An intergrowth of zircon and xenotime, formed at ca. 2.09 Ga, was significantly altered after incorporation as a restite into pegmatite at ca. 370 Ma (Piława Górna, Góry Sowie Block, SW Poland; Budzyń et al., 2018). Alteration involved fluid-induced coupled dissolution-reprecipitation processes, which resulted in compositional alteration and development of patchy zoning and porosity in the xenotime and the rim of zircon. Diffusion-reaction processes affected the metamict core of zircon and resulted in nano- to microscale patchy zoning and submicron-scale porosity. This study evaluates the alteration processes with respect to structural and compositional characteristics by using TEM and LA-ICPMS trace element analysis.

Nanoscale observations revealed nanoporosity in the metamict core of zircon and a continuation of patchy zoning on a submicron level, which resulted from heterogeneous metamictization correlating with variation in U and Th contents. The altered xenotime and the zircon rim are dominated by microporosity filled with a variety of secondary phases such as U, Th, Pb and Fe rich oxides and silicates. In rare cases, secondary PbS formed nano inclusions in zircon, occasionally surrounded by amorphous apatite. Aside of known substitution mechanisms in xenotime, such as thorite and cheralite components, a correlation of Zr with LREE and Si contents indicates substitution of the zircon component. Furthermore, the zircon-xenotime interface revealed dissolution pits, filled with secondary zircon that formed at the expense of primary xenotime via coupled dissolution-reprecipitation reactions. This indicates local penetration of the fluid-mineral reaction front into xenotime. Major (Si, Zr and P) and trace elements, including U, Th and Pb, which are geochronologically relevant, have been mobilized in the metamict core of zircon due to alteration induced by an alkali-rich fluid with high activities of F, Na and Ca. The altered xenotime and porous rim of zircon were affected by alteration induced by a fluid containing Fe, which resulted in precipitation of Fe-rich phases, such as Fe-oxides and silicates often accompanied by relevant contents of Pb. In conclusion, nanoscale structural observations and LA-ICP-MS trace element data support the complex geochronological implications of the altered zircon-xenotime intergrowth, emphasising the necessity of understanding alteration processes of zircon and xenotime taking into account element transport and thus the disturbance of their geochronological clock.

Acknowledgements: This work was supported by the National Science Centre grant no. 2017/27/B/ST10/00813.

References:

BudzyńB., Sláma J., Kozub-Budzyń G.A., Konečný P., HolickýI., RzepaG.,Jastrzębski M. (2018) Lithos 310-311, 65-85.

How to cite: Tramm, F., Wirth, R., Budzyń, B., Sláma, J., Schreiber, A., and Birski, Ł.: TEM and LA-ICP-MS constraints on fluid-induced alteration of a zircon-xenotime intergrowth in pegmatite from Piława Górna (the Góry Sowie Block, SW Poland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-124, https://doi.org/10.5194/egusphere-egu21-124, 2021.

Uranium-lead dating of zircon has been used extensively in geochronological studies based on the widespread occurrence of zircon and its resistance to chemical and physical weathering. Previous research has shown that despite their apparent robustness, many zircons contain evidence for recrystallisation, such as the replacement of the primary oscillatory zoning by unzoned zircon. This replacement is characterised by rims, patches and embayments of unzoned zircon which can either completely replace the primary zoning or preserve faint remnants within the unzoned zircon.  In some samples, the unzoned zircon contains lower U and Pb concentrations, implying that the zircon U-Pb age may be reset during the replacement (Pidgeon, 1992). Interestingly, zircons have also been found in which there is no apparent difference in U-Pb age between the zoned and unzoned zircon (Schaltegger et al., 1999). To better understand the replacement of zoned by unzoned zircon, it is important to study the microstructures present within recrystallised zircon to understand possible mechanisms causing recrystallisation. Multiple mechanisms may explain the trace element distribution within (partially) recrystallised zircon: annealing of radiation damaged (metamict) zircon, annealing of lattice strain imposed by alternating U concentrations in oscillatory zoning, enhanced diffusion along fast-diffusivity pathways (such as low-angle subgrain boundaries or fractures) and coupled dissolution-reprecipitation.  The mechanism(s) by which zircons recrystallise remain poorly understood, as well as the effect of the formation of different microstructures on corresponding zircon U-Pb dates. Understanding these phenomena is therefore of vital importance for correctly interpreting U-Pb ages in zircon.

This work focusses on investigating the microstructures that are present within recrystallised zircons from both metamorphic and igneous environments from the Jack Hills, Australia (Pidgeon, 1992) and the island of Lewis and Harris, Scotland (Van  Breemen  et  al.   1971). Suites of zircons from these areas have been imaged with cathodoluminescence, which is a powerful tool for obtaining high resolution images of the internal structures of zircons. Within these suites, zircons are present which show complex zoning patterns and (partial) recrystallisation; these will be studied in greater detail using EDS, EBSD and SHRIMP. Preliminary results of EDS on the inclusions show that inclusions are composed of feldspars, thorite, quartz and apatite, which were most likely included during the primary crystallisation of the zircon. EBSD measurements will provide additional data on the crystallographic orientation of recrystallized zones and the state of metamictization of the zircons, and may show if zircon has deformed crystal-plastically forming subgrain boundaries.

References

Pidgeon, R. T. (1992). Recrystallisation of oscillatory zoned zircon: some geochronological and petrological implications. Contributions to Mineralogy and Petrology, 110(4), 463-472.

Schaltegger, U., Fanning, C. M., Günther, D., Maurin, J. C., Schulmann, K., & Gebauer, D. (1999). Growth, annealing and recrystallization of zircon and preservation of monazite in high-grade metamorphism: conventional and in-situ U-Pb isotope, cathodoluminescence and microchemical evidence. Contributions to Mineralogy and Petrology, 134(2-3), 186-201.

Van Breemen, O., Aftalion, M., & Pidgeon, R. (1971). The age of the granitic injection complex of harris,outer hebrides.Scottish Journal of Geology,7(2), 139–152.

How to cite: Huijsmans, J., Hamers, M., Drury, M., and Lee, J.: Zircon recrystallisation microstructures andthe implications for U-Pb dating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3100, https://doi.org/10.5194/egusphere-egu21-3100, 2021.

Thermally activated processes can be described mathematically by the Arrhenius equation. The Meyer-Neldel Rule (MNR), or compensation law, linearly relates the pre-exponent term to the logarithm of the excitation enthalpy for processes that are thermally driven in an Arrhenian manner. This empirical rule was observed in many areas of materials science, in physics, chemistry, and biology. In geosciences it was found to uphold in hydrogen diffusion (Jones 2014a) and proton conduction (Jones 2014b) in minerals.

Trapped charge dating methods that use electron spin resonance (ESR) or optically or thermally stimulated luminescence (OSL and TL) are based on the dose-dependent accumulation of defects in minerals such as quartz and feldspar. The thermal stability of these defects in the age range investigated is a major prerequisite for accurate dating, while the accurate determination of the values of the trap depths and frequency factors play a major role in thermochronometry applications. 

The correlation of kinetic parameters for diffusion has been very recently established for irradiated oxides (Kotomin et al. 2018). A correlation between the activation energy and the frequency factor that satisfied the Meyer–Neldel rule was reported when the thermal stability of [AlO₄/h⁺]⁰ and [TiO₄/M⁺]⁰ ESR signals in quartz was studied as function of dose (Benzid and Timar-Gabor 2020). Here we compiled the optically stimulated luminescence (OSL) data published so far in this regard, and investigated experimentally the thermal stability of OSL signals for doses ranging from 10 to 10000 Gy in sedimentary quartz samples. We report a linear relationship between the natural logarithm of the preexponent term (the frequency factor) and the activation energy E, corresponding to a Meyer-Neldel energy of 45 meV, and a deviation from first order kinetics in the high dose range accompanied by an apparent decrease in thermal stability. The implications of these observations and the atomic and physical mechanisms are currently studied.

References

Benzid, K., Timar Gabor, A. 2020. The compensation effect (Meyer–Neldel rule) on [AlO₄/h⁺]⁰ and [TiO₄/M⁺]⁰ paramagnetic centers in irradiated sedimentary quartz. AIP Advances 10, 075114.

Kotomin, E., Kuzovkov, V., Popov, A. I., Maier, J., and Vila, R. 2018. Anomalous kinetics of diffusion-controlled defect annealing in irradiated ionic solids. J. Phys. Chem. A 122(1), 28–32

Jones, A. G. (2014a), Compensation of the Meyer-Neldel Compensation Law for H diffusion in minerals, Geochem. Geophys. Geosyst., 15, 2616–2631

Jones, A. G. (2014b), Reconciling different equations for proton conduction using the Meyer-Neldel compensation rule, Geochem. Geophys. Geosyst., 15, 337–349

How to cite: Kabacińska, Z., Timar-Gabor, A., and Guralnik, B.: Meyer-Neldel Rule on thermal stability parameters (trap depth and frequency factor) of luminescence signals in quartz, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10775, https://doi.org/10.5194/egusphere-egu21-10775, 2021.

Inclusions in garnets from the river Lešnica alluvion (Cer mountain area, Serbia),  were investigated in an effort to study their distribution within the garnet host and to estimate the mechanism of their origin. Garnets are often occurring in the Lešnica alluvion in a form of loosely separated crystals with preserved crystalline forms and as mildly rounded broken grains [1]. Their mineralogical determination was previously published by Milošević et al, [1]. Crystals, that have been extracted and separated from the sandy fraction, have exhibited the presence of various types of inclusions in their structure. Single and multiphase inclusions in the garnets were examined optically by petrographic methods followed by SEM-EDS method, applied for the chemical analyses of the individual inclusion, and LA-ICP-MS applied to determine distribution and content of trace elements in the host garnet.

Results from SEM-EDS method show that garnets are of the spessartine-almandine type with the incorporation of irregular inclusions determined as rare earth elements (REE) minerals (monazite, xenotime, columbite-tantalite) and accessory minerals that usually incorporate REE (titanite, apatite, and zircon) together with uranium oxide minerals. Other single-phase inclusions are often quartz and rutile. Size of inclusion varieties from grain to grain, between 5 and 40 µm, while their distribution doesn’t follow any pattern, random distribution. It has been noted that zircon and uranium oxide minerals are often found coupled and as multiphase inclusions while monazite, xenotime and columbite-tantalite minerals are observed as separate, single, inclusions. Chondrite normalized REE in the host garnets plotted on spider diagram show extreme depletions of large ion lithophile elements (LILE) and enrichment in high field strength elements (HFSE), with negative Ce, Nd and Eu anomaly. Single-phase and multiphase inclusions that are occurring in the same garnet host with a random distribution are suggesting different genetic relations.

[1] Milošević M., Kostić B., Vulić P., Jelić I. 2019. Garnets from river Lešnica alluvion, mountain Cer. II Kongres Geologa Bosne i Hercegovine sa medjunarodnim učešćem, Pp. 306-311

How to cite: Milošević, M. and Kostić, B.: Single and multi-phase inclusions in garnets from the Lešnica alluvion in the Internal Dinarides, Serbia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2423, https://doi.org/10.5194/egusphere-egu21-2423, 2021.

Along with some other Na-minerals, carbonophosphates indicate a high initial Na activity in carbonatite and kimberlite melts, which is beneficial for petrological reconstructions. Because carbonophosphates are capable of incorporating large-ion lithophile and rare earth elements (REEs) in their structure, they can participate in the transport of these elements. Moreover, due to the presence of both [PO₄]³⁻ and [CO₃]²⁻ groups in carbonophosphates, these mineral phases play an important role in the Earth's global carbon and phosphate cycles. With all these properties, carbonophosphates have long attracted the attention of geologists. Raman spectroscopy appears to be one of the most suitable tools for their diagnosis, since they commonly present in rocks as small inclusions in other mineral grains. Despite this profit, only a few publications contain Raman characteristics of either natural or synthetic carbonophosphates.

We studied and compared Raman spectra of three natural carbonophosphate phases (sidorenkite, bonshtedtite, and bradleyite) with the general formula Na₃MCO₃PO₄ (M = Mn, Fe, and Mg, correspondingly). These spectra showed from 21 to 24 vibrational bands, of which the two most intense (963±5 cm^-1 и 1074±3 cm^-1) correspond to the ν1(P–O) and ν1(C–O) modes. These two bands split due to the occurrence of isomorphic impurities. It was found that the crystallographic orientation of the sample influences the intensity of most bands. A natural increase in the Raman shift was observed for most bands assigned to the same vibrations (the smallest shift in the spectrum is characteristic of sidorenkite, an intermediate - of bonshtedtite, and the largest - of bradleyite).

We propose the following algorithm for the diagnosis of carbonophosphates:

• Checking minerals for belonging to the group of carbonophosphates by the main bands and the characteristic profile of the spectrum;
• Testing the hypothesis that the mineral of question is bradleyite based on the analysis of the estimated shift of the main bands;
• Diagnosis of a mineral species by peaks located between the main bands;
• Validation of the diagnostics by considering the position of the bands at 185±9 cm^-1, 208±7 cm^-1, 255±5 cm^-1, and 725±6 cm^-1.

The proposed algorithm allows one to perform Raman diagnostics of carbonophosphates in inclusions even in the absence of EPMA data. In the study of carbonatites, kimberlites, and other rocks, the diagnostics of the mineral species of the carbonophosphate group can be important in the petrological aspect.

This research was funded by the Russian Science Foundation, grant number 19-77-10039.

How to cite: Fomina, E., Kozlov, E., Sidorov, M., and Bocharov, V.: A Raman spectroscopic study of the natural carbonophosphates Na3MCO3PO4 (M = Mn, Fe, and Mg), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1528, https://doi.org/10.5194/egusphere-egu21-1528, 2021.

Raman spectroscopy represents a novel methodology of characterising plant-fire interactions through geological history, with enormous potential. Applications of Raman spectroscopy to charcoal have shown that this is an effective method of understanding intensity changes across palaeofire regimes. Such analyses have relied on the determination of appropriate Raman parameters, given their relationship with temperature of formation and microstructural changes in reference charcoals. Quantitative assessments of charcoal microstructure have also been successfully applied to the assessment of carbonaceous maturation under alternate thermal regimes, such as pyroclastic volcanism. Palaeowildfire systems in association with volcanism may present a complex history of thermal maturation, given interactions between detrital charcoals and volcanogenic deposition. However, whilst palaeofire and volcanic maturation of carbonaceous material are well understood individually, their interaction has yet to be characterised. Here we present the first analysis of palaeofire charcoals derived from volcanic ignition utilising Raman spectroscopy. Our results indicate that complex interactions between volcanism and palaeofire systems may be better understood by the characterisation of charcoal microstructure, alongside palaeobotanical and ecosystem studies. Understanding the unique relationship between wildfires and volcanism, and the impact that this has on the fossil record, may better assist our understanding of wildfire systems in deep history. Further still, this highlights the potential for better understanding the socioecological impacts of modern and future wildfire systems closely associated with volcanic centres. 

How to cite: Theurer, T., Muirhead, D., Jolley, D., and Mauquoy, D.: The Potential Applications of Raman Spectroscopy in Unravelling Complex Palaeowildfire Ecosystems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2626, https://doi.org/10.5194/egusphere-egu21-2626, 2021.

In recent decades increasing evidence was found for life under extreme conditions, e.g., near black smokers on the ocean floor. The synthesis and stability of vital molecules like adenosine triphosphate (ATP) and adenosine diphosphate (ADP) are essential to maintain the metabolism of all known organisms. The lifetime of these molecules in water is limited by the non-enzymatic hydrolysis reaction that becomes dominant at elevated temperatures. A better understanding of this mechanism will provide us insights of life at extreme conditions.

Previous studies determined the hydrolysis rate constants of ATP for several compositions, temperatures and pressures using quench experiments and subsequent analysis. So far, it was not tested whether quench artefacts might have affected those results. Therefore, the current study was performed to develop a method to follow the reaction in-situ with a high sampling rate at elevated temperatures. A confocal micro-Raman spectrometer and a hydrothermal diamond anvil cell were used to perform experiments at elevated temperatures and vapour pressure. Spectra were obtained in the range of 660 cm^-1 to 1157 cm^-1 as a function of time. Different solutions of ATP and ADP were measured at 353 K, 373 K, and 393 K, at starting pH values of 3 and 7. First findings are consistent with previous studies and show that with decreasing pH value the hydrolysis rate increases. The data indicate hydrolysis rate constants in the magnitude of 10^-3 s^-1 by 393 K, 10^-4 s^-1 by 373 K and 10^-5 s^-1 by 353 K. These initial observations show that this technique produces reliable kinetic data on this reaction. It also provides much better sampling statistics than quench experiments. 

The high reaction rates suggest that a mechanism exists to regulate this reaction at higher temperatures, which is necessary to allow metabolism under extreme conditions. Moreover, it is commonly known that ATP interacts with various metal ions with different effects on the reaction rate. An application of this method would be the quantification of the hydrolysis rate constant in chemically more complex systems.

How to cite: Moeller, C., Schmidt, C., Guyot, F., and Wilke, M.: A new in-situ method to determine the hydrolysis rate constant of adenosine triphosphate (ATP) by application of Raman spectroscopy in a hydrothermal diamond anvil cell, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3419, https://doi.org/10.5194/egusphere-egu21-3419, 2021.

Rapid development of in situ experimental techniques provides researchers with new opportunities to model geological processes, which take place deep in the Earth’s interior. Raman spectroscopy is considered a powerful analytical tool for investigation of the samples subjected to high pressures in a diamond anvil cell, since in such experiments phase assemblages can be determined in real time using measured Raman spectra.

In this study, we describe experimental methods for in situ observation and spectroscopic analysis of fluids and minerals, which constitute environment for diamond growth, at the upper mantle pressure conditions. Experiments were conducted in the externally heated, “piston-cylinder” type diamond anvil cell at pressures exceeding 6 GPa and temperatures up to 600 degree C. Phase relationships and fluid speciation were monitored during experiments to reconstruct the environment and mechanism of inclusions formation. Compared to other analytical tools, commonly used in combination with diamond anvil cell apparatus, Raman spectroscopy offers several advantages, such as short sample preparation time, non-destructive characterization of the phases observed in the sample chamber and relatively short measurement time.

This work was supported by grant No. 20-77-00079 from the Russian Science Foundation.

How to cite: Chertkova, N., Spivak, A., Zakharchenko, E., Litvin, Y., Safonov, O., and Burova, A.: In situ Raman spectroscopic technique for high-pressure studies of mineral and fluid inclusions formation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7530, https://doi.org/10.5194/egusphere-egu21-7530, 2021.

Organic carbon in rocks undergoes nanostructural changes when exposed to increased temperatures or strain. These changes can be identified using Raman spectroscopy, giving information about thermal maturity and strain conditions. However, it is well documented that in a heterogeneous rock, strain can be highly localised, evident in microstructural variations such as strain shadows, sub-grain development, twinning, and the rotation and alignment of crystal axes. In this study we map microstructural textures in deformed calcite through optical microscopy and EBSD of calcite crystal axes. This textural map is compared to mapped Raman spectral parameters of organic carbon particles in the same thin section. A comparison of the maps allows assessment of the extent to which Raman spectral parameters and hence carbon nanostructure is influenced by strain at a sub-mm scale. The study highlights the sensitivity of organic carbon nanostructure to sub-mm scale changes in strain localisation within a single deformed carbonate sample.

How to cite: Kedar, L., Bond, C., and Muirhead, D.: Strain-related carbon ordering on a sub-mm scale: a comparison of carbonate microfabrics and organic carbon nanostructure within a single sample., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9921, https://doi.org/10.5194/egusphere-egu21-9921, 2021.

Raman Spectroscopy is increasingly being used to better understand a range of Earth Science processes. Notable recently is the application of Raman Spectroscopy to carbonaceous material in strained rocks. Here we investigate the changes in Raman Spectral response in strained material relative to an unstrained equivalent, drawing on examples from the published literature and our own work. We consider inconsistencies in the relative changes in Raman Spectral parameters of strained material and their potential causes. In doing so we look at some of the current methods for determining Raman Spectral parameters in rocks and what they might tell us about the strain state of carbon in a single rock sample. Finally, we consider the implications for use of Raman Spectroscopy of carbonaceous material as a geothermometer as well as a future potential strain gauge. 

How to cite: Bond, C., Kedar, L., and Muirhead, D.: Raman Spectroscopy as a potential strain gauge, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11092, https://doi.org/10.5194/egusphere-egu21-11092, 2021.

The North Tanzanian Divergence (NTD) is the prolongation of the eastern branch of the East African Rift and is a place of intense volcanism. Numerous volcanoes erupted deep subalkaline to highly alkaline magmas, including the particular active natrocarbonatite Oldoinyo Lengai. On the North-South axis (Natron to Manyara basins), three highly alkaline volcanoes, Pello Hills, Lashaine and Labait, erupted melilite magmas that originated from low degree of partial melting of asthenospheric mantle (depth > 120 km). The particularity of these volcanoes is that they sampled numerous mantle xenoliths during ascent. This represents a unique opportunity to study the composition and the rheology of lithospheric mantle. Mantle xenoliths are deep garnet-bearing peridotites (120 km depth), amphibole and phlogopite peridotites and phlogopitites. They contain abundant hydrous minerals as isolated crystals or veins that attest to an important metasomatism beneath the NTD. Previous geochemical and petrological studies have highlighted interactions of alkaline magmas and the thick cratonic lithosphere as metasomatic agent. However, the presence and composition of magmas, the degree of metasomatism, and the role of metasomatism on mantle rheology below the NTD is still debated.

To characterize these previous parameters, in this study we performed geochemical and petrophysical analyses on metasomatized, fertile and refractory mantle xenoliths from Labait (on-craton volcano) and Pello Hills (in-rift volcano). Using mineral compositions and thermobarometer calibrations, we estimated the depth of mantle xenoliths between 40 and 140 km (14 to 47 kbar) and temperatures from 930 to 1340°C. EBSD analysis on thin sections indicate that peridotites and amphibole/phlogopite-bearing mantle xenoliths display a moderate to strong deformation induced crystal preferred orientation. In contrast, weak mineral orientations have been observed in phlogopite-amphibole-clinopyroxene-bearing veins. Calculation of seismic properties using MTEX program show that peridotites are seismically anisotropic, up to 12.4% for P-wave velocity (Vp) and 6.8% for S-wave velocity (Vs). The Vp and Vs in hydrous veins are lower than in peridotites (Vp: 7.5-7.9 and 8.3-9.6 km/s; Vs: 4.4-4.6 and 5.0-5.3 km/s respectively) and therefore the Vp and Vs velocities decrease with the increasing proportion of metasomatic minerals. We estimate that a peridotite with 20 vol.% metasomatic vein has a velocity decrease of 3.5% for Vp and 2.9% for Vs, compared to a fertile peridotite.

These geochemical and petrophysical approaches are important to understand P- and S-wave propagation in the lithospheric mantle beneath the NTD and more specifically in metasomatized lithospheric mantle. The new in situ data and models from mantle xenoliths will be compared to tomographic acquisition and discussed in term of temperature, presence of melt or metasomatism processes. Both petrophysical and geophysical data will help to precisely determine the structure and rheology of the lithospheric mantle, which may control the propagation of the rift at early stage rifting between the Tanzanian craton and the mobile Proterozoic belts.

How to cite: Clutier, A., Parat, F., Gregoire, M., Gibert, B., Gautier, S., and Tiberi, C.: Geochemical and petrophysical characterization of mantle metasomatism beneath the North Tanzanian Divergence, East African rift., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10603, https://doi.org/10.5194/egusphere-egu21-10603, 2021.

Cameroon Volcanic Line (CVL) is located in the western part of equatorial Africa and consists of volcanoes which were active from Eocene to recent, stretching ca. 1700 km from the Atlantic in the SW into the African continent in the NE. The continental part of the CVL is located on the Neoproterozoic Central African Orogenic Belt and is situated between the Congo craton and Sahara/Western Africa craton. Mantle peridotite xenoliths which occur locally in lavas of the CVL come from the spinel facies only, suggesting a relatively shallow lithosphere-asthenosphere boundary (LAB). This is supported by seismic studies, showing the LAB at 90-100 km.

In order to understand better the evolution of the lithospheric mantle beneath the CVL, we studied xenolith suite (16 xenoliths) from Befang in the Oku Massif (Tedonkenfack et al., submitted). The Befang xenoliths are almost entirely lherzolites which have cataclastic to weakly porphyroclastic texture. Harzburgites and websterites occur subordinately. Spinel is interstitial and has amoeboidal shape. The studied peridotites (14 lherzolites, 1 harzburgite) consist of minerals with almost constant composition (olivine Fo_88.7-90.3, orthopyroxene Al 0.17-0.19 atoms per formula unit (a pfu), clinopyroxene Al 0.28-0.30 a pfu, spinel Cr# dominantly 0.09-0.11). Spinel of Cr# 0.15 occurs in one of the lherzolites, whereas that occurring in harzburgite has Cr# 0.19. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the EBSD-studied subset of 8 samples (one harzburgite and 7 lherzolites). Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of the fabric of host rock.

These data, thermometry, phase relationships and phase equilibria diagrams suggest that the Befang mantle section was refertilised by MORB-like melt at pressures 1.0-1.4 GPa and temperatures slightly above 1200 – 1275 ºC. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the fabric of protolith. On the other hand, the LREE-depleted clinopyroxene shows discordant orientation relative to olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the melt. The major element and REEs composition of pyroxenes occurring in the Befang peridotites indicate chemical reequilibration at temperatures 930 – 1000 ºC. Trace element modeling shows that websterites can be linked to Cenozoic volcanism. We speculate that they form veins in the lithospheric mantle. Our study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process, which contrasts with the incompatible element-enriched melts typically invoked in within-plate settings.

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). Submitted.

How to cite: Puziewicz, J., Tedonkenfack, S. S. T., Aulbach, S., Ntaflos, T., Kaczmarek, M.-A., Kukula, A., Matusiak-Małek, M., and Ziobro, M.: Evolution of lithospheric mantle beneath mobile belt between two cratons: An example from the Oku Massif, Cameroon Volcanic Line (W Africa), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1670, https://doi.org/10.5194/egusphere-egu21-1670, 2021.

Migration of metals such as gold, silver and copper through the subcontinental lithospheric mantle (SCLM) can be tracked by the investigation of sulfides in mantle xenoliths. Therefore, to understand relations between the metal migration and metasomatism of silicate phases in the SCLM beneath SW Poland we studied sulfides in a set of mantle ultramafic xenoliths with variable metasomatic history. The xenoliths occur in the Cenozoic alkaline mafic volcanic rocks from the SW Poland (N Bohemian Massif).  

The studied sulfides occur in mantle rocks of variable history: 1) strongly depleted (group A0) to weakly metasomatized peridotites (Group A1); 2) strongly melt-metasomatized peridotites (Group B); 3) pyroxenites (Group C; for details of group definition see Matusiak-Małek et al., 2014, JoP). The metasomatism was of mixed silicate/carbonatite nature. The sulfides are either interstitial or enclosed in the silicates and form mostly globular monosulfide solid solution-chalcopyrite (mss-Ccp) assemblages typical of igneous sulfides separated and crystallized from mafic magmas, with mss partially re-equilibrated to exsolutions of pentlandite (Pn) and pyrrhotite (Po) when temperature dropped to <600°C (e.g., Craig and Kullerud, 1969, Econ. Geol. Monogr.).

The sulfide abundances increase from Group A (≤ 0.008 vol.‰) through Group B (up to 0.060 vol. ‰) to Group C (up to 0.963 vol.‰) xenoliths. The sulfides of Groups C (Po_15–99Pn_0–20Ccp_0–70)and B (Po_0–85Pn_14–100Ccp_0–27) are generally poorer in Ni compared to Group A (Po_0–74Pn_24–100Ccp_0–35). Consequently, Ni/(Ni+Fe) in the Group C pentlandites (0.41–0.52) is lower than in those in Group A (0.45–0.69). Moreover, the sulfide grains of Group B are enriched in chalcophile elements (e.g., the median content of Zn is 90 ppm) compared to sulfides from Groups C (52 ppm Zn) and A (51 ppm of Zn). The same relations occur in PGE contents, e.g., Pt in Group B is 1.6 ppm, while in Groups C and A it is 0.1 and 1.3 ppm, respectively.  Observed differences in δ⁵⁶Fe between the Groups are probably due to modal composition of bulk sulfide grains between Groups A (Ni-rich), B and C (Fe-Cu-rich). As no difference is observed between the grains of the same composition, any fractionation of Fe isotopes in sulfide melt seems to be possible only upon its differentiation from Ni-rich to Fe-Cu-rich.

The host peridotites were affected by strong depletion as the degree of partial melting was possibly ~30%. Thus, the observed enhanced sulfide modes in the metasomatized peridotites (Groups A1 and B) are most likely brought by the metasomatic melt. This is also evidenced by their Fe-Cu-rich composition, similar to that of the sulfides from the pyroxenites. In this view, melt metasomatism likely affects the chalcophile and highly-siderophile metal budget of the continental lithosphere.

The measurements of Fe isotopic ratios were financed from funds for years 2020-2024 within program “Diamond Grant” (DI2019 0093 49), the LAICPMS measurements were financed from 2016/23/N/ST10/00288 to J.C., and the EPMA analyses were done within the frame of the Polish-Austrian project WTZ PL/16 and WTZ PL 08/2018.

How to cite: Mazurek, H., Ciazela, J., Matusiak-Małek, M., Pieterek, B., Puziewicz, J., Lazarov, M., Horn, I., and 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.

Late Carboniferous/early Permian mafic volcanic rocks occurring in Scotland carry a broad spectrum of peridotitic and pyroxenitic xenoliths. The latter provide evidence of magmatic processes in the lower crust and the lithospheric mantle. In this study we present textural and compositional data on twenty-eight pyroxenitic xenoliths from six localities from southern Scotland (Midland Valley and Southern Uplands Terranes).

Most are interpreted as adcumulates (varying in grain size from fine to coarse) although some others are mesocumulates. They include both clinopyroxenites and websterites with variable amounts of olivine; phlogopite is present in only one sample. Cores of greenish clinopyroxene in three of the olivine clinopyroxenites are enveloped by brownish clinopyroxene, while one composite xenolith comprising coarse-grained olivine clinopyroxenite in sharp contact with harzburgite. Five groups, based on textural and mineralogical features were distinguished. Representatives of more than one group can be present in a single locality.

Most of the samples from the same textural group share similar chemical composition. In general, the clinopyroxenes are Ti,Al-diopside/augite with Mg#=0.74-0.86; where clinopyroxenes are zoned the rims have lower Mg# and higher Al content. The orthopyroxene is an Al (±Cr)-enstatite with Mg#=0.78-0.89, olivine (Fo_76-77) is relatively NiO-rich (0.16-0.29 wt.%). In clinopyroxenites the pyroxenes are LREE-enriched (La_N/Lu_N=1.31-3.17) with convex-upward REE patterns (Sm_N/Lu_N=2.48-7.37).

The temperatures and pressures of clinopyroxene crystallization in most of the clinopyroxenites are 1220-1300°C and 1.08–1.30 GPa (Putirka, 2008), respectively. Only the composite xenolith and the coarse-grained clinopyroxenites recorded higher pressures (1.42 and 1.65-2.03 GPa, respectively). As the Moho beneath S Scotland is located at ~35 km (corresponding to ~1 GPa; Davis et al., 2012), most of the clinopyroxenites are considered to come from the uppermost portions of lithospheric mantle or lowermost continental crust; the coarse-grained clinopyroxenites and the composite xenolith sample lithospheric mantle.

Clinopyroxenites from the southern Scotland crystallized from alkaline basaltic magmas similar to those that entrained  them. Whilst Downes et al. (2007, 2001) had previously suggested this for clinopyroxenites from Midland Valley localities, our studies show that crystallization of mafic melts was more widespread. Strong chemical and textural variations in the pyroxenites together with relatively constant PT conditions of crystallization suggest that they formed either from melts of slightly different composition, perhaps in response to magma chamber processes such as magma replenishment and/ or mixing. While, the presence of mafic cumulates points to possible crustal underplating beneath S Scotland, the presence of a high-pressure clinopyroxenites and composite clinopyroxenitic-peridotitic xenolith imply that some of the pyroxenites originated in the lithospheric mantle.

Davis et al. (2012). Geoph.J. Int., 190, 705-725.

Downes et al., (2007). J. Geol. Soc., 164, 1217-1231.

Downes et al. (2001). Lithos, 58, 105-124.

Putirka et al. (2008). Rev. Min. Petr., 69, 61-120.

This study was funded by Polish National Science Centre to MMM no. DEC-2016/23/B/ST10/01905. EPMA analyses were done within the frame of the Polish-Austrian project WTZ PL/16 and WTZ PL 08/2018.

How to cite: Matusiak-Małek, M., Matczuk, P., Upton, B. G. J., Ntaflos, T., Aulbach, S., Puziewicz, J., and Kukuła, A.: Pyroxenitic xenoliths from southern Scotland and what they tell us., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8810, https://doi.org/10.5194/egusphere-egu21-8810, 2021.

Melt inclusions of very unusual nature occur in garnets of eclogites of the Granulitgebirge, Bohemian Massif. This is one of the first direct characterization of a preserved metasomatic melt responsible for the formation of eclogites enclosed in garnet peridotites. The inclusions are micrometric, from glassy to fully crystalized as nanogranitoids and randomly distributed in the garnet core. Nanogranitoids contain kumdykolite/albite, phlogopite, osumilite and kokchetavite with a variable amount of quartz, pyroxene, carbonate and rare white mica. The melt has a granitic composition rather than basaltic or tonalitic/trondhjemitic as would be expected from the partial melting of ultramafic or mafic rocks and it is as well hydrous and peraluminous. The trace elements composition is also unusual for melts in mantle rocks with elements typical of continental crust (Cs, Li, B, Pb and Rb) and subduction zone (Th and U). Similar signatures, i.e. continental crust and subduction, are visible also in the whole rock trace elements in the form of high amounts of LILE and U. The eclogite major elements composition is similar to a Ca- and Fe - rich mafic rock akin more to the crust than to the mantle.

The peculiar melt composition and the lack of a clear residue of a melting reaction in the eclogites suggest that this melt is external, i.e. metasomatic. It infiltered the peridotites during subduction of the continental crust at mantle depth and aided the transformation of basic layers, already in the peridotite, to eclogite. In addition, similar trace elements patterns to the melt reported here can be found in the so-called durbachite -ultrapotassic melanosyenite present in the high-grade Variscan basement- and in the garnet peridotites and garnet pyroxenites of the T-7 borehole. In both case metasomatism was suggested but the agent was just inferred based on the geochemical signature. All these occurrences suggest that mantle contaminated by melts from deeply subducted continental crust is widespread beneath the Bohemian Massif.

How to cite: Borghini, A., Ferrero, S., O'Brien, P. J., Wunder, B., and Laurent, O.: Pristine metasomatic melt preserved in mantle rocks of the Bohemian Massif, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14751, https://doi.org/10.5194/egusphere-egu21-14751, 2021.

In Central Evia island (Aegean-Greece) serpentinized ultramafic rocks appear as elongated thrust sheets or in the form of olistostromes incorporated within Maestrichtian-Paleocene flysch. These are crosscut by well-developed rodingite dykes that were derived from four main protoliths that include i) Boninites, ii) Island-arc Tholeiitic Basalts and Gabbros, iii) Alkaline basalts and iv) Calc-alkaline basalts. They mainly comprise of minerals that include (hydro)garnet + chlorite + clinopyroxene ± vesuvianite. Accessory minerals include spinel ± calcite ± prehnite ± amphibole ± orthopyroxene ± olivine ± quartz ± opaque Fe-Ti oxides. Rodingites that were formed at the expense of boninites and island-arc tholeiitic rocks were likely formed within a single rodingitization stage, since garnet is mainly grossular-rich and relict primary clinopyroxene has been preserved. The rodingitization of the alkaline and calc-alkaline basalts seems to have occurred as a multi-stage metasomatic process that occurred during the exhumation of the mafic-ultramafic mantle wedge complex. This resulted in the development of late-stage andradite, vesuvianite and in some cases of chlorite during derodingitization. In this case, successive reaction zones with variability in the participating mineral phases were developed.  Geochemical results reveal remarkable rare earth element (REE) enrichments, especially in the inner zones, likely being the result of successive diffusion and element transfer. Few rodingites are characterized as calcite-bearing, whose stable ¹³C-¹⁸O isotopic data points to the restricted involvement of late-stage mixed hydrothermal and seawater-related carbonation processes.

How to cite: Karkalis, C., Magganas, A., Koutsovitis, P., and Ntaflos, T.: Rodingitization of mafic rocks from Central Evia (Greece) associated with serpentinite exhumation: Evidence from Petrological, Geochemical and Isotopic data , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3319, https://doi.org/10.5194/egusphere-egu21-3319, 2021.

Extensive magmatic activities were developed in  Central and Western Anatolia,  since middle miocene to quaternary times,   the most primitive lavas are situated in eastern end of Central (Sivas) and also western (Kula) Anatolia, besides Kula basalts are  one of the most recent basaltic rocks together with  basalts  from south-central Anatolia.   Although the magmatism is generally   observed at several different  locations, the recent   basaltic rocks in both of the regions   seem to be derived from  the melting  of the peridotite and pyroxenite  source  domains and the latter one  was ignored in previous studies as source component.

 The previous studies indicate that many of the basaltic rocks from Central and Western Anatolia  are related with spinel-garnet transition, but typical Tb/Yb(N) (>1.8; [1]) and Zn/Fe   (separates peridotite-derived (Zn/Fe <12; [2]) and pyroxenite-derived (Zn/Fe 13-20); [2] melts)  Co/Fe  ratios of the basaltic rocks from  several volcanic centers from Central and Western Anatolia  reveal that   melting from the single  source component  are not solely capable of  the producing  basaltic  rocks. 

 Sr-Nd and Pb isotopic  compositions  clearly display the distinction  of samples which are  linked to    asthenospheric source. The lead isotopic systematic  shows  no siginificant differences  among the Central and Western Anatolian basalts,  of all the samples are above the NHRL line and close to EM II  mantle component,  Sr- Nd  isotopes  also display similar compositions as well, the majority of the samples are in and close to mantle array,   but the  Sr isotopic composition   of  Miocene aged  Gediz and Simav lavas have high radiogenic values. 

Tb/Yb(N),  Zn/Fe ratios  and   as well as the Pb isotopic  compositions and REE-based melting model reveal  that Sivas, Erciyes Hasandağ, and Develidağ samples in central Anatolia,  and Kula, Gediz basalt in western Anatolia  seem to be  derived from the amalgamated melting of  pyroxenite and peridotite sources,   besides,  the sources melting is capable of  the producing     elemental variations in  basaltic rocks related with either lithospheric delamination or lithospheric  unstability

• 1.Wang et al., 2002, J.Geophys.Res.vol:107,ECV 5 1-21
• 2 .Le Roux, et al.,2011,EPSL, vol:307, 395-408

This study is financially supported by Hacettepe University, BAB project no: FHD-2018-17283

How to cite: Kurkcuoglu, B. and Yürür, T.: Sr-Nd-Pb isotopic significance of mantle source components from Central and Western Anatolia:  Melting  evidences   from peridotite and pyroxenite source  domains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12162, https://doi.org/10.5194/egusphere-egu21-12162, 2021.

Pyroxenites constitute the major form of heterogeneity in the upper mantle. Their occurrence in supra-subduction zone settings is mostly testified by veins and layers in refractory ophiolitic peridotites, where they represent a crucial witness of melt migration in the forearc/subarc environment [1,2]. The New Caledonia ophiolite hosts one of the largest forearc mantle section worldwide, providing a unique perspective into upper mantle processes. The sequence is dominated by ultra-depleted harzburgites [3], locally overlain by mafic-ultramafic cumulates [4,5,6]. The harzburgites are highly refractory residues that register a multi-phase evolution, including fluid-assisted melting in a forearc environment and contamination by fluid- and melt inputs triggered by Eocene subduction [1]. Pyroxenitic rocks intruding the harzburgites are only known in the Bogota peninsula shear zone, which records HT deformation along a paleotransform fault [7]. In this contribution, we report a comprehensive petrological and geochemical characterization on a new set of pyroxenites from this locality. The pyroxenites (~5-15 cm-thick) generally cut the peridotite foliation at variable angles, but concordant, locally boudinaged, layers also occur. Pyroxenite textures range from cumulitic to porphyroclastic or granoblastic-polygonal. The studied samples mostly consist of amphibole-bearing (5-44 vol.%) websterites, with variable amounts of orthopyroxene (27-67 vol.%) and almost constant clinopyroxene contents (~ 25-29 vol.%). Minor olivine-bearing orthopyroxenites are also present. Accessory phases include high-Ca (An= 82-86 mol%) plagioclase, Cr-rich spinel (Cr# = 50-61), sulfides and, occasionally, apatite. Pyroxenes displays high Mg# (Mg# Opx= 91-92; Mg# Cpx= 84-93), coupled with low Al2O3 contents (0.97-1.92 wt% and 1-2.42 wt% for orthopyroxene and clinopyroxene, respectively). Amphibole is high Mg# edenite. Application of conventional pyroxene thermometry yield equilibration temperatures ranging between 930-1040°C, comparable to the enclosing harzburgites (~ 950°C), whereas amphibole-plagioclase geothermometer provides lower temperatures (~ 800°C). Bulk rock composition of the websterites show variable Mg# (82-91) and REE concentrations ranging between 1 to 10 times chondritic values. They are characterized by flat to LREE-depleted (LaN/SmN 0.28-0.92) patterns, coupled to weak MREE-HREE fractionation (GdN/YbN = 1.73-1.92) and Eu negative anomalies. By contrast, orthopyroxenites display notably lower concentrations (0.1≤REE≤1 chondrite abundances). As a whole, clinopyroxene REE patterns of the websterites mirror bulk rocks at higher absolute values. Putative melts in equilibrium with clinopyroxene indicate strongly enriched compositions (up to 300 times chondritic values) coupled to variable LREE-HREE fractionation (LaN/LuN = 3-19) and flat to fractionated HREE (GdN/LuN 1-2). Such enriched liquids, which show some analogies with pre-obduction adakite-like dikes [8], have never been recorded in the MTZ cumulitic sequence of the New Caledonia ophiolite and shed new light on the magmatic activity in the early stage of subduction. 

[1] Varfalvy, Canad Mineral, 1997, 35 (2), 543-570.
[2] Berly et al., J. Petrol., 2006, 47(8), 1531-1555.
[3] Secchiari et al., Geosc. Front., 2020, 11(1), 37–55. [4]. 
[4] Marchesi et al., Chem. Geol., 2009, 266, 171-186.
[5] Pirard et al., J. Petrol., 2013, 54, 1759–1792.
[6] Secchiari et al., Contrib. Mineral. Petrol., 2018, 173(8), 66.
[7] Chatzaras et al., Geology, 2020, 48 (6): 569–573.
[8] Cluzel et al., Terra Nova, 2006, 6, 395–402.

How to cite: Ferrari, E., Secchiari, A., Montanini, A., and Cluzel, D.: Supra-subduction mantle pyroxenites in an infant subduction system: the New Caledonia ophiolite record., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15299, https://doi.org/10.5194/egusphere-egu21-15299, 2021.

Within the Samail Ophiolite, Oman, there are intervals of listvenite outcrops between layers of serpentinite zones above the basal thrust zone, atop the metamorphic sole. Near the base of the ophiolite mantle section, some peridotites underwent 100% carbonation from metasomatic introduction of CO₂-bearing fluids <200°C to form listvenites during the time of emplacement (97 ± 29 Ma, Falk and Kelemen, 2015). The carbonate rocks comprise mostly magnesite and/or dolomite, quartz, Cr-spinel, and Fe-(hydr)oxides; with carbonates as the sole Mg-minerals and quartz as the only silicate phase. The aim of this study is to chemically and petrographically investigate the Fe-bearing minerals within the fluid-altered mantle rocks in drill core samples from hole BT1B of the ICDP Oman Drilling Project. Sequential chemical extractions are useful for recognizing iron pools based on the minerology. We investigated the quantities of Fe-oxide/hydroxide phases through a series of chemical extractions (Poulton and Canfield, 2005) via atomic absorption spectroscopy in addition to optical microscope, SEM/EDS, EPMA/WDS and ICP analysis. Extractions performed at room temperature and one at 50°C included: carbonate-associated Fe (sodium acetate) targeting siderite, HCl-extractable Fe(II), reducible oxides (citrate-dithionite) targeting hematite and possible goethite, and magnetite (oxalate). Carbonate-based Fe in the listvenites from a sodium acetate extraction ranges from 12-28 mg/g, while the same extraction performed at 50°C for twice as long resulted in higher proportions of carbonate-associated Fe (15-35 mg/g). Easily reducible iron quantities from the diluted HCl solution extraction display the lowest overall Fe fractions (0.75-5.5 mg/g) following the room temperature acetate and 0.63-1.7 mg/g after the 50°C acetate extraction. Fe in reducible oxides extracted by dithionite ranged from 1.4-15 mg/g with similar result after both a room-temperature acetate and a 50°C acetate step. Oxalate extraction succeeding the room-temperature acetate yielded magnetite concentrations of 1.9-8.0 mg/g, while the increased temperature and time in the first step (acetate extraction) were followed by significantly lower amounts of Fe extracted by oxalate (0.47- 3.6 mg/g). Additionally, the same extractions were performed on a pure siderite sample from Greenland. For siderite samples crushed a week prior to analysis, the carbonate-associated Fe in sodium acetate extract was 165±17 mg/g; the sidenote yielded 42 wt% of overall extracted Fe (392±33 mg/g). This is only slightly lower than the expected 48.2 wt% of Fe for a pure siderite sample. Dilute HCl extractions display results of 126±5.4 mg/g, dithionite solution extracted 25±0.5 mg/g and oxalate proportions were 76±9 mg/g. Due to possible oxidation of siderite to magnetite occurring during the time between powdering the samples and analysis, the full dissolution of siderite may not be fully represented in only the acetate. Microprobe data shows a total amount of FeO in carbonates as 1.3-10.8 wt%. This is more than or similar to the acetate and HCl proportions of Fe which represent carbonate associated minerals in the listvenites. Data obtained from EMPA and ICP will additionally be discussed in relation to the Fe-oxide phases with relation to the listvenites minerology.

How to cite: Severin, Z., Till, J. L., and Phase 1 Science Party, O. D. P.: Sequential geochemical extractions and mineralogy of Fe-bearing minerals in carbonatized mantle rocks in the Samail Ophiolite, Oman , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15840, https://doi.org/10.5194/egusphere-egu21-15840, 2021.

During the Upper Jurassic-Lower Cretaceous times the western margin of Gondwana in southern Patagonia experienced extreme lithospheric extension and generation of rift and marginal back-arc basins. The ophiolitic complexes of the Rocas Verdes basin comprises incomplete ophiolite pseudostratigraphy lacking ultramafic rocks. The Tortuga Ophiolitic Complex, the southernmost seafloor remnant of the Rocas Verdes basin, record the most advanced evolutionary stage of the back-arc basin evolution in a mid-ocean ridge-type setting. The base of the Tortuga Complex consists of massive and layered gabbros, most of which are two pyroxene and olivine gabbros, leucogabbros, and clinopyroxene troctolites intruded by dikes of basalt and diabase with chilled margins. We present new major and trace element composition of clinopyroxene from the gabbros and sheeted dikes complexes to assess the geochemical affinity of parental basaltic magmas. Clinopyroxene in gabbros is mostly augite and have Al contents of 0.06-0.14 a.p.f.u. and Mg# of 80-92. Clinopyroxene in dolerites in the sheeted dike unit (augite and diopside) have Al content of 0.11-0.12 a.p.f.u. and Mg# of 85-92. Some immobile trace elements (e.g. Zr, Ti, Y) are sensitive to the degree of partial melting and mantle source composition, and can be used as a proxy for distinguishing tectonic environments. The Ti+Cr vs. Ca diagram, coupled with moderate-high TiO₂ content of clinopyroxene (0.4-1.4 wt.%) suggests their generation in mid-oceanic ridge-type environment (cf. Beccaluva et al., 1989).  The high Ti/Zr ratios (of ~4-11) coupled with low Zr contents (~0.2-1.1) are expected for higher degrees of partial melting or for melting of more depleted mantle sources. Conversely, low Zr/Y ratios (0.05-0.13) plot between the range of arc basalts. Chondrite-normalized REE patterns in clinopyroxene display a strong depletion of LREE compared to HREE and have an almost flat pattern in the MREE to HREE with a positive Eu (Eu*= 0.9-1.1) anomaly, indicating that clinopyroxene crystallized from a strongly depleted mid-ocean-ridge-type basalt, formed by extensive fractional melting of the mantle source and/or fractional crystallization and accumulation of anhydrous phases. The general trend of the incompatible trace elements patterns exhibit depletion in LILEs, minor HFSEs depletion, positive anomaly of Rb and negative anomalies in Ba, Zr, Ti and Nb, consistent with their generation from a refractory mantle source barely influenced by subduction components derived from the oceanic slab. This agrees with basalt generation in a back-arc basin located far away from the convergent margin. This study was supported by the Fondecyt grant 1161818 and the Anillo Project ACT-105.

How to cite: Torres Garcia, F., Calderón, M., Fadel Cury, L., Theye, T., Opitz, J., Rojo, D., Hopfenblatt, J., and Fuentes, F.: Trace element composition of clinopyroxene in gabbros and dolerites of the Tortuga Ophiolitic Complex, southernmost Patagonia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14475, https://doi.org/10.5194/egusphere-egu21-14475, 2021.

Quantifying the volatile content of the lunar interior is valuable for understanding the formation, thermal evolution, and magmatic evolution of the Earth and Moon. Petrological modelling and geochemical measurements have been used to study the volatile composition of the lunar interior. Improvements to analytical instruments have facilitated more precise measurements of the volatile content of lunar samples and meteorites, however, several problems remain with these measurements, hence, the volatile content of lunar magmas has yet to be constrained with certainty. We propose a volcanological approach for inferring the volatile contents of different lunar magmas.

            A terrestrial magma ascent model has been modified for lunar applications. Numerous parameters were adjusted for lunar conditions, including: magma major element composition, from low-Ti (green and yellow glasses) to high-Ti (orange, red, and black glasses); H₂O content; CO content; gravity; and pressure. The model calculated values for gas exsolution, viscosity, mass flow rate, and several other ascent processes, from a depth of 10 km to the surface. Using these results, we will assess the effect of varying magmatic volatile content on lunar magma ascent processes. We will also compare and contrast our results with existing models for lunar magma ascent, as well as models for magma ascent on other planetary bodies. Future work will involve modelling eruptions, using results from the magma ascent model, and verifying the results of the models using images and digital elevation models of the lunar surface.

How to cite: Lo, M., La Spina, G., Joy, K., Polacci, M., and Burton, M.: Modelling the ascent of picritic lunar magmas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10624, https://doi.org/10.5194/egusphere-egu21-10624, 2021.

The Earth-Moon system and its formation is a topic of great scientific interest, and great debate over the past decades. The giant impact hypothesis is the currently accepted model to explain the formation of our moon. Accordingly, a mars-sized impactor collides with the proto-earth. This giant impact vaporized a significant portion of the impactor and the proto-earth, creating a large accretionary disk from which the moon subsequently formed. Currently, there is a large effort to build reliable thermodynamic descriptors for the building materials of the two bodies involved in the impact. Understanding the behavior of major rock-forming minerals under these extreme conditions is vital for increasing the accuracy of these models.

Magnesium oxide, MgO, is one of the fundamental building blocks for rocky planets. It is an archetype material of ionic solids and a well-known refractory material. Because of its relevance it has been studied extensively; experimental and theoretical results have been produced up to pressures of 800 GPa and temperatures reaching 20000 K. These pressure and temperature regions are of great interest for the planetary sciences, studying planetary interiors. The transformation of the face-centered B1 phase to the body-centered B2 phase and the associated melting curve have been modelled numerous times. In contrast, we know very little of the liquid behaviour of MgO under pressure, let alone at the low pressures found in accretionary disks.

Here we investigate the low-density high-temperature regime characteristic of after-shock isentropic release. We explore the subcritical and the supercritical regimes of MgO using ab initio molecular dynamics. We determine the position of the critical point and examine the structural and transport properties in the sub- and supercritical regimes. We find an elevated critical temperature in comparison with previously studied magnesium-silicates, in agreement to the refractory nature of MgO. Furthermore, we provide insight into the speciation of liquid MgO and the liquid-gas separation. We see a shift in Mg-O speciation towards lower degrees of coordination as the temperature is increased from 4000K to 10000K. This shift in speciation is less pronounced at higher densities. The majority of the chemical species forming the incipient gas phase consist of isolated Mg and O ions and some MgO and O₂.

This research was supported by the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818 – IMPACT to RC). We acknowledge access to supercomputing facilities via eDARI stl2816, PRACE RA4947, and Uninet2 NN9697K grants.

How to cite: Bögels, T. and Caracas, R.: The behaviour of MgO in a giant impact setting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1123, https://doi.org/10.5194/egusphere-egu21-1123, 2021.

The prevailing theory of the origin of the Moon is the giant impact hypothesis, in which a Mars-sized impactor collides with the proto-Earth in the late stage of accretion, and the Moon is subsequently formed from the proto-lunar disk made of the ejected materials. As the laboratory-scale experiments are not able to simulate planetary-scale impacts, our understanding of the giant impact mostly comes from hydrodynamic simulations. However, the results of these simulations heavily depend upon the available equation of state to describe the thermodynamic response of the constituent materials of the proto-Earth and impactor to shock waves.

Iron as a building block material of the terrestrial planets naturally received significant attention. But the major effort has been put to determine its phase diagram up to the Earth’s core conditions (126-360 GPa and 3000-7000 K) and beyond. The studies of iron at low densities are still scarce and the position of the critical point (CP) is uncertain. As the liquid-vapor dome ends at CP, the position of the latter determines the time evolution of the proto-lunar disk during its condensation.

In order to assess whether the core of the planets undergoes significant vaporization during a giant impact, we employ ab initio molecular-dynamics simulations to explore iron over a wide density region encompassing the critical point (CP) and the Hugoniot lines of the shocked iron cores. We determine the critical point of iron in the temperature range of 9000-9350 K, and the density range of 1.85-2.40 g/cm³, corresponding to a pressure range of 4-7 kbars [1]. This implies that the iron core of the proto-Earth may become supercritical after giant impacts. We show that the iron core of Theia partially vaporized during the Giant Impact. Part of this vapour may have remained in the disk, to eventually participate in the Moon’s small core. Similarly, during the late veneer stage a large fraction of the planetesimals have their cores undergoing partial vaporization. This would help to mix the highly siderophile elements into magma ponds or oceans.

References:

[1] Z. Li, R. Caracas, F. Soubiran, Partial core vaporization during Giant Impacts inferred from the entropy and the critical point of iron, Earth Planet. Sci. Letters, 2020, https://doi.org/10.1016/j.epsl.2020.116463

How to cite: Li, Z., Caracas, R., and Soubiran, F.: Partial core vaporization during giant impacts inferred from the entropy and the critical point of iron, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1145, https://doi.org/10.5194/egusphere-egu21-1145, 2021.

Metamorphic rocks on the Moon are an important yet under-studied suite of lunar lithologies that have been identified in the Apollo and lunar meteorite collections [1]. These rocks, with granoblastic textures, are generally referred to as granulites; however, unlike their terrestrial counterparts, they are considered to represent the products of only high-temperature (> 1000 ^oC) thermal metamorphism that completely re-crystallised their protolith(s). Lunar granulites are commonly sub-divided into two main compositional groups related to their protolith lithologies. The Fe-granulites, found at most Apollo landing sites, are generally accepted to derive from metamorphosed plagioclase-rich igneous cumulates, termed the ferroan anorthosite (FAN) suite. The FAN suite are important lithologies as they represent products of the primary lunar crust. The Mg-granulites are found mostly at the Apollo 16 landing site and within lunar meteorite samples; the protolith(s) of this latter group is not well understood [2].  Early studies have linked the protolith to secondary magmatic intrusions into the primary anorthositic crust (termed the Mg-suite); however, recent studies have tentatively connected the protolith to a Mg-rich variation of the primary crustal plagioclase cumulates (termed the MAN suite). The occurrence of MANs is controversial, it is unclear how the MAN suite fits into canonical lunar crustal formation models [3]. To investigate the protoliths of the granulite suites, we report in situ trace- and minor-element abundances for olivine and pyroxene grains within Fe- and Mg-granulites, determined by LA-ICP-MS and EPMA respectively. Trace-element data presented here indicate that the Mg-granulites are compositionally similar to the MAN suite. Furthermore, by comparing plagioclase trace-element data with peak metamorphic temperatures (calculated using two-pyroxene thermometers [4]), we find no relationship between metamorphic temperature and diagnostic trace-element signatures suggesting that both granulite suites experienced similar thermal metamorphic conditions. Additionally, we estimate the duration of metamorphic heating using experimentally derived diffusion rates of minor elements in minerals,  (such as Ca in olivine [5]). Both the calculated cooling rates and peak metamorphic temperatures can set constraints on the metamorphic heat source responsible for thermally annealing the Fe- and Mg-granulites. Specifically, we are able to assess whether the granulites formed as a result of shallow (<1 km) burial of the protolith by impact melt sheets or hot, impact-generated fall-back breccias [6]; or deep (> 1km) contact metamorphism of the protolith due to the emplacement of magma chambers or upwelling plutons within the lunar crust [7].

[1] Lindstrom & Lindstrom, 1986, JGR, 91(B4), 263-276 [2] Treiman et al. 2010. MaPS, 45, 163-180. [3] Gross et al. 2014, EPSL, 388, 318-328. [4] Brey & Köhler, 1990, J Pet, 31, 1353-1378. [5] Dohmen et al, 2007, PCM, 34, 389-407. [6] Cushing et al. 1999, MaPS, 34, 185-195. [7] Hudgins et al. 2011, Am Min, 96, 1673-1685.

How to cite: Pernet-Fisher, J., Hartley, M., and Joy, K.: Trace and minor element variations in lunar granulites: Insights into lunar metamorphic conditions., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12352, https://doi.org/10.5194/egusphere-egu21-12352, 2021.

Chondrules - major constituent of chondrites (primitive meteorites) - belong to the first object formed in the solar system. They are millimetre-sized igneous objects resulting from partial to complete fusion and are divided into main families: non-porphyritic and porphyritic (Gooding and Keil, 1981); the latter one is more abundant in chondrites. This study aims to reproduce thermal histories of macro-porphyritic olivine chondrules (PO) and to better constrain (thermal, temporal) the conditions reigning in the early solar system.

In general, PO chondrules are composed of numerous euhedral crystals of olivine and/or pyroxene suggesting an initially melting below their liquidus temperatures. By contrast, in our study, the macro-porphyritic olivine chondrule displays only one large euhedral olivine. The low number of olivine crystals indicates that chondrule suffered an initial step of superheating, limiting nucleation process (Lofgren, 1988; Hewins et al., 1988). Moreover, embayments observed in euhedral olivine show that olivine crystal began to growth rapidly and then the growth-rate decreased during the cooling. Therefore, our petrographic investigation proposes a first high temperature stage (ΔT_liq = +10 °C) followed by a slow cooling.

To test this thermal history, experiments are performed to determine degree of superheating and cooling rate effect (i) on nucleation rate and (ii) on morphology of olivines formed during cooling. Preliminary results seem to confirm that macro-porphyritic olivine chondrules result from the slow cooling of a superheated initial chondritic liquid (Varela et al., 2006). Then these results allow to precise the beginning of the igneous processes (minimum thermal temperature and cooling rate) and to discuss the complete thermal evolution of the chondrule, by considering all other reaction textures observed in this chondrule: peritectic and oxidation reactions, quench texture and aqueous alteration.

References:

Gooding et al., (1981) Meteoritics, 16, No. I; Hewins et al., (1988) Meteoritics, 25, 309-318; Lofgren, (1988) Geochim. & Cosmochim. Ada, 50, 1715-1726; Varela et al., (2006) Icarus, 178 (2), 553–569.

How to cite: Auxerre, M., Faure, F., and Lequin, D.: Superheating and cooling rates effects on olivine growth in chondritic liquid: experimental and petrographic approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1230, https://doi.org/10.5194/egusphere-egu21-1230, 2021.

The crystallographic orientation of antiperthite (squared alkali feldspar inclusions grow inside plagioclase host) in Tiantangzai monzogranite from Dabie Mountain was investigated. The morphology of alkali feldspar inclusions is hexahedron, three pairs of parallel faces are controlled by the (010), (001) and (110) planes of the host plagioclase, respectively. Some plagioclase develops albite polysynthetic twin, defined the twinned individuals as Pl(1) and Pl(2), respectively; some alkali feldspar inclusions are related by Carlsbad twin, the twinned individuals are also defined as Kfs(1) and Kfs(2), respectively. Pl(1) is oriented similarly to Kfs(1). The topotaxial relationship between Pl(2) and Kfs(1) is similar to albite-twin. The topotaxial relationship between Kfs(2) and Pl(1) is similar to Carlsbad-twin. Kfs(2) and Pl(2) would form a topotaxial relationship similar to Carlsbad-albite-twin. Pl(1) generally becomes thinner or disappears in the regions where alkali feldspar inclusions developed. The development sequence of the alkali feldspar inclusions and the polysynthetic albite twin needs to be further investigated. Electron microprobe line scanning shows a homogeneous K, Ca and Na distribution in a single plagioclase grain with inclusions developed, suggesting that the origin of alkali feldspar inclusion may not be related to exsolution. The fractures in the host plagioclase are well developed, but most fractures do not pass through the embedded alkali feldspar. The precipitated alkali feldspar may be a result of alkali-bearing fluids penetrating through fractures and replacing plagioclase. The rim of some larger anhedral alkali feldspar inclusions has many voids, the local average misorientation map indicates there is a rectangular area with low misorientation difference inside the anhedral inclusions. The anhedral alkali feldspar inclusions are presumed to form by secondary replacement on top of the original rectangular inclusions.

How to cite: Song, Y. and Zhao, S.: Topotaxial intergrowth and origin of antiperthite in monzogranite , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13814, https://doi.org/10.5194/egusphere-egu21-13814, 2021.

Magnetite micro-inclusions in silicate minerals are important carriers of the remanent magnetization of rocks. Their shape orientation relationships (SOR) and crystallographic orientation relationships (COR) to the host crystal are of interest in the context of the bulk magnetic properties of the inclusion-host assemblage. We investigated the SOR and COR of magnetite (MT) micro-inclusions in plagioclase (PL) from oceanic gabbro using correlated optical microscopy, scanning electron microscopy, Electron backscatter diffraction analysis and Transmission electron microscopy.

In the mm-sized PL crystals of the investigated gabbros MT is present as equant, needle- and lath-shaped (sub)micrometer sized inclusions. More than 95% of the needle-shaped inclusions show SOR and specific COR to the plagioclase host. Most of the needles are elongated perpendicular to one of the MT{111} planes, which is aligned parallel to one of the (112), (1-12), (-312), (-3-12), (150), (1-50) or (100) planes of plagioclase. These inclusions are classified as “plane-normal type”. The needle elongation parallel to MT<111>, which is the easy direction of magnetization, ensures high magnetic susceptibility of these inclusions. The underlying formation mechanism is related to the parallel alignment of oxygen layers with similar lattice spacing across the MT-PL interfaces that are parallel to the elongation direction [1].

Apart from the SOR and the alignment of a MT{111} with one of the PL low index planes, the MT crystals rotate about the needle elongation direction. The rotation angles are statistically distributed with several maxima representing specific orientation relationships. In some cases one of the MT<001> axes is aligned with PL[14 10 7] or PL[-14 10 -7], which ensures that FeO₆ octahedra of MT well fit into channels // [001] of PL, which are formed by six membered rings of SiO₄ and AlO₄ tetrahedra [2]. This COR is referred to as the “nucleation orientation” of magnetite with respect to PL. There are several other possibilities to fit FeO₆ octahedra into the [001] channels of PL, but the alignment stated above allows for the additional parallel alignment of one of the MT{111} with one of the above mentioned low index lattice planes of PL. MT crystals with one of these nucleation orientations can undergo directional growth to develop laths and needles. MT crystals with other nucleation orientations that do not allow for the parallel alignment of MT{111} with the above mentioned PL lattice planes, do not significantly grow and form the equant inclusions.

For some needles one or more of the MT{011} planes that are parallel to the needle elongation direction, are aligned with low-index planes of plagioclase such as PL (112), PL(150), PL(1-50) etc., and form MT facets. This situation corresponds to achievement of the best possible match between the two crystal lattices. This can either be generated during primary growth or during re-equilibration of the micro-inclusions and the plagioclase host.

Funding by RFBR project 18-55-14003 and Austrian Science fund (FWF): I 3998-N29 is acknowledged.

Reference

[1] Ageeva et al (2020) Contrib. Mineral. Petrol. 175(10), 1-16.

[2] Wenk et al (2011) Am. Min. 96, 1316-1324

How to cite: Ageeva, O., Bian, G., Habler, G., and Abart, R.: Orientation relationships between magnetite micro-inclusions and plagioclase host , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12665, https://doi.org/10.5194/egusphere-egu21-12665, 2021.

REE orthoarsenates and orthophosphates are common accessory minerals characterized by the general chemical formula REEXO₄, where REE represents one of the lanthanides (La-Lu series), Y, Sc, Ca or Th, whereas X stands for As, P or Si. In the framework of a long-term project on the high-T/high-P crystal-chemistry and phase-stability of REE-bearing minerals, the high-pressure behavior of chernovite-(Y) (nominally YAsO₄), xenotime-(Y) (nominally YPO₄) gasparite-(Ce) (nominally CeAsO₄) and monazite-(Ce) (nominally CePO₄), has been studied. Chernovite-(Y) and xenotime-(Y) show a HREE- (Gd-Lu series) and Y-enrichment, and the same tetragonal symmetry (space group I4₁/amd), whereas gasparite-(Ce) and monazite-(Ce) share the same LREE (La-Eu) enrichment and monoclinic cell (space group P2₁/n). All these minerals occur at Mt. Cervandone (Western Alps, Italy), a renowned Alpine REE-bearing mineral deposit. The crystal chemistry of the four minerals has been studied via EPM-WDS analysis. Excluding gasparite-(Ce), which formation is bound to the replacement of the mineral synchisite-(Ce) (CaCe(CO₃)₂F), a sensible enrichment in Gd and Ho is observed. Moreover, the majority of the chernovite-(Y) show a variable amount of ThO₂, up to 13 wt%, and phosphorous as substitute for arsenic in almost every proportion. In the case of the monoclinic series between monazite-(Ce) and gaparite-(Ce), no solid solution has been observed. Experiments at high-pressure were performed by in situ synchrotron X-ray diffraction using a diamond anvil cell. The high-pressure behavior of single crystals of xenotime-(Y), gasparite-(Ce) and monazite-(Ce) has been studied up to ~20 GPa, whereas that of chernovite-(Y) has been studied by powder diffraction up to 8.20(5) GPa. A II-order Birch-Murnaghan equation of state was fitted to the V-P data, within the phase stability field of the minerals, yielding the following bulk moduli: K_P0,T0 = 125(3) GPa (β_V0 = 0.0080(2) GPa^-1) for chernovite-(Y); K_P0,T0 = 145(2) GPa (β_V0 = 0.0069(1) GPa^-1) for xenotime-(Y);  K_P0,T0 = 106.7(9) GPa (β_V0 = 0.0094(1) GPa^-1) for gasparite-(Ce), K_P0,T0 = 121(2) GPa (β_V0 = 0.0083(1) GPa^-1) for monazite-(Ce). K’ = ∂K_V/∂P = 4 (fixed) for all the minerals. Deformation mechanisms, at the atomic scale, were described on the basis of structure refinements.  

Acknowledgments: This research was partly funded by the PRIN2017 project “Mineral reactivity, a key to understand large-scale processes” (2017L83S77).

How to cite: Pagliaro, F., Lotti, P., Guastoni, A., Comboni, D., Gatta, G. D., Rotiroti, N., and Milani, S.: High-pressure crystal chemistry of four natural REE(As,P)O4 minerals from Mt. Cervandone, Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5066, https://doi.org/10.5194/egusphere-egu21-5066, 2021.

Chemical signatures of magnetite are commonly used to track the evolution of mineralizing systems in many geological settings. However, the impact of deformation processes on magnetite chemistry remains still underexplored. Here, we report a rare case of composite crystals consisting of magnetite and magnesioferrite recording different degrees and styles of deformation in order to evaluate how deformation promotes chemical modification. The samples employed in this study come from two different Mg-skarn iron deposits (i.e., El Robledal and San Manuel) from the Serranía de Ronda (SW Spain). Chemical data acquired by Electron Probe Microprobe Analyzer (EPMA) and Field Emission Scanning Microscopy (FESEM) are contrasted against microstructural data obtained by using Electron Back-Scattered Diffraction (EBSD). Our results show that magnesioferrite crystals [Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.22-0.46 and Fe³⁺# (Fe³⁺/Fe³⁺+Al³⁺) = 0.99-1.00] from El Robledal deposit are characterized by a ductile deformation that led to different crystallographic orientation domains along with the replacement of magnesioferrite by magnetite (Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.51-0.99 and Fe³⁺ (Fe³⁺/Fe³⁺+Al³⁺) =0.98-1.00] via coupled dissolution – reprecipitation. A replacement of magnesioferrite [Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.43-0.64 and Fe³⁺ (Fe³⁺/Fe³⁺+Al³⁺) = 0.99-1.00] by magnetite Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.78-1.00 and Fe³⁺# (Fe³⁺/Fe³⁺+Al³⁺) = 0.98-1.00] via a coupled dissolution – reprecipitation mechanism is also preserved in the composite (i.e., zoned) crystals from the San Manuel deposit, which was additionally overprinted by an additional recrystallization event as a result of grain boundary migration recrystallization. Our results show that deformation in a fluid-assisted deformation regime has induced chemical modification of the original magnesioferrite aggregates as well as strain localization. This close physicochemical link offers new avenues of interpreting the chemical signatures of Mg-Fe oxides, utilizing their microstructurally controlled variation or lack thereof.

How to cite: González-Pérez, I., Noval-Ruiz, S., González-Jímenez, J. M., Gervilla, F., Fanlo, I., and Tornos, F.: Evaluating the effects of deformation on the chemistry of composite magnesioferrite-magnetite crystals by means of EBSD, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10025, https://doi.org/10.5194/egusphere-egu21-10025, 2021.

How to cite: Szucs, A. M., Stavropoulou, A., O'Donnell, C., Davis, S., and Rodriguez-Blanco, J. D.: Mechanisms of bastnasite formation: replacement of calcite by rare earth carbonates., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-61, https://doi.org/10.5194/egusphere-egu21-61, 2021.

Major, minor and trace element analysis using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been applied to a broad range of mineral samples for characterization, mineral resources prospection, tracing and provenance determination, radiometric dating and studies on mineral formation conditions. In this study, we present a state-of-the-art LA-ICP-Time-Of-Flight-MS (LA-ICP-TOF-MS) technique for multi-element analysis of gem-quality Cu-bearing tourmaline from Brazil, Mozambique and Nigeria, with a special focus on elemental correlation among and within various provenances.

A TOF-MS obtains a full mass spectrum from ⁷Li⁺ to ²³⁸U⁺ simultaneously with an improved mass resolving power. These advantages over other conventional ICP-MS setups allow the TOF users to apply a novel concept of “first measure, then determine” which elements are of interest for the analysis of geological samples. Since the TOF-MS technique requires no/limited a priori knowledge about the sample before measurement, this technique can be beneficial for studying elements which occur infrequently in the minerals and for analysing full elemental composition in unidentified inclusions.

Multi-element composition of more than 400 Cu-bearing tourmaline samples (majority elbaite, Na-rich) was analysed using LA-ICP-TOF-MS that cover various colors, qualities and provenances available in the gem and jewellery trade. In order to investigate the elemental correlation, a non-linear unsupervised dimension reduction was performed on the high dimensional multi-element dataset using t-distributed stochastic neighbor embedding (t-SNE) algorithm. An unsupervised calculation works solely with the elemental concentrations and without labels of data points, for example color or provenance. The clusters in the geochemical data visualization indicates elemental similarity of various samples. We found that t-SNE algorithm is better than principle component analysis (PCA) algorithm in maintaining intrinsic elemental correlation from the original high dimensional space and embedding such information onto low dimensional datasets for visualization. Therefore, the t-SNE method excels in distinguishing within-group elemental similarities from between-group similarities. The separation of subgroups achieved with t-SNE is in agreement with the confirmed geographic provenances.

Additionally, a unique type of Cu-bearing liddicoatite (Ca and REE-rich) was recently discovered near Maraca in Mozambique (Nampula area). Since they have been reported so far only from this occurrence, this type of tourmaline is especially interesting to study how elements correlated during tourmaline formation. Applying t-SNE calculation on these samples, we have found two groups (or four subgroups) of these tourmaline samples. When multi-element concentration was plotted, it can be seen that light-REEs (La to Nd) have an apparent correlation with Ca concentration, however a negative correlation was observed between mid-REEs (Sm to Ho) and Ca. A correlation of Na to Bi and Th was also observed.

In a rare four-color (pink, purple, blue, green) Cu-bearing tourmaline sample from Quintos mine in the state of Rio Grande do Norte, Brazil, multi-element analysis was conducted along a profile across the entire color variation, from the core of the crystal (pink) to the rim of the crystal (green) to monitor elemental variations and correlations throughout the crystal growth process of this tourmaline within the pegmatite.

How to cite: Wang, H. A. O., Krzemnicki, M. S., Büche, S., Degen, S., Franz, L., and Schultz-Guttler, R.: Multi-Element Correlation Analysis of Cu-bearing Tourmaline using LA-ICP-Time-Of-Flight-MS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16170, https://doi.org/10.5194/egusphere-egu21-16170, 2021.

Stability relations of the REE-bearing accessory phases and alteration processes in the cancrinite-bearing nepheline syenite from the Čistá pluton (the center of the upper-crustal Tepla–Barrandian unit, Bohemian Massif, Czech Republic) were studied. Observations of rock microtextures, quantitative analyses of minerals and compositional X-ray mapping were performed using electron probe microanalysis (EPMA). The primary REE-bearing accessory minerals assemblage includes monazite-(Ce) associated with gadolinite-group minerals (i.e. gadolinite-(Ce) and gadolinite-(Y)), which were partially replaced by britholite-(Ce), bastnäsite-(Ce), aggregates of fine-grained REE-bearing phases (possibly fluorapatite and/or britholite-(Ce)) and, rarely, cerianite. K-feldspar and albite form intergrowths or symplectites with REE-phases in the investigated reaction microtextures. Furthermore, the zircon crystals demonstrate oscillatory zoning and/or extensive patchy zoning due to alteration processes. The alteration of accessory minerals are interpreted as driven by K- and Na-bearing alkali fluids with high CO₂ activity during late- to post-magmatic processes.

Acknowledgements: This work was supported by the National Science Centre research grant no. 2017/27/B/ST10/00813.

How to cite: Jaranowski, M., Budzyń, B., Kozub-Budzyń, G. A., Sláma, J., and Klomínský, J.: Stability relations of monazite-(Ce), gadolinite-(Ce), gadolinite-(Y), britholite-(Ce) and bastnäsite-(Ce) during late- to post-magmatic processes in nepheline syenite (Čistá pluton, Czech Republic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-820, https://doi.org/10.5194/egusphere-egu21-820, 2021.

The pressure-temperature conditions are transient in time and space during tectonic processes. To understand the complete P-T history of crustal domains examining the mineral paragenetic sequences and zoning profiles of minerals from diverse lithologies in the domain is necessary. But in highly tectonised crustal domains establishing time equivalence between far-spaced samples is difficult. To overcome this, a mylonite sample with closely spaced layers of different mineralogy collected from the South Maharashtra Shear Zone located along the north of Western Dharwar Craton (Rekha and Bhattacharya, 2014) was studied. The mylonite has four mineralogically distinct layers of few millimeters width containing garnet porphyroblasts of distinct zoning pattern separated by quartz layers. Layer-1 has two domains on the basis of the relative abundance of quartz; Layer-1A with more quartz and less flaky minerals and Layer-1B with less quartz and more flaky minerals. Layer-1A is composed of quartz>biotite>plagioclase>chlorite>K-feldspar with syn- to post-tectonic garnet porphyroblasts and the fabric is defined by shape preferred biotite-chlorite aggregates, recrystallized plagioclase and quartz ribbons.Layer-1B is relatively quartz poor and plagioclase>biotite>chlorite>K-feldspar aggregates rich domain as compared to L1A with biotite-chlorite aggregates and recrystallized plagioclase defined fabric.Prehnite elongated parallel to schistosity present but not very common. Layer-2 is very thin with amphibole-biotite±chlorite defined foliation and consists of plagioclase-K-feldspar-quartz with large garnet porphyroblast ofsyn to post-tectonic origin. Chlorites are mainly present near to garnet. Layer-3 is composed of biotite-calcite-plagioclase-chlorite-quartz with syn/post-tectonic garnet porphyroblast and the foliation is defined by biotite-chlorite aggregates, recrystallize plagioclase, calcite grains aligned parallel to the foliation and elongated quartz grains.Layer-3 is separated from the quartz layers on both sides by the formation of thin hornblende layers arranged parallel to the foliation. Very few hornblende grains found within the layer aligned parallel with the fabric defining minerals. Large pre-tectonic muscovite grains are preserved in Layer-3 and are altered to epidote along the margins of the grain. Layer-4 consists of hornblende, calcite, quartz with few plagioclase, K-feldspar and post tectonic garnet porphyroblast. The fabric is defined by the long axis of amphibole and calcite grains aligned parallel to it. Later biotite-prehnite grains formed at high angle to the fabric defining minerals. Conventional geothermobarometers were used for P-T estimation and it varies from 450-560°C and 6 kbar for Layer-1A, 445-550°C and 7 kbar for Layer-1B, 475-570°C and 6 kbar for Layer-2, 450-575°C and 7-8 kbar for Layer-3 and 450-5500°C and 7-9 kbar for Layer-4 at reference temperature of 500°C and pressure of 6kbar. Though different layers have distinctly different mineral assemblages there is hardly any variation in the P-T conditions which implies the original bulk rock composition was different for different layers not the P-T conditions of deformation.

Keywords: Mylonite, Western Dharwar Craton, Geothermobarometry

How to cite: Praharaj, P. and Rekha, S.: Role of P-T conditions and bulk rock composition in the mineralogical variations in millimeter scale: a study from South Maharashtra Shear Zone, western India , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9966, https://doi.org/10.5194/egusphere-egu21-9966, 2021.

Microporous minerals have many industrial applications, from filtration to contaminant immobilization. Natural and synthetic minerals, including zeolites, clays, and silica aerogel, represent a few examples of microporous minerals with distinctive structures, surface charges, and porosity. Analysis and comparison of their crystal structures are necessary to determine how each mineral may be suited for contaminant uptake. Here we assessed the structure of microporous minerals, specifically rowleyite, clinoptilolite, vermiculite, and silica aerogel.  Raman spectroscopy, X-ray fluorescence, and X-ray powder diffraction were used to create and model atomic mineral structures to visualize atomic and macroscope features. Taking into account pore size and surface charge each mineral was reviewed to find the best fit with regards to heavy metal uptake, mainly Pb (lead). Overall, we provide a comparative framework to assess microporous minerals that will inform future flow-through experiments for heavy metal uptake.

How to cite: Osorio, M., Oze, C., and Celestian, A.: Comparison of Microporous Minerals for Potential Contaminant Uptake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12619, https://doi.org/10.5194/egusphere-egu21-12619, 2021.

To determine the influence of the historic factory of electrodes and ferroalloys on the Šibenik bay sediments, XRPD analysis were carried out. The factory was established in the city of Šibenik, on the coast of the Krka River estuary, and produced calcium carbide, and later electrodes and ferroalloys. It was active from 1900 until 1995 [1]. During that time, a large amount of produced tailings were stored nearby and on the shore of the estuary. Due to the presence of the strong winds (bora and sirocco), which can reach up to 130 km/h, the tailings material could be transported to long distances [2].

Samples of tailing were collected at the location of the former factory, which is a tailing hill today, samples of dust were collected from the rooftop of the factory in the 1980s. Other samples were taken on a 1 km distant beach in the Šibenik bay  (Beach A) and a 19 km distant beach on the island in the outer Šibenik archipelago (Beach B). Both beaches are located south-west of the factory. The samples from the beaches were taken with a corer at different depths: 0 – 3 cm, 3 – 5 cm, around 5 cm. The sample from 3 – 5 cm depth was not analysed.

Bulk sample and a fraction <63 µm were analysed on X-Ray Diffractometer. The XRPD analysis of the sediments from Beach B in the outer Šibenik archipelago shows that calcite and quartz are the most abundant phases. This mineral composition shows that distant islands were not affected by aeolian transportation of the factory dust and tailing. In the bulk samples from Beach A, in the uppermost part (0 – 3 cm depth) mineral components are calcite, aragonite, calcium manganite, bustamite ferroan and carbon, while calcite, quartz, aragonite, calcium manganite and manganosite are present in the fraction <63 µm. The sample from the depth of 5 cm at the same beach, shows calcite, aragonite and Mn-oxide, while fraction <63 µm lacks in Mn-oxide.

A bulk sample of tailings shows mineral components: calcite, quartz, calcium manganite, bustamite ferroan and gypsum which corresponds to the previous research [3], and there is also manganese silicon, manganese silicide, carbon and amorphous phase [4]. A fraction <63 µm of the tailing, shows the following mineral phases: calcite, quartz, calcium manganite and bustamite ferroan, as presented in previous research [3]. Analysis of the rooftop dust shows three phases: carbon, bustamite ferroan and manganosite, which does not correspond to the data given from the factory [3].

From the presented results, it could be concluded that the historic factory influenced sediments in the Šibenik bay, however, its influence was not detected on the Beach B 19 km to the SW, which opens the question of reach and distance to which tailings can be transported by sea and/or wind.

This work has been supported in part (samples collection) by Croatian Science Foundation under the project lP-2019-04-5832.

How to cite: Huljek, L., Fajković, H., and Kwokal, Ž.: Reach of pollution and sediment correlation with the tailings in Šibenik Bay (Croatia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-870, https://doi.org/10.5194/egusphere-egu21-870, 2021.

The volcanic complex Bolshoi Semiachik is characterized by intensive hydrothermal activity which is expressed by presence of thermal fields with gas-steam jets (T up to ~ 140 ºC), boiling pots (T up to ~ 100 ºC), warm lakes (T up to ~ 90 ºC) and ground (T up to ~ 97 ºC) . The circulating hydrothermal solution is rich in ammonium, sulfate and locally in carbonate. To date, little is known about surface mineralogy that occurs at the geothermal fields of the volcanic complex Bolshoi Semiachik. The major geological expeditions were carried out there in the 1960`s, and there was also some additional research carried out in the 1980`s. The study of minerals occurring at the surface of geothermal fields is relevant for planetary science since similar minerals are suggested for Mars and Europa (Jupiter moon) and geochemistry since such environments of mineral formation are very specific.

In the summer 2020 the expedition of the Institute of volcanology and seismology has been organized in order to monitor thermal fields and to conduct mineral and water samples for study. Here we report the first data on mineral identification of processed samples (at about 50). At that moment, minerals have been identified by powder X-ray diffraction and electron-microprobe analyses.

The surface of Bolshoi Semiachik geothermal fields is covered by clay minerals with montmorillonite that is rich in disseminated pyrite being the most abundant. Among salt minerals the common phases are sulfates: halotrichite-, copiapite and voltaite-group minerals, alunogen, gypsum and native sulphur. The SiO₂ polymorphs: tridymite, cristobalite are also found at the geothermal field surface. In the zone called Central Crater chalcantite has been found in association with rhomboclase and tridymite. Some samples with zeolite-group mineral - laumontite were also found, which at the moment is identified less reliably. The central (high temperature) part of deposits around steam-gas jet is composed of dickite in association with sulphur and quartz covered by alunogen and halotrichite efflorescent. The rim (at about 1 meter from the center) is composed of smectites, marcasite and natroalunite. This zonation is likely caused by pH which is lower at the central part where the steam unloads and increases at the peripheral area around the steam-gas jet.

Acknowledgment. The study has been supported by RFBR project # 20-35-70008. We are grateful to Volcanoes of Kamchatka for letting us to conduct the field works at Bolshoi Semiachik thermal fields. Experimental works on mineral identification have been carried out using Analytical Centre of IViS and Research Park of SPbU.

How to cite: Zhitova, E., Ismagilova, R., Sergeeva, A., Nazarova, M., Nuzhdaev, A., Kuznetsov, R., Bolshakov, I., and Bukhanova, D.: Minerals of Bolshoi Semiachik geothermal fields (Central Kamchatka, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7462, https://doi.org/10.5194/egusphere-egu21-7462, 2021.

The role of microorganisms (lichens, micromycetes and bacteria) in the formation of biominerals is widely known (Purvis, 2008; Vlasov et al., 2020). In the fall of 2019, we organized an expedition to the area of Tolbachik volcano (cones 1, 2, 3 and Mount 1004), Kamchatka, Russia, and collected 120 samples of volcanic rocks with biofilms. The volcanic cones of Tolbachik concentrate a wide variety of elements and are a type-locality of more than 300 minerals (Vergasova and Filatov, 2012; Siidra et al., 2017; Pekov et al., 2018). Lichen species are widespread in the volcanic fields of Kamchatka, Russia (Kukwa et al., 2014).  The goal of this work was to search for and study biominerals associated with lichens.

As a result of our research, calcium oxalates (whewellite and weddellite) and copper oxalates (moolooite) associated with lichens were found. Whewellite was found in the lichens Psylolechia leprosa and Sarcogyne hypophaea. Whewellite and weddellite were found together in the lichen Rinodina gennarii. Pyroxene (diopside) and plagioclase (anorthite) sourced calcium for the oxalates formation. Whewellite accumulates in apothecia in the form of whitish masses, consisting of lamellar crystals of 5-6 microns in size and their stacked intergrowths. Weddellite forms bipyramidal crystals of 2-10 microns in size. Moolooite was found in lichens Acarospora squamulosa and Lecanora polytropa (together with whewellite). The source of copper is tenorite, atacamite and copper-rich silicates (products of basalt processing by fumaroles). Moolooite forms lamellar crystals and intergrowths up to 5-6 microns in size. An interesting feature of oxalate formations in the Lecanora polytropa lichen is a high lead content, which has never been previously recorded in natural oxalates. Linarite and pyromorphite are most likely the source of lead. Chemical analysis showed that "nests" of calcium oxalates can contain up to 6 wt% PbO, while "nests" of copper oxalate - no more than 1 wt% PbO. The results obtained indicate the possibility selective sorption of lead and suggest the possibility of replacing calcium with lead in the oxalates. The studies of the location forms of lead in biofilms are in progress. The exact form of lead has not yet been established. Linarite and pyromorphite are most likely the source of lead. This research was supported by Russian Science Foundation grant (19-17-00141) and performed at the resource centers of St. Petersburg State University (MM, XRD, Geomodel).

Fedotov S.A. (ed.). Great fissure Tolbachik eruption (1975-1976, Kamchatka) // Moscow: Nauka. 1984. 637 p.

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Pekov I.V. et al. // Acta Cryst. 2018. B74. P. 502–518.

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Siidra O.I. et al. // European Journal of Mineralogy. 2017. 29. 3. P. 499–510.

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Vlasov D.Yu. et al. In: Aspergillus niger: pathogenicity, cultivation and uses, Nova Science Publishers, New York. 2020. P. 2-121.

How to cite: Chernyshova, I., Vereshchagin, O., Marina, Z., Dmitry, H., Dmitry, V., and Olga, F.-K.: Ca, Cu and Pb solubilization and biomineralization by microorganisms: case study from Kamchatka, Russia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14392, https://doi.org/10.5194/egusphere-egu21-14392, 2021.

The most famous of natural occurring iron-nickel alloys are kamacite, taenite and tetrataenite, forming iron meteorites. Normally, they have significant platinum-group elements (PGE) content being a result of high siderophile behaviour of the latter. In spite of native iron and nickel having been described in terrestrial rocks, the most abundant Fe-Ni mineral in Earth’s crust is awaruite (Ni₃Fe). Current work represents the preliminary results of testing the ability of awaruite to concentrate PGE.

Awaruite is a widespread accessory mineral of ultramafic complexes. Its formation is usually assessed to the serpentinization of olivine which produces reductive fluid. The latter reacts with nickel sulfides and produces awaruite. Several reports of awaruite occurring together with platinum-group minerals (PGM) are present in the literature. In the Ural-Alaskan type complexes of Koryak Highlands (Far East Russia), such cases are abundant. Textural investigations of such complexes discovered a diverse array of serpentine–related mineralization, including isoferroplatinum in chlorite matrix, isoferroplatinum–amphibole intergrowths, and a wide range of PGE, Fe and Cu alloys formed in serpentine veinlets together with awaruite and base metal sulfides. This provides evidence of the relation between awaruite and platinum mineralization.

LA-ICP-MS has been used to reveal the PGE content in awaruite and coexisting sulfides. Grains from the placers related to the Galmoenan complex of Ural-Alaskan type were used for this study. The analysis revealed that sulfides may bear significant PGE admixture. Unexpectedly, the most abundant impurity is Os. Its content varies from 0.7 to 538 ppm. The shape of the time-resolved spectra of some samples indicates the possible presence of solid inclusions which concentrate Os. However, most of them, including those with 538 ppm Os, exhibit plain time-resolved spectra suggesting homogeneous Os distribution. Contents of other PGE are moderate: up to 8.3 ppm Pt, 1.4 ppm Pd, 4.3 ppm Ru, 0.25 ppm Rh and 2.6 ppm Ir.

Some awaruite grains also show relatively high Os content (up to 89 ppm), but time-resolved spectra of them exhibit clear evidence of mineral inclusions presence. In one case, Os spike coincides with the S spike, suggesting that Os is incorporated into the sulfide phase. In the case of spikeless spectra, Os content is always below the detection limit (b.d.l.). Rhodium content also is always b.d.l., while Ru content reaches 0.44 ppm, Ir – 0.08 ppm, and Pt – 0.03 ppm. The only element explicitly showing significant and homogenous presence in the awaruite is Pd, that content reaches 5.8 ppm in one analysis and 0.2–1.1 in many others.

These data indicate that in the studied case, awaruite mineralization is accompanied by the formation of PGM, while its role as a direct PGE concentrator is moderate and restricted to the first tenths ppm of Ru and Pd. Sulfides have shown much more impressive ability in concentrating PGE. Their selective enrichment in Os is a novelty and demands explanation.

Author thanks Evgeniy Sidorov and Dima Kamenetsky for the assistance. CODES of UTAS is greatly acknowledged for the LA-ICP-MS analyses. This work was supported by the Russian Foundation for Basic Research (RFBR) grant No 20-05-00290 A.

How to cite: Kutyrev, A.: Awaruite (Ni3Fe) as a platinum-group elements concentrator: Preliminary data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5432, https://doi.org/10.5194/egusphere-egu21-5432, 2021.

The laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) is a unique method for local analysis that allows studying mineral grains in situ. The aims of these geochemical researches are to estimate concentrations and distributions of PGE and other siderophilic and chalcophilic elements in ore minerals from complex deposits in the Arctic region (Fennoscandian Shield), using the LA-ICP-MS local analysis of trace elements. Pyrite, pentlandite, pyrrhotite and other sulfides are important for determining platinum-group elements.

In situ analyses of sulfide crystals were carried out on polished thin sections by ICP-MS. The electron (LEO-1415) and optic (LEICA OM 2500 P, camera DFC 290) spectroscopy was applied to study the morphology of the samples. Analytical points on sulfide minerals were selected using microelectronic and optical images.

PGE and other elements (As, Bi, Cd, Cr, Co, CuFe, Ni, Se, S, Sn, Sb, Pb, Re, Te, Tl, Zn, Hf, Th, U, REE) were measured by ICP-MS, using an ELAN 9000 DRC-e (Perkin Elmer) quadrupole mass spectrometer equipped with a 266 nm UP-266 MAСRO laser (New Wave Research). NIST 610, NIST 612 and tandem graduation (using solutions), considering sensitivity coefficients of isotopes were used to check the accuracy of estimations. Fe, Ni and Cu were used as internal standards, being most evenly distributed elements in minerals, when concentrations of elements in sulfides were calculated. The estimates were carried out, using inter-laboratory standards of chalcopyrite, pentlandite and pyrrhotite, which had been preliminarily prepared and studied using microprobe analysis (Cameca MS-46).

Data on concentrations of PGE, Au and Ag in sulfides, including data on their distribution in minerals, are crucial in studying the origin of noble metals in sulfide ores and interpreting formation settings of complex deposits. Estimated concentrations of other trace elements provide an essential supplement to geochemical data. Received data are new data (LA-ICP-MS) of Pt-Pd and Cu-Ni reefs of the Monchegorsk ore areas (2.5 Ga) with prospected commercial deposits. Elaborated LA-ICP-MS techniques were applied to provide in situ measurements of noble metals (PGE, Au, Ag), as well as siderophilic and chalcophilic elements, in sulfide minerals in order to study their distributions in chalcopyrite, pentlandite and pyrite from the Pechenga and Allarechka Cu-Ni deposits (1.98 Ga), Fedorova Tundra and Severny Kamennik PGE deposits (2.5 Ga).

The scientific researches are supported by RFBR Grant No 18-05-70082, scientific themes 0226-2019-0032 and 0226-2019-0053.

How to cite: Drogobuzhskaya, S., Bayanova, T., and Novikov, A.: Geochemical study in situ (LA-ICP-MS) of ore minerals from Paleoproterozoic layered PGE intrusions in the north-eastern Fennoscandian Shield, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12593, https://doi.org/10.5194/egusphere-egu21-12593, 2021.

Carbonatitic magmatism and metasomatism are rare in Great Britain & Ireland. However, REE-Nb minerals were identified in impure marbles and calc-silicates on the Aird of Shin and Arscaig near Lairg, Scotland. They belong to the Palaeoproterozoic Shin Group, a supercrustal succession of amphibolites, banded silicic gneisses, marbles and calc-silicates. The Shin Group is one of several Palaeoproterozoic to Neoproterozoic marble inliers in the North Highlands of Scotland that present evidence of Caledonian orogen carbonatitic metasomatism. The Proterozoic Bayan Obo ore complex in China was similarly deposited as a dolomite-limestone and later subject to alkali intrusions and carbonatitic metasomatism during the Caledonian orogeny. The Bayan Obo complex hosts REE-Nb-Fe carbonatitic fine-grained dolomites, REE-Nb deficient coarse dolomites, carbonatitic dykes, limestones and dolostones. The Aird of Shin marble mineralogy comprises niobium and tantalum Ca-bearing oxides, scheelite, strontian barite, ilmenite, REE-bearing monazite, REE-epidote and Fe-Mo sulphides in an impure Na-Fe-K calcite fabric. The Arscaig Qtz-Na-K calc-silicates are enriched in REE-bearing monazite, Mg-Fe chlorite and Fe-oxides, with minor REE-bearing xenotime, Mn-Fe garnet and strontian barite. The REE-Nb Aird of Shin marble and the REE-phosphate bearing Arscaig calc-silicates are comparable with carbonatitic mineral phases in the Bayan Obo complex. This study adds support to previous recognition of Caledonian carbonatitic magmatism and carbonatitic metasomatism of Proterozoic limestones and calc-silicates in Scotland. 

How to cite: Heptinstall, E. and Parnell, J.: Carbonatitic REE-Nb-Fe mineralisation in the Palaeoproterozoic Shin Group marble and calc-silicates, Loch Shin, Scotland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1190, https://doi.org/10.5194/egusphere-egu21-1190, 2021.

Porphyry Cu ore deposits are a rare product of arc magmatism that often form spatiotemporal clusters in magmatic arcs. The petrogenetic evolution of igneous rocks that cover the temporal window prior to and during porphyry Cu deposit formation may provide critical insights into magmatic processes that are key in generating these systems. This study documents the magmatic evolution of the Palaeocene-Eocene Yarabamba Batholith, Southern Peru, that was incrementally assembled between ~67 and ~59 Ma and hosts three, nearly contemporaneous, giant porphyry Cu-Mo deposits that formed at 57-54 Ma (Quellaveco, Toquepala and Cuajone). Whole-rock geochemistry, U-Pb geochronology and zircon trace element chemistry are reported from Yarabamba rocks that span the duration of plutonic activity, and from six porphyry intrusions at Quellaveco that bracket mineralisation. A change in whole-rock chemistry in Yarabamba intrusive rocks to high Sr/Y, high La/Yb and high Eu/Eu* is observed at ~60 Ma which is broadly coincident with a change in vector of the converging Nazca plate and the onset of regional compression and crustal thickening during the first stage of the Incaic orogeny. The geochemical changes are interpreted to reflect a deepening of the locus of lower crustal magma evolution in which amphibole ± garnet are stabilised as early and abundant fractionating phases and plagioclase is suppressed. Zircons in these rocks show a marked change towards higher Eu/Eu* (>0.3) and lower Ti (<9 ppm) compositions after ~60 Ma. Numerical modelling of melt Eu systematics and zircon-melt partitioning indicates that the time series of zircon Eu/Eu* in these rocks can be explained by a transition from shallower, plagioclase-dominated fractionation to high-pressure amphibole-dominated fractionation at deep crustal levels from ~60 Ma. Our modelling suggests that any redox effects on zircon Eu/Eu* are subordinate compared to changes in melt composition controlled by the fractionating mineral assemblage. We suggest that growth and intermittent recharge of the lower crustal magma reservoir from ~60 Ma produced a significant volume of hydrous and metallogenically fertile residual melt which ascended to the upper crust and eventually generated the three giant porphyry Cu-Mo deposits at Quellaveco, Toquepala and Cuajone from ~57 Ma. Our study highlights the importance of high-pressure magma differentiation fostered by strongly compressive tectonic regimes in generating world-class porphyry Cu deposits.

How to cite: Nathwani, C., Simmons, A., Large, S., Wilkinson, J., Buret, Y., and Ihlenfeld, C.: Petrological and zircon chemical record of arc magma evolution from long-lived batholith construction to giant porphyry copper deposit formation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-851, https://doi.org/10.5194/egusphere-egu21-851, 2021.

The Late Cretaceous to Eocene Sistan suture zone in southeastern Iran separates the Lut continental block in the west from the Afghan continental block in the east. A major belt of Oligocene to Miocene igneous rocks occurs between the cities of Zahedan and Nehbandan, stretching for ~200 km from south to north parallel to the border with Pakistan and Afghanistan. Known porphyry Cu mineralization is associated with the intrusions and intrusive complexes at Kuh-e Janja (16.5+2.0 Ma), Kuh-e Seyasteragi (19.2+ 1.4 Ma), Kuh-e Assagie (27.5+2.0 Ma), and Kuh-e Lar (32.8+3.0 Ma).

Small intrusions and intrusive complexes in the Zahedan-Nehbandan magmatic belt are mostly intermediate to felsic in composition and have calc-alkaline or shoshonitic affinities. Associated volcanic and volcaniclastic rocks are common. The igneous rocks are hosted by deformed late Cretaceous to Eocene flysch sequences that formed in the Sefidabeh forearc basin developed during the subduction and closure of the Sistan ocean. The geochemical composition of the intrusive rocks and their ages suggest that igneous activity and related mineralization in the Zahedan-Nehbandan magmatic belt may have formed as a result of post-collisional processes. The locations of the intrusive centers in the Kuh-e Assagie and Kuh-e Lar may be controlled by strike-slip faults, which are major post-collisional structures.

The recent discovery of the Janja porphyry Cu-Au-Mo deposit below Quaternary alluvial terraces highlights the exploration potential of the Zahedan-Nehbandan magmatic belt. In addition to post-collisional porphyry deposits, other deposit types such as skarns, polymetallic veins, or epithermal deposits may be hidden below the regionally extensive Quaternary cover.

How to cite: Soleymani, M., Niroomand, S., Rajabi, A., Monecke, T., and Modabberi, S.: Metallogeny of the Zahedan-Nehbandan magmatic belt and implications to porphyry Cu exploration in southeastern Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-249, https://doi.org/10.5194/egusphere-egu21-249, 2021.

Knowledge of molybdenum (Mo) speciation under hydrothermal conditions is a key for understanding the formation of porphyry deposits which are the primary source of Mo. Existing experimental and theoretical studies have revealed a complex speciation, solubility and partitioning behavior of Mo in fluid-vapor-melt systems, depending on conditions, with the (hydrogen)molybdate (HMoO₄^-, MoO₄^2-) ions and their ion pairs with alkalis in S and Cl-poor fluids [1-3], mixed oxy-chloride species in strongly acidic saline fluids [4, 5], and (hydrogen)sulfide complexes (especially, MoS₄^2-) in reduced H₂S-bearing fluids and vapors [6-8]. However, these available data yet remain discrepant and are unable to account for the observed massive transport of Mo in porphyry-related fluids revealed by fluid inclusion analyses demonstrating 100s ppm of Mo (e.g., [9]). A potential missing ligand for Mo may be the recently discovered trisulfur radical ion (S₃^•-), which is predicted to be abundant in sulfate-sulfide rich acidic-to-neutral porphyry-like fluids [10]. We performed exploratory experiments of MoS₂ solubility in model sulfate-sulfide-S₃^•--bearing aqueous solutions at 300°C and 450 bar. We demonstrate that Mo can be efficiently transported by S₃^•--bearing fluids at concentrations ranging from several 10s ppm to 100s ppm, depending on the fluid pH and redox, whereas the available data on OH-Cl-S complexes cited above predict negligibly small (<100 ppb) Mo concentrations at our conditions. Work is in progress to extend the experiments to wider T-P-composition range of porphyry fluids and to quantitatively assess the role of S₃^•- in Mo transport by geological fluids.

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How to cite: Kokh, M. A., Laskar, C., and Pokrovski, G. S.: The effect of the trisulfur radical ion on molybdenum transport by hydrothermal fluids, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3318, https://doi.org/10.5194/egusphere-egu21-3318, 2021.

Dharwar Craton in southern India hosts several gold bearing greenstone belts including the well-known Kolar and Hutti. Among them, the Gadag greenstone belt in the western part of Dharwar Craton contains many potential gold mines. It has three different lode systems named western, central and eastern lodes. These lodes are spatially distributed as linear groups along the shear zone with distinct lithological assemblages. Tourmaline is one of the most common hydrothermal minerals present in the alteration zones apart from chlorite, muscovite and sericite. These tourmalines show two textural association (i) occur as isolated, euhedral grains along the mylonitic foliation defined by chlorite, muscovite, sericite, quartz and carbonates (ii) occurrences of anhedral bizarre shaped tourmaline grains along with carbonate and quartz. Though texturally different, compositionally both the tourmalines are similar. They are dravite in nature with high Al_tot (6.02 to 6.56 apfu), low Na (0.42 to 0.88 apfu) and medium X-vacancies (0.08 to 0.57 apfu). The predominance of Fe²⁺ (high Fe²⁺/Fe³⁺) and low Na in the tourmaline crystal structure indicates low saline, reduced ore fluid of metamorphic origin that is responsible for gold mineralization in Gadag.

Microthermometric study of aqueous, carbonic and aqueous-carbonic inclusions from the auriferous lodes at Gadag reveal low to medium saline (0.04 to 9.59 NaCl equiv.)  H₂O-NaCl-CO₂±CH₄ ore forming fluid. Presence of trace amount of methane content within the carbonic inclusion indicates mineralization occurred at reducing environment. Thus, fluid inclusion results consistent with the tourmaline chemistry and strongly supports the metamorphic origin of ore fluids that responsible for gold mineralization at Gadag.

How to cite: Pal, D., Chinnasamy, S. S., and Rekha, S.: Ore fluid characteristics at Gadag Gold Field, Dharwar Craton, southern India: Evidences from tourmaline chemistry and fluid inclusion study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12132, https://doi.org/10.5194/egusphere-egu21-12132, 2021.

The Rosas Shear Zone (RSZ) is a 1 km thick brittle-ductile shear zone that outcrops in the Variscan fold and thrust belt foreland of SW Sardinia, where several important ore deposits were mined in the last century. The RSZ lies in the footwall and strikes parallel to the NE-dipping regional thrust that separates the Variscan foreland from the nappe zone. Two thrusts that developed along the limbs of two km-scale overturned antiforms, with NE-dipping axial plane, bound the RSZ. The folds show a SW-facing direction and a well-developed axial plane cleavage, and affect a lower Cambrian-upper Ordovician stratigraphic succession mainly made, from bottom to top, by a sequence about 200 m thick of dolostones and massive limestone followed by 50 m of marly limestones overlain by about 150 m of sandstones, pelites and siltstones, finally unconformable capped by conglomerates and siltstones, ranging in thickness from a few to 200 m. Differently, within the RSZ the bedding is completely transposed along the cleavage and its internal structure is characterized by anastomosing thrusts that affect the stratigraphic succession defining map-scale slices mainly consisting of dolostones and limestones embedded into the siliciclastic formations. It is noteworthy the occurrence of a NE-dipping, up to 100 m thick gabbro-dyke that postdates the deformation phases and that can be related to the exhumation of the chain during late Carboniferous-Permian times.

In the whole area, contact metamorphic and metasomatic processes selectively affected the Cambrian carbonate tectonic slices, originating several skarn-type orebodies. Mineralized rocks display the mineralogical assemblages and textures of Fe-Cu-Zn skarns, with relicts of anhydrous calcic phases related to the prograde metamorphic stage (garnet, clinopyroxene, wollastonite), frequently enclosed in a mass of hydrous silicates (actinolitic amphibole, epidote) and magnetite related to the retrograde metasomatic stage, in turn followed by chlorite, sulfides, quartz and calcite associated to the hydrothermal stage. Metasomatic reactions also involved mafic rocks, producing a mineral association marked by clinopyroxene, amphibole, epidote, prehnite and Ba-rich K-feldspar. Sulfide ores are made of prevailing sphalerite, chalcopyrite and galena, with abundant pyrite and pyrrhotite and minor tetrahedrite and Ag-sulfosalts. Garnets are andraditic/grossularitic, distinctly zoned and optically anisotropic. Field surveys pointed out the tight structural controls on skarn and ore formation. On a local scale, the gabbro emplacement along high- to low-angle NNW-SSE structures bordering the carbonate tectonic slices accentuate the effects of contact metamorphism, and metric to decametric mineralogical zonation (garnet→pyroxene→wollastonite) are recognized. On a larger scale, extensive hydrothermal fluid circulations involved the structures of the RSZ. Infilling of metasomatic fluids in carbonate tectonic slices is fault-controlled and aided by the increase in permeability due to the alteration of prograde silicates. The causative intrusion related to skarn ores belongs to the early Permian (289±1 Ma) ilmenite-series, ferroan granite suite which intrudes the RSZ about 3 km east from the studied area. The Fe-Cu-Zn skarn ores of Rosas are best interpreted as distal, structurally-controlled orebodies, connected to large-scale circulation of granite-related fluids in the km-sized plumbing system represented by the RSZ.

How to cite: Deidda, M. L., Attardi, A., Cocco, F., Fancello, D., Funedda, A., and Naitza, S.: Shear zone development and structurally-controlled skarn ore mineralization in the Rosas district, SW Sardinia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2806, https://doi.org/10.5194/egusphere-egu21-2806, 2021.

The Freiberg district, located in the eastern part of the Erzgebirge, Germany, hosts one of the largest series of epithermal polymetallic vein deposits in Europe. The present study aims to decipher mineralogical and geochemical zoning on the vein- and district-scale and to constrain the underlying ore-forming processes. Detailed petrographic investigations, geochemical analyses and fluid inclusion studies are carried out on several vertical vein profiles within the Freiberg district in order to develop a district-scale metallogenic model. Five different mineral associations related to Permian magmatic-hydrothermal activity have been recognized within the Freiberg epithermal vein system exhibiting a distinct district-scale and vein-scale zonation. The central part of the Freiberg district is dominated by sphalerite-pyrite-quartz and galena-quartz±carbonate associations with a mean silver grade of 769 g/t (n=65). Similar base metal-rich assemblages also predominate the deepest vein intersections (>300 m below ground level) in the peripheral sectors of the Freiberg District. Vein infill at intermediate depth and peripheral positions in the district is, in contrast, dominated by a sphalerite-Ag-sulfides-carbonate association. This association is marked by an abundance of carbonate gangue and significantly higher silver grades (mean = 4800 g/t; n=25). Veins in the shallowest and most peripheral parts (depth <150 m b.g.l.) of the Freiberg district are dominated by a Ag-sulfide-quartz association with a mean Ag concentration of 4900 g/t (n= 56). Silver is mainly hosted by sulfosalts and fahlore but significant concentrations may also be associated to Ag-sulfide inclusions in galena. Even shallower, the veins comprise a stibnite-quartz association with distinctly low Ag contents (410 g/t Ag, n=4). Fluid inclusions related to the various associations yield consistent salinities in the range of 0.1 to 6.0 % eq. w(NaCl). The homogenization temperature, however, progressively decreases from about 320°C for quartz associated with proximal sphalerite-pyrite-quartz mineralization, down to ~170°C for quartz related to distal Ag-sulfide-quartz association. The general formation of the Freiberg epithermal veins is related to the continuous evolution of a magmatic-hydrothermal system in time and space. Silver deposition is most likely triggered by boiling and associated cooling and volatile-loss, which results in a distinct carbonate horizon (typically at ~500 m depth b.g.l. for peripheral parts) with significantly elevated Ag grades (sphalerite-Ag-sulfides-carbonate association).

How to cite: Swinkels, L., Schulz-Isenbeck, J., Frenzel, M., Gutzmer, J., and Burisch, M.: Spatiotemporal zonation of the Freiberg Ag-Pb-Zn-(Cu) epithermal system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2137, https://doi.org/10.5194/egusphere-egu21-2137, 2021.

High demand for specific chemical elements from the group of rare earth elements (REE) has led to a detailed prospection and geochemical analysis of a previously known but unexploited bauxite deposit. The Upper Eocene karst bauxite within exploitation field Mamutovac, located in the municipality of Promina in the Dalmatian Hinterland (Croatia), is such a deposit, with estimated reserves of 112,000 tone.

In order to determine REE distribution pattern in the Mamutovac Ia deposit, a 25meter core was obtained by exploration drilling, down to the deposit footwall that is composed of Upper Cretaceous rudist limestone. For this study 23 subsamples were singled out, on average, per each meter of a core. 

The degree of lateritization is determined by the Al₂O₃–SiO₂–Fe₂O₃ composition diagram (after Schellman, 1986), and lateritization varies from moderate to strong, with a lower degree of lateritization in a lower part of the core, down from 15 m.  Two different genetic classification systems indicate the origin of the bauxite is mafic, basaltic igneous rocks.            

Main mineral phases in the bauxite core samples were determined using X-ray powder diffraction (XRPD) analysis. The mineral phases through the whole core are similar, with boehmite, gibbsite, hematite, and anatase as the main phases. Additional mineral phases determined in the core are kaolinite, goethite, and rutile. 

Results of geochemical analysis obtained by inductively coupled plasma emission/mass spectrometry (ICP-ES/MS) indicate an inhomogeneous distribution of REE through the core, with two main trends: from 0-15m and from 15-25m, with some elevation of REE abundances in the lower part of the core. In the upper part of the core,  total REE content (∑REE), including Y and Sc, ranges between 352 and 630 ppm (average 500 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (∑LREE/∑HREE) ratios reach up to 10.2. For lower part ∑REE (including Y and Sc) ranges between 569 and 813 ppm (average 676 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (∑LREE/∑HREE) ratios are up to 9.82. Singificant enrichment of LREE compared to HREE is present due to the fact that HREE are highly mobile in an alkalic karst environment and consequently removed through drainage channels. The most abundant REE is Ce. Within interval, 0-15m Ce ranges between 149.3-264.9 ppm (average 210.7 ppm), while within the interval 15-25m Ce ranges 152.7-301.7 ppm (average 219.56 ppm).

Correlation analysis shows no correlation between Sc and other REE and no significant correlation between Ce and other REE or potential bearing oxides. The correlation between Sc and Al₂O₃ or Fe₂O₃ suggests that Sc is likely bound to Al-oxyhydroxides and Fe-oxyhydroxides. Correlation between REE (Sc free) and P₂O₅ indicates REE (Sc free) are probably contained in REE-bearing phosphates. 

This activity has received funding from the European Institute of Innovation and Technology (EIT), a body of the European Union, under the Horizon 2020, the EU Framework Programme and Research and Innovation.

How to cite: Teskera, D., Fajković, H., Ilijanić, N., Tomašić, N., Gizdavec, N., Andrea, Č., and Slobodan, M.: Geochemical characteristics of Croatian prospective Bauxite deposit Mamutovac, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-905, https://doi.org/10.5194/egusphere-egu21-905, 2021.

Serpentine veins are ubiquitous in hydrated and deformed ultramafic rocks, and have previously been used to track fault kinematics and understand the evolution of environmental conditions during vein formation. However, difficulties in unambiguously identifying and mapping serpentine types at sub-micron to mm scales has limited our understanding of vein precipitation kinetics and growth histories. Using recently developed techniques of Raman spectroscopy mapping, combined with scanning- and transmission-electron microscopy, we describe a new type of mineralogically banded serpentine crack-seal vein in six samples from different settings around the world. In all of the studied samples, individual bands comprise a thin layer (~0.4–2 µm) dominated by chrysotile and a much thicker layer (~0.5–30 µm) dominated by polygonal serpentine/lizardite. Existing field and experimental data suggest that disequilibrium conditions immediately following crack opening may favour rapid precipitation of chrysotile along one of the crack margins. Subsequently, diffusional transport of elements favours slower precipitation of polygonal serpentine/lizardite which leads to crack sealing. The similarities in layer thicknesses and mineralogy exhibited by samples collected from extension and shear veins, dilational jogs, foliation surfaces, and the margins of phacoids, suggest that a common set of processes involving crack opening and sealing are active in a range of different structural sites within serpentinite-dominated shear zones, potentially associated with frequent and repetitive stress drops such as those recorded during episodic tremor and slow slip.

How to cite: Tarling, M. S., Smith, S. A. F., Rooney, J. S., Viti, C., and Gordon, K. C.: Serpentine crack-seal veins: a unique record of fluid conditions during faulting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-425, https://doi.org/10.5194/egusphere-egu21-425, 2021.

How to cite: McGrath, J., Piazolo, S., Morgan, R., and Elliott, J.: Field evidence for fluid facilitated fracturing and Dissolution-Precipitaion creep explains observed off-fault tremor and continuous deformation: Field examples from the Alpine Fault, New Zealand , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8214, https://doi.org/10.5194/egusphere-egu21-8214, 2021.