GMPV5.1

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The surfaces of all the grass biomass samples contained a variety of geogenic (quartz, carbonates, clay minerals, feldspars) and anthropogenic (usually metal-bearing) particles directly attached to the biomass tissues. These smelter-derived particles are predominantly slag fragments enriched in various contaminants, droplets of metals/sulfides, and, in the case of the biomass from Kabwe, newly formed aggregates of submicrometric anglesite (PbSO₄) crystals. Heavy mineral fractions were obtained from all biomass samples to better understand the solid-phase speciation of contaminants. In Tsumeb, the key metal-hosting minerals/phases on biomass were Cu-Fe sulfides, arsenolite (As₂O₃) and metal-bearing slag glass. In Selebi Phikwe pyrrhotite (Fe_1-xS), pyrite (FeS₂), pentlandite [(Fe,Ni)₉S₈] and chalcopyrite (CuFeS₂) were predominant. Samples from Kabwe were composed of galena (PbS), pyrite (FeS₂), sphalerite (ZnS), chalcopyrite (CuFeS₂) and anglesite (PbSO₄) and in Luanshya, the particulates were mainly formed by phases from the Cu-Fe-S ternary system. The mineralogy of particulates collected in the grass samples was similar to that in the corresponding topsoil samples. The knowledge of solid-phase speciation is of key importance for determining the fate of contamination in such environments.

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

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

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

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

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

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