Earth and Fe(III)-reducing microorganisms might be key inhabitants of the deep and hot biosphere [1, 2]. Since microbial Fe cycling is typically accompanied by Fe isotope fractionation, stable Fe isotopes (δ56Fe) are used as tracer for microbial processes in modern and ancient marine sediments [3, 4]. Here we present Fe isotope data for dissolved and sequentially extracted sedimentary Fe pools from subseafloor sediments that were recovered during International Ocean Discovery Program Expedition 370 from a 1,180 m deep hole drilled in the Nankai Trough off Japan where temperatures of up to 120°C are reached at the sediment-basement interface. The expedition aimed at exploring the temperature limit of microbial life and identifying geochemical and microbial signatures that differentiate the biotic and abiotic realms [5, 6]. Dissolved Fe (Fe(II)aq) is isotopically light throughout the ferruginous sediment interval but some samples have exceptionally light δ56Fe values. Such light δ56Fe values have never been reported in natural marine environments and cannot be solely attributed to microbially mediated Fe(III) reduction. We show that the light δ56Fe values are best explained by a Rayleigh distillation model where Fe(II)aq is continuously removed from the pore water by diffusion and adsorption onto Fe (oxyhydr)oxide surfaces. While the microbially mediated Fe(II)aq release has ceased due to an increase in temperature beyond the threshold of mesophilic microorganisms, the abiotic diffusional and adsorptive Fe(II)aq removal continued, leading to uniquely light δ56Fe values. These findings have important implications for the interpretation of Fe isotope records especially in deep subseafloor sediments.

 

References:

[1] Vargas, M. et al., 1998. Nature 395: 65-67.

[2] Kashefi, K. and Lovley, D.R., 2003. Science 301: 934-934.

[3] Beard, B.L. et al., 1999. Science 285: 1889-1892.

[4] Anbar, A.D. and Rouxel, O., 2007. Annu. Rev. Earth Planet. Sci. 35: 717-746.

[5] Heuer, V.B. et al., 2017. In Proc. IODP Volume 370.

[6] Heuer, V.B. et al., 2020. Science 370: 1230-1234.

How to cite: Köster, M., Staubwasser, M., Meixner, A., Kasemann, S. A., Manners, H. R., Morono, Y., Inagaki, F., Heuer, V. B., Kasten, S., and Henkel, S.: Uniquely low stable iron isotopic signatures in deep marine sediments caused by Rayleigh distillation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6603, https://doi.org/10.5194/egusphere-egu23-6603, 2023.

EGU23-7883 | ECS | Posters on site | BG2.1

Effects of different slurry application techniques on Nitrogen Use Efficiency (NUE) in an extensive grassland 

Sebastian Floßmann, Kaiyu Lei, Sigrid van Grinsven, Jörg Völkel, Ingrid Kögel-Knabner, and Michael Dannenmann

Optimized slurry management targeted to increase nitrogen use efficiency (NUE) can be fundamental for limiting fertilizer N losses from agricultural grasslands causing eutrophication of ground- and surface water as well as air pollution. However, a holistic assessment of both agronomic and environmental impacts including key soil functions is still missing. This study aims to provide such information by assessing the impacts of traditional vs. modern slurry application techniques on NUE, hydrological and gaseous N losses, productivity and fodder quality, soil organic nitrogen formation and total N balances.  In a plot-scale grassland experiment 15N enriched slurry was applied after the first cut in early summer. The application treatments included: (1) traditional slurry broadcast spreading under dry weather; (2) application like (1) followed by a heavy rainfall event to increase slurry infiltration into soil; (3) broadcast spreading of slurry diluted with water; (4) injection of slurry into soil via shallow slits; and (5) injection of slurry into soil via deep slits. Variant (4) and (5) represent modern trailing shoe injections requiring extensive machinery. Fates of fertilizer N such as plant uptake, immobilization in soil and microbial biomass as well as NO3 leaching were investigated by 15N tracing approaches in order to create full N balances. For this, biomass harvest and soil sampling were conducted after a growth period of 2 months. Here, we will present first results of our work that are expected to provide highly relevant decision support for grassland management. 

How to cite: Floßmann, S., Lei, K., van Grinsven, S., Völkel, J., Kögel-Knabner, I., and Dannenmann, M.: Effects of different slurry application techniques on Nitrogen Use Efficiency (NUE) in an extensive grassland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7883, https://doi.org/10.5194/egusphere-egu23-7883, 2023.

EGU23-8103 | ECS | Orals | BG2.1

Lysimeter-based full N balance as a tool to test field N2 flux measurements 

Irina Yankelzon, Lexie Schilling, Nicole Wrage-Moennig, Arne Tenspolde, Ulrike Ostler, Klaus Butterbach-Bahl, Lorenz Hartl, Rainer Gasche, Amanada Matson, Reinhard Well, Clemens Scheer, and Michael Dannenmann

Measuring soil dinitrogen (N2) emissions is notoriously challenging under field conditions. Hence, N2 emissions represent a significant uncertainty in the nitrogen mass balance of terrestrial ecosystems. The 15N gas flux (15NGF) method is the only method currently available for directly quantifying N2 emissions in situ. However, this method has rarely undergone independent validation under field conditions. In this study, our objectives were to: (1) Quantify N2 emissions and their role in the fertilizer N mass balance of a wheat rotation using the 15NGF method (2) Verify the obtained quantities of N2 emissions using a mass balance approach and (3) Verify the temporal N2 emission dynamics at the soil-atmosphere interface using vertical soil profiles of 15N2 enrichment.

To achieve these objectives, we grew winter wheat in lysimeters and applied 15N enriched mineral fertilizers via fertigation in three doses (sum 170 kg N ha-1). We then analyzed gaseous (NH3, N2O, N2) and hydrological N losses, as well as fertilizer N fates in plant and soil, and 15N2 enrichment in soil air.

Our results showed that N2 emissions directly measured using the 15NGF method amounted to 30 ± 4 kg N ha-1, which was equivalent to 18 ± 3 % of the applied fertilizer N. These measurements agreed with unrecovered fertilizer N obtained from the 15N fertilizer mass balance, although the latter had large inherent uncertainty (21 ± 21 kg N ha-1). N2O emissions, however, were negligible (0.14 ± 0.02 kg N ha-1). The temporal variability of measured N2 emissions after fertilizer additions was generally well explained by 15N2 enrichment in soil gas.

Overall, we provide independent validation of the 15NGF method in measuring N2 emissions in the field and highlight the significant role of these emissions in the nitrogen balance of crop systems. Our data also suggest that soil gas measurements in combination with diffusion modeling could serve as an alternative method for quantifying N2 emissions. These results should encourage a wider application of the 15NGF method in order to improve our understanding of N2 emissions and reduce the current uncertainties in estimates of these emissions.

How to cite: Yankelzon, I., Schilling, L., Wrage-Moennig, N., Tenspolde, A., Ostler, U., Butterbach-Bahl, K., Hartl, L., Gasche, R., Matson, A., Well, R., Scheer, C., and Dannenmann, M.: Lysimeter-based full N balance as a tool to test field N2 flux measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8103, https://doi.org/10.5194/egusphere-egu23-8103, 2023.

Identifying and quantifying sources and cycling of nitrogen is important for understanding not only aquatic ecosystems but also planning water resource management, mitigating urban and agricultural pollution, and optimizing government policy. Stable isotopes of dissolved nitrate and nitrite (δ15N, δ18O and δ17O) have been useful in distinguishing between the diverse nitrogen sources and sinks and help understand large scale global ocean processes as well as revealing major changes in agricultural land use and urbanization. 

Despite the strength of dissolved nitrate and nitrite stable isotope analysis, the strong barrier for uptake using the favored contemporary methods (bacterial denitrifier and Cd-azide reaction) due to the laborious multi-step methods, maintenance of anerobic bacterial cultures and use of highly toxic chemicals has limited the analysis to highly specialized laboratories. We evaluate the performance of the Elementar EnvirovisION using the new Titanium (III) reduction method (Altabet et al., 2019) for one step conversion of nitrate into N2O for IRMS analysis.   

The EnvirovisION has been developed for high performance analysis of CO2, N2O and CH4 and dissolved nitrate. The system has the capacity to be rapidly customized for specific needs with options for dual GC columns supporting the Weigand ‘heart-cut’ N2O method (Weigand et al., 2016) and sequential N2 and N2O analysis from a single atmospheric sample. 

How to cite: Barker, S., Preece, C., Berstan, R., and Seed, M.: Analysis of dissolved nitrate stable isotopes using the one-step Ti (III) reduction method and Elementar EnvirovisION System  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8338, https://doi.org/10.5194/egusphere-egu23-8338, 2023.

EGU23-9366 | Posters on site | BG2.1

Temporal and spatial variations in the isotope hydrobiogeochemistry (H, C, O, S, Ra) of a managed river draining a lowland towards the Baltic Sea 

Michael E. Böttcher, Cátia M. Ehlert von Ahn, Christoph Malik, Julia Westphal, Benjamin Rach, Carla Nantke, Anna-Kathrina Jenner, Rhodelyn Saban, Vera Winde, and Iris Schmiedinger

The flow path of a river draining a lowland in the southern Baltic Sea, the Warnow River, was investigated to evaluate its freshwater composition as a source of dissolved substances to regional coastal waters. A spatial study was carried out once to follow the variations from the source to the estuary. A temporal study in the composition as a function of the season, during 6 years (2017-2022), was carried out at a site just before the river reaches the estuary. Surface water was sampled to analyze major and tracer elements, stable (H, C, O, S), and unstable (Ra) isotopes. The results show that the composition of the Warnow River along the flow path is controlled by a complex interplay between in-situ processes, exchange with the atmosphere, diffuse groundwater, and surface water inlets. On a temporal scale, pH, nutrient, and redox sensitive trace element concentrations are strongly impacted by pelagic primary production in spring. During summer and autumn, influences occurred by benthic microbial activity, associated diffusive release from soils/sediments, and surface water inlets. Throughout the investigation period, the Warnow River was a source of isotopically light CO2 to the atmosphere and DIC to the estuarine waters. The delivered DIC concentrations seem to vary with the season due to changes in biological pelagic and benthic activity. DOC was derived from a mixture of C3 organic sources and fertilizers. From concentration-discharge relationships, examples of dilution, mobilization, and chemostasis trends were found. Discharge-controlled seasonal trends are superimposed by system-internal processes and the hydrological consequences of river and drainage management. Our analysis thus provides new insights into the controls on the variations of water and solutes in a managed river at the land-sea interface as part of the regional hydrological cycle of a lowland catchment coastal water system.

 

The study was supported by the DFG research training group BALTIC TRANSCOAST, DAAD ,  and the BMBF project CARBOSTORE/COOLSTYLE

How to cite: Böttcher, M. E., Ehlert von Ahn, C. M., Malik, C., Westphal, J., Rach, B., Nantke, C., Jenner, A.-K., Saban, R., Winde, V., and Schmiedinger, I.: Temporal and spatial variations in the isotope hydrobiogeochemistry (H, C, O, S, Ra) of a managed river draining a lowland towards the Baltic Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9366, https://doi.org/10.5194/egusphere-egu23-9366, 2023.

EGU23-10139 | ECS | Posters on site | BG2.1 | Highlight

The influence of high evaporative conditions on peat-forming mosses in the Antarctic Peninsula 

Danielle Jones, Dulcinea Groff, and David Beilman

Low-elevation coastal ecosystems of the northern Antarctic Peninsula are responding to rapid climate change by expansion of ice-free areas and increased vegetation cover. The record-setting air temperatures during the austral summer of 2020 provided an opportunity to evaluate the sensitivity of peat-forming and carbon accumulating mosses to conditions with high evaporative demand, a departure from the typical wet, cold, and windy conditions of the northern Antarctic Peninsula. Mosses are sensitive to environmental change and have been used as archives of paleoclimate information where few terrestrial records exist. However, it is still unclear how much of an influence increased evaporative demand, source water variation, or microclimate can have on moss leaf cellulose. We collected environmental waters and moss surface samples to explore the influence of microclimate, persistent snowmelt, and evaporation on moss tissue waters and cellulose for two moss species, Chorisodontium aciphyllum and Polytrichum strictum. Using the δ18O isotope values of moss tissue waters and leaf alpha-cellulose from surface samples, we compared the enrichment found in mosses to the enrichment in local water sources.  

δ2H and δ18O isotopes of moss tissue waters ranged from -87 to -23 and -10.6 to 0.6, respectively, indicating significant enrichment relative to our environmental water samples (δ2H values of -98.3 to -48.7 and δ18O values of -12.1 to -5.21) and long-term summer precipitation (February, δ2H values of -66.9 ± 15.9‰ and δ18O values of -8.11 ± 2.20‰, Vernadsky Station). Negative correlations between δ18O of moss water and the daily average and maximum relative humidity (on the day of collection) (r = -0.44; p < 0.001 and r = -0.62; p < 0.001, respectively) suggest that conditions resulting in high evaporative demand may have a dominant effect and imprint on the δ18O of moss cellulose. We found no relationship between δ13C values of alpha-cellulose, which reflect changes in CO2 diffusivity with moisture conditions, and microclimate variables or average temperature and relative humidity on the day of sample collection. This is possibly the result of discrepancies between peak growth and seasonal peaks in cumulative evaporation leading the tissues to incorporate multiple seasons. The isotope values of moss waters likely reflect the anomalously warm summer on the Antarctic Peninsula, as indicated by the divergence from moss water lines published in non-record-setting summers. Although the δ18O values of moss tissue waters are a proxy for the composition of δ18O values of summer precipitation, it is critical to consider the imprint of high evaporative conditions, in addition to summer precipitation composition, when reconstructing past environmental conditions using cellulose from peat archives. 

How to cite: Jones, D., Groff, D., and Beilman, D.: The influence of high evaporative conditions on peat-forming mosses in the Antarctic Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10139, https://doi.org/10.5194/egusphere-egu23-10139, 2023.

EGU23-11001 | ECS | Orals | BG2.1

Development of new proxies for sulfurization and paleo-environmental conditions using a Rock-Eval coupled to MC-ICPMS 

Hadar Cohen-Sadon, Yoav Oved Rosenberg, Shimon Feinstein, and Alon Amrani

The sulfur (S) cycle is directly linked to the global carbon and iron cycles. Sulfur plays an important role in the preservation of organic matter (OM) over geological time scales. Assimilatory and dissimilatory sulfate reductions (ASR and DSR, respectively) are the main processes shaping the sulfur cycle and carry different sulfur isotopic fractionation (-1 to -3 ‰, and -20 to -75 ‰, respectively). The reduced S species produced by DSR react during early diagenesis with OM (sulfurization) to form organic-S, and/or with iron (Fe) to form pyrite. Although in most cases organic- and pyritic-S have a common origin (i.e., DSR), organic-S in marine sediments is typically 34S enriched relative to its co-existing pyrite by up to 40 ‰ (global average is ~10‰). This isotopic difference is assumed to depend on specific paleo-environmental conditions and different sulfurization pathways (open-closed system for sulfate, Fe availability, redox state, OM type, etc.). Different sulfurization pathways may affect the type and distribution of S-bonds in sedimentary OM and thus can strongly affect the structure and character of sedimentary OM.

Recently, new instrumentations and methods were developed for the rapid determination of organic- and pyritic-S concentrations and δ34S values using a Rock-Eval analyzer (RE) coupled to a MC-ICPMS. A new parameter, Tmax-S (the temperature at maximum peak of organic-S generation), was suggested to represent the organic-S thermal stability in pyrolysis conditions. Applying this parameter to thirteen organically rich and thermally immature samples of various geological settings and paleo-environmental origins revealed several interesting empirical correlations. The Tmax-S value was found to differ among the rocks and to linearly correlate (R2=0.98) with the percentage of pyrolyzed organic-S out of the total organic-S in the rock. Moreover, Tmax-S was strongly correlated with the distribution of sulfidic and thiophene compounds in the rock (R2=0.87). This suggests that Tmax-S may be used as a tool to evaluate the distribution of different S-bonds in the organic molecule, and, as a proxy, their sulfurization and paleoenvironmental conditions.

The rock samples' Tmax-S values also correlate with their isotopic difference between organic- and pyritic-S (Δ34Sorganic-pyrite; R2=0.76). The Δ34Sorganic-pyrite values of the rocks extended between 1 to 40‰ where marine samples characterized by low Tmax-S values (~400-450 °C) and large Δ34Sorganic-pyrite values (~20-40‰) and lacustrine samples by high Tmax-S values (~450-480 °C) and small Δ34Sorganic-pyrite values (~1-5‰). This correlation further supports the link between paleo-environmental conditions, specific sulfurization pathways, and the organic-S structures (represented by Tmax-S). It may shed light on some fundamental questions regarding the role of S isotopic distribution between pyrite and OM during deposition and diagenesis.

How to cite: Cohen-Sadon, H., Rosenberg, Y. O., Feinstein, S., and Amrani, A.: Development of new proxies for sulfurization and paleo-environmental conditions using a Rock-Eval coupled to MC-ICPMS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11001, https://doi.org/10.5194/egusphere-egu23-11001, 2023.

EGU23-12808 | Orals | BG2.1

Exploring new protocols for bulk off-line fluid inclusion extraction for the analysis of δ13C-CH4 using a Cavity Ring-Down Spectroscopy (CRDS) analyzer. 

Orlando Sébastien Olivieri, Alberto Vitale Brovarone, Jens Fiebig, Francesco Ressico, Valentina Marassi, Sonia Casolari, and Olivier Sissmann

For decades, the search for terrestrial abiotic CH4 has been a central quest in geology and astrobiology. Most of this research has focused on crustal fluid samples collected at surface seeps, hydrothermal vents, and wells. Nonetheless, in such open systems processes like mixing with shallow biotic CH4, oxidation, and diffusion can lead to large uncertainties in the initial composition of deeply originated CH41. Extracting natural CH4 from fluid inclusions entrapped in minerals could overcome the effects of shallow contamination occurring in natural open systems and shed light on the origin of deep CH4 in a wide variety of geodynamic settings2,3.  

In this abstract, we present a novel approach for bulk off-line fluid inclusion extraction for the analysis of δ13C-CH4 using a Cavity Ring-Down Spectroscopy (CRDS) analyzer (Picarro G2201-i). Two fluid extraction techniques were compared: ball milling in ZrO2 jars and sample crushing in a stainless-steel sealed tube under a piston. The accuracy and precision of the different protocols was evaluated with blanks, CH4 isotopic labelling and interlaboratory comparisons.   

Blanks and isotopically labelled tests with the ball milling technique suggested that milling speed, and duration, and sample mass and type may strongly affect the CH4 concentrations and isotopic compositions measured by the CRDS analyser. These effects are mainly ruled by the blank production of CH4 –demonstrated by gas chromatography analyses– and potentially other molecules induced by frictional heating. The blank gases may cause interference effects on the absorption bands detected by the CRDS analyser. This effect was marked by a large offset in the δ13C-CH4 measured in the high-range analytical modes of the Picarro G2201-i. The magnitude of the interference was inversely correlated to the CH4 concentration.Other processes such as CH4 diffusion and adsorption may play a role in the observed changes in CH4 concentrations and isotopic compositions. Experimental conditions involving high CH4 concentrations and sample mass could well reproduce CH4 isotopic composition. 

Crushing in a sealed stainless-steel tube produces lower blank levels compared to ball milling, nevertheless the crushing efficiency and CH4 release is lower due to smaller rock sample size.   

The presented ball milling protocol provides a simple and fast way to extract and accurately analyse CH4 hosted in fluid inclusions even if great care should be considered for samples with low CH4 concentrations where contamination and interferences can potentially alter the CH4 isotopic signature of natural samples.   

 

References 

  • 1 - Young et al. (2017). 10.1016/j.gca.2016.12.041 
  • 2 - Klein et al. (2019). 10.1073/pnas.1907871116 
  • 3 - Grozeva et al. (2020). 10.1098/rsta.2018.0431 

 

This work is part of project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 864045).    

How to cite: Olivieri, O. S., Brovarone, A. V., Fiebig, J., Ressico, F., Marassi, V., Casolari, S., and Sissmann, O.: Exploring new protocols for bulk off-line fluid inclusion extraction for the analysis of δ13C-CH4 using a Cavity Ring-Down Spectroscopy (CRDS) analyzer., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12808, https://doi.org/10.5194/egusphere-egu23-12808, 2023.

EGU23-13490 | ECS | Posters on site | BG2.1

New insights into benthic nitrogen cycling using natural-abundance stable isotopes measurements 

Alessandra Mazzoli, Cameron M. Callbeck, Tim J. Paulus, Claudia Frey, Jakob Zopfi, Sergei Katsev, Donald E. Canfield, and Moritz F. Lehmann

Marine and lacustrine benthic habitats represent hotspots of nitrogen (N) turnover, with many N transformation processes occurring simultaneously, and at high rates. More specifically, sedimentary microbial reduction of nitrate to dinitrogen (N2), and other modes of N2 production (e.g., anammox), are the most important sinks of fixed N in aquatic environments. Natural abundance stable isotope ratio measurements can be employed to help disentangling N-loss mechanisms, given that the isotope effects (e) associated with each process are well studied.

In our study, we surveyed an array of lacustrine and marine benthic environments and assessed the isotopic composition (d15N and d18O) of porewater ammonium (NH4+) and nitrate (NO3-) – the key substrates driving the various N transformation pathways, such as denitrification, anammox, nitrification and dissimilatory nitrate reduction to ammonium (DNRA). We further examined how benthic N isotope dynamics vary in different sedimentary regimes, with distinct organic matter (OM) mineralization rates. We expect the relative importance of the various N pathways to affect the NH4+ and/or NO3- isotope pools differentially.

Our preliminary porewater d15N-NH4+ results suggest a diverse pattern with regard to the isotope enrichments between oligotrophic lakes, characterized by relatively strong depth gradients, and eutrophic lakes, where no significant depth gradient was observed. We hypothesize that this distinction could be attributed to different organic N availability and/or anammox contributions in the surveyed environments. Furthermore, we compared rate measurements (based on 15N addition experiments) to the N and O nitrate isotopic signatures to quantify processes, such as denitrification and DNRA. To investigate N isotope fractionation within the narrow nitracline, we employed the whole-core squeeze method, which provided a high-resolution porewater NO3-profile. Using this method, we found that the calculated community nitrate consumption e values at the nitracline (eelim_porewater) showed strong variability among the surveyed settings. We attribute such variation to shifts in the relative importance of denitrification versus DNRA and anammox between lakes of different trophic states. Overall, eelim_porewater wasconsiderably below 25‰ – the value generally reported for the biological isotope effect of denitrification (edenit).

How to cite: Mazzoli, A., Callbeck, C. M., Paulus, T. J., Frey, C., Zopfi, J., Katsev, S., Canfield, D. E., and Lehmann, M. F.: New insights into benthic nitrogen cycling using natural-abundance stable isotopes measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13490, https://doi.org/10.5194/egusphere-egu23-13490, 2023.

EGU23-13891 | ECS | Orals | BG2.1

There and back again: Combining hydrogen and strontium isotopes refines the trans-Saharan migratory patterns of the butterfly Vanessa cardui 

Megan Reich, Sana Ghouri, Samantha Zabudsky, Gerard Talavera, and Clement Bataille

Migratory insects serve an important role to ecosystems and economies as they participate in the long-distance transfer of nutrients, pollen, and biomass. However, migratory insects are understudied, especially compared to birds and mammals, partially because traditional tracking techniques (e.g. mark-recapture, biologgers) are often ineffective for insects because insects are small, short-lived, and numerous. Thus, isotope geolocation has become an effective tool for studying dispersing insects. The painted lady butterfly (Vanessa cardui (L.)) is a virtually cosmopolitan species that was recently found to make regular, annual multi-generational migrations across the Sahara Desert. Previous work geolocating painted ladies with hydrogen isotopes has shown early spring migratory movements of painted ladies from sub-Saharan Africa to Mediterranean Europe and autumn movements to the sub-Sahara from Europe. However, these previous works using hydrogen isotopes were unable to offer refined estimates of natal origin due to the inherent limitations of the technique. Here, we update previous hydrogen isotope-based geographic assignment by (1) using an updated model of hydrogen isotope variations across the landscape (i.e., isoscape), (2) combining with strontium isotope-based geographic assignment, and (3) expanding the number of geolocated butterflies to include capture locations on both sides of the Sahara Desert across different years. Using this method, we spatially refine previous estimates of the natal origins of successful trans-Saharan migrants and estimate the distances that successful migrants travelled. Overall, this study demonstrates the advantages of combining hydrogen and strontium isotopes for the geographic assignment of migratory butterflies and further advances our understanding of long-distance insect migration.

How to cite: Reich, M., Ghouri, S., Zabudsky, S., Talavera, G., and Bataille, C.: There and back again: Combining hydrogen and strontium isotopes refines the trans-Saharan migratory patterns of the butterfly Vanessa cardui, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13891, https://doi.org/10.5194/egusphere-egu23-13891, 2023.

EGU23-14655 | ECS | Posters on site | BG2.1

Unravelling the formation paths of amorphous hydroxyaluminosilicates and hydrous ferric silicates: Evidence from silicon isotopes 

Franziska M. Stamm, Andre Baldermann, Daniel A. Frick, Dorothee Hippler, and Martin Dietzel

Silicate mineral weathering and the resulting formation of clay minerals are key processes at the Earth’s surface. Reverse weathering reactions regulate the evolution of ocean pH and chemistry, atmospheric carbon dioxide budget, soil formation and associated nutrient and element transfer within local and global biogeochemical cycles. A key element released during weathering processes is silicon (Si), that enters the biogeochemical cycle as dissolved silicic acid (Si(OH)4 or DSi). During the transport of DSi through the hydro-, bio-, pedo- and lithosphere towards the ocean, DSi is involved in the formation of new silicate minerals (i.e., clay minerals) in particular in the critical zone (CZ). Here, DSi is frequently precipitating as gel-like, amorphous phases such as short range ordered hydroxyaluminosilicate phases (HAS: e.g., allophane) or as hydrous ferric silicates (HFS: e.g., hisingerite). These highly reactive minerals are known precursors to the formation of important soil clay minerals e.g., within the smectite group.

The individual reaction pathways and the environmental controls underlying HAS and HFS formation within the CZ are not yet well constrained. Si isotope fractionation throughout HAS and HFS formation is a key tool to decode and assess such enigmatic reaction mechanisms. Therefore, a series of allophane-hisingerite precipitation experiments has been performed to investigate Si isotope fractionation to potentially resolve mechanisms and conditions underlying the formation of HAS and HFS phases. Kinetic and equilibrium Si isotope fractionation between reactive fluid and solid phases are studied at high temporal resolution. Isotope exchange mechanisms are investigated using the three-isotope method, which is a novel proxy to trace the direction and the progress of low-temperature water-mineral/rock interactions.

How to cite: Stamm, F. M., Baldermann, A., Frick, D. A., Hippler, D., and Dietzel, M.: Unravelling the formation paths of amorphous hydroxyaluminosilicates and hydrous ferric silicates: Evidence from silicon isotopes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14655, https://doi.org/10.5194/egusphere-egu23-14655, 2023.

EGU23-15191 | Orals | BG2.1

Determining the relevance of common mycelial networks in the nitrogen nutrition of plants adapted to semi-arid ecosystems 

Alberto Andrino, Asunción Morte, Francisco Arenas, Aline Figueiredo, Leopold Sauheitl, Alfonso Navarro, Ángel L. Guarnizo, Georg Guggenberger, and Jens Boy

Plants in semi-arid environments have adapted to scarce nitrogen (N) resources by becoming more efficient at using and taking it up, or by relying on symbiotic organisms. Common mycelial/mycorrhizal networks (CMNs) may help plants access and assist to a spatio-temporal redistribution of resources in soil. While CMNs have been extensively investigated in temperate forests and grasslands, their importance in semi-arid environments is still uncertain. This study evaluates the existence and importance of CMNs in N translocation in semiarid environments, using Helianthemmum almeriense as the host plant mycorrhized with Terfezia claveryi. We hypothesize that the presence of CMNs is a response mechanism to N scarcity due to soil heterogeneity. Through this mechanism, host plants and mycorrhizal fungi provide redistribution of N, playing a determinant role at all spatial scales, from the facilitation of seedling establishment to the persistence and coexistence of different plant communities. To test our hypothesis, we designed a mesocosm that allowed only hyphae to cross into an adjacent compartment. Three different tests were used to assess the existence and directionality of CMN. In the first test (T1), an adult plant was labeled with 15N and on the other side, only unlabeled soil was present. In this way, we could check if the mycorrhizal fungus tends to homogenously distribute the 15N to places where there is no other plant. In the second test (T2) we had an adult plant and in the adjacent compartment, four-week-old seedlings that were already mycorrhized with mycelium coming from the compartment with the adult plant. In this case, the 15N marker was applied where the adult plant was located, and we checked whether there was a transfer of 15N to the seedlings. In T3, we used a set of mesocosms equal to T2, but this time 15N was applied on the side where the seedlings were located. The idea was to determine whether the distribution of the 15N was proportional to the size of the plant that could receive it. The three types of mesocosms were sampled before labeling (day 0), 7 and 14 days after labeling. Our results reveal that 15N translocation to adjacent compartments occurred in all three tests, but in significantly different amounts. The translocation of 15N was significantly higher in those tests where there was a plant in the adjacent compartment (Tests 2 and 3) compared to T1. We also found that the contribution (%) of 15N to the total plant N pool was significantly higher for one-month-old seedlings in both T2 and T3, compared to adult plants. Under controlled greenhouse conditions, we have shown that the mycelium seems to act as an effective hub for N translocation, but we have not found the amounts transferred under our experimental conditions to be nutritionally remarkable. Our results should be further evaluated under natural conditions, to verify whether this N transfer has a greater nutritional significance than that found under controlled conditions, and also whether this CMN may play a more important role in signaling between plants adapted to semi-arid regions.

How to cite: Andrino, A., Morte, A., Arenas, F., Figueiredo, A., Sauheitl, L., Navarro, A., Guarnizo, Á. L., Guggenberger, G., and Boy, J.: Determining the relevance of common mycelial networks in the nitrogen nutrition of plants adapted to semi-arid ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15191, https://doi.org/10.5194/egusphere-egu23-15191, 2023.

EGU23-16065 | Posters on site | BG2.1

Isotopic tracking of condensation, infiltration and interstitial water to detect microbial activity in caves 

Angel Fernandez-Cortes, Tamara Martin-Pozas, Soledad Cuezva, Fernando Gazquez, David Benavente, Juan Carlos Cañaveras, Cesareo Saiz-Jimenez, and Sergio Sanchez-Moral

Water plays a key role in the colonization and ecology of microorganisms in natural subterranean environments since it controls their metabolic activity and the microbe-mineral interactions. In turn, microbial activity leaves its signature in groundwater. For instance, the aerial hyphae of Actinobacteria colonizing cave-rock surfaces and sediments act as vapour condensation nuclei and facilitate the retention of interstitial water in the porous system of rocks, sediments and speleothems.

Here, we present the results of exhaustive monitoring of cave waters from Pindal Cave (northern Spain), a shallow and well-ventilated cave on the coastline, with extensive microbial colonization on the sediments and walls surfaces. This study sheds light on the detection of biosignatures based on stables isotopes of cave waters and controlled by underground-dwelling microorganisms. The isotopic composition (d18O and dD) of seepage waters (fast drips, soda straws and gours) and condensation droplets were determined by cavity ring-down spectroscopy (CRDS). An analytical set-up based on a CRDS analyser coupled to an Induction Module enabled the step-heating of moonmilk deposits and other substrates with distinct degrees of microbial colonization, and the selective release of their interstitial water for isotope analyses.

The δ18O and δD values of the in-cave waters correlate linearly (δD=7.71·δ18O+12.28; R2=0.97), like the Local Meteoric Water Line (δD=7.00·δ18O+6.77; R2=0.92, based on the of isotopes composition of regional rain). The offset of d-excess between the cave waters and the LMWL would indicate a significant recharge by occult precipitation linked to local coastal fogs. The isotopic composition of dripping water,  -5.7‰ [-6.7 to -4.8 ‰] for  d18O and -31.3‰ [-39.0 to -22.7 ‰] for dD, agree with the water samples from the gours located far from the cave entrance, with some slight deviations indicating evaporation processes or sudden contributions of meteoric water due to flash-flood events.

The δ18O and δD values of condensation water collected from non-colonized surfaces are -5.4‰ [-5.9 to -4.5 ‰] and –28.4‰ [-32.9 to -21.3 ‰], respectively. This isotope composition is similar to the contemporary infiltration water, which suggests that condensation mostly comes from autochthonous vapour generated from in-cave waters. The Actinobacteria mats quickly absorb the condensation water and it is then retained during long periods on the rock surface. Thus, in the case of microbial induced deposits like moonmilk, condensate water becomes a reservoir of interstitial water exposed to isotopes fractionation linked to the microbial metabolism processes. Indeed, the δ18O and δD values of this interstitial water correlate linearly with the rest of the in-cave waters but show a distinctive composition with higher δ18O and δD values compared to the infiltration water and condensation droplets; -3.6‰ [-4.4 to -2.0 ‰] and –18.9‰ [-27.2 to -10.8 ‰], respectively. These findings lead to exploring the potential use of water isotopes as a tool for indirectly assessing microbial activity and its role in the water balances in underground ecosystems.

Research funded by PID2019-110603RB-I00 – SUBSYST and PID2020-114978GB-I00 projects

How to cite: Fernandez-Cortes, A., Martin-Pozas, T., Cuezva, S., Gazquez, F., Benavente, D., Cañaveras, J. C., Saiz-Jimenez, C., and Sanchez-Moral, S.: Isotopic tracking of condensation, infiltration and interstitial water to detect microbial activity in caves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16065, https://doi.org/10.5194/egusphere-egu23-16065, 2023.

EGU23-16235 | ECS | Orals | BG2.1 | Highlight

Isotope biogeochemistry of the carbon-iron-sulfur cycle in a temperate coastal peatland after flooding by brackish seawater 

Rhodelyn Saban, Michael Ernest Boettcher, Anna Kathrina Jenner, Sara Elizabeth Anthony, Gerald Juransinski, Catia Ehlert von Ahn, Patricia Roeser, and Iris Schmiedinger

Soils from a coastal peatland (Drammendorf,  southern Baltic Sea) were investigated for the biogeochemical impact of flooding with brackish seawater. The peatland was rewetted in late 2019 through the partial removal of a dyke and brackish water with high sulfate concentration from a lagoon (Kubitzer Bodden) allowed to intrude into the peatland. Soil cores were retrieved about 2 and 3 years after the initial rewetting event. Pore waters were extracted from soil cores using rhizons and samples were analyzed besides physical parameters for major ions, nutrients, water stable isotopes, dissolved inorganic carbon (DIC) concentrations, and stable isotopes in C and S species. Solid phase samples were analyzed for contents of CNS and acid-extractable metal and nutrient species, and the stable isotope composition of acid-volatile sulfide (AVS), chromium-reducible sulfide (CRS, pyrite).Results from the post-event campaigns are compared with pre-flooding conditions. Poree water generally showed a trend towards freshening with depth as remains from the pre-flooding conditions. . Different sites are furthermore characterized by different amounts of diagenetically released dissolved inorganic carbon (DIC). A mixing evaluation of ẟ13C-DIC signatures together with major ion concentrations reveals potential DIC sources, like organic matter/methane oxidation, carbonate dissolution and mixing with seawater-derived DIC. DIC from the dissolution of minor soil carbonates may lead to a relative enrichment of 13C in DIC. Brackish water intrusion and cation exchange are reflected by the downward gradients in pore water compositions, with Na and Mg decreasing and Ca increasing with depth. Soil organic carbon is dominating with inorganic carbon being a minor fraction in most parts. Dissolved pore water sulfate and high total sulfur in the top soils with decrease downward trends further reflect the importance of post-event enhanced sulfur cycling leading to characteristic sulfur isotope signatures. AVS is depleted in the top soils with highest contents at about 5 cmbsf. Pyrite sulfur dominates and show different enrichment zones with the sediment columns. Contents in CRS contents covary with TOC, indicating that the benthic diagenetic system is controlled by organic matter availability, as in normal marine sediments.  The study demonstrates the role of electron acceptor availability for benthic carbon cycling, and the kinetics of biogeochemical interactions upon oxidation of reduced carbon, mineral authigenesis/dissolution, and ion exchange processes. The results of implications for coastal processes in the humid climate zone during times of increasing seawater level rise.

 

 

How to cite: Saban, R., Boettcher, M. E., Jenner, A. K., Anthony, S. E., Juransinski, G., Ehlert von Ahn, C., Roeser, P., and Schmiedinger, I.: Isotope biogeochemistry of the carbon-iron-sulfur cycle in a temperate coastal peatland after flooding by brackish seawater, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16235, https://doi.org/10.5194/egusphere-egu23-16235, 2023.

EGU23-16361 | ECS | Posters on site | BG2.1

Comparison of two isotope-based methods to quantify nitrification rates in estuaries 

Vanessa Russnak, Sophie Kache, Maren Voss, and Kirstin Dähnke

Estuaries are important biogeochemical reactors that can remove dissolved inorganic nitrogen (DIN, mostly nitrate) from the water column, but can also generate nitrate via remineralization and subsequent nitrification of organic matter in the water column. To assess this regeneration of nitrate, an important nutrient source for phytoplankton that contributes to eutrophication, various isotope-based laboratory methods are in use.

In this study, we compare two commonly used stable-isotope-based techniques to measure nitrification in estuarine water, the isotope dilution method and the addition of 15N-ammonium. Both measure the isotope enrichment in nitrate but have drastically different incubation times. We apply both methods in the estuary of the Elbe River and evaluate the drawbacks and advantages of each method to develop application recommendations.

Our results indicate that nitrification measurements using isotope dilution are less variable between stations, but suggest that rates are overestimated at high phytoplankton activity. On the counter side, the addition of 15N-ammonium as a tracer apparently overestimates nitrification in heterotrophic settings, probably because substrate addition stimulates nitrification. The adequate measurement technique must this be carefully chosen depending on the selected study site.

Funding information  - This study has been carried out and was financially supported by the BMBF “Blue-Estuaries” project (grant no. 03F0864C)

How to cite: Russnak, V., Kache, S., Voss, M., and Dähnke, K.: Comparison of two isotope-based methods to quantify nitrification rates in estuaries, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16361, https://doi.org/10.5194/egusphere-egu23-16361, 2023.

EGU23-16727 | ECS | Posters on site | BG2.1

The isotope effect of benthic N removal in two Swiss lakes 

Tim J. Paulus, Alessandra Mazzoli, Claudia Frey, Jakob Zopfi, Cameron Callbeck, and Moritz F. Lehmann

Aquatic sediments play a critical role in moderating the availability of fixed nitrogen (N) in the biosphere. Microbial N cycling processes, such as denitrification and anammox, contribute to fixed‑N removal as N2 gas from lakes and the ocean. N‑isotopic measurements of dissolved inorganic N (e.g., nitrate (NO3-)) can provide insights into the different sources, sinks, and pathways of N, if the associated N isotope signatures/effects are constrained. While substantial work has been done to resolve N‑loss using microbial metagenomic‑based approaches and rate measurements, how nitrogen‑loss processes imprint natural‑abundance isotopes of 15N and 18O of NO3- remains largely understudied in freshwater lake sediments. Current marine evidence suggests that water column denitrification involves high NO3- isotope effects (>20‰). In contrast, the marine NO3- isotope effect of sedimentary denitrification is suppressed at the level of the sediment‑water interface (apparent N/O isotope effect, εapp <5‰). How anammox affects εapp in either marine or freshwater systems, is completely unknown. This study aims to achieve a deeper understanding of NO3- N and O isotope fractionation during benthic N transformation and sedimentary N‑loss (including anammox), and its ultimate expression in the water column of freshwater lakes. We also investigate how εapp values may vary with environmental conditions (e.g., trophic state) that affect the reactivity and amount of organic matter in the sediments, as well as the balance between benthic N‑cycle reactions.

The two study sites Lake Baldegg (eutrophic) and Sarnen (oligotrophic), were chosen because of their contrasting trophic states. We conducted a suite of experiments with sediment cores collected at different times of the year to assess the sedimentary εapp in these two lakes. More specifically, we carried out whole‑core incubations under oxic/anoxic conditions and examined the change 15N/14N and 18O/16O of NO3- with net NO3- depletion in the overlying water. We integrated natural‑abundance N and O isotope measurements with 15N‑label based N transformation‑rate measurements, to understand how the phenology and differential combination of the different N transformation pathways may modulate εapp. We demonstrate that nitrification, DNRA, denitrification, anammox and organic matter remineralization overlap spatially in the sediments of Lake Sarnen. In contrast, these processes are, in parts, spatially decoupled in Lake Baldegg. Moreover, the relative importance of anammox versus denitrification is significantly greater in Lake Baldegg. In both lakes the net N isotope effect of sedimentary NO3- consumption is strongly underexpressed at the ecosystem level, with NO3-‑N εapp values systematically below 4‰. In Lake Sarnen the NO3- N‑vs.‑O isotope signature followed a 1:1 trend, whereas in Lake Baldegg a systematically higher ratio was observed. This suggests that, while in Lake Sarnen, the NO3- N and O isotope signatures are dominated by NO3- reduction, NO3- regeneration (e.g., by nitrification or anammox) overprints the NO3- isotopic signature of net denitrification under the more eutrophic conditions in Lake Baldegg.

How to cite: Paulus, T. J., Mazzoli, A., Frey, C., Zopfi, J., Callbeck, C., and Lehmann, M. F.: The isotope effect of benthic N removal in two Swiss lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16727, https://doi.org/10.5194/egusphere-egu23-16727, 2023.

GMPV2 – The mantle-surface connection (in partnership with GD)

EGU23-243 | ECS | Orals | GMPV2.1

Reappraisal of the geodynamic evolution of the mantle massifs of the Ivrea-Verbano Zone based on new field, petrochemical and geochronological data 

Abimbola Chris Ogunyele, Mattia Bonazzi, Alessio Sanfilippo, Alessandro Decarlis, and Alberto Zanetti

The Ivrea-Verbano Zone (IVZ) is the westernmost sector of the Southern Alps. It is constituted by granulite-to-amphibolite-facies continental crust representing the basement of the Adria plate. The IVZ contains many orogenic mantle peridotites. The largest mantle bodies are aligned along the Insubric Line at the lowest stratigraphic units, in contact with mafic-ultramafic crustal intrusives. Mantle bodies in the central and southern sectors of IVZ are spinel lherzolites with spinel dunites and variable amount of clinopyroxenite, websterite and subordinate anhydrous/hydrous gabbroic bodies (e.g. the Baldissero, Balmuccia, Premosello peridotites). Conversely, modally-metasomatised spinel harzburgites with large dunite bodies and phlogopite-and-amphibole-bearing websterites (e.g. the Finero peridotite) crop out in the northern IVZ.

The constant association of the IVZ mantle peridotites with High-T shear zones suggests that none of them was emplaced into the crust by mantle diapirism. Alternative hypotheses involve emplacement at the crustal level at the onset of the Mesozoic extensional regime or tectonic addition to accretionary wedges of Paleozoic subduction zones. Recent gravimetric and seismic data converge in indicating that high-density rocks are very close to the surface near the Insubric Line, thus supporting the possibility that the largest mantle peridotites may be a direct expression of the underlying subcontinental mantle.

This contribution focuses on new field, petrographic, geochemical and geochronological data, to address some relevant issues, such as the nature of the spinel lherzolite (refractory residue vs. refertilised mantle), the origin of pyroxenites and gabbros, the relationships with the associated crustal intrusives and the record of Mesozoic tectono-magmatic events.

The final goal is to provide new insights into the geodynamic evolution of the mantle bodies and the mantle-crust systems at the Laurasia-Gondwana margin, defining in particular how the mantle heterogeneity acquired during Paleozoic may have governed the rifting process of the Adria margin in Jurassic times.

How to cite: Ogunyele, A. C., Bonazzi, M., Sanfilippo, A., Decarlis, A., and Zanetti, A.: Reappraisal of the geodynamic evolution of the mantle massifs of the Ivrea-Verbano Zone based on new field, petrochemical and geochronological data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-243, https://doi.org/10.5194/egusphere-egu23-243, 2023.

Even though the southern Indian Dharwar craton hosts several kimberlites, lamproite, and lamprophyre fields of the Mesoproterozoic age, mantle-derived peridotitic xenoliths are very rare and are often highly altered and poorly preserved. Due to these constraints, xenolith-based direct mantle investigations have been limited beneath the Indian cratons. In this study, we report extensive geochemical analyses on peridotite xenoliths from the P3 kimberlite pipe of the Wajrakarur kimberlite field from the Eastern Dharwar craton (EDC). With the help of major and trace element compositions of the garnets and clinopyroxenes, this study aims to characterize the mantle below EDC and to comment on its evolution.

During this study, 57 peridotite xenoliths were identified. P-T estimates were carried out using garnet compositions. Based on the vertical distribution of garnets on a projected depth, it is observed that the upper part of the lithosphere is composed mostly of lherzolites(G9) with few harzburgites (G10), whereas the base of the lithosphere is dominated by Ti-Metasomatized garnets(G11).

Garnet compositions show an anomaly in the TiO2 content, which is marked by a sudden increase in TiO2 at ~160 km of depth. This depth coincides with an increased concentration of G11 garnets. Zr/Hf vs Ti/Eu plot for garnets shows that carbonatitic and kimberlitic fluids are involved in metasomatizing the SCLM. The Mg# and Cr# values suggest that the lithosphere gets more depleted with increasing depth. Clinopyroxene compositions show the presence of two types. Type 1 is enriched in LREE than the Type 2 clinopyroxenes showing the metasomatic enrichment.

The depth range of the studied peridotite xenoliths indicates sampling of the mantle from ~170 to 190 km of depth, indicating a 190 km thick LAB at 1.1 Ga. However, geophysical studies show a present-day estimate of a ~110 to 120 km thick lithosphere. This further indicates about 70-80 km of delamination of the lithospheric keel in post-Mesoproterozoic times. Such large-scale delamination of the lithosphere might be possible due to the increased frequency of mantle plumes, convective erosion, and the heavily metasomatized nature of the SCLM.

How to cite: Daimi, Z. and Dongre, A.: Evolution of the lithospheric mantle beneath Eastern Dharwar craton of Southern India: constraints from peridotite xenoliths from P3 kimberlite pipe of the Wajrakarur, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-293, https://doi.org/10.5194/egusphere-egu23-293, 2023.

EGU23-2720 | Orals | GMPV2.1

Preservation of the water concentration in mantle xenoliths. The cases of Peylenc & Ray Pic volcanoes (FMC) 

Jannick Ingrin, Konstantinos Thomaidis, and Maria Drouka

The ability of xenoliths to preserve water lithospheric signatures remains an unsolved question for many years. We report water content in olivine and pyroxenes of peridotite xenoliths from Peylenc and Ray Pic volcanoes (French Massif central, FMC). On each site xenoliths were sampled from products of an explosive eruption (volcanic breccia and pyroclastic deposit) and an effusive eruption (frozen magma chamber and a lava flow).

In Peylenc, the xenoliths from the breccia have systematically more water than the xenoliths from the basalt quarry: ol 1-9, opx 60-95 and cpx 250-380 wt. ppm H2O versus ol <0.2, opx 20-55 and cpx 110-240 wt. ppm H2O.

In Ray Pic, water content in xenoliths from the lava flow is independent of its location in the lava: ol < 1, opx 190-270 and cpx 430-640 wt. ppm H2O. Results suggest that the cooling and solidification of the lava had no impact on water content.

The xenoliths from the pyroclastic deposit have systematically more water: ol 3-12, opx 330-460 and cpx 810-890 wt. ppm H2O. These values are either comparable with or lower than the values reported previously from the same locality1.

The study shows that xenoliths recovered from explosive eruptions have higher water content than the ones from effusive eruptions, but also that water content can be different from one explosive event to another.

Conclusion is that water content can rapidly be reset during magma degassing prior to eruption. Degassing controls water content of xenoliths.

Among the xenoliths studied, several have spectral signatures different from others. This different spectral signature has also been reported from other volcanoes2, 3. The coexisting of different spectral signatures, which have not been erased during degassing, are probably the only OH signatures fully preserved from depth.

1 Azevedo-Vannson S.,et al. Chemical Geology 575 120257 (2021)

2 Denis C.M.M. et al. Lithos 226 256-274 (2015)

3 Patkó L. et al. Chemical Geology 507 23-41 (2019)

How to cite: Ingrin, J., Thomaidis, K., and Drouka, M.: Preservation of the water concentration in mantle xenoliths. The cases of Peylenc & Ray Pic volcanoes (FMC), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2720, https://doi.org/10.5194/egusphere-egu23-2720, 2023.

EGU23-2760 | Posters on site | GMPV2.1

Geology, geochemical typification and petrogenic model of formation of Middle Paleozoic metabasites of the Khrami crystalline massif (Georgia) 

David Shengelia, Tamara Tsutsunava, Giorgi Beridze, and Irakli Javakhishvili

The Khrami crystalline massif is located in the northern part of the Lesser Caucasus, in the Black Sea - Transcaucasian terrane. The massif outcrops Middle Paleozoic metabasites, which crosscut the Precambrian gneiss-migmatite complex and, in turn, are cut by Late Variscan granites. These metabasites have not experienced Precambrian prograde HT/LP (720-770°C, P<1.5 kbar) regional metamorphism, although retrograde LT/LP (T≈430-5100C, P≈0.6-1 kbar) metamorphism, associated with the Sudetian orogeny has been recorded. According to the presented geological data, the age of metabasites is within the Cambrian and Upper Paleozoic. Considering the analogy between the metabasites spread in the Dzirula crystalline massif, which is exposed in the same terrane, and the metabasites of the Khrami massif, the age of the latter is most likely Middle Paleozoic (Shengelia et al., 2022). The metabasites of the Khrami massif are represented by veins (1-60 m) and stock-shaped bodies (80-800 m) of fine-grained ophitic gabbro, gabbro-diabases and diabases of various thicknesses. They are cut by numerous granite veins and penetrated by thin quartz-feldspar injections. The paragenesis of the high-temperature magmatic stage - Cpx+Pl78-84 has been preserved in metabasites in some places; Further, under the conditions of greenschist facies, the paragenesis Ab+Act(Tr)+Chl+Ep±Qz develops. According to the petrogenic diagrams Na2O+K2O – SiO2, the metabasites of the Khrami massif belong to the formations of the subalkaline series (Irvine and Baragar, 1971), correspond to basalts and andesite-basalts (Le bas et al., 1986) and basalts and picrites (Cox et al., 1979). This is confirmed by the data of diagrams Zr/Ti-Nb/Y (Pearce, 1996) and Zr/TiO2 – Yb/Y (Winchester, Floyd, 1977). According to the Na2O+K2O–FeO*-MgO (Irvine and Baragar, 1971), a great part of the metabasites is of tholeiitic composition, and only a small part is of calc-alkaline composition. On the diagram Fe*-SiO2 (Frost et al., 2008) the dots denoting metabasites are completely disposed in the magnesian field. According to the TiO2 - Zr/(P2O5*104) diagram (Winchester, Floyd, 1976), the metabasites correspond to tholeiite basalts. According to the diagram V-Ti/1000 (Shervias, 1982), the metabasites belong to the MORB genetic formation, and according to the diagram Cr-Y (Pearce, 1982), they belong mainly to the VAB, and also to the MORB. According to the ratio MnO-TiO2/10-P2O5 (Mullen, 1983), dots of mafic rocks are located in the island-arc tholeiitic field. Thus, the Middle Paleozoic metabasites of the Khrami crystalline massif are represented by shallow subvolcanic magmatites predominantly of andesite-basalt and tholeiite-basalt groups of the tholeiitic series. They correspond to the MORB and VAB genetic groups.

How to cite: Shengelia, D., Tsutsunava, T., Beridze, G., and Javakhishvili, I.: Geology, geochemical typification and petrogenic model of formation of Middle Paleozoic metabasites of the Khrami crystalline massif (Georgia), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2760, https://doi.org/10.5194/egusphere-egu23-2760, 2023.

EGU23-2878 | Posters on site | GMPV2.1

Peridotite xenoliths from Stöpfling in Hessian Depression (Germany) revisited 

Jacek Puziewicz, Sonja Aulbach, Magdalena Matusiak-Małek, Theodoros Ntaflos, and Małgorzata Ziobro-Mikrut

The Hessian Depression in Germany represents the northern continuation of the Upper Rhine Graben and is known for Cenozoic alkaline basaltic lavas. Many of these carry peridotite xenoliths of mantle origin, which were studied mainly in the  80-ies of the XX century (Hartmann & Wedepohl 1990 and references therein). These studies documented mantle lithosphere melting followed by metasomatism. Here we describe the xenoliths from the Stöpfling quarry near Homberg upon Efze. The quarry has been recultivated and sampling is not possible now, our samples come from the archival collection of the Department of Geochemistry of the University of Göttingen. In this abstract, we give an overview of newly collected major- and trace-element mineral-chemical data from 11 xenoliths.

The xenoliths from Stöpfling are spinel-facies lherzolites and harzburgites. They consist of aggregates of few coarse (typically 4-6 mm across) grains of olivine and orthopyroxene embedded in fine-grained matrix of olivine, ortho- and clinopyroxene and spinel. Coarse-grained aggregates represent fragments of protogranular texture and are volumetrically prevailing. Spinel is commonly interstitial and has amaeboidal morphology. Locally, centimetre-thick layers of websterites cross-cut the peridotites. Hartmann & Wedepohl (1990) report traces  (<1 vol. %) of phlogopite in 2 of 12 lherzolites they studied.

The major element composition of olivine is strikingly homogeneous in all studied rocks (91±0.5 % forsterite and 0.40 wt. %. NiO), Ca content is < 500 ppm. Orthopyroxene is mildly aluminous (0.10-0.17 atoms of Al per formula unit, [pfu]) as is clinopyroxene (0.12-0.25 atoms Al pfu). Spinel Cr# [= Cr/(Cr+Al)] varies from 0.18 to 0.46. Clinopyroxene coexisting with spinel of low Cr# is Al-rich and contains 1600-2200 ppm Ti, whereas that coexisting with spinel of higher Cr# is less aluminous and contains 600-1200 ppm Ti. Clinopyroxene coexisting with spinel of Cr# 0.46 is extremely impoverished in Ti (50 ppm). The REE patterns of clinopyroxene in most samples are above the primitive-mantle (PM) level, are LREE-enriched and flat at MREE-HREE. Those extremely depleted in Ti show a decrease from HREE towards MREE, the contents of which are below PM level, and are strongly LREE-enriched.

Peridotites from Stöpfling consist of olivine which chemical homogeneity  across the xenolith suite supposedly records melt depletion. The variable content of Al in orthopyroxene from different samples probably is due to subsequent refertilization event(s) involving silicate melt, whereas the REE characteristics of clinopyroxene suggests that it was additionally cryptically  metasomatized. The unaffected olivine composition indicates low ratio of metasomatic agent to protolith.

Acknowledgements. JP is grateful to G. Wörner for enabling access to the xenoliths from Stöpfling that were originally collected by H. Wedepohl and are now archived at the Geochemistry and Isotope Geology Division of the Geoscience Center at University Göttingen (GZG).

Funding. This study originated thanks to the project of Polish National Centre of Research 2021/41/B/ST10/00900 to JP.

References:

Hartmann G., Wedepohl. K.H. (1990): Metasomatically altered peridotite xenoliths from the Hessian Depression (Nortwest Germany). Geochim. Cosmochim. Acta 54: 71-86.

How to cite: Puziewicz, J., Aulbach, S., Matusiak-Małek, M., Ntaflos, T., and Ziobro-Mikrut, M.: Peridotite xenoliths from Stöpfling in Hessian Depression (Germany) revisited, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2878, https://doi.org/10.5194/egusphere-egu23-2878, 2023.

EGU23-4252 | Orals | GMPV2.1

Evidence for the effects of subduction in Triassic lavas from the Northern Peloponnese (Greece): A mineralogical, geochemical and isotopic (Sr-Nd) approach 

Petros Koutsovitis, Konstantinos Soukis, Sotirios Kokkalas, Andreas Magganas, Theodoros Ntaflos, Yirang Jang, and Sanghoon Kwon

Triassic volcanism in Greece is mainly associated with the rift phase of the Neotethys that resulted in the formation of E-MORB and OIB alkali basalts, which are widespread throughout the Hellenic mainland[1]. In most of the outcrop localities (e.g. Pindos, Koziakas, Othris, Argolis) these basalts are closely related in the field with other more differentiated volcanics that display a clear subduction signature [1,2]. In the Northern Peloponnese and specifically from the localities of Drakovouni, Palaiohouni and Perachora, three types of lavas were identified: basaltic andesites, andesites and rhyodakites, which are fine to medium grained and displaying either porphyritic or even equigranular textures in the more felsic varieties. These lavas were classified based on their Si, Na and K contents, as well as their Nb/Y vs. Zr/Ti ratios, which were subjected to rather restricted metasomatic processes (LOI:1.1-3.7, partial albitization and uratilization). Based on their potassium contents, as well as upon the AFM geochemical ternary plot and their FeO/MgO ratios, they are geochemically classified as calc-alkaline volcanics, clearly being affected by subduction-related processes. The latter is confirmed by: presence of magmatic magnesiohornblende in all types of lavas at variable amounts, enhanced Th/Yb contents (2.4-4.1), LREE enrichments [(La/Yb)CN=6.2-10.0], lower normalized values of Th and U compared to Nb and Ta, positive K and Pb anomalies, negative Ti anomalies in the PM-normalized diagrams, noticeable LILE enrichments (e.g. Cs, Rb, Ba).

Fractional crystallization played a significant role in the differentiation processes. This is confirmed by: presence of primary clinopyroxene and amphibole in the basaltic andesites whose modal composition significantly decreases in the andesites and rhyodakites (only accessory amphibole), relatively strong correlation between Sc/Y with CaO/Al2O3 (R2 = 0.91), positive correlation between P2O5/TiO2 and (La/Yb)N (R2 = 0.87), higher Cr and Ni contents in the least differentiated lavas, increase of Nb/Yb in the highly fractionated lavas, increasing Eu negative anomalies from the compositionally basic to the felsic varieties (basaltic andesites EuCN/Eu*= 0.73-0.80; andesites EuCN/Eu* = 0.63-0.74, rhyodakites EuCN/Eu* = 0.51-0.61). Apart from fractional crystallization, crustal assimilation (AFC processes) likely played an additional role during differentiation, shown by the strongly positive correlation between SiO2 and Nb/Yb (R2 = 0.92). The Sr-Nd isotopic data further confirm the effect of crustal contamination and AFC processes, with lower 143Nd/144Nd and higher 87Sr/86Sr ratios for the rhyodakites compared to the andesites and basaltic andesites.

References: [1]Koutsovitis, P., Magganas, A., Ntaflos, T., Koukouzas, N., Rassios, A.E., Soukis, K., 2020. Petrogenetic constraints on the origin and formation of the Hellenic Triassic rift-related lavas. Lithos 368-369, 105604, [2] Pe-Piper, G., Piper, D.J.W., 2002. The Igneous Rocks of Greece. Borntraeger, Stuttgart, pp. 1–645.

How to cite: Koutsovitis, P., Soukis, K., Kokkalas, S., Magganas, A., Ntaflos, T., Jang, Y., and Kwon, S.: Evidence for the effects of subduction in Triassic lavas from the Northern Peloponnese (Greece): A mineralogical, geochemical and isotopic (Sr-Nd) approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4252, https://doi.org/10.5194/egusphere-egu23-4252, 2023.

EGU23-4404 | ECS | Orals | GMPV2.1

First noble gases measurements in lherzolites from Mt Vulture volcano: new constraints on the mantle below Italy 

Laura Italiano, Antonio Caracausi, Gabriele Carnevale, Michele Paternoster, and Silvio G. Rotolo

Mount Vulture is a stratovolcano (age 0.75-0.14 Myr) located in southern Italy, which despite being at the same latitude of Vesuvius and Phlegreian Fields, has several peculiarities about its setting and erupted magma composition. Indeed, if compared to other Italian Quaternary volcanoes, it is the only one located east of the Apennine Front, about 100 km off the axis of the Campanian Magmatic Province (Peccerillo et al., 2017). Furthermore, although being a quiescent volcano (last eruption dated 0.14 Myr), previous studies (e.g., Caracausi et al., 2015, Bragagni et al., 2022) have shown extremely high CO2 emissions (4.85 × 108 mol yr-1), which are likely related to the carbonatitic volcanism of its final phase of activity, as well as some petrological aspects in the erupted products pointing to a mantle source metasomatism.

Recently, investigations on Vulture mantle xenoliths (Carnervale et al., 2022) revealed CO2-rich fluid inclusions (FIs) that indicate a primary depth of bubbles entrapment in olivine and pyroxene phenocrysts coinciding with the regional crust-mantle boundary (27-30km).

This research focuses for the first-time noble gases isotopes (He, Ne, Ar) in FIs from lherzolite enclaves from Mt. Vulture tephra. The He isotopic ratios (as R/Ra; R is the 3He/4He ratio of the sample and Ra the same ratio in air), are between 6.2 and 5.4 ± 0.08. These values are lower than the signatures of the MORB upper mantle (8 ± 1Ra) and overlap the values of the Sub Continental Lithospheric Mantle (SCLM, 6.1 ± 0.9Ra). The Ne isotopic signatures (20Ne/22Ne and 21Ne/22Ne) are in the field of the MORB values.

The He-Ne-Ar systematics is consistent with a SCLM source feeding the magmatism of the Vulture volcano. However, considering the noble gases He-Ne-Ar, in Vulture xenolites this mantle source has affinities with that feeding the volcanic activities of Mt. Etna (Nakai et al., 1997; Correale et al., 2014). This inference bears some evidence about the similitudes of the mantle below these two volcanic systems that is affected by mantle metasomatism, which is likely also responsible for the large CO2 fluxes and the carbonatitic magmatism (Bragagni et al., 2022). New measurements of the noble gases in free gases from the two volcanoes together with a detailed comparison between the geochemistry and petrography of the Vulture and Etna most primitive products will provide new constraints on the mantle typology below the two volcanoes and its relationship with the geodynamical evolution of the central Mediterranean.

References

Bragagni et al., 2021, Geology

Carnevale et al. (2022). Geophys. Res. Lett.

Caracausi et al. (2015). Earth Planet. Sci Lett.

Correale et al., 2014. Lithos

Nakai et al., (1997). Earth Planet. Sci Lett.

Peccerillo, A. (2017). Advances in Volcanology. Springer, Cham.

How to cite: Italiano, L., Caracausi, A., Carnevale, G., Paternoster, M., and Rotolo, S. G.: First noble gases measurements in lherzolites from Mt Vulture volcano: new constraints on the mantle below Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4404, https://doi.org/10.5194/egusphere-egu23-4404, 2023.

EGU23-4569 | ECS | Posters on site | GMPV2.1

The origin of hydrous amphibole in the subcontinental lithospheric mantle beneath the Southern Alps of New Zealand 

Nadine Cooper, James Scott, Marco Brenna, Marshall Palmer, Malcolm Reid, Claudine Stirling, and Petrus le Roux

Peridotite xenoliths provide valuable insight into lithospheric mantle conditions, composition, and evolution. The origin of amphibole in the lithospheric mantle and whether amphibole melts to produce alkaline intraplate magmas is a highly debated topic. Large areas of the lithospheric mantle forming Earth’s youngest continent, Zealandia, have chemical compositions comparable to Archean mantle lithosphere but Re-Os isotope and bulk rock data indicate that lithosphere stabilisation occurred in the Mesozoic. Some areas of this refractory lithospheric mantle have been metasomatized, with one of the clearest occurrences being MARID-like veins in xenoliths in alkaline intraplate magmas in the Southern Alps of New Zealand. These xenoliths contain abundant veinlets composed of amphibole, phlogopite, clinopyroxene and apatite in rocks that have average olivine compositions exceeding Mg# 92 and spinel Cr# 70. The latter indicates that these peridotites have undergone >25% partial melting prior to metasomatism.

Using a combination of quantitative scanning electron beam methods, trace element and in-situ laser ablation inductively coupled mass spectrometry (LA-ICP-MS) analysis, and conventional 87Sr/86Sr isotope analysis by solution, we seek to establish the origin of hydrous phases in this mantle lithosphere. The benefit of inspecting formerly highly depleted peridotites is that the chemistry of the metasomatic agent, which is typically enriched in incompatible elements, is less diluted than in the cases where melts infiltrate fertile lithosphere. Although minor Fe-diffusion has occurred within the studied host rock, the bulk compositions of the veins are picro-basaltic. The mica separates, measured by solution chemistry, are today more radiogenic than the in-situ diopside and amphibole analyses, however, we find that the age-corrected ~25 Ma, 87Sr/86Sr initials fall in a tight cluster of very depleted mantle-like ratios from 0.7027 to 0.7056. Although the fluids appear to have sub-alkaline bulk compositions, the amphibole trace elements are enriched in HFSE and lack depleted Nb components.

The data suggests that these basaltic veins are not arc-related and do not derive from melting of subducted sediment, but also have no direct genetic link to the host alkaline melts. If this latter interpretation is correct, then the injection of hydrous veins was not part of a continuous process that resulted in alkaline magmatism, although they may have been subsequently melted to give rise to alkaline magmas with depleted mantle-like isotopic characters. 

How to cite: Cooper, N., Scott, J., Brenna, M., Palmer, M., Reid, M., Stirling, C., and le Roux, P.: The origin of hydrous amphibole in the subcontinental lithospheric mantle beneath the Southern Alps of New Zealand, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4569, https://doi.org/10.5194/egusphere-egu23-4569, 2023.

EGU23-4686 | ECS | Posters on site | GMPV2.1

Evolution of the African Mantle Domain and its enriched signal: perspective from pre-200 Ma ophiolites 

Piero Azevedo Berquo de Sampaio, Zheng-Xiang Li, Luc Serge Doucet, and Hamed Gamaleldien

Earth’s mantle is highly heterogeneous, with mantle-derived rocks sampling depleted and enriched domains both in intraplate settings and along spreading ridges. The most notorious isotopic anomaly is the DUPAL anomaly, where an overall strong recycled isotopic signature occurs. Studies on Tethyan and Paleo-Tethyan ophiolites have shown the persistence of “DUPAL signature” in those oceans, which paleogeographic reconstructions place on approximately the same position as the present-day Indian Ocean and thus argue for a long-lived “DUPAL signature” in the mantle. The origin of the DUPAL anomaly is controversial, with many studies pointing to it being a primordial feature. More recently, however, it has been shown that plume products in the African Mantle Domain (AMD), of which the DUPAL anomaly region is a part of, generally bear a more enriched signal than plume-related rocks in the Pacific Mantle Domain. This observation has been hypothesized to be related to the formation of the Pangea supercontinent above the present-day AMD, and therefore offering a geodynamic scenario capable of explaining the origin of the enriched isotopic signature of the AMD. However, present-day ocean crust record is limited in time, extending to 200 Ma at maximum, younger than the formation of Pangea at ca. 320 Ma. To investigate the oceanic record of mantle enrichment further back in time and test the influence of supercontinent cycle on the composition of the AMD, it is necessary to utilise preserved oceanic terranes in orogenic belts. In this study we compiled isotopic data from preserved oceanic terranes related both to the formation of the AMD, starting from the assembly of Gondwana till the duration of Pangea, including that of the Mozambique, Adamastor, Goias-Pharusian, Iapetus, Rheic, Qilian-Shangdan, Paleo-Tethys, Meso-Tethys and Neo-Tethys paleo-oceans. Neodymium isotopic data is the most widely available for these ophiolites. The Nd isotopic data indicates a progressively more depleted signal before Gondwana formation until it reaches a maximum and stays relatively stable until shortly after Pangea break-up, where noticeable decrease in depletion occurs. Lead isotopic data is less readily available, existing data nevertheless allow to observe an increase in Th/U ratio during Gondwana formation. Taken together, these observations indicate an increase in recycled continental components in the mantle source of the AMD ophiolites. We envisage this to be evidence for mantle enrichment during the formation of Gondwana and Pangea within the AMD. New isotopic analyses are still needed to paint a clearer picture of the interplay between the supercontinent cycle and mantle geochemistry.

How to cite: Azevedo Berquo de Sampaio, P., Li, Z.-X., Doucet, L. S., and Gamaleldien, H.: Evolution of the African Mantle Domain and its enriched signal: perspective from pre-200 Ma ophiolites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4686, https://doi.org/10.5194/egusphere-egu23-4686, 2023.

EGU23-4995 | ECS | Posters on site | GMPV2.1

The composition and origin of sulfides in peridotitic xenoliths from Ruddon’s Point (Fife, Scotland) 

Hubert Mazurek, Magdalena Matusiak-Małek, Hannah S.R. Hughes, and Brian J.G. Upton

Permian mafic volcanic rocks occurring in southern terrains of Scotland (United Kingdom) are rich in peridotitic xenoliths providing insight into the composition of the Subcontinental Lithospheric Mantle (SCLM) beneath this area. Peridotites from the Ruddon’s Point (Fife) xenolith suite form four textural groups: (1) protogranular and (2) porphyroclastic lherzolites, (3) equigranular wehrlites and (4) lherzolites transitional between protogranular and equigranular peridotites. The SCLM beneath southern Scotland was affected by reaction with an alkaline melt resulting in clinopyroxene crystallization (wehrlitization) and decrease of Fo in olivine from primary (protogranular and porphyroclastic) lherzolites (Fo88.5-90.0) through transitional to equigranular (Fo80.0-85.0) peridotites (Matusiak-Małek et al., 2022).

The sulfides occurring in the peridotites form oval, elongated or irregular grains enclosed in pyroxenes and olivine, or interstitial between these phases. The abundance of sulfides  increases from the transitional lherzolites (mean = 0.009 vol.‰), through equigranular and porphyroclastic peridotites (0.026 and 0.029 vol.‰, respectively) to protogranular lherzolites (0.050 vol.‰). Sulfide minerals present in all textural groups are pentlandite (Pn) and chalcopyrite (Ccp). There is generally an absence of pyrrhotite (Po), but protogranular and “transitional” lherzolites contain minor amounts. Porphyroclastic lherzolites occasionally contain millerite (Mlr) and covellite (Cv). The sulfides from the equigranular and protogranular peridotites are more enriched in Cu-, and depleted in Ni-phases (Po0Pn71Ccp29 and Po4Pn68Ccp27, respectively) in comparison to sulfides from the porphyroclastic and transitional peridotites (Po0Pn80Ccp20 and Po6Pn83Ccp12, respectively). The Cu/(Cu+Fe) is homogenous in sulfides of all the textural types, whereas Ni/(Ni+Fe) in pentlandite is homogenous only in transitional and equigranular peridotites (0.64–0.65 and 0.55–0.59, respectively) in contrast to porphyroclastic and protogranular ones (0.54–0.68 and 0.52–0.64, respectively). The only significant difference in trace element composition of sulfides appears in the concentrations of Co and Zn which  are  4894 ppm and 2214 ppm, respectively, in the protogranular peridotites, compared to 30090 ppm and 1391 ppm, respectively, in the transitional peridotites.

The more primitive protogranular and porphyroclastic lherzolites  are characterized by the highest sulfide abundances in comparison to the sulfides from melt-metasomatized equigranular wehrlites, with no significant differences  in sulfide mineral and chemical (major and trace elements) composition between groups. Thus, activity of the alkaline silicate melts responsible for wehrlitization of the primary lherzolites seems not to influence the sulfide enrichment in the SCLM beneath S Scotland. The presence of Cv and Mlr in lherzolites suggests alteration by hydrothermal, post-volcanic activity, affecting the xenoliths after the exhumation to the surface by basaltic lavas.

Matusiak-Małek, M., Kukuła, A., Matczuk, P., Puziewicz, J., Upton, B.J.G., Ntaflos, T., Aulbach, S., Grégoire, M., Hughes H.S.R. (2022). Evolution of upper mantle and lower crust beneath Southern Uplands and Midland Valley Terranes (S Scotland) as recorded by peridotitic and pyroxenitic xenoliths in alkaline mafic lavas. 4th EMAW TOULOUSE 2021 Book of Abstracts.

How to cite: Mazurek, H., Matusiak-Małek, M., Hughes, H. S. R., and Upton, B. J. G.: The composition and origin of sulfides in peridotitic xenoliths from Ruddon’s Point (Fife, Scotland), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4995, https://doi.org/10.5194/egusphere-egu23-4995, 2023.

EGU23-9276 | ECS | Orals | GMPV2.1

Unlocking the secrets of the Archean cratonic mantle through garnet Lu-Hf geochronology 

Kira Musiyachenko, Matthijs Smit, Maya Kopylova, and Andrey Korsakov

The sub-continental lithospheric mantle (SCLM) of Archean cratons represents the depleted and buoyant residue left behind after crust extraction. The history of the SCLM is notably complex in all cratons, often recording multiple episodes of melting and metasomatism. Garnet is a prime target for studying this history, as it provides thermobarometric constraints and hosts incompatible trace elements that can help identify melting and refertilization. Placing the rich geological record of mantle garnet in time is crucial for resolving cratonic evolution. Robust age constraints from garnet have nevertheless been difficult to obtain. Isolating enough analyte material for Lu-Hf or Sm-Nd chronometry is challenging for small xenoliths of highly depleted mantle rock. Age estimates are typically based on external or two-point isochrons with limited statistical robustness and geological interpretability. Moreover, chronometer systematics are principally not well constrained for the conditions and processes of the mantle. The question of which assemblages and chemical features of the Archean SCLM are actually of the Archean age is often left unanswered. To address this, we used ultralow-blank Lu-Hf chronometry, in concert with trace element analysis, on a targeted analysis of texturally and compositionally different mantle xenoliths from three Archean cratons (Slave, Kaapvaal, and Siberian Cratons).

The samples analyzed in this study represent a variety of garnet-bearing lithologies: clinopyroxene-rich fertile lherzolite, harzburgite (both granular and sheared), and orthopyroxenite with pyrope in exsolution lamellae. These samples were chosen, as they capture various stages of mantle evolution, from initial melting and subsolidus equilibration to shearing and metasomatic re-equilibration. We were able to obtain multi-point internal Lu-Hf isochrons for all lithologies, including those with extremely depleted compositions. The Lu-Hf ages span the history of the SCLM, from the Mesoarchean to the ages of kimberlite eruption. The oldest ages were obtained from lithologies depleted in Ca and clinopyroxene, i.e., exsolved orthopyroxenites and harzburgites from the Kaapvaal and Siberian Cratons. Lherzolites provided younger ages corresponding to metasomatic events, some of which could be linked to synchronous magmatic episodes in the overlying crust.

The data show that compositional and geochronological signatures in garnet can be retained on billion-year time scales. Static and dynamic recrystallization, and metasomatism – rather than temperature alone – control these signatures in garnet. The exsolution of pyrope in Ca-depleted Kaapvaal and Siberian orthopyroxenites is now confirmed to have occurred in the Archean. The geochemistry and petrology of these particular samples thus can constrain the P-T evolution that led to the development of the early continents.

How to cite: Musiyachenko, K., Smit, M., Kopylova, M., and Korsakov, A.: Unlocking the secrets of the Archean cratonic mantle through garnet Lu-Hf geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9276, https://doi.org/10.5194/egusphere-egu23-9276, 2023.

EGU23-10026 | Posters on site | GMPV2.1

Geochemical characteristics of mafic rocks from the Edessa ophiolite (North Greece): Implications for their petrogenesis 

Aikaterini Rogkala, Petros Petrounias, Petros Koutsovitis, Panagiota P. Giannakopoulou, Panagiotis Pomonis, and Konstantin Hatzipanagiotou

The Edessa ophiolite complex represents remnants of oceanic lithosphere which was thrust out of one or more ocean basins during Upper Jurassic to Lower Cretaceous time. Petrographic, geological and geochemical evidences indicate that this ophiolite complex consists of both mantle and crustal suites. It includes lherzolites, serpentinised harzburgites with high degree of serpentinisation, diorites, gabbros, diabase dolerites and basalts. We present here new data on mineral compositions and geochemistry in mafic rocks. The basalt displays N-MORB composition, having enhanced TiO2 (1.9-2.4 wt.%) and flat REE patterns, whereas the gabbros show E-MORB affinities, having moderate to high Ti content (TiO2 = 1.1-1.2 wt.%) with strong LREE-HREE fractionations. Such geochemical enrichment from N-MORB to E-MORB composition indicates mixing of melts derived from a depleted mantle and fertile mantle source at the spreading centre. On the other hand, diorites and partially diabase dolerites display SSZ-type composition with low Ti content (TiO2 = 0.1-0.7 wt.%) and depleted LREE pattern with respect to HREE. They also display high Ba/Zr, Ba/Nb and Ba/Th ratios relative to primitive mantle, which strongly represents the melt composition generated by partial melting of depleted lithospheric mantle wedge influenced by hydrous fluids derived from subducting oceanic lithosphere in a forearc setting. Based on these geochemical evidence, we suggest that mid ocean ridge (MOR) type mafic rocks (basalts and gabbros) from the Edessa ophiolite represent the section of older oceanic crust which was generated during the opening of the Axios Ocean. Conversely, the diorites and diabase dolerites represent the younger oceanic crust which was formed at the forearc region by partial melting of the depleted mantle wedge modified by hydrous fluids released from the subducting oceanic slab.

How to cite: Rogkala, A., Petrounias, P., Koutsovitis, P., Giannakopoulou, P. P., Pomonis, P., and Hatzipanagiotou, K.: Geochemical characteristics of mafic rocks from the Edessa ophiolite (North Greece): Implications for their petrogenesis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10026, https://doi.org/10.5194/egusphere-egu23-10026, 2023.

EGU23-10058 | Posters on site | GMPV2.1

A monazite- and REE-rich apatite-bearing mantle xenolith from Pleiku, central Vietnam 

Christoph Hauzenberger, Jürgen Konzett, Bastian Joachim-Mrosko, and Hoang Nguyen

Primitive mantle rocks usually contain rare earth elements (REE) in very low concentrations. Here we report an occurrence of monazite associated with REE-rich apatites in a carbonate-bearing wehrlite xenolith from Pleiku, central Vietnam. The sampled xenolith displays an equigranular matrix of rounded olivine grains. Texturally primary orthopyroxene, clinopyroxene and spinel are notably absent. Scattered within the olivine matrix two types of domains are present: domain-I contains numerous blocky clinopyroxene grains within a matrix of quenched silicate melt and is associated with a second generation of olivine, small euhedral spinel and rare grains of carbonates. Both apatite and monazite may be present. Domain-II typically contains abundant irregularly shaped patches of carbonate associated with quenched silicate melt, secondary olivine, spinel, and clinopyroxene. No phosphate phases are observed within type-II domains. Monazite occurs in different generations: monazite I is found as very small rounded to elongate grains included in primary olivine, partly crosscut by fine melt veinlets, monazite II as large grains up to 300 x 200 µm in size with embayed grain boundaries and monazite III as very small euhedral and needle-like crystals in silicate melt pools. For apatite two textural types occur: apatite I forms lath-shaped to rounded crystals up to 200 x 50 µm in size, apatite II is present within silicate melt pools of type-I domains where it forms euhedral needle-like to equant grains. Some of the apatite II crystals may have cores of monazite III. Monazites show compositional variation mainly with respect to ∑REE2O3 (63-69 wt%) and ThO2 (1.1-5.3 wt%) and only minor variations in P2O5 (29-32 wt%) SiO2 (<0.05-0.4 wt%) and CaO (0.2-0.4 wt%) Apatites are characterized by strongly variable and high REE2O3 and SiO2 contents (4-27 wt% ∑REE2O3,0.6-6.8 wt% SiO2) as well as with significant Na2O (0.3-1.5 wt%), FeO (0.1-1.8 wt%), MgO (0.2-0.6 wt%) and SrO (0.2-0.9 wt%) contents. F and Cl contents are in the range 1.9-3.0 wt% and 0.2-0.8 wt%, respectively. Based on textural evidence and chemical composition of the metasomatized mineral phases an initial stage of metasomatism is proposed which was triggered by a P-REE-CO2-rich agent with low aH2O resulting in the co-precipitation of carbonates as patches and along micro-veins and of phosphates in a peridotite assemblage. A subsequent second stage is characterized by pervasive infiltration of an alkali-rich basaltic melt into the carbonate + phosphate-bearing assemblage. The presence of monazite prior to silicate melt infiltration is indicated by narrow melt veins crosscutting monazite I grains. Reactions of the silicate melt with the pre-existing phases led to the formation of domains-I and -II and changed the composition of the infiltrating melt towards phonolitic-trachytic composition. The second stage led to partial breakdown and recrystallization of monazite and apatite.

How to cite: Hauzenberger, C., Konzett, J., Joachim-Mrosko, B., and Nguyen, H.: A monazite- and REE-rich apatite-bearing mantle xenolith from Pleiku, central Vietnam, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10058, https://doi.org/10.5194/egusphere-egu23-10058, 2023.

EGU23-12712 | ECS | Orals | GMPV2.1

Peridotite xenoliths from the Udachnaya-East kimberlite: windows onto the evolution of the Siberian sub-cratonic lithospheric mantle 

Federico Casetta, Igor Ashchepkov, Luca Faccincani, Rainer Abart, and Theodoros Ntaflos

Peridotite xenoliths from kimberlites are useful tools for exploring the architecture and composition of the thick sub-cratonic lithosphere, and thus understanding the long-term evolution of the Earth’s mantle. However, the continuous infiltration of kimberlite-related melts and fluids prior to - and during - the transport of mantle-derived fragments towards the surface makes it difficult to extract information about the original texture and chemistry of the mantle rocks and the deep-seated metasomatic processes.

In this study, fresh spinel- to garnet-bearing peridotite xenoliths from Udachnaya-East were studied to unveil the nature and composition of the lithospheric mantle beneath the Siberian craton. The studied samples have mostly harzburgitic to dunitic composition, even though lherzolites and rare wehrlites are also found. Occasionally, harzburgites are orthopyroxene-rich (up to 40 vol.%) or garnet-rich (up to 30 vol.%). The texture of the peridotites is extremely variable, ranging from protogranular to highly recrystallized and/or sheared. In spinel-bearing rocks, primary olivine is Mg- and Ni-rich (Fo90-93; NiO = 0.34-0.46 wt%), orthopyroxene has Mg# of 92-94 and Al2O3 in the range of 0.3-3.0 wt%, while clinopyroxene is Mg-rich (Mg# 94-96), with Al2O3 comprised between 1.0 and 3.5 wt%. In garnet-bearing peridotites, olivine ranges from Mg- and Ni-rich (Fo92; NiO = 0.45 wt%) to Fe-rich and Ni-poor (Fo87; NiO = 0.25 wt%), while pyroxenes have Mg# from 93 to 87-88 and comparatively low Al2O3 contents (orthopyroxene: 0.5-1.1 wt%; clinopyroxene: 0.8-2.2 wt%). High-precision electron microprobe analyses complemented by thermo- and oxy-barometric models were used to reconstruct the thermo-chemical log of the Siberian sub-cratonic mantle, in comparison to what proposed by Liu et al. (2022). Textural-compositional studies of the reaction zones enabled to discriminate the secondary-formed minerals with composition ascribable to the liquid line of descent of kimberlite-related melts at Udachnaya (Casetta et al. 2023) from those formed during melt/fluid-rock reactions taking place in the mantle before xenoliths’ entrainment by the host kimberlites. Altogether, our results enable to trace the P-T-X evolution experienced by the Siberian mantle, opening a window onto the comprehension of the interactions between kimberlitic-related fluid/melts and the sub-cratonic lithosphere.

 

Casetta, F., Asenbaum, R., Ashchepkov, I., Abart, R., & Ntaflos, T. (2023). Mantle-Derived Cargo vs Liquid Line of Descent: Reconstructing the P–T–fO2–X Path of the Udachnaya–East Kimberlite Melts during Ascent in the Siberian Sub-Cratonic Lithosphere. Journal of Petrology, 64(1), egac122.

 Liu, Z., Ionov, D. A., Nimis, P., Xu, Y., He, P., & Golovin, A. V. (2022). Thermal and compositional anomalies in a detailed xenolith-based lithospheric mantle profile of the Siberian craton and the origin of seismic midlithosphere discontinuities. Geology.

How to cite: Casetta, F., Ashchepkov, I., Faccincani, L., Abart, R., and Ntaflos, T.: Peridotite xenoliths from the Udachnaya-East kimberlite: windows onto the evolution of the Siberian sub-cratonic lithospheric mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12712, https://doi.org/10.5194/egusphere-egu23-12712, 2023.

EGU23-13627 | ECS | Posters on site | GMPV2.1

The impact of melt impregnation on the genesis of mantle peridotites from Puke Massif (Mirdita Ophiolite, Albania) revealed by geochemical data 

Jakub Mikrut, Magdalena Matusiak-Małek, Michel Gregoire, Georges Ceuleneer, Kujtim Onuzi, and Jacek Puziewicz

The Mirdita Ophiolite (N Albania) consists of two meridional belts of different geochemical affinities: supra-subduction zone for the Eastern belt and mid-ocean ridge (MOR) for the western belt. Puke Massif described in this study is a mantle dome belonging to the MOR belt.

Structurally, the Puka Massif is interpreted as an Oceanic Core Complex formed of harzburgites cross-cut by dunitic channels grading to mylonitized plagioclase and amphibole bearing lherzolites with minor dunites and chromitites at the top of the section. The massif experienced an intense magmatic activity evidenced by gabbroic and pyroxenitic dykes. Field and petrographic evidences revealed that plagioclase, clinopyroxene and amphibole in lherzolitic mylonites crystallized from impregnating melts (Nicolas et al. 1999, 2017). Scientific question behind our study is whether this conclusion is confirmed by geochemical data.

Clinopyroxene from magmatic veins cross-cutting mylonites, has trace elements (TE) composition identical to that from the host peridotite. In general, 3 types of TE patterns can be identified in the veins and mylonites: 1. Strongly depleted (Yb=0.3-0.6x primitive mantle, PM, McDonough & Sun 1995); 2. Intermediate (Yb=1.1-4xPM); 3. Enriched (Yb=5-11xPM). The group 1 comprises only pyroxenites. Two relatively undeformed harzburgites occurring in the lowermost section of the mantle dome contain TE-poor clinopyroxene. One, which is amphibole-bearing, exhibits TE pattern resembling that in group 1, while the other one shows even more depleted signature, with Yb=0.8-1.3xPM and La <0.001xPM. Intrusive rocks from groups 2 and 3 are widespread in the whole massif while the occurrences of the depleted group are restricted to the lowermost sections. Rocks from different groups may occur within a single outcrop.

The TiO2 content in clinopyroxene mimics the TE-based division of the rocks. Clinopyroxene in the group 1 and harzburgites has TiO2<0.1 wt.%, whereas that from group 2 and 3 has 0.1<TiO2<0.5 wt.% and TiO2>0.5 wt.%, respectively. Similar relationships are observed in the composition of spinel, which has TiO2<0.1 wt.% in group 1 rocks, 0.1 - 0.25 wt.% in group 2 and between 0.1 and 2.0 wt.% in the group 3 rocks.

As magmatic rocks and deformed peridotites share common clinopyroxene TE trends, as well as similar Ti variations in clinopyroxene and spinel, geochemical data support impregnating origin of mylonites. Impregnating melts, differing in enrichment level, were active within whole massif; only the most depleted seem to be restricted to some of its parts. Only internal or easternmost harzburgites could have escape magmatic impregnations; these samples are relatively undeformed and have depleted melting-like TE trends. These findings are in agreement with melt impregnation origin of mylonites. Presence of the depleted lithologies supports primarily harzburgitic origin of the massif, later followed by mylonitization of some of its part. 

This study was financed as a project within program “Diamond Grant” (DI 024748).

How to cite: Mikrut, J., Matusiak-Małek, M., Gregoire, M., Ceuleneer, G., Onuzi, K., and Puziewicz, J.: The impact of melt impregnation on the genesis of mantle peridotites from Puke Massif (Mirdita Ophiolite, Albania) revealed by geochemical data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13627, https://doi.org/10.5194/egusphere-egu23-13627, 2023.

EGU23-14795 | ECS | Posters on site | GMPV2.1

The lithospheric mantle beneath Devès volcanic field – case study of mantle xenoliths from Mt. Briançon (Massif Central, France) 

Małgorzata Ziobro-Mikrut, Jacek Puziewicz, Sonja Aulbach, and Theodoros Ntaflos

The 3.5-0.5 Ma Devès volcanic field is located in the “southern” mantle domain of the French Massif Central (MC), which originated by partial melting, likely followed by refertilization by melts from the upwelling asthenosphere [1, 2]. However, the extent of melting versus degree of refertilization remains unclear. In order to obtain new insights into this fundamental question, we studied a large mantle xenolith population (n – 21) from a cinder cone in the NW of Devès, the Mt. Briançon nepheline basanite. Extensive use of EMPA and LA-ICP-MS allowed us to gather a comprehensive and representative dataset. Here, we present preliminary interpretations. Ongoing EBSD analyses will provide further data to confirm or correct our hypothesis.

The lithospheric mantle (LM) beneath the Devès is heterogeneous. It contains lherzolite with clinopyroxene (cpx) exhibiting REE patterns with relatively flat Lu-Eu and variable LREE-depletion. The coexisting spinel (spl) is highly aluminous (Cr# 0.09-0.15). By analogy with prior work [2], we suggest that cpx and spl were added to the rock by a MORB-type melt [2]. Those lherzolites probably represent refertilized LM similar to the Lherz massif [3], which obscures the original degree of depletion.

A distinct mantle region below the Devès is represented by harzburgites and cpx-poor lherzolites containing cpx with REE patterns that show moderately increasing Lu-Sm and steeply increasing towards La. The coexisting spl has medium to high Cr# (0.17-0.28). We suggest that this lithology was not refertilized by MORB-like melts, but records some other metasomatic event(s).

A single harzburgite xenolith contains LREE-enriched cpx similar to those described above, but of significantly lower element abundances. This harzburgite is the most magnesian in the entire suite, with olivine Fo ~91.2% and Mg# in pyroxenes ~0.92 (vs Fo 88.5-90.4% and Mg# 0.88-0.91 for other peridotites). Pyroxenes have the lowest Al, Fe, Ti, Na contents in the whole suite and spinel is the most chromian (Cr# ~0.43). This rock resembles harzburgites from the northern domain of the MC, interpreted as a relatively depleted residue of partial melting [4].

This study was funded by Polish National Science Centre to MZM (UMO-2018/29/N/ST10/00259).

References:

[1] Lenoir et al. (2000). EPSL 181, 359-375.

[2] Puziewicz et al. (2020). Lithos 362–363, 105467.

[3] Le Roux et al. (2007). EPSL 259, 599–612.

[4] Downes et al. (2003). Chem Geol 200, 71–87.

How to cite: Ziobro-Mikrut, M., Puziewicz, J., Aulbach, S., and Ntaflos, T.: The lithospheric mantle beneath Devès volcanic field – case study of mantle xenoliths from Mt. Briançon (Massif Central, France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14795, https://doi.org/10.5194/egusphere-egu23-14795, 2023.

EGU23-16528 | Posters on site | GMPV2.1

Megacryst suites in kimberlite 

Daniel Schulze

Large, single crystals (> 1cm) are a familiar component of mantle xenolith suites of many kimberlites.  Confusion between different suites exists in the literature, however, which affects petrogenetic models, and some clarification is warranted.  Megacrysts of the Cr-poor suite[1] are most common.  Cr-poor silicates (garnet, clinopyroxene, orthopyroxene, olivine) are characterized by lower Mg/(Mg+Fe) and Cr2O3 and higher TiO2 values than typical mantle peridotite minerals.  Strong geochemical trends in most occurrences of Cr-poor megacryst suites (e.g., concomitant decrease in Mg/(Mg+Fe) and Cr2O3) are interpreted by most authors as the result of fractional crystallization of a kimberlite, or kimberlite-like, magma.   

The Cr-rich megacryst suite, comprising garnet, clinopyroxene, orthopyroxene and olivine, but not ilmenite, was described from the Sloan/Nix kimberlites in northern Colorado[1].  Constituent minerals, all four of which are essential to the definition of the suite, are characterized, in part, by high and restricted values of Mg/(Mg+Fe) and wt% Cr2O3 (e.g., 0.791 to 0.837 and 6.1 to 13.0, respectively, in garnet [2]).  Elsewhere, large crystals with Mg/(Mg+Fe) and Cr2O3 values higher than Cr-poor suite minerals do occur, but none correspond to the Sloan-Nix Cr-rich suite in paragenesis, size and/or composition[2].  For example, almost no garnet megacrysts described as “Cr-rich” or “high-Cr” from other localities (e.g., refs 3-6) contain >6 wt% Cr2O3 and even garnets with <2 wt% Cr2O3 are termed “Cr-rich” or “high-Cr”.  Most, or all, of these so-called “Cr-rich garnet megacrysts” are simply xenocrysts from coarse-grained peridotite. 

The “Granny Smith” suite, first described from Kimberley and Jagersfontein [7], is dominated by Cr-clinopyroxene associated with phlogopite (and ilmenite at Kimberley), with uncommon olivine or rutile.  Garnet and orthopyroxene do not occur in this suite, which is neither equivalent to nor a subset of the Cr-rich megacryst suite.  Other suites dominated by Cr-clinopyroxene, also not shown to coexist with garnet and orthopyroxene, have been described from Orapa and Bobbejaan [6] and Grib [8], though analogies have been drawn with the Cr-rich megacryst suite despite compositional and paragenetic differences.  A similar megacrystalline assemblage (Cr-cpx, ilmenite, phlogopite, olivine) has been described from Attawapiskat [9] and at Balmoral megacrysts of Cr-cpx occur with ilmenite, Nb-Cr rutile and zircon [10].

All of these suites of Cr-cpx +/- ilmenite, rutile, phlogopite, olivine, zircon (lacking garnet/opx), though varied, have more in common with each other than with the Cr-rich megacryst suite.  All might be best termed “Granny Smith”, and may have common origins.  The only feature they share with the Sloan-Nix Cr-rich megacryst suite is the presence of large chromian clinopyroxene.  Use of such populations as equivalents of the Sloan-Nix Cr-rich megacryst suite in mantle petrogenetic schemes can lead to faulty conclusions. 

References:  1) Eggler et al. (1979) The Mantle Sample, 2) Schulze (2022) Goldschmidt Conf. Abstr., 3) Hunter and Taylor (1984) Am. Min., 4) Kopylova et al. (2009) Lithos, 5) Bussweiller et al. (2018) Min. Pet., 6) Nkere et al. (2021) Lithos, 7) Boyd et al. (1984) GCA, 8) Kargin et al. (2017) Lithos, 9) Hetman (1996) MSc., 10) Schulze, unpub. data. 

How to cite: Schulze, D.: Megacryst suites in kimberlite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16528, https://doi.org/10.5194/egusphere-egu23-16528, 2023.

Integrating petrography and mineral chemistry data with the determination of volatiles concentration and isotopic fingerprint in fluid inclusions (FI) in ultramafic xenoliths is a novel approach which provides crucial information on the nature and evolution of the lithospheric mantle, together with important insight into how and where volatiles are stored and/or migrate through the lithosphere.

In this work, we investigated a new suite of ultramafic peridotite xenoliths from the Massif d’Ambre by integrating petrography, mineral and glass chemistry and the concentrations of volatiles [CO2 and noble gases (He, Ne and Ar)] in fluid inclusions (FI) hosted in olivine (Ol), orthopyroxene (Opx) and clinopyroxene (Cpx). The Massif d’Ambre is a Cenozoic stratovolcano located in northern Madagascar originated upon intense volcanic activity from ~12 to ~0.85 Ma, and the area is characterized by the widespread occurrence of mantle xenoliths, mostly, but not restricted to, spinel lherzolites and subordinately pyroxenites, which are hosted in mafic volcanic rocks. The new suite comprises 18 lherzolites, 11 harzburgites, 2 dunites, 3 wehrlites and 1 Ol-clinopyroxenite. Based on their petrographic and textural features, the suite was divided into five distinct groups: group 1A (protogranular to porphyroclastic textures), group 1B (large and porphyroclastic olivines), group 2 (infiltrated dunites and wehrlites), group 3 (cumulate-textured wehrlites) and group 4 (Ol-clinopyroxenite). Xenoliths are modally and compositionally heterogeneous and a clear separation can be observed between groups 1A-1B and groups 2-3, as testified by the large forsterite range of olivine (Fo88.4 – 93.2 vs Fo78.7 – 89.1, respectively), the Mg# of orthopyroxene (89.5 – 93.2 vs 82.7 – 87.3, respectively) and clinopyroxene (90.9 – 95.2 vs 81.4 – 89.9, respectively). This systematics corroborates the distinct origin of the groups, with xenoliths belonging to 1A-1B having the most refractory character and reflecting high extents (up to 30%) of melt extraction, while groups 3-4 xenoliths reflecting less depleted or re-fertilized mantle portions. Based on glass analyses, we propose that a carbonatitic or carbonated alkaline agent may have interacted with some portion of the source mantle, in agreement with Coltorti et al. (2000). The noble gases in FI hosted in Ol, Opx and Cpx exhibit 3He/4He ratio corrected for air contamination (Rc/Ra values) ranging from 5.90 Ra to 7.05 Ra, which is below the typical MORB-like upper-mantle value (8 ± 1 Ra). Furthermore, the great majority of xenoliths exhibits 4He/40Ar* ratios between ca. 0.2 to 0.8.

The major element distribution in mineral phases together with the systematic variations in FI composition will be used to place constraints on the origin and evolution (in terms of melting and metasomatism) of this portion of the mantle below the Massif d’Ambre and will be exploited to obtain a possible timeline for the petrological events that have characterized this lithospheric mantle portion.

Coltorti M., Beccaluva L., Bonadiman C., Salvini L. & Siena F. 2000. Glasses in mantle xenoliths as geochemical indicators of metasomatic agents. Earth Planet Sc. Lett., 183, 303–320.

Keywords: mantle xenoliths; lithospheric mantle; metasomatism; Massif d’Ambre

How to cite: Faccini, B., Faccincani, L., Rizzo, A. L., Casetta, F., and Coltorti, M.: Combining volatiles measurements in fluid inclusions with petrology of ultramafic xenoliths from the Massif d'Ambre: unravelling the nature and evolution of the northern Madagascar Sub-Continental Lithospheric Mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16798, https://doi.org/10.5194/egusphere-egu23-16798, 2023.

EGU23-17587 | Orals | GMPV2.1

Crustal rhyolite melts at mantle depths 

Luigi Dallai, Gianluca Bianchini, Riccardo Avanzinelli, Mario Gaeta, Etienne Deloule, Claudio Natali, Andrea Cavallo, and Sandro Conticelli

Melts with rhyolite compositions originate from partial melting of crustal rocks or extensive differentiation of basaltic melts, at temperatures in the range of 800 °C. Accordingly, they are confined to the shallow continental crust. Nevertheless, experimental studies have demonstrated that dacite-rhyolite melts can be generated at higher temperature (> 1000°c) and pressure (>2 GPa), by partial melting of continental crustal lithotypes, but direct evidence for their occurrence has never been found. This implies that rhyolite melts may be produced at mantle conditions either by subduction of sedimentary material or exhumation of subducted continental crust.

Ephemeral rhyolite melt inclusions were found preserved in peridotite xenoliths from Tallante (Betic Cordillera, southern Spain) that are remnants of a supra-subduction mantle wedge. Here, the interaction of silica-rich melts with peridotite generated hybrid mantle domains, characterized by the occurrence of millimetre-sizes felsic veins with crust-like Sr-Nd-Pb-O- isotope compositions. The “Tallante” composite xenoliths were found among a wide population of peridotitic xenoliths, and display extreme compositional and isotopic heterogeneities both within the ambient peridotite and within the felsic veins. The latter consist of orthopyroxene, plagioclase, and quartz, and they are separated from the surrounding peridotite by an orthopyroxene-rich reaction zone. In their mineral phases, rhyolite glass inclusions and interstitial films associated to quartz crystals were observed. Petrological evidence and thermodynamic modelling indicate that rhyolite melts were originated by partial melting of near an-hydrous garnet-bearing metapelites at temperatures above 1000 °C. Partial melting was likely triggered by near-isothermal decompression during rapid exhumation of previously subducted crustal slivers. The melts reacted with the ambient lithospheric mantle at lower temperature (900 °C) and produced orthopyroxene, followed by plagioclase, quartz, and phlogopite. On the basis of chemical characteristics, it is hypothesized that potassic (HK-calc-alkalic to shoshonitic) and  ultrapotassic magmas may originate from metasomatic mantle sources generated from the interaction of crustal rhyolitic melts with mantle peridotite.

How to cite: Dallai, L., Bianchini, G., Avanzinelli, R., Gaeta, M., Deloule, E., Natali, C., Cavallo, A., and Conticelli, S.: Crustal rhyolite melts at mantle depths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17587, https://doi.org/10.5194/egusphere-egu23-17587, 2023.

EGU23-3560 | PICO | GD2.2

Mineralogical and geochemical characteristics of lamproite minerals of the Murunsky massif. 

Igor Ashchepkov, Nikolai Vladykin, Irina Sotnikova, Nikolai Medvedev, Nikolai Karmanov, and Natalia Alymova

Minerals from leucite lamproites of the Murunsky alkaline massif (Vladykin, 2000; 2005; Vladykin, 2009) were analyzed by electron microscopy in the sections of 700 grains of minerals (IGM SB RAS) and LA ICP MS (IIC SB RAS) - 40 grains. Pyroxenes, amphiboles, various micas including varieties of the Ba type, leucites and nephelines, Ba and K feldspars, eudialyte, barite, stroztianite, ilmenites, Cr- spinelides, Ti magnetites, apatites, tourmaline, and various carbonates and sulfides: pyrrhotite, petlandite, chalcopyrite, murunite, smithsonite, galena.

 

Pyroxenes are divided into 3 groups from diopsides to augites and aegirines, revealing a continuous series of compositions according to MgO (Fig. 1). Amphiboles K-richterites and arfversonites, and Ca-Fe ackermanites. Complete ranges from phlogopites to biotites have been established among micas. The proportion of Ba micas is significant. In the diagram  genetic digram (Minchell, 1995 )(Fig. 2) falls into the field of ailikites or orangeites,  and lamproites. Leucites and nephelines occurs  friquiently. Numerous apatites are characterized by Ca-Sr substitution and noticeable F contents (to 3%). K-type eudialytes and a mineral close to priderite were found.

 

In the TRE diagrams (Fig.3), pyroxenes are characterized by La-enriched ~200-250 weakly inclined spectra of La/Ybn (2-3) that spread out in the HREE wing. Amphiboles of the K-Na-Ca are characterized show inclined spectra with Ho-Tm depression,  LILE peaks elevated Zr, Hf, Y and Ta-Nb minima. The more alkaline amphiboles are characterized by reduced REE concentrations, more  elevated Zr-Hf. Ultra-alkaline amphiboles (richterite and arfvedsonite) have higher REE contentswith characteristic U-shaped spectra, very high LILE contents high peaks of Sr, Zr, Hf. Phlogopites have oblique U-shaped spectra with a sharp peak Eu interference Ti. Very high LILE with a peak at Va, Sr, Y, Pb are typical.

Low REE and especially LREE with a peak of Eu are characteristic of leucites. U, Sr, Pb peaks are also characteristic, and HFSE vary. The REE spectra of K-Ba feldspars are similar to those of phlogopite. High peaks of LILE, Sr, Pb, Y are expressed on spiderdiagrams

Judging by the peculiarities of mineral trends, lamproites are the result of low degrees melting  under the influence of plume melts of a mantle deeply metasomatized by subduction processes. Pyroxenes are end–to-end minerals, at an early stage their compositions were controlled by fractionation of olivine and then saturated SiO2 silicates. Further fractionation led to enrichment with rare elements P, Sr, F. In amphiboles, the growth of REE was accompanied by the accumulation of Zr, Hf, while Nb, Ta were removed during the deposition of T-magnetite. Grant RBRF 19-05-00788.

How to cite: Ashchepkov, I., Vladykin, N., Sotnikova, I., Medvedev, N., Karmanov, N., and Alymova, N.: Mineralogical and geochemical characteristics of lamproite minerals of the Murunsky massif., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3560, https://doi.org/10.5194/egusphere-egu23-3560, 2023.

EGU23-3860 | PICO | GD2.2 | Highlight

Mineralogy and geochemistry of the kimberlite xenocrysts from the Anabar region, Yakutia, Russia 

Sergey Kostrovitsky, Igor Ashchepkov, Nikolai Medvedev, Nikolai Karmanov, and Natalia Alymova

Kimberlitic xenocrysts: garnets, pyroxenes, ilmenites, spinels from Anabar region were analyzed by EPMA and LAICPMS.

Reconstructed mantle sections of t Anabar region published (Ashchepkov et al., 2001; 2016; 2019; 2022 show in general, the relative rarity of sub-Ca pyropes  in lower part of the section and the frequency of wehrlite associations in the upper part. Pyroxenite -eclogite lens from 3 to 5 GPa is widely represented in most sections. Ilmenite trends are not long. In several pipes amphiboles from Cr-hornblendes to Cr-richterites were detected.

In the Anabar region (Khardakh and Staro-Rechensky fiedls) The REE patterns of  garnets are characterized by high variations in the spectra, with elevated LREE and HFSE minima, peaks of U, Pb, associated with subduction fluid flows. Pyroxenes are characterized by inclined REE spectra of La/Ybn ~15 to 20 and with varying HREE with subduction-related Ba, U, Pb peaks. But pyroxenes with plume related spectrums of with smooth spider diagrams (SD) are often found in pyroxenite lens.

Garnets from the Kuranakh field (Malokuonamskaya, Losi, Trudovaya, Universitetskaya etc) are divided into dunite-garburgite with low REE and LREE enrichment and wehrlite with convex REE maximum Gd, Eu and high concentrations of HREE often enriched in Th , U varying Ta-Nb and always low Zr-Hf.  Clinopyroxenes from the Malokuonamskaya pipe often have a local minimum of HREE and variations in the slope and enrichment of the REE spectra. On the CD, the peaks of Ba are varying, they show Ta, Nb enrichment and minima in Zr-Hf.

The garnets from the Universitetskaya pipe are mainly lherzolite-harzburgite with signs of subduction genesis (U peaks), and wide variations of HFSE sometime with Zr–Hf enrichment, due aqueous metasomatism. Clinopyroxenes are generally more diverse in REE spectra, Nb peaks with wide variations of Ba, Th-U and HFSE are common on CD

The Losi dike has a high content of perovskites, with highly enriched spectra with a slope with a decrease in highly charged and Pb and ilmenites with high and inclined REE spectra due to fractionation of proto-kimberlite (essentially carbonatite) melt. The eclogitic minerals with Eu anomalies and peaks of U, Ba and low HFSE are common.

In most mantle sections, ancient subduction sings are recorded in pyrope garnets, an partially adakite metasomatism in pyroxenes. Later they were modified by the action of plume carbonatite melts. The middle pyroxenite-eclogite lens originated as the boundary of the crust in ancient Archaic times. The upper wehrlitic part of the section arose during the melting of the pyroxene lens in the middle part and the migration of melts to the upper part. Protokimberlite metasomatism is not very pronounced. No signs of the supposed delamination of the lithosphere (Griffin et al, 2005) were found in the sections, which was also proved by Opx-Gar thermobarometry under the Duken field (Ashchepkov, 2003). The lower part of the section is depleted  so garnet and pyroxenes are rare and reflect low-temperature geotherm.

 

Grant RBRF 19-05-00788.

 

How to cite: Kostrovitsky, S., Ashchepkov, I., Medvedev, N., Karmanov, N., and Alymova, N.: Mineralogy and geochemistry of the kimberlite xenocrysts from the Anabar region, Yakutia, Russia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3860, https://doi.org/10.5194/egusphere-egu23-3860, 2023.

EGU23-6727 | PICO | GD2.2 | Highlight

Geochemical interaction between slab-derived melts and mantle at high pressure in subduction zones 

Nadia Malaspina, Giulio Borghini, Stefano Zanchetta, and Simone Tumiati

The fate of crust-derived melts at warm subduction zones and the transport mechanism of crustal components to the supra-subduction mantle is still matter of debate. Borgo outcrop of Monte Duria Area (Adula-Cima Lunga unit, Central Alps, Italy) is an excellent case study of melt-peridotite interaction occurred under a deformation regime at high pressure, that enabled the combination of porous and focused flow of eclogite-derived melts into garnet peridotites. Migmatised eclogites are in direct contact with retrogressed garnet peridotites and experienced a common high pressure (2.8 GPa - 750 °C) and post-peak (0.8–1.0 GPa - 850 °C) static equilibration. The contact is marked by a tremolitite layer, also occurring as boudins parallel to the garnet layering in the peridotites, derived from a garnet websterite precursor after the interaction between eclogitic melts and peridotites at high pressure. LREE concentrations of retrogressed websterites along a 120 m length profile starting from the eclogite-peridotite contact to the inner part of the peridotite, show a progressive enrichment coupled with a peculiar fractionation. Numerical modelling assuming the eclogitic leucosome as the starting percolating melt reproduces the REE enrichment and LREE-HREE fractionation observed in retrogressed websterites bulks within the first 30 m by two steps of melt-peridotite reaction: a high peridotite assimilation at eclogite-peridotite boundary, followed by reactive melt percolation within the peridotite assuming variable amounts of olivine assimilation and pyroxene + amphibole/phlogopite crystallisation. The numerical simulation aims to model the effect of interaction between crust-derived melts produced by partial melting of mafic slab component with suprasubduction mantle peridotites at sub-arc depths. The comparison between the REE composition of the retrogressed garnet websterites along the profile and the result of our model suggests that reactive melt infiltration at HP is a plausible mechanism to modify the REE budged of mantle peridotites that lie on top of the subducting crustal slab, which show peculiar LREE “spoon-like” fractionations. Moreover, the melt/peridotite interaction and the percolation of slab-derived melts into the overlying mantle may strongly modify the overall REE abundance and LREE/HREE fractionation (e.g., CeN/YbN) of the residual crustal melt within the first 30 m of slab/mantle interface.

How to cite: Malaspina, N., Borghini, G., Zanchetta, S., and Tumiati, S.: Geochemical interaction between slab-derived melts and mantle at high pressure in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6727, https://doi.org/10.5194/egusphere-egu23-6727, 2023.

EGU23-6901 | ECS | PICO | GD2.2 | Highlight

Three-dimensional Lithospheric Resistivity Structure and Thermal State of the North China Craton 

Baochun Li and Gaofeng Ye*

The North China Craton (NCC) has been affected by the subduction and roll-back of the Paleo-Pacific Plate in the Mesozoic. To study the thinning of the lithosphere and the melting of the NCC, a three-dimensional (3-D) resistivity model of the lithosphere is obtained from a magnetotelluric sounding (MT) deployed in the NCC (Figure 1). In addition, the cause of the low resistivity of the upper mantle of the NCC can be solved by the Nernst-Einstein Equation and the Arrhenius Equation which is used to establish the relationship between the resistivity and temperature. Moreover, the Hashin-Shtrikman (HS) boundary conditions limit the range of electrical conductivity of mixed minerals (Figure 2). Based on the 3D resistivity structure, the temperature and melt fraction model, the lithospheric resistivity of the north of 37.5°N in the Ordos Block (OB), the southern Taihang Uplift (THU) and the Luxi Uplift (LXU) are as low as 1 Ωm which the upper mantle temperature is in the range of 1400 - 1550 °C, and the melt fraction is 1-10% in the high-temperature regions. According to the resistivity model and the thermal state, the westward subduction and roll-back of the Paleo-Pacific Plate provided conditions for upper mantle melting in the LXU and the Bohai Bay Basin (BBB). It also made the Tanlu Fault Zone (TLFZ) and THU channels for the upwelling, and the front of the Paleo-Pacific Plate stagnant slab is blowing the THU. With the remote tectonic stress of the Paleo-Pacific Plate and the Indian Plate, anticlockwise rotation of the OB induced the low resistivity of grabens and rifts around the OB (Figure 3). Moreover, upper mantle volatiles (H2O and CO2) and slight carbonatite melts significantly lower the mantle melting temperature.

* This work was supported by National Natural Science Foundation of China (Grants 41974112 and 40434010) and project SINOPROBE on sub-project SINOPROBE-01.

Reference:

Dong, S..T. Li. (2009). SinoProbe: the exploration of the deep interior beneath the Chinese continent. Acta Geologica Sinica, 83(7), 895-909.

Hirschmann, M. M. (2010). Partial melt in the oceanic low velocity zone. Physics of the Earth and Planetary Interiors, 179(1), 60-71.

Zhao, G..M. Zhai. (2013). Lithotectonic elements of Precambrian basement in the North China Craton: Review and tectonic implications. Gondwana Research, 23(4), 1207-1240.

Figure 1 Simplified s tectonic map of the North China Craton (modified from Zhao and Zhai (2013)); Map of MT profiles and sites, in which blue dots represent MT stations in this study, supported by the “SINOPROBE” project (Dong and Li, 2009). TNCO: Trans-North China Orogen 

Figure 2 Schematic diagram of dynamic changes of water and carbon dioxide during heating and melting of upper mantle minerals. NAMs means nominally anhydrous minerals; the “Calculate” in the dashed box is the calculation category of this study; the criterion for determining the interconnection of melts was proposed by Hirschmann (2010).

Figure 3 Schematic diagram of the possible formation mechanisms of the North China Craton inferred from the crustal and upper mantle 3-D resistivity model derived from this research.

How to cite: Li, B. and Ye*, G.: Three-dimensional Lithospheric Resistivity Structure and Thermal State of the North China Craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6901, https://doi.org/10.5194/egusphere-egu23-6901, 2023.

EGU23-8651 | PICO | GD2.2

Ancient mantle metasomatism in West Ykukite field Northern Yakutia 

Denis Iudin, Igor Ashchepkov, Svetlana Babushkina, Oleg Oleinikov, and Nikolai Medvedev

 

 

 

In the subcratonic lithospheric mantle (SCLM) beneath Leningrad pipe (West Ukukit field), Yakutia garnet thermobarometry allows us to identify seven horizons (paleo subduction slab). Microprobe data for Cr-bearing amphiboles >500 grains from mantle xenoliths and concentrates reveal a broad range of compositions changing from Cr- pargasitic hornblendes to pargasites, edinites, kataforites, К-richterites with increasing pressure determined with new amphibole thermobarometer.  The low pressure (LP) Cr-hornblendes and pargasites compiles the high-temperature branch (90-60 mw/m2) from 3.5 GPa to Moho traced by basaltic cumulates. In the middle part of SCLM edinites mark 35 to 40 mw/m2 geotherms. In the middle part of SCLM edinites mark 35 to 40 mw/m2 geotherms. At high pressures kataforites also vary in thermal conditions. Richterites near the lithosphere base trace both low –and high temperature convective branches.

 Age samples of aillikites estimated by 40Ar/39Ar age using the method described in detail by A. Travin et al. [40]. Quartz ampoules with samples were irradiated in the Cd-coated channel of a reactor (BBP-K type) at the Tomsk Polytechnic Institute. The gradient of the neutron flux did not exceed 0.5% of the sample size. Step-heating experiments were carried out in a quartz reactor with an external heater. The blank for 40Ar (10 min at 1200°C) was not higher than 5×10–10 cm3. Ar was purified using Ti and ZrAl SAES getters. The isotopic composition of Ar was measured on a Micromass Noble Gas 5400 mass spectrometer (analyst Yudin D.S.). The results of the dating of the phlogopite grains and amphiboles occurred in the intergroup with the Phl are shown the (Figure 1). The phlogopie from the spinel lherzolite 2665 Ma corresponding to the final stge of the craton formation. Similar age was determined for the Phl from Udachnaya. The age of the intergrowth of the Amph-Phl from the sample Ol-151 is splitting. The high temperature part with the age 1368Ma may be reffered to the global activization of the plume and accretion magmatism activity found in many World regions [42] including Siberia. The more yanger plateo is close to the 380-400 Ma which is just corresponds to the Devonian plume magmatism? And the small plateau ~210 Ma refer to Triassic The . As well in the sample Ol-112 the older one 370 Ma plateo just give Devonian age. And one of the younger 160 Ma corresponds to the Jurassic stage of kimberlite volcanism.

Presence of the Phl with the 2.6 Ga referring to the major event of the crust generaion corresponding to the beginning of mertasomatic H2O bearing metasomatic processes recorded in the mantle xenoliths in the World proves the common model of the appearance of water in the mantle  at the last stages of the continental growth, The other two peaks  400 -380 Ma and 160 Ma may be referred to the plume kimberlite magmatism and even to the protokimberlite stage (latest one). 

RBRF grant 19-05-00788

How to cite: Iudin, D., Ashchepkov, I., Babushkina, S., Oleinikov, O., and Medvedev, N.: Ancient mantle metasomatism in West Ykukite field Northern Yakutia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8651, https://doi.org/10.5194/egusphere-egu23-8651, 2023.

The small plutons of anorthosite and associated gabbronorite exposed near Barabar hills form a component of Chotanagpur granite gneiss complex (CGGC) in eastern India. Plagioclase (>90 vol %) make up the majority of anorthosite rock with minor mafic minerals (amphibole, mica), while orthopyroxene (>40 vol %), plagioclase (40-50 vol %) and clinopyroxene (>20 vol %) make up the associated gabbronorite. These are cumulate rocks with anorthosite and gabbronorite showing adcumulate and mesocumulate textures, respectively. Compositionally, plagioclase ranges from anorthite to labradorite (An60-96) in anorthosite and from oligoclase to bytownite (An50-70) in gabbronorite. In gabbronorite, the clinopyroxene composition ranges from diopside to augite (En36-43 Fs12-15 Wo43-47), and the orthopyroxenes are hypersthene (Wo39-40 En46-50 Fe10–21).

Anorthosite show enrichment of LILE (Rb, Ba, Sr, Th, Pb) with respect to the HFSE (Zr, Ti, Nb and display enrichment in LREE ((La/Yb) N = 2.78-15.29) with positive Eu anomaly (Eu/Eu* = 1.29-3.45) and variable MREE. A flat to depleted trend for HREE ((Sm/Yb) N = 1.02-2.95) is observed for anorthosites. Associated gabbronorites show enrichment of LREE ((La/Yb) N=1.99-4.93), depleted HREE ((Sm/Yb) N = 0.88-3.24) with negative to positive Eu anomaly (Eu/Eu* = 0.78-2.95). Also, the gabbronorite shows enrichment of LILE (Rb, Ba, Sr, Th, Pb) compared to HFSE (Zr, Ti, Nb). Clinopyroxenes of gabbronorite have low REE abundances (53.29-60.29 ppm). Clinopyroxenes are depleted in light rare earth elements (LREEs) (La/Yb) N = 0.75–0.80 and depleted in LILEs such as Ba, Sr. and also exhibit negative anomalies in Zr and Ti.

REE composition of gabbronorite clinopyroxene is constrained between TMF = 15-30% calculated using the equilibrium distribution method (EDM). This is substantiated by whole rock parental melt REE composition calculated using the concentration ratio approach (Nernst equation), the result of which is consistent with those made using EDM. In chondrite normalized plot, the estimated parental melt display (1) near-horizontal trend from Lu to Gd at rock/chondrite = ~100, (2) negative anomaly at Eu, (3) gradual rise from Sm to Ce and (4) slight dip from Ce to La.

How to cite: Negi, P., Belousov, I., Danyushevsky, L. V., Saikia, A., and Ahmad, M.: Anorthosite and associated gabbronorite plutons of Barabar hills in Chotanagpur granite gneiss complex (CGGC), eastern India: Estimation of parental melt for gabbronorite using equilibrium distribution method (EDM), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10859, https://doi.org/10.5194/egusphere-egu23-10859, 2023.

The suggested olivin thermometry for mantle peridotite and zenolith (Hoog et al., 2010, Bussweller et al., 2017) allow correct estimation of the temperatures using high precision data obtained by LA ICP MA or even EPMA inn hjigh resolution. IN this version we tried to obtain the pressure eestimates using the inversion of the Ol thermometer to barometer. And also we substituted the CaO by MnO withe essential correction. In this variant  I received the pair of the Ol thermometer and Mn - in - olivine barometer which allow to work not only with the high resolution data but with the routine analyses and obtain not bad estimates for the see of data for the Udachnaya, Zarnotsa, Aykhal and other pipes (Ashchepkov et al., 2010-2021) and even fo the diamond inclusions (Ashchepkov et al., 2021-2023). RBRF grant 19-05-007888

How to cite: Ashchepkov, I.: New formulation of the olivine thermobarometer for mantle xenoliths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12275, https://doi.org/10.5194/egusphere-egu23-12275, 2023.

The study of mantle xenoliths from kimberlite pipes allows to establish the composition, evolution processes and thermal condition of the lithospheric mantle under ancient cratons. The Mirny kimberlite field belongs to the diamond-bearing kimberlite fields in the center of the Siberian craton. The collection of mantle xenoliths from the Mir pipe (57 samples) was investigated by authors. Four main petrographic groups were identified: peridotites (Grt lherzolites), Grt websterites, Grt clinopyroxenites and eclogites. The pyroxenite xenoliths attract the special attention.   

Garnets from lherzolites and websterites are also characterized by a relatively high Mg# content (75–83) and low TiO2 contents (up to 0.2 wt %). Eclogites are characterized by high-calcium (3.78 - 9.46 wt.%) and high-iron (7.77 - 17.20 wt.%) composition of garnet getting into the ​​wehrlite paragenesis area. Thus, the lithospheric mantle under the Mirny kimberlite field differs from the lithospheric mantle under other diamondiferous fields (for example, Udachnaya kimberlite pipe). The Mirny mantle xenoliths are characterized by the pyroxenites widespread development (up to 50%), the low-Ti composition and deformed lherzolites absence.

In addition, websterites and lherzolites show a wide range of crystallization parameters (600 - 1200°C; 2 - 6 GPa) probably due to their gradual cooling after magmatic crystallization and the exsolution structures formation. Clinopyroxenites are characterized by narrow variations in the P-T crystallization parameters (812 - 960°C; 3-4 GPa) indicated their later crystallization from asthenospheric melts. Eclogites are characterized by relatively low calculated temperature parameters (720–840°C; 2.2–3.7 GPa) confirming their origin in subduction zones at shallow depths. The sporadic calculated values for websterites and clinopyroxenites are locating within the diamond stability area. The use of the Opx - thermobarometer (in samples founding Opx) revealed 2 trends in the crystallization of orthopyroxene. Crystallization of individual Opx grains in websterites occurred earlier than Cpx with higher P-T parameters - higher by ~100С and ~0.5 Ha. The second trend (pressure reduction with a slight decrease in temperature) notes the formation of Opx decay structures in an initially homogeneous crystal of monoclinic pyroxene. Minerals from pyroxenites demonstrate a wide development of melting processes in the lithospheric mantle in the south of the Siberian craton Craton and the formation of megacrystalline pyroxene cumulates. The origin of eclogites is assumed from subducted oceanic crust marking the subduction component in the process of formation of the lithospheric mantle.

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

How to cite: Kalashnikova, T. and Kostrovitsky, S.: The metasomatic processes and thermal condition of lithosphere mantle under the center of Siberian craton: evidences of pyroxenite xenoliths from Mir kimberlite pipe , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12888, https://doi.org/10.5194/egusphere-egu23-12888, 2023.

EGU23-16857 | PICO | GD2.2

Tracing of evolution of carbonatite and silicate melts of the Belo-Ziminsky alkaline-ultrabasic carbonatite massif by mineralogy and geochemistry 

Sergey Zhmodik, Igor Ashchepkov, Olga Kiseleva, Dmitry Belyanin, Irina Sotnikova, Nikolai Medvedev, and Nikolai Karmanov

The Belo-Ziminsky alkaline-ultrabasic carbonatite massif contain dolomite, and calcite ankerite carbonatites essential part , syenites, melteigites and iolites cut by aillikite dikes of several generations (Ashchepkov et al., 2020; Doroshkevich et al., 2014-2021 etc). We analyzed  >4000 mineral grains by electron microscope in all types of rocks and >230 grains by  LA ICP MA  All rocks of the massif are derived from one type of mantle melt that was close to aillikite and formed at a level of >5 GPa in the mantle.

According to the nature of the PGE spectra –  and by serpentinized xenoliths in aillikites, this melt drained metasomatized enriched peorvskites and hydrogenated mantle and was initially very rich in HFSE. Above, at the level of the crust and the upper part of the mantle, the melt began to separate under liquation. In the lower and middle crust, several (3) magmatic chambers were probably formed sequentially, which separated various carbonate and silicate melts, and from dolomite to ankerite melts, judging by the slope, the number of grains in the source decreased, that is, the melts became less deep and more fractionated.

These trends are reflected both in the composition of pyroxenes from aillikites  and in the PTX diagram . All this led to significant variations in rocks and their rare-earth spectra of all rocks

 

How to cite: Zhmodik, S., Ashchepkov, I., Kiseleva, O., Belyanin, D., Sotnikova, I., Medvedev, N., and Karmanov, N.: Tracing of evolution of carbonatite and silicate melts of the Belo-Ziminsky alkaline-ultrabasic carbonatite massif by mineralogy and geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16857, https://doi.org/10.5194/egusphere-egu23-16857, 2023.

Shallowing of slabs during their descend into the upper ~200 km of the mantle, i.e. flat subduction, can be associated with extensive geochemical, structural, and dynamic modification of the continental lithosphere. Anomalously buoyant oceanic lithosphere, overthrusting, and interactions with cratonic keels have been suggested to explain flat slabs, but the dynamics of flat slab subduction remain to be fully understood. Here, we explore self-consistent flat-slab subduction using the finite element code ASPECT with adaptive mesh refinement and a free surface boundary condition. We focus on the role of the structure of the overriding continental plate including the role of keels. Results show that flat slabs arise when the subduction interface is weak and the overriding continental lithosphere is positively buoyant, leading to trench rollback. Substantiating previous work, we also observe that a strong continental keel further enhances flat slab formation. Our results also indicate that as the slab flattens, regions of pronounced subsidence and extension develop within the foreland region, on top of more typical, larges-scale subsidence recorded within the continental interior. Regional uplift and subsidence of the overriding plate are not only linked to flat slab emplacement and removal, but also affected by slab dynamics of the shallow upper mantle. Our work can contribute to a better understanding of continental deformation including sediment transport on continent-wide scales.

How to cite: Grima, A. G. and Becker, T.: Modeling the interactions between slab dynamics and continental overriding plate deformation during flat subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1322, https://doi.org/10.5194/egusphere-egu23-1322, 2023.

EGU23-1559 | Orals | GD4.2

Horizontal and vertical slab tearing as different stages of a self-sustaining process developing in a non-collisional setting with oblique subduction 

Alexander Koptev, Nevena Andrić-Tomašević, Giridas Maiti, Taras Gerya, and Todd Ehlers

Slab break-off is usually referred to as an early collisional process driven primarily by the slowing of the subduction rate as negatively buoyant oceanic lithosphere detaches from positively buoyant continental lithosphere that is attempting to subduct. In this context, slab tearing (or slab break-off propagation) is traditionally attributed to continental corner dynamics, when the subducting plate first detaches in the area of continental collision and then the slab window opens toward the adjacent segment of the convergence boundary, where ocean-continent subduction continues. Another important process, previously thought to be independent of slab break-off and horizontal slab tearing, is a fragmentation of the subducting slab along vertical planes perpendicular to the convergence direction. Previous numerical studies have linked this vertical slab tearing to pre-existing weakness within the subducting plate and/or abruptly changing convergence rates along the trench.

In our study, we use a 3D thermo-mechanical numerical approach to study slab tearing in a non-collisional geodynamic context. The effects of subduction obliquity angle, age of oceanic slab, and partitioning of boundary velocities have been investigated. We show, for the first time, that horizontal and vertical slab tearing are different stages of the same process, which can develop in a self-sustained manner in a non-collisional environment of oblique ocean-continent subduction. Even with an initially absolutely homogeneous oceanic plate and laterally unchanging and temporally constant boundary velocities, the obliquity of the active margin appears to be a sufficient factor to trigger complex system evolution, which includes the transition from horizontal to vertical slab tearing along with additional processes such as retreat and rotation of the trench, decoupling of the overriding and downgoing plates by upwelling asthenosphere in the mantle wedge (also termed “delamination”), initiation of new subduction, and formation of a transform fault.

Our results show striking similarities with several features – such as trench curvature, subduction zone segmentation, magmatic production, lithospheric stress/deformation fields, and associated topographic changes – observed in many subduction zones (e.g., Marianas, New Hebrides, Mexico, Calabrian).

How to cite: Koptev, A., Andrić-Tomašević, N., Maiti, G., Gerya, T., and Ehlers, T.: Horizontal and vertical slab tearing as different stages of a self-sustaining process developing in a non-collisional setting with oblique subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1559, https://doi.org/10.5194/egusphere-egu23-1559, 2023.

Subduction of oceanic lithosphere has been proposed as the main driving mechanism for plate tectonics for decades and it represents a key process for the geochemical cycles on Earth. However, the physical processes and melting that occur as the subduction zone began foundering and evolved to reach a mature stage is still debated. The Izu-Bonin-Mariana (IBM) intra-oceanic subduction zone, that represents the boundary between the Pacific Plate and the Philippine Sea, is an ideal natural laboratory to study subduction zone processes from their inception to their stabilization. The rock record produced in IBM reveals a rapid compositional variability in slab-fluid tracers as well as in mantle depletion-enrichment over a short timescale (within 1 to 5 Ma of subduction inception). Despite this geochemical evolution, it is still highly debated whether IBM initiated as a forced or spontaneous subduction zone, i.e. induced by or in the absence of horizontal forcing, respectively.

Here, we conducted 2D high-resolution petrological-thermomechanical subduction models that include spontaneous deformation, erosion, sedimentation and slab dehydration processes, as well as melting, assuming a visco-plastic rheology using the i2VIS code. We aimed to model the initiation and the early stage of IBM with ultra-low horizontal forcing and inception triggered by transform collapse. Our new numerical model proposes a viable scenario for the transition from juvenile to mature subduction zone. This evolution includes initiation by gravitational collapse of the slab and the development of a near-trench spreading, the gradual build-up of a return flow of asthenospheric mantle and the progressive maturation of the volcanic arc. Our numerical results of mantle depletion within the mantle wedge and the overall subduction history of IBM are compared further with seismological and geochemical evidences.

How to cite: Ritter, S., Balázs, A., Ribeiro, J., and Gerya, T.: Magmatic Fingerprints of Subduction Initiation and Mature Subduction of the Izu-Bonin-Mariana Subduction Zone: Numerical Modelling and Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2071, https://doi.org/10.5194/egusphere-egu23-2071, 2023.

EGU23-2103 | Orals | GD4.2

Scaling of Free Subduction on a Sphere 

Neil Ribe, Alexander Chamolly, Gianluca Gerardi, Stephanie Chaillat, and Zhong-hai 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 (BEM) to study free (gravity-driven) subduction in axisymmetric and 3-D geometry, with a focus on determining the dimensionless parameters that control the dynamics. The axisymmetric model comprises a shell with thickness h and viscosity η1 subducting in an isoviscous planet with radius R0 and viscosity η2. The angular radius of the trench is θt. Scaling analysis based on thin-shell theory reveals two key dimensionless parameters: a `flexural stiffness' St = (η12)(h/lb)3 that is also relevant for flat plates, and a new `dynamical sphericity number' ΣD = (lb/R0)cotθt that is unique to spherical geometry. Here lb is the `bending length', or the sum of the lengths of the slab and of the seaward flexural bulge. The definition of ΣD implies that the dynamical effect of sphericity is greater for small plates than for large ones; we call this the `sphericity paradox'. By contrast, the purely geometric effect of sphericity is opposite, i.e. greater for large plates than for small ones. The dynamical and geometrical effects together imply that sphericity significantly influences subduction at all length scales. We confirm the scaling analysis using BEM numerical solutions, which show that the influence of sphericity on the slab sinking speed (up to a few tens of percent) and on the hoop stress (up to a factor of 2-3) is largest for small plates such as the Juan de Fuca, Cocos and Philippine Sea plates. We next study a 3-D model comprising a plate bounded by a ridge and a semicircular trench subducting in a three-layer earth consisting of an upper mantle, a lower mantle and an inviscid core. We examine the linear stability of the shell to longitudinal perturbations corresponding to buckling, and determine a scaling law for the most unstable wavelength that we compare with the observed shapes of northern/western Pacific trenches. 

How to cite: Ribe, N., Chamolly, A., Gerardi, G., Chaillat, S., and Li, Z.: Scaling of Free Subduction on a Sphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2103, https://doi.org/10.5194/egusphere-egu23-2103, 2023.

EGU23-2573 | ECS | Posters on site | GD4.2

Numerical modelling of mantle exhumation in inverted rift systems 

Frank Zwaan, Sascha Brune, Anne Glerum, John Naliboff, and Dylan Vasey

The tectonic exhumation of mantle material is a well-known phenomenon and may occur during both rifting and subsequent (large-scale) basin inversion. However, the processes leading to the exhumation of dense and therefore negatively buoyant (sub-)lithospheric mantle material remain poorly understood. We therefore conducted a series of thermomechanical simulations using the geodynamics code ASPECT (coupled with FastScape for the inclusion of surface processes) testing the impact of various parameters on mantle exhumation in inverted rift systems.

We find that rift duration strongly impacts mantle exhumation, both during the rift phase, as well as during subsequent inversion. When only limited rifting is applied, the dense mantle material cannot reach the surface as the overlying crustal layers remain connected. Basin inversion then tends to create a symmetric pop-up structure by reactivating rift boundary faults, and the dense mantle material is forced down by the thickening of low-density crustal layers on top of it. Only after certain amount of extension, the crust is sufficiently thinned so that mantle material can be exhumed. This mantle material may then remain near the surface or be further exhumed during basin inversion. Such further mantle exhumation is favoured if asymmetric reactivation of the rift basin occurs, so that mantle material is thrust on top of the downgoing plate.

The establishment of such asymmetric orogenic systems allowing for efficient mantle exhumation is further promoted by having only short-lived tectonic quiescence between rifting and inversion, so that no thermal equilibration of the exhumed mantle domain can occur. As a result, the rift basin remains a weakness that is readily exploited during inversion. Longer periods of tectonic quiescence restore the strength of the lithosphere, so that delayed inversion generates more symmetric structures, with limited opportunities for mantle exhumation.

Within this tectonic context, erosion efficiency is another key factor. First, more efficient erosion during inversion removes crustal material so that the mantle can be exhumed (even in symmetric orogenic systems). Second, efficient erosion also leads to the development of asymmetric orogenic systems, thus doubly contributing to mantle exhumation. Somewhat similarly, high plate velocities during inversion introduce larger amounts of crustal material into the system, which erosion cannot remove in a timely manner, whereas slow plate velocities allow erosion more time to remove material. Hence, mantle exhumation is positively correlated to erosion efficiency, and is negatively correlated to plate velocities during inversion

Finally, serpentinization of mantle material can occur close to the Earth’s surface (i.e. in the uppermost kilometres) and strongly reduces the material’s density and brittle strength. Although our models so far only show a limited effect of serpentinization, the overall weakness of serpentinized mantle material at the rift basin floor seems to reduce localization of inversion-related deformation, thus generating more symmetric inversion systems with limited mantle exhumation.

How to cite: Zwaan, F., Brune, S., Glerum, A., Naliboff, J., and Vasey, D.: Numerical modelling of mantle exhumation in inverted rift systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2573, https://doi.org/10.5194/egusphere-egu23-2573, 2023.

The Mariana convergent margin provides the environment where a natural process brings materials from great depths directly to the surface. The Mariana forearc contains the only current active serpentine mud volcanism in a convergent margin setting. Here, serpentinite mud volcanoes are numerous, large (averaging 30 km diameter and 2 km high) and active. They are composed principally of unconsolidated flows of serpentine muds containing clasts of serpentinized mantle peridotite and several other lithologies, such as blueschist materials derived from the subducting slab.

IODP Expedition 366 recovered cores from three serpentinite mud volcanoes at increasing distances from the Mariana trench subduction zone along a south-to-north transect: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). These cores consist of serpentinite mud containing lithic clasts and minerals derived from the underlying forearc crust and mantle, as well as from the subducting Pacific Plate. Fluids upwell within these mud volcanoes at a rate that is in excess of the mud matrix. Such fluids originate from the downgoing plate but are highly altered, are reducing and have pH values in the range of 9 to 12.5.

For the purposes of this study ultramafic and mafic rock clasts from the flanks and summits of both Asùt Tesoru and Fantangisña Seamounts were analyzed in order to reconstruct processes of fore-arc mantle alteration, fluid activity and fluid-rock interaction. Additionally, several samples from Asùt Tesoru Seamount consisting of cryptocrystalline serpentine mud with commonly occurring lithic clasts (>2 mm) in different amounts and size were investigated.

In general the mineral paragenesis of the serpentinized peridotite clasts, including mainly lizardite and chrysotile serpentine group minerals, along with brucite as well as andradite, and the apparent absence of high-temperature phases such as antigorite and anthophyllite, tentatively constrains an upper temperature limit of 200 – 300 °C. However, the presence of fine-grained matrix antigorite associated with lizardite suggests metamorphic temperature of at least 340 °C.

Hydrogarnet is a common secondary, hydrothermal mineral phase in the studied samples and it defines a serpentinization temperature of c. 230 °C. Garnet crystals with subhedral habitus and almost pure andraditic composition are found within a carbonate matrix. However, also Cr-rich garnets are common within the serpentinite clasts. They are subhedral to anhedral and contain chromite inclusions with similar composition to the unaltered chromites in the same sample. These textural observations suggest a secondary origin for the Cr-rich garnets as well, most probably related to hydrothermal fluids that infiltrated the ultramafic protolith. The formation of Cr-rich garnet after Cr-rich spinel is usually associated with hydrothermal or metasomatic reactions, although the precise mechanism of formation remains unclear. Generaly Cr-rich hydrogarnets in serpentinites crystallize below 400 °C, which is in line with the obtained metamorphic conditions and indicate an overall evolution of a hydrothermal fluid from c. 350 °C (antigorite in serpentinites) to c. 100 °C and below.

How to cite: Kurz, W., Miladinova, I., Krenn, K., and Hilmbauer-Hofmacher, T.: Fore-arc mantle alteration, fluid activity and fluid-rock interaction revealed from Serpentinite Mud Seamounts at the Mariana Convergent Margin System (IODP Expedition 366), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2657, https://doi.org/10.5194/egusphere-egu23-2657, 2023.

EGU23-2981 | Orals | GD4.2

Magmatic response to the subduction initiation of Early Cretaceous Nidar Ophiolite Complex, eastern Ladakh, NW Himalaya 

Takeshi Imayama, Akinori Sato, Dripta Dutta, Yasuaki Kaneda, Shota Watanabe, Takeshi Hasegawa, Masayo Minami, Yuki Wakasugi, Shigeyuki Wakaki, and Yi Keewook

Early Cretaceous Nidar Ophiolite Complex (NOC, eastern Ladakh) is associated with the north-dipping supra-subduction of the Neo-Tethyan Ocean along the Indus suture zone. The supra-subduction zone ophiolite formed in the forearc setting records the magmatic response to the subduction initiation, but the magmatic evolution in the NOC is poorly constrained. The low-Ti gabbros have low SiO2 in whole-rock composition and high Mg# in clinopyroxene. They also record highly depleted magma In contrast, dolerites and basalts have relatively higher SiO2 in whole-rock composition and lower Mg# in clinopyroxene, with flat REE patterns accompanied by fractional crystallization. Significant variation in Yb content relative to Tb/Yb ratio also supports fractional crystallization from gabbros to basalts. In Th/Yb-Nb/Yb diagram, all samples plot in the region from the MORB type to the island arc tholeiite. The Nd-Sr isotopes and high Ba/La ratio suggest that the NOC was originally derived from a single depleted mantle source similar to the MORB and was subsequently affected by hydrothermal alteration, resulting in greenschist- to lower amphibolite-facies overprint to form albite, actinolite, epidote and chlorite. Detrital zircon U-Pb ages from volcanic sediments associated with the NOC concentrated at ca. 136 Ma, representing the timing of the main magmatic phase in the NOC. Our data, combined with the geochronological and geochemical data in previous studies, suggest that the low-Ti, highly depleted magma in the NOC was firstly generated at extensional spreading in the upper plate during subduction initiation, and then changed to island arc tholeiite composition with the development of the subduction zone during Early Cretaceous.

How to cite: Imayama, T., Sato, A., Dutta, D., Kaneda, Y., Watanabe, S., Hasegawa, T., Minami, M., Wakasugi, Y., Wakaki, S., and Keewook, Y.: Magmatic response to the subduction initiation of Early Cretaceous Nidar Ophiolite Complex, eastern Ladakh, NW Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2981, https://doi.org/10.5194/egusphere-egu23-2981, 2023.

EGU23-3130 | ECS | Orals | GD4.2

Micro to Macroscale: the three-dimensional network characteristics of serpentinite dehydration veins 

Austin Arias, Andreas Beinlich, Lisa Eberhard, Marco Scambelluri, Timm John, Alissa Kotowski, and Oliver Plümper

On Earth, subduction zones facilitate the cycling of volatiles between the Earth’s surface and interior. Volatile cycling has significant effects on the long-term state of the Earth’s climate and tectono-magmatic events, including volcanism and earthquakes. A key stage in the volatile cycle is the devolatilization of the subducting oceanic lithosphere, in which volatiles can escape the previously hydrated rocks. However, it is not well known how efficiently volatiles are transported at this stage. To better understand how volatiles escape at these conditions, we have analyzed the dehydration-related vein networks of the Erro-Tobbio meta-serpentinites (ET-MS), Italy. The ET-MS display well preserved networks of metamorphic olivine veins. These veins are the result of the dehydration reaction of antigorite and brucite to produce H2O and olivine. However, due to the low permeability of serpentinite at depth, the dehydration reaction requires the formation of self-organizing vein networks to allow the produced fluid to escape [1]. Thus, the metamorphic olivine veins in ET-MS may be used as a proxy for fluid flow pathways. We took a multiscale approach to analyzing the network architectures. For microscale (~16 µm voxel size) and mesoscale (~200 µm voxel size) resolutions, X-ray tomography methods are sufficient to visualize the three-dimensional structure of the networks. However, for large scale observations these methods are inapplicable. To solve this, we apply a novel workflow to analyze outcrop scale (~10 m) network systems in three dimensions using only two-dimensional data. By training a generative adversarial network (GAN) with two-dimensional data conditioned by spatial orientation, we can generate statistically representative three-dimensional networks that mimic those of the ET-MS. These representations also display similar characteristics in their respective pore-network-models. With this method, it is possible to produce reasonable three-dimensional approximations of the ET-MS vein networks using only photogrammetry data of the outcrops. In turn, this allows us to extract metrics, such as permeability, that describe the volatile transport efficiency of the ET-MS, and further, how these characteristics change at a broad range of scales.  

[1] Plümper et al. (2017) Nature Geoscience 10(2), 150-156. 

How to cite: Arias, A., Beinlich, A., Eberhard, L., Scambelluri, M., John, T., Kotowski, A., and Plümper, O.: Micro to Macroscale: the three-dimensional network characteristics of serpentinite dehydration veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3130, https://doi.org/10.5194/egusphere-egu23-3130, 2023.

EGU23-4422 | Posters on site | GD4.2

From Subduction Initiation to Polarity Reversal: Zircon Age and Geochemical Constraints from Solomon Islands 

Rashmi Battan, Truong Tai Nguyen, Sun-Lin Chung, Tsuyoshi Komiya, Shigenori Maruyama, Andrew Tien-Shun Lin, Hao-Yang Lee, and Yoshiyuki Izuka

Intra-oceanic arc’s collision with an oceanic plateau plays a crucial role in the development of complex tectonic setting and induce subduction polarity reversal. Despite several studies and investigations, the origin and timing of subduction initiation in Solomon Island Arc (SIA) is still ambiguous. This study presents first robust zircon U-Pb ages and in-situ Hf isotope data from Choiseul, Santa Isabel (SI) and New Georgia Group (NGG), three major islands of SIA. Magmatic zircons and Hf isotope data from one gabbro sample, geochemically identical to N-MORB with Nb, Ta depletion in spidergram yielded 46 ± 1 Ma, which we decipher as the timing of Stage I magmatism by subduction of Pacific plate and subduction initiation in Choiseul. Six Choiseul andesites gave a mean age 206Pb/238U of 0.7 Ma, with εHf(t) values from +9 to +15 which represents the youngest crystallization age of Stage II magmatism with typical island arc-like signatures and a depleted mantle source. Detrital zircons from two sand sample yielded a population of mean age ranging from 0.3-0.7 Ma, 10 Ma and 48-46 Ma with εHf(t) values +9 to 15, +11 to +12 and +11 to +14 respectively and third sample has yielded a mean age 207Pb/206Pb 2.6 Ga and 500-1600 Ma with εHf(t) values -8 to +9, probably associated with Australian-type source indicating presence of a continental fragment beneath SIA. 

Similar ages of ca. 2.6 Ma have been obtained from inherited zircons from three gabbroic dyke sample from Santa Isabel with εHf(t) values +1 to +9 whereas one gabbroic dyke sample yields 110 ± 1 Ma, with εHf(t) values +14 to + 16 which we interpret as the basement age of SI.

U-Pb dating of zircons from mafic to felsic rocks along NGG, covered mostly by Quaternary eruptive lavas. The youngest age population indicate Late Pliocene-Pleistocene 206Pb/238U ages, 2.5-1.5 Ma, interpreted as  zircon crystallization ages of Stage II arc magmatism resulting from subduction of the Solomon Sea plate, as those of Choiseul Andesite. The first U-Pb age from ca. 36.8±0.5 Ma granite on Ghizo Island in New Georgia Group, revealing Late Eocene-aged magmatic zircon. This age represents the magmatic emplacement as the basement of plutonic rock from NGG that has not been reported before.

We conclude that, (i) The Solomon Islands has a Cretaceous basement preserved in SI. (ii) The timing of subduction initiation and Stage I N-MORB type tholeiitic magmatism in SIA is 46 Ma followed by episodic eruptions from the early Eocene to late Eocene. (iii) Oligocene (30-20 Ma) magmatic hiatus, probably the time of subduction polarity reversal from subduction of Pacific plate to subduction of Solomon Sea plate. (iv) Stage II island arc magmatism initiated at 20-18 Ma in NGG to youngest emplacement age of Pliocene to Pleistocene in Choiseul as well as in NGG. (v)Abundant Archean zircons are present in samples from all three islands, indicate presence of micro-continent beneath Islands of Solomon. We are still working on the whole rock isotopic analysis to better constrain the tectonic and magmatic evolution of SIA.

How to cite: Battan, R., Nguyen, T. T., Chung, S.-L., Komiya, T., Maruyama, S., Lin, A. T.-S., Lee, H.-Y., and Izuka, Y.: From Subduction Initiation to Polarity Reversal: Zircon Age and Geochemical Constraints from Solomon Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4422, https://doi.org/10.5194/egusphere-egu23-4422, 2023.

EGU23-4644 | ECS | Orals | GD4.2

Are the long-lasting isotope trends in central Patagonia independent from slab dynamics and upper-plate architecture? 

Marie Genge, César Witt, Massimiliano Zattin, Delphine Bosch, Olivier Bruguier, and Stefano Mazzoli

Shifts in isotopic and trace element composition in magmatic zircon are commonly related to internal forcing independent of plate parameters (e.g., crustal thickness, delamination), or external factors that are governed by parameters of the down-going plate, particularly the slab dip. U-Pb geochronology, trace elements and Hf-O isotope analyses on detrital zircon from central Patagonia (45 °S – 48 °S) were used in this study as fingerprint for monitoring slab dip variations and related processes (e.g., arc migration, slab rollback) as well as upper-plate stress regime evolution. According to literature, main geodynamic events include: (i) two shallow slab episodes during late Triassic and late Early Cretaceous – early Paleogene times, the latter characterized by significant contraction; (ii) two phases of slab rollback during Jurassic – Early Cretaceous and late Paleogene, associated to a steep slab configuration, extensional processes and crustal thinning; (iii) a slab window episode during the Paleogene; and (iv) a Miocene contractional phase following an increase of plate convergence rates. Although slab dynamics seems structurally related with upper-plate architecture, it appears to exert little to null control on the magmatic arc reservoirs. Indeed, our results, integrated with published data from a larger area (40 °S – 52 °S), show long-lasting trends ( > 70 Ma) in the isotopic and trace elements record, that are mostly independent of these events. We thus consider that other processes, eventually coeval, controlled the enrichment of magmas and may overtake the influence of slab dip and upper-plate architecture on the isotopic and trace elements signature. These other processes include subduction erosion, ridge subduction, subduction of a younger slab, potential slab tearing, and/or change in convergence rates that affects mantle flow. 

How to cite: Genge, M., Witt, C., Zattin, M., Bosch, D., Bruguier, O., and Mazzoli, S.: Are the long-lasting isotope trends in central Patagonia independent from slab dynamics and upper-plate architecture?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4644, https://doi.org/10.5194/egusphere-egu23-4644, 2023.

EGU23-4710 | Orals | GD4.2

Controls on the Dynamics of Subducting Slabs in a 3-D Spherical Shell Domain 

Rhodri Davies, Fangqin Chen, Saskia Goes, and Lior Suchoy

It has long been recognised that the shape of subduction zones is influenced by Earth’s sphericity, but the effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics: most existing studies have been executed in a Cartesian domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their applicability. There are therefore many outstanding questions relating to the key controls on the dynamics of subduction. For example, do predictions from Cartesian subduction models hold true in a spherical geometry? When combined, how do subducting plate age and width influence the dynamics of subducting slabs, and associated trench shape? How do relic slabs in the mantle feedback on the dynamics of subduction? These questions are of great importance to understanding the evolution of Earth's subduction systems but remain under explored.

In this presentation, we will target these questions through a systematic geodynamic modelling effort, by examining simulations of multi-material free-subduction of a visco-plastic slab in a 3-D spherical shell domain. We will first highlight the limitation(s) of Cartesian models, due to two irreconcilable differences with the spherical domain: (i) the presence of sidewall boundaries in Cartesian models, which modify the flow regime; and (ii) the reduction of space with depth in spherical shells, alongside the radial gravity direction, the impact of which cannot be captured in Cartesian domains, especially for subduction zones exceeding 2400 km in width. We will then demonstrate how slab age (approximated by co-varying thickness and density) and slab width affect the evolution of subducting slabs, using spherical subduction simulations, showing that: (i) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates; (ii) wider slabs can develop along-strike variations in trench curvature due to toroidal flow at slab edges, trending toward a `W'-shaped trench with increasing slab width, and (iii) the width effect is strongly modulated by slab age, as age controls the slab's tendency to retreat. Finally, we will show the diverse range of ways in which remnant slabs in the mantle impact on subduction dynamics and the evolution of subduction systems.

How to cite: Davies, R., Chen, F., Goes, S., and Suchoy, L.: Controls on the Dynamics of Subducting Slabs in a 3-D Spherical Shell Domain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4710, https://doi.org/10.5194/egusphere-egu23-4710, 2023.

EGU23-5078 | Posters virtual | GD4.2

Subduction of bathymetric irregularities along active margins: insights from numerical modeling 

Vlad Constantin Manea, Marina Manea, and Lucian Petrescu

Oceanic plates are far from homogeneous, and a large number of bathymetric discontinuities such as seamounts of different sizes are transported along by plate motion towards the mid ocean trenches and beyond. Seamounts currently colliding with plate margins show a major role in shaping the forearc morphology, and several studies even suggest that they might be related with seismicity. However, it is not clear what happens after seamounts are subducted, they can be accreted to the forearc, carried down into the subduction zone and recycled into the deep mantle, or a mix of the two scenarios. Using high-resolution two-dimensional thermomechanical numerical simulations, we investigate subduction processes of oceanic plates with a heterogeneous structure marked by a series of basaltic seamounts arranged in a chain like structure. We solve the 2D momentum, continuity and energy equations with the finite differences coupled with PIC (particle-in-cell) method. Our models also incorporate a depth-dependent, realistic non-Newtonian visco-elasto-plastic rheology, and plasticity is implemented using a yield criterion which limits the creep viscosity. Preliminary results show that initially seamounts preserve they structure when impacting with the trench. Their integrity is partially conserved until they subduct to a depth of about 25-30 km when they finally start to succumb to the great deformations and stresses along the slab interface. We observed that the lower part of the seamount continuously deforms and amalgamates along the slab interface. The upper part is detached and incorporated into the forearc structure. The subsequent seamounts that trail the first seamount, follow the same deformation pattern, and the top of them are maintained in the highly deformed forearc region. Our preliminary modeling results confirm that seamount subduction represent a key tectonic process that influences on a long-term time scale the structure and evolution of subduction zones.

How to cite: Manea, V. C., Manea, M., and Petrescu, L.: Subduction of bathymetric irregularities along active margins: insights from numerical modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5078, https://doi.org/10.5194/egusphere-egu23-5078, 2023.

The subduction zone interface is a shear zone of varying thickness that defines the boundary between the subducting slab and overriding plate. The rheology of this shear zone controls several important aspects of subduction dynamics, but accurately estimating its rheology can be complex due to the wide range of subduction materials and their varying rheological properties. Of particular importance is the relative strengths of metasedimentary and metabasic rocks at various temperature and pressure conditions. To better understand these rheological contrasts in naturally deformed rocks, we are conducting field and microstructural work in the Eclogite Zone in the Tauern Window, Austria. The eclogite zone preserves intercalated metamafic (metabasalt and metagabbro) and metasedimentary (quartzite, garnet mica schist, marble and calc-schist) rocks that were subducted and exhumed to the surface as a single structural unit. Using high resolution drone imaging, 2D structural mapping, and 3D structural modeling, we have documented map-scale relationships between metamafic and metasedimentary rocks in the Eissee region near Matrei. Our mapping demonstrates that the mafic eclogites consistently define slabs, lenses and boudins of up to 2 km in along-strike length and 0.2 km in thickness, embedded within the metasedimentary units, all of which are relatively uniformly deformed to very high strain. This suggests that eclogitized metamafic rocks persisted as rheological heterogeneities within the subduction channel through both the subduction and exhumation paths. Additionally, we are using microstructural observations to document the deformation mechanisms of individual rock units and to understand the weakening mechanisms that allowed some of the eclogites to break down from boudins to strongly foliated layers intercalated with the metasediments. At the interface between select metasedimentary and eclogite units there is a marked rheological change in eclogite rheology, likely due to fluids leached from the metasedimentary rocks, resulting in strain localization and increased foliation development within eclogite layers from meter to micron length scales. Integration of our mapping, outcrop, and microstructural observations will provide insights into the length scales of rheological heterogeneity on the deep interface and large-scale geodynamics of subduction through influencing the bulk viscosity of the interface.

How to cite: Tokle, L., Behr, W., Braden, Z., and Cisneros, M.: Persistence of initial lithological heterogeneity to deep subduction conditions: Implications for the rheology of the subduction zone interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5162, https://doi.org/10.5194/egusphere-egu23-5162, 2023.

EGU23-5221 | ECS | Orals | GD4.2

The role of sediments on subduction dynamics and geometry: insights from numerical modeling 

Silvia Brizzi, Thorsten Becker, Claudio Faccenna, Whitney Behr, Iris van Zelst, Luca Dal Zilio, and Ylona van Dinther

It is widely recognized that sediments play a key role for subduction. For example, sediments subducted along the shallow seismogenic plate interface are thought to influence seismic coupling and the occurrence of megathrust earthquakes, as well as the morphologies of accretionary prisms. Due to their weakening and/or lubricating effect, subducted sediments are also thought to promote faster plate speeds. However, global observations are not clear-cut on the relationship between the amount of sediments and plate motion. Here, we use 2D thermomecanical models to investigate how incoming plate sediments can influence subduction dynamics and geometry. We find that thick sediments can promote slower subduction due to an increase of the shear stress along the plate interface as the accretionary wedge gets wider, and a decrease of slab pull as more buoyant material is subducted. Our results also show that the larger interface shear stress and slab buoyancy due to thick sediments increase the slab bending radius. This study offers a new perspective on the role of sediments on large-scale subduction dynamics, suggesting that sediment buoyancy and wedge geometry might also affect plate motion and geometry.

How to cite: Brizzi, S., Becker, T., Faccenna, C., Behr, W., van Zelst, I., Dal Zilio, L., and van Dinther, Y.: The role of sediments on subduction dynamics and geometry: insights from numerical modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5221, https://doi.org/10.5194/egusphere-egu23-5221, 2023.

EGU23-5229 | ECS | Posters on site | GD4.2

Modeling fluid-driven seismic cycles in subduction zones 

Betti Hegyi, Luca Dal Zilio, Whitney Behr, and Taras Gerya

Various geological and geophysical observations from different subduction zones attest to the importance of pore pressure fluctuations and fluid flow in triggering regular earthquakes, slow slip events and tectonic tremors. We use the Hydro-Mechanical Earthquake Cycle (H-MEC) code to model fluid-driven earthquake cycles in a subduction megathrust environment. The code uses  a finite differences-marker in cell method, and couples solid rock deformation with fluid flow. The code solves the mass and momentum conservation equations for both solid and fluid phases, with the addition of gravity and temperature-dependent viscosity. The brittle/plastic deformation is resolved through a rate-dependent strength formulation and the development of slip instabilities is governed by compaction-induced pore fluid pressurization. With such code we can demonstrate how the fluid pressurization can lead to localisation of deformation with slip rates up to m/s in a fully compressible poro-visco-elasto-plastic media. The models can reproduce all slip modes observed in nature from regular earthquakes to transient slow slip phenomena to aseismic creep. Here we investigate various controls on dominant slip mode and their expected distributions and interactions along a subduction interface model setup. Our initial results show that the dominant slip mode depends on porosity, permeability, plastic dilatation and viscosity of the matrix. An increase in the porosity will lead to aseismic deformation in the form of slow slip events and creep. We also investigate the effects of inclusions (clasts) along the subduction channel, acting as stress heterogeneities, with physical properties different from the subduction channel. We attempt to understand the role of inclusions with different viscosities and permeabilities embedded in the matrix. With this numerical framework, we can better understand fluid-driven seismicity, and the effects of fluids on long-term geodynamic processes. Our study also contributes to better understand the role of fluid pressure cycling in seismic and aseismic deformation in subduction zone environments, as well as provides new insights in the role of stress heterogeneities within the frictional-viscous shear zone. 

How to cite: Hegyi, B., Dal Zilio, L., Behr, W., and Gerya, T.: Modeling fluid-driven seismic cycles in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5229, https://doi.org/10.5194/egusphere-egu23-5229, 2023.

EGU23-5747 | Orals | GD4.2

Subduction invasion polarity switch (SIPS):  A new mechanism of subduction initiation, with an application to the Scotia Sea region 

Wouter P. Schellart, Vincent Strak, Anouk Beniest, Joao C. Duarte, and Filipe M. Rosas

The initiation of subduction remains an enigmatic process and a variety of conceptual models has been proposed to explain such initiation. Conceptual models have been tested with geodynamic models and have been applied to various subduction settings around the globe. None of these tested models, however, are applicable to the Scotia subduction zone in the Southern Atlantic (also referred to as South Sandwich subduction zone), where subduction started in the Late Cretaceous/Early Cenozoic in a pristine ocean basin setting devoid of other subduction/collision zones. How this subduction zone initiated remains intensely debated, as exemplified by the variability of published plate tectonic reconstructions. We present new tectonic reconstructions of the Scotia region involving a relatively simple middle-Late Cretaceous plate boundary configuration that involves a new mechanism of subduction initiation, Subduction Invasion Polarity Switch (SIPS). SIPS involves a long-lived, wide and deep subduction zone (South American-Antarctic subduction zone) that imposes major horizontal trench-normal compressive deviatoric stresses on the overriding plate. The overriding plate consists of a narrow continental lithospheric (land) bridge at the trench (Cretaceous-Early Cenozoic Antarctica-South America land bridge) with oceanic lithosphere behind it (Weddell Sea-Atlantic Ocean). The stresses cause shortening and thrusting at the continent-ocean boundary in the backarc region of the overriding plate, forcing oceanic lithosphere under continental lithosphere, starting the subduction initiation process, and eventually leading to a new, self-sustaining, subduction zone (Scotia subduction zone) with an opposite polarity (dipping westward) compared to the long-lived subduction zone (dipping eastward). The model thus involves invasion of a new subduction zone into a pristine ocean basin (Atlantic Ocean), with the primary driver being a long-lived subduction zone in another ocean basin (Pacific Ocean). To test the physical viability of the SIPS model, we have conducted numerical geodynamic simulations of buoyancy-driven subduction. Numerical results demonstrate that the SIPS model is viable, with compressive stresses in the overriding plate resulting from strong trenchward basal drag induced by subduction-driven whole-mantle poloidal return flow and compression at the subduction zone plate boundary due to the high resistance of the subduction zone hinge of the long-lived subduction zone to retreat westward. Subduction initiation starts in the overriding plate after ~100 Myr of long-lived subduction, eventually resulting in the formation of a new, opposite-dipping, subduction zone. Notably, this new subduction zone develops at the continent-ocean boundary for models without and with a pre-imposed weak zone. Apart from the Scotia Sea region, the SIPS model might also be applicable to subduction initiation that has occurred elsewhere in the geological past (e.g. the New Caledonia, Lesser Antilles-Puerto Rico, Rocas Verdes and Arperos subduction zones), and that is presently in a very early stage of development in the Japan Sea.

How to cite: Schellart, W. P., Strak, V., Beniest, A., Duarte, J. C., and Rosas, F. M.: Subduction invasion polarity switch (SIPS):  A new mechanism of subduction initiation, with an application to the Scotia Sea region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5747, https://doi.org/10.5194/egusphere-egu23-5747, 2023.

EGU23-6155 | Orals | GD4.2

Dynamics of multiple microcontinent accretion during oceanic subduction 

Zoltán Erdős, Susanne Buiter, and Joya Tetreault

Microcontinent accretion during oceanic subduction is one of the main contributors to continental crustal growth. Many of the continental mountain belts we find today were built from accretionary orogenesis, for example, the Cordillera of the west coast of the Americas, the European Alps, and the Australian Lachlan orogen. Continental growth can also be observed in modern accretionary orogens such as the Pacific accretionary belt, with the collision of the Philippine microplate, and the Taiwan-Luzon-Minduro Belt. In many of these systems, multiple bathymetric highs, such as microcontinental terranes, island arcs, or oceanic plateaus, are accreted before full oceanic closure, thus significantly altering the subduction zone before continental collision occurs.
The process of accretion implies a complex balance of multiple geodynamic forces that can result in either microcontinent subduction, microcontinent accretion, or subduction stalling (which could lead to the initiation of an altogether new subduction zone). The most important driving forces in this system are the slab-pull force arising from the negative buoyancy of the down-going slab and the far-field force which is the result of large-scale plate-motions external to the subduction zone. These forces are counteracted (among others) by friction along the subduction interface and the buoyancy of the downgoing microcontinent. The resulting net forces control the overall stress-field of the overriding plate as well as the state of stress and potential deformation of any further microcontinents embedded within the oceanic lithosphere that are not yet in the subduction zone. 
When multiple microcontinents are embedded in the subducting oceanic plate, the friction along the subduction interface and its temporal variations can take a crucial role. The accreting microcontinents have a first order effect on the length and the rheology of the subduction channel, thereby controlling the interface friction. The fate of the microcontinents (e.g. full or partial accretion, or subduction) also affects the overall buoyancy of the slab, altering the balance of forces through the slab-pull.
Using 2D thermo-mechanical experiments with the finite-element software SULEC-2D, we explore the roles of the structure and rheology of multiple accreting microcontinents (controlling their integrated strength) as well as the velocity of the subducting plate (controlling the far-field and the slab-pull force) to better understand how accretion of crustal units can modify the subduction zone and affect later continental collision. Our setup is comprised of a subducting oceanic basin surrounded by two continents. In this setup the oceanic plate is either “empty” or one or two microcontinents are embedded within it.
Our first results show that microcontinent accretion is promoted by the presence of a weak rheological detachment layer within the microcontinent. In turn, strong coupling of the microcontinental crust to its host-lithosphere promotes terrane subduction and may ultimately lead to the stalling of subduction. Moreover, the behavior of the microcontinents during accretion and subsequent continental collision has a first order effect on the structural style of the resulting orogen as the rheology of the microcontinents controls the degree of localization of deformation in the subduction channel.

How to cite: Erdős, Z., Buiter, S., and Tetreault, J.: Dynamics of multiple microcontinent accretion during oceanic subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6155, https://doi.org/10.5194/egusphere-egu23-6155, 2023.

EGU23-6363 | ECS | Posters on site | GD4.2

200 Ma of magmatism along the northern border of the West African Craton during Pan-African convergence 

Alex Bisch, Antoine Triantafyllou, Gweltaz Mahéo, Jamal El Kabouri, Olivier Bruguier, Delphine Bosch, Julien Berger, Jérôme Ganne, and Frédéric Christophoul

Convergence zones are marked by a variety of settings that may follow each other in modern-day tectonics, including compressive phases such as subduction, obduction, collision but also extensive ones such as back-arc opening or stress-relaxation during orogenesis. Hence, the protracted evolution leading to a super-continent block amalgamation may be difficult to decipher and so may be the forcings on external enveloppes such as volcanism or erosion caused by the different phases.

This question arises critically at the time of the Pan-African Orogenesis (1-0.5 Ga) assembling Gondwana, a time of supposedly dramatic and diachronical changes for external envelopes: glaciations of debated scales, deposition of various Banded Iron Formations, first (Ediacarian) fauna, replacement by Cambrian faunas. Our goal is to explore in detail the geodynamical succession leading to the amalgamation of blocks along the northern margin of the West African Craton (WAC), outcropping in the Central Anti-Atlas region, Morocco. This region is characterized by the occurrence of extended convergence-related magmatism, ophiolite emplacement and basins fillings (including BIF) during Cryogenian and Ediacaran periods.

Data obtained from compilation of cartographic work, whole-rock geochemistry and datation reveals a polyphased but still poorly constrained evolution through proxies of continentality (εNd) and of crustal thickness (Sr/Y ratio). We present new data spanning metamorphic petrology, basin stratigraphy, coupled datation and trace element analysis in detrital zircons in order to better understand the evolution of the geodynamic, magmatic and drainage systems. We propose a geodynamic scenario based on these data:

  • Development of an early oceanic arc (760-720 Ma) with juvenile magmatic signature (3<εNd(t)<7), its accretion on the WAC is followed by an episode of calc-alkaline magmatism (710-700 Ma).

  • Second arc development (700-670 Ma) only seen in detrital and inherited zircons, its accretion at 670 Ma is followed by late-orogenic magmatism (660-650 Ma) associated with decreasing crustal thickness (from 70 to 25 km).

  • Third arc development on the newly formed continent margin (640-600 Ma) until oceanic closure and collision. Intense late orogenic magmatism occurs (590-570 Ma), coeval with the decreasing crustal thickness (from 100 to 30 km).

  • A late phase of calc-alkaline is recorded (570-550 Ma) at constant and regular crustal thickness (25 km). A 550 Ma compressive event is recorded, very few calc-alkaline follows.

  • The onset of Cambrian with the development of a large passive margin capping the whole region. This change coincides with disappearance of ice-house climate evidence from the global sedimentological record.

How to cite: Bisch, A., Triantafyllou, A., Mahéo, G., El Kabouri, J., Bruguier, O., Bosch, D., Berger, J., Ganne, J., and Christophoul, F.: 200 Ma of magmatism along the northern border of the West African Craton during Pan-African convergence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6363, https://doi.org/10.5194/egusphere-egu23-6363, 2023.

EGU23-6505 | ECS | Posters on site | GD4.2

Global inversion and parametrization for building tomographic velocity models 

Umedzhon Kakhkhorov, Børge Arntsen, Wiktor Waldemar Weibull, and Espen Birger Raknes

Traveltime tomography is applied to investigate seismic structures of the Earth's subsurface. An accurate tomographic velocity model is important for a high-resolution waveform velocity building and its availability is one of the main components to mitigate the nonlinear inverse problem. We present a new methodology of obtaining velocity models for traveltime tomography studies. We found a way to get a highly accurate first-arrival traveltime tomography in combination with global optimization. The role of global optimization is twofold: to find initial solutions that are close to ‘truth’, and to guide tomographic inversion towards a geologically consistent model that explains the data. The main advantage of our workflow is a data-driven approach avoiding the use of a conventional layer-based parameterization and incorporation of manual interpretations into the velocity model. 

To date, a few geophysical studies have been focused on developing data-driven and a labour non-intensive regional tomographic velocity model building workflow. In our study, we present the tomographic velocity model building workflow as a combination of first-arrival traveltime tomography and global optimization. Global optimization allows to search for velocity parameters and depth to interfaces in the larger search area with a higher chance of convergence. After defining the geometry of main layers and general velocity trends, traveltime tomography with a bi-cubic B-spline model parameterization can be fitted to further update the velocity model. Our approach allows obtaining a highly accurate velocity model which can be used for seismic depth migration and as a starting model for a FWI seismic imaging. The workflow is developed and applied to synthetic and field regional seismic datasets. 

The developed methodology is applied for a shallow seismic engineering data and regional Ocean Bottom Seismic data. We identify four key components that lead to building an accurate tomographic velocity model: (i) understanding prominent horizons and possible velocity distribution of a layer within the study area. (ii) Performing ray penetration test to define offset ranges which carry the velocity information for the defined layers. (iii) Determining inversion schema to a perform global search for the velocity trends and major boundaries, and a local search to update lateral velocity variation. (iv) Iteratively update a set of defined layers (i.e., sediment, igneous crust and basement) in a top-down manner. 

How to cite: Kakhkhorov, U., Arntsen, B., Weibull, W. W., and Raknes, E. B.: Global inversion and parametrization for building tomographic velocity models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6505, https://doi.org/10.5194/egusphere-egu23-6505, 2023.

Intermediate-depth earthquakes in many subduction zones occur in two distinct layers, forming an upper and a lower seismic zone separated vertically by an aseismic or weakly seismic region. This setting is widely known as Double Seismic Zone (DSZ). Notably, intermediate-depth seismicity in Northern Chile shows a pattern of intraslab seismicity which is distinct from the aforementioned conventional DSZ. Here, two parallel seismicity planes are present in the updip part of the slab, but at a depth of ∼80–90 km, there is a sharp transition to a highly seismogenic volume of 25–30 km thickness, which closes the gap between the two seismicity planes.

While such an observation is unique to Northern Chile, understanding the processes behind the formation of this feature should provide important constraints on the mineral processes that govern seismicity in DSZs as well as the role and involvement of fluids. As seismic velocities contain important information about mineralogy and fluid content, we aim at a high-resolution characterization of the seismic wavespeeds of the Northern Chile subduction zone, mainly focusing on the subducting Nazca slab. Data from the seismic stations of the permanent IPOC (Integrated Plate boundary Observatory Chile) deployment in the Northern Chile forearc form the backbone of the dataset, but are complemented by several temporary deployments that span shorter time sequences as well. We use the seismicity catalog of Sippl et al. (2018) that contains >100,000 earthquakes and 1,200,404 P- and 688,904 S-phase picks for the years 2007 to 2014, and limit our analysis to events that have more than 14 P-arrivals as well as more than 7 S-arrivals. Constraining the hypocentral depth range to 40-155 km and the longitude range to 68° W- 72°W, we perform local earthquake tomography using the FMTOMO algorithm (Rawlinson et. al., 2006) with a dataset of 10102 events comprising 163,359 P- and 113,036 S- phase picks.

We present first 3D models of P- and S-wavespeeds from the Northern Chile forearc between about 18.5° S and 24.5° 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 in order to derive the optimal settings for the inversion.

 

The presented seismic velocity distribution will eventually be compared with theoretical wavespeeds that are forward calculated assuming different mineralogical compositions in order to narrow the range of possible reactions that may be occurring at depth.

 

How to cite: Hassan, N. and Sippl, C.: Looking deep into the subducting Nazca plate under the Northern Chile forearc with local earthquake tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6845, https://doi.org/10.5194/egusphere-egu23-6845, 2023.

EGU23-7182 | Orals | GD4.2

Upper-plate shortening and Andean-type mountain-building in the context of mantle-driven oceanic subduction 

Robin Lacassin, Tania Habel, Anne Replumaz, Benjamin Guillaume, Martine Simoes, Thomas Geffroy, and Jean-Jacques Kermarrec

To explore the conditions that lead to mountain-building in the case of an oceanic subduction, we conduct analog experiments (with silicon putty upper and lower plates, glucose syrup upper mantle) where subduction is driven by slab pull but also by an underlying mantle flow. Here, plate displacement is not imposed as in most models, but is controlled by the overall balance of forces in the system. We simulate three scenarios: no mantle flow (slab-pull driven subduction), mantle flow directed toward the subducting plate, and mantle flow directed toward the overriding plate. In the case of this latter scenario, we also test the influence of pre-existing rheological contrasts in the upper plate to best reproduce natural cases where inheritance is common. Our experiments show that when plate convergence is also driven by a background mantle flow, the continental plate deforms with significant trench-orthogonal shortening (up to 30% after 60 Myr), generally associated with thickening. We further identify that upper plate shortening and thickening is best promoted when the mantle flow is directed toward the fixed overriding continental plate. The strength of the upper plate is also a key factor controlling the amount and rates of accommodated shortening. Deformation rates increase linearly with decreasing bulk strength of the upper plate, and deformation is mostly localized where viscosity and strength are lower. When compared to the particular natural case of the Andes, our experiments provide key insights into the geodynamic conditions that lead to the building of this Cordilleran orogen since the Late Cretaceous - Early Cenozoic.

 

How to cite: Lacassin, R., Habel, T., Replumaz, A., Guillaume, B., Simoes, M., Geffroy, T., and Kermarrec, J.-J.: Upper-plate shortening and Andean-type mountain-building in the context of mantle-driven oceanic subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7182, https://doi.org/10.5194/egusphere-egu23-7182, 2023.

EGU23-7188 | ECS | Orals | GD4.2

How a subducting plateau impacts regional and global tectonics? 

Yang Liu, Nicolas Coltice, Laetitia Le Pourhiet, and Ziyin Wu

Plateau subduction is a common process at different plate convergent margins, and they often modify subduction and affect slab behaviour. However, fewer studies have been conducted in the intraoceanic subduction context, and the physical and rheological parameters involved imply a strong hypothesis on the initial conditions (thermal state, no flow in the mantle, no interaction with the tectonic network). Here, we use global three-dimensional spherical mantle convection models to investigate the potential impacts of a subducting plateau on subduction zones and plate reorganization from regional to global scales in a fully self-consistent plate-like tectonics system. Our models show that plateaus with different sizes (length, width and thickness) can locally slow down the trench retreat rate. A larger plateau prevents trench migration, eventually terminating the subduction. The buoyancy of plateaus is found to influence the shape of the trench. Low buoyancy plateaus do not deform the trench as they subduct while in models with buoyant plateaus, the trench advances landward in front of a plateau forming an arcuate shape in the map. This arcuate shape of the trench is further enhanced with decreasing buoyancy and increasing viscosity. If the oceanic plateau has a higher yield stress, it will always drive the formation of the arcuate trench before fully subducted, regardless of the buoyancy. The simulations suggest that any single plateau rheology variable (buoyancy, or yield stress) except the viscosity can influence trench migration behaviour on a regional scale. We will also explore how plateau subduction modifies the global tectonic evolution over 100 My.

How to cite: Liu, Y., Coltice, N., Le Pourhiet, L., and Wu, Z.: How a subducting plateau impacts regional and global tectonics?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7188, https://doi.org/10.5194/egusphere-egu23-7188, 2023.

EGU23-7211 | Orals | GD4.2 | Highlight

How do subduction zones spread over Atlantic-type oceans? 

João C. Duarte, Nicolas Riel, Patricia Cadenas, Filipe M. Rosas, J. Kim Welford, and Boris Kaus

There is a long-standing mystery regarding how subduction zones enter internal Atlantic-type oceans to complete their Wilson cycle. While the process of subduction initiation is challenging to tackle, the Atlantic is a natural laboratory that allows understanding of some of the different stages of the process of invasion of new subduction zones. Three different subduction zones seem to be entering the Atlantic from different edges: the Caribbean Arc, the Scotia Arc and around the Iberia Peninsula. While the first two examples constitute fully developed subduction zones, it is unknown how they will propagate in the future. Will they spread intra-oceanically or will the subduction migrate along the Atlantic passive margins? Iberia is a good place to investigate the processes involved in the formation of new subduction zones. There have been places of aborted subduction (along the Cantabrian margin), places of incipient subduction (North, West and Southwest Iberia) and there is a subduction arc currently propagating into the Atlantic Ocean (the Gibraltar Arc). We will focus on this last case. Last year, we presented a numerical model that showed that the Gibraltar Arc may indeed further propagate into the Atlantic. This year, we present new models that investigate the factors controlling such propagation. We test different parameters such as the presence of weak zones in the adjacent margins and in the oceanic lithosphere (fracture zones) to obtain insights into the main factors controlling the first stages of propagation of new subduction zones in Atlantic-type oceans.

 

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- IDL

How to cite: Duarte, J. C., Riel, N., Cadenas, P., Rosas, F. M., Welford, J. K., and Kaus, B.: How do subduction zones spread over Atlantic-type oceans?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7211, https://doi.org/10.5194/egusphere-egu23-7211, 2023.

EGU23-7314 | ECS | Orals | GD4.2

Trench retreat rates in narrow subduction zones controlled by overriding plate thickness 

Pedro J. Gea, Flor de Lis Mancilla, Ana M. Negredo, and Jeroen van Hunen

Subducting slabs are the main drivers of plate motion and flow in Earth’s mantle. Thus, much effort has been put into understanding the main factors controlling slab dynamics and subduction-induced mantle flow. Slab width (W) has been shown to have a major role in controlling the subduction dynamics and more specifically, the trench motion (e.g., Stegman et al., 2006; Schellart et al., 2007). Both numerical modelling experiments and retreat velocities observed in wide subduction zones show that the trench retreat velocity (VT) decreases as the slab is wider. However, observations on natural narrow subduction zones (W ≤ 1000 km, e.g. Calabria, Gibraltar, Scotia) do not show a direct relation between W and VT, thus indicating that other factors, still poorly understood, may play a more relevant role on trench retreat velocities. The aim of this work is to identify which are these factors that exert a dominant control. To accomplish this, we use self-consistent 3D numerical subduction models to systematically evaluate the effect of slab width, strength of coupling with the lateral plate and overriding plate thickness on trench motion. In contrast to what happens in moderate to wide subduction zones, our simulations show that slab width has little influence on trench retreat velocity for narrow subduction zones, which is a robust result for different viscous couplings at the lateral slab edge.  On the contrary, our results indicate that the major influence is exerted by the thickness of the overriding plate, with the trench retreat velocities decreasing noticeably as the plate thickness increases. These results are in agreement with retreat velocities observed in narrow subduction zones showing no direct relation with slab width, but an inverse dependence on overriding plate thickness.

 

References

Schellart, W. P., Freeman, J., Stegman, D. R., Moresi, L., and May, D. (2007). Evolution and diversity of subduction zones controlled by slab width, Nature, 446(7133), 308–311. doi:10.1038/nature05615

Stegman, D. R.; Freeman, J.; Schellart, W. P.; Moresi, L.; May, D. (2006). Influence of trench width on subduction hinge retreat rates in 3-D models of slab rollback, Geochemistry Geophysics Geosystems, 7(3), Q03012–. doi:10.1029/2005gc001056

How to cite: Gea, P. J., Mancilla, F. D. L., Negredo, A. M., and van Hunen, J.: Trench retreat rates in narrow subduction zones controlled by overriding plate thickness, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7314, https://doi.org/10.5194/egusphere-egu23-7314, 2023.

EGU23-7467 | ECS | Posters on site | GD4.2

Combined natural and numerical-modeling constraints on subduction interface strength at deep metamorphic conditions 

Ana Lorena Abila, Whitney Behr, and Jonas Ruh

The integrated stress magnitude or bulk effective viscosity of subduction interface shear zones is a key component of both long- and short-term subduction dynamics. Current constraints on average subduction interface viscosity come from laboratory flow laws for subduction-related rock types and range from 1018 Pa.s (quartz-rich lithologies) to 1023 Pa.s (metabasaltic lithologies) for typical subduction strain rates and viscous subduction interface conditions (e.g. T between 400-900 °C). However, this viscosity range is based on end-member flow laws, which means it likely overestimates the true range in viscosity that is possible along the subduction interface. In nature, subduction shear zones are commonly a mixture of multiple rock types in various distributions (e.g. clast-matrix melanges); and furthermore, natural shear zones show a range in width from place to place, suggesting varying strain rates. Our goal in this study is to place more precise bounds on the global range of shear zone viscosity (or integrated shear stress) for natural subduction shear zones at deep subduction conditions. To do so, we curated a set of 9 geologic maps of eclogite facies shear zones from existing literature, focusing on those that a) show minimal retrogressive overprint, b) have defined shear zone widths, and c) have well-constrained PT conditions. These maps were digitized and implemented in a simple shear visco-elasto-plastic numerical model with constant strain rate (10-12 s-1) boundary conditions and experimentally constrained flow laws assigned to each rock type, including eclogite (eclogite mafic blocks), wet quartz (quartz-rich blocks, schists, gneisses), blueschist (blueschist mafic blocks), wet olivine (peridotites), antigorite (serpentinites), and aragonite (calcareous blocks). Numerical experiments  ran for a restricted amount of time steps to assure  steady-state stress/viscosity (<10 ky). Resulting integrated shear stresses and viscosities were then compared for the different example shear zones. Initial results indicate that natural shear zones should exhibit effective viscosities that vary by at least 1-2 orders of magnitude at a specific temperature, depending on the distribution of weak vs. strong blocks and the matrix rheology. Additional results and statistical analysis of all of the shear zones will be presented at the meeting. 

How to cite: Abila, A. L., Behr, W., and Ruh, J.: Combined natural and numerical-modeling constraints on subduction interface strength at deep metamorphic conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7467, https://doi.org/10.5194/egusphere-egu23-7467, 2023.

EGU23-8492 | Orals | GD4.2

Understanding the role of structural inheritance and flat slab geometry in Central Andes 

Michael Pons, Constanza Rodriguez Piceda, Stephan V. Sobolev, Magdalena Scheck-Wenderoth, and Manfred R. Strecker

The Sierras Pampeanas (29 - 35°S) located south of the Altiplano-Puna plateau above the Chilean subduction zone, consist of uplifted foreland basement blocks that are an expression of the eastward propagation of compresive deformation. Their presence is one of the most enigmatic features of the Andes. The formation of these ranges is considered an end member of the thick-skinned foreland deformation style, which involves the deformation of the sedimentary cover and the crystalline basement. At 33°S, the onset of compression occurs at 22Ma, and the change between thin and thick skinned deformation style at 16Ma. However, the mechanism responsible for this evolution remains controversial. Two main hypotheses have been proposed to explain this evolution. The first one atributes the change in foreland deformation style to the setting of the Pampean flat slab at 12 Ma, which is contemporanous to the southward migration and subduction of the Juan Fernandez hotspot ridge at 33S. Alternatively, it has been proposed that the reactivation of pre-existing structures inherited from pre-Neogen tectonic events could better explain the onset of deformation about 10 Ma before the arrival of the flat-slab. To resolve this controversial debate, we have developed a data-driven 3D geodynamic model using the FEM geodynamic code ASPECT. We incorporated the present-day geometrical and thermal configuration of the southern central Andes and the flat-slab from previous models. This approach allowed us to study the structural and thermomechanical factors responsible for the location of deformation in the Sierras Pampeanas (e.g., topography, temperature and composition, strength of the lithosphere and velocity of the plates).  Moreover,  we investigated the role of the geometry of the Nazca plate on the foreland deformation, and proposed a new mechanism ("flat slab conveyor)" that reconciles the timing of the main geological events (onset of shortening, change in tectonics style of deformation of the foreland, growth of the topography, cessation of volcanic activity, uplift of the basement, and propagation of the deformation). This work expands our understanding of how plates interact at convergent boundaries, in particular at the subduction zones, and how and where deformation is expressed at the surface of the the upper continental plate.

How to cite: Pons, M., Rodriguez Piceda, C., Sobolev, S. V., Scheck-Wenderoth, M., and Strecker, M. R.: Understanding the role of structural inheritance and flat slab geometry in Central Andes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8492, https://doi.org/10.5194/egusphere-egu23-8492, 2023.

EGU23-8670 | Posters on site | GD4.2 | Highlight

The role of subduction in the formation of Pangean oceanic large igneous provinces 

Philip Heron, Erkan Gün, Grace Shephard, Juliane Dannberg, Rene Gassmöller, Erin Martin, Aisha Sharif, Russell Pysklywec, R. Damian Nance, and J. Brendan Murphy

Large igneous provinces (LIPs) have been linked to both surface and deep mantle processes related to supercontinent formation. During the formation, tenure, and breakup of Pangea, the most recent supercontinent, there is a noted contemporaneous increase in the number of emplacement events of both continental and oceanic LIPs. There is currently no clear consensus on the origin of LIPs, but the most widely recognized hypothesis relates their formation to crustal emplacement of hot plume material originating in the deep mantle. The interaction of subducted slabs with the lowermost mantle thermal boundary and subsequent return-flow is a key control on plume generation. This mechanism has been explored for LIPs below the interior of a supercontinent (e.g., continental LIPs). However, a number of LIPs related to Pangea formed at the supercontinent’s exterior (e.g., Ontong Java Plateau in the Pacific Ocean), with no consensus on their formation mechanism. In this research, we consider the dynamics of global-scale supercontinent processes resultant from numerical models of mantle convection, and analyse whether circum-supercontinent subduction could generate both interior (continental) and exterior (oceanic) deep-mantle plumes. Our 2-D and 3-D numerical models show that subduction related to the supercontinent cycle can reproduce the location and timing of the Ontong Java Plateau, Caribbean LIP, and potentially the Shatsky Rise, when relating these LIPs to a deep mantle exterior plume. The findings here highlight the importance of taking into consideration mantle dynamics in every stage of the supercontinent cycle.

How to cite: Heron, P., Gün, E., Shephard, G., Dannberg, J., Gassmöller, R., Martin, E., Sharif, A., Pysklywec, R., Nance, R. D., and Murphy, J. B.: The role of subduction in the formation of Pangean oceanic large igneous provinces, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8670, https://doi.org/10.5194/egusphere-egu23-8670, 2023.

EGU23-8910 | ECS | Orals | GD4.2

Intra-Plate Deformation of the Pacific: Evidence from Oceanic Plateaux and Geodynamic Models 

Erkan Gün, Russell Pysklywec, Philip Heron, Gültekin Topuz, and Oğuz Göğüş

The theory of plate tectonics acknowledges that drifting lithospheric plates are rigid and do not undergo substantial deformation except near or at plate boundaries. However, studies have shown that intra-plate deformation is a feature for continental lithosphere and can originate from different mechanisms such as lithospheric drips, delamination, and in-plane stresses. On the other hand, there is not well-known understanding of tectonic deformation within the interior of ocean plates. We compile data to show there is geological and geophysical evidence documenting that the drifting Pacific plate has been undergoing appreciable extensional deformation at the locations of its oceanic plateaux. Namely, the Ontong Java, Shatsky Rise, Hess Rise, and Manihiki plateaux show extensive evidence for normal faults, horst-graben structures, and extension related magmatic activity at a significant distance from plate boundaries. Furthermore, this deformation occurred after the initial emplacement of their associated large igneous provinces (LIPs) and before their arrival to subduction zones.

We present numerical geodynamic experiment results demonstrating that terranes embedded in ocean plates can undergo extensional deformation prior their accretion to the overriding plate due to slab-pull (e.g., a “subduction pulley”).  Our numerical models show that the subduction pulley is also a valid mechanism for the extensional deformation of the Pacific oceanic plateaux even at remote locations from the plate boundaries. For instance, tensional stress originated from down-going slabs can be transmitted through strong oceanic lithosphere over long distances (>1000 km) and deform the plate at its weak oceanic plateaux regions. The numerical experiments further demonstrate that high crustal thickness reduces the bulk strength of ocean lithosphere at the location of oceanic plateaux and makes them susceptible to slab-pull related extension—manifesting on the surface as intra-ocean plate deformation.

How to cite: Gün, E., Pysklywec, R., Heron, P., Topuz, G., and Göğüş, O.: Intra-Plate Deformation of the Pacific: Evidence from Oceanic Plateaux and Geodynamic Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8910, https://doi.org/10.5194/egusphere-egu23-8910, 2023.

Although positive buoyancy of young lithosphere near spreading centers does not favor spontaneous subduction, subduction initiation occurs easily near ridges due to their intrinsic rheological weakness when plate motion reverses from extension to compression. It has also been repeatedly proposed that inherited detachment faults may directly control the nucleation of new subduction zones near ridges subjected to forced compression. However, recent 3D numerical experiments suggested that direct inversion of a single detachment fault does not occur. Here we further investigate this controversy numerically by focusing on the influence of brittle-ductile damage on the dynamics of near-ridge subduction initiation. We self-consistently model the inversion of tectonic patterns formed during oceanic spreading using 3D high-resolution thermomechanical numerical models with strain weakening of faults and grain size evolution. Numerical results show that forced compression predominantly reactivates and rotates inherited extensional faults, shortening and thickening the weakest near-ridge region of the oceanic lithosphere, thereby producing ridge swellings. As a result, a new megathrust zone is developed, which accommodates further shortening and subduction initiation. Furthermore, brittle/plastic strain weakening has a key impact on the collapse of the thickened ridge and the onset of near-ridge subduction initiation. In contrast, grain size evolution of the mantle only slightly enhances the localization of shear zones at the brittle-ductile transition and thus plays a subordinate role. Compared to the geological record, our numerical results provide new helpful insights into possible physical controls and dynamics of natural near-ridge subduction initiation processes recorded by the Mirdita ophiolite of Albania.

How to cite: Liu, M. and Gerya, T.: Forced subduction initiation near spreading centers: effects of brittle-ductile damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9669, https://doi.org/10.5194/egusphere-egu23-9669, 2023.

EGU23-9814 | Orals | GD4.2

Molybdenum Isotope Systematics of the Kamchatka Subduction Zone System 

Matthias Willbold and Gerhard Wörner

Molybdenum (Mo) isotopes in magmatic rocks are a promising tool in high-temperature isotope geochemistry. In particular, basalts from subduction zones that are geochemically controlled by mass transfer through slab-fluid addition have systematically higher δ98Mo values (i.e. measured 98Mo/95Mo ratio in a sample relative to that in a standard) than the depleted mantle (δ98Mo = –0.21‰). In these rocks, the elevated δ98Mo values are linked to high Pb/Ce and high (238U/230Th) ratios and can be reconciled by the addition of isotopically heavy Mo via a slab fluid component1,2. So far, these systematics are best expressed in subduction zone basalts from the Mariana and Izu arc systems that also form coherent mixing trends between fluid-enriched mantle domains in δ98Mo versus 143Nd/144Nd and 176Hf/177Hf space1,2.

The Kamchatka arc system represents the northernmost expression of the W-Pacific convergent margin. Volcanic front lavas are dominated by slab-to-mantle mass transfer through fluid transport, whereas subduction of the Emperor seamount ridge gives rise to back-arc basalts with a geochemical and isotopic affinity to within-plate basaltic rocks3.

Here, we report δ98Mo data for 47 basalts from an E-W transect across the Kamchatka peninsula that have previously been analysed for their major, trace element, radiogenic and stable isotope data. The δ98Mo data extent the trend defined by samples from the Marianas and Izu arcs starting from moderately high δ98Mo and Pb/Ce values towards sub-depleted mantle δ98Mo and mantle-like Pb/Ce ratios that indicate the presence of a source component formed by partial melts of a rutile-bearing mafic crust4.

The common geochemical and isotopic trends formed by the combined Mariana – Izu – Kamchatka datasets suggest a surprisingly uniform Mo isotope composition of a subduction zone fluid endmember for more than 5000 km along-strike of the Circum-Pacific subduction zone system. Our data also confirm the presence of an enriched source component in the Kamchatka mantle wedge, possibly originating from the subducted Emperor seamount chain5.

1Freymuth, H., et al., EPSL 432, 176-186 (2015). 2Villalobos-Orchard, J., et al., GCA 288, 68-82 (2020). 3Churikova, T., et al. JPet 42, 1567-1593 (2001). 4Chen, S., et al., Nat. Comm. 10, 4773 (2019). 5Shu,Y., et al.,Nat. Comm. 13, 4467 (2022).

How to cite: Willbold, M. and Wörner, G.: Molybdenum Isotope Systematics of the Kamchatka Subduction Zone System, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9814, https://doi.org/10.5194/egusphere-egu23-9814, 2023.

EGU23-9902 | ECS | Orals | GD4.2

Origin of S-type granites in the forearc accretionary complex of the East Kunlun Orogenic Belt, northern Tibetan Plateau 

Xiang Ren, Yunpeng Dong, Dengfeng He, and Christoph Hauzenberger

A forearc environment is usually characterised by a relatively low geothermal gradient and hence little magmatic activity occurs. However, S-type granites were discovered within the forearc accretionary complex of the East Kunlun Orogenic Belt. The S-type granites intruded into an upper amphiolite facies partially migmatitic crystalline basement in form of dikes and sills at ca. 440 Ma which corresponds to the transition of the Proto-Tethyan to the Paleo-Tethyan realm in the northern Tibetan Plateau. The observed granites contain either garnet + biotite + muscovite or garnet + muscovite: (1) muscovite granite is strongly peraluminous with an aluminous saturation index (ASI) of more than 1.1 (ASI = molar [Al2O3/(Na2O+K2O+CaO]) and has high-K calc-alkaline characteristics, low Sr/Y (1.9–16.1) and LaN/YbN (1.85–13.2) ratios. (2) Two-mica granite is moderately peraluminous (ASI = 1.02–1.09), has high Ca and low K contents as well as high Sr/Y (16.8–67.7) and LaN/YbN(10.9–33.3) ratios. Other trace element contents and their ratios also show striking differences with high Sr (207–324 ppm) content and CaO/Na2O (0.47–0.96) ratio, and a low Rb/Sr (0.04–0.32) ratio for two-mica granite, but low Sr (63–126 ppm) content and CaO/Na2O (0.08–0.20) ratio, and a high Rb/Sr (0.56–2.53) ratio for muscovite granite. The observed differences are due to different protolith chemistries and melting mechanisms. Based on melting experiments of metasedimentary rocks (Patiño Douce and Harris, 1998), muscovite granite was most likely produced by dehydration melting of a metapelitic source and the two-mica granite by H2O-fluxed melting of a metagreywacke. Zircon Hf isotopes of the two S-type granites have εHf(440 Ma) values of -6.85 to +12.02 indicating the involvement of a mantle-derived magma which probably triggered the anatexis of supracrustal rocks deposited in a forarc regime. Coveal adakites with a younging westward trend as well as mafic rocks have been reported in this accretionary complex, which together with anatexis and metamorphism of accreted material support the occurrence of a slab window beneath the forearc accretionary complex of the East Kunlun Orogenic Belt during subduction of the Tethyan oceanic slab.

 

References

Patiño Douce, A.E., Harris, N., 1998. Experimental constraints on Himalayan anatexis. Journal of Petrology 39, 689–710.

How to cite: Ren, X., Dong, Y., He, D., and Hauzenberger, C.: Origin of S-type granites in the forearc accretionary complex of the East Kunlun Orogenic Belt, northern Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9902, https://doi.org/10.5194/egusphere-egu23-9902, 2023.

EGU23-10756 | Orals | GD4.2

Time dependent slab temperatures, metamorphism, and mechanical properties: Insights from dynamic subduction models 

Adam Holt, Cailey Condit, Valeria Turino, Gabe Epstein, Ryan Stoner, and Victor Guevara

The thermal structure of subduction zones enacts a first-order control on many geological processes and properties, including the locus and degree of slab devolatilization, and the associated densities and strengths of subducting material. Modeling studies with fixed subduction geometries and plate velocities have been used to map out how various subduction parameters affect the pressure-temperature conditions of slabs and, in turn, the depths of major dehydration reactions. However, there is abundant geological evidence that slab properties, and the associated temperatures, evolve over few-Myr timescales. In this study, we use numerical subduction models to target this time dependence. Specifically, we focus on the styles and drivers of thermal transience and the imprint of this on subducting slab dehydration and slab strength.

Specifically, we have developed 2-D and 3-D subduction models that enable slab properties to evolve through time in a dynamically consistent fashion using the ASPECT finite element code1-3. We use these models to investigate: i) the extent to which slab thermal conditions – and the associated metamorphic reactions and slab strength – evolve throughout the lifetime of a subduction zone, ii) the effects of first-order subduction zone properties on this evolution, and iii) the degree to which three-dimensionality (i.e., the presence of a slab edge) impacts this evolution. Regardless of imposed basic subduction parameters (e.g., plate ages, crustal strengths), our model subduction zones exhibit highly time-dependent thermal evolutions. The slab top, for example, exhibits rapid cooling during initiation and slower cooling subsequently, with along-strike temperature variations of up to ~40°C in the 3-D models. This thermal transience has fundamental implications for the geophysical and geochemical evolution of subduction zones; it manifests in a strong time dependence of dehydration depths and magnitudes and, in turn, substantial variability in slab strength. 

 

1: Bangerth, W., Dannberg, J., Gassmoeller, R., & Heister, T. (2020). ASPECT v2.1.0, Zenodo. https://doi.org/10.5281/ZENODO.3924604

2: Heister, T., Dannberg, J., Gassmöller, R., & Bangerth, W. (2017). High accuracy mantle convection simulation through modern numerical methods - II: Realistic models and problems. Geophys. J. Int., 210(2), https://doi.org/10.1093/gji/ggx195

3: Holt, A. F., & Condit, C. B. (2021). Slab temperature evolution over the lifetime of a subduction zone. Geochem., Geophys., Geosys., 22, doi:10.1029/2020GC009476.

How to cite: Holt, A., Condit, C., Turino, V., Epstein, G., Stoner, R., and Guevara, V.: Time dependent slab temperatures, metamorphism, and mechanical properties: Insights from dynamic subduction models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10756, https://doi.org/10.5194/egusphere-egu23-10756, 2023.

EGU23-10847 | Posters on site | GD4.2 | Highlight

Reconstructing slab dip through deep time to explain pulses in kimberlite eruptions 

Ben Mather, Dietmar Müller, Christopher Alfonso, Maria Seton, and Nicky Wright

The recycling of oceanic lithosphere at subduction zones constitutes the largest driving force of plate tectonic motion. The angle at which subducting plates enter the mantle influences the magnitude of this force, the distribution of subduction-related earthquakes, intensity of volcanism, and mountain building. However, the factors that control subduction angle remain unresolved. We develop a novel formulation for calculating the subduction angle based on trench migration, convergence rate, slab thickness, and plate density which reproduces the present-day dynamics of global subduction zones. Applying this formulation to reconstructed subduction boundaries from the Jurassic to present day, we relate subduction angle combined with slab flux to pulses in kimberlite eruptions. High rates of subducting slab material trigger mantle return flow that stimulates fertile reservoirs in the mantle. These convective instabilities transport slab-influenced melt to the surface at a distance inbound from the trench corresponding to the subduction angle. Our deep-time slab dip formulation has numerous potential applications including modelling the deep carbon and water cycles, and an improved understanding of subduction-related mineral deposits.

How to cite: Mather, B., Müller, D., Alfonso, C., Seton, M., and Wright, N.: Reconstructing slab dip through deep time to explain pulses in kimberlite eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10847, https://doi.org/10.5194/egusphere-egu23-10847, 2023.

EGU23-10944 | ECS | Orals | GD4.2

Seismic Evidence of Slab Segmentation and Melt Focusing Atop the 410-km Discontinuity in NE Asia 

Jung-Hun Song, Seongryong Kim, and Junkee Rhie

The geometry of subducting slabs is largely controlled by mantle rheology and time evolving processes of surface plate boundaries. Imaging of a detailed slab distribution and its surrounding can provide information of physical, chemical, and dynamical properties of the upper mantle. Based on new high-resolution 3-D tomography of subducting Pacific slab in northeast Asia, we revealed a prominent gap within the stagnant portions of the slab showing an abrupt change in its lateral trends that follow the trace of plate junctions associated with plate reorganization at the western Pacific margin during the Cenozoic. Focused partial melting above the slab gap was inferred based on the spatial coincidence between the high Vp/Vs anomaly and the negative reflectivities above the 410-km discontinuity from local receiver function studies. The slab gap is possibly filled with low-velocity anomalies within the MTZ as evidenced by wavefield focusing of teleseismic body waves and absolute velocity imaging from previous studies. We explain the spatial coincidence between the low-velocity anomaly within the MTZ and the focused melt layer above the MTZ by the process of mantle dynamics related with secular variation of slab geometries by tearing. Isolated low-velocity anomalies within the MTZ imaged by seismic tomography without previous thermal disturbances (e.g., hot plume) are suggested to be the products of distinct MTZ compositions disturbed by former nearby slab subductions. Our results suggest a close dynamical relationship between the subducting slab and the MTZ, which promotes the formation of multi-scale chemically distinct domains in the deeper upper mantle.

How to cite: Song, J.-H., Kim, S., and Rhie, J.: Seismic Evidence of Slab Segmentation and Melt Focusing Atop the 410-km Discontinuity in NE Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10944, https://doi.org/10.5194/egusphere-egu23-10944, 2023.

EGU23-11018 | ECS | Posters on site | GD4.2

Magmatic arc compositions governed by climate change: A biogeodynamic perspective from the Eastern Equatorial Pacific 

Carlos Errázuriz-Henao, Arturo Gómez-Tuena, Mattia Parolari, and Marion Weber

Magmatic arcs modulate global climate over geological timescales through outgassing and rock weathering, but recognizing the fingerprints of climate change in arc magmas remains challenging. Based on a detailed reconstruction of oceanographic, atmospheric, and climatic processes since the middle Miocene, as well as an extensive geochemical database of Miocene and active arc-front magmas from the Trans-Mexican Volcanic Belt, Central American Volcanic Arc, and the North Andean Colombian Arc we developed a conceptual framework by which biogeochemical proxies in oceanic sediments can be tracked down to the composition of arc magmas. Using this framework, we show that the well-documented increases in biologically mediated authigenic Ba and U contents of seafloor sediments from the Eastern Equatorial Pacific (EEP) at the onset of the so-called “carbonate crash” (12–9 Ma) were triggered by an escalation in biological productivity and an augmented efficiency of respiratory carbon storage. We suggest that the temporal modification of the oceanic carbon cycle was regulated by the synchronous formation of three wind-powered seasonal upwellings systems —Tehuantepec, Papagayo, and Panama— that developed in the context of steepening meridional temperature gradients, intensified atmospheric circulation and global climate cooling since the Middle Miocene. Sediments deposited in the context of these newly established upwelling systems became anomalously enriched in authigenic U and Ba not only in comparison to older sediments, but also with respect to geographically adjacent areas of the EEP where vigorous upwellings are absent. These peculiar environmental conditions thus produce a heterogeneous ocean floor that upon subduction and eventual interaction with the mantle wedge creates arc volcanoes with compositional fluctuations that mimic those of the ocean sediments. These findings indicate that the oceanographic and biogeochemical effects of climate change can be engraved on the continental crust and mantle.

How to cite: Errázuriz-Henao, C., Gómez-Tuena, A., Parolari, M., and Weber, M.: Magmatic arc compositions governed by climate change: A biogeodynamic perspective from the Eastern Equatorial Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11018, https://doi.org/10.5194/egusphere-egu23-11018, 2023.

EGU23-11540 | ECS | Orals | GD4.2

Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles 

Stephen Hicks, Lidong Bie, Catherine Rychert, Nicholas Harmon, Saskia Goes, Andreas Rietbrock, Songqiao Wei, Jenny Collier, Timothy Henstock, Lloyd Lynch, Julie Prytulak, Colin Macpherson, David Schlaphorst, Jamie Wilkinson, Jonathan Blundy, George Cooper, Richard Davy, and John-Michael Kendall

Volatiles expelled from subducted plates promote melting of the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonised lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Qκ-1/Qµ-1 > 0.6) and VP/VS (>1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids towards the back-arc. The strongest attenuation (1000/QS~20), characterising melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper plate properties, past tectonics, and resulting melt pathways collectively condition volcanism.

How to cite: Hicks, S., Bie, L., Rychert, C., Harmon, N., Goes, S., Rietbrock, A., Wei, S., Collier, J., Henstock, T., Lynch, L., Prytulak, J., Macpherson, C., Schlaphorst, D., Wilkinson, J., Blundy, J., Cooper, G., Davy, R., and Kendall, J.-M.: Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11540, https://doi.org/10.5194/egusphere-egu23-11540, 2023.

EGU23-11688 | ECS | Posters on site | GD4.2

Numerically modelling along-strike rheologic variations in 3D subduction zones 

Derek Neuharth, Whitney Behr, and Adam Holt

Because subduction zones can extend thousands of kilometers along-strike, many previous studies have used 2D subduction models which inherently assume homogeneity along-strike. However, in nature we see that subduction zones are often heterogeneous along-strike and can exhibit significant variations in the subducting plate age, thickness, and viscosity, trench location, as well as in the geometry of the overriding plate. While 2D models can test large system-wide changes to these parameters by assuming homogeneity along-strike, how variabilities in the geometry and rheology interact with each other in a three-dimensional setting is poorly understood.

To understand how along-strike variations affect an evolving subduction zone, we developed self-consistent 3D subduction models using the finite element code ASPECT. The models include a thermally-defined subducting plate and overriding plate, and a constant-viscosity crust/interface. We vary two primary parameters along-strike: 1) the viscosity of the interface shear zone and 2) the thickness of the overriding plate, which affects the interface shear zone length. We explore how varying each of these parameters affects the subduction, convergence, and trench rollback velocities, slab morphology, and the stress distribution and topography formation within the overriding plate.

We find that along-strike variations to the interface viscosity or overriding plate thickness has only minor effects on the slab morphology and convergence velocities, but largely affects the surface stress distribution. While variations in the overriding plate thickness or interface viscosity do not affect the convergence velocity along-strike, having a thicker overriding plate or stronger interface leads to a reduction in the system-wide convergence velocity. Despite the similar velocities along-strike, slab morphology changes along-strike, with lower dips seen in regions with a greater overriding plate thickness or weaker interface viscosity. Most importantly, along-strike changes to either parameter results in significant differences in the surface stress distribution. Higher stresses build within the side that has a thicker overriding plate or stronger interface. This increase in stresses results in greater topography, with a maximum variation along-strike of up to ~1.2 km.

How to cite: Neuharth, D., Behr, W., and Holt, A.: Numerically modelling along-strike rheologic variations in 3D subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11688, https://doi.org/10.5194/egusphere-egu23-11688, 2023.

EGU23-13467 | Orals | GD4.2

Processes related to the rift-to-collision transition in the eastern Betics as revealed by low-temperature thermochronology on magmatic, U-Pb dating and clumped isotopes on calcite-filled veins 

Frédéric Mouthereau, Marine Larrey, Louise Boschetti, Nicolas Beaudoin, Stéphanie Brichau, Nick Roberts, Damien Huyghe, Matthieu Daëron, Véronique Miegebielle, and Sylvain Calassou

The Alboran margin in the Betics formed as a result of backarc crustal thinning oblique to the direction of the slab retreat. The history of sediment infill, subsidence and faulting reveals extension at upper crustal levels operated from the Serravallian-early Tortonian to the late Tortonian (14-8 Ma) synchronously with Ca-K magmatism. Only recently, around 8 Ma, the retreating slab detached resulting in the onset of the tectonic inversion of the margin. Here we report new apatite (U-Th)/He thermochronological analyses from Cabo de Gata magmatic province, and new U-Pb dating, Oxygen (O) and carbon (C) stable isotopic analyses of calcite-filled veins from the Tabernas basin combined with fluid temperatures determined by clumped isotope D47 analyses. U-Pb ages from 8.56 ± 0.21 to 4.88 ± 0.45 Ma are remarkably synchronous with late alkaline Tortonian-Messinian magmatic events and post-Messinian uplift. Low-temperature thermochronology confirms that magmatic edifices cooled below sea-level at around 8-7 Ma, and then slowly exhumed onshore during shortening along the Carboneras fault and regional kinematic reorganisation associated with slab detachment. C and O isotopic compositions (-17.23‰ to -9.08‰ for O and -15.77‰ to -1.60‰ for C, in V-PDB) of calcite veins are close to carbonates endmember of the Alpujárride basement. The O and C isotopes trend highlights a burial where all δ18O and δ13C calcite have depleted values compared with host rocks indicating a higher temperature of calcite precipitation (estimated at 83.7°C) and an increasing organic matter degradation with depth. The concordance on ages suggests that deep processes including mantle delamination and hot mantle triggered CaCO3 fluid precipitation and uplift during the transition from extension to onset of tectonic inversion. The deep mantle processes related to the 8 Ma event impacted not only the uplift of the Alboran basin that caused the Messinian Salinity Crisis that is well recorded in the Betics, but also the recent uplift of Iberia and Western Europe.

How to cite: Mouthereau, F., Larrey, M., Boschetti, L., Beaudoin, N., Brichau, S., Roberts, N., Huyghe, D., Daëron, M., Miegebielle, V., and Calassou, S.: Processes related to the rift-to-collision transition in the eastern Betics as revealed by low-temperature thermochronology on magmatic, U-Pb dating and clumped isotopes on calcite-filled veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13467, https://doi.org/10.5194/egusphere-egu23-13467, 2023.

EGU23-13615 | ECS | Orals | GD4.2

Lithospheric Controls on the Distribution of Porphyry Copper Deposits 

Simon Stephenson, Mark Hoggard, Marcus Haynes, Karol Czarnota, and Krystian Czado

Lithospheric structure in subduction settings controls the distribution of thermal, compositional and rheological interfaces.  It therefore plays a key role in the generation, fractionation and transport of subduction-related melts that are a vital ingredient of the formation of porphyry copper deposits.  Renewed efforts to understand the linkage between lithospheric structure and the location, grade and endowment of porphyry copper deposits has raised the possibility of using crustal and lithospheric mantle structure as an exploration tool.  One example is a suggested relationship between the genesis of porphyry copper deposits – known to be associated with evolved, silica-rich magmas – and the thickness of the crust.  Here, using a new compilation of spot measurements, we explore the utility of crustal thickness as an exploration tool for porphyry copper deposits.

How to cite: Stephenson, S., Hoggard, M., Haynes, M., Czarnota, K., and Czado, K.: Lithospheric Controls on the Distribution of Porphyry Copper Deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13615, https://doi.org/10.5194/egusphere-egu23-13615, 2023.

EGU23-13902 | ECS | Posters on site | GD4.2

Multi-scale numerical modelling of subduction interface rheology 

Paraskevi Io Ioannidi and Wouter Pieter Schellart

The physical nature and the rheology of the subduction interface play an important role in the deformation of the overriding plate, the degree of locking of the subduction zone plate boundary, and the rate of subduction. Here, we employ the Finite Element Method (FEM) to determine the effect of matrix rheology on the bulk interface deformation. We use the open-source particle-in-cell FEM code Underworld (Moresi et al., 2007) to create synthetic 2D visco-plastic models of the subduction interface that deform by simple shear. The models comprise meter-scale blocks of continental affinity encompassed within a metasedimentary matrix. We investigate the effect of constant, Newtonian, and non-Newtonian matrix viscosities on the deformation and stress distribution in the models for large finite shear strains. We vary the percentage of block concentration from 10% to 65%, as well as the shear velocity while making sure the strain rates produced remain within the interseismic range, and we calculate strain localization and stresses within the models. Finally, we use the same viscosity formulations in large-scale 2D models of a subduction zone to investigate their influence on upper plate deformation and subduction rate during the interseismic stage. With this multi-scale analysis, we gain insight into how the same rheological law can affect deformation at different scales.

How to cite: Ioannidi, P. I. and Schellart, W. P.: Multi-scale numerical modelling of subduction interface rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13902, https://doi.org/10.5194/egusphere-egu23-13902, 2023.

EGU23-14047 | ECS | Posters on site | GD4.2

The growth of Turkish – Iranian Plateau and comparative models for understanding the deformation on the overriding plate during plateau formation 

Uğurcan Çetiner, Jeroen van Hunen, Oguz H. Gogus, Mark B. Allen, and Andrew P. Valentine

The Arabia-Eurasia collision, which started during Late Eocene (~35 Ma) or afterward across the Bitlis-Zagros suture, resulted in the formation of the Turkish – Iranian Plateau. Even though the average elevation throughout the plateau is around 2 km, the lithospheric structures between East Anatolian and the Iranian parts may be different. For instance, seismological studies suggest that East Anatolia is underlain by anomalously low-speed anomalies/hot asthenosphere whereas the Iranian part is associated with a rather thick (>200 km in some places) and strong lithosphere. Therefore, the area may be regarded as two distinct regions, namely, the East Anatolian Plateau and the Iranian Plateau. The growth of the plateau is mostly attributed to slab break-off combined with crustal shortening. Other processes often associated with the collision are lithospheric delamination and tectonic escape of microplates. These hypotheses suggested for the growth of the plateau are yet to fully explain the dualistic nature of the lithosphere in a region where elevations are roughly similar. In this work, by using 2D numerical experiments we aim to investigate the physical, geometric, and rheological parameters affecting the deformation of the plate during pre-, syn-, and post-collision. Our preliminary model results show an extension (up to ~70 km) on the terrane that is dragged behind the subducting plate, while the overriding plate undergoes shortening during the collision. The collision results in ~100 km of underthrusting in 50 Myrs which is in the range for the measured amounts of underthrusting across the plateau. We aim to expand the study by creating comparative model sets (i.e., models representing East Anatolia vs. models representing Iran) with a parameterization of varying lithospheric structures (e.g., different crust and mantle thicknesses), and strength profiles, which will help us to understand the kinematics and dynamics of such orogenic growth.

How to cite: Çetiner, U., van Hunen, J., Gogus, O. H., Allen, M. B., and Valentine, A. P.: The growth of Turkish – Iranian Plateau and comparative models for understanding the deformation on the overriding plate during plateau formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14047, https://doi.org/10.5194/egusphere-egu23-14047, 2023.

EGU23-14049 | Orals | GD4.2

A 3-D numerical investigation of the impact of buoyant features on subduction dynamics and stress 

Lior Suchoy, Saskia Goes, Fangqin Chen, and D. Rhodri Davies

The subduction of positively buoyant features has been suggested to cause flat or shallow dipping slabs, the formation of cusps in trench geometry and periods of reduction or full cessation of arc magmatism. Additionally, recent earthquake data indicates that the subduction of the Hikurangi plateau near New Zealand causes a rotation of intraplate stresses. In this study, we present a series of multi-material 3-D simulations of free subduction to investigate how subduction of buoyant elongated features, or ridges, impact downgoing plate velocities, trench motions, slab morphology and intraplate stress regime. We examine how these parameters are affected by the age of the subducting plate and the relative buoyancy and position of the buoyant ridge. We find that buoyant ridges change slab sinking and trench retreat rates and locally rotate intraplate stresses. These, in turn, modify the evolution of slab morphology at depth and trench shape at the surface, as trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young and weak plates, the change in trench shape is more localised than on old and strong plates. We observe slab shallowing around the ridge only in young plates, while the stronger pull by the more negatively buoyant old plates causes slab steepening near the buoyant ridge. Buoyant ridges on old plates which are located near stagnating or advancing regions, typical in wide slabs, modify trench behaviour more strongly than ridges in other regions of the trench. Bending-related intraplate earthquakes are more likely in older plates where higher stress is accumulated and the rotation due to the buoyant ridge is more widespread than for younger plates. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the formation of a flat slab, a variation in expressions also observed on Earth.

How to cite: Suchoy, L., Goes, S., Chen, F., and Davies, D. R.: A 3-D numerical investigation of the impact of buoyant features on subduction dynamics and stress, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14049, https://doi.org/10.5194/egusphere-egu23-14049, 2023.

EGU23-14144 | ECS | Orals | GD4.2

Insights into slab detachment dynamics from 0D to 3D numerical experiments   

Andrea Piccolo, Marcel Thielmann, and Arne Spang

Slab detachment is a process that has been invoked to explain rapid uplift, deep seismicity and magmatic activity in several active orogens (e.g., Alps, Himalaya). The negative buoyancy force associated with a slab at depth and its progressive removal during detachment results in a reorganization of forces within the lithosphere and the detaching slab. However, it is not yet clear to which extent slab detachment is the primary cause of the different observations. Deciphering the impact of slab detachment on the observations mentioned above therefore requires a thorough understanding of the physical processes controlling deformation within and around the detaching slab. 

Here, we employ numerical models to investigate the nonlinear coupling between mantle flow and slab detachment. Due to the three-dimensional nature of slab detachment and the variety of involved processes, it is difficult to pinpoint the first order controls on the time scale of this process. As a first step, we therefore develop a simplified 0D necking model that describes the temporal evolution of the thickness of a detaching slab, additionally taking into account the effects of the nonlinear coupling between upper mantle and detaching slab. This allows us to derive a set of nondimensional numbers which ultimately control the slab detachment process.  

Based on these findings, we then use 2D and 3D numerical models to further determine higher dimensional geometrical effects on slab detachment. Results show that the predictions from the 0D experiments predict the 2D and 3D experiments sufficiently well if simple slab geometries are used. For more complex slab geometries, higher dimensional results deviate from the 0D predictions. Nevertheless, the combination of 0D and 2D/3D numerical models allows to efficiently determine first order controls on slab detachment and thus also on specific geological observations such as seismicity and surface response. 

How to cite: Piccolo, A., Thielmann, M., and Spang, A.: Insights into slab detachment dynamics from 0D to 3D numerical experiments  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14144, https://doi.org/10.5194/egusphere-egu23-14144, 2023.

Continental collision zones form at convergent plate boundaries after negatively buoyant oceanic lithosphere subducts entirely into the Earth's mantle, whereafter collision ensues, and colliding continents are sutured together. In models of free subduction, the volume of the preceding and adjacent negatively buoyant oceanic lithosphere controls the system's driving force and dynamics. To investigate the dynamics of long-term continental subduction, indentation and collisional boundary migration and associated slab dynamics we designed large-scale numerical models of subduction-and-collision including two sets of modelled depths: whole mantle (2880 km) and upper mantle + partial lower mantle (960 km) and varying the trench parallel length ratio (1.5 - 2) of the indenting continental lithosphere (~2300 km) and adjacent oceanic lithosphere. In this contribution, we present the contrasting evolution of continental subduction and indentation coupled with adjacent oceanic slab rollback focusing on the different slab dynamics observed by varying the depth of the mantle in the models. Intriguingly, the whole mantle models show sustained continental indentation and concurrent deep continental subduction to mid-low upper mantle depths resulting in deep slab tearing at the subducted continental margin and shallow slab tearing at the trench parallel boundaries of the continental plate. In addition, the models also show continental underthrusting beneath the overriding plate and underplating of the continent, coeval with indentation and adjacent oceanic slab rollback. Together, these results provide insights into the India-Eurasia collision zone where the prolonged northward indentation of India during the last 50 Myrs and the rollback of the Sunda slab appear linked.

How to cite: Laik, A., Schellart, W., and Strak, V.: Protracted continental subduction, indentation and collisional boundary migration coupled with adjacent oceanic slab-rollback and slab detachment in large-scale buoyancy-driven 3D whole-mantle scale numerical models of subduction-and-collision., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14232, https://doi.org/10.5194/egusphere-egu23-14232, 2023.

EGU23-15571 | Orals | GD4.2 | Highlight

Sharpening our community research on the initiation of subduction zones 

Fabio Crameri

Current research on how, when, and where subduction zones initiate (one of the key, long-lasting open questions in the Earth Sciences) spans a multitude of (if not all) Earth and Planetary Science disciplines, engages most geoscientists at least once during their career, occupies research vessels and supercomputers, remains a steady appearance in overarching science journals, and often is considered the holy grail of our field.

It is maybe not surprising that the study of subduction zone initiation (SZI) has therefore created a multitude of different research approaches and divided sub-disciplines applying specific methodologies and field-specific jargons and terms, of which neither is understood across sub-discipline boundaries any longer. To make it worse, a few leading SZI researchers have stopped acknowledging each other’s work, even scientifically.

Within all sub-disciplines that exploit the rock record, plate reconstructions, geophysical measurements like seismic tomography, and theoretical and numerical modelling, we have never learned more about the formation of subduction zones than in the past couple of years. As a community, however, we failed to bring the dispersed knowledge (and sources of information) to a common ground and progress: Numerous numerical models on passive margin SZI made some geoscientists believe that it is the most likely place for SZI to occur. Misleading terminology made others believe that SZI can occur "spontaneously" or that "fore-arc basalts" (FABs) are formed in fore-arcs.

With the community-based, community-driven, community-accessible Subduction-Zone Initiation (SZI) Database (www.SZIdatabase.org), we turn the helm towards a more unified, collaborative approach again. We provide the most extensive and detailed collection of current, trans-disciplinary SZI data (and from just this, a wealth of new insights), suggest a commonly-accessible SZI-related terminology, and offer a platform for community-wide, always-on discussion (see Crameri et al., 2020).

Everything is put in place to reunite, and not loose track of, all our individual efforts and advances, so we, as a community, can learn and understand more about this enigmatic, truly cross-disciplinary hallmark of our fascinating planet.

 

Crameri, F., V. Magni, M. Domeier, G.E. Shephard, K. Chotalia, G. Cooper, C. Eakin, A.G. Grima, D. Gürer, A. Király, E. Mulyukova, K. Peters, B. Robert, and M. Thielmann (2020), A transdisciplinary and community-driven database to unravel subduction zone initiation, Nature Communications, 11, 3750. doi:10.1038/s41467-020-17522-9

How to cite: Crameri, F.: Sharpening our community research on the initiation of subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15571, https://doi.org/10.5194/egusphere-egu23-15571, 2023.

At mid-oceanic ridges, mantle temperature and magma supply influence the structure of the neo-volcanic zone. Due to the large Romanche offset, a strong “cold edge” effect is present at its eastern intersection with the Mid-Atlantic Ridge. This effect decreases with the distance from the transform fault, making this region an ideal area to study the impact of the thermal gradient on the architecture of the neo-volcanic zone. We analyzed seafloor videos and photos from submersible dives, as well as bathymetry and backscatter data collected during the SMARTIES cruise (2019), from the Ridge-Transform Intersection (RTI) to approximately 80 km to the south of it. We produced maps at local and regional scales and quantified the morphology of volcanoes (height, diameter, height/diameter ratio, volume and surface). Visual observations have showed that the seafloor is mainly made up of pillows or elongated pillows and rare massive lava flows. Within 30 km of the RTI, the neo-volcanic area is characterized by clusters of volcanoes, affected by faults trending N120-130° E, oblique to the extension and to the transform fault orientation, and by faults trending E-W. At 30 km to 50 km from the RTI, the Central segment displays a robust volcanic ridge oriented N150°E built by a pilling of volcanoes and narrow ridges. Its eastern and southern parts are old and characterized by oblique faults and narrow ridges (N130-140°E), while the northwest portion is more recent, faults and ridges are almost normal to the extension. The southernmost segment, located at 80 km from the RTI, is orthogonal to the spreading direction and asymmetric, bounded at the west by a detachment fault. Recent volcanic edifices were observed from the center of the segment to the base of the detachment. Our observations suggest that the neo-volcanic area is fed by more and more magma from north to south. This increase in magma supply is marked by a more structured volcanic axis, volcanoes that are more voluminous and a change in the orientation of the segments and faults. Changes in the orientation of faults and off-axis abyssal hills also reveal variations in the magmatic supply over time.

How to cite: Grenet, L., Maia, M., Hamelin, C., Briais, A., and Brunelli, D.: Construction of the neo-volcanic area of a slow-spreading ridge in a cold mantle context: Mid-Atlantic Ridge Eastern Intersection with Romanche Transform Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-742, https://doi.org/10.5194/egusphere-egu23-742, 2023.

EGU23-869 | ECS | Orals | GD5.2

Gravity signature in the mid-ocean ridge-transform system: Insights from deep mantle rheology and shallow crustal structure 

Sibiao Liu, Zhikui Guo, Lars Rüpke, Jason P. Morgan, Ingo Grevemeyer, and Yu Ren

Gravity signals over the mid-ocean ridge-transform system reflect the distribution of underlying crustal and upper mantle mass anomalies. The gravity measurement, especially ‘residual’ gravity anomalies, relies on the gravitational corrections of both seafloor relief and lithospheric thermal structure. Lithospheric thermal correction typically uses a 1D plate cooling approximation or a 3D passive flow model that assumes isoviscous mantle rheology. As this rheological approximation is oversimplified and physically complex, how sensitive gravity anomalies are to an increasingly complex/accurate approximation for mantle rheology is still unresolved. Here we systematically examine the residual gravity anomaly discrepancies caused by assumptions of different mantle rheologies on 16 natural ridge-transform systems ranging from ultraslow- to fast-spreading. Our calculations show that estimated residual gravity anomalies are significantly lower (e.g., ~21 mGal lower at mid-ocean ridges) in the isoviscous flow models than in the static plate cooling models, primarily due to the effects of lateral heat advection and conduction. When the assumed mantle rheology is changed from uniform viscosity to a non-Newtonian viscosity with brittle weakening in cooler (faulting) regions, the mantle upwelling intensifies and local near-surface temperature generally increases, resulting in an increase in the residual anomaly. This increase is distributed uniformly along the ultraslow-and slow-spreading ridge axes, but is concentrated along transform faults at intermediate- and fast-spreading ridges. The amount of the rheology-induced gravity difference is most closely linked to transform age offset instead of spreading rate or transform offset length alone. Our analysis reveals that oceanic transform faults exhibit higher gravity anomalies than adjacent fracture zones, which may reflect thinner crust in the transform deformation zone.

How to cite: Liu, S., Guo, Z., Rüpke, L., Morgan, J. P., Grevemeyer, I., and Ren, Y.: Gravity signature in the mid-ocean ridge-transform system: Insights from deep mantle rheology and shallow crustal structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-869, https://doi.org/10.5194/egusphere-egu23-869, 2023.

EGU23-1567 | ECS | Orals | GD5.2 | Highlight

Evolution of Icelandic rift zones geometry as result of MOR-plume interaction 

Viacheslav Bogoliubskii, Evgeny Dubinin, and Andrey Grokholsky

Rift zones of Iceland large igneous province (LIP) have complicated interior geometric pattern expressing in several parallel extension centers. It significantly differs from adjacent Reykjanes (RR) and Kolbeinsey (KR) mid-oceanic ridges (MOR) that only have small overlappings between separate neovolcanic centers. At small scale, rift zones connect with each other by broad transform zones with distributed strain pattern instead of typical narrow transform faults. Those transform zones have very different structure varying from simple book-shelf fault zones of South Iceland seismic zone to sophisticated system of magmatic and amagmatic structures of Tjörnes transform zone. The whole system drastically differs from typical structure and geometry of ultra-slow MOR. Iceland rift zone evolution commenced at 25 Ma and strongly influenced by thermal pulses of Iceland plume each 6-7 My and slightly asymmetric spreading. Another challenge of this region lies in asymmetric thermal influence of Icelandic plume. RR is affected by plume at distance of at least 800 km, whereas Kolbeinsey ridge at distance of ca. 600 km. To reveal the ridge-plume interaction through Iceland evolution and possible causes of Icelandic plume influence asymmetry we used a method of physical modelling. The extending setting comprises mineral oils mixture that have numerical resemblance with oceanic crust in density, shear modulus and thickness. Two-layered model have elastic bottom layer, brittle top one and local heating source (LHS) corresponding to Icelandic plume pulses. The first experiment type configuration includes two sections corresponding to RR and KR. At their joint, the LHS melts the modelling lithosphere creating analogue of LIP. The LHS periodically switched on and transported to another position, which is similar to plume pulses in asymmetric spreading conditions. The general pattern of each cycle is as following. Initially within LIP two rift branches propagate to each other forming an overlapping. A block between two rift branches rotates as horizontally as vertically. These blocks express in Iceland topography as uplifted peninsulas of its northwestern part. In some time, overlapping transforms to oblique transfer zone and rift zones change their structure of several extension centers to one-axis structure and have direct connection. Then new plume pulse rejuvenates the cycle. If incipient offset between rift branches is quite small, then overlapping structure passes to oblique transform zone with several extension centers and small overlappings. Thermal pulses of less volumes have considerable influence as well, but current data cannot permit to correctly them. As a result, we created a conceptual model of Iceland rift zones evolution also using data of other researchers. The second model had the same initial configuration, but thermal pulses extend downward to modelling Reykjanes ridge. This migration caused by density heterogeneities of upper layers due to deep thermal differences. The resulting geometry is very similar to natural one. There are different segmentation pattern at both spreading ridges and some rift zones. Developed transform zones confine rotating blocks and have structure varying from book-shelf fault zone to overlapping as in nature. We infer that modeled asymmetry and origination can reflect the natural ones.

How to cite: Bogoliubskii, V., Dubinin, E., and Grokholsky, A.: Evolution of Icelandic rift zones geometry as result of MOR-plume interaction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1567, https://doi.org/10.5194/egusphere-egu23-1567, 2023.

EGU23-1879 | Posters on site | GD5.2

Ocean Bottom Seismic Survey 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. The aim of this work is to better understand the lithospheric structure beneath the rare ultraslow-spreading ridges, using as example the Knipovich Ridge along its spreading direction. Ultraslow spreading ridges are characterized by a low melt supply. At spreading rates below 20 mm/y, conductive cooling effectively reduces the mantle temperature and results in less melt produced at larger depths. 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. This profile is a prolongation of the previously acquired profile AWI-20090200 (Hermann & Jokat 2013) and together allow for the modeling of ~535 km long transect crossing the Knipovich Ridge from the American to the European plate. Seismic record sections were analyzed with 2D trial-and-error forward seismic modeling. 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 Survey in the Knipovich Ridge area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1879, https://doi.org/10.5194/egusphere-egu23-1879, 2023.

EGU23-2230 | ECS | Orals | GD5.2 | Highlight

Highly Asymmetric Seismicity in a System of Tectonic Extension and Hydrothermal Venting at the Mohn-Knipovich Ridge Bend 

Matthias Pilot, Marie Eide Lien, Vera Schlindwein, Lars Ottemoeller, and Thibaut Barreyre

In recent years hydrothermal vent systems were found in unexpectedly high abundance along ultraslow spreading ridges, despite their overall decreased magma supply. Thin oceanic crust and resulting shallow heat sources can drive hydrothermal fluid circulation and detachment faults can act as fluid pathways, resulting in e.g., serpentinization of the oceanic crust. So far, no long-term recording of seismicity around hydrothermal vent systems along ultraslow spreading ridges have been reported. Here, we present results from a ~1-year local Ocean Bottom Seismometer deployment between 2019 - 2020 at Loki’s Castle hydrothermal vent field (LCVF) along the Arctic Mid Ocean Ridge. LCVF is located at a water depth of ~2500m on top of the axial volcanic ridge (AVR) at the Mohn-Knipovich Ridge bend where spreading is highly asymmetric from west to east.

For the processing we use a combination of an automatic event detection algorithm (Lassie), a deep-learning phase picking model (PhaseNet) and partial manual re-evaluation of phase picks. Additionally, selected clusters of events are cross-correlated and relocated using hypoDD. The resulting earthquake catalogue consists of a total of 12368 events with 6719 manually re-evaluated and 5649 automatically picked events.

From the results we see that most of the plate divergence at the Mohn-Knipovich Ridge bend is accommodated by a young detachment fault west of the AVR. Most of the seismicity occurs between depths of ~2-8km in a bended band that steepens up to 70° with depth and follows the local topography. However, the described detachment fault differs from reported mature detachment faults at the Mid-Atlantic Ridge or Southwest Indian Ridge. Within the footwall we observe episodical, clustered seismicity with extensional faulting mechanisms, indicating that the detachment could be cross-cut by normal faults. Along strike, the seismicity of the fault plane appears highly heterogeneous, with the central part showing only sparse seismicity at depths below 3km while other segments show episodical shallow seismicity. Towards LCVF seismicity below the AVR increases and the maximum depth of earthquakes shallows by about ~2km. This could indicate the presence of a shallow heat source below LCVF as a driving factor for the hydrothermal circulation.

How to cite: Pilot, M., Lien, M. E., Schlindwein, V., Ottemoeller, L., and Barreyre, T.: Highly Asymmetric Seismicity in a System of Tectonic Extension and Hydrothermal Venting at the Mohn-Knipovich Ridge Bend, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2230, https://doi.org/10.5194/egusphere-egu23-2230, 2023.

The significant discrepancy between the observed conductive heat flow and predictions by thermal models for oceanic lithosphere younger than 50 Ma is generally interpreted to result from hydrothermal circulation between basement outcrops. Numerical simulations of fluid flow between such outcrops performed in previous studies revealed that establishing horizontal pressure gradients to sustain a hydrothermal siphon requires high aquifer permeabilities and a contrast in the outcrops’ transmittance, which is the product of the outcrop permeability and the area of outcrop exposure. However, most previous studies focused on the model parameters needed to sustain a hydrothermal siphon, while the physical processes that create the horizontal pressure gradients in the first place remain poorly constrained.

In order to shed more light on the physics behind outcrop-to-outcrop flow, a simple synthetic 2D model of two outcrops connected by a permeable aquifer was set up. Fluid flow modelling was done by using hydrothermalFoam, a hydrothermal transport model, that is based on the open-source C++ computational fluid dynamics toolbox OpenFOAM. Our initial simulations focus on variations of the permeability of the outcrops and the aquifer. The results reveal two key points that are essential to generate a flow: First, the outcrops permeability has a fundamental effect on its average pressure. High permeabilities lead to a rather "cold" hydrostatic pressure regime with lower temperatures and hence higher average pressures. Lower outcrop permeabilities are accompanied with a rather "warm" hydrostatic pressure regime characterized by higher temperatures and lower average pressures. Secondly, fluid convection in the aquifer is necessary to establish a siphon flow. Therefore, the aquifer permeability must be sufficiently high to overcome Darcy resistance and yet low enough to prevent the flow from being solely diffusive.

How to cite: Kremin, I., Guo, Z., and Rüpke, L.: The effect of permeability on the pressure regime in 2D outcrop-to-outcrop submarine hydrothermal flow models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2737, https://doi.org/10.5194/egusphere-egu23-2737, 2023.

The Earth System appears increasingly interconnected and hydrothermal discharge at back smoker vent sites is not only visually appealing, it also sustains unique ecosystems, generates large polymetallic sulfide deposits, and modulates ocean biogeochemical cycles. At slow spreading ridges, fault zones seem to provide stable preferential fluid pathways resulting in the formation of the ocean’s largest sulfide deposits. The TAG hydrothermal mound at 26°N on the Mid-Atlantic Ridge (MAR) is a typical example located on the hanging wall of a detachment fault. It has formed through distinct phases of high-temperature fluid discharge lasting 10s to 100s of years throughout at least the last 50,000 years and is one of the largest sulfide accumulations on the MAR. Yet, the mechanisms that control the episodic behavior, keep the fluid pathways intact, and sustain the observed high heat fluxes of possibly up to 1800 MW remain poorly understood. Previous concepts involved long-distance channelized high-temperature fluid upflow along the detachment but that circulation mode is thermodynamically unfavorable and incompatible with TAG's high discharge fluxes. Here, based on the joint interpretation of hydrothermal flow observations and 3-D flow modeling, we show that the TAG system can be explained by episodic magmatic intrusions into the footwall of a highly permeable detachment surface. These intrusions drive episodes of hydrothermal activity with sub-vertical discharge and recharge along the detachment. This revised flow regime reconciles problematic aspects of previously inferred circulation patterns and allows to identify the prerequisites for generating substantive seafloor mineral systems.

How to cite: Guo, Z., Rüpke, L., and Tao, C.: Detachment-parallel recharge explains high discharge fluxes at the TAG hydrothermal field-Insights from 3D numerical simulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2767, https://doi.org/10.5194/egusphere-egu23-2767, 2023.

EGU23-3138 | ECS | Orals | GD5.2

Oceanic transform faults offshore São Tomé and Príncipe highlighted by integrated density and magnetic modeling of the crust 

Peter Haas, Myron Thomas, Christian Heine, Jörg Ebbing, Andrey Seregin, and Jimmy van Itterbeeck

The Eastern Gulf of Guinea hosts several buried Cretaceous-aged oceanic fracture zones. 3D broadband seismic data acquired offshore São Tomé and Príncipe revealed a complex crustal architecture. Mapped oceanic fracture zones show low-angle reflectors that detach onto or eventually cross through the Moho boundary, overlain by strong reflectors that are interpreted as transform process related extrusive lava flows. Here, we use a high resolution shipborne free-air gravity and total field intensity magnetic data set to reassess whether previously defined seismic models of the crust are in conformity with potential field data. The study area is located offshore São Tomé with a size of c. 150x150 km. Using the software IGMAS+, we model the gravity and magnetic properties of the crust (i.e. density and susceptibility) in 3D. Long record length seismic sections plus mapped seismic horizons, which include bathymetry, sediments, upper and lower crust, are used as constraints. While the general trend of the free-air anomaly can be explained within a range of expected crustal densities, the magnetic field anomaly reflects high residuals that are predominantly oriented parallel to the transform faults. This indicates that gravity and magnetic data cannot be explained by the same simple source geometry. Therefore, we first perform sensitivity tests to isolate the source of the residual magnetic anomaly, followed by a structural analysis along the transform faults with special emphasis to the extrusive lava flows in the crustal domain. Our final model reconciles seismic horizons and potential field data and will stimulate a discussion on the architecture and evolution of transform faults and their signatures in different data sets.    

How to cite: Haas, P., Thomas, M., Heine, C., Ebbing, J., Seregin, A., and van Itterbeeck, J.: Oceanic transform faults offshore São Tomé and Príncipe highlighted by integrated density and magnetic modeling of the crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3138, https://doi.org/10.5194/egusphere-egu23-3138, 2023.

EGU23-3562 | ECS | Posters on site | GD5.2

Deformation along the Oceanographer Transform Fault from fault mapping and thin section analysis 

Anouk Beniest, Katharina Unger Moreno, Lizette Dedecker, Bente Schriever, and Thor Hansteen

The Oceanographer Transform Fault is an oceanic transform fault that offsets a segment of the Atlantic Mid-Oceanic Ridge (MOR), southwest of the Azores. We investigate how deformation is accommodated along an active transform through the interpretation of fault patterns and geomorphological features on high resolution bathymetry and a petrological and kinematic analysis of thin sections.

The bathymetric interpretation yielded six different domains which consisted of 1) the main transform zone with E-W running strike-slip faults, 2) the NNE-SSW oriented MOR valley, 3) the abyssal domain hosting NNE-SSW oriented normal faults that bound the abyssal hills, 4) the abyssal domain hosting NE-SW oriented faults, oriented obliquely to the mid-oceanic ridge and the main transform valley, 5) a volcano- and lava flow rich domain and 6) a shallow domain with corrugations oriented perpendicular to the MOR with little volcanic cover.

The thin section analysis reveals a complete ophiolitic sequence, including serpentinized peridotite, gabbro and basalt with varying degrees of alteration. Samples retrieved from depths >3500 m show that deformation occurs mainly in the ductile domain through bulging and sub-grain rotation of plagioclase, lamellar feldspar formation (in gabbro), shearing and recrystallisation of gabbro and serpentinization of peridotite. Brittle deformation manifests itself through fracturing of crystals, displacement of plagioclase sub-crystal domains and veining. Especially gabbroic samples show a decrease in serpentinized veins with decreasing depth. Basalts are found only at shallow depth, seemingly covering gabbro, appearing not to be affected by deformation at all, only occasional cracks filled with pristine calcite are observed.

The combination of geomorphological features identified on high-resolution bathymetry maps and the petrological and kinematic analysis of thin sections showed that deformation along the transform fault differs from the deformation that happens at the MOR. Deformation at the MOR is characterized by 1) axis-parallel normal faulting, pulses of volcanism, resulting in elongated ridges and volcanic cones on the ocean floor and the formation of dykes under magma-rich circumstances, and core complex exhumation during magma-starved periods that occurred between 1.8 – 4.2 Ma and around 7.5 Ma along the southwestern MOR segment of the OTF and 2) heavily sheared zones that extend obliquely from the MOR-transform intersection into the adjacent older plate. Deformation at the transform fault is accommodated through serpentinization at depths deeper than 3000 m, leading to pop-up structures in the main transform zone and causing fracturing in the overlying gabbro, allowing hydrothermal fluids to heavily alter deeper rocks and migrate to shallower depths with decreasing alteration of the oceanic crust with decreasing depth.

We hypothesize that the transform fault itself at depth accommodates stresses to a large extent via serpentinization processes in response to strike-slip tectonic activity in a very narrow band in the active, deepest part of the main transform zone. Deformation patterns other than serpentinization and serpentinite veining that are observed in rock samples along the transform fault are the result of earlier tectonic activity that took place during or shortly after the formation of the rock at the MOR.

 

How to cite: Beniest, A., Unger Moreno, K., Dedecker, L., Schriever, B., and Hansteen, T.: Deformation along the Oceanographer Transform Fault from fault mapping and thin section analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3562, https://doi.org/10.5194/egusphere-egu23-3562, 2023.

EGU23-4289 | Posters on site | GD5.2 | Highlight

Oceanic crustal structure at ODP Site 1256 from seismic wide-angle tomography and down-hole logging 

Ingo Grevemeyer, Timothy J. Henstock, Anke Dannowski, Milena Marjanovic, Helene-Sophie Hilbert, Yuhan Li, and Daman A. H. Teagle

Our view on the structure of oceanic crust is largely based the interpretation of seismic refraction and wide-angle experiments, revealing that the upper basaltic crust (layer 2) is a region of strong velocity gradients. In contrast, the lower gabbroic crust (layer 3) is relatively homogeneous, although it generally displays a gentle increase in velocity with depth. Furthermore, the upper crust has been sub-divided into layer 2A, composed of extruded basalts, and layer 2B, formed by basaltic sheeted dikes. Site 1256, drilled during the Ocean Drilling Program (ODP) into the upper crust and later extended into the uppermost gabbroic crust during the Integrated Ocean Drilling Program (IODP), is among the deepest drill sites sampling intact oceanic crust. It is the only site world-wide that crossed the entire basaltic upper crust, reaching plutonic rocks at ~1.35 km below the top of the basement, recovering 150 m of dominantly gabbroic rocks at the base of the hole. Three campaigns of down-hole logging at hole 1256D provided a unique set of high-resolution sonic-log velocities of seismic layer 2 and from the uppermost top of seismic layer 3. However, Hole 1256D was drilled at a site with rather limited seismic data coverage, especially lacking seismic refraction and wide-angle profiling. During a seismic survey of the RRS JAMES COOK in the Guatemala Basin in December of 2022, a seismic profile with 12 Ocean-Bottom-Seismometers spaced at 7 km intervals, receiving signals from a tuned airgun array of 4500 cubic-inches shot at 150 m spacing was collected. The data provide excellent seismic records to derive a detailed sound-velocity model of the oceanic crust at the drill site from tomographic travel time inversion of first arrivals (Pg, Pn) and a prominent wide-angle reflection from the crust-mantle boundary (PmP) or seismic Moho. The results show that the seismic structure along the 115 km long line is extremely homogeneous. The velocity-depth profile from tomography further provides an excellent low-frequency match of the down-hole logging observations, supporting that modern seismic data are a powerful remote sensing tool to study the oceanic crust and lithosphere. An interesting observation is that the thickness of the oceanic crust at Site 1256 is extremely thin at only 4.6 to 5.1 km, compared to a global average thickness of about 6 km. This appears to be a regional feature supported by another seismic profile about 150 km north-eastwards. The thin crust agrees with a weak seismic event at ~6.8 s two-way travel time (twtt), i.e., ~1.6 s twtt below basement obtained from re-processing 6-km-long streamer data from the ODP pre-site survey at Site 1256.

 

How to cite: Grevemeyer, I., Henstock, T. J., Dannowski, A., Marjanovic, M., Hilbert, H.-S., Li, Y., and Teagle, D. A. H.: Oceanic crustal structure at ODP Site 1256 from seismic wide-angle tomography and down-hole logging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4289, https://doi.org/10.5194/egusphere-egu23-4289, 2023.

EGU23-4327 | ECS | Posters on site | GD5.2

High-resolution upper crustal structure from OBH data at the TAG Hydrothermal Field, 26°N on the Mid-Atlantic Ridge 

Szu-Ying Lai, Gaye Bayrakci, Bramley Murton, and Tim Minshull

The Trans-Atlantic Geotraverse (TAG) segment at 26°N on the Mid Atlantic Ridge (MAR) is notable for hosting hydrothermal mounds and seafloor massive sulphide deposits. At the slow-spreading MAR, detachment faulting plays an important role in controlling the seafloor morphology. In this study, we investigate the seismic velocity in the upper crust at a finer scale than previously possible, and its relationship to fault structures.

We used short-offset ocean bottom hydrophone (OBH) data collected during the Meteor 127 cruise in 2016. The survey was designed mainly to study the hydrothermal mounds. We chose a NW-SE trending, 11-km long wide-angle seismic profile that crosses a detachment breakaway identified from AUV bathymetry and seismic reflection profiles. The source was a G-gun array of 760 c. inch towed at 6 m depth. The shot spacing was 12 s (15-20 m) with four OBHs at 1.3 km spacing.

A two-dimensional P-wave velocity model was generated by first-arrival travel-time tomography using the TOMO2D code. We used as our starting model the average 1D velocity depth function of a slice along our profile through Zhao et al’ s (2012) three-dimensional velocity model. Our final tomographic model reveals crustal velocities from 3.4 km/s to 5 km/s for the upper 600 m below seabed. Most of the profile lies beneath the eastern valley wall, where a corrugated detachment surface crops out. Beneath the detachment surface in our profile, we observed an increased velocity of 6.5 km/s at 1.5 km below seabed. Our velocity model suggests that the west-dipping normal fault exhumes lower crust of velocity up to 6.5 km/s.

How to cite: Lai, S.-Y., Bayrakci, G., Murton, B., and Minshull, T.: High-resolution upper crustal structure from OBH data at the TAG Hydrothermal Field, 26°N on the Mid-Atlantic Ridge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4327, https://doi.org/10.5194/egusphere-egu23-4327, 2023.

EGU23-5648 | Posters on site | GD5.2

Temporal variation in spreading processes at the Eastern Romanche-Mid-Atlantic Ridge intersection 

Marcia Maia, Anne Briais, Lorenzo Petracchini, Marco Cuffaro, Marco Ligi, Daniele Brunelli, Lea Grenet, and Cédric Hamelin

We studied the east intersection between the Romanche transform fault (TF) and the Mid-Atlantic ridge using bathymetry and gravity anomalies, to investigate the temporal evolution of the ultra-cold ridge-transform intersection. Our results reveal a complex ridge axis, with evidence of a significant decrease in the along-axis melt supply towards the RTI but also since ~10 Ma.

Over a 100 km distance south of the RTI, the ridge axis is formed by three spreading segments offset by large non-transform discontinuities. Large detachment faults mark the present-day spreading style at the RTI, while magma supply increases away from the Romanche intersection. Axial and near-axis fault patterns reveal a marked obliquity, especially in the north and center of the study area.In lithosphere older than 10 Ma, the ridge axis appears to form a single spreading segment between the Romanche and Chain TFs, perpendicular to the spreading direction, with relatively regular abyssal hills. From around 10 to 3 Ma, oceanic core complexes (OCCs) developed in the northern part of the ridge axis south of the Romanche TF.  The complexity of the ridge axis appears to have increased in the last 3 Ma, with ridge obliquity accompanying axial instabilities and ridge jumps.  At least three eastward ridge relocations were identified immediately south of the Romanche TF, rupturing a series of OCCs located in the African plate, east of the ridge axis. This pattern could reflect a progressive decrease in the melt supply, in particular since 3-5 Ma. This may be related to a significant reduction of the ridge spreading rate as seen from kinematic models which allowed the cooling effect of the large offset Romanche TF to dominate the spreading processes in the area.

How to cite: Maia, M., Briais, A., Petracchini, L., Cuffaro, M., Ligi, M., Brunelli, D., Grenet, L., and Hamelin, C.: Temporal variation in spreading processes at the Eastern Romanche-Mid-Atlantic Ridge intersection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5648, https://doi.org/10.5194/egusphere-egu23-5648, 2023.

The eastern Southwest Indian Ridge (SWIR) is a melt-poor end-member region of the global MOR system. The available magma focuses to axial volcanoes, leaving >50 km-wide, nearly amagmatic ridge sections, where seafloor spreading occurs via large offset detachment faults. We present map to outcrop scale observations of the deformation associated to one of these detachments, in the 64°35'E region of the SWIR. This active detachment fault presently has a horizontal offset of ~4 km (Cannat et al., 2019), and accommodates nearly all the plate divergence (14 km/million year; Patriat and Segoufin, 1988). We focus on the lower slopes of the footwall, where this active fault currently emerges at an angle of ~35°. The emergence is traceable across a length of ~20 km on side-scan sonar and shipboard bathymetry data. It locally shows undulations at a wavelength of ~1-4 km. High-resolution bathymetry at and near the emergence area shows two morphological domains. In one domain, the exhumed fault surface bears distinct corrugations that trend at an 18° to 33° angle to the spreading direction, extends up to 300 m, are spaced by ~15-300 m, and are ~1 m to ~40 m in amplitude. In the other domain, the exhumed fault is not corrugated. Remotely operated vehicle (ROV) dive observations at the outcrop scale show discrete planar fault planes and brecciated and fractured rock forming the top ~1-4 meters of the corrugated exposures. In contrast, the non-corrugated fault exposures show up to ~8 m of gouge-bearing micro-brecciated domains, including several up to 1 m thick horizons of semi-brittle sheared serpentinites. Dive observations further suggest that: (1) there are several sigmoidal intercalations of such gouge-bearing horizons forming the upper few tens of meters of the non-corrugated fault zone, and (2) the horizons of sheared serpentine originated as brittle cracks that served as hydrous fluid pathways into the fault damage zone. We propose: (1) that the absence of corrugations is related to the overall weaker semi-brittle rheology of the emerging fault in this domain, compared to the purely brittle corrugated domain; and (2) that the two domains represent damage developed in distinct conditions of temperature and hydrothermal fluid availability. At the broader map scale, the non-corrugated domain to the east emerges about 1.2 km farther south than the corrugated domain, and the trace of emergence thus draws an indentation between the two domains. Given the ~35° fault emergence angle in the two domains, we infer that their across-fault distance is ~650 m. The detachment damage zone may thus be at least that broad, and comprised of distinct, probably anastomosing domains of more localized deformation, which would preferentially be exposed at the seafloor. This damage zone anatomy would be consistent with seismic refraction observations (Momoh et al., 2017) in the area.

How to cite: Mahato, S. and Cannat, M.: Anatomy of a detachment fault damage zone at a nearly amagmatic mid-ocean ridge: observations from outcrop to map scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6200, https://doi.org/10.5194/egusphere-egu23-6200, 2023.

EGU23-7119 | ECS | Posters on site | GD5.2

Immature transform plate boundaries in the Northeast Pacific: Constraints from ocean bottom seismology 

Yu Ren, Dietrich Lange, and Ingo Grevemeyer

Plate tectonics defines oceanic transform faults as long-lived tectonics features. In the Pacific Ocean their traces, called fracture zones, can easily be identified as several thousands of kilometer-long features in bathymetric and gravity field data. However, today none of the fracture zones in the North Pacific are directly linked to any mid-ocean ridge-transform fault. This feature is related to the subduction of the Farallon spreading center and a major change in the direction of plate motion several millions of years ago. Consequently, ridge segmentation is adjusting to a new tectonic framework. The Blanco transform fault system (BTFS) in the northwest off the coast of Oregon is one of the newly evolving transform faults. It is highly segmented and shows strong similarities with other segmented oceanic transform systems, such as the Siqueiros in the East Pacific Rise, which developed from a pre-existing transform fault subjected to a series of extensional events due to a documented change in spreading direction. However, plate tectonic reconstructions suggested that the BTFS developed from at least two large ridge offsets rather than a single transform fault, emerging from a series of ridge propagation events after the plate reorientation at ~5 Ma.
We used one year of ocean-bottom-seismometer data from the Blanco Transform OBS Experiment (2012-2013) and high-resolution multibeam bathymetry, aeromagnetic, and gravity datasets to study the seismotectonic behavior and tectonic evolution of the BTFS. Interestingly, all available datasets provide no evidence for the existence of either transform faults or fracture zones around the BTFS before 2 Ma, supporting that there were no pre-existing transform faults before the initiation of the BTFS. Therefore, we suggest the BTFS developed from two broad transfer zones instead of pre-existing transform faults. We present seismicity and focal mechanisms for stronger manually-picked events.  Furthermore, the seismic data were picked with a phase picker learned with a large OBS training dataset. The resulting seismicity of ~8,000 events reveals the present-day deformation of the fault system with very high spatial resolution, and supports substantial along-strike variations, indicating different slip modes in the eastern and western BTFS. Seismic slip vectors suggest that the eastern BTFS is a mature transform fault system accommodating the plate motion. At the same time, the western BTFS is immature as its re-organization is still active. The BTFS acts as a natural laboratory to yield processes governing the development of transform faults away from continental rift zones.

How to cite: Ren, Y., Lange, D., and Grevemeyer, I.: Immature transform plate boundaries in the Northeast Pacific: Constraints from ocean bottom seismology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7119, https://doi.org/10.5194/egusphere-egu23-7119, 2023.

EGU23-7479 | Posters on site | GD5.2 | Highlight

Off-axis compression triggered by a seafloor spreading event on the Northern Mid-Atlantic Ridge, 54ºN 

Jean-Arthur Olive, Göran Ekström, W. Roger Buck, Zhonglan Liu, Javier Escartín, and Manon Bickert

Mid-ocean ridges are quintessential sites of extensional deformation, where large-magnitude compressional seismicity is rare and typically confined to transpressional ridge-transform intersections. Here we report on a recent, unusual seismic sequence that included 12 thrust faulting events with magnitudes up to 6, ~25 km off-axis on both sides of the Mid-Atlantic Ridge (MAR) at 54ºN. These compressional events were preceded by a rapidly-migrating swarm of extensional on-axis earthquakes with M≥4.2. We relocated a total of 124 earthquakes and calculated their focal mechanisms using a surface wave-based method. We then modeled the stress state of the ridge flanks to construct a mechanically-consistent interpretation of the sequence, and discuss its significance in terms of seafloor spreading processes.

The sequence started on September 26th, 2022 at 6:07 UTC with a M4.8 normal faulting earthquake at 54º01’N on the Northern MAR, ~125 km north of the Charlie-Gibbs fracture zone. Over 80 normal faulting earthquakes (4.5≤M≤5.8) occurred over the next 3.5 days, with locations steadily migrating southward at ~0.6 km/hr. Earthquake locations form a narrow band that closely follows the axial valley of the symmetric, abyssal hill-bearing 53º30N segment, which is bound by non-transform offsets both to the north and south. Extensional seismicity continued in this band for ~27 more days without a clear propagation pattern. 80 hours into the earthquake swarm, a magnitude-5.7 thrust earthquake occurred ~25 km east of the extensional band. Between September 29, 2022 and January 4, 2023, 11 more thrust events occurred on N-S striking planes east and west of the axis, outlining two narrow bands ~25 km away from the neovolcanic zone. Some of these events seem well aligned with off-axis normal fault scarps, suggesting a possible reactivation of these faults on both flanks.

To better understand this remarkably symmetric pattern of off-axis compression, we model the absolute stress state of the ridge flanks, and the relative stress changes imparted by the on-axis extensional event. 2-D visco-elasto-plastic simulations of slow mid-ocean ridges show that unbending of the lithosphere as it moves out of the axial valley imparts horizontal compression in the cross-axis direction within ~10 to ~40 km away from the ridge axis, and down to ~3 km below seafloor. While this deviatoric compression can reach the brittle yield stress, the associated strain rates are so low that a seismic manifestation of this phenomenon should be extremely rare. On the other hand, the on-axis intrusion of a vertical dike up to a depth of ~5 km below seafloor can put the shallow axis in tension while imparting excess compression on the shallow lithosphere ~25 km off-axis on both sides. Our preferred interpretation is therefore that the extensional swarm represents the southward migration of a blind dike within the neovolcanic axis, which drove both ridge shoulders to compressional failure. Off-axis shortening may thus be an integral component of seafloor spreading that usually operates aseismically, but can be highlighted by certain types of on-axis intrusion events.

How to cite: Olive, J.-A., Ekström, G., Buck, W. R., Liu, Z., Escartín, J., and Bickert, M.: Off-axis compression triggered by a seafloor spreading event on the Northern Mid-Atlantic Ridge, 54ºN, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7479, https://doi.org/10.5194/egusphere-egu23-7479, 2023.

EGU23-7653 | ECS | Posters on site | GD5.2

Earthquake relocations and three-dimensional VP, VS and VP/VS along the fast-slipping Gofar oceanic transform fault, East Pacific Rise. 

Clément Estève, Yajing Liu, Gong Jianhua, and Wenyuan Fan

Fast-slipping mid-ocean ridge transform faults are characterized by quasi-periodic seismic cycles with typical inter-event times of 5 to 8 years. In particular, the Gofar transform fault (GTF) of the East Pacific Rise, generates a MW ~ 6 earthquake every 5 to 6 years on short (~20 km) along-strike segments separated by a barrier zone. Therefore, the GTF presents the opportunity to investigate the relation between fault structure and material properties of this fault to earthquake processes. Here, we perform a joint inversion of P- and S-wave arrival times from local earthquakes to develop three-dimensional seismic velocity models (VP, VS and VP/VS) of the easternmost and westernmost segments (G1 and G3, respectively). The velocity models reveal that G3 is characterized by a more heterogeneous fault zone velocity structure compared to G1. Sharp velocity contrasts are observed along G3 interpreted to reflect along-strike variations in material properties. G1 is characterized by large low-velocity anomaly extending through the entire oceanic crust with subtle along-strike variations. The 2020 Mw 6.1 earthquake occurred within a low VP, low VS and high VP/VS patch along G1 whereas the 2008 Mw 6 earthquake occurred on sharp VP, VS and VP/VS contrast. We also note similarities between the two fault segments. In particular, rupture barrier zones are characterized by a high rate of seismicity and a rapid decrease following the mainshock. We also note the occurrence of deep seismicity in low VP/VS patches beneath the rupture barrier zones, which may indicate sea-water infiltration at 10 to 14 km depth below sea level.

 

How to cite: Estève, C., Liu, Y., Jianhua, G., and Fan, W.: Earthquake relocations and three-dimensional VP, VS and VP/VS along the fast-slipping Gofar oceanic transform fault, East Pacific Rise., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7653, https://doi.org/10.5194/egusphere-egu23-7653, 2023.

The domal structure in the core of the Troodos ophiolite exposes lower crustal (gabbro suite) and mantle rocks (ultramafic province). This structure is part of a fossil ridge-transform intersection (RTI), where an extinct spreading axis meets the fossil oceanic transform, namely the Arakapas transform. A major feature in the RTI system is the Troodos Forest-Amiandos Fault (TAF), an off-axis and axis parallel fault that was active during the Cretaceous seafloor spreading. Here we investigate the deformation across the TAF by measuring paleomagnetic vectors from 34 sites in the gabbro suite around the domal ultramafic core. Special emphasize was along an E-W transect that crosses the TAF south of the sheeted dike complex and north of the ultramafic province. We also compiled dike dips along an E-W strip (6 km wide) north of the gabbro suite. All results were compared to previous paleomagnetic studies from the sheeted dikes and the gabbro suite. Accordingly, we have found that rotations in the gabbro are very similar to those in the sheeted dikes, suggesting coupling of the upper and the lower oceanic crust during axial deformation of seafloor spreading. All rotation axes were horizontal and parallel to the dike strikes, i.e., parallel to the extinct spreading axis. Rotations increase gradually towards the TAF from both sides, eastward in the footwall and westward in the hanging wall. The most plausible scenario is an upward and downward deflection in the footwall and the hanging wall, respectively, similarly described theoretically for the early stages of detachment development. The orientations of the rotation axes of all paleomagnetic vectors indicate spreading-related deformation. This suggests that the relative uplift of the deep-seated rocks was by the development of a young detachment during seafloor spreading rather than serpentinite diapirism. The detachment occurrence in the outside-corner is explained here by the shift from orthogonal to curved axis, inferred from sheeted dike orientations.

How to cite: Abelson, M., Kamahaji, L., Shaar, R., and Agnon, A.: Lithosphere deflection on a juvenile oceanic detachment during seafloor spreading promoted the exposure of the mantle rocks of the Troodos ophiolite – inferences from gabbro paleomagnetism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8330, https://doi.org/10.5194/egusphere-egu23-8330, 2023.

EGU23-9093 | Orals | GD5.2 | Highlight

Oceanic transform faults revisited with models and data 

Lars Ruepke, Ingo Grevemeyer, Zhikui Guo, Sibiao Liu, Ming Chen, Jason Morgan, and Colin Devey

Plate tectonics describes oceanic transform faults as conservative strike-slip boundaries, where lithosphere is neither created nor destroyed. Seafloor accreted close to ridge-transform intersections (RTI) has therefore been expected to follow a similar subsidence trend with age as lithosphere that forms away from RTIs. Our recent combined analysis of high-resolution bathymetric data, satellite gravity, and three-dimensional numerical models from transform faults segmenting mid-ocean ridges across the entire spectrum of spreading rates challenges this concept.  One striking observation is that transform faults are systematically deeper than their adjacent fracture zones. Gravity data suggests that the underlying reason may be changes in crustal thickness, with transform valleys having thin and fracture zones ‘normal’ crustal thicknesses. Another observation is that outside corner crust often shows symmetric abyssal hills with intact flat top volcanoes, while the inside corner regions show intense and oblique tectonic deformation. Furthermore, so-called J-shaped ridges, volcanic ridges that bend towards the active transform, show that magmatic accretion occurs predominantly along the spreading axis, ‘feeling’ the rotating stress field only in the direct vicinity of the RTI. While these observations do show some dependence on spreading rate, they can be identified across a wide range of opening rates, suggesting that they are expressions of processes inherent to transform faulting.

In this contribution, we will review these observations before presenting numerical 3-D thermo-tectono-magmatic models designed to elucidate the underlying processes. These models use a dilation term to mimic magmatic accretion and resolve visco-elasto-plastic deformation. The simulations show that the tectonic deformation axis, the axis of plate separation, becomes oblique at depth resulting in extension and crustal thinning within the transform deformation zones. Complementing simulations that account for magmatic accretion and hydrothermal cooling show that a skew can develop between this oblique deformation axis and the axis of magmatic accretion, implying a possible disconnect between the main diking direction and the direction of tectonic deformation. Taken all evidence together, oceanic transform faulting appears to be much more complex than pure strike-slip motion. It shows a surprisingly complex pattern of tectonic faulting and hints at spill-over magmatism at the RTI.  Crustal accretion at ridge transform intersections may therefore be fundamentally different to accretions elsewhere along mid-ocean ridges.

How to cite: Ruepke, L., Grevemeyer, I., Guo, Z., Liu, S., Chen, M., Morgan, J., and Devey, C.: Oceanic transform faults revisited with models and data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9093, https://doi.org/10.5194/egusphere-egu23-9093, 2023.

EGU23-9241 | ECS | Orals | GD5.2

Geological overview of the Oceanographer Transform Fault 

Katharina A. Unger Moreno, Colin W. Devey, Lars Rüpke, Anouk Beniest, Thor H. Hansteen, and Ingo Grevemeyer

Recent studies on oceanic transform faults, one of the three fundamental types of plate boundaries, has suggested that they may not be purely conservative features and that the crust formed adjacent to them (on the "inside corners" of the ridge-transform intersection) may differ in structure and composition significantly from outside-corner crust. Here we present a geological map of the Oceanographer Transform (Atlantic Ocean, southwest of the Azores) created by combining an interpretation of multibeam bathymetry, rock sampling and seafloor visual observations. We find that outside- and inside-corner crust at the ridge transform intersection have distinctive morphologies and petrography: the outside corner shows rough seafloor, from which only pillow basalts are recovered, extending all the way to the fracture zone. The inside corners, in contrast, are characterized by both rough, basaltic seafloor and regions that are much smoother, from which serpentinized peridotite are often recovered. The width of the inside-corner region showing this variable morphology, bathymetry and petrography seems to vary over time from 10 to 25 km. In two places, oceanic core complex crust is recognized close to the transform in this inside-corner region. We emphasize that plate production at the inside corner appears to occur via a variety of magmatic and amagmatic processes.

How to cite: Unger Moreno, K. A., Devey, C. W., Rüpke, L., Beniest, A., Hansteen, T. H., and Grevemeyer, I.: Geological overview of the Oceanographer Transform Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9241, https://doi.org/10.5194/egusphere-egu23-9241, 2023.

EGU23-9688 | Orals | GD5.2

Segmented Mantle Melting, Lithospheric Rheology and Transform Fault Formation 

Fernando Martinez and Richard Hey

Mantle melting along mid-ocean ridges occurs in a segmented manner.  Melting and melt extraction are greatest within ridge segment interiors but near segment ends mantle upwelling decreases, cooling increases and melt extraction becomes inefficient.  Owing to the strong influence of water on mantle rheology, these effects have important consequences for the strength of oceanic lithosphere.  Residual mantle formed in ridge segment interiors is melt-depleted and dehydrated forming strong rheological bands.  Near segment ends, however, the formation of low-degree hydrous melts predominates, and these are inefficiently extracted from the mantle.  On solidification, these hydrous melts can re-fertilize surrounding mantle with water due to the high diffusivity of hydrogen in mantle material. This results in weak hydrous bands of mantle material near segment ends.  Thus, segmented mantle melting creates a corresponding segmented oceanic mantle rheological structure that favors the localization of shear deformation in the weak bands near segment ends.  Further strain localization within these weak zones may then facilitate additional weakening processes along discrete narrow transform fault zones. We Illustrate our model with geophysical observations from the Reykjanes Ridge and northern Mid-Atlantic Ridge south of Iceland.  The Reykjanes Ridge is a ~1000 km long linear axis without transform faults.  Rapid propagation of melting anomalies along its linear axis precludes a stable magmatic segmentation as shown by its linear mantle Bouguer anomaly.  Immediately south of the Reykjanes Ridge, the northernmost segments of the Mid-Atlantic Ridge have prominent mantle Bouguer anomaly lows indicating stable cells of segmented mantle melting. Transform and non-transform discontinuities immediately form at the ends of the mantle Bouguer anomaly lows.  This model can be extended to explain the occurrence (or absence) of transform faults over the full range of spreading rates from ultra-slow to ultra-fast ridges.

Reference: Martinez, F., and R. Hey (2022), Mantle melting, lithospheric strength and transform fault stability: Insights from the North Atlantic, Earth and Planetary Science Letters, 579, doi:10.1016/j.epsl.2021.117351.

How to cite: Martinez, F. and Hey, R.: Segmented Mantle Melting, Lithospheric Rheology and Transform Fault Formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9688, https://doi.org/10.5194/egusphere-egu23-9688, 2023.

Lithospheric inheritance is known to strongly influence the spatial and temporal patterns of continental deformation in all geodynamic contexts, emphasizing the role of rheological feedbacks between time-spaced geodynamic events. In principle, the transition from continental rifting to sea-floor spreading at diverging plate boundaries marks a threshold beyond which these long-term feedbacks no longer apply. This is because sea-floor spreading is accompanied by the creation of new lithosphere from melting and cooling of the underlying and uprising mantle, which should make lithospheric inheritance negligible at oceanic plate boundaries. However, whether and how lithospheric inheritance continues to affect oceanic plate boundary processes after the continental rifting to sea-floor spreading transition is reached has so far not been explored in detail.

As a young oceanic rift that broke up the Arabia-Nubia Shield and its mosaic of Proterozoic accreted blocks, the Red Sea (RS) represents an ideal case to study these specific lithospheric inheritance effects. We performed a quantitative morpho-structural analysis designed to track along-axis variations of the magmato-structural architecture of the RS plate boundary and to explore its relationships with the inherited structures of the rifted continental plates. Specifically, faults and sea-floor morphology have been mapped over the post-5.3Ma extent of oceanic crust from Global Multiresolution Synthesis (including multibeam surveys) bathymetry. The structural and magmatic patterns have then been extracted by quantifying four metrics: the axial depth, the slope of the central-trough flanks, the proportion of exposed volcanic sea-floor, and the distribution of normal-fault offsets.

This analysis reveals that anomalously deep segments bounded by steeper-than-average flanks bound the central RS in the North and South. Furthermore, it shows that this specific axial topography occurs where the structural pattern locally switches from regularly-spaced and moderate-displacement (~400m) normal faults to one dominant large-displacement (~1200m) fault as well as coinciding with a lower proportion of volcanic sea-floor (15-20% versus 70% on average along the rest of the axis). This distinct magmato-structural signature is commonly interpreted to reflect a decreased fraction of plate separation accommodated magmatically along slow and ultra-slow spreading ridges, in agreement with tectono-magmatic interaction models: individual faults that form near the axis remain active longer and accumulate more displacement when this fraction decreases. On the other hand, a decreased magma input would result in a thinner crust, and thus isostatically account for the anomalous depth of these segments.

The location of these two magma-starved segments appears unrelated to variations in spreading rate or to the segmentation of the RS axis, but stands in the prolongation of two major Proterozoic suture zones within the Arabia-Nubia Shield. On the Arabian side, both of these two inherited structures coincide with a rise of the lithosphere-asthenosphere boundary (LAB) as mapped from S-to-P receiver functions. We therefore propose that on-axis magma starving results from local outward spreading of the upper-mantle upwelling, in turn driven by its off-axis channeling along the LAB topographic highs. Thereby, heat and eventually melts would be transferred from beneath the axis to beneath the onshore suture zones, possibly fueling the Plio-Pleistocene volcanic activity observed there.

How to cite: Moulin, A. and Jónsson, S.: Lithospheric inheritance controls on early sea-floor spreading: new insights from magmato-structural patterns along the Red Sea axis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11070, https://doi.org/10.5194/egusphere-egu23-11070, 2023.

EGU23-11239 | ECS | Posters on site | GD5.2

Characteristics of the George V and Tasman Transform Fault systems, South-East Indian Ridge, and implications for mantle dynamics. 

Rim Jbara, Anne Briais, Etienne Ruellan, Georges Ceuleneer, and Marcia Maia

The George V and Tasman Transform Fault Systems (TFS) are major, right-stepping offsets of the South-East Indian Ridge between 140°E and 148°E. The George V TFS (~140°E) has an offset of about 300 km, and the Tasman TFS (~148°E) an offset of about 600 km. These TFS have multiple shear zones with intra-transform ridge segments (ITRS), mostly unmapped yet. We present the results of the analysis of geophysical and petrological data collected during the STORM cruise (South Tasmania Ocean Ridge and Mantle), completed with global data sets including satellite-derived gravity and bathymetry, and earthquake distribution. The swath bathymetry data cover some parts of the shear zones and only a few of ITRSs. They reveal a complex interaction between tectonic processes at the plate boundary and near-axis volcanic activity along and across the transform faults. In both the George V and Tasman TFS the western ITRS are shallower than the eastern ones, and they appear to receive a lot more magma supply. These western ITRS display off-axis volcanism observed on swath bathymetry or suspected from free-air gravity anomaly highs. In both TFS also, the western shear zone consists of two segments separated by a tectonic massif which we interpret to represent a push-up resulting from transpression along the transform. The mechanism involved in generating the transpression is a lengthening of the western ITRS to the west due to its high magma supply, leading to an overlap between the ITRS and the ridge segment immediately to the west of the TFS, that is in a mechanism similar to the processes currently uplifting the mylonitic massif along the St. Paul TF in the Equatorial Atlantic. The bathymetric and backscatter maps of the western George V TFS also reveal a series of recent off-axis oblique volcanic ridges. Rocks dredged on one of these ridges consist of picrites (i.e. basalts rich in olivine phenocrysts). These observations suggest that both TFS are not magma starved like many mid-ocean ridge transforms, but are the locus of significant primitive melt supply. Such an unexpected production of high-Mg melt might be related to the presence of a mantle thermal anomaly beneath the easternmost SEIR, the result of regional extension following clockwise rotations of the spreading direction, and/or to a western flow of mantle across the TFS. Some of the ITRS actually appeared after changes in the Australia-Antarctic plate motion.

How to cite: Jbara, R., Briais, A., Ruellan, E., Ceuleneer, G., and Maia, M.: Characteristics of the George V and Tasman Transform Fault systems, South-East Indian Ridge, and implications for mantle dynamics., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11239, https://doi.org/10.5194/egusphere-egu23-11239, 2023.

EGU23-11852 | Orals | GD5.2 | Highlight

Accretion of fast-spreading oceanic crust: benefits from large-scale sampling in the Oman ophiolite in combination with cores drilled by the ICDP Oman Drilling Project 

Jürgen Koepke, Dieter Garbe-Schönberg, Dominik Mock, and Sven Merseburger

Based on a newly established profile through fast-spreading oceanic crust of the Oman ophiolite and on cores drilled within the ICDP Oman Drilling Project (OmanDP), we present here the results of 12 years research, focusing on the nature of the magmatic accretion of the deep crust beneath fast-spreading mid-ocean ridges. We established a 5 km long profile through the whole plutonic crust of the Oman ophiolite by systematic outcrop sampling in the Wadi Gideah (Wadi Tayin Block near Ibra), providing the reference frame for the 300 to 400 m long OmanDP drill cores GT1 and GT2 (lower crust, mid-crust), as well as CM1 and CM2 (crust-mantle boundary) drilled into the same area.
The results allow implication on the mechanism of accretion of fast-spreading lower oceanic crust. Depth profiles on bulk rock and mineral compositions, crystallization temperature and microstructures combined with petrological modeling reveal insights into the mode of magmatic formation of fast-spreading lower oceanic crust, implying a hybrid accretion mechanism. The lower 2/3 of the crust (mainly layered gabbros) was formed via the injection of melt sills and in situ crystallization. Here, upward moving fractionated melts mixed with more primitive melts through melt replenishments, resulting in an upward differentiation trend. Since the fraction of crystallization is only small, upmoving melts could easily transport the latent heat produced by deep crystallization upward. The upper third of the gabbroic crust is significantly more differentiated, in accord with a model of downward differentiation of a parental melt originated from the axial melt lens sandwiched between the gabbroic crust and the sheeted dike complex. While the 5 km long profile shed light on the overall magmatic accretion process, the Oman DP drill cores showing ~ 100% recovery allowing high density sampling provide incredible details on the magmatic accretion process. Examples are the identification of individual melt sills from which the layered gabbro section has been formed (drill core GT1) or the detailed observation of olivine accumulation at the base of the crust (drill cores CM1/CM2).

How to cite: Koepke, J., Garbe-Schönberg, D., Mock, D., and Merseburger, S.: Accretion of fast-spreading oceanic crust: benefits from large-scale sampling in the Oman ophiolite in combination with cores drilled by the ICDP Oman Drilling Project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11852, https://doi.org/10.5194/egusphere-egu23-11852, 2023.

EGU23-12073 | Orals | GD5.2

Tectonics controls on melt production and crustal architecture during nearly amagmatic seafloor spreading 

Leila Mezri, Javier García-Pintado, Marta Pérez-Gussinyé, Zhonglan Liu, Wolfgang Bach, and Mathilde Cannat

At ultra-slow ridges, tectonics, hydrothermalism, serpentinization and magmatism interact to build the oceanic crust. How this heterogenous crust forms and relates to faulting remains poorly understood, but is key for elucidating hydrothermal flow patterns and their implications for ocean-lithosphere element exchange. Along the melt-poor Southwest Indian Ridge (SWIR) at 64°30' East, crustal thickness varies across the ridge strike, with crustal thickening attributed to serpentinization extending downward along detachment faults, DFs. This observation calls into question the commonly assumed relationship between local crustal thickening and magma-supply increase. Here we use 2D numerical models to analyze how coupled tectonics, mantle melting, magma emplacement and serpentinization interact. Our model includes hydrothermal cooling, ocean loading, and the oceanic crust density. We reproduce the observed bathymetry at SWIR, 64°30'E, which is shaped by alternating DFs formed in flip-flop mode. Our results show that the offset and duration of DFs are controlled by ocean loading and crustal density. Importantly, shallow faulting and deeper mantle flow are coupled: long-lived DFs result in relatively slower mantle upwelling, lower melt supply, but crustal thickening due to deeper serpentinization, ~5 km, consistent with the observed thick ultramafic crust in nature. In between alternating DFs, mantle upwelling is faster, melt supply higher, and serpentinization shallower, < 2km. Since magmatic crustal thickness is overall very small, 1.5-2 km, changes in faulting-induced serpentinisation depth, are the main cause for observed variations in crustal thickness, 2-7 km. We conclude that, at melt-poor ridges, tectonics controls both crustal thickness variations and melt supply oscillations.

How to cite: Mezri, L., García-Pintado, J., Pérez-Gussinyé, M., Liu, Z., Bach, W., and Cannat, M.: Tectonics controls on melt production and crustal architecture during nearly amagmatic seafloor spreading, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12073, https://doi.org/10.5194/egusphere-egu23-12073, 2023.

The ultramafic Rainbow Massif hosts the high-temperature (HT) Rainbow hydrothermal site, venting H2, CH4 and Fe-rich fluids that support unique macro- and microbial ecosystems. This Massif also sustained low-temperature (LT) hydrothermal circulation associated to fossil bivalve communities, identified at two sites, Clamstone and Ghost City, with 14C and U-Th dates of 25.5 and 110 kyrs, respectively. Furthermore, the Massif is also underlain by seismic reflectors interpreted as stacked melt lenses, the potential heat source for fossil and active hydrothermal outflows. To understand the diversity, controls, and history of ultramafic-related hydrothermal circulation, and how these different systems are sustained over time, the Arc-en-Sub cruise (May 2022) conducted (1) a compliance experiment to determine if deep-seated reflectors are melt-bearing at depth, (2) extensive bathymetric mapping (70 km2) and magnetic surveying with the Autonomous Underwater Vehicle (AUV) IdefX, and (3) extensive geological observations, sampling, and seafloor imaging (3D and photomosaicing) with the Remotely Operated Vehicle (ROV) Victor, along ~100 km of bottom tracks.

Preliminary cruise results reveal corrugated detachment fault surfaces along its western flank, and confirm that the massif is associated with a detachment system rooting westwards, along the S-AMAR ridge segment. The AUV microbathymetry also shows a complex tectonic history of oblique high-angle normal faulting, small-scale detachment faulting, and late strike-slip deformation, with temporal changes yet to be analyzed.

ROV observations and sampling confirmed the dominance of ultramafic rocks in the massif substrate, and revealed previously unknown hydrothermal sites, both active and fossil. First, in addition to Rainbow, we have identified several active sites of a new type, with LT fluids venting at temperatures from a few degrees above ambient seawater, and up to 70°C. This discovery significantly extends the style and areal exposures of present-day activity well beyond the HT Rainbow hydrothermal field (> 10 km2). Second, we have identified numerous fossil carbonate and sulfide hydrothermal chimneys at various locations on the massif that are sometimes in close spatial association, suggesting a temporal evolution of local hydrothermal style. Third, fossil bivalve communities are found over much broader areas than previously described (hundreds of m2), extending along the summit of the Massif and its western flank, demonstrating an extensive, and pervasive diffuse flow in the past. Dating of these sites within a detailed structural framework will constrain the timing and duration of these different hydrothermal events to better evaluate their relationships and their links to the magmatic and structural evolution of the massif. These preliminary cruise results already show complex spatio-temporal dynamics of fluid flow, resulting in a far more varied and widespread hydrothermal activity than expected on ultramafic-hosted environment along mid-ocean ridges. These results also provoke further consideration of the impact of ultramafic hydrothermal systems on thermal and chemical ocean-lithosphere exchanges.

 

How to cite: Escartin, J. and Andreani, M. and the Arc-en-Sub Science Party: Diversity and dynamics of ultramafic-hosted hydrothermal activity at mid-ocean ridges : first results from the Arc-en-Sub oceanographic cruise, Rainbow Massif, 36°14’N MAR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13265, https://doi.org/10.5194/egusphere-egu23-13265, 2023.

EGU23-13725 | ECS | Posters on site | GD5.2

Detachment fault growth modulated by brittle softening and ductile flow in amagmatic (ultra)slow-spread oceanic lithosphere 

Antoine Demont, Jean-Arthur Olive, and Mathilde Cannat

Large-offset detachment faults are common at slow-spreading mid-ocean ridges (MORs). They are typically thought to form in ridge portions that receive a moderate supply of magma. However, they are also found along certain sections of ultraslow-spreading MORs that are largely amagmatic, and feature unusually cold and thick (>15 km) brittle lithosphere. Here we combine geological observations and numerical simulations to assess how these unusual conditions enable and modulate the growth of detachments.

We simulate amagmatic seafloor spreading using 2-D thermo-mechanical models with self-consistent thermal evolution. The brittle lithosphere is modeled as a Mohr-Coulomb elasto-plastic material whose friction decreases with accumulated plastic strain. Ductile deformation is parameterized through experimentally-derived olivine flow laws.

We first investigate how the strength contrast between the fault zone and surrounding lithosphere affects tectonic styles. Geological observations suggest fault zones have lower effective friction coefficients due to serpentinization and fluid circulation.  Evidence for grain size reduction in  ultramafic rocks also suggests additional ductile weakening. In our simulations, varying the strength contrast between faults and lithosphere leads to 3 regimes:  (1) a stable detachment that migrates toward its hanging wall; (2) the sequential growth of horsts bound by two active antithetic faults; and (3) “flip-flopping” detachments that cross-cut each other, comparable to those documented in the natural case. A greater contrast in friction and/or cohesion favors the stable detachment mode, which is consistent with previous studies.

We next focus on the specific effect of a strong, viscous lower lithosphere on brittle deformation in the upper lithosphere. We do so by comparing simulations that use dry olivine flow laws for rocks hotter than ~700ºC with models in which the brittle lithosphere sharply transitions into a low-viscosity asthenosphere. We find that a strong lower lithosphere favors more distributed faulting and shifts the transition to the stable detachment regime to greater strength contrasts.

We also investigate the impact of pervasive fluid circulation in the shallow axial lithosphere, which manifests as active hydrothermal sites. We parameterize its mechanical and thermal effect, i.e., reducing the effective normal stress through a hydrostatic fluid pressure and efficiently cooling young lithosphere. While the latter strongly modulates the depth to the brittle-ductile transition, we find that the former has small effect on tectonic styles, akin to a slight weakening of unfaulted lithosphere.

Finally,  extensive mass wasting is also documented at mid-ocean ridge detachments, but its potential effect on tectonics remains poorly known. We implement diffusive erosion of the model's free surface, which promotes a transition from the stable to flip-flopping detachment regime. This is possibly due to a modulation of topographic stresses.

Overall, because of the delocalizing effect of a strong ductile lithosphere, the growth of detachments at cold, amagmatic MOR sections requires some degree of rheological weakening, both in the brittle and ductile domains. We find, however, that even moderate frictional weakening (e.g., a friction coefficient of 0.4) which can be attributed to serpentinization of the fault zone, can be sufficient to promote large-offset faulting, a process that may be aided by mass redistribution at the seafloor.

How to cite: Demont, A., Olive, J.-A., and Cannat, M.: Detachment fault growth modulated by brittle softening and ductile flow in amagmatic (ultra)slow-spread oceanic lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13725, https://doi.org/10.5194/egusphere-egu23-13725, 2023.

EGU23-13813 | Posters on site | GD5.2

Morphological and geochemical evolution of the eruptive activity along axial volcanic ridges in the Northern section of the Reykjanes ridge. 

Morgane Le Saout, Colin W. Devey, Dominik Palgan, and Thorsten S. Lux

The Reykjanes Ridge is a segment of the slow-spreading Mid-Atlantic Ridge interacting with the Iceland plume. The 900 km long segment consists in “en echelon” axial volcanic ridges. They are typically 3-6 km wide, 20-30 km long, 200-500 m high, and overlap with each other over a distance of, on average, 1/3 of their length.  The Reykjanes ridge AVRs have been the subject of several studies and are the base of numerous models of AVRs evolution. However, most of these studies are based on bathymetry with a resolution > 20 m and sidescan data > 5 m, with no geochemical component. Thus, small temporal variations of the accretionary processes, especially changes in eruptive activity and magma composition, are still not well constrained. We here retrace the development of AVRs using high-resolution data combined with lava flow composition. During the MSM75 expedition in 2018, four AVRs between 62.95ºN and 63.20ºN were mapped at the resolution of 5 m. At the 63.08ºN AVR, bathymetric and backscatter data are combined with side-scan sonar data (with a 50 cm resolution) acquired with an autonomous underwater vehicle (AUV Abyss from GEOMAR) and near-bottom video from six remotely operated vehicle dives (ROV Phoca from GEOMAR) to: 1) delineate individual lava flows and tectonic structures, 2) determine flow morphologies (i.e., lobate flows, hummocky flows, hummocky ridges, seamounts), 3) locate extrusion sources, and 4) determine the chronology of the geological events. In addition, the composition of samples collected via ROV and wax corer is used to determine the geochemical evolution of the AVR. Around 200 flow units with distinct morphologies and stages of sedimentation were delineated. Our study reveals that major changes in the flow morphology at 63.08ºN is correlated with changes in flow composition. The AVR development appears to have initiated with the emplacement of seamounts aligned along an eruptive fissure. This was followed by a period of relatively high-extrusion rate / low viscosity eruptions leading to the emplacement of lobate flows. A decrease in extrusion rate and/or increase in viscosity results in the transition from lobate to hummocky morphology. In the last stage, the volcanic activity focuses along numerous narrow hummocky ridges. The similarity of the morphology distribution on several neighboring AVRs in this region indicates comparable evolutions.

How to cite: Le Saout, M., Devey, C. W., Palgan, D., and Lux, T. S.: Morphological and geochemical evolution of the eruptive activity along axial volcanic ridges in the Northern section of the Reykjanes ridge., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13813, https://doi.org/10.5194/egusphere-egu23-13813, 2023.

EGU23-13869 | Posters on site | GD5.2

High-resolution geomorphological studies of a Red Sea Rift segment in Hadarba Deep 

Nico Augustin, Morgane Le Saout, Cora K. Schiebener, and Froukje M. van der Zwan

The mid-ocean rift in the Red Sea is recently regaining attention in the geosciences due to the possibility of investigating this young ocean in more detail than ever by state-of-the-art methods and modern deep-sea instrumentation. During the first AUV surveys of the Red Sea rift in Spring 2022, we collected multibeam bathymetry, backscatter, sub-bottom, and water column data over a 9 km long ridge segment in the Hadarba Deep between 22.49°N and 22.56°N to investigate the volcano-tectonic processes of this mid-ocean ridge. This area's total spreading rate of about 12 mm per year is defined as ultra-slow spreading. The high-resolution hydroacoustic data of the used Kongsberg Hugin Superior AUV (operated by Fugro) revealed more than 100 individual lava flows with different stages of sedimentation. The oldest lava flows are buried under 3-4 m of sediment, indicating ages of up to 28 ka. A dome volcano with a 2.5 km diameter and an average height of 300 m dominates the mapped area but has been inactive for at least ~8.4 ka. Several younger lava flows show recent episodes of volcanism along the rift axis. However, their sediment cover is below the vertical sub-bottom-profiler resolution of about 10 cm and thus might be only a few hundred years old or younger. We will present our geomorphological maps, analyses, and statistics that reveal a moderately faulted, ultra-slow spreading MOR segment in the Red Sea with a surprisingly large amount of magmatic extension and show implications for the formation history of this ridge segment.

How to cite: Augustin, N., Le Saout, M., Schiebener, C. K., and van der Zwan, F. M.: High-resolution geomorphological studies of a Red Sea Rift segment in Hadarba Deep, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13869, https://doi.org/10.5194/egusphere-egu23-13869, 2023.

EGU23-14327 | Orals | GD5.2

Seismic constraints on the evolution of hydrothermal circulation beneath Lucky Strike volcano, Mid-Atlantic Ridge 

Soumya Bohidar, Wayne Crawford, and Mathilde Cannat

Lucky Strike volcano is the central edifice of the Lucky Strike segment, Mid-Atlantic Ridge. Its summit overlies an axial magma chamber (AMC), 3-3.8 km beneath the seafloor, and hosts one of the largest known deep-sea hydrothermal fields. Local seismicity beneath the hydrothermal field has been monitored since 2007 as a part of the EMSO (European Multidisciplinary Seafloor and water column Observatory)-Azores observatory by 5 OBSs with yearly redeployments. In a 12-year (2007-2019) earthquake catalog (noncontinuous), we observe continuous low magnitude seismicity (ML ~ -1 to 0), focused mainly 0.5-2 km above the AMC, suggesting that thermal contraction of rocks, possibly combined to deformation induced by volume changes during hydrothermal alteration, at the base of a single limb along-axis hydrothermal cell is the primary source of this seismicity. We thus interpret the seismicity clusters, with horizontal extent 1200 to 1800 m2, as zones of enhanced heat extraction, in the lower part of the hydrothermal downflow zone.

We present the evolution of this hydrothermally-induced seismicity over the 12 years of the catalog. We observe three lateral 400-800 m shifts of the main seismicity clusters. The first and second shifts are small and could be explained by a fortuitous combination of network-based biases, picking error and/or change in the shallow seismic velocity structure of the volcano. The third shift, occurring during a catalog gap between June 2013 and April 2015, is ~800 m eastward and corresponds to a change in the seismicity distribution from a patch above the AMC to a vertical pipe-like pattern, indicating a real change in the hydrothermal circulation. We propose that this shift is driven by recent magmatic injections above the AMC, and/or to the opening of new tectonic cracks, enhancing local permeability and allowing for more efficient cooling above the shallower region of the AMC roof.

We also observe three Higher Seismic Activity (HSA seismic rate > 18 events/week) periods: April-June 2009, August-September 2015, and April-May 2016. The 2009 HSA period was the most intense: it lasted ~13 weeks, starting with a relatively higher magnitude event (ML = 1.7), and culminating in June after another higher magnitude (ML = 1.8) event. Most of the events clustered 0 to 1 km above the AMC reflector, with a few deeper events (down to only 800 m below the AMC reflector) during the culmination period. Although we do not have focal mechanisms to test this hypothesis, we propose that this HSA period resulted from tectonic events opening enhanced local permeability channels for downgoing hydrothermal fluids, and leading to higher heat extraction by the hydrothermal system.

How to cite: Bohidar, S., Crawford, W., and Cannat, M.: Seismic constraints on the evolution of hydrothermal circulation beneath Lucky Strike volcano, Mid-Atlantic Ridge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14327, https://doi.org/10.5194/egusphere-egu23-14327, 2023.

EGU23-14452 | Posters on site | GD5.2

Spatial association between talc-rich mineralization and sulfide-bearing deposits in a newly discovered inactive and weakly actie fields (Mid-Atlantic Ridge) 

Ewan Pelleter, Cecile Cathalot, Stéphanie Dupré, Mathieu Rospabe, Thomas Giunta, Boissier Audrey, Sandrine Cheron, Mickael Rovere, Robin Bonnet, Paco Ferrand, Laetitia Leroy, Yoan Germain, Vivien Guyader, Jean-Pierre Donval, and Yves Fouquet and the Ewan Pelleter

Since 1977 and the discovery of the first high temperature (HT) hydrothermal vent, more than 300 sites are known (about 600 including inferred ones). Among these hydrothermal sites, the talc-rich deposit is the most recent class of hydrothermal system discovered on the seafloor [1]. Only three talc-rich deposits have been described so far: (i) the active Von Damm Vent Field (VDVF), (ii) the inactive St Paul’s and (iii) Conrad fracture zones deposits [2]. These hydrothermal sites are associated with lower crustal rocks and/or serpentinized peridotites and might be widespread at slow or ultraslow spreading ridge. However, no clear spatial or temporal relationship of this new class of hydrothermal system and the “black smoker”-like system has been highlighted.

 During the HERMINE (March-April 2017) and HERMINE2 (July-August 2022) cruises [3], [4], two hydrothermal areas with talc-rich deposits have been discovered during Nautile HOV dives. The first one (23°N) is an inactive hydrothermal area located 28km northwest of the Snake Pit vent field (25km west of the axial rift). At least two deposits have been observed: (i) a talc-silica deposit and (ii) a fully oxidized SMS-type deposit characterized by copper concentrations up to 3.3wt.%. The second hydrothermal area (26°N) is composed of one large and weakly-active deposit composed of silica-sulfides rocks and at least two small talc-silica deposits. To our knowledge, this is the first time that such a spatial relationship has been described between these two classes of deposits. The preliminary results on these newly discovered hydrothermal field will be presented here.

 

[1] Hodgkinson et al. (2015) Nat.. Commun 6:10150

doi: 10.1038/ncomms10150 .

[2] D’Orazio et al. (2004) Eur. J. Mineral. 16, 73-83

[3] Fouquet and Pelleter (2017), https://doi.org/10.17600/17000200

[4] Pelleter and Cathalot (2022),

https://doi.org/10.17600/18001851

How to cite: Pelleter, E., Cathalot, C., Dupré, S., Rospabe, M., Giunta, T., Audrey, B., Cheron, S., Rovere, M., Bonnet, R., Ferrand, P., Leroy, L., Germain, Y., Guyader, V., Donval, J.-P., and Fouquet, Y. and the Ewan Pelleter: Spatial association between talc-rich mineralization and sulfide-bearing deposits in a newly discovered inactive and weakly actie fields (Mid-Atlantic Ridge), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14452, https://doi.org/10.5194/egusphere-egu23-14452, 2023.

EGU23-15377 | ECS | Orals | GD5.2

Significant variability in 87Sr/86Sr and d88/86Sr in Hess Deep Rift lithologies due to hydrothermal alteration. 

Utpalendu Haldar, Simontini Sensarma, and Ramananda Chakrabarti

Hydrothermal alteration of seafloor basalts alters its elemental and isotopic composition. Studies on dredged basalts and ophiolite sequences using stable O, K, and radiogenic Sr [1,2,3] isotopes have documented the effect of seafloor alteration on such lithologies. Experimental studies of basalt-seawater interaction have also demonstrated exchange of Sr isotopic signatures between these two phases [4] while limited data for altered oceanic crust suggests incorporation of heavier Sr isotopes [5]. To further our understanding of the behaviour of Sr during seafloor alteration in natural settings, we measured 87Sr/86Sr and δ88/86Sr in a suite of variably altered lithologies from Hess Deep Rift (HDR), which include basalt, norite, gabbro and troctolite.

Radiogenic Sr (87Sr/86Sr) was measured using TIMS (Thermo Scientific, Triton Plus), using internal normalization while stable Sr isotopes (δ88/86Sr, reported relative to NIST SRM 987) were measured using a double spike (84Sr-87Sr) TIMS technique, both at the Centre for Earth Sciences, IISc, Bangalore. The δ88/86Sr values of the HDR samples (0.308-0.810 ‰) are higher than the bulk silicate Earth (BSE) value (0.27 + 0.05 ‰) [6]; some samples show δ88/86Sr values higher than modern-day seawater value (0.386 ‰) [e.g., 7]. The 87Sr/86Sr varies from ~0.703 in unaltered samples to ~0.709 in altered samples, the latter close to the modern-day seawater value. Overall, our data suggests incorporation of heavier isotopes of Sr in altered oceanic crustal samples; the heavier than seawater δ88/86Sr values observed in some samples reflect formation of new mineral phases, consistent with high δ88/86Sr observed in anhydrite formed in laboratory experiments of basalt-seawater interaction[4].

[1]. Lamphere et al. (1981) Journal of Geophysical Research: Solid Earth86(B4), pp.2709-2720; [2]. McCulloch et al. (1981) Journal of Geophysical Research: Solid Earth86(B4), pp.2721-2735; [3]. Parendo et al. (2017) Proceedings of the National Academy of Sciences114(8), pp.1827-1831; [4]. Voigt et al. (2018) Geochimica et Cosmochimica Acta240, pp.131-151; [5] Klaver et al. (2020) Geochimica et Cosmochimica Acta288, pp.101-119; [6] Moynier et al. (2010) Earth and Planetary Science Letters300(3-4), pp.359-366; [7]. Ganguly and Chakrabarti 92022) Journal of Analytical Atomic Spectrometry37(10), pp.1961-1971.

How to cite: Haldar, U., Sensarma, S., and Chakrabarti, R.: Significant variability in 87Sr/86Sr and d88/86Sr in Hess Deep Rift lithologies due to hydrothermal alteration., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15377, https://doi.org/10.5194/egusphere-egu23-15377, 2023.

EGU23-16161 | Orals | GD5.2 | Highlight

The role of magma supply in fragmentation of oceanic lithosphere 

Adina E. Pusok, Yuan Li, Richard F. Katz, Tim Davis, and Dave A. May

Observations suggest that the oceanic lithosphere is shaped by dike intrusions and faulting in proportions that depend on the spreading rate (Carbotte et al., 2016). Yet it remains unclear how the interplay between magmatism and faulting during seafloor spreading affects mid-ocean ridge (MOR) axial morphology, fault spacing, and the pattern of abyssal hills (Buck et al., 2005, Huybers et al., 2022). Here we present two-phase flow numerical models of oceanic lithosphere extension that reconcile the nonlinear brittle behaviour of the lithosphere with mantle melting and magma transport through the lithosphere. 

Fast-spreading ridges show symmetric normal faulting and axial highs, while slow-spreading ridges show an asymmetric fault pattern and axial valleys. Previous work has focused on explaining the MOR fault pattern by tectonic or magmatic-induced deformation. In the first scenario, faults result from tectonic stretching of the thin axial lithosphere during amagmatic periods (Forsyth 1992), while in the second scenario, dike-injection may create stresses that activate extensional faults (Carbotte et al., 2016). Current state-of-the-art models (i.e., Buck et al., 2005) use a single-phase formulation for the deformation of oceanic lithosphere in which a prescribed axial dike may accommodate both magmatic and tectonic extension. In these models, the fault pattern depends on M – the fraction of plate separation rate that is accommodated by magmatic dike opening. While M-models are able to explain a number of observations, M represents a simple parameterization of complex fracture dynamics of sills, dikes, and faults. In particular, M-value models neglect fault–dike interaction and other modes of melt transport and emplacement in the lithosphere (Keller et al., 2013). 

Here we build a 2-D oceanic lithosphere extension model that incorporates a new poro- viscoelastic–viscoplastic theory with a free surface (Li et al., in review) to robustly simulate plastic representations of dikes and faults in a two-phase magma/rock system. We hypothesise that magma supply controls the pattern of dike–fault interaction in oceanic extension settings. We present simplified model problems to compare results with those from M-value models. These enable us to address the significance of M in terms of fundamental magma and lithospheric processes. We then focus on development of fault patterns, magma pathways and crustal production at fast-/slow-spreading ridges.

 

References

Buck et al., 2005, Nature, doi:10.1038/nature03358.

Carbotte et al., 2016, Geol. Soc. London, doi:10.1144/SP420.

Forsyth, 1992, Geology, doi:10.1130/0091-7613(1992)020<0027:FEALAN>2.3.CO;2.

Huybers et al., 2022, PNAS, doi:10.1073/pnas.2204761119.

Keller et al., 2013, GJI, doi:10.1093/gji/ggt306.

Li, Y., Pusok, A., Davis, T., May, D., and Katz, R., (in review). Continuum approximation of dyking with a theory for poro-viscoelastic–viscoplastic deformation, GJI.

How to cite: Pusok, A. E., Li, Y., Katz, R. F., Davis, T., and May, D. A.: The role of magma supply in fragmentation of oceanic lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16161, https://doi.org/10.5194/egusphere-egu23-16161, 2023.

On-going work on the Samail Ophiolite Volcanogenic Massive Sulfide (VMS) deposits and Oman Drilling Project (OmanDP) drill cores provide insights on sulfur and metal cycling during hydrothermal alteration and critical differences between ophiolitic and modern oceanic crust.

The volcanic section is pervasively overprinted by low-T oceanic metasomatism leading to variably depleted sulfur in sulfide (TSsulf) concentrations reflecting leaching and oxidation of magmatic sulfides. Secondary sulfides incorporated mostly basaltic sulfur with minor sulfur addition via open-system bacterial sulfate reduction (BSR).

The sheeted dyke-gabbro transition (OmanDP GT3 drillhole) records a change from BSR open-system processes (d34S>-12.8‰) towards addition of heavy hydrothermal sulfur via thermochemical sulfate reduction ~4km above the Moho Transition Zone-MTZ. Downward progression from d34S=+13.6‰ to ~MORB values suggest decreasing water/rock ratios during hydrothermal alteration. Here, near complete recrystallization under greenschist/amphibolitic facies conditions (no magmatic sulfides), coupled with strong sulfur (TSsulf>2 ppm) and copper leaching (>1 ppm), document the high-T reaction zone of the hydrothermal system overlying the axial melt lens, where S and metals are sourced to form VMS deposits. Although multiple sulfur isotope systematics for Oman VMS ores indicates a deep S-source within the range of GT3 reaction zone (d34S ~4‰), REE patterns and trace metal endowments in the ores suggest that the footwall lavas are also a source of metals, in addition to those leached from the deep reaction zone. Crucially, metal leaching and S-isotopic shifts are far more extensive than those reported on in-situ oceanic crust, implying a net addition of seawater-S ~30% to the upper crustal section.

Differences between in-situ and ophiolitic lower crustal sections are seemingly less pronounced: the foliated and layered gabbros (GT2-GT1 drillholes) preserve small S-isotopic shifts relative to MORB, implying that formation of secondary sulfides involved minor S-seawater input (~7%) and mostly redistribution of magmatic-S. Wide fault zones of convincing oceanic origin preserve sulfates with composition similar to Cretaceous seawater (d34S~+18‰) supporting the role of focused fluid flow corridors during deep crustal cooling. TSsulf and Cu+Ni concentrations increase throughout the lower crust while strong Cu+S leaching characterize tectonized and low-T hydrothermally overprinted domains. Above the MTZ, the primitive layered gabbros and intercalated ultramafics (CM1 drillhole- Sequence SI) record metal and TSsulf enrichments related with magmatic sulfide saturation/segregation from mantle melts upon entering the crust. Incompatible element rich pegmatoidal dikelets crosscutting SI include late, high-fS2 sulfides formed during low-T BSR (δ34S>-25.8‰).

The MTZ comprises 90m of fully serpentinised dunite (SII) underlain by dunite with rodingitized gabbro (SIII). The SII-dunites show vanishing TSsulf and Cu concentrations, consistent with desulfurization producing alloy-bearing mineral assemblages formed during extremely low fS2-fO2 conditions, typical of early serpentinization stages. The dunites mark the onset of increasing S-isotopic shifts towards the SIII-rodingites The occurrence of both sulfides (δ34S=+1.4, +56.9‰) and sulfates (δ34SSO4=+19.4, +36.5‰) with δ34S>>Cretaceous seawater sulfate can be explained by input of fluids at the top of SII-dunites which composition progressed towards extreme heavy values during closed-system, multi-staged evolution.

AJ acknowledges WWU International Visiting Scholars and EU-H2020 Marie Sklodowska-Curie #894599 Fellowships, and FCT I.P./MCTES PIDDAC–UIDB/50019/2020- IDL.

How to cite: Jesus, A. P.: Sulfur and metal fluxes in the oceanic crust: the Samail  ophiolite as proxy for fast spreading ridges., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17478, https://doi.org/10.5194/egusphere-egu23-17478, 2023.

EGU23-434 | Posters on site | GD1.3

Neogene Mantle Dynamics of Western Mediterranean Region Constrained by Basalt Geochemistry and Residual Depth Anomalies 

Chia-Yu Tien, Nicky White, John Maclennan, Benedict Conway-Jones, and Megan Holdt

There is considerable interest in combining a range of geophysical, geochemical and geomorphic observations with a view to estimating the amplitude, wavelength and depth of mantle thermal anomalies on a global bases. Here, we wish to explore how forward and inverse modelling of major, trace and rare earth elements can be exploited to determine melt fraction as a function of depth for a mantle peridotitic source. Our focus is on an area that includes the Iberian Peninsula where previous work shows that long-wavelength topography is probably generated and maintained by sub-plate thermal anomalies which are manifest by negative shear-wave velocities. Geological and geomorphic studies suggest that this dynamic support is a Neogene phenomenon. 48 newly acquired Neogene basaltic samples from Spain were analyzed and combined with previously published datasets. Both major element thermobarometry and rare earth element inverse modelling are applied to estimate melt fraction as a function of depth. In this way, asthenospheric potential temperature and lithospheric thickness can be gauged. These estimates are compared with those obtained from calibrated shear-wave tomographic models. Our results show that potential temperatures and lithospheric thicknesses are 1250-1300 °C and 65-70 km, respectively. These values broadly agree with calibrated tomographic models which yield values of 1300-1350 °C and 45-70 km. We conclude that a region encompassing Iberia is dynamically supported by a combination of warm asthenosphere and thinned lithosphere. This conclusion broadly agrees with independently obtained residual depth anomalies which indicate that the Western Mediterranean region probably has moderately positive dynamic support.

How to cite: Tien, C.-Y., White, N., Maclennan, J., Conway-Jones, B., and Holdt, M.: Neogene Mantle Dynamics of Western Mediterranean Region Constrained by Basalt Geochemistry and Residual Depth Anomalies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-434, https://doi.org/10.5194/egusphere-egu23-434, 2023.

EGU23-650 | ECS | Posters on site | GD1.3

Dynamic mantle support beneath West Antarctica's Ice Sheets: Insights from geophysical and geochemical observations 

Aisling Dunn, Nicky White, Robert Larter, Simon Stephenson, and Megan Holdt

Transient mantle processes generate and maintain topographic variations which cannot be accounted for by crustal isostatic effects.  Accurately constraining the importance of dynamic topography across Antarctica will yield valuable insights into spatial and temporal patterns of mantle convection that inform studies of key boundary conditions for ice sheet models, such as heat flux and palaeotopography. Global studies largely neglect Antarctica because of complications associated with ice cover. In contrast, regional studies tend to oversimplify the problem by exploiting gridded datasets that ignore crustal density variations. Residual elevations, calculated by isolating and removing isostatic contributions to observed topography, enable the amplitude and wavelength of dynamic support to be gauged. Here, the results of analysing legacy (i.e. refraction) and modern (i.e. wide-angle) seismic experiments, onshore receiver functions, as well as a regional shear-wave crustal tomographic model are presented. In this way, a comprehensive suite of spot measurements (n = 195) across West Antarctica are calculated which, in conjunction with a recently augmented database of residual depths in the surrounding Southern Ocean (n = 1106), permit spatial variations of residual topography to be quantified. Positive residual anomalies (1 - 2 km) from the Transantarctic Mountains, Marie Byrd Land and the Antarctic Peninsula are consistent with regions of slow shear-wave velocity anomalies within the upper mantle, positive free-air gravity anomalies, and Cenozoic intraplate basaltic volcanism, indicating that topographic support is attributable to mantle convective processes. Lithospheric thicknesses derived from inverse modelling of basaltic rare-earth element concentrations show that elevated topography coincides with thinned lithosphere, further attesting to the relationship between positive residual elevation and mantle convective upwelling. Steepened geothermal gradients associated with regions of plate thinning have significant implications for the delivery of heat flux to the base of the West Antarctic Ice Sheet.

How to cite: Dunn, A., White, N., Larter, R., Stephenson, S., and Holdt, M.: Dynamic mantle support beneath West Antarctica's Ice Sheets: Insights from geophysical and geochemical observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-650, https://doi.org/10.5194/egusphere-egu23-650, 2023.

EGU23-773 | ECS | Orals | GD1.3

The influence of mantle-lithosphere interaction on the evolution of relief formation and drainage networks 

Fabian Christopher Dremel, Jörg Robl, Bjarne Friedrichs, and Christoph von Hagke

Remnants of the Variscan mountain belt can be found today throughout North America, North Africa, Europe, and Asia, which are typically characterized by hilly to mountainous topography. Since the topography of the Variscan orogen was already levelled in the Permian by post-orogenic erosion and thermal subsidence, processes independent of Variscan convergent tectonics must be responsible for the observed high topography. Central Europe encompasses several landscapes showing extensive post Variscan relief rejuvenation, including from west to east the Massif Central, the Vosges Mountains and Black Forest, and the Bohemian Massif. However, despite their spatial proximity, the underlying processes that led to uplift and relief rejuvenation could not be more different. For the Massif Central, mantle plume activity has been proposed, while continental rifting has been held responsible for uplift of the Black Forest and Vosges Mountains. Uplift of the Bohemian Massif has been attributed to the forebulge of the Alpine orogeny, or slab dynamics in the eastern Alps, respectively.

The aim of this study is to investigate the relationship between different uplift scenarios, relief formation and the response of the drainage system to spatial and temporal variations in uplift rates, focusing on the Massif Central, Black Forest and Vosges as well as the Bohemian Massif. The spatial and temporal succession of uplift rates as well as denudation rates in response to post orogenic uplift will be analysed based on an extensive compilation of low-temperature thermochronological data. Geomorphological analyses include the plan view and profile geometry of river networks, i.e., normalised steepness indices, across divide χ gradients and river orientation.

Although the underlying processes are different, relief rejuvenation is a striking feature in these mountain ranges. Low relief surfaces at higher elevations contrast with lower reaches, with deeply incised rivers and migrating knickpoints indicating temporal variations in uplift rates over the last millions of years. Furthermore, the organisation of river networks varies within the mountain ranges, highlighting the influence of underlying processes on the evolution of drainage networks. The Massif Central shows a radial, star-shaped drainage pattern with rivers steepening towards the centre of the plume related uplift. The Upper Rhine Graben is dominated by rift flank retreat governing drainage divide migration. This is expressed by short, steep rivers draining into the graben and long, low gradient rivers on the side facing away from the rift valley. The Bohemian Massif features a bowl-shaped topography, with tributaries of the Moldau (Vltava) draining north. However, the southern side of the Bohemian Massif drains into the Danube in short tributaries with steep lower reaches. These analyses in combination with thermochronometry pave towards constraining timing and spatial extent of the rejuvenation signal. Ultimately, this will allow for making inferences on the underlying driving mechanisms.

How to cite: Dremel, F. C., Robl, J., Friedrichs, B., and von Hagke, C.: The influence of mantle-lithosphere interaction on the evolution of relief formation and drainage networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-773, https://doi.org/10.5194/egusphere-egu23-773, 2023.

EGU23-788 | ECS | Posters on site | GD1.3

Observed Dynamic Topography and Cenozoic Magmatism of the Eastern Seaboard of Australia 

Philippa Slay, Nicky White, Megan Holdt, and Simon Stephenson

Topography and bathymetry on Earth is both isostatically and dynamically supported. The isostatic signal is dominantly controlled by variations in the thickness and density of crust and lithospheric mantle. Therefore the challenge is to identify the dynamic component of topographic support, which is caused by sub-plate density anomalies arising from convective mantle processes. Here, we exploit an observationally-led approach to determine residual (i.e., dynamic) topography across the Australian continent and its margins. Compilations of receiver function analyses, wide-angle/refraction seismic surveys and deep seismic reflection profiles are used to determine both crustal velocity structure and depth to Moho. A published compilation of laboratory measurements is used to convert crustal velocity into density. In this way, residual topography is carefully isolated and combined with existing offshore measurements. Australia’s isolation from plate boundaries combined with rapid northward translation suggest that long-wavelength dynamic topography is controlled primarily by the interaction of sub-plate convection and plate motion. Large-scale positive dynamic topography occurs along the eastern seaboard, which coincides with slow shear-wave velocity anomalies, positive long-wavelength gravity anomalies and Cenozoic basaltic magmatism. Geochemical modelling of both age-progressive and age-indepedent basalts suggests that the eastern seaboard is underlain by positive asthenospheric temperature anomalies and dramatically thinned lithosphere. These inferences are consistent with calibrated tomographic models, which show that the lithosphere is 60 km thick. In general, the pattern of continental dynamic topography is consistent with residual bathymetric anomalies from oceanic lithosphere surrounding Australia.

How to cite: Slay, P., White, N., Holdt, M., and Stephenson, S.: Observed Dynamic Topography and Cenozoic Magmatism of the Eastern Seaboard of Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-788, https://doi.org/10.5194/egusphere-egu23-788, 2023.

EGU23-843 | ECS | Posters on site | GD1.3

Global Analysis of lithosphere-asthenosphere dynamics using a revised plate cooling model 

Megan Holdt, Nicky White, and Fred Richards

A global understanding of the evolution of oceanic lithosphere yields key insights about lithosphere-asthenosphere interaction. An important starting point is that age-depth and heatflow measurements provide the fundamental constraints for progressive cooling of oceanic lithosphere. When jointly inverting these measurements to identify an optimal plate model, the robustness of the result is predicated upon their quality, number and global distribution. Here, we exploit a revised and extensively augmented database of accurate age-depth measurements (n = 10,874) and a published database of heatflow measurements (n = 3,753). These databases are jointly modelled using both analytical and numerical methodologies to obtain a plate model, which has an average asthenospheric temperature of 1325±50oC and a lithospheric thickness of 105±10 km. These recovered values agree with independent geochemical and seismic constraints of mantle potential temperature and lithospheric thickness. This revised plate cooling model is used to improve our understanding of lithosphere-asthenosphere interaction.  First, we use plate cooling to measure residual depth anomalies, which are a reliable proxy for mantle dynamic topography. Our results demonstrate that dynamic topography varies on wavelengths as short as 1000 km with amplitudes of ±1 km. Secondly, we combine plate cooling with the depth distribution of oceanic intraplate earthquakes to identify the isothermal surface above which brittle elastic behaviour occurs. Finally, we demonstrate that age-depth and heatflow measurements exhibit a sustained flattening from ~60 Ma, suggesting that resupply of heat from the asthenosphere is an essential component of the lithosphere-asthenosphere system. Our database of accurate residual depth measurements is used to explore links between mantle dynamics, asthenospheric temperature anomalies extracted from earthquake tomographic models, and basaltic melting. 

How to cite: Holdt, M., White, N., and Richards, F.: Global Analysis of lithosphere-asthenosphere dynamics using a revised plate cooling model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-843, https://doi.org/10.5194/egusphere-egu23-843, 2023.

EGU23-1257 | ECS | Orals | GD1.3

Separation of signal components in global gravity models 

Betty Heller-Kaikov, Roland Pail, and Martin Werner

Vertical movements of the Earth’s surface represent mass displacements, which cause a temporal gravity signal that can be measured by dedicated satellite gravity missions such as the GRACE or GRACE-FO missions. Especially observations of vertical movements that are caused by mantle dynamic processes would enable to constrain numerical mantle convection models using geodetic data sets, thereby improving our understanding about the physical behavior of the Earth’s interior.

Using satellite gravity data to observe the above-mentioned vertical movements poses two main challenges:

First, the small amplitudes of the geoid trend signals induced by mantle dynamic signals require data accuracies and record lengths that will only be met by future satellite gravity missions. Indeed, it is known from previous simulation studies that temporal gravity signals produced by mantle convection will be detectible in future double-pair satellite gravity missions such as the planned Mass Change and Geoscience International Constellation (MAGIC).

The second challenge to make use of gravity data sets for constraining geophysical mantle models is the extraction of the signal of interest from the total gravity signal. While temporal gravity data sets include the cumulative mass displacement signal, the problem of how to separate the superimposed signals produced by phenomena in the hydrosphere, cryosphere, atmosphere, oceans and solid Earth is still unsolved.

In this contribution, using the gravity signals given by the updated ESA Earth System Model, we address the task of signal separation in temporal gravity data and present two approaches for it. To this end, the knowledge of the spatial and temporal characteristics of the individual signal components is exploited by applying principal component analysis as well as a machine learning approach.

How to cite: Heller-Kaikov, B., Pail, R., and Werner, M.: Separation of signal components in global gravity models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1257, https://doi.org/10.5194/egusphere-egu23-1257, 2023.

How the surface plates link to mantle slabs is fundamental for paleo-tectonic reconstructions and has implications on mantle dynamics. Assuming a simplified, vertical sinking slab, many tomography-based studies have vertically projected the surface features into the mantle, arguing for the tectonic explanations of mantle structures or vice versa. In contrast, geodynamic models continue to suggest that slabs can be laterally transported by a few hundred kilometers up to ~6000 km near the core-mantle boundary. The dynamics of mantle slabs remain controversial.

The Caribbean mantle has recently been suggested for vertical slab sinking. However, a vertically sinking slab at a near-stationary eastern Caribbean trench would require slab buckling in the mantle, because at least 1,200 km subduction needs to be accommodated within the upper 660 km mantle. Yet, mantle tomographies show expected (~100 km) slab thickness with limited slab thickening or buckling. With no need for a priori assumption on mantle dynamics, here, we used a slab-unfolding approach to restore and re-interpret the slab structures of the Lesser Antilles slab underneath the Caribbean. Our results show that the slab structure can be alternatively explained with limited intra-plate deformation if the slab was transported northwestward by ~900 km after subduction. Such lateral transportation in the mantle is possibly due to the physical connection with the North American plate, whose northwestward motion since the Eocene has been dragging the slab toward the same direction. We also provided our tectonic explanations on the edges and gaps of the slabs, supporting previous work that pre-existing weak zones and plate boundaries determine the fragmentation of the Lesser Antilles slab. The slab unfolding approach used in this study has the potential to be applied to other subduction zones, with no need for a priori assumption on mantle dynamics (i.e., vertical slab sinking) for future tomography-based analysis.

How to cite: Chen, Y.-W. and Wu, J.: Lesser Antilles slab reconstruction suggests significant northwestwards lateral slab transportation underneath the Caribbean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1352, https://doi.org/10.5194/egusphere-egu23-1352, 2023.

EGU23-1983 | ECS | Posters on site | GD1.3

Cenozoic history of North Atlantic surface motions: Implications for asthenosphere flow processes 

Zhirui Ray Wang, Giampiero Iaffaldano, and John Hopper

Mantle convection is a fundamental process that shapes Earth’s surface, as it provides driving and resisting forces for horizontal motions of tectonic plates, as well as for inducing non-isostatic vertical motion --- commonly termed “dynamic topography”. Growing geologic constraints of past plate motion variations and dynamic topography have led to better understanding of the history of mantle flow induced surface expression. Ultimately, the existence of a thin, mechanically weak asthenosphere allows geodynamicists to link such observables to mantle flow properties in the context of Couette/Poiseuille flow. Here we utilize publicly available geological and geophysical data sets to study Cenozoic plate kinematic changes and the spatial-temporal evolution of dynamic topography in the North Atlantic region. We employ quantitative, analytical Couette/Poiseuille flow models to link the inferred surface motion history to asthenosphere flow properties underneath. Our efforts aim at disentangling the role of asthenospheric channelized flow in influencing the Cenozoic surface expression of North Atlantic region.

How to cite: Wang, Z. R., Iaffaldano, G., and Hopper, J.: Cenozoic history of North Atlantic surface motions: Implications for asthenosphere flow processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1983, https://doi.org/10.5194/egusphere-egu23-1983, 2023.

EGU23-2575 | ECS | Orals | GD1.3

Pressure-driven upper-mantle flow in the Indo-Atlantic Realm since the Upper Jurassic inferred from continent-scale hiatus surfaces and oceanic spreading rate variations 

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

Mantle convection is a fundamental process responsible for shaping the tectonic evolution of the Earth. It is commonly perceived that mantle convection is difficult to constrain directly. However, it affects the horizontal and vertical motion of the lithosphere. The former is observed in the spreading rates, while the latter leaves various imprints in the geological record. In particular, the positive surface deflections driven by mantle convection create erosional/non-depositional environments, which induce gaps (hiatus) in the stratigraphic record (i.e., an absence or thinning of a sedimentary layer). Modern digital geological maps allow us to map long-wavelength no-/hiatus surfaces at continental scale systematically.

Here we compare our continent-scale hiatus mapping to plate motion variations in the Atlantic and Indo-Australian realms from the Upper Jurassic onward. In general, we find the datasets correlate except when plate boundary forces may play a significant role. There is a timescale on the order of a geologic series, ten to a few tens of millions of years (Myrs), between the occurrence of continent-scale hiatus and plate motion changes. This is consistent with the presence of a weak upper mantle. Furthermore, we find significant differences in the spatial extent of hiatus patterns across and between continents, which means they cannot simply be explained by eustatic variations but should be linked to variations in the upper-mantle flow.

Our results highlight the importance of geological datasets to map the temporal evolution of geodynamic processes in the deep Earth. Also, they imply that different timescales for convection and topography in convective support must be an integral component of time-dependent geodynamic Earth models. Studies of horizontal and vertical motion of the lithosphere to track past mantle flow would provide powerful constraints for adjoint-based geodynamic inverse models of past mantle convection.

How to cite: Vilacís, B., Hayek, J. N., Stotz, I. L., Bunge, H.-P., Friedrich, A. M., Carena, S., and Clark, S. R.: Pressure-driven upper-mantle flow in the Indo-Atlantic Realm since the Upper Jurassic inferred from continent-scale hiatus surfaces and oceanic spreading rate variations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2575, https://doi.org/10.5194/egusphere-egu23-2575, 2023.

It is generally accepted that East Asian mantle dynamics has been dominated by subduction and downwelling since Mesozoic times (e.g. Müller et al. (2016)). However, seemingly in contrast to this history, a variety of observations indicate a presence of anomalously hot asthenospheric material beneath East Asia during the late Cenozoic. First of all, tomographic models consistently reveal an extensive network of seismically slow anomalies at asthenospheric depths, which align spatially with a recent (< 30 Ma) phase of intraplate volcanism. The influence of this positively buoyant material at the surface is further highlighted by induced dynamic uplift, which is recorded in the geological record through an inter-regional sedimentary hiatus during the late Eocene—Oligocene. Residual topography studies additionally find swells of dynamic uplift throughout this region in the present day. Global mantle circulation models (MCMs) show that these observations can be reproduced in a subduction-dominated region by the spillover of anomalously hot asthenospheric material from the adjacent Pacific domain during ridge subduction events. In particular, the subduction of the Izanagi-Pacific ridge at ~55 Ma provides a large window through which Pacific asthenosphere could have flowed into East Asia. We test this hypothesis by comparing these MCMs to a variety of geological observations, including the distribution of sedimentary hiatus and intraplate volcanism during the late Cenozoic. We additionally compare the present-day distribution of hot material predicted by these models with the recently published full waveform inversion tomographic model of the region, Sinoscope 1.0, which highlights the distribution of seismically slow anomalies beneath the region. We find an encouraging match between asthenospheric flow predicted by these models and the observations considered, showing this to be a viable new hypothesis in explaining these observations. The mechanism of hot asthenospheric build-up during subduction and release during slab window opening may not be limited to East Asia, and could reconcile observations of intraplate volcanism and dynamic uplift in convergent regions more generally. 

How to cite: Brown, H., Ma, J., Colli, L., and Bunge, H.-P.: The influence of slab window asthenospheric flow on intraplate volcanism, dynamic uplift, and present-day mantle heterogeneity in East Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3213, https://doi.org/10.5194/egusphere-egu23-3213, 2023.

Geological maps contain a large amount of information that can be used to constrain geodynamic models, but which has been often overlooked by the geodynamic community. Particularly significant are unconformable geologic contacts at continental scales: what is usually perceived as a lack of data (material eroded or not deposited) becomes instead part of the signal of dynamic topography.

We were able to use geological maps to constrain the dynamic processes in the mantle beneath Africa by understanding its Cenozoic elevation history, and by using it to distinguish between different uplift and subsidence scenarios. This was accomplished by mapping the spatio-temporal patterns of geological contacts at the series level using continental-scale geological maps, under the assumption that continental-scale unconformable contacts are proxies for vertical motions and for paleotopography. We also mapped the present-day elevation of marine sediments for each series.

We found that significant differences exist in interregional hiatus surfaces. For example, the total unconformable area at the base of the Miocene expands significantly compared to the base of the Oligocene, strongly suggesting that most of Africa underwent uplift in the Oligocene. In southern Africa there are no marine Oligocene or Pleistocene sediments, suggesting that this region reached a high in the Oligocene, subsided in the Miocene and Pliocene, and has been high again since late Pliocene to Pleistocene. More generally, to reproduce the pattern of marine sedimentation in Africa that we mapped, sea level increases between 300 and at least 500 m above present level would be required. These are well in excess of the maximum 150 m eustatic sea level rise that has been postulated by several authors for the Cenozoic. Our results therefore support a dynamic origin for the topography of Africa. Specifically, the time-scale of geologic series (at most a few tens of millions of years) is comparable to the spreading-rate variations in the south Atlantic, which have been linked to African elevation changes through pressure-driven upper mantle flow.

How to cite: Carena, S., Friedrich, A., and Bunge, H.-P.: Geological hiatus surfaces across Africa in the Cenozoic: implications for the timescales of convectively-maintained topography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3508, https://doi.org/10.5194/egusphere-egu23-3508, 2023.

It is well known that increasing pressure and temperature along upper-mantle geotherms combine to produce a zone of low seismic wave speeds. Beyond such behaviour arising from the anharmonicity of the crystal lattices of the constituent minerals, viscoelastic relaxation may result in further reduction of the wave speeds, along with appreciable attenuation of seismic waves. In order to better constrain such sub-solidus relaxation in olivine-dominated lithologies, we have recently prepared and tested in torsional forced oscillation several new specimens of synthetic polycrystalline olivine (Fo90 olivine buffered by ~5 wt% En90). These specimens were prepared by hot pressing sol-gel precursor powder encapsulated within metal foils (of Ni70Fe30 or Pt) at high temperature (1200-1350ºC) and pressure (300 MPa). Enclosure within Ni-Fe foil yields relatively reducing anhydrous conditions and average grains sizes d ≤ 5 μm. The more oxidising and hydrous conditions associated with Pt encapsulation are conducive to grain growth to at least 20 μm. Our forced-oscillation methods have been refined by replacement of the polycrystalline alumina control specimen with single-crystal sapphire, discontinuation of the use of Ni-Fe foils at the ends of the specimens in favour of direct contact with alumina torsion rods, and selective use of austenitic stainless steel as an alternative to the usual mild-steel material for the enclosing jacket. Such testing of fine-grained olivine polycrystals at periods of 1-1000 s and shear strain amplitudes < 10-5 has consistently revealed an essentially monotonically period- and temperature-dependent high-temperature background. The onset of high-temperature anelastic relaxation involves a superimposed dissipation peak of only modest amplitude plausibly attributed to elastically accommodated grain-boundary sliding. Grain-size sensitivity is incorporated into a Burgers type creep-function model fitted to the (G,Q-1) data for multiple specimens through power-law grain size dependencies of the key characteristic times. The Maxwell time τM, varying as d-mV, defines the transition from anelastic to viscous background behaviour, and τP ~ d-mA, the centre of the distribution of relaxation times for the dissipation peak. The data for the newly prepared pure synthetic specimens of 4-22 mm grain size, tested with the refined experimental methodology, require mV ~ 3 and mA < 1.5. These inferences are consistent with micromechanical models for grain-boundary sliding, but yield markedly stronger grain-size sensitivity than previously reported. However, mapping of the tested samples by electron back-scattered diffraction indicates that the density of geometrically necessary dislocations, responsible for lattice curvature, decreases systematically with increasing grain size, raising the possibility that any contribution from dislocation damping might enhance the apparent grain-size sensitivity. A preliminary extrapolation of the new model for grain-size sensitive viscoelastic relaxation in dry, melt-free dunite to upper-mantle conditions of grain size and pressure suggests shear modulus relaxation < 2% and dissipation Q-1 < 0.01 – thus unable to account for seismological observations of the mantle beneath young oceanic lithosphere and in subduction zones. Uncertainties in such extrapolation will be discussed, along with other factors that might enhance sub-solidus viscoelastic relaxation including the segregation of trace-element impurities to olivine grain boundaries, and the influence of oxygen and water fugacities. 

How to cite: Jackson, I., Qu, T., and Faul, U.: Seismic wave dispersion and attenuation within the asthenosphere: the role of sub-solidus viscoelastic relaxation revisited, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4014, https://doi.org/10.5194/egusphere-egu23-4014, 2023.

EGU23-4053 | Orals | GD1.3 | Highlight

Influence of the Asthenosphere on Earth Dynamics and Evolution 

Mark Richards, Lawrence Cathles, Willy Fjeldskaar, Adrian Lenardic, Barbara Romanowicz, and Johnny Seales

The existence of a thin, weak asthenospheric layer beneath Earth’s lithospheric plates is consistent with existing geological and geophysical constraints, including Pleistocene glacio-isostatic adjustment, modeling of gravity anomalies, studies of seismic anisotropy, and post-seismic rebound. Mantle convection models suggest that a pronounced weak zone beneath the upper thermal boundary layer (lithosphere) may be essential to the plate tectonic style of convection found on Earth. The asthenosphere is likely related to partial melting and the presence of water in the sub-lithospheric mantle, further implying that the long-term evolution of the Earth, including the apparently early onset and persistence of plate tectonics, may be controlled by thermal regulation and volatile recycling that maintain a geotherm that approaches the wet mantle solidus at asthenospheric depths.

How to cite: Richards, M., Cathles, L., Fjeldskaar, W., Lenardic, A., Romanowicz, B., and Seales, J.: Influence of the Asthenosphere on Earth Dynamics and Evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4053, https://doi.org/10.5194/egusphere-egu23-4053, 2023.

EGU23-4232 | Orals | GD1.3

Geophysical modelling of vertical motion processes constrained by geodetic and geological observations (UPLIFT) 

Hans-Peter Bunge, Yi-Wei Chen, Anke Friedrich, and Roland Pail and the UPLIFT Team

Vertical motion of the Earth’s lithosphere (uplift) occurs on different spatial and temporal scales. Commonly assumed to be primarily related to plate tectonic mechanisms and isostatic adjustment, it has become clear that mantle related forcing and in particular mantle plumes are a significant contributor to uplift events in many regions of the world, making vertical motions a powerful probe into sublithospheric processes. Significant improvements of observational methods (e.g. satellite missions) and publicly-accessible databases (e.g. digital geological maps) make it now feasible to map vertical motions from geodetic to geologic time scales. This in turn provides invaluable constraints to inform key, yet uncertain, parameters (e.g. rheology) of geodynamic models. Such models also contribute powerful insight into complex landscape evolution processes at interregional to continental scales. Here we report on a new (starting date April 2022) Research Training Group (RTG) 2698, with 10 individual dissertation projects and a Post-doc project, funded by the German Research Foundation. An interdisciplinary approach of Geodynamics, Geodesy and Geology aims to answer questions related to how the interaction of exo- and endogenic forcing shapes a diverse array of earth processes from landscape evolution to the occurrence of earthquakes. The RTG uses a combined interpretation of interdisciplinary observations with different spatial and temporal sensitivity, in conjunction with physical models, to disentangle different uplift mechanisms, including the plume, plate and isostatic mode, based on their specific spatial and temporal patterns. We will give an overview on the key philosophy and main architecture of the RTG. Core components include an integrated geophysical process model, composed of an adjoint geodynamic model that accounts for seismic tomography and mineralogy, coupled with a landscape evolution model, with the lithosphere as a filter function, and targeted observations that include geodetic (geometric and gravimetry) data to reflect contemporary uplift processes combined with high precision, geological, magnetostratigraphic and geomorphologic data to reflect uplift processes and sedimentation rates on geological time scales. The modeling will be complemented by a thorough uncertainty analysis and an enhanced visualization of the key results.

How to cite: Bunge, H.-P., Chen, Y.-W., Friedrich, A., and Pail, R. and the UPLIFT Team: Geophysical modelling of vertical motion processes constrained by geodetic and geological observations (UPLIFT), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4232, https://doi.org/10.5194/egusphere-egu23-4232, 2023.

EGU23-4286 | ECS | Orals | GD1.3 | Highlight

Meteorological Tools for Assessing Mantle Flow-related Dynamic Topography Maps 

Ayodeji Taiwo, Hans-Peter Bunge, and George Craig

Construction of robust mantle flow trajectories plays an important role in understanding the parameters that govern mantle convection and relating them to geologic observables. In the past, the assessment of constructed trajectories focused majorly on metrics targeted at the mantle volume whilst neglecting the surface manifestations of mantle convection in the form of dynamic topography. However, an increasing amount of interest is being built around linking convection to surface effects, including dynamic topography. As such, it is vital to study ways in which mantle flow trajectories can be assessed via their dynamic topography predictions. Commonly used assessment and comparison metrics such as root-mean-square errors, suffer from the so-called double penalty problem --- a dynamic topography prediction that does not match a reference observation one-to-one is penalized twice: first as a miss and second as a false alarm. It is therefore attractive to investigate metrics that overcome this problem. Here, we introduce an object-based approach, first applied in meteorology, and show that this approach is not only amenable to studying dynamic topography, but that it also overcomes the double penalty problem whilst providing accurate model assessment.

How to cite: Taiwo, A., Bunge, H.-P., and Craig, G.: Meteorological Tools for Assessing Mantle Flow-related Dynamic Topography Maps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4286, https://doi.org/10.5194/egusphere-egu23-4286, 2023.

EGU23-4326 | ECS | Posters on site | GD1.3

TerraNeo: Ongoing development of a scalable mantle convection code for exascale computing 

Eugenio D'Ascoli, Hamish Brown, Nils Kohl, Marcus Mohr, and Hans-Peter Bunge

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 rheology, and testable preconditions, such as dynamic topography. The vertical deflections predicted by such models may then be tested against the geological record. Considering realistic Earth-like Rayleigh numbers (∼ 108) a resolution of the thermal boundary layer on the order of ∼ 10 km is necessary considering the volume of the Earth’s mantle. Simulating Earth’s mantle convection at this level of accuracy requires solving sparse indefinite systems with more than a trillion degrees of freedom, computational feasible on exascale HPC systems. This can only be achieved by mantle convection codes providing high degrees of parallelism and scalability. Earlier approaches from applying a prototype framework using hierarchical hybrid grids (HHG) as solvers for such systems demonstrated the scalability of the underlying concept for future generations of exascale computing systems. In consideration of 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 parallelization 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 a resolution on the order of ∼ 1 km.

How to cite: D'Ascoli, E., Brown, H., Kohl, N., Mohr, M., and Bunge, H.-P.: TerraNeo: Ongoing development of a scalable mantle convection code for exascale computing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4326, https://doi.org/10.5194/egusphere-egu23-4326, 2023.

EGU23-5023 | ECS | Posters on site | GD1.3

A theory for mega-dyke propagation as driven by hotspot topography. 

Timothy Davis and Richard Katz

How can mega-dykes propagate hundreds of kilometres laterally through the crust? These blade-shaped dykes are enormous geological structures characterised by widths up to 100 metres. Ernst and Baragar (1992) showed that mega-dykes propagate away from a point at the centre of the dyke swarm. The magma for such dykes is believed to originate from a hotspot impinging on the base of the lithosphere, and this process typically precedes rifting events (Ernst, 2001; Srivastava et al., 2019). Current models do not adequately explain the mechanisms driving the propagation and termination of mega-dykes. We hypothesise that mega-dyke propagation is driven by the gradient in gravitational potential energy associated with the topography of a hotspot swell.

We present an analytical model linking the length of mega-dykes to the dimensions of a topographic swell above a hotspot. Our model accounts for various energy sources, including magma-source pressure and gravitational potential energy, and energy sinks such as viscous dissipation, elastic wall-rock deformation, and fracturing at the dyke tip. We define the ground surface deformation above a hotspot using an analytical model (Morgan, 1965) and demonstrate, in this context, that the dyke width scales with distance from the magma source. The final dyke length is computed by finding the point at which the sum of energy sources becomes less than the energy sinks. Furthermore, we explore the trade-offs between parameters controlling the swell size and the final length of a mega-dyke. We tentatively apply our findings to observed mega-dyke swarms and investigate the hot-spot sizes required to produce the observed lengths of these structures.

References

Ernst, R.E. and Baragar, W.R.A., 1992. Evidence from magnetic fabric for the flow pattern of magma in the Mackenzie giant radiating dyke swarm. Nature, 356(6369), pp.511-513. doi:10.1038/356511a0

Ernst, R.E., 2001. The use of mafic dike swarms in identifying and locating mantle plumes. Geological Society of America Special Papers, 352, p.247-265. doi:10.1130/0-8137-2352-3.247

Morgan, W.J., 1965. Gravity anomalies and convection currents: 1. A sphere and cylinder sinking beneath the surface of a viscous fluid. Journal of Geophysical Research, 70(24), pp.6175-6187. doi:10.1029/JZ070i024p06175

Srivastava, R.K., Ernst, R.E. and Peng, P. eds., 2019. Dyke swarms of the world: A modern perspective. Springer Geology. doi:10.1007/978-981-13-1666-1

How to cite: Davis, T. and Katz, R.: A theory for mega-dyke propagation as driven by hotspot topography., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5023, https://doi.org/10.5194/egusphere-egu23-5023, 2023.

EGU23-5621 | Orals | GD1.3

How post-Caledonian burial, exhumation and peneplanation shaped the scenery of Fennoscandia 

Peter Japsen, Paul F. Green, Johan M. Bonow, James A. Chalmers, Ian R. Duddy, and Ilmo Kukkonen

The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides limited documentation of the post-Caledonian history. But a more complete understanding can be obtained by also considering evidence of rocks that were formerly present but have since been removed (‘missing section’).

We report apatite fission-track data and associated thermal history constraints in 331 samples of Precambrian basement, Phanerozoic sediments and igneous rocks from outcrops and boreholes (up to 6 km depth) from Norway, Sweden and Finland, which define multiple episodes of cooling over the last billion years.

We are therefore able to establish a post-Caledonian history of Fennoscandia involving repeated episodes of kilometer-scale burial and exhumation with key episodes of exhumation beginning during late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene. The effects of these episodes are documented in the stratigraphic record and as prominent peneplains. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasizing the tectonic nature of the history.

Results from Finland record events also recognized in Norway and Sweden (though less pronounced) and are thus not consistent with long-term cratonic stability. We interpret the lack of preserved Phanerozoic sedimentary cover in Finland to be due to complete removal during multiple episodes of denudation. For example, our results show that about 2 km of Cambrian to Middle Triassic sediments covered the Sub-Cambrian Peneplain in southern Finland prior to the onset of Middle Triassic exhumation. In southern Scandinavia, Miocene exhumation led to formation of a peneplain which in Pliocene times was uplifted and dissected, producing the modern landscape, also by exhuming older peneplains from below their protective cover rocks.

The Carboniferous to Cretaceous exhumation episodes affected Fennoscandia as well as East Greenland, however, post-breakup episodes affected the conjugate margins of the NE Atlantic differently. Whereas Neogene uplift began in the early Miocene in Fennoscandia, it began in the late Miocene in Greenland. Pliocene uplift affected both margins at about the same time. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here.

 

References

Bonow & Japsen, 2021, Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic. GEUS Bulletin.

Green et al., 2022a, Episodic kilometre-scale burial and exhumation and the importance of missing section. Earth-Science Reviews.

Green et al., 2022b, The post-Caledonian thermo-tectonic evolution of Fennoscandia. Gondwana Research.

Japsen & Chalmers, 2022, The Norwegian mountains: the result of multiple episodes of uplift and subsidence. Geology Today. https://doi.org/10.1111/gto.12377

Japsen et al., 2018, Mountains of southernmost Norway: uplifted Miocene peneplains and re-exposed Mesozoic surfaces. Journal of the Geological Society, London.

Japsen et al., 2021, Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic. GEUS Bulletin.

Lidmar-Bergström et al., 2013, Stratigraphic landscape analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence. Global and Planetary Change.

How to cite: Japsen, P., Green, P. F., Bonow, J. M., Chalmers, J. A., Duddy, I. R., and Kukkonen, I.: How post-Caledonian burial, exhumation and peneplanation shaped the scenery of Fennoscandia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5621, https://doi.org/10.5194/egusphere-egu23-5621, 2023.

EGU23-6676 | ECS | Orals | GD1.3

Ray-theoretical and finite-frequency seismic traveltime predictions for tomographic filtering of 3D mantle circulation models 

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

Linking geodynamic models to observations from seismology is essential for improving our understanding of the present-day thermodynamic state of the mantle. From the geodynamic perspective, 3D mantle circulation models (MCMs) yield physically relevant predictions of the global distribution of buoyancy forces, while complementing information is available from seismic data and tomography that can reveal the location and morphology of mantle heterogeneity. Investigating this powerful interplay in a fully synthetic framework has great potential. It allows us to make robust interpretations of mantle structure provided that quantitatively meaningful comparisons can be made. This especially relates to the magnitudes of heterogeneity that can not be effectively constrained by the individual modelling approaches.

Following this general concept, there are two possible links: 1) synthetic seismic data can be predicted from the MCM and statistically be compared against observed data. 2) the MCM gets modified by a tomographic operator (informing us about spatially variable seismic resolution and, if applicable, model uncertainty), and subsequently this filtered version gets compared against the corresponding tomographic image from real observations.

Here, we discuss these two strategies together based on observed data for S-wave cross-correlation traveltime residuals that have been applied to global seismic tomography. Taking the same set of source-receiver configurations, synthetic traveltime predictions are computed in a state-of-the-art MCM using ray theory (RT), paraxial finite-frequency kernels (FFK), as well as cross-correlation measurements on synthetic seismograms (SPECFEM). The latter requires computationally demanding 3D-wavefield simulations using SPECFEM3D_GLOBE for an earthquake catalog comprising over 4,200 teleseismic events.

These data sets can be used for tomographic filtering by application of the generalized inverse operator of the actual tomographic model. Filtered MCMs derived from the differently predicted data sets appear largely similar on a global scale with regards to the shape and amplitudes of imaged mantle heterogeneity. This is observed despite the lack of more accurate wave physics in RT or FFK and possible measurement errors for the SPECFEM data that, although being computed in a synthetic case, can not be completely ruled out. Stronger differences between filtered models appear in regions of higher image resolution where model uncertainty by propagated data errors can play a more prominent role.

We discuss the impact of the different filtering strategies by comparing filtered models to the original MCM and synthetic traveltime residuals to the underlying real observations. The results strongly highlight the need for incorporating both resolution and model uncertainty in combined tomographic-geodynamic studies.

How to cite: Freissler, R., Schuberth, B. S. A., and Zaroli, C.: Ray-theoretical and finite-frequency seismic traveltime predictions for tomographic filtering of 3D mantle circulation models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6676, https://doi.org/10.5194/egusphere-egu23-6676, 2023.

EGU23-7226 | ECS | Posters on site | GD1.3

The effect of asthenosphere’s rheology on mantle and surface tectonics : the role of composite rheology 

Maelis Arnould, Tobias Rolf, and Antonio Manjón-Cabeza Córdoba

Earth’s upper mantle rheology controls lithosphere-asthenosphere coupling and thus its surface tectonics. Although rock deformation experiments and seismic anisotropy measurements indicate that dislocation creep can occur in the Earth's uppermost mantle, the role of composite rheology (including both diffusion and dislocation creep) on global-scale mantle dynamics and surface tectonics remains largely unexplored.

Here, we investigate the influence of composite rheology on the planform of convection and on the planetary tectonic regime as a function of the lithospheric yield strength in numerical models of mantle convection with plate-like tectonics. We show that the consideration of composite rheology in the upper mantle leads to the self-generation of a discontinuous asthenosphere evolving fast, with a low-viscosity and a maximal thickness that depend on the rheological parameters for diffusion and dislocation creep. In mobile-lid models, the spatio-temporal evolution of the asthenosphere is mainly controlled by the location of slabs and plumes that generate regions of mantle deforming dominantly through dislocation creep. Moreover, the low upper-mantle viscosities caused by composite rheology produce substantial and contrasting effects on surface dynamics. For a strong lithosphere (high yield stress), the large lithosphere-asthenosphere viscosity contrasts promote stagnant-lid convection, while the increase of upper-mantle convective vigor enhances plate mobility for low lithospheric strength (small yield stress). We further show that composite rheology does not facilitate the onset of plate-like behavior at large lithospheric strength due to decoupling between the asthenosphere and the lithosphere.

How to cite: Arnould, M., Rolf, T., and Manjón-Cabeza Córdoba, A.: The effect of asthenosphere’s rheology on mantle and surface tectonics : the role of composite rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7226, https://doi.org/10.5194/egusphere-egu23-7226, 2023.

EGU23-8412 | Orals | GD1.3

Shallow Asthenospheric Volumes Beneath Cenozoic Volcanic Provinces in the Circum-Mediterranean: Evidence From Seismic Tomography And Integrated Geophysical-Petrological Thermochemical Modelling 

Amr El-Sharkawy, Thor H. Hansteen, Carlos Clemente-Gomez, Javier Fullea, Sergei Lebedev, and Thomas Meier

During the Cenozoic, the Circum-Mediterranean has experienced extensive and widespread igneous magmatism (i.e. intraplate, subduction-related and mixed-origin) that reflects the response of the upper mantle to the geodynamic evolution of this area. The exact origin of the volcanic activities and its relation to the underlying thin lithosphere especially in the continental regions have been long-lasting debated. We investigate the structure of the lithosphere and the sub-lithospheric mantle in the Circum-Mediterranean using regional high-resolution 3-D surface wave tomography and integrated geophysical-petrological thermochemical modelling of the temperature field and explore the relation to the occurrence intraplate and mixed-origin volcanic provinces (IMVPs).

We define 9 shallow asthenospheric volumes (SAVs) across the Circum-Mediterranean upper mantle that form an almost interconnected belt of reduced shear wave velocities starting from the western Mediterranean to the Middle East and surrounding the Calabrian, Adriatic, Alpine slabs, however only interrupted by the eastern Mediterranean thick oceanic lithosphere. The SAVs are characterized by pronounced variations in shear-wave velocity not only laterally but also vertically between 70 and 300 km depths. Results from integrated geophysical-petrological thermochemical modelling show that the low velocities of the SAVs correspond to areas of thinned lithosphere (i.e., 1300 ºC at about 60-80 km depth) and anomalously warm asthenosphere (down to 300 km approximately) with respect to the average ambient mantle geotherm. A remarkable correlation between these areas and locations of IMVPs is observed with a mean lateral distance of < 100 km separating any SAV to the neighboring IMVP. The maximum separating distances are in order of ~ 350 km indicating a dense network of volcanic provinces above the shallow SAVs.

The origin of the SAVs is related either to asthenospheric upwelling caused by slab rollback and decompressional melting during the formation of the back-arc basins (i.e., Agean-Anatolia, Pannonian, Moesian, Western Mediterranean) or to lithospheric thinning and rifting (Middle East and Rhone-Rheine areas). For the origin of the remaining SAVs (Adriatic, Central European, North Africa), other processes, i.e. thermal erosion feed by input from deep mantle sources, are suggested. According to the oldest ages of the IMVPs in the Circum-Mediterranean, the development of the SAVs started at least about ~ 60 - 70 Ma ago and accelerated in the Neogene.

How to cite: El-Sharkawy, A., Hansteen, T. H., Clemente-Gomez, C., Fullea, J., Lebedev, S., and Meier, T.: Shallow Asthenospheric Volumes Beneath Cenozoic Volcanic Provinces in the Circum-Mediterranean: Evidence From Seismic Tomography And Integrated Geophysical-Petrological Thermochemical Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8412, https://doi.org/10.5194/egusphere-egu23-8412, 2023.

EGU23-9490 | Orals | GD1.3

Coupling Models of Plate Motion History, Mantle Convection and the Geodynamo to explain long-term Geomagnetic Field Behavior 

Juliane Dannberg, Daniele Thallner, Rene Gassmoeller, Courtney Sprain, Frederick LaCombe, and Chloe Ritchie

Mantle convection and plate tectonics are crucial mechanisms for keeping conditions at the Earth’s surface in a suitable range for life. One important mantle process is the transport of heat out of the Earth’s outer core, which impacts the geodynamo that generates Earth’s magnetic field. This interaction makes it possible to use changes in the paleomagnetic record to infer the past dynamics of the Earth’s mantle and core.

We here couple a plate reconstruction, 3d global mantle convection models, and geodynamo simulations to quantify the largest possible influence of mantle heat transport on the magnetic field at the Earth’s surface. To constrain the core-mantle boundary heat flux, we set up compressible global mantle convection models using the geodynamic modeling software ASPECT, with material properties computed based on a mineral physics database. We prescribe the velocities at the surface using a plate reconstruction that describes plate motion history throughout the last 1 billion years, encompassing the complete cycle of supercontinent assembly and dispersal. This boundary condition imposes the location of subducted slabs in the model, which then sink down and interact with the thermal/thermochemical boundary later at the base of the mantle, affecting the amplitude and pattern of the heat flux out of the core and how it changes over time. Our models show that the distribution of hot and cold regions changes in terms of location, shape and number throughout the supercontinent cycle, depending on subduction location. Our results indicate that structures at the core-mantle boundary fluctuate and might have looked very differently throughout Earth’s history.

We then select endmember scenarios of core-mantle boundary heat flux patterns and amplitudes to apply them as boundary conditions to thermally driven numerical geodynamo simulations. To assess how well these simulations reproduce Earth’s long-term magnetic field behavior, we apply the Quality of Paleomagnetic Modeling criteria. This allows us to systematically explore the impact of the most extreme variations of CMB heat flux on the geodynamo and to determine if extreme anomalies in the paleomagnetic record, like the extreme weak field period in the Ediacaran, could be caused by mantle dynamics alone or if they require other mechanisms, such as the nucleation of the Earth’s inner core.

Our work shows how integrating multidisciplinary datasets into modeling studies improves our understanding of the mantle’s role in regulating the magnetic field throughout Earth's history, allowing us to re-evaluate the causes of variations in paleomagnetic data.

How to cite: Dannberg, J., Thallner, D., Gassmoeller, R., Sprain, C., LaCombe, F., and Ritchie, C.: Coupling Models of Plate Motion History, Mantle Convection and the Geodynamo to explain long-term Geomagnetic Field Behavior, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9490, https://doi.org/10.5194/egusphere-egu23-9490, 2023.

EGU23-9743 | ECS | Posters on site | GD1.3

Linking thermal and seismic mantle structure in the light of uncertain mineralogy and limited tomographic resolution 

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

Mantle convection is primarily driven by gravitational forces acting on thermally buoyant structures in Earth's interior. The associated vertical stresses generate phases of uplift and subsidence of the surface, leaving observable traces in the geologic 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 geologic observations. These so-called mantle flow retrodictions are emerging as powerful tools that have the potential to allow for tighter constraints on the inherent physical parameters.

To contain meaningful information, the inverse models require an estimate of the present-day buoyancy distribution within the mantle, which can be derived from seismic observations. By using thermodynamically self-consistent models of mantle mineralogy, it is possible to convert the seismic structure of global tomographic models to temperature. However, both seismic and mineralogical models are significantly affected by different sources of uncertainty and often require subjective modelling choices, which can lead to different estimated properties. In addition, due to the complexity of the mineralogical models, the relation between temperature and seismic velocities is highly nonlinear and not strictly bijective: In the presence of phase transitions, different temperatures can result in the same seismic velocity, further complicating the conversion between the two parameters.

 

Using a synthetic closed-loop experiment, we investigate the theoretical ability to estimate the present-day thermal state of Earth's mantle based on tomographic models. The temperature distribution from a 3-D mantle circulation model with earth-like convective vigour serves as a representation of the "true" temperature field, which we aim to recover after a set of processing steps. These steps include the “forward and inverse” mineralogical mapping between temperatures and seismic velocities, using a thermodynamic model for pyrolite composition, as well as applying a tomographic filter to mimic the limited resolution and uneven data coverage of the underlying tomographic model. Owing to imperfect knowledge of the parameters governing mineral anelasticity, we test the effects of changes to the anelastic correction applied in forward and inverse mineralogical mapping. The mismatch between the recovered and the initial temperature field carries a strong imprint of the tomographic filter. Additionally, we observe systematic errors in the recovered temperature field in the vicinity of phase transitions. Our results highlight that, given the current limits of tomographic models and the incomplete knowledge of mantle mineralogy, amplitudes and spatial scales of a temperature field obtained through global seismic models will deviate significantly from the true state. Strategies to recover the present-day buoyancy field must be carefully selected in order to minimize additional uncertainties.

How to cite: Robl, G., Schuberth, B., Papanagnou, I., and Thomas, C.: Linking thermal and seismic mantle structure in the light of uncertain mineralogy and limited tomographic resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9743, https://doi.org/10.5194/egusphere-egu23-9743, 2023.

EGU23-10217 | ECS | Posters on site | GD1.3

High-resolution mantle flow models reveal importance of plate boundary geometry and slab pull forces on generating tectonic plate motions 

Arushi Saxena, Juliane Dannberg, and Rene Gassmoeller

Plate tectonics can explain several geological and geophysical phenomena on Earth, and a number of mantle flow models have been developed to investigate the underlying plate tectonic forces. However, these models have come to contradictory conclusions on the balance between the resisting and driving forces. Additionally, they have used the same simplified model to represent the geometry of the plates, and therefore the impact of plate boundary geometry on surface deformation remains unknown.

To address these issues, we have developed high-resolution global instantaneous mantle convection models based on recent geophysical constraints with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different plate boundary configurations. We find a good fit to the observed GPS data for models with plate boundaries that are 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5×1017 and 5×1018 Pa s for all plate boundary configurations. We also find that the model with plate boundaries defined by the Global Earthquake Model (GEM, Pagani et al., 2018)—featuring open plate boundaries with discrete lithospheric-depth weak zones in the oceans and distributed crustal faults within continents—achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point-wise velocity residual of 1.87 cm/year. These results show that Earth’s plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents.

Our models also quantify the contributions to the plate driving forces originating from heterogeneities in the upper mantle and the lower mantle, respectively, finding that the slab-pull in the top 300 km alone contributes ~70% of the total plate speeds. Noting the importance of slab pull as a major plate driving force, we further investigate the influence of subduction zone and slab geometry on surface plate motions and their fit to GPS data. Specifically, our models compare a simplified slab structure to a more detailed representation of slabs based on the Slab2 database (Hayes et al., 2018), and reaffirm that a realistic slab geometry is a crucial factor in the transmission of slab pull forces to the plate.

How to cite: Saxena, A., Dannberg, J., and Gassmoeller, R.: High-resolution mantle flow models reveal importance of plate boundary geometry and slab pull forces on generating tectonic plate motions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10217, https://doi.org/10.5194/egusphere-egu23-10217, 2023.

EGU23-10292 | ECS | Posters on site | GD1.3

Earth’s Wandering Rotation Axis as a Diagnostic for Global Mantle Convection Models 

Christopher M. Calvelage, Lorenzo Colli, Jonny Wu, and Yi-An Lin

Dynamic topography is the change in topography that arises from viscous flow within the Earth’s mantle. As such, dynamic topography is sensitive to past mantle flow states. Making predictions of dynamic topography through time often relies on complex mantle convection models. To better constrain mantle convection models, we compare their implied True Polar Wander (TPW) paths for a range of model parameters. TPW is the re-orientation of a planetary solid body with respect to its rotation axis and may be produced by large scale mass redistributions on the Earth’s surface or within the mantle that perturb the Earth’s moment of inertia.

Here we compare TPW histories estimated from two global plate tectonic reconstructions that were assimilated into the TERRA mantle convection code: (1) the widely-used Earthbyte global plate model (‘corrected R’ Matthews et al., 2016); and (2) TOMOPAC-22, a newly developed global plate tectonic model of the circum-Pacific using structurally-restored slabs from mantle seismic tomography (Wu et al., 2022). The time series of geodynamically-modeled mantle states are used to calculate synthetic TPW paths from perturbations in components of Earth’s moment of inertia from mass redistribution within the mantle; multiple (>10) viscosity-depth profiles were considered. We test these modeled TPW paths by comparing them against published paleomagnetic observations (Torsvik et al., 2012; Besse and Courtillot, 2002). Predicted TPW for plate Model 1 ranges widely (~90°) in azimuth from 120°W to 59°E with no consistent pattern across viscosity profiles. TPW rates reach maximums of 1.1°/Myr with excursions of ~25°. In contrast, predicted paths for Model 2 cluster within a smaller ~30° azimuthal range centered around ~29°E irrespective of the viscosity profile.  Predicted maximum rates were up to ~2°/Myr with excursions of up to 30°. Temporally, predicted paths for Model 2 drift toward northern Russia and then veer towards Greenland. Depending on the viscosity profile used some predicted TPW paths undergo stillstands from ~80 to ~30 Ma.  Ultimately, most model scenarios show longitudinal misfits up to 60° with observed paleomagnetic data; modeled TPW rates were within observed and theoretical ‘speed limits'. We discuss similarities and differences between our preliminary TPW history results and paleomagnetic observations, with a goal of developing an effective TPW test for constraining geodynamic parameters, plate tectonic reconstructions, and dynamic topography through time.

How to cite: Calvelage, C. M., Colli, L., Wu, J., and Lin, Y.-A.: Earth’s Wandering Rotation Axis as a Diagnostic for Global Mantle Convection Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10292, https://doi.org/10.5194/egusphere-egu23-10292, 2023.

EGU23-10376 | Posters on site | GD1.3

Daisy chain method applied to mapping the asthenosphere 

Lawrence Cathles, Willy Fjeldskaar, and Aleksey Amantov

The discovery of very rapid uplift rates under areas recently de-glaciated and the realization that such rapid uplift can stabilize ice sheets has generated interest in determining the properties of the asthenosphere.  The asthenosphere is also important to plate tectonics, and to the proper interpretation many important Earth observations.  The current approach to determining the properties of the asthenosphere is to calculate the observed rate of uplift in an area for a great many deglaciation and earth models, calculate the difference between the observed and calculated uplift rates and histories, and find the earth model (with error bars) that best matches the observations.  A faster, simpler, and in some ways better assessment method is to compute the isostatic adjustment response to a loading history consisting of linear segments.  This method determines the central response time from the dimensions of the load, the loading history, the lithosphere flexural rigidity (often not important), and the present rate of uplift.  The last can be easily measured today with GPS in INSAR.  Asthenosphere properties are indicated by the central response time so determined. The Daisy chain method will be described, evaluated against data and conventional modeling in northern Norway, and then applied to infer asthenosphere properties in a number recently-deglaciated continental localities.

How to cite: Cathles, L., Fjeldskaar, W., and Amantov, A.: Daisy chain method applied to mapping the asthenosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10376, https://doi.org/10.5194/egusphere-egu23-10376, 2023.

EGU23-11908 | ECS | Posters on site | GD1.3

Imaging 3-D electrical conductivity structure under US constrains lateral variations in the mantle water content 

Federico Daniel Munch and Alexander Grayver

Electrical conductivity variations provide unique constraints on chemistry, mineralogy, and physical structure of the crust and mantle. As a physical property, conductivity is highly sensitive to the presence of even small amounts of melt and water (i.e., hydrogen). Here, we present a new 3-D electrical conductivity model (MECMUS-2022) derived by inverting data from ~1300 USArray MT stations covering ∼80% of the contiguous United States on a quasi-regular 70-km grid. The use of a novel multi-scale imaging approach and locally refined meshes allows us to consistently incorporate a large range of spatial scales and image 3-D electrical conductivity distribution from the surface down to mantle transition zone. We find conductivity variations that correlate with known continental structures such as due to the active tectonic processes within the western United States (e.g., Yellowstone hotspot, Basin and Range extension, and subduction of the Juan de Fuca slab) as well as the presence of deep roots beneath cratons. We further interpret conductivity variations in terms of the upper mantle water content by coupling electrical conductivity with constrains on mantle thermo-chemical structure derived from the analysis of seismic data (in the form of P-to-s and S-to-p receiver functions). Further, we explore the links between electrical conductors and lithospheric controls on occurrence of critical mineral deposits.

How to cite: Munch, F. D. and Grayver, A.: Imaging 3-D electrical conductivity structure under US constrains lateral variations in the mantle water content, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11908, https://doi.org/10.5194/egusphere-egu23-11908, 2023.

EGU23-14852 | Orals | GD1.3 | Highlight

Whole Mantle Convection with Two Structures and Timescales of Flow 

Jason P. Morgan, Ya-Nan Shi, and Paola Vannucchi

Mantle convection has often been debated to be either a mode of ‘top-to-bottom’ whole mantle convection, or flow within separated geochemical ‘reservoirs’ such as a denser layer often proposed to be the origin of lower mantle LLSVPs. Here we propose a straightforward resolution in which plate tectonic downwelling is linked to a ~3000 km-broad N-S circumglobal ‘ring’ of higher-than-average seismic wavespeeds in the lower mantle that has been recognized since the first global models of non-radial seismic structure. In the high-viscosity lower mantle, subduction-linked downwelling occurs at speeds of <~1.3 mm/yr, which is the origin of the long-known ~1.7Ga ‘isochrons’ seen in both hotspot and mid-ocean ridge volcanism.  This ~3000 km-wide great-circle ring of slow downward flow is associated with two antipodal axial spokes of twice-as-fast but still very slow largescale upward flow in the ‘LLSVP’ regions. In addition to this background pattern of large-scale lower mantle circulation, upward counterflow to plate subduction preferentially takes material from a warmer D’’ thermal boundary layer at the core-mantle boundary through ~10-20 mantle plumes that feed a sublithospheric plume-fed asthenosphere. In the lower mantle, the relatively warmer and lower viscosity plumes preferentially rise through and are slowly attracted towards the LLSVP regions by the low-order mode of slow lower mantle flow, with plume-conduits further warming their surrounding LLSVP lower mantle.

In this contribution we review the seismological and geochemical observations that support this scenario of two interlocking modes of whole mantle convection with very slow flow in the lower mantle that is linked to and pierced by much faster flow in a D’’-plume-asthenosphere upward flow circuit. We then present 3-D thermomechanical models designed to elucidate under what conditions this mode of flow can arise from a highly variable viscosity mantle with both internal heating and significant heatflow across the core-mantle boundary. Finally we briefly touch on some further implications of this scenario for Earth’s radial mantle structure, supercontinent evolution, the geoid, and the geodynamo.

How to cite: Morgan, J. P., Shi, Y.-N., and Vannucchi, P.: Whole Mantle Convection with Two Structures and Timescales of Flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14852, https://doi.org/10.5194/egusphere-egu23-14852, 2023.

EGU23-15266 | ECS | Posters on site | GD1.3

Testing Dynamic Topographic Predictions of Mantle Convection Models Using Global Palaeobiological Datasets 

Conor O'Malley, Gareth Roberts, James Panton, Huw Davies, and Victoria Milanez Fernandes

Over geological timescales, aside from isostatic processes arising from crustal thickness variations, flow within the mantle has long been recognised to generate a significant component of Earth's topography, i.e. "dynamic topography". Therefore, geological and geophysical evidence of Earth's surface deflection can provide spatio-temporal evidence of deep Earth processes, if tectonic/crustal processes are accounted for. Mantle convection models can be used to calculate past and present dynamic topography in a number of ways, with the aim of matching surface observations to improve our understanding of mantle properties and flow characteristics. We analyse the global spatio-temporal patterns of dynamic topography predicted by a suite of models run using the TERRA code, which solves the Stokes and energy equations for mantle flow within a spherical shell. Both compressible/incompressible models are analysed, for a range of mantle viscosity structures. We calculate dynamic topography using two widely-used methods, focussing on the present-day where the pattern of dynamic topography is constrained in greatest detail. First, we examine dynamic topography using instantaneous surface stress calculated from full-resolution 3-D TERRA output. Secondly, model output is transformed into the spherical harmonic domain, and density anomalies at depth are propagated to surface stress variations, and therefore topographic deflections, using analytic sensitivity kernels i.e. the propagator matrix method. Each method makes subtly different assumptions about boundary conditions and mantle structure and properties. We demonstrate that uplift predictions calculated using each method can be compared with observational estimates derived from palaeobiological data, oceanic residual depth measurements, and continental gravity anomalies. We highlight key similarities and differences between dynamic topographic predictions from each method across a suite of mantle convection models, and identify correlation/misfit with observational constraints.

How to cite: O'Malley, C., Roberts, G., Panton, J., Davies, H., and Milanez Fernandes, V.: Testing Dynamic Topographic Predictions of Mantle Convection Models Using Global Palaeobiological Datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15266, https://doi.org/10.5194/egusphere-egu23-15266, 2023.

EGU23-15494 | ECS | Posters on site | GD1.3

Dynamic topography and satellite gravity data joint inversion using Reduced Order Models (DYGIRO) 

Olga Ortega-Gelabert, Javier Fullea, Mariano S. Arnaiz-Rodríguez, and Sergio Zlotnik

Geophysical observables, such as surface elevation, gravity field anomalies, seismic data, surface heat flow, etc, are essential pieces of information used to make inferences about the structure and dynamics of the Earth’s interior. Simultaneously fitting different observable datasets is crucial in order to obtain consistent models. Among geophysical data, gravity data from ESA’s GOCE satellite mission provides key information in properly constraining the Earth’s density distribution. WINTERC-G is a new global thermochemical model of the lithosphere and upper mantle (currently being extended into the transition zone and lower mantle) based on terrestrial and satellite gravity data (Fullea et al., 2021). The inversion procedure behind WINTERC-G has two main steps. In step 1, a 1D column-wise inversion of surface wave tomographic, surface elevation (isostasy) and heat flow data is performed. Then, in step 2, the output model from step 1 is used as prior information for the inversion of the gravity field data (filtered geoid anomalies and gravity gradients from GOCE at satellite height) to refine the 3D crustal density and upper mantle composition. The model predicts a residual, non-isostatic topography that can be considered as a proxy for dynamic topography.

However, within a rigorous framework, dynamic topography cannot be simply taken as a non- isostatic residual, but it should be explicitly computed (i.e. solving the Stokes equation for a given rheological and density distribution) and consistently integrated into the joint inversion of the gravity field and the terrestrial observation with feedback from both the static and dynamic parts. The goal of DYGIRO project is to add a third step into the global WINTERC-G inversion scheme that consistently integrates dynamic topography as an additional model constrain.

We present here the first steps of such integration at global scale. To do that, the dynamic topography is computed by solving the Stokes flow problem associated with the current WINTERC-G model down to the transition zone. The dynamic topography thus obtained is coupled with the static thermochemical model constrained by gravity and seismic data within an iterative scheme where the observed surface elevation coincides with the model’s isostatic plus dynamic elevation contributions. The high computational cost associated with the large- scale 3D flow computations will be alleviated by means of Reduced Order Models. Such models are based on the idea of creating surrogate models that approximate the solution at a much lower computational cost.

 

Fullea, J. Lebedev, S., Martinec, Z., Celli, N. L. (2021). WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical-petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data, Geophysical Journal International, 226(1), 146–191.

How to cite: Ortega-Gelabert, O., Fullea, J., Arnaiz-Rodríguez, M. S., and Zlotnik, S.: Dynamic topography and satellite gravity data joint inversion using Reduced Order Models (DYGIRO), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15494, https://doi.org/10.5194/egusphere-egu23-15494, 2023.

EGU23-15545 | ECS | Orals | GD1.3

Amplification of sub-lithospheric dynamics by melt migration during plume-lithosphere interaction 

Björn H. Heyn, Grace E. Shephard, and Clinton P. Conrad

The interaction of mantle plumes with continental or cratonic lithosphere can result in (large-scale) volcanism and continental breakup, but these consequences seem to be limited to tectonic settings with pre-existing weak zones. In contrast, most parts of continental plume tracks, or their hypothesized tracks, show no extrusive magmatism. To reconcile this, our previous work has shown that even in the absence of melt, sustained plume-lithosphere interaction leads to lithospheric thinning, followed by elevated surface heat flux about 40-140 million years after the thermal anomaly in the mantle disappears. Therefore, melt-free continental plume tracks can be initially identified by a reduced lithosphere thickness, and later by an increased surface heat flux that temporally and spatially follows the thinned lithosphere.

Yet, even if melt is not erupted, variable amounts of melt may still be generated at the base of the lithosphere above the plume, and this melt can impact local dynamics. In order to assess the role of melt in plume-lithosphere interactions, we have developed a recent suite of numerical models of mantle convection that include melting/freezing and melt migration. Our results indicate a much stronger time-dependence of models with melt compared to models without melt. In particular, small-scale convection at the base of the lithosphere becomes more vigorous, which leads to patterns that feature more localized and larger amplitude lithospheric removal and stronger asymmetry across the plume track. The generation of melt in a thinned area has a self-enhancing effect; more melt thins the lithosphere faster, resulting in more melt generation. However, the effect of thinning for a moving plate is limited, both with respect to the affected area and the time during which this local thinning can be sustained. As a result, the surface heat flux pattern, which is a long-pass filtered image of the lithosphere thinning, does not change significantly compared to a case without melt. However, melt migration brings heat closer to the surface, which increases the amplitude of the heat flux anomaly, and reduces the delay time following lithosphere thinning. The amplification of local dynamics by melt migration is especially pronounced if the plume interacts with pre-existing topography of the lithosphere-asthenosphere boundary (LAB), e.g. steps in lithospheric thickness. Depending on the LAB topography, multiple events of melt generations and magmatic intrusion can be generated by a single plume over tens of millions of years . Such a scenario may explain the pulse-like prolonged activity of the High Arctic Large Igneous Province (HALIP; which erupted between 130-85 Ma) and potentially an early phase of an Iceland plume track under Greenland (pre-62 Ma).

How to cite: Heyn, B. H., Shephard, G. E., and Conrad, C. P.: Amplification of sub-lithospheric dynamics by melt migration during plume-lithosphere interaction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15545, https://doi.org/10.5194/egusphere-egu23-15545, 2023.

EGU23-15705 | Orals | GD1.3

Analyzing geological maps at the continental scale 

Anke M Friedrich

Geological maps are essential products of geological work that display the results of generations of field geologists’ work. Most original geological maps are generated and utilized at local scales. At regional scales, geological maps have gained practical significance ever since William Smith’s 1815 geological map of England exemplified the robust nature of mapping and correlating strata beyond local scales. However, by comparison, geological maps compiled at continental scales appear to be of limited use outside of geological circles. They are often oversized, inhibiting their practical use, so they decorate our geoscience hallways and lecture halls with their beautiful colors and general esthetic appearance. Few outsiders can even read these maps. Their unique color-coding, the multiple non-diverging color schemes, and their complex legends further inhibit non-geologists from being able to recognize the enormous knowledge stored in these maps. I present an analysis of continent-scale geological maps by visualizing time not represented by the rock record (hiatus) and examining the dimensions of hiatal surfaces at interregional scales. The maps yield significant variability in sizes and space-time patterns of hiatal surfaces, a behavior expected in light of interregional-scale processes induced by both the plate and the plume mode of mantle convection. However, to rigorously test models of mantle convection, the temporal resolution of continent-scale maps must be increased to stages level, i.e., the temporal scale at which tectonic processes occur. In addition, synthesis of geological data on continent-scales requires the development and application of event-based stratigraphic-framework mapping.

How to cite: Friedrich, A. M.: Analyzing geological maps at the continental scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15705, https://doi.org/10.5194/egusphere-egu23-15705, 2023.

EGU23-16368 | ECS | Orals | GD1.3

Can Correcting for Mantle Dynamics Reconcile Divergent Plio-Pleistocene Sea-Level Estimates? 

Fred Richards, Sophie Coulson, Mark Hoggard, Jacqueline Austermann, Blake Dyer, and Jerry Mitrovica

Estimates of global mean sea level (GMSL) during past warm periods provide a key constraint on ice-sheet sensitivity to future climate change and inform projections of long-term sea-level rise. Measurements from the most recent periods of enhanced warmth are especially valuable since these intervals represent the closest climatic analogues to near-future conditions. Considerable focus has therefore been placed on reconstructing sea-level during the Mid-Pliocene Warm Period (MPWP; 3.3–3.0 Ma) and the Last Interglacial (~129–116 ka), periods characterised by mean temperatures 2­–3 °C and ~1 °C above preindustrial levels, respectively. Many GMSL estimates have been obtained from palaeoshoreline deposits since these geomorphic proxies provide a more direct and potentially more precise constraint on past sea-level than stable isotope records. However, estimates from different sites differ by several metres due to spatially variable vertical crustal motions caused by geodynamic processes, including glacial isostatic adjustment and dynamic topography.

To tackle this issue, we integrate a suite of Australian sea-level markers and geodynamic simulations into a probabilistic inverse framework to quantify and remove the effect of vertical crustal motions at a continental scale. We find that dynamic topography accounts for most of the observed MPWP sea-level marker deflection and is also significant for the LIG. After correcting for this process and glacial isostatic adjustment, we obtain a revised MPWP GMSL estimate of +16.0/10.4–21.5 m (50th/16th–84th percentiles). We also find that post-LIG dynamic topography may account for several metres of relative displacement across the Great Barrier Reef, potentially reconciling discrepant GMSL estimates from this region. Recalibration of sea-level projections with these revised estimates suggests a more stable Antarctic Ice Sheet under future warming scenarios and appears to rule out recent high-end forecasts.

How to cite: Richards, F., Coulson, S., Hoggard, M., Austermann, J., Dyer, B., and Mitrovica, J.: Can Correcting for Mantle Dynamics Reconcile Divergent Plio-Pleistocene Sea-Level Estimates?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16368, https://doi.org/10.5194/egusphere-egu23-16368, 2023.

EGU23-16771 | Orals | GD1.3

Feedbacks between sea-floor spreading,trade winds and precipitation in the Southern Red Sea 

Kurt Stüwe, Jörg Robl, Syed Turab, Pietro Sternai, and Fin Stuart

Feedbacks between climatic and geological processes are highly controversial
and testing them is a key challenge in Earth sciences. The Great Escarpment of
the Arabian Red Sea margin has several features that make it a useful natural
laboratory for studying the effect of surface processes on deep Earth. These
include strong orographic rainfall, convex channel profiles versus concave
swath profiles on the west side of the divide, morphological disequilibrium in
fluvial channels, and systematic morphological changes from north to south
that relate to depth changes of the central Red Sea. Here we show that these
features are well interpreted with a cycle that initiated with the onset of
spreading in the Red Sea and involves feedbacks between orographic precipitation,
tectonic deformation, mid-ocean spreading and coastal magmatism.
It appears that the feedback is enhanced by the moist easterly trade
winds that initiated largely contemporaneously with sea floor spreading in the
Red Sea.

How to cite: Stüwe, K., Robl, J., Turab, S., Sternai, P., and Stuart, F.: Feedbacks between sea-floor spreading,trade winds and precipitation in the Southern Red Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16771, https://doi.org/10.5194/egusphere-egu23-16771, 2023.

EGU23-17312 | ECS | Posters on site | GD1.3

Using Earth’s free oscillations to assess mantle circulation models 

Anna Schneider, Bernhard Schuberth, Paula Koelemeijer, Federica Restelli, and Christophe Zaroli

For a thorough understanding of the impact of mantle convection on vertical motions of the lithosphere, computational modeling plays a crucial role. Mantle circulation can be modeled by solving the equations of motion of a fluid using Earth-like input parameters assimilating plate motions at the surface in discrete steps through time. Thus, a realistic Earth model relies on the robustness of the inserted information. However, apart from the general difficulty of inferring deep Earth’s properties, also the plate tectonic model introduces uncertainty. Especially the linking of relative plate motions to absolute position relies on controversial assumptions such as fixity of structures in the mantle (e.g., plumes or Large-Low-Shear-Velocity Provinces) or the association between subducted plates at depth and high velocity regions in tomographic images. The latter specifically are restricted by non-uniqueness and the need to regularize the inversions, distorting structures and damping heterogeneity amplitudes.

In order to infer secondary results from an MCM, it is thus important to validate the model against independent observations. Here, we employ Earth’s free oscillations that feature global sensitivity to 3-D structure for model assessment, complementing our earlier work using seismic body wave data. To this end, the temperature field of a published MCM is converted to seismic velocity with the help of a thermodynamic model of mantle mineralogy. An effective forward approach for the computation of normal mode data from synthetic Earth models is the calculation of splitting functions, describing the distortion of characteristic frequency peaks in the spectrum induced by even degree structural heterogeneity. A general problem is that the sensitivity of normal modes with depth often shows oscillatory behaviour preventing a straight forward relation of frequency shifts to structure in a certain depth range. This can be mitigated by combining kernels of several modes via a Backus-Gilbert approach to obtain focused sensitivity in pre-specified depth ranges of the mantle. For testing the significance of relevant model differences in splitting function data, geometrical alterations mimicking changes in the absolute reference frame and viscosity were applied to a pre-computed MCM. Current results indeed indicate that normal mode data are sensitive to such model changes within their respective uncertainty ranges.

How to cite: Schneider, A., Schuberth, B., Koelemeijer, P., Restelli, F., and Zaroli, C.: Using Earth’s free oscillations to assess mantle circulation models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17312, https://doi.org/10.5194/egusphere-egu23-17312, 2023.

EGU23-17452 | ECS | Orals | GD1.3

Retrodicting flow of the early Cenozoic mantle: perspectives from an adjoint modelling approach 

Siavash Ghelichkhan, Hans-Peter Bunge, and Jens Oeser

Convection in the mantle provides the primary forces that shape the long wavelength structure of the Earth's surface
through dynamic topography. These forces have long been known as the cause of key events in the Cenozoic era: the
termination of large-scale marine inundation in North America in the Palaeocene, the late Tertiary rise of Africa
relative to other continents and the long-wavelength tilting of Australia since the late Cretaceous. It is an
overarching goal in geodynamics to construct reliable models that can retrodict (make predictions about the past)
these key events correctly. This year marks the 20th anniversary since the introduction of adjoint modelling as a
powerful method to retrodict mantle flow. Using the adjoint method, various datasets are assimilated to optimize
dynamic earth models by deriving the necessary gradient information. Here we explore a suite of eight high-resolution
(about 670 million finite elements), compressible, global mantle flow retrodictions going back to 50 Ma. Our
retrodictions involve the dynamic effects from an upper mantle low-viscosity zone, assimilate a past plate-motion
model for the tangential surface velocity field, probe the influence of two different present-day mantle state
estimates derived from seismic tomography, and acknowledge the rheological uncertainties of dynamic Earth models
by taking in four different realizations for the radial mantle viscosity profile, two of which were published
previously. The retrodictions show for the first time that key Cenozoic events emerge jointly as part of global
Cenozoic mantle flow histories. We show that the retrodicted mantle flow histories are sensitive to the present-day
mantle state estimate and the rheological properties of the Earth model, meaning that this input information is
testable with inferences gleaned from the geological record. Retrodictions allow one to track material back in
time from any given sampling location, making them potentially useful, for example, to geochemical studies. Our
results call for improved estimates of non-isostatic vertical motion of the Earth’s surface — provided, for
instance, by basin analysis, seismic stratigraphy, landform studies, thermochronological data or the sedimentation
record — to constrain the recent mantle flow history and suggest that mantle flow retrodictions may yield synergies
across different Earth science disciplines.

How to cite: Ghelichkhan, S., Bunge, H.-P., and Oeser, J.: Retrodicting flow of the early Cenozoic mantle: perspectives from an adjoint modelling approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17452, https://doi.org/10.5194/egusphere-egu23-17452, 2023.

GMPV3 – Earth and terrestrial planets: formation, early history, and planetary interiors (in partnership with PS and GD)

EGU23-76 | Posters on site | GD3.1

Artificial chemical weathering of basaltic rock under the earth surface conditions of the present and the Proterozoic era 

Shoichi Kobayashi, Yukiko Takahashi, and Jun Naohara

In order to compare the mineral chemical effects of acid rain on surface materials under the present oxygen level and the early Proterozoic or late Archean low oxygen (before the GOE) environmental conditions, artificial chemical weathering experiments using an improved Soxhlet extraction apparatus were conducted for basalt, which had already been covered on the early earth’s surface. Some dozens of polished basalt plates put in the extraction chamber were reacted to HCI, H2S04 and HN03 solutions at pH 4, and CO2 saturated water, and distilled water at 50℃ for a different period of time up to 950 days in an open system. In the experiment under the low oxygen condition (5×10⁻⁴ PAL), the whole extraction apparatus was placed in the acrylic glove box, and oxygen was removed by the deoxidizer, and it was carried out in the nitrogen gas flow. The basalt was composed mainly of olivine as a phenocryst, and plagioclase, clinopyroxene, ilmenite and glass as a groundmass. The extracted sample solutions were collected, and analyzed using ICP-MS. Morphological, chemistry and altered product of each mineral surface were studied by SEM, EPMA, XRD and microscopy techniques.

Under both the low oxygen before the GOE and the present oxygen concentration conditions, SEM images showed remarkable dissolution of olivine surface by the H2SO4, HNO3 and HCl solutions. The (Mg + Fe)/Si on the olivine surface and (Na + Ca + K)/ (Al + Si) on the plagioclase surface decreased significantly with increasing experimental period. In chemistry of the extracted solutions, molar ratios of many elements such as Mg, K and Zn tend to be high in the three acidic solutions at pH 4, and low by the CO2 saturated water and distilled water. The molar ratio is calculated by dividing the cumulative total mole of each extracted element by the mole of individual element in the unaltered basaltic rock. The ratios of Fe, Mg, Ni, Zn and Co near 70 pm in ionic radius are high, and reflect the dissolution from the octahedral coordination of olivine. The ratios of Ca, Na, Sm, Ce, La and Sr near 110 pm are high, and reflect the dissolution from the cavities within the framework of plagioclase. Under the low oxygen condition, major elements such as Fe and Mn, and minor ones such as Zn tend to dissolve easily in all extraction solutions. Ce and Eu in REE, and Nb, Ti, Y and Zr in HFS elements are soluble in pH 4 HCl and H2SO4, CO2 saturated water and distilled water under the low oxygen condition. The results suggest that easily extracted elements under the low-oxygen condition of the early Proterozoic or late Archean influenced the evolution of continental crust, land and ocean, and may have contributed to the formation of the early Earth's surface environment.

How to cite: Kobayashi, S., Takahashi, Y., and Naohara, J.: Artificial chemical weathering of basaltic rock under the earth surface conditions of the present and the Proterozoic era, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-76, https://doi.org/10.5194/egusphere-egu23-76, 2023.

The Proterozoic orogenic belts incorporated in and around the present-day continents preserve complex magmatic, metamorphic, and geophysical signatures of the ancient supercontinents. One such orogenic belt, the Eastern Ghats Belt (EGB) is amalgamated with the Archean cratons of India along a crustal-scale suture zone known as the Terrane Boundary Shear Zone (TBSZ). The continental margin – orogenic belt interfaces, such as the TBSZ, are the black boxes of ancient tectonic processes, since they are rheologically weakened crustal discontinuities that undergo intense deformation and metamorphism recording the complete orogenic history. There have been two schools of thought on the age of final amalgamation of the EGB with the Bastar craton, as the TBSZ records two major tectonothermal events at ~950Ma and ~550Ma, coeval with the formation of supercontinents Rodinia and Gondwana, respectively. The age and mechanism of this amalgamation have implication on the crustal architecture of the Proterozoic supercontinents.

Recent studies confirmed the presence of felsic and mafic granulites of Archean Sm-Nd model ages (3.3 – 3.1 Ga) from the TBSZ that have undergone high-pressure granulite facies metamorphism. It is speculated that these rocks are of Bastar craton in origin and the underthrusting of the Bastar craton beneath the EGB, during the final collision, led to the high-pressure metamorphic conditions. In this communication, we have carried out a comparative petrological and geochemical investigation of the Archean felsic rocks (Grt-bearing charnockites) from the TBSZ and the Hbl-Bt granites from the adjacent regions of the Bastar craton to understand origin and tectonic significance of the charnockites. The garnet-bearing charnockites from the TBSZ are characterised by coarse grained Grt + Opx + Pl + Qz + Kfs + Hbl + Bt ± Ilm. The Hbl-Bt granites of the Bastar craton, adjacent to the TBSZ, are characterized by coarse grained Hbl + Bt + Qz + Kfs + Pl, with small Opx grains forming around Hbl in few places at the interface. The Grt-bearing charnockites and the Hbl-Bt granites are both ferroan and metaluminous to slightly peraluminous in nature. The high concentrations of trace elements, high Y/Nb (>1.2) ratio and pronounced negative anomalies of Eu, Sr and Ti in both the rocks are characteristic of A2-type within plate granitoids, similar to the other reported granitoids from the Bastar craton. The strong similarity in the geochemistry of Grt-bearing charnockites and Hbl-Bt granites along with the available Archean model ages of the charnockites indicate that the Grt-bearing charnockites of the TBSZ are granulite-facies equivalents of the Hbl-Bt granites and hence represent the remnants of cratonic margin in the TBSZ. This geochemical study along with the Tonian ages (~950 Ma) from monazite cores and inclusions in garnet within the co-exposed metapelites in the suture zone indicate that the Bastar craton underthrusted beneath the EGB during the formation of Rodinia. The ~500 Ma ages reported from the strongly recrystallized monazite rims might represent the reactivation of the intracontinental suture zone due to the far-field stress from the Kuunga orogeny (~530 – 490 Ma) during the formation of East Gondwana.

How to cite: Padmaja, J., Sarkar, T., and Dasgupta, S.: Geodynamic significance of the Archean A-type granites exposed along the western margin of a Proterozoic orogenic belt: Insights on the final docking of the Eastern Ghats Belt with the Indian subcontinent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-363, https://doi.org/10.5194/egusphere-egu23-363, 2023.

EGU23-377 | ECS | Posters on site | GD3.1

How flat subduction and the upper plate rheology control the deformation of the North China craton 

Açelya Ballı Çetiner, Oğuz Göğüş, and Jeroen van Hunen

The longevity of the cratonic lithosphere is controlled by its buoyancy, strength, and the viscosity contrast with that of the underlying sub-lithospheric mantle. A number of geodynamic models show that the style and characteristic of lithospheric removal/thinning mechanisms over cratons (i.e. whether delamination, drip, or hydration weakening) are accounted by their geological history and geodynamic evolution. For example, the question of which process(es) control lithospheric removal from beneath the Wyoming and North China cratons still enigmatic. To address this problem, we are using 2D numerical models to investigate how lithospheric mantle of the North China Block has been thinned in which geological, geophysical and petrological studies refers the areas as key example of cratonic destruction/removal that occurred (120-80 Ma). Considering the geological evolution of North China region, the main focus of the study is to investigate the effects of a set of parameters (e.g., viscosity, buoyancy and thickness) for the base of cratons which is likely weakened by fluids released from the subducting oceanic plate. Our preliminary results show that movement of the subducting plate is sensitive to the parameters affecting the stability of the lithosphere whereas overriding plate is mainly affected by viscosity. If the base of the cratonic lithospheric mantle is dense, thick and relatively less viscous, it forces oceanic slab to rollback, else the overlying plate slides through the base of the cratonic mantle. The model results with stagnated oceanic plate at the transition zone with low viscosity cratonic base is responsible for the deformation of the cratonic roots.

How to cite: Ballı Çetiner, A., Göğüş, O., and van Hunen, J.: How flat subduction and the upper plate rheology control the deformation of the North China craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-377, https://doi.org/10.5194/egusphere-egu23-377, 2023.

EGU23-1941 | Orals | GD3.1 | Highlight

Giant impacts and the origin and evolution of continents 

Tim Johnson, Christopher Kirkland, Yongjun Lu, Hugh Smithies, Michael Brown, and Michael Hartnady

Earth is the only planet known to have continents, although how they formed and evolved is not well understood. Using the oxygen isotope compositions (SIMS) of dated magmatic zircon, we show that the Pilbara Craton in Western Australia, Earth’s best-preserved Archaean (4.0–2.5 Ga) continental remnant, was built in three stages. Stage 1 zircons (3.6–3.4 Ga) form two age clusters with one-third recording submantle δ18O, indicating crystallization from evolved magmas derived from hydrothermally-altered basaltic crust similar to that in modern-day Iceland. Shallow melting is consistent with giant meteor impacts that typified the first billion years of Earth history. Giant impacts provide a mechanism for fracturing the crust and establishing prolonged hydrothermal alteration by interaction with the globally extensive ocean. A giant impact at around 3.6 Ga, coeval with the oldest low-δ18O zircon, would have triggered massive mantle melting to produce a thick mafic–ultramafic nucleus. A second low-δ18O zircon cluster at around 3.4 Ga is contemporaneous with spherule beds that provide the oldest material evidence for giant impacts on Earth. Stage 2 (3.4–3.0 Ga) zircons mostly have mantle-like δ18O and crystallized from parental magmas formed near the base of the evolving continental nucleus. Stage 3 (<3.0 Ga) zircons have above-mantle δ18O, indicating efficient recycling of supracrustal rocks. That the oldest felsic rocks formed at 3.9–3.5 Ga, towards the end of the so-called late heavy bombardment, seems unlikely to be a coincidence.

How to cite: Johnson, T., Kirkland, C., Lu, Y., Smithies, H., Brown, M., and Hartnady, M.: Giant impacts and the origin and evolution of continents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1941, https://doi.org/10.5194/egusphere-egu23-1941, 2023.

EGU23-2083 | ECS | Posters on site | GD3.1

Waveform Tomography of the Antarctic Plate 

Ee Liang Chua and Sergei Lebedev

The Antarctic continent is a complex assemblage of geological units, ranging from Archean cratons in the east to a Cenozoic assembly of Mesozoic terranes in the west. Present are also the failed Lambert rift system, the inactive West Antarctic rift system and intraplate volcanism in Marie Byrd Land. Covered almost entirely by ice sheets, Antarctica's highly heterogeneous lithospheric structure and its upper mantle are among the least well-studied regions of the Earth’s interior.

The past two decades have seen a significant rise in the number of seasonal and temporary deployments as well as new permanent stations, supplementing and improving the still sparse station coverage in Antarctica. This provided a considerable improvement in both the quantity and quality of seismic data available for the Antarctic continent and its surrounding regions. We assemble a very large dataset of 0.8 million waveform fits, comprising all publicly accessible broadband data in the Southern Hemisphere, with sparser coverage elsewhere, for the best possible sampling of the Antarctic Plate’s crust and the upper mantle.

The new S-wave velocity tomographic model of the crust and upper mantle of Antarctica is computed using the Automated Multimode Inversion (AMI) scheme. AMI first extracts structural information from the surface, S- and multiple S-waves as sets of linearly independent equations. These equations are then combined into a single large linear system that is solved to obtain a tomographic model of the Antarctic crust and upper mantle. We observe the clear delineation of East and West Antarctica by a strong velocity gradient that bisects the continent extending from Coats Land to Victoria Land, following the Transantarctic Mountains. West Antarctica is observed to be underlain by low S-wave velocity anomalies connecting the Antarctic Peninsula, the Amundsen Sea Coast and Marie Byrd Land. The highest S-wave velocity anomalies are observed in central-eastern Antarctica, most of which is underlain by thick, cold cratonic lithosphere. Our tomography maps the boundaries of Antarctica’s cratonic lithosphere and, also, substantial intra-cratonic heterogeneity. It also reveals the patterns of the lithosphere-asthenosphere interactions beneath the cratons and the neighbouring Cenozoic terranes and offers new evidence on the origins of the Transantarctic Mountains and the intraplate volcanism in West Antarctica.

How to cite: Chua, E. L. and Lebedev, S.: Waveform Tomography of the Antarctic Plate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2083, https://doi.org/10.5194/egusphere-egu23-2083, 2023.

The Acasta Gneiss Complex (AGC) in northwestern Canada is home to the oldest known evolved (felsic) rocks on Earth, dating back to around 4.03 billion years (Ga). These rocks preserve evidence for multiple episodes of magmatism, metamorphism, and deformation, offering insights into the geological processes that shaped the Earth's crust throughout the Archean and late Hadean. However, the metamorphic pressure–temperature (P–T) conditions of this complex remain poorly constrained. In this study, we use phase equilibria modelling and in situ garnet Lu-Hf geochronology to analyse two garnet-bearing tonalitic gneisses in the AGC, providing the first quantitative P–T constraints for a late Paleoarchean tectono-metamorphic event in the AGC. Our results indicate metamorphic peak conditions of approximately 725-780°C and 4.5-6.2 kbar, with limited partial melting (<7 vol.%) of the felsic gneisses at these crustal levels. In situ Lu-Hf garnet geochronology suggests that this metamorphic event occurred between 3.3-3.2 Ga, consistent with previous findings of high-grade metamorphism at that time. Isotopic disturbance of garnet at approximately 1.9 Ga is interpreted to reflect partial resetting of the Lu-Hf systematics in response to fluid-present re-equilibration during the Paleoproterozoic Wopmay orogeny. Our study extends the limited dataset of published P–T data for Mesoarchean and older metamorphic rocks and shows that tonalitic gneisses in the AGC evolved along a high apparent thermal gradient of 125-150°C/kbar.

How to cite: Kaempf, J., Johnson, T., Clark, C., Brown, M., and Rankenburg, K.: Pressure–temperature conditions and age of metamorphism in the Archean Acasta Gneiss Complex: constraints from phase equilibrium modelling and in situ garnet Lu-Hf geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2207, https://doi.org/10.5194/egusphere-egu23-2207, 2023.

EGU23-2391 | ECS | Posters virtual | GD3.1

Cratonic Lithosphere Delamination and Relamination Explain the Temporal Variation of Cratons 

Lihang Peng, Lijun Liu, and Liang Liu

Cratonic lithosphere delamination has been frequently suggested in recent studies. However, the fate of the delaminated Sub-Cratonic Lithospheric Mantle (SCLM) has not been thoroughly investigated. Here, we use 2D numerical models to study the evolution of initially delaminated SCLM whose density is initially larger than that of the ambient mantle. Our simulations reveal that after the dense lithospheric segments sink into the hot mantle, the increase of thermal buoyancy and/or removal of the dense components reverse their trajectory, and most of these segments eventually relaminate to the base of the above lithosphere. The time needed for the relamination process to complete is 100-300 Myr since initial delamination, with the exact value depending on the buoyancy of the SCLM and the mantle viscosity. Both delamination and relamination could generate a rapid hundred-meter to kilometer scale surface uplift. After the relamination, the subsequent cooling of the SCLM causes gradual subsidence by ~2 km. This model provides a novel explanation for the observed Phanerozoic vertical motion of many cratons as well as the origin of the enigmatic intracratonic basins, arches, and domes in the upper cratonic crust. According to our models, the delamination-to-relamination evolution mode could occur repeatedly during the past one billion years, as could reconcile the apparent long-term intactness of cratonic crusts and the temporal variations of cratonic topography.

How to cite: Peng, L., Liu, L., and Liu, L.: Cratonic Lithosphere Delamination and Relamination Explain the Temporal Variation of Cratons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2391, https://doi.org/10.5194/egusphere-egu23-2391, 2023.

EGU23-2404 | ECS | Orals | GD3.1

Using banded iron formations to understand habitable conditions on the early Earth 

Claire Nichols, Benjamin Weiss, Athena Eyster, Craig Martin, Adam Maloof, Nigel Kelly, Mike Zawaski, Stephen Mojzsis, Bruce Watson, and Daniele Cherniak

Earth is the only known inhabited world in our solar system. Criteria essential for planetary habitability include surface liquid water, a stable atmosphere, and a magnetic field. While the rock record suggests Earth has fulfilled these criteria for at least 4 billion years (Ga), both its environment and life have evolved over time. The Great Oxygenation Event (GOE), which occurred ~2.5 Ga ago, drastically altered the chemistry of the oceans and atmosphere. Decoding environmental and magnetic signals recorded in rocks prior to the GOE is essential for understanding the conditions under which life first emerged.

An ideal target for investigating surface conditions prior to the GOE are banded iron formations (BIFs), which precipitated directly from ancient oceans. However, BIFs have been significantly altered since their formation, and it is unclear whether a record of their depositional environment remains.  The present day mineralogy is dominated by magnetite, but it remains to be established how this relates to the precipitates deposited on the seafloor. Additionally, in spite of magnetite's ideal magnetic properties, BIFs are avoided for paleomagnetic analysis because the timing of magnetization is uncertain. It is vital to constrain the magnetic field record leading up to the GOE because it may have influenced atmospheric hydrogen loss, contributing to rapid surface oxidation.

We present paleomagnetic field tests from the Isua Supracrustal Belt that suggest a record of Earth’s 3.7-billion-year (Ga) old (Eoarchean) magnetic field is preserved in the banded iron formation in the northernmost northeast region of the belt. Our results are supported by radiometric Pb-Pb dating of magnetite from the same banded iron formation.  We show that the Pb-magnetite system has a closure temperature below 400 °C for the magnetite grain size range observed in the banded iron formation, suggesting the rocks have not been significantly heated since magnetization was acquired. This temperature range is well below the Curie temperature of magnetite (580 °C), suggesting Eoarchean magnetization has not been thermally overprinted by subsequent metamorphism.  Passed paleomagnetic field tests suggest the rocks have also avoided chemical overprints. We recover an ancient magnetic field strength, supporting previous studies that argue Earth’s magnetic field has been active throughout most of its history although variations in its strength remain poorly constrained.

How to cite: Nichols, C., Weiss, B., Eyster, A., Martin, C., Maloof, A., Kelly, N., Zawaski, M., Mojzsis, S., Watson, B., and Cherniak, D.: Using banded iron formations to understand habitable conditions on the early Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2404, https://doi.org/10.5194/egusphere-egu23-2404, 2023.

EGU23-2429 | Orals | GD3.1 | Highlight

The Malolotsha Klippe: Large-Scale Subhorizontal Tectonics Along the Southern Margin of the Archean Barberton Greenstone Belt, Eswatini 

Christoph Heubeck, Tonny Bernt Thomsen, Benjamin D. Heredia, Armin Zeh, and Philipp Balling

Whether Archean tectonics were horizontally or vertically dominated is controversially discussed because arguments bear on the kinematics and thermal state of the Archean mantle and constrain the mode of formation of the earliest continental crust. Highly deformed strata of Archean greenstone belts figure prominently in this debate because they record long periods of time and multiple deformation phases. Among the best-preserved greenstone belts counts the Barberton Greenstone Belt (BGB) of southern Africa. Geological mapping of part of the southern BGB in Eswatini (Swaziland), combined with U-Pb zircon dating, shows that the region preserves a tightly re-folded imbricate thrust stack in which metavolcanic and -volcaniclastic strata of the Onverwacht Group, deposited at 3.34–3.29 Ga, have been thrust on top of ca. 3.22 Ga siliciclastic strata of the Moodies Group. The structurally highest element, the Malolotsha Syncline, forms a tectonic klippe of substantial size and is >1,450 m thick. Forward modeling of a balanced cross section indicates that this thrust stack was part of a northwestward-verging orogen along the southern margin of the BGB and records a minimum horizontal displacement of 33 km perpendicular to its present-day faulted, ductily strained and multiply metamorphosed margin. Because conglomerate clasts indicate a significantly higher degree of prolate strain which extends further into the BGB than at its northern margin, late-stage tectonic architecture of the BGB may be highly asymmetrical. Our study documents that the BGB, and perhaps other Archean greenstone belts, preserves a complex array of both vertically- and horizontally-dominated deformation styles that have interfered with each other at small regional and short temporal scales.

How to cite: Heubeck, C., Thomsen, T. B., Heredia, B. D., Zeh, A., and Balling, P.: The Malolotsha Klippe: Large-Scale Subhorizontal Tectonics Along the Southern Margin of the Archean Barberton Greenstone Belt, Eswatini, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2429, https://doi.org/10.5194/egusphere-egu23-2429, 2023.

We present the result of an integrated petrological and geophysical 3D modelling of the lithospheric mantle over the West and Central African rift system. For modelling, the integrated geophysical and petrological forward modelling software LitMod3D has been used. The initial geometry of the model is based on the Moho depth and base lithosphere of the global model WINTERC-G, and the sediment thickness from the global model Crust1.0 and the available seismic Moho depth have been used for validation. The model is fitted to satellite gravity gradients and the Bouguer anomaly calculated from the XGM2019e-2190 model. Different classes of mantle composition data have been considered and by iteratively trying to compute the best fitting between different modelled and observed signals, the final models of density, velocity and temperature distributions have been estimated. 

The model shows lateral transitions curved shape, extending horizontally for about 50km, between the West and Central African rift system, and the surrounding Congo craton and West African craton. More in detail, the results show the lateral and vertical variation of density, temperature and velocity in respect between the different lithospheric mantle domains. We notice the absence of a clear signature of the Saharan meta-craton, making this area more similar to the West and Central African rift system than the bordering cratons. Moreover, the modelled density profile shows a continuous depth dependent gradient under the rift system, but three steps in the depth profile under the cratons, suggest a layering of the lithospheric mantle with respect to its density gradient, which can be interpreted as metasomatism of the lower lithospheric mantle.

How to cite: Fosso Teguia M, E. E. and Ebbing, J.: Integrated 3D modelling of the lithospheric mantle under the West and Central African rift system and surronding., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3477, https://doi.org/10.5194/egusphere-egu23-3477, 2023.

EGU23-4246 | ECS | Orals | GD3.1 | Highlight

When and how did Earth’s earliest continents first emerge above the oceans? 

Priyadarshi Chowdhury, Peter A. Cawood, and Jacob A. Mulder

The emergence of continents above sea-level marks a pivotal junction in Earth’s evolution that fundamentally changed the chemistry of the atmosphere and oceans, which was critical to establishing a habitable planet. However, when and how the first subaerial continental landmasses formed remains contentious. Abrupt changes in proportion of submarine vs subaerial volcanism and in the oxygen isotopic ratios of shales and zircons at the Archean-Proterozoic transition (2.5 billion years ago, Ga) are invoked to argue for global continental emergence around that time (e.g., Kump and Barley, 2007; Bindeman et al., 2018). However, direct evidence for an earlier episode of continental emergence comes from ~3.0-2.7 Ga paleosols (like the Nsuze paleosol) and terrestrial sedimentary strata that formed atop stable cratons (cf. Eriksson et al., 2013). This attests continental emergence > 2.5 Ga, at a time when the operation of modern plate tectonics is debated.

To help resolve these issues, we focussed on the cratons like the Singhbhum and Kaapvaal cratons since they host widespread Mesoarchean terrestrial to shallow marine clastic strata and paleosols, which suggests early (> 2.5 Ga) continental emergence on Earth. We studied how crustal thickness and composition of these cratons evolved through time leading to their emergence, by linking the Paleo-to-Mesoarchean sedimentary and magmatic records of these cratons (Chowdhury et al., 2021). First, we studied the conglomerate-sandstone-shale successions that are uncomforably lying on the cratonic basement and determined their depositional ages to constrain the timing of the continental emergence. Then we analysed the chemistry of the tonalite-trondhjemite-granodiorite (TTG) suite of felsic rocks and performed petrogenetic modelling to quantify the evolution of crustal thickness and P-T conditions of crust formation, which elucidated the underlying mechanism and tectonic environment of emergence.

Our results show that the studied cratons became emergent between ca. 3.3-3.1 Ga due to progressive crustal thickening and maturation driven by granitoid magmatism. The cratonic crust  became chemically mature and extremely thick (45-50 km) by 3.2-3.1 Ga, such that isostatic compensation led to their rise about the sea level. Modelling of the TTG chemistry further elucidated that these TTGs formed at hotter thermal conditions characteristic of a thickened Archean crust atop a zone of rising mantle. Hence, we propose that emergence of stable continental crust began at least during the late Paleoarchean to early Mesoarchean and was driven by the isostatic rise of their magmatically thickened, SiO2-rich crust without the help of plate tectonics (Chowdhury et al., 2021). We further surmise that such early episodes of emergence caused important changes in Earth’s early surficial environments including promoting transient atmospheric-oceanic oxygenation (O2-whiffs) and CO2 drawdown leading to glacial events.

Reference:

Bindman et al., 2018. Nature 557, 545–548.

Chowdhury et al., 2021. PNAS 118, e2105746118.

Eriksson et al., 2013. Gondwana Research 24, 468–489.

Kump and Barley, 2007. Nature 448, 1033–1036.

How to cite: Chowdhury, P., Cawood, P. A., and Mulder, J. A.: When and how did Earth’s earliest continents first emerge above the oceans?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4246, https://doi.org/10.5194/egusphere-egu23-4246, 2023.

EGU23-4566 | Posters on site | GD3.1

On tectonic modes of the early Earth 

Peter Cawood, Priyadarshi Chowdrury, Jack Mulder, Chris Hawkesworth, Fabio Capitanio, Prasanna Gunawardana, and Oliver Nebel

The Earth has evolved into a habitable planet through ongoing and complex cycling. Decades of field studies, geochemical analyses and computational approaches to integrate data into feasible geodynamic models reveal that Earth’s evolution was not linear but evolved in discrete phases. The timing of changes between these phases, their loci within Earth’s crust or between discrete cratonic terranes, and most importantly the drivers or tipping point for these changes, remain elusive.

Integrating the record from the continental archive with knowledge of the ongoing cooling of the mantle and lithospheric rheology (parametrized for its evolving thermal state) allows us to determine that a number of different tectonic modes operated through the early history of the Earth. The temporal boundaries between these proposed different phases in tectonic mode are approximate, transitional, and correspond with the first recording of a key feature of that phase.

Initial accretion and the moon forming impact resulted in a proto-Earth phase (ca. 4.57-4.45 Ga) likely characterized by a magma ocean. Its solidification produced the primitive Earth lithosphere that extended from ca. 4.45-3.80 Ga, which based on the very minor fragments preserved in younger cratons provides evidence for intra-lithospheric reworking, but which also likely involved intermittent and partial recycling of the lid through mantle overturn and meteoritic impacts. Evidence for craton formation and stabilization during the primitive (ca. 3.8 Ga to 3.2 Ga), and juvenile (ca. 3.2 Ga to 2.5 Ga) phases of Earth evolution likely reflects some degree of coupling between the convecting mantle and a lithosphere initially weak enough to favour an internally deformable, squishy-lid behaviour. These regions of deformable lithosphere likely oscillated spatially and temporally with regions of more rigid, plate like, behaviour leading to a transition to global plate tectonics by the end of the Archean (ca. 2.5 Ga). Evidence for assembly of rigid cratonic blocks in the late Archean along with their subsequent rifting and breakup followed by their reassembly along major linear orogenic belts in the Paleoproterozoic marks the clear inception of the supercontinent cycle in response to a plate tectonic framework of oceans opening and closing.

Since solidification of the magma ocean early in Earth history, the available record suggests some degree of mantle-lithosphere coupling. The development and stabilization of cratons from 3.8-2.5 Ga provides evidence for the progressive development of rigid lithosphere and represents the inexorable precursor to the development of plate tectonics.

How to cite: Cawood, P., Chowdrury, P., Mulder, J., Hawkesworth, C., Capitanio, F., Gunawardana, P., and Nebel, O.: On tectonic modes of the early Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4566, https://doi.org/10.5194/egusphere-egu23-4566, 2023.

EGU23-4744 | ECS | Orals | GD3.1 | Highlight

Pb isotope heterogeneities in the mantle and links to the supercontinent cycle 

Sheree Armistead, Bruce Eglington, Sally Pehrsson, and David Huston

Isotopic proxies such as Hf, Nd and Pb are widely used to understand the evolution of Earth’s crust and mantle. Of these, Pb isotopes are particularly sensitive to crustal influences, and the extraction of mantle melts. We present a global compilation of Pb isotope data from syngenetic Volcanogenic Massive Sulphide (VMS) deposits, which allow us to track the evolution of Pb isotopes in deposits that are associated with dominantly back-arc and extensional oceanic settings through time.

Unradiogenic Pb isotope signatures, specifically low model source µ (238U/204Pb) values, in some Archean cratons have long been recognised, yet their origin remains elusive. For example, sulphides from the c. 2.7 Ga Abitibi Belt in the Superior Province of Canada require long-lived (> 500 my) evolution of a source component to generate the Pb isotope signatures observed. Other isotope systems, such as Lu-Hf and Sm-Nd, show relatively juvenile signatures for the Abitibi Belt, suggesting decoupling of the different systems. Low µ values are evident in ore deposits and rocks from the Archean to modern settings but are most prominent in Archean settings because of their associated low 207Pb/204Pb values, unlike for younger times.

Pb isotope data at a global and broad temporal scale show that periods with distinct low µ values have a marked cyclicity that coincides with the supercontinent cycle. We propose that during supercontinent assembly, portions of older unradiogenic, Pb-rich mantle are tapped and incorporated into VMS deposits. Pb, possibly enriched in sulphides, can explain the apparent decoupling of Pb from silicate-controlled isotope systems like Hf and Nd. We suggest that the source of this unradiogenic mantle component formed during the previous supercontinent cycle when large volumes are extracted from the mantle to form (radiogenic) crust and an unradiogenic residue, which most likely resides in the lithospheric mantle although some may also be present as discrete ‘pods’ in the circulating mantle. This process provides a mechanism to explain isolation of source regions for several hundred million years, as required to generate the low µ values, until later tapping during a subsequent supercontinent amalgamation cycle.

The low µ values in the c. 2.7 Ga Abitibi Belt represent the best-known Archean occurrence of this signature, indicating that their unradiogenic source relates to a major mantle extraction event that would have occurred at least 500 my earlier, i.e. at about 3.2 Ga.

How to cite: Armistead, S., Eglington, B., Pehrsson, S., and Huston, D.: Pb isotope heterogeneities in the mantle and links to the supercontinent cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4744, https://doi.org/10.5194/egusphere-egu23-4744, 2023.