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The compositional diversity of volcanic rocks revealed by NASA’s MESSENGER at the surface of Mercury has been interpreted to result from partial melting of a heterogenous sulfur-rich Mercurian mantle. However, melting relations and the composition of partial melts for iron-free and sodium-rich mantle, together with the effect of sulfur as a key volatile, have not yet been studied in detail. In this study we present results from high-pressure and high-temperature experiments on the mineralogical and geochemical evolution of the mantle residue and melting products of primitive deep Mercury’s mantle with two starting compositions differing by their Mg/Si ratios. Both compositions have sulfur added as FeS. Experiments were conducted using a multi-anvil press under reduced conditions (by controlling the Si/SiO2 ratio of the starting composition) at pressures of 3 and 5 GPa.The residual mantle of Mercury with the lower Mg/Si ratio of 1.02 contains olivine + orthopyroxene above ~15 wt% melting at 3 and 5 GPa, and olivine disappears at melting over ~30 wt.% at 5 GPa. The Mercurian mantle with the Mg/Si of 1.35 contains olivine + orthopyroxene in the residue above ~15 wt% melting at 3 and 5 GPa, and olivine only when the melting degree is over ~50 wt.%. Our experiments also show that the majority of chemical composition of the High-Magnesium region (HMR) can result from ~25±15 wt.% melting of a deep primitive mantle. Further work will enable us to evaluate the compositional diversity of the mantle that is needed to explain the broad range of surface lavas. We also aim at understanding the role of the highly refractory residual mantle as a controlling factor for the end of major volcanic activity on Mercury at 3.5 Ga.

Alkaline magmatism is an important chemical end-member of magmatic activity that typically occurs in response to small volume melting of asthenospheric- and/or lithospheric mantle material in intra-continental settings. Understanding trace element partitioning and phase equilibria during alkaline magmatism can therefore provide constraints on intra-continental geodynamic settings. However, the partitioning of trace elements between alkaline melts and their dominant equilibrium mineral phases remains poorly constrained. Feldspathoids in particular have received limited attention with regards to their trace element contents, hampering our ability to interpret geochemical trends in alkaline magmatic systems. In this study, we performed a series of 1 atmosphere experiments in a gas-mixing furnace using a variety of highly alkaline (Na2O + K2O = 4.15–14.97 wt%) and silica-undersaturated (SiO2 = 36.73–45.96 wt%) lava compositions from Nyiragongo, Democratic Republic of Congo, in order to investigate the partitioning behaviour of trace elements in minerals from alkaline magmas. Experimental runs were performed with oxygen fugacity buffered at both QFM (quartz-fayalite-magnetite equilibrium) and QFM + 1 and cover a range of geologically-relevant temperatures (1025–1200 °C). The quenched products of these experiments contained leucite, nepheline, melilite, clinopyroxene, olivine, and rhönite crystals, of which glass-crystal pairs were analysed for rare earth elements, large-ion lithophile elements, and high-field-strength elements. Leucite and nepheline host considerable quantities of large-ion lithophile elements but take up negligible amounts of more highly charged cations. Åkermanitic melilite readily incorporates mono- to trivalent cations with a preference for light over heavy rare earth elements, but incorporates only select divalent cations. Rhönite and clinopyroxene have analogous partitioning behaviours, with a strong preference for heavy over light rare earth elements. Fractionation modelling using the reported partitioning behaviours reproduces the 2021 eruption products of Nyiragongo, with 48% fractionation from an olivine-melilitic parental melt composition. Crystallization of trace-element poor feldspathoid amplifies pre-existing high LREE/MREE ratios of the parental magma and progressively increase trace element abundances for all but monovalent cations.

Piston-cylinder assemblies exhibit inhomogeneous pressure distributions and biases compared to the theoretical pressure applied to the hydraulic press because of the thermal and mechanical properties of the assembly components. Whereas these effects can partially be corrected by conventional calibration, systematic quantification of friction values remain very sparse and results vary greatly among previous studies. We performed an experimental study to investigate the behavior of the most common cell assemblies, i.e., talc [Mg3Si4O10(OH)2], NaCl, and BaCO3, during piston-cylinder experiments to estimate the effects of pressure, temperature, run duration, assembly size, and assembly materials on friction values. Our study demonstrates that friction decreases with time and also partially depends on temperature but does not depend on pressure. We determined that friction decreases from 24 to 17% as temperature increases from 900 to 1300 °C when using talc cells, indicating a friction decrease of ~2% per 100 °C increase for 24 h experiments. In contrast, friction becomes independent of time above 1300 °C. Moreover, at a fixed temperature of 900 °C, friction decreases from 29% in 6 h runs to 21% in 48 h runs, corresponding to a decrease of friction of 0.2% per hour. Similar results obtained with NaCl cell assemblies suggest that friction is constant within error, from 8% in 9 h runs to 5% in 24 h runs. At 900 °C, possible steady-state friction values are only reached after at least 48 h, indicating that friction should be considered a variable for shorter experiments. We establish that assembly materials (and their associated thermomechanical properties) influence the friction correction more than the dimensions of the assembly parts. Finally, we show that the use of polytetrafluoroethylene film instead of conventional Pb foil does not modify friction but significantly reduces the force required for sample extraction, thus increasing the lifetime of the carbide core, which in turn enhances experimental reproducibility.

To better understand the role and extent of inter-mineral diffusion during subsolidus processes, we investigated the iron and magnesium isotopic compositions of olivine, orthopyroxene, and chromite separates from the Peridotite Zone of the Stillwater Complex. Olivine and orthopyroxene show limited Mg isotopic variations, with δ26Mg values ranging from −0.40 to −0.26‰ and from −0.29 to −0.22‰, respectively. In contrast, chromite displays extremely large Mg isotopic variations, with δ26Mg values ranging from −0.05 to +0.84‰. The δ56Fe values of olivine and orthopyroxene range from 0.00 to +0.17‰ and −0.04 to +0.06‰, respectively, whereas those of chromite range from −0.09 to +0.13‰. Most olivine-orthopyroxene pairs in our samples show no clear Fe-Mg isotopic differences, whereas silicate and coexisting chromite pairs plot away from theoretically predicted equilibrium lines, indicating disequilibrium inter-mineral fractionation. Higher δ56Fe values in silicates than in chromite and significantly higher δ26Mg values in chromite than in silicates indicate that subsolidus re-equilibration is responsible for the observed disequilibrium Fe-Mg isotope fractionation. We develop a quantitative model based on the investigated olivine and chromite to reproduce the observed kinetic Fe-Mg isotope fractionations. Our model results indicate a systematic difference between the Fe and Mg isotope fractionation factors, β, of olivine (βFe ≈ 0.27 and βMg ≈ 0.16) and chromite (0.03

Since the end of socialism in Mongolia, migration processes have dramatically increased. The lack of investment in the rural infrastructures and the repetition of zud have pushed the most vulnerable herders towards the capital Ulaanbaatar and its outskirts. They encounter tremendous difficulties in having access to private property and seem condemned to move relentlessly from enclosure to enclosure (hashaa) in the hope of finding a less precarious place to settle in the city. The main purpose of this article is to show how difficult it is for some families of herders to leave their homeland and settle in another place. These difficulties are first described from the point of view of the relationships women and men entertain with the spirits of the land (savdag) after migrating to a new place. I will try to show how the realisation of homeland paintings (nutgyn zurag) help, to some extent, to maintain relationships with these spirits and the homeland as a whole. Finally, I describe the impossibility for some new migrants to settle permanently and to get used to the city of Ulaanbaatar, dasah.

Introduction: The IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory generates mid-infrared spectra for the ESA/JAXA BepiColombo mission to Mercury. Onboard is a mid-infrared spectrometer (MERTIS-Mercury Radiometer and Thermal Infrared Spectrometer), which will allow to map the mineralogy in the 7-14 µm range [1, 2]. In order to interpret the future data, a database of laboratory spectra is assembled at the Institut für Planetologie in Münster (IRIS) and the DLR in Berlin. So far, we have studied for this purpose natural mineral and rock samples (e.g. 3, 4), impact melt rocks (e.g. 5, 6, 7) and meteorites (e.g. 8, 9, 10, 11). Furthermore, surface processes like regolith formations and space weathering were of interest (e.g. 12, 13, 14). Synthetic analogue materials have become one of the foci of our work, since they allow to produce ‘tailor-made’ materials based on remote sensing data and/or modelling and experiments. These are closer than natural terrestrial materials, which formed usually under different conditions as expected on Mercury [e.g. 1]. We synthesized analogs for surface regions of Mercury and other planetary bodies (15, 16, 17). In this part of our study, we present mixtures based on phase equilibria of peridotite and partial melt compositions which were studied under hermean mantle conditions - temperature, pressure, oxygen fugacity (18,19,20). These experiments suggested that the crustal mineralogy should be dominated by variable abundances of plagioclase, olivine, clino- and orthopyroxene, with unconstrained proportions of silicate glass. Based on the model mineralogy of representative results, we produced mineral/glass mixtures based on the Low-Mg Northern Volcanic Plains (NVP)(Y121, Y131, Y172), High-Mg NVP (Y143, Y144), Smooth Plains (Y140, Y143, Y144), Inter crater Plain and Heavily Cratered Terrains (IcP-HCT) (Y126, Y131, Y132, Y146), and High-Mg Province (Y126, Y131, Y146) [20]. Samples and Techniques: We conducted diffuse reflectance studies of sieved size fractions (0-25 µm, 25-63 µm, 63-125 µm and 125-250 µm) under vacuum conditions, ambient heat, and variable geometries. We used a Bruker Vertex 70v with A513 variable geometry stage. The results will be made available in the IRIS Database [1]. Results: First results show the Christiansen Feature (CF), a characteristic, easy to identify reflectance low (or emission high) ranging from 7.9 µm to 8.2 µm (always average of all size fractions). The Transparency Feature (TF), typical for the finest size fraction (0-25 µm) is in many mineral mixtures less pronounced than for pure mineral phases. Here the individual TF of the components result in a broad feature. The resulting spectra can be divided into three groups – such as dominated by a single glass feature at 9.6 – 9.9 µm, a second groups with forsterite bands 9.4 µm- 9.5 µm, 10.2 µm, 10.6 µm, 11.9 µm and 15.9 µm-16 µm, and a third dominated by pyroxene bands at 8.9-9.1 µm, 9.4-9.5 µm, 9.9 µm, 10.2 µm, 10.4-10.5 µm, 10.6 µm, 10.8-11 µm 11.1-11.3 µm and 11.4-11.6 µm. Plagioclase features, even when the phase is dominating the composition, are usually ‘overprinted’ by forsterite and pyroxene bands. Discussion: A classic way to connect an easy to identify spectral feature in the mid-infrared to the chemical bulk composition is using the CF and the SiO2 content. Both show a strong correlation for both terrestrial rocks [21] and a variety of synthetic analogue samples from earlier studies in this project [15, 16, 17] (Fig.1). Summary & Conclusion: In a next step, we will study these mixtures under more realistic conditions, i.e., high vacuum and high temperature, in order to better simulate the hermean surface. Also, these mixtures will be used to test spectral unmixing routines, which allow to identify abundances of single minerals in a complex mixture of phases. References: [1] Hiesinger et al. (2020) Space Sci. rev. 216, 110 [2] Benkhoff et al. (2022) Space Sci. Rev. 217, 90 [3] Reitze et al.(2020) Min. Pet. 114, 453-463 [4] Reitze et al.(2021) EPSL 554, 116697 [5] Morlok et al.(2016) Icarus 264, 352-368 [6] Morlok et al.(2016) Icarus 278, 162-179 [7] Reitze et al.(2021) JGR (Planets) 126, e06832 [8] Weber et al. (2016) MAPS 51, 3-30 [9] Morlok et al. (2017) Icarus 284, 431-442 [10] Morlok et al. (2020) MAPS 55, 2080-2096 [11] Martin et al. (2017) MAPS 52, 1103-1124 [12] Weber et al. (2020) EPSL 530, 115884 [13] Weber et al. (2021) EPSL 569, 117072 [14] Stojic et al. (2021) Icarus 357, 114162 [15] Morlok et al. (2017) Icarus 296, 123-138 [16] Morlok et al. (2019) Icarus 324, 86-103 [17] Morlok et al. (2021) Icarus 361, 114363 [18] Charlier et al. (2013) EPSL 363, 50-60 [19] Namur et al. (2016) EPSL 439, 117-128 [20] Namur and Charlier (2017) Nature Geosci. 10, 9-13 [21] Cooper at al. (2002) JGR 107, 5017-5034 [22] Morlok et al. (2020) Icarus 335, 113410 Figure 1: Comparison of the Christiansen Feature (CF), a characteristic reflectance low, to the SiO2 bulk composition. The results from this study (red circles) fall along the regression line for terrestrial intermediate rocks.

International audience; Ilmenite-, magnetite- and clinopyroxene−melt trace element partition coefficients were investigated experimentally as a function of oxygen fugacity and melt composition in a range of synthetic ferrobasaltic bulk compositions. The experiments were performed at a constant temperature (1080 °C) and pressure (1 atm) over a range of oxygen fugacity (fO2) conditions from ca. 2 log units below to ca. 2 log units above the FMQ buffer. The partitioning behaviour of the divalent cations Zn, Mn, Co and Ni are found to be controlled by the degree of polymerisation of the coexisting melt; the partitioning behaviour of rare earth elements, Y and Sc can be explained well by the lattice strain model and the partitioning of the high-field strength elements Zr, Hf, Ta and Nb is influenced by the TiO2 content of the melt. Vanadium partitioning is strongly influenced by oxygen fugacity and a series of linear regression equations are presented to express the dependence of the mineral−melt partitioning behaviour of the multivalent cation V on oxygen fugacity. Furthermore, calibration of the partitioning of vanadium between magnetite-ilmenite pairs as an oxybarometer is proposed and applied to a ferrobasaltic layered intrusion—the Skaergaard intrusion—to provide an estimate of oxygen fugacity.

Introduction In light of the low oxygen fugacity inferred for Mercury, it is expected that Si is the dominant light constituent of Mercury’s core, potentially combined with smaller amounts of C and S. Depending on specific assumptions on Mercury’s oxidation state and bulk composition (for example, assuming a CB or EH chondrite-like bulk composition), geochemical estimates for the amount of Si, C, and S in Mercury’s core differ [1,2]. The concentration of light elements in Mercury’s core can be assessed independently from geochemical inferences using geophysical measurements. Geodetic constraints on the interior mass distribution of Mercury are derived from Mercury’s (close proximity to a) Cassini state 1 [3]. The compositional range of Mercury’s core for which the mass distribution of the planet is in agreement with geodetic measurements can be examined by planetary interior structure modelling [4-6]. Such interior structure modelling requires a composition-dependent parametrisation of the thermodynamic properties of metallic core alloys. Experimental measurements of density and of ternary Fe-Si-C liquids at high pressures have been lacking, although they are crucial to constrain the compositional range of Mercury’s core, and of bulk Mercury, using geodetic information of the planet. We experimentally measured the density and P-wave velocity (VP) of Fe-Si-C liquid metallic mixtures at high pressure, and investigated the feasible range of Mercury’s core composition in light of present geodetic constraints by interior structure modelling. Methods Density measurements of Fe-Si-C liquid metals are performed at high-pressure and high-temperature by X-ray absorption techniques with a Paris-Edinburgh (PE) press at beamline ID-27 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Binary Fe-Si sample powder is loaded into a cylindrical diamond (C) sample container, which saturates the sample in C. X-ray absorption profiles of the C-saturated Fe-Si-C metallic liquid sample are obtained in-situ, and of the quenched sample after the experiment ended and brought to ambient conditions. The density of the recovered samples is measured by hydrostatic weighing at the IPGP in Paris, France. The density of the liquid sample at experimental conditions is derived by combining the density of the quenched sample and the post-situ X-ray absorption profile with the in-situ X-ray absorption profile, using the Beer-Lambert law for X-ray absorption. Ultrasonic VP measurements of Fe-Si liquid metals are performed at high-pressure and high-temperature with a PE press at beamline 16-BMB of the Advanced Photon Source (APS) synchrotron facility, in Argonne, Illinois. Ultrasonic signals of 20 MHz, 25 MHz, and 30 MHz are generated and received in-situ by a lithium niobite transducer located at the top of the setup. Vertical wave reflections at the top and at the bottom of the sample are recorded and used to determine the vertical two-way travel time of the ultrasonic wave through the sample. The sample length is determined from radiographic images that are collected in situ. The ultrasonic sound speed (VP) through the sample is calculated using the sample length and the two-way travel time of sound waves. The samples that are successfully recovered from both the density experiments and the VP experiments are analysed by electron microprobe at the Institute for Mineralogy in Münster, Germany. A ternary ideal mixing model (FESIC) is fitted to the Fe-Si-C liquid metal density and data obtained by us and to data available in literature. This mixing model is implemented in spherically symmetric interior structure models of Mercury that are constrained by the normalized moment of inertia of Mercury I=0.346±0.014 MR2 and that of its outer solid shell Im=0.1475±0.006 MR2 [3]. The thermal profile is taken linear in the upper part (assumingly conductive) of the core, and adiabatic lower in the core. An Fe-Si-C solid inner core is considered where temperature is below the melting temperature of the liquid alloy. The mantle and an assumed 40 km thick curst are parametrized as single density spherical shells with fixed density ratio. Results Figure 1 compares the obtained density and VP measurements with the FESIC mixing model. The results confirm previous studies that VP of Fe-rich liquid metal increases and the density decreases with increasing concentration of Si. For the C-saturated density measurements, the decrease of C with increasing Si concentration confirms that the solubility of C in Fe-Si metals decreases with increasing concentration of Si. In the VP experiments, the sample was not loaded in a C-saturated environment. Nonetheless, we did detect a small amount of C in the sample with ~10wt%Si. The bulk-core compositions of interior structure models, constrained by the I and Im mentioned above, are compared to estimated core composition from by geochemical methods [1] from assuming a bulk composition of Mercury similar to an EH chondrite or CB chondrites (figure 2). The Si and C concentrations of Mercury’s core that are estimated from assuming a CB-like bulk composition of Mercury are consistent with the core composition of interior structure models with the central value of I (0.3458·MR2). A EH chondrite-like bulk composition of Mercury is thought to have a large core concentration of Si, and can only be met with an obliquity of Mercury at the upper end of the uncertainty limit, the planet is cold, and the inner core is large. The latter is inconsistent with the deep-dynamo explanation for Mercury’s broad-scale low-intensity magnetic field [7]. This study is published and openly accessible [8]. Acknowledgements We acknowledge the Marie Sklodowska-Curie grant No 845354 awarded to JSK and the BRAIN-be program grant (BR/143/A2/COME-IN) to TVH. The X-ray absorption measurements were performed at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. The APS is operated by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. [1] Steenstra E. S. and W. van Westrenen (2020) Icarus, 340, 113621 [2] Vander Kaadden et al. (2020) JGR:Planets, 125(5), e2019JE006239 [3] Margot et al. (2012) JGR:Planets, 117(E12), E00L09 [4] Hauck et al. (2013), JGR:planets, 118(6), 1204-1220 [5] [Rivoldini A. and T. Van Hoolst (2013) Earth Planet. Sci. Lett., 377-378, 62-72 [6] Knibbe J. S. and W. van Westrenen (2015) JGR:Planets, 120(11), 1904-1923. [7] Christensen, U. (2006) nature, 444(7122), 1056-1058. [8] Knibbe et al. (2021), JGR:Planets, 126(1), e2020JE006651.

Introduction: The IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory at the Institut für Planetologie in Münster produces a database of mid-infrared spectra for the ESA/JAXA BepiColombo mission to Mercury. The MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument onboard the BepiColombo Mercury Planetary Orbiter allows mapping spectral features in the 7-14 µm range, with a spatial resolution of about 500 meters [1,2]. In addition to a variety of natural terrestrial and meteoritic materials for the comparison of the expected results, we started using synthetic analogues based on the chemical composition of Mercury measured by MESSENGER. This allows to produce infrared spectra of bodies from which no material as returned samples or meteorites is available so far [3-5]. Advanced modelling based on the chemistry of Mercurian lavas and high-temperature experiments to simulate the mantle formation and the crystallization of lavas at the surface resulted in prediction for modal mineral compositions for distinct surface regions [6-8]. This allows to produce synthetic mixtures of minerals and glass representative for these hermean regions. Samples & Techniques: For the first round of mixing studies of powdered samples, sample compositions were selected from modal compositions based on experiments covering the dominant mineralogically diverse, 3.6–3.5 Gyr old volcanic smooth plains regions on Mercury [6,7]. The experimental conditions (for details see [7,8]) were temperatures between 1170-1360°C and highly reducing conditions (ΔIW of -4.9 to -6.2). Of the run products described in [7], we picked modal compositions covering a wide range of phase compositions, ranging from pure glass to the most crystalline composition modelled (crystalline content from 9-58 wt%). The analogues were prepared using mixtures of synthetic glass material based on hermean compositions [7-9] and natural crystalline forsterite, enstatite, diopside and plagioclase, with compositions in the range that was observed in the petrological experiments [7]. All materials were sieved into 4 size fractions before (0-25 µm, 25-63 µm, 63-125 µm, 125-250 µm), and the analogue mixtures composed directly from the size fractions. Diffuse reflectance mid-infrared spectra were made with a Bruker Vertex 70 infrared system using a Cooled MCT detector. Analyses of the powders were made at low pressure (10-3bar) to reduce atmospheric bands from 2-20 µm. For calibration, a diffuse gold standard was used for ratioing, to guarantee low noise, we integrated 512 scans for each spectrum. Spectral features of interest are the Christiansen Feature (CF), a characteristic reflectance low that also serves as proxy for the bulk composition; the Transparency Feature (TF), typical and indicator for the finest grain size fraction (0-25 µm); and the Reststrahlen Bands (RBs), the molecular vibration modes. Results: In the range of interest for MERTIS (7-14 µm), the entirely glassy end member shows a simple spectrum with a strong RB at 9.6 µm, a CF at 7.9 µm and the TF at 11.77 µm [4]. Increased crystalline content (9 wt% forsterite, 91 wt% glass) in sample ID 345 Smooth Plains has two RB appearing at 9.6 µm and 10.5-10.6 µm, and a weaker RB at 10.2 µm. The CF is at 7.9-8 µm, the TF at ~11.7 µm. Sample ID 344 Smooth Plains contains several crystalline species (5 wt% forsterite, 2 wt% diopside, 28 wt% plagioclase and 11 wt% enstatite). This results in a feature-rich spectrum, with RBs at 9.5 µm, 9.9 µm, 10.2 µm, 10.5 µm, 10.8 µm, 11.1 µm and 11.3-114 µm. The CF is found at 7.8-7.9 µm, the TF is at 11.7 µm. The crystalline-rich end member ID 343 Smooth Plains has only 42 wt% glass components with 6 wt% forsterite, 11 wt% diopside, 34 wt% plagioclase and 7 wt% enstatite. RBs are seen at 9.4 – 9.6 µm, 9.9 µm, 10.2 µm, 10.5 µm, 10.8 µm and 11.3 µm. The TF is at 11.6 µm, the CF at 7.9 - 8 µm. Discussion: Spectra show increasing RB features with decreasing content of glass (Fig.1). However, a comparison of the finest size fractions (0-25 µm) (Fig.2) of the 4 samples shows astonishingly similar spectra, basically the smooth glass spectra of with relatively weak RB on top, with the spectrum dominated by the TF. This could make distinguishing of such spectra of a continuum of similar composition difficult. Contrasts between the spectra are stronger at the larger grain size fractions (>25µm), where the RB features are stronger. Variations in band intensities between the different samples – particular the high intensity of the ID 344 Smooth Plains spectrum – could be results of a highly reflective component (Enstatite?) or indicator of insufficient mixing of the phases. Summary & Conclusions: We will continue by mixing further samples based on the hermean surface models and experiments [7], with the aim to have series of samples representative for each of the terranes. Future spectral unmixing models will test if the individual mineral components can be extracted by modelling form the spectra. References: [1] Benkhoff J. et al. (2020) Planetary and Space Science 58, 2-20 [2] Hiesinger H. et al. (2020) Planetary and Space Science 58, 144–165 [3] Morlok et al. (2020) Icarus 335, 113410 [4] Morlok et al. (2019) Icarus 324, 86-103 [5] Weber et al. (2020) Earth and Planetary Science Letters 530, 115884 [6] Weider S.Z. et al. (2015) Earth and Planetary Science Letters 416, 109-120 [7] Namur and Charlier (2017) Nature Geoscience 10, 9-15 [8] Namur O. et al. (2016) Earth and Planetary Science Letters 448, 102-114 [9] Nittler L.R. et al. (2018) Mercury: The View after MESSENGER. Cambridge University Press, Cambridge, pp. 30-51. Figure 1. Mid-infrared diffuse reflectance spectra of 4 size fractions. CF: Christiansen Feature, TF: Transparency Feature. Figure 2. Mid-infrared diffuse reflectance spectra of the 0-25 µm size fractions.

To investigate chromium diffusion kinetics in ultramafic cumulate minerals, we analyzed the Cr elemental and isotopic compositions of olivine, orthopyroxene, and chromite from the Stillwater layered intrusion. Core-to-rim compositional profiles reveal that Cr elemental concentrations decrease from 60 to 20 ppm in olivine and from 5000–4600 to 2700–2400 ppm in orthopyroxene. These zoned Cr distributions in olivine and orthopyroxene suggest that Cr was lost by diffusion into the melt. Olivine and orthopyroxene have δ53Cr values ranging from –0.09 to 0.25‰ and from –0.11 to 0.07‰, respectively, higher than the values of coexisting chromite (–0.23 to –0.07‰). This isotopic disequilibrium can be explained by diffusion-driven kinetic fractionation during cooling. The preferential diffusion of light Cr isotopes from silicate minerals to the melt resulted in isotopically heavier olivine and orthopyroxene, but the kinetic diffusion between chromite and melt negligibly affected the isotopic compositions of chromite grains due to their high Cr concentrations. Modeling results based on the observed Cr contents and isotopic compositions of silicate minerals constrain the cooling time of the Peridotite Zone in the Stillwater magmatic system to have been 10–100 kyr.

Experimental measurements of density by X-ray absorption and of P-wave velocity by ultrasonic techniques of liquid Fe-(

Enrichment of subduction derived magmas in chalcophile and siderophile elements plays a key role in the formation of economically important ore deposits. Melting of mantle wedge peridotite induced by fluxing slab-derived fluids is the first step in the chemical transfer from the slab to melts (Spandler and Pirard, 2013). Changes in redox conditions, sulfur content, amount of fluid, and P-T conditions affect the elements partitioning between melts and residual phases (Dale et al., 2009; Li and Audetat, 2012; Perchuk et al., 2018; Rielli et al., 2018). However, to date there is a few systematic data on mineral-melt partitioning for economically important elements during partial melting of peridotite in mantle wedge conditions.We determined experimentally mineral-melt partition coefficients for a range of chalcophile and siderophile elements (V, Co, Cu, Zn, As, Se, Mo, Ru, Rh, Pd, Ag, Cd, Sb, Re, Os, Ir, Pt, Au, Tl, Bi) at different P-T conditions. Slightly serpentinized peridotite (3 wt.% H2O; Debret et al., 2013) was used as a starting material for all experiments. A set of experiments with 1 wt.% of FeS added to the peridotite was also performed in order to study the effect of S on element partitioning. Starting materials were doped with 100-200 ppm of targeted elements. The experiments were performed at pressures of 1-2 GPa and at temperatures between 1100 and 1300°C in end-loaded 0.5” piston-cylinder apparatus in the newly established high-pressure laboratory at the University of Liege (Belgium). In order to avoid Fe-loss, chemical reduction and volatile loss of experimental charges, double Au80Pd20 capsules pre-saturated with Fe were used. Major and trace element composition in synthesized experimental products were measured by electron microprobe and LA-ICP-MS respectively.In this study, we report a wide range of partition coefficients determined between coexisting silicate, oxide, sulfide minerals and melt as a function of P-T and S content. The results provide further insights into mobility of economically important elements during genesis of ore-forming magmas in subduction settings.References:Spandler and Pirard (2013) Lithos, 170-171, 208-223 Dale et al. (2009) GCA, 73 (5), 1394-1416 Li and Audetat (2012) EPSL, 355-356, 327-340 Perchuk et al. (2018) Lithos, 302-303, 203-223 Rielli et al. (2018) EPSL, 497, 181-192 Debret et al. (2013) Chem. Geol., 357, 117-133

Introduction: The purpose of the IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory is to produce laboratory spectra for the mid-infrared spectrometer MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) on the ESA/JAXA BepiColombo mission to Mercury. This device will map the mineralogy of the hermean surface spectral features in the 7-14 µm range, with a spatial resolution of ~ 500 meters [1,2]. For the interpretation the data from MERTIS, we need laboratory spectra for comparison. A wide range of natural mineral and rock samples such as terrestrial impact rocks and meteorites [e.g., 3-5] was studied for this purpose. Since we do not have natural samples from surface of Mercury, we produced synthetic analogs based on MESSENGER data and laboratory experiments [6-9]. A central component for such mixtures will be glass to replicate material formed by impact events and lava extrusion and explosive volcanism (i.e., pyroclastic debris) [e.g. 10]. We present results of our ongoing study of synthetic glasses. These synthetic glasses will be studied in the mid-infrared to obtain spectra for the IRIS database, the material will also used for future mixtures and experiments. Samples and Techniques: Sample Production: In order to simulate the petrologic evolution of magmas on early Mercury, we synthesized analog material under controlled temperature, pressure and oxidation state [7-9]. The glass was produced following a procedure described in [11] with the oxidation state controlled by exposing the sample to a CO-CO2 gas-mixture equivalent to four orders of magnitude below the iron-wüstite buffer (IW-4). For in-situ studies we selected run products from earlier, similar laboratory experiments [9]. Infrared Spectroscopy: For the bulk powder FTIR diffuse reflectance analyses, powder size fractions 0-25 µm, 25-63 µm, 63-125 µm, and 125-250 µm were measured, in addition to a polished sample. We used a Bruker Vertex 70 v infrared system with a MCT detector at the IRIS laboratories at the Institut für Planetologie in Münster. Analyses were conducted under low pressure to reduce atmospheric bands, analyses were made in reflectance from 2-20 µm. FTIR microscope analyses for in-situ studies in polished blocks and thin sections were conducted using a Bruker Hyperion 1000/2000 System at the Hochschule Emden/Leer. We used a 250×250 µm sized aperture. In addition, a Perkin-Elmer Spotlight-400 FTIR spectrometer at the University of Manchester was used to map samples using an adjoining Focal Plane Array (FPA) mapping unit with a resolution of 6.25 µm × 6.25 µm. Results: Figure 1 gives an example of an area mapped using micro-FTIR. Sample 131_1 is based on the MESSENGER derived composition of the Mercurian High Magnesium Regions (HMg) [9]. Spectra in Fig.2 are of the Mg-poor (5.2 wt%) glassy component in this sample. Compared with spectra of glasses based on the Inter Crater Planes (ICP) (21.5 wt% MgO), 123_3 (17.7 wt% MgO) and 126_3 (12.2 wt% MgO), we see generally spectra typical for glassy materials. The single Reststrahlenband (RB) shifts with increasing MgO from 9.3 µm to 9.9 µm, and the CF from 7.9 µm to 8.2 µm. The two examples for bulk powders (Fig.3) have low MgO contents: 1.6 wt% (Low Mg C) and 4.7 wt % (Low Mg B) [9]. Different grain size fractions show intensity correlated with increasing grain size (Fig. 3). The RB and CF features are basically similar for all size fractions, but an characteristical Transparency Feature (TF) appears in the finest fraction (0-25 µm). The Low Mg B sample has the TF at 11.7 µm, the CF at 7.8 µm and the RB at 9.4 µm. Low-Mg C shows the CF from 7.6 µm to 7.7 µm, the RB at 9.2 µm – 9.3 µm and a TF at 11.6 µm. Summary & Conclusions: The sieved size fractions of the bulk glass material show typical features for highly crystalline materials. They follow a trend of band shifts for CF and RB towards longer wavelengths with increasing MgO contents [3,4]. We will present further glasses cover higher MgO contents (>6 wt%) to provide material for the whole range of expected Mercurian regolith glass compositions [7-9]. However, for a complete picture of the hermean surface, we expect mixtures of glassy and crystalline material. This will be the next step in our study, where we will obtain spectra of mixtures representing various regions on Mercury [e.g.7,8]. Furthermore, the impact of space weathering, which changes the structural and thus spectroscopic properties of grain surfaces will be taken into account [12,13,14]. References: [1] Rothery D.A. et al. (2020) Space Space Rev. 216, 66 [2] Hiesinger H. et al. (2020) in prep. [3] Morlok et al. (2020) Icarus 335, 113410 [4] Morlok et al. (2019) Icarus 324, 86-103 [5] Weber et al. (2020) Earth and Planetary Science Letters 530, 115884 [6] Weider S.Z. et al. (2015) Earth and Planetary Science Letters 416, 109-120 [7] Namur and Charlier (2017) Nature Geoscience 10, 9-15 [8] Namur O. et al. (2016) Earth and Planetary Science Letters 448, 102-114 [9] Namur O. et al. (2016) Earth and Planetary Science Letters 439, 117-128 [10] Fasset C.I. (2016) Journal of Geophysical Research: Planets 121, 1900-1926 [11] Renggli C. and King P. (2018) Rev.Min.Geochem 84, 229-255 [12] Weber I. et al. (2020) Earth & Planetary Science Letters 530, 115884 [13] Stojic et al. (2020) Icarus (submitted) [14] Stojic et al. (2020) LPSC 51, 1875

Mercury's crust has a complex structure resulting from a billion years of volcanism. The surface variations in chemical composition have been identified from orbit by the spacecraft MESSENGER. Combining these measurements with laboratory experiments on partial melting, we estimate which variations in surface density and degree of mantle melting are required to produce surface rocks. If the surface density is representative of the deep crustal density, more than one half of crustal thickness variations in the northern hemisphere are explained by lateral variations in mantle melting. The crust is thin below the magnesium-poor Northern Volcanic Plains whereas the thickest crust is found in the magnesium-rich region located at mid-northern latitudes in the Western Hemisphere. The magnesium-rich region is thus not due to an early impact but rather to extensive mantle melting. The thickness-melting relation has also been observed for the oceanic crust on Earth and might be a common feature of terrestrial planets., Comment: 11 pages of main text, 37 pages with supplements; 3+12 figures, 1+1 tables

Cet article propose d’analyser une maniere singuliere dont les attaques de loups sur les troupeaux en Mongolie sont interpretees par les eleveurs nomades. La perte d’animaux domestiques est parfois consideree comme un don aux loups et plus particulierement a l’esprit maitre du territoire et des animaux sauvages. La question posee dans cet article est la suivante : pourquoi les eleveurs operent-ils ce « retournement » d’une perte, resultant d’un acte de predation, en un « don » ? La reponse a cette question met en jeu une conception singuliere de l’environnement, la circulation d’un bien symbolique nomme hishig, qui se traduit par les termes de « grâce » ou de « fortune », et la notion bouddhiste de « merite », buyan.

The Wajilitag and Puchang intrusive complexes of the Tarim large igneous province (TLIP) are associated with significant resources of Fe–Ti oxide ores. These two mafic–ultramafic intrusions show differences in lithology and mineral chemistry. Clinopyroxenite and melagabbro are the dominant rock types in the Wajilitag complex, whereas the Puchang complex is generally gabbroic and anorthositic in composition with minor plagioclase–bearing clinopyroxenites in the marginal zone. Disseminated Fe–Ti oxide ores are found in the Wajilitag complex and closely associated with clinopyroxenites, whereas the Puchang complex hosts massive to disseminated Fe–Ti oxide ores mainly within its gabbroic rocks. The Wajilitag intrusive rocks are characterized by a restricted range of initial 87Sr/86Sr ratios (0.7038–0.7048) and positive eNd(t) (+0.04 − +3.01), indicating insignificant involvement of continental crustal contamination. The slightly higher initial 87Sr/86Sr ratios (0.7039–0.7059) and lower eNd(t) values (−1.05 − +2.35) of the Puchang intrusive rocks also suggest that the isotopic characteristics was controlled primarily by their mantle source, rather than by crustal contamination. Both complexes have Sr–Nd isotopic compositions close the neighboring kimberlitic rocks and their hosted mantle xenoliths in the TLIP. This indicates that the ferrobasaltic parental magmas were most probably originated from partial melting of a metasomatized subcontinental lithospheric mantle, modified recently with subduction–related materials by the impingement of the ascending mantle plume. The recycled subduction–related materials preserved in the lithospheric mantle could play a key role in the formation of the parental Fe–rich magmas in the context of an overall LIP system. The distinct variations in mineral assemblage for each complex and modeled results indicated that the Wajilitag and Puchang complexes experienced different crystallization path. Fe–Ti oxides in Wajilitag joined the liquidus earlier in the crystallization sequence, especially relative to the crystallization of plagioclase. This is attributed to the relatively high TFeO, TiO2 and initial H2O contents of the parental magma. In combination with definitive field and petrological evidence, the enrichment of highly incompatible elements (e.g., Zr, Hf, Nb and Ta) and the depletion of rare earth elements in the Fe–Ti oxide ores is consistent with the plausible interpretation that the ores could be formed by fractional crystallization and crystal accumulation of the Fe–Ti oxide crystals from the ferrobasaltic parental magmas. A considerable amount of the Fe–Ti oxides in the Puchang has transported and sunk from higher up in the chamber to the underlying unconsolidated silicate crystal pile. The highly dense Fe–Ti oxide crystal slurries further tended to effective accumulate Fe–Ti oxides to form high–grade Fe–Ti oxide ore bodies, and subsequent rapid collapse and intrusive into lower lithologies within the complex under a H2O–rich environment during the late–stage of magmatic differentiation. The development of massive Fe–Ti oxide ores in the case of the Puchang, could plausibly result from a combination of the protracted differentiation history of a Fe highly enriched parental magma and the later addition of external H2O from the country rocks (e.g., carbonates) to the slowly cooling magma chamber.

We have synthesized and analyzed by mid-infrared reflectance spectroscopy silicate glasses that are representative for the glasses on the surface of Mercury. The glass compositions are based on high-pressure laboratory experiments and the resulting compositions of the glass phase. The spectra are of interest for investigating the surface of Mercury using the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument on board of the ESA/JAXA BepiColombo mission.Both powdered fractions and polished blocks have been analyzed. Powdered size fractions of 0–25 μm, 25-63 μm, 63-125 μm, and 125–250 μm were measured in reflectance in the thermal infrared (2–20 μm). Spectra for powdered bulk glasses (1.6 wt% - 19.0 wt% MgO) show a single, dominating Reststrahlenband (RB, 9.3–9.8 μm), a Christiansen Feature (CF; 7.6 μm - 8.1 μm), and a size dependent Transparency Feature (TF; 11.6–11.9 μm). Micro-FTIR analyses of polished blocks of glasses (3.4–26.5 wt% MgO) have characteristic bands at 7.8–8.2 μm (CF), and 9.3–9.9 μm (RB). Only few olivine crystalline features were observed.Spectral features correlate with compositional characteristics, e.g. SiO2 content or SCFM (SiO2/(SiO2 + CaO + FeO + MgO) index. The strongest correlation between band features CF and the strong RB are with Mg/Si. No simple mixture of glass spectra from this study is able to reproduce the entire ground based spectrum of the surface of Mercury. However, Mg-rich glasses reproduce identified features at 8.5 μm, 9.9 μm and 12.4 μm.

Cumulate rocks of the Upper Main Zone and Upper Zone (UUMZ) of the Bushveld Complex, South Africa, contain the world's major resources of Fe-Ti-V ±, hosted in Ti-magnetite and apatite, and are commonly considered as having crystallized from the last major injection of magma into the magma chamber. In this study, we present the petrography, modal proportions, whole-rock major element chemistry (260 samples), electron microprobe data (∼10 000 analyses for plagioclase, olivine, and pyroxene), and compiled analyses of Cr in magnetite (239 samples) for the UUMZ sampled over 2.1 km of the Bierkraal drill cores in the western limb of the Complex. The UUMZ section exhibits a broad normal fractionation trend upwards, but a series of reversals to more primitive anorthite contents in plagioclase, Mg# in pyroxenes and olivine, Cr in whole-rocks and Cr in magnetite separates are observed, accompanied by the appearance or disappearance of various minerals. Anorthosite or leucogabbro layers are closely linked to these reversals; the reversals in An % of plagioclase are used as boundaries to divide the UUMZ into 18 cycles. These cycles are interpreted as indications of magma chamber replenishment by plagioclase-laden magmas (up to 20 vol. % plagioclase) and are also marked by spikes in Cr content. In addition, abundant Fe-Ti oxide-bearing plagioclase-rich rocks are identified in the lower half of the UUMZ. These have crystallized from a hybrid melt produced by the mixing of a new plagioclase-bearing magma batch and the resident magma. Further crystallization of this hybrid liquid may lead to the formation of magnetite layers in the lower part of the UUMZ. The Bushveld UUMZ therefore grew by multiple emplacements of crystal-laden magmas coming from deep-seated chambers. Slow cooling in a shallow chamber explains the systematic bottom-up compositional evolution in the cumulate pile within individual cycles. The residual melt reached silicate liquid immiscibility soon after the saturation of apatite. Thereafter, segregation of conjugate Fe-rich and Si-rich melts and crystallization of the paired melts produces cumulates with a smooth upward decrease in Fe-Ti oxides, whereas plagioclase mode increases in each apatite-bearing cycle. A comparison of systematic geochemical analyses and a detailed lithological stratigraphy between the Bushveld limbs demonstrates the possible connectivity between the western and eastern Upper Zone but indicates notable differences from the Bellevue section of the northern limb.

In this study we experimentally assess whether the bulk composition of the Kiruna-type iron–fluorine Vergenoeg deposit, South Africa (17 wt.% SiO2 and 55 wt.% FeOtot) could correspond to an immiscible Fe-rich melt paired with its host rhyolite. Synthetic powder of the host rhyolite was mixed with mafic end-members (ore rocks) in variable proportions. Experimental conditions were 1–2 kbar and 1010 °C, with a range of H2O and F contents in the starting compositions. Pairs of distinct immiscible liquids occur in experiments saturated with fluorite, under relatively dry conditions, and at oxygen fugacity conditions corresponding to FMQ−1.4 to FMQ+1.8 (FMQ = fayalite-magnetite-quartz solid buffer). The Si-rich immiscible liquids contain 60.9–73.0 wt.% SiO2, 9.1–12.5 wt.% FeOtot, 2.4–4.2 wt.% F, and are enriched in Na2O, K2O and Al2O3. The paired Fe-rich immiscible melts have 41.0–49.5 wt.% SiO2, 20.6–36.1 wt.% FeOtot and 4.5–6.0 wt.% F, and are enriched in MgO, CaO and TiO2. Immiscibility does not develop in experiments performed under water-rich (aH2O > 0.2; a = activity) and/or oxidized (>FMQ+1.8) conditions. In all experiments, solid phases are magnetite, ±fayalite, fluorite and tridymite. Our results indicate that the rocks from the Vergenoeg pipe crystallized in a magma chamber hosting two immiscible silicate melts. Crystallization of the pipe from the Fe-rich melt explains its extreme enrichment in Ca, F and Fe compared to the host rhyolitic rocks. However, its low bulk silica content compared to experimental Fe-rich melts indicates that the pipe formed by remobilization of a mafic crystal mush dominated by magnetite and fayalite. Segregation of evolved residual liquids as well as the conjugate immiscible Si-rich melt produced the host rhyolite. The huge amount of fluorine in Vergenoeg ores (∼12 wt.% F) can hardly be explained by simple crystallization of fluorite from the Fe-rich silicate melt (up to 6 wt.% F at fluorite saturation). Instead, we confirm a previous hypothesis that the fluorite enrichment is, in part, due to the migration of hydrothermal fluids.

An experimental study of the microstructural evolution of an immiscible basaltic emulsion shows that the Fe-rich liquid forms homogeneously nucleated droplets dispersed in a continuous Si-rich liquid, together with droplets heterogeneously nucleated on plagioclase, magnetite, and pyroxene. Heterogeneous nucleation is likely promoted by localised compositional heterogeneities around growing crystals. The wetting angle of Fe-rich droplets on both plagioclase and magnetite increases with decreasing temperature. Droplet coarsening occurs by a combination of diffusion-controlled growth and Ostwald ripening, with an insignificant contribution from coalescence. Characteristic microstructures resulting from the interaction of immiscible Fe-rich liquid with crystal grains during crystal growth can potentially be used as an indicator of liquid unmixing in fully crystallised natural samples. In magma bodies < ~ 10 m in size, gravitationally driven segregation of immiscible Fe-rich droplets is unlikely to be significant.

Cet article propose d’analyser différentes attitudes et discours moraux, à priori contradictoires, actualisés autour de la mise à mort d’un mouton, d’une vache et d’un loup parmi des éleveurs nomades de Mongolie. La mise à mort d’un animal domestique, contrairement à celle d’un animal sauvage, est toujours empreinte de sobriété. Pour les éleveurs, selon les fragments de l’idéologie bouddhiste en vigueur, la mise à mort d’un animal domestique est associée aux idées de pollution (buzar) et de péché (nügel). De manière contrastée, la mise à mort d’un animal sauvage, et plus particulièrement d’un loup, fait l’objet d’une grande joie. Un éleveur chanceux à la chasse est dit « vertueux », « méritant » (buyantaj) et doté d’un haut potentiel vital (hijmor’). En mobilisant la notion mongole de fortune (hišig), j’analyse la coexistence de différents types de moralité liés à la mise à mort d’un mouton, d’une vache et d’un loup., This article analyzes a priori contradictory attitudes and discourses related to the killing of a sheep, a cow, and a wolf among Mongolian nomadic herders. Contrary to the killing of a hunted animal, the killing of a domestic animal is always sad and sober. For the herders, according to their understanding of Buddhist ideology, the killing of a domestic animal is associated with the ideas of pollution (buzar) and sin (nügel). In a contrasted way, the killing of a hunted animal, and more particularly a wolf, is joyful. A good hunter is perceived as a “virtuous” and “meritorious” person with high vital potential (hijmor’). In relation to the Mongolian notion of “fortune” (hišig), I analyze the coexistence of different types of morality linked to the killing of a sheep, a cow, and a wolf., Este artículo propone analizar diferentes actitudes y discursos morales, a priori contradictorios, actualizados en torno al asesinato de una oveja, una vaca y un lobo entre los pastores nómadas de Mongolia. La matanza de un animal doméstico, a diferencia de la de un animal salvaje, siempre es sobria. Para los criadores, de acuerdo con los fragmentos de la ideología budista actual, la matanza de un animal doméstico está asociada con las ideas de contaminación (buzar) y pecado (nügel). En contraste, matar un animal salvaje, especialmente un lobo, constituye una gran alegría. Se dice que un criador afortunado en la caza es "virtuoso", "merecedor" (buyantaj) y está dotado de un alto potencial vital (hijmor'). Al movilizar el concepto mongol de fortuna (hišig), analizo la coexistencia de diferentes tipos de moral relacionados con el asesinato de una oveja, una vaca y un lobo.

© 2016 Elsevier B.V.. The Bushveld Complex (South Africa) is the largest layered intrusion on Earth and plays a considerable role in our understanding of magmatic differentiation and ore-forming processes. In this study, we present new geochemical data for apatite-hosted multiphase inclusions in gabbroic cumulates from the Bushveld Upper Zone. Inclusions re-homogenized at high-temperature (1060-1100 °C) display a range of compositions in each rock sample, from iron-rich (35 wt.% FeOtot; 28 wt.% SiO2) to silica-rich (5 wt.% FeOtot; 65 wt.% SiO2). This trend is best explained by an immiscible process and trapping of contrasted melts in apatite crystals during progressive cooling along the binodal of a two-liquid field. The coexistence of both Si-rich and Fe-rich immiscible melts in single apatite grains is used to discuss the ability of immiscible melts to segregate from each other, and the implications for mineral and bulk cumulate compositions. We argue that complete separation of immiscible liquids did not occur, resulting in crystallization of similar phases from both melts but in different proportions. However, partial segregation in a crystal mush and the production of contrasting phase proportions from the Fe-rich melt and the Si-rich melt can be responsible for the cyclic evolution from melanocratic (Fe-Ti-P-rich) to leucocratic (plagioclase-rich) gabbros which is commonly observed in the Upper Zone of the Bushveld Complex where it occurs at a vertical scale of 50 to 200 m. ispartof: EARTH AND PLANETARY SCIENCE LETTERS vol:443 pages:108-117 status: published

In his book, Lawrence W. Gross, who is an Anishinaabe Indian, explores the ways in which Anishinaabe American Indians strive to maintain their worldview and culture after the American colonisation ...

In this study we investigate the likeliness of the existence of an iron sulfide layer (FeS matte) at the core-mantle boundary (CMB) of Mercury by comparing new chemical surface data obtained by the X-ray Spectrometer onboard the MESSENGER spacecraft with geochemical models supported by high-pressure experiments under reducing conditions. We present a new data set consisting of 233 Ti/Si measurements, which combined with Al/Si data show that Mercury's surface has a slightly subchondritic Ti/Al ratio of 0.035 ± 0.008. Multiphase equilibria experiments show that at the conditions of Mercury's core formation, Ti is chalcophile but not siderophile, making Ti a useful tracer of sulfide melt formation. We parameterize and use our partitioning data in a model to calculate the relative depletion of Ti in the bulk silicate fraction of Mercury as a function of a putative FeS layer thickness. By comparing the model results and surface elemental data we show that Mercury most likely does not have a FeS layer, and in case it would have one, it would only be a few kilometers thick ( 13 km ). We also show that Mercury's metallic Fe(Si) core cannot contain more than ∼1.5 wt.% sulfur and that the formation of this core under reducing conditions is responsible for the slightly subchondritic Ti/Al ratio of Mercury's surface.

© 2018 Elsevier Ltd We present crystallization experiments on silicate melt compositions related to the lunar magma ocean (LMO) and its evolution with cooling. Our approach aims at constraining the primordial internal differentiation of the Moon into mantle and crust. We used graphite capsules in piston cylinder (1.35–0.80 GPa) and internally-heated pressure vessels (

The origin of iron oxide-apatite deposits is controversial. Silicate liquid immiscibility and separation of an iron-rich melt has been invoked, but Fe–Ca–P-rich and Si-poor melts similar in composition to the ore have never been observed in natural or synthetic magmatic systems. Here we report experiments on intermediate magmas that develop liquid immiscibility at 100 MPa, 1000–1040 °C, and oxygen fugacity conditions (fO2) of ∆FMQ = 0.5–3.3 (FMQ = fayalite-magnetite-quartz equilibrium). Some of the immiscible melts are highly enriched in iron and phosphorous ± calcium, and strongly depleted in silicon (, The origin of iron oxide-apatite deposits remains enigmatic and controversial. Here, the authors perform experiments on intermediate magmas and show that increasing aH2O and fO2 enlarges the two-liquid field thus allowing the Fe–Ca–P melt to separate easily from host silicic magma and produce iron oxide-apatite ores.

Dissolved silica (DSi) plays an important biogeochemical role in the fjords of northern Chilean Patagonia (44–48°S), where it drives high biogenic productivity and promotes carbon burial. It is generally believed that the DSi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology, climate, topography, vegetation, and meltwater input. In northern Chilean Patagonia several authors have proposed that the postglacial volcanic ash soils (andosols) may play a significant role in the high supply of DSi to the regional fjords. To assess the influence of andosols on DSi concentrations in north Patagonian rivers, we mapped andosol thickness and compared our results with river chemistry. The mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes. The andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes, reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material. Mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes, i.e. high amounts of amorphous material, plagioclase, K-feldspar, and pyroxene. Down-profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth, resulting from weathering of the volcanic parent material. For the five studied watersheds, a highly positive correlation (R2=0.98) was found between average andosol thickness and DSi concentrations, suggesting that andosol thickness is the main parameter affecting DSi concentrations in north Patagonian river systems. On seasonal timescales, increased precipitation (winter) and glacial meltwater (summer) input can significantly reduce DSi concentrations. We argue that the weathering of andosols constitutes the most important source of DSi to the lakes and fjords of northern Chilean Patagonia, explaining the particularly high regional rates of biogenic silica production. Copyright © 2015 John Wiley & Sons, Ltd.

International audience; We have performed piston–cylinder experiments on a primitive martian mantle composition between 0.5 and 2.2 GPa and 1160 to 1550 °C. The composition of melts and residual minerals constrain the possible melting processes on Mars at 50 to 200 km depth under nominally anhydrous conditions. Silicate melts produced by low degrees of melting (

Martian meteorites are the only samples available from the surface of Mars. Among them, olivine-phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores (Fo 70–85) and rims richer in Fe (Fo 45–60). The Northwest Africa 1068 meteorite is one of the most primitive “enriched” shergottites (high initial 87 Sr/ 86 Sr and low initial e 143 Nd). It contains olivine crystals as magnesian as Fo 77 and is a major source of information to constrain the composition of the parental melt, the composition and depth of the mantle source, and the cooling and crystallization history of one of the younger magmatic events on Mars (∼180 Ma). In this study, Fe-Mg isotope profiles analyzed in situ by femtosecond-laser ablation MC-ICP-MS are combined with compositional profiles of major and trace elements in olivine megacrysts. The cores of olivine megacrysts are enriched in light Fe isotopes ( δ 56 Fe IRMM-14 = −0.6 to −0.9‰) and heavy Mg isotopes ( δ 26 Mg DSM-3 = 0–0.2‰) relative to megacryst rims and to the bulk martian isotopic composition ( δ 56 Fe = 0 ± 0.05‰, δ 26 Mg = −0.27 ± 0.04‰). The flat forsterite profiles of megacryst cores associated with anti-correlated fractionation of Fe-Mg isotopes indicate that these elements have been rehomogenized by diffusion at high temperature. We present a 1-D model of simultaneous diffusion and crystal growth that reproduces the observed element and isotope profiles. The simulation results suggest that the cooling rate during megacryst core crystallization was slow (43 ± 21 °C/year), and consistent with pooling in a deep crustal magma chamber. The megacryst rims then crystallized 1–2 orders of magnitude faster during magma transport toward the shallower site of final emplacement. Megacryst cores had a forsterite content 3.2 ± 1.5 mol% higher than their current composition and some were in equilibrium with the whole-rock composition of NWA 1068 (Fo 80 ± 1.5). NWA 1068 composition is thus close to a primary melt (i.e. in equilibrium with the mantle) from which other enriched shergottites derived.

NASA’s MESSENGER spacecraft has revealed geochemical diversity across Mercury’s volcanic crust. Near-infrared to ultraviolet spectra and images have provided evidence for the Fe2+-poor nature of silicate minerals, magnesium sulfide minerals in hollows and a darkening component attributed to graphite, but existing spectral data is insufficient to build a mineralogical map for the planet. Here we investigate the mineralogical variability of silicates in Mercury’s crust using crystallization experiments on magmas with compositions and under reducing conditions expected for Mercury. We find a common crystallization sequence consisting of olivine, plagioclase, pyroxenes and tridymite for all magmas tested. Depending on the cooling rate, we suggest that lavas on Mercury are either fully crystallized or made of a glassy matrix with phenocrysts. Combining the experimental results with geochemical mapping, we can identify several mineralogical provinces: the Northern Volcanic Plains and Smooth Plains, dominated by plagioclase, the High-Mg province, strongly dominated by forsterite, and the Intermediate Plains, comprised of forsterite, plagioclase and enstatite. This implies a temporal evolution of the mineralogy from the oldest lavas, dominated by mafic minerals, to the youngest lavas, dominated by plagioclase, consistent with progressive shallowing and decreasing degree of mantle melting over time. The MESSENGER spacecraft has revealed geochemical diversity across Mercury’s surface. Magma crystallization experiments suggest a crustal mineralogy consistent with a transition towards shallower and cooler mantle melting conditions.

International audience; The Sveconorwegian late-orogenic magmatism of southern Norway (970-916 Ma) consists of two magmatic suites: the Hornblende-Biotite-Granitoids (HBG) suite and the Anorthosite-Mangerite-Charnockite (AMC) suite of the Rogaland Anorthosite Province (RAP), characterized by opx-bearing lithologies. The Farsund body comprises elements of both suites that display mingling relationships. The main facies, mostly charnockitic, contains orthopyroxene whereas a subordinate granitic facies comprises hornblende and biotite. U-Pb (zircon) isotopic data show overlapping ages of 931 ± 2 Ma for the charnockitic facies and 926 ± 4 Ma for the granitic facies. Both facies display similar extent of differentiation demonstrating that the granitic facies was not derived by fractionation from the charnockitic one. Mineralogical, geochemical and petrological data indicate that the charnockitic facies belongs to the AMC suite and the granitic facies, to the HBG suite. Strontium, Nd and Pb isotopic data show that the Farsund intrusion was emplaced at the boundary between two different lithotectonic units that are separated by the Farsund-RAP shear zone. This shear zone likely favored the emplacement of the magmas. Most of the assimilation occurred in the lower crust whereas limited differentiation likely took place in the upper crust.

International audience; The Lac Tio hemo-ilmenite ore body crops out in the outer portion of the 1.06 Ga Lac Allard anorthosite, a member of the Havre-Saint-Pierre anorthosite suite from the Grenville province of North America. It is made up of ilmenitite (commonly with more than 95% hemo-ilmenite) associated with noritic lithologies and anorthosite. The present study compares the magnetic fabric of the ore body, as deduced from anisotropy of magnetic susceptibility (AMS) measurements, with the crystallographic and shape fabrics, obtained from lattice-preferred orientation (LPO) and shape-preferred orientation (SPO) measurements made using electron backscattered diffraction (EBSD) and 3D image analysis, respectively. Room-temperature hysteresis measurements, thermomagnetic curves and values of the bulk magnetic susceptibility reveal a magnetic mineralogy dominated by a mixed contribution of hemo-ilmenite and magnetite. The hemo-ilmenite grains display a LPO characterized by a strong preferred orientation of the basal (0001) plane of ilmenite along which hematite was exsolved. This LPO and the magnetic fabric fit well (angle between the crystallographic c-axis and the axis of minimum susceptibility ≤ ca. 15° for most samples), and the latter is thus strongly influenced by the hemo-ilmenite magneto-crystalline anisotropy. A magnetite SPO, concordant with the hemo-ilmenite LPO, may also influence and even dominate the magnetic fabric. The rock shape fabric is coaxial with the magnetic fabric that can thus be used to perform detailed structural mapping. Interpretation of the magnetic fabric and field structural data suggests that the Lac Tio ore body would be a sag point at the margin of the Lac Allard anorthosite, deformed by ballooning during the final stage of diapiric emplacement of the anorthosite body.

L’auteur analyse les rapports objectifs et subjectifs que des éleveurs nomades vivant dans l’ouest de la Mongolie entretiennent avec une portion de territoire qu’ils nomment leur « pays natal » (törsön nutag). L’attachement à ce lieu n’est pas seulement établi à la naissance, il s’actualise et se développe à travers des actions rituelles quotidiennes, occasionnelles et annuelles. L’auteur aborde les libations quotidiennes destinées aux esprits du territoire, les offrandes faites à ces esprits au camp d’hiver pendant les célébrations du Nouvel An, et l’effacement de certaines traces sur le sol lors de déménagements. Il s’agit de montrer que des actions rituelles véhiculent une certaine idée de fixité et d’ancrage dans le territoire alors que la mobilité est au cœur de l’élevage extensif de moutons et de chèvres pratiqué par les éleveurs. Cet article vise à montrer que mouvement et fixité sont complémentaires dans l’attachement au pays natal. The author analyses the objective and subjective relationships that nomadic herders living in West Mongolia entertain with a part of land, which they call their “homeland” (törsön nutag). The attachment to the homeland is not only established at birth, but also actualised and developed through daily, occasional and annual ritual actions. The author describes the daily libations to the spirits of the land, the offerings made to these spirits at the winter encampment during the New Year celebrations and the erasing of some traces left on the ground when the herders move to another pasture. Some ritual practices convey an idea of fixity and rooting in the land whereas mobility is at the heart of the extensive rearing of sheep and goats. This article aims at showing that movement and fixity are complementary aspects of the attachment to the land.