GMPV – Geochemistry, Mineralogy, Petrology & Volcanology

GMPV1.1 – Advances in analytical and experimental techniques in mineralogical and geochemical research

EGU22-1186 | Presentations | GMPV1.1

Unraveling the secrets of the Earth through nanogeology: A correlative microscopy approach

Renelle Dubosq, David Schneider, Anna Rogowitz, and Baptiste Gault

Correlative analytical approaches involving high-spatial resolution microscopy techniques allow for the compositional measurements and spatial imaging of materials at the near-atomic scale. By combining electron backscatter diffraction (EBSD) mapping, electron channeling contrast imaging (ECCI), scanning transmission electron microscopy (STEM) and atom probe tomography (APT) on various geological materials such as minerals and glasses, we have successfully documented element mobility regulated by structural defects. Although these techniques were initially developed in the materials sciences, they are now being applied to a broad range of applications within many subdisciplines of geosciences including geochemistry, geochronology, and economic geology. In one set of experiments, we applied a correlative approach on naturally deformed pyrite from an orogenic gold mine in northern Canada to assess the impact of crystal-plastic deformation on the remobilization of trace elements. This study has led us to propose a new paragenetic model for metallic ore deposits in which deformation creates nanostructures that act as traps for base- and precious-metals. By applying our approach on pyrite that is rich with fluid inclusions, we have also documented two processes that led to proposing a new fluid inclusion-induced hardening model, which is in contrast to the more commonly reported weakening effect of fluids on minerals. To broaden the applications of our approach, we have applied the same suite of analytical techniques to a synthetic andesitic glass to assess whether nanoscale chemical heterogeneities can act as nucleation sites for gas bubbles. The combined results demonstrate the existence of nanoscale chemical heterogeneities within the melt and at the bubble-melt interface supporting the hypothesis that homogeneous nucleation could in fact be a variety of heterogeneous nucleation. The interactions between trace elements and structural defects plays a vital role in determining the mechanical properties of minerals, particularly in fluid-rich environments. These sub-nanometer scale exchanges consequently control meso- to tectonic-scale geological processes. Our research work not only demonstrates the latest advancements in analytical microscopy resolving long-standing geological problems but also brings us closer to bridging the gap between the fields of materials sciences and geosciences.

How to cite: Dubosq, R., Schneider, D., Rogowitz, A., and Gault, B.: Unraveling the secrets of the Earth through nanogeology: A correlative microscopy approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1186, https://doi.org/10.5194/egusphere-egu22-1186, 2022.

EGU22-2517 | Presentations | GMPV1.1

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

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

Understanding earth materials is critical to creating a sustainable, carbon-neutral society. Earth materials control the feasibility of subsurface energy storage, geothermal energy extraction, and are a source of critical elements for future-proof battery technologies. Perturbations to geological systems can also result in hazards, such as human-induced earthquakes. If we want to tackle the current, pressing scientific questions related to sustainable development for a circular economy, there is an urgent need to make multi-scale, multi-dimensional characterisations of earth materials available to a broad spectrum of earth-science disciplines. In addition to the society-relevant topics, the properties of earth materials determine how the Earth workson the most fundamental level.To overcome this challenge, 15 European facilities for electron and X-ray microscopy join forces to establish EXCITE. EXCITE is a Horizon Europe infrastructure project, and enables access to high-end microscopy facilities and to join the knowledge and experience from the different institutions. By doing so, EXCITE will develop community-driven technological imaging advancements that will strengthen and extend the current implementation of leading-edge microscopy for earth-materials research. In particular, the EXCITE strategy is to integrate joint research programmes with networking, training, and trans-national access activities, to enable both academia and industry to answer critical questions in earth-materials science and technology. As such, EXCITE builds a community of highly qualified earth scientists, develops correlative imaging technologies providing access to world-class facilities to particularly new and non-expert users that are often hindered from engaging in problem-solving microscopy of earth-materials.This presentation gives an overview EXCITE, its activities and open calls, and the progress of the first year of the project.

How to cite: Walter, S., Cnudde, V., Plümper, O., and ter Maat, G.: EXCITE: A European infrastructure to promote electron and X-ray microscopy of Earth materials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2517, https://doi.org/10.5194/egusphere-egu22-2517, 2022.

EGU22-3234 | Presentations | GMPV1.1

In-situ nanoscale geochemical characterization of organic matter in shale by AFM-IR

Ke Wang, Lin Ma, and Kevin G. Taylor

Due to the fine-grained nature of shale, organic matter particles are generally micro- and nano-scale in size. Functional groups differ between different organic matter types and as such provide unique chemical information for organic matter. Micro-FTIR can provide direct measurement to characterize sample features at the micrometer scale. However, optical diffraction limits its application at the nanometer scale. As a non-destructive high-resolution scanning probe technique, atomic force microscopy (AFM) is very powerful in nanoscale research and has been widely used in the fields of polymers, semiconductors, electrochemistry and biology. To provide a better combination of AFM’s unique advantages with nanoscale chemical analysis, the AFM-IR technique has been developed in recent years and also attracted the attention of geologists to explore the application in geological materials.

In this research, AFM-IR which is a quite new technique in geological research was used to investigate the in-situ geochemical characteristics of organic matter in shale. Nanoscale molecular composition of individual organic particles was captured nondestructively, and the distribution of typical functional groups was displayed via 2D IR mapping. In our samples, both alginite and inertinite display chemical homogeneity. The former is dominated by oxygenated and aliphatic contents which indicates a higher hydrocarbon generation potential, whereas the latter is dominated by aromatic carbon. In contrast, migrated solid bitumen particles show compositional heterogeneities at the nanometer scale as some are aromatic-rich and others are aliphatic-rich. Finally, linking this advanced nanochemical technique to potential applications in subsurface energy was explored. This research demonstrates that AFM-IR is a powerful tool to examine the in-situ nanoscale geochemical characteristics of different organic matter types, which can also provide implications for energy applications.

How to cite: Wang, K., Ma, L., and Taylor, K. G.: In-situ nanoscale geochemical characterization of organic matter in shale by AFM-IR, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3234, https://doi.org/10.5194/egusphere-egu22-3234, 2022.

Hydrous lattice point defects (OH defects) in quartz (SiO2) occur through coupled substitution of Si4+ with a trivalent cation (most commonly Al3+) and a hydroxyl group (OH-). These impurities can be used to investigate its host rock’s crystallization history and may therefore also serve as a tracer for sediment provenance analyses, but are also economically relevant (e.g., high purity quartz sources).

Transmission infrared (IR) spectroscopy has proven to be a very effective method to analyze OH defects down to concentrations of a few weight parts per million water equivalent. This technique, however, requires thin (100 to 200 µm), polished quartz wafers that are cut perpendicular to the crystallographic c-axis. Preparation of a statistically significant number (i.e. > 100) of grains using this approach is very time consuming and requires a skilled operator. Furthermore, IR spectral analysis so far does not follow a standardized protocol, possibly introducing individual biases and hampering reproducibility of as well as comparability between datasets.

In this work, we present a new, standardized procedure for sample preparation, measurement, and data analysis of OH defects in quartz. Sample preparation and IR measurements are significantly sped up and simplified and require relatively little specialized laboratory equipment. Additionally, our data analysis is performed largely automated and based on spectral deconvolution and generation of synthetic spectra before quantification, ensuring quick generation of reproducible results. This new protocol may therefore be another step towards making OH defect analysis accessible to a wider range of geoscientific fields.

How to cite: Jaeger, D. and Stalder, R.: Quantification of OH in quartz via infrared spectroscopy – new protocol for sample preparation and spectral analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4954, https://doi.org/10.5194/egusphere-egu22-4954, 2022.

EGU22-7132 | Presentations | GMPV1.1

Setup to study the electronic structure of iron-bearing compounds in situ at conditions of the Earth’s lower mantle 

Christian Albers, Robin Sakrowski, Georg Spiekermann, Lélia Libon, Max Wilke, Nicola Thiering, Hlynur Gretarsson, Martin Sundermann, Johannes Kaa, Metin Tolan, and Christian Sternemann

The determination of the electronic structure of iron-bearing compounds at high pressure and high temperature (HPHT) conditions is of crucial importance for the understanding of the Earth’s interior and planetary matter. Information on their electronic structure can be obtained by X-ray emission spectroscopy (XES) measurements, where the iron’s Kβ1,3 emission provides information about the spin state and the valence-to-core region focusses on the coordination chemistry around the iron and its electronic state. Furthermore, resonant XES (RXES) at the iron’s K-edge reveals even more detailed information about the electronic structure [1].

We present a setup to investigate the electronic structure of iron-bearing compounds in situ at HPHT conditions using XES and RXES. The HPHT conditions are accomplished by diamond anvil cells (DACs) in combination with a portable double-sided Yb:YAG-laser heating setup [2]. The spectroscopy setup contains a wavelength dispersive von Hamos spectrometer in combination with a Pilatus 100K area detector [3]. This setup provides a full Kβ1,3 emission spectrum including valence-to-core emission in a single shot fashion. In combination with a dedicated sample preparation and use of highly intense synchrotron radiation of beamline P01 at PETRA III, the duration of the measurements is shortened to an extend that in situ XES, including valence-to-core, as well as in situ spin state imaging becomes feasible. The use of miniature diamonds [4] enables RXES measurements at the Fe-K edge. By using different analyzer crystals for the von Hamos spectrometer, simultaneous Kα and Kβ detection are feasible, which provides L-edge and M-edge like information.

The presented sample is siderite (FeCO3), which is in focus of recent research as it is a candidate for the carbon storage in the deep Earth. Siderite exhibits a complex chemistry at pressures above 50 GPa and temperatures above 1400 K resulting in the formation of carbonates featuring tetrahedrally coordinated CO4-groups instead of the typical triangular-planar CO3-coordination. These carbonates are well understood on a structural level but information on their electronic structure is scarce [5-7]. We present information on the sample’s spin state at in situ conditions of about 75 GPa and 2000 K XES Kβ1,3 imaging  as well as RXES measurements for low and high pressure siderite at ambient temperature conditions for Kα and Kβ emission.

[1] M. L. Baker et al., Coordination Chemistry Reviews 345, 182 (2017)

[2] G. Spiekermann et al.,  Journal of Synchroton Radiation, 27, 414 (2020)

[3] C. Weis et al., Journal of Analytical Atomic Spectroscopy 34, 384 (2019)

[4] S. Petitgirard et al., J. Synchrotron Rad. , 24, 276 (2017)

[5] J. Liu et al., Scientific Reports, 5, 7640 (2015)

[6] M. Merlini et al., American Mineralogist, 100, 2001, (2015)

[7] V. Cerantola et al., Nature Communications 8, 15960 (2017)

How to cite: Albers, C., Sakrowski, R., Spiekermann, G., Libon, L., Wilke, M., Thiering, N., Gretarsson, H., Sundermann, M., Kaa, J., Tolan, M., and Sternemann, C.: Setup to study the electronic structure of iron-bearing compounds in situ at conditions of the Earth’s lower mantle , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7132, https://doi.org/10.5194/egusphere-egu22-7132, 2022.

EGU22-13173 | Presentations | GMPV1.1

Chemical Analysis of Trace Elements at the Nanoscale in Samples Recovered from Laser-Heated Diamond Anvil Cell Experiments

Ingrid Blanchard, Sylvain Petitgirard, Vera Laurenz, Nobuyoshi Miyajima, Max Wilke, Dave Rubie, Sergey S. Lobanov, Louis Hennet, Wolfgang Morgenroth, Rémi Tucoulou, Valentina Bonino, Xuchao Zhao, and Ian Franchi

High pressure and high temperature experiments performed with laser-heated diamond anvil cells (LH-DAC) are being extensively used in geosciences in order to study matter at conditions prevailing in planetary interiors. Due to the size of the apparatus itself, the samples that are produced are extremely small, on the order of few tens of micrometers. There are several ways to analyze the samples and extract physical, chemical or structural information, using either in situ or ex situ methods. Here, we will compare two nanoprobe techniques, namely nano X-ray fluorescence (nano-XRF) and Nanoscale secondary ion mass spectrometry (NanoSIMS), that can be used to analyze samples synthetized in LH-DAC and recovered using Focused Ion Beam. The two techniques are very different in various aspects, the most important one being that nano-XRF is a deeply penetrative but nondestructive method, whereas NanoSIMS is a surface sensitive and destructive method. The second major difference between the two techniques is that NanoSIMS can probe isotopes, whereas nano-XRF cannot. With both, it is possible to obtain the spatial distribution of chemical elements in the samples.

We used these two nanoprobes to retrieve elemental concentrations and ratios of dilute moderately and highly siderophile elements (few tens of ppm) in quenched experimental melts relevant for the formation of the core of the Earth. We will show those results and discuss the importance of proper calibration for the acquisition of quantifiable results. We have also performed metal–silicate partitioning experiments in which tungsten and molybdenum were incorporated. Those experiments are especially relevant to understand the core–mantle differentiation of the Earth, about 4.5 billion years ago. We will first present and compare metal–silicate partition coefficient obtained by both nano-XRF and NanoSIMS, and second also with results obtained independently by electron microprobe.

How to cite: Blanchard, I., Petitgirard, S., Laurenz, V., Miyajima, N., Wilke, M., Rubie, D., Lobanov, S. S., Hennet, L., Morgenroth, W., Tucoulou, R., Bonino, V., Zhao, X., and Franchi, I.: Chemical Analysis of Trace Elements at the Nanoscale in Samples Recovered from Laser-Heated Diamond Anvil Cell Experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13173, https://doi.org/10.5194/egusphere-egu22-13173, 2022.

EGU22-6179 | Presentations | GMPV1.1

Constraining P-T conditions using a SEM Automated Mineralogy based workflow – an example from Cap de Creus, NE Spain

Richard Wessels, Thijmen Kok, Hans van Melick, and Martyn Drury

The spatial distribution of mineral phases in a thin section provides information about the mineral reactions and deformation history of the sample. This information is often difficult to obtain using classical optical microscopy or SEM analyses, as the spatial resolution is too small to provide the necessary overview. SEM Automated Mineralogy (AM) delivers false colour mineral phase maps at the full thin section scale. Combined with full-sized PPL and XPL thin section scans, this provides an exceptional high-resolution overview of the mineral content and microstructures. Moreover, SEM-AM provides quantitative information about the mineral and bulk rock compositions, which can subsequently be used in thermodynamic modelling to establish P-T conditions for the entire, or a subset of, the rock sample.

The structural geology group at Utrecht University recently acquired a SEM-EDS system with Automated Mineralogy capabilities. The accuracy of the EDS system was compared against WDS microprobe measurements, while the SEM-AM based bulk rock composition of the thin section was compared against XRF data from the corresponding sample dummy. Subsequently, the SEM-AM bulk rock composition was used as input for thermodynamic modelling using Perple_X. Independent temperature estimates were established using; i) SEM-EBSD based CPO results on quartz, in conjunction with the quartz recrystallization mechanisms and recrystallized grain size; and ii) titanium-in-quartz using nano-SIMS analyses. Further constraints on fluid-rock-melt interactions were obtained by using LA-ICP-MS.

This workflow is applied to samples from the Cap de Creus region in northeast Spain. Located in the axial zone of the Pyrenees, the pre-Cambrian metasediments underwent HT-LP greenschist- to amphibolite-facies metamorphism, are intruded by pegmatite bodies, and overprinted by greenschist-facies shear zones. The SEM-AM workflow allowed to further constrain the prograde and retrograde P-T conditions in the different metamorphic zones. In addition, at the thin section scale, the results show temporal and spatial variations in the mineral reactions that occurred.  

In the near future, this workflow will be refined and included in the broader correlative microscopy workflow that will be applied in the H2020-funded EXCITE project (https://excite-network.eu/), a European collaboration of electron and x-ray microscopy facilities and researchers aimed at structural and chemical imaging of earth materials. The data will be made available in a FAIR manner through the EPOS (European Plate Observing System) data publication chain (https://epos-msl.uu.nl/).

How to cite: Wessels, R., Kok, T., van Melick, H., and Drury, M.: Constraining P-T conditions using a SEM Automated Mineralogy based workflow – an example from Cap de Creus, NE Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6179, https://doi.org/10.5194/egusphere-egu22-6179, 2022.

EGU22-6787 | Presentations | GMPV1.1

Self-supervised Automated Mineralogical and Chemical Analysis for Hyperspectral Datasets

Po-Yen Tung, Hassan Sheikh, Matthew Ball, Farhang Nabiei, and Richard Harrison

Identification of unknown micro- and nano-sized mineral phases is commonly achieved by analysing chemical maps generated from hyperspectral datasets, particularly scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX). However, the accuracy and reliability are limited by subjective human interpretation and instrumental artefacts in the chemical maps. At the same time, machine learning has emerged as a powerful method to overcome the roadblocks. Here, we propose a self-supervised machine learning approach to not only identify unknown phases but also unmix the overlapped chemical signals of individual phases with no need for user expertise in mineralogy. This approach leverages the guidance of gaussian mixture modelling (GMM) clustering fitted on an informative latent space of pixel-wise elemental data points modelled using a neural network autoencoder, and deconvolutes the overlapped chemical signals of phases using non-negative matrix factorisation (NMF). We evaluate the reliability and the accuracy of the new approach using two hyperspectral EDX datasets. The first dataset was measured from an intentionally fabricated sample, where seven known mineral particles are physically overlapping with each other as well as the substrate. Without any prior knowledge, the proposed approach successfully identified all major phases and recovered the original chemical spectra of the individual phases with high accuracy. In the second case, the dataset was collected from a potential vehicular source of particulate matter air pollution, where identification of the individual pollution particles is complicated by the complex nature of the sample. The approach once again was able to identify the potential Fe-bearing ultrafine particles and isolate the background-subtracted elemental signal. We demonstrate a robust approach that potentially brings a significant improvement of mineralogical and chemical analysis in a fully automated manner. In addition, the proposed analysis process has been built into a user-friendly Python code with graphical user interface (GUI) for ease of use by general users.

How to cite: Tung, P.-Y., Sheikh, H., Ball, M., Nabiei, F., and Harrison, R.: Self-supervised Automated Mineralogical and Chemical Analysis for Hyperspectral Datasets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6787, https://doi.org/10.5194/egusphere-egu22-6787, 2022.

EGU22-9146 | Presentations | GMPV1.1

The origins of volatile organic sulfur compounds in natural gas reservoirs

Ilya Kutuzov, Chunfang Cai, and Alon Amrani

Volatile organic sulfur compounds (VOSC) are known to occur in natural gas and petroleum reservoirs. These compounds are typically accompanied by H2S which together, degrade the quality of the petroleum, complicate production due to corrosion of piping, and pose a health risk to workers and local communities. The origins of both H2S and VOSC in natural gas are only partially understood with the latter being analyzed in only a few cases and its formation processes virtually unknown. Nevertheless, several studies have linked VOSC to H2S in processes such as thermochemical sulfate reduction (TSR) and kerogen cracking. Hence, VOSC have the potential to act as a proxy for the natural gas and H2S origins, in-situ TSR and fluid migration pathways.

To better understand the pathways of VOSC formation in natural gas reservoirs, we analyzed natural gas samples (Permian reservoirs, Sichuan Basin, China) and performed a series of pyrolysis experiments. The results of the experiments between methane (CH4) and H2S at 360°C for 4-96 hours revealed the only VOSC formed is methanethiol (MeSH) which was identified at ppm concentrations in all experiments. The δ34S values of the MeSH were 2 to 3‰ heavier than the initial H2S. For comparison, Meshoulam et al., (2021) reported that the reaction between H2S and pentane (i.e. “wet gas”) that yielded a variety of VOSCs from thiols to methyl-thiophenes in the gas phase and up to methyl-benzothiophenes in the liquid phase. The analysis of natural gases showed that the samples contain a large variety of thiols and sulfides. The diversity of VOSC identified carries some resemblance to that observed by Meshoulam et al., (2021) and may suggest these VOSC are the result of in-reservoir reaction of C2+ hydrocarbons with H2S. The analysis of δ34S values of the VOSCs showed they cover a range between +10 to +30‰ while most samples had their VOSC in a narrower range of approximately 8‰. Generally, samples show a positive correlation between H2S content and VOSCs concentration- thereby implying VOSCs formation in the gas-phase. The δ34S of thiols in five of the samples covered a narrower isotopic range of about 2‰ while the sulfides in the samples spread over a large isotopic range of up to 10‰. This observation suggests the thiols are in isotopic equilibrium with their associated H2S while the sulfides are not. The reason for this difference is unclear. Further analysis will shed more light on isotopic fractionations between VOSC and H2S and will thus allow identification of H2S origins in the studied area.

[1] Meshoulam, A., Said-Ahmad, W., Turich, C., Luu, N., Jacksier, T., Shurki, A., Amrani, A., 2021. Experimental and theoretical study on the formation of volatile sulfur compounds under gas reservoir conditions. Organic Geochemistry, 152, 104175

How to cite: Kutuzov, I., Cai, C., and Amrani, A.: The origins of volatile organic sulfur compounds in natural gas reservoirs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9146, https://doi.org/10.5194/egusphere-egu22-9146, 2022.

EGU22-3987 | Presentations | GMPV1.1

40Ar/39Ar In-Situ Dating of Altered Mafic Rocks in the Karoo Large Igneous Provinces.

Clémentine Antoine, Richard A. Spikings, Sean P. Gaynor, and Urs Schaltegger

Dating of the extrusive parts of large igneous provinces has been a challenge because of the lack of mineral phases that can be dated by high-precision techniques. This is the case for the rapidly emplaced Drakensberg lavas, part of the Karoo LIP in South Africa and Lesotho. The circulation of hot fluids through the lava stack during rapid emplacement of continental flood basalts develops relatively high degrees of fracturing and alteration of the rocks, which often results in the re-opening of isotopic systems and inaccurate dates. This alteration occurs on varying length scales, from the outcrop to the micrometric scales, creating Argon loss in minerals of interest for 40Ar/39Ar dating (i.e. plagioclase) and making the procedure of separation for step-heating 40Ar/39Ar a tedious and sometimes ineffective task. Here, we re-approach measuring 40Ar/39Ar by directly analyzing leached and unleached thin sections without having to go through mineral separation, and therefore effectively eliminating the mixing issue of mechanically separating the plagioclase crystals. Half of each plagioclase aliquot was leached in acid, and then irradiated at the TRIGA reactor (Oregon State). We used a 193nm excimer UV-laser attached to a noble gas extraction and purification line, and an Argus VI mass spectrometer at the University of Geneva on thick sections for in-situ analysis. Plagioclase separates from the same Karoo lava flow samples were previously analyzed for 40Ar/39Ar geochronology using step heating, on aliquots of both leached and unleached plagioclase separates, using the same noble gas analytical equipment. This allows for a direct comparison of the in-situ­ analysis, testing the potential differences between the two different analytical systems and a potential way of assessing differences in accuracy between the two. Preliminary results show that accurate ages can be achieved by this technique at the cost of a larger precision.  

How to cite: Antoine, C., Spikings, R. A., Gaynor, S. P., and Schaltegger, U.: 40Ar/39Ar In-Situ Dating of Altered Mafic Rocks in the Karoo Large Igneous Provinces., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3987, https://doi.org/10.5194/egusphere-egu22-3987, 2022.

Next generation, high-resolution datasets to assess the dynamics of geological systems are becoming increasingly important to answer scientific questions that require higher spatial and temporal resolution than the current state-of-the-art. Such questions involve the couplings and feedbacks between tectonic, climatic, and surficial processes that constitute a heavily debated topic in Earth-Systems research. Over the last decades, the insufficient temporal resolution of conventionally derived (U-Th)/He thermochronometric datasets has limited the necessary quantification to track recent changes in erosion rates and relief—two metrics essential to reconstruct the past dynamics of landscapes and evaluate the relative contribution of surface and tectonic processes on erosion.

To overcome this limitation, the ERC-funded COOLER project aims to further the development of high-resolution, ultra-low temperature thermochronology by setting up a world-leading 4He/3He laboratory at the University of Potsdam. The centerpiece of the newly established laboratory is a split-flight-tube multi-collector gas-source sector mass spectrometer from Thermo Scientific™ connected to a sample-gas preparation bench, which includes He gas purification equipment along with a diode laser for stepped-heat sample degassing. Important topics of research the instrument will be utilized for include 1) investigation of the glacial imprint on topography, 2) characterization of the couplings between tectonic activity and topographic relief development in response to glaciation, and 3) quantification of glacial erosion relative to fluvial erosion in mountain belts. In addition to serving researchers and students at the University of Potsdam and collaborating institutions, the facility will provide analytical, research, and educational opportunities within the frame of the COOLER project to researchers from across the globe through external workshops.

To illustrate the capabilities of the new laboratory, we present our analytical and experimental methodologies used to obtain reliable high-resolution 4He/3He datasets. We focus on accuracy and cross-calibration to ensure minimal analytical bias in our measurements. Growing efforts in the (geo)science community are aimed at establishing best standardization practices and ensuring consistencies between laboratories and/or communities. Accordingly, we focus on ensuring that our methodologies are leading toward a noble-gas standardized method to compare mass spectrometry capabilities over various laboratories, and analytical techniques among the noble-gas communities. Accordingly, our standardized approach, coupled with analytical automation will lead to significant improvement in the accessibility and efficiency of routine 4He/3He analyses for geologic applications.

How to cite: Amalberti, J., van der Beek, P., Colleps, C., and Bermard, M.: New high-resolution 4He/3He laboratory at the University of Potsdam: Toward standardized approaches for efficient and reliable routine 4He/3He analyses for thermochronology applications., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7412, https://doi.org/10.5194/egusphere-egu22-7412, 2022.

EGU22-4301 | Presentations | GMPV1.1

Beyond Vienna: MS/MS Option for the Neoma MC-ICP-MS.

Grant Craig, Jenny Roberts, Markus Pfeifer, Claudia Bouman, Nicholas Lloyd, and Johannes Schwieters

The isotope composition of rainfall provides information on the initial isotope composition of the moisture source, conditions during evaporation and condensation of water vapor, and the rain-out history of an air-parcel. A standard method to analyze the rainfall isotope composition is by using Cavity Ring Down Spectrometry (CRDS). The accuracy of the analysis highly depends on the water isotope standards used, which determines the degree to which absolute values from different labs can be compared. The amount of international water isotope standards like VSMOW2 and SLAP2 primary water standards is extremely limited; therefore the International Atomic Energy Agency recommends calibrating in-house water isotope standards once a year by using VSMOW2 and SLAP2. The isotope range between VSMOW2 and SLAP2 is extreme, with 55.5‰ for d18O and 427.5‰ for d2H. The isotope range used in a sequence poses a problem for CRDS techniques that are characterized by significant memory effects.

In this study, we compare the behaviors of two different CRDS systems: a Picarro L2140i and a LGR WIA 35EP. We evaluate the relation between isotope differences of subsequent samples and the memory effect. We show that after 100 injections, memory effects may still be visible in hydrogen. Even when the isotope composition of subsequent injections of the same standard or sample does not show a trend anymore, the raw isotope data seems biased towards the isotope composition of multiple different samples or standards run prior. Running long sequences of for example 1100 injections in high precision 17O mode, also requires several vaporizer septa changes. The timing of a septa change is important, because opening the vaporizer allows water vapor from the atmosphere to enter the otherwise closed system, from which it takes approx. 20 injections to recover to the prior absolute values. Here we aim to provide a more practicle approach to a calibration sequence architecture and number of injections per primary and in-house standards, taking into account the potential drift of the analyzers.

How to cite: Wassenburg, J. A. and Sinha, N.: Improving calibrations of in-house water isotope standards using CRDS and OA-CRDS: memory effects versus drift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11603, https://doi.org/10.5194/egusphere-egu22-11603, 2022.

EGU22-626 | Presentations | GMPV1.1

Triple oxygen isotope fractionation of carbonate during carbonate precipitation and acid digestion

Pallab Roy, Amzad Laskar, and Mao-Chang Liang

Stable oxygen isotopic composition (δ18O) of CO2 produced from carbonates in natural archives is a useful proxy for paleo precipitation and paleo temperature reconstruction. However, there exist multiple factors controlling the δ18O values, the applications of the δ18O alone for paleoclimate studies are thus limited. Anomaly in 17O in carbonates, expressed by Δ′17O=1000*ln(δ17O/1000+1)-λ*1000*ln(δ18O/1000+1) is another proxy to independently constrain aspects of climatic variables such as precipitation source variation and kinetic effects during carbonate precipitation. However, to use 17O anomaly for such studies, the triple oxygen isotope fractionation exponent (θ= lnα17/lnα18) must be known precisely. Knowledge of this parameter is central to emerging applications of carbonate triple oxygen isotopes to paleoclimate and paleo-hydrology studies. Though a number of theoretical and experimental studies have been carried out in the last few years, there remains no consensus on 𝛳 value for carbonate-water system, likely due to kinetic isotope fractionation during precipitation.

Here, we measured Δ′17O in synthetic carbonates as well as in the water from which the carbonates are precipitated to check how reliable the Δ′17O value of the parent water can be reconstructed from the carbonates or carbonate-digested CO2. To determine θcarbonate_CO2-water for precipitated carbonates, we synthesized carbonates in the laboratory at temperatures ranging from 10 ⸰C to 66 ⸰C using passive/active CO2 degassing method. Triple oxygen isotope compositions of the water were determined using water-CO2 equilibration followed by CO2-O2 exchange method and of the carbonate (CO2 liberated by acid digestion) using CO2-O2 exchange method. We analyzed our isotope data for their possible kinetic isotope effect and determined the 𝛳carbonate_CO2-water value for precipitated carbonates. We find that most of our synthetic carbonate samples did not attain the equilibrium. The 𝛳carbonate_CO2-water increases as the disequilibrium effect increases. We determined the θcarbonate_CO2-water from the samples precipitating in equilibrium. Furthermore, we do not find any differences in the 𝛳carbonate_CO2-water value for carbonate precipitated in equilibrium at 25 ⸰C and 35 ⸰C. An important issue of using Δ′17O in carbonates is to resolve the 𝛳acid for acid digestion which is resolved in the present study. Additionally, we determined the temperature dependent variation in 𝛳acid and find no significant changes between 0 ⸰C and 70 ⸰C.

How to cite: Roy, P., Laskar, A., and Liang, M.-C.: Triple oxygen isotope fractionation of carbonate during carbonate precipitation and acid digestion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-626, https://doi.org/10.5194/egusphere-egu22-626, 2022.

EGU22-3540 | Presentations | GMPV1.1

Protracted U-Pb age spectra from complex zircon crystals resolved using high-precision geochronology and selective sample pre-treatment

Urs Schaltegger, Sean P. Gaynor, Melissa Ruiz, and Alexey Ulianov

Geochronology is fundamental for the understanding of rates and mechanisms of Earth processes, including tectonics, crust formation, ore formation and magmatism. Analytical techniques are mostly applied to the mineral zircon, particularly LA-ICPMS and ID-TIMS dating, which offer the required accuracy, precision and analytical throughput to solve outstanding scientific questions. However, zircon can record multiple geological events within discrete crystallographic domains, so it is crucial to ensure that measurements are completed using optimal precision and accuracy while specifically targeting crystal domains of interest to resolve potentially complex zircon systematics. We explore here a case where the combination of xenocrystic and autocrystic growth zones within same crystals, together with decay damage related lead loss, leads to apparently protracted age spectra, which can erroneously be interpreted in terms of magmatic evolution.

We present LA-ICP-MS and ID-TIMS U-Pb zircon data from a Variscan, 335 Ma old granodiorite from the Alpine basement in the Aar massif (Switzerland), which highlight the potential complexities present in zircon samples and address the need for careful zircon pre-treatment. CL imagery of zircon reveals minor but pervasive secondary alteration, leading to the observed excess scatter in LA-ICPMS dates. Chemical abrasion (CA) as a pre-treatment prior to LA-ICPMS analysis significantly reduces this scatter. CA-ID-TIMS analyses of zircon from this sample yield extremely high precision due to very high radiogenic/common Pb ratios (Pb*/Pbc), with significant 206Pb/238U scatter. Due to the elevated precision of these analyses, it is possible to resolve a linear discordance for these data. This indicates that Pb-loss is not the only age component observed, and the volume of zircon analyzed via CA-ID-TIMS does not purely reflect Variscan igneous crystallization. Since CL images also show thin and poorly visible metamorphic rims, we carried out a physical abrasion (PA) pre-treatment prior to chemical abrasion to isolate the Variscan zircon zones from later Alpine overgrowth for CA-ID-TIMS analysis. We interpret a high-precision PA-CA-ID-TIMS 206Pb/238U age of 335.479 ± 0.041/0.096 Ma (internal non-systematic/external systematic error; MSWD=0.27) as best estimate for Variscan zircon crystallization for this sample. This age overlaps with the result of CA-LA-ICPMS analyses when properly accounting for the total analytical uncertainty, including matrix effects on concentration ratio standardization.

From these data we conclude: (1) mixing of two age components in zircon may lead to an apparent protracted range in 206Pb/238U age, which can be resolved if isotope analyses yield very high Pb*/Pbc ratios and thus are very precise. At lower precision zircon age spectra can be erroneously interpreted as reflecting protracted growth, since they will overlap concordia due to elevated 207Pb/235U uncertainties, as well as in between individual 206Pb/238U ages. (2) By combining physical and chemical abrasion, we can resolve the observed complexities, by selectively analyzing zircon domains of interest while simultaneously mitigating diffusive Pb-loss. (3) This study shows how analytical precision may dramatically impact on scientific interpretation, as less precise data can easily be mistaken to reflect prolonged magmatic growth, rather than two-component mixing with xenocrystic material. This difference can significantly impact the interpreted lifespan of magmatic systems.

How to cite: Schaltegger, U., Gaynor, S. P., Ruiz, M., and Ulianov, A.: Protracted U-Pb age spectra from complex zircon crystals resolved using high-precision geochronology and selective sample pre-treatment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3540, https://doi.org/10.5194/egusphere-egu22-3540, 2022.

GMPV2.1 – Evolution of the Earth's upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites

EGU22-517 | Presentations | GMPV2.1

Metal migration and ore minerals across the crust-mantle transition zone (Oman DP ICDP holes CM1A, CM2B)

Dariusz Marciniak, Ciążela Jakub, Jesus Ana, Pieterek Bartosz, Koepke Jürgen, Strauss Harald, Lazarov Marina, Horn Ingo, Słaby Ewa, Prell Marta, and Blutstein Konrad

Holes CM1A and CM2B of the International Continental Scientific Drilling Program (ICDP) Oman Drilling Project (OmanDP, https://www.omandrilling.ac.uk/)  drilled  through  the Moho  Transition  Zone  (MTZ).  CM1A is composed  of layered gabbro (0–160 meters below surface, mbs), dunite (160–310 mbs), and harzburgites (310–405 mbs), whereas CM2B contains dunite (20–120 mbs) and harzburgites (120–300 mbs). The drillholes provided an unprecedented opportunity to study the behavior of metals in the MTZ, where arriving primitive MORB melts  extensively  react  with  the  mantle.  Here,  melts, typically  enriched  with  sulfur and  chalcophile  elements,  are supposed to enrich the mantle and lower crust with sulfides (Gonzalez-Jimenez et al., 2020 – Ore Geol. Rev.; Ciążela et al., 2018 - GCA).          

            Modal sulfide content increases downwards the gabbro sequence from ~0.004 vol.‰ to ~1.0 vol.‰ but decreases again from 0.8 vol.‰ to 0.01 vol.‰ in the lower part of the MTZ and in the harzburgite of the upper mantle. This is reflected in the S concentration increasing from 341 ± 17 ppm, 2sd (standard deviation = σ) to  832  ±  37  ppm,  2sd,  in  the  gabbro  section  and  decreasing  downwards  from  the middle part of  Moho into harzburgites from 475 ± 21, 2sd ppm to 63 ± 3 ppm, 2σ. The sulfides in olivine gabbro from MTZ are mostly (56–87% of all sulfides) pyrrhotite-pentlandite-chalcopyrite assemblages indicating the magmatic origin. Sulfides in layered gabbro sequence are consisted of similar magmatic assemblages (36-100%) with minor chalcopyrite, bornite, heazlewoodite, chalcocite, millerite, siegenite and sphalerite with secondary origin. In dunite and harzburgite sequences sulfides are exclusively hydrothermal.

Based on EMPA and LA-ICPMS measurements, Zn, Co and Cu seem to reach their maximum concentrations in magmatic sulfides from the MTZ. Although, no significant differences are observed between the Fe isotope signatures in magmatic pyrrhotites from the lower crust (–0.73 to –0.24, 2sd [‰] of δ56Fe) and the MTZ (–0.73 to –0.53, [‰] of δ56Fe), we found different δ56Fe for pyrrhotite (–0.24‰) and chalcopyrite +0.36‰ within the same sulfide grain. The bulk signature of δ56Fe for this grain is –0,12‰ being in accordance with the mass balance calculated δ56Fe 0.025‰ ± 0.025‰ of the mantle (Craddock et al., 2013 – Earth Planet. Sci. Lett).

            The  enrichment in sulfides and selected metals (Zn, Co, Cu) towards the  MTZ  might  result  from  melt-mantle  reaction  as  we  proposed previously for the slow-spread oceanic lithosphere based on the Kane Megamullion Ocean Core Complex (Ciążela et al., 2018 - GCA).  In the CM1A/2B ultramafic rocks: dunites and harzburgites, most sulfides are, however, secondary, formed by the same secondary fluids which caused the pervasive serpentinization. To verify whether these sulfides replaced the primary magmatic sulfides or were brought from late-stage seawater-derived fluids, we plan to measure sulfur in whole-rocks and in situ and more iron isotopes in sulfides in situ. Preliminary δ56Fe signature isotope data give us evidence for magmatic origin of the sulfides from upper part of the MTZ section.

How to cite: Marciniak, D., Jakub, C., Ana, J., Bartosz, P., Jürgen, K., Harald, S., Marina, L., Ingo, H., Ewa, S., Marta, P., and Konrad, B.: Metal migration and ore minerals across the crust-mantle transition zone (Oman DP ICDP holes CM1A, CM2B), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-517, https://doi.org/10.5194/egusphere-egu22-517, 2022.

EGU22-328 | Presentations | GMPV2.1

New constraints on the origin of metal enrichment at the crust-mantle boundary from the Ivrea-Verbano Zone, NW Italy

Bartosz Pieterek, Jakub Ciążela, Riccardo Tribuzio, Magdalena Matusiak-Małek, Andrzej Muszyński, Harald Strauss, Marina Lazarov, Stefan Weyer, Ingo Horn, Thomas Kuhn, and Izabella Nowak

Copper deposits or sulfide enrichment have been found along the crust-mantle transition zones in ophiolites and along the oceanic Moho. However, scarcity of suitable exposures limits our knowledge on the migration of chalcophile metals across the subcontinental crust-mantle boundary. This study aims to provide new constraints on the migration of sulfide-associated chalcophile metals at the transition between the subcontinental mantle peridotites of the Balmuccia massif and lower crustal gabbronorites of the Mafic Complex (Ivrea-Verbano Zone, NW Italy).

An ~80-m-thick zone composed of interlayered pyroxenites and gabbronorites (Contact Series; CS) showing igneous contact with the mantle peridotites was sampled along the Val Sesia river, near the Isola village. We investigated a transect from the mantle peridotites (rich in pentlandite) through the CS to the lower crustal gabbronorites (rich in pyrrhotite or pyrite). The CS zone comprises three sampling sites located 0–5 m (CS1), 65–70 m, and 75–80 m from the mantle peridotites and is characterized by the along-transect Mg# variations (Mg# of 71–57). The mantle peridotites are sulfide poor (average of 0.12 vol.‰), in contrast to the CS rocks (up to 7.8 vol.‰). The enhanced sulfide abundances in mafic rocks of the CS correlate with higher S, Cu, Ag, and Cd contents. This sulfide- and chalcophile-rich metal zone within the CS ends ~75 m away from the margin of mantle peridotites implying a probable thickness of the enrichment zone. Sulfides from mantle peridotites and CS1 are pyrrhotite-(troilite)-chalcopyrite-(cubanite)-pentlandite assemblages of magmatic origin, which is supported by δ34S ranging from –0.6‰ to +1.8‰ (average of 0.0‰; cf., Oeser et al., 2012 – Chemical Geology).

The in-situ Fe isotope signatures of polyphasic sulfide grains from CS1 show a strong fractionation between the various phases. The δ56Fe values of pyrrhotites are negative ranging from –0.8‰ to 0.0‰, whereas chalcopyrite exhibit positive values of 1.3–1.7‰. The mass balance calculations of the δ56Fe for the bulk composition of the sulfide grains from CS1 show unfractionated (magmatic or mantle) values of 0.0 ± 0.2‰ (cf., Craddock et al., 2013 – EPSL).

The stagnant melts at the crust-mantle boundary extensively react with the mantle yielding enrichment in sulfides and chalcophile elements, which is known to yield enrichment in sulfides (Ciazela et al., 2018 - GCA; Patkó et al., 2021 - Lithos). However, the contact between the Balmuccia mantle peridotites and the lower continental crust of the Mafic Complex is highly heterogeneous with alternating layers of pyroxenites and gabbronorites. These layers may have formed from distinct magma batches as suggested by the along-transect Mg# variations. Therefore, the mechanism of observed enrichment in sulfides and chalcophile elements probably involves several stages of melt-peridotite and melt-pyroxenite reactions. These might explain the exceptionally large ~75-m-thick sulfide-rich horizon observed at the CS. Our results indicate that substantial chalcophile metal inventory is trapped at the CS. Assuming they behave the same at the Moho level, this would explain the relative deficit of these elements in the continental crust when compared its bulk composition to the composition of primitive mantle melts.

This research was funded by the NCN Poland (2018/31/N/ST10/02146)

How to cite: Pieterek, B., Ciążela, J., Tribuzio, R., Matusiak-Małek, M., Muszyński, A., Strauss, H., Lazarov, M., Weyer, S., Horn, I., Kuhn, T., and Nowak, I.: New constraints on the origin of metal enrichment at the crust-mantle boundary from the Ivrea-Verbano Zone, NW Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-328, https://doi.org/10.5194/egusphere-egu22-328, 2022.

EGU22-2217 | Presentations | GMPV2.1

Metal enrichment in refertilized subcontinental lithospheric mantle: insight from the ultramafic xenoliths from the volcanic rocks of the Oku Volcanic Group (Cameroon) 

Hubert Mazurek, Magdalena Matusiak-Małek, Jakub Ciazela, Bartosz Pieterek, Jacek Puziewicz, and Sylvin S.T. Tedonkenfack

Sulfides hosted by peridotites from Befang (Oku Volcanic Group, Cameroon) xenolith suite can play an important role in tracking migration of strategic metals such as Au, Ag, or Cu through the subcontinental lithospheric mantle (SCLM) beneath the Central African Orogenic Belt. Most peridotites are lherzolites, which are subdivided into two main groups differing by crystallographic preferred orientation (CPO) and rare-earth element (REE) composition of clinopyroxene. Group I is characterized by light REE (LREE)-depleted clinopyroxene (re-)crystallized during percolation of metasomatic melt. Group II contains LREE-enriched clinopyroxene with the CPO representing deformation before percolation of the melt (Tedonkenfack et al., 2021). Lherzolites of group I  are interpreted to be metasomatized by MORB-like melts coming from  Depleted MORB Mantle (DMM). Peridotites of  group II are interpreted to be a protolith for the group I ones.

The sulfides form oval to slightly elongated grains enclosed usually in orthopyroxene, or rarely in clinopyroxene and olivine. They are composed of pyrrhotite (Po), pentlandite (Pn), and chalcopyrite (Ccp). Pyrrhotite is mostly predominant, whereas Pn forms exsolution lamellae in Po or massive crystals separating Po from Ccp. Chalcopyrite is present on the rims of grain or penetrates through the entire grain, occasionally containing cubanite exsolutions. The Group I lherzolites contain more sulfides (up to 0.031 vol.‰), with larger grains (range: 14−250 µm, 57 µm on average) compared to the Group II sulfides (up to 0.002 vol.‰, range: 12−45 µm, 27 µm on average respectively). Sulfides from Group I are richer in Po, and especially Ccp (Po77Pn12Ccp11 on average) compared to Group II (Po72Pn23Ccp4 on average). Ni/(Ni+Fe) in pyrrhotite from Group I (0.14–0.43) is more heterogeneous compared to group II (0.20–0.37).

Enrichment in Po and Ccp in the Befang Group I xenoliths suggests a significant role of melts in transporting sulfur and metals. Observed refertilization by DMM-derived melts may affect the chalcophile and highly siderophile metal budget of the SCLM. The degree of refertilizaton seems to depend on temperature and therefore is moderate in Befang (up to 0.031 vol.‰) with moderate temperatures of orthopyroxene-clinopyroxene equilibration (938–997°C; Tedonkenfack et al, 2021). In lower temperatures of Opx-Cpx equilibration (810–970°C), we observe higher sulfide abundances (up to 0.062 vol.‰), whereas in higher temperatures (1010–1120°C) lower sulfide abundances (up to 0.00048 vol.‰; Mazurek et al., 2021).

 

This study was supported by the Diamond Grant project 093/DIA/2020/49.

 

References

Mazurek, H., Ciazela, J., Matusiak-Małek, M., Pieterek, B., Puziewicz, J., Lazarov, M., Horn, I., Ntaflos, T.: Metal enrichment as a result of SCLM metasomatism? Insight from ultramafic xenoliths from SW Poland., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15992, https://doi.org/10.5194/egusphere-egu21-15992, 2021

Tedonkenfack SST., Puziewicz J., Aulbach S., Ntaflos T., Kaczmarek M-A., Matusiak-Małek M., Kukuła A., Ziobro M.: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Contributions to Mineralogy and Petrology, 176: 37.

How to cite: Mazurek, H., Matusiak-Małek, M., Ciazela, J., Pieterek, B., Puziewicz, J., and Tedonkenfack, S. S. T.: Metal enrichment in refertilized subcontinental lithospheric mantle: insight from the ultramafic xenoliths from the volcanic rocks of the Oku Volcanic Group (Cameroon) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2217, https://doi.org/10.5194/egusphere-egu22-2217, 2022.

EGU22-6901 | Presentations | GMPV2.1

Melt metasomatism and enrichment in metals in the uppermost Earth’s mantle

Jakub Ciazela, Bartosz Pieterek, Dariusz Marciniak, Hubert Mazurek, Levente Patko, and Ewa Slaby

Cu-rich sulfide deposits of economic importance in ophiolites such as Troodos in Cyprus or Semail in Oman often occur along the crust-mantle transition zones (e.g. Begemann et al., 2010). Although secondary sulfides formed during serpentiniztion now prevail, the relicts of primary magmatic sulfides indicate the igneous nature of enrichment in sulfides at the oceanic Moho level. Crust-mantle transition zones in situ in the oceans are suggested to be enriched in sulfides and many chalcophile (e.g. Cu, Zn, Pb, Se, Te) metals via melt-mantle reaction (Ciazela et al., 2017; 2018). The enrichment in sulfides seems to be ubiquitous along the crust-mantle transition zone (Ciazela et al., 2018) and might be expected even at the continental Moho. This is possible as sulfides precipitate during melt-mantle reaction independently on pressure. The process seems to work at low pressures of the oceanic crust-mantle transition zone (0.1–0.2 GPa) (Marciniak et al., this session; Ciazela et al., 2018), medium pressures of the continental crust-mantle transition zone (~1.0 GPa) (Pieterek et al., this session), and in high pressures related to various melt-metasomatized mantle xenoliths (up to 2.5 GPa) (Mazurek et al., this session; Patkó et al., 2021). Metal refertilization due to variable melt-peridotite reactions at the crust-mantle transition zone and along melt channels in the upper mantle may affect the local, regional, and even global metal mass balance of the oceanic and continental lithosphere. The distribution of mantle sulfides is heterogeneous. The zones of enrichment in metals occur mostly at the crust-mantle transition or in melt-modified mantle rocks along melt channels in the upper mantle. These zones are important for subsequent ore formation in secondary processes. In the oceans, especially along slow-spreading ridges, shallow magmatic sulfide horizons are penetrated by hydrothermal fluids operating along faults to form massive sulfides on the seafloor. On land, the re-mobilization of the mantle sulfides horizons by sulfide-undersaturated melts or by buoyant CO2 bubbles can contribute to the formation of porphyry and related epithermal mineral deposits.

Begemann F., Hauptmann A., Schmitt-Strecker S. and Weisgerber G. (2010) Lead isotope and chemical signature of copper from Oman and its occurrence in Mesopotamia and sites on the Arabian Gulf coast. Arab. Archaeol. Epigr. 21, 135–169.

Ciazela J., Dick H. J. B., Koepke J., Pieterek B., Muszynski A., Botcharnikov R. and Kuhn T. (2017) Thin crust and exposed mantle control sulfide differentiation in slow-spreading ridge magmas. Geology 45, 935–938.

Ciazela J., Koepke J., Dick H. J. B., Botcharnikov R., Muszynski A., Lazarov M., Schuth S., Pieterek B. and Kuhn T. (2018) Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR). Geochim. Cosmochim. Acta 230, 155–189.

Patkó L., Ciazela J., Aradi L. E., Liptai N., Pieterek B., Berkesi M., Lazarov M., Kovács I. J., Holtz F. and Szabó C. (2021) Iron isotope and trace metal variations during mantle metasomatism: In situ study on sulfide minerals from peridotite xenoliths from Nógrád-Gömör Volcanic Field (Northern Pannonian Basin). Lithos 396397, 106238.

How to cite: Ciazela, J., Pieterek, B., Marciniak, D., Mazurek, H., Patko, L., and Slaby, E.: Melt metasomatism and enrichment in metals in the uppermost Earth’s mantle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6901, https://doi.org/10.5194/egusphere-egu22-6901, 2022.

The Mirdita Ophiolite in northern Albania forms a ~240 km long and ~40 km wide zone within Dinaric-Hellenic belt. It marks suture after Neo-Tethyan Ocean closure. The chemical diversity of volcanic crustal rocks led to its division into two zones: the eastern one is interpreted to have Supra-Subduction Zone (SSZ) origin, whereas the western zone exhibits Mid-Ocean Ridge (MOR) affinity. More than a dozen of ultramafic massifs occur along the entire length of the ophiolite.

In this study we focus on chemical diversity of peridotites from two adjacent massifs, Kukes and Puka, which have SSZ and MOR affinities, respectively. The Kukes Massif is composed of a sequence from harzburgites at its base to clinopyroxene-poor dunites at the top, followed by pyroxenitic and peridotitic cumulates at the mantle/crust transition zone. The Puka massif is a mantle dome, composed of harzburgites and plagioclase/amphibole lherzolites (locally mylonitzed) and it is interpreted as a former oceanic core complex (OCC; Nicolas et al. 2017). Both massifs are pervasively penetrated by pyroxenitic and gabbroic veins and are serpentinised to variable degree.

Chemical composition of minerals varies between samples and lithologies, as well as between massifs. Olivine from the Kukes harzburgites has higher Fo values and NiO contents than that from dunites (Fo89.5-92 and NiO 0.31-0.52 wt.% vs. Fo88.1-91.2 and NiO 0.15-0.30 wt.%, respectively). Clinopyroxene has Mg#92.5-95.1 and Al=0.03-0.08 apfu in harzburgite, while interstitial dunite clinopyroxene has Mg#94-98 and Al below 0.03 apfu. Harzburgite orthopyroxene has Mg#90.1-91.8 and Al=0.03-0.08 apfu. Chromian-spinel has Cr#0.55-0.72 and Mg#0.46-0.56 in harzburgites and Cr#0.63-0.86 and Mg#0.25-0.48 in dunites, moreover in dunites it often exhibits chemical zonation with Cr# increasing to core. Chemical composition of minerals changes gradually in the scale of single outcrop, with Fe content increasing toward veins.

The Puka peridotites have more enriched composition. Olivine has Fo87.8-90.8 and NiO=0.25-0.43 wt. %, clinopyroxene has Mg#90.1-93.3 and Al=0.05-0.15 apfu, orthopyroxene has Mg#88.5-91.0 and Al=0.03-0.1 apfu, while spinel has Cr#0.38-0.55 and Mg#0.42-0.57, with single sample of Cr#0.60-0.75 and Mg#0.33-0.52. Plagioclase is Ca-rich (77-95 An), amphibole – occurring in some lherzolites – has composition of pargasite-tremolite.

Differences in lithological and chemical composition are visible between peridotites from both massifs, which correspond with diversity of crustal rocks and suggest that also mantle sections of the ophiolite record different origin. Peridotites from Kukes are harzburgites and dunites pointing to their refractory nature. The depleted peridotites were further affected by intensive magmatic veining. Infiltration of the melt triggered gradual enrichment in Fe of the silicates and chemical zonation of spinel. This process is well visible in dunites, where changes of Fe contents can be followed on distances of few meters. As metasomatic modification has a limited range, most of chemical differences have to be related with different protolith, but further studies are required to reconstruct rocks evolution.

Protolith of Puka peridotites is more fertile compared with Kukes, but reaction between veins and host lherzolite was not observed, and mylonitization led to Al depletion in pyroxenes.

This study was financed from scientific funds for years 2018-2022 as a project within program “Diamond Grant” (DI024748).

How to cite: Mikrut, J., Matusiak-Małek, M., and Puziewicz, J.: Preliminary insights into lithological and chemical diversity in Mirdita Ophiolite peridotite massifs – Kukes and Puka case studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9560, https://doi.org/10.5194/egusphere-egu22-9560, 2022.

EGU22-13175 | Presentations | GMPV2.1

Xenolith-based thermal and compositional lithospheric mantle profile of the central Siberian craton

Dmitri Ionov, Zhe Liu, Paolo Nimis, Yigang Xu, and Alexander V. Golowin

Many aspects of structure and thermal state of >200 km thick cratonic lithospheric mantle (CLM) remain unclear because of insufficient sampling and uncertainties of pressure (P) and temperature (T) estimates. An exceptionally detailed record of equilibration temperature and composition for the central Siberian craton in the 60–230 km depth range was obtained using new and published petrographic and in-situ chemical data for ~200 garnet peridotite xenoliths from the Udachnaya kimberlite. The thermal profile is complex with samples between 35 and 40 mW/m2 model conductive geotherms as well as hotter layers in the middle and at the base (190–230 km) of the CLM. A previously unknown mid-lithospheric zone includes rocks up to 150° hotter than ambient geotherm, with high modal garnet and cpx, low-Mg# and melt-equilibrated REE patterns. We posit that hot domains with enriched compositions may form at depths where ascending melts stall (e.g., due to loss of volatiles and/or redox change) and react with wall-rock harzburgites. By contrast, we find no rocks rich in volatile-rich metasomatic amphibole, mica or carbonate, nor layers composed of peridotites with distinct melt-extraction degrees. The CLM base contains both coarse and variably deformed rocks heated and re-worked (Mg#Ol down to 0.86) by localized interaction with asthenospheric melts.

How to cite: Ionov, D., Liu, Z., Nimis, P., Xu, Y., and Golowin, A. V.: Xenolith-based thermal and compositional lithospheric mantle profile of the central Siberian craton, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13175, https://doi.org/10.5194/egusphere-egu22-13175, 2022.

Uncommon Ba-Cl-rich phases including Ba-Cl micas and Cl-phosphates have been found in garnet pyroxenites as a part of the matrix or in polyphase inclusions in garnets. Polyphase inclusions are rich in carbonates (dolomite, magnesite, norshetite), phosphates (Cl-apatite, goryainovite (Ca2PO4Cl), monazite) and other silicates (spinel, amphibole, orthopyroxene, clinopyroxene, margarite, aspidolite, scapolite, cordierite). The inclusions appear as chains crosscutting garnet crystals and their presence is not linked with any chemical zoning in the host garnet.

The Ba-Cl-rich mica has composition ranging from Ba-rich phlogopite to chloroferrokinoshitalite and to oxykinoshitalite. The mica present in the matrix correspond to Ba-rich phlogopite with low Cl contents and occur together with celsian and low-Cl hydroxyl apatite. The mica in the polyphase inclusions ranges to almost pure chloroferrokinoshitalite and oxykinoshitalite endmembers and coexists either with Cl-apatite (Cl = 1.2 apfu) or rarely goryainovite containing up to 2.5 wt% of SrO. This is second world occurrence of goryainovite and first evidence that Ca can be partially replaced by Sr in this mineral.

Special attention was paid to the composition trends of the Ba-Cl-rich micas. These are mainly related to the XFe ratio, which correlates positively with Cl, Ba, and Al and negatively with Si and Na. Positive correlation of Cl with Ba and XFe leads to the formation of mica with composition Ba0.95K0.03Fe2.69Mg0.37Al1.91Si2.02Cl1.98, XFe0.88, which is the most Cl-rich mica so far described from natural samples (10.98 wt% Cl) and is very close to the theoretical formula of chloroferrokinoshitalite BaFe3Al2Si2O10Cl2. The positive correlation of Ba with Al and their negative correlation with Si and K is corresponding to the coupled substitution Ba1Al1K-1Si-1 linking the composition of phlogopite and kinoshitalite. Composition trend related with the Ti-content shows that Ti correlates positively with Ba but negatively with Cl, XFe, and with the sum of Mg and Fe. It implies that Ti is incorporated into mica in coordination with O (Ti1O2(Mg,Fe2+)-1(OH)-2) and it leads to the formation of oxykinoshitalite (BaMg2TiSi2Al2O12). Since the incorporation of either Cl or Ti + O correlates with XFe content of mica, XFe ratio can be the crucial factor controlling the ability of mica to incorporate Cl into its crystal lattice. In some cases, two micas with contrasting composition corresponding closer to chloroferrokinoshitalite or oxykinoshitalite coexist in one polyphase inclusion, demonstrated by distinct content of XFe, Ti and Cl (for example: XFe0.20:0.77, Ba0.48:0.63, Ti0.35:0.02, Cl0.27:1.45). This could imply the existence of an immiscibility between the composition trends of chloroferrokinoshitalite and oxykinoshitalite .

Such Ba, Cl and K-rich phases are atypical for garnet pyroxenite. Their presence may be caused by the injection of fluid/melt of crustal source during subduction and subsequent exhumation processes or may be related to earlier mantle metasomatism. The presence of Cl-rich phases together with carbonates indicates extremely high activity of Cl and CO2 in the metasomatizing fluid/melt that interacted with garnet pyroxenites.

How to cite: Zelinková, T., Racek, M., and Abart, R.: Compositions of Ba-Cl-rich micas and other uncommon phases related to metasomatism of garnet pyroxenite (Gföhl unit of the Moldanubian Domain, Bohemian Massif), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7935, https://doi.org/10.5194/egusphere-egu22-7935, 2022.

EGU22-1865 | Presentations | GMPV2.1

Preliminary data on mantle xenoliths from the Wum maar, Oku Volcanic Group, Cameroon Volcanic Line (West Africa)

Jacek Puziewicz, Sonja Aulbach, Mary-Alix Kaczmarek, Anna Kukuła, Theodoros Ntaflos, Magdalena Matusiak-Małek, Sylvin S. T. Tedonkenfack, and Małgorzata Ziobro-Mikrut

The Wum maar is located in the Oku Volcanic group, part of continental sector of the Cameroon Volcanic Line (CVL) in west Africa, which consists of volcanoes active from Eocene to recent. The continental part of the CVL is located on the metamorphic-igneous basement of the Neoproterozoic Central African Orogenic Belt (CAOB), which originated during Gondwana assembly. Some of the CVL lavas contain spinel-facies peridotite and pyroxenite xenoliths giving insight into the mantle lithosphere underlying the CAOB.

We studied xenolith suite (19 xenoliths) from the Wum maar, comprising 14 lherzolites and 5 websterites. The half of lherzolites (7) consist of minerals with fertile composition (olivine Fo89, orthopyroxene Al 0.16-0.19 atoms per formula unit, clinopyroxene Al 0.28-0.31 a pfu, spinel Cr# 0.08-0.13). Clinopyroxene is REE-depleted and has 87Sr/86Sr ratios of 0.7017-0.7021. A reconnaissance study of crystal preferred orientation (CPO) by EBSD shows that at least in part of the rocks the clinopyroxene fabric is very weak, suggesting that its crystallization post-dates the primary deformation event recorded by the olivine-orthopyroxene framework. A smaller part of lherzolites (5) contains clinopyroxene the CPO of which fits that of the olivine-orthopyroxene framework, is LREE-enriched and has 87Sr/86Sr ratios of 0.7027-0.7028. One of these lherzolites contains amphibole (pargasite), which forms aggregates and schlieren and texturally is later than olivine-pyroxene host. CPO of amphibole, ortho- and clinopyroxene is decoupled from that of olivine in that rock. Two lherzolites have slightly depleted mineral compositions (olivine Fo90-91, orthopyroxene Al 0.15 apfu, clinopyroxene Al 0.25 a pfu, spinel Cr# 0.18).

Websterites are dominated by orthopyroxene (Al 0.20-0.21 a pfu) whereas clinopyroxene (Al 0.30-0.31) is subordinate, and is characterized by LREE-depletion and 87Sr/86Sr ratios of 0.7019-0.7020. Spinel occurring in websterites is aluminous (Cr# 0.04-0.06), in some samples subordinate olivine (Fo90) occurs. One of the xenoliths consists of millimetric monomineral layers of pyroxenes and olivine chemically identical to those occurring in websterites.  

The mineral chemical data coupled with mineral fabrics suggest that lherzolites with LREE-depleted clinopyroxene could have originated by late crystallization caused by melt metasomatism. The metasomatic agent is probably best represented by websterites, which contain LREE-depleted clinopyroxene with similar, depleted 87Sr/86Sr of 0.7019-0.7020 (compare to DM value of 0.7026, Workman and Hart 2005), confirming earlier findings of refertilization of the regional lithospheric mantle by highly depleted melts (Tedonkenfack et al. 2021). The addition of amphibole was connected with recrystallization of ortho- and clinopyroxene and with significant change of its 87Sr/86Sr signature to more radiogenic values.

Funding. This study originated thanks to the project of Polish National Centre of Research NCN 2017/27/B/ST10/00365 to JP. The bilateral Austrian-Polish project WTZ PL 08/2018 enabled extensive microprobe work.

References:

Tedonkenfack SST, Puziewicz J, Aulbach S, Ntaflos T., Kaczmarek M-A, Matusiak-Małek M, Kukuła A, Ziobro M: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Contributions to Mineralogy and Petrology 176: 37.

Workman RK, Hart SR (2005) Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231: 53-72.

How to cite: Puziewicz, J., Aulbach, S., Kaczmarek, M.-A., Kukuła, A., Ntaflos, T., Matusiak-Małek, M., Tedonkenfack, S. S. T., and Ziobro-Mikrut, M.: Preliminary data on mantle xenoliths from the Wum maar, Oku Volcanic Group, Cameroon Volcanic Line (West Africa), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1865, https://doi.org/10.5194/egusphere-egu22-1865, 2022.

EGU22-4351 | Presentations | GMPV2.1

Preliminary characteristics of mantle xenoliths from Mt. Briançon (Massif Central, France) - missing information about the lithospheric mantle beneath Devès volcanic field

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

The 3.5-0.5 Ma Devès volcanic field consists mainly of nepheline basanite rocks. The underlying Variscan basement is a part of the western Moldanubian Zone (an allochton of the European Variscan orogen, probably the Gondwana margin). The Devès volcanic field is located in the “southern” mantle domain of Massif Central (MC), which consists of fertile lithospheric mantle (LM) little affected by partial melting [1]. These characteristics probably resulted from intense metasomatism by melts coming from the upwelling asthenosphere [2].

Despite the rich literature dealing with the LM beneath the Devès volcanic field, some textural and geochemical details remain obscure. We studied a large xenolith population (n – 21) from Mt.Briançon (NW of the Devès volcanic field) with extensive use of EMPA and LA-ICP-MS in order to obtain a comprehensive and representative data set, and here present the preliminary findings.

The Mt.Briançon xenoliths are typically oval in shape and vary in size from 4 to 13 cm. The host rocks are tuff and scoria deposits. The xenoliths are mostly anhydrous spinel lherzolites rich in clinopyroxene (cpx, modal content up to 28%) and scarce harzburgites. One xenolith consists of olivine clinopyroxenite in contact with peridotite. The peridotites exhibit serial texture or different stages of porphyroclastic texture. In some xenoliths elongated spinel is arranged in streaks.

Most of the three major phases in the peridotites are homogenous at the grain and xenolith scale. Olivine Fo is typically 88.5-90.4% in the whole suite, and NiO content is 0.35-0.43 wt.%. Orthopyroxene (opx) has Mg# 0.89-0.91 and 0.128-0.217 atoms of Al per formula unit (apfu). Cpx has Mg# 0.88-0.91 and Al content of 0.208-0.316 apfu and spinel Cr# is highly variable in the whole suite (0.09-0.28). In contrast, one harzburgite (sample 4025) has olivine with higher Fo (~91.2%), opx with higher Mg# (~0.92) and lower Al content (0.111-0.116 apfu), cpx with Mg# ~0.92 and Al content of ~0.145 apfu, and spinel Cr# of ~0.43 and Mg# of ~0.75.

The main observed REE pattern in peridotite cpx is relatively flat Lu-Eu and slightly, but variably depleted in lighter REE. In several xenoliths cpx exhibits various REE patterns, transitioning from LREE-depleted to relatively flat or slightly LREE-enriched, while a few samples contain cpx with REE abundances moderately increasing Lu-Sm and steeply increasing towards La. The majority of peridotite opx REE patterns are moderately decreasing in Lu-Sm and more steeply decreasing towards La, whereas a less common opx pattern is similar to the previous one in Lu-Nd, but much less depleted in lighter REE. This opx coexists with LREE-rich cpx.

This study confirms that the LM beneath Mt.Briançon is mostly lherzolitic and quite fertile in terms of major elements. Ongoing work, utilizing the diversity of lithologies and pyroxene REE patterns, combined with detailed major-element and REE thermometry and with textural observations, will provide detailed insights into the microstructural, thermal and metasomatic history of the LM beneath the MC.

 

This study was funded by Polish National Science Centre to MZM (UMO-2018/29/N/ST10/00259).

 

References

[1] Uenver-Thiele L. et al. (2017). JPetrol 58, 395–422.

[2] Puziewicz J. et al. (2020). Lithos 362–363, 105467.

How to cite: Ziobro-Mikrut, M., Puziewicz, J., Aulbach, S., Ntaflos, T., and Matusiak-Małek, M.: Preliminary characteristics of mantle xenoliths from Mt. Briançon (Massif Central, France) - missing information about the lithospheric mantle beneath Devès volcanic field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4351, https://doi.org/10.5194/egusphere-egu22-4351, 2022.

EGU22-5617 | Presentations | GMPV2.1

Kilometre-scale isotopic heterogeneity in abyssal peridotites from the Doldrums Fracture Zone (Mid Atlantic Ridge, 7-8ºN).

Camilla Sani, Alessio Sanfilippo, Alexander A. Payve, Felix Genske, and Andreas Stracke

In Nd-Hf isotopic space the great majority of the global abyssal peridotites plot in the field defined by global MORBs. However, Hf isotope ratios by far exceeding those in ridge basalts, are locally observed in abyssal peridotites showing that the Earth’s mantle is more heterogeneous that inferred from ridge basalts [1]. Mantle peridotites exposed at the Doldrums Fracture Zone at the Mid Atlantic Ridge (7-8° N) reveal that such heterogeneity coexists on a kilometre-scale. Abyssal peridotites from the northern part of the Doldrums FZ domain can be grouped into residual peridotites and melt-modified (refertilized) samples [2]. New Nd-Hf isotopic data show that the refertilized peridotites preserve highly radiogenic Hf values (εHf up to 101) associated with MORB-like Nd isotopes (εNd up to 12), reflecting partial resetting of ancient highly depleted mantle by recent melt-rock interaction. On the other hand, despite a very depleted incompatible element compositions, the residual peridotites have Nd-Hf isotope ratios similar to the local MORB (εNd = 7-12 and εHf =12-19). They most likely reflect highly depleted mantle that has been entirely reset by reaction with extracted or retained melts, and hence developed with only modest incompatible element depletion until recent melting at the Mid Atlantic ridge axis, which led the strong incompatible element depleted of these peridotites. The kilometre-scale association of such isotopically heterogeneous domains suggests that the upper mantle exposed in this portion of Atlantic formed by a combination of ancient melting and melt-rock reaction processes, preceding its emplacement below the present-day Mid Atlantic ridge axis.

 [1] Stracke, A., et al., 2011. Abyssal peridotite Hf isotopes identify extreme mantle depletion. Earth and Planetary Science Letters, 308(3-4), pp.359-368. [2] Sani, C., et al., 2020. Ultra-depleted melt refertilization of mantle peridotites in a large intra-transform domain (Doldrums Fracture Zone; 7–8° N, Mid Atlantic Ridge). Lithos, 374, p.105698.

How to cite: Sani, C., Sanfilippo, A., Payve, A. A., Genske, F., and Stracke, A.: Kilometre-scale isotopic heterogeneity in abyssal peridotites from the Doldrums Fracture Zone (Mid Atlantic Ridge, 7-8ºN)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5617, https://doi.org/10.5194/egusphere-egu22-5617, 2022.

EGU22-5414 | Presentations | GMPV2.1

Magmatic processes at rifted margins: Preliminary results from peridotites of the Diamantina zone (SW Australia)

Mélanie Ballay, Marc Ulrich, and Gianreto Manatschal

Keywords: magma-poor rifted margin, refertilization, partial melting, mantle-melt interaction

Although magmatic processes are of primary importance for the understanding of lithospheric breakup, many first order questions remain, such as: how, when, where and how much magma is produced during final rifting; what are the conditions and controlling processes of magma production; how does magma percolate and interact with the lithospheric mantle; and how and when does magma focus, how is it extracted and how does it interact with the extensional processes during final rifting and breakup? Answering to these questions is a prerequisite to understand lithospheric breakup and formation of a new plate boundary, which is among the least understood plate tectonic processes at present.

In this study we present preliminary petrological results from mantle rocks dredged from the SW Australia ocean-continent transition (OCT, Diamantina zone). We analyzed pyroxene and spinel compositions from these peridotites to identify mantle domains and mantle-melt reactions during rifting and breakup. The chemical composition of clinopyroxenes shows two distinct populations: a first generation characterized by low (Sm/Yb)N ratios and no Eu anomalies, while a second generation shows interstitial textures and flat HREE patterns with a deep negative Eu anomaly. These two populations of clinopyroxenes suggest that the peridotites from the Diamantina zone record two distinct events: a first cooling event that is followed by magma infiltration. This is further supported by equilibrium temperatures calculated on the two clinopyroxene generations showing that the first population equilibrated at lower temperatures (900°C ± 30°C) corresponding to a subcontinental geotherm, while the second generation equilibrated at higher temperatures (1100°C ± 100°C), and was likely liked to the entrapment of MORB-type melts in the plagioclase stability field at low pressure (~5kbar) during magma infiltration.  

The exhumation path of the Diamantina peridotites determined in our study is similar to those of refertilized peridotites from the present-day Iberia and fossil Alpine Tethys OCTs, suggesting that refertilisation processes occurring at magma-poor rifted margins during final rifting and breakup are not dependent from the inherited nature of the subcontinental mantle.

How to cite: Ballay, M., Ulrich, M., and Manatschal, G.: Magmatic processes at rifted margins: Preliminary results from peridotites of the Diamantina zone (SW Australia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5414, https://doi.org/10.5194/egusphere-egu22-5414, 2022.

EGU22-9331 | Presentations | GMPV2.1

Mantle metasomatism recorded upon bimodal chromitites (E. Chalkidiki, Greece): a tool to unravel metasomatic processes

Petros Koutsovitis, Alkiviadis Sideridis, Pavlos Tsitsanis, Federica Zaccarini, Basilios Tsikouras, Christoph Hauzenberger, Tassos Grammatikopoulos, Luca Bindi, Giorgio Garuti, and Konstantin Hatzipanagiotou

Nea Roda and Gomati ultramafic bodies (east Chalkidiki, north Greece) consist of both Cr- and Al- podiform chromitites, which are highly altered. Their PGE geochemistry and subsequently PGE-mineralogy (PGM) demonstrate abnormal element concentrations with an enrichment in PPGE (Pd, Pt), leading to high Pd/Ir ratios. Secondary PGM and base metal assemblages are dominated by Sb and As, whereas primary phases form sulphides. At a more mature stage, desulphurization of the aforementioned phases led to formation of native metals. Diopside hosted within diopsidite and chromitite show both an alkaline melt- and a fluid- rock interaction, depicted by LREE enrichment. The temperature of the metasomatic fluids was lower than 600oC, as recorded by chlorite and garnet geothermometry. A raise in fluid mobile elements (FME: B, Sb, Li, As, Cs, Pb, U, Ba and Sr) is noted in the whole rock and clinopyroxene analysis. All these characteristics along with the distinctive spinel textures (porous, zoned grains) point to a metasomatic event during subduction that led to the post-magmatic modification of the chromitites and the mantle section causing a LREE, Pb, As, Sb, Pd and Pt enrichment. 

How to cite: Koutsovitis, P., Sideridis, A., Tsitsanis, P., Zaccarini, F., Tsikouras, B., Hauzenberger, C., Grammatikopoulos, T., Bindi, L., Garuti, G., and Hatzipanagiotou, K.: Mantle metasomatism recorded upon bimodal chromitites (E. Chalkidiki, Greece): a tool to unravel metasomatic processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9331, https://doi.org/10.5194/egusphere-egu22-9331, 2022.

EGU22-3865 | Presentations | GMPV2.1

Formation of corona structures from the troctolitic gabbros of Chainigund, Kargil, Ladakh, NW Himalayas, India: Petrological implications

Shivani Harshe, Mallika Jonnalagadda, Raymond Duraiswami, Mathieu Benoit, Michel Grégoire, and Nitin Karmalkar

Well-developed corona structures are observed and described in detail in the cumulate troctolites from Chainigund village, Kargil. The gabbro-troctolite unit is situated 5 km NW of Kargil city and consists of gabbros, troctolites, and anorthosites with doleritic dykes cross-cutting the unit at places. The host gabbros are fresh and display both fine and coarse-grained varieties. Troctolites occur as pods and veins within the gabbro and are composed of plagioclase (77-80 vol%), olivine (10-16 vol%), pleonaste spinel (6-8 vol%), amphiboles (2 -3 vol%) and opaques (0.5-2vol %). Both olivines and plagioclases are unzoned with spectacular coronas around the olivines (Fo 74.9-76.7) at the contact with plagioclase feldspar (An90.6-95.2). From center outwards, the discontinuous reaction series consists of the following members: Olivine, enstatitic orthopyroxene, magnesio-hornblende (Amph1) enclosed by a symplectitic rim of pargasite (Amph2) and pleonaste spinel and concludes at the plagioclase interface i.e. Ol-Opx-Amph1-Amph2-Spl-Plg. The mineral textures of the corona structure indicate formation in the presence of an interstitial fluid trapped between cumulus olivine and plagioclase. The reaction of this fluid with the olivine resulted in a rim of peritectic orthopyroxene around olivine which was subsequently replaced to form Amph 1 between the orthopyroxene and plagioclase. This is evident by the horse-shoe shaped outline and intermingling boundary shared by orthopyroxene and Amph 1. The formation of outer Amph 2 and spinel symplectite layers could be attributed to the replacement of precursor clinopyroxene and plagioclase at high temperatures (1050-1150° C ± 40° C). The Amph-Spl symplectites, presence of oxidizing conditions (magnetite and ilmenite), discontinuous reactions and local or short-range diffusion phenomena thus indicate that the corona structures are a result of metasomatic interaction of cooling magma with the previously formed minerals.

Keywords: Corona structures; troctolite gabbro; olivine- plagioclase contact; Kargil; Ladakh; India.

How to cite: Harshe, S., Jonnalagadda, M., Duraiswami, R., Benoit, M., Grégoire, M., and Karmalkar, N.: Formation of corona structures from the troctolitic gabbros of Chainigund, Kargil, Ladakh, NW Himalayas, India: Petrological implications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3865, https://doi.org/10.5194/egusphere-egu22-3865, 2022.

EGU22-199 | Presentations | GMPV2.1

Evaluation of elastic geobarometry of spinel inclusions in olivine and its application to mantle xenoliths

Yuuki Hagiwara, Ross Angel, Mattia Gilio, Junji Yamamoto, and Matteo Alvaro

The determination of the pressure and temperature (P-T) history experienced by mantle xenoliths, especially the pressure, is essential for elucidating the physicochemical layering structure of the uppermost mantle. However, the lack of continuous reactions between solid solution minerals with large volume changes in spinel-lherzolites makes it difficult to apply conventional geobarometry based on mineral chemistry. Here, elastic geobarometry (Angel et al., 2014; Angel et al., 2017), a complementary technique for determining equilibrium P-T conditions of rocks, was applied to spinel inclusions in olivine in a spinel-lherzolite xenolith.

To utilize elastic geobarometry, reliable equations of state (EoS) for the host mineral and inclusion are essential. Although the EoS for mantle olivine is well constrained by Angel et al. (2018), detailed studies on the EoS for spinel are scarce. Therefore, we firstly conducted a comprehensive review of previous studies investigating the temperature and/or pressure dependence of volume, bulk modulus, and heat capacity, and then determined the EoS for end member spinel using EoSfit7c (Milani et al., 2017).

Next, using Raman spectroscopy, we attempted to estimate the residual pressure of spinel inclusions (Pinc) trapped in olivine in a mantle xenolith from Ennokentiev, Sikhote-Alin, Far Eastern Russia (see Yamamoto et al. (2012) for the chemical composition of the sample). As a result, the peaks of the spinel inclusions were always shifted to higher wavenumbers than those of the unstrained reference spinel crystal from the same xenolith, but only Eg (~410 cm-1) and A1g (~750 cm-1) peak positions could be measured with sufficient accuracy for quantitative analysis of residual pressure. When Pinc was estimated using relation between spinel peak position and pressure reported by Chopelas and Hofmeister (1991), the data obtained from the center of the inclusion showed positive Pinc from both A1g and Eg peaks, and they agreed within error. However, it is desirable to use the A1g peak for the calculation of Pinc because 1) the Eg peak has low Raman scattering intensity, 2) depending on the crystal orientation of the host olivine, the Eg peak of spinel could interfere with the B3g peak of olivine, and 3) the Eg peak is expected to be sensitive to the differential stress because the Pinc calculated from the Eg peak obtained from the edge of the inclusion is unusually higher than that calculated from the A1g peak. Since positive residual pressures were obtained from all the inclusions investigated, by combining the EoS of spinel constrained in this study and measured Pinc, spinel inclusions trapped in olivine can be expected to be a new method for estimating the depth provenance of spinel-bearing peridotite.

 

References

Angel et al. (2014) Am Mineral, 99, 2146-2149; Angel et al. (2017) Am Mineral, 102, 1957-1960; Angel et al. (2018) Phys Chem Miner, 45, 95-113, Chopelas and Hofmeister (1991) Phys Chem Miner, 18, 279-293; Milani et al. (2017) Am Mineral, 102, 851-859; Yamamoto et al. (2012) Tectonophysics, 554-557, 74-82.

How to cite: Hagiwara, Y., Angel, R., Gilio, M., Yamamoto, J., and Alvaro, M.: Evaluation of elastic geobarometry of spinel inclusions in olivine and its application to mantle xenoliths, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-199, https://doi.org/10.5194/egusphere-egu22-199, 2022.

EGU22-9457 | Presentations | GMPV2.1

Composition of lithospheric mantle beneath southern margin of East European Craton evidenced by peridotitic xenoliths from Scania, S Sweden.

Magdalena Matusiak-Małek, Jakub Mikrut, Jacek Puziewicz, Anna Kukuła, Theodoros Ntaflos, Sonja Aulbach, Leif Johansson, and Michél Grégoire

Southern Sweden (Scania region) is located in the peripherical parts of the East European Craton (EEC). In the Mesozoic, up to three pulses of volcanic activity took place between 191 and 110 Ma (Bergelin et al., 2006, IJES; Tappe et al., 2016, GCA). Some of the alkali basaltoids carry ultramafic, mafic and felsic xenoliths (Rehfeldt et al, 2007, IJES). In this study, we focused on the evolution of the lithospheric mantle sampled by anhydrous, spinel-facies lherzolites, harzburgites, and subordinate dunites.

Based on the Fo content in olivine, the peridotites were classified into three groups. Group X peridotites are characterized by Ca-rich olivine (890-1470 ppm) with Fo=91.1-91.7.  Enstatite has Mg#=91.5-91.9 and Al=0.16-0.22 atoms per formula unit (apfu), while the Cr-augite has Mg#= 90.8-91.2 and Al=0.21-0.28 apfu. Clinopyroxene is chemically homogenous in terms of trace elements and is LREE-enriched with positive Eu-anomaly. The Nd and Sr isotopic ratios in clinopyroxene are 143Nd/144Nd=0.512548 (εNd=2.63) and  87Sr/86Sr=0.704237, respectively. Olivine in group Y peridotites is Ca-poor (<951 ppm) and has Fo=89.5-91.1, enstatite has Mg#=89.7-91.7, and Al content of 0.084-0.169 apfu. The Cr-diopside has Mg#=90.8-93.5 and Al=0.118-0.232 apfu. Trace element patterns in clinopyroxene allow subdivision of this group into two subgroups: subgroup Y1 – with heterogeneous LREE-enriched clinopyroxene, and subgroup Y2 – with homogenous LREE-enriched clinopyroxene; both groups are characterized by a positive Eu anomaly, but in subgroup Y1 it is significantly more pronounced. The Nd and Sr isotopic ratios in clinopyroxene from subgroup Y1 are 143Nd/144Nd=0.512624–0.512644 (εNd=4.13-4.52) and 87Sr/86Sr=0.703027–0.703100, therefore significantly more depleted than group X. In group Z peridotite the Fo content in olivine is 88.1-89.1, the Mg# in enstatite is 89.1-89.5 and its Al content is 0.19-0.20 apfu. The Mg# of Cr-diopside is 88.5-89.4 and the Al content is 0.24-0.25 apfu. The trace elements contents in clinopyroxene is homogenous and the REE pattern is flat at values double that in the primitive mantle.         

 The highest equilibration temperatures were estimated for the group X xenoliths, where TWES=1101-1110 °C (Witt-Eickschen and Seck, 1991, CMP) and TBK=1214-1241 °C (Brey and Köhler, 1990, JoP).  The temperatures calculated for group Y xenoliths are TWES=875-1033 °C and TBK=872-1027 °C and do not significantly differ between subgroups. Temperatures recorded by the group Z sample are TWES=1040-1056 °C and TBK=1065-1081 °C.

The composition of group X peridotites suggests their metasomatism by a high-temperature mafic melt resembling the basaltoids from Scania. Alternatively, they may represent high-pressure cumulates, as suggested by their coarse-grained texture. The group Y peridotites record cryptic metasomatism of a significantly depleted peridotite (melt extraction ranging typically between 25 and 30%) by a carbonatitic melt. The carbonatitic metasomatic agent was fractionating chromatographically from REE-, Th- and U-rich in subgroup Y2 to -poor in those elements in subgroup Y2. The group Z peridotite possibly represents depleted peridotite which was further metasomatized by a mafic melt. The lithospheric mantle beneath the marginal part of EEC has a complex composition, which is however different from a typical cratonic mantle.

 

Founded by Polish National Science Centre grant no. UMO-2016/23/B/ST10/01905 and WTZ PL 08/2018.

How to cite: Matusiak-Małek, M., Mikrut, J., Puziewicz, J., Kukuła, A., Ntaflos, T., Aulbach, S., Johansson, L., and Grégoire, M.: Composition of lithospheric mantle beneath southern margin of East European Craton evidenced by peridotitic xenoliths from Scania, S Sweden., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9457, https://doi.org/10.5194/egusphere-egu22-9457, 2022.

EGU22-4679 | Presentations | GMPV2.1

Deciphering multiple metasomatism beneath Mindszentkálla (Bakony-Balaton Highland Volcanic Field, western Pannonian Basin) revealed by upper mantle peridotite xenoliths

Levente Patkó, Zoltán Kovács, Nóra Liptai, László E. Aradi, Márta Berkesi, Jakub Ciazela, Károly Hidas, Carlos J. Garrido, and István J. Kovács

The Bakony-Balaton Highland Volcanic Field (BBHVF), where Neogene alkali basalts and their pyroclasts host a great number of upper mantle xenoliths, is situated in the western part of the Pannonian Basin. One of the barely investigated xenolith localities of the BBHVF is Mindszentkálla. In the BBHVF, most of the xenoliths have lherzolitic modal composition, however, the Mindszentkálla locality is dominated by harzburgites. In addition to the homogeneous coarse-grained harzburgite xenoliths, we collected composite and multiple composite (with more than two different domains) xenoliths that represent small-scale heterogeneities. Harzburgite, interpreted as the host rock, is crosscut by dunitic, orthopyroxenitic, apatite-bearing websteritic, and amphibole-phlogopite-bearing veins.

To understand the evolution of the conspicuously complex mantle beneath Mindszentkálla, in situ major and trace element analyses were carried out on all rock-forming minerals. The major element chemistry of silicate minerals in the harzburgite wall rock and dunite veins show lower basaltic element (Fe, Mn, Ti, Na) contents with respect to the orthopyroxenitic and websteritic veins. The rare earth elements display flat or spoon-shaped patterns in the harzburgitic clinopyroxenes, whereas the websteritic clinopyroxenes and the amphiboles of the amphibole-phlogopite vein are enriched in light rare earth elements.

The observed textural and geochemical features indicate that the Mindszentkálla xenoliths could have gone through significant mineralogical and compositional modifications in at least two events. During the first event, the lherzolitic mantle was metasomatized most likely by a silica-rich melt, which could have resulted in orthopyroxene-rich peridotitic lithology. The metasomatizing Si-rich melt is likely related to a former subduction event.

The second metasomatic event led to the formation of dunite, orthopyroxenite, apatite-bearing websterite, and amphibole-phlogopite-bearing veins. These lithologies are likely the products of interactions between volatile-enriched, asthenosphere-derived basaltic melts and the peridotite wall rock, or they represent the high-pressure crystallization of such melts. The ascent of these mafic melts may have happened shortly before the xenolith entrapment during the Neogene basaltic volcanism.

How to cite: Patkó, L., Kovács, Z., Liptai, N., Aradi, L. E., Berkesi, M., Ciazela, J., Hidas, K., Garrido, C. J., and Kovács, I. J.: Deciphering multiple metasomatism beneath Mindszentkálla (Bakony-Balaton Highland Volcanic Field, western Pannonian Basin) revealed by upper mantle peridotite xenoliths, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4679, https://doi.org/10.5194/egusphere-egu22-4679, 2022.

EGU22-3733 | Presentations | GMPV2.1

Basaltic rocks from the Vardar ophiolite (North Macedonia): new insights on the metasomatism of sub-arc upper mantle using geochemical and stable isotope data

Valentina Brombin, Edoardo Barbero, Emilio Saccani, Nicola Precisvalle, Sonja Lepitkova, Ivica Milevski, Igor Ristovski, Igor Milcov, Gorgi Dimov, Costanza Bonadiman, and Gianluca Bianchini

In the upper mantle, volatiles control its composition, partial melting conditions, as well as the ascent rate of the formed melts. As consequence, volatile composition of the mantle is, in turn, recorded in the melts and, therefore, in the erupted basaltic rocks. Despite their importance, origin, budget, and fluxes of the volatiles in the upper mantle are poorly constrained. It is well known that the main input of mantle volatiles, such as carbon (C) and sulphur (S), represents components released from the subducting slab, e.g., oceanic rocks and sediments, whose have characteristic isotopic signatures. In this view, studies of isotopic ratios of volatiles of subduction-related magmatic rocks could be used to identify the chemical components released by the subducting slab metasomatizing the upper mantle. To confirm this hypothesis, we investigated the major and trace element composition, as well as the C and S elemental contents and isotopic ratios of subvolcanic and volcanic rocks of the Vardar ophiolites of North Macedonia, which represent remnants of the Mesozoic Tethyan oceanic lithosphere formed in supra-subduction zone tectonic settings.

The ophiolites were sampled at Lipkovo and Demir Kapija localities, in the northern and southern part of North Macedonia, respectively. Based on whole-rock major and trace element composition, two main groups of rocks can be distinguished: i) Group 1 rocks, which are subalkaline basalts with backarc affinity and ii) Group 2 rocks, which are calc-alkaline basalts with arc affinity. The petrogenetic modelling based on trace and Rare Earth Elements, indicates that Group 1 mantle sources were affected by limited metasomatic processes by slab-released components, in particular aqueous fluids and sediment melts, whereas the Group 2 mantle sources were strongly metasomatized by sediment melts and adakitic melts. Accordingly, the Group 1 rocks exhibit C-enriched and S-depleted isotopic signature, indicating a minor involvement of melts from the subducting sediments. On the other hand, the C-depleted and S-enriched isotopic signatures of the Group 2 rocks suggest a major involvement of melts derived from the subducting sediments rich in organic matter and sulphate phases Therefore, both geochemical and isotopic data of the subvolcanic and volcanic samples of the North Macedonia ophiolites show that the sub-arc mantle sources are more affected by slab-released fluids than those of the backarc basin, which are more distal from the trench. Thus, combining the geochemical and isotopic data of subvolcanic and volcanic samples of complex geological framework can contribute to reconstruct the geodynamic scenarios, such as that of the Vardar ophiolites in the Dinaric-Hellenic belt. In addition, this approach may be useful to better understand the global geodynamic cycles of volatiles reconstructing their origin, budget, and isotopic composition, and understand the impacts on climate and environment from local to global scale.

How to cite: Brombin, V., Barbero, E., Saccani, E., Precisvalle, N., Lepitkova, S., Milevski, I., Ristovski, I., Milcov, I., Dimov, G., Bonadiman, C., and Bianchini, G.: Basaltic rocks from the Vardar ophiolite (North Macedonia): new insights on the metasomatism of sub-arc upper mantle using geochemical and stable isotope data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3733, https://doi.org/10.5194/egusphere-egu22-3733, 2022.

EGU22-13428 | Presentations | GMPV2.1

Transition from “orogenic-like” to “anorogenic” geochemical affinity in Mesozoic post-collisional magmatism: evidence from alkali-rich dykes from Ivrea-Verbano Zone (Southern Alps)

Abimbola Chris Ogunyele, Tommaso Giovanardi, Mattia Bonazzi, Maurizio Mazzuccheli, Alessandro De Carlis, Anna Cipriani, and Alberto Zanetti

Dyke swarms intruding the mantle–continental crust transition of the Adria plate as documented by the Ivrea-Verbano Zone (IVZ, Southern Alps) represent a unique opportunity to investigate the evolution of mantle melts from Late Paleozoic to Mesozoic in the post-collisional Variscan realm. Thus, we present new petrological and geochemical data of dyke swarms cropping out in the Finero Phlogopite Peridotite mantle unit. Dykes are from a few cm to >1 m thick and cut at a high angle the mantle foliation.

The dyke swarms are composed of cumulus phlogopite-bearing amphibole peridotite, hornblendite, diorite and anorthosite. Many dykes are composite, showing variable proportions of melanocratic and leucocratic layers. Volatiles overpressure during the late magmatic stage is testified by plastic flow and development of a porphyroclastic structure by deformation of early cumulates and by the widespread segregation of a fine-grained mica matrix. The dyke swarms show mineralogical and geochemical features varying between two end-member series.

A dyke series is characterized by Al-rich pargasite (Al2O3 up to 18 wt.%) and phlogopite, associated with apatite, calcite, sulphides and sometimes sapphirine. The amphiboles show i) large LILE and LREE contents, ii) negative Nb, Ta, Zr and Hf anomaly and iii) isotopic oxygen composition heavier than the mantle interval, which support the occurrence of recycled continental crust components in the parent melts and impart an overall “orogenic” affinity.

The second series mainly consists of Al-poorer pargasite, phlogopite and albite (An 8-10), associated with apatite, monazite, ilmenite, zircon, Nb-rich oxides and carbonates. Mineral compositions and assemblages indicate that the parent melts were strongly enriched in Fe, Na, H2O, P and C. Amphiboles are still enriched in LILE and LREE, but show extreme enrichments in Nb, Ta, Zr and Hf. As a whole, the petrochemical features point to an “anorogenic” alkaline affinity. Zircons from the “anorogenic” dykes are mostly anhedral, with homogenous internal structure or sector zoning. The strongly positive εHft (average of +10) of zircons and the Sr isotopic composition of amphiboles (0.7042) point to a derivation of such “anorogenic” melts from mildly enriched mantle sources. Concordant 206Pb/238U zircon ages for “anorogenic” dykes vary from 221 ± 9 Ma to 192 ± 8 Ma. Some dykes show both “orogenic” and “anorogenic” affinities, thus recording different pulses of mantle melts and metasomatic overprinting. As a whole, the dyke swarms show a transition from “orogenic” to “anorogenic” affinity indicating re-opening of dykes’ conduits for the melt ascending, pointing to a progressive change of the mantle sources of the Mesozoic magmatism of the Southern Alps.

How to cite: Ogunyele, A. C., Giovanardi, T., Bonazzi, M., Mazzuccheli, M., De Carlis, A., Cipriani, A., and Zanetti, A.: Transition from “orogenic-like” to “anorogenic” geochemical affinity in Mesozoic post-collisional magmatism: evidence from alkali-rich dykes from Ivrea-Verbano Zone (Southern Alps), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13428, https://doi.org/10.5194/egusphere-egu22-13428, 2022.

In the Alpine orogen of the north Aegean region, the eastern Rhodope Zone consists of widespread high-grade metamorphic basement exposed in Bulgaria and Greece. In this high-grade basement, the lithologically variegated upper unit contains meta-ultramafic bodies, which are considered as dismembered Precambrian meta-ophiolite association (Kozhoukharova 1984). In the same unit, the voluminously predominant amphibolites, having mafic igneous precursors of boninitic-tholeiitic affinity, are in turn considered of Precambrian-Paleozoic island arc origin (Haydoutov et al. 2004), or part of the amphibolites of Ordovician age have back-arc origin (Bonev et al. 2013). The upper unit, together with the overlying Circum-Rhodope belt Jurassic ophiolite, constitutes the hanging wall of the Eocene extensional system consisting of meta-granitoids with Carboniferous protoliths in the footwall. Here, we report on the geochemistry of the amphibolites from the upper unit in Bulgaria and Greece, and discuss their composition and tectonic setting, which might shed a light on the mid-late Paleozoic-early Mesozoic tectonic architecture of the region.

The amphibolites occur intercalated with para- and ortho-metamorphic lithologies within the upper unit. Texturally, they are represented mainly by massive or banded amphibolite and garnet-bearing amphibolite. The bulk mineral assemblage contains amphibole and plagioclase ± quartz ± garnet ± epidote-clinozoisite ± chlorite ± sphene ± rutile, which resulted from the main metamorphic overprint in amphibolite-facies and variable retrogression to greenschist-facies. The meta-mafic rocks cover the range of basalt to andesite composition, with elevated MgO, variable alkali and low-K contents, having mainly tholeiitic to weak calc-alkaline affinity. The range of TiO2 defines two groups of high-Ti (>1%) and low-Ti (<1%) meta-mafic rocks. Mostly flat to slightly LREE-depleted chondrite-normalized patterns characterize the high-Ti group, which overlaps N-MORB and E-MORB compositions. The low-Ti group exhibits pronounced LREE-depleted and fractionated REE patterns, rarely U-shaped boninitic-like pattern. N-MORB-normalized trace element profiles define high LILE/HFSE ratios, moderate to strong HFSE and HREE depletion of the low-Ti group, and close to N-MORB to slightly enriched HFSE-HREE trend of the high-Ti group. A negative Nb anomaly characterizes part of the low-Ti group, whereas other samples from both groups show no Nb anomalies and have contents higher than N-MORB. On various trace element discrimination diagrams the majority of high-Ti group meta-mafic rocks display clear MORB affinity and few samples plot in the WPB field of oceanic island tholeiites, whereas low-Ti meta-mafic rocks show island arc tholeiite (IAT) affinity or have transitional MORB/IAT signature. 

The compositional diversity of the meta-mafic rocks from the upper unit with MORB, transitional MORB/IAT and IAT affinity, in turn call for the origin of the protoliths in a paired ocean ridge-island arc environment, and thus could hints their supra-subduction zone origin in an island arc/back-arc setting.

 

References

Bonev, N., Ovtcharova-Schaltegger, M., Moritz, R., Marchev, P., Ulianov, A. 2013. Geod Acta 26, 3-4, 207-229.

Haydoutov, I., Kolcheva, K., Daieva, L., Savov, I., Carrigan, Ch.  2004. Ofioliti, 29, 2, 145-157.

Kozhoukharova, E. 1984. Geologica Balc., 14, 4, 9-36.

 

Acknowledgements: The study was supported by the NSF Bulgaria KP-06-N54/5 contract.

How to cite: Bonev, N., Dotseva, Z., and Filipov, P.: Geochemistry and tectonic significance of meta-ophiolitic mafic rocks in the high-grade metamorphic basement of the eastern Rhodope Zone, Bulgaria-Greece, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1863, https://doi.org/10.5194/egusphere-egu22-1863, 2022.

EGU22-9103 | Presentations | GMPV2.1

Features of the composition and structure of the lithospheric mantle of the Upper Muna field.

Igor Iakovlev, Vladimir Malkovets, and Anastasia Gibsher

Peridotite xenoliths are of great interest for research, since their composition is closest to the simulated compositions of the upper mantle, and they also make it possible not only to determine the conditions for the formation of these rocks, but also the degree of metasomatic processing of the diamondiferous keel, as well as the thickness and distribution area of diamondiferous rocks in the lithospheric mantle.

The Middle Paleozoic (D3-C1) diamondiferous kimberlite pipe Komsomolskaya-Magnaya was chosen as the object of research. This is one of the diamondiferous pipes of the Siberian platform, which contains many unchanged xenoliths of peridotite rocks.

We studied a collection of 180 peridotite xenoliths of the Komsomolskaya-Magnitnaya pipe, of which 104 belong to dunite-harzburgite paragenesis, 74 to lherzolite and 4 websterites. Also, we studied a large number of minerals from the concentrate material of the Komsomolskaya-Magnitnaya kimberlite pipe.

A high proportion (~ 30%) of peridotites with high magnesian olivines (Mg #> 93 mol%) indicates the presence of a block of highly depleted rocks in the lithospheric mantle.

We noted a high proportion of garnets with S-shaped REE distribution spectra (~ 60%), as well as garnets belonging to the harzburgite-dunite paragenesis in accordance with the CaO-Cr2O3 diagram. It indicates a moderate role of metasomatic changes associated with silicate melts, as well as interaction with carbonatite melts enriched in LREE.

In addition, kimberlite indicator minerals (KIM) (garnets, chrome spinels, ilmenites) were studied, sampled directly from 7 geophysical anomalies, 6 new kimberlite bodies, and kimberlite pipes Interkosmos, Kosmos-2, 325 years of Yakutia, belonging to the Upper Muna field. These data provide more information on the composition of the lithospheric mantle within the entire Upper Muna field.

For several kimberlite bodies, a high proportion of KIM of the diamond association is noted, however, for most kimberlite bodies, signs of a high degree of secondary metasomatic processes are noted, which negatively affect the preservation of diamond in the lithospheric mantle.

Cr-spinels from various kimberlite bodies of the Upper Muna field attract special attention. In addition to the typical peridotite Cr-spinels, there are Cr-spinels that follow the magmatic trend (Sobolev, 1974) and have extremely low contents of aluminum and titanium. The genetic identity of these Cr-spinels is still unknown.

Was done precise pressure (P)-temperature (T) estimation using single-clinopyroxene thermobarometry (Nimis, Ta). Was obtained mantle paleogeotherm.  Data was received about surface heat flux ~34–35mW/m2, 225–230 km lithospheric thickness, and 110–120 thick “diamond window” for the Upper Muna field (Dymshits et al, 2020).

  • Dymshits A. M., Sharygin I. S., Malkovets V. G., Yakovlev I. V., Gibsher A. A., Alifirova T. A., Vorobei S. S., Potapov S. V., Garanin V. K. Thermal state, thickness, and composition of the lithospheric mantle beneath the Upper Muna kimberlite field (Siberian Craton) constrained by clinopyroxene xenocrysts and comparison with Daldyn and Mirny fields // Minerals. 2020. V. 10. P. 549.
  • Sobolev N.V., Deep inclusions in kimberlites and the problem of the composition of the upper mantle // Novosibirsk: Nauka, 1974.

How to cite: Iakovlev, I., Malkovets, V., and Gibsher, A.: Features of the composition and structure of the lithospheric mantle of the Upper Muna field., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9103, https://doi.org/10.5194/egusphere-egu22-9103, 2022.

EGU22-3525 | Presentations | GMPV2.1

Multi-mineral study of lithospheric metasomatism in N-Tanzania: Mantle source characterization of the carbonatite magmas 

Valentin Casola and Lydéric France

GMPV2.2 – Metamorphism, fluids, and melts in subduction zones: Mass transfer and carbon mobility

EGU22-13287 | Presentations | GMPV2.2

Reconciling extensive mantle hydration at subduction trenches and limited deep H2O fluxes

Diane Arcay, Nestor Cerpa, and José Alberto Padrón-Navarta

The long-term global sea level depends on the balance of H2O exchanges between the Earth's mantle and the surface through both volcanism (mantle degassing) and subduction of hydrous minerals (mantle regassing). The estimates of H2O fluxes by the current thermopetrological subduction models predict that regassing exceeds degassing by 60%, which may lead to a sea-level drop of at least a hundred meters in the last 540 Ma [Parai & Mukhopadhyay, 2012, Earth Planet. Sc. Lett., 317, 396-406. https://doi.org/10.1016/j.epsl.2011.11.024. These models further imply a moderate ( Tg/Myr) global input of H2O at the subduction trenches. In contrast, geological constraints suggest a near-steady state of long-term sea level while geophysical observations advocate for a larger global H2O input, especially given the large amounts of hydrated lithospheric mantle that are inferred at present-day subduction trenches. To address this paradox, we revise the subduction-H2O flux calculations using recently published experimental data on natural hydrated peridotites at high-pressure conditions, which suggest that all hydrated phases destabilize below 800˚C for pressures higher than 8 GPa [Maurice et al., 2018, Contrib. Mineral. Petrol, 173(10), 86. https://doi.org/10.1007/s00410-018-1507-9 ]. Our reassessed thermopetrological models show that a prominent global H2O input ( Tg/Myr), mainly conveyed by the layer of subducted serpentinized mantle, is compatible with a limited global H2O retention in subducted slabs at mid-upper mantle depths ( Tg/Myr), including in models that consider some worldwide variability of the input serpentine. We also show that the global H2O retention at mid-upper mantle depths is only driven by the hydrated mantle of coldest subducting plates. Overall, our models show that the present-day global water retention in subducting plates beyond mid-upper mantle depths barely exceeds the estimations of mantle degassing, and thus quantitatively support the stable-sea level scenario over geological times.

How to cite: Arcay, D., Cerpa, N., and Padrón-Navarta, J. A.: Reconciling extensive mantle hydration at subduction trenches and limited deep H2O fluxes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13287, https://doi.org/10.5194/egusphere-egu22-13287, 2022.

EGU22-2584 | Presentations | GMPV2.2

Multidimensional Analysis of Serpentinite Dehydration Networks and Implications for Volatile Flux in Subduction Zones 

Austin Arias, Andreas Beinlich, Lisa Eberhard, Marco Scambelluri, and Oliver Plümper

Subduction zones are principal pathways for the cycling of volatiles such as  hydrogen and carbonfrom the Earth’s surface to the mantle and back to the atmosphere. This cycling has significant long-term effects on Earth’s climate. However, the processes that lead to volatile release during subduction and total volatile fluxes are poorly understood. In our study, we will quantify and characterize the network architecture of dehydration pathways exhibited as mineralized olivine-bearing metamorphic veins in the exhumed meta-serpentinites from the Erro-Tobbio unit, Italy [1]. Applying network analytical methods and graph theory both macroscopically and microscopically can provide the mode of propagation and describe the controlling factors affecting the evolution of these dehydration networks. Furthermore, multiscale observations can confirm the scalability of the vein network and if quantitative results such as permeability or volatile flux can be extrapolated to larger scales.

Along with 2-D network analysis, these vein networks will be analyzed in 3-dimensions using X-ray tomography and sophisticated machine-learning methods, such as generative adversarial networks. The results of both will be compared, which can then assure whether current machine-learning methods can effectively create statistically equivalent copies of these networks. Lastly, the synthesis of 2-D and 3-D multiscale results should provide meaningful parameters for accurate calculations of volatile flux during the dehydration of subducting slabs. 

 

[1] Plümper et al. (2017) Nature Geoscience 10(2), 150-156.

How to cite: Arias, A., Beinlich, A., Eberhard, L., Scambelluri, M., and Plümper, O.: Multidimensional Analysis of Serpentinite Dehydration Networks and Implications for Volatile Flux in Subduction Zones , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2584, https://doi.org/10.5194/egusphere-egu22-2584, 2022.

EGU22-877 | Presentations | GMPV2.2

Magnesium isotopic composition of back-arc basin lavas and its implication for the recycling of serpentinite-derived fluids

Yi Ding, Xianglong Jin, Xiaohu Li, Zhenggang Li, Jiqiang Liu, Hao Wang, Jihao Zhu, Zhimin Zhu, and Fengyou Chu

Dehydrated fluids expelled from serpentinized mantle in the subducted slab are gradually recognised as a vital role in generating arc magmatism and element cycling in the Earth. However, it remains not clear about their recycling at various depth in subduction zones and if slab serpentinite-derived fluids contribute to the genesis of lavas from the back-arc basins. Here, we study the magnesium (Mg) isotopic compositions of lavas from the Okinawa Trough (OT) and Lau basin (LB) as Mg isotopes have shown great potential to trace dehydration of slab serpentinites in recent years. Overall, lavas from the OT and LB have averagely heavier Mg isotopic compositions relative to the mid-ocean ridge basalt (MORB) mantle, which could be attributed to the involvement of slab serpentinite-derived fluids rather than crustal assimilation or input of subducted sediments as indicated by the isotopic modelling results. The δ26Mg values of the southern OT (SOT) and southern LB (SLB) are generally higher than the middle OT (MOT) and northern LB (NLB), respectively, with an average of -0.11 ± 0.06‰ (2SD, n=5) for the SOT, -0.20 ‰ ± 0.04 (2SD, n=5) for the MOT, -0.13 ‰ ± -0.08 for the SLB (2SD, n=6) and -0.19 ‰ ± 0.06 (2SD, n=10) for the NLB. The binary modelling results have shown that various amounts of serpentinite-derived fluids could explain the variations in Mg isotopic compositions observed in the OT and LB. Combined published δ26Mg values in subduction zones with our data, the thermal structure of inter-subduction zone may play a first control on the signal of Mg-rich serpentinite-derived fluids. By contrast, the contributions of these fluids to different segments in a specific subduction zone may depend on the slab depth beneath magmatic activity sites.

How to cite: Ding, Y., Jin, X., Li, X., Li, Z., Liu, J., Wang, H., Zhu, J., Zhu, Z., and Chu, F.: Magnesium isotopic composition of back-arc basin lavas and its implication for the recycling of serpentinite-derived fluids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-877, https://doi.org/10.5194/egusphere-egu22-877, 2022.

EGU22-11697 | Presentations | GMPV2.2

Sulfur in the slab: A sulfur-isotopes and thermodynamic-modeling perspective from exhumed terranes

Jesse Walters, Alicia Cruz-Uribe, and Horst Marschall

Sulfur is a key element in the subduction zone-volcanic arc system; however, the mechanism(s) that recycle sulfur from the slab into the overlying volcanic arc are debated. Here we summarize recent advances in quantifying this component of the deep sulfur cycle. First, primary metamorphic or inherited sulfides in oceanic-type eclogites are only rarely observed as inclusions and are typically absent from the rock matrix. Additionally, sulfides are relatively common in rocks metasomatized at the slab-mantle interface by slab-derived fluids during exhumation. Combined, these two observations suggest that sulfur loss from subducted mafic crust is relatively efficient. Thermodynamic modeling in Perple_X using the Holland and Powell (2011) database combined with the Deep Earth Water model suggests that the efficiency and speciation of sulfur loss varies depending on the degree of seafloor alteration prior to subduction and the geothermal gradient of the slab. In relatively cold subduction zones, such as Honshu, slab-fluids derived from subducted mafic crust are predicted to exhibit elevated concentrations of HSO4-, SO42-, HSO3-, and CaSO4(aq), whereas hot subduction zones, such as Cascadia, are predicted to produce slab fluids enriched in HS- and H2S at lower pressures. The oxidation of sulfur expelled from subducted pyrite is balanced by the reduction of Fe3+ to Fe2+, consistent with the low Fe3+/SFe of exhumed eclogites relative to blueschists and altered oceanic crust. Where oxidized S-bearing fluids are produced, they are anticipated to interact with more reduced rocks at the slab-mantle interface and within the mantle wedge, resulting in sulfide precipitation and significant isotopic fractionation. The δ34S values of slab fluids are estimated to fall between -11 and +8 ‰. Rayleigh fractionation during progressive fluid-rock interaction results in fractionations of tens of per mil as oxidized species are depleted and sulfides are precipitated, resulting in δ34S values of sulfides that easily span the -21.7 to +13.9 ‰ range observed in metasomatic sulfides in exhumed high-pressure rocks. However, in subduction zones where reduced species prevail, the S isotopic signature of slab fluids is expected to reflect their source and will exhibit a narrower range in δ34S values. As a result, the δ34S values measured in arc magmas may not always be a reliable indicator of the contribution of different components of the slab, such as sediments vs. AOC. Additionally, the impact of S recycling on the oxygen fugacity of arc magmas is expected to vary both spatially and temporally throughout Earth history.

How to cite: Walters, J., Cruz-Uribe, A., and Marschall, H.: Sulfur in the slab: A sulfur-isotopes and thermodynamic-modeling perspective from exhumed terranes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11697, https://doi.org/10.5194/egusphere-egu22-11697, 2022.

EGU22-11784 | Presentations | GMPV2.2

Elemental and lithium isotopic signature of fluids in metapelites from ancient subduction zones

Kristijan Rajic, Hugues Raimbourg, Antonin Richard, Catherine Lerouge, Romain Millot, and Clement Herviou

The objective of this work is to study the fluid rock-interactions at low metamorphic grade in subduction zones. We focused in particular on the evolution of metapelites from the base of the seismogenic zone (⁓250℃) to the down-dip transition to the aseismic domain (⁓330℃). In the three examples examined here (Kodiak Complex in Alaska, Shimanto Belt in Japan, the French Alps), we followed the variations in mineralogy, trace element budget, as well as fluid inclusion elemental and isotopic (δ7Li) composition.

In the Kodiak and Shimanto belt, the mineralogy remains constant with temperature increase, with the dominance of phyllosilicates (white mica and chlorite), quartz and plagioclase. In more deformed zones of higher-T samples (330 ± 16℃ and 3 ± 0.4 kbar for Kodiak and 320 ± 14℃ and 3.9 ± 0.4 kbar for Shimanto belt) quartz and plagioclase are completely dissolved, while large white mica and chlorite grains crystallized. Also, the chlorite/white mica ratio is higher with temperature increase.

White mica is a main host for B, LILE and to smaller extent for Li. Plagioclase hosts the same elements but in lower concentrations. Chlorite is a main host for Li ± B and quartz hosts Li to smaller extent than chlorite and mica. Bulk rock analysis revealed partial loss in B, Rb, Sr and Cs with temperature increase, in contrast to the retention of Li and Ba. Mass balance based on trace element concentrations of individual phases and their proportion point to a reorganization of elements released during quartz and plagioclase dissolvement and phyllosilicate recrystallization: Rb, Cs and Ba released from plagioclase are incorporated in higher grade mica, Li released from mica and quartz is incorporated into chlorite. In the lack of newly formed phase as a host, B and Sr are probably released into a fluid.

The salinity at 250°C is around 2wt.% NaCl eq., i.e. lower than original pore-filling seawater. The freshening can be accounted for by smectite dehydration and transformation into illite. From 250 to 330°C, a salinity increase is observed, up to 3.5wt.%, possibly related to the chlorite crystallization requiring higher amount of water. The fluid is highly enriched in fluid-mobile elements in comparison with seawater. δ7Li values of fluid inclusion leachates are distinct for each locality: +8.1 to +17.07‰, in the Kodiak, +2.53 to +10.39‰ in the Shimanto belt and -1.54 to +9.54 ‰ in the western Alps. δ7Li of fluids is independent of other parameters, such as temperature or Li concentration.

Mineral reactions and fluid-mobile elements concentration in phases point to overall a local redistribution of fluid-mobile elements between phases, except for minor release of B and Sr. Lithium isotopes, which show that δ7Li of fluid is possibly buffered by host rock, confirm the fact that the rocks behaved to a large extent as a closed system during burial and subsequent exhumation.

How to cite: Rajic, K., Raimbourg, H., Richard, A., Lerouge, C., Millot, R., and Herviou, C.: Elemental and lithium isotopic signature of fluids in metapelites from ancient subduction zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11784, https://doi.org/10.5194/egusphere-egu22-11784, 2022.

EGU22-9783 | Presentations | GMPV2.2

Titanium isotopic fractionation of arc derived melts and cumulates

Julian-Christopher Storck, Nicolas David Greber, Alexandra Müller, Thomas Pettke, and Othmar Müntener

Mechanisms such as crystallization differentiation, subduction erosion, delamination, or relamination that are responsible for the formation and modification of modern crust with an on average andesitic composition are actively debated (Hacker et al. 2015). Isotope fractionation associated with igneous processes is documented for many non-traditional stable isotope systems, making them promising tools to advance our understanding of modern arc crust formation. Titanium isotopes are especially promising, as volcanic and plutonic arc rocks show a trend from light to heavy isotope values with increasing SiOconcentration due to the fractionation of minerals with light Ti isotopes.

We present new Ti isotope data on medium K calc-alkaline to shoshonitic magmatic differentiation suites from the Adamello Batholith (N-Italy), Kos (Agean arc), Torres del Paine (Patagonia) and the Dolomites (N-Italy) in addition to crust-derived mafic cumulates. The Ti isotopic composition of dacites and granites range between δ49TiOL-Ti ≈ 0.3 to 1.1‰, with heavier values for more alkaline granitic melts in agreement with published data (Hoare et al. 2020). Mafic cumulates from related and additional localities are overall isotopically lighter than (their) granitic counterparts ranging between δ49TiOL-Ti ≈ -0.15 and +0.08‰. Cumulates of studied crustal sections enriched in Fe-Ti oxides (>5 modal %) show δ49Ti values lighter than the depleted MORB mantle (DMM, δ49TiOL-Ti ≈ +0.002 ± 0.007‰) and counterbalance the isotopically heavy composition of felsic rocks. The occurrence of cumulates heavier than DMM may have several reasons: (i) “heavy” cumulates may represent late-stage relicts of progressive magma differentiation containing trapped intercumulus melt or (ii) they experienced overprinting, e.g., by mafic rejuvenation.

We therefore find that the Ti isotopic composition of cumulate rocks and likely also the magmatic lower continental crust is influenced by their mineralogical composition. How this impacts the Ti isotopic composition of the bulk continental crust in the light of delamination and relamination processes needs further work.

 

REFERENCES

Hacker, B. R., Kelemen, P. B., & Behn, M. D. (2015). Continental lower crust. Annual Review of Earth and Planetary Sciences43, 167-205.

Hoare, L., Klaver, M., Saji, N. S., Gillies, J., Parkinson, I. J., Lissenberg, C. J., & Millet, M. A. (2020). Melt chemistry and redox conditions control titanium isotope fractionation during magmatic differentiation. Geochimica et Cosmochimica Acta282, 38-54.

How to cite: Storck, J.-C., Greber, N. D., Müller, A., Pettke, T., and Müntener, O.: Titanium isotopic fractionation of arc derived melts and cumulates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9783, https://doi.org/10.5194/egusphere-egu22-9783, 2022.

EGU22-11854 | Presentations | GMPV2.2

Iron mobility in slab-derived hydrous silicate melts at sub-arc conditions

Carla Tiraboschi, Rohrbach Arno, Klemme Stephan, Berndt Jasper, and Sanchez-Valle Carmen

Aqueous and saline fluids have a fundamental role in subduction zones and represent a major vector of mass transfer from the slab to the mantle wedge. In this setting, assessing the mobility of redox sensitive elements, such as iron, in aqueous fluids and melts is essential to provide insights on the oxygen fugacity conditions of slab-derived fluids and the oxidation state of arc magmas.

We experimentally investigate the solubility of magnetite and hematite in water-saturated haplogranitic melts, which represent the felsic melt produced by subducted eclogites. Experiments were conducted at 1–2 GPa and temperature ranging from 700 to 950 °C employing an endloaded piston cylinder apparatus. Single gold capsules were loaded with natural hematite, magnetite and synthetic haplogranite glass. Two sets of experiments were conducted: a first set with pure H2O and a second set with a 1.5 m H2O-NaCl solution. After quench, the presence of H2O in the haplogranite glass was verified by Raman spectroscopy, while iron and major element contents were determined by electron microprobe analysis.

Results show that a significant amount of FeO is released from magnetite and hematite equilibrated with hydrous melts, up to 1.96 ± 0.04 wt% at 1 GPa and 950 °C. In the presence of NaCl, we observed an increase in the amount of iron in the haplogranite glass, e.g. from 1.04 ± 0.12 wt% to 1.50 ± 0.31 wt% of FeOtot at 800 °C. These concentrations are substantially higher than the iron solubility in aqueous and saline fluids predicted by thermodynamic modelling (DEW model, Sverjensky et al., 2014), likely due to formation of Fe- and Si-bearing complex in the haplogranite-bearing fluid at run conditions. Our results suggest that hydrous melts can effectively mobilize iron from Fe-oxides even at relatively low-pressure conditions. Slab-derived hydrous melts can thus represent a valid agent for mobilizing iron from the subducting slab to the mantle wedge, and can strongly influence the geochemical cycles of Fe and the redox conditions of subduction zone fluids.

 

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

How to cite: Tiraboschi, C., Arno, R., Stephan, K., Jasper, B., and Carmen, S.-V.: Iron mobility in slab-derived hydrous silicate melts at sub-arc conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11854, https://doi.org/10.5194/egusphere-egu22-11854, 2022.

EGU22-13297 | Presentations | GMPV2.2

Experimental constraints on the nature of multiphase solid inclusions and their bearing on mantle wedge metasomatism, Bohemian Massif

Antonio Acosta Vigil, Jana Kotková, Renata Copjaková, Richard Wirth, and Jörg Hermann

Fluids are the primary agents for mass transfer in subduction zones. These fluids can be captured as primary inclusions within minerals crystallizing during subduction processes. Some of these inclusions, referred to as multiphase solid inclusions (MSI), are characterized by the high proportion and variety of minerals, hence by a high concentration of solute in the trapped fluid. Kotková et al. (2021) have described primary MSI in garnets of subduction-related ultra-high pressure (UHP) peridotites (P-T of 1030-1150 ºC/3.6-4.8 GPa) of the Bohemian Massif. MSI range in size between ≈5-40 µm and are mostly composed of hornblende, the barian mica kinoshitalite, dolomite and magnesite. MSI have been interpreted as trapped residual liquids produced after partial UHP crystallization of carbonate-silicate melts that now form garnet pyroxenite veins in the peridotites. Experimental re-melting of MSI is the best procedure to investigate the precise nature of trapped fluids. We have conducted re-melting experiments of MSI present in garnets of a lherzolite, taking the inclusions to P-T around their entrapment conditions at or close to host rock peak P-T, 4-4.5 GPa and 1000-1225 ºC. The inclusions (re-)crystallized into a garnet fringe at the boundary between inclusions and host garnet, barian mica and carbonatite melt towards the center of the inclusion, and a large irregular and empty space in between the garnet fringe and the central silicate-carbonate component. Microstructures and mass balance indicate that the empty space was occupied by a Na-K-Cl-F-rich saline aqueous fluid (brine). Hence experiments did not produce a single melt at any experimental conditions, but systematically show the stability and coexistence of barian mica + carbonatite melt + brine at the entrapment conditions, and a garnet fringe indicating reaction between trapped fluids and host garnet. This suggest that growing garnet trapped a carbonatite melt and a saline aqueous fluid coexisting in the matrix, together with solid crystals of barian mica likely produced by metasomatism of the percolating fluids through the host peridotite. It is intriguing, however, that neither single mica crystals nor separate former carbonate melt and brine have been found included in garnets. Mass balance shows that carbonate melt is the main host for incompatible elements such as Ba. This presentation will discuss the bearings of the experimental results on the nature and origin of these MSI, potential links to diamond formation and their implication on mass transfer processes in subduction zones.

Kotkova et al. (2021) Lithos 398-399, 106309

How to cite: Acosta Vigil, A., Kotková, J., Copjaková, R., Wirth, R., and Hermann, J.: Experimental constraints on the nature of multiphase solid inclusions and their bearing on mantle wedge metasomatism, Bohemian Massif, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13297, https://doi.org/10.5194/egusphere-egu22-13297, 2022.

EGU22-3092 | Presentations | GMPV2.2

New rutile and titanite phase stability constraints at subsolidus conditions in a mafic system

Inês Pereira, Kenneth Koga, and Emilie Bruand

Rutile, titanite and ilmenite are the most common Ti-bearing minerals found in metamorphic rocks of variable grades. Rutile and titanite, in particular, are extremely useful minerals as they can be dated using U-Pb, and Zr concentrations are calibrated as geothermometers for both minerals, making them valuable petrochronometers. Previous experimental studies on MORB composition [1] established that titanite is more stable at LT-LP, rutile at HP (> 12 kbar), while ilmenite at HT-LP metamorphic conditions. Despite these phase stabilities, the natural occurrence of rutile at LP (< 12 kbar) and titanite at HP (> 20 kbar) and ilmenite at both HP and LP indicates strong uncertainties on our current understanding about their stabilities. [2] demonstrated a non-trivial compositional effect mainly driven by CaO content, on the titanite-out reaction for granitoid compositions (2-4 kbar). For MORB compositions, experimental constraints are currently lacking in the 400-600 ºC temperature range.

Here we present the results of a set of experiments run in a piston-cylinder apparatus using a gold capsule with a NNO oxygen fugacity buffer. We tested multiple starting materials, with different Ti/Ca values, including: 1) a pulverised eclogite (MORB composition) powder with titanite and rutile as well as a few initial eclogitic silicate mineral seeds, promoting nuclei for mineral overgrowth, 2) the same eclogite, glassed and pulverised in the lab, with fewer product seeds, and some of these with added Ti powder; 3) a different MORB powder with crushed titanite and kaersutite seeds. More than 30 experiments were conducted, with pressure ranging between 12 and 23 kbar, and temperature between 400 and 750 ºC in water-saturated conditions and using a cold pressure-seal capsule technique. Due to the challenging LT experiments, equilibrium is not attained, but dissolution and precipitation features are often observable. Epidote is one of the first minerals to nucleate and grow when the initial water content is > 10 wt%, and crystallisation is followed by amphibole. We show that when Ti/Ca is high, rutile is stable even at lower pressures, and when Ti/Ca is low, titanite seeds appear metastable even at higher pressures (19 kbar) and low temperatures. This is in agreement with petrological observations (i.e. peak titanite reported in blueschist rocks). At lower water saturation conditions (10 wt%), reactions are more sluggish, but successful experimental assemblies show that at 600 ºC and 14 kbar titanite seeds become unstable and start reacting with the basalt bulk rock powder to form ilmenite. We found that H2O content, as well as Ti/Ca ratios appear to influence the stability of these Ti-phases in a mafic system. These results can be used to constrain the stabilities of rutile, titanite and ilmenite, which in turn elucidate the P-T-X conditions that these accessory minerals are able to record.

[1] Liou, et al. (1998). Schweiz. Mineral. Petrog. Mitt., 78, 317-335. [2] Angiboust, S., & Harlov, D. (2017). Am. Min., 102, 1696-1708.

How to cite: Pereira, I., Koga, K., and Bruand, E.: New rutile and titanite phase stability constraints at subsolidus conditions in a mafic system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3092, https://doi.org/10.5194/egusphere-egu22-3092, 2022.

EGU22-6180 | Presentations | GMPV2.2

New zircon U-Pb geochronology from the Ketilidian orogen of South Greenland

Rikke Vestergaard, Tod Waight, Andreas Petersson, Heejin Jeon, and Martin Whitehouse

The Paleoproterozoic Ketilidian orogen in South Greenland (1.85-1.73 Ga) is interpreted to be the result of northwards-dipping oblique subduction of an oceanic plate beneath the Archaean continental crust of the North Atlantic Craton. The Ketilidian orogen was part of the subducted-related magmatism and accretionary orogenic belt named the Great Paleoproterozoic Accretionary Orogen that existed along an active margin stretching through Laurentia (North America and South Greenland) to Baltica (Northeast Europe), which formed the supercontinent Columbia/Nuna. Thus, the orogeny represents part of an important episode of crustal growth and preservation in Earth’s history. The Central Domain of the orogeny is dominated by the plutonic remnants of a magmatic arc (the Julianehåb Igneous Complex (JIC), ca. 1.85-1.80 Ga), which eventually grew sufficiently large and stable to subsequently uplift and unroof, to produce rocks interpreted to represent erosional fore-arc deposits that are preserved to the south in the Southern Domain. Between ca. 1.80 Ga and 1.76 Ga, the fore-arc was subjected to metamorphism of amphibolite to granulite facies, and was subsequently intruded by post-tectonic granites (including rapakivi variants) of the Ilua Suite (1.75-1.73 Ga). We present new zircon U-Pb SIMS ages for granitic and metasedimentary rocks sampled at a regional scale in a traverse stretching NW to SW through the Central and Southern Domains of the Ketilidian Orogen in South Greenland. Previous studies have distinguished two pulses of magmatism in the JIC, an early event at ca. 1.85-1.83 Ga and a later phase at ca. 1.80-1.78 Ga. Our JIC samples are dominated by the late stage (<1.83 Ga) with most ages concentrated at 1.8 Ga, suggesting that the main volume of crust in the western portion of the arc was generated over a relatively short period. Ages for the Ilua Suite agree well with previous studies. Zircon age distributions in the metasedimentary rocks of the Southern Domain are consist with detritus dominantly sourced from the JIC, however the presence of small populations of older zircons (up to 2.8 Ga) not observed as inherited zircons in the JIC, indicates that older crustal components also eroded into the fore-arc. These U-Pb zircon results are part of an ongoing larger investigation combining O-Hf isotope compositions in zircon, coupled with whole rock geochemical and isotope data. This research will provide the first thorough geochemical and petrogenetic investigation of the timing, across arc variations, and source components involved in the formation and evolution of South Greenland as well as its contribution in one of the worldwide peaks of continental crustal growth.

How to cite: Vestergaard, R., Waight, T., Petersson, A., Jeon, H., and Whitehouse, M.: New zircon U-Pb geochronology from the Ketilidian orogen of South Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6180, https://doi.org/10.5194/egusphere-egu22-6180, 2022.

EGU22-11108 | Presentations | GMPV2.2

Eclogite-hosted metamorphic veins in the Münchberg Massif (Germany)

Johannes Pohlner, Afifé El Korh, Reiner Klemd, Thomas Pettke, and Bernard Grobéty

Eclogite-hosted metamorphic veins mark former fluid migration pathways during a subduction-exhumation cycle, and allow to trace fluid-mediated element transfer across lithologies, to ultimately metasomatize the mantle wedge. Fluids can be generated by dehydration reactions at different P-T conditions in various lithologies, all influencing how different chemical constituents are dissolved and re-precipitated. Here we present a study of eclogite-hosted quartz-rich metamorphic veins in the Variscan Münchberg Massif. The eclogites probably represent subducted continental crust that was variably hydrated and subjected to amphibolite facies conditions before reaching eclogite facies peak conditions of ca. 3 GPa and 700°C.

Isolated, mm-sized quartz pockets with euhedral high-pressure minerals are common in the Münchberg eclogites, but continuous veins that may have allowed focused fluid flow beyond specimen scale are rare. Nevertheless, where such veins occur, they can contain high-pressure minerals such as garnet and omphacite, but also rutile, zircon, and allanite, indicating high field strength-element (HFSE) mobility at least on the specimen scale. Garnet- and omphacite-bearing veins are typically 1-10 mm thick with average crystal sizes of 1 mm and less. A different vein type is mostly similar in thickness, but consists of quartz + phenocrysts (sometimes >1 cm long) of kyanite, phengite, and/or rutile. Symplectite-rich selvages surrounded by mostly fresh host eclogite are common.

Oxygen isotope thermometry of quartz-garnet, quartz-phengite, and quartz-kyanite pairs yield temperatures around 700°C, interpreted to represent vein crystallization. δ18O values of vein quartz (+6.1 to +10.5‰) from all vein types are identical to δ18O values of host rock quartz (the latter were predicted from mass balance modelling at 700°C based on host rock δ18O values from +4.0 to +7.9‰). While it is evident that the garnet- and omphacite-bearing veins were formed under eclogite facies conditions, pressures are uncertain for the quartz-rutile, quartz-phengite, and quartz-kyanite veins. Still, vein formation at relatively high pressures seems probable, as solubilities of chemical components tend to increase with pressure, facilitating HFSE mobilization from the source rock. We propose that internal fluids were generated by dehydration of phengite and/or zoisite and/or amphibole from the eclogites. Isolated quartz-rich pockets formed in eclogites that may have released only small amounts of fluid, whereas continuous metamorphic veins were formed in eclogites that produced more fluid, probably reflecting a more intense hydration before eclogite facies metamorphism. The internal origin of the fluids supported by oxygen isotope evidence argues against fluid transport over large distances. The fluids may have largely remained in place before being consumed for symplectite formation upon retrogression to amphibolite facies conditions.

How to cite: Pohlner, J., El Korh, A., Klemd, R., Pettke, T., and Grobéty, B.: Eclogite-hosted metamorphic veins in the Münchberg Massif (Germany), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11108, https://doi.org/10.5194/egusphere-egu22-11108, 2022.

EGU22-3423 | Presentations | GMPV2.2

Metasomatism between serpentinite and pelitic schist in the Yuli belt, eastern Taiwan: fluid-rock interactions during subduction metamorphism

Dominikus Deka Dewangga, Chin-Ho Tsai, Hao-Yang Lee, Yoshiyuki Iizuka, Wen-Han Lo, and Chi-Yu Lee

Metasomatic rocks in orogenic mélanges bear critical information about fluid-rock interactions and element mobilities during subduction processes. The Yuli belt contains a few mélange units that crop out high-pressure blocks of metaigneous rocks and serpentinites enclosed in metasedimentary rocks. Metasomatic rocks are found along contacts between the serpentinites and metasedimentary rocks. However, the protolith and formation of those metasomatic rocks are largely unknown. Meter-scale metasomatic zones occur at the contact between pelitic schists (PS) and serpentinites (SP) in the Tsunkuanshan area. Five zones from PS to SP are newly identified: (I) chlorite-albite schist, (II) amphibole-albite rock, (III) albite-chlorite schist, (IV) epidote-chlorite schist, and (V) chlorite-talc schist. Minor garnet and amphibole (glaucophane core - barroisite mantle - actinolite rim) are present in the zone I and II, respectively. Field and petrographic observations combined with whole-rock major elements data suggest that this rock association likely was formed by chemical exchanges between the SP and PS. However, the zone II shows enrichment of Si, Na, and Ca, but Al depletion relative to the other metasomatic rocks. This anomaly might be due to infiltration of external fluids. Rare earth element patterns of the PS, zone I, II, III, and IV are similar, indicating a similar protolith origin. Hence, the original boundary between the PS and SP is likely between the zone IV and V. We estimate the chemical mass balance from the PS to the metasomatic rocks (zone I, II, III, and IV) using the sparse isocon method (Kuwatani et al., 2020). The result shows that the chemical components in zone I, III, and IV are gained relative to the PS, whereas those in zone II are of loss. We interpret that the zone I, III, IV, and V were produced by diffusive exchanges of components between the PS and SP, whereas formation of the zone II was likely created by Na-Ca rich fluid infiltrations. The newly-found occurrence of glaucophane within the zone II indicates fluid-rock interactions during subduction metamorphism.

Keywords: Chemical mass balance, sparse isocon method, Na-Ca rich fluids, Yuli belt.

How to cite: Dewangga, D. D., Tsai, C.-H., Lee, H.-Y., Iizuka, Y., Lo, W.-H., and Lee, C.-Y.: Metasomatism between serpentinite and pelitic schist in the Yuli belt, eastern Taiwan: fluid-rock interactions during subduction metamorphism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3423, https://doi.org/10.5194/egusphere-egu22-3423, 2022.

EGU22-1215 | Presentations | GMPV2.2

Experimental constraints on low temperature dehydration induced by mineral reactions in calcite-bearing ophicarbonates

Lisa Eberhard, Oliver Plümper, and Daniel J. Frost

It is generally accepted that subduction zones are important sites for element recycling into the Earth’s mantle. This does in particular also include carbon, which is transported in the form of organic carbon and carbonates. While organic carbon is expected to effectively fix carbon in the slab, carbonates are often entitled as an important CO2 source for arc magmatism. The exact composition of the total subducted carbon load, in terms of oxidised and reduced carbon material, changes between different slabs and consequently the total released carbon varies significantly among suduction zones. An important mechanism for carbon release is the dissolution of carbonates in aqueous fluids. Ophicarbonates, containing both serpentine and carbonate minerals, are thus of special interest: The fluid released through serpentine dehydration reactions interacts with carbonates and causes the release of carbon. However, to better constrain the carbon release it is essential to understand the release of fluid in carbonated systems.

In this study we present a detailed experimental analysis on the effect of carbonates on the fluid release from serpentinites. We performed multi-anvil experiments on model ophicarbonates. Our starting material was a mixture between natural antigorite and Ca-carbonate and/or graphite. We also conducted thermodynamic calculations on various serpentinite-carbonate systems. Our experimental results show that serpentine dehydrates at temperatures <600 °C at 2.5 GPa, which is lower with respect to uncarbonated serpentinites. For a serpentinite with 20 wt% CaCO3 the dehydration of serpentine thus takes place at 50 - 60 km depth. In the absence of CaCO3 the fluid is released at 60 - 70 km depth. In cold subduction zones this shift in dehydration depth is even more extreme: In a carbonated system the serpentine was found to dehydrate at 80 - 110 km depth, in comparison to 110 - 130 km depth in the uncarbonated system. We found that this shift is mainly due to Ca-Mg exchange reactions between the carbonate and silicate fraction. The experimental run products show distinct dehydration mineralogy, forming Ca-silicates and Mg-bearing carbonates. In combination with mass balance calculations we show that the total carbonate-fraction does not decrease over the whole experimental temperature range. In conclusion, serpentinites with a high Ca-carbonate content are expected to dehydrate earlier in the subduction zones, whereas the carbon remains in the slab. The presence of Ca-carbonate thus has the potential to prevent subduction of water into deeper levels of the Earth’s mantle.

How to cite: Eberhard, L., Plümper, O., and Frost, D. J.: Experimental constraints on low temperature dehydration induced by mineral reactions in calcite-bearing ophicarbonates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1215, https://doi.org/10.5194/egusphere-egu22-1215, 2022.

EGU22-3929 | Presentations | GMPV2.2

Carbonation of peridotites along the basal thrust of the Semail Ophiolite (OmanDP Hole BT1B): insights from Fe and Zn isotopes

Thierry Decrausaz, Marguerite Godard, Baptiste Debret, and Isabelle Martinez

The formation of carbonated serpentinites (serpentine, Mg-Ca carbonates) and listvenites (quartz, Mg-carbonate) by reactions between exhumed mantle peridotites and percolating CO2-bearing fluids is a major sink for carbon from spreading ridges to ophiolites and orogenic suture zones. During ICDP Oman Drilling Project, the transition from the base of the Semail Ophiolite to its metamorphic sole was drilled at Hole BT1B (Wadi Mansah), allowing to recover ~200 m of variously carbonated serpentinites and listvenites, and underlying metabasalts. Mineralogical and geochemical investigations indicate that carbonation at the expense of the Wadi Mansah peridotites was triggered by the migration of multiple fluid batches along the basal thrust at shallow depths and low temperatures (50-250 °C). To better constrain the impacts of fluid source(s) and protolith compositions on reaction pathways and oxidation state during carbonation, we carried out iron and zinc isotopes study of 19 variously carbonated peridotites (13 listvenites, 5 carbonated serpentinites, one serpentinized harzburgite) and of 6 underlying metamorphic samples from Wadi Mansah area (including 3 BT1B samples).

The partially serpentinized harzburgite and carbonated serpentinites have δ56Fe and δ66Zn compositions ranging between -0.05 – +0.06 ‰ and -0.11 – +0.15, respectively, overlapping that of previously analysed abyssal (δ56Fe: -0.15 – +0.11 ‰; δ66Zn: +0.12 – +0.62 ‰), ophiolitic (δ56Fe: -0.27 – +0.14 ‰; δ66Zn: -0.56 – +0.38 ‰), orogenic (δ56Fe: -0.06 – +0.12 ‰; δ66Zn: +0.03 – +0.55 ‰), and fore-arc (δ56Fe: -0.26 – +0.09 ‰) peridotites. In contrast, listvenites display highly variable δ56Fe and δ66Zn values, between -0.33 – +0.2 ‰ and -0.46 – +0.64 ‰ respectively. Iron isotopes compositions show a positive correlation with bulk iron contents. Zinc isotope compositions are positively correlated to δ13CTC values, suggesting a high mobility of Zn in carbonate-bearing fluids. The lightest δ66Zn values were measured in listvenites with minor amounts of fuchsite (Cr-mica), that often display evidences for breakdown of Cr-spinel. Metamorphic sole samples display isotopic compositions typical of mafic rocks (δ56Fe: +0.01 – +0.24 ‰; δ66Zn: +0.24 – +0.47 ‰), in agreement with an oceanic crust-derived protolith (MORB, δ56Fe: +0.06 – +0.18; δ66Zn: +0.27 – +0.30 ‰).

Our results suggest an important control of the protolith chemistry and complexation with dissolved carbon in reactive fluids on the Fe and Zn isotopes compositions.

How to cite: Decrausaz, T., Godard, M., Debret, B., and Martinez, I.: Carbonation of peridotites along the basal thrust of the Semail Ophiolite (OmanDP Hole BT1B): insights from Fe and Zn isotopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3929, https://doi.org/10.5194/egusphere-egu22-3929, 2022.

EGU22-9996 | Presentations | GMPV2.2

Metaserpentinite carbonation and decarbonation reactions during subduction metamorphism and subsequent tectonic exhumation

Vicente López Sánchez-Vizcaíno, José Alberto Padrón-Navarta, Casto Laborda-López, María Teresa Gómez-Pugnaire, Manuel Dominik Menzel, and Carlos Jesús Garrido

In subduction zones, serpentinite-hosted ophicarbonates and their main dehydration and decarbonation reactions linked to prograde metamorphism are relatively well understood. On the contrary, the geological conditions and processes leading to the carbonation of subduction-zone metaserpentinites by fluid–rock interactions remain poorly constrained. At different arc depths, the reaction of decarbonation fluids derived from marble and carbonate‐bearing sediment with slab and mantle wedge serpentinites, as well as tectonic mixing and deformation along subduction zone interface, may produce magnesite-bearing rocks with a bulk composition similar to that of ophicarbonates. Subsequently, these hybrid metasomatic lithologies will undergo decarbonation reactions at prograde or retrograde conditions which may influence the cycling of C and other volatiles from the slab to the mantle wedge and the global estimates of C fluxes at convergent margins. This can be evaluated through the study of exposed paleo-subduction metamorphic suites.

Here we investigate the tectonic, textural and mineralogical evolution of marble layers and magnesite-rich lenses hosted in chlorite harzburgite (Chl-harzburgite) in the Cerro Blanco ultramafic massif (Nevado-Filábride Complex, Betic Cordillera, S. Spain), which records high-pressure alpine subduction metamorphism as evidenced by the transition from antigorite serpentinite (top of the body) to Chl-harzburgite (bottom) due to high-pressure deserpentinization. Chl-harzburgite is separated from a gneiss and mica schist crustal sequence by a footwall of strongly heterogenous mylonite (around 20 m thick) encompassing: transposed, foliated and brecciated marble layers, foliated Chl-harzburgite lenses (in some cases completely transformed to retrograde serpentinite), centimetre to several decimetre thick boudins of idiomorphic coarse to very coarse magnesite aggregates, associated to chlorite and magnetite and enveloped by the mylonitic foliation, and, finally, abundant almost monomineralic amphibole aggregates. We interpret this mylonite zone as a detachment leading to the exhumation of the Cerro Blanco massif after reaching peak subduction metamorphic conditions that formed the Chl-harzburgite assemblage.

Combined field, EDS-SEM, and EPMA data obtained from a detailed cross-section sampling of this mylonite zone reveal that, locally, metamorphic equilibrium was reached between Chl-harzburgite and the transformation products of the magnesite boudins during the mylonite foliation development. Thermodynamic modelling of these assemblages allows inferring the relationship between deformation and metamorphic conditions during exhumation, including possible decarbonation reactions.

We thank the Universidad de Jaen 1263042 FEDER-UJA grant, funded by the European Social Fund and the European Regional Development Fund.

How to cite: López Sánchez-Vizcaíno, V., Padrón-Navarta, J. A., Laborda-López, C., Gómez-Pugnaire, M. T., Menzel, M. D., and Garrido, C. J.: Metaserpentinite carbonation and decarbonation reactions during subduction metamorphism and subsequent tectonic exhumation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9996, https://doi.org/10.5194/egusphere-egu22-9996, 2022.

EGU22-13148 | Presentations | GMPV2.2

Rupture of serpentinized mantle wedge by self-promoting carbonation: insights from Sanbagawa metamorphic belt

Atsushi Okamoto, Ryosuke Oyanagi, Kazuki Yoshida, Masaoki Uno, Hiroyuki Shimizu, and Madhusoodhan Satish-Kumar

The slab-mantle interface is one of the most active sites of fluid-rock interaction, which affects the mass transfer and mechanical properties along subduction zone megathrust. However, the effects of CO2 fluids and carbonation/decarbonation reactions on seismic activity are still poorly understood. In addition, although mantle peridotite is known as a large sink of CO2, the nature of carbonation at mantle wedge condition remains unconstrained. In this study, we show the characteristics of carbonation of serpentinite body from the Sanbagawa metamorphic belt, Kanto Mountain, Japan [1]. The Higuchi serpentinite body (8 x15 m) is mainly composed of antigorite, and has not relics of olivine and pyroxenes. Massive antigorite parts are segmented by talc + carbonates (magnesite, dolomite and calcite) veins. At the boundary between serpentinite body and pelitic schists, actinolite-chlorite schist and chlorite rocks were formed. The location, depleted composition of Cr-rich spinel in the Higuchi body and temperature of ~400 ˚C of carbonation suggest that this body was originated from the leading edge of the mantle wedge. The carbon and oxygen stable isotope compositions of carbonates within the Higuchi body reveal that carbonic fluid was derived from carboniferous materials in sediments. Carbonation of serpentinite body is characterized by gains of CO2, silica and Ca, and losses of H2O and Mg. The thermodynamic calculations on mineral-fluid equilibria reveal that (1) the carbonic fluid produced under the oxidizing conditions (QFM +0.3) explains the systematic mineralogical variations within the Higuchi body, and that (2) carbonation of serpentinite proceeded with solid volume contraction, high fluid pressure and high mobility of Mg, which is largely consistent with the experimental carbonation at the mantle wedge condition [2]. This is consistent with the tree-like patterns of carbonate veins within the Higuchi body. Brittle failure to form carbonate veins was followed by a viscos flow of carbonate and talc. We infer that episodic infiltration of oxidizing fluids causes self-promoting carbonation of mantle wedge with solid volume change, which could affect the mechanical properties of slab-mantle interface.

[1] Okamoto, A, et al., 2021. Com Env Earth, 58, 4831-4839. doi.org/10.1038/s43247-021-00224-5

[2] Sieber et al. 2020. J. Petrol., 1-24. doi: 10.1093/petrology/egaa035

How to cite: Okamoto, A., Oyanagi, R., Yoshida, K., Uno, M., Shimizu, H., and Satish-Kumar, M.: Rupture of serpentinized mantle wedge by self-promoting carbonation: insights from Sanbagawa metamorphic belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13148, https://doi.org/10.5194/egusphere-egu22-13148, 2022.

EGU22-11350 | Presentations | GMPV2.2

Hydrocarbon-bearing fluid migration produces brecciation at high pressure condition in subduction

Francesco Giuntoli, Alberto Vitale Brovarone, and Luca Menegon

It has been recently proposed that high-pressure genesis of abiotic hydrocarbon can lead to strain localization in subducted carbonate rocks1. However, the mechanical effects of the migration of these hydrocarbon-bearing fluids on the infiltrated rocks still need to be constrained.

In this study, we investigate omphacitite (i.e. omphacite-rich rock) adjacent to an high-pressure methane source from the Western Italian Alps (Italy) using a multiscale and analytical approach including petrographic, microstructural, X-ray compositional mapping and electron backscatter diffraction analyses (EBSD). In the field, omphacitite bands are 1-5 metres thick and tens of metres long and are adjacent to carbonate rocks affected by high-pressure reduction and methane production.

Hand specimens and thin sections display a brecciated structure, with omphacitite fragments ranging in size from a few microns to several centimetres, surrounded by a matrix of jadeite, omphacite, grossular, titanite, and graphite. X-ray compositional maps and cathodoluminescence images highlight oscillatory zoning and skeletal (jackstraw) textures in jadeite, omphacite and garnet in the matrix, suggesting a fast matrix precipitation under plausible disequilibrium conditions. CH4 and H2 are found in fluid inclusions in the jadeite grains. This feature suggests a potential link between the genesis of CH4 in the adjacent carbonate rocks and the brecciation event.

EBSD analysis was performed on omphacitite clasts close to their borders, where omphacite grain size varies between a few microns and a maximum of 100 microns. Those omphacite grains display no crystallographic preferred orientation, abundant low angle boundaries and low (< 5°) internal lattice distortion. We interpret these textures as formed by pervasive and diffuse micro-fracturing related to the brecciation occurring at high pore fluid pressure, reaching sub-lithostatic values. This study suggests that at high-pressure conditions in subduction zones, the genesis and migration of hydrocarbon-bearing fluids can trigger fracturing in adjacent lithotypes.

1Giuntoli, F., Vitale Brovarone, A. & Menegon, L. Feedback between high-pressure genesis of abiotic methane and strain localization in subducted carbonate rocks. Sci. Rep. 10, 9848 (2020).

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

 

How to cite: Giuntoli, F., Vitale Brovarone, A., and Menegon, L.: Hydrocarbon-bearing fluid migration produces brecciation at high pressure condition in subduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11350, https://doi.org/10.5194/egusphere-egu22-11350, 2022.

The role of subduction zones has been considered critical to understand carbon fluxes among the Earth’s reservoirs. At plate margins, most of the carbon is stored in carbonate sediments. Nevertheless, the past decade saw an increasing focus also on reduced carbon - kerogen and graphite – to understand its role in the deep carbon cycle. Most of reduced carbon derive from seafloor organic-rich sediments, even if, a little portion can form by decarbonation during metamorphism.

In the Palaeoproterozoic supracrustal rocks of the Lewisian Complex, graphitic marbles were found in a mixed succession of metasediments at Gott Bay, Island of Tiree (Scotland). Such marbles show bedding-parallel slip surfaces associated with chlorite that are absent in other marbles on the island that are devoid of graphite. Marbles and schists-hosted graphite were analysed showing marked differences in carbon isotopic composition and structural ordering measured by means of Raman spectroscopy.

Petrographic and chemical evidence support the hypothesis of an abiotic origin of the marble-hosted graphite and the mechanisms that led to its formation could explain the heavy isotopic composition of many Proterozoic marbles in the world.

 

 

 

 

How to cite: Schito, A., Parnell, J., Muirhead, D., and Boyce, A.: Evidence of abiotic graphite formation in Proterozoic marbles of the Lewisian Complex: mechanisms and consequences for the deep carbon cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5014, https://doi.org/10.5194/egusphere-egu22-5014, 2022.

High-pressure COH fluids have a fundamental role in a variety of geological processes. Their composition in terms of volatile species can control the solidus temperature, carbonation/decarbonation reactions, and influences the amount of solutes generated during fluid-rock interaction at depth. Over the last decades, several systems have been experimentally investigated to unravel the effect of COH fluids at upper mantle conditions. However, fluid composition is rarely tackled as a quantitative issue, and rather infrequently fluids are analyzed in the same way as the associated solid phases in the experimental assemblage. A comprehensive characterization of carbon-bearing aqueous fluids in terms of composition is hampered by experimental difficulties in synthetizing and analyzing high-pressure fluids, without altering their composition upon quench.

Recently, improved ex situ techniques have been proposed for the analyses of experimental COH fluids, leading to significant advancement in synthetic fluids characterization. The development of customized techniques in order to investigate these fluids, in terms of volatile speciation and dissolved solute load, allowed to elucidate some of the processes involving carbon at high-pressure conditions and to assess its influence in the mantle wedge.

Some of the recently developed techniques employed for ex situ quantitative analyses of carbon-saturated COH fluids will be presented, such as the capsule piercing QMS technique (Tiraboschi et al., 2016) and the cryogenic LA-ICP-MS technique (Kessel et al., 2004; Tiraboschi et al., 2018). The capsule piercing QMS technique allow to measure the main uncharged volatile species in the COH system (i.e., H2O, CO2, CH4, H2, O2, CO), while the cryogenic LA-ICP-MS technique permits to measure the amount solutes generated by mineral dissolution in COH fluids, in terms of mol/kg.

The results obtained by employing these analytical strategies indicate that a quantitative approach to COH fluid analyses is a fundamental step to understand the effect of carbon-bearing fluids at upper mantle conditions and to ultimately unravel the deep cycling of carbon.

 

Kessel, R., Ulmer, P., Pettke, T., Schmidt, M. W. and Thompson, A. B. (2004) A novel approach to determine high-pressure high-temperature fluid and melt compositions using diamond-trap experiments, Am. Mineral., 89(7), 1078–1086.

Tiraboschi, C., Tumiati, S., Recchia, S., Miozzi, F. and Poli, S. (2016) Quantitative analysis of COH fluids synthesized at HP–HT conditions: an optimized methodology to measure volatiles in experimental capsules, Geofluids, 16(5), 841–855.

Tiraboschi, C., Tumiati, S., Sverjensky, D., Pettke, T., Ulmer, P. and Poli, S. (2018) Experimental determination of magnesia and silica solubilities in graphite-saturated and redox-buffered high-pressure COH fluids in equilibrium with forsterite + enstatite and magnesite + enstatite, Contrib. to Mineral. Petrol., 173(1), 1–17.

How to cite: Tiraboschi, C.: Carbon-saturated COH fluids in the upper mantle: what ex situ experiments tell us about carbon at high-pressure and high-temperature conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11725, https://doi.org/10.5194/egusphere-egu22-11725, 2022.

EGU22-5782 | Presentations | GMPV2.2

Deep subduction of continental crust contributes to mantle metasomatism and deep carbon cycle

Alessia Borghini, Gautier Nicoli, Silvio Ferrero, Patrick J. O'Brien, Oscar Laurent, Laurent Remusat, Giulio Borghini, and Sula Milani

The garnet in the ultra-high pressure (UHP) eclogites of the Erzgebirge (Bohemian Massif, Germany) trapped primary inclusions of metasomatic melt originated by the partial melting of the continental crust. The study of these inclusions alow us to estimate the contribution of the subducted continental crust to mantle metasomatism and deep carbon fluxes. The inclusions are randomly distributed in the inner part of the garnet, they are micrometric and occur as both polycrystalline, i.e. nanogranitoids, and glassy, often with a shrinkage bubble. Nanogranitoids consist of kumdykolite, quartz, kokchetavite, biotite, white mica, calcite and rare graphite. The inclusions share their microstructural position in the garnet with inclusions of polycrystalline quartz interpreted as quartz pseudomorph after coesite that indicate the entrapment at UHP conditions. The melt composition, measured on glassy inclusions and rehomogenized nanogranitoids, is granitic. The melt is also hydrous, slightly peraluminous and the trace element enrichments observed are consistent with an origin from the continental crust, testified by the high amount of incompatible elements such as Cs, Pb, Th, U, Li and B. Similar signatures were also reported elsewhere in the Bohemian Massif, e.g. in other metasomatic melts hosted in HP mantle eclogites, in metasomatized mantle rocks and in post-collisional ultrapotassic magmatic rocks, suggesting that mantle metasomatism from melts originated in the continental crust is widespread in the orogen.

The melt H2O and CO2 contents were measured with the NanoSIMS. The CO2 values in particular were corrected reintegrating the vapor contained in the shrinkage bubble and are in average 19552 ± 772 ppm, the highest content of CO2 measured so far in crustal melt inclusions. The modelled endogenic carbon flux associated with the subduction of the continental crust of the Variscan Orogenic Cycle is 22 ± 8 Mt C yr-1. This flux within error is similar to the endogenic carbon fluxes in the serpentinized mantle (~ 14 Mt C yr-1) and to the exogenic fluxes in mid-oceanic ridges (~ 16 Mt C yr-1) and arc volcanoes (~ 24 Mt C yr-1). Hence, in collisional settings, deeply subducted continental crust carried a large amount of volatiles to the mantle and the lower crust. Due to the absence of post collisional arc volcanism, most of these volatiles remained trapped in the root of mountain belts. This long-term storage of the carbon in the orogen roots prevents ultimately the closure of the carbon cycle.

How to cite: Borghini, A., Nicoli, G., Ferrero, S., O'Brien, P. J., Laurent, O., Remusat, L., Borghini, G., and Milani, S.: Deep subduction of continental crust contributes to mantle metasomatism and deep carbon cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5782, https://doi.org/10.5194/egusphere-egu22-5782, 2022.

EGU22-9318 | Presentations | GMPV2.2

Subducted Carbon in the Earth’s lower mantle: The fate of magnesite

Lélia Libon, Georg Spiekermann, Melanie Sieber, Johannes Kaa, Serena Dominijanni, Mirko Elbers, Ingrid Blanchard, Christian Albers, Nicole Bierdermann, Wolfgang Morgenroth, Karen Appel, Catherine McCammon, Anja Schreiber, Vladimir Roddatis, Konstantin Glazyrin, Rachel Husband, Louis Hennet, and Max Wilke

Subduction of carbon-bearing phases throughout Earth’s history may be an important mechanism of sourcing carbon to the Earth’s lower mantle. As carbon has very low solubility in mantle silicates, it is primarily present in accessory phases such as carbonates, diamond, or metal carbides. Previous studies indicate that more than half of the carbonate contained in the oceanic crust may survive metamorphism and dehydration in the sub-arc and reach the lower mantle, even though the oxygen fugacity in the deep mantle may not favour their stability [1]. Indeed, the presence of carbonate in ultra-deep diamond inclusions provides evidence for carbonate subduction at least down to the transition zone [2].

The carbonate phases present in the lower mantle depend on their bulk composition, the oxygen fugacity, and on their stability at a given pressure and temperature. Results from high-pressure experiments show that magnesite (MgCO3) can be stable up to deep lower mantle conditions (∼80 GPa and 2500 K) [3]. Accordingly, magnesite may be considered the most probable carbonate phase present in the deep Earth. Experimental studies on magnesite decarbonation in presence of SiO2 at lower mantle conditions suggest that magnesite is stable along a cold subducted slab geotherm [4, 5]. However, our understanding of magnesite’s stability in contact with bridgmanite [(Mg,Fe)SiO3],  the most abundant mineral in the lower mantle, remains incomplete.

Hence, to investigate sub-solidus reactions, melting, decarbonation, and diamond formation in the system MgCO3-(Mg,Fe)SiO3, we conducted a combination of high-pressure experiments using multi-anvil press and laser-heated diamond anvil cells (LH-DAC) at conditions ranging from 25 to 70 GPa and 1300 to 2100 K.

Multi-anvil experiments at 25 GPa and temperatures below the mantle geotherm (1700 K) show the formation of carbonate-silicate melt associated with stishovite crystallization, indicating incongruent melting of bridgmanite to stishovite, in accordance with the recent finding of Litasov and Shatskiy [4]. LH-DAC data from in situ X-ray diffraction show crystallization of bridgmanite and stishovite. Diamond crystallization is detected using Raman spectroscopy. A melt phase could not be detected in situ at high temperatures.

Our results suggest a two-step process that starts with melting at temperatures below the mantle geotherm, followed by crystallization of diamond from the melt produced.  Therefore, we propose that subducted carbonate-bearing silicate rocks will not remain stable in the lower mantle and will instead melt at upper-most lower mantle conditions, fostering diamond formation. Our study also provides additional evidence that diamond production is related to carbonated melt. Consequently, the melting of recycled crust and chemical transfer to the surrounding mantle will hinder the transport of carbon deeper into the lower mantle.

[1] Stagno et al. (2015) Contrib. Mineral. Petrol. 169(2), 16.
[2] Brenker et al. (2007) EPSL 260(1-2), 1-9.
[3] Binck, et al. (2020) Physical Review Materials, 4(5),1-9.
[4] Litasov & Shatskiy (2019) Geochemistry International, 57(9), 1024-1033.
[5] Drewitt, et al. (2019). EPSL, 511, 213-222.

How to cite: Libon, L., Spiekermann, G., Sieber, M., Kaa, J., Dominijanni, S., Elbers, M., Blanchard, I., Albers, C., Bierdermann, N., Morgenroth, W., Appel, K., McCammon, C., Schreiber, A., Roddatis, V., Glazyrin, K., Husband, R., Hennet, L., and Wilke, M.: Subducted Carbon in the Earth’s lower mantle: The fate of magnesite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9318, https://doi.org/10.5194/egusphere-egu22-9318, 2022.

EGU22-3611 | Presentations | GMPV2.2 | Highlight

Perturbation of the deep-Earth carbon cycle in response to the Cambrian Explosion

Andrea Giuliani, Russell N. Drysdale, Jon D. Woodhead, Noah J. Planavsky, David Phillips, Janet Hergt, William L. Griffin, Senan Oesch, Hayden Dalton, and Gareth R. Davies

Earth’s carbon cycle is strongly influenced by subduction of sedimentary material into the mantle. The composition of the sedimentary subduction flux has changed considerably over Earth’s history, but the impact of these changes on the mantle carbon cycle is unclear. Here we show that the carbon isotopes of kimberlite magmas record a fundamental change in their deep-mantle source compositions during the Phanerozoic Eon. The 13C/12C of kimberlites prior to ~250 Myr preserves typical mantle values, whereas younger kimberlites exhibit lower and more variable ratios – a switch coincident with a recognised surge in kimberlite magmatism. We attribute these changes to increased deep subduction of organic carbon with low 13C/12C following the Cambrian Explosion when organic carbon deposition in marine sediments increased significantly. These observations demonstrate that biogeochemical processes at Earth’s surface have a profound influence on the deep mantle, revealing an integral link between the deep and shallow carbon cycles.

How to cite: Giuliani, A., Drysdale, R. N., Woodhead, J. D., Planavsky, N. J., Phillips, D., Hergt, J., Griffin, W. L., Oesch, S., Dalton, H., and Davies, G. R.: Perturbation of the deep-Earth carbon cycle in response to the Cambrian Explosion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3611, https://doi.org/10.5194/egusphere-egu22-3611, 2022.

GMPV5.1 – Solving geoscience problems using mineralogy

The Wanshan tribe is in the Maolin district of Kaohsiung City in Taiwan. This area belongs to the Chaochou Formation within the Lushan Slate Belt. Its terrain is hillslope and stream terrace with slate and argillite rock-composition. The geological features of this area include slope angle greater than 30 degrees, colluvium, and serious erosion, which had a debris flow during the Morakot typhoon (2009). The area is currently classified as a massive potential landslide region and is still in a slow slip (creeping).

In this study, mineralogical and microstructural techniques were applied to investigate the slope stability of this area, e.g. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), optical microscope (OM), scanning electron microscopy (SEM), and microcomputer tomography (micro-CT). A 40 m-depth rock-core was drilled at the field site and the core samples were prepared for related measurements and experiments. The rock-core composed of fresh slates and weathered slates.

Based on XRD and OM analyses, the mineral phases in this area included quartz, illite, chlorite, muscovite and feldspar. The weathered core-sample had a more content ratio of clay minerals compared to that in the fresh slate core-sample. The FTIR results exhibited that the weathered core-samples had a higher water content than that in the fresh slate samples. With the help of SEM and micro-CT, it can be observed that the weathered core-sample had many longitudinal fractures, however, the fresh slate core-sample just had the slate cleavage.

It is so interesting that the lithology of rock-core changed into a dense fresh slate at the depth of 20 m; it suggested that this rock-layer is more impermeable to water. The weathered rock is favorable for water infiltration and then induced rock weathering, which could weaken the mechanical strength of this rock-layer. It is known that the lithology variation/change of rock-layers preferred to accumulate water, and it was easy to become a weak interface-layer. Therefore, we should pay attention to the fluctuation of groundwater level in this area and the drainage system needs to be well done.

How to cite: Hung, C. S. and Chen, Y. H.: Study on slope stability of Maolin area in Kaohsiung (Taiwan) using mineralogical and microstructural techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3511, https://doi.org/10.5194/egusphere-egu22-3511, 2022.

EGU22-3992 | Presentations | GMPV5.1 | Highlight

Low-level shock metamorphism induced by lightning

Tze-Yuan Chen, Li-Wei Kuo, Steven Smith, Ching-Shun Ku, Ching-Yu Chiang, Dennis Brown, and Marianne Negrini

Cloud-to-ground lightning can result in high-temperature metamorphism of rocks, forming rock fulgurite. Here, we characterize a rock fulgurite on granitic gneiss from Kinmen Island, Taiwan, and demonstrate that high-pressure metamorphic features can be also generated by lightning. With the lightning monitoring system, we detected a lightning event with a peak current of 162 kA and the associated fulgurite. We conduct microanalytical methods on rock fulgurite, including optical microscope, scanning electron microscope with electron backscatter diffraction (EBSD), focused ion beam-transmission electron microscopy, and in-situ synchrotron Laue diffraction analyses. The fulgurite is characterized by an up to 200 μm thick glassy crust overlying host rock for around 10 square meters. Within the glassy crust, typical high-temperature features, such as vesicles, relic mineral fragments, and reduced oxidation-state iron oxides spheres, can be recognized. Below the glassy crust, EBSD analysis documents phase transformation (from monoclinic to triclinic) and planar features (exsolution lamellae) of alkali feldspar (sanidine) grains. Synchrotron Laue diffraction analysis indicates that these planar features are parallel to the (100) plane and preserve residual stress of up to 1.57 GPa, well above the 0.38 GPa recorded in feldspar grains (reference sample from borehole cores) that are not affected by lightning. The findings, including glassy crust, phase transformation and planar features of alkali feldspar grains, and high residual stress, suggest that lightning can result in both high-temperature and high-pressure metamorphic features. Because these assemblages are reminiscent of shock metamorphic textures produced by meteorite impact, we interpret them to be shock-related features. Given that the recognition of shocked minerals (with planar features) and glasses are both parts of the set of diagnostic criteria for meteorite impacts, in the absence of a broader suite of criteria, we recommend caution, since our identification of the Kinmen Island fulgurite indicates lightning can result in low-level shock metamorphic features.

How to cite: Chen, T.-Y., Kuo, L.-W., Smith, S., Ku, C.-S., Chiang, C.-Y., Brown, D., and Negrini, M.: Low-level shock metamorphism induced by lightning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3992, https://doi.org/10.5194/egusphere-egu22-3992, 2022.

Nanoscale apatite inclusions in xenotime: witness of Pb mobility

Cilva Joseph1, 2, Denis Fougerouse1, 2, Steven M. Reddy1, 2, Aaron Dodd3, Steven Denyszyn4, David W. Saxey2, William D.A. Rickard2

1School of Earth and Planetary Sciences, Curtin University, Perth, Australia

2Geoscience Atom Probe Facility, John de Laeter Centre, Curtin University, Perth, Australia

3Microscopy and Microanalysis Facility, John De Laeter Centre, Curtin University, Perth, Australia

4School of Earth Sciences, University of Western Australia, Perth, Australia

Discordant ages as measured by 206Pb/238U and 207Pb/235U ratios in various geochronometers are common. Several mechanisms have been proposed to explain discordant ages in different minerals. These include loss of radiogenic Pb, mixing of different age domains within a mineral, and intermediate daughter radioisotope disequilibrium. Xenotime (YPO4) is a geochronometer used to date different geological processes, such as diagenesis, metamorphism, and hydrothermal events. However, xenotime commonly yields small degrees of discordancy (<3%) by high precision geochronology techniques. To investigate the mechanism responsible for slightly discordant xenotime analyses, two ~1000 Ma crystals (z6413 and Y1) from Ontario and Western Australia were analysed using atom probe tomography (APT) and transmission electron microscopy (TEM) which provide sub-nanometre scale chemical and crystallographic analysis of minerals. Both samples have not undergone significant metamorphism (T < 300°C) after crystallisation. Combined APT and TEM results revealed the presence of nanoscale apatite [Ca5(PO4)3(F,Cl,OH)] inclusions and crystal dislocations in the xenotime grains. APT data indicates that the apatite inclusions are rich in radiogenic Pb and that the dislocations are decorated with Ca, Cl and H. Nanogeochronology of xenotime by APT indicate that the apatite inclusions likely formed by exsolution during the cooling of crystals, capturing radiogenic Pb. Dislocations in the crystals may have acted as fast diffusion pathways leading to radiogenic Pb-loss and caused the U-Pb system disturbance.

How to cite: Joseph, C.: Nanoscale apatite inclusions in xenotime: witness of Pb mobility, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11558, https://doi.org/10.5194/egusphere-egu22-11558, 2022.

EGU22-1195 | Presentations | GMPV5.1

Annealing experiments on zircons: influence of lattice orientation and metamictization.

Irene Morales, José Francisco Molina, Pilar Montero, Fernando Bea, and Aitor Cambeses

Zircon derived from crustal rocks can survive dissolution into basic melt during rock assimilation and magma hybridization if shielded in mafic phenocrysts or minerals from non-disaggregated xenoliths. Under these conditions, zircon can be subject to thermal shock that triggers recrystallization of metamict domains and reaction with its hosted mineral inclusions. In this work, we simulate this process by performing thermal annealing experiments on zircon grains with a variable degree of metamictization. The results show recrystallization of metamict domains, melting of multi-phase mineral inclusions, nanopores formation, and microcracking propagation by thermo-elastic stress. Highly metamict zircon with elevated common-Pb and radiogenic-Pb loss, which were impossible to date with SHRIMP, lost all their common-Pb and some radiogenic-Pb upon annealing, producing well-fitted discordias with significant upper intercept age. The porosity enhances intracrystalline melt mobility, leaching out impurities. Baddeleyite was formed at temperatures below the thermal decomposition of pure zircon by two mechanisms: (1) incongruent zircon dissolution into molten mineral inclusions with a high CaO/SiO2 ratio (2) recrystallization of metamict domains aided by silica migration from the reaction site.

How to cite: Morales, I., Molina, J. F., Montero, P., Bea, F., and Cambeses, A.: Annealing experiments on zircons: influence of lattice orientation and metamictization., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1195, https://doi.org/10.5194/egusphere-egu22-1195, 2022.

The Yanchang Formation of the Upper Triassic in the Jiyuan area in the central and western parts of the Ordos Basin is one of the main oil and gas enrichment areas in the basin. However, the tight sandstones of the Yanchang Formation have long been controversial on mineral genesis, formation age and sediment source. The distribution and variation characteristics of detrital zircon ages were studied using LA-ICP-MS dating and geochemistry testing of the detrital zircons from sandstones. The source of detrital zircons of different age components is identified, and difference of tectono-paleogeographic environments is analyzed. The main conclusions can be drawn as follows. Cathodoluminescence images show that most detrital zircon have a zonal structure. Rare Earth Element distribution models show that the sandstone is rich in HREE and is short of LREE, and all of models are left-dipping patterns. The Th/U values of detrital zircon show that most of the values are greater than 0.4, and a few are less than 0.1.The above geochemical testing results show that the source of detrital zircon is mainly magmatic rocks, followed by metamorphic rocks, and the ages of detrital zircons are reliable.The age results show that there exist three age stages of the Yanchang Formation detrital zircons, i.e., 228- 379 Ma, 1650- 1915 Ma, 2400- 2560 Ma, corresponding to the tectonic movements of indosinian, Hercynin, middle- late Lüliang movement and early- middle Wutai movement.By comparing the isotopic ages for the plutons in and around research areas, the tight sandstone of the Yanchang Formation in the central and western parts of the Ordos Basin derive from the Daqing Mountains-Wula Mountains, Yinshan Mountains and Jining areas in the north-northeast of the Ordos Basin.The sedimentary rocks source from gneissic granite in the late Neoarchean, ancient TTG gneiss and granulite in the early Paleoproterozoic, the khondalite belt in the Lüliang Movement, and the magmatic rock in the Indosinian and Hercynian.

How to cite: Wu, K.: The study of detrital zircon geochronology, geochemistry and tectonic-sedimentary significance of Upper Triassic Yanchang Formation in  central and western Ordos Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6046, https://doi.org/10.5194/egusphere-egu22-6046, 2022.

The Late Cretaceous igneous rocks within the south-western part of the Pannonian Basin basement (Croatia) occur in two areas: at the north-western part of Mt. Papuk (Pp; covering the area of ~10km2) and at Mt. Požeška Gora (Pg; area of ~30 km2). The predominant rocks are rhyolites and basalts, with pyroclastic material to a lesser extent. Additionally, smaller granite body crops out on Pg. The specific magma geochemistry (A-type signature) and age (~82 Ma) recently refined on acidic varieties (granite and rhyolite) indicate the beginning of the tectonic transition in this area from compression to extension.

In the reconstruction of magma evolution, inclusions captured in zircon grains represent valuable material that provides additional information. Zircon grains extracted from the samples of acidic rocks (rhyolites and granites) are quite small, usually less than 100 µm in the longer axis, with an average aspect ratio of 2.1:1. The grains are euhedral, with an external morphology defined by {100} prisms and {101}>{211} bipyramids. Such a primitive external zircon morphology suggests a magma source in the lower crust or upper mantle. The high Zr-saturation temperature and Ti-in-zircon temperature (~780 °C for Pp, ~910 °C for Pg) also suggest a deep source processes and material. The zircon grains are colourless and highly transparent, comprising solid inclusions suitable for analysis with the Raman spectrometer. The inclusions are euhedral-subhedral, mostly less than 10–15 µm in diameter. They are randomly oriented with the respect to the host zircon crystal growth structure. The following inclusions in zircons were detected by Raman spectrometer: anatase, kokchetavite, kumdykolite, apatite and hematite. In respect to characteristics of magma crystallisation, we have found important that anatase represents a TiO2 polymorph formed at lower igneous temperatures, but its crystallisation compared to rutile is favoured by rapid crystallisation. The kokchetavite and kumdykolite are polymorphs of KAlSi3O8 and NaAlSi3O8, respectively. Recent research show that they represent metastable phases in melt inclusions as a consequence of rapid crystallisation. Apatite detected in zircon dominantly resembles F-apatite. A high F content is indicative of magma formed by partial melting of upper mantle material, while hematite inclusions indicate an oxidising environment for the magma at the time of hematite crystallisation. In addition to the inclusions, the rapid uplift of the Late Cretaceous acidic magma is supported by the occurrence of hematite with crystallographically oriented ilmenite exsolutions and perthite found in Pg granite as well as zircon aspect ratios.

In conclusion, the inclusions found in the zircon, which were protected from later equilibration with the melt or alteration by fluids, confirm a deep magma source (upper mantle/lower crust) and represent independent mineralogical evidence indicating rapid uplift and emplacement of a hot mantle/crust transition level magma with early-crystallised zircon into the upper crustal level. The rapid uplift was possible due to the formation of accompanying extensional deep-rifts in the course of the tectonic transition from compression to extension.

How to cite: Schneider, P. and Balen, D.: Rapid uplift of Late Cretaceous acidic magma from northern Croatia deciphered by studying inclusions in zircon using Raman spectroscopy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3895, https://doi.org/10.5194/egusphere-egu22-3895, 2022.

EGU22-7905 | Presentations | GMPV5.1

The influence of the synthesis procedure on the morphology of REE-enriched Pb-apatite (pyromorphite) 

Julia Sordyl, Karolina Rybka, Klaudia Dziewiątka, Anna Jędras, Mateusz Skalny, Kacper Staszel, Adam Tomczak, Kamil Urbański, and Maciej Manecki

Synthetic REE-enriched Pb-apatites are potentially important materials in the industry. The size and morphology of the crystals can influence the physical properties, and therefore affect technological processes. The conditions of the synthesis can determine the size and morphology of the crystals. Lead apatite Pb5(PO4)3Cl (analogue of mineral pyromorphite) was chosen for this study because the morphology of its crystals shows particular sensitivity to changes in synthesis conditions or solution composition. The addition of REE elements was used because there are reports that the morphology of synthetic Ca-apatite crystals depends on the presence of REE elements. Therefore, in the present study, synthesis by solution mixing at room temperature was carried out and the change in morphology of the precipitated pyromorphite crystals was observed as a function of solution chemistry (presence or absence of La or Sm) and concentration, pH, and mixing parameters. Powder X-ray diffraction (XRPD) was used to identify the phase composition of precipitates, scanning electron microscopy (SEM) to examine the morphology of the crystals, and energy-dispersive X-ray spectroscopy (EDS) for analysis of the elemental composition of analyzed crystals.

XRPD results showed that pyromorphite was identified in all samples. No changes in the crystalline structure were observed (hexagonal system, P63/m space group, typical for apatites). Also, EDS analyses showed that the chemical composition remained unchanged despite the morphological differences and the studied REEs (La or Sm) were incorporated into the structure in similar amounts in all precipitates. SEM images indicated that both the size and morphology of the pyromorphite crystals were sensitive to small modifications of the synthesis conditions. The size ranged from 2 µm up to 500 µm. Stirring resulted in smaller crystals than precipitation in the still water column. Crystals appeared in the form of long hexagonal needles (both single and cross-twinned), or slightly rounded, elongated and spear-like rods, or flower-like forms and intergrowths. The presence of REE caused elongation parallel to crystallographic c axis and formation of long needles compare to stubby hexagonal rods in the control sample.

The variation in size and morphology of Pb-apatites synthesized by the precipitation in aqueous solutions in different conditions were reported for the first time. Further research is needed to explain the contributing factors.

Slight changes in the synthesis protocol strongly affect the size and shape of Pb-apatite crystals. Therefore, determining the optimal conditions for the synthesis of homogeneous and well-formed crystals could be of great importance in the potential future applications of these materials.

This research was funded by NCN research grant no. 2019/35/B/ST10/03379.

How to cite: Sordyl, J., Rybka, K., Dziewiątka, K., Jędras, A., Skalny, M., Staszel, K., Tomczak, A., Urbański, K., and Manecki, M.: The influence of the synthesis procedure on the morphology of REE-enriched Pb-apatite (pyromorphite) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7905, https://doi.org/10.5194/egusphere-egu22-7905, 2022.

EGU22-11489 | Presentations | GMPV5.1

Apatite in the Upper Zone of the Bushveld (Western Limb)- evidence for a rejuvenated magma at the height of Layer 21?

Richard James Roberts, Tawnee Britt, and Callum Hetherington

The occurrence of apatite and its trace element geochemistry in a borehole core through the Upper Zone from the Western Limb of the Bushveld is reported here (BK1). Apatite displays cyclic behaviour in the upper portion of the Upper Zone, appearing and disappearing several times. Two “spikes” of apatite, where apatite appears in abundance and then disappears suddenly, occur below the magnetitite layer noted as Layer 21, and are marked by a pronounced negative Eu anomaly in the apatite REE profile. The apatite intervals above Layer 21 are marked by sudden appearance and gradual disappearance, and have no Eu anomaly. Previous studies on the UZ in the Eastern Limb have noted this difference in REE profiles and have explained it either as a consequence of the trapped liquid shift, or as an indication of massive liquid immiscibility in the chamber at the level of Layer 21. We propose an alternative solution, in which a rejuvenated magma is injected into the magma chamber at or just below the level of Layer 21. This new rejuvenated magma is likely genetically related to the previous magma but is much higher in Fe and depleted in V compared to the previous magma, and is responsible for the formation of Layer 21 (8m thick), a layer considerably thicker than any other magnetitite layer, including the Main Magnetite Layer. The influx of a new magma is clear in the largest compositional shifts in the Upper Zone across layer 21, shown in the compositions of orthopyroxene (Mg#=25 below; Mg#=49 above), plagioclase (An#=47 below; #An=58 above), and olivine (Mg#=20 below; Mg#=40 below), as well as in the occurrence of liquid immiscibility only in the magma above Layer 21. In this model, the Eu anomaly created by plagioclase fractionation in the apatite below Layer 21 has been diluted by the addition of new magma which has not experienced prolonged fractionation of plagioclase.

How to cite: Roberts, R. J., Britt, T., and Hetherington, C.: Apatite in the Upper Zone of the Bushveld (Western Limb)- evidence for a rejuvenated magma at the height of Layer 21?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11489, https://doi.org/10.5194/egusphere-egu22-11489, 2022.

EGU22-12289 | Presentations | GMPV5.1

Determining the coherent solvus for alkali feldspar

David Heuser, Elena Petrishcheva, Gerlinde Habler, Ge Bian, Christian Rentenberger, Christian Leopold Lengauer, and Rainer Abart

Alkali feldspar is one of the most common rock forming minerals in magmatic and metamorphic rocks. It forms a solid-solution between the sodium and potassium end members. At temperatures above about 600°C alkali feldspar shows continuous miscibility. Towards lower temperatures, a miscibility gap exists. When cooled from super-solvus temperatures into the two phase region of the phase diagram, alkali feldspar of intermediate composition exsolves forming coherently intergrown lamellae of Na-rich and K-rich alkali feldspar, a microstructure referred to as perthite. The compositions and the characteristic widths of the exsolution lamellae reflect the cooling history. For a quantitative retrieval of cooling rates the thermodynamics of the solid solution including the effect of coherency strain and Na-K interdiffusion, which determines the coarsening kinetics, must be known.

Four alkali feldspars with different degrees of Al-Si ordering were investigated, namely Madagascar Orthoclase, Volkesfeld Sanidine, Zillertal Adular and Zinggenstock Adular. For each feldspar a ther- modynamic mixing model describing the strain free solvus was derived from feldspar-NaCl-KCl salt Na-K partitioning experiments performed at 800°C, 900°C and 1000°C. The models show increasing non-ideality with increasing degree of Al-Si ordering. The corresponding coherent solvi and spinodes were calculated using the strain energy function of Robin (1974).

The coarsening kinetics was obtained from exsolution experiments. To this end, each alkali feldspar was shifted to intermediate compositions by exchange with NaCl-KCl melt at 900°C for 35 days and subsequently tempered at 440°C, 480°C, 520°C and 560°C for 4, 8, 16, 32, 64, 128 or 256 days. Analyses of the run products by pXRD revealed splitting of reflections of the lattice planes that are subparallel to the lamellae subparallel to (-801), a feature that is diagnostic for coherent exsolution in feldspar. TEM investigation of foils extracted perpendicular to the crystallographic b-axis revealed fully coherent lamellae and lamellar widths between 8 and 30 nm. Lamellae growth rates were obtained from the time series experiments. For a given annealing time and temperature Madagascar Orthoclase shows relatively sharp and thick lamellae as compared to the other three feldspars. The coherency strain was derived from a comparison of the lattice parameters determined for the Na-rich and the K-rich lamellae by pXRD measurements of the experimental products with those of strain free feldspar as given by Kroll et al. (1986). The strain energy density calculated for the coherent intergrowth is by a factor of two smaller than the one given by Robin (1974).

Kroll, H., Schmiemann, I., and Cölln, G. (1986). Feldspar solid solutions. American Mineralogist, 71:1–16.

Robin, P.-Y. F. (1974). Stress and strain in cryptoperthite lamellae and coherent solvus of alkali feldspars. Am Mineral, 59:1299–1318.

How to cite: Heuser, D., Petrishcheva, E., Habler, G., Bian, G., Rentenberger, C., Lengauer, C. L., and Abart, R.: Determining the coherent solvus for alkali feldspar, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12289, https://doi.org/10.5194/egusphere-egu22-12289, 2022.

EGU22-3747 | Presentations | GMPV5.1

Experimental measurement of P-wave velocities across the α→β quartz at lower continental crust pressure and temperature conditions

Arefeh Moarefvand, Julien Gasc, Damien Deldicque, Loïc Labrousse, and Alexandre Schubnel

Polymorphic mineral phase transitions play an important role in the dynamics of the Earth’s crust and mantle. The quartz α→β transition, one of the most common, is a displacive transition which has been studied for over a hundred year and has been detected up to 3 GPa by several experimental methods. In thermodynamics databases, the α→β phase transition of quartz is generally associated with a significant change in elastic properties, and a corresponding shift of seismic wave velocities. Several seismological studies have used the transition to estimate the temperature profile of the lower crust. However, the elastic properties of quartz at high-pressure and temperature remain poorly known, particularly within at β-quartz field. Indeed, because the transition is so called a lambda-transition, it is impossible to simply extrapolate room pressure measurements at high pressure and temperature.

Here, experiments were performed within a 3rd generation Griggs-type apparatus, equipped with active and passive acoustic monitoring (Moarefvand et al. 2021). In this set-up, two ultrasonic transducers (5-10 MHz) allow us to measure p-wave velocities at in-situ P-T conditions. Experiments were carried out on 10mm long cored rock samples of Arkansas Novaculite (grain size of 3-6 µm), under hydrostatic pressure conditions ranging from 0.5 to 1.25 GPa and temperatures from 200 to 900°C, i.e. effectively crossing the quartz α→β phase transition. The transition was directly observed as a minimum in p-wave velocities, preceded by an important softening of velocities as temperature was getting close to the transition temperature. However, the p-wave velocities measured beyond the transition, in the β-quartz field, were lower than that predicted by thermodynamic databases. Two additional experiments were carried out on Novaculite, at 0.5 and 0.8 GPa confining pressures, using the acoustic emission (AE) set-up, in order to investigate whether these low velocities could be related to damage (microcracking) triggered by the transition, but no significant peak of acoustic emission was observed near the transition temperature. Novaculite samples were then analyzed using Electron Back-Scatter Diffraction (EBSD) and a prevalence of Dauphiné twinning was observed on all the samples that underwent the transition at HP-HT.

Finally, four additional experiments were realized on quartz single-crystals to investigate the effect of grain boundaries and the evolution of anisotropy during the transition. Again, the velocities observed in the β-quartz field, were lower than that predicted by thermodynamic databases. Microstructural analysis of these samples revealed the importance of cracking, in particular in the direction parallel to the c-axis.

Taken together, our results show that the velocity change due to the transition known at low pressure might be less important at higher pressure than that predicted by thermodynamic databases. If true, this important result needs to be confirmed using alternative methodologies, as it would imply that velocity changes related to the α→β quartz transition at lower crustal conditions might be lower than that observed by seismologists in thickened continental crust.

References:

Moarefvand, Arefeh, et al. "A new generation Griggs apparatus with active acoustic monitoring."
Tectonophysics816 (2021): 229032.

How to cite: Moarefvand, A., Gasc, J., Deldicque, D., Labrousse, L., and Schubnel, A.: Experimental measurement of P-wave velocities across the α→β quartz at lower continental crust pressure and temperature conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3747, https://doi.org/10.5194/egusphere-egu22-3747, 2022.

EGU22-6398 | Presentations | GMPV5.1

Helium partitioning between mantle and the core at the early Earth

Ozge Ozgurel and Razvan Caracas

Noble gases are geochemical tracers, providing information about the formation of our planet and serving as a record of conditions in Earth history. Each noble gas has at least one stable non-radiogenic isotope, which is residue either of Big Bang or supernovas, and at least one stable radiogenic isotope, product of nuclear decay reactions from unstable heavier isotope of another element. The ratio of non-radiogenic and radiogenic isotopes of the noble gases arriving at the surface are essential to understand processes occurring on various timescale in the Earth interior.

The isotopic signature of the noble gases in the mid-ocean ridge basalts (MORBs) are different than in the ocean island basalts (OIB) such as in Iceland, Hawaii, Galapagos, Réunion, or Samoa. One such example is the high 3He/4He ratio observed in OIB, which are explained as a signature of the core, which in this case becomes a hidden geochemical reservoir. Here, we study the Helium partitioning between molten pyrolite and liquid iron, which represent proxies for the crystallizing magma ocean and the growing core, respectively. We employ molecular dynamics simulations based on the density functional theory as implemented in the VASP package. We perform the simulations at several temperatures and pressures that sample the magma ocean adiabat.

These calculations will allow to derive some trends on the preference of Helium on the silicate or iron melts. In the long term, they will confirm or inform the existence of a hidden reservoir deep inside the Earth, to position it in space, and to determine its formation in time.

We acknowledge support from the Research Council of Norway, project number 223272. RC acknowledges support from the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818 – IMPACT) and access to supercomputing facilities via the eDARI gen6368 grants, the PRACE RA4947 grant, and the Uninet2 NN9697K grant.

How to cite: Ozgurel, O. and Caracas, R.: Helium partitioning between mantle and the core at the early Earth, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6398, https://doi.org/10.5194/egusphere-egu22-6398, 2022.

EGU22-3168 | Presentations | GMPV5.1

Thermodynamic analysis of the olivenite-libethenite solid solution

Juraj Majzlan, Martin Števko, Alexandra Plumhoff, Edgar Dachs, and Artur Benisek

Minerals of the olivenite-libethenite [Cu2(AsO4)(OH)-Cu2(PO4)(OH)] group appear at many sites with secondary copper oxysalts. Their structural arrangement seems to be particularly stable and is also found in minerals in other classes, such as in andalusite or kieserite. Thermodynamic properties of the end members were investigated before and suggest that olivenite is the most stable Cu arsenate. In this contribution, we inspected in a detail the solid solution series between olivenite and libethenite.

Samples used in this work were synthetic, prepared from aqueous solutions with Cu(NO3)2, (NH4)H2PO4, and Na2HAsO4. Chemical composition of the members of the olivenite-libethenite solid solution were determined by ICP-OES. The relative proportions of the cations (As/P) differ little from the initial ratios in the parental solutions. For libethenite and a few solid-solution members, the orthorhombic space group Pnnm was taken for the refinement of the powder XRD data. For olivenite and the remaining, most solid-solution members, the monoclinic space group P21/n yielded slightly better results. Acid solution calorimetry in 5 N HCl showed that the solid solution is thermodynamically non-ideal, with positive enthalpies of mixing. The data indicate slight asymmetry and can be fit by a function Hex = Xoli·Xlib [A + B(Xoli – Xlib)], where Xoli and Xlib are the mole fractions of olivenite and libethenite component, respectively, and A = 6.27±0.16 kJ·mol–1, B = 2.90±0.5 kJ·mol–1. The asymmetry and positive excess enthalpies of mixing are confirmed by autocorrelation analysis of Fourier-transform infrared spectra. The results are interpreted as a local heterogeneity that arises from strain relaxation around cations with different sizes (As5+/P5+) in the intermediate members. The length scale of the heterogeneity corresponds to the wavelength of the phonons, on the order of one or a few unit cells. A distinct feature in the Hex data is the sudden drop of the mixing enthalpies between Xlib = 0.7 and 0.8. This feature can be explained by a subtle symmetry change in the solid solution from orthorhombic to monoclinic. The energetic difference between these two configurations is 0.9 kJ·mol–1. Excess entropies are zero within the uncertainties of the measurements, with one exception (at Xlib = 0.2). Excess volumes show a complicated, non-linear dependence on Xlib. Addition of PO4 into olivenite causes contraction of the unit cell, as expected for substitution of a smaller for a smaller cation. On the other side of the solid solution, addition of AsO4 into olivenite causes expansion of the unit cell. The variations of Vex are related to the interplay of cation-size differences and the small driving force between the two related (orthorhombic/monoclinic) structure. The olivenite-libethenite solid solution is non-ideal but the deviation from ideality is too small for a development of a miscibility gap. In nature, the As/(As+P) ratio in such minerals is controlled by geochemical rather than thermodynamic factors.

How to cite: Majzlan, J., Števko, M., Plumhoff, A., Dachs, E., and Benisek, A.: Thermodynamic analysis of the olivenite-libethenite solid solution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3168, https://doi.org/10.5194/egusphere-egu22-3168, 2022.

EGU22-4407 | Presentations | GMPV5.1

Effect of the relative humidity on the oxidation of arsenopyrite and löllingite

Petr Drahota, Vojtěch Ettler, Adam Culka, Jan Rohovec, and Radim Jedlička

Humidity is an important factor in sulfide oxidation as it has been shown that sulfide minerals weather differently depending on the humidity. Arsenopyrite (FeAsS) and löllingite (FeAs2) concentrates were placed under six relative humidities (RH) between 75% and 100% for 40 months and then studied using XRD, EMPA, Raman microspectrometry, and chemical extractions. Results of our experiments showed that oxidative dissolution of arsenopyrite and löllingite concentrates led to formation of different mineral assemblages in different amounts. Oxidative dissolution of arsenopyrite concentrate led to formation of poorly crystalline ferric arsenate (PCFA) and minor elemental sulfur, while oxidation of löllingite concentrate resulted in formation of well crystalline scorodite (FeAsO4·2H2O) and arsenolite (As2O3). Our data indicated that high levels of sulfate in arsenopyrite concentrate (released from sulfide oxidation) triggered fast precipitation of PCFA and retarded its transformation to scorodite. Effect of the RH on the mineralogy of oxidation products was negligible; however, quantity of newly formed oxidation products was function of RH. The data indicated that oxidation kinetics of arsenopyrite and löllingite concentrates were relatively similar and low (corresponding up to 3.5 % of the sulfide/arsenide) at RH≤94%, but löllingite concentrate oxidized much faster (up to 10×) at RH levels close to 100%.

How to cite: Drahota, P., Ettler, V., Culka, A., Rohovec, J., and Jedlička, R.: Effect of the relative humidity on the oxidation of arsenopyrite and löllingite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4407, https://doi.org/10.5194/egusphere-egu22-4407, 2022.

EGU22-11602 | Presentations | GMPV5.1

Thermal degradation of biological carbonates

Pedro Álvarez-Lloret, Adriana Torres-Mansilla, and Luis Monasterio-Guillot

The study of mineral decarbonation mechanisms is of great interest for its application to various geological and industrial processes. Biomineralization is a phenomenon by which living organisms are able to produce mineral phases, the most abundant of which are calcium carbonates and phosphates. Among the more abundant polymorphs of calcium carbonate are calcite and aragonite, being the most thermodynamically stable structures under biological environments (Weiner & Addadi, 1997). In general, mineral phases formed by biologically controlled mineralisation processes have lower crystallinity characteristics than their geological analogues. In the current communication, the thermal degradation of biogenic calcium carbonates is comparatively studied with their respective ones of geological origin. During the transformation, chemical and microstructural alterations occur from the original polymorphs of biogenic calcite (eggshell; Gallus gallus) and aragonite (mollusc shell; Ruditapes philippinarum) to the final calcium oxide mineral phase. The samples were gradually heated from room temperature to 1100°C in order to remove the water content and organic matter components contained in the biogenic phases and to induce progressive mineral decarbonation. The kinetics of these compositional transformations were analysed by means of differential scanning calorimetry (DSC). Different analytical techniques, such as attenuated total reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), were used for the chemical and structural characterisation of the mineral transformation of these phases. During thermal degradation, changes are observed in the molecular composition of these biogenic phases related to the distortion of the carbonate group and its association with the organic components. Furthermore, the mineral decarbonation process of calcium carbonates involves different structural transformation mechanisms that depend on the modification of unit cell parameters, thermal expansion coefficients and microstructural reorganisation (Rodriguez-Navarro et al., 2009). Accordingly, CaCO3 crystalline structures are transformed from the original calcite and aragonite phases to the cubic structure of lime, with a calcite-aragonite transformation prior to decarbonation explained by the reorientation of the CO3 group towards Ca and by changes in the packing of the Ca atoms, followed by the increase of the unit cell volume (Antao & Hassan, 2010). The results show some significant differences during mineral transformation depending on their geological or biological origin. The characterization of this mineral decarbonation process has important implications in natural and industrial processes (i.e., cement production, CO2 capture).

  • Weiner, S.; Addadi, L. (1997) Design strategies in mineralized biological materials. Journal of Materials Chemistry, 7(5), 689-702.
  • Rodriguez-Navarro, C.; Ruiz-Agudo, E.; Luque, A.; Rodriguez-Navarro, A.B.; Ortega-Huertas, M. (2009) Thermal decomposition of calcite: mechanisms of formation and textural evolution of CaO nanocrystals. American Mineralogist 94, 578–593.
  • Antao, S. M., Hassan, I. (2010) Temperature Dependence of the Structural Parameters in the Transformation of Aragonite to Calcite, as Determined from in Situ Synchrotron Powder X-Ray-Diffraction Data. Canadian Mineralogist 48, 1225– 1236.

How to cite: Álvarez-Lloret, P., Torres-Mansilla, A., and Monasterio-Guillot, L.: Thermal degradation of biological carbonates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11602, https://doi.org/10.5194/egusphere-egu22-11602, 2022.

EGU22-9668 | Presentations | GMPV5.1

Lithium element partitioning among haplogranitic melt, fluid and quartz

Edgar Alejandro Cortes Calderon, Ben S. Ellis, and Peter Ulmer

Lithium (Li) is a key element in the production and development of high energy density storage technology. The boost in production of battery-powered vehicles has, as a result, increased Li demand. Felsic magma reservoirs are commonly linked to Li-bearing ore deposits as their major source of Li. Understanding the processes that may affect the Li inventory in magmas is, thus, crucial to improve exploitation of Li resources. We performed experiments using haplogranitic glass shards and quartz cores between 60-150 MPa and 750-950 ºC, involving fluids with salinities ranging 0.3 to 4.4 NaCleq m in externally heated MHC pressure vessels. Quartz cores were used in all experiments to trap synthetic fluid inclusions at equilibrium conditions by in-situ thermal-shock. Li partitions weakly into quartz, DLiquartz/melt ~ 0.02, with no apparent variation with studied pressures and temperatures within analytical error. LA-ICP-MS analyses on natural quartz from this study and published data show that Li concentrations in quartz from “hot and dry” rhyolites (e.g. Mesa Falls Tuff, Lava Creek Tuff, Weinheim Rhyolite) are higher than “cold and wet” rhyolites (e.g. Kos Plateau Tuff, Bandelier Tuff, Bishop Tuff, Young Toba Tuff, Oruanui Rhyolite), 25 ± 6 and 6 ± 5 ppm (n = 5300) in average respectively. Our DLiquartz/melt experimental results are one order of magnitude lower than natural dry-rhyolites but similar to the apparent DLiquartz/melt derived from natural samples in H2O-saturated systems, where hydrogen seems to play a more important role charge-balancing Al in point defects of quartz than Li. While Li is slightly incompatible with single-phase intermediate density fluids, Li partitions relatively strongly into hydrosaline fluids (HSF), DLiHSF/melt 5-12, within the two-phase fluids coexistence surface, with the highest values in the high temperature experiments. Although Li in HSF increases with temperature and, in turn, with chlorinity of the HSF, such a scenario does not affect greatly the inventory of Li in the run melts. The higher the temperature of the studied system at a given pressure, the lower the proportion of HSF with respect to low density vapor fluid (LDVF) in the system. Such topological consequence limits the “effective” extraction of lithium by fluids in felsic magma reservoirs to very constrained regions in pressure, temperature and fluid composition. As a result, extremely and ubiquitous high Li degassing from rhyolitic melts based on the Li concentration offset between re-homogenised melt inclusions and groundmass glass must be carefully revisited.

How to cite: Cortes Calderon, E. A., Ellis, B. S., and Ulmer, P.: Lithium element partitioning among haplogranitic melt, fluid and quartz, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9668, https://doi.org/10.5194/egusphere-egu22-9668, 2022.

EGU22-2645 | Presentations | GMPV5.1

On the link between granites and pegmatites: the case study of the Li-rich mineralization from Castillejo de Dos Casas (Salamanca, Spain)

Encarnación Roda-Robles, Idoia Garate-Olave, Jon Errandonea-Martin, Alfonso Pesquera, and Pedro Gil-Crespo

In the Castillejo de Dos Casas area (C2C) (Central Iberian Zone) different granitic (Villar de Ciervo granite) and pegmatitic units of Variscan age occur intruded into the Neoproterozoic-Cambrian metasediments of the Schist Greywacke Complex (SGC). These units include: (1) biotite-rich porphyritic granite; (2) two-mica granite; (3) muscovite ± tourmaline ± phosphates-rich, leucogranites; (4) barren to Li-rich aplite-pegmatite cupola; and, (5) Li-rich aplite-pegmatite dykes. Except (1), all these units are highly peraluminous (A/CNK in the range of 1.18-2.23), Ca-poor (0.09-0.87 wt% CaO), and P-rich (0.29-3.11 wt% P2O5). Units (4) and (5) are heterogeneous, showing different mineral associations. The most common consists of a fine-grained matrix of quartz, plagioclase and Li-mica, where coarser feldspar crystals grow perpendicularly to the contacts, and topaz, montebrasite, Fe-Mn-phosphates, petalite, elbaite, cassiterite and Nb-Ta oxides are accessory. A layered texture is also locally observed.

The origin of pegmatitic melts is somehow controversial. For decades they have been considered the residual portions originated by the fractional crystallization of granitic magmas (e.g. London, 2008). However, lately the anatectic model, which proposes that pegmatitic melts originate directly by low degrees of partial melting, is gaining more followers among pegmatite researchers (e.g. Simmons et al., 2016).

In the case of C2C, the aplite-pegmatite cupola is located over the two-mica granite and close to the leucogranitic units, whereas the aplite-pegmatite dykes intrude concordantly into the SGC materials, over and close to the granitic/pegmatitic cupola. These spatial relationships strongly suggest the existence of a petrogenetic link between granitic and pegmatitic units. Whole-rock data show a gradual decrease in the Ca, Fe, Mg, Ti, Ba, Y and REE contents and K/Rb ratio with fractionation, from units (1) to (5), parallel to an increase in Al, Mn, P, Li, F, Rb, Cs, Sn, Nb and Ta. Similarly, chemical composition of main mineral phases shows gradual changes from the less evolved unit (1) to the most fractionated one (5). A continuum is observed for micas, with a progressive Li, F, Rb and Cs increase, parallel to a K/Rb decrease. Alkali feldspars show a gradual decrease of the K/Rb ratio for K-feldspar and of Ca for plagioclase; whereas tourmaline becomes Li-richer and Fe-poorer from (3) to (5) (it has not been identified in units (1) and (2)). Therefore, taking into account the spatial relationships of the 5 units, as well as their chemistry at whole-rock and mineral scales, the most feasible origin for the pegmatitic melts in the C2C area corresponds to the fractionation of a parental granitic melt that well could correspond to the unit (1) of the Villar de Ciervo granite, and that would evolve through the units (2), (3) and (4), up to the most fractionated unit (5) of the Li-rich aplite-pegmatite dykes.

 

London, D., 2008. Pegmatites. Canadian Mineralogist, Special Publication n° 10, pp. 347.

 

Simmons, W., Falster, A., Webber, K., Roda-Robles, E., Boudreaux, A., Grassi, L.R., Freeman, G., (2016): Bulk composition of Mt. Mica pegmatite, Maine, USA: implications for the origin of an LCT type pegmatite by anatexis. Can. Mineral. 54, 1053-1070.

How to cite: Roda-Robles, E., Garate-Olave, I., Errandonea-Martin, J., Pesquera, A., and Gil-Crespo, P.: On the link between granites and pegmatites: the case study of the Li-rich mineralization from Castillejo de Dos Casas (Salamanca, Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2645, https://doi.org/10.5194/egusphere-egu22-2645, 2022.

EGU22-5329 | Presentations | GMPV5.1

Preliminary results of Unidirectional Solidification Textures recorded by the aplite-pegmatites from Tres Arroyos (Badajoz, Spain) and the story they tell

Idoia Garate-Olave, Encarnación Roda-Robles, Pedro Pablo Gil-Crespo, Jon Errandonea-Martin, Alfonso Pesquera, and Nora Santos-Loyola

One of the most characteristic attributes of pegmatitic rocks is their anisotropic fabric with a great variety of textures, including not only a broad range of crystal sizes, but also different types of unidirectional crystal growths such as the so-called Unidirectional Solidification Textures (UST). In the Tres Arroyos Pegmatite Field (Central Iberian Zone of the Iberian Massif), apart from comb-textures, the alternation of aplitic and pegmatitic layers (with variable modal proportions) parallel to the contacts with the host rocks occur commonly all across the pegmatitic dykes. The origin of the layering in these bodies is still enigmatic.

In the case of Tres Arroyos, the strong undercooling of the system could be produced by a combination of different factors, including a sudden drop of pressure favoring the exsolution of a fluxing components-bearing aqueous fluid from the pegmatitic melt, and a marked temperature decrease of the pegmatitic melt due to its intrusion into significantly colder host rocks. The reduced thickness of the studied dykes (average of 2 m) would promote to the development of nonequilibrium textures along the entire width of the dykes. The variation of the crystal size (≈2-3 orders of magnitude) through different layers constituting the dykes reflects changes in the nucleation density and crystal growth rate during crystallization. The occurrence of dykes with several alternating thin pegmatitic and aplitic layers could be the result of cyclical changes induced by the competition between crystal growth rate and nucleation rate. The simplest layering patterns observed in Tres Arroyos, with alternating quartz-rich and plagioclase-rich bands, or alternating lepidolite-rich and albite-rich layers, could be explained by a diffusion-controlled oscillatory nucleation model, whereas the understanding of more complex layering patterns would need a more comprehensive study.

How to cite: Garate-Olave, I., Roda-Robles, E., Gil-Crespo, P. P., Errandonea-Martin, J., Pesquera, A., and Santos-Loyola, N.: Preliminary results of Unidirectional Solidification Textures recorded by the aplite-pegmatites from Tres Arroyos (Badajoz, Spain) and the story they tell, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5329, https://doi.org/10.5194/egusphere-egu22-5329, 2022.

Libethenite and olivenite present itself as a particularly interesting candidates for a photocatalyst due to its unique structure. One of the features of copper hydroxy- phosphates and -arseniates is the presence of bridging hydroxyl (OH) groups shared between neighboring Cu atoms. In materials used in photoelectrochemical applications, the role of surface OH groups and OH-related defects is often variable and depends on the material system and reaction of interest. For instance, OH groups can improve photocatalytic activity by forming OH radicals or act as an important intermediate in the catalytic reaction. As such, the presence of the OH group inherent in the crystal structure of the material may lead to potentially interesting behavior. Seven compounds of the libethenite Cu2(OH)PO4 – olivenite Cu2(OH)AsO4  solid solution series were synthesized at 70 °C from aqueous solutions and characterized using XRD, SEM–EDS and FTIR and Raman. The substitution effect of [PO4]3- anions by [AsO4]3- on systematic changes in lattice parameters and spectral properties has been explained based on correlation between chemical composition and the peak positions. The substitution results in systematic linear increase in unit cell parameters and unit cell volume. Isomorphic substitutions are apparent in IR and Raman as a change in the position and intensity of bands derived from phosphates, arsenates and hydroxyl ions. Isomorphic substitutions of As for P in the solid solution series change the bond length and geometry. Investigation into materials that contain intrinsic OH groups may lead to better understanding of these processes and impact for photocatalytic properties. These studies will help determine the potential of libethenite Cu2(OH)PO4 – olivenite Cu2(OH)AsO4 isomorphic series as photocatalysts.

How to cite: Waluś, E. and Manecki, M.: Hydroxyl group of libethenite Cu2(OH)PO4 – olivenite Cu2(OH)AsO4 solid solution series - vibrational spectroscopic study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9288, https://doi.org/10.5194/egusphere-egu22-9288, 2022.

EGU22-7167 | Presentations | GMPV5.1

Mineralogy of particles deposited on biomass and in soils from various smelter-polluted sites

Marek Tuhý, Vojtěch Ettler, Juraj Majzlan, and Stefan Kiefer

For this investigation, biomass and soil samples from several smelter areas in sub-Saharan Africa were used. Grass samples and topsoils were collected in the Tsumeb area in northern Namibia (Cu-smelter, former mine), Selebi-Phikwe in Botswana (Ni-Cu mine and smelter), Luanshya in the Zambian Copperbelt (Cu mine and smelter), and Kabwe in central Zambia (Pb-Zn mine and smelter). Metal(loid)s concentration in soils and grass were generally in the order of hundreds to thousands mg/kg.

The surfaces of all the grass biomass samples contained a variety of geogenic (quartz, carbonates, clay minerals, feldspars) and anthropogenic (usually metal-bearing) particles directly attached to the biomass tissues. These smelter-derived particles are predominantly slag fragments enriched in various contaminants, droplets of metals/sulfides, and, in the case of the biomass from Kabwe, newly formed aggregates of submicrometric anglesite (PbSO4) crystals. Heavy mineral fractions were obtained from all biomass samples to better understand the solid-phase speciation of contaminants. In Tsumeb, the key metal-hosting minerals/phases on biomass were Cu-Fe sulfides, arsenolite (As2O3) and metal-bearing slag glass. In Selebi Phikwe pyrrhotite (Fe1-xS), pyrite (FeS2), pentlandite [(Fe,Ni)9S8] and chalcopyrite (CuFeS2) were predominant. Samples from Kabwe were composed of galena (PbS), pyrite (FeS2), sphalerite (ZnS), chalcopyrite (CuFeS2) and anglesite (PbSO4) and in Luanshya, the particulates were mainly formed by phases from the Cu-Fe-S ternary system. The mineralogy of particulates collected in the grass samples was similar to that in the corresponding topsoil samples. The knowledge of solid-phase speciation is of key importance for determining the fate of contamination in such environments.

This study was supported by the Czech Science Foundation (GAČR project no. 1-23794J) and a grant from the Endowment Fund of the Faculty of Science, Charles University, attributed to M. Tuhý. The Charles University team was partially supported by the institutional funding from the Center for Geosphere Dynamics (UNCE/SCI/006).

How to cite: Tuhý, M., Ettler, V., Majzlan, J., and Kiefer, S.: Mineralogy of particles deposited on biomass and in soils from various smelter-polluted sites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7167, https://doi.org/10.5194/egusphere-egu22-7167, 2022.

EGU22-268 | Presentations | GMPV5.1

Impact of post-depositional transformation on sedimentary rocks and implications for paleoenvironmental studies: Evidence from  Mesoproterozoic (1.1 Ga) sediments from the Taoudeni basin, Mauritania

Mohamed Ghnahalla, Abderrazak El Albani, Ahmed Abd Elmola, Olabode M. Bankole, Claude Fontaine, Timothy W. Lyons, Chenyi Tu, Mohamed Salem Sabar, Alain Trentesaux, and Alain Meunier

Understanding and reconstruction of the paleo-condition dynamics linked to biological evolution in Earth history remain a big challenge because a majority of the ancient rocks have been affected by secondary modification processes, including tectonic, metamorphic, and hydrothermal activities. This study examines the influence of magmatic intrusion on sediment composition and paleo-environmental reconstruction from two drill cores (S1 and S2) drilled into the shallow-marine Mesoproterozoic (~1.1 Ga) El Mreiti Group of northeast Taoudeni Basin, Mauritania. Petrographic and mineralogical data show that the S1 drill core, intruded by dolerite sill, consists of a series of metamorphic minerals, including pyroxene, graphite, pyrrhotite, garnet, zeolite, talc, and saponite in sediments within the contact aureoles of the dolerite sill, indicating the influence of contact metamorphism and associated hydrothermal activities. The dominance of low-temperature minerals and the absence of metamorphic minerals in the S2 drill core sediments demonstrate that they are largely preserved and were only affected by high-grade diagenetic modifications. The anomalous enrichments of the Fe and redox-sensitive trace elements (RSTEs) in sediments within the vicinity of the dolerite sill coincide with increasing pyrrhotite contents, suggesting the transfer and remobilization of the RSTEs via thermal decomposition of pyrite to pyrrhotite during metamorphism and hydrothermal processes at elevated temperatures. This is supported by the absence of hematite, low Th/U ratios, and increasing Eu anomaly values in the dolerite sill and contact aureoles. This study reinforces the importance of screening and assessment of samples for post-depositional alteration effects before being used for the reconstruction of paleo-redox conditions in modern and ancient sedimentary rocks.

How to cite: Ghnahalla, M., El Albani, A., Abd Elmola, A., M. Bankole, O., Fontaine, C., W. Lyons, T., Tu, C., Sabar, M. S., Trentesaux, A., and Meunier, A.: Impact of post-depositional transformation on sedimentary rocks and implications for paleoenvironmental studies: Evidence from  Mesoproterozoic (1.1 Ga) sediments from the Taoudeni basin, Mauritania, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-268, https://doi.org/10.5194/egusphere-egu22-268, 2022.

EGU22-9879 | Presentations | GMPV5.1

Effect of Clay Mineralogy on Hill Slope Weathering

Arnab Kumar Pal, Siddharth Garia, and Archana M Nair

The shallow subsurface is prone to the dynamic influence of anthropogenic and environmental processes. To understand the influence, it is essential to quantify the rate of weathering across the depth profile. Chemical weathering rates for landscapes are difficult to quantify due to the non-uniqueness of the timescales over which weathering occurs. The rate of chemical weathering is generally observed to increase with physical erosion and weathering. Clay, a weathering product of rock mass, mainly contributes to this chemical weathering. Therefore, understanding the effect of clay mineralogy is significant in understanding this weathering environment. It is noticeable that intense rainfall in northeastern India mainly contributes to the weathering of the rock mass. Hence, the present study investigates the mechanism by examining the chemical weathering profile across the regolith depth. The primary objective of this study is to highlight that clay minerals have a significant role in the surface and subsurface weathering process across hillslope. Thus, for the analysis purpose, undisturbed soil samples were collected from the top 20 meters of the sediment column in a hillslope of northeastern India, inside IIT Guwahati campus, Assam at a regular 5-meter interval using the auger drilling technique. X-ray diffraction (XRD) was used to identify the clay mineralogy. Clay mineral was separated from the actual soil sample by following the USGS standard manual (extracting <2μm fraction) after treating with Hydrogen peroxide (H2O2) solution to remove organic matter. Organic matter was removed as it may cause background interference and prevent parallel orientation of clay minerals. It is observed that illite is the dominant clay mineral, followed by kaolinite and chlorite. Illite content decreases significantly with depth, while kaolinite and chlorite content increases slightly with depth. This variation may be attributed to climatic conditions, rainfall distribution across the year, resulting in deep infiltration. Mineral fluid interaction along with variation in climatic and environmental conditions subsequently causes clay mineral alteration. The accumulation of clay minerals and their alteration forms a zone of mechanical and chemical weakness, causing soil mass movement across hillslope. Thus, it can be concluded that mineralogical and geochemical analysis is essential for determining landscape sensitivity to erosion and weathering processes of hillslope areas.

How to cite: Pal, A. K., Garia, S., and Nair, A. M.: Effect of Clay Mineralogy on Hill Slope Weathering, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9879, https://doi.org/10.5194/egusphere-egu22-9879, 2022.

EGU22-5274 | Presentations | GMPV5.1

ION4RAW: Improving metal recovery in Cu-Pb-Zn-(Au-Ag) ore deposits through inventory of by-products and critical raw materials

Pauline Moreau, Isabelle Duhamel-Achin, Blandine Gourcerol, Philippe Lach, Catherine Lerouge, Nicolas Maubec, Philippe Négrel, and Guillaume Wille

Long-term management of the mineral resource supply incorporating anthropogenic environmental impacts is crucial for sustaining human society. This is especially true for recovery of by-products and critical raw materials (CRM) whose production is often unable to respond quickly to rapid changes in consumption trends. As part of European H2020 research and innovation, the ION4RAW project aims at obtaining reliable estimates of by-products and CRM, and at developing ionometallurgy processes to improve their extraction from primary resources. Targeted metals are by-products (Te, Se, Re and Mo) and CRM (Bi, Ge, In, Co, Pt, Sb) in 5 selected Cu-Ag-Au ore deposits through the world (Cononish Gold mine, Scotland; Cobre Las Cruces and El Valle Boinas, Spain; El Porvenir and Cerro Lindo, Peru). The final objective of this study is to determine the carrier minerals of CRM and by-products, the variability of their chemistry, their distribution and quantification, in order to improve their recovery during ore treatment processes. We currently inventory by-products and CRM by characterizing ores and gangue, using a multi-technical approach (bulk chemistry and X-Ray diffraction, optical and scanning electron microscopic observations, µX-ray fluorescence mapping, EPMA spot analyses and laser ablation-ICP-MS). We present here the preliminary results of El Porvenir and El Valle Boinas that are two calcic skarn-related deposits defined by their garnet composition.

 

El Porvenir (Peru), owned by Nexa Resources, is a Pb-Zn ore deposit associated with andradite–bearing skarn, exploited in an underground mine located in the Western Cordillera of the Andes mountain range in central Peru.

El Valle-Boinas (Spain), owned by Orvana Minerals Corp, is a Cu-Au ore deposit associated with a grossular-bearing skarn, exploited in an underground mine located in Cantabrian Mountains, 60 km southwest from Aviles in Spain.

Mineralogical investigations indicate that the major ore consists of chalcopyrite, galena, sphalerite, pyrite with minor pyrrhotite, tennantite-tetrahedrite–series minerals and tellurides. The electron microprobe allows analyzing micron-sized metal-carrier minerals, including electrum, Bi-Pb sulfosalts, hessite [Ag2Te], stannoidite, determining the composition of tennantite-tetrahedrite-series minerals (argentotennantite containing up to 12 wt% Ag and 5 wt% Bi) and detecting traces in major ore at a detection limits of 200-1000 ppm (for example, galena significantly contains Ag, Sb and Te). The laser ablation-ICP-MS was tested at maximum power of the laser and at different beam diameters adapted to the grain sizes (from 85 to 10 µm). Laser ablation-ICP-MS analyses with a beam diameter of 10 µm confirms EPMA data and allows detecting lower metal contents, such as Se, Rh, Pd, In, Te, in main ore minerals at detection limits of the ppm.

How to cite: Moreau, P., Duhamel-Achin, I., Gourcerol, B., Lach, P., Lerouge, C., Maubec, N., Négrel, P., and Wille, G.: ION4RAW: Improving metal recovery in Cu-Pb-Zn-(Au-Ag) ore deposits through inventory of by-products and critical raw materials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5274, https://doi.org/10.5194/egusphere-egu22-5274, 2022.