¹Johannes M.Meusburger,¹Martin Ende,¹Philipp Matzinger,¹Dominik Talla,¹Ronald Miletich,¹Manfred Wildner
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113459]
¹Institut für Mineralogie und Kristallographie, Althanstraße 14, 1090 Wien, Austria
Copyright Elsevier

The high-pressure behaviour of hydrated magnesium sulfate kieserite, MgSO₄⋅H₂O, has been investigated on isothermal compression at T = 295 K up to 8.3 GPa hydrostatic pressure. The crystal properties of synthetic endmember single crystals were investigated using a high-pressure diamond anvil cell by means of in-situ X-ray diffraction and vibrational spectroscopy methods. The experimental study reveals a second-order phase transition from the monoclinic (C2/c) α-phase to a triclinic (P 1¯) β-form at a transition pressure of 2.72 GPa. Elastic properties as determined from precise lattice parameters yield static elasticities as described by third-order Birch-Murnaghan equations of state with V₀ = 355.5(4) ų, K₀ = 48.1(5) GPa, K’ = 8.1(6) for the low-pressure polymorph (α-MgSO₄⋅H₂O), and V₀ = 355.8(1.8) ų, K₀ = 49.3(5.5) GPa, K’ = 4.8(1.0) for the high-pressure polymorph (β-MgSO₄⋅H₂O). The nature of the phase transition and its reversibility on pressure release make it seem unlikely that the β-polymorph can be recovered at surface conditions on any icy satellite, although in the context of impact events it is proposed to exist, but only on a limited time scale before re-transforming to α-MgSO₄⋅H₂O. With respect to the icy mantles of Ganymede and Callisto, the depth profile of Ganymede following the established thermal gradients suggest a stability field only for α-MgSO₄⋅H₂O being relevant to the presumable conditions in the icy mantle. In contrast, the depth profile for Callisto, as corresponding to maximum pressures of approximately 5 GPa, crosses the α-to-β-transition boundary and make the high-pressure polymorph a promising candidate rock-forming mineral for the deep icy mantle of the outermost Galilean moon. In particular the material parameters reported for the α and β form of MgSO₄⋅H₂O are fundamental to compute the icy mantle dynamics and accurately determine the radial density structure in models of Ganymede and Callisto.

¹Emily J.Foote,¹David A.Paige,²Michael K.Shepard,³Jeffrey R.Johnson,⁴Stuart Biggar
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113456]
¹University of California Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567
²Bloomsburg University, 400 E. Second St., Bloomsburg, PA 17815, Bloomsburg, PA
³Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, 200-W230, Laurel, MD 20723-6005
⁴College of Optical Sciences, University of Arizona, 1630 E. University Blvd., P.O. Box 210094, Tucson, AZ 85721-0094
Copyright Elsevier

We have acquired a comprehensive laboratory bidirectional measurements of Apollo 11 and Apollo 16 lunar soil samples and have successfully fit photometric models to the laboratory data and have determined the solar spectrum averaged hemispheric reflectance as a function of incidence angle. The Apollo 11 (sample 10084) and 16 (sample 68810) soil samples are two representative end member samples from the Moon, dark lunar maria and bright lunar highlands. We used our solar spectrum averaged albedos in a thermal model and compared our model-calculated normal bolometric infrared emission curves with those measured by the LRO Diviner Lunar Radiometer Experiment. We found excellent agreement at the Apollo 11 site, but at the Apollo 16 site, we found that the albedos we measured in the laboratory were 33% brighter than those required to fit the Diviner infrared data. We attribute this difference at Apollo 16 to increased compaction and decreased maturity of the laboratory sample relative to the natural lunar surface, and to local variability in surface albedos at the Apollo 16 field area that are below the spatial resolution of Diviner.

¹Gregory J.Archer,¹Gregory A.Brennecka,² Philipp Gleißner,³Andreas Stracke,²Harry Becker,¹Thorsten Kleine
Earth and Planetary Science Letters 528, 115841 Link to Article [https://doi.org/10.1016/j.epsl.2019.115841]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
²Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstrasse 74-100, 12249 Berlin, Germany
³Institut für Mineralogie, University of Münster, Corrensstrasse 24, 48149 Münster, Germany
Copyright Elsevier

We report ¹⁸²W and ¹⁴²Nd isotopic compositions, ¹⁸⁷Re–¹⁸⁷Os systematics, and abundances of highly siderophile elements (HSE: Re, Os, Ir, Ru, Rh, Pt, Pd, and Au) for a suite of komatiites and basalts from the ∼3.3Ga Ruth Well Formation and the ∼3.45Ga Warrawoona Group of the Pilbara Craton, Western Australia. The ¹⁸²W compositions from all samples are indistinguishable from each other, and more radiogenic than modern bulk silicate Earth, with a mean μ¹⁸²W value of +9.1±4.2 (2SD). By contrast, the ¹⁴²Nd values for all samples are indistinguishable from each other and terrestrial standards, with a mean μ¹⁴²Nd value of −1.6±3.2 (2SD). The ¹⁴⁶Sm–¹⁴²Nd and ¹⁸⁷Re–¹⁸⁷Os systematics are consistent with chondritic Sm/Nd and Re/Os ratios in the mantle source during the lifetime of ¹⁸²Hf, and the observed ¹⁸²W excesses therefore cannot be accounted for by early Hf–W fractionation by magma ocean processes, neither by silicate liquid-crystal fractionation nor by high P–T metal-silicate equilibration. The estimated abundances of HSE in the mantle source, however, are significantly lower than modern bulk silicate Earth, with only 51±9% (1SD) of modern bulk silicate Earth abundances. These results are consistent with a partial lack of late-accreted material within the Pilbara source at ∼3.3Ga to account for the ¹⁸²W excesses. Further, widespread ¹⁸²W excesses of similar magnitude in other Archean mantle-derived rocks worldwide strongly suggests that a common process, most likely incomplete addition of late-accreted material, was responsible. The apparent mismatch between late-accreted ¹⁸²W–HSE systematics for some other localities likely reflects either the inherent difficulties associated with estimating source HSE abundances, and/or dissociation of W and HSE by mantle processes. Finally, the combined average ¹⁸²W–HSE systematics of Archean samples indicate that the pre-late accretion BSE likely had a μ¹⁸²W value similar to that of the lunar mantle, which strongly suggests post-giant impact Earth–Moon equilibration and indicates that the Moon formed after ¹⁸²Hf extinction.

¹Hill, P.J.A.,¹Banerjee, N.R.,^1,2Ali, A.,¹Jabeen, I.,¹Osinski, G.R.,¹Longstaffe, F.J.
Journal of Mass Spectrometry 54, 667-675 Link to Article [DOI: 10.1002/jms.4381]
¹Department of Earth Sciences and Centre for Planetary Science and Exploration, The University of Western Ontario, 1151 Richmond Street N, London, ON N6A 5B7, Canada
²Earth Sciences Research Centre (ESRC), Sultan Qaboos University (SQU), Al-Khoudh, Muscat, Oman

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¹Balan, E.,¹Créon, L.,¹Sanloup, C.,¹Aléon, J.,²Blanchard, M.,¹Paulatto, L.,¹Bureau, H.
Chemical Geology 525, 424-434 Link to Article [DOI: 10.1016/j.chemgeo.2019.07.032]
¹Sorbonne Université, CNRS, IRD, MNHN, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), 4 place Jussieu, Paris cedex 05, 75252, France
²Géosciences Environnement Toulouse (GET), Observatoire Midi-Pyrénées, Université de Toulouse, CNRS, IRD, UPS, 14 avenue E. Belin, Toulouse, 31400, France

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^1,2Run-Lia Pang,²Dennis Harries,¹Kilian Pollok,^1,3Ai-Cheng Zhang,^2,4Falko Langenhorst
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125541]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China
²Institute of Geosciences, Friedrich Schiller University Jena, D-07745 Jena, Germany
³CAS Center for Excellence in Comparative Planetology, China
⁴Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawai’i 96822, USA
Copyright Elsevier

Shock-induced Ti-rich melt pockets in a basaltic eucrite Northwest Africa (NWA) 8003 were studied using scanning and transmission electron microscopy. Unique mineral assemblages consisting of clinopyroxene, ilmenite, vestaite, corundum, and kyanite are observed. Among them, vestaite and corundum in NWA 8003 are first reported to occur in eucrite meteorites. Petrographic and chemical evidences indicate that the Ti-rich melt pockets have formed by in-situ melting of ilmenite, plagioclase, pyroxene, and possibly minor silica and apatite nearby. The temperature rise and melting were caused by the high shock impedance contrast at interfaces between ilmenite and other phases with a distinctly lower density. Crystallization pressure, temperature and cooling time of the Ti-rich melt pockets in NWA 8003 are constrained to be ∼0.9–∼10 GPa, ∼1300–∼1730 °C, and < 1 ms (5–50 μm in size), respectively.

¹Doreen Schmidt,¹ Kilian Pollok,² Gabor Matthäus,²Stefan Nolte,^1,3FalkoLangenhorst
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125542]
¹Institute of Geoscience, Friedrich Schiller University, Carl-Zeiss-Promenade 10, 07745, Jena, Germany
²Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University, Albert-Einstein-Straße 15, 07745, Jena, Germany
³Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawai’i, 96822, USA
Copyright Elsevier

Space weathering by micrometeoroid bombardment is a cosmic phenomenon on atmosphere-free celestial bodies, a process that is expected to particularly overprint planetesimals and cosmic dust in debris discs. We reproduced micrometeoroid impact craters by femtosecond pulsed laser irradiation on oriented enstatite single crystals (En₉₃Fs₇) to investigate the deformation behavior and its orientation dependence. All microcraters show typical bowl shaped morphologies, a glass surface layer with splash like ejecta material and subsurface layering. Although we could reproduce melting and vaporization as typical space weathering effects in the enstatite experiments, there is no formation of agglutinate particles or metallic nanoparticles (npFe⁰). The shock effects in the deformation layer consist of planar structures like microfractures and cleavages, amorphous lamellae, stacking faults and clinoenstatite lamellae. Their activation and/or orientation depends on the shock direction. In special orientations we observe the activation of glide systems along specific low indexed crystallographic planes. Due to the short timescale and the high strain rates, the most prominent effect is the failure of enstatite by microfracturing along non-rational crystallographic planes. Common deformation mechanisms reported in meteorites like the formation of clinoenstatite lamellae via shearing along [001] (100) occur less frequently. Shear is apparently the dominant mechanism in the formation of the above-mentioned effects and causes also their modification by frictional heating. The wide-spread formation of amorphous lamellae is, for example, interpreted to be the result of this shear heating along planar structures. We interpret this unconventional deformation behavior as a consequence of the small spatial and temporal scale of the experiments, resulting in a short-lived spherical shock wave with high deviatoric stresses in contrast to a long pressure pulse and quasi-hydrostatic compression in large scale impacts that produce typical shock features.

¹M.Gellissen,¹A.Holzheid,¹Ph.Kegler,²H.Palme
Geochemistr< (Chemie der Erde)  (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125540]
¹Institut für Geowissenschaften, Universität Kiel, Germany
²Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt / Main, Germany
Copyright Elsevier

We have studied the evaporation of Na, K and Mn from Al-Na-K- and Mn-rich silicate at various conditions. Total alkali oxide contents ranged from 5 to 20%. The evaporation rate of Na increases with temperature and decreasing oxygen fugacity and decreases with duration of heating. The loss of K is in all cases less pronounced than for Na. Heating in an evacuated vacuum furnace is more effective in removing Na and K from melt droplets than in furnaces with one atm gas flow of air or gas mixtures controlling the oxygen fugacity. The strong pumping required to keep the vacuum removes Na and K atoms very effectively. In all experiments, the rate of evaporation is determined by quasi-equilibrium between a thin layer of Na and K rich gas above the molten silicates. The results of the experiments are in agreement with several other studies.

In experiments with more than one sample in the furnace, equilibration of Na- and K-rich samples with Na- and K-poor samples occurred rapidly, mediated by the ambient gas phase.

The results of experiments with Mn in starting compositions showed much stronger losses of Na than Mn under a variety of conditions.

Thus the nearly chondritic Mn/Na ratios in the Earth cannot be the result of evaporation of Na and Mn in Earth-making materials, as the Mn/Na ratios in evaporation residues would be much higher than chondritic ratios. Such evaporation processes may have occurred in the parent material of Moon, Vesta and Mars.

The data suggest, in agreement with earlier hypotheses, that the high and variable contents of Na and K in chondrules require a gas phase high in Na and K equilibrating with chondrule melts. The volume of nebular gas parental to a certain type of chondrites was heated and Na and K were lost from the chondrule precursors to the gas phase. Subsequently the nebular parcel was compressed leading to higher partial pressures of Na and K. Flash heating then produced chondrule melts which incorporated some of the gaseous Na and K and then cooled rapidly. The large range of Na and K contents in chondrule melts reflects very local enrichments of Na and K in the gas phase. Despite these variations bulk chondritic meteorites have well defined bulk Na and K contents, implying a closed system during formation of chondrule and matrix.