EGU General Assembly 2024  

While the deep Earth is not directly accessible, it can be explored by laboratory experiments under high-pressure and -temperature (P-T) combined with geophysical observations and geodynamical modeling. We conduct experiments using a laser-heated diamond-anvil cell (DAC) which can generate static high P-T beyond conditions at the center of the Earth. Combining such DAC experiments with in-situ X-ray observations at synchrotron sources and thermal/electrical conductivity measurements and ex-situ textural and chemical characterizations of recovered samples, we have been trying to uncover the structures, chemical compositions, physical properties, dynamics, and evolution of the deep Earth and planetary interiors. The lowermost part of the Earth’s mantle, sometimes called the D” layer, have been the most enigmatic region inside our planet, but the discovery of its main constituent crystals of post-perovskite dramatically improved our understanding of this mysterious layer. Recent hot debates on the core include its thermal conductivity and the mechanism of its convection that have sustained the planetary magnetic field since early history of the Earth. In addition, the Earth’s core is known to include substantial amounts of light elements such as sulfur, silicon, oxygen, carbon, and hydrogen, but its exact chemical composition has been highly controversial since Birch (1952). Hydrogen could be one of the important core light elements when considering that a large amount of water may have been delivered to the growing Earth and hydrogen is strongly siderophile (iron-loving) under high pressure. Nevertheless, the phase diagram and properties of iron hydrides are little known since hydrogen is least soluble into iron at ambient conditions. I will introduce these high-pressure studies on the deep mantle and core materials including our recent work on iron hydrides and discuss the possible ranges of Earth’s core composition.

How to cite: Hirose, K.: Exploring the deep Earth and planetary interiors by high-pressure experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1663, https://doi.org/10.5194/egusphere-egu24-1663, 2024.

The Moon is thought to have been covered initially by a deep magma ocean, its gradual solidification leading to the formation of the aluminium-rich plagioclase-bearing highland crust. We performed the first high-pressure, high-temperature experimental study of the mineralogical and geochemical evolution accompanying the full solidification of a lunar magma ocean (LMO) and provide new constraints on the presence of water in the early lunar interior. In a dry Moon, plagioclase appears after 68 per cent solidification and yields a crust with a thickness of ~68km¹, well above the lunar crustal thickness suggested by recent GRAIL mission gravitational data (34–43 km). Water-bearing experiments show a delay in the start and lowering of the volume of plagioclase formed during LMO crystallization, as observed previously for terrestrial magma. Using crustal thickness as a hygrometer we conclude that at least ~800 ppm water was present in the Moon at the time of LMO crystallization, indicating the Earth-Moon system was water-rich from the start^2,3.

Water does not only have remarkable effects on early LMO evolution, but also on the properties of Earth’s mantle rocks, however, how and how much transporting water into the deep Earth is still debated due to high mantle temperatures. Subduction of oceanic lithosphere transports surface H₂O into the mantle. Recent studies proved that stishovite and post-stishovites as high-pressure phases of SiO₂ have the potential to carry weight percent levels of water into the Earth’s interior along the geotherm of the subducting oceanic crust⁴. Regression of our experimental data indicates an H₂O storage capacity in stishovite of ~3.5 wt% in the transition zone and shallow lower mantle, decreasing to about 0.8 wt% at the base of the mantle⁵. As slabs subducted to the deepmost mantle, dehydration of these dense hydrous silica phases (DHS) can potentially change physicochemical properties of the Earth’s mantle by reducing melting point, forming new high-pressure phases and enhancing the oxygen fugacity heterogeneity of lower mantle⁶.

References:

[1] Lin Y., Tronche E. J., Steenstra E. S., and van Westrenen W. Experimental constraints on the solidification of a nominally dry lunar magma ocean. Earth Planet. Sci. Lett. 471, 104–116 (2017).

[2] Lin Y., Tronche E. J., Steenstra E. S., and van Westrenen W. Evidence for an early wet Moon from experimental crystallization of the lunar magma ocean. Nat. Geosci. 10, 14–18 (2017).

[3] Lin Y., Hui H., Xia X., Shang S., and van Westrenen W. Experimental constraints on the solidification of a hydrous lunar magma ocean. Meteorit. Planet. Sci. 55, 207–230 (2020).

[4] Lin Y., Hu Q., Meng Y., Walter M. and Mao H.-K. Evidence for the stability of ultrahydrous stishovite in Earth’s lower mantle. Proc. Natl. Acad. Sci. U. S. A. 117, 184–189 (2020).

[5] Lin Y et al. Hydrous SiO₂ in subducted oceanic crust and H₂O transport to the core-mantle boundary. Earth Planet. Sci. Lett. 594, 117708 (2022).

[6] Lin Y. and Mao H. K. Dense hydrous silica carrying water to the deep Earth and promotion of oxygen fugacity heterogeneity. Matter Radiat. Extremes 7, 068101 (2022).

How to cite: Lin, Y.: Effects of water on the evolution of the Early Moon and deep Earth investigated by experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4803, https://doi.org/10.5194/egusphere-egu24-4803, 2024.

Lake Tziscao is one of the water bodies belonging to Lagunas de Montebello National Park, located in the south-southeastern part of the state of Chiapas, Mexico. Its importance lies in its great tourist activity due to its size and nearby human settlement, which is why there are numerous anthropogenic factors that promote the transformation of natural areas within it.

In this work, PHREEQC software was used to perform inverse hydrogeochemical modeling, with which the predominant hydrogeochemical processes of the site were identified and estimated using 20 sampling points distributed along Lake Tziscao.

Prior to the execution of the model, a statistical analysis, simplification and graphic representation of samples, as well as a site analysis were carried out, whose comparison results coincide with the presence of calcic-magnesic bicarbonate type waters, suggesting the feasibility of the proposed model.

Modeling results indicate that the main processes present in the water-rock interaction in the area are: hydration of anhydrite and subsequent dissolution-precipitation of gypsum in large proportion, minimal transfer or equilibrium in carbonate minerals and halides such as calcite, dolomite, sylvite and halite, nonetheless, the concentrations of elements such as nitrogen and phosphorus within the water body suggest anthropogenic pollution sources, while the relatively low salinity indicates that the waters are poorly evolved or have been transported to a lesser extent.

How to cite: González Herrera, C. R. and García Villanueva, L. A.: Identification of hydrogeochemical processes through inverse modeling in PHREEQC in Lake Tziscao, belonging to the Montebello lagoon system in Chiapas, Mexico., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-26, https://doi.org/10.5194/egusphere-egu24-26, 2024.

Geochemical sampling has limitations due to budget constraints and restricted access to certain areas. This results in some regions being unsampled, making it difficult to generate comprehensive geochemical anomaly maps and distinguish between background values and anomalies. To address this, different interpolation models have been developed, such as inverse distance weighting (IDW) and kriging techniques. However, both IDW and kriging only consider the horizontal distance between samples and ignore elevation changes, which is important in real-world terrains. This effect is most pronounced in mountainous terrains. To address this, we propose a new interpolation technique called Inverse Radius Weighting (IRW). IRW factors in both horizontal distance and elevation changes between sample pairs, resulting in more accurate predictions. Detailed elevation data is available for the entire globe in the form of digital elevation maps from the Shuttle Radar Topography Mission (SRTM) and other sources. In this research, both IDW and IRW models were applied to soil samples in Cyprus. A comparative analysis between IDW and IRW models showed that IRW gives more accurate predictions, especially in terrains with complex morphologies. IRW's ability to account for topographical influences makes it the preferred choice in such scenarios.

How to cite: Sadeghi, B., Morrison, S., Eleish, A., and Klump, J.: Inverse Radius Weighting (IRW) interpolation model: A new interpolation considering morphology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1348, https://doi.org/10.5194/egusphere-egu24-1348, 2024.

In regional or local scale geochemical mapping, the choice of sampling media and analytical methods will be influenced by the source, form, mobility and spatial distribution of elements being mapped. For environmental monitoring and mineral exploration there are potential advantages in using plant organs rather than regolith materials as the sampling media, including the capacity of plants to sample large volumes of underlying regolith and the averaging of their biogeochemical composition over timeframes extending from months to years. The limited use of plant organs in geochemical mapping relates partly to perceived complicating factors such as variability between plant species, seasonal variability in some plant organs and analytical costs.

Needle samples from over 4,000 cypress pines (C. glaucophylla) in the highly mineralised Cobar Basin in central New South Wales have been analysed by both ICPMS and pXRF. The study spanned regional mapping using samples collected adjacent to roads and tracks, and detailed grids and traverses across 36 mineral prospects and deposits. For various major and trace elements, there is strong correlation between results obtained by total digestion ICPMS and by portable XRF, including direct pXRF analysis of unprocessed samples in the field.

There are distinct lithological influences on variation in the background values for various elements, including Au and Pb, noting that the majority of mineral deposits are structurally hosted within the Devonian sandstone and siltstones regionally intruded by felsic intrusives. There is an extensive zone of elevated base and precious metal values in the needles between the Peak Au mine site and the city of Cobar which was the focus of mineral processing for many decades. Highly elevated values for Ag, Au, Pb, Zn, Ni, Co, W and/or REE occur above known mineral deposits, depending on deposit style, and commonly display more consistent geochemical spatial patterns than in regolith samples. Pines in general typically restrict uptake of Cu in the needles to within the range of 3–12 ppm due to its function as an important trace nutrient.

How to cite: Schifano, J., Cohen, D., and Rutherford, N.: Pining for an Anomaly: Exploration and environmental assessments using regional and local scale biogeochemical patterns in the Cobar Region, Australia., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1404, https://doi.org/10.5194/egusphere-egu24-1404, 2024.

The nuclear forensics is one of the pillars in the architecture of nuclear security, as a response to criminal acts and illicit trafficking involving nuclear materials or other radioactive materials. ENEA is participating in international table-top exercises organized by the Nuclear Forensics International Technical Working Group (ITWG), a community whose aim is to advance the scientific discipline of nuclear forensics supporting the development of national capabilities. The “Galaxy Serpent” is a set of virtual international web-based exercises, focused on the development of National Nuclear Forensic Libraries (NNFLs). The aim is to increase national awareness of the technical challenges associated with the development of a National Nuclear Forensic Library (NNFL) and how it can be a valuable support for investigating crimes and/or illicit activities involving nuclear or radioactive materials.

The ENEA CBRN team participated in the Galaxy Serpent exercise, version 3, focused on the investigation on imported uranium ore concentrate materials. The used approach, the tools and the main outcomes will be presented. The scenario was dealing with the interception of a transport vehicle attempting to leave the country carrying radioactive materials out of regulatory control (MORC). In fact, further inspection revealed geological sources within some labelled containers and the isotopic analysis performed on these materials determined the sources to be uranium ore concentrate (UOC). The ENEA CBRN team was tasked to check whether this material was consistent with the material used within its country. The assessments have been carried out using Rare Earth Element (REE) patterns as main fingerprint of the geochemical affinity classes. REEs can be used to verify the origin of the samples and some process they have experienced as they are water insoluble and present in very low concentration in water, so they really reflect the original chemistry of the source. In addition, variations in their concentration could be indicative of technological processes aimed at the recovery of some elements that have different high technology applications. The use of statistical tools for the extrapolation of forensic information are presented and discussed.

The exercise had the dual purpose of testing, on the one hand the team’s skill level and the type of tools necessary for a response in the mitigation of chemical, biological, radiological, nuclear and risks (CBRN), and on the other hand, to prepare tools and procedures that may also involve other actors at national level, in particular in response to radiological risk.

How to cite: Telloli, C., Ottaviano, G., Rocchi, F., Padoani, F., and Rizzo, A.: Nuclear Forensic of Uranium Ore Materials out of Regulatory Control: The Galaxy Serpent exercise v3, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1715, https://doi.org/10.5194/egusphere-egu24-1715, 2024.

Anthropogenic Pb originated from leaded petrol and high temperature industrial activities is still a major contamination issue to various compartments in the urban environment, including soil and road dust. Human exposure to Pb near Pb-contaminated areas involves incidental ingestion of soil and road dust and inhalation of resuspended solid particles. Volos is a medium-sized industrialized city, located in central Greece, surrounded by steel and cement factories. The geochemical reactivity, fractionation and bioaccessibility (both oral and inhalable) of Pb in selected soil (n=10) and road dust (n=10) samples were investigated through a variety of laboratory chemical methods comprising the dilute HNO₃ extraction, the BCR sequential extraction procedure, the simple bioaccessibility extraction test (SBET) and a simulated lung fluid (SLF solution, artificially lysosomal fluid). In addition, the Pb isotopic composition of both total and bioaccessible Pb was determined to identify the Pb sources and examine potential differences of Pb solubilization in terms of its origin when interacting with simulated human stomach and lung fluids.

Lead was found in highly reactive forms in both road dust and soil (medians 83% and 69% of total contents, respectively). The majority of Pb was found to be associated with the sum of the acid soluble (F1), reducible (F2) and oxidizable (F3) fractions (median 72% of total contents for both soil and road dust), indicating that Pb has a high remobilization potential from the solid matrix. The oral bioaccessibility (%) of Pb was higher than the inhalation one (medians 49% and 37% of the total content), respectively), highlighting the soil and dust ingestion as the primary route of Pb exposure. The isotopic analyses of total Pb in soil and road dust (²⁰⁶Pb/²⁰⁷Pb = 1.144 to 1.192) suggest that the predominant anthropogenic Pb source is industrial Pb from the steel plant, with minor contributions of Pb derived from vehicular emissions. Interestingly, we found significant differences in the isotopic ratios between total and bioaccessible Pb (²⁰⁶Pb/²⁰⁷Pb = 1.130 to 1.152), demonstrating that Pb solubilized by the simulated gastric and lung extractions is principally anthropogenic. High Pb bioaccessibilities (%) accompanied a shift towards lower ²⁰⁶Pb/²⁰⁷Pb ratios. Moreover, ²⁰⁶Pb/²⁰⁷Pb ratios of both total and bioaccessible Pb exhibited significantly negative correlations with Pb reactive fractions (%), showing that natural Pb is linked to low Pb release from the soil and road dust matrix. Overall, Pb isotopes provide deep insights into the connection between Pb bioaccessibility and reactivity with Pb sources in soil and road dust from industrial environments.

References

Kelepertzis, E., Chrastný, V., Botsou, F., Sigala, E., Kypritidou, Z., Komárek, M., Skordas, K., Argyraki, A. 2021. Tracing the sources of bioaccessible metal(loids) in urban environments: A multidisciplinary approach. Science of the Total Environment 771: 144827.

How to cite: Kelepertzis, E., Kypritidou, Z., Chrastný, V., and Komárek, M.: Geochemical occurrence of Pb in soil and road dust from an industrialized urban environment: Fractionation, bioaccessibility and isotopic composition , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1834, https://doi.org/10.5194/egusphere-egu24-1834, 2024.

Provenance studies of flint artefacts provide important means for interpreting raw material procurement strategies, which testify to the level of expertise and environmental knowledge of prehistoric people. Due to its importance, different approaches and methods have been used in order to address this topic, which often makes it difficult to compare different studies. During the recent years we have been exploring the potential of bulk rock composition of flint measured using inductively coupled mass-spectrometry (ICP-MS) for provenance studies. Through the systematic sampling of flint from all across Israel (now archived at the Geological Survey of Israel, as part of the developing national flint collection) and the investigation of a large suite of trace elements, we have been developing a robust approach for determining the provenance of flint. By sampling several specimens from each locality and measuring a large array of elements, we additionally address the variability of compositional data in natural rock sources, and develop a statistical framework for evaluating the uncertainty involved in the provenancing of flint. These developments have been applied in recent case studies in key archaeological sites, and shed new light on the old question of flint provenance in prehistory.

How to cite: Ben Dor, Y., Finkel, M., Sharon, G., Tirosh, O., Bar, O., and Ben-Yosef, E.: Recent advances in flint provenance studies in Israel developed by combining geochemical and statistical perspectives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2817, https://doi.org/10.5194/egusphere-egu24-2817, 2024.

Local glaciers and ice caps in the Northern Hemisphere and the Greenland Ice Sheet (GrIS) have recently been suggested to be important parts of the Arctic mercury (Hg) budget. Based on ice-core data, the recently estimated total glacial Hg pool is approximately 2,400 tons, approximately 97% of which is in Greenland¹. With Hg concentrations in pre-industrial ice being significantly lower than in ice formed during the 19th and 20th centuries, the dominating source of glacial Hg and input to the Arctic Hg budget is ascribed to long-range transport of anthropogenic Hg emissions².

Alarming concentrations of Hg in meltwater from the western margin of the GrIS were recently reported³. With Hg concentrations reported as being 100 - 1000 times higher than what is known for other freshwater systems of Greenland and a postulated increase in Hg export to downstream environment following climate warming and asserted global importance of Hg fluxes from the GrIS, these extraordinary concentrations and conclusions calls for independent verification.

In our current study⁴, we expand the sampling of subglacial meltwater from 21 representative outlets at GrIS in 2021 and 2022 to get a better scientific basis for conclusions on the magnitude of glacial Hg sources in Greenland. Results from our study consistently show that both total and dissolved Hg concentrations in glacial meltwater over space and time are very low (generally <10 pM) and that an extremely elevated Hg concentration range (up to 4000 pM recently reported³) cannot be reproduced.

In contrast to what was previously reported³, we find that meltwater from below the GrIS is very low in Hg; has minor implications for the global Hg budget and pose only a very limited risk for local communities and the natural environment of Greenland.

References:

• A. Dastoor, et al. (2022), Arctic Mercury Cycling. Nature Reviews Earth & Environment 3, 270–286 (2022). https://doi.org/10.1038/s43017-022-00269-w.
• AMAP. AMAP Assessment 2021: Mercury in the Arctic. Arctic Monitoring and Assessment Programme (AMAP),1- 324.
• J. R. Hawkings et al (2021) Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet. Nature Geoscience 14, 496–502 (2021). https://doi.org/10.1038/s41561-021-00753-w.
• Jørgensen et al (2024) Large mercury release from the Greenland Ice Sheet invalidated. Science Advances, in press.

How to cite: Jørgensen, C. J., Søndergaard, J., Larsen, M. M., Kjeldsen, K. K., Rosa, D., Sapper, S. E., Heimbürger-Boavida, L.-E., Kohler, S. G., Wang, F., Gao, Z., Armstrong, D., and Albers, C. N.: No evidence for large mercury release from the Greenland Ice Sheet: recent conclusions on global mercury budget invalidated. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4005, https://doi.org/10.5194/egusphere-egu24-4005, 2024.

The study of ancient aqueducts shows us how past societies used water resources such as rivers, lakes, springs and groundwater. Such resources were tested for their quality, captured, sometimes diverted or abandoned, or supported by a new source. The efficient management of ancient water supply systems was adapted to societal needs, to the chosen environment and to change in climate and population dynamics, similar to factors shaping our modern water management. The in-situ carbonate deposits of ancient water supply systems reflect characteristics of the water resources and aquifers used, and therefore constitute an archive with considerable research potential, particularly for better understanding of ancient water management, palaeo-environment, and water scarcity.

            Ancient aqueducts were long-lived structures, with recorded operation periods of up to 800 years such as the more than 400 km long Valens aqueduct of Constantinople. However, carbonate sequences are often shorter because of cleaning. The Valens aqueduct has a double channel to allow cleaning without interruption of the water supply, and shows only 27 years of carbonate deposits. A carbonate sequence of 250 years is documented for the ancient city of Nemausus, which correlates with the actual documented years of operation. This is because some aqueducts were built wide enough to allow smooth operation without being cleaned of carbonate for most of their length. The aqueduct of Arelate was modified by reallocation of branches and expansion, probably in response to increasing and changing demand of water. In at least 50 years of carbonate stratigraphy, this aqueduct shows periodic variations in the aquifer.

            As the focus of this paper we discuss the Roman aqueduct of Divona, which shows evidence of regular cleaning, repairs, modifications and even timing of maintenance, captured in aqueduct carbonate. The d¹⁸O profile of the carbonate stratigraphy shows a cyclicity that is inferred to reflect annual water temperature variations in the channel. This cyclicity was used to determine the timing of maintenance. The aqueduct operated for centuries but the preserved profile shows 88 years of operation, interrupted by two plaster repair events, representing time breaks in water supply of at least several months. Not less than 14 carbonate removal events were recognized, which took place in fall, spring, or winter but never in summer, with an interval of 1 to 5 years. Carbonate removal from channels was done rapidly, in less than one month, since stable isotope cycles show no indication of a long-term interruption in the water supply. The last maintenance was done only three years before the final abandonment of the water supply, showing that continued operation of the aqueduct was planned but was not fulfilled. This micro-story shows how a historical water management operated and adapted to water scarcity and population growth and decline, similar to modern days. Frequent cleaning of aqueduct carbonate and repairs are examples of what we call today “sustainable” water management.  

Ancient aqueducts carbonates are models to study aspects of past water management and adaptations to crisis, and provide a vision for the future of water availability and climate change.

How to cite: Sürmelihindi, G. and Passchier, C.: Lessons learned from the maintenance of ancient aqueducts through their carbonate archives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4708, https://doi.org/10.5194/egusphere-egu24-4708, 2024.

The project focuses on a provenance study carried out on Zeus/Owl bronze coins, coming from the Greek colony of Velia in southern Italy, and dating back to the 3rd century BC. Chemical elemental composition and lead isotope analyses were carried out at the Laboratori Nazionali del Gran Sasso-INFN by using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and TIMS (Thermal Ionization Mass Spectrometry) techniques. Lead isotope ratios of the coin samples were compared with data from various ore deposits in the main Mediterranean areas documented in existing literature. Additionally, the elemental composition was examined to establish distinctive geological characteristics aiding in identifying the provenance sources of the studied coins. The majority of the coins exhibited an isotope signature of the lead, that makes up the alloy, overlapping with multiple clusters in the Aegean Greece area (Syros, Kea, Antiparos, Serifos and Sifnos) and the Spain South-East area (Cartagena-Mazarron and Almeria). Six coins displayed an uncertain provenance, suggesting the possibility of mixing and/or metal recycling. Notably, one coin demonstrated overlap with both Spain South-East and Tuscany clusters, indicating a shared provenance probability. Regarding the results of the elemental analysis, the main elements that make up the coins alloy are copper, lead and tin. The Pb content ranges considerably from a minimum of 0.5% to a maximum of 24.9%, while the concentration of Cu ranges from a minimum of 73.3% to a maximum of 93.5% and that of Sn ranges between 1.7% and 10.3%. This information contributes to the reconstruction of historical trade routes, enhancing our understanding of the dynamics of metal supply and socio-economic relationships in Velia.

Keywords: Provenance study; Isotopes; Ancient Coins; Ore Deposit; TIMS

How to cite: Ercoles, I., Castorina, F., Nisi, S., Carbone, F., Pardini, G., and Trincherini, P. R.: Provenance Analysis of Zeus/Owl bronze Coins from Velia: A Comprehensive Study using ICP-MS and TIMS Techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5724, https://doi.org/10.5194/egusphere-egu24-5724, 2024.

Consumers' growing attention on food composition, quality and origin has sparked a renewed interest in food traceability. The use of isotopic markers of territoriality helps emphasize the connection between agricultural products and their specific geographical area of origin, linked both to the soil-to-plant continuity of elemental composition and to contribution from airborne substances assimilated directly by the shoot. Asparago di Altedo PGI is an exclusive product of the Eastern area of Emilia-Romagna region, between Via Emilia and the Adriatic coast. Sandy-based territories favour the emergence of asparagus turions but include significant variations from sandy-clayey loam soils to lean sandy soils, forming a gradient from the inland to the coast. This research aims to detect a potential asparagus diversification driven by soil and environmental characteristics in the province of Ferrara, useful for further defining the product's typicality with respect to the area of origin. For the selected fields (Malborghetto, Mezzano, Bosco Mesola, Mesola, Lagosanto, Volania, Valli Basse), soil and plant sampling took place from May to the early days of June 2023. As an outgroup, samples of common green asparagus cultivated in Abruzzo region (Central Italy) were collected. The turions were transported to the laboratory for analyses of the fast chlorophyll fluorescence induction, a non-destructive near-instantaneous method for physiological plant assessment. Subsequently, soil and asparagus samples were dried and powdered for isotopic analyses. Soil diversification was characterized through pH and chemical analysis of major and trace elements using X-ray fluorescence. To assess the influence of the environment/soil on asparagus, δ¹³C and δ¹⁵N isotopic ratios, as well as the C/N ratio, were analyzed on soils and plants using an elemental analyzer associated with an IRMS spectrometer. PCA analysis showed that the soils could be distinguished based on geochemical factors and, for some fields, even at a resolution of a few tens of kilometres. For instance, the abundance of Na₂O separated the coastal fields from those of inland, and the soil samples of the Malborghetto field stood out from the others due to a higher concentration of certain heavy metals (Cr, Ni, Pb). Soil diversification was also attributable to anthropic interventions in the reclamation of the lagoon areas in some parts of the Ferrara province. An interesting correspondence was found between soil diversity and chlorophyll fluorometric parameters. In particular, although the photosynthetic functionality of the plants was very good in all fields, it was possible to distinguish the asparagus samples based on their origin: for example, the most performing asparagus was from Mesola regardless of the cultivar. Work is still in progress to get a more complete picture of the soil-to-plant continuity in relation to the environmental characteristics of the examined fields.

How to cite: Marrocchino, E., Aliprandi, E., Martina, A., Tassinari, R., and Ferroni, L.: Isotopic and functional markers for the assessment of territoriality: the case study of Asparago di Altedo PGI in the province of Ferrara (NE Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6499, https://doi.org/10.5194/egusphere-egu24-6499, 2024.

Lithium (Li) stands as a critical mineral resource, finding applications across various industries such as new energy, medicine, and optoelectronics (Bowell et al., 2020). Fluorite emerges as a strategic mineral, playing a pivotal role as a significant non-metal resource in various countries (Kesler et al., 2012). Recently, significant discoveries of fluorite and lithium have been made within the Early Permian strata in the Liuzhi area of the southwestern Yangtze Block, China, with reserves reaching a large scale (fluorite > 400 Kt; lithium > 100 Kt). This discovery suggests a potentially new type of lithium deposit unrelated to magmatism, sedimentary, or brine-related origins. The rare mineral system exhibiting fluorite and lithium associations holds substantial economic value and research significance. This study aims to investigate the origin of the Pingqiao F-Li deposit in the Liuzhi area through field geological investigation, mineralogy and element geochemistry, with the intention of discovering similar deposits elsewhere.

The fluorite in the study area demonstrates an apparent hydrothermal origin, with fluorine deriving from deep F-rich strata and fluid-mediated water-rock reactions (Zou et al., 2021, 2022). Similarly, the lithium ore body origin from hydrothermal characteristics, being preserved on both sides of a fault, with decreasing Li content moving away from the fault (Zou et al., 2022). Abundant silicified alteration was observed within the deposit, indicating significant hydrothermal activity. Lithium concentration is found within quartz resulting from silicification, indicating the presence of significant Li within the hydrothermal system. Cookeite stands out as the primary carrier mineral for lithium in this deposit (Hui et al., 2021). Cookeite formation occurs in medium- and low-temperature (Guo et al., 2019), aligning with the homogenization temperature of fluorite fluid inclusion (110-240 ℃, Zou et al., 2022). In conclusion, both the fluorite and lithium within the Pingqiao F-Li deposit likely originated from hydrothermal processes.

Keywords: Fluorite-lithium; Southwest Yangtze Block; Origin; hydrothermal

References

Bowell, R.J., Lagos, L., De Los Hoyos, C.R., Declercq, J., 2020. Classification and characteristics of natural lithium resources. Elements. 16, 259–264.

Guo, W.M., Wang, D.H., Li, P., Li, J.K., Shu, Z.M., Zhang, W.S., 2019. Sb-Li assemblages: Rare assemblages of mineralization and the occurrence of lithium. Acta Geol. Sin. 93, 1296–1308 (in Chinese with English abstract).

Hui, B., Gong, D.X., Chen, W., Lai, Y., 2021. Study on the occurrence of lithium in sedimentary lithium deposits in Liuzhi area Guizhou Province. Nonfer Metals (mineral pro sect). 2, 1–4 (in Chinese with English abstract).

Kesler, S.E., Gruber, P.W., Medina, P.A., Keoleian, G.A., Everson, M.P., Wallington, T.J., 2012. Global lithium resources: Relative importance of pegmatite, brine and other deposits. Ore Geol. Rev. 48, 55–69.

Zou, H., Li, Q.L., Bagas, L., Wang, X.C., Chen, A.Q., Li, X.H., 2021. A Neoproterozoic low-δ18O magmatic ring around South China: Implications for configuration and breakup of Rodinia supercontinent. Earth Planet. Sci. Lett. 575, 117196.

Zou, H., Xiao, B., Gong, D.X., Huang, C.C., Li, M., Yu, L.M., Tian, E.Y., Liu, C.M., Chen, H.F., Hu, C.H., 2022. Origin and tectonic setting of Pingqiao fluorite-lithium deposit in the Guizhou, southwest Yangtze Block, China. Ore Geol. Rev. 143, 104755.

How to cite: Zou, H., Xiao, B., and Gong, D.-X.: Origin of Pingqiao fluorite-lithium deposit in Guizhou, southwest Yangtze Block, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7053, https://doi.org/10.5194/egusphere-egu24-7053, 2024.

Our research presents a thorough analysis of climatic and environmental transformations in the Central Dnieper Basin (CDB) during the Middle and Late Pleistocene. It focuses on the study of glacial features left by the Dnieper lobe of the Saalian ice sheet and the co-occurring loess covers, as expressions of Pleistocene climatic fluctuations and landscape changes.
The research includes a detailed analysis of loess distribution, revealing a clear contrast between isolated loess patches in the northern lowlands and a continuous, thick loess cover in the south, especially from the latitude of Kyiv. These covers contain well-developed paleosols, reflecting interglacial changes, which form the basis for deep chronostratigraphic correlations on a regional and supra-regional scale. A key element of the study is resolving unresolved stratigraphic issues of the Pleistocene in Ukraine, with particular emphasis on the chronostratigraphic position of loess and paleosol units in the context of global climatic stages.
The main aim of the research is to identify local environmental influences on recorded Quaternary events following the deglaciation of the Dnieper lobe, to reconstruct the interactions between landscape changes post-glacial retreat and aeolian systems, and to establish a comprehensive and reliable stratigraphy for the Quaternary deposits of the Central Dnieper area. The methodology includes the application of a wide range of multidisciplinary techniques, including detailed grain size distribution and chemical composition analysis, advanced colourimetric measurements, paleomagnetic studies and luminescence dating. The research is based on original and older (palynological) studies on the Pleistocene, highlighting the importance of loess-palaeosol sequences in reconstructing the environmental history of the region.
The CDB, located at the juncture of the Dnieper Upland and Dnieper Lowland, provides unique insights into glacial, fluvial, and loess accumulation. Research includes detailed lithological and pedological sediment characterizations at key geological sites. Results of laboratory analysis clarify transport, deposition, and transformation processes of glacial and aeolian materials, indicating significant loess autochthony. Thermal and precipitation data from pollen analysis of mineral-soil sediments highlight the climatic condition's spatial and temporal variability in the CDB. Biome analysis shows varied landscape mosaics in each cycle, with no total deforestation in climatic pessima or complete afforestation in interglacial optima. These findings offer new insights into the CDB's complex Pleistocene stratigraphy, evidencing the last ice sheet's advance in the Dnieper valley during MIS8, and its link to ana- and kataglacial L3 loess sedimentation phases. They also emphasize the local variability and diversity of soil cover evolution and transformation after the glacial retreat, influenced by the post-glacial topography.
Our research significantly broadens the understanding of environmental changes in the Middle and Late Pleistocene in the CDB, contributing to the development of stratigraphic models and paleoenvironmental reconstructions on both regional and global scales.
Research carried out as part of the grant of National Science Centre, Poland as the project no. 2018/31/B/ST10/01507 entitled “Global, regional and local factors determining the palaeoclimatic and palaeoenvironmental record in the Ukrainian loess-soil sequences along the Dnieper River Valley – from the proximal areas to the distal periglacial zone”.

How to cite: Łanczont, M., Mroczek, P., Komar, M., Nawrocki, J., and Standzikowski, K.: Deciphering Middle-Late Pleistocene environmental changes: a multidisciplinary approach to Middle Dnieper loess-palaeosol sequences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8265, https://doi.org/10.5194/egusphere-egu24-8265, 2024.

Transition from fossil fuels to renewable energies is key to reduce human CO2 emissions, in order to cope global warming. As well as the need of technological progress, this raise the needs for metal resources. Some commodities are likely to experience very strong growth of their demand over the coming decades such as Lithium (Li), Aluminum (Al), Cobalt (Co), Nickel (Ni), Copper (Cu), and Rare Earth Elements (“REE”), due to their uses in “green” energy technologies.

The EU-funded “MADITRACE” project aim for the development of traceability methods and certification systems for four critical raw material (CMR): lithium, graphite, cobalt and REEs, in order to integrate sustainable provenance of materials into a Digital Product Passport (DPP) for batteries and vehicles. In the particular case of lithium, a previous study has shown that the deposit type -‘Hard rock’ or Salar- origin of a lithium material can be tracked through the supply chain up to the battery using lithium isotopic analysis¹. Nevertheless, some processes can affect this signature. In addition, these analyses requires high-cost instruments and are time-consuming. In order to verify in the future the provenance of a batch of raw material, traceability tools must be resilient to processes and mixing. They should also be more democratized and faster to set-up.

In this regard, the project focuses on the development of the combination of rapid and easy-to-use on-site analysis for routine screening as well as laboratory verification in case of anomalies during the provenance verification of a lithium product. This relies on conventional geo-physico-chemical analysis such as mineralogy, major and trace element compositions, as well as isotopic analysis. The methods investigated includes hyperspectral spectroscopy, IR spectroscopy, LUXREM (XRF-XRD coupling, in development) as well as conventional X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD), Laser Induced Breakdown Spectroscopy (LIBS), (Laser Ablation) Inductively Coupled Plasma Mass Spectrometry ((LA)-QQQ-ICP-MS), (Laser Ablation)  Multi-Collector Inductively Coupled Plasma Mass Spectrometry ((LA)-MC-ICP-MS) and Thermal Ionization Mass Spectrometry (TIMS).

• Desaulty, A. M. et al. Tracing the origin of lithium in Li-ion batteries using lithium isotopes. Nat Commun 13, (2022).

How to cite: Moradell-Casellas, A., Desaulty, A.-M., Monfort-Climent, D., Perret, S., Guerrot, C., Kloppmann, W., Lafaurie, N., Gilardi, N., Delchini, S., Maubec, N., and dezes, M.: Lithium geochemical traceability: development of a multi-criteria approach using on-site and laboratory technologies for the implementation of a battery digital product passeport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9041, https://doi.org/10.5194/egusphere-egu24-9041, 2024.

The Almadén mercury mining district, located in South-central Spain, has been the most important producer of this element worldwide, until the cessation of exploitations in year 2003. The environmental consequence of this activity affects an area of some 250 km², coincident both with a geological structure (the Almadén syncline) and a river basin (the Valdeazogues river and tributaries). The old cinnabar (HgS) mines and mineral showings are scattered in the syncline and in the basin, favouring a wide distribution of the elements in the soils and sediments, as reported by previous publications from this research group and partners.

Crayfish (Procambarus clarkii) is an exotic river crab, with has replaced the autochthonous one  (Austropotamobius pallipes) due to its voracity. It is very common all along the Valdeazogues river and tributaries, and it is captured and consumed by local population in summertime, when it is easily captured in the ‘tablas’, water accumulated in river pods during the cessation of water running due the stational drought. Preliminary data on the Hg contents in this species, obtained in year 2005 reach up to 9,060 ng g^-1 (in muscle) and 26,150 ng g^-1 (in hepatopancreas), according to some previous publications of this research group.

In this communication we present new data on this issue, obtained during the year 2022 along the Valdeazogues river and in some of its tributaries. In this research, 330 crayfish (sizes between 7 and 12 mm) were captured from upstream of the El Entredicho open pit mine to downstream of the confluence with the Guadalmez river (about 36.3 km), as well as the Los Álamos stream, and the Azogado stream, both tributaries of the Valdeazogues. All specimens were analysed by Zeeman effect atomic absorption spectrometry.

The overall results showed maximum values of 3,567 ng g^-1 of total Hg in muscle tissue, with a mean value for the district of 1,617 ± 920 ng g^-1. In hepatopancreas which is an organ of the digestive tract with functions of absorption and storage of nutrients, as well as synthesis of digestive enzymes, the maximum value is very similar: a maximum of 3,590 ng g^-1, while the mean is slightly lower, 1,025 ± 1,028 ng g^-1. For the whole population, the relationship of Hg content in muscle tissue and hepatopancreas with size is not appreciable, probably because they are organisms of fast grown, and there is no general relationship between age and size. On the other hand, there is a relationship between Hg in hepatopancreas and salts contents and total Hg concentration in the nearby sediments.

How to cite: Higueras, P., Barquero, J. I., Bakale, F., Esbrí, J. M., and García Ordiales, E.: Bioaccumulation of mercury in muscle tissue and hepatopancreas in red crayfish (Procambarus clarkii) in a transect of the Valdeazogues river and tributaries, Almadén Hg mining district, south central Spain. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9369, https://doi.org/10.5194/egusphere-egu24-9369, 2024.

Asturias, located in northern Spain, is a region with a rich history of mining and metallurgical activities intertwined with coal and metals. The Hg-mining district situated in the centre of this region was the Spain’s second-largest Hg manufacturer from 60s to 70s. Several areas were affected by the presence of Hg, specifically in the “El Terronal” mine, which stands out as one of the most affected areas, primarily due to mining and subsequent pyrometallurgical processing.

A pilot-scale remediation using nanoscale zero-valent iron (nZVI) was conducted on a soil plot with a Hg concentration of 1500 mg/kg in “El Terronal”. The nZVI proved to be an exceptional amendment for Hg immobilization, revealing an 86% reduction in Hg mobility within 72 hours of applying the nZVI, sustained over a period of 32 months. Nevertheless, the long-term effects and mechanisms of Hg remediation remain not fully understood. In light of this, the present work focused on elucidating Hg speciation changes 6 years after the application of nZVI in a Hg-polluted soil under field conditions.

Soil samples were taken from both the treated plot and an adjacent untreated plot before nZVI application and after 6 years. Initially, a simplified USEPA Method 3200, involving sequential extraction, was used to evaluate the Hg mobility. Subsequently, the identification of Hg species was conducted using a mercury temperature programmed desorption (HgTPD) device. Based on preliminary results, the reference database for mercury compounds in this work were HgO, cinnabar (HgS), metacinnabar (HgS), HgCl₂, HgSO₄, corderoite (Hg₃S₂Cl₂), Hg complexed to humic acid, and Hg adsorbed to goethite. Furthermore, X-ray absorption spectroscopy was employed to complement the study of mercury speciation. In this regard, soils and patterns were prepared as pellets from finely ground and homogenized powder. The Hg L_III-edge spectra XANES were collected in transmission and fluorescence modes at 70-80 K on CLAESS beamline (ALBA synchrotron).

The concentration of Hg in the mobile fraction was below detection limit in both samples, treated and untreated soils. However, a decrease on the semi-mobile fraction was found from 57% to 39% in the treated soil with nZVI respect to the untreated soil. This result is in accordance with the Hg immobilization reported at the beginning of the field remediation. With respect to HgTPD, the Hg species identified corresponds to Hg bound to S. On the other hand, the data treatment by linear combination fits of the Hg L_III-edge spectra XANES demonstrated that the Hg solid speciation in the treated and untreated soil samples is similar, mainly dominated by cinnabar, metacinnabar, and Hg adsorbed to goethite. This result, may indicate that the Hg mobile is associated to a minor phase, not quantifiable, or to a Hg immobilization from all phases without preference.

In summary, the mobility of Hg is linked to only a minor fraction of the total concentration of these elements in the soil, with this metal being predominantly associated with cinnabar, metacinnabar and goethite. Consequently, the complete observation of the effects of immobilization processes on Hg speciation was hindered by resolution limitations.

How to cite: Baragaño, D., López-Toyos, L., Simonelli, L., López-Antón, M. A., and Ratié, G.: Remediation of mercury-polluted soil in a mining area using nanoscale zero-valent iron, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9549, https://doi.org/10.5194/egusphere-egu24-9549, 2024.

A key aspect for the evaluation of environmental and health risk associated with mercury (Hg) contamination is the assessment of its speciation, which can influence the mobility and bioavailability of this element in the environment. The evaluation of Hg speciation in soils and sediments of contaminated sites is commonly based on selective sequential extraction (SSE) methods, which, however, have certain disadvantages: they do not allow for a specific removal of Hg species, are generally time-consuming and characterised by a low reproducibility. An easy-to-use alternative to SSE may be represented by thermo-desorption (TD) technique, where different Hg species can be identified according to their specific release temperature during a gradual heating. The aim of this study was to evaluate the potential application of TD for the risk assessment associated with Hg occurrence in alluvial soils at some sites in the Friuli-Venezia Giulia Region (NE Italy) affected by past Hg inputs related to mining and, to a lesser extent, industrial activities. At each site, surface and deep soil samples (n≥12) were collected and analysed for total Hg concentration and Hg speciation through TD. Speciation analyses were performed by means of a Hg atomic absorption spectrometer (Lumex RA915M) coupled with a pyrolysis attachment (PYRO-915+). This setup allows for a continuous monitoring of Hg released during the sample heating. Calculations of risk associated to Hg volatilisation, leaching, and ingestion were performed using the relative amount of non-cinnabar (non-α-HgS) compounds determined through TD, considered as potentially mobile. Results were then compared with those obtained through the application of a SSE method commonly used for the assessment of Hg speciation in the investigated area. Almost all samples analysed through TD showed the occurrence of non-mobile red cinnabar (α-HgS), confirming the remarkable legacy of the mining source. Generally, although a slightly higher abundance of potentially mobile Hg forms was obtained through TD than SSE, the calculated risk resulted “acceptable” (hazard index < 1) using data from both techniques. Besides, it must be stressed that calculation performed through TD data are based on a larger number of samples, thus providing a greater representativeness of the mobility of the Hg species and associated risk in the investigated area. Considering also the good reproducibility of data obtained through TD and its celerity and accuracy in Hg species discrimination, the proposed approach could be considered as a valid and relatively low expensive tool for risk assessment at Hg contaminated sites. This is especially true for sites such as former Hg mining areas characterised by the occurrence of α-HgS, easily discriminable through TD.

How to cite: Floreani, F., Pavoni, E., Petranich, E., Antonini, P., Mauri, M., and Covelli, S.: Mercury speciation in soils through thermo-desorption technique as a rapid screening tool for risk assessment procedure at mercury-contaminated sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10434, https://doi.org/10.5194/egusphere-egu24-10434, 2024.

The occurrence of gaseous mercury pollution has to be identified and monitored through innovative methods and techniques, which would serve as a step toward strengthening the knowledge of the mechanisms of mercury dispersion in the atmosphere, in accordance with the provisions of the Minamata Convention on Mercury. Consequently, the aim of this work is to present the very first data obtained by directly and continuously measuring GEM (Mercury Elemental Gas) in the lower atmosphere through an original assembly of a UAV (Unmanned Aerial Vehicle, a heavy-lift octocopter) and a Lumex^® RA-915M (a portable spectrometer for gaseous mercury). A few sites pertaining to both the mining facilities of the former Hg-mining area of Abbadia San Salvatore (Mt. Amiata, Italy) and the surrounding urban zones were selected to test the performance and effectiveness of the UAV-Lumex^® combination at different heights. The octocopter agility and directional versatility, able to stop at selected altitudes, and the Lumex^® great sensitivity made it possible to shed light on the variability of GEM concentrations and to represent its distribution via dot-map graphical visualization, providing a tridimensional picture of GEM profiling during the flights. This approach allows checking in near real-time whether the guideline concentrations are eventually exceeded. More specifically, the acquisition system was optimized through: i) the use of a stand-alone GPS as a synchronization tool for Lumex^® and UAV GPS data; ii) the connection of a vertical sampling tube to the Lumex^® inlet to overcome the strong airflows of the UAV rotors; iii) the use of batteries for power supply to avoid the release of exhaust gases. Moreover, all flights were standardized based on previously acquired data thanks to the method accuracy and the UAV pilot experience, allowing reprogramming and repeating the routes in different times. The results showed significant concentration variations between the urban and the most contaminated mining area, and highlighted the differences when the flight was repeated at a later date.

How to cite: Cabassi, J., Lazzaroni, M., Giannini, L., Mariottini, D., Nisi, B., Meloni, F., Rappuoli, D., and Vaselli, O.: Investigating the 3D distribution of GEM (Gaseous Elemental Mercury) in the lower atmosphere via a UAV (Unmanned Aerial Vehicle) - Lumex® assemblage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10879, https://doi.org/10.5194/egusphere-egu24-10879, 2024.

The concept of Terroir, developed with respect to grape and wine, can be generalized to define the inseparable link between an agri-food product and its territory of origin as a determining element for its economic valorisation. While the terroir certainly impacts on physiological and compositional aspects of a crop, an important influence is due to the species diversification in cultivars. Therefore, both environment/soil and cultivar participate in defining the geographical authenticity of crops.

Geochemical-isotopic techniques are a powerful tool to authenticate a crop with respect to its geographical origin. The integration of multi-elemental analyses with the determination of isotopes such as carbon (δ¹³C) and nitrogen (δ¹⁵N) can allow a detailed mapping of the geographical origin of agricultural products. The stable isotopes of light elements present in crops offer a unique form of ‘isotopic signature’ that reflects the geochemical conditions of the soil together with the metabolic specificity of the plants (photosynthesis, N assimilation). This is crucial not only to authenticate the plant provenance, but also to support protected designations of origin (PDOs) and geographical indications (PGIs), strengthening the consumer’s confidence in the authenticity and quality of products.

In this first report, we have combined geochemical-isotopic and chlorophyll fluorimetric analyses of two red chicory (“radicchio rosso”, cv. Chioggia and cv. Treviso) cultivars typical of the Emilian coastal environment, but not yet recognized as PGI, different from analogous crops in Veneto Region. An effort in this respect is motivated by the special geochemistry of sandy coastal soils, which tend to be dry and exposed to salinisation phenomena.

Soil was thoroughly characterized based on its chemical-physical properties, including XRF analysis of major elements. A detailed analysis of elements in soil and plants was performed by ICP-MS-QQQ down to ultra-trace elements, and EA-IRMS analysis was done for the evaluation of C and N isotopic ratios. Plant phenotyping, based on chlorophyl fluorescence indexes, was performed to highlight the physiological specificities of the two cultivars, to put in relation with the stable isotope profile of light atoms.

The comparative results of the geochemical composition of the plant organs evidenced a cultivar-specific fractionation of some elements: cv. Chioggia had higher element absorption capacity than cv. Treviso, and both cultivars share an attitude to concentrate P, Cu and Mo. Upon translocation of elements from roots to leaves, especially the rare earth elements showed the specificity of the two cultivars, which can be differentiated based on the concentration of lanthanides as compared to the soil. A better use of mineral nutrients could be supported by higher photosynthetic performance in cv. Treviso than cv. Chioggia.

This research, to be further implemented, can constitute a useful database for the reconstruction of the geochemical-isotope profile for the geographical traceability of “radicchio rosso” and the possible further promotion of this crop in Ferrara province.

This research was allowed by phD fellowship granted by EUROPEAN SOCIAL FUND P L U S - The ESF+ 2021-2027 Programme of the Regione Emilia Romagna

How to cite: Martina, A., Aquilano, A., Ferroni, L., and Marrocchino, E.: Geochemical-isotopic and fluorimetric analyses for the characterization of two red chicory varieties in sandy coastal soil of the Ferrara province (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10952, https://doi.org/10.5194/egusphere-egu24-10952, 2024.

Volcanic eruptions are unpredictable and present a significant challenge for volcanic crisis management, primarily due to the variety of eruptive styles, ranging from effusive to explosive. By elucidating the dynamics of magma ascent, with a focus on degassing, we can better understand of the interconnections between petrological characteristics, geochemical and geophysical signals, volcanic hazards, and volcano monitoring. To this aim, lithium (Li), which has a high mobility in both silicate melts and crystals, has been used as a geospeedometer to monitor short-time processes, such as syn-eruptive magma ascent and degassing and post-eruptive processes (cooling). Yet, to appropriately interpret Li data in crystals from volcanic deposits, a clear understanding of the Li behavior and partitioning between the crystal-melt-fluid phases during an eruption is essential. Most of the Li partitioning data rely on glass inclusions and their host minerals, which do not always guarantee equilibrium conditions. Experimental data are largely missing, especially in the case of silica-rich hydrated magmas. Therefore, we provide Li contents and partitioning via phase-equilibrium experiments for analyzable-sized plagioclases crystallized from Li-bearing H2O-saturated rhyolitic melts at pressures from 50 to 150 MPa and temperatures of 800 and 875 °C. In addition to its applications in volcanology, this research could yield valuable information for assessing the economic viability of lithium in felsic deposits, specifically those with rhyolitic/granitic compositions (as highlighted by Benson et al., 2017), and in magmatic fluids. Moreover, it holds futuristic potential for extracting lithium directly from these fluids.

How to cite: Dupont de Dinechin, M., Martel, C., Balcone-Boissard, H., Rusiecka, M., Champallier, R., and Deloule, E.: Experimental Investigation of Lithium Partitioning among Plagioclase, Rhyolitic Melt, and H2O Vapor, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14481, https://doi.org/10.5194/egusphere-egu24-14481, 2024.

This research work focuses on reconstructing the anthropogenic fingerprint of the past 150 years through the high-resolution analysis of trace organic compounds preserved in Antarctic ice.

Over the decades, numerous persistent and semi-volatile organic pollutants were largely used in several industrial activities. Some of them proved to be highly toxic, posing a serious threat to human health and natural ecosystems. Consequently, international bans and agreements were established to reduce their industrial production. As a result, restrictions on one compound have led to increased emissions of other chemical substitutes. A rise-and-fall trend in the concentrations between well-established and emerging pollutants is expected in response to international legislative measures. High resistance to biodegradation and semi-volatility promote the long-range atmospheric transport of these molecules, which reach remote areas such as polar regions, where they accumulate as a result of cold condensation processes.

The extraction site GV7 (70°41' S, 158°51' E, 1950 m a.s.l.) is highly significant since it presents a high snow accumulation rate (241 ± 13 mm we yr-1). This feature, rare in recent archives, enables the analysis of trace organic compounds that would otherwise require considerably high amounts of matrix. The ice core (length: 50 m; diameter: 100 mm) is an ideal archive to investigate the “Great Acceleration” since it spans the last 150 years.

The novel analytical method specific for snow and ice applied in this work allows to recognize the evolution of a single compound over time in response to international bans and social changes. The multi-proxy approach adopted allows to identify trends in well-established and new generation organic pollutants as well as personal care products. More specifically, fragrances are compounds of increasing interest since they provide information on use and consumption related to changes in household and social habits.

Solid-phase extraction (SPE) combined with gas chromatography coupled with triple quadrupole mass spectrometry (GC-MS/MS) enable to significantly increase the analytical signal. In addition, samples were entirely processed in a stainless-steel clean room to reduce contamination, achieve low detection limits, and obtain high-resolution data.

Results show a change in the concentration of each compound on a time frame of 150 years. Since this is a pilot study, the processes involved in the transport and deposition of the analytes in deep ice are not yet fully understood and need further investigation. It is necessary to take into consideration possible changes in the use and consumption of organic molecules and potential variations in atmospheric transport.

Previous studies provide data on personal care products on surface snow, which are essential for a broader interpretation of the processes involved.

How to cite: Genuzio, G., Vecchiato, M., Argiriadis, E., Spolaor, A., Frezzotti, M., Barbante, C., and Capodaglio, G.: Trace organic compounds in an Antarctic ice core: a high-resolution analysis to reconstruct the anthropogenic fingerprint, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15658, https://doi.org/10.5194/egusphere-egu24-15658, 2024.

Mine dumps are man-made geological formations characterized by unique chemical, particle-size, bacterial, and physical and mechanical features, representing deposits or cumuli of crushed, grounded and roasted material. Processing plants of metallic poli-sulfide ore deposits have contributed to pollute soils and surface and ground waters in many areas worldwide. The southern sector of the Apuan Alps (northern Tuscany, Italy) hosts a number of small pyrite ± barite ± iron-oxide orebodies that have been exploited since at least the Middle Age, whose activity ceased at the end of the 20^th century. The most important mining areas were those distributed along a 10 km-long NE-SW strip in high Hg contents the southern portion of the Apuan Alps. In this framework, the Rezzaio treatment plant (Valdicastello Carducci, Pietrasanta), dismissed since 1991, was the site where ore bodies hosted within the metamorphic rocks of the Apuane Unit, mainly from Monte Arsiccio, Pollone and Buca della Vena mines were treated. The materials extracted from these mines were barite and iron oxides (both hematite and magnetite) used as weighting agents as drilling mud during petroleum drilling wells. Abandoned mining tunnels and dumps and plants for mineral treatment are still present in the area, posing a series of environmental threats. Our study focused on assessing the impact due to mercury contamination released by the treatment plant of Rezzaio by the past-mining activity. The aims of this study were to (1) determine the concentration of Gaseous Elemental Mercury (GEM or Hg0) in air and interstitial soil inside and outside the plant, including the working areas and the edifices where the workers were operating (e.g., offices, laboratory, rock storage); (2) assess the total amount of Hg in the top- and sub-soils, mostly developed on a small mining dump and (3) quantify the release of Hg by soil leaching tests by Milli-Q water. According to WHO and the Italian Legislative Decrees, the GEM values in air and outside the plant and in the plant edifices and mining structure are below the Recommended Exposure Limit. The spatial distribution of Hg indicates that up to 88 mg/kg were recorded in the top- and sub-soils, the highest contents being found on the small mining dump that is partly the bank of a creek. However, in most cases the concentration of Hg leachate were < 1µg/L, suggesting that mercury is likely trapped within crystalline silicate structures recalcitrant to chemical weathering. These results suggest that despite the high contents, mercury is not apparently playing a critical role as a contaminant in the Rezzaio area, being hosted in relatively insoluble minerals.

How to cite: Barbara, N., Meloni, F., Cabassi, J., and Vaselli, O.: Mercury contamination in a former mining plant of NW Tuscany (central Italy)  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15864, https://doi.org/10.5194/egusphere-egu24-15864, 2024.

Mining activities have a severe impact on fluvial systems. The dispersion of huge amounts of heavily polluted wastes contribute to mining-related river pollution due to runoff. Pollutants distribution in fluvial systems is controlled by the interplay between weather conditions (e.g., flooding events), geomorphic processes, and anthropic activities affecting sediments supply, erosion, transport, and (re-) deposition. Mercury (Hg) is listed as a critical contaminant due to its high toxicity, mobility, and persistence in the environment. Its use is progressively banned. As a result, Hg mining is now limited to a few countries. However, legacy mine wastes are still releasing Hg into the environment, particularly to fluvial systems. The Monte Amiata Mining District (MAMD, Southern Tuscany) was the 3rd largest Hg producer worldwide. Four river basins drain the MAMD. Among them, the Paglia River (PR) basin drains the SE sector of the MAMD, covering an area of 1320 km². The widespread Hg pollution and the low resilience to contamination of this river basin was demonstrated in previous studies. Extreme flooding events redistributed huge amounts of polluted sediments across the catchment. The Hg flux discharged by PR to the Tiber River, and ultimately to the Mediterranean Sea, was estimated around 11kg/y. However, this estimate is based on spot samplings. In this study, the relationship between Hg transported by particulate (Hg_p), total suspended solids (TSS) and water turbidity (Tb_w) for PR was investigated to set up a method for the calculation of Hg fluxes from TSS and Tb_w monitoring. Water samples were collected in different hydrological conditions between 2022 and 2023. Samples were taken along the PR, upstream and downstream of the Elvella creek confluence (ECC), a tributary that is not polluted by Hg, to evaluate its effects on the Hg budget. The samples were filtered and the TSS collected on the filters were analyzed for Hg. Part of the samples were analyzed also for Tb_w to investigate the relationship between TSS and Tb_w. TSS ranged between 1.3 and 621.4 mg/L, whereas Hg varied between 0.8 and 321.8 ng/L. Tb_w varied between 12.2 and 358 NTU and a linear relationship was found between TSS and Tb_w. The highest Hg and TSS values were measured during the recession phase of flooding events, whereas the lowest ones were found during low flow conditions. A linear relationship was also found between Hg and TSS. Hg was higher in the upstream samples than in those collected downstream the ECC, confirming that Hg source is the heavily polluted PR basin. The relationship between the two parameters could be applied to the indirect, continuous measurement of Hg fluxes discharged by PR with an automated TSS/Tb_w sensor. Such monitoring would allow assessing the variability of Hg pollution and transport across the PR basin in real time especially in case of flooding, that are expected to become more frequent due to climate change, leading to an increase of Hg delivery to the Mediterranean Sea.

How to cite: Nannoni, A., Annese, V., Fornasaro, S., Morelli, G., Ciani, F., Monnanni, A., Lattanzi, P., Rimondi, V., Costagliola, P., and Fagotti, C.: Particle-bound mercury transport across a mine-polluted fluvial system: towards a simple method to measure Hg flux from the Monte Amiata Mining District (Southern Tuscany, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16063, https://doi.org/10.5194/egusphere-egu24-16063, 2024.

Geochemical prospecting is a valuable tool for investigating the influence of the geological context on the composition of stream sediment and determining the existence of any natural or anthropogenic geochemical anomaly within a river catchment basin. Several indices have been proposed in scientific literature to assess sediment's environmental quality and the ecological condition of catchment basins. In environmental studies, these indices are usually based on applying ratios among the raw geochemical composition of the sediment at the sampling location and a value assumed as a reference for the undisturbed conditions (Background/baseline). However, the reference values are often determined while overlooking the potential influence of river dynamics on the variability of sediment composition, and this can compromise the robustness of the contamination assessment.

As a matter of fact, the chemical composition of a stream sediment sample is representative of the relative upstream catchment basin. The Sample Catchment Basin (SCB) method, which accounts for the dynamic nature of rivers, has been largely used in literature to correct the dilution effect impacting the composition of stream sediment, aiming at determining reliable geochemical background values to be used for mineral prospecting.

The main purpose of the study was to check if the use of the correction of the dilution effect to determine background values could also improve the performance of some contamination indices, favouring a more effective and accurate assessment of the environmental degradation affecting a river basin.

The Sarno River, known for its susceptibility to contamination from urban and industrial sources, served as a pertinent case study. A total of 96 samples were used to define the zone of influence of each sample through the elaboration of geomorphological and hydrological features; then, the background concentrations of each element were estimated by calculating the weighted average element content based on the areal proportions of lithologic units in each sample catchment basin. The values deriving from this step were then used as a reference to calculate the degree of contamination for each SCB.

The contamination indices were calculated and mapped by using both non-diluted and dilution-corrected background data.

A comparative analysis was performed among the results obtained to assess if sensitive changes occurred to the spatial and statistical distribution of used indices and to determine if an improvement in performance could be obtained.

 This study represents a methodological benchmark for future research focusing on environmental risk assessment of stream sediment.

How to cite: Iannone, A., Guarino, A., Pacifico, L. R., and Albanese, S.: Can contamination indices performance be improved by accounting for the dilution effect when dealing with stream sediments? A case study from southern Italy., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16836, https://doi.org/10.5194/egusphere-egu24-16836, 2024.

In this research. we identified the provenance of lead flux used in the production of the glaze of unique, high‐quality late medieval stove tiles from the northern part of the Carpathian Basin and elaborated and evaluated a fast preparation process to measure Pb isotope ratios in high‐Pb glazes. A total of 24 stove tiles from seven archaeological sites in present‐day Hungary and Slovakia were analysed.

We compared three different methods of preparation to determine the Pb isotopes ratio from high-Pb glazes. Method 1 consisted of the dissolution of bulk chips of glaze, dilution of the solution and mass spectrometric analysis without Pb purification. Method 2 collected a tiny amount of glaze material from the surface with acid‐impregnated swabs, subsequent dilution and direct analysis of the sample solution. Method 3 used solutions from method 1, extraction of Pb by ion‐exchange chromatography and analysis of the purified Pb. Each preparation method produced similar Pb isotope ratios. Results demonstrate that the Pb isotope ratios are independent of the preparation methods. Therefore, we recommend using the simplest method of surface sampling of high-lead glazes with swabs (method-2). It is a fast procedure that requires less effort in the laboratory with the benefit of preserving the integrity of cultural heritage objects.

The majority of the Pb isotope ratios fall into one group and shows a strong overlap with the lead ore deposits of the Krakow-Silesia mining region. The imported Pb was used not only in the liquation process to separate silver from the copper ore mined in the territory of the Slovak Ore Mountains, but also in the preparation process of the glazes of most of the stove tiles analysed that were produced in the region. The lead ore locally mined in the Slovakian Ore Mountains may have been used, possibly mixed with Pb derived from Poland, only for the green glazes of some Csábrág/Čabraď and Ipolyság/Šahy tiles. The Pb isotope ratios of some of the tiles excavated in Eger are similar to the Pb isotope data of the Triassic Bleiberg‐type Pb‐Zn ore deposits, indicating a potential use of lead imported from Austria.

How to cite: Horváth, A., Palcsu, L., Bajnóczi, B., and Györkös, D.: Comparison of rapid preparation methods for lead isotope analysis of high-lead ceramic glazes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17034, https://doi.org/10.5194/egusphere-egu24-17034, 2024.

Understanding the transfer of contaminants from soil to plants, especially agricultural products, is essential in environmental science, particularly in the context of risk assessment and the development of sustainable agricultural practices. The estimation of transfer factors (TFs) (Singh et al., 2011), which quantify the uptake of elements or pollutants by plants from the surrounding soil, serves as a crucial parameter in evaluating potential ecological and human health risks, as these elements could enter the food chain (Ozhovan and Kremenetskiy, 2018).

For this study, the Transfer Factors soil-to-plant were estimated using the bioavailable concentrations (Guarino et al., 2022) of Potentially Toxic Elements (PTEs) identified by Italian law (D.lgs. 152/2006) in the agricultural soils and the elemental concentration in the primary agricultural products (PAP). These latter are freshly harvested fruits and vegetables, which retain their integrity and freshness as they have not undergone significant processing, collected across the entire region through the Campania Trasparente project (www.campaniatrasparente.it).

The aim of this study was to compare various Transfer Factors (TFs) among the most numerous vegetal species and potentially highlight different behaviours. A robust multivariate statistical approach, such as Robust Principal Component Analysis (RPCA) was applied to the TFs, and a multiple regression, using the stepwise method, was performed, with Principal Components as dependent variables and soil physical parameters (grain size, organic matter, pH, cation exchange capacity, salinity, electrical conductivity) as independent variables.

Our findings reveal distinct patterns in the soil-to-plant transfer factors for various elements, emphasizing the role of soil properties, plant species, and environmental conditions. Results reveal that, within the Campania region, the highest TFs for the most vegetal species are associated with Zn and Cu. Specifically, RPCA indicates a positive correlation between Zn and Co TFs. In the end, the multiple regression analysis highlights that clay presence and cation exchange capacity are the primary soil physical factors influencing TFs across different plant species.

This integrated approach could provide a comprehensive understanding of soil-plant transfer processes and the impact of soil physical parameters on TFs in regional cultivations. The study helps better understand the impact of soil physical parameters, such as cation exchange capacity (CEC), grain size, organic matter, etc., on vegetal species growth. It can lead to well-informed decisions regarding crop selection, fertilizer application, irrigation, and other factors.

References:

Guarino, A., Albanese, S., Cicchella, D., Ebrahimi, P., Dominech, S., Pacifico, L.R., Rofrano, G., Nicodemo, F., Pizzolante, A., Allocca, C., Romano, N., De Vivo, B., Lima, A., (2022). Factors influencing the bioavailability of some selected elements in the agricultural soil of a geologically varied territory: the Campania region (Italy) case study. Geoderma 428, 116207.

Jaswant Singh, Suraj K. Upadhyay, Rajaneesh K. Pathak & Vidhu Gupta (2011). Accumulation of heavy metals in soil and paddy crop (Oryza sativa), irrigated with water of Ramgarh Lake, Gorakhpur, UP, India, Toxicological & Environmental Chemistry, 93:3, 462-473.

Ozhovan M, Kremenetskiy A. (2018). Transfer Factors: Concepts and Applications in Soil-Plant Systems. Boca Raton, FL: CRC Press.

How to cite: Pacifico, L. R., Guarino, A., Iannone, A., Pizzolante, A., Esposito, M., Brambilla, G., and Albanese, S.: Comprehensive analysis and multivariate statistical approach of Transfer Factors soil-to-plant estimated from bioavailable concentrations in agricultural products: the case study of the Campania region (Southern Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17147, https://doi.org/10.5194/egusphere-egu24-17147, 2024.

In the past 20 years, the occurrence of tungsten-related health and safety incidents has drawn the close attention of scholars to the toxicity of tungsten and its health and environmental effects. The upper limit of tungsten concentration in water, its mobility and toxicity are all closely related to its speciation. Although polytungstates have been proven to be more toxic and migratory than monomeric tungstates, there is limited information about their abundance in natural environments due to the lack of a reliable analytical approach for determination. In this study, we conducted a simultaneous analysis of monomeric and polymeric tungsten species in natural water using reverse-phase ion pair chromatography coupled with inductively coupled plasma mass spectrometry. Polytungstates and five monotungstates, including tungstate as well as mono, di, tri, and tetrathiotungstate, were chromatographically separated within 35 min of using ethanol (12 - 48% gradient) as the mobile phase. The detection limit of polytungstates was 1.50 µg/L. Although common for the analysis of metals, experimental studies based on electrospray ionization - high resolution mass spectrometry (ESI-HRMS) have indicated that samples containing polytungstates should not be acidified, as it could result in the transformation of monotungstates to artifact polytungstates. Overall, our study offers an effective method for the analysis of various tungsten species, especially polytungstates, at environmentally relevant concentrations.

How to cite: Zhao, Q. and Hu, S.: Reverse phase ion pair chromatography coupled with inductively coupled plasma mass spectrometry as a method for tungsten speciation in natural waters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17460, https://doi.org/10.5194/egusphere-egu24-17460, 2024.

The distribution of Li and its two stable isotopes among mantle minerals has been widely used in the past to decipher the physical and chemical state of the Earth’s interior through geological time-scales. Hence in this study, using a combination of Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) we study the mechanism of incorporation and distribution of Li ion and its two isotopes (⁶Li and ⁷Li) in the olivine (M₂SiO₄, M:Mg,Fe) lattice as a function of temperature and Fe concentration. Li is known to occupy both interstitial and substitutional sites in olivine (Dohmen 2010, GCA). Our calculations indicate that Li, Fe²⁺ and Fe³⁺ prefer to occupy the smaller and less distorted M1 site. A positive correlation between Fa-content and Li concentration is suggested.

Calculation of isotopic fractionation of Li between the interstitial and substitutional sites of forsterite shows that the heavier isotope gets populated in the interstitial sites of olivine. Incorporation of Fe is found to enhance the extent of fractionation. Our study hence emphasizes the importance of considering the influence of Fe, even if it is present in small concentrations, while determining the isotopic fractionation of minor and trace elements in mantle minerals. We also offer valuable insights into the microscopic origin of the role played by Fe in modulating the isotopic fractionation of Li in mantle minerals.

How to cite: Chatterjee, S., Mondal, R., Pramanik, C., Ghosh, P., and Saha-Dasgupta, T.: Influence of Fe on the distribution and isotopic fractionation of Li in olivine: A first-principles study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18016, https://doi.org/10.5194/egusphere-egu24-18016, 2024.

Mercury (Hg) represents one of the top ten chemical elements of significant public concern according to the World Health Organization. In 2013, the Minamata Convention was established aiming to reduce, control and possibly eliminate the use and release of mercury in the environment. The Global Mercury Assessment 2018 estimated annual global mercury anthropogenic emissions at around 2200 tons, while the contributions of primary natural sources (e.g., volcanic activity) appear significantly uncertain.

The aim of this study is to better constrain the origin and quantity of mantle-derived Hg by integrating the current available data from experimental petrology, geochemical analyses of sedimentary rocks the Hg anomaly of which is linked to large-scale magmatic events, chemical data of igneous rocks and Hg measurements from volcanoes and minerals by in situ and in satellite remote sensing.

The volcanic Hg is known to be characterized by an atmospheric residence period of 0.5-2 years (Bagnato et al., 2007) that allows it to distribute over the globe in the form of Hg⁰ and Hg²⁺.Inizio modulo The oxidation of Hg⁰ to Hg²⁺ causes mercury to dissolve into aqueous fluids. Part of Hg directly migrates to the atmosphere, precipitate into sedimentary basins and eventually long-term sequestrate in marine sediments (Grasby et al., 2019).

Sharp Hg anomalies have been detected in several stratigraphic layers with concentrations varying from 20 ppb (La Bédoule, France) to 90 ppm (Grane field, southern Viking Graben, Norwegian North Sea) to be representative of mass extinction anoxic and Large Igneous Province events (i.e. Greater Ontong Java and North Atlantic Igneous Province) such as Selli oceanic anoxic event and Palaeocene-Eocene Thermal Maximum, respectively (Grasby et al., 2019 and reference therein). The analyses of current Hg volcanic emissions along with stratigraphic geochemical anomalies highlight transport processes of deeply seated Hg of mantle origin (Shen et al., 2023). The interior of Earth is proposed to store about 10 ppb of Hg (BSE model, McDonough and Sun 1995) within a variety of igneous rocks both intrusive (peridotites, pyroxenites and gabbros) and effusive (basalts), the majority of which (about 5 ppb) is hosted by ophiolites (Canil et al., 2015).

Further, the current global volcanic Hg flux ranges from 0.6 ton·yr^-1 to over 1000 ton·yr^-1 (Edwards et al., 2021) pointing out the high volatility of mantle-derived Hg that is confirmed by the established link between volatile-driven LIP events and Hg anomalies distributed worldwide. Additional sources of natural Hg emissions are represented by hydrothermal mineralization (e.g. cinnabar) that testify the dominant role of SO₂ and H₂S emissions in volcanic and hydrothermal systems, respectively.

We will present a preliminary database of global Hg concentration that allows to model the deep Hg cycle based on the effect of magma-mineral element distribution and the role of pressure-temperature-mantle redox state through space and time.

How to cite: Benedetti, F., Marras, G., Brandano, M., Calabrese, S., Bosi, V., Ricciardi, A., and Stagno, V.: An updated database of mercury emissions based on remote sensing, geochemical surveys and laboratory experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18436, https://doi.org/10.5194/egusphere-egu24-18436, 2024.

Stalagmites in karstic caves may serve as paleoclimate proxies, especially in regions missing glacial ice cores or other continental proxies. Specifically, the laminae revealed in a stalagmite cross-sectional cut can be related to the past upstream flows and soil coverage above the cave. The shape of these laminae, and therefore of the stalagmite top surface, thus change over time in response to variable environmental conditions. However, the effect of the past flows on such shape variability remains poorly understood. Previous models describing stalagmite growth thus involved strong simplifying assumptions regarding the aerodynamics and hydrodynamics of drops impacting stalagmites in caves. For instance, drops were assumed to always land at the apex of the stalagmite, thereby feeding the thin residual film covering it in one central point, while it was recently shown that the drop impacting position is sometimes scattered over several centimeters, which may have a non-negligible effect on stalagmite width [1]. The concave shape exhibited by some stalagmites was also associated with drops splashing at impact, while most drop impacts in caves lead to splashing and cannot, therefore, be related to a particular stalagmite shape [2]. Another assumption of previous stalagmite growth models is that the thin residual film lying on top of the stalagmite remains uniform in time and space, which may not always be accurate.

We thus propose to study the evolution of this residual film in time and space. Starting from an initially dry stalagmite, the film thickens because of the liquid brought by the successive drops, until it reaches a steady state. The thickness of the film at steady-state results from the balance between the incoming flow of drops falling on the stalagmite, and the film depletion through gravity-driven drainage. If this drop inflow is interrupted, only the drainage remains. We are interested in assessing the effect of the main factors influencing the film thickness evolution during these three phases, namely: (i) the underneath stalagmite shape, and (ii) the drop dripping frequency, i.e., the amount of liquid brought over a certain time. To achieve this, we record film thickness measurements during the filling, stationary and sole drainage phases on actual stalagmites, both in caves and in a lab setting. The caves provide a great diversity of shapes while the lab measurements allow to systematically vary the drop dripping frequency. We complete these measurements by a reduced-order modeling of the film thickness in time and space, using Reynolds lubrication equation expressed in curvilinear coordinates to account for the various existing stalagmite profiles. We obtain a good agreement between the experimental measurements and the results provided by the model with a set of parameters representing adequately the stalagmites of our dataset. We finally show that, depending on the stalagmite shape, considering the film as uniform in time and space may remain a valid assumption, but this is not always the case.

[1] Parmentier J. et al, P. R. Soc. A. (2019), https://doi.org/10.1098/rspa.2019.0556
[2] Parmentier J., Terrapon V. and Gilet T., Phys. Rev. Fluids (2023), https://doi.org/10.1103/PhysRevFluids.8.053603

How to cite: Parmentier, J., Terrapon, V., and Gilet, T.: Gravity-driven drainage of a thin film on a stalagmite , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18537, https://doi.org/10.5194/egusphere-egu24-18537, 2024.

The present work is based on a full-scale project for the treatment of port sediments with high Hg concentrations. The port area of this work is located in the Principality of Asturias (northern Spain). Preliminary studies for the implementation of a dredging activity on the sediments of the Llanes port showed Hg concentrations in the sediments ranging from 0.19 to 1.13 µg g^-1, with an average of 0.81 µg g^-1. This Hg average concentrations exceeds the legal threshold in Spanish territory for returning dredged sediment to the sea, so that according to current legislation it must be extracted from the coastal system and managed on land, generating a substantial loss of a significant volume of sediment in the system. In order to improve a circular economy and to be able to manage these Hg-contaminated materials to be dredged more efficiently, laboratory-scale tests verified that the Hg contamination was mostly found in the finets fraction <63µm. With these previous results and with regional governmental support, the company EXCADE S.L. in collaboration with the University of Oviedo designed and built a full-scale plant based on the treatment of contaminated sediments by cyclone for the efficient removal of the fine contaminated fraction.  Between June and August 2023, a total of 8,000 m³ of contaminated sediments from this port area were processed in a first phase through this treatment plant. The particle size and the Hg concentrations in the treated material were monitored every two working days, and after the treatment of all the material, four representative samples of the total volume treated were sent to an external laboratory to validate the results obtained during the procedure. The monitoring results showed that the treated material had fine material concentrations of less than 5%, and that the Hg concentration ranged from 0.05 to 0.13 µg g^-1, which resulted in a 7-fold reduction of the initial average Hg concentration in the sediments. The same occurred with the results from the external laboratory that showed that the treated material had fine material concentrations of less than 5%, and that the Hg concentration ranged from 0.13 to 0.17 µg g^-1. These Hg concentrations in the treated material were within the legal range in Spanish territory, which is why the treated material was authorized for deposit at sea. Throughout 2024, the same procedure will be carried out on 12,000 m³ of new contaminated by Hg material to be dredged to validate the results of this first real-scale experience for the treatment of sediments contaminated by high Hg concentrations.

How to cite: garcia-Ordiales, E., Barquero Peralbo, J., Navarro Murillo, E., Rico Fernandez, P., and Cienfuegos Suarez, P.: Experiences in a full-scale cyclone plant treatment of Hg-contaminated port sediments., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18550, https://doi.org/10.5194/egusphere-egu24-18550, 2024.

Materials research applied to archaeological ceramic artefacts has garnered widespread interest among scientists, architects, engineers, and archaeologists focused on safeguarding architectural heritage. These ancient structures within historic city centers encapsulate the distinctive history and visual essence of each city across different eras. Assessing both old and new materials following damage to these historical edifices becomes crucial for predicting their behaviour during restoration. This endeavour not only aims to analyze and preserve these artifacts but also aims to explore the knowledge and craftsmanship involved in their creation and use. Characterizing building materials primarily targets preservation and restoration goals, encompassing the origins of historical raw materials, understanding archaeological artifact changes, determining original firing methods, and reconstructing manufacturing technologies. Bricks and ceramics, resembling fired artificial rocks, retain geological imprints from their claystone origins, impacted by local geological settings influencing material availability and building techniques. Take, for instance, Ferrara, a Medieval city in Northeast Italy, strategically positioned between the Adriatic Sea and the Po alluvial plain. Its prosperity during the Renaissance under the Estense family was bolstered by extensive modifications to the city, predominantly utilizing locally abundant silico-clastic sediments for construction.

The focus of this research on historical bricks and terracotta decorations from prominent Medieval and Renaissance buildings in Ferrara is to understand the composition of these ancient materials to aid in planning effective restoration treatments, identifying causes of decay, selecting suitable replacement materials, and avoiding incorrect restoration choices. Analyzing the chemical and geological attributes of these materials provides valuable insights into their manufacturing techniques and origins. Moreover, by comparing obtained data with regional sediment records, it has been possible to ascertain the nature and sources of the original raw materials.

How to cite: Marrocchino, E. and Vaccaro, C.: Geochemical characterization of bricks and terracottas used in historical monuments in Ferrara (Italy): Reference to raw materials and production technique, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19518, https://doi.org/10.5194/egusphere-egu24-19518, 2024.

Riparian vegetation plays an important role in fluvial ecosystems. River drainage in abandoned mine sites is often source of heavy metals through transport of contaminated sediments. In those areas riparian vegetation may take up contaminants from riverbanks soil, acting as a temporary storage of metals. In this study, the potential mercury (Hg) in plants growing on soil anomalous in Hg was quantified to evaluate its storage effectiveness, and the potential as a secondary Hg source to the atmosphere in case of fire, or upon anthropic utilization as biomass.
Riparian trees along a section of the Paglia River (Tuscany, Italy), draining the abandoned Monte Amiata Hg mining district, the 3rd Hg producer worldwide in the past, were sampled from the riverbanks. The riparian vegetation is occasionally cut during bank maintenance, and the resulting wood may end up into wood chips for solid biofuel. Poplars (Populus spp.) are the most abundant species naturally widespread along the Paglia riverbanks, together with Robinia spp. and Quercus spp.. 
Cores of trunks (8/10 cm long, 0.5 cm diameter) from 50 trees were sampled from fives sites using a drill corer. At each site, a soil sample was collected. 
In soils, Hg ranged from 3.5 to 52.8 mg/kg, above the Italian limit for soil (1 mg/kg; D.Lgs.152/2006). Preliminary data in trees, show Hg ranges between 0.5 and 93 ug/kg. Anomalous Hg concentrations (195-353 ug/kg) in few samples are probably associated to soil particles trapped in the tree barks. Except for these values, Hg concentrations in trees are below the recommended Hg limit (100 ug/kg) for high quality solid biofuels (European EN ISO 17225, 2021), thus posing little to moderate impact on the value of the locally harvested wood chips and the potential health risk for Hg0 emissions. On the other hand, in case of wildfires, Hg stored in trees bole wood (about 0.6 kg estimated in the studied area) can be released from the burning trees and from the subjacent soil. Thus, vegetation represents a potential secondary source of Hg₀ to the atmosphere. Results highlight the importance in similar contaminated areas of metals fate investigation in soil and plants to assess the actual risks to the surrounding environment (biota, human health, and animals) posed by Hg emissions in case of fire, or for example by biomass used for energy production. Remediation strategies in these areas should include a wise management of riparian vegetation as a tool for mitigation of Hg release in the environment.

How to cite: Morelli, G., Ciani, F., Costagliola, P., Fagotti, C., Lattanzi, P., Monnanni, A., Nannoni, A., and Rimondi, V.: Quantification Of Mercury (Hg) In Riparian Trees Along The Paglia River, Monte Amiata Hg Mining District (Italy): Implications For A Sustainable Environmental Management And Risks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19595, https://doi.org/10.5194/egusphere-egu24-19595, 2024.

The EU-funded CRM-geothermal project aims to integrate the extraction of critical raw materials and geothermal heat from deep geothermal reservoirs. Within the project, extraction technologies and their economic and environmental feasibility are tested and evaluated across several geological regions in Europe and East Africa.

  The focus of this study is the North German Basin, a typical sedimentary basin that initiated rifting in the late Carboniferous period, accumulating various sediments to a thickness of up to 10–12 km. Located in central Europe it stretches over an area from Poland to the Netherlands, traversing across North Germany.

The succession is beginning with Permian volcanic rocks at the base, and overlain by alternating layers of mud-, silt- sandstones and evaporates; some of which have already been identified for geothermal energy extraction (e.g. Neustadt-Glewe, Schwerin, and Potsdam). Up to now, the extraction of lithium (Li) has not been explored, despite the existence of elevated Li concentrations occurring in formation fluids of the Rotliegend and Bunter sandstone.

In this study the potential content of selected critical and valuable elements (Li, Sr, Cu) and their availability in various formations of the North German Basin was assessed. For this purpose, cuttings from different formation rocks from one deep well (GrSk04/05; 4000 m depth) were first analyzed for bulk concentrations of these elements. Most promising samples (with Li up to 74 ppm, Cu up to 214 ppm, and Sr with up to 2334 ppm) were selected from Muschelkalk, Bunter sandstone (Dethfurt), Zechstein (Ohre), Permian Rotliegend sandstone (Hannover), and volcanic rocks)  for a sequential extraction. This method provides indication on the type of elemental bonding within minerals, allowing to estimate the availability and sustainability of the CRM in the respective formation fluids.

How to cite: Regenspurg, S., Thomas, A., Stammeier, J. A., Schiepersky, F., Scheck-Wenderoth, M., and Kieling, K.: Critical raw materials from geothermal fluids: Potential in the North German Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19791, https://doi.org/10.5194/egusphere-egu24-19791, 2024.

Mercury is a worldwide contaminant, with a usual concentration range of 10 to 100 μg kg^-1 in the marine/oceanic sediments. The Bohai Sea, the largest gulf in China, is nearly enclosed by densely populated and industrialized land and connects to the northwestern Pacific Ocean via the Bohai Strait. The sediment core (profile) may record anthropogenic mercury history. A 476-cm sediment core was collected and sectioned into 1-cm slices, which were analyzed for mercury and conservative tracer scandium. Mercury content ranged from 14.4 to 35.5 μg kg^-1 while scandium content ranged from 9.57 to 13.1 μg kg^-1. Overall, mercury content increased from the sediment profile base up to top while scandium content decreased, showing that anthropogenic activities around the bay led to mercury enrichment and accumulation in the sediment. In details, mercury content in the sediment ranged from 14.4 to 17.4 μg kg^-1 and averaged 16.3 μg kg^-1 from 476-cm depth up to 351-cm depth. This average mercury content is considered as its geochemical base level in the bay. From 351-cm depth up to 181-cm depth, mercury content in the sediment ranged from 16.6 to 20.1 μg kg^-1 and averaged 18.4 μg kg^-1. The fluctuations in mercury content in this period might be related to climate change. Mercury content in the sediment slowly increased from 16.9 μg kg^-1 at 181-cm depth to 22.8 μg kg^-1 at 38-cm depth, which is supposed to be related to anthropogenic activities. Afterwards, mercury content in the sediment rapidly increased from 22.8 μg kg^-1 at 38-cm depth to 35.1 μg kg^-1 at 21-cm depth and fluctuated between 33.4 and 35.5 μg kg^-1 from 21-cm depth up to 9-cm depth. This rapid and high mercury enrichment and accumulation in the sediment is connected to the intensive anthropogenic activities around the bay. Subsequently, mercury content in the sediment decreased to 26.3 μg kg^-1 at 5-cm depth and then increased to 29.0 μg kg^-1 at the depth of 0-1 cm. Therefore, the mercury concentration profile in the 476-cm sediment core records the anthropogenic mercury pollution history in the Bohai Sea and can be used to estimate anthropogenic mercury mass and accumulation flux in the sediment.

This study was funded by the National Natural Science Foundation of China (42277366).  

How to cite: Lin, C., Ouyang, W., He, M., Liu, X., and Wang, J.: Vertical concentration profile of mercury in a 476-cm sediment core from the Bohai Sea: Inferring anthropogenic influence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20063, https://doi.org/10.5194/egusphere-egu24-20063, 2024.

The abandonment of industrial waste frequently leads to acid drainage affecting groundwater and severely impacting the environment or urban infrastructure. The severe impacts of the acid drainage are related, besides the extremely low pH reached in the affected waters, to the subsequent mobilization and spread of toxic heavy metals such as As, Fe, Cu, Cd, Ni, Pb, and Zn in highly oxidizing environments. The hydrogeology and hydrochemistry of an urban area in Al-Mozara (Zaragoza, Spain), built over an old industrial zone with pyrite roasting waste deposits that experienced acid drainage problems, has been investigated and modelled. Drilling and piezometer construction, and groundwater samples taken during the activities of the SAGE4CAN project, revealed the existence of a perched aquifer within old sulfide mill tailings, where the building basements interrupted the groundwater flow leading to a water stagnation zone that reached extreme acidity values (pH < 2), by drastically increasing the reaction times. A groundwater flow reactive transport model was developed with the software PHAST to reproduce flow and groundwater chemistry, to be used as a predictive tool for guiding and selecting the optimal remediation actions. The model reproduced the measured groundwater chemistry by simulating the kinetically controlled pyrite and portlandite dissolution. Further, the model predicts that an extreme acidity front (pH < 2), coincident with the Fe (III) pyrite oxidation mechanism taking dominance, is propagating by 30 m/year. The incomplete dissolution of residual pyrite (up to 18 % dissolved by the end of the simulations) predicted by the model indicates that the acid drainage in this aquifer is limited by the flow regime rather than by sulfide availability. The construction of additional water collectors between the recharge source and the stagnation zone has been proposed, together with periodical pumping out of acid water from the stagnation zone. The study findings are expected to serve as a useful background for the assessment of acid drainage and remediation techniques in urban areas by numerical modelling, since urbanization of old industrial land is rapidly increasing worldwide. 

How to cite: Jiménez, J., Marazuela, M. Á., Baquedano, C., Martínez-León, J., Sanchez Navarro, J. Á., Cruz-Pérez, N., Santamarta, J. C., and García-Gil, A.: Reactive transport model of an extreme acidic perched aquifer within roasted pyrite waste in a fully urbanized area (Zaragoza, Spain) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20228, https://doi.org/10.5194/egusphere-egu24-20228, 2024.

Quercus ilex is a vascular plant, a tree of large size, which is one of the most common species present in central Spain. Almadén (Ciudad Real province, South-central Spain) is the centre of a mining area active since prehistoric times, particularly for mercury, but also for others potentially toxic elements (PTEs: Pb, Zn, Ag, Cu), and in this area the Q. ilex constitutes woods, as well as the so called ‘dehesas’, a characteristic landscape with these trees scattered with variable density in pasture areas.

In this work we have sampled and analysed Hg and other PTEs (data not shown here) in the leaves from a wide area, of some 2,300 Km², located around the Almadén mine and site. A total of 88 samples were taken, prepared, and analysed, using the Atomic Absorption Spectrometry with Zeeman effect combined with a process pyrolisation, with a LUMEX RA-915 series equipment.

The area corresponds to the southernmost Central Iberian Zone of the Iberian Hesperian Massif, characterized by Palaeozoic and Pre-Palaeozoic substrates. In particular, the samples are distributed in three geological subdomains: the Almadén syncline in the north, the Alcudia anticline in the centre and the Guadalmez syncline in the south. Siliciclastic Paleozoic detrital rocks are in the majority in both synclines, while the pre-Paleozoic rocks of the Alcudia anticline are mainly dominated by schists and greywackes. 

Mercury uptake by plants occur through their leaves, and it accumulates in these, as proven empirically and experimentally. Besides, the presence of Hg in the atmosphere depends on the eventual presence of discrete sources, such as mines or dumps, or on the Hg emissions from contaminated soils.

Our results show that Hg concentrations in Q. ilex leaves are conditioned by the presence of discrete sources in the Almadén syncline (the Hg mines present in this region), with a mean value of 197 ng/g ± 169, reaching even 1,000 ng/g in areas close to the main sources of atmospheric Hg. On the other hand, in the Alcudia Valley (99 ng/g ± 170) and the Guadalmez syncline (64 ng/g ± 192) the concentrations are lower and show a certain variability that may be related to the possible presence of the element in the soil in the form of anthropogenic contamination, as this research team has demonstrated in recent scientific publications.

How to cite: Barquero Peralbo, J. I., Esbrí Víctor, J. M., Ntutumu, D. M., Minang, C. M., Lorenzo Álvarez, S., González Valoys, A. C., and Higueras, P.: Regional distribution of mercury in the leaves of Quercus ilex in the Almadén area (Spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20759, https://doi.org/10.5194/egusphere-egu24-20759, 2024.

Four jellyfish species, ctenophoran Mnemiopsis leidyi and scyphozoan Cotylorhiza tuberculata, Chrysoara hysoscella and Rhizostoma pulmo were collected in summer of 2017 in the Gulf of Trieste (northern Adriatic Sea) and analysed for Hg and other metal(loid)s to assess their bioaccumulation and biomonitoring potential. No significant differences in Hg levels (0.06-0.22 µg/g dry mass) were observed between the studied species but all significantly concentrated Hg well above the dissolved Hg seawater levels (5 ng/L) of the gulf. The studied species have diverse diets consisting primarily of various plankton groups. C. hysoscella feeds mainly on mesozooplankton (>200 µm) R. pulmo and C. tuberculata mostly consume microzooplankton (50-200 µm) while M. leidyi preys on various organism (and particles) in the water column. In addition, C. tuberculata harbours autotrophic endosymbionts (microalgae). Considering their feeding behaviour, it appears that studied jellyfish species do not bioaccumulate Hg, nor other metal(loid)s, along the pelagic food web. Hence, the Hg levels in jellyfish are probably the consequence of the dissolved metal (passive and active) uptake. Moreover, the methodological approach analysing the jellyfish freeze-dried samples containing salt can distort the real picture and the Hg/C_org. ratio could better describe the metal level in the gelatinous organism. However, considering the high Hg bioconcentration factor (log BCF >5), jellyfish can be used aa a useful bioindicator for Hg, and other metal(loid)s, dissolved in seawater.     

Keywords: Jellyfish, coastal waters, mercury, bioconcentration, contamination, bioindicator

How to cite: Faganeli, J., Tjasa, K., Darja, M., Alenka, M., and Ingrid, F.: Mercury in the coastal pelagic food web: phytoplankton, zooplankton and jellyfish, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22463, https://doi.org/10.5194/egusphere-egu24-22463, 2024.

Identifying the impurities that promote the selection of specific twin laws of gypsum has relevant implications for the geological studies aimed at interpreting the gypsum depositional environments both in ancient and modern deposits, and overall, on Mars surface, where “swallowtail” gypsum twin habit has been recently observed. However, because of the limited knowledge of morphological, crystallographic, and optical characteristics of the five twin laws of gypsum, relatively little has been done to understand which impurities exert a critical role in the selection of different twin laws and how this may impact our awareness about their occurrence in nature. Typically, the 100-contact twin law has been the only twin law of gypsum known so far in nature. However, some sedimentological-stratigraphic studies suggested this might not be the only widespread one. In this work, we firstly provide a geometric-crystallographic background of the five twin laws of gypsum, allowing researchers to recognize the twin laws only by the measurement of i) their re-entrant angle value and ii) the extinction angle formed between the two individuals using crossed polarizers in optical microscopy. Moreover, we show specific crystal growth laboratory experiments designed to improve our understanding of different habits and twin laws of gypsum occurring with and without the addition of carbonate ions in solution. The main results suggest that the different orientation of primary fluid inclusions with respect to the twin plane, and the main elongation of the sub-crystals making the twin, are a useful tool to distinguish between 100 and -101 twin laws, whose geometry is otherwise very hard to distinguish, especially in rock samples. Moreover, gypsum twins obtained by crystal growth laboratory experiments are compared with those detected in natural environments and the occurrence of the -101 twin law is suggested occurring in evaporitic-sedimentary environments. These results provide new insights into the mineralogical implications of twinned gypsum crystals and their potential use as a tool for a deeper comprehension of the natural gypsum deposits.

How to cite: Cotellucci, A., Otálora, F., Canals, À., Criado-Reyes, J., Pellegrino, L., Bruno, M., Aquilano, D., Garcia-Ruiz, J. M., Dela Pierre, F., and Pastero, L.: New insights on gypsum twinned crystals: mineralogical implications for natural gypsum deposits, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-176, https://doi.org/10.5194/egusphere-egu24-176, 2024.

When exposed to high-temperature conditions (~1670°C), zircon crystals (ZrSiO₄) decompose according to the reaction: ZrSiO₄→ZrO₂+SiO₂ [2,8]. Under optical and electron microscopes, decomposed zircons are easily identified by the presence of bright rims of baddeleyite (ZrO₂) surrounding the unaltered primary crystal core (ZrSiO₄). Due to the high temperatures needed for this reaction to occur (i.e., exceeding the highest temperatures normally reached by magmatic processes or wildfires on the Earth’s surface), finding decomposed zircons in natural glass has become a handy unequivocal way to relate natural glass to extreme processes like meteoritical impacts [1], airbursts [6], or lightning [3]. If recognizing fulgurites (i.e., products of lightning) is more easily done because of their morphology, the identification of impact glasses can be problematic, especially when they are not associated with a known impact crater. This work aims to demonstrate the reliability of zircon decomposition as a geothermometer, used to identify impact (or airbursts) glasses.

Through high-temperature experiments, we show that the decomposition of zircons can occur in natural systems at lower temperatures than the ones predicted by models. At T=900-1000°C (P=1 bar, exposed to air), in the presence of Ca-sulfates and NaCl-rich soil called ‘caliche’ (from the Atacama Desert, chosen for its relation with one of the most recent debated case, that of Pica glass – [4,5,6,7]), zircons decomposed forming the typical bright rims. Using FEG-SEM-EDS, Raman spectroscopy, and TEM (on thin foils prepared using FIB), however, we show that the Zr-rich rim mineralogy in our experiments differs from previous petrographic descriptions, with assemblages of baddeleyite, baddeleyite + Ca-Zr-oxide, or only Ca-Zr-oxide.

In conclusion, we demonstrate that decomposed zircons could also result from lower temperature processes than impacts or airbursts and should be used more carefully in assessing the origin of glasses. Also, we suggest that a more detailed mineralogical characterization of decomposed zircons (rarely done after their detection) is needed to correctly assess the formation conditions of samples containing such rims.  

References

[1] El Goresy A., 1965. Baddeleyite and its significance in impact glasses. Journal of Geophysical Research, 70:3453-3456.

[2] Kaiser A., et al., 2008. Thermal stability of zircon (ZrSiO4). Journal of the European Ceramic Society, 28:2199-2211.

[3] Kenny G.G. and Pasek M.A., 2021. The response of zircon to the extreme pressures and temperatures of a lightning strike. Scientific Reports, 11:1560.

[4] Roperch P., et al., 2017. Surface vitrification caused by natural fires in Late Pleistocene wetlands of the Atacama Desert. Earth and Planetary Science Letters, 469:15-26.

[5] Roperch P., et al., 2022. Widespread glasses generated by cometary fireballs during the late Pleistocene in the Atacama Desert, Chile: COMMENT. Geology, 50.5:e550.

[6] Schultz P.H., et al., 2022. Widespread glasses generated by cometary fireballs during the late Pleistocene in the Atacama Desert, Chile. Geology, 50.2:205-209.

[7] Schultz P.H., et al., 2022. Widespread glasses generated by cometary fireballs during the late Pleistocene in the Atacama Desert, Chile: REPLY. Geology, 50:e551.

[8] Timms N.E., et al., 2017. A pressure-temperature phase diagram for zircon at extreme conditions. Earth-Science Reviews, 165:185-202.

How to cite: Musolino, A., Devouard, B., Rochette, P., Roperch, P., Zanetta, P.-M., Seydoux-Guillaume, A.-M., Ferry, D., and Campos, A.: Decomposed zircons: A reliable geothermometer to identify impact and airburst glasses?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-565, https://doi.org/10.5194/egusphere-egu24-565, 2024.

The Karkonosze granite (~320–312 Ma) is interpreted as a syn-collisional to magmatic arc intrusion. It is known for distinct symptoms of post-magmatic activity, including formation of intragranitic pegmatites observed in Szklarska Poręba quarry with overprinted W–Sn–Mo–Bi hydrothermal mineralization (e.g., Kozłowski et al., 1978; Pieczka & Gołębiowska, 2012).

Tin mineralization in the granite quarry at Szklarska Poreba is represented by cassiterite (Karwowski et al., 1972), Sn-rich titanite, malayaite, stokesite, and rare tin sorosilicates – kristiansenite, kozłowskiite and silesiaite (Evans et al., 2008;  Pieczka et al., 2022, 2023) The presence of all the above-mentioned mineral phases was confirmed by chemical microanalysis using the electron probe microanalyzer JEOL SuperProbe JXA-8230 and structure refinement. Cassiterite was recognized in an association mainly with scheelite, molybdenite, wolframite, chalcopyrite, and pyrite. These minerals crystallized from high-temperature aqueous fluids, subsequently followed by sulphide-rich stage (Karwowski et al., 1973). Sn-rich titanite, forming an isomorphic series with malayaite, CaTi[SiO₄]O–CaSn[SiO₄]O, shows chemical heterogeneity, with a maximum SnO₂ content up to 15.88 wt% (32 mol% Sn end-member), and elevated Nb₂O₅ (up to 9.85 wt%), Ta₂O₅ (up to 7.88 wt%), and Sc₂O₃ (up to 1.90 wt%). Malayaite is close to the pure Sn end-member, it contains up to 97 mol% Sn end-member with minor Fe, Nb, Ta contents. Stokesite, CaSnSi₃O₉·2H₂O, occurs as a rim grown around the outermost parts of Sn-rich titanite crystals, veinlets cutting cassiterite, and in direct contact with fluorite. Its crystals were also observed on surfaces or within fractures in bismuthinite.

The initial source of Sn was related to the final stage of pneumatolytic processes, in the granitic complex with successive development during hydrothermal activity. Fluid inclusion studies indicate that cassiterite crystalized at temperatures of 515–470ºC (Kozłowski et al., 2002).

The precipitation of Sn-rich titanite was likely initiated under elevated metal activities at slightly lower temperatures and high oxygen fugacity.

Stokesite, representing the final stage of the Sn assemblage, slowly crystallized in free spaces, was found in a direct contact with fluorite, which homogenization temperature in the Szklarska Poręba assemblage was estimated at 159-172 ^oC (Kozłowski & Matyszczak, 2022). Therefore, stokesite and fluorite may have formed during the same stage of hydrothermal processes. Since no alterations had been observed on the cassiterite grains, a secondary source of tin for later Sn-rich minerals was excluded.

How to cite: Mil, K., Gołębiowska, B., Włodek, A., and Pieczka, A.: Tin mineralization in post-magmatic processes: a case of post-magmatic activity in the Szklarska Poręba Huta quarry, Lower Silesia, SW Poland , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-764, https://doi.org/10.5194/egusphere-egu24-764, 2024.

The volcanic landscapes of Iceland's Westfjords are marked by the intriguing presence of Plagioclase Ultraphyric Basalts (PUBs), distinctive lava formations that are a focal point of this research. Characterized by plagioclase contents so high (up to 50-60%) that they approach the crystallinity of a crystal mush, these formations offer a unique opportunity to explore the extreme end of lava crystallinity and the influence of abundant large plagioclase crystals on lava viscosity and flow. The main aim of this research is to understand how the abundance of large plagioclase crystals influences the viscosity and flow of lavas at the extreme end of lava crystallinity, as well as better understand the origin of the crystal cargo. The interplay between the crystals and the magma is crucial for better understanding the origins and flow characteristics of these volcanic formations. This is achieved through an interdisciplinary approach, combining petrographical and geochemical analyses, including Inductively Coupled Plasma (ICP) for major element trace element analysis, with Anisotropy of Magnetic Susceptibility (AMS) to determine the flow direction within the lava. This comprehensive method provides insights into the crystallization conditions of magmas and minerals, as well as the textural and compositional characteristics of the plagioclase crystals. The outcomes of this research are not only crucial for understanding the unique aspects of the Westfjords’ volcanic regions but also have significant implications for predicting volcanic hazards and refining magma dynamics models, thereby enhancing our ability to mitigate the impacts of volcanic activity.

How to cite: Jones, P., Caracciolo, A., Marshall, E. W., and Piispa, E. J.: Understanding the flow dynamics of a Plagioclase Ultraphyric Basalt- a case study from the Westfjords, Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1209, https://doi.org/10.5194/egusphere-egu24-1209, 2024.

The study of iron-magnesium silicates within rocky planetary interiors has been a cornerstone of mineralogy, petrology and planetary science, offering insights into the composition and evolution of celestial bodies. The talk will present an exploration of the current understanding of these silicates and critically examines the question: Have we truly discovered them all?

Recent advancements in analytical techniques, including high-pressure experiments and computations, have challenged conventional assumptions about the ubiquity and diversity of iron-magnesium silicates. During the talk, key discoveries on Earth, Mars, and other celestial bodies will be reviewed revealing unexpected mineralogical variations and prompting a reevaluation of existing models.

How to cite: Bindi, L.: Iron-magnesium silicates in rocky planetary interiors: Have we really discovered them all?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1725, https://doi.org/10.5194/egusphere-egu24-1725, 2024.

Rare earth elements (REE) are essential in many green, modern technologies and play a critical role in a more sustainable future [1]. However, there is a substantial risk to their supply as the availability of REE deposits with minable concentrations are limited [2]. A better understanding of the mechanisms controlling REE concentration in minerals would have applications in more efficient practices as well as REE separation techniques and recycling.

Our study investigated the reaction of multi-component REE (La, Ce, Pr, Nd, and Dy) aqueous solutions with carbonate grains of dolomite, aragonite and calcite at hydrothermal conditions (21-210 °C). Two different solutions were prepared (i) a solution with equal concentrations of each of the five REE: (ii) a solution with the concentrations of the five REEs normalized to a Post Archean Shale standard (PAAS), to mimic the rare earth element concentrations in continental crust and natural fluids.

The interaction between the REE bearing fluids with each of the carbonate grains resulted in the replacement of the host carbonate grain with a series of REE minerals following a complex crystallization sequence (lanthanite → kozoite → bastnasite → cerianite). We have found that for most of the experiments at 165 °C, when using the equal concentration solutions, the crystallization of kozoite was promoted and the REE ratio in the newly formed solids was similar to the REE ratio in solution. In contrast, when PAAS solutions were used, REE-bearing crystals were zoned or had a heterogenous distribution of REEs, often coupled with the formation of discreet REE phases (e.g., cerianite). In addition, chemical signatures indicating the presence of metastable REE-bearing phases that transformed to more thermodynamically stable polymorphs were found in multiple samples as well as symplectite textures formed by the reaction of adjacent phases. Overall, our experiments demonstrate that the polymorph selection, crystallization pathway, the kinetics of mineral formation and the chemical texture of the newly formed rock during the mineral-fluid interaction process are dependent on the REE concentrations in solution, their ionic radii, temperature, time, and solubility of the host grains.

References

[1] Sinding-Larsen, R., Wellmer, F.W.,. Non-renewable resource issues: Geoscientific and societal challenges, Non-Renewable Resource Issues: Geoscientific and Societal Challenges 2012.

[2] Jordens, A., Cheng, Y.P., Waters, K.E.,. A review of the beneficiation of rare earth element bearing minerals. Miner. 2013 Eng. 41, 97-114.

How to cite: Maddin, M., Rateau, R., Szucs, A. M., Terribli, L., and Rodriguez-Blanco, J. D.: Complex Multi-Stage Replacement Reactions in the REE-CaCO3 System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2001, https://doi.org/10.5194/egusphere-egu24-2001, 2024.

Charnockite is an orthopyroxene-bearing felsic rock and an important constituent of the deep crust, thus, it holds significant importance in uncovering crustal growth and differentiation mechanisms. However, its generation and preservation remain debated. By focusing on mineral records, we here aim to provide a more detailed understanding of these issues. The Gaozhou charnockite in the Yunkai terrane of South China was chosen for extensive mineralogical studies and thermodynamic modeling. The Gaozhou charnockite contains granulitic enclaves, and mineral assemblages within charnockite can be divided into three phases, with the peak phase mainly composed of orthopyroxene, and minor biotite. Meanwhile, the charnockite and enclaves show comparable compositions of biotite and orthopyroxene. Embayed textures and high TiO₂ content in biotite grains suggest high-temperature anatexis. On the other hand, the orthopyroxenes with inclusions and high Al₂O₃ content indicate peritectic origin. Moreover, reaction intergrowths of biotite with orthopyroxene grains have also been observed, suggesting that these grains were generated by the consumption of biotite. The Gaozhou charnockite has much lower zircon water content (135 ppm, median) as compared to that of the contemporary Opx-free granites (202-643 ppm, medians) in the Yunkai terrane, indicating dry primary parental melts. In addition, phase equilibria modeling constraints peak anatexis conditions at 860-870 ℃/6.2-7.0 kbar. Peritectic orthopyroxenes must have been generated by the incongruent melting of biotite under high-temperature granulitic facies in the lower crust. Subsequently, these grains were entrained and migrated by low water content melts to the upper crust. Therefore, overall observations favor a model of selective entrainment of source materials at a low magma water environment for the generation of the Gaozhou charnockite.

How to cite: yang, H. and Yao, J.: Generation of the charnockite by residua entrainment in water-deficient melts: insights from minerals composition and H2O-in-zircon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2231, https://doi.org/10.5194/egusphere-egu24-2231, 2024.

Quartz, the most common mineral constituent of the Earth’s continental crust, undergoes the displacive α-β transformation at pressures and temperatures of the lower crustal conditions. This transition is associated with important variations in the thermodynamic properties (such as thermal expansion and isothermal bulk modulus) and is therefore thought to cause important seismic velocity contrasts that are distinguished by seismic tomography. The α-β transition is characterized by a non-linear increase in volume with temperature and an abrupt variation in bulk modulus, which, at the transition, drops from about 70 GPa to nearly zero within 10-15 K. Although well-known at room pressure, the behavior of quartz across the transition at high pressure, i.e., at Earth-relevant conditions, remains largely unexplored.

In this work, we have characterized this transition at high P-T conditions by means of X-ray diffraction and acoustic measurements. The experiments were performed at the European Synchrotron Radiation Facility (ESRF, beamline ID06) using a multi anvil press up to 3 GPa and 1400 °C. The measured velocities show a strong decrease of V_p toward the phase transition, followed by a steep increase in the β-field, reaching values higher than those in the α-field. In our data, this increase is not as large as that predicted by thermodynamic models using the known elastic properties of quartz (e.g., Abers and Hacker 2016). As anticipated, V_s is rather constant throughout the transition, resulting in major variations in the V_p/V_s ratio. The unit cell volume was calculated from the collected diffraction patterns. Contrary to the well-documented negative thermal expansion of quartz in the β-field at room pressure, the unit cell volumes obtained at high-pressure show a slight continuous volume increase during heating after the phase transition.

In conclusion, we document here that the behaviour of quartz across the α-β transition at high P-T is different from what has been previously predicted, which is likely a consequence of the poor knowledge of β-quartz thermo-elastic properties at high P-T. This could affect the interpretation of seismic data in the deep crust, which is currently based on extrapolations of the room-pressure behavior of the α-β quartz transition.

How to cite: Mingardi, G., Gasc, J., Ardit, M., Alvaro, M., and Schubnel, A.: What can we learn from X-ray diffraction and seismic velocities across the alpha-beta quartz transition at lower crust conditions? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2301, https://doi.org/10.5194/egusphere-egu24-2301, 2024.

In order to explore the favorable reservoir characteristics and diagenetic evolution laws of the Cretaceous Kukebai Formation in the Kekeya area of the southwestern Tarim Basin, and provide theoretical basis for oil and gas exploration and development in the study area, comprehensive data such as core, cast thin sections, and carbon and oxygen isotopes were used to carry out the classification of diagenetic facies types and the study of diagenetic evolution models. The results indicate that the reservoir of the Kukebai Formation in the study area is mainly composed of feldspar lithic sandstone and lithic feldspar sandstone, with mainly developed diagenetic processes such as compaction, cementation, and dissolution. The diagenetic stage is in the middle diagenetic stage A. The Kukebai Formation reservoir mainly develops four types of diagenetic facies: moderately compacted dissolution facies, moderately compacted cementation facies, strongly compacted compaction facies, and strongly cemented facies. Among them, the strong compacted phase becomes a dense reservoir due to mechanical compaction in the early stage of diagenesis, and is mainly distributed in the sand mud interbedded layers of sedimentary microfacies between river channels and estuarine dams; The strongly cemented phase is densified in the early diagenetic stage due to the precipitation of a large amount of carbonate cement, mainly developed in the sand mud interbedded layers near the mud end of underwater distributary channels and the sedimentary microfacies of estuarine dams; The dissolution effect of medium compacted dissolution phase sandstone is strong, and the reservoir properties are the best, mostly appearing in the upper part of distributary channel sand bodies with strong sedimentation and water accumulation dynamics; The medium compacted and cemented sandstone has moderate compaction, and the reservoir properties are relatively good. It mainly develops in the lower part of distributary channel sand bodies with strong hydrodynamics. There are two types of favorable reservoirs in the study area, namely the medium compacted cementation phase and the medium compacted dissolution phase sandstone.

How to cite: Wang, H. and Zhang, L.: Reservoir characteristics and diagenetic evolution of Kukebai Formation in Kekeya area, Southwest Depression of Tarim Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2730, https://doi.org/10.5194/egusphere-egu24-2730, 2024.

Serpentines are among the most abundant hydrous minerals in oceanic lithospheres formed by hydrothermal alteration of ultramafic mantle rocks (i.e. peridotites). Antigorite – the high temperature and pressure variety of serpentine – is considered to be the dominant water carrier within down-going oceanic slabs. The successive dehydration of antigorite during subduction of partially serpentinized oceanic lithospheres is strongly associated with the water cycle in the upper mantle and is expected to play an important role in the generation of arc magmatism (Ulmer & Trommsdorff, 1995; Schmidt & Poli, 1998), and influence rheological properties of oceanic slabs by processes such as dehydration embrittlement which is thought to trigger intermediate-to-deep focus earthquakes (Jung et al., 2004; Ferrand et al., 2017).

Antigorite is a hydrous phyllosilicate known for its polysomatism: The number of SiO₄ tetrahedra m along its a-cell periodicity. Previous electron microscopy studies reported the existence of antigorite within a wide range of m values (~13-23) depending on the pressure (P) and temperature (T) conditions (Mellini et al., 1987; Wunder et al., 2001). However, there is a lack of the combined structural and thermodynamic evidence about the stability of the different antigorite polysomes along the P,T-paths of subducting oceanic lithospheres.

We use a theoretical mineral physics approach based on first principles density functional theory calculations to quantify the phase diagrams of the terminal dehydration reactions of antigorite with different m-values between 13-19 under subarc depth P,T conditions. Our results elucidate the significance of the compositional variations of antigorite on the dehydration of serpentinized oceanic slabs during the progressive stages of subduction.

How to cite: Ritterbex, S. and Plümper, O.: First principles investigation of the effect of compositional variations on the terminal breakdown of antigorite in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2878, https://doi.org/10.5194/egusphere-egu24-2878, 2024.

In November 2023, the European Union reached a provisional agreement on an European Critical Raw Materials Act, which encourages the local production, processing, and recycling of critical elements, notably the rare earth elements (REE). While indispensable for the green energy transition, their production is notoriously environmentally damaging, and efforts are being made to reduce this environmental footprint, for example via the use of secondary REE sources from waste or by the application of green chemistry and circular economy principles.

In this study, we investigated the potential of hen eggshell calcite waste to be recycled for the uptake of REE from industrial and waste streams. We interacted commercial eggshells with 50 mM multi-REE (La, Nd, Dy) solutions at 25 to 205 °C between three hours and three months. The resulting products were characterized by powder XRD and Rietveld refinement for quantitative phase identification; SEM electron imaging for structural characterization; SEM energy dispersive spectroscopy for elemental mapping and quantification of major and minor elements; and laser ablation ICP-MS for trace element mapping.

We observe a pervasive diffusion of the REE inside the eggshell calcite, along pathways formed by the intracrystalline organic matrix and calcite crystal boundaries, and without any partitioning of La, Nd and Dy. At 90 °C, calcite is observed dissolving and being replaced by kozoite spherulites, reminiscent of natural kozoite crystals. At 165 °C and 205 °C, an interface coupled dissolution-precipitation mechanism is observed, resulting in the complete dissolution of the calcite and its pseudomorphic replacement by polycrystalline kozoite. At 205 °C, kozoite itself is slowly replaced by hydroxylbastnäsite, the stable form of rare earth hydroxycarbonate, following a crystallization pathway previously established with inorganic calcite. Minor REE zoning at the eggshell grain scale is also observed, hinting at a potential use for REE separation.

Our results demonstrate two potential applications of eggshell waste for the sustainable recovery of REE from aqueous solutions: at low temperatures, as a mixed organic-inorganic adsorbent and absorbent; and at higher temperatures as an efficient sacrificial template for the precipitation of rare earth hydroxycarbonates.

How to cite: Rateau, R., Drost, K., Maddin, M., Szucs, A., Terribili, L., Guyett, P., and Rodriguez-Blanco, J. D.: Sustainable recovery of rare earth elements with eggshell waste calcite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2915, https://doi.org/10.5194/egusphere-egu24-2915, 2024.

The interactions between clay minerals and organic matter, specifically adsorption, are widely recognized as a crucial mechanism for promoting the preservation of organic matter within sedimentary environments. This paper discusses the genesis and adsorption of clay minerals, especially their influence on the process of organic matter enrichment in sedimentary environments. The composition of clay minerals found in sediments serves as an indicator of both the climatic and lithological characteristics of the provenance area. Smectite formation is favored in mafic provenance, while the coexistence of illite and chlorite suggests cold and arid conditions. Additionally, an abundance of kaolinite indicates intense chemical weathering of the provenance area. The physical and chemical properties of clay minerals and organic matter significantly influence adsorption. Smectite is thought to adsorb more organic matter due to its greater surface area. Selective adsorption of high molecular weight, aromatic, and aliphatic compounds dissolved organic matter onto mineral surfaces may have played a role in kerogen formation. Moreover, the preservation of organic matter via clay mineral adsorption is intricately linked to the sedimentary environment. Disparities in nutrient elements during the clay minerals synsedimentary period can impact biological productivity. Furthermore, the pH and solution metal ions of the water column influence the quantity and type of organic matter adsorbed. The contribution of adsorption to organic matter preservation is influenced by redox conditions, and this contribution can be observed through density separations. Additionally, we present several recommendations for future research. Firstly, diagenesis alters the clay mineral assemblage in sedimentary rocks. However, it may be possible to reconstruct the clay mineral assemblage based on morphological, mineralogical, and chemical composition characteristics. Secondly, studies have indicated that clay minerals can facilitate the precipitation of carbonate minerals, providing insights into the formation of abiotic carbonate minerals. Finally, the practical applications of clay minerals in shale oil and gas exploration are underscored, such as their ability to predict sweet-spot areas and control reservoir properties.

How to cite: Zhao, T., Xu, S., and Gou, Q.: Differential adsorption of clay minerals: Implications for organic matter enrichment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3030, https://doi.org/10.5194/egusphere-egu24-3030, 2024.

Upon heating, the glass transition is a temperature interval over which an unrelaxed glass transforms to a supercooled liquid relaxed on the experimental time scale. The term standard glass transition temperature (T_g) refers to the temperature at which the viscosity is 10¹² Pa s [1]. One of the many reasons why T_gis important in geosciences is that it successfully parametrizes models of silicate melt viscosity over the temperature range of magmatic systems [2]. The pressure-dependence of T_g of a given silicate glass/melt is thus a crucial parameter that can provide insights into the viscosity of the corresponding natural silicate liquid in the Earth’s mantle. Although the detection of the glass transition at 1 atm is relatively straightforward, high-pressure measurements present challenges mainly because of the miniscule sample volume available for probing. As a consequence, previous high-pressure measurements of T_g in silicate glasses/melts were carried out in large-volume devices at P < 2-3 GPa [3,4], drastically losing the sensitivity to detect glass transition at higher pressures. The emerging picture is that in silicates systems the pressure-dependence of T_g is governed by the glass/melt structure, specifically the number of non-bridging oxygens (NBO) per tetrahedron (TET). Apparently, the T_g of polymerized glasses (NBO/TET < 1) decreases with pressure, while the T_g of depolymerized glasses (NBO/TET > 2) increases with pressure [3,4]. One unanswered question is how these trends are affected by pressure-induced structural changes in the glass, such as the rearrangement of the TET network or the increase in Si and Al coordination by O (i.e., progressive decrease of TET associated with the increase of higher coordination polyhedra). Extending the pressure range of T_g measurements to P > 2-3 GPa is needed to address this question. Yet, to the best of our knowledge, no successful attempt has been made to constrain glass transition temperatures in silicate systems in a diamond anvil cell device. At EGU 2024, we will report on ongoing time-controlled optical experiments in laser-heated diamond anvil cells which reveal spectroscopic discontinuities in Fe-bearing basaltic glasses over the glass transition. We will attempt to link these discontinuities to T_g in order to model the viscosity of basaltic melts at mantle P-T.

References

[1]        B. Mysen and P. Richet, Silicate Glasses and Melts (Elsevier, 2019).

[2]        M. Cassetta, D. Di Genova, M. Zanatta, T. B. Ballaran, A. Kurnosov, M. Giarola, and G. Mariotto, Sci. Rep. 11, 13072 (2021).

[3]        M. Rosenhauer, C. M. Scarfe, and M. Virgo, Carnegie Inst. Wash. Yearb. 78, 556 (1979).

[4]        N. S. Bagdassarov, J. Maumus, B. Poe, A. B. Slutskiy, and V. K. Bulatov, Phys. Chem. Glasses 45, 197 (2004).

How to cite: Lobanov, S. S. and Speziale, S.: Optical probing of glass transition at high pressure allows whole-mantle silicate melt viscosity models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3365, https://doi.org/10.5194/egusphere-egu24-3365, 2024.

Concrete is one of the most sought-after materials in our time, second only to water in importance to developed and emerging nations alike. It has been a crucial component of major infrastructure projects for thousands of years. In the year 2022 alone, China, the largest producer of concrete, manufactured approximately 2.1 million metric tons of cement, a key ingredient in modern concrete formulations. Various concrete mixes, tailored for specific applications, have been perfected and are widely used in the industry. In broad terms, concrete consists of about three-fifths sand and rock fragments (aggregates), one-fifth cement, and one-fifth water. This combination makes it the world's most widely used building material, particularly for large structures which are reinforced with steel rods. Aggregates can be sourced from crushed rock or naturally occurring sand and gravel, but the type of aggregate used significantly influences the overall properties and robustness of the final product. The mineralogical composition of the rock itself is closely related to the quality and resilience of the concrete. Understanding the mineralogy and chemistry of the lithotypes used allows for predicting their interaction with other concrete constituents, preventing undesirable chemical reactions. Such reactions can compromise the safety and resilience of the finished product, and ultimately prevent the use of materials that would otherwise perform poorly. Among the many concrete pathologies that may arise from the use of inadequate raw materials, internal sulfate attack (ISA) mainly occurs when sulfide-bearing aggregates are used. This leads to complex chemical reactions resulting in the oxidation of sulfide phases and the release of sulfur into the cement paste. Consequently, severe cracking and internal swelling significantly compromise concrete integrity. The European standard (EN 12620:2008) is a widely used guideline that recommends a total sulfur content in aggregates not exceeding 1.0 wt.%. This threshold is reduced to 0.1 wt.% when pyrrhotite is detected in the lithotype to be used as an aggregate. Given that pyrrhotite is the second most common sulfide found in nature, it is crucial to identify and quantify the various sulfide minerals that may be present and to understand how they can affect finished concrete structures. The use of automated mineralogy, represented by software systems such as QEMSCAN, emerges as a powerful solution for identifying and quantifying pyrrhotite and any other sulfide phases in aggregates for concrete. It is a scanning electron microscope (SEM)-based system that uses backscattered electron (BSE) image segmentation and simultaneous acquisition of energy-dispersive X-ray (EDS) spectra to classify mineral phases using a pre-defined list of mineral spectra. Preliminary results from QEMSCAN analysis of both thin sections and mounts comprised of ground rock of different grain sizes have been promising. This SEM-based system can analyze whole rock samples and crushed aggregates, providing accurate results over different size intervals. Despite the expected negative correlation between sample grain size and pyrrhotite content, the results vary from 2.71 to 5.59 wt.% for total pyrrhotite content in the analyzed samples. Moreover, when averaged over all grain sizes, these results align with those obtained through traditional optical petrography.

How to cite: Titon, B., Duchesne, J., and Fournier, B.: Use of automated mineralogy for the quantification of pyrrhotite in concrete aggregates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4169, https://doi.org/10.5194/egusphere-egu24-4169, 2024.

Carbonate-rich shale in salt lakes has become a potential target for petroleum exploration. A full understanding of storage space development characteristics is the basis for the efficient development of this kind of shale. In this study, the complex mineral composition and multiple pore structure of a typical carbonate-rich shale from the Paleogene Xin’gouzui Formation in the Jianghan Basin were systematically analyzed. The mixed shale and dolomitic shale were the main lithofacies types in the study area. Both of them were dominated by interparticle (interP) pores. However, their pore sizes are noticeably different. Pores with a size of <100 nm are the main compositions of the mixed shale, with an average volume proportion of 78.24%. Conversely, the dolomitic shale develops mainly micro-sized pores and micro-fractures, with a ratio of 70.46%. The difference in pore structure for different types of shales is closely associated with mineral composition. When particles of different sizes are mixed, most of the interP pores are prone to be filled by fine minerals (e.g., clay), resulting in relatively small pore sizes for the mixed shale. Homogeneous carbonate minerals are favorable for the residual of larger size interP pores. However, recrystallization and secondary enlargement of carbonate minerals can also lead to a significant decrease in pore diameter of interP pores. With these results, a storage space development model for different lithofacies shales was established. This work is crucial to further reveal the reservoir mechanisms and hydrocarbon scales of an argillaceous dolomite reservoir.

How to cite: Gou, Q. and Lu, Y.: Petrography and mineralogy control the nm-μm-scale pore structure of  lacustrine carbonate-rich shales of  China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4492, https://doi.org/10.5194/egusphere-egu24-4492, 2024.

Introduction:  Hydrated silica has been detected from orbit in Jezero crater [Tarnas et al., 2019] and holds great promise for the astrobiology science goals of the M2020 mission and the MSR Program. Early entombment within an hydrated silica matrix has been shown to minimize the molecular degradation of microorganisms during advanced diagenesis [Alleon et al., 2016a,b; Alleon et al., 2018].

On sol 0910, a float rock was automatically selected by the AEGIS system after a rover drive when entering the margin unit from the Jezero delta top. The target is a light-toned partially buried float with lustrous appearance.

LIBS: The chemistry of 9/10 points reveal a homogeneous composition, enriched in SiO₂. The average SiO₂ for these 9 points is 75.0 wt.% while the average total of quantified oxides is 83.5 wt. %.  

VISIR reflectance: The reflectance spectra share an overall blue slope, and exhibit absorptions at 1.9 µm (H₂O), 2.2 µm (X-OH) and 1.4 µm (OH & H₂O). The chemistry derived from LIBS (mean Al₂O₃< 2 wt.%) leads to the attribution of the 2.2 µm band to Si-OH. All such absorptions are present within spectra of terrestrial hydrated silica.

What type of hydrated silica? The reflectance spectra show that this target contains both Si-OH and molecular water. The position of absorption bands departs from what is typically observed for opals and chalcedony is at present the closest spectral analogue in term of band depths and position.

What origin? A 2.2 µm band has been observed in the IR spectra from the fan top and the margin unit, together with carbonate signatures. The LIBS derived chemistry of the targets suggest that this 2.2 band is related to hydrated silica. This suggests that the formation of the hydrated silica is associated with carbonate formation (locally or in the catchment) and that AEGIS_0910A may have the same origin. One possible scenario that is being investigated is that this silica material could represent the precipitates from a fluid that dissolved the ubiquitous olivine found in Jezero floor and delta, and concomitantly precipitated carbonates that are abundant in delta-rocks and the marginal unit ([Calvé et al., LPSC 2024; Wiens et al., LPSC 2024]).

Here, IR spectroscopy reveals that this hydrated silica-rich material is more crystalline that the hydrated silica deposits previously reported on Mars from orbit and in situ at Marias Pass, Gale crater [Pan et al., 2021; Gabriel et al., 2022; Ruff et al., 2011; Rapin et al., 2018].

Summary: Two independent lines of evidence, IR and LIBS, reveal that the float rock analyzed on sol 910 is made of hydrated silica. This target is unique so far in the SuperCam dataset (> 500 targets), but may be linked to high SiO₂ points observed in the carbonate-rich delta bedrock units. Based on IR, this rock seems more akin to a micro-crystalline type silica, in contrast to previous observations of silica from the ground. Such a target may have trapped and preserved biosignatures, together with unique information on the paleoenvironmental conditions of the Jezero crater.

How to cite: Beck, P. and the Supercam and M2020 team members: Multi-spectroscopic detections of hydrated-silica in the Jezero crater   , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4623, https://doi.org/10.5194/egusphere-egu24-4623, 2024.

Greenhouse gases, especially CO₂, have been increasing worldwide. To address this issue, carbon capture and storage (CCS) technology has been researched and developed to decrease atmospheric CO₂ concentrations. Among the various methods studied, mineral carbonation is an emerging technique that involves the reaction between Ca-Mg-Fe bearing basaltic rocks and CO₂ to store it in the rocks through the formation of carbonate minerals. The CarbFix project in Iceland is an example of this method. However, there is still much to learn about the physicochemical relationships between water, dissolved ions, and growing crystals in complex multicomponent systems at the atomic and nanoscale, which are essential for the successful implementation of CCS in basaltic reservoirs.

One of the methods being explored in this study involves the utilization of supercritical CO₂, which is achieved above the critical temperature and pressure of 30.97 °C and 73.773 bar, respectively. Under these conditions, CO₂ exhibits both liquid and gaseous properties. This work shows the results of an experiment conducted in basaltic crystals and basaltic glasses at the temperature and pressure range of 100 and 200 ºC, and 64 to 79 bar, to investigate the reaction between CO_2(sc), water, natural forsterite and basaltic glass, which have demonstrated that under these conditions we have the partial dissolution of the previous mineralogical phases, and the subsequent formation of new alteration phases, but also the precipitation of carbonates with Ca, Mg and Fe. We will compare our results with studies of carbonation of synthetic forsterite.  

How to cite: Pierozzi, A., Rateau, R., Orlando, A., Borrini, D., and Rodriguez Blanco, J. D.: Carbonation experiment of basaltic crystals and glasses using supercritical CO2 under different PT conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4658, https://doi.org/10.5194/egusphere-egu24-4658, 2024.

Fluocerite is a rare earth element (REE) fluoride mineral with chemical formula (REE)F₃. It is found in nature as an accessory mineral in magmatic-hydrothermal REE ore deposits, including alkaline complexes and carbonatites, where is associated with REE fluorocarbonates (i.e. bastnasite, parisite, synchysite), REE-bearing fluorite, cerianite, monazite and xenotime. Due to its relatively scarcity in these deposits, fluocerite kinetics and mechanisms of crystallisation, its role in REE fractionation and as phase for the evolution of magmatic-hydrothermal REE mineralizing systems have not received a lot of attention in the past years. Recently instead, fluocerite is gaining interest as it was suggested to be a precursor phase of bastnasite. Bastnasite is one of the most important minerals for the extraction of REE, indispensable in modern world because of their wide range of hi-tech industry and in clean energy applications. For this reason, illuminating the mechanisms of fluocerite crystallization and its role in the evolution of REE deposits could significantly enhance our understanding of the genesis of REE fluorocarbonates. 
The present study has two main objectives: 1) To study the kinetics and mechanisms of the fluocerite formation at temperatures ranging from ambient to low hydrothermal (up to 200 °C) 2) To demonstrate in situ that fluocerite reacting in the presence of a CO₃-rich solution can transform into REE fluorocarbonates in hydrothermal conditions. 
For the first purpose, fluocerite was synthesized by reacting pure fluorite (CaF₂) powder with REE-bearing solutions at different temperatures. To achieve the second objective, synthetic fluocerite was reacted with Na₂CO₃ solutions at hydrothermal conditions up to 200 °C. Samples of solids were taken at specific time intervals to follow the ongoing of the crystallisation reactions. The nature of crystallising solids, their quantification and growth morphology were determined with a combination of powder X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive microscopy (SEM-EDS).
Our results showed that the fluocerite crystallisation rate decreases proportionally with the REE atomic number and increases with increasing T. The activation energy of crystallisation is similar irrespective of the REE used in the synthesis (~75 KJ/mol) while the activation energy of nucleation increases with the REE atomic number (80 - 96 KJ/mol). All fluocerites reacted with the CO₃-bearing solutions transformed into bastnasite at all temperature, also forming cerianite in the Ce-bearing experiments. 

How to cite: Terribili, L. and Rodriguez-Blanco, J. D.: Mechanistic insights into the fluorite-fluocerite-bastnasite transformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4694, https://doi.org/10.5194/egusphere-egu24-4694, 2024.

Mineral replacement reactions are essential for the understanding of the genesis and chemistry of REE-bearing carbonatite deposits. Many of these reactions involve interaction of Ca-Mg and REE carbonate phases, leading to the formation of minerals with complex compositions and structures.

This study explores the oriented surface precipitation of REE carbonates during the interaction of individual and multiple REE-bearing aqueous solutions with calcite and aragonite (CaCO₃) at low hydrothermal conditions (25-220 °C). This mineral-fluid interaction is translated into a temperature-dependent solvent-mediated surface precipitation and subsequent pseudomorphic mineral replacement of the CaCO₃ seeds by newly formed REE carbonates. This complex replacement sequence includes the crystallisation of metastable kozoite (orthorhombic REECO₃OH) via the formation of individual spindle-shaped crystals following a transient non-random orientation on the surface of the host grains, gradually covering their full surfaces.

Our experiments show that the likelihood of formation of the oriented overgrowth and its stability are controlled by structural constraints which in turn depend on four factors: temperature, ionic radii and ionic potential of the REE in the system, and dissolution rate of the host CaCO₃ minerals. Also, we demonstrate that REE elements can be rapidly immobilized as REE hydroxicarbonates, even at low hydrothermal conditions. An explanation of the epitaxial overgrowth’s configuration and the atomic arrangement of the structures of the CaCO3 polymorphs and REE-kozoite will be discussed. 

[1] Szucs AM et al. Reaction Pathways toward the Formation of Bastnäsite: Replacement of Calcite by Rare Earth Carbonates. Crystal Growth & Design, 2021;21(1):512–527.
[2] Szucs AM et al. Targeted Crystallization of Rare Earth Carbonate Polymorphs at Hydrothermal Conditions via Mineral Replacement Reactions. Global Challenges. 2022;2200085.

How to cite: Rodriguez-Blanco, J., Szucs, A. M., Rateau, R., Maddin, M., and Terribili, L.: Temporal growth of epitaxial layers in the CaCO3-REECO3OH system during mineral replacement processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4776, https://doi.org/10.5194/egusphere-egu24-4776, 2024.

This study delves into the continental organic-rich shale of the Shahejie Formation in the Lijin Sag, Dongying Sag, Bohai Bay Basin, with a focus on exploring the diverse array of methods and approaches utilized to study minerals. By employing an assortment of analytical techniques, including XRD diffraction, scanning electron microscope observation, QEMSCAN scanning, organic matter type detection, TOC testing, and thermal maturity tests, we elucidate the material composition, lithofacies type, and lithofacies combination of the organic-rich shale. Moreover, our investigation incorporates comprehensive imaging logging, core scanning, thin section observation, SEM, CT scanning, FIB-SEM, porosity analysis, nuclear magnetic resonance, high-pressure mercury injection, and gas adsorption to characterize the pores and fractures of shale reservoirs at different scales. The controlling factors influencing the spatial development and evolution of shale reservoirs are thoroughly discussed. In addition, we conducted conventional pyrolysis and multi-temperature pyrolysis experiments to study the shale oil content in different occurrence states. This allowed us to clarify the oil-bearing properties and occurrence characteristics of the shale. Lastly, based on our research findings and the comprehensive evaluation of the oil-bearing capacity and production performance of wells with different productivity in the study area, we not only discuss the law of shale oil enrichment but also establish a model for shale oil enrichment. This study serves as an important contribution to understanding the diversity of methods employed in the study of minerals, particularly in the context of continental organic-rich shale reservoirs. It offers valuable insights for guiding regional shale oil exploration endeavors.

How to cite: Gao, B., Xu, S., Zhang, Z., and Zhao, T.: Exploring the diversity of methods in the study of minerals: a case study on organic-rich shale in the Shahejie Formation, Bohai Bay Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5725, https://doi.org/10.5194/egusphere-egu24-5725, 2024.

Omphacitic clinopyroxenes exhibit widespread occurrence in various geological settings and rock types, making them promising candidates for Raman elastic geothermobarometry applications. Raman elastic geobarometry uses the deformation recorded by mineral inclusions to determine the pressure and temperature conditions under which they were entrapped. Raman scattering, which is highly sensitive to structural deformations, provides valuable insights into the variations in crystal structure that occur due to heating or compression. While several host-inclusion systems have been investigated, clinopyroxene inclusions have not been extensively studied. Therefore, the application of Raman elastic geobarometry to omphacites in different mineral hosts necessitates an accurate calibration of Raman-peak positions against hydrostatic pressure.

Natural omphacite crystals can exhibit cationic ordering associated with crystallization temperature, which affects their elastic behaviour. To address these aspects, we conducted a study on natural ordered (P2/n) and experimentally disordered (C2/c) omphacite crystals from Münchberg Massif (Germany). In situ high-pressure Raman spectroscopy measurements were performed using a diamond anvil cell. As expected, the frequencies of the modes increased with increasing pressure. By examining omphacite crystals with varying degrees of order obtained through isothermal annealing experiments, we observed that progressive cationic disorder primarily led to peak broadening, while changes in Raman peak positions were predominantly influenced by pressure variations.

Additionally, the chemical composition of omphacites influences the Raman-peak positions and their pressure evolution. Therefore, we analysed Fe³⁺-rich omphacites from Lugros and Camarate (Bétic Cordilleras, SE Spain), and Voltri (Italy) along with synthetic iron-free omphacites. This analysis is an initial step towards the chemical calibration of omphacites using Raman spectroscopy.

To gain a deeper understanding of the elastic behaviour of modes suitable for elastic geobarometry, we simulated the Raman spectrum of a fully ordered omphacite (Jd₅₀Di₅₀ composition) at different pressures using ab initio Hartree-Fock/Density Functional Theory simulations. The simulated data exhibited excellent agreement with experimental spectra, enabling us to comprehend the pressure dependence of specific modes. Leveraging these findings, we can calculate the entrapment pressure of omphacite inclusions still confined within their host rocks by determining Raman shifts of the main peaks alongside changes in cation order.

Our results provide valuable insights into the calibration and application of Raman elastic geobarometry for omphacitic clinopyroxenes. By considering the influence of chemical composition and cationic ordering, we have enhanced our understanding of the elastic behaviour of omphacite and its potential for geobarometric calculations. These findings offer a valuable tool for determining the pressure and temperature conditions of geological processes involving omphacitic clinopyroxenes.

How to cite: Baratelli, L., Mihailova, B., Prencipe, M., Cámara, F., and Alvaro, M.: Raman elastic geobarometry: investigating cation order in omphacitic clinopyroxenes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5885, https://doi.org/10.5194/egusphere-egu24-5885, 2024.

Abstract

Functional groups (e.g. alcohol, hydroxyl, carboxyl etc.) of soil organic matter are responsible for soil properties like cation exchange capacity or wettability. Functional groups can be characterized by spectroscopic procedures like Fourier transform infrared (FTIR) spectroscopy since the infrared light can introduce vibration modes within the groups. Only the light of an energy similar to the bonding energy of the C=O bond, for example, causes the absorption bands of the functional groups to show up at typical wavenumber (WN) regions in FTIR spectra. However, when the C=O group interacts with cations, the bonding energy may change thereby affecting the WN region of the absorption band. This change in WN (following organic matter (OM)-cation interaction) may limit procedures of automated spectral interpretation, which are mostly based on fixed ranges -determined from textbooks, or sets of single wave numbers determined by statistical approaches.

Our study aims to quantify the effect of OM-cation interactions on the spectral features (intensity and WN region of C=O absorption bands) in FTIR spectra. To quantify the effect of OM-cation interactions on defined functional groups as far as possible, we study mixtures of polygalacturonic acid (PGA; as a model substance for soil organic matter) with different polyvalent cations (Ca²⁺, Fe^³+, Al^³+) at different concentrations.

PGA-cation mixtures with different cation concentrations were prepared, freeze dried, and characterized using FTIR spectroscopy (KBr technique). A proton-cation exchange at the carboxylic acid groups during PGA-Cation interaction gives rise to a COO- band in FTIR. Since the cation effect is found in an earlier study to be stronger for the COO- band (1620-1550 cm^-1) as compared to the C=O band, the interpretation of the FTIR spectra focuses on the COO- band. Compared to spectra of pure PGA, the spectra of all PGA-cation mixtures show a significant positive correlation between COO- band intensity and cation concentration. Additionally, a shift in the maximum of COO- band towards lower WN was observed for all cations, which depends on the kind of cations and increased with cation concentration.

Increase in intensity of the COO- band and the shift in WN region of COO- band maxima confirms changes in FTIR spectral features with cation addition and that those changes depend on the type of cation. The results suggest that type and concentration of cation should be considered when interpreting FTIR spectra of organic matter since both, change in intensity and shift in the WN of the band maxima, could restrict procedures of automated spectral interpretation, which mostly rely on fixed ranges (from textbooks), or sets of single wave numbers determined by statistical approaches. For a deeper understanding on the relation between OM-cation interactions, organic matter with increasing heterogeneity and complexity need to be studied.

How to cite: Bhattarai, N. and Ellerbrock, R. H.: Spectral characterization of organic matter is affected by polyvalent cations interaction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5906, https://doi.org/10.5194/egusphere-egu24-5906, 2024.

Constant development of high and green technologies makes rare earth elements (REE) more viable than ever. Relative scarcity of REE and lack of proper substitutes increase the demand for inexpensive and efficient methods of their recovery. Some new methods and technologies have been already proposed but their effectiveness leaves much to be desired. Most recently, precipitation in form of lead apatite has been proven to provide with very high levels of REE removal from aqueous solutions.

Substitution of REE in apatites has been broadly studied for calcium–phosphate apatite specimens, while lead–phosphates have been usually omitted. Recent studies suggested that precipitation of Pb and individual REE, induced by the presence of phosphates and Cl ions, results in near complete removal of cations from solutions in the form of REE-containing pyromorphite Pb₅(PO₄)₃Cl. The goal of this study was to optimize the procedure. 

Pyromorphite (Pym) was precipitated from a solution of phosphoric acid (1:1) containing REE (each element at the concentration of 15 ppm) by addition of NaCl and Pb(NO₃)₂ (powder). The addition was conducted 5 times with very small amount of Pb relative to phosphates: 1/200, 1/100, 1/50, 1/20 and 1/10 of Pb needed for complete reaction with phosphoric acid. The amount of Cl was used in 1.5 times excess with respect to stoichiometric Pb. Each time solids and solutions were separated and sampled for the analysis.

The synthesis was carried out under atmospheric pressure, at an ambient temperature of about 21°C and at pH=3. Powder X-ray diffraction (XRPD) was used to identify the obtained phases, scanning electron microscopy (SEM) to examine the morphology of the crystals, energy-dispersive X-ray spectroscopy (EDS) for analysis of the elemental composition of solids, while solutions were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-OES).

Most REE are removed already at the first, lowest dose of Pb: more than 99% of La, Ce, Pr, Nd, Sm, Eu, and Gd; between 90 and 96% of Tb, Dy, Ho, and Er; between 80 and 50% of Tm, Yb, and Lu; 46% of Sc, 86% of Y, and 98% of Th disappear from the solution. After the third addition, REE are removed completely (except for Sc, which required 5 amendments). All these elements were removed from solution by precipitation of REE-containing Pym. An admixture of "phosphoschultenite" PbHPO₄ also appears in the precipitate, which most likely does not contain REE (or contains much less than Pym).

These preliminary results indicate strong affinity of REE with Pym structure. In contrast to previous findings (Sordyl et al., 2023), a fractionation of REE was observed. Further analyses are in demand for better understanding of the mechanism of these processes which will allow for optimization of industrial applications.

This research was funded by National Science Centre research grant no. 2021/43/O/ST10/01282.

References:

Sordyl, J., Staszel, K., Leś, M., & Manecki, M. (2023). Removal of REE and Th from solution by co-precipitation with Pb-phosphates. Applied Geochemistry, 158, 105780. https://doi.org/10.1016/j.apgeochem.2023.105780

How to cite: Staszel, K. and Manecki, M.: First evidence of strong REE compatibility with pyromorphite Pb5(PO4)3Cl, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8290, https://doi.org/10.5194/egusphere-egu24-8290, 2024.

The NASA Perseverance rover is exploring Jezero crater on Mars since february 2021 [1]. Perseverance’s main goal is to investigate the past geologic and environmental conditions of Jezero crater and seek evidence of past life. For this, the rover has characterized the local geology of the crater floor and is presently working in an ancient river delta. Then, Perseverance will explore the crater rim, and possibly some regions outside of the crater. In addition, the rover selects and collects the most compelling samples that will be retrieved and brought back to Earth by a future mission (NASA/ESA Mars Sample Return project) for more detailed study.

Perseverance uses a panel of spectroscopic tools based on the analysis of sunlight reflectance in the visible and near-infrared domains (MastcamZ, SuperCam), deep-UV (SHERLOC) and time-resolved (SuperCam) Raman, Laser Induced Breakdown Spectroscopy - LIBS (SuperCam) and X-ray fluorescence (PIXL). Some instruments can analyze the chemistry and mineralogy of rocks remotely up to several meters [2-3] while others work close to the rock for higher spatial resolution (~100 mm) and better textural control [4-5]. The rover is operated nearly every day and sends data almost immediately to Earth.

On the crater floor, Perseverance found igneous rocks: basaltic lava or pyroclastic flows [6] covering an olivine-rich cumulate [4,7]. The magmatic mineral assemblage, including the textural relationships, was carefully described: mostly Fe-rich pyroxenes in the basaltic flows, and a cumulate composed of dominant olivine with augite and pigeonite, as well as some phosphates and (Cr-)Ti-Fe-oxides in both units. The bulk of these rocks is weakly altered but Fe-Mg carbonates [8], sulfates [5] and various phyllosilicates [9] were detected showing that fluid-rock interactions locally occurred. After the crater floor, Perseverance began exploring the sedimentary rocks in the Jezero western fan, which is still in progress. On the fan, some float rocks show intense alteration to kaolinite followed by metamorphism [10].

Perseverance instruments which have an original design optimized for lightness, resistance to extreme conditions and performance will be introduced. Doing spectroscopy on Mars is challenging but these instruments have worked perfectly so far. A large amount of data, including some first-time achievements on Mars, have been collected and will be summarized with special emphasis on spectroscopic data.

[1] Farley et al., Science, 2022 ; [2] Bell et al., Science Advances, 2022 ; [3] Wiens et al., Sciences Advances, 2022 ; [4] Liu et al., Science, 2022 ; [5] Scheller et al., Science, 2022 ; [6] Udry et al., JGR Planets, 2023 ; [7] Beyssac et al., JGR Planets, 2023 ; [8] Clavé et al., JGR Planets, 2023 ; [9] Mandon et al., JGR Planets, 2023 ; [10] Royer et al., LPSC 2024.

How to cite: Beyssac, O.: Spectroscopy on Mars with NASA Perseverance rover, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8479, https://doi.org/10.5194/egusphere-egu24-8479, 2024.

Quartz is ubiquitous within continental crust and can virtually be found within all rock types (plutonic, metamorphic and sedimentary). During erosion, weathering and sedimentation processes, it has a very high preservation potential and is often used to trace sediments production and transport dynamics. The QUARTZ project (Multi-methods characterization of quartz for source-to-sink tracing in alluvial sediment and dosimetry approaches – French ANR) aims to use quartz as a tracer for sediment sourcing river dynamics by combining conventional characterization method such as Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Laser Induced Breakdown Spectroscopy (LIBS), and Cathodo-Luminescence (CL), with dosimetric methods, such as Electronic Spin Resonance (ESR) and Optically Stimulated Luminescence (OSL) which are more classically used for Quaternary sediment dating. To this end, one must define a robust quartz chemico-structural and dosimetric signature that can be compared from one sample to the other. We also aim to better understand ESR, OSL, and CL signals controlled by structural quartz defects. These can be either intrinsic (e.g. dislocations, missing/supplementary O or Si), or extrinsic (foreign atoms), each technique being more or less sensitive to these different defects.

In this study, we apply this multi-method approach to the various bedrock lithologies of the Strengbach catchment (ca.40 km²) draining a low mountain range located in the easternmost France (Vosges). These are largely dominated by crystalline metamorphic and plutonic rocks, with secondary Triassic sandstones (Buntsandstein). Bedrock samples have been treated mechanically and chemically to extract quartz grains. These grains have been analyzed using ESR and OSL techniques and mounted on thick sections (100 µm) for CL, LA-ICP-MS, and LIBS analyses. 100-µm thick-sections were used to prevent quartz tearing apart under LA-ICP-MS laser beam. Quartz characterization was completed by the study of whole-rock bedrock thick sections, analyzed with CL, LA-ICP-MS and LIBS approaches.

Preliminary results allow identifying specific quartz chemico-structural signatures not only depending on rock type (gneiss, granite, sandstone) but also on formation process (magmatic, recrystallized, metamorphic or sedimentary). Further comparison between quartz analysis in whole rock and in separated grains samples permit to assess the impact of the chemical treatment on the quartz signatures and to identify quartz populations likely to be more represented in the alluvial sediments produced by the different lithologies. Finally, ongoing analyses point out the complex contribution of trace elements to OSL, ESR and CL signals.

How to cite: Aupart, C., Lerouge, C., Lach, P., Trichard, F., Boulay, M., Rizza, M., Valla, P., Voinchet, P., Rixhon, G., and Tissoux, H.: Quartz chemico-structural characterization: a tool for sediment source tracing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8723, https://doi.org/10.5194/egusphere-egu24-8723, 2024.

In this study, investigated the geology, mineralogy, petrography and geochemistry of metavolcanic rocks in northern Ilgın (Konya). There are two Paleozoic and Mesozoic metamorphic rock groups in the study area. Alluvium and Neogene sediments are unconformably layered over these rocks. Paleozoic metamorphic group include metasediments and metacarbonates. This metamorphic group consist of metaconglomerate at their base and continue upward as metasandstone, metaquartzite, phyllite, schist, metachert, and metacarbonate at the top. Mesozoic metamorphic group consists of metasediments, metacarbonates, and metavolcanic rocks. There is metaconglomerate at the base and continue upward shale, metasandstone, and metacarbonate at the top. The main difference between the two groups is that the Mesozoic metamorphic group contains metavolcanic rocks. These metavolcanic rocks, which are the main subject of this study, occur at five different locations within the study area. These are Dereköy – Kurtlukaya Hill, Küçüktokmak Hill, Kocatokmak Hill, Göleç Hill, and Avdan Village. Metavolcanic rocks are commonly observed as massive metalavas, but in some areas they exhibit a significant degree of foliation. These rocks include quartz, feldspar, and muscovite. In some areas, quartz veins cut the rocks, and in others, iron oxides are observed. The metavolcanic rocks that are the main target of this study are metariolitic - alkaline metariolitic rocks. The rocks have undergone slight metamorphism, and foliation is clearly visible in some samples. The rocks consist of an average of 40-50% matrix and 50-60% quartz, alkali feldspar, muscovite and plagioclase minerals and exhibit a hemicrystalline porphyritic texture. The matrix of the rocks consists of fine-grained quartz, alkali feldspar and sericite minerals. These rocks’ SiO₂ contents vary between 63.60-71.97%; K₂O contents vary between 3.4-10.52%; Al₂O₃ contents vary between 15.78-18.56%; Fe₂O₃ contents vary between 0.94-4.26% and TiO₂ contents vary between 0.02-0.57%. The rocks are calc-alkaline and shoshonitic in character. In addition, the rocks are peraluminous and silica-saturated. Trace element analysis shows that Ba is present in high concentrations (88–391 ppm) in  the rocks. Samples from Avdan and Dereköy have high Zr values (424–597 ppm) and Rb values (190–360 ppm). Eu values ​​(0.06–0.55) are low in all samples. Low Eu and high Ba are state that crustal contamination. The spider diagrams shows a decrease in Sr, Hf, and Ti elements, especially Eu, and an increase in other elements in the rocks. The negative anomalies observed in Sr and Eu elements indicate that fractional crystallization of feldspars. Enrichment of elements such as Th, Nb, and Zr indicate that crustal contamination. These rocks exhibit a relatively LREE-rich, HREE-poor composition, and show fractionation from LREEs to HREEs in normalized distribution pattern according to chondrite. The formation of the rocks includes fractional crystallization, assimilation-fractional crystallization, magma mixing and crustal contamination events. Ilgın metavolcanic rocks were formed as a result of magmatic activity that developed simultaneously with the collision after orogeny in the within plate environment.

Keywords: Geochemistry, Ilgın/Konya, metavolcanic rocks, petrography, Turkey.

How to cite: Sarıkaya, O. and Özdamar, Ş.: Petrography and Geochemistry of the North of Ilgin (Konya) Metavolcanic Rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9462, https://doi.org/10.5194/egusphere-egu24-9462, 2024.

Photocatalysis is a promising water purification technology, that harnesses the power of light-induced reactions to degrade contaminants. Utilizing visible light in the reactions is imperative, as it comprises a significant portion of the solar spectrum, which aligns with sustainable practices. Graphitic carbon nitride (g-C₃N₄) is a photocatalyst active in visible light, characterized by high chemical and thermal stability, ease of synthesis, and relatively low cost. However, its performance is limited by charge carrier mobility and charge recombination. These limitations might be addressed by synthesizing heterostructures, i.e. composites containing two or more semiconductors. Heterojunctions between g-C₃N₄ and layered double hydroxides (LDH) have shown increased photocatalytic efficiency. LDH are crystalline, hydrotalcite-like materials that enhance the charge separation and light absorption by the heterostructure. These materials can be obtained through various synthesis methods, including coprecipitation and hydrothermal treatment, influencing their properties. Thus, this study aimed to compare heterostructures obtained by different synthesis routes and asses their photocatalytic efficiency.

Three synthesis methods were used to obtain Zn-Cr LDH/g-C₃N₄ heterostructures: coprecipitation, adsorption/coprecipitation, and hydrothermal treatment. For g-C₃N₄ preparation, melamine was heated at 550°C for 5 h. The coprecipitation method involved dissolving zinc and chromium nitrates in DI water, then adding it to a suspension of g-C₃N₄, while simultaneously adding a solution of NaOH and Na₂CO₃. The adsorption/coprecipitation method was based on adding zinc and chromium nitrates to a g-C₃N₄ suspension, then after 30 minutes adding a solution of NaOH and Na₂CO₃. The hydrothermal method included dissolving zinc and chromium nitrates in the g-C₃N₄ suspension, adding NaOH and Na₂CO_3, then placing the suspension in an oven for 24 h at 100°C. The obtained materials were characterized by XRD, SEM/TEM, XPS, TRFL, N₂ adsorption/desorption, and photoelectrochemical measurements. The photocatalytic activity of heterostructures was assessed in batch experiments in aqueous solutions containing 1 ppm of estrone, with a 150 W LED lamp as a source of visible light.

The XRD patterns of obtained materials confirmed the formation of layered phases. The hydrothermal heterostructure was characterized by sharper reflections, which suggested higher structural order and/or larger crystallites. The average specific surface values (S_BET) showed that the hydrothermal composite was characterized by the highest S_BET - 124 m²/g. This indicated its higher porosity, compared to the materials obtained by other methods. The TRFL studies proved that the heterojunctions have lower recombination rates and longer lifetimes of charge carriers. The results of photochemical measurements suggested superior electronic conductivity and charge transfer efficiency for the hydrothermal heterostructure. The determined photoelectrochemical properties agreed well with the photocatalytic activity of heterostructures, which was the highest for the hydrothermal composite. This material led to a 99.5% estrone concentration loss after 60 minutes of reaction, in comparison to 49.9% and 75.8% loss assessed for the materials obtained by coprecipitation and adsorption/coprecipitation, respectively. The results of this study demonstrated the advantage of using the hydrothermal method to obtain LDH/g-C₃N₄ heterostructures with a high efficiency of pollutant photodegradation from aqueous solutions.

This research was funded by the AGH University of Science (Krakow, Poland), grant number 16.16.140.315.

How to cite: Jędras, A., Matusik, J., Dhanaraman, E., Fu, Y.-P., and Cempura, G.: Zn-Cr LDH/g-C3N4 heterostructure for estrone photodegradation: what is the effect of synthesis methods on materials’ properties and degradation efficiency?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9600, https://doi.org/10.5194/egusphere-egu24-9600, 2024.

The widespread occurrence of zearalenone (ZEN) in a variety of grain products and animal feed, coupled with its capacity to accumulate in the food chain, poses a significant health risk for both humans and animals. Its ability to induce estrogen-like effects may disrupt the body's estrogen levels, thereby contributing to reproductive system diseases, even at very low concentrations. The removal of ZEN from aqueous environment is predominantly challenging due to its weakly polar nature, compounded by its high thermal stability. Photodegradation, especially when applying mineral-based photocatalysts, stands out as a promising strategy for environmentally friendly mycotoxin removal. It not only demonstrates cost-effectiveness but also entails the production of negligible secondary pollutants.

Our research employed platy kaolinite (M), synthetic calcined kaolinite nanotubes (MNC), and halloysite purchased from Sigma-Aldrich (HS) as supports for TiO₂, g-C₃N₄, or combination of TiO₂/g-C₃N₄ semiconductors. Each synthesis was designed to consistently yield ~20 wt% of the semiconductor or its mixture in the samples, maintaining a TiO₂ to g-C₃N₄ ratio of 1:1. The sol-gel method was used for TiO₂ synthesis [1], while porous g-C₃N₄ nanosheets were prepared by heating melamine at 550°C, with the addition of ammonium chloride in a 1:1 ratio. The structural, textural, morphological, and light absorption properties of the obtained samples were characterized through XRD, N₂ adsorption/desorption, UV-Vis DRS spectroscopy, Raman spectroscopy, SEM, and TEM..

The UV-induced photodegradation kinetics experiments (365 nm, 10 mW/cm²) were carried out at a consistent initial ZEN concentration of ~10 ppm. ZEN concentrations were determined with high-pressure liquid chromatography (HPLC). The TiO₂-loaded photocatalysts exhibited the slowest photodegradation kinetics, resulting in the final removal of ~41.9% by the M-based sample, ~63.4% by the HS-based sample, and ~86.9% by the MNC-based sample. Conversely, the impregnation with g-C₃N₄ and TiO₂/g-C₃N₄ led to materials exhibiting the fastest kinetics, effectively removing over ~99.9% of the initial ZEN concentration. Notably, the nanotubular-based photocatalysts demonstrated slightly faster kinetics than those observed for the M-based materials and were comparable to those noted for the pure g-C₃N₄. Analogous experiments under visible light irradiation highlighted the synergistic effect for the combination of  both semiconductors, characteristic of Z-scheme heterojunction structures. Among the MNC-based samples, the least efficient photodegradation was demonstrated by the g-C₃N₄-containing sample (~13.7%), slightly higher for the TiO₂-containing sample (~20.3%), and the most efficient removal was observed for the sample containing both semiconductors (~36.6%).

The conducted experiments revealed a significant potential of kaolinite and halloysite nanotubes as carriers for semiconductors in the effective removal of ZEN from aqueous solutions. Future aspects of our research will involve detailed investigations into the degradation pathways of ZEN and the electrochemical characterization of the materials used.

This project was supported by the National Science Centre Poland, under a research project awarded by Decision No. 2021/43/B/ST10/00868.

References:
[1] Dziewiątka K., Matusik J., Trenczek-Zając A., Cempura G. (2023). TiO₂-loaded nanotubular kaolin group minerals: The effect of mineral support on photodegradation of dyes as model pollutants. Applied Clay Science, Elsevier, volume 245, 107123. 

How to cite: Dziewiątka, K., Matusik, J., and Cempura, G.: Efficient photodegradation of zearalenone: Unraveling the potential of photocatalysts based on kaolin group minerals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9623, https://doi.org/10.5194/egusphere-egu24-9623, 2024.

Diffuse Reflectance Infrared Fourier Transform Spectroscopy (FTIR DRIFT) is a widely used method for investigating soil organic materials. The existing literature suggests variations in sample preparation techniques for soil analysis. Notably, the powdering and drying method may influence the presence of organic materials, clay minerals, and carbonates. These minerals are occasionally found as coatings on different mineral surfaces and sometimes as part of the matrix within soil aggregates. This study examined four topsoils of distinct types from Hungary: Arenosol, Leptosol, Gleysol, and Phaeozem (WRB2022). The samples were pulverized both to < 250 µm and < 63 µmAnd also various procedures for drying were used: 1-hour drying sessions at 50 °C, 100 °C, 150 °C, 200 °C, and 250 °C, as well as overnight drying at 50 °C, 100 °C, and 150 °C. Additionally, samples were measured without undergoing extra drying at room temperature. This study aimed to focus on significant organic material bands.

Pulverization has a more pronounced effect on FTIR DRIFT spectra in soils with aggregates, furthermore, when the original soils contain a higher proportion of sand fraction. The drying method affects the measured absorbance values at the highlighted wavenumbers with an underlined influence on the aliphatic components range. Support of the National Research, Development, and Innovation Office (Hungary) under contract K142865, and Eötvös Loránd Research Network SA41/2021 are gratefully acknowledged.

How to cite: Szalai, Z., Karlik, M., Jakab, G., Vancsik, A., Hatvani, I. G., Cseresznyés, D., and Király, C.: Effect of sample preparation on the FTIR DRIFT spectra in the case of soils with different organic material content, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10421, https://doi.org/10.5194/egusphere-egu24-10421, 2024.

Similar to Ca-apatites, carbonate substitutions are also possible in Pb-apatites although they are still not fully characterized [1,2]. Therefore, for the first time, a comprehensive comparison of the IR spectra of synthetic Pb-apatite analogs has been carried out with a detailed examination of the rather often ignored carbonate substitutions. CO₃^2- ions can be substituted in the apatite structure in two different positions: by substitution of an anion located in the X-position in the channel, such as OH- or halogen (A-type substitution), or by substitution of an anion in the tetrahedral position, such as PO₄^3- or AsO₄^3- (B-type carbonate substitution). This can be illustrated by the following chemical formula: Pb_10-y(Na,K)_y[(PO₄)_6-y(CO₃)_y][(X)_2-2x(CO₃)_x], where x≈y. IR studies have shown that in apatites prepared at high temperature, most of the carbonates are located in the channel. Under low-temperature environmental conditions, the formation of AB-carbonated Pb apatites is much more plausible [3]. Some Pb apatites, such as fluoride apatites e.g. Pb₁₀(AsO₄)₆F₂, do not tend to incorporate carbonate at all, at least not during precipitation from solutions with CO₃^2- concentrations similar to environmental (pCO₂=10^-3.5 atm). This is likely due to the greater ordering in apatite channels, where the fluoride anion occupies the mirror plane.

In the present work, various Pb-apatites containing As and V were prepared by precipitation from an aqueous solution in the presence of Na⁺ cations at room temperature and open to the air. The type of A- or B- carbonate substitution was determined in IR spectra collected at room temperature based on asymmetric stretching of the carbonate (ν₃) and out-of-plane bending (ν₂) modes. The high-frequency component of the ν₃ region of the A-type carbonate for Pb apatites showed the greatest variability with chemical composition. For example, in Pb₁₀(AsO₄)₆OH_0.86(CO₃)_0.07 hydroxylmimetite, the bands at 1462 and 1421 cm^-1 are attributed to A-type carbonate substitution, while the bands occurring at 1385 and 1348 cm^-1 are associated with B-type. Compared to lead phosphates and vanadates, carbonate bending oscillations ν₂ at 870 cm^-1 are not apparent in arsenate Pb apatites due to overlap with the As-O stretching mode. In situ IR measurements were also carried out during temperature rise to 500 °C to determine the thermal stability of individual carbonate substitutions in the Pb-apatite structure. In general, most Pb-apatites begin to release carbonates around 300 °C. As the temperature increases, bands in the ν₂ and ν₃ carbonate regions begin to disappear until the apatite structure completely disintegrates.

References

[1] Yoder, C. H., Bollmeyer, M. M., Stepien, K. R., & Dudrick, R. N. (2019). The effect of incorporated carbonate and sodium on the IR spectra of A-and AB-type carbonated apatites. American Mineralogist: Journal of Earth and Planetary Materials, 104(6), 869-877.

[2] Kwaśniak-Kominek, M., Manecki, M., Matusik, J., & Lempart, M. (2017). Carbonate substitution in lead hydroxyapatite Pb₅(PO₄)₃OH. Journal of Molecular Structure, 1147, 594-602.

[3] Lempart, M., Manecki, M., Kwaśniak-Kominek, M., Matusik, J., & Bajda, T. (2019). Accommodation of the carbonate ion in lead hydroxyl arsenate (hydroxylmimetite) Pb₅(AsO₄)₃OH. Polyhedron, 161, 330-337.

How to cite: Puzio, B. and Manecki, M.: Carbonates substitution in lead apatites – IR spectroscopic study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11495, https://doi.org/10.5194/egusphere-egu24-11495, 2024.

Jarosite, a hydrous K-rich sulfate mineral, was found in fine-grain quantities on the Martian surface by the Opportunity rover in 2004. Jarosite found in some terrestrial settings can form a complete solid solution with ammoniojarosite through substitution of the ammonium ion (NH₄⁺) which replaces K⁺ within its crystal structure. Requiring water and acidic conditions to form, jarosite stands as a potential indicator of ancient N-bearing environments on the Martian surface. The Mars Perseverance rover is currently exploring the Martian surface with analytical instrumentation that may be capable of detecting N-rich jarosite, including the SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) and the PIXL (Planetary Instrument for X-ray Lithochemistry) detectors. To investigate the detection of N in jarosite with Raman and X-ray spectroscopy, we analyzed several terrestrial samples of jarosite and ammoniojarosite using laser Raman spectroscopy and electron-excited Wavelength Dispersive X-ray Spectroscopy (WDS). Comparison of high wavenumber regions of Raman spectra with WDS spectra of N K-α X-rays on the same samples will be used to investigate detection and quantification of N as ammonium in jarosite.

How to cite: Bushmaker, S., Nachlas, W., and Bonamici, C.: X-ray and Raman spectroscopy of jarosite and ammoniojarosite from several terrestrial localities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12017, https://doi.org/10.5194/egusphere-egu24-12017, 2024.

Apatite is a ubiquitous mineral in plutonic carbonatites (magmatic carbonate-rich rocks) and associated rock types (Chakhmouradian et al., 2017). Carbonatites are enriched in incompatible elements such as P and rare earth elements (REE), which are accommodated into apatite structure among many other elements (e.g., Hughes and Rakovan, 2015), making apatite a suitable tracer for changes in magmatic-hydrothermal geochemistry.

Sokli carbonatite complex, located in eastern Lapland, Finland, is the westernmost intrusion of the Kola Alkaline Province (Vartiainen, 1980 and references therein). The Sokli complex encompasses multiple generations of carbonatite magmatism, which compositionally span from calcite carbonatite to dolomite carbonatite to late-stage Ba, Sr, REE-enriched dolomite-rich veins. Carbonatites are associated with several generations of phoscorites, exotic magnetite-apatite cumulates typically found in carbonatite complexes. Apatite is present in most rock types in the complex, from an accessory to a rock-forming mineral.

The Sokli complex has been studied for decades (O’Brien and Hyvönen, 2015), but the composition and role of magmatic apatite has not been discussed in detail outside of phosphorous mineralization studies. Previous studies indicate that with progressive fractionation the concentrations of Ba, Sr, REE, and F increase in whole-rock and mineral compositions (O’Brien and Hyvönen, 2015 and references therein). Questions that still remain open include whether apatite has recorded the proposed different magmatic and metasomatic stages and if apatite chemistry could provide arguments for the proposed liquid immiscibility relationship between carbonatites and phoscorites (Lee et al., 2004).

A variety of apatite-bearing rock types from the Sokli complex were sampled. The composition of apatite will be studied in situ for major and trace elements with electron microprobe analyzer (EPMA) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS), respectively.

References cited:

Chakhmouradian, A.R., Reguir, E.P., Zaitsev, A.N., Couëslan, C., Xu, C., Kynický, J., Mumin, A.H., Yang, P., 2017. Apatite in carbonatitic rocks: Compositional variation, zoning, element partitioning and petrogenetic significance. Lithos 274–275, 188–213.

Hughes, J. M., Rakovan, J. F. 2015. Structurally robust, chemically diverse: apatite and apatite supergroup minerals. Elements 11, 165–170.

Vartiainen, H., 1980. The petrography, mineralogy and petrochemistry of the Sokli carbonatite massif northern Finland. Geological Survey of Finland, Bulletin 313.

O’Brien, H., E. Hyvönen. 2015. The Sokli carbonatite complex in Maier, W.D., Lahtinen, R., O’Brien, Hugh (Eds.), Mineral Deposits of Finland. Elsevier. 305–325.

Lee, M.J., Garcia, D., Moutte, J., et al., 2004. Carbonatites and phoscorites from the Sokli complex, Finland. In: Wall, F., Zaitsev, A.N. (Eds.), Phoscorites and Carbonatites from Mantle to Mine: The Key Example of the Kola Alkaline Province. The Mineralogical Society of Britain and Ireland, London, 133–162.

How to cite: Karvinen, S., Beier, C., and Heinonen, A.: Apatite in the Sokli carbonatite complex, Finland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12115, https://doi.org/10.5194/egusphere-egu24-12115, 2024.

Exploring the Raman oxygen isotope signatures of calcite and vaterite

Oxygen isotope tracers have been increasingly used to differentiate between solid-state and fluid-mediated mineral transformation pathways (e.g., Julia et al. 2023). When ¹⁸O enrichment within oxyanion bearing minerals is analysed using Raman spectroscopy, the kinetically hindered formation of different isotopologues can also provide an in-situ timer for these processes (King et al. 2014). However, at present we assume that each isotopologue band in the vibrational spectrum has an equivalent intensity when present at the same concentration within the crystal structure. Here we test this hypothesis by exploring the vibrational spectra of two important oxyanion-bearing minerals, calcite and vaterite. These are polymorphs of CaCO₃ and reflect a metastable, transition phase and the thermodynamically most stable mineral expected in many natural systems found at the Earth’s surface.

Here we have used a joint experimental and theoretical approach to demonstrate that isotopic substitution changes both band positions and band intensities to different extents, depending on the vibrational spectroscopy method used and the bands examined. Density functional theory simulations (King et al. 2022) show that for calcite, the most intense Raman bands, the υ₁ symmetrical stretching, related to individual isotopologues are found to have very similar intensities and are not affected by changes in isotopologue distribution within the material. Splitting of some bands due to changes in symmetry correlate to observed effects in experimentally produced ¹⁸O enriched calcite.In contrast, vaterite vibrational bands were found to change more extensively upon isotope substitution, thus they can only be used to evaluate relative changes in the ¹⁸O concentration within the material. These results are expected to contribute to a deeper und less ambiguous understanding of evaluating isotopic enrichment effects in the vibrational spectra of calcium carbonates.

Julia et al. 2023 Chemical Geology, 621, 121364.

King et al. 2014 Crystal Growth & Design, 14, pp. 3910.

King et al. 2022 Crystals, 13, 48.

How to cite: King, H. E. and Živković, A.: Exploring the Raman oxygen isotope signatures of calcite and vaterite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12281, https://doi.org/10.5194/egusphere-egu24-12281, 2024.

The understanding of the vitrification processes encompasses all the fields between geo- and material- sciences. Glass represents a non-equilibrium picture of its parental super-cooled liquid (SCL) and the last melt fraction quenched after a volcanic eruption. The SCL is usually read as a system that moves away from equilibrium without having enough time to explore the phase-space. In these conditions it is unable to find new configurations, causing a drop of the thermodynamic equilibrium and a glass is formed. This system is named non-ergodic and at eruptive temperatures represent a key component that may experiences fragmentation [1]. This particular state is generally referred to the thermal interval preceding the glass transition temperature (T_g, T at which the viscosity is 10¹² Pa s) and the monitoring of its micro-structural evolution requires the less invasive experimental technique. With this regard we have used the deep UV-Raman spectroscopy to investigate a set of silicate model-glasses, loaded with different iron contents. This spectroscopic approach allows for the acquisition of fluorescence-free spectra with a maximized signal in the high-wavenumber region (between 850-1300 cm^-1) thus providing the finest conditions for the assessment of the tetrahedral arrangement through the Qⁿ deconvolution analysis (n represents the number of bridging oxygens) [2]. Here we correlate the trend of each Qⁿ unit with temperature across the T_g-interval. Our results display a clear T-dependent rearrangement of the Qⁿ distribution in function of iron content. Our finding, supported by differential scanning calorimetry, thermal dilatometry, Mössbauer, FTIR and ATR measurements, may deliver helpful insights into the thermal-dependent microstructural evolution through the T_g-interval and the viscous behavior of silicate SCLs.

• _{[1] D. B. Dingwell, Science 273, 1054 (1996).}
• _{[2] M. Cassetta, B. Rossi, S. Mazzocato, F. Vetere, G. Iezzi, A. Pisello, M. Zanatta, N. Daldosso, M. Giarola, and G. Mariotto, Chem. Geol. 644, 121867 (2024).}

How to cite: Cassetta, M., D'Amico, F., Rossi, B., De Bona, E., Sambugaro, A., Biesuz, M., Almeev, R., Vetere, F., Giordano, D., Enrichi, F., Daldosso, N., and Mariotto, G.: In-situ structural analysis of silicate supercooled liquids through deep-UV Raman spectroscopy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12774, https://doi.org/10.5194/egusphere-egu24-12774, 2024.

Determining the habitability of planets remains a fundamental question in science and society. In this study, we harness network theory to explore the unique patterns exhibited by minerals and their mineralizing environments in both biotic and abiotic contexts throughout the evolution of Earth and other terrestrial bodies in our solar system [1-. By examining mineralogical networks across diverse planetary systems, including early solar system bodies, the early Hadean Earth (closely related to modern-day Mars), plate tectonics, and modern Earth, we gain valuable insights into Earth's history and the factors that have shaped the development and sustainability of life. Our investigation reveals distinct characteristics within biotic networks, setting them apart from their abiotic counterparts.

This research significantly advances our understanding of the intricate interplay between Earth and life. Network analysis offers deeper insights into the connections between minerals and living systems, providing invaluable perspectives on the emergence and co-evolution of life on our planet. Moreover, our findings contribute to identifying and characterizing planetary biosignatures, essential for the search for extraterrestrial life. Recognizing these unique patterns within biotic networks lays the groundwork for developing targeted exploration strategies for detecting potential biosignatures and interpreting the complexities of planetary environments.

Our innovative network analysis of minerals and mineralizing environments sheds new light on the relationships between Earth and life. By delving into the intricate connections within biotic and abiotic systems, we deepen our understanding of Earth's dynamic history and enhance our knowledge of potential habitats for life beyond our planet.

How to cite: Morrison, S., Prabhu, A., Hazen, R., Wong, M., Giovannelli, D., and Eleish, A.: Characterizing life influence on Earth's mineralogy via mineral network analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14196, https://doi.org/10.5194/egusphere-egu24-14196, 2024.

There is a constant search for materials that could be used as geochemical barriers and fillers for radioactive waste storage containers. One of effective methods of immobilizing toxic elements is their precipitation in the form of sparingly soluble crystalline phases. The purpose of this study was to test the effectiveness of co-precipitation of Th from aqueous solutions in the form of crystalline lead phosphates. Such phases have high stability and low solubility and the presence of Pb has an additional effect on reducing the radiation.

Three sets of experiments were carried out by adding reagents into a solution containing non-radioactive Th at a concentration of 400 ppm:

(A) a solution containing PO₄^3- ions (at a concentration of 1 g/L);

(B) a solution containing Pb²⁺ and a solution containing PO₄^3- ions (at concentrations of 3.5 g/L and 1 g/L, respectively) added dropwise simultaneously;

(C) solutions containing Pb²⁺, PO₄^3-, and Cl^- ions (at concentrations of 3.5 g/L, 1.0 g/L, and 0.12 g/L, respectively) added dropwise simultaneously.

All experiments were repeated at pH = 3, 5 and 7. No reaction occurred in experiment (A), while in experiments (B) and (C) the solid phases crystallized, and the Th concentration dropped from 400 to about 0.05 ppm. In the absence of Cl (experiment B), the reaction at pH=3 led to the formation of "phosphoschultenite" PbHPO₄ while at pH = 5 and 7 Th-bearing hydroxylpyromorphite Pb₅(PO₄)₃OH was formed. In the presence of Cl ions (experiments C), Th-bearing pyromorphite Pb₅(PO₄)₃Cl was formed over the entire pH range. Th was removed from solution by coprecipitation with Pb and incorporation of Th into lead phosphate structure.

The results showed that Pb must be present for Th to be effectively immobilized from solution in the form of phosphate phases. The presence of Cl is not as important as the presence of Pb in terms of removal efficiency, but it may be crucial for the long-term stability of the precipitated phases, since Pb₅(PO₄)₃Cl has higher stability and lower solubility than Pb₅(PO₄)₃OH. These findings pave the way for development of potential innovative techniques for immobilizing Th from waste and contaminated solutions, which could have implications for the safety and long-term viability of various nuclear waste disposal programs. This research was funded by National Science Center research grant no. 2021/43/O/ST10/01282.

How to cite: Manecki, M., Wrona, P., Brzoska, A., and Staszel, K.: Immobilization of radioactive Th by coprecipitation with lead apatites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14330, https://doi.org/10.5194/egusphere-egu24-14330, 2024.

Arsenic is a world-wide serious health problem occurring in various types of rocks, soil, and contaminated water resources. However, it is not always an acute health problem, as concentrations are often comparably low. But recently, it gained increasing attention with the introduction of new laws in Germany (and the EU) regarding the deposition of excavated sediments, e.g., in the context of the construction of tunnels or the mining of gravel and sand etc. The decision on whether excavated material can be used as backfill or needs landfilling depends on the analysis and classification relative to specified limit values. In the latter scenario, this can result in a significant increase in costs. It is mandatory to determine the heavy metals and arsenic (among other parameters) in the solid sample and to produce and analyze an eluate of the sample to identify soluble harmful elements that could potentially contaminate the groundwater.

At a first glance, arsenic contents in solid and in eluate often show erratic patterns, which could not be explained. In clastic sediments, an often observed (weak) correlation between arsenic and iron in solid analyses led to the assumption that arsenic is bound in iron-hydroxides. However, a comprehensive examination of the chemistry and mineralogy of a large number of samples did not reveal any clear correlations. Therefore, we studied drill-core samples and sediment profiles of poorly consolidated Miocene clastic sediments, including gravel, sands, clay and silt from different areas of the Northern Alpine foreland basin (mostly from the Munich and Ingolstadt areas).

Based on geochemical analyses, we found different “arsenic-types”: Some samples show the expected correlation pattern for arsenic in the solid and the eluate. Some samples, however, show high arsenic in the solid and low arsenic concentrations in the eluate. Also, remarkably, samples with rather low arsenic contents in the solid and high arsenic in the eluate were observed. No systematic correlation with other chemical elements or with macroscopic characteristics, e.g. grain size, could be identified. Our detailed mineralogical investigation of more than 30 samples showed that XRD analysis, which is usually used to identify the mineralogy in the finest fraction, is not sufficient to explain this behavior. Therefore, we separated all mineral phases (also in the clay fraction) and analyzed their mineral chemistry (in particular their arsenic content) with SEM, their texture with high-resolution Keyence microscopy (2000x), and combined the results with extensive leaching experiments.

Our results imply that mineralogy is the key to understanding the elution behavior of arsenic. Regarding the binding characteristics of arsenic, three different mineral types can be distinguished: 1) Fe-, Si- and Al-Hydroxides (minor tourmaline, apatite and zircon) can bind arsenic relatively well (no arsenic in the eluate), 2) chlorite and mica can adsorb high amounts of arsenate but with a weak bond (high As in eluate) and 3) smectite which releases its arsenate step-by-step with the increasing degree of swelling. The study showed that only with a detailed mineralogical and mineral-chemical analysis profound predictions on the elution behavior of arsenic can be made.

How to cite: Aßbichler, D., Weichselgartner, N., Diesner, N., Kayalar, M., Otte, C., Heuss-Aßbichler, S., Tautenhahn, S., and Friedrich, A. M.: Mineralogy – the key to understanding and predicting the elution behavior of arsenic , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14683, https://doi.org/10.5194/egusphere-egu24-14683, 2024.

Gemological reports have gained a crucial role in today’s gemstone trading because they provide buyers and sellers with information regarding gem features, which in turn can be translated to monetary value. Although there is information about technics to separate Colombian emeralds from other countries, not much information is available about how to differentiate emeralds from the Western Belt (COC), and those from the Eastern Belt (COR), two main produced zones in Colombia, those districts more recognized are, Muzo and Chivor, respectively. This work aims to show the advances made in one of the techniques used in a gemological laboratory to determine the origin of emeralds.
The analysis of fluid inclusions via Raman spectroscopy can yield beneficial information regarding the chemical properties of mineral systems. Primary fluid inclusions trapped by emerald permit us to know the chemistry and the thermobarometric conditions of the mineralizing fluids. Fluid inclusions are usually three-phase inclusions with contain three or more phases including liquids, gases, and salt (halite). Sometimes they are multiphase with solids such as calcite. The gas phases are typically CO2, N2, and CH4 (Cheilletz et al., 1994; Giuliani et al., 1993; Giuliani et al., 1995; Romero & Hernandez, 1999; García-Toloza et al., 2017). Raman spectra of CO2 exhibit two bands near 1285 cm-1 and 1385 cm-1, this feature is well-known as the Fermi doublet (Fernandez, 1983; Howard-Locke, 1971); the distance between these bands is proportional to the fluid density (Rosso & Bodnar, 1995; Song Y. et al., 2003). 
The data of ∆ Fermi doublet suggest that values below 103.1 are exclusive from the COR, whereas there is an overlap from 103.1 to 103.4. Additionally, the position of the two main CO2 bands varies significantly between the two Colombian belts. The location of peaks from the COR are found at lower energy levels. Thus, this method may be used to estimate the provenance of some populations, the Fermi doublet is not only helpful to differentiate between the Colombian emerald belts but also between Colombian emeralds from samples from Brazil and Afghanistan.

How to cite: Garcia-Toloza, J., Betancur, C., Alvarado, H., and Cedeño, C. J.: Raman spectroscopy analysis of fluid inclusions as a tool in determination of origin of Colombian emeralds., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14692, https://doi.org/10.5194/egusphere-egu24-14692, 2024.

The Styrian Basin, situated in the transition zone between the Pannonian Basin and the Eastern Alps, is believed to have formed above a lithospheric wedge, which have been affected by a subduction. The Late Miocene-Pliocene alkali basalts sampled the subcontinental lithospheric mantle beneath the area, bringing mantle xenoliths to the surface (e.g., [1] [2]). These xenoliths are amphibole-rich, indicating extensive modal metasomatism at mantle depth. Our goal is to better understand the possible fluid and melt-related processes in these xenoliths by studying fluid and melt inclusions in them. In the studied samples, one category of xenoliths contains both fluid and melt inclusions (co-entrapped), while the other contains only fluid inclusions. We carried out 3D confocal Raman mapping, Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), Electron Microprobe Analysis (EMPA), and Scanning Electron Microscope with Energy Dispersive Spectroscopy (SEM-EDS). Our primary objectives are to 1) gain insights into the nature of metasomatic agents based on fluid and melt inclusions and 2) test the applicability of 3D Raman mapping on inclusions. The studied inclusions are primary (fluid inclusions) and pseudosecondary (fluid and melt inclusions), occurring in orthopyroxene, clinopyroxene, and amphibole. The fluid inclusions are irregular to negative crystal-shaped (3-100 μm), whereas melt inclusions are glass-rich with rounded to negative crystal shapes (4-15 μm).

A series of 3D Raman mapping on these fluid inclusions has revealed complex phase assemblages comprising fluid and solid phases (magnesite, silicate glass, pyrite, talc, anhydrite, and nahcolite). The fluid is dominated by CO₂ (up to 99.3 mol%) and H₂O (up to 8.7 mol%). EMPA indicates that the trapped silicate glass in the melt inclusions is H₂O-bearing (up to 3.3 wt%) and exhibits an evolved composition (i.e., trachyandesitic composition with SiO₂ between 54.31-60.65 wt%) relative to the host basalt of the studied xenoliths.

We discovered pargasitic amphiboles within SiO₂-rich glass in the melt inclusion that co-entrapped with the CO₂-H₂O-rich fluid phase (where H₂O content is likely high relative to mantle fluids). This strongly suggests that amphiboles were likely crystallized from an immiscible SiO₂-rich melt and CO₂-H₂O-rich fluid that could have been circulating in the mantle wedge above a subducted slab. This immiscible component is suggested to be a metasomatic agent that modified this mantle portion beneath the Styrian Basin.  Furthermore, this study revealed that the laser-induced heating effect could overestimate sulfides in the 3D Raman models, while silicate glass could be underrepresented due to its low Raman scattering properties. However, complementary FIB-SEM serial slicing provides a clear outline of silicate glass in fluid inclusions. Despite these limitations, 3D Raman mapping has proven to be a powerful tool for unravelling complex phase assemblages in inclusions.

This research was supported by the NKFIH_FK research fund nr. 132418 to M. Berkesi. Part of this research was funded by the Doctoral School of Earth Sciences of the University of Pécs.

References:

[1]. Aradi et al., 2019; Földtani Közlöny, 149 (1). pp. 35-49.

[2]. Aradi et al., 2017; Tectonics, 36, 2987–3011.

Keywords: 3D Raman mapping, complex inclusions, mantle metasomatism, subduction zone, Styrian Basin.

How to cite: Myovela, J. L., Aradi, L. E., Spránitz, T., Hegedűs, M., Konečný, P., Kovács, J., and Berkesi, M.: Unravelling metasomatic agent in amphibole-rich upper mantle xenoliths from the Styrian Basin (W-Carpathian Pannonian Region): Insights from 3D Raman mapping of complex inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16706, https://doi.org/10.5194/egusphere-egu24-16706, 2024.

Earthquakes result from the brittle failure of rocks at depths and are primarily induced by far-field tectonic stresses. Despite this general understanding, the atomic-scale mechanisms triggering brittle failure in dry ductile crustal rocks remain elusive. Quartz, a widespread mineral in the lower crust, undergoes an instantaneous polymorphic transformation from the α to β phase under pressure and temperature conditions aligning with estimates for several lower-crustal paleo-earthquakes, recorded as pseudotachylytes. The α–β quartz transition is characterized by displacive reversibility. As α–quartz approaches the transition temperature (T_c = 847 K for a free quartz crystal at atmospheric pressure) under constant pressure, its volume increases nonlinearly without abrupt jumps. However, near the phase-transition temperature, the bulk modulus of quartz exhibits a notable drop from approximately 30 GPa to nearly zero, followed by an abrupt rise to over 70 GPa within 10 K temperature range (Lakshtanov et al., 2007).

Near the α–β transition, quartz inclusions within garnet hosts should develop substantial differential strain, thereby imposing strong differential stresses on the surrounding host crystal. We used in situ high-temperature Raman spectroscopy on quartz inclusions in garnet to monitor the structural deformation and atomic dynamics across the phase transition. The temperature-dependent behaviour of the phonon wavenumbers (ω) in quartz inclusions, particularly the hardening and disappearance of a minimum in ω(T) for A modes near 208 and 464 cm^-1 (related to the α–β phase transition), along with the persistence of Raman activity at ~128 cm^-1 and ~355 cm^-1 above T_c, confirms the accumulation of abnormally high strain in confined quartz grains near the anticipated phase transition. The stored elastic energy in the inclusion is subsequently released through the inclusion-host boundary into the host during the α–β transition. This release causes the garnet around the quartz inclusion to fracture or, in some instances, shatter due to the significant differential stresses forming within the inclusion at its transition. Notably, inclusions of apatite and zircon within the same garnets remain unchanged under the same conditions, thereby excluding the possibility of fracturing being caused by the host garnet itself.

Our experiments show that the α–β transition of a single quartz inclusion in garnet is sufficient to fracture the host phase in a laboratory environment. This process can be upscaled to quartz-bearing rocks at lower crustal conditions and might provide the initial mechanical instabilities necessary to trigger ductile and/or brittle deformation in quartz-bearing rocks, eventually leading to earthquakes.

References

Lakshtanov, D.L., Sinogeikin, S.V., Bass, J.D., 2007. High-temperature phase transitions and elasticity of silica polymorphs. Physics and Chemistry of Minerals 34, 11-22.

How to cite: Gilio, M., Morana, M., Angel, R. J., Mihailova, B., and Alvaro, M.: High-temperature Raman spectroscopy of quartz inclusions in garnet: a tool to investigate lower crustal rheology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16793, https://doi.org/10.5194/egusphere-egu24-16793, 2024.

Sulfuric acid speleogenesis (SAS) is a general cave formation process in carbonate rocks in the presence of sulfuric acid. Such caves are mainly formed at and above the water table by abiotic or/and biotic oxidation of hydrogen sulfide (H₂S). One possible source of H₂S may be volcanic activity. The oxidation of H₂S produces sulfuric acid that immediately reacts with carbonate host rock, producing replacement gypsum and CO₂.

The Western Cordillera in the Peruvian Andes, characterized by volcanic and tectonic activity, features substantial travertine deposits. Among the most interesting and, at the same time, less known are the Mulapampa travertines located in the vicinity of the active Ampato-Sabancaya Volcanic Complex (ASVC). There are numerous collapse sinkholes in the travertine cover, and within three of them, caves have been found. discovered in three of them. Particularly interesting is the Gruta con lago cave, the bottom of which is located at the level of the current water table (ca. 40 m below ground level). It does not have the characteristic morphology of active SAS caves, but several speleogenetic by-products – mainly thick gypsum deposits – are typical of such features.

Mineralogical studies of sediment samples from the lake at the bottom of Gruta con lago corroborated the sulfuric acid genesis of the cave. Native sulfur was detected in those samples, among others. Microscopic examination of native sulfur crystals reveals traces of substantial corrosion attributable to the activity of sulfur bacteria. In the same cave lake's bottom sediments, framboidal pyrites formed inside the biofilms (presumably of sulfate-reducing bacteria) were found. Common secondary minerals in SAS caves, such as barite or celestine, are present on the cave bottom and walls.

This research was funded by the National Science Centre (Poland), grant No 2020/39/B/ST10/00042, and the Institute of Earth Sciences, University of Silesia, Poland.

How to cite: Tyc, A., Ciesielczuk, J., Gaidzik, K., and Powolny, T.: Sulfuric acid speleogenetic by-products and secondary minerals in caves of the Mulapampa travertines (Western Cordillera, Andes, Peru), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17099, https://doi.org/10.5194/egusphere-egu24-17099, 2024.

The Dellen impact structure is located in a ca. 20 km wide basin filled by two lakes in the east central Sweden. The complex structure is covered by a thick moraine deposit, and most impact melted material can be found as loose blocks and boulders scattered throughout the moraine. Geophysical measurements show the presence of a coherent impact melt body about 9 km wide and 200-500 m thick for which impact ages  between 90, 110, to 140 Ma were determined [1]-[2]. 

The impact melt glass (commonly referred as dellenite) consisting of phenocrysts of subhedral orthopyroxene (Wo₄En₆₃Fs₃₃), skeletal plagioclase (average An₅₉Ab₃₈Or₃), and euhedral magnetite within a glassy matrix of rhyolitic composition. MicroFTIR measurements performed in the glass matrix and euhedral glass blebs within the skeletal plagioclase show the presence of 1.4 wt% water in the rhyolitic glass. We estimated that the dellenite vitrified at ca. P=200-300 bar by comparing the glass water content  with the water solubility of a similar composition silicate melt following  Papale's model [3].

Dellenite orthopyroxene was studied by polarized FTIR spectroscopy, Mössbauer spectroscopy, single crystal X-ray diffraction and EMPA. They are iron rich enstatite (Wo₄ En₆₃ Fs₃₃) with a Fe³⁺/Fe_tot ratio of 1.6%. They have very weak to absent OH vibrational bands in the IR spectra, corresponding to H₂O contents ranging from 0 to 39 ppm H₂O, a variability suggesting H loss during post-formation processes, which may occur via the relatively fast redox reaction Fe²⁺ +OH^- =Fe³⁺ +O^2- +½H₂. 

In volcanic pyroxenes H loss may be a common process occurring at different moments from crystallization to post-eruption. However, H incorporation in pyroxene is associated with point defects governed by slow kinetics diffusion rates, which are retained in the structure when H is lost. By reversing the redox reaction the original H content of pyroxene can thus be recovered by thermal annealing experiments under reducing conditions [4]-[5].

In order to restore H that was possibly lost, dellenite pyroxenes were thermally annealed under hydrogen atmosphere (at 1 Atm) in a horizontal glass-tube furnace by thermal annealing experiments at 700°C for 17 hours. FTIR spectra were recorded after each heating step. All the samples increased their hydrogen content and the final average water content is 77 ppm. 

Cation partition as derived by the SC-XRD and EMPA were used to calculate the orthopyroxene closure temperature (Tc) which is expression of the cooling rate for the cpx-host rock. Preliminary results point to a high Tc (833°C) due to a quite fast host-rock cooling rate. 

A tentative model for the evolution of the rhyolitic portion of the Dellen impact melt is under development merging geophysical data with our experimental data on water content of pyroxene and glass, and pyroxene geospeedometry.  

References:

[1]Henkel H (1992) Tectonophysics 216, 31-40

[2]Mark DF Lindgren P Fallick AE (2014) Geological Society of London Special Publication 378, 349-366

[3]Papale P (1999) Am Mineral 84, 477-792

[4]Weis FA Skogby H Stalder R (2016)  Am Mineral 101(10): 2233-2247

[5]Nazzareni S Barbarossa V Skogby H Zanon V Petrelli M (2020)  CMP 175:87

How to cite: Nazzareni, S., Giuli, G., and Skogby, H.: Dellen crater impact melt rock: pyroxenes as a proxy for melt thermal history and water content, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17632, https://doi.org/10.5194/egusphere-egu24-17632, 2024.

The mantle transition zone (MTZ) is known to be potentially hydrated as laboratory
experiments have shown that the two major mineral phases namely wadsleyite (β-M₂SiO₄ ;
M: Mg, Fe) and ringwoodite (γ-M₂SiO₄; M: Mg, Fe) can accommodate significant amounts of
water in the form of hydroxyl ions in their crystal structure. Direct in-situ evidence of the
MTZ being (at least locally) hydrated has been derived from natural diamonds containing
hydrous ringwoodite inclusions (Pearson 2014, Nature). Hence, in this study, we have
investigated the crystal structure and the thermoelastic properties of Fe-bearing ringwoodite
as a function of temperature, pressure, and water content (0 wt%, 1.56 wt%, 3.3 wt%) using a
combination of first-principles density functional theory (DFT) and quasi-harmonic
approximation (QHA). Our calculation reveals that hydration in general causes a reduction in
the sound wave velocity of ringwoodite. However, the ‘reduction’ brought in by hydration is
significantly suppressed at pressures corresponding to the lower part of the MTZ.
Consequently, the sound wave velocities for the 1.56 wt% water-containing ringwoodite
model is found to become very similar to the sound wave velocities of the anhydrous
ringwoodite. However, when the water concentration is increased further to ~3.3 wt%, the pressure-induced
suppression at lower MTZ pressures though present is not significant. These findings indicate that though seismic
waves may not be able to precisely decipher the state of hydration of the lower part of MTZ
when the water concentration is less than 1.56 wt%, it is still robust enough to locate regions
of very high water concentration ~ 3.3 wt%.

How to cite: Mondal, R., Shukla, G., and Chatterjee, S.: Are seismic waves robust enough to detect the presence of water in the lower part of the mantle transition zone?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17688, https://doi.org/10.5194/egusphere-egu24-17688, 2024.

At high temperatures, alkali feldspar consists of a continuous solid-solution between the Na (albite) and K (K-feldspar) end members. Below about 600°C, a miscibility gap opens, the limits of which are determined by the so-called solvus. Alkali feldspar of intermediate composition tends to exsolve when cooled from temperatures of magmatic or metamorphic crystallization, forming an intergrowth of Na- and K-rich lamellae, a microstructure referred to as perthite. Initially, coherency is maintained across the lamellar interfaces and it may be preserved over geological times. Since the lattice parameters of alkali feldspars strongly depend on composition, the exsolution lamellae must be strained to maintain coherency at the interfaces. The elastic energy required to strain the lamellae counteracts exsolution and equilibrium compositions of coexisting coherent exsolution lamellae define a coherent solvus which lies below the solvus for strain-free phase equilibria. Segregation of Na and K and subsequent lamellar coarsening is achieved by thermally activated Na-K interdiffusion. Therefore, compositions and widths of the exsolution lamellae could be used to reconstruct cooling histories. Knowing the shape and position of the coherent solvus is key for the corresponding geo-speedometry applications.

To determine the coherent solvus, initially homogeneous disordered, gem-quality alkali feldspar was annealed at temperatures between 440°C and 560°C and at atmospheric pressure, which caused it to exsolve into coherently intergrown 10 to 20 nm wide lamellae, the compositions of which were directly determined with atom probe tomography.

The application of different annealing times showed that thermodynamic equilibrium was reached during the experiments. The obtained lamellar composition define points on the coherent solvus, which were for the first time measured directly for alkali feldspars.

Additionally, equilibrium Na-K partitioning experiments between NaCl-KCl melt and the same alkali feldspars as used for the exsolution experiments were performed at atmospheric pressure and at temperatures between 800°C and 1000°C to calibrate a thermodynamic mixing model supplemented by a model for the elastic energy required for coherent exsolution. The coherent solvus calculated from the thermodynamic model and the directly measured coherent solvus are in excellent agreement. This indicates that the developed models provide an adequate description of phase equilibria in coherent lamellar intergrowth. The directly measured coherent solvus and the models form a solid base for potential applications of geo-speedometry in coherently exsolved alkali feldspars.

How to cite: Heuser, D., Dubosq, R., Bian, G., Petrishcheva, E., Habler, G., Gault, B., Lengauer, C. L., Rentenberger, C., and Abart, R.: The coherent solvus of disordered alkali feldspar determined with atom probe tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18335, https://doi.org/10.5194/egusphere-egu24-18335, 2024.

In the drive to develop more fuel-efficient aircraft engines to reduce the environmental impact of flying, engines are being designed to run much hotter. This is leading to a greater range of damaging interactions between the engine components and mineral dusts ingested into the engine during flight. To mitigate the effects of these interactions there is a critical need to understand mineral transformations (e.g., polymorphic changes, melting, glass transition), reactions, and mineral properties under much more extreme rates of heating and cooling than have been examined previously. Recent technological advances allow differential scanning calorimetry (Flash DSC) measurements to be made on small samples at temperatures of up to 1000 ℃, at heating/cooling rates of up to 50000 K/s, rates which comparable to those experienced by mineral dust particles inside a jet engine. Here we present two case studies, relevant in the engine context, that illustrate the capabilities of Flash DSC measurements.

A number of minerals ingested into aircraft engines undergo polymorphic transformations as they are rapidly heated inside the engine and these can have a profound effect on the accumulation rate of dust deposits on engine components. In our first case study we show the effect of heating/cooling-rate on the α - β-quartz transformation at rates between 10 to 10000 K/s (ambient pressures). During heating the temperature of the transformation increases from 573 to 608 ℃ over this heating-rate range, and the kinetics of the transformation are significantly modified.

Dust deposits may undergo melting inside an engine and infiltrate the porous coatings that are applied to engine components for thermal protection. This prevents the coatings expanding and contracting in response to temperature changes which, in turn, leads to their failure. Hence a knowledge of the viscosity of the melts (and hence infiltration-rate) and how this varies with temperature is important. Conventional methods of measuring viscosity are unable to access a considerable temperature range in which changes occur within the sample (e.g., crystallization) over the timescale of the measurement. The temperature dependence of viscosity may, however, be obtained from the heating-rate dependence of the glass transition temperature, and this is a measurement that can be made extremely rapidly by Flash DSC. In the second case study we show the temperature-dependence of viscosity over a temperature range previously inaccessible, for two CMAS melts that have compositions representative of those that are found in aircraft engines.

How to cite: Bai, Y., Covey-crump, S., Bojdo, N., Jones, M., and Pawley, A.: Differential scanning calorimetry measurements of mineral transformations at the extreme heating and cooling-rates experienced by mineral dusts ingested into aircraft engines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18687, https://doi.org/10.5194/egusphere-egu24-18687, 2024.

Dedolomitization is a geological process where dolomite undergoes transformation into calcite via the influx of aggressive Ca-rich solutions derived from various sources (e.g., evaporite dissolution). This conversion can take place in diverse environments. Our study focuses on a unique occurrence of dedolomite within a cave environment in the Mravljetovo brezno v Gošarjevih rupah cave located in central Slovenia. The cave walls exhibit distinctive yellowish and reddish crusts and covers that originated from dedolomitization process developed within this cave system.

Macro- and microscopic observations reveal that yellowish lithologies are of sedimentary origin, where dominating dedolomite (i.e., replacive calcite) is associated by mainly detrital particles with a high content of quartz, muscovite, clay minerals, and lithoclasts. In contrast, red lithologies are associated with the transitional zone between sedimentary layers and the host rock dolomite, featuring peculiar calcite crystals with abundant pore space and intercrystalline iron oxides and clay. The transitional zone itself consists of a calcite mosaic with smaller dolomite remnant embedded within the calcite structure.

The primary objective of this study is to conduct a comprehensive mineralogical analysis (XRD, SEM-EDS, EMPA, μXRF, CL, and Raman spectroscopy), aiming to recognize their interrelationships and utilize them as proxies for understanding the processes leading to dedolomitization.

Dedolomitization is evidenced by the abundance of corroded dolomite rhombs infilled with calcite, coupled with the development of moldic (dissolution-related) porosity, and subsequent crystallization of vein calcite. Detrital quartz reveals embayed crystal boundaries, as well as rounded lithoclasts enriched in clay-group species (e.g., illite). Subordinate detrital apatite, rutile, and zircon were also recognized. Besides, some mineral phases of authigenic origin were detected based on their habits and textural relationships. These include clay-group species (i.e., kaolinite, illite, and/or possible mixed-layer clays), as well as S- and Na-rich apatite, and fluorite. The formation of dedolomite was followed by the decrease of Mg and increase of Fe as evidenced by elemental mapping. These changes can reflect oxidizing conditions and subsequent precipitation of Fe³⁺ in hematite or goethite/lepidocrocite mineral phases that stained dedolomitized regions red to yellow.

Furthermore, we seek to investigate the potential influence of these mineralogical dynamics on cave formation and speleogenesis. All these findings can contribute to a better understanding of geological and geochemical mechanisms governing dedolomitization processes within cave environments.

This work is funded by the Slovenian and Polish research agencies (ARRS and NCN) through the bilateral Polish-Slovenian research project CEUS (project code in Slovenia: N1-0226; project code in Poland: 2020/39/I/ST10/02357).

How to cite: Gaidzik, K., Šarc, F., Ciesielczuk, J., Martín Pérez, A., Košir, A., Otoničar, B., Powolny, T., Tyc, A., Johnston, V., and Gebus-Czupyt, B.: Mineralogical study of dedolomitization in cave environments –the Mravljetovo brezno v Gošarjevih rupah cave, central Slovenia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19040, https://doi.org/10.5194/egusphere-egu24-19040, 2024.

The magmatic-hydrothermal transition is an important but poorly-understood process in the formation of Sn-W, Nb-Ta and Li deposits associated with evolved granites and pegmatites. Theory predicts that boron isotopes will fractionate between magma and fluid, so the magmatic-hydrothermal transition may be recorded in the borosilicate mineral tourmaline, which is widespread and common in these kinds of deposits. The key information needed to interpret the tourmaline record is the B-isotope fractionation between granitic melts and the fluids derived from them but former experimental studies on B-isotope fractionation between the relevant phases are not in agreement (e.g. Kowalski and Wunder, 2018, Maner and London, 2018).

This study fills this gap by an experimental, multivariant approach. We synthesized a glass of haplogranitic composition (Ab40Or25Qtz35) and produced variants of water content (0, 4 and 6 wt%), aluminum saturation (ASI 0.7, 1, 1.3) and boron concentration (2 and 5 wt%). For each composition we determined the coordination environment of B in the glass and the fractionation of B isotopes between the respective melt and aqueous fluid at near-solidus temperature. The first part of the study was the chemical characterization and analysis of B coordination in the glasses. The NMR analysis of 11B indicates that the coordination of 11B is dominantly trigonal in all glasses, but there is an increase of tetrahedral coordination with increasing boron concentration and water content. Fluid-melt fractionation experiments are ongoing and first results will be presented.

References:
• Kowalski, P., Wunder, B. (2018). Boron isotope fractionation among vapor–liquids–solids–melts: Experiments and atomistic modeling. In: Marschall, H., Foster, G. (eds) Boron Isotopes. Advances in Isotope Geochemistry. Springer-Verlag, Berlin-Heidelberg, volume 7, pages 33–69
• Maner, J. L., London, D. (2018) Fractionation of the isotopes of boron between granitic melt and aqueous solution at 700 °C and 800 °C (200 MPa), Chemical Geology, Volume 489, Pages 16-27

How to cite: Rauscher, J., Wunder, B., Wilke, M., Trumbull, R., Jahn, S., Sieber, M. J., Michaud, J., Pohl, F., Scicchitano, M. R., Fechtelkord, M., and Appelt, O.: Exploring boron isotope fractionation during interaction of silicate melts and hydrous fluids: an experimental approach concerning ore formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20076, https://doi.org/10.5194/egusphere-egu24-20076, 2024.

A fundamental observation regarding oceanic subduction systems is that the starting material of subduction (MORB) is less oxidized than a major end-product (primitive magma in arcs), likely as a result of infiltration of mantle source regions by oxidized components from the subducted slab. Important redox-sensitive elements in slabs are S, C, H, and transition elements such as Fe and Mn. Fe is important because it is volumetrically significant, and release of other redox agents by dehydration reactions in subducted altered oceanic crust is controlled in part by Fe³⁺/∑Fe. Lawsonite (Lws) and epidote-group minerals (EGMs) are hydrous Ca-Al silicates that are key phases in subduction-zone H₂O and element cycling owing to their composition and abundance, and the Lws-EGM transition has been linked to significant changes in fluid composition. Fe is a major component in most EGMs and a more minor but common component in Lws. Fe in Lws and metamorphic EGMs is generally assumed to be entirely Fe³⁺ that substitutes for Al in octahedral sites. However, results of Fe-XANES analyses for Lws and EGMs in blueschist and eclogite were acquired at the European Synchrotron Radiation Facility and show a wide range of Fe³⁺/∑Fe. Results for Lws appear robust because there are no signs of beam damage during analysis and there does not appear to be a strong orientation effect (linear dichroism). EGMs similarly show no beam damage effects but, in contrast to Lws, show significant variation in XANES spectra and resulting calculated Fe³⁺/∑Fe as a function of orientation. Although Fe in some Lws analyzed is entirely Fe³⁺, Lws and EGMs from New Caledonia blueschists contain substantial Fe²⁺. Work is in progress to determine what controls Fe³⁺/∑Fe in Lws and EGMs, but a preliminary conclusion is that Fe²⁺ in these phases in subducted oceanic crust may be greater than currently known, with implications for phase equilibria calculations and understanding of subduction redox conditions and processes.

How to cite: Whitney, D., Hanel, S., Wilke, M., and Rosa, A.: Variation in Fe2+ / Fe3+ in hydrous silicates in subducted oceanic crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20603, https://doi.org/10.5194/egusphere-egu24-20603, 2024.

The Mahakoshal Supracrustal Belt (MSB) marks the northern margin of the Central Indian Tectonic Zone (CITZ) along which are sutured the northern and southern crustal blocks of India. Monazite U-Th-Pb total ages in the Dudhi granite from a sample at the southern margin of the MSB are reported here. Although the age of the MSB was constrained between 1.8 and 2.2 Ga, a more precise upper age limit of ~2.1 Ga was proposed later. The present sample shows signatures of extensive hydrothermal alteration resulting in the replacement of orthoclase by oligoclase accompanied by precipitation of carbonate and microcrystalline silica. The monazites yield seven age peaks starting from 2053±65 Ma to 1457±39 Ma, suggesting multiple resetting of the ages. The most intense peaks are at 1951±19 Ma (n=29), 1851±20 Ma (n=20) and 1787±25 Ma (n=12), with only three points in the 2053±65 Ma population. Most likely, the Dudhi granite represents partial melting of the basement to the MSB at 2053±65 Ma and constrains the maximum age of the MSB, corroborating the upper age limit suggested earlier.

How to cite: Mondal, A., Mallick, S. P., and Pruseth, K. L.: Monazite age constraint on the Mahakoshal Supracrustal Belt, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-136, https://doi.org/10.5194/egusphere-egu24-136, 2024.

The behaviour of rare earth elements (REE), U-Pb, Sm-Nd, and Sr-Sr isotope compositions in accessory minerals provides a unique opportunity to track fluid sources and investigate trace element mobilization during fluid-assisted metamorphism. Metapelites of the Southern Marginal Zone (SMZ), Limpopo Belt (Bandelierkop formation), South Africa, experienced a ca. 2.7 Ga granulite-facies event in which the rocks underwent anatexis. The southern portion of the SMZ contains dispersed fragments of retrogressed metapelites with ubiquitous amphibolite facies assemblages including biotite, orthoamphibole, kyanite and a 2^nd generation of garnet replacing cordierite, equilibrated under 660-600ºC and ≥ 0.6GPa. The hydrated metapelites contain graphite intergrown with the retrograde assemblages, indicating a mixed H₂O-CO₂ fluid and a rock-dominated system. However, the source of the fluids that caused the retrogression remains unclear. Previous studies suggested that hydrating fluids were originally internally derived from the crystallizing in-situ melts, in sediments containing biogenic graphite, or that an externally derived CO₂ and H₂O-bearing fluid infiltrated the metapelites through shear zone systems. For the latter, some studies have proposed that this occurred during uplift of the granulite directly after Neo-Archean peak metamorphism, while others have used rutile U-Pb ages of ca. 2.1 Ga to argue for Paleoproterozoic retrogression.

This study investigated the geochemistry of garnet, apatite, and monazite from the hydrated zone metapelites to understand the origin of the fluids. Garnet trace elements show two distinct populations described as Grt1 (Eu/Eu*=0.36) and Grt2 (Eu/Eu*=1.55). Monazite shows relatively homogeneous REE pattern for distinct samples with a slight variation in HREE and negative Eu anomaly (Eu/Eu*=0.20-0.38). As for apatite the REE pattern is variable and distinct within and between samples (Eu/Eu*=0.36-0.37). 2741 Ma to 2707 Ma U-Pb monazite ages suggest that the amphibolite-facies assemblages are mainly related to the ca. 2.7 Ga granulite-facies event. U-Pb apatite dating yielded younger ages ranging from ca. 2057 Ma to 2047 Ma. Sm-Nd isochron of apatite yielded an initial ¹⁴³Nd/¹⁴⁴Nd (0.50950 ± 0.00100; 2s; n = 21; MSWD = 4.6) equivalent, within uncertainties, to the monazite initial ¹⁴³Nd/¹⁴⁴Nd (0.50882 ± 0.00030; 2s; n = 30; MSWD = 0.81). Monazite and apatite preserved its primary 2.7 Ga Sm-Nd isotope signature, but the U-Pb apatite system was reset at ca. 2.05Ga by solid-state diffusion. Thus, apatite reacted in the presence of a disequilibrium fluid in the Neo-Archean, as evidenced by the REE chemical variation, but did not experience dissolution/reprecipitation processes.  

We propose that the retrogressed zone of the SMZ experienced a Neo-Archean peak granulite-facies followed by amphibolite-facies retrogression, in which an internally derived fluid interacted with the metapelites. This is supported by published Sm-Nd bulk rock compositions that follow the same evolution trend as these samples, indicating a closed system history in the retrogressed zone of the SMZ. The rocks also record a Paleoproterozoic, lower-temperature, amphibolite-facies re-heating event, responsible for the resetting of the apatite. Initial ⁸⁷Sr/⁸⁸Sr = 0.7130±0.0014 (2s; n = 19; MSWD = 13) indicates a continental origin for the fluids that crystallized the apatite.

How to cite: Mazoz, A., Stevens, G., Moyen, J.-F., Gonçalves, G., Ferreira, A., and Santos, R. V.: Unravelling fluid-rock interaction in the hydrated zone of the Southern Marginal Zone of the Limpopo Belt - South Africa: a geochemical investigation based on U-Pb geochronology and Sm-Nd isotope composition of monazite and apatite in metapelites , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-791, https://doi.org/10.5194/egusphere-egu24-791, 2024.

Calcite is a common syn-kinematic precipitate in upper crustal fault zones coating slickensides, forming slickenfibers, and infilling veins. Structural and geochemical analyses of fault-related calcites can be used to unravel the source, distribution, and mixing of parental fluids in association with past fault activity. Identifying deeply sourced fluids through syn-kinematic calcites is of paramount importance, as the correlation of the ascent of deep sourced fluids with strong earthquakes, may allow using hydrogeochemical modifications in groundwater as potential seismic precursors. In this study, we investigate the origin of syn-kinematic paleo-fluids that circulated along the Val d’Agri faults, in southern Italy. These faults bound an intermontane basin topping the largest onshore oil field in Western Europe. Since the Val d’Agri Basin is affected by natural seismicity and low magnitude oil production induced earthquakes, it is necessary to assess the potential threats of hydrocarbon fault leakage at shallow crustal levels. With this aim, we collected about 350 syn-tectonic calcites along high-angle extensional-transtensional fault zones. By combining macro- and micro- scale structural observations with carbonate isotopes (C, O, clumped, and Sr) and rare earth elements and yttrium (REY) geochemistry, we identified 5 fluid sources: (1) meteoric waters in geochemical and thermal disequilibrium with the host rocks, which interacted with superficial soil; (2) meteoric waters in geochemical disequilibrium and thermal equilibrium with the host rocks, which had limited interaction with the host rocks; (3) buffered fluids in geochemical and thermal equilibrium with the host rocks; (4) high temperature fluids in geochemical equilibrium and thermal disequilibrium with the host rocks, which ascended from the carbonate hydrocarbon reservoir; (5) hot meteoric waters in thermal and geochemical disequilibrium with the host rocks, which mixed with the deeply sourced fluids. The presence of multiple fluids is consistent with an open fault-related circulation system, which allowed mixing of shallow and deep fluids through the high-angle extensional-transtensional Val d’Agri faults. Given the societal and economic issues of this area, the recognized involvement of deep fluids during past fault activity is crucial for the context of oil exploration and production as well as for environmental monitoring. Furthermore, this suggests that the Val d’Agri Basin is an ideal region to explore fluid-fault relationships throughout the entire seismic cycle through local seismicity records and continuous groundwater monitoring.

How to cite: Schirripa Spagnolo, G., Bernasconi, S., Aldega, L., Castorina, F., Agosta, F., Billi, A., Prosser, G., Smeraglia, L., and Carminati, E.: The Isotope and REY geochemistry of fault-related calcites document syn-kinematic fluid distribution along the Val d’Agri faults (southern Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1982, https://doi.org/10.5194/egusphere-egu24-1982, 2024.

Magmatic activities in sedimentary basins provides abnormal heat sources and exert significant impact on the regional temperature field. In previous studies, the anomalous thermal effects of magmatic activities of multiple scales were studied. Small-scale intrusions (cm-m) can conduct high-temperature thermal baking of surrounding strata within tens to hundreds of meters. Basin-scale heat flow anomalies caused by mantle plume upwelling have also received increasing attention. In contrast, the thermal effects of large igneous plutons (several km to tens of km) have received little attention. A few studies have shown that the large intrusive bodies can affect the temperature field within a range of tens of kilometers. The Permian large igneous province is widely distributed in the Tarim Basin, forming several large plutons. The Manalik pluton is a large intrusive body in the northwestern Tarim, with a long diameter of up to 40 km. We have measured the clumped isotope of different calcite fabrics from the Ordovician carbonate intervals surrounding the contact aureoles of Manalik pluton. In-situ U-Pb dating will be applied to these fabrics to provide starting anchors for thermal history modeling using solid-state reordering models of carbonate clumped isotope. In addition, Silurian sandstones from the same area were collected for zircon (U-Th)/He age measurement and subsequent thermochronological thermal history inversion. Compared with conventional thermal indicators applied in deeply buried strata (e.g., vitrinite reflectance), the integration of the two thermochronological tools (Δ47/U-Pb and zircon U-TH/He) holds the advantage in more accurately quantifying the abnormal thermal effects of kilometer-scale intrusive bodies. The experimental results show that zircon (U-Th)/He and clumped isotope jointly constrain temperatures exceeding 200°C in Well Shengli 1 and Well Yingmai 35, which are closest to the Manalik pluton; the thermal anomalies identified in Well Yudong 2 are as high as 220°C; Well Yingmai 2 Well and Yingmai 34, which are far away from the igneous intrusion, were not affected by the thermal contact aureoles of Manalik pluton during the Permian period, and the current burial temperature is the highest paleogeothermal temperature experienced in historical periods. Based on the zircon (U-Th)/He and U-Pb/Δ47 simulation results, we reveal that the Manalik pluton has a significant thermal baking effect on the area within 20km, and the maximum temperature in the area close to the igneous pluton can exceed 220°C. The results of this study provide typical cases and inspiration for identifying and quantifying the thermal effects of contact aureoles in other basins where large igneous pluton are developed.

How to cite: Maimaiti, A., Tian, J., Cong, F., and Wang, Q.: Quantifying the anomalous thermal effects of contact aureoles of a large pluton in the Tarim Basin: Constraints from clumped isotope thermometry, in situ calcite U-Pb dating, and zircon U-Th/He thermochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2777, https://doi.org/10.5194/egusphere-egu24-2777, 2024.

The Tethyan Phosphogenic Province is one of the widest of its kind, representing an outstanding period of phosphate deposition principally in the Upper Cretaceous-Eocene period. The main aim of this study is to compare the Turkish phosphorites occurring along the southern side of the Neo Tethyan Ocean due to suitable seawater temperature and upwelling oceanic currents with Albanian phosphorites were deposited in higher latitudes and colder climates, in the same ocean. The Şemikan (Türkiye) phosphorites consist mainly of cream-coloured (CCP) and locally reddish phosphorites (RP) occurring as lenses or concordant blankets within high-grade cream phosphorites. Based on microscopic examination, cream-coloured phosphorites consist of phosphatic pellets, intraclasts, bioclasts (fossilized shark teeth, ostracods etc.) and nonphosphatic components, with texture changing from wackestone to packstone, testifying shallow marine depositional environment. Whereas, Gusmari (Albania) phosphorites consist of laminated phosphorites (LP), of mudstone/wackestone texture, with planktonic foraminifera Globotruncanidae, where the phosphate is sedimentary, and alternating laminae of phosphate and pelagic carbonate. Besides this, under SEM-EDS, 5µm crystals of the major ore of uranium, UO₂, were evidenced for the first time in LP. The mineralogical analyses showed that the CCP consisted of carbonate-rich fluorapatite, minor calcite and quartz. The RP consisted predominantly of carbonate-rich fluorapatite, hydroxyapatite, montmorillonite, and minor quartz. The LP consisted predominantly of calcite, carbonate-rich fluorapatite, hydroxyapatite, and traces of quartz. The mean P₂O₅ content of the CCP is 29%, RP and LP 14%, which is lower than that of other well-known global phosphorite deposits. The CaO content of the CCP, RP and LP ore is also higher than that of other global deposits because of a calcite matrix between phosphorite pellets. Based on preliminary results of trace elements CCP, RP and LP show a general trace element scarcity compared to the trace element averages of the world’s average phosphorites. The main reason for this deficiency is the rapid sedimentation or high burial rate in the sedimentary basin, which prevents the replacement of carbonate-rich fluorapatite by trace elements.

How to cite: Fociro, A., Öztürk, H., Sinojmeri, A., Cansu, Z., Moisiu, L., Çelik, Y., Nazaj, S., and Prifti, I.: Petrographic and Geochemical Analysis of Upper Cretaceous Phosphorites in Şemikan, Turkey and Gusmari, Albania: Insights into Depositional Environments and Palaeoceanographic Conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2875, https://doi.org/10.5194/egusphere-egu24-2875, 2024.

Crystals grow in supersaturated solutions. A mysterious counterexample is dolomite CaMg(CO₃)₂, a geologically-abundant sedimentary mineral that does not readily grow at ambient conditions, not even under highly supersaturated solutions. Using atomistic simulations, we show that dolomite initially precipitates a cation-disordered surface, where high surface strains inhibit further crystal growth. However, mild undersaturation will preferentially dissolve these disordered regions, enabling increased order upon reprecipitation. Our simulations predict that frequent cycling of a solution between supersaturation and undersaturation can accelerate dolomite growth by up to seven orders of magnitude. We validate our theory with in situ liquid cell TEM—directly observing bulk dolomite growth following pulses of dissolution. This mechanism explains why modern dolomite is primarily found in natural environments with pH or salinity fluctuations. More generally, it reveals that the growth and ripening of defect-free crystals can be facilitated by deliberate periods of mild dissolution. [Kim et al., Science: adi3690 (2023)]

How to cite: Sun, W.: Dissolution enables dolomite growth near ambient conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3567, https://doi.org/10.5194/egusphere-egu24-3567, 2024.

The Rb-Sr dating system has long been recognised as being susceptible to thermal perturbation. Its so-called closure temperature (T_C) in biotite, the lowermost temperature at which interstitial diffusion of radiogenic ⁸⁷Sr is no longer facilitated, is ca. 400 ˚C, much lower than e.g., the commonly used U-Pb system in zircon in excess of 900 ˚C. Newly developed in-situ analyses or Rb-Sr isotope systematics in biotite using a collision cell mass spectrometer (ICP-MS/MS) have now enabled rapid dating using multiple grains and with high spatial resolution (on a single grain scale). This now allows making use of the thermal characteristics of this dating tool. However, the modes and degrees of isotope reset are still poorly understood. Here, we analyse rocks from the Kohler Range in Antarctica for their Rb-Sr systematics in biotite. The plutonic rocks formed as part of the active Permian Gondwana margin (ca. 280-260 Ma). Whilst two samples record their original Permian age, two other samples yield cretaceous ages (~100 Ma), consistent with regional magmatic activity during the breakup of Gondwana. Two samples with mixed populations of micas confirmed a partial reset in this rock, and thereby the full reset for the Cretaceous ages. An intriguing aspect is that reset is predominant in spot analyses with higher Rb/Sr, making these sections apparently more prone to thermal reset, likely through higher diffusion potentials. We interpret the resetting of the system as a response to thermal perturbation of the igneous rocks with no apparent petrographic footprint. It is demonstrated that in-situ Rb-Sr dating of igneous micas in plutons can be used to date magmatic flare-ups in rocks that can be hundreds of millions of tears older. The technique thus holds immense potential to decipher the thermal histories of terranes that otherwise remain undetected and may be used to shed new light on a large number of suspect Rb-Sr (mixed?) ages with no apparent geologic meaning.

How to cite: Nebel, O., Ali, Z., and Raveggi, M.: Magmatic flare-up recorded in Rb-Sr reset-ages during Gondwana break-up, Kohler Range, Marie Byrd Land, Antarctica , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4508, https://doi.org/10.5194/egusphere-egu24-4508, 2024.

Phosphorites are well-known, worldwide, for accommodating a significant amount of U relative to other sedimentary rocks, due to the crystal structure of apatite where U substitutes Ca. In Albania, uranium-bearing Lower Jurassic phosphorites form a distinctive horizon identified across the entire Ionian zone. Two different types of U-bearing phosphatic deposits are identified within the Lower Jurassic carbonate succession in Albania; one, stratigraphically younger, layered and parallel to carbonate strata and the other due to infiltration in older, brecciated carbonates. The first type consists of lenticular shape deposits of limited lateral extension intercalated in thin-shelled bivalve packstone/rudstone, possibly corresponding to the Toarcian Bositra-rich organic rich “Posidonia” shales of Austria and Germany. The phosphatic horizon is confined by dark gray J₂ limestone on the top, while the bottom shows signs of an early erosion. Their extent varies from 5-10 m to 100-160 m, while their thickness varies from 0.3 to 6 m. The radioactivity measurements indicate that the intensity of gamma radiation varies from 0.6 to 1.66 µSv/h, while the uranium content varies from 50 to 230 ppm, the highest values corresponding to the P₂O₅ peak of 32.66%. The second type of phosphorite mineralization developed in a widespread horizon throughout the Ionian zone. Its extension varies from 1.5 to 8 km, composed of continuous zones up to 0.5-1 km with some small interruptions. Uranium-bearing phosphatic deposits occur as the infiltrated matrix of breccias (caused by hydraulic or tectonic stress, not of sedimentary origin) made of angular clasts of Pliensbachian inner carbonate platform facies of the J₁ (peloidal and oncoidal packstone/grainstone with Siphovalvulina foraminifers and Palaeodasycladus mediterraneous dasyclad algae). The intensity of gamma radiation varies from 0.5 to 1.1 µSv/h, uranium content varies from 50 to 150 ppm and the P₂O₅ highest peak is 15%. In accordance to the first data achieved, the uranium-bearing phosphorites of Early Jurassic age in Albania formed in deep, oxygen-depleted marine conditions as suggested by the abundance of thin-shelled bivalves. The well-documented early Toarcian Oceanic Anoxic Event driven by an increase in nutrients linked to high volcanic emissions of CO₂ may have favoured the formation of the phosphate deposits. The intensive tectonic events associated with the Alpine Tethys Ocean opening during the Early and Middle Jurassic should be the main factor causing the brecciation and controlling the formation of later infiltration mineralization.

How to cite: Sinojmeri, A., Fociro, A., Della Porta, G., Grieco, G., and Beqiraj, S.: Preliminary insights on uranium-bearing Jurassic phosphorites of the Ionian zone, Albania, their distribution and genesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5344, https://doi.org/10.5194/egusphere-egu24-5344, 2024.

The Dizi series formed on the southern passive margin of a small oceanic basin on the Southern Slope of the Greater Caucasus and is exposed in the structural zone of the same name. The series is composed of metaterrigenous phyllite-like and volcanogenic rocks of the Devonian-Triassic age; marbles also are quite widespread in the series. During the Variscan orogeny, all rocks of the series underwent low-temperature regional metamorphism; later, in the Middle Jurassic time, intensive contact metamorphism took place. The object of presented research is marble, found in the rocks of the series both in the form of lenses and blocks. Interest in the study of marbles spread in the Dizi series is caused by several factors, namely, there is still no consensus on the position of marbles in the series, their detailed geochemical study has not been carried out, and the conditions of their formation have not been determined. There is an opinion that the Dizi series represents part of the Triassic Upper Karakaya complex, which was probably deposited in the forearc of the southern margin of Laurasia. The marbles are included in the series as exotic blocks of shallow marine Carboniferous and Permian limestone, most likely formed in Gondwana. During the study of the Dizi series marbles petrographic and geochemical research methods were applied. Petrographic characteristics of the marbles from all outcrops show a similar mineral composition, and structure and texture as well. The authors analyzed the main components, RE, and REE of the Dizi series marbles. The ratios Ca VS Mg, Mg/Ca VS SiO₂, and Sr VS Mg/Ca show that the protolith of the marbles was pure limestone. The reconstruction   of the deposition conditions of the marble protolith, based on the concentrations of Sr, Rb, and Ba, indicates the formation of limestones in the conditions of the continental margin. The Ce-negative anomaly observed in the marble samples is possibly due to the existence of an oxygenated marine environment, probably of shallow water conditions. These conditions fully correspond to the tectonic interpretation of geochemical data from other metasedimentary rocks of the series. The results of the presented studies confirm that the marbles under consideration were formed in situ, together with the other rocks of the Dizi series in the conditions of the continental slope and its foot on the southern passive margin of a small oceanic basin of the Southern Slope of the Greater Caucasus.

How to cite: Javakhishvili, I., Tsutsunava, T., and Beridze, G.: About the marbles of the Dizi series (Greater Caucasus): geochemical features, the nature of the protolith, and paleoecological conditions of their formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5609, https://doi.org/10.5194/egusphere-egu24-5609, 2024.

Microbialite development in the Ediacaran Qigebrak Formation of the Tarim Basin, Northwest China: An examination of characteristics, distribution, and paleoceanographic reconstruction

Xudong Chen^1,2, Qilu Xu^1,2

• National Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China;
• School of Geosciences, China University of Petroleum (East China), Qingdao, 266580, China

The Upper Ediacaran Qigebrak Formation in the Tarim Basin of NW China preserves abundant and well-preserved microbialites with primary textures. These provide valuable insights into Precambrian sedimentology and paleoceanography. Our study focuses on elucidating the relationship between paleoceanic conditions and the development of these microbialites to understand their Precambrian origin.

A comprehensive analysis of Ediacaran outcrops in the northwestern Tarim Basin identified 12 distinct microbialite types, ranging from mafic (F1) to flat-laminated stromatolite (F12). These comprise F2 (micrite dolomite), F3 (granular dolomite), F4 (bonded sand debris dolomite), and spongiomicrobialite variants (F5-F7). Additionally, we observed F8 (fenestral tectonic thrombolites), F9 (micrite thrombolites), and diverse stromatolite dolomites (F10-F12). Their occurrence is spatially distributed: F1 and F2 in the nearshore supratidal low-energy zone; F3, F4, and F7 in granular beach and microbial mound zones; F5 and F8 in the environmental transition zone; F6 and F11 in the lower intertidal high-energy zone; F10 predominantly in the upper subtidal high-energy zone; and F9 and F12 in both upper intertidal and lower subtidal low-energy zones.The shale-normalized REE patterns of these microbialites exhibit weak negative Ce anomalies, weak positive Eu anomalies, and positive La anomalies, suggestive of suboxic seawater deposition. Their chemical signatures, characterized by low V, Ni, and Co concentrations, high Sr content, and Sr/Cu ratios exceeding 50, collectively indicate warm and arid paleoclimatic conditions. Compared to F9, F6, F10, and F11 show lower V/(V+Ni) values, higher Mg/Ca ratios, and stronger LREE and MREE deficits, suggesting formation in shallower, more dynamic, saline, and oxygenated waters.

Our findings offer fresh perspectives on the formation mechanisms of Precambrian microbial rocks and paleo-oceanic reconstruction.

How to cite: Chen, X. and Xu, Q.: Microbialite development in the Ediacaran Qigebrak Formation of the Tarim Basin, Northwest China: An examination of characteristics, distribution, and paleoceanographic reconstruction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5704, https://doi.org/10.5194/egusphere-egu24-5704, 2024.

Dating Quaternary carbonates and phosphates beyond the range of U-series geochronology is challenging, but recent studies have shown potential using the method of LA-ICP-MS U-Pb geochronology. Terrestrial materials altered and produced by pedogenic processes are particularly challenging, as they are usually rich in common Pb and poor in U; however, they provide some of the rare opportunities to directly date important archaeological artefacts. Our aim is to advance the age constraints of the hominin presence in the Zarqa Valley, Jordan, an important geomorphological feature with the oldest hominin artefact outside Africa. Along with new Ar-Ar geochronology of sequence-bounding basalts and new palaeomagnetic constraints, our approach is to: (1) review published U-Pb data of 2019; (2) conduct LA-ICP-MS U-Pb analyses in various pedogenic carbonates (calcrete) that cap the artefact-bearing deposits along with mammoth fossil remains; and (3) review the regional ²³⁴U/²³⁸U activity ratio estimate required for calculation of accurate U-Pb ages.

A previous attempt to date hominin artifacts in the valley yielded an age of 1.98 ± 0.20 Ma for calcrete material, which is a weighted mean of several individual U-Pb isochrons derived from laminated calcretes, cracks, pore spaces and cement, and corrected by an initial ²³⁴U/²³⁸U activity ratio of 1.5 ± 0.5. We calculated an alternative, statistically favourable, age based on pooling the data into a single Tera-Wasserburg regression, resulting in 1.93 ± 0.44 Ma.

Our LA-ICP-MS analysis thus far has not yielded a new significant age, but we have focussed on understanding the U and Pb compositions in a range of materials, including calcretes, rhizoliths, fossil coatings and Mammalian fossils. Biogenic spherulite laminae in laminar calcrete have higher U (0.56 ± 0.064 ppm) and lower Pb contents (0.61 ± 0.15 ppm) compared to abiogenic cracks and cement (0.33 ± 0.084 and 0.9 ± 2 ppm, respectively). Although far from desirable for U-Pb geochronology, for now, the spherulite laminae seems to be the most suitable micromorphology to date calcrete. Coarse spar of rhizoconcretions have very low U contents (0.07 ± 0.35 ppm), leading to unfavourable U/Pb ratios. Two fragments of a mammoth molar from an artefact-bearing deposit have been analysed; one is part of the crown having dentine and enamel, and the other one is dentine of the root. The crown and root fragments have high U concentrations of 33 ± 11 and 13.7 ± 9.9 ppm, respectively, but with their high Pb contents they still yield a low spread in U/Pb ratios and very imprecise lower intercept ages. Using LA-ICP-MS mapping to better identify areas of alteration, we pooled U-Th-Pb spot data from regions with low Y (<5 ppm), Mn (<50 ppm), Al (<100 ppm), Th (< 0.05 ppm) and high P (> 7200 ppm), which correlated with the central portion of the dentine. These data yielded an age, using the combined U-Pb and Th-Pb calculation, of 1.9 ± 1.1 Ma; although very imprecise, it shows potential for further refinement.

How to cite: Cerqueira, J. C., Roberts, N. M. W., Scardia, G., Parenti, F., Ladeira, F., and Neves, W.: U-Pb geochronology of Quaternary pedogenic carbonates and teeth from archaeological sites of Zarqa Valley, Jordan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5861, https://doi.org/10.5194/egusphere-egu24-5861, 2024.

Detrital geochronology is a powerful tool to interrogate the sedimentary archive of (paleo-)hinterland tectonism, metamorphism, and exhumation, and can also be applied to modern river sediment as a first-pass tool to establish regional bedrock ages. The popular zircon U-Pb detrital geochronometer has seen widespread adoption for these tasks (4,173/5,100 results for the search term detrital geochronology also contain the term zircon U-Pb; Clarivate Analytics Web of Science). However, zircon fertility is strongly biased to intermediate to felsic source rocks. Moreover, zircon crystallization is volumetrically limited in metamorphic terranes which do not achieve anataxis (e.g., Moecher & Samson, 2006), and is typically restricted to rim overgrowths which are vulnerable to mechanical destruction during fluvial transport, and which are challenging to detect and analyse (e.g., Campbell et al., 2005).

Therefore, it is desirable to develop complementary provenance tools for sub-anatectic settings, as well as tools targeting more abundant rock-forming minerals for use with small-volume samples (e.g., drillcore). Established alternative detrital phases include the U-Pb system in apatite, monazite, titanite, and garnet. The advent of LA-ICPMS systems equipped with mass-filtered online reaction cells now also permits the routine use of β-decay systems by overcoming parent-daughter isobaric interferences. These include Lu-Hf in garnet and apatite, and Rb-Sr in K-phases including K-feldspar and mica (Rösel & Zack, 2022; Woods 2016). K-phases are also amenable to conventional Ar-Ar detrital geochronology.

Here, we present case studies of emerging detrital provenance techniques, with particular application to modern and past orogenic systems.

Campbell, I., et al., 2005. Earth Planet. Sci. Lett. 237, 402-432,  doi: 10.1016/j.epsl.2005.06.043

Moecher, D., & Samson, S., 2006, Earth Planet. Sci. Lett. 247, 252–266, doi: 10.1016/j.epsl.2006.04.035

Rösel, D., & T. Zack, 2022. Geostandards and Geoanalytical Research 46.2, 143-168, doi: 10.1111/ggr.12414.

Woods, G. 2016. Agilent Application Note. Agilent Technologies, Cheadle.

How to cite: Mark, C., Neofitu, R., O'Sullivan, G., Glorie, S., Zack, T., Rösel, D., Barfod, D., Chew, D., Daly, J. S., Clift, P., and Najman, Y.: Mountains from sand grains: Advances in detrital provenance applied to orogens, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9818, https://doi.org/10.5194/egusphere-egu24-9818, 2024.

The fault system within petroliferous basins plays a pivotal role in governing the migration, accumulation, and preservation of oil and gas resources. Accurate determination of the timing of fault activities is critical for reconstructing the history of tectonic evolution and for the analysis of hydrocarbon systems. Conventionally, this determination is achieved through the analysis and interpretation of seismic data. However, this method's effectiveness is often constrained by the quality of the seismic data, typically yielding only an approximate timeframe for fault activity. This limitation poses significant challenges in precisely identifying the periods of fault activity, which is essential for the analysis of their impact on hydrocarbon accumulation. Calcite, a commonly developed vein mineral in response to fault activities, is noteworthy in this context. The use of LA-ICP-MS U-Pb dating for fault vein calcite has been established as an effective technique to reveal time information of fault activity. The Tuoputai area, situated within the Tarim Basin, is recognized as one of the exploration hotspots with a complex tectonic evolution history. In particular, the strike-slip faults connecting Lower Cambrian source rocks with Ordovician carbonate reservoirs are instrumental in hydrocarbon migration and accumulation. In this study, the TP39 fault zone in the Tuoputai area, recognized for its rich hydrocarbon content, was selected for detailed analysis. We initially analyzed seismic data to obtain the approximate period of fault activity, followed by LA-ICP-MS U-Pb dating of calcite veins from core samples, to precisely determine the fault activity time. Additionally, the study incorporated the analysis of oil fluid inclusions in the calcite veins to comprehensively analysis the impact of fault activities on hydrocarbon accumulation. The seismic data indicated that the TP39 fault zone has mainly experienced three activity periods, including the Caledonian (542-416 Ma) to Hercynian (416-251 Ma), Indosinian (251-199.6Ma) and Himalayan (65.5 Ma-present) periods. In situ U-Pb dating of calcite veins from Ordovician reservoir cores in two wells within the fracture zone yielded ages of 446.79±2.67 Ma, 443.63±1.31 Ma, and 278.23±2.11 Ma, defining two significant active events in the TP39 fault zone during the Late Caledonian (~440 Ma) and Late Hercynian (~280 Ma), respectively. Furthermore, fluid inclusion analysis in calcite veins revealed a high prevalence of yellowish-green and bluish-green fluorescent oil inclusions, followed by blue fluorescent oil inclusions. The corresponding Th results from coexisting water inclusions indicated that the mainly phases of crude oil charging occurred during the Late Caledonian and Late Hercynian periods, followed by the Himalayan period, correlating well with the U-Pb dating results. This indicated that the fault activity during the Late Caledonian and Late Hercynian periods opened pathways for crude oil migration from the source rocks to the reservoirs. This study used the absolute dating method to constrain the activity time of the fault, demonstrating its impact on hydrocarbon accumulation, which is of great significance to basin structural research and oil and gas exploration.

How to cite: Xie, H. and Tian, J.: Fault activity history under absolute age constraints and its impact on hydrocarbon accumulation: A case study of the Tuoputai area in the Tarim Basin, China , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10059, https://doi.org/10.5194/egusphere-egu24-10059, 2024.

The mantle section of the ophiolite sequence is composed of ultramafic rocks, abundant in magnesium silicates. When exposed to crustal depths, these minerals become thermodynamically unstable and often interact with fluids of different provenance and chemistry. Ophiolite-hosted carbonates are one of the most widespread secondary phases resulting from interactions between silicates and CO₂-rich fluids. There is ample evidence that carbonation of ultramafic rocks can occur in various geological settings and across a broad range of P-T conditions (Plümper & Matter, 2023). Therefore, accurately identifying the source of the fluids responsible for carbonation could contribute to a more comprehensive understanding of the long and complex evolution of the ophiolites.

In this study, we investigate carbonates hosted by the two ultramafic massifs (Szklary and Braszowice) of the Central Sudetic Ophiolite (CSO) (NE Bohemian Massif). This ophiolitic complex represents a late Devonian oceanic lithosphere formed in the slow-spreading regime. The complex story of the CSO includes prograde metamorphism, reaching its climax within the amphibolite facies, emplacement of syn- and post-Variscan magmas, as well as tropical weathering event(s) in the Cenozoic. Carbonate mineralization appears mostly as extensive veins and vein-like structures within partially serpentinized peridotites and serpentinites. The vast majority of veins in both localities exhibit a high modal abundance of cryptocrystalline magnesite accompanied by chalcedony or quartz. Field investigations revealed that carbonate veins containing magnesite-dolomite and calcite-dolomite are comparatively less common occurrences and they are mostly seen in the Braszowice ophiolitic fragment. In some samples, hydrous magnesium silicates co-occur with the studied carbonates. Based on both bulk and single-spot chemical composition (ICP-MS/ES and LA-ICP-MS) of carbonates, discrepancies and similarities have been observed between two ultramafic massifs. The concentrations of several trace elements (Ni, Al, Mn, Sr, Ba, Fe) noticeably vary between Szklary and Braszowice. Moreover, varied chemical compositions have been pinpointed among veins sampled at different depths. Strontium isotope composition was analyzed for fraction dissolved in HCl. At least two groups of carbonate veins can be distinguished based on their ⁸⁷Sr/⁸⁶Sr ratios. Veins sampled from the Braszowice pit floor, exhibiting Mgs or Mgs ± Dol or Cal ± Dol paragenesis, consistently display 0.7064 - 0.7065 values. Carbonate veins located at shallow depths in Braszowice and Szklary, primarily composed of cryptocrystalline Mgs or Mgs ± Qz, show ⁸⁷Sr/⁸⁶Sr values ranging from 0.7070 to 0.7113 suggesting input from fluids derived from the continental crust. Our research indicates a level of complexity in the formation of ophiolite-hosted carbonates including several stages of their formation as well as several sources of carbonating fluids.

Plümper, O., & Matter, J. (2023). Olivine—the alteration rock star. Elements, 19(3), 165-172.

Funding: Research financially supported by NCN PRELUDIUM project 2022/45/N/ST10/00879

How to cite: Cieślik, B., Pietranik, A., Kierczak, J., Lacinska, A., and Ettler, V.: Multistage carbonation of the Variscan ophiolite? Insights from geochemical and isotopic diversity of ophiolite-hosted carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11037, https://doi.org/10.5194/egusphere-egu24-11037, 2024.

Temperature is recognized as the only dominant factor that affects the opening and closing of isotope system, based on which thermochronology has well developed. However, there are some research shows that stress could also matter. The muscovite K-Ar ages of Sanbagawa (Japan) schists are consistently younger with increasing deformation extent (Tetsumaru, 1988), which revealed that tectonic deformation can have influence on isotopic ages. On a microscopic scale, elements like Pb can redistribute in zircon lattice during dislocation (Piazolo,2015). The behaviors of isotopic systems in dating minerals under stress involve the fundamental problem of isotopic chronology. The application of it can be very wide, it allows us to get the deformation age directly if we choose the right deformed minerals in the right way. Some of the works such as fault, fold and ductile shear zone dating by our lab has been published (Yu Wang, 2010, 2016, 2020). What role does stress play in isotope diffusion which in turn affects ages is what we are eager to know. We designed a set of experiments using three axles press to work on undeformed K-feldspars with known age (126Ma) to test the effects. Rock mechanics experiments, field observation and isotopic dating are combined to give us an insight to it.

How to cite: Chen, X. and Wang, Y.: Effect of tectonic stress on isotopic systems in dating minerals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11149, https://doi.org/10.5194/egusphere-egu24-11149, 2024.

The Bristol Channel Basin (BCB) is a small continental rift basin that developed along the eastern margin of the North-Atlantic during the Mesozoic. Relatively minor basin inversion occurred during the Cenozoic. It has been extensively studied due to the exceptional exposure of faults along both margins of the basin. Widespread calcite mineralisation of overprinting fracture networks documents fluid partitioning along these structures over time. However, the temporal evolution of deformation has been constrained solely from the relative timing of structures in the field and through comparisons with other basins in the region. This has made detailed modelling of how structures have evolved during basin development and later inversion problematic. In this study we succesfully use U-Pb carbonate geochronology on low U samples (<1ppm) to constrain the absolute timing of fault development, whilst also assessing fluid source evolution with stable isotope and fluid inclusion data. Absolute dating of calcite slickenfibres in the fault cores of extensional, thrust and strike-slip faults in the East-Quantoxhead - Kilve region reveals the precise timing of different phases of deformation within the BCB for the first time.

New age data show that extensional faulting occurred from ca. 154-118 Ma. Strike-slip faults formed ca. 47-21 Ma, with thrust faults forming ca. 46-35 Ma. The results show Late Jurassic – Early Cretaceous E-W extension with a vertical σ₁, followed by Eocene – Miocene N-S contraction with σ₁ now being ~horizontal. New age determinations provide much greater insight into the longevity of these structural phases, as well as how fluid nature and composition has evolved over time. Stable isotope data captures fluid source evolution, with δ13C & δ18O values being more negative in the older extensional faults, and becoming more positive over time in the later contractional features. Reactivated structures show evidence for deeper fluid sources, shown by relatively hotter fluid inclusion temperatures within these faults.

Constraining the development of different fault populations within the BCB increases our understanding of the evolution of regional stress within southern England and can be extrapolated to nearby basins. Understanding the historical partitioning of fluid flow through different fault populations has practical applications for understanding where produced and/or injected fluids will flow when a reservoir is exploited today, such as in an Enhanced Geothermal System (EGS).

How to cite: Connolly, J., Anderson, M., Mottram, C., Price, G., and Sanderson, D.: Using U-Pb Carbonate Geochronology to constrain the timing of fault development and fluid source evolution in an inverted continental rift basin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11865, https://doi.org/10.5194/egusphere-egu24-11865, 2024.

Carbonates (calcite, aragonite, dolomite) are a minor component (often below 4 vol. %) of CM carbonaceous chondrites and formed during the aqueous alteration of their asteroidal parent bodies in the first few million years of Solar System history. The chemical and isotopic composition of these minerals are a valuable source of information on the conditions of alteration, potentially providing information on the composition and temperature of asteroidal fluids.

We report the carbon triple oxygen and carbonate clumped isotope compositions of six CM chondrites (Allan Hills 83100, Cold Bokkeveld, LaPaz Icefield 031166, Lonewolf Nunataks 94101, Murchison, Scott Glacier 06043), which span a range of degrees of aqueous alteration. To avoid issues due to the brecciated nature of these meteorites, gas aliquots produced by a single acid digestion were used to measure both the clumped isotopes and the triple oxygen isotope compositions. Where both calcite and dolomite are present, stepped acid dissolution allows us to measure their isotopic compositions separately.

We found that the Δ¹⁷O values range from -1 to -2.6‰, with a 0.6‰ difference between coexisting calcite and dolomite that indicates precipitation from distinct fluids. Crystallization temperatures range from 5 to 50⁰C for calcite and 75 to 100⁰C for dolomite. CM chondrites often contain several generations of carbonates with ranges in isotopic compositions that can be determined by ion probe. Because our method relies on the bulk extraction of carbonate phases, the measured values are the modes of the distributions for each meteorite, which has to be considered carefully in their interpretation. The isotopic composition of the alteration fluids can also be calculated for each meteorite and carbonate phase. We find that their δ¹⁸OvsSMOW ranges from -6.6 to +2.3‰, with no clear relationship with temperature or the δ¹³C of the carbonates, indicating a variety of starting isotopic compositions for the alteration fluids.

The main pattern that emerges is that chondrites with a higher degree of alteration (based on their petrology) have carbonates with lower Δ¹⁷O and higher crystallization temperatures, which is consistent with a prograde reaction in a largely closed system, and with dolomite forming after calcite in our samples.

How to cite: Clog, M., Lindgren, P., Lee, M. R., and Modestou, S.: The thermal and aqueous evolution of CM carbonaceous chondrite meteorites revealed by triple oxygen and clumped isotope compositions of their carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11910, https://doi.org/10.5194/egusphere-egu24-11910, 2024.

In south-western Martinique (Lesser Antilles), the Pointe Burgos Basaltic monogenetic strombolian cone and lava flow cut through a porphyritic dacitic lava dome (Morne Champagne) dated at 617 ± 52 ka (Germa et al., 2011). An exceptional feature of the basaltic lava flow is the occurrence of about 4% of large (up to 2 cm) quartz crystals. Previous studies suggested that quartz xenocrysts had been added to the basaltic magma upon mechanical magma mixing with the cooled shallow dacitic reservoir, with a 9:1 ratio. Indeed, plagioclase phenocrysts (>1 cm) present resorbed surface and reaction rims, a well-known evidence of crystal remobilization. However, no other textural evidence of magma mixing is visible in the basaltic edifice. Moreover, the quartz crystals present unusual habits, are heavily cracked, and appear as filling voids in the basalt. This led us to investigate the age of the basaltic eruption and of the quartz crystals to propose a scenario for the xenocrysts’ origin.

The groundmass of the basaltic lava flow was K-Ar dated at 379 ± 25 ka, therefore ~240 ka after the eruption of the dacitic dome that it cuts through. Such a long time difference suggests that magma in the shallow reservoir was completely solidified when the basaltic magma ascended through it. Therefore, we would have expected to see also enclaves of dacite included in the basalt. Thermoluminescence (TL) dating allows for estimating the time since mineral formation or the last heating of a mineral above ~350 °C, thus representing an ideal tool to test whether the quartz xenocrysts formed synchronously with lava flow, or if they were formed later as substitutional minerals or void fillings. Here, we used red TL in combination with several protocols for dose determination, yielding consistent results. For assessing the dose rate, we took into account the quartz xenocrysts’ size distribution, the radioelement concentration of the basaltic matrix and the sites’ erosive evolution. The latter is particularly important because the basaltic matrix is comparatively poor in radioactivity so that the share of the cosmic dose rate becomes important. We obtain preliminary TL ages of 345 ka (with a total erosion of 20 m) and 377 ka (with an erosion of 50 m), each with a ~7% uncertainty. This result emphasizes the importance of reconstructing the lava flow geometry for answering the research question. As we believe that scenario (1) is more plausible, our results indicate the xenocrysts were likely formed post-eruption, challenging the initially suggested model of magma mixing and favouring secondary precipitation or mineral substitution. In case of TL resetting through geothermal activity, the age would represent the cooling following its cessation. However, given the xenocrysts’ pseudomorphic habit, it appears more likely that they represent secondary precipitates from hydrothermal fluids in voids left by strong geothermal alteration of the basaltic host rock.    

References

Germa, A., Quidelleur, X., Lahitte, P., Labanieh, S., Chauvel, C., 2011. The K–Ar Cassignol–Gillot technique applied to western Martinique lavas: a record of Lesser Antilles arc activity from 2 Ma to Mount Pelée volcanism. Quat. Geochronol. 6, 341-355.

How to cite: Schmidt, C., Germa, A., Quidelleur, X., King, G., and Jaimes Gutiérrez, R.: Age and origin of quartz xenocrysts in a basaltic lava flow in Martinique , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13041, https://doi.org/10.5194/egusphere-egu24-13041, 2024.

Intrusions of the Navajo Volcanic Field (NVF) contain eclogite xenoliths that record processes related to the subduction of the Farallon plate beneath the Colorado Plateau. Previous geochronological work sparked controversies about their origin, especially whether they are derived from oceanic crust of the Farallon plate, or from older continental lithosphere, based on occasional Proterozoic zircon U-Pb ages. Moreover, the mechanisms and timescales of the recorded high-pressure processes, including several stages of fluid metasomatism, are largely unknown. We study the U-Pb systematics of garnet, zircon and rutile by LA-ICP-MS in order to achieve a refined petrochronologic interpretation of the NVF eclogites.

The eclogite xenoliths are hosted by serpentinized ultramafic microbreccia (SUM) which intruded the Colorado Plateau at ~30 Ma as a consequence of extensive hydration of the lithospheric mantle by Farallon slab-derived fluids. In contrast to kimberlite-borne eclogite xenoliths, which often contain garnet and omphacite only, those of the NVF additionally contain ubiquitous rutile, and often pyrite, phengite, zoisite pseudomorphs after lawsonite (with rare lawsonite relics), accessory monazite, and rare coesite. Based on this assemblage, peak P-T conditions around 4 GPa and 600°C are estimated. Subsequent rapid uplift in the sub-solidus SUM is not thought to have caused significant further heating. Except for a few instances where a mid-ocean ridge basalt-like bulk chemical composition is essentially preserved, the xenoliths are strongly overprinted by several metasomatic events in the eclogite facies. Most notably, this involved interaction with a Na-Si-S-rich fluid, probably of crustal origin, and a later (just prior to exhumation) serpentinite-derived fluid.

All our U-Pb rutile data as well as published U-Pb monazite data (~29 Ma) agree with the ~30 Ma SUM formation age. The majority of the U-Pb zircon analyses predate the rutile data by not more than several Myr, with a minority of older ages forming a continuum to the late Cretaceous. Unlike some earlier studies, we did not obtain any Proterozoic U-Pb zircon ages. The garnet U-Pb dates, which are mostly from pre-metasomatic zones, partly agree with the zircon dates within uncertainty, but sometimes predate the zircon dates from the same sample by up to several tens of Myr.

Despite moderate peak metamorphic temperatures (~600°C), rutile remained an open system for Pb until exhumation. Garnet and zircon are resistant to Pb volume diffusion at these temperatures, however, the zircon ages appear to be largely reset during fluid metasomatism, as also indicated by often high common Pb contents. Due to the absence of preserved igneous zircon ages, the protolith origin remains uncertain. Garnet, which grew mostly before metasomatism, seems to provide robust ages of initial eclogitization, which may have been diachronous in our sample suite. Geochronological evidence implies that several tens of Myr passed between initial eclogitization and exhumation of the xenoliths.

How to cite: Pohlner, J. E., Hao, S., Albert, R., Gerdes, A., Schulze, D. J., Helmstaedt, H., and Aulbach, S.: Garnet, zircon and rutile U-Pb systematics of eclogite xenoliths from the Navajo Volcanic Field (USA), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13231, https://doi.org/10.5194/egusphere-egu24-13231, 2024.

The Cryogenian period represents a critical interval in Earth’s history, characterized by drastic tectonic and environmental changes. Evidence of low-altitude glacial deposits from this time has been recognized globally, alluding to the most extensive icehouse regimes known on our planet. These conditions of successive global freezing and warming during the Neoproterozoic have been dubbed as ‘Snowball Earth’ events. Importantly, the Cryogenian may have played a key role in the accelerated evolution of early life, as microorganisms became more complex and abundant after this period. Consequently, it is important to constrain the absolute timing, duration, and termination of these glacial and interglacial events. Despite their significance, robust, direct dating of Cryogenian sections remains challenging. The most accurate way to constrain these units is through dating of interbedded volcanics. However, they are not present across all sections globally, making correlations difficult to establish.

As such, we present a novel strategy to address this issue by directly dating a broad array of Cryogenian carbonates through an in situ U-Pb mapping approach. Our case study includes inter-glacial and post-glacial carbonates from sections in Australia, Oman, and Greenland. We show that this method allows for the concurrent collection of geochemical, petrographic, and geochronological information at sufficient precision to address key geological questions. Geochemical proxies such as elevated Mn/Sr ratios and Al or Si can be used to filter areas affected by alteration or detrital input, respectively. Secondary phases such as veins and overgrowths can also be petrographically avoided as an advantage of the spatially coherent mapping technique. Regions that yield enrichment in U and best spread in U–Pb ratios can be preferentially selected. Triaging such datasets and spatial information can help identify subdomains within a sample that is most suitable for dating, maximizing the success rate of this approach. The technique is capable of yielding age precision of ±1% depending on the concentration of U, the range in radiogenic isotopes, and the number of pixels that make up an analytical point.  

How to cite: Subarkah, D., Collins, A., Löhr, S., Nixon, A., Blades, M., Farkas, J., Lloyd, J., Klaebe, R., Gilbert, S., and Virgo, G.: Direct dating of global Cryogenian sections by in situ U–Pb mapping of carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14298, https://doi.org/10.5194/egusphere-egu24-14298, 2024.

Carbonatite has enormous potential for rare earth element resources, typically enriched in light rare earth elements, and has attracted increasing attention from geologists and economists. However, there are a small number of documented instances of carbonatite-related heavy rare earth elements enrichment. The Jialu carbonatites in the Qinling orogenic belt (central China) are characterized by the enrichment of heavy rare earth elements compared with typical global carbonatites. The carbonatites are dominantly comprised of calcite, quartz, sulfate, K-feldspar, minor sulfides, and rare earth minerals such as monazite, bastnäsite, parisite, and xenotime, with two mineralization stages including the early quartz-K-feldspar-calcite stage (Stage I) and the late sulfide-rare earth mineral-calcite stage (Stage II). The rare earth element contents of Stage I calcite are higher than those of the Stage II, especially heavy rare earth elements. Calcite from the different mineralization stages exhibits variable chondrite-normalized REE patterns, with the heavy rare earth elements and rare earth element abundances (134–1023 ppm) decreasing from the early to the late stage owing to the crystallization of xenotime. The δ¹³C (−5.39‰ to −6.68‰) and slightly higher δ¹⁸O (10.77‰ to 12.60‰) values for calcite from the Jialu carbonatites generally deviate from the values observed in the primary carbonatite field, which may be a result of Rayleigh-type fractionation. LA–ICP–MS U–Pb dating shows the lower-intercept ages of 243.8 ± 5 and 237.6 ± 1.3 Ma for the monazite and xenotime, respectively, with the weighted average ²⁰⁶Pb/²³⁸U ages of 240.9 ± 6 and 239.2 ± 1.3 Ma. These results indicate that the Jialu deposit was concurrent with Triassic carbonatite magmatism and rare earth element mineralization observed on the southern margin of the North China Craton. This implies that this region may have great rare earth element mineralization potential.

How to cite: Li, F., Zeng, Q., Fan, H., and Yang, K.: Unusual heavy rare earth elements enrichment and mineralization age in the Jialu deposit from the Qinling Orogen, central China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14613, https://doi.org/10.5194/egusphere-egu24-14613, 2024.

In the northernmost part of the Romanian Carpathians, the Maramureș region exposes several tectonic units comprising remnants of the Mesozoic Ceahlău - Severin Ocean. The “Black Flysch” unit contains a mafic complex extended in the Middle – Late Jurassic interval. These are covered by Upper Jurassic–Lower Cretaceous sediments, which include deep-water carbonates and siliciclastic deposits in the “Black Flysch” Nappe and mainly turbidites in the Ceahlău unit, which belong to the Outer Dacide nappe system.

The U-Pb age distribution spectra of detrital zircons obtained from the samples collected from the “Black Flysch” and Ceahlău tectonic units exhibit similarities within the range of 180–3,000 Ma. Significant peaks have been noticed at around ~460, 580–620, ~320, 180–200, and 950–1,100 Ma. Within the ‘Black Flysch’ Nappe prevail Ordovician ages (~460 Ma) associated with the Bucovinian Nappe basement. Conversely, in the Ceahlău Nappe, the Late Neoproterozoic peak (~600 Ma) holds greater significance, corresponding to the sediments of the Eastern European Platform and the paragneiss of the Bucovinian Nappe. The East European Craton contributes insignificantly as source area, given the minimal percentage of inherited ages surpassing 1 Ga.

How to cite: Lazar, C., Roban, R. D., and Ducea, M.: Provenance of the North Eastern Carpathian thrust sheet deposits based on geochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14745, https://doi.org/10.5194/egusphere-egu24-14745, 2024.

Chemical composition heterogeneity in carbonate rocks ranging from the microscale to several meters preclude their direct age determination. Therefore, stepwise dissolution of several bulk rock samples or subsamples of an individual specimen can provide information on the primary composition of the carbonate material and refine the resulting Pb–Pb age. A millimetre-thick carbonate-rich (white) and shale-rich (black) layer from the Rohtas Formation, Lower Vindhyan Group, was divided into eight subsamples each and subjected to three leaching steps. The first leachate (L1) was discarded, and subsequent leachates, L2 and L3, were obtained after 24 hours of leaching in 0.6M HBr. A Pb-Pb isochron age of 1666±25 Ma (n=23, MSWD=13) is obtained by regressing L2 and L3 leachates from both layers. Since initial leachates (e.g., L2) contain epigenetically altered carbonate material, data points in the ²⁰⁷Pb/²⁰⁴Pb vs ²⁰⁶Pb/²⁰⁴Pb plot are well correlated but show a large scatter. In contrast, regressing only the L3 leachates of both layers yielded a Pb-Pb isochron age of 1644±49 Ma (n=12, MSWD=7), with a reduced scatter and comparable with earlier published work. Increasing the number of leaching steps minimizes the degree of scatter and significantly improves the precision of the obtained Pb-Pb age. Two subsamples from phosphoritic stromatolite-bearing carbonate rocks of the Tirohan Dolomite from the Jankikund river section, Lower Vindhyan Group, were subjected to seven leaching steps, of one hour each, in 0.5M HBr. The Pb isotopic composition of the carbonate material dissolved in five steps (L3 to L7) was regressed to yield an isochron age of 1579±16 Ma (n=10, MSWD=1.3). The Pb-Pb age of the Tirohan Dolomite Member obtained by multi-step leaching in this study is indistinguishable within error from an earlier reported age ^[1] of 1650±89 Ma (n=5, MSWD=89), moreover shows a better correlation of the ²⁰⁷Pb/²⁰⁴Pb vs ²⁰⁶Pb/²⁰⁴Pb data. All the analyses were performed in static mode on a Thermo-Fisher Neptune Plus MC-ICPMS. The instrumental mass fractionation was corrected using both thallium-spiking and sample-standard bracketing. Furthermore, a generalized power law correction was applied to the ²⁰⁴Pb-corrected ratios of unknown samples using the ²⁰⁵Tl/²⁰³Tl ratios of the bracketing NBS-981 standards. The two-stage mass bias corrected ratios were then normalized by the ratios of NBS-981 during each analytical session. The long-term isotopic ratios of NBS-981 standard (n=71) are ²⁰⁶Pb/²⁰⁴Pb= 16.9371±0.0026 (2σ), ²⁰⁷Pb/²⁰⁴Pb= 15.4906±0.0046 (2σ), ²⁰⁸Pb/²⁰⁴Pb= 36.7042±0.0113 (2σ).

[1] Bengtson, S., Belivanova, V., Rasmussen, B., Whitehouse, M. (2009). The controversial “Cambrian” fossils of the Vindhyan are real but more than a billion years older. Proceedings of the National Academy of Sciences, 106(19), 7729-7734.

How to cite: Nandi, A., Vadlamani, R., and Bera, M. K.: Improving the precision of Pb-Pb ages of carbonate rocks by implementing stepwise dissolution techniques: A case study from the Lower Vindhyan Group, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14937, https://doi.org/10.5194/egusphere-egu24-14937, 2024.

Geochronological data on ore-bearing minerals can constrain the absolute ages and duration mineralising processes. Of the tungsten-bearing minerals, wolframite is the most promising geochronometer for these mineral systems, but high precision ages are hampered by common Pb and intra-grain heterogeneity. We present ID-TIMS and LA-ICP-MS U-Pb isotope data of wolframite , combined with milli scale (SEM-EDS) and microscale (LA-ICP-MS) element maps and nanoscale (FIB-TEM) chemical and structural images to elucidate the complex geochemical behaviour of this mineral and the implications for U-Pb geochronology.

During this study, three new U-Pb reference materials have been developed with ages of ca 158 Ma, 289 Ma and 325 Ma; these are available to interested laboratories. The best precision obtained by ID-TIMS was 1.24%, whilst we estimate the best possible precision for LA-ICP-MS ages to be ca 1.8%. Apart for analytical uncertainties, the main contributor to age uncertainty is the poor dispersion in U-Pb data (for Discordia fitting) and unknown common Pb composition for ID-TIMS data, and micron-scale heterogeneity for LA-ICP-MS data.

Microscale (LA-ICP-MS maps) to nanoscale (FIB-TEM) imaging techniques show large chemical and structural heterogeneity of wolframite related to the complex geological environments in which it is precipitated and altered. Trace element mapping highlights oscillatory and sector zoning not typically observed when using traditional SEM-based techniques. The variable distribution of the analysed elements (Fe, Mn, Sc, Nb, Ta, Y, Pb, Th and U for this study) can be explained both by coupled substitution and changing fluid chemistry recorded within a single wolframite crystal. The nano-scale structure of a strongly altered wolframite is characterised by rare ca 10x10 nm non-symmetric zones of amorphous crystal structure, and bands of elongate (ca 100 x 20 nm oval-shaped) low density zones that we consider representing porosity developed during rapid crystallisation of wolframite.

Although no real intra-grain age dispersion is observed in the analysed samples, the precision of U-Pb ages is strongly affected by the local chemical and structural characteristics of the wolframite. Most notably, the concentration of ²³⁸U and ²³⁸U/²⁰⁴Pb can vary by an order of magnitude within a zone smaller than a typically laser ablation spot (e.g., 100 µm).

How to cite: Carr, P., Romer, R., Chew, D., Wirth, R., and Mercadier, J.: Nano to milli scale characteristics of wolframite ([Fe,Mn]WO4)  and their implications for U-Pb geochronology of tungsten-bearing mineral deposits, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14940, https://doi.org/10.5194/egusphere-egu24-14940, 2024.

A schist and a marble are used to investigate ⁴⁰Ar and Sr behaviour in white mica that show distinct records of deformation and fluid-mediated chemical exchange. The rocks were obtained from the upper level of the Middle Allochthon in the northern Scandinavian Caledonides. They underwent eclogite-facies metamorphism (2.4-2.6 GPa/590-660°C) at c. 486-481 Ma and were deformed during juxtaposition with the overlying Upper Allochthon in lower amphibolite/greenschist facies conditions at c. 430-420 Ma. Deformation of the schist is recorded by anastomosing shear bands that delimit polymineralic lenses of white mica, quartz, garnet, and apatite. White mica are only locally deformed along shear bands but show irregular zoning indicative of dissolution-reprecipitation, with high-celadonite zones (X_Cel: 0.22) generally enveloped by low-celadonite zones (X_Cel: 0.09). Fluid activity during rock deformation is evinced by the presence of chlorite in shear bands and surrounding partially retrogressed garnet, as well as dissolution-reprecipitation of plagioclase. Mobilization of trace elements is evident, with low-celadonite zones enriched in V, Sr, Nb, Ba and depleted in Li, Ti, Co, Zn relative to high-celadonite zones. The former also shows slight enrichment of average B (35.9 µg/g) compared to the latter (27.2 µg/g), but δ¹¹B values are the same for both zones (-13.5 and -13.6 ‰), suggesting locally-derived fluids. Deformation and foliation development of the marble is characterized by shape preferred orientation of calcite and white mica. The mica show variable grain size and are all deformed, highlighted by electron channeling contrast imaging that reveals abundant µm-scale kink bands within individual grains, a feature that is significantly less apparent in the schist mica. The marble mica show uniform high-celadonite content (X_Cel: 0.28), representing preservation of high-pressure mica chemistry during deformation. They show no trace element variations, except for a decrease B content with δ¹¹B values (36.3 µg/g and -18.1 ‰ to 15.5 µg/g and -22.0 ‰), which may be explained by heterogeneous devolatilization and preferential loss of ¹¹B during high-grade metamorphism. Thus, it is evident the mica remained closed to chemical exchange during deformation. The white mica ⁴⁰Ar/³⁹Ar dates from the schist are dispersed (491 ± 4 Ma to 427 ± 4 Ma), with the older dates typically provided by high-celadonite zones, and vice versa. The marble mica yielded a similar range of dates (486 ± 4 Ma to 428 ± 4 Ma), with finer-grains yielding younger dates. Weighted averages of single-spot Rb/Sr dates show a similar pattern for the schist (high-celadonite: 485 ± 8 Ma; low-celadonite: 427 ± 15 Ma). However, Rb/Sr dates from the marble mica only reproduce the older population of dates (481 ± 4 Ma) regardless of grain size. These results demonstrate that loss of ⁴⁰Ar from white mica can be facilitated by either fluid-mediated chemical exchange or deformation, but re-equilibration of Sr isotopes to reset Rb/Sr dates requires fluid-driven processes in lower amphibolite/upper greenschist facies conditions.

Research funded by NCN grant no. UMO-2021/40/C/ST10/00264 (C.J. Barnes), supported by “Juan de la Cierva” Fellowship JFJC2021-047505-I by MCIN/AEI/10.13039/501100011033 and CSIC (M. Bukała)

How to cite: Barnes, C., Zack, T., Gerdes, A., Dubosq, R., Camacho, A., Rösel, D., and Bukała, M.: Examining the behaviour of Sr and 40Ar in white mica in response to deformation and fluid-mediated chemical exchange, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15171, https://doi.org/10.5194/egusphere-egu24-15171, 2024.

Faults and related fractures have been studied for decades due to their potential in providing insights into past and present crustal deformation processes, climate evolution, seismology, and hydrology among others. Carbonates are very common syn-tectonic minerals that occur along fault planes or in fault-related fractures forming slickenfibres and veins (Roberts and Holdsworth, 2022). The ability of carbonates to incorporate uranium during their precipitation allows the application of in-situ carbonate U-Pb radioisotopic dating via LA-ICP-MS (Roberts et al., 2020). The integration of this method with the more conventional petrography and biostratigraphy holds strong potential in resolving the timing of brittle structure development. A robust pre-dating screening protocol using a multi-disciplinary approach, including structural, microstructural, petrographic, and isotopic characterization has been implemented to link carbonate precipitation event to fault kinematics.

This approach has been applied to the central Southern Alps (Northern Italy), where Early Jurassic rift-related faults are preserved despite their later involvement in the Alpine orogeny. Fieldwork and sampling focused on the Amora Fault (Bergamo, Italy), a rift-related N-S normal fault of the Jurassic Lombardian basin. Structural and paleostress analysis led to the identification of several mesoscopic N-S trending normal faults and veins both in the hanging wall and footwall of the Amora Fault, indicating an E-W extension. The fault is cross-cut by middle Eocene E-W trending magmatic bodies, which, in turn, are cross-cut by Alpine thrust faults. The Amora Fault and related minor faults also show strike-slip reactivation related to N-S Alpine compression.  

Sampling focused on the Norian to Lower Jurassic succession in the hangingwall and footwall of the main fault plane, where carbonate syn-tectonic veins and slickenfibres are present. Structural analysis allowed relating the structures to either the rifting or the Alpine reactivation.

Microstructural and petrographic analyses assisted by cathodoluminescence on 21 samples revealed the occurrence of several carbonate phases. Elemental analyses (Ca, Mg, Fe, Sr) and O-C stable isotope analyses confirmed the circulation of different fluids. U-Pb dating on the carbonate phases provided four age clusters, each connected to a tectonic phase: (1) Early to Middle Jurassic carbonates precipitated in rift-related structures from a fluid with a δ¹³C buffered by the host-rock. (2) Early Cretaceous carbonates possibly related to the late stage of rifting activity. (3) Late Cretaceous carbonates precipitated from a meteoric fluid during the early stages of the Alpine orogeny. (4) Oligo-Miocene carbonates connected to the strike-slip reactivation of rift-related normal faults.

The integration of field-based and stratigraphic observations with carbonate geochemistry and geochronology allowed the recognition of a complex reactivation history for the Amora Fault.

References

Roberts, N.M.W., Drost, K., Horstwood, M.S., Condon, D.J., Chew, D., Drake, H., Milodowski, A.E., McLean, N.M., Smye, A.J., Walker, R.J., and Haslam, R., 2020. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb carbonate geochronology: strategies, progress, and limitations. Geochronology 2, 33–61.

Roberts, N.M.W, and Holdsworth, R.E., 2022. Timescales of faulting through calcite geochronology: A review. Journal of Structural Geology, 158, 104578.

How to cite: Rocca, M., Zanchetta, S., Mangenot, X., Gasparrini, M., Berra, F., Deschamps, P., Guihou, A., and Zanchi, A.: Carbonate U-Pb geochronology as a tool to unravel complex fault evolution: an example from the central Southern Alps (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15293, https://doi.org/10.5194/egusphere-egu24-15293, 2024.

               Within the first five years of the initial introduction of multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) with the VG Elemental Plasma 54 the potential for the technique to be applied to Isotope Cosmochemistry applications had already been recognized¹. Early work focused on the ¹⁸²Hf-¹⁸²W chronometer, which had up until the introduction of MC-ICP-MS, been extremely difficult to measure with existing thermal ionization mass spectrometry (TIMS) techniques due to the extremely high first ionization potential of W.

In the following 25 years the use of MC-ICP-MS for Isotope Cosmochemistry applications has expanded to numerous other isotopic systems, including, but not limited to ²⁶Al-²⁶Mg, ¹⁴⁶Sm-¹⁴²Nd and ⁶⁰Fe-⁶⁰Ni, not just ¹⁸²Hf-¹⁸²W.  A general feature of these measurements is typically a reliance on excellent precision, on the order of a few ppm, 2RSD [2]. The high count rates required to achieve such excellent precision take time in order to achieve. Excellent precision over such time scales require a high performance mass spectrometer, capable of high sensitivity, stable throughout the course of the measurement and equipped with a low-noise detection array.

For over 20 years Thermo Fisher Scientific has pioneered developments in multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). The latest generation Thermo Scientific™ Neoma™ MC-ICP-MS, blends cutting-edge and field proven technology from the Ultra™ HR-IRMS and iCAP Qnova™ Series ICP-MS [3] and has the capability to complement and enhance Isotope Cosmochemistry applications [4]. Here we report our investigations into using the Neoma MC-ICP-MS and Neoma MS/MS MC-ICP-MS for a selection of Isotope Cosmochemistry application, including high precision Mg, Fe, Cu, Zn and W measurements.

[1] A. Halliday, D. Lee, J. Christensen, M. Rehkämper, W. Yi, X. Luo, C. Hall, C. Ballentine, T. Pettke, C. Stirling, Geochimica et Cosmochimica Acta, 1998, 62, 919-940.

[2] S. Goderis, R. Chakrabarti, V. Debaille, J. Kodolányi, 2016, J. Anal. At. Spectrom., 2016, 31, 841-862.

[3] Thermo Fisher Scientific, 2020, BR30600-EN 0520C: Neoma Multicollector ICP-MS [pdf], Thermo Fisher Scientific.

[4] Z. Deng, M. Schiller, M. G. Jackson, M-A. Millet, L. Pan, K. Nikoljsen, N. S. Saji, D. Huang, M. Bizzarro, Nature, 2023, 621, 100-104

How to cite: Craig, G., Pfeifer, M., Williams, N., Mournier, L., Bouman, C., and Lloyd, N.: High precision isotope ratio analysis for Cosmochemistry applications using the Thermo Scientific Neoma MC-ICP-MS., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15680, https://doi.org/10.5194/egusphere-egu24-15680, 2024.

U–Pb and U–Th geochronology of zircon in igneous rocks provides key information about the age, longevity, and assembly rates of magma reservoirs. Historically, the available analytical resolution limited these insights to an averaged “age” of a magmatic system. With dramatic improvements in analytical techniques over the last two decades, it has become possible to resolve extended records of zircon crystallisation within a single igneous sample, which can extend prior to its eruption or subsurface solidification by as much as a million years. In some magmatic systems these age spectra mirror those produced in zircon solubility models, reflecting monotonous cooling of a magma reservoir, whilst in others they may take other shapes indicative of a more complex interplay of processes [1,2]. Isolating the effect of these processes can be challenging since many analytical and geological factors also play a role. Such geological processes may include magma recharge or truncation of zircon crystallization by melt extraction.

In this study, we compiled high-precision zircon U-Pb dates from volcanic, plutonic and porphyry copper systems. We use the Wasserstein metric as a dissimilarity measure to compare distributions between all compiled age spectra. Dimensionality reduction of the resulting dissimilarity matrix reveals that plutonic systems have contrasting age spectra to volcanic and porphyry copper systems. Plutonic systems typically exhibit age spectra skewed towards older ages whereas volcanic and porphyry systems are skewed towards younger ages.

We adopt a bootstrap modelling approach to explain these differences, which allows the modelling of the effects of the number of sampled zircons, analytical uncertainties, magmatic recharge, mixed age domains and a truncation of crystallisation. The effects of multiple magmatic recharge events combined with truncation by volcanic eruption/dyke formation appear to be the most likely explanation for the young skew of volcanic and porphyry copper age spectra. Truncation of zircon crystallization alone appears to be incapable of explaining the full difference. Recognising the contrasting zircon age spectra between volcanic and plutonic systems is critical to improve eruption age estimation and interpretations of zircon compositions in petrological studies.

[1] Keller, C.B., et al., GPL, 2018. 31–35.

[2] Tavazzani, L., et al., EPSL, 2023. 623, 118432.

How to cite: Nathwani, C., Tavazzani, L., Szymanowski, D., Virmond, A., Markovic, S., and Chelle-Michou, C.: Controls on high precision zircon U-Pb age spectra in magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15969, https://doi.org/10.5194/egusphere-egu24-15969, 2024.

Geochronological methods play a pivotal role in unraveling the evolution of volcanic fields, providing insights into eruption timescales and recurrence. In the Quaternary Eifel volcanic field, with >300 maars and scoria cones, dating volcanic events remains challenging due to the scarcity of suitable materials for conventional dating methods. A promising approach to determine accurate eruption ages is to apply (U-Th)/He geochronology to zircon extracted from partially re-melted crustal xenoliths^1,2, which in case of Eifel maars are co-deposited with country-rock derived lithics and juvenile lapilli. However, the reproducibility of the method, if applied to xenoliths of different origin, age, composition, and texture, has not been studied for a single explosive eruption.

We collected >250 crustal xenoliths from >35 centers of the East and West Eifel volcanic fields. Coupled petrological investigation and zircon geochronology (U-Pb and U-Th) of a subset of these xenoliths reveal their diversity regarding protolith types (plutonic vs. low- to high-grade metamorphic), zircon crystallization ages (200 ka to 3 Ga) and degree of pyrometamorphic overprint (variable abundances of glass and vesicles, and crystal breakdown reaction textures). (U-Th)/He dating of the previously U-Th-Pb dated crystals (zircon-double-dating, ZDD) was performed to determine eruption ages for these centers.

Here, we focus on a xenolith suite (n = 8) from the Gemündener Maar and E-Schalkenmehrener Maar, two vents within a maar cluster known as Dauner Maar group. Tentative eruption ages of 20 to 30 ka were estimated from considerations on paleoclimate and crater morphology^3,4, and ESR xenolithic quartz dates of 30 ± 4 ka⁵. The pyroclastic deposits are rich in diverse zircon-bearing crustal xenoliths and thus, offer an ideal testbed to investigate how critical parameters such as xenolith rock type, zircon crystallization age, grain morphology, structure and chemical composition determined by Raman analysis and cathodoluminescence imaging, among others, could influence the measured (U-Th)/He ages. The investigated xenoliths comprise both magmatic and metamorphic protoliths with varying degree of pyrometamorphic overprint. Zircon U-Pb ages range from 115 ± 4 Ma to 2731 ± 66 Ma. Preliminary (U-Th)/He dates of individual xenoliths agree with the expected eruption age range, underscoring the feasibility of the method. A detailed analysis of parameters potentially affecting (U-Th)/He systematics in zircon ages is ongoing.

[1] Blondes, M.S., Reiners, P.W., Edwards, B.R., Biscontini, A., 2007, Dating young basalt eruptions by (U-Th)/He on xenolithic zircons: Geology, 35, 17–20.
[2] Ulusoy, İ., Sarıkaya, M.A., Schmitt, A.K., Şen, E., Danišík, M., Gümüş, E., 2019, Volcanic eruption eye-witnessed and recorded by prehistoric humans: Quat Sci Rev, 212, 187–198.
[3] Büchel, G., 1993, Maars of the Westeifel, Germany: Paleolimnology of European Maar Lakes, 49, 1–13.
[4] Lange, T., Cieslack, M., Lorenz, V., Büchel, G., 2022, Chronological sequence of volcanic eruptions in the SE part of the Westeifel Volcanic Field during the Weichselian Glaciation: Jber Mitt Oberrhein Geol Ver, 104, 313– 365.
[5] Woda, C., Mangini, A., A. Wagner, G., 2001, ESR dating of xenolithic quartz in volcanic rocks: Quat Sci Rev, 20, 993–998.

How to cite: Sturm, A., Schmitt, A. K., Danišík, M., and Dunkl, I.: Assessing the reproducibility of (U-Th)/He geochronology of xenolithic zircon: Insights from the Quaternary Eifel intraplate volcanic field, Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16158, https://doi.org/10.5194/egusphere-egu24-16158, 2024.

Cassiterite (SnO₂) is one of the dominant ore phases in tin-tungsten bearing magmatic-hydrothermal deposits. It can contain high uranium contents and usually hosts low levels of common Pb, making it one of the best U-Pb geochronometers among ore minerals [1]. The widespread use of in-situ techniques to obtain crystallization ages for cassiterite, however, is limited by a paucity of accurately characterized reference materials (RMs). Such shortage is mostly caused by the difficulty of achieving closed-system acid decomposition of this mineral, which represents the foundation of isotope dilution techniques, necessary for accurate and precise determination of U-Pb isotopic composition using thermal ionization mass spectrometry (TIMS) techniques.

In this contribution, we present a new set of U-Pb isotopic compositions of two cassiterite samples from the archetypal Variscan Sn-W greisen deposits of Panasqueira (Portugal) and Krasno (Czechia) obtained with an updated protocol of complete HBr decomposition of cassiterite in the presence of a U-Pb tracer, followed by U and Pb purification, and TIMS analyses. Previous to dissolution, the U-Pb isotopic compositions of the same cassiterite aliquots are characterized via laser-ablation-inductively coupled-mass spectrometry (LA-ICP-MS) and each cassiterite fragment is imaged with an ultra-fast washout laser ablation system to obtain high-resolution maps of the content and distribution of key trace elements (e.g. U, Pb, Fe, REE).

These two samples show variable but high U concentrations (2-20 ppm) and produce U-Pb isochron ages with 1% precision and low dispersion. We compare these new materials with established RMs (Yankee [2]; AY-4 [3]) and discuss their usability as primary reference materials for microbeam applications.

[1] Neymark, L. A., et al., Chemical Geology. 2018, 483, 410-425.

[2] Carr, P.A., et al., Chemical Geology. 2020, 539, 119539.

[3] Yuan, S., et al., Ore Geology Reviews. 2011, 43, 235–242.

How to cite: Tavazzani, L., Szymanowski, D., Carr, P., Guillong, M., Buret, Y., Cortes-Calderon, E. A., Mercadier, J., and Chelle-Michou, C.: Two new cassiterite reference materials for in-situ U-Pb dating from the European Variscan metallogenic belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16536, https://doi.org/10.5194/egusphere-egu24-16536, 2024.

Recent years have seen a rise in applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to elemental and isotopic analysis of a wide range of geological materials, with a true explosion of in situ geochronology. Standardising such analyses relies on a homogeneous matrix-matched primary reference material (RM) whose ablation, transport and ionisation characteristics will result in fractionating elements and isotopes in the same way as in the unknown of interest.

One of the current frontiers of LA-ICP-MS geochronology – U–Pb dating of carbonates – suffers from a lack of such a material. Because the currently used primary RMs (e.g. WC-1 [1]) are heterogeneous in both age and U/Pb ratio, isotopic ratios are corrected on an isochron (whole-sample) basis rather than for each individual analytical spot, which imposes excess uncertainty on all U–Pb ages obtained this way. The U–Pb carbonate geochronology community is thus in urgent need of homogeneous reference materials for wide distribution. Ideally, such a RM should match the ablation behaviour of the unknown carbonate and consequently all matrix effects, including the amount and depth progression of inter-element laser induced elemental fractionation (LIEF), can be corrected directly, as is standard in e.g. zircon U–Pb geochronology.

We present a method for preparing synthetic RMs that uses a natural rock starting material which is milled to nano-powder, homogenised, and recrystallised using high-pressure, high-temperature apparatuses. In this way, natural sample heterogeneity is removed through milling, while textural coarsening is aimed at generating ablation behaviour similar to that of routine unknown samples.

Initial tests of synthetic calcite materials demonstrate the ability to achieve homogeneity at the spatial scale of a typical LA-ICP-MS laser spot size (80–110 µm typical for calcite U–Pb), while the ablation rate and LIEF are comparable to those of a range of commonly used calcite RMs. This suggests that experimental manufacturing of recrystallised carbonate is a promising avenue to obtain primary RMs that will allow spot-by-spot correction of LIEF in U–Pb analyses, thereby significantly reducing the reliance on heterogenous natural calcite RMs and improving the precision and accuracy of this analytical method.

Finally, this approach may serve as a blueprint for larger-scale production of primary RMs for a variety of matrices and isotopic systems for which there are no natural RMs characterised by the necessary homogeneity or availability.

[1] Roberts, N.M.W., et al., Geochemistry Geophysics Geosystems, 2017, 18(7): 2807-2814.

How to cite: Szymanowski, D., Kueter, N., Guillong, M., Tavazzani, L., and Akker, I. V.: Synthesising homogeneous carbonate reference materials for in situ U–Pb calcite geochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16896, https://doi.org/10.5194/egusphere-egu24-16896, 2024.

More and more similar Grenvillian orogeny-related late Mesoproterozoic detrital zircon age peaks reported from ca. 1.0 Ga strata among the Rodinia blocks make paleogeography reconstruction of the North China Craton more puzzling. In this work, we compile detrital zircon U-Pb data of the late Mesoproterozoic–early Neoproterozoic strata in the eastern North China Craton (ENCC) with coeval or older rock units from the potential provenances (e.g. North Australia, Siberia, Laurentia and India/Greater India cratons and the North Atlantic region), and present inverse Monte Carlo modelling. The result confirmed that ca. 1.0 Ga ENCC–North Australia Craton connection is most plausible, which is first quantitatively evaluated.

How to cite: Zhang, W., Xu, W., Liu, P., Liu, C., and Liu, F.: Eastern North China Craton–North Australia Craton connection at 1.0 Ga through detrital zircon modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16928, https://doi.org/10.5194/egusphere-egu24-16928, 2024.

High-precision (CA-ID-TIMS) U-Pb geochronology of individual growth zones of zircon has been a long-awaited milestone in the geochronological community. Focused ion beam (FIB) and femtosecond (fs) laser machining monitored in real time by CL-SEM both show promise as techniques for physical extraction of target zircon domains in preparation for spatially resolved ID-TIMS dating. In this contribution, we test a novel laboratory protocol for zircon microsampling using an in-house multi-ion plasma (Ar-Xe) FIB and fs laser, and showcase first µID-TIMS zircon dates. We first examine the chemical impacts of protective metal coatings (Cr, Pt-Pd and C) used for ion milling on the U-Pb systematics of a low-Pb and a low-U zircon. We then present high-resolution transmission electron microscope (TEM) images of a zircon surface irradiated by ion and fs laser beams to show the contrasting extent of structural damage induced by the two techniques at standard microsampling conditions. Potential Pb-loss/U-gain in the nanometer-wide ion damaged layer in zircon is mapped by atom probe tomography (APT). Subsequently, we showcase the FIB workflow for extracting a number of microsamples of the Mud Tank and GZ-7 reference zircon spanning the sizes expected in future applications using natural zircon. We present first results of spatially resolved high resolution (µID-TIMS) dating of the Mud Tank and GZ-7 microsamples, and explore the achieved analytical accuracy and precision. Finally, we discuss the feasibility of conducting a µID-TIMS study on natural zircon given zircon features (i.e., age, U content, and volume of target domain) and research objective, and discuss benefits and limits to our approach.

How to cite: Markovic, S., Wotzlaw, J.-F., Szymanowski, D., and Chelle-Michou, C.: µID-TIMS: A Focused Ion Beam (FIB)–Femtosecond (Fs) Laser Microsampling Protocol for Spatially Resolved High-Precision Zircon Geochronology , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17149, https://doi.org/10.5194/egusphere-egu24-17149, 2024.

Elemental analyzers (EA) are the go-to sample introduction instrument for light stable isotope analyses of solid materials. Sample preparation is labor intensive and time consuming, with high associated consumable and equipment cost. Sample recovery is impossible in case of malfunctioning, i.e., no repeat analysis when sample amount is restricted.

In the same way, Laser ablation (LA) is traditionally considered a sample introduction technique for Inductively Coupled Plasma Mass Spectrometry (ICP MS) where plasma-based instrumentation will ionize and measure with a high degree of accuracy and precision the aerosol generated during the ablation process.

In this contribution we present an innovative method of measuring C stable isotopic ratios of carbonates by hyphening two instruments that are not usually found in the same lab. We coupled a laser ablation system (Teledyne Photon Machines Fusions CO2) equipped with a specially designed ablation chamber (Terra Analitic isoScell Δ100) to a Cavity Ring Down Spectrometer (Picarro G2201-i) to perform spatially resolved, highly accurate and precise measurements of both inorganic (stalagmite) and bioaccumulated (freshwater bivalve) carbonate samples. This novel system requires minimal sample preparation, allows for in-situ sequential and repeat sampling, all while eliminating the need to individually prepare samples.

How to cite: Stremtan, C., Wozniak, J., Puscas, C. M., and Tamas, T.: Laser Ablation – Cavity Ring Down Spectrometry, a new method for the in-situ analysis of δ13C of organic and inorganic carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17192, https://doi.org/10.5194/egusphere-egu24-17192, 2024.

Well-characterized matrix-matched reference materials are an indispensable requisite for mineral dating by LA-ICPMS. Recently, the in-situ U-Pb dating of low-U minerals (<20 µg/g) has emerged as a cutting-edge technique in the field of geochronology. The methodology has especially been applied to carbonate and garnet, although other minerals such as sulfate, ilmenite, staurolite, etc., are likely dateable by the same technique. However, the ability to expand this technique to such phases is hampered by the scarcity of reliable reference materials, creating a strong need for investigating and developing appropriate materials with well-constraint ages and homogeneous isotopic compositions.

During the last few years, the FIERCE laboratory has been investigating reference materials for garnet dating. Analysing garnet crystals from different localities and of various U and Pb contents, we found that four garnet localities have the potential to become reference materials for in-situ U-Pb studies. On the one hand, the availability of garnet crystals is sufficient to be distributed to laboratories worldwide. On the other hand, the garnet crystals analysed at FIERCE are relatively homogeneous, except for specific domains like rims, which showed slightly different ages (Millonig et al., 2023). The studied specimens come from Balochistan, with an approximate age of 45 Ma; Mongolia (ca. 130 Ma); Mali (black variety, different to the popular “Red-Mali”, age of ca. 200 Ma) and the Lake Jaco district in Mexico (pink variety, ca. 35 Ma). For this contribution, we have done an intra-crystal, inter-crystal and inter-session comparative study of the different localities, analysing multiple crystals from each locality over multiple analytical sessions. The potential reference materials analyses have been cross-calibrated against garnet crystals of known age (ID-TIMS age) and yield reproducible ages between different analytical sessions. Furthermore, garnet from the four localities will also be analysed by TIMS to provide independent age constraints.

How to cite: Beranoaguirre, A., Millonig, L. J., Stifeeva, M. V., Albert, R., Marschall, H., and Gerdes, A.: Potential matrix-matched reference material for in-situ garnet U-Pb dating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18378, https://doi.org/10.5194/egusphere-egu24-18378, 2024.

Understanding the stability of carbonates under high pressure and temperature is essential for modelling the carbon balance and cycle in the deep Earth. In the presence of an H₂O-containing fluid, the melting curve of carbonates can be strongly reduced to a lower temperature. Since magnesite is an important carbonate host in the Earth's mantle, the melting curve of magnesite in the presence of an H₂O-containing fluid is of particular interest.

Here we report results from in situ synchrotron energy dispersive X-ray diffraction experiments and use texture observations from ex situ falling sphere experiments in the brucite-magnesite system between 1 and 12 GPa. We define the dehydration and melting curve of brucite and elucidate the stability of magnesite in the presence of a liquid and periclase.

The observed liquidus provides information on the fate of magnesite-bearing rocks in subduction zones. Our results show that magnesite remains stable under typical subduction zone gradients even when infiltrated by hydrous fluids released by dehydration reactions during subduction. We conclude that magnesite can be subducted to depths below the arc and beyond. Our results therefore have important implications for the carbon budget of the Earth's mantle and its role in the regulation of the carbon cycle.

How to cite: Sieber, M. J., Reichmann, H. J., Farla, R., and Koch-Müller, M.: Stability of magnesite (MgCO3) in the presence of a hydrous fluid in the upper mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18595, https://doi.org/10.5194/egusphere-egu24-18595, 2024.

Continental breakup leads to formation of new oceanic gateways, evolution of ocean bathymetry, and, in many cases, emplacement of large igneous provinces (LIPs). Changes in ocean circulation, volcanic CO₂ emissions, and alteration of freshly emplaced ocean crust associated with these events were likely drivers of global-scale Cretaceous climate change. Yet, the precise timing and nature of Cretaceous continental rifting and submarine LIP eruptions remain largely unconstrained. The Agulhas Plateau (AP), along with Maud Rise (MR) and Northeast Georgia Rise (NEGR), are thought to constitute a once contiguous submarine LIP that was emplaced in the gateway between the incipient South Atlantic, Southern Ocean, and Indian Ocean basins during the breakup of Africa and East Antarctica. International Ocean Discovery Program (IODP) Expedition 392 recovered sedimentary and igneous rocks from the Agulhas Plateau, southwest Indian Ocean, including basaltic pillow lavas at IODP Site U1582, located on the northernmost edge of the plateau. Calcite veins and infills hosted in pillow lavas can provide insights into the timing and chemical environment of post-magmatic fracturing, fluid circulation, submarine weathering and carbonation of the LIP. We present in-situ U/Pb ages (n=12) of the calcite veins determined via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), clumped isotope (Δ₄₇) compositions (n=6) and ⁸⁷Sr/⁸⁶Sr ratios to investigate the timing and temperature of calcite precipitation. U/Pb geochronologic dates for vein calcite and infill are reproducible and yield Cenomanian to Turonian ages, consistent with shipboard nannofossil biostratigraphic age constraints for sediments intercalated between the pillows. Reproducible clumped isotopic paleotemperatures range from ~19 to 26°C, with a calculated δ¹⁸O value for precipitating fluids of ~-2 to +1‰ Vienna Standard Mean Ocean Water (VSMOW). The ranges of both these values are consistent with ambient mid-Cretaceous marine waters and, when combined with the age constraints for the basalt and sediments, support rapid weathering and carbonation of the submarine LIP following post-eruptive cooling. U/Pb geochronology of calcites at IODP Site U1582, refined by Sr isotope stratigraphy, provide a minimum age for the Agulhas Plateau. These data constrain the timing of the formation of a paleobathymetric restriction at the gateway between several incipient Cretaceous ocean basins, and have implications for geochemical interactions between mafic igneous rocks and seawater through the life cycle of a Cretaceous LIP.

How to cite: Gürer, D., Jones, M. M., Bohaty, S. M., Bernasconi, S. M., Nana Yobo, L., and Roberts, A. P.: Agulhas Plateau large igneous province emplacement and carbonation constrained by in-situ U-Pb dating, Sr isotope geochemistry and clumped isotope thermometry of calcite veins in basaltic basement at IODP Site U1582, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19239, https://doi.org/10.5194/egusphere-egu24-19239, 2024.

Understanding fluid processes is crucial for understanding the magmatic and metamorphic evolution of rocks, as well as mineral transport and deposition. Targeted in situ geochronology of minerals which have interacted with fluids allow us to investigate the temporal evolution of these fluid systems. Combined with trace element analysis or stable isotope analysis it is possible to gain insight into the nature of source of mineralising fluids. These results contribute to modelling and understanding of mineral systems which can be used for targeting mineral deposits.

Early results of this work are presented based on situ Lu-Hf geochronology applied to garnet and apatite associated with a variety of mineral deposits from Finland. The mineral deposits are hosted in rocks are variable age (Archean to Proterozoic) and all were affected by the Svecofennian orogeny (1.92-1.78 Ga) causing deformation, metamorphism and/or remobilisation.

The Siilinjärvi P deposit hosted in a 2.61 Ga carbonatite (Karhu et al., 2001) presents apatite ages ranging from 2050 to 2260 Ma and calcite ages of 1800 to 1920 Ma indicating potentially several phases of fluid remobilisation which may be prior to or during the Svecofennian orogeny.

The Kiviniemi Sc deposit is hosted in a garnet bearing ferrodiorite (1857 ± 2 Ma, U-Pb zircon; Halkoaho et al 2020). In situ Lu-Hf analysis of garnet produces an age of 1824 ± 18 Ma and for apatite an age of 1835 ± 19 Ma.

Garnet and apatite geochronology has also been applied to Li bearing pegmatites in the Somera-Tammela pegmatite province in Southern Finland. Garnet gave an age of 1801 ± 53 Ma and apatite gives 1835 ± 26 Ma. A second sample produced a nearly identical apatite age of 1835 ± 15 Ma.

Two garnets were sampled from inferred Archean deposits, the Sotkamo silver Mine is hosted in the Tipasjärvi Greenstone Belt and the Hosko gold deposit hosted in the Ilomantsi Greenstone Belt. In Sotkamo garnet from a quartz vein hosting base metal mineralisation produced a Lu-Hf age of 1870 ± 27 Ma. Two garnet samples were dated from the Hosko gold deposit, in mineralised sediments, garnet associated with vein quartz produced an age of 1837 ± 4 Ma. A granitic vein cross-cutting the ore hosting sediments gave an age of 2620 ± 7 Ma, although this sample clearly recorded a resetting event with younger ages obtained from the rim.

Despite only have the age results so far, it is clear that the Svecofennian orogeny had a strong impact on mineral systems, reworking of deposits thought to be Archean.

Halkoaho, T., Ahven, M., Rämö, O.T., Hokka, J., Huhma, H., 2020, https://doi.org/10.1007/s00126-020-00952-2

Karhu, J.A., Mänttäri, I., Huhma, H., 2001. Radiometric ages and isotope systematic of some Finnish carbonatites. University Oulu, Res. Terrea, Ser. A. No. 19.8.

How to cite: Cutts, K., Szentpeteri, K., Karvinen, S., Glorie, S., Käpyaho, A., and O'Brien, H.: In situ Lu-Hf dating of garnet and apatite as a means to understand fluid processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19715, https://doi.org/10.5194/egusphere-egu24-19715, 2024.

The Tabei uplift is located in the northern part of the Tarim Basin, while the Lunan area is in the eastern part of Tabei uplift. The dryness coefficients of natural gas range from 0.62 to 0.99 (average: 0.92), the methane contents range from 30.42% to 96.4% (average: 85.10%), and the methane carbon isotopes range from -47.30‰ to -33.80‰ (average: -36.96‰) in the Lunnan area. Compared with the actual regional thermal evolution of the source rock, the natural gas exhibits excessively heavy dryness coefficients and methane carbon isotope characteristics. To investigate the genesis of heavy methane carbon isotopes and dry gas in different areas of the Tabei Uplift. Natural gas chemical composition and carbon isotope were used to analyze the genesis of natural gas, basin modeling was conducted to reconstruct the natural gas generation process, and the geologic causes of this phenomenon are discussed. The results show that the natural gas is primary cracking gas and sourced from marine type II kerogen. The dryness coefficient, methane carbon isotopes, and source rock maturity gradually increases from the west to the east. Instantaneous effects led to the dry gas and relative heavy methane carbon isotopes generated at a low maturity level. The current natural gas in the Ordovician reservoirs was all generated during the Himalayan orogeny. Long period pause of the gas generation between the two hydrocarbon generation phases is the main cause for the instantaneous effects.

How to cite: Liu, X., Tian, J., Liu, Z., and Cong, F.: The generation mechanism of deep natural gas, Tabei uplift, Tarim Basin, Northwest China: insights from instantaneous and accumulative effects, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2342, https://doi.org/10.5194/egusphere-egu24-2342, 2024.

Serpentinite carbonation contributes to the deep carbon (C) cycle. Recently, geophysical and numerical studies have identified considerable hydrothermal alterations in deep bending faults beneath outer-rise regions, implying potentially significant C storage in the slab mantle. However, quantitative determination of C uptake in outer-rise regions is lacking. Here, we experimentally constrained the serpentinite carbonation in H₂O–CO₂–NaCl fluids under bending fault conditions to estimate C uptake in the slab mantle. We found that serpentinite carbonation produced talc and magnesite along the serpentinite surface. The porous reaction zones (49.2% porosity) promoted the progress of the carbonation reaction through a continuous supply of CO₂-bearing fluids to the reaction front. Strikingly, NaCl effectively decreased the serpentinite carbonation efficiency, particularly at low salinities (< 5.0 wt%), which is likely attributed to the reduction in H₂O and CO₂ activities (a_H2O and a_CO2) and transport rate of reactants, the change in pH of fluids, and the enhancement of magnesite solubility. We fitted an empirical equation for the reaction rate of serpentinite carbonation in bending faults and found that this reaction could contribute to a flux of 25–100 Mt C/yr in subduction zones. Our results shed new light on the deep C cycle and the serpentinite carbonation in environments with high salinities.

How to cite: Huang, Y., Okumura, S., Matsumoto, K., Takahashi, N., Tang, H., Wu, G., Tsujimor, T., Nakamura, M., Okamoto, A., and Li, Y.: Importance of mantle serpentinite carbonation in bending faults for the deep carbon cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5003, https://doi.org/10.5194/egusphere-egu24-5003, 2024.

Coupled dissolution-precipitation reactions have been studied extensively recently for their ability to retain elements of interest into a stable solid form that can sequester potentially toxic elements. This is achieved through the initial dissolution of a substrate mineral in a fluid containing the target (often toxic) element. The dissolution leads to the supersaturation of a boundary layer at the mineral surface with respect to another solid phase containing the element of interest¹. When the relative solubilities of the different minerals (in the aqueous fluid at the reaction interface) and their molar volume difference allow it, a coupled dissolution-precipitation can lead to the pseudomorphic replacement of the original substrate². We tested this reaction for CaCO₃ and cadmium (Cd) containing solutions as calcite (CaCO₃) and otavite (CdCO₃) form an almost perfect solid solution. We compared the reaction in similar solutions with different types of CaCO₃: calcite single crystal, Carrara marble (polycrystalline calcite) and aragonite single crystals. For single calcite crystals, the reaction in a Cd-solution passivates the crystal’s surface due to the epitaxial growth of a (Ca,Cd)CO₃ solid solution layer of low solubility. However, the random orientation of the grains in the Carrara marble samples and the change of crystal structure for the aragonite crystals modified the mechanism and allow the replacement of CaCO₃ by (Ca,Cd)CO₃ to take place³. Hydrothermal experiments and in situ fluid-cell atomic force microscopy (AFM) were used to observe the reaction both at room temperature and high pressure and temperature (200°C). In addition to SEM, BSE and EDX observations, synchrotron X-ray microtomography images were acquired on Carrara marble and aragonite samples at different stages of the reaction in order to gather more information about the replacement mechanism and the extent of Cd-uptake achievable through this process. The extent of the reaction was shown to be similar for the different solution concentrations used and limited in the case of Carrara marble. The porosity closes fast after the start of the reaction blocking the fluid pathways necessary for the reaction to proceed. The reaction in the aragonite samples seems to progress mainly through a reaction-induced fracture network probably created by the stress caused by the crystallographic structural differences between parent and product phases. Overall, these results demonstrate the capacity of CaCO₃ to trap and store cadmium into a solid phase by a mechanism of coupled dissolution-precipitation.

(1)        Putnis, C. V.; Putnis, A. A Mechanism of Ion Exchange by Interface-Coupled Dissolution-Precipitation in the Presence of an Aqueous Fluid. Journal of Crystal Growth 2022, 600, 126840. https://doi.org/10.1016/j.jcrysgro.2022.126840.

(2)        Pollok, K.; Putnis, C. V.; Putnis, A. Mineral Replacement Reactions in Solid Solution-Aqueous Solution Systems: Volume Changes, Reactions Paths and End-Points Using the Example of Model Salt Systems. American Journal of Science 2011, 311 (3), 211–236. https://doi.org/10.2475/03.2011.02.

(3)        Julia, M.; Putnis, C. V.; King, H. E.; Renard, F. Coupled Dissolution-Precipitation and Growth Processes on Calcite, Aragonite, and Carrara Marble Exposed to Cadmium-Rich Aqueous Solutions. Chemical Geology 2023, 621, 121364. https://doi.org/10.1016/j.chemgeo.2023.121364.

How to cite: Julia, M., Putnis, C. V., Renard, F., and Plümper, O.: Potential sequestration of toxic elements: the specific example of cadmium and carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5717, https://doi.org/10.5194/egusphere-egu24-5717, 2024.

The presence of ophiolitic mélanges in the Indonesian archipelago has been acknowledged as pivotal for the paleo-tectonic reconstruction of the Southeast Asia Region (southwestern Sundaland). However, the occurrence of rodingite as an integral component of ophiolite in Indonesia has not been thoroughly documented. The rodingites within the Ciletuh Ophiolitic Mélanges in Western Java are notably fresh and widespread, providing a valuable opportunity to initiate comprehensive research on rodingites, particularly focusing on the interplay of metasomatism between serpentinite and meta-gabbro. These metasomatic processes can provide valuable insights into reconstructing the evolution of P-T conditions and elemental transfer involving fluids in a subduction zone. This study aims to focus on field occurrences, petrography, whole-rock geochemistry, with the application of P-T pseudosection modeling to describe their metamorphic conditions.

Rodingitized gabbro in Ciletuh occur as dykes intersecting serpentinized peridotite with sharp and diffuse contact. These dykes are controlled by faults in direction opposite perpendicular or diagonal to the shearing direction of serpentinites. Sheared-foliated rodingite and serpentinite are common, usually forming boudinages. Rodingites are classified into six types which are: (1) Fine to medium grain clinopyroxene rich, (2) Fine to medium grain hydrogarnet rich, (3) Coarse grain, (4) Schistose, (5) Diffused serpentinite-rodingite at peripheral dyke, and (6) Diffused serpentinite-rodingite embedded within serpentinite.  Type (1) to (3) are dykes which mostly composed by garnetized plagioclase (47-49%) and clinopyroxene (29-32%), orthopyroxene (20%), olivine (<3%), epidote (<5%), zoisite (<3%) with minor spinel and magnetite (2-4%). Type (4) is comprised of foliated mineralogical domains such as carbonate-rich and chlorite-rich domain. Types (5) and (6) are characterized with diffused contact of rodingite (hydrogarnets) and chloritized serpentinite. Chlorite reaction zones can be encountered at the contacts between rodingite and serpentinite, typically indicated by the presence of chloritized groundmass, chloritized serpentine mesh, chlorite and hydrogarnet veinlets, as well as partial clinopyroxene rim around hydrogarnet.

The general whole rock geochemical characteristics of rodingitized gabbro are indicated by low SiO₂ content (34-42 wt%), high CaO (3-16 wt%), high MgO (17-32 wt%), medium Al₂O₃ (5-10 wt%), and FeOt (5-18 wt%), with high LOI (5-10 wt%). Significant whole rock geochemical variations characterize the serpentinite-rodingite reaction zones in both the sharp dykes (Type 1-3) and diffused (Type 5-6) contact. Serpentinite near the reaction zone exhibits enrichment in Al₂O₃, CaO, but depletion in MgO, FeO, and SiO₂. Conversely, rodingitized gabbro experiences enrichment in MgO, slight enrichment in FeO, and depletion in CaO and Al₂O₃.  

P-T psedosection models show that rodingitization occured concurrently with serpentinization during medium to low-grade metamorphism at temperatures ranging from 200 to 490˚C. This process involved diffusional metasomatism with fluids derived from serpentinization and metamorphism of gabbro (e.g., Ca, Mg, and Al), considering the addition of H₂O and other potential fluids during the exhumation of ophiolitic mélanges in the subduction slab.

How to cite: Ikhram, R., Hoshide, T., Ohba, T., and Rosana, M. F.: Rodingite Occurrence in Ciletuh Ophiolitic Mélange Complex (Indonesia): Evidence of Fluid-Rock Interaction in Subducted Oceanic Crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8161, https://doi.org/10.5194/egusphere-egu24-8161, 2024.

It is now widely known that the fluids play a major role in the formation and evolution of the Earth´s crust. Fluids and melts formed by dehydration-melting reaction of muscovite, biotite and amphibole during prograde metamorphism can have a profound effect on the trace element and isotope composition on the crustal sources of magmas.

However, while the phase relations of these reactions as well as the textural and mineralogical evidence of fluid-rock interaction in high-grade metamorphic complexes are well studied, the mechanisms of the onset of fluid and melt generation by the dehydration melting along with the transport and geochemical impact of these mobile phases onto anhydrous minerals at the grain scale remain unclear.

We investigated the mechanisms of local reactions involved in the incipient dehydration/melting processes at different temperatures, the sequence of reactions and the interaction of the fluid and/or melt with the anhydrous mineral phases, by conducting analogue heating experiments of rock cylinders in a vertical furnace. The rock samples used in the experiments were granitoids and gneisses from the Iberian Massif (Spain) with variable content of biotite and muscovite. They were cut into cylinders with dimensions of about 3x20 cm and placed into a vertical furnace. The experiments were done under thermal gradient at sub- and supersolidus conditions (600-1200^oC) at ambient pressure in an inert atmosphere of N₂ and last up to 8 days.

First results show that significant compositional and textural changes in biotite and muscovite were produced in experimental runs at temperatures >850^oC. Muscovite experienced dehydration melting breakdown to ultrabasic, very peraluminous melts with higher Na and lower K than the starting muscovite, small grains of aluminosilicates and large vesicles. Biotite underwent subsolidus dehydration, resulting in the formation of spinel and/or Fe-Ti oxides and alkali-rich aqueous fluid. Notably, K-feldspar did not nucleate at the dehydration site; instead, excess K and other incompatible elements (Li, Rb, Cs, Ba) were transported by fluids released from biotite and muscovite. These fluids subsequently induced metasomatic reactions in plagioclase, transforming it into K-feldspar. Additionally, Ca released from plagioclase contributed to the formation of titanite after ilmenite. The metasomatic changes were facilitated by fluid migration along micropores that were present in the starting plagioclase, highlighting the intricate processes involved in mica driven metamorphism and metasomatism. A second type of melt was generated with increasing temperature, characterized by higher silica and more granitic-like compositions, suggesting the involvement of quartz and feldspars in the melting reactions.

Although the experimental pressure conditions are much lower than those inside the crust, these analogous experiments allow us to investigate the mechanism by which fluids and melts are segregated from the reaction sites and the influence of rock texture. In these analogue experiments the breakdown of hydrous minerals is enhanced because they are outside their P-T stability fields. Besides, the formation of gas is maximized since its solubility in the melt is very low. Therefore, it allows us to investigate the importance of vesiculation in the creation of pathways for fluid and melt migration.

How to cite: Repczynska, M. M., Cambeses, A., Molina, J. F., Montero, P., and Bea, F.: Experimental insights into fluid and melt generation by dehydration reactions of micas with implications for crustal processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9404, https://doi.org/10.5194/egusphere-egu24-9404, 2024.

Sediment-hosted Cu deposits are a significant global source of copper. This study employs a mineral system approach, focusing on basin-scale groundwater flow as a key mechanism for Cu transport from source to trap. Numerical experiments using the open-source IC-FERST code investigate the controls on Cu transport in the Katangan Basin, Central African Copperbelt. The models developed for early and late stages of basin evolution incorporate fluid flow, heat and solute transport, and dynamic mesh optimization to enhance computational efficiency.

The early-stage model, corresponding to the salt deposition period, attributes the formation of saline brine to a dense residual phase resulting from evaporite formation. In the late-stage model, corresponding to Cu mobilization and mineralization, Cu dissolution and mineralization are simulated using a partition coefficient informed by experimental data.

Results reveal that density gradients induced by salinity and temperature variations play a crucial role in initiating convective groundwater flow. Highly saline, dense brines generated during salt deposition or dissolution form complex, downward-propagating plumes influenced by flow instabilities and geologic heterogeneity. Permeable faults and fractures in basement rocks enable groundwater to percolate, potentially mobilizing Cu from intra- or extra-basinal source rocks. Salinity and temperature gradients drive upwelling plumes, transporting Cu from deeper source rocks to shallower, organic-rich sedimentary rocks where mineralization occurs.

How to cite: Bahlali, M., Woitischek, J., Jacquemyn, C., Purkiss, M., and Jackson, M.: Integrated Modeling of Cu-Rich Fluid Migration and Mineralization in the Katangan Basin, Central African Copperbelt: Insights from Numerical Experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11453, https://doi.org/10.5194/egusphere-egu24-11453, 2024.

A set of small iron oxide-apatite (IOA) ore bodies have been discovered within polydeformed and polymetamorphosed metasedimentary rocks on Prins Karls Forland, Svalbard. A complex tectonothermal history resulted in the development of various ore structure, varying from brecciated to mylonitised. Generally, the IOA ores are divided into two major geochemical subtypes: (1) fluorapatite-bearing with predominant low-Th monazite, and (2) F-Cl apatite-bearing with predominant high-Th monazite. Initial alteration of the ores resulted in liberation of REE and P from the apatite and redeposition as small (<30 mm), rounded monazite and xenotime crystals. REE and P in solution were likely transported during deformation that probably enhanced the transportation process. In fact, both the iron oxides and phosphates in the intensively deformed ores show features characteristic of fluid-assisted dissolution-reprecipitation creep. Subsequent stages of alteration caused either Th-enrichment of the monazite or even full replacement of low-Th monazite by a high-Th variety. In some of the ore bodies the original fluorapatite incorporated Cl, Mn, and Sr likely due to interaction with a Cl-rich fluid from the surrounding gabbroic and metasedimentary host rocks. The huge variability in the textures and the mineral assemblages from the ore bodies most likely reflect interaction with compositionally variable fluids that were liberated during the protracted tectonothermal evolution of the entire metamorphic complex. Hence, it is concluded that the IOA ores formed as a product of Fe, P, Ca, and REE fractionation from hypersaline fluids associated with the surrounding gabbros and metasedimentary rocks indicating that the ores were subjected to fluid activity during at least one metamorphic event.

How to cite: Majka, J., Maraszewska, M., Harlov, D. E., Manecki, M., Schneider, D. A., Broska, I., and Myhre, P. I.: Complex metamorphic and metasomatic history recorded by REE-phosphates in apatite-iron oxide ores from Svalbard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11520, https://doi.org/10.5194/egusphere-egu24-11520, 2024.

The circulation of toxic elements through soils, sediments and aquatic environments remains a significant environmental problem, which implies several, often unrecognized health risks. Dissolution and precipitation reactions that result in formation of sparingly soluble crystalline compounds containing toxic elements e.g. As, appear to be a promising strategy for reducing their chemical mobility and bioavailability (Magalhães, 2002; Wang et. al., 2013).

In this study, the processes occurring at the interface of anglesite and solutions containing AsO₄^3- ions were investigated. The results provide insight into the mechanism of As immobilization on the mineral surface through transformation of labile form into less reactive and more thermodynamically stable phases. Synthetic anglesite powder and fragments of natural anglesite crystals (Tsumeb, Namibia) were reacted for up to 3 months with solutions containing AsO₄^3- (50 mg As/l) in the presence of Cl^- ions at pH range 2 - 8. The experiments were conducted at room temperature (20 ^oC) or in the autoclave (120 ^oC).

Rapid sequestration of As from the solution was associated with precipitation of mimetite Pb₅(AsO₄)₃Cl: over 66% of As was removed within 24 hours. After 7 days of the reaction, the concentration of As decreased from 50 to less than 11 mg As/L. The concentration of Pb²⁺ ranged from 0.6 mg Pb/L at pH 8 to 20 mg Pb/L at pH 2. Both, homogeneous and heterogeneous precipitation of mimetite was observed, and some anglesite crystals were covered by incrustations. At pH=2, mimetite was associated with schultenite PbHAsO₄.

Scanning Electron Microscopy observations of the natural crystals surface, indicated that the reaction of As-containing solutions with anglesite at pH 4-8, involves dissolution of PbSO₄, resulting in formation of etch pits, followed by precipitation of randomly intergrown mimetite as a loosely bound crust. The crust was formed in the vicinity but is separated from anglesite surface. In contrary, at very acidic conditions (pH=2), anglesite is replaced by a secondary phase as a result of a coupled dissolution and precipitation, leading to formation of lead arsenate pseudomorph. Surprisingly, temperature had no significant effect on the reaction, while the pH control is of great importance and determines the mechanism.

References:

Magalhães, M. C. F. (2002). Arsenic. An environmental problem limited by solubility. Pure and Applied Chemistry, 74(10), 1843–1850.

Wang, L., Putnis, C. V., Ruiz-Agudo, E., King, H. E., & Putnis, A. (2013). Coupled dissolution and precipitation at the cerussite-phosphate solution interface: Implications for immobilization of lead in soils. Environmental science & technology, 47(23), 13502-13510.

This research was funded by AGH University of Kraków project No 16.16.140.315.  

How to cite: Stępień, E. and Manecki, M.: Arsenate aqueous solution – anglesite PbSO4 interface: dissolution, precipitation, and arsenic sequestration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11970, https://doi.org/10.5194/egusphere-egu24-11970, 2024.

Water, a principal component of Earth’s fluids, interacts with rocks in ways that profoundly influence lithospheric phenomena. These interactions are fundamental to both geochemical and geodynamic processes, extending their impact to areas of societal importance such as subsurface energy extraction and storage, and the formation of vital metal deposits for green energy technology. Additionally, the interplay between fluids and rocks significantly affects the Earth's carbon cycle, influencing atmospheric CO₂ levels, climate, and overall planetary habitability. The traditional perspective suggests that fluids move through the lithosphere without being affected by the unique properties that emerge when matter is confined to the nanoscale. Contradicting this view, our research reveals that rocks involved in a variety of lithospheric processes consistently show nanoporosity, primarily with pores smaller than 100 nanometers. Within these small spaces, water behaves differently than it does in larger environments. Through molecular dynamics simulations, we have quantified water's relative permittivity—a critical factor in its geochemical behavior— when confined in natural nanopores. Our findings demonstrate that, under a wide range of lithospheric conditions, from ambient to extreme temperatures up to 700 °C and pressures up to 5 GPa, water's permittivity within these nanopores significantly deviates from that in its bulk state. Our thermodynamic equilibrium models indicate that this difference markedly reduces mineral solubility and alters ion speciation in natural settings. These pore-size-dependent properties may exert a primary influence on rock reactivity and the evolution of aqueous geochemistry during fluid-rock interactions.

How to cite: Plümper, O., Chogani, A., King, H. E., and Tutolo, B.: Nanopore Influence on the Geochemical Properties of Water in Earth's Lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12279, https://doi.org/10.5194/egusphere-egu24-12279, 2024.

Fluid-aided mineral replacement plays a key role in metamorphic reactions and metasomatic mass transfers. Within the scope of this study we investigate the role of pore space evolution in the hydrothermal phase transition from gypsum to bassanite. We monitored the partial dehydration of gypsum to bassanite in-situ using an X-ray-transparent flow-through reaction cell (Kahl et al., 2016) during long-term hydrothermal percolation experiments. By repeated, intermittent X-ray microtomography (µ-CT) scans, we surveyed the evolution of the porous system created by the dissolution-reprecipitation process. The quantitative 3D image analysis of the obtained 4D image material shows that incipient bassanite formation takes place in domains well within the interior of the gypsum crystal, presumably located along nano- or microcracks (i.e. at the scale of grain boundaries of the selenite host, and maybe enhanced due to the presence of fluid inclusions), and not directly at the gypsum – fluid interface. After larger volumes of interconnected pores have formed in later stages of the experiment, bassanite nucleation becomes insignificant and bassanite growth is now the dominant fixation mechanism of hemihydrate. The fabric of the final reaction product is controlled by these later-stage elongate bassanite crystals that are oriented along [001] of the former gypsum crystal. Careful data analysis reveals that processes which strongly depend on transient characteristics of the fluid-hosting fabric component are easily obliterated from the rock record. Concerning the predictive numerical simulation of mineral replacement processes in general, these results reveal that the boundary conditions underlying mineral nucleation may not be deduced from observations of the resulting fabric of mineral growth.

Kahl, W.-A., Hansen, C., and Bach, W. (2016) A new X-ray-transparent flow-through reaction cell for a mu-CT-based concomitant surveillance of the reaction progress of hydrothermal mineral-fluid interactions. Solid Earth, 7(2), 651-658.

How to cite: Kahl, W.-A., Hansen, C., Murshed, M. M., Bach, W., and Garcia, J. M.: Porosity evolution determines available reaction mechanisms in water-rock interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12899, https://doi.org/10.5194/egusphere-egu24-12899, 2024.

The interpretation of mineral equilibria and reactions in rocks assumes uniform hydrostatic pressure across all phases. However, such condition is typically not satisfied in geological systems that are composed of multiple phases that are in contact with one another.  Stress gradients and non-hydrostatic stresses are to be expected in rocks in the lithosphere, even in the presence of fluids. This complexity challenges the reliability of existing hydrostatic thermodynamic models, and, currently, there is still no accepted theory for evaluating the thermodynamic effect of non-hydrostatic stress on reactions [e.g. 1, 2, 3, 4].

Molecular dynamics (MD) allows us to investigate first-order phase transitions in solid-liquid systems under stress, without the a-priori assumption of a specific thermodynamic potential [5]. With MD simulations the energy of the system, the pressure of the fluid, the stress of the solid, as well as the overall melting and crystallization process can be monitored until the stressed system attains the equilibrium conditions. Our findings indicate that under differential stress, the mean stress of the solid deviates progressively from the pressure of the fluid with which it is in equilibrium. At low differential stresses, deviations from the reference hydrostatic equilibrium are small, allowing accurate phase equilibria predictions by considering the fluid pressure as a proxy for equilibration pressure, as suggested by previous experimental investigations [6].

In the presence of substantial non-hydrostatic stresses, equilibrium between solid and fluid occurs at a fluid pressure significantly higher than hydrostatic thermodynamics predicts. However, the stressed system becomes unstable and a rim of a quasi-hydrostatically stressed solid eventually crystallizes around the initial highly stressed solid core. During the crystallization, the total stress balance is preserved until the newly formed solid-solid-fluid system reaches again a stable equilibrium. At the final equilibrium conditions only the low-stressed solid is exposed to the fluid, bringing back the equilibrium fluid pressure close to the value expected for the equilibrium at homogeneous hydrostatic conditions. Therefore, our results suggest that models describing equilibria and reactions in minerals and rocks under stress can assume that phase equilibria are accurately predicted by using the fluid pressure as a proxy of the equilibration pressure.

References

[1] Frolov, T., & Mishin, Y. 2010: Effect of nonhydrostatic stresses on solid-fluid equilibrium. I. Bulk thermodynamics. Physical Review B - Condensed Matter and Materials Physics, 82(17), 1–14.

[2] Hobbs, B. E., & Ord, A. 2015: Dramatic effects of stress on metamorphic reactions. Geology, 43(11), e372.

[3] Tajčmanová, L., Vrijmoed, J., & Moulas, E. 2015: Grain-scale pressure variations in metamorphic rocks: Implications for the interpretation of petrographic observations. Lithos, 216–217, 338–351.

[4] Wheeler, J. 2014: Dramatic effects of stress on metamorphic reactions. Geology, 42(8), 647–650.

[5] Mazzucchelli M., Moulas E., Kaus, B., Speck T. submitted: Fluid-mineral equilibrium under stress: insight from molecular dynamics. American Journal of Science.

[6] Llana-Fúnez, S., Wheeler, J., & Faulkner, D. R. (2012). Metamorphic reaction rate controlled by fluid pressure not confining pressure: Implications of dehydration experiments with gypsum. Contributions to Mineralogy and Petrology, 164(1), 69–79.

How to cite: Mazzucchelli, M. L., Moulas, E., Schmalholz, S. M., Kaus, B., and Speck, T.: Precipitation in fluid-mineral systems under differential stress investigated through molecular dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13089, https://doi.org/10.5194/egusphere-egu24-13089, 2024.

Fluid flow within the continental crust, and the concomitant fluid-rock interactions, are likely responsible for mass transfer and significant change in bulk rock chemistry (i.e. metasomatism). Strain localization and formation of ore deposits are very commonly associated to metasomatism. Metasomatic processes are studied combining petrology, geochemistry, fluid inclusion analysis and/or thermodynamic modelling (P-T-X). To model and quantify the mass and fluid flux integrated with time, the driving forces and controlling factor, such as fluid chemistry (solubility, speciation, chlorinity …), P-T conditions and phase relations, the degree of disequilibrium between the fluid and the host-rock must be clearly identified.

This study focuses on phase relations modelling during metasomatic processes based on the mineralogical and chemical characterisation of metasomatic rocks from the Tauern Window. Samples are amphibole- and chlorite-bearing micaschists resulting from the transformation of a granodiorite under amphibolite conditions (550-570°C and 0.5-0.6 GPa). The studied outcrop is similar to some extent to Mg-metasomatic rocks reported in several localities in the Alps, including Dora Maira, Gran Paradiso or Monte Rosa and summarised in Ferrando (2012). Although all the localities reported in Ferrando (2012) and the Tauern window have their own characteristics (eg. different P-T conditions, fluid chemistry, mineralogy, age...), they also share similar features. For instance, the gain in Mg with respect to the protolith is systematically coupled with a gain in fluid, and a loss of Ca, Na and sometimes Si. This shared feature suggests that a unique and simple process must be involved in all these localities.

Thermodynamic models are developed using chemical potentials of perfectly mobile components of the system as variable (µi), following the definition of Korzhinskii (1959). It means that the chemical potential of the mobile component (MgO, CaO, Na2O, SiO2, H2O) is controlled by the environment, which we consider here as an externally-derived fluid. The computed projections and pseudo-sections show that the reequilibration of the granodiorite with the externally-derived fluid (high µMgO and low µCaO, µNa2O, µSiO2) induce a series of metasomatic reactions leading to the breakdown of the granodiorite assemblage into amphibole, then muscovite-chlorite and eventually talc. From these models, it is possible to quantify the amount of mass lost and gained along the defined reequilibration path and eventually estimated the required fluid flux.

How to cite: Amiot, M., Goncalves, P., and Choulet, F.: Phase relation modelling associated with metasomatic processes in open systems: application to an example of Mg-metasomatism from the Neves area, Tauern window, Eastern Alps., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14807, https://doi.org/10.5194/egusphere-egu24-14807, 2024.

In the upper crust, rock deformation commonly occurs in the presence of aqueous fluids, which are known to alter the material's response to stress. These fluids facilitate dissolution and precipitation, driving changes in the mineral composition and texture. The interaction between dissolution-precipitation and deformation in the upper crust has been studied in various natural geological cases, through experimentation, and modeling. Recently, there has been increased emphasis on understanding the role of fluids in deformation at the nanoscale. This experimental study aims to comprehend the effects of deformation on dissolution and precipitation at the nanoscale, specifically at the boundary between individual mineral grains.

Our research has focused on understanding quartz dissolution and precipitation at the grain boundary scale at hydrostatic pressures and temperature conditions representative of the upper 5 km of the crust. We report preliminary findings from our experiments on nano-milled quartz crystals, representing natural grain boundary geometry, in contact with different aqueous solutions in a closed system. The pH, salinity, and concentration of Si in solution were systematically altered to assess their impact on dissolution rates. By using ¹⁸O-doped solutions, coupled with nanoscale secondary ion mass spectrometry and atomic force microscopy, we can track the dissolved and re-precipitated material, and monitor the changes in the geometry of the nano-milled quartz surface. This constitutes the initial step in our effort to further explore and quantify the effects of differential stress at the grain boundary. Additionally, we present results from a pilot study designed to test how differential normal stress impacts asperity dissolution within quartz-quartz contacts. These experiments aim to improve our understanding of dissolution rates in relation to pressure solution, a significant deformation mechanism in sedimentary and fault rocks.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie initial training network (FluidNET) grant agreement no. 956125.

How to cite: Billarent-Cedillo, A., Jefferd, M., King, H. E., Hangx, S., and Plümper, O.: Nanoscale experiments of intergranular dissolution-precipitation to understand deformation mechanisms in the upper crust.  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16710, https://doi.org/10.5194/egusphere-egu24-16710, 2024.

Reactive transport of solutes in porous media involving dissolution/precipitation reactions may alter the physical properties of intact rocks, such as porosity and permeability. Such processes are difficult to predict and characterize due to heterogeneity at the pore scale, caused by the intimate coupling of chemical and transport processes. So far, experimental studies have mainly focused either on chemical aspects, using short time batch or microfluidic experiments, or on transport, using a porous medium in classical counter diffusion cells. The former approach offers a large flexibility in selecting and modifying parameters like pH, ionic strength, and element concentrations, and thereby allows the systematic derivation of chemical data such as mineral precipitation and dissolution at ex-situ conditions. The latter approach allows studying changes of (bulk) rock transport properties under realistic (in-situ) conditions over longer times, with limited knowledge of pore scale physical and chemical parameters, which may vary in space and time. Therefore, each of these methods limits a full characterization of the evolution of chemistry and transport properties in a realistic porous medium, particularly near the clogging zones that may form due to precipitation.

In this study, we present a methodology that allows the full chemical and physical characterization of reactive transport processes within a porous medium at the microscopic scale (1-10 um). We present experimental datasets that record, the chemical and physical evolution in 300 mm tapered glass capillaries filled with silica gel, in which precipitation of CaCO₃ polymorphs has been induced via counter diffusion of Na₂CO₃ and CaCl₂ reservoir solutions. Two counter diffusion systems, one containing 1 mM ZnCl₂ in the CaCl₂ titrant, the other without Zn, were prepared and evolved for three years. Optical microscopy and synchrotron-based techniques (micro XRF/XRT/XRD, micro XANES and SAXS) were used to characterize the system at selected times (1, 6, 12, 24, 36 months). In both experiments the precipitation of several calcite and/or vaterite crystal aggregates collectively reduced the gel porosity and formed clogging zones in the central part of the capillary. The data obtained for the Zn-free system show that vaterite crystals formed in the calcium rich part of the capillary (i.e., on the side of the CaCl₂ titrant) remain stable for the entire duration of the experiment without converting to the more stable calcite. In the Zn-doped system, the vaterite crystals remain stable for 1 year and start to dissolve afterwards. The carbonate ions released via vaterite dissolution did not lead to the formation of new CaCO₃ precipitates in the Ca-rich part of the capillary. Instead, a zinc hydroxy carbonate phase is formed.

Through this study, we show for the first time the evolution of a clogging zone in a porous medium at the microscopic scale over an extended period and under truly undisturbed in-situ conditions. Our results show that small concentrations of Zn²⁺ ions in the pore water have a strong effect on the precipitation/dissolution kinetics of CaCO₃ polymorphs, as well as on their crystal morphology.

How to cite: Rajyaguru, A., Curti, E., Ferreira Sanchez, D., Appel, C., and Grolimund, D.: Zinc(II) ions under diffusive regime controls the stability of vaterite: Derivation of pore scale chemical dynamics near CaCO3 clogging interface via coupled micro-XRF/XRD/XANES and SAXS imaging., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17340, https://doi.org/10.5194/egusphere-egu24-17340, 2024.

The Rolvsnes Granodiorite, comprising the major extent of the northern part of Bømlo Island, Western Norway, has been proposed to be an onshore analogue to the weathered basement rocks at Utsira High hosting significant petroleum resources. A total of 205 meters of core in three boreholes was collected crosscutting both fault zones and apparently tectonically undisturbed rocks. Four distinct lithologies were identified in the drillholes: A medium-grained (grano-)diorite, a range of biotite granites, a porphyritic granite, and aplites/pegmatites. All rock types display evidence of hydrothermal alteration as either pervasive discoloration or more localized veining. Early propylitic alteration of the granodiorite is easily observed macroscopically as distinct greening, caused by primary amphibole being replaced by epidote, and calcic plagioclase cores being altered to epidote+muscovite+quartz. The extent and transition of the alteration steps can be observed in the hyperspectral logs. A second generation of epidote can be observed as 1-2 mm veins crosscutting all lithologies. With decreasing temperature and/or higher fluid/rock ratio, biotite is altered to chlorite. Late infiltration of carbonic fluids is evident from calcite veins cutting former alteration types, and ankerite/Fe-rich dolomite + Fe-oxide veins associated with open fractures. 

The clay mineralogy is dominated by smectite and kaolinite, and several meter long sections of the drill cores are near or completely disintegrated from drilling and core handling due to the high smectite content. Kaolinite and smectite may occur together as alteration products, but in open fractures kaolinite is found as infilling in vugs and fractures lined with quartz or associated with the Fe-carbonates, with little or no smectite. This indicates that during late fluid circulation in the faults, kaolinite was precipitated directly from the fluid, and that smectite in the smectite-rich zones was a part of a low temperature pervasive alteration event.

K-Ar dating of the clay-rich alteration zones from this and former studies show a large range of ages, with the ages of the finest (<0.1 µm) fraction ranging from 31 Ma to 281 Ma. The oldest ages are likely mixed or inherited from early events, but apparent clusters around 30-50, 110-140, 200-210, and 265-280 Ma may provide indications of periods of low temperature alteration.   

How to cite: Drivenes, K., Knies, J., Kurz, T., Margreth, A., and Schonenberg, J.: From high-T Hydrothermal Alteration To Near-Surface Weathering – The Alteration History of the Rolvsnes Granodiorite, W Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19351, https://doi.org/10.5194/egusphere-egu24-19351, 2024.

The alteration of ferroan brucite, a common by-product of serpentinization, has been proposed as a H₂ source at low temperature. Here, synthetic ferroan brucite with Fe/(Fe+Mg) = 0.2 was reacted with pure water at temperatures ranging from 348 to 573 K in 29 experiments either conducted in gold capsules or Ti-based reactors. H₂ production monitoring with time and characterization of the reaction products revealed the occurrence of the following reaction: 3 Fe(OH)₂^brucite = Fe₃O₄ + H₂ + 2 H₂O. This reaction proceeds completely in ~ 2 months at 378 K and is thermally activated. The small grain size of the synthetic brucite (40-100 nm) is similar to observations in natural samples, and is probably responsible for the high reaction rate measured. H₂ production reached a plateau and Fe-bearing brucite also precipitated as a reaction product, suggesting the achievement of equilibrium. The thermodynamic properties of Fe(OH)₂ were refined based on the experimental dataset and differ by less than 5 % from previous estimates. However, ferroan brucite is predicted to be stable at an hydrogen activity one order of magnitude lower than previously calculated. As a result, significant H₂ production during ferroan brucite alteration at low temperature requires efficient fluid renewal. Such a mechanism strongly differs from olivine serpentinization which can occur even at high activity in H₂ and thus with limited water renewal.

How to cite: Malvoisin, B., Carlin, W., Brunet, F., Lanson, B., Findling, N., Lanson, M., Jeannin, L., Fargetton, T., and Lhote, O.: New thermodynamic and kinetic constraints on H2 production during ferroan brucite reaction at low temperature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20271, https://doi.org/10.5194/egusphere-egu24-20271, 2024.

Fluid migration within the Earth's crust significantly influences the development of shear zones. The Bergen Arcs have been a focal point for investigating the localization of rheologically weaker zones that facilitate shear zone formation, with various hypotheses proposed (Jamtveit et al. 2019; Incel et al. 2022). These zones may originate from seismic events, inducing brittle fracturing and creating pathways for mineral re-equilibration and ductile deformation.

This research concentrates on the island of Krossøy, located in the northernmost part of the Bergen Arcs, Western Norway, offering a unique perspective on deformation, textural evolution, and metamorphism compared to the extensively studied southern regions of Holsnøy and Radøy (Austrheim 1987; Mukai et al. 2014; Moore et al. 2020). Krossøy exposes anorthosites from the old granulitic basement, intruded by a series of subparallel mafic granulitic dykes forming a distinctive "dyke swarm," not documented elsewhere in the Bergen Arcs. We present our results on microstructural analysis through Electron Backscattered Diffraction (EBSD) and, mineral and chemical evolution using Electron Microprobe analysis (EMPA).

Given the plagioclase-rich nature of anorthosites, our results delineate the chemical and textural evolution of feldspars, tracing their journey from early-stage granulitic anorthosite formation approximately 930 Ma ago to the development of Caledonian mylonite (440-420 Ma) during shear zone activity under amphibolite facies conditions. By examining the fluid pathways, we seek to determine their relationship with the formation of rheologically weaker areas in the crust and how the dynamic interplay between fluid infiltration and deformation mechanisms may play an important role by changing the metamorphic conditions, textures and mineral assemblages in the rocks.

Austrheim, H. (1987). Eclogitization of lower crustal granulites by fluid migration through shear zones. Earth and Planetary Science Letters, 81(2–3), 221-232.

Incel, S., Labrousse, L., Hilairet, N. et al. (2022). Reaction-induced embrittlement of the lower continental crust. Geology, 47(3).

Jamtveit, B., Petley‐Ragan, A. et al. (2019). The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust. Journal of Geophysical Research: Solid Earth, 124(8), 7725-7755.

Moore J., Beinlich A., Piazolo S., Austrheim H. and Putnis A. Metamorphic differentiation via enhanced dissolution along high permeability zones. Journal of Petrology 61, 10, egaa096 (2020)

Mukai, H., Austrheim, H., Putnis, C. V., and Putnis, A. (2014). Textural Evolution of Plagioclase Feldspar across a Shear Zone: Implications for Deformation Mechanism and Rock Strength Journal of Petrology, 55(8), 1457-1477.

How to cite: Hernández Filiberto, L., Austrheim, H., and Putnis, A.: Fluid pathways and metamorphic evolution in the northern part of the Bergen Arcs: the island of Krossøy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20323, https://doi.org/10.5194/egusphere-egu24-20323, 2024.

During active rifting, whenever magmatism is present, magma emplacement on the upper crust is usually controlled by brittle structures reactivating an inherited tectonic fabric. In the southeastern Brazilian margin, a Cretaceous NE-SW tholeiitic dyke swarm follows the trend of the Neoproterozoic Ribeira Belt. However, in the coastal area of Rio de Janeiro, it crosscuts orthogonally the Paleoproterozoic orthogneisses of the Cabo Frio Tectonic Domain. In order to investigate how these South Atlantic rift structures formed orthogonally to the inherited host fabric, detailed structural analysis on two key areas was performed, using geological mapping with high-resolution drone images, analyzing the relation of brittle structures, diabase dykes and host rocks. The main set of faults and fractures is oriented parallel to the NE-SW diabase dykes. Dykes bifurcate or change direction abruptly following faults and fractures. Three paleostresses regimes were characterized: (1) a strike-slip transtension with NNE-SSW and NE-SW strike-slip faults; (2) an extensional transtension with oblique NNE-SSW and ENE-WSW faults; and (3) a pure extension with NNE-SSW and ENE-WSW normal faults. The tholeiitic dykes were emplaced during phases 2 and 3 continuously. Syn-kinematic secondary minerals formed on the cataclasites and the host rocks by fluid interaction. Calcite, epidote, chlorite and iron oxide compose a low-grade metamorphism of Ca-, Fe- and Mg- assemblage. These minerals also registered different phases of deformation during paleostresses regimes, with crystallization/precipitation facilitated by thermal injection of the tholeiitic magmas. Increase in permeability of the host rocks by formation of faults and fractures also contributes for the fluid migration, thus contributing with hydrothermal alteration on the upper crust. These mineral reactions also corroborated with the weakening of the continental crust, allied with the increase of dilatant slip surfaces. The combination of these tectonic and hydrothermal processes enabled the emplacement of the NE-SW Serra do Mar Dyke Swarm into the Cabo Frio Tectonic Domain, disregarding the NW-SE inherited tectonic fabric.

How to cite: B. Khater, B., S. Schmitt, R., L. C. Pires, G., and F. Palmeira, A.: Magma Emplacement during active rifting in the upper crust: kinematics and petrology of diabase and host rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20669, https://doi.org/10.5194/egusphere-egu24-20669, 2024.

How to cite: Demirkaya, İ., Topuz, G., and Wang, J.-M.: Unusually slow cooling of metamorphic rocks in an orogenic belt: A case from the Bolu Massif (NW Turkey) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14, https://doi.org/10.5194/egusphere-egu24-14, 2024.

The pre-Pennsylvanian metasedimentary units (Cosoltepec Formation) of the Acatlán Complex in southern Mexico represent 70-90% of the exposed surface of this complex. The metasedimentary units mainly consist of metapelites, metapsammites and quartzites, as well as sparse pillow basalts and doleritic dikes (Ortega-Gutiérrez et al., 1978). The tectonostratigraphic evolution of these rocks remains a controversial issue in the pre- and post-Orogenic tectonics of the Acatlán Complex. As part of these units, this paper analyses El Pitayo Lithodeme, a low-grade metamorphic unit exposed at Guadalupe Allende (formerly El Pitayo) area, 20-25 km SE of Izúcar de Matamoros, Puebla State, which up to now has not been described in detail.

El Pitayo Lithodeme, located in the westernmost sector of the Complex, consists of fine-grained metapelites and metapsammites, quartzites, radiolarites, sericite-chlorite schist and interbedded metabasalts, which together suggest a deep-water depositional basin. Structurally, the sequence has a predominant N-S trending and penetrative axial plane foliation, associated with isoclinal folding, and it is bordered by faults. El Pitayo Lithodeme is overthrusted by blue schists (Casitas Lithodeme) and apparently it is juxtaposed by lateral faults with the eclogitic rocks of the Piaxtla Suite, in the westernmost sector of the Acatlán Complex.

By U-Pb geochronology of detrital zircons from metasediments, a maximal age of middle Cambrian (ca. 513 Ma, major peak age of the younger zircon grains) for the refilling of the “El Pitayo” basin was estimated, with detrital materials from Pan-African (ca. 500-605 Ma) and Grenvillian orogens (ca. 910-1325 Ma). On the other hand, a K-Ar (laser ablation) age of 234 ± 3 Ma was obtained for white micas from metasedimentary rocks, which can be interpreted as the age of low-grade metamorphism, or as a cooling age related to exhumation processes linked to the Late Triassic tectonic event during the break-up of western Pangea. Furthermore, thermobarometric analyses (chlorite geothermometer and pseudosection modelling) suggest that the greenschist facies metamorphism occurred at P-T conditions, for which no quantitative values have been estimated previously for the low-grade metamorphic rocks of the Acatlán Complex.

Thus, the El Pitayo Lithodeme, by its lithology and the structural position between high-pressure Mississippian rocks of the Piaxtla Suite at the westernmost sector the Acatlán Complex, is considered a key unit that with more detailed information will surely allow more robust correlations with other low-grade metamorphic units and will undoubtedly help to better understand about the pre- and post-Pangea tectonic evolution of the Acatlán Complex, southern Mexico.

How to cite: González-Ixta, Y. and Elías-Herrera, M.: Lithodeme El Pitayo, a Palaeozoic meta-volcanosedimentary unit of the Acatlán Complex, southern Mexico and its importance in pre- and post-Pangea tectonic evolution., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-368, https://doi.org/10.5194/egusphere-egu24-368, 2024.

Increasing evidence shows that, even where mid-ocean ridge serpentinization is widespread, significant volumes of fresh mantle are subducted. A part of these rocks may remain dry, or experienced subduction-related serpentinization. Once serpentinites are exhumed after a whole subduction cycle, it is challenging to determine timing and conditions of serpentinization. However, these may be constrained by investigating lithologies that are coupled with serpentinized peridotitic massifs from the mid-ocean ridge stage, such as gabbroic rocks. Here, we focus on variably transformed gabbroic rocks in the Monte Maggiore massif (Alpine Corsica, France). This body formed along a slow-spreading center of the Piemonte-Ligurian Basin in the Jurassic, and was subsequently subducted to blueschist-facies conditions. In the Monte Maggiore massif there is ample evidence for fluid–rock interaction processes. The most evident one is a serpentinization front of the peridotitic units where serpentinization degrees vary from < 10 to 100 %. Weakly serpentinized domains preserve rather fresh brown amphibole-bearing gabbroic rocks with only partial blueschist-facies metamorphic overprint. Instead, intensely serpentinized domains embed metasomatized gabbros such as rodingites.

To constrain timing and conditions of fluid circulation in the Monte Maggiore massif, we applied a multi-methodological approach to characterize the nature of metasomatic fluids and to date the timing of fluid–rock interaction in selected metasomatic and hydrated rocks. Low Cl contents (< 0.009 wt. %) measured by electron probe microanalyzer in late-magmatic brown and green amphibole in a Jurassic Ti-gabbro dike cutting the peridotitic units indicates that, after emplacement of the dike, this gabbro underwent alteration driven by magmatic water. This process was accompanied by titanite crystallization at the expenses of primary ilmenite and is dated at ca. 163 Ma by titanite LA-ICP-MS U–Pb geochronology. However, the formation of the Monte Maggiore serpentinization front recorded by rodingite-forming minerals and grossular-jadeite assemblage in partially re-equilibrated gabbros is dated at ca. 34 Ma and 47 Ma by LA-ICP-MS U–Pb geochronology of garnet.

Our data pinpoint at least two phases of fluid circulation in the Monte Maggiore unit, which span the entire evolution of the ophiolitic massif from rifting to high-pressure metamorphism during the Alpine orogeny. Notably, our geochemical and geochronological data rule out that any of these hydration phases were driven by seawater infiltrating the ocean floor, suggesting that mid-ocean ridge serpentinization contributed to a negligible extent to the overall hydration of the Monte Maggiore ophiolite. Conversely, our data suggest that serpentinization occurred primarily in subduction setting. Considering the role of subduction-derived serpentinization in transferring chemical species (e.g., C–O–H) feeding microbial activity in supra-subduction mantle regions, our evidence bears important implications for our understanding of the deep bio-geochemical cycle.

How to cite: Peverelli, V., Olivieri, O. S., Beranoaguirre, A., Cannaò, E., Ressico, F., Pastore, Z., Gerdes, A., and Vitale Brovarone, A.: Missing seawater in the hydration record of a peridotite massif from mid-ocean ridge to subduction (Monte Maggiore, Alpine Corsica, France), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-879, https://doi.org/10.5194/egusphere-egu24-879, 2024.

The Köli Nappe Complex in the Scandinavian Caledonides of Sweden originated as terranes within the Iapetus Ocean, derived from subduction-related magmatic and basin systems. The Krutfjellet Nappe in Västerbotten, Sweden and the Gasak Nappe in Nordland, Norway are both part of the Upper Kӧli Nappes. Siliclastic, carbonate and volcanic protoliths underwent metamorphism up to amphibolite facies, in places involving extensive migmatisation which is not found in other Kӧli Nappe units. Owing to a lack of previous studies, the exact age and origins of these migmatites is currently unknown. Foliations and early folds in the metasediments are cut by c. 445-434 Ma intrusions [1], followed by a regional metamorphic overprint which is assumed to be Scandian. Monazites and zircons from pelitic migmatites in the Norra Storfjället lens of the Krutfjellet Nappe, and monazites from pelitic schists and gneisses in the Sulitjelma area of the Gasak Nappe were dated in-situ using LA-ICP-MS.

Monazites yield Th-U-Pb concordia ages of between 428-424 Ma. Individual concordant analyses span between 443-416 Ma. The monazites yield a large proportion of discordant analyses which fall on discordia lines at high angles to the concordia curve, interpreted to be due to the presence of initial Pb in the monazites. Lower intercept ages range between 428-416 Ma. These isotopic monazite ages are younger than the majority of EPMA Th-U-total Pb ages obtained for the Krutfjellet Nappe in the same grains [2]. The monazites often have complex zoning patterns in Y and REEs, however this zoning appears to be decoupled from the Th-U-Pb isotopic systems. We suggest that the monazites from the Krutfjellet and Gasak Nappes underwent metamorphism and/or fluid-related alteration at between 428-416 Ma, associated with assembly of the Caledonian orogenic wedge. This may have involved pervasive resetting of older monazites through dissolution-reprecipitation, leading to contamination with initial Pb and decoupling of the Th-U-Pb system from Y and REE zoning. The actual age of migmatisation still remains uncertain.

Zircons yield a spectrum of U-Pb dates which appear to be predominantly detrital. The majority are Mesoproterozoic to earliest Neoproterozoic (1600-900 Ma) and a small number around 600-550 Ma. A significant proportion of dates are discordant. These discordant dates often occur in grains which have a spongey, mottled appearance, indicating that the zircons have also experienced some alteration (metamictisation?). Lower discordia intercepts are poorly constrained, but appear to be Ordovician to Silurian. A zircon included in kyanite produced a single concordant date of 440 Ma, which matches the age for nearby earliest-Silurian intrusions [1]. On the basis of this so-far limited zircon dataset we tentatively propose that these rocks underwent migmatisation at c. 440 Ma, perhaps associated with enhanced heat flow from rift-related magmatism, but the monazite age record has been severely overprinted during subsequent Scandian orogenic wedge assembly and translation and its associated lower-grade metamorphism.

Funded by the National Science Centre (Poland) grants no. 2021/41/N/ST10/04298 and 2021/41/B/ST10/03679.

[1] Stephens, M.B. 2020. GSL Memoirs, 50, 549–575.

[2] Carter, I. S. M., Cuthbert, S. & Walczak, K. 2023. EGU Gen. Assem.

How to cite: Carter, I., Cuthbert, S., and Walczak, K.: Enigmatic migmatites from the North Scandinavian Caledonides: Unpicking the metamorphic history of the Upper Kӧli Nappes using in-situ (Th)-U-Pb dating of monazite and zircon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-968, https://doi.org/10.5194/egusphere-egu24-968, 2024.

Mineral host-inclusion systems can retain crucial information regarding their geologic history. For example, we can determine their formation conditions in terms of pressure (P) and temperature (T) from elastic geobarometry. In particular, it is possible to determine the strain acting on the inclusion when still entrapped in its host by measuring changes in the Raman-peak positions with respect to those of a free crystal, which are interpreted through the inclusion phonon-mode Grüneisen tensors (Grüneisen 1926).  The calculated inclusion strains can then be used in an elastic model to calculate the pressure and temperature conditions of entrapment. A simple case is when an anisotropic crystal is contained within a quasi-isotropic host, such as quartz in garnet. When this host-inclusion system is subjected to changes in P and T the host crystal will impose a uniform strain on the inclusion, which will in turn develop deviatoric stresses. In this scenario the symmetry of the inclusion mineral is preserved and the strains in the inclusion can be measured via Raman spectroscopy using the phonon-mode Grüneisen tensor approach.

             However, a more complex situation arises when the host-inclusion system is fully anisotropic, Such as when a quartz inclusion is entrapped in a zircon host, because symmetry breaking of the inclusion occurs as P and T change. In this case, the effect of symmetry breaking on the frequencies of phonon modes is not known and may be different from the case of structural phase transitions involving soft modes.

             Therefore, we calculated the expected deformations for a quartz inclusion in a zircon host in multiple orientations and at various geologically relevant P-T conditions. We then performed ab initio Hartee-Fock/Density Functional Theory simulations on α-quartz with the selected range of strains to (i) determine the role of the symmetry breaking strains in a completely anisotropic host-inclusion system and (ii) evaluate the possible application of the phonon-mode Grüneisen tensor when the symmetry is broken. Our results show the changes in the positions of the Raman modes produced by strains that are expected for symmetry broken quartz inclusions in zircon are generally similar to those that would be seen if the quartz inclusions remained truly trigonal in symmetry. Therefore, the Grüneisen components for trigonal alpha quartz can be used for Raman elastic geothermobarometry in anisotropic host-inclusion systems without introducing significant errors.

 Acknowledgements: This work has been partially supported by the PRIN-MUR project “THALES” Prot.2020WPMFE9_003 and the National Science Foundation under Award No. (1952698) to JPG.

References: Grüneisen, E., 1926. Zustand des festen K¨orpers. Handbuch der Physik 1, 1–52.

How to cite: Murri, M., Gonzalez, J. P., Mazzucchelli, M. L., Prencipe, M., Mihailova, B., Angel, R. J., and Alvaro, M.: Anisotropic host-inclusion systems: the role of symmetry breaking strains, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1263, https://doi.org/10.5194/egusphere-egu24-1263, 2024.

In the Moroccan Eastern Meseta, the High Moulouya Batholith (HMB), which spans an area of approximately 2400 km2, is partially hidden by the Meso-Cenozoic cover. The HMB was emplaced in Cambro-Ordovician metasedimentary rocks that had undergone greenschist facies metamorphism (Chl+Mus+Qtz+Pl+Kfs). These hosting rocks were then affected by HT-BP superimposed contact metamorphism linked to HMB emplacement. Four metamorphic zones were identified, delineating four isograds corresponding to four main metamorphic reactions. These zones include the biotite zone, cordierite zone, andalusite zone, and sillimanite zone. 

The biotite zone exhibits a mineral assemblage of Bt+Mus+Chl+FK+Qtz (±Pl ± Grt), marking the introduction of biotite through the discontinuous monovariant reaction: Chl+Qtz+FK+H2O=Bt+Mus . In the cordierite zone, the composition includes Bt+Mus+Crd+Chl+FK+Qtz (±Pl), and the reaction leading to Crd formation is: Chl+Bt+Mus+Qtz = Crd+FK+H2O. The successive development of aluminum silicates characterizes the andalusite and sillimanite zones, each associated with specific isograds corresponding to the following reactions: (Sill)+Qtz+H2O, Mus+Qtz=FK+And (Sill)+H2O, and/or And=Sill.

The obtained results, using pseudosection modelling as well as petrogenetic grid calculations, allow to precise better the HMB emplacement PT conditions. Biotite appears at a temperature of 400°C, cordierite at 500 to 520°C and andalusite at 580 to 600°C. The stability field of the andalusite-sillimanite paragenesis allows constrains the pressure at 2.6 to 2.9 Kb, which is considered constant for the entire metamorphic aureole. Therefore, the granitoids of the HMB were emplaced at a depth of 8.5 to 9.5 km, developing a contact aureole for temperatures ranging from 400 to 625°C. Moreover, 2D gravity modelling revealed that the HMB has a laccolithic shape with a thickness ranging from 3 to 5 km. The presence of numerous feeders suggests that the emplacement of the HMB occurred through a dyking process.

How to cite: Elabouyi, M., Driouch, Y., Dahire, M., Ntarmouchant, A., Jeddi, E. M., Mali, B., Laguenini, F., and Belkasmi, M.: Contact metamorphism, PT conditions and model of the emplacement of the High Moulouya batholith (Moroccan Variscan Meseta). Insights from thermodynamic and gravity modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2616, https://doi.org/10.5194/egusphere-egu24-2616, 2024.

Triassic collisional assemblage between the North China Block (NCB) and South China Block (SCB) along the Qinling Orogen still remains controversy in timing and process. As an indicator, collision-type granulite well records textural evidences of orogenic crustal alteration induced by continental collision. Located at the narrowest part of the Qinling Orogen, the Foping gneiss dome exposed pelitic and mafic granulites, migmatite and granitoids, which are critical to understand the Triassic tectonic evolution history of the Qinling Orogen. Representative pelitic granulite, mafic granulite, and pelitic schist samples from the Foping dome were selected to obtain the P-T-t paths to reveal the collision timing and process, through an integrated study of petrography, mineral chemistry, estimation of P/T conditions and U-Pb geochronological dating. Our results indicate that these granulites experienced granulite facies peak metamorphism at 6.2-7.4 kbar/ 805-855 °C and followed by retrograde metamorphism at 3.4-4.7 kbar/ 605-715 °C with characteristic of clockwise P-T paths. The pelitic schist underwent peak and retrograde stages at P/T conditions of 4.9-5.1 kbar/ 590-605 °C and 3.5-3.7 kbar/ 510-520 °C, respectively, and consisting clockwise P-T paths. Zircon U-Pb dating gives an inherited age of ca.580-573 Ma, which indicates the protoliths of the Foping granulites probably derived from Neoproterozoic. In addition, it also generates a peak metamorphic age of ca.247-240 Ma, revealing the collision onset of the Qinling Orogen at Early-Middle Triassic. Integrated results of zircon and monazite U-Pb analyzing yield retrograde age at ca.208-198 Ma, constraining the collision termination at Late Triassic. Together with the previous studies in the Qinling-Dabie Orogen, we propose that the collision between the SCB and the NCB occurred in the Qinling Orogen, and it is coeval with the collision time of late Permian-Middle Triassic in the Dabie Orogen, and ends at ca.208-198 Ma. Then the > 70^o main clockwise rotation occurred in Jurassic-Cretaceous probably.

How to cite: You, J. and Yang, Z.: Triassic collision of the Qinling Orogen: Evidence from granulite metamorphism of the Foping gneiss dome, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2977, https://doi.org/10.5194/egusphere-egu24-2977, 2024.

This study reports phase relations and U – Th – Pb_totalin-situ monazite geochronology of two-pyroxene granulite and high iron oxide bearing garnet-orthopyroxene granulite from the Karimnagar Granulite Belt, Eastern Dharwar Craton, India. The two-pyroxene granulite samples with granoblastic texture are composed of quartz, plagioclase, orthopyroxene, and clinopyroxene as major mineral phases, and biotite, zircon, ilmenite, and monazite occur as accessory phases. Small anhedral coronal orthopyroxenes surround the clinopyroxene megacryst and inclusions of clinopyroxene occur in orthopyroxene. Locally, biotites overgrow orthopyroxene and clinopyroxene along their rims. Garnet-orthopyroxene granulites are composed of orthopyroxene, garnet, spinel, quartz, plagioclase feldspar, hematite-magnetite, and ilmenite. Small, rounded orthopyroxene inclusions in garnet and anhedral coronal garnets surrounding orthopyroxene were observed. Spinels are hercynitic in composition. Ilmenite and tiny grains of spinel (~30 μm) occur as exsolve phases in magnetite. Magnetite separates spinel from garnet and orthopyroxene. The following metamorphic reactions can be proposed from the mineral assemblage:

• Cpx megacryst + Pl = metamorphic Opx + Cpx (Two-pyroxene granulite)
• (a) Opx ± Ilm + Pl → Coronal Grt + Qtz, (b) Al-rich magnetite→ Magnetite + Spinel (Hercynite), Ti-rich magnetite → Magnetite+ Ilmenite  (High iron oxide garnet-orthopyroxene granulite).

The result from petrography, phase equilibria, and thermometry of the two-pyroxene granulite predicts that metamorphic orthopyroxene becomes stable at 0.65 Gpa - 950^oC along a cooling path, and biotites overgrow orthopyroxene at 650 ^oC (0.65 GPa). Similarly, the result from grt-opx granulite implies a cooling path where coronal garnet becomes stable at 800 ^oC-0.65 Gpa.

The U-Th-Pb analysis of monazite grains in pyroxene (38 analysis) and feldspar (25 analysis) from two-pyroxene granulite shows the oldest and youngest peak at 2635 ± 90 Ma and 2449 ± 44 Ma, respectively. The monazite in pyroxene (46 analysis) and quartz (14 analysis) from garnet-orthopyroxene granulite exhibits the oldest peak at 2449 ± 14 Ma and a tiny youngest peak at 1987 ± 29 Ma. Another sample of garnet-orthopyroxene (40 analyses) displays the oldest and youngest peaks at 2574 ± 32 Ma and 2448 ± 25 Ma, respectively.

The late Neoarchean peak at ~2600 Ma retrieved from the pyroxene granulite and high iron oxide bearing garnet-orthopyroxene granulite is probably the protolith emplacement age of granulite, correlated with the accretion of Eastern Dharwar Craton and Bastar Craton as a part of extended Ur assembly. The early Paleoproterozoic peak at ~2450 Ma implies the formation of coronal garnet and metamorphic orthopyroxene during a cooling path.

How to cite: Satpathi, K. and Nasipuri, P.: Phase relations and monazite geochronology of two-pyroxene granulite and high iron oxide bearing garnet-orthopyroxene granulite from Karimnagar Granulite Belt: its importance in Neoarchean-Paleoproterozoic metamorphism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3113, https://doi.org/10.5194/egusphere-egu24-3113, 2024.

Using innovative methodological developments applied to the geosciences, such as "split-stream" LASS-HR-MC-ICP-MS technique, we present new geochemical results focusing on high-grade granulite facies rocks from the Iforas Granulitic Unit (IGU, Hoggar Mountains, NE Mali). This unit represents a high grade metamorphic terrane that has been only poorly studied yet. The aim of this study is to understand how granulites provide information on crustal growth processes and, in the context of the IGU, to test whether the processes identified can be integrated into global geodynamic reconstructions during the Palaeoproterozoic. Granulites can contain various U-Pb datable minerals such as zircon, monazite, rutile or apatite. These minerals record, to varying degrees (influence of temperature and/or fluids, nature of the protolith), the events that the granulites have undergone. From a global point of view, the main results of this study show that the major events recorded within the IGU have affected this unit uniformly. Five major events were identified on the basis of the nine rocks studied in detail, and correspond respectively to the following periods: c. 2.06-1.99 Ga, c. 1.95-1.96 Ga, c. 1.86-1.90 Ga, c. 1.76 Ga and c. 1.70 Ga. Present results suggest that the basement is mostly formed by leptynite and orthogneiss of Late Rhyacian age at c. 2.05 Ga. This basement was affected by two major phases corresponding to two successive but distinct granulite facies events at c. 2.0 Ga and c. 1.90 Ga. The first high-grade event is followed by an exhumation event concomitant to erosional processes and sedimentary deposition. The second high-grade metamorphic event occurred at c. 1.90 Ga and is contemporaneous to gabbonoritic magma intrusion. A retrograde amphibolite/greenschist facies metamorphism followed at 1.76-1.78 Ga. This study also highlighted the influence of fluid phases in granulitic rocks and their potential importance in supercontinent break-up. The thermal evolution of the IGU ended with cooling until c. 1.7 Ga. Finally, the Pan-African event did not affect the U-Pb system of zircon, monazite and especially rutile and apatite in the granulitic rocks studied, suggesting that the IGU represents a preserved segment of Paleoproterozoic granulitic crust.

How to cite: Bosch, D., Bruguier, O., Caby, R., Monchal, V., and Pinon, H.: Significance of high-grade metamorphic events in the Tuareg Shield and its implication for evolution of the Columbia Supercontinent, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4159, https://doi.org/10.5194/egusphere-egu24-4159, 2024.

Major- and trace-element zoning in metamorphic garnet can provide useful insights into the metamorphic evolution of the host rocks, in particular when it is coupled with microstructural investigation and thermodynamic modelling. Mylonitic micaschists along the Posada-Asinara Shear Zone in the Axial Zone of the Sardinia Variscan chain contain garnet porphyroblasts with four distinct growth zones (core, mantle, rim and outer rim). The porphyroblasts, enveloped by the S2 foliation, preserve an internal foliation defined by the orientation of the quartz, occasionally arranged in a sigmoidal pattern, suggesting rotation during growth. A large garnet porphyroblasts was investigated by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) mapping. The major element compositional variation follows a bell-shaped zoning, with Ca and Mn contents progressively decreasing, and Fe and Mg increasing, from the core (Alm₄₅Grs₂₅ Prp₁Sps₂₉) to the outer rim (Alm₈₆Grs₃Prp₁₁Sps₁). The trace element compositional profiles show a central enrichment area for the heaviest REE (Tm, Yb, Lu), corresponding to the garnet core. Elements with lower atomic number (Er, Ho and Y) show a similar enrichment in the mantle. Elements with even lower atomic numbers (Tb, Gd, Eu and Sm) are depleted in the core and mantle, but their content increases in broad shoulders in the garnet rim. The outer rim of the garnet is depleted in all REE. Trace element mapping also shows an annular enrichment zone in Y, Sc, Dy, Ho, Er and Tm at the mantle-rim boundary superimposed on the general compositional zoning. The REE distribution in the garnet growth zones reflects continuous growth controlled by diffusion-limited REE uptake. The Y + HREE annular enrichment zone is interpreted as a decrease in growth rate and  represents a short-lived episode in the garnet growth history. The clockwise P-T path, reconstructed by isochemical P–T phase diagrams and refined by the CZGM software (Faryad and Ježek, 2019, Lithos 332-333, 297-295) is divided into two distinct stages. The first, prograde stage is recorded by the compositional variation of garnet core and mantle, while the second stage reflects rim growth during exhumation. The core + mantle and the rim growth are separated by a decrease in garnet growth rate. The last part of the P-T path has been reconstructed from the rock mineral assemblage, which includes staurolite + biotite.

How to cite: Cruciani, G., Fancello, D., Franceschelli, M., and Rubatto, D.: Major- and trace-element zoning in garnet from mylonitic micaschists of NE Sardinia, Italy: implications for garnet growth and P-T history, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4628, https://doi.org/10.5194/egusphere-egu24-4628, 2024.

This study presents geochemical (major and trace elements, Pb-Sr-Nd isotopes on whole rocks) and geochronological (U-Pb on zircon) analyses on granitoids and volcanics from the Hounde Greenstone Belt (HGB). The HGB is one of the three Greenstone Belts outcropping in the southwestern part of Burkina Faso with, from east to west, the Boromo, Houndé and Banfora Greenstone belts. All three greenstone belts are separated by granitic domains and are mined for gold. In the HGB, the preserved sequence is constituted by a 6 km thick basaltic and gabbroic pile followed upward by intermediate (andesite) to felsic (rhyolite) volcanics with intercalated volcaniclastic and sedimentary material. Fine-grained sediments are more and more abundant upward. The HGB is limited on the East by the N-S Boni shear zone, which controlled deposition of “Tarkwaian-type” detrital sediments (conglomerate, sandstones and phyllites).

Geochemical analyses indicate that the oldest dated plutonic samples (2195 ± 6 and 2183 ± 7 Ma) have a trondhjemitic affinity and metaluminous or peraluminous character. Similar ages at 2172 ± 5 and 2191 ± 5 Ma were also obtained on volcanics (andesite and rhyolite) from within the HGB indicating coeval development of GB and basement rocks. The trondhjemite have geochemical characteristics consistent with magma production in a convergent plate setting and the 2.20 – 2.17 Ga period is interpreted as corresponding to arc build-up and thickening of the arc crust. Cross-cutting leucocratic veins in the trondhjemite indicates partial melting of the arc crust at 2144 ± 6 Ma, which may be related either to a regional metamorphic event or triggered by the gradual thickening of the crustal section. Granites and granodiorites (and their volcanic equivalents) yield younger ages in the range 2132 ± 3 Ma to 2095 ± 9 Ma, and geochemical features typical of volcanic arc granites although the youngest granitoids, in the 2120 – 2100 Ma range, indicate a syn-collisional setting. Nd isotope data show large variations (eNd ranging from +0.7 to +14.5) and a broad general trend of increasing eNd values with decreasing ages. This trend may reflect increasing proportions of juvenile mantle-derived material to the source regions of the younger granitoids. However some samples have significantly older T_DM model ages ranging from 2310 to 2430 Ma suggesting the involvement of early Birrimian components that could have been added to the source regions, either by assimilation at lower crustal levels or by sediment subduction.

How to cite: Bruguier, O., Bosch, D., Caby, R., Baratoux, L., and Jessell, M.: Timing and geodynamical setting of Paleoproterozoic events in the Birrimian of the West African Craton: Insights from the Hounde Greenstone Belt (SW Burkina Faso), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4756, https://doi.org/10.5194/egusphere-egu24-4756, 2024.

Eclogites are a characteristic product of subduction-driven metamorphism and generally regarded as mineralogical evidence for modern-style plate tectonics. Consequently considerable effort has been expended to determine when eclogite appeared in the geological record, including claims of Archaean-aged eclogite.  One area of such contention is the Belomorian Orogenic Belt in NW Russia.  There are two schools of thought regarding Belomorian high pressure metamorphism.  One is that metamorphism occurred at c. 2.7 Ga, representing potentially the oldest occurrence of eclogite (eg Volodichev et al 2021; Minerals, 11, 1029).  The other view is that high pressure metamorphism occurred at around 2 Ga, forming part of the global set of c. 2.Ga eclogites (eg Yu et al., 2017; Journal of Metamorphic Geology, 35, 855-869). 

A combination of sample-scale X-ray mapping, laser ablation ICPMS and Time-of-Flight mapping has been used to delineate two generations of garnet in a sample from the well-studied Stolbikha Island locality in the Belomorian Belt.  The sample contains voluminous diopside-plagioclase symplectites whose re-integrated composition is consistent with the former presence of pyroxene with X_jd ~ 0.26-0.3. The symplectites overprint hornblende that probably formed during melt crystallisation.  The cores of the older generation garnet are comparatively HREE rich, and give an in-situ laser ablation Lu-Hf age of 2490 ± 40 Ma.  The second generation garnet is comparatively HREE depleted, and gives a Lu-Hf age of 1875 ± 86 Ma.  The comparatively large uncertainties reflect low Lu concentrations in the analysed garnets.  Both generations of garnet preserve partially relaxed major element zoning, and given the apparent diffusivities of major elements relative to Lu and Hf, it is probable both derived ages are meaningful.  An important difference between the two garnet generations is the presence of rutile inclusions in younger garnet and their absence in older garnet.   P-T modelling suggests c. 2.5Ga metamorphism occurred at c. 6-8kbar at temperatures > 750°C. For the younger mineral assemblage, P-T modelling taking into account the presence of the older garnet as well as the inferred clinopyroxene composition, combined with Zr-in rutile thermometry from rutile-qtz-zircon clusters in c. 1875 Ma garnet, gives c. 1.5 GPa and 700°C.   

The results indicate Belomorian Orogen high pressure metamorphism occurred at c.1875 Ma, confirming the conclusions of other workers (eg Yu et al 2017) that high pressure metamorphism is Palaeoproterozoic in age.  However we find no evidence for notably elevated pressures (> 2GPa) for the metamorphism at c. 1875 Ma as suggested by some previous workers, or evidence for high pressure metamorphism at c. 2.7 Ga. The Belomorian high-P rocks belong to the now globally distributed suite that records the emergence of eclogite in the initial stages of Nuna assembly. The general emergence of eclogite in the geological record at around 2 Ga probably reflects a combination of subduction into a cooler mantle and continental processes that facilitated preservation. 

How to cite: Hand, M., Brown, D., Glorie, S., He, X., Gilbert, S., and Payne, J.: In-situ garnet Lu-Hf geochronology from the contentious Belomorian high-pressure rocks., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4969, https://doi.org/10.5194/egusphere-egu24-4969, 2024.

Subduction zones are critical sites for recycling of Li and B into the mantle. The way of redistribution of Li and B and their isotopes in subduction settings is debated, and there is a lack of detailed studies on Li and B partitioning between minerals of different types of eclogites and their host rocks. We present Li and B concentration data of minerals and Li and B whole-rock isotope data for low-T and high-T eclogites and their phengite schist host rocks from the Changning–Menglian suture zone, SW China. Omphacite controls the Li budget in both the low-T and high-T eclogites. Low-T eclogites have Li and δ⁷Li values (8.4–27.0 ppm, –5.5 to +3.2 ‰) similar to their phengite schist host rocks (8.7–27.0 ppm, –3.8 to +3.0 ‰), suggesting that Li was added to low-T eclogites from the phengite schists. In contrast, high-T eclogites have much lower δ⁷Li values (–13.2 to –5.8 ‰) than the phengite schists, reflecting prograde loss of Li or exchange with wall rocks characterized by low δ⁷Li values. Phengite and retrograde amphibole/muscovite are the major B hosts for low-T and high-T eclogites, respectively. The budgets and isotopic compositions of B in eclogites are affected by the infiltration of fluids derived from phengite schists, as indicated by eclogite δ¹¹B values (–15.1 to –8.1 ‰) overlapping with the values of the phengite schists (–22.8 to –9.5 ‰). Lithium and B in eclogites are hosted in different mineral phases that may have formed at different stages of metamorphism, implying that the contents and isotopic compositions of Li and B may become decoupled during subduction-related fluid-mediated redistribution. We suggest a mineralogical control on the redistribution of Li and B in eclogites during subduction and the exchange of Li and B with the immediate wall rocks. The observed contrasting Li and B isotopic signatures in eclogites are likely caused by a fluid-mediated exchange with different types of wall rocks during both prograde metamorphism and exhumation.

How to cite: Wang, D., Romer, R., Liu, F., and Glodny, J.: The behavior of Li and B isotopes in high-T and low-T eclogites enclosed by phengite schists, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5469, https://doi.org/10.5194/egusphere-egu24-5469, 2024.

Understanding the relationship between ultra-high-pressure (UHP) metamorphic rocks and their surrounding country rocks is crucial for interpreting the tectono-metamorphic dynamics within orogenic belts. This study focuses on the Changning–Menglian orogenic belt in Southeast Tibet to delineate the subduction history of the Paleo-Tethys Ocean. We integrate garnet Sm–Nd and Lu–Hf dating, rutile/zircon U–Pb geochronology, phase equilibria modeling, and thermobarometry to examine high-pressure eclogites and surrounding metasediments. Pseudosection modeling and conventional thermobarometry suggest a clockwise pressure-temperature (P–T) path for the eclogite, from ~1.4 GPa/~505–530 °C to ~2.4–2.8 GPa/~600–640 °C, followed by decompression to <~0.7 GPa. The micaschists reached peak conditions of 2.0–2.2 GPa and 570–620 °C. Lu–Hf dating yields ages of around 236–241 Ma for the eclogites and 249–251 Ma for the micaschists. Sm–Nd dating indicates a similar age range for the eclogites (236–242 Ma) but yields slightly younger ages for the micaschists (~240 Ma). These results imply a brief period of garnet growth in the eclogites, suggested by Rayleigh-fractionation-style Lu zoning and a rimward increase in Sm concentration within garnet. In contrast, the micaschists exhibit a more prolonged garnet growth period of approximately 10 Myr. The comparable peak metamorphic conditions and high-pressure metamorphic ages in both rock types suggest they underwent a concurrent subduction-exhumation cycle. Magmatic zircon U–Pb dating establishes the protolith age of the metabasaltic rocks at ca. 247 Ma. The multi-mineral geochronological data indicate a rapid transition from oceanic divergence to convergence within the orogenic belt around 250 Ma. These findings, along with previous geochronological data on continental subduction, point to a brief ~20 Myr cycle involving the formation, deep burial (exceeding 75 km), and subsequent ascent to the shallow crust of the Paleo-Tethys oceanic rocks. This evidence supports a continuous transition from oceanic to continental subduction within the region.

How to cite: Zhou, Y., Cheng, H., Peng, Z., Fu, Y., and Du, K.: Metamorphic P–T-t path and tectonic implications of the eclogite from Changning–Menglian orogenic belt, southeastern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5883, https://doi.org/10.5194/egusphere-egu24-5883, 2024.

Corona textures in high-grade metamorphic rocks, characterized by specific mineral assemblages, have been extensively studied, yet their direct dating remains a challenge. In an effort to ascertain the formation time and duration of corona textures, we undertook a comprehensive petrochronological study, utilizing garnet Lu–Hf and Sm-Nd alongside zircon U–Pb dating, on a corona-bearing granulite from the Miyun area in the North China Craton. This region, situated at the intersection of the Archean Eastern Block and the Paleoproterozoic Trans-North China Orogen, provides valuable insights into polymetamorphic processes.

Through pseudosection modeling and conventional thermobarometry, we determined that the corona texture—predominantly garnet, with minor clinopyroxene and quartz—formed at approximately 0.9 GPa and 740 °C. This was followed by retrogression at ~0.5 GPa and 670 °C, leading to the growth of amphibole and biotite. Lu–Hf dating of garnet gave an age of 1864 ± 3 Ma, significantly younger than the metamorphic zircons' U–Pb age of ca. 2454 Ma. This discrepancy suggests a disequilibrium in rare earth elements (REE) between garnet and zircon. Comparative analysis of REE concentrations in zircon and garnet, along with experimental data and lattice strain modeling, indicated that zircons deviated from the equilibrium array, implying their (re)crystallization independent of garnet. The preservation of Lu zoning in garnet suggests that the Lu–Hf date reflects the period of garnet growth, approximating the time of anhydrous corona assembly formation.

The U–Pb zircon age of ca. 2454 Ma indicates an earlier, distinct Archean metamorphic event, which is a common feature in high-grade metamorphic rocks throughout the Eastern Block of the North China Craton. The garnet Sm–Nd dating, yielding an age of 1817 ± 6 Ma, aligns with the amphibole-biotite Lu–Hf date of 1819 ± 16 Ma, indicating a gap of approximately 47 Myr from the garnet Lu–Hf date. This suggests a phase of rapid growth followed by fast cooling. The coinciding ages of garnet Sm–Nd and amphibole-biotite Sm–Nd and Lu–Hf, given their different closure temperatures, point to more than mere cooling, indicating the formation of anhydrous coronae around 1.86 billion years ago, followed by hydrous retrogression ca. 1.82 Ga.

The presence of both Paleoproterozoic and Archean ages in the Miyun granulites correlates with significant tectonic episodes in the Trans-North China Orogen and the Eastern Block, respectively. This correlation suggests that the Miyun region experienced overlapping metamorphic events associated with both these tectonic units. Our approach, integrating Lu–Hf and Sm–Nd dating, is particularly effective for rocks with explicit textures, enabling precise extraction of temporal intervals in metamorphic processes.

How to cite: Du, K., Cheng, H., Dragovic, B., and Cao, C.: Integrated garnet and zircon petrochronology of corona formation in high‐grade rocks from granulite‐facies rocks in the North China Craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6042, https://doi.org/10.5194/egusphere-egu24-6042, 2024.

Plate tectonics represents a forefront of research in earth sciences, with the establishment of modern-style plate tectonics remaining one of the key unresolved issues. Debates continue about its initiation, with estimates ranging from the Hadean to the Neoproterozoic or Cambrian periods, spanning nearly Earth's entire history. The North China Craton (NCC), as one of the world's oldest cratons, encapsulates a geological history from 3.8 to 1.8 billion years ago, offering valuable insights into early Earth's evolution. Recent work by Ning et al. (2022) highlighted eclogite-facies garnet clinopyroxenite in the Eastern Hebei terrane of the NCC, dated at over 2.47 billion years, suggesting the presence of modern-style plate tectonics by the end of the Archean era.

To further investigate the timing and metamorphic processes of the garnet clinopyroxenite, we conducted a comprehensive garnet and zircon petrochronological study. The garnet clinopyroxenite is primarily composed of clinopyroxene and garnet, with accessory minerals including plagioclase, quartz, titanite, magnetite, and ilmenite. Garnet compositional profiles show minimal chemical zonation, with a gradual decrease in X_Prp (0.27–0.23) from core to rim, indicative of diffusional resorption driven by retrogression. Conventional thermobarometric calculations suggest peak metamorphic conditions between 761–833°C and 1.0–1.1 GPa, not reaching eclogite-facies. Zircon analysis revealed depleted LREE, positive Ce, and negative Eu anomalies, with most zircons indicating a metamorphic age of 2478 ± 12 Ma. A subset of zircons provided a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 1770 ± 11 Ma, displaying flat HREE patterns potentially coexisting with garnet. U–Pb data suggest the Eastern Hebei terrane's garnet clinopyroxenite records Neoarchean (ca. 2.50 Ga) and Paleoproterozoic (ca. 1.8 Ga) metamorphic ages. However, the diverse range of zircon U–Pb ages and their ambiguous textural associations complicate the correlation of P–T conditions with specific timeframes. Thus, the peak metamorphic conditions of garnet clinopyroxenite, as estimated by conventional thermobarometry, cannot be conclusively dated to either ca. 2.50 Ga or ca. 1.8 Ga. This ambiguity limits the evidence for Archean eclogite-facies metamorphism. Future garnet-whole rock Sm–Nd/Lu–Hf isochron analysis may offer more definitive dating of metamorphic events and enhance understanding of the garnet clinopyroxenite's thermal history.

How to cite: Yang, R. and Cheng, H.: Garnet and zircon petrochronological study of the garnet clinopyroxenite from Eastern Hebei terrane，North China Craton——no evidence for Archean eclogite-facies metamorphism？, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7780, https://doi.org/10.5194/egusphere-egu24-7780, 2024.

Crustal evolution of the North Tianshan during the late Paleozoic remains controversial due to the lack of structural and metamorphic constraints. We present new structural, petrological and geochronological data of the Xiaopu metamorphic complex (XMC) to address this issue. The XMC shows a well-preserved Buchan-type metamorphic sequence made of garnet, andalusite-staurolite and sillimanite zones. Structural observations indicate that garnet, sillimanite, andalusite and staurolite grew syn-kinematically during a transtensional event (D2). Inclusion trails in garnet cores oriented at high angle with the external foliation probably record an earlier deformation stage (D1). Synchronous ductile normal faults and thrusts (D3) overprinted previous structures and control the exhumation of the metamorphic complex. LA-ICP-MS zircon U-Pb ages of pre-D2 gneissic granodiorite, syn-D2 granitic dikes and post-D2 diorites constrain the occurrence of D2 between 332 and 305 Ma. Apatite U-Pb ages of mylonitic rocks from the ductile fault indicate that D3 occurred at ~285 Ma. Phase modelling and geothermobarometers were used to estimate the pressure-temperature (P-T) conditions of the XMC. Peak conditions show progressive temperature increase from andalusite-staurolite schists (~580 °C) to sillimanite migmatites (~680 °C) at nearly constant pressure (~4 kbar), suggesting a significant thermal effect of nearby large intrusive bodies. The schists display a pre-peak heating with slight decompression and the migmatites show retrograde cooling and decompression to ~600 °C and ~3 kbar. Their P-T paths and high/T and low/P thermal regimes are in line with an extensional setting. Monazite U/Th-Pb ages of 313-311 Ma for sillimanite-bearing schists and migmatites suggest monazite growth during the retrogression. ⁴⁰Ar/³⁹Ar ages of mica from sillimanite schists are in the range of 298-275 Ma, consistent with a later cooling and exhumation associated with D3. These data reveal the crustal transtension during the middle to late Carboniferous (~330-310 Ma) and cooling and exhumation during the early Permian (~285 Ma) of the North Tianshan arc. Such transtensional tectonics probably facilitated decompression melting of the lower crust and lithospheric mantle of the arc. Subsequent ascent and emplacement of the resulting melt could yield high thermal gradient, produce partial melting of the mid-crustal rocks and promote crustal exhumation. 

How to cite: Ni, X., Wang, B., Soret, M., Cluzel, D., Chen, Y., Liu, J., and Faure, M.: Crustal transtension and associated high-T/low-P metamorphism in the North Tianshan Arc, NW China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9315, https://doi.org/10.5194/egusphere-egu24-9315, 2024.

Eclogites have provided important constraints on the processes of plate subduction, collision and the overall tectonic evolution of orogens. The Gubaoquan eclogite is the only one identified in the Beishan Orogenic Belt, which constitutes the southernmost part of the Central Asian Orogenic Belt. The protolith age and tectonic setting of the eclogite and associated rock units remain ill-constrained. U–Pb dating of the eclogite indicates a Neoproterozoic age of 887 ± 7 Ma for its protolith age and an Ordovician age of 461 ± 15 Ma for the eclogite facies metamorphism. Detailed U-Pb ages of zircons, monazites, rutiles and apatites from the eclogite and country rocks suggest that they have experienced multiple metamorphic events in the Neoproterozoic and Paleozoic, which are inferred to correlate with retrograde metamorphism during the later exhumation. The protoliths of the Gubaoquan eclogite are of continental origin, and along with the extensive distribution of the Neoproterozoic arc-related rocks probably resulted from assembly of Rodinia. This work was financially supported by the National Natural Science Foundation of China (41730213 and 41890831), Hong Kong RGC GRF grants (17307918), HKU Internal Grants for Member of Chinese Academy of Sciences (102009906) and for Distinguished Research Achievement Award (102010100), Northwest University Excellent Doctoral Thesis Cultivation Program (YB2023003), and from the Australian Research Council (FL160100168).

How to cite: Wang, T., Cawood, P. A., Diwu, C., and Zhao, G.: Neoproterozoic-Early Paleozoic evolution of the southern Central Asian Orogenic Belt: constraints from eclogites in the Beishan Orogenic Belt (NW China), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9385, https://doi.org/10.5194/egusphere-egu24-9385, 2024.

Early Mesozoic evolution and geodynamic processes of the South China Block remain controversial and its rheology is not well understood. The granites and migmatites exposed in the Yunkai massif preserve important records of middle crust mechanical behavior during Indosinian orogeny. They show a significant strength decreasing of the crust during this period, further affecting the rheological behavior of the entire lithosphere in South China. In order to better understand the Early Mesozoic evolution and geodynamic processes of the South China Block, we conducted detailed studies on structural geology, multi-minerals geochronology and P-T estimate on Mesozoic migmatites and granitoids in the Yunkai massif. Three tectonic/metamorphic events are identified. The main one corresponds to the development of a regional NE-SW extension. It constitutes a dome-like structure with amphibolite-facies metamorphism during 243–237 Ma (D1), followed by a rapid cooling to ~300 °C within ~20 Ma. Conventional mineral thermobarometers constrain the D1 metamorphism at 665–692 °C and 6.1–6.2 kbar, indicating an upper amphibolite – granulite facies metamorphism. Based on the phase equilibrium modelling, the grossular component (X_Grs=0.12–0.13) in the garnet core, Ti content (X_Ti=0.15–0.17) of biotite and An value (An=0.84–0.86) of plagioclase in the matrix define a peak P–T condition at 780–810 °C and 6.8–7.0 kbar within the stability field of the observed assemblage, indicating a mid-crustal high-temperature metamorphism. Combined with the field structural relationships, geochemical similarity and inherited zircons, the protoliths of the D1 amphibolite-facies metamorphism are of Silurian (<427 Ma) greywacke and magmatic rocks. Due to the strong reworking during the Early Mesozoic and only a few of these previous records were preserved in the metamorphic rocks by the zircon cores and several monazites. Thereafter, the D1-deformed granites and migmatites are crosscut by Late Jurassic (~157 Ma) greenschist-facies NE-SW dextral strike-slip faults (D2). Both of the above rock units are reworked by a later local vertical shearing (D3). Combined with published age data, our results documented a late local metamorphism of 10 Ma with respect to the regional magmatism, suggesting a magma-induced high temperature metamorphism. We propose that this magma-induced mid-crustal flow and high-temperature metamorphism are in response to the Indo-China collision and the westward subduction of the Paleo-Pacific Plate. Our new results provide new insights on partial melting and its implications on mid-crust rheological behavior during orogenic processes.

How to cite: Liu, J., Wang, B., Cochelin, B., Lu, S., Shu, L., Gumiaux, C., Chen, Y., Raimbourg, H., Faure, M., and Ni, X.: Early Mesozoic magma-induced mid-crustal flow and high-temperature metamorphism in the Yunkai massif, South China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9918, https://doi.org/10.5194/egusphere-egu24-9918, 2024.

In southern Madagascar two main tectono-metamorphic events, corresponding to the East African Orogeny (ca. 630–610 Ma) and the Kuunga Orogeny (ca. 580–515 Ma) were recognized. An early structures include recumbent folds and sub-horizontal foliation S₁ that were transposed during a regional east–west shortening resulting into north–south-oriented upright folds, with horizontal axes and new vertical axial planar foliations S₂. This second deformation event is coeval with the development of a network of vertical ductile shear zones such as the Ejeda SZ, Ampanihy SZ, Beraketa SZ, Ihosy SZ, Zazafotsy SZ and Tranomaro SZ. These megascale 15–25 km-wide intracrustal near-vertical N-S or NW-SE trending strike-slip ductile shear zones crosscut the entire high-grade metamorphic basement of southern Madagascar and separate lower-strain domains where complex fold interference patterns are visible. These high-strain zones developed between 580 and 530 Ma with a slight diachronism from the west to east and south to north and are coeval with melting and UHT/HT granulite facies conditions. The granulite facies metamorphism is widespread throughout the whole basement in all lithologies, in the southern part reaching peak conditions of 900–1000°C at 6–10 kbar and slightly lower temperature conditions (≤800°C) to the west, north, and in the Ikalamavony fold-thrust belt to the north–northeast. Importantly, the shear zones reveal large fluid/melt transfer from the depth that caused extensive fluid/melt rock interaction (in the shear zone as well as in the surrounding basement) that resulted in localized charnockitisation of the granulites. The melt/fluid flux here was structurally controlled and seems to be penetrative throughout the basement rocks. This offers a unique opportunity to study fluid-assisted pervasive melt migration controlled by localized deformation across the whole crust. In this context, our objective is to investigate the tectonometamorphic changes occurring in the intensely deformed high-grade lower to middle crust located in southern Madagascar. Additionally, we seek to delineate the chronological connection between the deformations and high-temperature metamorphism (U)HT, along with the associated processes of crustal anatexis and magmatism.

How to cite: Rarivoarison, H. N., Hasalová, P., Andriamamonjy, A. S., Miha, T., Štípská, P., Závada, P., Martelat, J.-E., and Schulmann, K.: Tectono-metamorphic evolution and crustal-scale shear zone origin in the high-grade crust of southern Madagascar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10343, https://doi.org/10.5194/egusphere-egu24-10343, 2024.

This petrological study involves a detailed examination of blueschists and other LT-HP metamorphic rocks which were tectonically emplaced within the mafic – ultramafic belt of the Nan River suture zone of northern Thailand. The blueschists do not contain garnet, lawsonite, jadeite or pumpellyite and, therefore, are assigned to the epidote – blueschist subfacies. Associated meta-cherts sometimes contain piemontite or bright blue winchite. Thrust sheets of blueschists interlayered with greenschists occur in two localities: one large outcrop is patchily exposed west of Uttaradit city, the other 135 km to the north along two stream sections on the southern flank of Doi Phuk Sung. In addition, rather rare float samples of garnet – white mica ± blue amphibole gneisses have been found in one of the Doi Phuk Sung stream sections and on three different point bars of the Wa River, ca. 40 km further to the north. These gneisses are given the field term “exotics” as their outcrop is unknown and obviously of higher metamorphic grade than any other rocks exposed in the region. The blueschists contain the mineral assemblage Amp (glaucophane – riebeckite, barroisite – winchite) + Ep + Wm + Chl + Ab + Qz ± Ttn ± Rt ± Zrn. The greenschists are typically composed of Amp (actinolite, barroisite) + Chl + Ep + Ab + Qz +Wm ± Ttn ± Rt ± Hem. The “exotics” fall into three groups based on their mineralogy: (1) Grt – Wm + Ab + Chl + Qz ± Stp ± Ep ± Ttn ± Aln ± Zrn ± Ap; (2) Amp (hornblende) – Grt – Wm + Ab + Chl + Qz ± Stp ± Ep ± Ttn ± Aln ± Zrn ± Ap; and (3) Amp (glaucophane – riebeckite, barroisite, winchite) – Grt – Wm + Ab + Chl + Qz ± Stp ± Ep ± Ttn ± Aln ± Zrn ± Ap. The blueschists and greenschists from both localities show identical history of 3 phases of deformation and relative timing of mineral growth. Evidence of D1, preserved as rootless isoclinal folds of quartz rich seams, was almost entirely destroyed by the development of an intense pervasive schistosity during D2, associated with tight to isoclinal folds. D3 produced a crenulation cleavage with little recrystallisation. The peak P-T conditions of blueschists were estimated by constructing pseudosections, indicating temperatures of approximately 450 to 500 °C and pressures of 0.8 to 1.2 GPa. The exotics preserve direct evidence of gneissic segregation banding and a single deformation event. In many cases amphiboles are visually zoned with green cores and violet – blue rims. This is interpreted to indicate that they originated in the greenschist/amphibolite facies and then passed into the blueschist/eclogite facies. Garnets are generally fractured and fragmented and usually display strong prograde compositional zoning where Xprp and Xalm are increasing, Xgrs and Xsps decreasing from core to rim. Peak P-T conditions were estimated by using the Grt-Amp thermometer and calculated pseudosections with temperatures of approximately 550-600°C and pressures of 0.8 to 1.2 GPa.

How to cite: Sawasdee, P., A. Hauzenberger, C., and E. Booth, J.: LT-HP metamorphic rocks from the Nan River suture zone, Thailand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10898, https://doi.org/10.5194/egusphere-egu24-10898, 2024.

Apatite, an abundant accessory mineral in igneous and metamorphic rocks, may accommodate appreciable amounts of trace elements including U, Pb and REE and is thus a useful U-Pb geochronometer and tracer of high-temperature metasomatism. Since apatite is susceptible to recrystallization, new growth and fluid-induced chemical changes, a good understating of the U-Pb system closure in apatite at variable geological conditions is required to correctly interpret apatite U-Pb ages. In this research, we delve into the behavior of apatite in marine phosphorites metamorphosed at sanidinite facies conditions to constrain U-Pb systematics in apatite under extreme high-T low-P conditions.

We sampled non-metamorphosed, metamorphosed, and hydrothermally altered marine phosphorites from the Mottled Zone pyrometamorphic complex exposures in the Hatrurim Basin, Israel. Petrographic study of the samples was followed by in -situ measurement of major (EMPA) and trace element compositions and U-Pb dating (LA-ICP-MS) of apatite.

Our results show that during the pyrometamorphic event apatite recrystallized and incorporated carbonate, silica, and sulphate into its crystal lattice. Thermally derived apatite recrystallization resulted in a submillimeter-scale Pb isotopic homogenization, inheritance of common lead of very low ²⁰⁷Pb/²⁰⁶Pb ratio from the U-rich, biogenic apatite precursor, and contemporaneous U-Pb system closure of apatite on a wider scale. The Miocene and Pliocene U-Pb ages of apatite coincide with previously known ⁴⁰Ar/³⁹Ar and K-Ar ages of the Mottled Zone pyrometamorphic event (Gur et al., 1995). Post-metamorphic interaction of high-T metamorphosed phosphorites with carbonate-, uranyl- and vanadate-rich fluids resulted in U and V enrichment of apatite, as well as redistribution of REE.

The results of our research shed new light on the timing and extent of the Mottled Zone pyrometamorphic event, contribute to understating the behavior of biogenic apatite under extreme high-T, low-P conditions, and exemplify the utilization of apatite in meta-sedimentary rocks for dating thermal events including combustion metamorphism.

How to cite: Segall, Z., Katzir, Y., Vapnik, Y., and Elisha, B.: U-Pb Dating of Apatite in Sanidinite-Facies Pyrometamorphosed Rocks from the Hatrurim Basin, Israel, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11568, https://doi.org/10.5194/egusphere-egu24-11568, 2024.

Interaction between fluids and different rock types at the subducting slab interface directly influences deep volatile recycling processes. Recent studies [1] suggest that an influx of reduced fluids from graphite-bearing metapelites can promote deserpentinization at lower temperatures and modify the intrinsic redox capacity of the released fluid. Here we report a newly discovered high-pressure deserpentinization front ­– Cerro Pingano (Betic Cordillera, Spain), located 20 km north of the type locality of Cerro del Almirez [1] – where additional observations involving carbonate-bearing chlorite-harzburgites further support the influx of C-bearing fluids concomitantly to deserpentinization. This small body (<0.5 km²) is hosted within a metasedimentary sequence of graphite-bearing mica schists and marbles which together underwent an Alpine high-pressure metamorphism. Antigorite (Atg-)serpentinite (without carbonate) is separated from Chl-harzburgite (enriched in magnesite) through a sharp boundary of chlorite (Chl-)serpentinite that can be traced across a ~50 cm wide reaction front.

Atg-serpentinite shows an S-C fabric with a strong crystallographic preferred orientation (CPO) characterized by [001]_Atg perpendicular to the foliation. Although the transformation to Chl-harzburgite is associated with fabric weakening, the low-strain olivine, orthopyroxene, and tremolite show a remarkable distribution of the poles to their (010) perpendicular to the compositional layering. Magnesite [0001] axes are distributed perpendicular to the layering, and petrographic observations indicate textural equilibrium between Ol + Opx + Chl + Tr + Mag. The transformation of Atg-serpentinite to Chl-harzburgite is also associated with a decrease of Fe³⁺/ΣFe and a measurable increase of C, Na, and K content in bulk chemistry, suggesting an interaction with externally derived fluids.

We tested this hypothesis with thermodynamic modelling of the fluid-rock interaction between the host-rock derived fluids and Atg-serpentinites. Thermodynamic models of graphite-bearing mica schist predict dehydration due to chloritoid and chlorite breakdown, and release of highly reducing CH₄ + CO₂-bearing fluids. Open-system infiltration models show that host-rock derived fluids could effectively reduce the serpentinite bulk composition, consistently with the observed decrease of Fe³⁺/ΣFe between Atg-serpentinites and Chl-harzburgites. The infiltration-induced reduction shifts the stability of Chl-harzburgite mineral assemblage to temperatures ~50°C lower than predicted by closed-system models without external fluids input.

While the microstructural record suggests that Chl-harzburgite fabric was inherited from the Atg-serpentinite precursor, the changes in bulk chemistry and redox conditions result from interaction with highly reductive aqueous fluids derived from host graphite-bearing mica schists. Hence, we infer that the record of specific prograde metamorphic reactions may reflect changes in redox conditions, not necessarily associated uniquely with P-T changes. The redox contrast between the reduced fluids and prograde dehydrating serpentinites thus represents a new way to precipitate carbonates that can be further subducted and may devolatilized beyond subarc depths.  

[1] Padrón-Navarta, J.A. et al. (2023) Nat. Geosci.

Research funded by RUSTED project PID2022-136471N-B-C21 & C22 funded by MICIN/ AEI/10.13039/501100011033 and FEDER program, and “Juan de la Cierva” Fellowship JFJC2021-047505-I by MCIN/AEI/10.13039/501100011033 and CSIC (M. Bukała).

How to cite: Bukała, M., Padrón-Navarta, J. A., Menzel, M. D., Hidas, K., Sánchez-Vizcaíno, V. L., and Garrido, C. J. G.: The effect of modulated deserpentinization on the deep carbon cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12237, https://doi.org/10.5194/egusphere-egu24-12237, 2024.

Accurately constraining the timing and tempo of specific metamorphic events is necessary to constrain the rates of important geodynamic processes, such as burial and exhumation in orogens and devolatilization in subduction zones. Accessory phase petrochronology is a popular tool employed to constrain the age and duration of metamorphic processes, including mineral nucleation and deformation fabric development. While accessory phases can produce robust dates, their thermodynamic data is often poorly constrained, requiring careful petrographic analysis to link dates to the pressure-temperature-deformation histories of metamorphic rocks. The dating of rock-forming minerals, like garnet and plagioclase, is typically more resource intensive than accessory phase petrochronology, but allows for directly linking dates to specific metamorphic events. Here, we consider the results of monazite accessory phase U-Th-Pb chemical dating with that of Sm-Nd dating of garnet from the Manhattan Schist, New York City, to explore how the synthesis of these two methods can be used to constrain robust tectonic histories.

The Manhattan Schist is a Laurentia-derived aluminous pelite historically thought to record polymetamorphism characterized by: 1) upper amphibolite facies metamorphism and anatexis associated with the Taconic Orogeny (~520-470 Ma) and 2) lower grade overprinting during the Acadian orogeny (~416-360 Ma). This interpretation, however, is based on correlation with seemingly similar units elsewhere in New England rather than direct study of the Manhattan Schist, and is called to question by the data presented here.

This work explores three samples, MAT-2017-01a, GWB-03, and CRT-06. All samples are grt-ky-bt-ms migmatites, that record a four-stage metamorphic history: 1) garnet growth starting at ~550°C and 4-6 kbar, 2) burial and heating to kyanite-grade anatexis at 700-750°C and 7-11 kbar, 3) ~1-2 kbar of isothermal exhumation to sillimanite (fibrolite) stability, and 4) continued exhumation to ~700°C and ~6 kbar. Monazite grains in all samples occur both in the matrix and as inclusions in garnet. Metamorphic monazite dates are dominated by a ~465 ±30 Ma (n=15) age consistent with growth during the Taconic Orogeny, with only a single date at ~383 ±25 Ma found in CRT-06. Bulk garnet Sm-Nd dating via TIMS in MAT-2017-01a, however, yields a late Acadian age of ~386 ±3.68 Ma (n=5, MSWD=0.94). The low MSWD coupled with the preservation of major element growth zoning in garnet, suggests that this value represents a single garnet age population reflective of growth at peak or near-peak conditions, entirely during the Acadian orogeny.

Taken as a whole, our results suggest that the Manhattan schist experienced: 1) early greenschist facies metamorphism during the Taconic orogeny recorded in metamorphic monazite, and 2) peak metamorphism associated with collision and burial in the Acadian orogeny recorded in garnet. Additionally, the sample-to-sample heterogeneity in monazite ages within the same lithology suggests that monazite growth is controlled by (sub)cm-scale processes. Therefore, future studies should investigate multiple samples of the same formation, if not the same outcrop, before making tectonic interpretations based on accessory phase petrochronology.

How to cite: Castro, A., Walker, S., Thomas, J. B., Jaret, S. S., Brunet, I., and Morin, K. D.: Insights from the Application of Accessory and Major Phase Petrochronology from the Manhattan Schist, NYC, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12609, https://doi.org/10.5194/egusphere-egu24-12609, 2024.

Temperature predictably controls mineral stability during metamorphism, and exerts first-order influence on rock viscosity during deformation, but the co-evolution of temperature-dependent metamorphic mineralogy and rock rheology is poorly understood. Thermally-controlled metamorphic-mechanical feedbacks must lead to strain localization during plate boundary formation. However, geologic observations from horizontally-forced, newly-destructive, intra-oceanic subduction plate boundaries consistently present a rheological paradox: hot rocks are strong and cold rocks are weak. 

Observations from geo-/thermochronology and metamorphic thermobarometry demonstrate that following a stage of initially slow, forced convergence along a hot plate interface when the slab tip resists downward translation, the lower plate suddenly collapses into the mantle. After this catastrophic collapse, subduction becomes self-sustaining (i.e., slab pull is established), stable, and cold. The physical mechanism triggering collapse is unknown, though geological studies show that collapse occurs contemporaneously with rapid cooling of the nascent plate contact and depression of slab-parallel isotherms, or “refrigeration”. These observations imply that hot rocks are strong (i.e., viscously sticky), and cold rocks are weak (i.e., viscously lubricating). It is puzzling why the resistance phase would be characterized by the highest temperature metamorphism, since high-temperature rocks are commonly viscously weak; furthermore, plate boundary “unzipping” and lithosphere-scale localization only occur during the rapid refrigeration phase, when rocks should, to a first order, be stiffer and less deformable. What mechanism(s) overcome stiffening, such that a temperature decrease leads to rock weakening, strain localization, and successful subduction initiation? 

Here, we compare microstructures from metamorphic rocks that formed along ancient hot, warm, and cold plate interfaces that correspond to different stages in the evolution of subduction zone formation from initiation to self-sustaining. We conclude that refrigeration drives changes in metamorphic mineral stability, distributions of strain-accommodating minerals, fluid content, and deformation mechanisms, which together dramatically weaken the developing plate boundary. We use flow laws and paleopiezometry to bracket ductile rock strength and demonstrate that cooling at the time of inferred slab collapse causes a minimum 3 order of magnitude viscosity reduction from ~10²¹ to 10¹⁸ Pa-s—the most drastic change in viscosity over a subduction zone’s lifetime. The viscosity reduction leads to a series of dynamic feedbacks, namely: interface decoupling and accelerated plate rates; increased and sustained interface cooling; and stabilization of a wetter, weaker interface. Our ‘refrigeration weakening’ hypothesis embodies a coupled metamorphic-mechanical process that is inherent to the evolution of common oceanic crust, and successfully explains observed changes in upper plate stress state, inferred slab velocity, and timing of proto-forearc seafloor spreading. If true, this mechanism motivates several new testable hypotheses regarding the dynamics of subduction zone development as a function of temperature changes in the modern Earth and throughout Earth’s history.  

How to cite: Kotowski, A., Seyler, C., and Kirkpatrick, J.: From hot and strong to cold and weak: How ‘Refrigeration Weakening’ facilitates strain localization during subduction initiation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12666, https://doi.org/10.5194/egusphere-egu24-12666, 2024.

Xenotime, a common accessory mineral in metasedimentary rocks, is reactive during metamorphism and can incorporate significant amounts of uranium, making it a promising target for in-situ U-Pb geochonology. However, small grain sizes and cryptic mineral zoning limit the applicability of this tool in low-grade metamorphic rocks thus far. Herein we present results from the dating of two low-grade metamorphic samples collected in the Tirolic-Noric Nappe System at the southern base of Dachstein and Hochschwab massifs (Eastern Alps, Austria). These weakly metamorphosed metasediments, in which sedimentary structures are preserved, underwent metamorphism during the Cretaceous Eo-Alpine event, resulting in a mineral assemblage consisting of chloritoid + pyrophyllite + muscovite + hematite + rutile + quartz that infers P-T conditions of ~350°C and 0.2-0.6 GPa.

Both samples contain accessory xenotime grains that typically range from 10 to 30 µm in diameter. SEM imaging and chemical mapping reveal systematic chemical zoning of most xenotime grains with a heterogeneous core and a distinct, 5-10 µm wide rim that is enriched in MREEs (Sm-Gd). We targeted each chemical domain of xenotime by in-situ LA-ICPMS U-Pb dating using a 5 µm beam diameter. In addition to U and Pb isotopes, Gd and Y concentrations were monitored. The majority of concordant U-Pb dates in both samples range between 632 and 250 Ma. These analyses exhibit low Gd/Y ratios consistent with the xenotime core composition and are therefore interpreted as an inherited population. Both samples exhibit a younger age cluster characterized by high Gd/Y ratios, corresponding to the MREE-rich xenotime rim. In the Hochschwab sample, the youngest cluster yields a concordia age of 134.2 ± 4.0 Ma (MSWD: 2.7, n: 7). Host-inclusion relationships of chloritoid and xenotime suggest coeval growth of the MREE-rich xenotime rim and chloritoid porphyroblasts, linking the U-Pb date to the growth of the main metamorphic assemblage. In the Dachstein sample, the youngest cluster yields a concordia age of 92.4 ± 1.5 Ma (MSWD: 2.9, n: 9). Xenotime and chloritoid are not observed in direct contact, and this sample is characterized by a pervasive crenulation cleavage, which postdates chloritoid growth. From the distribution and morphology of xenotime we conclude that dissolution-precipitation related to crenulation cleavage formation facilitated growth of the MREE-rich rim.

Our results suggest that several stages of xenotime precipitation occurred during protracted or multistage tectono-metamorphic activity in the Tirolic-Noric Nappe System during the Eo-Alpine metamorphic evolution, which is also corroborated by published geochronological data in the same unit. We also demonstrate that the constantly improving spatial resolution of LA-ICP-MS systems allows successful in-situ dating of minute xenotime growth zones, thus providing great potential to improve our understanding of processes during low-grade metamorphism.

How to cite: Hollinetz, M. S., McFarlane, C. R. M., Schneider, D. A., Huet, B., and Grasemann, B.: In-situ LA-ICP-MS U-Pb dating of lower greenschist facies xenotime, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14650, https://doi.org/10.5194/egusphere-egu24-14650, 2024.

Talc (nominally Mg₃Si₄O₁₀OH₂) is a Mg-dominant trioctahedral layered silicate with empty interlayer space that can accommodate minor quantities of Fe²⁺ and Mn²⁺ at the octahedral sites, replacing Mg. Given that talc is a common hydrous silicate mineral, containing up to 5.5 weight percent of H₂O and commonly occurring under a variety of geological conditions, it can contribute to the volatile cycling in the vicinity of subduction zones. Therefore, the deeper understanding of the temperature-induced talc breakdown into Mg-rich pyroxene and the role of Fe and Mn in the crystal structure of talc during its structural collapse can provide valuable information in several fields of Geosciences such as metamorphic petrology, geophysics, and environmental sciences. Moreover, the information from the dehydroxylation and thermal decomposition of talc can be applied beyond Geosciences; in particular, to understand the weathering processes and firing conditions of soapstone-based cultural-heritage objects. Moreover, the high-temperature atomic dynamics of Fe²⁺-bearing hydrous silicates with strong structural anisotropy, as probed by Raman spectroscopy,  can shed light on the thermal activation of charge carriers (delocalized H⁺ and e^-) and hence, on conductivity anomalies in the lithosphere (Bernardini et al., 2023).

In this study, we present the results of the thermally-induced changes in Fe²⁺- and Mn²⁺-containing talc in the temperature range of 100-1400 K by considering the framework (15-1215 cm^-1) and OH-stretching vibrations (3400-3800 cm^-1). For this purpose, two samples from Tyrol in Austria were examined, whose exact chemical formulas, particularly (Mg_2.93Fe²⁺_0.08Ni_0.01Si_4.04OH_1.81O_0.19) and (Mg_2.95Mn²⁺_0.07Fe²⁺_0.01Si_4.06OH_1.69O_0.31), were determined by wavelength-dispersive electron microprobe analysis (Aspiotis et al., 2023). We show that structural transformations at an atomic-scale level occur at different temperatures for the Fe²⁺- and Mn²⁺-containing talc samples, as the Raman peak position of the TO₄ stretching vibration at ~1050 cm^-1 starts deviating from the linear dependence with elevated temperatures at 1250 and 1150 K, respectively. In addition, the in situ Raman heating/cooling experiments demonstrate that the OH-stretching mode at ~ 3660 cm^-1 associated with a MgMgFe²⁺ or MgMgMn²⁺ local configuration vanishes at 1250K for both talc crystals but recovers when cooling down to room temperature, whereas the OH-stretching vibration at 3675 cm^-1 related to a MgMgMg triplet can still be identified at least at 1350 K. This reveals that reversible oxidation processes are related to Mn²⁺-bearing hydrous minerals besides those containing Fe²⁺. The complete irreversible thermal decomposition of talc occurs at 1400 K, where clinoenstatite is formed.

References

S. Aspiotis, J. Schlüter, F. Hildebrandt, B. Mihailova, J. Raman Spectrosc. 2023; 54, 1502.

S. Bernardini, G. Della Ventura, J. Schlüter, B. Mihailova, Geochem. 2023, 83, 125942.

How to cite: Aspiotis, S., Stoeck, L., Schlüter, J., and Mihailova, B.: In situ high-temperature Raman spectroscopy for the thermal decomposition of Mn2+- and Fe2+-bearing talc, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15106, https://doi.org/10.5194/egusphere-egu24-15106, 2024.

The Inthanon metamorphic core complex in northern Thailand comprises gneisses, schists, migmatites and calc-silicates which are intruded by a variety of granitoids of different age. New P-T estimates, U-Th-Pb total age and U-Pb age data of monazite indicate a multi stage history of the core complex.

Garnet mica-schists and gneisses are exposed in the western part of the Inthanon metamorphic core complex. Garnets show two episodes of growth, with some displaying garnet breakdown and corona formation containing plagioclase, quartz, biotite, and muscovite. The garnet core (grt1) records medium to high-grade metamorphism in the Late Triassic to the Early Jurassic. The second garnet growth (grt2) can be distinguished by a significantly lower Ca content and formed during a high-grade metamorphic event in the Late Cretaceous. Both garnet generations contain abundant inclusions of biotite, muscovite, and monazite, which are used for the reconstruction of the P-T-t history. The monazite included in grt1 yields an age of ~230 Ma. Metamorphic conditions during the first episode of garnet crystallization are 0.7–0.8 GPa at 530–570 °C. The second garnet growth occurred in the upper amphibolite facies at pressures of 0.4–0.5 GPa and temperatures of 640–670 °C. The monazite inclusions in grt2 and monazite within the garnet coronae yield an age of about 80 Ma. The monazite in the matrix, which exhibits complex chemical zoning indicative of recrystallization and re-precipitation during multiple stages of metamorphism, yields a main population at 230 Ma and a typical lead loss trend to a few clusters of 80 Ma dates.

Orthogneiss domains are characterized by a mylonitic texture with large K-feldspar augen and porphyroclasts surrounded by a fine-grained, foliated matrix of quartz and feldspar. This domain is mainly exposed in the core zone of the Inthanon complex and tends to become more mylonitic towards the east. Temperature conditions of 650–700 °C and 0.4 to 0.7 GPa were calculated by pseudosection modelling and using the Ti-in biotite-geothermometer. The monazite texture from the orthogneiss domain displays patchy zoning indicative of several resorptions and reprecipitations. The monazite exhibits an older age range of 230–210 Ma, with younger clusters yielding ca. 75 Ma, and shows a lead loss trend to ca. 30 Ma. The orthogneiss domain is extensively injected by concordant foliated biotite-garnet leucogranite with a monazite U-Pb age around 40 Ma. This age is considered as the upper age limit for the early stages of ductile shearing in the core complex.

Our data indicate that the Western Gneiss Belt in Thailand underwent several tectono-metamorphic events: (1) a medium P-T regional metamorphic phase in the Late Triassic to the Early Jurassic related to Sukhothai-Sibumasu collision (~200 Ma), followed by (2) a widespread younger overprint at upper amphibolite facies in the Late Cretaceous connected with local plutonic activity 75‑65 Ma. (3) Local Late Eocene–Oligocene magmatism and Chiang Mai basin development within deformation zones led to the emplacement of orthogneisses and local metamorphic overprint as seen e.g. in the Mae Ping and Three Pagoda shear zones.

How to cite: Santitharangkun, S., Hauzenberger, C. A., Skrzypek, E., Gallhofer, D., and Fritz, H.: P–T–t constraints on the Inthanon metamorphic core complex and implications for the evolution of the Western Gneiss Belt, northern Thailand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15425, https://doi.org/10.5194/egusphere-egu24-15425, 2024.

Based on petrological and geochronological studies of glaucophane-bearing schist in the Cenozoic Yuli metamorphic belt, Taiwan, as one of the world's youngest high-pressure (HP) terrane, we provide insights on the metamorphic ages, the metamorphic stages/microstructural fabrics, and the exhumation mechanisms of HP rocks.

In this study we conducted field surveys of well-preserved mesoscale amphibole facies ultramafic schist outcrops along the Mayuan River, located in the Juisui area. We also carried out microstructural analysis using a microscope and SEM-EDS on oriented thin sections to distinguish different deformation stages/fabrics, along with quantitative EPMA analysis of the chemical composition of amphibole and phengite mineral. Furthermore, two different grain sizes (0.18mm and 0.25mm) of phengite were used to conduct the ⁴⁰Ar/³⁹Ar step heating dating analysis to determine the metamorphic age.

Field observation identify S₂ as the main foliation, shallowly dipping to the northwest or northeast in the Mayuan River area. The amphibole schist represents the rim of the ultramafic blocks within the matrix of the albite-quartz-mica schist. We also find a right-lateral west dipping shearing fault zone occurred between these two schists.

By adopting main Phengite fabrics as S₂, in microstructure domain, the prograde to retrograde metamorphism (subduction to exhumation) of 5 stages were identified: 1) S_2-1, defined by rotated stubby subhedral phengite; 2) S₂, defined by Phengite ± Epidote ± Calcic-amphibole; 3) S₂₊₁, defined by Phengite ± Epidote ± Calcic-amphibole ± Chlorite; 4) S₂₊₂, defined by Phengite ± Calcic-amphibole ± Titanite ± Albite; 5) and post-S₂₊₂ phengite. The amphibole revealed varied zoned compositions and evidence of both “clockwise” (high-T to low-T) and “counterclockwise” (high-T low-P to high-P low-T) metamorphism from core to rim: from Pargasite to Edenite/Mg-Hb to Actinolite, Glaucophane to Winchite to Actinolite, and Pargasite to Winchite to Actinolite. Phengite grow in every 5 stages, and the ⁴⁰Ar/³⁹Ar dating yielded plateau ages of 10.7±1.6 Ma, 10.4±0.5 Ma, 8.8±0.6 Ma, 8.9±1.9 Ma, and 11.0±0.7 Ma, indicating cooling ages after the subduction stage with an estimated closure temperature of 410-420°C. One age spectrum showed a minimum age of 6.1 Ma, possibly representing a recrystallized age during exhumation.

This study reveals the P-T-t path of the amphibole schists in the rim of ultramafic rocks in the subduction channel from subduction to exhumation. The clockwise and counterclockwise P-T path of the zoned amphibole indicated the complicated exhumation mechanism, and the retrograde metamorphism occurred in 11~6 Ma.

How to cite: Pang, C.-H., Yeh, M.-W., Lee, J.-C., and Iizuka, Y.: Interpreted 11-6 Ma age of Retrograde Metamorphism in the subduction channel of the Yuli Belt, Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16362, https://doi.org/10.5194/egusphere-egu24-16362, 2024.

In complex continental back-arc settings, such as the Cycladic realm of southeast Greece, polymetallic mineralization can provide information about past tectonic events and help to reconstruct the architecture of the metamorphic basement. In the Cyclades archipelago, slab rollback generated Miocene crustal extension and the formation of metamorphic core complexes, where hydrothermal systems occurring in the upper crust track one of the latest events in the geodynamic evolution. Lead isotope ratios of galena (PbS) and Sr isotope ratios of barite (BaSO₄) of the polymetallic ore deposits, which are exposed on most of the islands, reveal two distinct sources of lead and strontium in the underlying basement of the core complexes. A clear division exists between ²⁰⁶Pb/²⁰⁴Pb≤18.84 and ⁸⁷Sr/⁸⁶Sr≥0.711 in the north-central Cyclades and ²⁰⁶Pb/²⁰⁴Pb≥18.84 and ⁸⁷Sr/⁸⁶Sr≤0.711 in the west Cyclades. This regional pattern corresponds with the exposures of the high-pressure/low-temperature Upper and Lower Cycladic Blueschist nappes on the islands, respectively. Moreover, the pattern follows the surface trace of the proposed synorogenic Trans-Cycladic Thrust, a subduction-related structure that imbricated the high-pressure units. In addition, the isotopic composition of the hydrothermal minerals indicate that the structurally lower Cycladic Basement has a stronger influence on the metal sources of deposits occurring in the hanging wall of the Trans-Cycladic Thrust than in the footwall. Observations featuring the isotopic signature of hydrothermal minerals are complemented by a compilation of new and published isotopic and geochemical whole-rock data of the basement rock types. This allows us to further interpret the geodynamic significance of the apparent heterogeneities in the exposed rocks of the metamorphic core complexes and correlate the scattered exposures of the metamorphic basement. Furthermore, regional patterns in the isotopic and geochemical signature of the basement lithologies help to reconstruct the nature of the continental margin prior to Cretaceous-Eocene subduction.

How to cite: Wind, S., Schneider, D., Hannington, M., Hector, S., and Patten, C.: Reconstructing the nature of the metamorphic basement in the Cyclades, Greece, by the isotopic signature of hydrothermal minerals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16493, https://doi.org/10.5194/egusphere-egu24-16493, 2024.

Mineral reactions determine rocks' physical and rheological properties, but whether these reactions occur close to or far from equilibrium, and whether they are continuous or pulsed, is generally unclear. Garnet, the Rosetta Stone of metamorphic processes, presents an unparalleled potential to track the timing and rate of such reaction sequences often recorded and preserved in its growth zones. Here, we used a combination of major and trace-element mapping of garnet to identify single growth zones linked to specific mineral reactions. We extracted each zone by laser microsampling to perform high-precision Lu-Hf chronology and investigate whether and to what extent garnet keeps up with tectonic processes. The analyses were done on a single 1.3 cm-sized garnet grain from a mica schist from the Schneeberg Complex, Italy. The garnet grain was chemically characterised by major- and trace-element mapping (EPMA, LA-ICPMS), and five compositionally distinct micro-domains were extracted using a laser mill. Each single zone was divided into multiple garnet aliquots to enable multi-point isochrons. The four inner zones, corresponding to ~ 85% of the total garnet volume, yielded identical ages with a weighted mean of 98.4 ± 0.1 Ma (2σ). The outermost zone shows a strong chemical contrast with the rest of the grain, yielding a resolvably younger age of 97.8 ± 0.3 Ma. The data show that garnet growth in metapelites may take less than 1 Ma and, within that short time, progresses in several pulses that last less than c. 200 kyr. Our results demonstrate that garnet growth may occur much faster than required for changes in P–T conditions caused by tectonic processes. Pulsed, ultrafast garnet growth occurred instead at isobaric and isothermal conditions, far removed from equilibrium, and resulted in high-flux fluid production. While challenging the equilibrium paradigm, this example provides a rare glimpse into reaction overstepping and the rapid pushes of the system to attain equilibrium during periods of efficient matrix element transport.

How to cite: Tual, L., Smit, M. A., Cutts, J. A., Musiyachenko, K., Kooijman, E., Majka, J., and Foulds, I.: Garnet growth in a geological blink of an eye: evidence from high-precision Lu-Hf chronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17461, https://doi.org/10.5194/egusphere-egu24-17461, 2024.

Bing Yu^1,2* , M. Santosh^1,3, Richard M. Palin², Cheng-Xue Yang¹

¹School of Earth Sciences and Resources, China University of Geosciences Beijing, No. 29 Xueyuan Road, Haidian District, Beijing 100083, China

²Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, United Kingdom

³Department of Earth Science, University of Adelaide, Adelaide SA 5005, Australia

*E-mails:eart0615@ox.ac.uk ; bing-yu@email.cugb.edu.cn

The existence of Earth's oldest supercontinent Ur is controversial due to be paucity of rock records related to early continent-building processes, particularly since juvenile felsic crust formed during the Early Archean (4.0–3.2 Ga) in many cases had been reworked or destroyed. The Paleo-Mesoarchean terranes are therefore of potential interest, the subduction-related arc magmatism and high-grade metamorphism in these regions can be used as important clues to trace the history of the assembly of Earth’s oldest supercontinent.

The Southern Granulite Terrane (SGT) in India is a collage of continental blocks ranging in age from Paleo-Mesoarchean through Neoarchean and Late Neoproterozoic-Cambrian, providing a near-complete record of the history of assembly and disruption of several supercontinents. The Coorg Block and the surrounding Mercara suture zone are important windows for tracing the history of the Ur supercontinent. We investigate the Coorg Block composed dominantly of charnockites and mafic granulites and the Mercara Suture Zone exposing extensive khondalites (granulite facies metapelites). The khondalite belt in the Mercara Suture Zone is currently the oldest known khondalite series, and zircon U-Pb data of detrital zircons indicate that the protoliths formed during the Paleoarchean (up to 3.5 Ga), with high-grade metamorphism at ca. 3.1 Ga, coinciding with the timing of assembly of supercontinent Ur. Phase equilibria modelling indicated a peak temperature of above ca. 900 °C and pressure up to 12 kbar. The charnockite suite (usually associated with mafic granulite enclaves) from the Coorg block ranges in age from Mesoarchean to late Neoarchean, with magmatic xenocrysts showing ages up to 3.5 Ga, this suggests that old crustal components are present in the crystalline basement. The peak of magmatic emplacement for the charnockite and gabbroic suites, both showing arc affinity, occurred at ~3.15 Ga and the arcs accreted onto the Dharwar craton to the north during the Neoarchean transition, building the ‘expanded Ur’. Mafic granulites formed by the underplating of basaltic magma derived through slab partial melting during subduction. The magmatic zircon core suggests Mesoarchean emplacement and the metamorphic zircons as well as monazite indicate collisional metamorphism at 3.0-3.1 Ga marking the assembly of the Ur supercontinent.   

We also combine our data with published results from other regions including Madagascar and East Antarctica, where remnants of the early crust are preserved in an attempt to reconstruct the Ur supercontinent. Our spatio-temporal analysis and model simulations suggest near-simultaneous assembly of the early crustal nucleic on the globe around ca. 3.1-3.0 Ga, although some parts of the supercontinent did not cratonize until the Late Mesoarchean.

Keywords: High-grade metamorphism; Zircon and monazite Geochronology; Ur supercontinent

Reference:
Yu et al., 2021. Gondwana Research 91: 129-151.
Yu et al., 2022. Precambrian Research 370: 106537.
Yang et al., 2023. Gondwana Research, 118, 1-36.

How to cite: Yu, B.: Mesoarchean crustal growth in the Coorg block and Mercara suture zone, southern India: evidence for reconstructing the Ur supercontinent, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17675, https://doi.org/10.5194/egusphere-egu24-17675, 2024.

Subduction erosion present in oceanic subduction zones has been reported recently in continental subduction-collision zones, but the response of the upper plate remains enigmatic. The Dabie-Sulu orogen is considered to have formed by deep northward subduction of the Yangtze Block (YB) beneath the North China Block (NCB). However, the Haiyangsuo complex within the Northern Sulu ultrahigh-pressure (UHP) belt has intriguingly been accepted as Neoarchean–Paleoproterozoic metamorphic basement from the NCB. We examined petrography, mineral chemistry and geochronological data for the Haiyangsuo mafic granulites to decipher their multiperiod metamorphic evolution. The mineral assemblage from the first episode features coarse-grained Grt1 + Cpx1 ± Opx1 ± Amp1 + Pl1 + Ilm that formed under high-temperature (HT) granulite-facies conditions (7.3–8.3 kbar and 830–895 ℃). The second episode produced “red-eye socket” Grt2 + Cpx2 + Pl2 ± Amp2 + Qtz + Rut generated during high-pressure (HP) granulite-facies metamorphism (12.2–17.2 kbar and 800–875 ℃). Grt1 contains high heavy rare earth elements (HREEs) and oxygen isotopes in equilibrium with late Paleoproterozoic metamorphic zircons, while Grt2 has lower HREEs and oxygen isotopes, similar to Triassic metamorphic minerals in the Dabie-Sulu orogen. P-T estimates from pseudosection modeling and geothermobarometry show that Triassic HP granulite-facies metamorphism was followed by rapid decompression and slow cooling; these rocks resemble but mostly differ from the UHP eclogites due to non-UHP conditions. The above characteristics collectively imply that the metamorphic basement from the NCB was subducted to lower crustal to upper mantle depths (50–60 km) while the YB was subducted deeply; thus, tectonic erosion can indeed occur during continental subduction and collision.

How to cite: Liu, L.: Tectonic erosion along a continental subduction-collision zone revealed by compositions and metamorphism of mafic granulite in the Sulu orogen, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18068, https://doi.org/10.5194/egusphere-egu24-18068, 2024.

Two NW-SE trending profiles across the Pleißing and Pulkau nappes were investigated in detail and 56 samples from the Pernegger trench, 31 samples from the Pulkau and 32 samples from the Thaya valleys recovered. The Pleißing nappe exhibits amphibole-gneiss, metapelite, orthogneiss / metatuffite and marble with the corresponding mineral assemblages of hornblende - mica - feldspar - quartz - titanite - ilmenite; staurolite - garnet - mica ± graphite ± turmaline ± monazite; mica - biotite -epidote -kalifeldspar – quartz - ilmenite ± garnet ± chlorite; and calcite - biotite -mica -quartz -epidote - titanite ± amphibole. Grt-amphibolites, partly retrograded to greenschists, metapelite / phyllonite, and orthogneiss / metatuffite are recognized in the Pulkau nappe with the mineral assemblages amphibole -epidote - chlorite - rutile - ilmenite -quartz - titanite; mica - biotite - garnet - hornblende -quartz -plagioclase -ilmenite - monazite ± staurolite; mica - biotite - chlorite -Kfeldspar -quartz -ilmenite -magnetite ± turmaline.

P-T estimates from the Thaya valley profile are 580-620 °C / 0.8-0.9 GPa for the Pleißing nappe and 600-640 °C / ca. 0.5-0.8 GPa for the Pulkau nappe. Two phase garnets occur in some grt-metapelite from the Pleißing nappe. Garnet cores indicate P-T conditions of ca. 550 °C / 0.5 GPa and garnet rims in equilibrium with matrix minerals give ca. 590 °C / 0.9 GPa. P-T estimates along the Pulkau valley are 590-630 °C and 0.8-0.9 GPa for the Pleißing nappe and 540-580 °C / 0.5-0.8 GPa for the Pulkau nappe.

U-Pb dating of monazite by LA-ICPMS yielded a metamorphic age of 331 ± 2Ma , similar to the younger monazite age group of Štípská et al. (2015). The Th-U-Pb ages obtained by electron microprobe are slightly younger at 317 ± 6 Ma, which may be related to Pb loss during monazite recrystallization. Zircons from two meta-tuffite samples, one from the Pleißing, the other from the Pulkau nappe yielded concordant ages of 587 ± 8 Ma and 592 ± 8 Ma, respectively, similar to the magmatic age of the Biteš gneiss. The sample from the Pleißing nappe contained in addition a second age group with 620 ± 8 Ma.

Based on our geothermobarometric results the Pleißing and Pulkau nappe experienced a nearly identical metamorphic overprint in the northern part of the Thaya window. A slight decrease in metamorphic grade is seen in the southern part of the Pulkau nappe, suggesting a decreasing metamorphic gradient from NE to SW.

Štípská, P., Hacker, B. R., Racek, M., Holder, R., Kylander-Clark, A. R. C., Schulmann, K., & Hasalová, P. (2015). Monazite dating of prograde and retrograde P–T–d paths in the Barrovian terrane of the Thaya window, Bohemian Massif. Journal of Petrology, 56(5), 1007-1035.

How to cite: Hauzenberger, C., Findl, M., Skrzypek, E., Gallhofer, D., Linner, M., and Fritz, H.: P-T-t evolution of the Pulkau and Pleißing Nappes, Thaya Window, Lower Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18090, https://doi.org/10.5194/egusphere-egu24-18090, 2024.

The present study integrates petrochemical analyses and phase equilibria modeling of rare Garnet-Al-Silicates (Kyanite-Sillimanite-Andalusite) - Staurolite ± graphite bearing anatectic metapelites to comprehend its tectono-metamorphic evolution from the Eastern Himalayan Syntaxis (EHS), NE India. Extensive field studies reveal the occurrence of high-grade metapelitic rocks as enclaves in the Trans-Himalayan Lohit group of rocks (migmatitic gneisses), Dibang Valley, Arunachal Pradesh, India. Quartz-garnet-kyanite-plagioclase represents the peak metamorphic assemblage, in which garnets (Fe-rich) occur as porphyroblast and kyanite exhibit long crystals embedded in polygonal quartz and feldspar. The presence of peritectic kyanite and overgrowth of muscovite corona over kyanite (back reaction of melt with Al-silicates) indicates melting in the metapelitic rocks. Additionally, the presence of hydrous phases (e.g., muscovite and biotite), in the matrix points towards a wet melting condition. Furthermore, the post-peak metamorphic history of the rocks can be characterized by the presence of sillimanite and andalusite formed during exhumation. Thermobarometric studies estimate the peak metamorphic conditions for the metapelite at T =650±25°C, P~8 Kbar. The P-T pseudosection analysis predicts the peak metamorphic condition for the metapelites at T~ 650°C, P=7-8 Kbar; with clockwise PT paths. This suggests a wet melting condition at T~ 680°C (Solidus) and P~8 Kbar for the high-grade metapelites possibly related to the India-Asia collision from the Eastern Himalayan Syntaxis of Arunachal Himalaya.

How to cite: Saikia, D., Ozha, M., and Shankar, R.: Metamorphic Evolution of Rare Garnet-Al-Silicates (Kyanite-Sillimanite-Andalusite)-Staurolite ± graphite bearing Anatectic Metapelites from Eastern Himalayan Syntaxis, NE India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20042, https://doi.org/10.5194/egusphere-egu24-20042, 2024.

The northern margin of the North China Craton is an important tectonic zone, bordered by the globe’s largest Phanerozoic accretionary orogen, the Central Asian Orogenic Belt. The Paleoproterozoic strata on the northern margin of the North China Craton (NCC) comprise a relatively intact low-grade (meta-)sedimentary sequence, but whether there are breaks in the sequence and the tectonic setting in which the sequence was deposited are uncertain. In this work, Lu–Hf isotopic, and zircon U–Pb geochronological analyses were performed on (meta-)sedimentary rocks from the Paleoproterozoic strata, to investigate the potential provenance, depositional age, and depositional environment, and discuss the likely tectonic setting of sedimentation on the northern margin of the NCC during the Paleoproterozoic. The distribution of detrital zircon ages shows that the lower meta-feldspathic sandstone unit of the Paleoproterozoic sequence was deposited after ca. 2.2 Ga, whereas the maximum depositional age of (meta-)quartz siltstone and quartzites were around 1.89 Ga and at from ca. 1.86 to 1.81 Ga, respectively. Integration of our U–Pb and Hf isotope data with data from the other regions of the NCC, indicate that the Paleoproterozoic strata have experienced a depositional environment between ca. 2.2–1.81 Ga in an extensional basin system. We further proposed that the northern margin of the NCC evolved from an extensional tectonic setting, possibly related to slab rollback. Subsequently, the Paleoproterozoic sequence was affected by a ~1.8 Ga metamorphic event to form these (meta-)sedimentary rocks in the region.

How to cite: Chen, N. H.-C.: Zircon U-Pb ages and Lu-Hf isotopes of Paleoproterozoic metasedimentary rocks in the North China Craton: Implications for its crust and evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1331, https://doi.org/10.5194/egusphere-egu24-1331, 2024.

The Angul-Tikarpara domain of the northern Eastern Ghats Province (EGP) of Eastern India is characterized by high-grade rocks like felsic gneiss, khondalite (garnet-sillimanite-K-feldspar-quartz bearing granulite), charnockite, mafic granulite and aluminous granulite (spinel-magnetite-hematite-garnet-cordierite-sillimanite-K-feldspar-quartz-biotite-plagioclase). Two distinct mineralogical varieties of mafic granulite are present as enclaves within felsic gneiss and coarse-grained charnockite. Type-A mafic granulite is composed of orthopyroxene, clinopyroxene, hornblende, plagioclase, magnetite, ilmenite, biotite, and/or garnet with a subordinate amount of quartz. Type-B mafic granulite, on the other hand, contains titanite along with clinopyroxene, plagioclase, hornblende, garnet, calcite, ilmenite, magnetite, and biotite. The present study is focused on the latter variety where the peak (M_A1) assemblage is represented by clinopyroxene, plagioclase, titanite, ilmenite, magnetite, calcite, and hornblende. Porphyroblastic clinopyroxene in the aforesaid assemblage is characterized by well-developed Al-zoning, with Al₂O₃-content being maximum at the core (5.3–3.8 wt.%) and minimum at the rim (3.6–0.22 wt.%). It appears that the high-aluminous core had stabilized at the peak stage, while the low-aluminous rim formed during the retrogressive stage characterized by decompression (M_A1R). From the zoning pattern, the peak M_A1 and M_A1R conditions were estimated to be 8.6‒6.8 kbar, ~850˚C, and 4.2‒3 kbar, 660 ˚C, respectively. During the decompression, subidioblastic titanite broke down to low-Al clinopyroxene (2.5-0.5 wt.% Al₂O₃) + ilmenite intergrowth surrounding the former phase. The decompression was associated with cooling during which coronal garnet grew surrounding porphyroblastic clinopyroxene, plagioclase, and calcite. Zn-bearing spinel was exsolved from magnetite during this stage. Phase diagram modeling of Type-B mafic granulite shows that M_A1 metamorphism occurred along a clockwise P-T trajectory. Further development of grossular-rich coronal garnet around hornblende suggests that the rock underwent a second prograde metamorphic event (M_A2). In the chondrite-normalized rare earth element (REE) diagram, Type-B mafic granulite shows a more fractionated pattern than Type-A mafic granulite.

Textural, thermobarometric, and phase equilibria data indicate that the metamorphic evolution of Type-B mafic granulite is comparable to the recently published P-T evolution of Type-A mafic granulite, aluminous granulite, khondalite, and fine-grained charnockite of the area where the M_A1 metamorphism involved decompression and associated cooling from ∼850^◦C, 7–8 kbar to ∼760^◦C, 4–5.8 kbar at ca. 1200 Ma and followed by subsequent prograde M_A2 metamorphism at ca. 990 Ma. This study provides additional evidence that the geological evolution of the Angul-Tikarpara domain is different than the rest of the EGP lying at the southern part of the Mahanadi Shear Zone (MSZ). The latter segment of the EGP is characterized by ultra-high temperature metamorphism (UHT) at ca. 1030–990 Ma which is absent in the present study area. Such contrasting ages and P-T evolution of high-grade rocks on either side of the MSZ confirm the fact that the shear zone represents a terrane boundary which was formed by juxtaposition of the Angul-Tikarpara domain with the EGP only after ca. 960 Ma.

How to cite: Banerjee, A., Ganguly, P., Bose, S., Sorcar, N., Mukherjee, S., and Das, K.: Reaction textures in titanite-bearing mafic granulite: Constraints on the metamorphic evolution of Angul-Tikarpara domain of the Eastern Ghats Province, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2374, https://doi.org/10.5194/egusphere-egu24-2374, 2024.

Eclogites and their constituents ubiquitously form part of kimberlite-borne xenolith and xenocryst suites. Their mineralogic, geochemical, stable and radiogenic isotope characteristics unambiguously point to a crustal protolith, likely derived from ancient spreading ridges [1]. Available P-T constraints and the frequent occurrence of accessory coesite and/or diamond [2] indicate ultrahigh-pressure metamorphism. Because cratonic eclogites occur globally, their compositions can provide invaluable insights into ancient geodynamics and mass cycles, for which the ages of their formation (rather than later metasomatic overprints) must be constrained. However, the accurate and precise age determination for cratonic eclogites – and the application of petrochronologic concepts in general – is hampered by the fact that (i) they were emplaced into the cratonic mantle lithosphere billions of years ago, after which their composition may have been altered, (ii) they last resided at mantle temperatures enabling diffusive (partial) isotopic equilibration of their mineral constituents, (iii) accessory minerals amenable to U-Pb dating are rare (except rutile, which invariably yields kimberlite eruption ages) and, if present, of  metasomatic origin, and (iv) they represent high-variance systems, often consisting of only garnet and omphacite and typically devoid of inclusions.

The recent advent of garnet U-Pb geochronology as applied to metamorphic rocks [3] opened a new door to obtaining accurate and precise ages for eclogites, including xenoliths from the Navajo Volcanic Field presumably sampling the Cretaceous Farallon plate [4]. However, preliminary work, using a multicollector ICPMS (Thermo Finnigan Neptune Plus) at the FIERCE laboratory (Goethe University Frankfurt), shows that even garnet from relatively cold (last equilibrated at ~815-1000°C; [5]) eclogite xenoliths from the Kaapvaal craton margin may have lost its original crystallisation age information. Garnet in these eclogites, which were likely emplaced during the Mesoproterozoic Namaqua-Natal orogeny, all yield U-Pb ages are within several 100 Ma of Cretaceous kimberlite eruption. This is in stark contrast to results for UHT granulite xenoliths from the Kaapvaal craton, which retain 3 Ga garnet U-Pb ages [6]. This may reflect low garnet U-Pb closure T in cratonic eclogite related to slow secular lithosphere cooling, as opposed to high closure T in granulite owing to fast cooling from magmatic or peak metamorphic T.

Available “conventional” ages for eclogitic xenoliths and diamonds from cratons globally reveal some systematics, indicating metamorphism around 2.9-2.6 Ga and again 2.0-1.8 Ga. These ages can be interpreted in the framework of the supercontinent cycle, whereby the Palaeoproterozoic ages reflect emplacement during assembly of Nuna-Columbia, and the Meso-/Neoarchaean ages reflect the amalgamation of the oldest cratonic nuclei into Earth’s first supercontinent, consistent with a global, linked plate tectonic network. In contrast, a temporal link to emplacement ages for TTGs is weak, suggesting that cratonic eclogite is not the complementary residue to Earth’s oldest continental crust [1].

[1] Aulbach and Smart 2023 AREPS; [2] Stachel et al. 2022 RIMG; [3] Millonig et al. 2020 EPSL; [4] Pohlner, Aulbach et al. in prep.; [5] Le Roex et al. 2020 JPet; [6] Shu, Beranoaguirre et al. in prep.

How to cite: Aulbach, S., Beranoguirre, A., Millonig, L., and Pohlner, J.: Acquisition and interpretation of ages from xenolithic mantle eclogites – the oldest records of subducted oceanic crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2810, https://doi.org/10.5194/egusphere-egu24-2810, 2024.

Cratonic margin basins are crucial in tracking the provenance characteristics. This study aims to characterize one of the Proterozoic basins in Southeastern India known as Pranhita Godavari (PG) basin. Nestled between the famous Dharwar and Bastar cratons, the PG basin is about 450 Km long NW-SE trending rift-related basin with a huge thickness of siliciclastics. The basin consists of three cycles of deposition. In this study, we characterize the geochemistry, U-Pb geochronology and Lu-Hf systematics of the detritus as well as the adjacent basement Gneiss in order to define the sediment source.

                        K₂O/Na₂O v SiO₂ and the Discriminant function diagrams (Verma & Armstrong-Altrin, 2013) indicate a passive margin setting for the sediments. Together with Eu/Eu*, the high La/Yb_N ratios (8.23-37.9) and LREE enriched and flat HREE patterns indicate a felsic source. The other geochemical indicators like TiO₂ versus Zr and Ni, Al₂O₃/TiO₂, Th/Co, La/Sc ratios along with high Th/U also indicate felsic continental sources.   The different weathering indices like CIA.PIA, and  ICV indicate moderate to slightly intense weathering of the source terrains producing mostly mature sediments.

The metamorphic zircons (average Th/U=0.88) from the basement Gneiss yield a Concordia age of 2490±6 Ma and a weighted mean age of 2490±6 Ma. Three magmatic zircon cores yield a weight mean average of 2677±36 Ma. Previous studies from the Bastar and Dharwar cratons also report the presence of 2.5 Ga old zircons.

The sediment was mainly sourced from the Paleoarchean to Mesoproterozoic sources with detrital zircon ages spread from 3571-1622 Ma. The Probability Density Plots show major peaks at 1842, 2498, 2637 Ma and minor peaks at 1637,3340, 3567 Ma. The Youngest detrital zircon method brackets the maximum depositional age of the Mulug Formation 1622±33 Ma.

The zircons from the basement gneiss of Peninsular Gneissic complex show negative Hf isotope values (εHf= -15.27 and 0.17). Similarly, the detrital zircons show negative values (εHf =-12.58-0.70) indicating their derivation from evolved sources.

The age peaks and the εHf composition from the Mulug formation perfectly match with the basement gneiss ages. This together with published literature indicates that the Mulug formation was deposited at ~1.6 Ga and was sourced from the eastern Dharwar and Bastar cratons

How to cite: Ganaie, A. M.: Detrital Zircon U-Pb Geochronology and Lu-Hf isotope systematics from the Pranhita Godavari basin: Implications for the Provenance and Mesoproterozoic tectonics  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3845, https://doi.org/10.5194/egusphere-egu24-3845, 2024.

The Jonnagriri greenstone belt (JGB) of eastern Dharwar craton is one of the unique and economically important greenstone belts of southern India. This greenstone sequence consists of metabasalts, meta-felsic volcanics and schistose meta-tuffs surrounded by granitoid intrusives. These intrusives are the only known granitoid in India that hosts orogenic type gold deposit in the Dona sector of JGB. In our present work, we are focusing on the granitoids emplaced surrounding the JGB that are broadly classified into two main groups; (i) The Pagadarayi granodiorite (PGD) and (ii) The Chennampalli granites (CGR). The present study is to examine the geochemical evolution, decipher the tectonic settings and determine the timing of emplacements of the granitoids using whole rock geochemistry and U-Pb zircon dating. This will also help us to understand the crustal architecture of the part of the eastern Dharwar Carton in the southern Indian peninsula. The PGD compositionally ranges from tonalite to granodiorite suits and the adjacent CGR ranges from granite to syenogranite suits of rocks. The petrogenetic evolution of these granitoid clearly showed a transition from calc-alkaline to a more fractionated potassic rich granite. The major oxide and trace element behavior showed that they are metaluminous to peraluminous in nature where the PGD are geochemically linked to the TTGs while the potassic rich CGR phase majorly shares its genetic link with hybrid and two-mica granites. The source of PGD suits of rocks is inferred to be an outcome of partial melting of TTG crust and the CGR suits are ferromagnesian deficit phase with an increase in K₂O/Na₂O due to crustal contamination, which indicates a result of crustally reworked magmatic phase. Therefore, an enrichment of LREE and LILE relative to HREE and HFSE with depletion of Nb-Ta-Ti notably is observed, which represents a convergent setting signature for these granitoids. The PGD suit of rocks dominantly showed I-type characteristics affirmed by their ASI index, and with the typical SiO₂, CaO and FeO contents, indicating that they are part of volcanic arc to island arc granitoid settings. The CGR showed distinctive characteristics of A₂ type granites due to its Y/Nb value ranging from 1.2 to 1.83 depicting a shallow depth subduction regime which are formed within the crust, indicating a within plate post-colliotional settings. Zircon U-Pb dating by LA-ICP-MS reveals that the first emplacement of PGD recorded a concordant emplacement age of 2651±14 Ma and the CGR yielded concordant ages of 2557±10 Ma and 2532±22 Ma respectively. This implies that the Jonnagiri granitoid represents an orogenic type tectonic settings where diversification in the mode of granitoid intrusion showed a change in volcanic-arc magmatism to within plate magmatism, from the older phase of tonalite-granodiorite emplacement to the successive younger potassic rich syenogranite emplacement. 

How to cite: Das, S. and Chinnasamy, S. S.: Granitoids of the Jonnagiri greenstone belt of eastern Dharwar craton: Constraints from geochemistry and U-Pb zircon geochronology., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6082, https://doi.org/10.5194/egusphere-egu24-6082, 2024.

The Earth's crust, an incredibly thin layer of rock encompassing the planet's outermost solid shell, plays a crucial role in sustaining human existence by housing vital natural resources. Moreover, actively engaged in a multitude of geological processes such as plate tectonics, volcanic activities, and erosion, it significantly molds landscapes and influences natural phenomena, thereby serving as a cornerstone in maintaining Earth's habitable conditions. However, substantial debate persists regarding the mechanisms governing the growth of continental crust, and the broader implications of its role within Earth's tectonic framework remain elusive. In this study, we sought to predict the historical evolution of crustal thickness during the Archean era using machine learning based on global geochemical data of igneous rocks. The model predicted that crustal thickness decreased progressively from approximately ~35km during the Paleoarchean period to a nadir of roughly ~33km in the Early Mesoarchean era. Subsequently, there was a trend of thickening observed from the Early Mesoarchean to the Neoarchean period. Our findings reveal a dynamic history of Archean crustal thickness characterized by an initial phase of thinning followed by subsequent thickening from the Paleoarchean to the Neoarchean. These fluctuations align cohesively with the transition from a pre-plate tectonic to a regime of sustained plate tectonics. The observed phenomena were attributed to the initiation of ultrathick primary crust formation, accompanied by a tectonic regime primarily influenced by Rayleigh–Taylor instabilities. The instabilities arising from an excessive buildup of primary crust likely played a pivotal role in causing the subsequent thinning of the continental crust, marking the transition phase towards a predominantly modern-style subduction.

How to cite: Zhang, Y., Liu, H., and Sun, W.: Machine Learning-Based Quantification of Archean Crustal Thickness (Moho Depth), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7316, https://doi.org/10.5194/egusphere-egu24-7316, 2024.

To understand the onset and evolution of cold subduction on Earth, detrital sedimentary rocks of Precambrian age, potentially derived from exposed high-P low-T metamorphic rocks can be investigated. This requires the estimation of peak metamorphic pressure and temperature, time of formation, and source lithology (P-T-t-X) of detrital single grains. Rutile is a common accessory mineral in subducted oceanic crust and one of the most likely minerals from subducted rocks to survive sedimentation processes. As single grain T-t-X estimates on rutile are possible, it is a prime candidate for the investigation of subduction processes through time.

We developed a method to identify rutile formed in modern cold subduction conditions, by combining in-situ polarised Fourier Transform Infrared Spectroscopy (FTIR) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).

Our study reveals a pressure-dependent variation in hydrogen content within metamorphic rutile, ranging from less than 10 to 2500 μg/g H₂O. Higher peak metamorphic pressures correspond to elevated H₂O contents, particularly noticeable in mafic low-temperature eclogite facies rutile, suggesting H-in-rutile can be used as a pressure indicator. Using Zr in rutile as a temperature indicator, H₂O/Zr ratios act as proxies for thermal gradients (P/T) in metamorphic rutile. When combined with low Nb, W, and Sn contents, typical of mafic protoliths, it is possible to identify modern-style cold subduction of mafic crust using trace element signatures in detrital rutile.

Therefore, detrital rutile can serve as a tracer for subduction conditions over time, as modern-style cold subduction signatures are preserved in rutile during weathering and sedimentary processes.  In this study, we test our novel approach on detrital rutile grains of sandstones and arkoses from the Torridon and Ardvreck Groups, Hebridean in NW Scotland. Our analysis reveals that some grains of the Torridon Group of late Proterozoic age (detrital ages ranging from 1.0 to 1.9 Ga; Pereira et al., 2020) exhibit high H₂O/Zr ratios and low total Nb+W+Sn contents, typical of low-T eclogite facies rutile. This implies that low-T eclogites which formed during cold subduction were likely exposed and eroded in the catchment of the sedimentary basins, indicating modern-style cold subduction during the Mesoproterozoic.  We propose that the combined measurement of H₂O and trace elements in detrital rutile is a powerful tool to search for remnants of cold subduction through the Earth’s history.

Pereira, I., Storey, C.D., Strachan, R.A., Bento dos Santos, T., Darling, J.R., 2020. Detrital rutile ages can deduce the tectonic setting of sedimentary basins. Earth Planet. Sci. Lett. 537, 116193. https://doi.org/10.1016/j.epsl.2020.116193

How to cite: Lueder, M., Hermann, J., Pereira, I., Tamblyn, R., and Rubatto, D.: Tracing modern-style cold subduction in the Proterozoic – evidence from H2O and trace elements in detrital rutile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7908, https://doi.org/10.5194/egusphere-egu24-7908, 2024.

Molecular modeling of the interaction between silica and water provides a better understanding of how water affects rocks and glasses at the nanoscale. Here, we parametrize a new classical dissociative force field for the water–silica system. We create a classical force field capable of reactive interactions between all chemical species in the water–silica system, using the same functional form by Vashishta et al. to describe bulk water, silica, and silica–water interactions. Using a hierarchical genetic algorithm as a global optimizer and the Nelder-Mead simplex algorithm as a local optimizer, we parameterized the Vashishta force field to reproduce the density, transport properties, and vapor-liquid properties of water. We then used the same method to obtain water–silica interaction parameters to reproduce gas phase orthosilicic geometry and silica surface properties such as silanol concentration, heat of immersion, and the wettability angle of water on a silica surface. For oxygen–silicon interactions in silica, we reuse an existing Vashishta potential parameter set that has been parameterized to reproduce bulk mechanical behavior, surface properties, and fracture properties. Our developed force field can be used to study processes such as dissolution, friction, and stress corrosion fracture in the presence of water over a wide range of thermodynamic conditions for larger-scale and longer-scale simulations.

How to cite: Camposano, A. V., Sveinsson, H. A., and Malthe-Sørenssen, A.: Machine Learning an All-Atom Empirical Force Field for a Water-Silica System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8283, https://doi.org/10.5194/egusphere-egu24-8283, 2024.

Predicting the physical properties of rock is critical for modeling mantle convection. Density changes are the main driving force for mantle convection, for example, while elasticity/seismic properties allow probing of mantle dynamics and structure. Pressure-temperature (PT) conditions predicted by numerical thermo-mechanical models are often mapped to pre-computed pseudosections calculated by Gibbs Free Energy Minimization (GFEM) programs (e.g., Perple_X; Connolly, 2009) to predict phase changes and the associated evolution of rock properties (e.g., density, seismic wave velocities, and fluid contents). In principle, GFEM programs could be coupled to numerical geodynamic simulations (at each point in space and for each timestep) to establish models where phase assemblages and rock properties evolve self-consistently. In practice, this is currently intractable because GFEM programs remain too slow (10²–10⁴ ms per node) to be coupled to high-resolution numerical geodynamic models. While parallelization of GFEM calculations can increase efficiency dramatically (e.g., MAGEMin; Riel et al., 2022), predicting rock properties recursively during a geodynamic simulation requires GFEM efficiency on the order of ≤ 10⁰–10^-1 ms to be feasible. As an alternative to the GFEM approach, this study demonstrates the efficiency of predicting target rock properties through pre-trained machine learning models (referred to as RocMLMs). In our initial test case, RocMLMs are trained to predict density, seismic wave velocity, and melt fraction for dry upper mantle rocks based on an array of 128 Perple_X pseudosections (with 128x128 PT resolution) derived from 3111 harzburgite and lherzolite samples retrieved from the Earthchem.org repository. The training dataset size was reduced from 128¹³ to 128³ PTX examples by transforming the 11 oxide components of X (bulk rock composition) into a single Fertility Index value representing the estimated degree of melt extraction from a primitive mantle source. We show that Decision Tree, K-Neighbors, and single-layer Neural Network algorithms can predict rock properties up to 10³ times faster than commonly-used GFEM programs (with some performance trade-offs), attaining the required efficiency of 10⁰–10^-1 ms. Our results imply that implementing dynamic evolution of rock properties in geodynamic simulations is now possible with RocMLMs. Future generations of RocMLMs will include hydrated systems and a larger array of mantle compositions (e.g., dunites and pyroxenites).

How to cite: Kerswell, B., Cerpa, N., Tommasi, A., Godard, M., and Padrón-Navarta, J. A.: RocMLMs: Predicting Rock Properties through Machine Learning Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8578, https://doi.org/10.5194/egusphere-egu24-8578, 2024.

Vp/Vs (or the Poisson's ratio) provides critical information to constrain the bulk crustal composition, stress state, and tectonic evolution. The crustal Vp/Vs beneath the seismic station can be effectively determined by the receiver function H-κ stacking technique. However, complex crustal structures often cause large uncertainty in Vp/Vs measurements. Additionally, Vp/Vs observations are sparse in many regions of the world due to the uneven distribution of seismic stations. While interpolation methods have been widely applied to obtain a continuous distribution of Vp/Vs, these results are not accurate enough and may be strongly biased by the interpolation artifacts. Therefore, reliable mapping of the Vp/Vs variation in the crust remains a major challenge in seismological study.

We present a machine learning approach to estimate the Vp/Vs using multiple geophysical datasets. This approach assumes that the Vp/Vs is related to the physical and chemical properties of the crust. Specifically, we implement a Gradient Boosted Regression Tree algorithm (XGBoost) to develop an optimal prediction model for North America. To train the model, we use Vp/Vs as the target values and a compilation of geophysical observations as the predictor variables. These measurements are composed of two types of data: (1) continuous data, such as crustal velocities and gravity anomalies; (2) categorical data (tectonic type). We use 80% of the measurements to train the model, and the remaining 20% to validate the model. We first examine the reliability of this method by predicting Vp/Vs for the United States, where extensive geophysical data are available. Overall, the model achieves a high R² value of 0.88 in all measured results versus prediction results, indicating robust prediction results at most locations. In the second, a more challenging test, we predict Vp/Vs for Canada where measurements are sparse and uneven, and the amount of data is only 14% of that in the United States. The results show an R² value of 0.87 between the measured and predicted values. Feature importance analysis indicates that crustal shear wave velocity and tectonic type contribute most significantly to reducing the loss function. The prediction results show that bulk Vp/Vs varies between 1.70 and 1.90 across Canada, with a mean value of 1.82.  The cratonic regions generally exhibit high (>1.80) Vp/Vs with a relatively small (<0.05) variation, whereas Proterozoic orogens are characterized by a large Vp/Vs variation from 1.75 and 1.90. The lowest Vp/Vs of 1.66 is observed in the Phanerozoic orogenic belts of Cordillera, contrasting sharply with the basement rocks (~1.90) beneath the Alberta foreland basin. Overall, our study highlights the capability of the machine learning in discovering complex relationships between multi-dimensional geophysical data sets and resolving crustal Vp/Vs in continents globally.

How to cite: Gao, X., Chen, Y., Zhang, Z., and Zhao, W.: Predicting Vp/Vs in North America with a Machine Learning Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9828, https://doi.org/10.5194/egusphere-egu24-9828, 2024.

The Southern Granulite Terrane (SGT) is an integral part of the Neoproterozoic Gondwana supercontinent. The Nilgiri block situated in the northern part of the SGT is characterized by Neoarchean magmatism. The major rock types found in the western part of the Nilgiri block include charnockite, hornblende biotite gneiss (HBG), pyroxenite, gabbro, amphibolite, mafic granulites, and granite. This study focuses on the geochemical signatures of major lithologies in the western Nilgiri block to understand the geological evolution within the broader Southern Granulite Terrane. Oxide data show charnockite samples with SiO₂ from 51 to 67 wt% and HBG with SiO₂ from 63 to 71 wt%. Normative Ab-An-Or classification diagrams indicate tonalitic and granodioritic signatures for charnockite and HBG, respectively. Both exhibit high Al₂O₃ (>15 wt%) and low K₂O (<3 wt%). Charnockites and HBG display a magnesian and calcic-to-calc-alkalic composition, while mafic granulite shows a low-K tholeiite and calc-alkali composition. Zr vs. Ti diagrams reveal a volcanic arc signature for charnockite, HBG, and mafic granulites. In the study area, Peralimala Granite (PG), Ambalavayal Granite (AG), and Kalpetta Granite (KG) are present as plutons. KG and PG are magnesian, while AG is ferroan. KG and PG have an alkali-calcic composition, which contrasts with the calc-alkalic nature of AG. Comparative analysis with charnockites from the eastern Nilgiri block shows variations in SiO₂ and Al₂O₃ content, with the western region exhibiting lower SiO₂ and higher Al₂O₃. HBG in the western part shows a slightly elevated Na₂O+K₂O value. The charnockite consistently shows depletion in Y, Cs, Ta, Th, and U, coupled with Zr, Ba, Pb, and La enrichment. Similarly, HBG displays depletion in Y, Ta, Th, and U and enrichment in Rb, Sr, Zr, and Ba. Both rock types consistently exhibit enrichment in LREE and depletion in HREE. Mafic granulites show depletion in Cs, Th, Ta, and U, along with Nb, Ba, and Pb enrichment, displaying a flat REE pattern without significant fractionation. KG and PG exhibit enriched LREE and depleted HREE, whereas AG displays a strong negative Eu anomaly and a flat REE pattern. KG and PG are enriched in Ba, K, and La, with depletion in Ta, Nb, Ti, and Y. Conversely, AG is enriched in Ba, K, and Sr, with minimal Rb content and depletion in Th, U, Ta, Nb, and Ti, suggesting AG partial melts formed from the deep crustal level or upper mantle region. Charnockite and HBG show an affinity towards Archean TTG, suggesting their formation through the partial melting of Archean-hydrated, low K-metabasic source rocks, resulting in garnet amphibolite restite. U-Pb zircon data reveals an age of 2555±15 Ma for charnockite and 2512±12 Ma for HBG, indicating Neoarchean magmatism. Discordant ages from HBG align on a Pb-loss trend toward the lower intercept age of ~1100 Ma, suggesting a Late-Mesoproterozoic thermal event. U-Pb zircon data of Kalpetta Granite gives an age of 544±5 Ma, implying a Pan-African thermal event. These findings highlight distinct magmatic and thermal events in the western Nilgiri block, including Neoarchean activity and notable Late-Mesoproterozoic and Neoproterozoic thermal events.

How to cite: Shamil, V. T. M., -Kumar, C. I., and -Kumar, M. S.: Insights into the Neoarchean Magmatic Evolution of the Western Nilgiri Block, Southern India., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10081, https://doi.org/10.5194/egusphere-egu24-10081, 2024.

The Belomorian eclogite province (BEP) of the eastern Fennoscandian Shield (Russia) is one of the oldest eclogite metamorphic complexes on Earth, providing an opportunity to study the most ancient subduction processes. The BEP gained prominence due to the numerous publications on petrology and geochemistry of Archean-Paleoproterozoic HP metamorphic rocks from Gridino, Salma, and Kuru-Vaara areas. Here, we present results from a detailed petrological study of a representative retrograde eclogite sample from a new HP locality in the Kem-Ludy Islands, where eclogites form lenticular bodies and have conformable contacts with country gneisses.

The studied retrograde eclogite sample has a massive structure with a fine- to medium-grained granoblastic texture. At least three metamorphic stages were identified in the rock based on the mineral assemblages. The pre-eclogite stage is indicated by epidote inclusions in the cores of garnet porphyroblasts. Garnet, matrix omphacite, and quartz represent peak metamorphism stage. Plagioclase-clinopyroxene symplectites after the omphacite and amphibole-plagioclase kelyphytes around the garnet were formed at the retrograde stage, while peak metamorphism minerals were then replaced to different extents by secondary amphibole during fluid-rock interaction.

The application of garnet-clinopyroxene geothermometer and clinopyroxene-plagioclase-quartz geobarometer assessed peak metamorphic temperature of 625-670°C and minimum pressure of 1.2-1.3 GPa, respectively. The retrograde stage corresponds to conditions of 600-725°C and 0.6-0.7 GPa as determined by garnet-amphibole, amphibole-clinopyroxene, amphibole-plagioclase geothermometers, and clinopyroxene-plagioclase-quartz and amphibole-plagioclase geobarometers.

The established P-T metamorphic evolution of the retrograde eclogite from Kem-Ludy area differs from most of the eclogites of Gridino and Salma areas by lower pressure at the peak of metamorphism and a lack of decompressional heating up to the UHT granulite facies conditions. Therefore, Kem-Ludy area likely pertains to another tectonic slice than Gridino and Salma areas, where the Neoarchean and Paleoproterozoic ages of HP metamorphism are under debate. Further investigation is needed to clarify the tectonic position of Kem-Ludy area.

Financial support of Russian Science Foundation project 23-77-00066.

How to cite: Grigorieva, V., Perchuk, A., Kozlovsky, V., and Sandalov, F.: Metamorphic evolution of eclogite of Kem-Ludy Islands, Early Precambrian Belomorian eclogite province, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10822, https://doi.org/10.5194/egusphere-egu24-10822, 2024.

The Late Archean Gadag greenstone belt (GGB) in the northern continuity of extensive Chitradurga greenstone belt in the western Dharwar craton has extensive meta volcano-sedimentary cover apart from older TTGs (Tonalite-trondhjemite-granodiorite), pink granite and other intrusives. The GGB encompasses a very unique and classical orogenic type gold deposit known as Gadag gold field (GGF) where auriferous lodes are hosted by metabasalt, greywacke and BIFs in western, central and eastern part of GGF respectively. In this study, we focus on the deformation history and P-T conditions of metamorphism of greenstone rocks which could have influenced in the generation of auriferous fluid in GGB. Two events of deformation were suggested in GGB so far where the first event (D1) is represented by NW-SE trending pervasive fabrics (S1) and schistocity, whereas the second event (D2) marking the regional disposition of NNW-SSE tectonic trend. This is further corroborated by microscopic evidences of Q-M microlithons development and garnet porphyroblast growth that is post tectonic to D1 deformation, syn-tectonic to early D2 and stage 2 porphyroblast development of non-rotating porphyroblast model in garnetiferous amphibolite in the north-eastern part of GGB. However, the matrix continued to get deformed and reached stage 6 in garnetiferous schist with dominant sinistral sense of shear in the southern part of GGB. The estimated peak metamorphic temperature of garnetiferous amphibolite using hornblende-plagioclase thermobarometry is 578 ± 21°C and the pressures are 7.1 ± 3kb and 7.4 ± 2.3kb. Garnet-biotite thermometric estimation for the same garnetiferous amphibolite from north eastern part of GGB yielded 525 ± 25°C indicating a lower amphibolite facies of metamorphism. The auriferous quartz veins were associated with both the D1 and D2 phases of deformation, and the genesis of this auriferous fluid may be related to lower amphibolite facies of metamorphism of these host rocks as evidenced from the fluid inclusion study.

Keywords: craton, P-T conditions, thermobarometry

How to cite: Saikia, M. J. and Chinnasamy, S. S.: Deformation history and P-T condition of metamorphism of Gadag greenstone belt of western Dharwar craton, southern India: Implications on the genesis of orogenic gold mineralisation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10873, https://doi.org/10.5194/egusphere-egu24-10873, 2024.

Combined with geophysical, geochronological and structural data, isotope geochemical proxies (including Pb, Nd, Hf and Sr) are commonly used to correlate basement terranes and hence to test and refine supercontinent configurations. In the case of Pb, many such studies rely on whole-rock isotopic data, which being time-dependent, can be difficult to interpret.

By contrast, feldspars, by virtue of their low U/Pb and Th/Pb ratios, have time invariant Pb isotope compositions. They are also modally abundant rock-forming minerals and are amenable to in situ analysis and textural discrimination. This study evaluates the utility of Pb isotopes in feldspar as a mechanism to identify terrane boundaries and evaluate large-scale continental reconstruction models.

We are systematically collating feldspar Pb isotope data from Archaean and Paleoproterozoic basement rocks in the North Atlantic region (Laurentia-Baltica and the intervening continental plateaux) from literature sources as well as new measurements from outcrop and offshore wellbores from Scotland, Norway, Greenland and Russia. 

A particular focus is on the Lewisian Complex of Scotland because these rocks are argued to link with terranes in both Greenland and Baltica. Our Pb isotopic data identify four Pb isotopic domains in Scotland.  The NAC, Nagssugtoqidian and Rinkian terranes are recognised onshore and offshore west of Shetland and correlate strongly with Greenland.  Moreover the boundaries between them are consistent with large-scale sutures proposed on other grounds although they do not support the traditional nine-terrane model for the Lewisian Complex [1]. Feldspar Pb isotopic data from the Kola Peninsula and northern Fennoscandia are consistent with the suggestion that the sub-Moine inliers (previously considered to have Archaean protoliths, equivalent to the Lewisian Complex) have an affinity with Baltica [2].

References:

[1] Kinny et al. (2005) Journal of the Geological Society, London 162, 175-186.

[2] Strachan et al. (2020) Geology 48, 1094-1098.

How to cite: Daly, J. S., Flowerdew, M., and Badenszki, E.: Mapping ancient geochemical terranes using feldspar Pb isotopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11081, https://doi.org/10.5194/egusphere-egu24-11081, 2024.

The work reports on the state-of-the-art and future perspectives of Machine Learning (ML) in igneous petrology and volcanology. To do that, it starts reviewing established methods that mainly concern clustering, dimensionality reduction, classification, and regression. Among them, clustering and dimensionality reduction are particularly valuable for decoding the chemical record stored in igneous and metamorphic phases and to enhance data visualization, respectively. Classification and regression tasks find applications, for example, in petrotectonic discrimination and geothermobarometry, respectively. The main core of the discussion will consist of depicting the next future for ML in petrological and volcanological applications. I propose a future scenario where ML methods will progressively integrate and support established petrological and volcanological methods in boosting new findings, possibly providing a paradigm shift. In this framework, the use of multimodal data, data fusion, physics-informed neural networks, and ML-supported numerical simulations, will play a significant role. Also, the use of ML hypotheses formulation and symbolic regression could significantly boost new findings. In the proposed scenario, the main challenges are: a) progressively link machine learning algorithms with the physical and thermodynamic nature of the investigated processes, b) make deep learning algorithms more transparent, as they often operate as “black boxes,” c) advance in exploring cutting edge tools that rise from researches in Artificial Intelligence, and overall, d) start a collaborative effort among researchers coming from different disciplines in research and teaching.

How to cite: Petrelli, M.: Machine Learning in Igneous Petrology and Volcanology: State-of-the-Art and Perspectives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13673, https://doi.org/10.5194/egusphere-egu24-13673, 2024.

Research on sampling and analysis of fluids and rocks within both continental and oceanic crusts has revealed a significant portion of Earth's prokaryotic biomass residing in the rock-hosted biosphere, extending to depths of several kilometers. This deep subsurface life within the lithosphere may host a substantial amount of Earth's biomass. However, more constrained estimates of this biomass are still lacking. In this study, we first determine the habitable volume of the lithospheric biosphere and then estimate its potential biomass. Temperature, a critical factor influencing the limits of life, is considered the primary focus in this context. We employ a machine learning approach to estimate the habitable volume of the lithosphere above the 122°C isotherm, which is considered the upper limit for prokaryotic life.

Our methodology involves selecting a range of geophysical and geological features that are thought to impact geothermal gradients. These include Moho depth, lithosphere-asthenosphere boundary (LAB) depth, topography, susceptibility, tectonic units, gravity mean curvature, vertical magnetic field, and distances to ridges, trenches, transform faults, young rifts, and volcanoes, as well as P-wave and S-wave velocities in the crust. We used a Gradient Boosted Regression Tree algorithm to develop two models correlating geothermal gradients in continental and oceanic settings with these geophysical and geological features. The models were applied to a binned grid with a 0.5° x 0.5° resolution, enabling the estimation of the depth to the 122°C isotherm for each grid based on the machine learning model's predictions of geothermal gradients.

Our results reveal substantial habitable volumes within the lithosphere. The habitable volume in the continental crust may account for about 7% of the total crustal volume, while in the oceanic crust, it could be around 5%. Given the cell density range of 10² to 10⁶ cells per gram in oceanic rocks and 10² to 10⁴ cells per gram in continental rocks, along with an estimated carbon mass of 2x10^-14 grams per cell, the lithospheric biomass is estimated to be between 0.008 and 33.2 Gt Carbon. For context, the biomass found in plants and marine microbes is estimated to be around 450 Gt Carbon and 2.9 Gt Carbon, respectively.

How to cite: Zhao, W. and Zhangzhou, J.: Estimating Biomass in the Lithosphere: A Machine Learning Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13794, https://doi.org/10.5194/egusphere-egu24-13794, 2024.

Throughout geological history, changes in metamorphic conditions plays a crucial role in reflecting the evolution of the tectono-thermal conditions of Earth. The determination of temperature and pressure conditions for evaluating metamorphism typically relies on a limited number of samples, and the testing and analysis process requires significant time and work for thin section preparation, thin section analysis, geochemical analysis, as well as pseudosection calculations based on thin section and geochemical constraints. Following these procedures, it is commonly assumed that localized results can represent thermobaric conditions at regional or even orogenic belt scales. This assumption holds true when metamorphism reflects rock burial depth (i.e., lithostatic pressure). However, on small spatial scales, deviational stresses resulting from tectonic extension or compression can induce structural underpressure or overpressure, thereby rendering this assumption invalid. Therefore, we introduce magnetic susceptibility (k) as a measure of material magnetization in an applied magnetic field. It exhibits two key characteristics: (i) Fe-Ti oxides in mafic rocks display a mineral phase sequence largely associated with changes in pressure, with approximate pressure ranges for ilmenite + magnetite (<6 kbar), ilmenite (6–12 kbar), rutile + ilmenite (~12 kbar), and rutile (>12 kbar); (ii) Magnetic susceptibility can be quickly and extensively measured to reflect variations in Fe-Ti oxide content within mafic rocks. Our findings demonstrate that Fe content decreases while Ti content increases with increasing pressure. Thus, as pressure increases during prograde metamorphism, Ti generally replaces Fe, and this process can be detected as systematic decreases in magnetic susceptibility. This pressure–susceptibility correlation is further corroborated by retrograde metamorphism, where k inversely increases with decreasing pressure during exhumation. Based on our comprehensive petrological and geophysical analysis of mafic rock samples collected from the Paleoproterozoic (ca. 1.8 Ga) Jiao–Liao–Ji Belt of the North China craton, including coupled thin section, geochemical, and thermal susceptibility (kT) fingerprinting of Fe-Ti oxides, we posit that magnetic susceptibility can serve as a reliable indicator for discerning metamorphic pressure. Furthermore, owing to its ease of rapid and extensive data acquisition in fieldwork settings, we contend that it can play a pivotal role in identifying potential deviations from lithostatic stress due to tectonic stress on either small and/or large spatial scales.

How to cite: Ou, Q. and Mitchell, R.: Ferromagnetism as a pressure proxy for metamorphism?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14364, https://doi.org/10.5194/egusphere-egu24-14364, 2024.

In his classic contribution “A Heat Pipe Mechanism for Volcanism and Tectonics on Venus” [1989, JGR 94, B3, 2779-2785], Turcotte applied O’Reilly and Davies’ [1981, GRL 8, 313-316] model for Io’s volcanic heat transport to Venus, and further speculated that this mechanism might explain a thick lithosphere inferred for Archean Earth. The latter idea – to consider heat-pipe cooling for Earth – then lay fallow until roughly 15 years ago, when one of us (Moore) argued in talks and manuscripts (all rejected) that the cold, thick, and strong lithosphere generated by heat-pipe cooling might offer an alternative to subduction tectonics for generating the “too-cold” Hadean zircons reported by Hopkins et al. [2008, Nature 456, 493-496]. With the additional realization that the heat-pipe cooling mechanism might similarly account for the rocks preserved from the first half of Archean time, the concept of an early heat-pipe Earth finally received broad consideration just over a decade ago [Moore & Webb, 2013 Nature 501, 501-505]. 

Heat-pipe cooling is a hot stagnant-lid cooling mode based on our understanding of the active volcano-tectonics of Jupiter’s moon Io [O’Reilly & Davies, 1981]. Heat-pipes are not plumes: heat-pipes are conduits channeling melts upwards through lithosphere, whereas plumes commonly span the whole crust and mantle and accordingly have relatively complex histories. The heat-pipe Earth hypothesis posits that during the first third of Earth history, rapid volcanism dominated cooling from the end of the magma ocean period to the onset of (episodic?) plate tectonics. During the heat-pipe period, voluminous mafic volcanism resulted in protracted resurfacing, causing quasi-continuous burial of cold, hydrated surface materials that (1) cooled a single-plate lithosphere and (2) generated tonalite-trondhjemite-granodiorite melts deep in the lithosphere. It is noteworthy that the burial of surface materials to mantle depths – long seen as a distinguishing characteristic of plate tectonics – is a hallmark of heat-pipe cooling.   

The past decade has seen abundant explorations and tests of the heat-pipe Earth hypothesis, as well as renewed interest in the heat-pipe cooling mechanism for other terrestrial bodies. This presentation will review major results and consider key critiques. Highlights include demonstrations that heat-pipe cooling viably explains: (a) the early histories of the lithospheres preserved at Mercury, Venus, Mars, and the Moon, and thus can be hypothesized as a universal cooling mechanism for early / hot terrestrial bodies in our Solar System and others [Moore et al., 2017 EPSL 474, 13-19; Peterson et al., 2021 Sci.Adv. 7:eabh2482]; (b) the Eoarchean development of the Isua supracrustal belt of southern West Greenland [Webb et al., 2020 Lithosphere 12, 166-179 and a collection of subsequent works], which was previously understood exclusively via plate tectonic models; (c) the initiation of a global plate network, as thinning and corresponding warming of lithosphere during waning heat-pipe cooling caused thermal expansion which overcame the tensional strength of the lithosphere [Tang et al., 2020 Nat.Comm. 11:3621]; and (d) Earth’s detrital zircon depositional records older than ~3.3 Ga [Zuo et al., 2021 EPSL 575:117182].  

How to cite: Webb, A. A. G., Moore, W. B., Zuo, J., Müller, T., Tang, C., Simon, J. I., Haproff, P. J., Leung, C. Y. E., Ganbat, A., Ramírez-Salazar, A., Piazolo, S., Wang, Q., Sorger, D., Chin, E. J., Johnson, T. E., McKenzie, N. R., Kirkland, C. L., Cheng, H. C. J., and Hauzenberger, C.: A decade of the heat-pipe Earth hypothesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14694, https://doi.org/10.5194/egusphere-egu24-14694, 2024.

The Son Valley Crystallines (SVC) of the Precambrian Chhotanagpur granite-gneiss complex (CGGC) of the Sonbhadra district Uttar Pradesh contain gneisses and migmatites which are highly deformed and metamorphosed. The study area encompasses different parts of SVC which are Arangapani, Kudri, Anjangira, Jarha, Nawatola, and Naktu. Here we found gneiss and migmatite except Nawatola and Naktu where we found felsic breccia. The foliation in migmatite is E-W but at places it changes to ENE-WSW. The leucosome part of the migmatite occasionally shows pinching and swelling and ptygmatic folding structures. Petrography of the leucosome of this gneiss and migmatite shows the dominance of microcline, orthoclase, quartz, and rare plagioclase with a minor amount of biotite and amphibole whereas the melanosome is dominated by biotite, rarely with amphibole and minor quartz and, feldspars. These rocks contain a higher amount of REE-bearing phases viz. zircon, garnet, apatite, titanite, monazite, and xenotime. The REE-bearing phases particularly zircon, monazite, and xenotime are found as inclusions mostly within biotite and occasionally in feldspars whereas apatite and titanite were found as inclusions exclusively within feldspars. Few zircon and monazite are found in intergranular space between different mineral grains. REE-bearing phases were analyzed in EPMA for total rare earth oxide (TREO) quantification and it was observed that TREO is 0.84 - 1.91 wt% (avg. 1.37 wt%) for apatite and titanite, and for monazite, it is 44.54 - 68.51 wt% (avg. 58.98 wt%). The chemical ages of monazite from Kudri migmatite is 1166 - 748 Ma (avg. 936 Ma; n=10) and Jarha gneiss is 1339 - 837 Ma (avg. 1088 Ma; n=13) these ages coincide with Grenville orogeny (c.1250 - 980 Ma). Hence, REE mineralization in the study area may be the result of the Grenville orogenic event. Most monazite grains are anhedral to elongate in shape and they are found as inclusion in biotite and feldspar however, some of the monazite grains are found in the intergranular space. These two contrasting modes of occurrences of monazite suggest an earlier dominantly of syngenetic (orogenic) mineralization and later with an epigenetic overprint. The geochemical analysis of these rocks shows high SiO₂ and low MgO, FeO, and CaO contents indicating a felsic source which is also supported by the TAS diagram in which most of the samples fall in the granite region. The A/NK vs A/CNK plot shows the rocks are peraluminous in nature. The tectonic discrimination diagram of Y vs Nb, Ta+Nb vs Rb, and Yb vs Ta suggests that most of the rock samples fall within the plate field with few in the volcanic arc and few in the syn-collisional setting which indicates the complexity of the terrain.

How to cite: Verma, A. and Chinnasamy, S. S.: The implication of Grenville orogeny on REE mineralization in migmatites and gneisses of Son Valley Crystallines Sonbhadra, Uttar Pradesh, North India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15661, https://doi.org/10.5194/egusphere-egu24-15661, 2024.

The South Delhi Fold Belt (SDFB) within the northwestern Indian Shield is a Proterozoic NE-SW trending fold belt. The western boundary of the SDFB is defined by the Phulad Shear Zone, formed during a transpression regime around 820-810Ma. Granite rocks of ~1Ga have been documented from the western part of the fold belt and are linked with the formation of the Rodinia Supercontinent. These granites are closely associated with gabbroic rocks. The present study focuses on the geochemistry of these granites and the mafic rocks, as well as their field structure and petrography.

The granites and the mafic rocks are confined to a narrow linear belt along the western part of the fold belt. Detailed field studies reveal that the foliations in the granites, mafic and mylonites within PSZ share a common stress regime and are broadly synchronous. Geochemically these granites are ferroan, calc-alkalic, metaluminous to weakly peraluminous and their classification in granite discrimination diagrams confirms A-type and within plate granite. The mafic rocks exhibit a compositional range from tholeiitic to calc-alkaline, with a trace element ratio resembling enriched mid-oceanic ridge basalt (E-MORB) type magma. The tectonic discrimination diagram suggests rift-related magmatism. Geochemical analysis of these bimodal magmatic compositions in the SDFB, encompassing both mafic rocks and A-type granites are typically associated with areas experiencing extensional tectonics, particularly rift-related magmatism. Integrating field structures, petrography and geochemistry of these granite and the mafic rocks suggests that the ~1Ga granite and the associated mafic rocks formed in an extensional regime and are not directly linked to the collisional assembly of the Rodinia Supercontinent. 

Keywords: South Delhi Fold Belt, Granite, Phulad Shear Zone, Rodinia supercontinent, Extensional regime

How to cite: Manna, A., Chatterjee, S. M., Roy, A., and Sarkar, A. K.: Geochemistry of ~1Ga granite and associated mafic rocks from the South Delhi Fold Belt, NW India, and its tectonic significance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16033, https://doi.org/10.5194/egusphere-egu24-16033, 2024.

Upper amphibolite- and granulite-facies metabasites, ubiquitous in Archaean and Proterozoic terranes, represent a critical source of information on the lower continental crust. Elucidating the metamorphism of these rocks provides insights into the processes occurring at depth throughout Earth’s history. However, despite a century of geochemical studies examining high-temperature metabasites in the rock record, several aspects of their phase equilibria remain enigmatic, complicating the development of reliable thermodynamic equations of state for key phases.

This problem exists in part because studies of natural rocks primarily aim to establish the pressure-temperature (P-T) conditions of their respective region. Whilst researchers typically examine the relationship between the geochemical composition of different phases in pursuit of these P-T estimates, observations are necessarily restricted to the bulk composition of their rock and the P-T conditions at which the minerals equilibrated. In contrast, when developing equations of state, a rigorous understanding of how mineral compositions vary for a wide range of pressures, temperatures, and bulk compositions is required. This study lays the groundwork for such an understanding of metabasic phase equilibria by compiling a database of geochemical analyses from studies of natural samples worldwide.

Whole rock compositions, phase assemblages, modal abundances, and mineral compositions have been extracted from over 100 studies in the literature to construct a database containing >1000 samples. First, we determine the median value for and examine the range in the major- and minor-element whole rock composition of metabasites. These values are then compared to several average basalt compositions from the literature. Second, we examine the range and variability in the composition of individual minerals and the partitioning of elements between them. Third, using wet chemical analyses from the database, we test the ability of current ferric iron estimation techniques to reproduce that measured in garnet, orthopyroxene, clinopyroxene, and amphibole. Future work will use this database to test the capability of new thermodynamic equations of state and make it available as a community resource.

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 850530).

How to cite: Forshaw, J., Green, E., and Lanari, P.: Upper amphibolite- and granulite-facies metabasites: the natural record, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17273, https://doi.org/10.5194/egusphere-egu24-17273, 2024.

Monazites crystallize along with silicate minerals, displaying microstructure characteristic of different recrystallization processes. They crystallize as the result of dislocation creep, dissolution creep or dissolution- precipitation creep, depending on pressure-temperature conditions and fluid composition. In dissolution- precipitation creep, newly formed grains replace pre-existing ones and appear as a distinct compositional domain under X-Ray and BSE images. Rock strain-fabric can be correlated with monazite-microstructure and dated using monazite-chemistry. Because it contains a significant amount of Th and U and lacks common Pb and continues to be used for Th-U-total Pb geochronology by chemical analysis in Electron Probe Microanalyser. As the closure temperature of monazite for Th-U-total Pb is ca. 800 °C; each domain retains its age of formation and can be used as geochronometer. Thus, monazite geochronology is used as an effective tool to constrain the timing of fabric development. Fourteen samples of Ambaji granulites of South Delhi Terrane, Aravalli Delhi Mobile Belt, NW India were used for the monazite geochronology and 306 analyses were performed. The microfabric of these samples has been studied to ascertain the category of strain fabric present in them.

The Ambaji granulite comprises pelitic, calcareous, and mafic granulites with several phases of granite intrusions, G_0-3. The granulites were deformed by three phases of folding, F_1–3, during South Delhi orogeny and marked by a subhorizontal pervasive fabric, S₁, axial planar to isoclinal-recumbent F₁ folds that developed during granulite facies metamorphism. S₁ is overprinted by discrete sets of subvertical shear zones associated with a mylonitic fabric, S₂, that were developed axial planar to NE-SW striking upright F₂ folds and facilitated exhumation of granulite facies rocks to the upper crust. The shear zones show early history of high-temperature thrust sense shear and late stage low-temperature sinistral shear. The NW-SE striking F₃ folds also affected the granulite facies rocks. Brittle strike slip, and normal fault (S_f fabric) that developed post F₃, led the final exhumation of the granulite facies rocks to the surface. The S₁ monazites are Y-depleted and recrystallized through dislocation creep, and the S₂-S_f monazites are Y-enriched and recrystallized through dissolution-precipitation creep. Different monazite population yielded distinct ages of circa 875-857, 834-778, and 764-650 Ma for S₁, S₂, and S_f strain, respectively, indicating that the South Delhi orogeny spanned 875-650 Ma overlapping with the early phase of the Pan-African orogeny or representing a transition between Grenvillian and Pan-African orogeny.

How to cite: Tiwari, S. K. and Biswal, T. K.: Monazite Geochronology of Deformational Strain Fabric and its Tectonic Implications of the Lower-Middle Crustal Rocks: A Case Study of Ambaji Granulite, NW India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18091, https://doi.org/10.5194/egusphere-egu24-18091, 2024.

We are exploring the origins of some of Earth’s oldest monazite minerals found in the Isua supracrustal belt of southern West Greenland. Monazite is the primary host for light rare earth elements, Th and U, and is a predominant accessory mineral in low Ca granites and metapelites. Its occurrence is controlled by the Al/Ca ratio of the host rock, and at lower metamorphic grade it may be preceded by allanite. Monazite does not form if the Al/Ca ratio falls below a certain threshold.
Rock types with a high Al/Ca ratio suitable for monazite formation are widespread in modern geological settings. Archean rocks, however, typically have a basaltic to ultramafic composition. Even Archean felsic igneous rocks such as TTGs generally exhibit relatively low Al/Ca ratios. Consequently, the composition of most Archean rocks essentially limits the growth of monazite, with apatite, allanite, titanite or zircon being the predominant accessory phases. Nonetheless, the Al/Ca ratio of some rocks must have exceeded the critical threshold during crustal differentiation, allowing the first monazites to be formed. The exact timing of when this happened, and which rocks were involved, is not known. Here we present evidence of very early monazite formation, as discovered in the Isua supracrustal belt (ISB) of southern West Greenland.
The "metapelitic" rock used for this study contains multiphase garnet porphyroblasts and exhibits two generations of monazite. Monazite found in garnet cores yield Th-U-Pb ages of ~3.6 Ga, placing these crystals among the oldest monazites known to date. The younger monazite generation found in the more peripheral parts of the garnet grains and in the rock matrix yields Th-U-Pb ages of ~2.7 Ga. These younger ages are consistent with recently published garnet ages that have been interpreted to record the dominant tectono-metamorphic event of the ISB (Eskesen et al., 2023, Geology 51, 1017–1021). A detrital origin of either monazite generation is unlikely because there are no other known occurrences of monazite in Isua and both monazite generations appear to have formed in their current host rock via a metamorphic overprint.
Due to the rocks’ pelitic bulk composition, they are interpreted as one of the oldest preserved clastic sedimentary rocks, consistent with a provenance consisting of ultramafic, mafic and felsic igneous rocks (Bolhar et al., 2005, GCA 69, 1555–1573). Alternatively, their composition can be interpreted as a metasomatic modification of a basaltic rock (Rosing et al., 1996, Geology 24, 43–46). In either case, the observed ~3.6 Ga monazite indicates a minimum age for the process that led to the high Al/Ca composition of the host rock, which in turn eventually allowed the growth of monazite in the Archean crust of the ISB. As for the hotly-debated matter of whether or not the Isua supracrustal belt hosts late Eoarchean metamorphism, the ~3.6 Ga data appears to potentially represent the first direct-dating evidence in support of this interpretation.

How to cite: Sorger, D., Müller, T., and Webb, A. A. G.: Primordial monazite growth in Archean “metapelites” of the Isua supracrustal belt, southern West Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18431, https://doi.org/10.5194/egusphere-egu24-18431, 2024.

The Eoarchean Isua supracrustal belt (ISB) in West Greenland comprises one of the oldest rock records, yet its geological evolution and geodynamic setting are still debated. Major order questions involve the timing and number of the tectono-metamorphic events leading to the formation of mineral assemblages and structures observed today. Interpreted cross-cutting relationships and crystallization ages of the Ameralik (mafic) dykes have been used to suggest an Eoarchean metamorphic age for the most pervasive event (e.g., Nutman et al., 2004, JGS 161, 421-430). Recent studies, in contrast, argue that this event is Neoarchean in age, as constrained via garnet (-plagioclase-hornblende) dating (e.g., Eskesen et al. 2023, Geology 51, 1017-1021; Ramírez-Salazar et al., unpublished data). In this study, we present data of eight garnet grains from two metapelitic samples from the eastern limb of the ISB to acquire further information about the metamorphic evolution. Both samples share a similar mineral assemblage, featuring a matrix predominantly composed of porphyroblastic garnet with ±chlorite, biotite, white mica, quartz, and ±plagioclase. The garnets exhibit a diversity of unevenly distributed inclusions dominated by quartz, plagioclase, white mica, chlorite, and ilmenite. Additionally, apatite, ±monazite, ±allanite, ±rutile, and ±zircon, as well as some iron-arsenide and -sulphide minerals, are abundant as inclusions. Textural evidence in combination with major and trace element zoning reveals three distinct garnet core to rim domains referred to as garnet I to garnet III. The porphyroblasts’ inclusion-rich cores (garnet I) are characterized by a bell-shaped spessartine component and heavy rare earth element zoning pattern, along with a relatively flat grossular and pyrope pattern. The garnet annuli (garnet II) are grossular-rich, with a constant or slightly increasing pyrope and spessartine components already at their minimum. Garnet II typically exhibits less inclusions. A drop in grossular together with an increase in pyrope components, and the virtual absence of inclusions mark the third garnet domain (garnet III). Our examination of the chemical, mineralogical, and textural characteristics across the different garnet domains reveals the growth of garnet through distinct mineral reactions under variable metamorphic conditions. These domains may be linked to either distinct metamorphic growth stages within a single event or disparate metamorphic events in the tectono-thermal history of the ISB. To unravel the chronological sequence of garnet growth, we present texturally resolved dating of individual garnet domains using the Sm-Nd isochron method.

How to cite: Wolf, J., Sorger, D., Ramírez-Salazar, A., Hauzenberger, C., Webb, A. A. G., Willbold, M., and Müller, T.: Unravelling the metamorphic history of the Isua supracrustal belt: A garnet-based study in West Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18808, https://doi.org/10.5194/egusphere-egu24-18808, 2024.

Delineating subsurface interfaces is a crucial step in site selection and characterization for various subsurface applications, such as the geologic carbon sequestration, the radioactive waste disposal and hydrocarbon exploration and production. 3D seismic surveys are widely used for identifying subsurface interfaces and geologic features. Due to the large volumes and the complexity of seismic data, manual interpretation of subsurface interfaces is extremely time-consuming, and the interpretation results can be greatly affected by the subjectivity of a particular interpreter. With the latest advances in deep neural networks (DNNs), automatic seismic interpretation methods based on DNNs emerged. Most of the DNN-based seismic interpretation methods are supervised learning methods, which require large amount of labeled data for network training. We have developed an unsupervised learning method with deep fully convolutional networks (FCNs) for rapid subsurface interface identification based on self-learning algorithms, which does not require manual data labeling and specific training datasets. The characteristics of subsurface interfaces are represented as numerical constraints added to the specially designed loss function for constructing the FCN model. Physical constraints are further applied in postprocessing the outputs of the FCN model to improve the resolution of the identified subsurface interfaces. Application of the unsupervised learning method on a real seismic dataset collected at a potential CO₂ storage site demonstrates that the proposed method yields rapid and accurate identification of subsurface interfaces with relatively strong acoustic impedance contrast in seismic images. The proposed approach may assist in automatic subsurface interface identification in real time and facilitate building geological models for subsurface applications.

How to cite: Wang, Z., Qi, S., Liu, Y., Zheng, B., Sun, P., and Han, Y.: Unsupervised Deep Learning for Rapid Subsurface Interface Identification using Geophysical Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19107, https://doi.org/10.5194/egusphere-egu24-19107, 2024.

The Eoarchean Isua supracrustal belt (ISB) in southern West Greenland exposes one of the oldest rock records on Earth. Its tectono-metamorphic evolution remains debated, particularly with respect to its timing and metamorphic peak conditions recorded by the various mafic to ultramafic lithologies. A first-order question is the presence or absence of metamorphic gradients within the belt. To that end, phase equilibria modelling combined with multiple geothermobarometric data by our group suggested a homogeneous distribution of peak metamorphic conditions (550-600 °C; 0.8-1.0 GPa). However, recent studies of a specific dunite lens from the ISB suggested different metamorphic conditions, varying from ultra-high pressure (UHP) to prograde low-pressure deserpentinization.

In this study, the metamorphism affecting ultramafic rocks from the specified lens B in the northwestern limb of the ISB is investigated along a transect from the rim towards the center of the lens. A total of four samples are examined for their petrography, mineral assemblages, and reaction textures, using EPMA, SEM, EBSD, ICP-MS data together with thermodynamic modelling.

Results reveal a strong foliation in the rim of the lens, with antigorite (X_Mg=0.91) + magnesite + magnetite ± ilmenite forming the stable assemblage. Deformation decreases towards the center of the lens, where antigorite (X_Mg=0.98) + fosterite (X_Mg=0.97) + magnesite + magnetite ± Ti-chondrodite/Ti-clinohumite form the observed assemblage.

The presence of accessory Ti-phases has been used as an indicator for retrograde decompression after UHP metamorphism through the breakdown reaction of Ti-chondrodite to form Ti-clinohumite. We present textural evidence of Ti-clinohumite being replaced by Ti-chondrodite, pointing to a different reaction along a cooling path at lower pressures. The presence of carbonate instead of brucite together with the absence of talc highlights the role of CO₂ – which must be assessed to accurately describe phase relations for the metamorphic evolution of ultramafic rocks. Thermodynamic modelling indicates that antigorite stability is strongly CO₂-dependent, limiting the stability of antigorite + magnesite to pressures < 1 GPa at X_CO2 > 0.005. EBSD analysis reveals clear evidence of olivine experiencing internal deformation, and thus preceding the growth of antigorite in the sample. A second observation further supports this finding: Magnetite, magnesite and Ti-humite phases are spatially associated with olivine breakdown reaction textures.

In summary, this study suggests that UHP conditions or deserpentinization are not required to explain the metamorphic records of these mafic lenses, thus removing a strong argument for the ISB to exhibit a metamorphic gradient and UHP rocks. Instead, we interpret the lens to exhibit a fluid-mediated reaction front that can be readily achieved at the homogeneous, amphibolite-facies conditions reported for the rest of the belt.

How to cite: Mueller, T., Wolf, J., Sorger, D., Piazolo, S., Hauzenberger, C., Zuo, J., and Webb, A.: Amphibolite facies conditions recorded in CO2-bearing fluid-mediated reaction fronts preserved in an ultramafic lens from the Isua supracrustal belt, southern West Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19290, https://doi.org/10.5194/egusphere-egu24-19290, 2024.