During the last week of this year, Cosmochemistry Papers will be on Christmas break. Normal service will commence on January, 2nd, after we have recovered.

Merry Christmas & Happy New Year to everyone and see you in 2019 !

¹A. J. King, ¹S. S. Russell, ¹P. F. Schofield, ²E. R. Humphreys‐Williams, ²S. Strekopytov, ³F. A. J. Abernethy, ³A.B. Verchovsky, ³M. M. Grady
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13224]
¹Planetary Materials Group, Department of Earth Sciences, Natural History Museum, , London, SW7 5BD UK
²Imaging and Analysis Centre, Natural History Museum, , London, SW7 5BD UK
³Department of Physical Sciences, The Open University, , Walton Hall, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

Jbilet Winselwan is one of the largest CM carbonaceous chondrites available for study. Its light, major, and trace elemental compositions are within the range of other CM chondrites. Chondrules are surrounded by dusty rims and set within a matrix of phyllosilicates, oxides, and sulfides. Calcium‐ and aluminum‐rich inclusions (CAIs) are present at ≤1 vol% and at least one contains melilite. Jbilet Winselwan is a breccia containing diverse lithologies that experienced varying degrees of aqueous alteration. In most lithologies, the chondrules and CAIs are partially altered and the metal abundance is low (<1 vol%), consistent with petrologic subtypes 2.7–2.4 on the Rubin et al. (2007) scale. However, chondrules and CAIs in some lithologies are completely altered suggesting more extensive hydration to petrologic subtypes ≤2.3. Following hydration, some lithologies suffered thermal metamorphism at 400–500 °C. Bulk X‐ray diffraction shows that Jbilet Winselwan consists of a highly disordered and/or very fine‐grained phase (73 vol%), which we infer was originally phyllosilicates prior to dehydration during a thermal metamorphic event(s). Some aliquots of Jbilet Winselwan also show significant depletions in volatile elements such as He and Cd. The heating was probably short‐lived and caused by impacts. Jbilet Winselwan samples a mixture of hydrated and dehydrated materials from a primitive water‐rich asteroid. It may therefore be a good analog for the types of materials that will be encountered by the Hayabusa‐2 and OSIRIS‐REx asteroid sample‐return missions.

¹. B. Verchovsky, ²S. A. Hunt, ³W. Montgomery, ³M. A. Sephton
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13231]
¹School of Physical Sciences, The Open University, , Walton Hall, Milton Keynes, MK7 6AA, UK
²Department of Earth Sciences, University College London, , London, WC1E 6BT, UK
³ Geochemistry Laboratory, Imperial College London, , London, SW7 2AZ, UK
Published by arrangement with John Wiley & Sons

Planetary noble gases in chondrites are concentrated in an unidentified carrier phase, called “Q.” Phase Q oxidized at relatively low temperature in pure oxygen is a very minor part of insoluble organic matter (IOM), but has not been separated in a pure form. High‐pressure (HP) experiments have been used to test the effects of thermal metamorphism on IOM from the Orgueil (CI1) meteorite, at conditions up to 10 GPa and 700 °C. The effect of the treatment on carbon structural order was characterized by Raman spectroscopy of the carbon D and G bands. The Raman results show that the IOM becomes progressively more graphite‐like with increasing intensity and duration of the HP treatment. The carbon structural transformations are accompanied by an increase in the release temperatures for IOM carbon and ³⁶Ar during stepped combustion (the former to a greater extent than the latter for the most HP treated sample) when compared with the original untreated Orgueil (CI1) sample. The ³⁶Ar/C ratio also appears to vary in response to HP treatment. Since ³⁶Ar is a part of Q, its release temperature corresponds to that for Q oxidation. Thus, the structural transformations of Q and IOM upon HP treatment are not equal. These results correspond to observations of thermal metamorphism in the meteorite parent bodies, in particular those of type 4 enstatite chondrites, e.g., Indarch (EH4), where graphitized IOM oxidized at significantly higher temperatures than Q (Verchovsky et al. 2002). Our findings imply that Q is less graphitized than most of the macromolecular carbonaceous material present during parent body metamorphism and is thus a carbonaceous phase distinct from other meteoritic IOM.

^1,2B.Laurent,¹C.R.Cousins,²M.Gunn,²C.Huntly,²R.Cross,^1,2E.Allender
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.12.031]
¹School of Earth and Environmental Sciences, North Street, University of St Andrews, St Andrews, Fife, UK, KY16 9AL
²Institute for Mathematics and Physics, Aberystwyth University, Aberystwyth
Copyright Elsevier

Detection of organic matter is one of the core objectives of future Mars exploration. The ability to probe rocks, soils, and other geological substrates for organic targets is a high priority for in situ investigation, sample caching, and sample return. UV luminescence – the emission of visible light following UV irradiation – is a tool that is beginning to be harnessed for planetary exploration. We conducted  UV photoluminescence analyses of (i) Mars analogue sediments doped with polyaromatic hydrocarbons (PAHs; <15 ppm), (ii) carbonaceous CM chondrites and terrestrial kerogen (Type IV), and (iii) synthetic salt crystals doped with PAHs (2 ppm). We show that that detection of PAHs is possible within synthetic and natural gypsum, and synthetic halite. These substrates show the most apparent spectral modifications, suggesting that the most transparent minerals are more conducive to UV photoluminescence detection of trapped organic matter. Iron oxide, ubiquitously present on Mars surface, hampers but does not completely quench the UV luminescence emission. Finally, the maturity of organic carbonaceous material influences the luminescence response, resulting in a reduced signal for UV excitation wavelengths down to 225 nm. This study demonstrates the utility of UV luminescence spectroscopy for the analysis of mixed organic-inorganic materials applicable to Mars exploration.

¹Vivian Z. Sun et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.12.030]
¹Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109
Copyright Elsevier

Concretions are prevalent features in the generally lacustrine deposits of the Murray formation in Gale crater. In this work, we document the morphologic, textural, and chemical properties of these concretions throughout 300 meters of Murray formation stratigraphy from Mars Science Laboratory observations between Sols 750-1900. We interpret these observations to constrain the timing and composition of post-depositional fluid events at Gale crater. We determine that the overall diversity of concretion morphology, size, texture, and chemistry throughout the Murray formation indicates that concretions formed in multiple, likely late diagenetic, episodes with varying fluid chemistries. Four major concretion assemblages are observed at distinct stratigraphic intervals and approximately correlate with major distinct chemical enrichments in Mg-S-Ni-Cl, Mn-P, and Ca-S, among other local enrichments. Different concretion size populations and complex relationships between concretions and veins also suggest multiple precipitation events at Gale crater. Many concretions likely formed during late diagenesis after sediment compaction and lithification, based on observations of concretions preserving primary host rock laminations without differential compaction. An upsection decrease in overall concretion size corresponds to an inferred upsection decrease in porosity and permeability, thus constraining concretion formation as postdating fluid events that produced initial cementation and porosity loss. The combined observations of late diagenetic concretions and distinct chemical enrichments related to concretions allow constraints to be placed on the chemistry of late stage fluids at Gale crater. Collectively, concretion observations from this work and previous studies of other diagenetic features (veins, alteration halos) suggest at least six post-depositional events that occurred at Gale crater after the deposition of the Murray formation.

¹Melissa Sims et al.(>10)
Earth and Planetary Science Letters 507, 166-174 Link to Article [https://doi.org/10.1016/j.epsl.2018.11.038]
¹Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA
Copyright Elsevier

The pressure-induced amorphization of the two endmembers of the plagioclase ((Na_1−xCa_x)Al_1+xSi_3−xO₈) solid-solution, anorthite (CaAl₂Si₂O₈) and albite (NaAlSi₃O₈), has been studied as a function of compression rate by means of time-resolved powder diffraction. Anorthite and albite were compressed in a diamond anvil cell to 80 GPa at multiple rates from 0.05 GPa/s to 80 GPa/s. The amorphization pressure decreases with increasing compression rate. This negative strain rate sensitivity indicates a change in deformation mechanism in the plagioclase solid-solution endmembers from brittle to ductile with increasing compression rate. The presented data support the previously proposed shear deformation mechanism for the amorphization of plagioclase. Furthermore, amorphization progresses over a wide pressure range suggesting heterogeneous amorphization, similar to observations based on recovered material from shock-compression experiments of plagioclase. Our experiments support the contention that amorphization pressures for plagioclase may occur at lower pressures than usually considered.

¹Tim Lichtenberg, ²Tobias Keller,³Richard F.Katz,⁴Gregor J.Golabek,¹Taras V.Gerya
Earth and Planetary Science Letters 507, 154-165 Link to Article [https://doi.org/10.1016/j.epsl.2018.11.034]
¹Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland
²Department of Geophysics, Stanford University, Stanford, CA 94305, United States
³Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, United Kingdom
⁴Bayerisches Geoinstitut, University of Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany
Copyright Elsevier

Rocky planetesimals in the early solar system melted internally and evolved chemically due to radiogenic heating from ²⁶Al. Here we quantify the parametric controls on magma genesis and transport using a coupled petrological and fluid mechanical model of reactive two-phase flow. We find the mean grain size of silicate minerals to be a key control on magma ascent. For grain sizes ≳1 mm, melt segregation produces distinct radial structure and chemical stratification. This stratification is most pronounced for bodies formed at around 1 Myr after formation of Ca, Al-rich inclusions. These findings suggest a link between the time and orbital location of planetesimal formation and their subsequent structural and chemical evolution. According to our models, the evolution of partially molten planetesimal interiors falls into two categories. In the magma ocean scenario, the whole interior of a planetesimal experiences nearly complete melting, which would result in turbulent convection and core–mantle differentiation by the rainfall mechanism. In the magma sill scenario, segregating melts gradually deplete the deep interior of the radiogenic heat source. In this case, magma may form melt-rich layers beneath a cool and stable lid, while core formation would proceed by percolation. Our findings suggest that grain sizes prevalent during the internal heating stage governed magma ascent in planetesimals. Regardless of whether evolution progresses toward a magma ocean or magma sill structure, our models predict that temperature inversions due to rapid ²⁶Al redistribution are limited to bodies formed earlier than ≈1 Myr after CAIs. We find that if grain size was ≲1 mm during peak internal melting, only elevated solid–melt density contrasts (such as found for the reducing conditions in enstatite chondrite compositions) would allow substantial melt segregation to occur.

¹Yann-Aurélien Brugier, ¹Jean Alix Barrat,²Bleuenn Gueguen, ¹Arnaud Agranier, ^3,4Akira Yamaguchi, ⁵Addi Bischoff
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.12.009]
¹Laboratoire Géosciences Océan (UMR CNRS 6538), Université de Bretagne Occidentale et Institut Universitaire Européen de la Mer, Place Nicolas Copernic, 29280 Plouzané, France
²UMS CNRS 3113, Université de Bretagne Occidentale et Institut Universitaire Européen de la Mer, Place Nicolas Copernic, 29280 Plouzané, France
³National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
⁴Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (the Graduate University for Advanced Studies), Tokyo 190-8518, Japan
⁵Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

The Ureilite Parent Body (UPB) was a C-rich planetary embryo disrupted by impact. Ureilites are fragments of the UPB mantle and among the most numerous achondrites. Zinc isotopic data are presented for 26 unbrecciated ureilites and a trachyandesite (ALM-A) from the same parent body. The δ66Zn values of ureilites range from 0.40 to 2.71 ‰ including literature results. Zinc isotopic compositions do not correlate with the compositions of olivine cores, with C and O isotopic compositions, with Zn abundances, nor with shock grades. The wide range of δ66Zn displayed by the ureilites is chiefly explained by evaporation processes that took place during the catastrophic breakup of the UPB. During breakup, the high temperatures of the UPB mantle allowed Zn to evaporate, regardless of the intensity the shock suffered by the ureilitic debris. For the most shocked of them, post-shock heating permitted greater evaporation, and heavier Zn isotopic compositions. The surface of the UPB was certainly much colder than the mantle before the breakup. Therefore, crustal rocks were probably less prone to Zn evaporation. ALM-A, the sole crustal rock analyzed at present, has a δ66Zn value (0.67 ‰) significantly higher than those of regular chondrites. This result indicates that its mantle source displayed already non-chondritic Zn isotopic compositions before the breakup of the UPB.

¹S.Marchi et al. (>10)*
Nature Astronomy (in Press) Link to Article [https://doi.org/10.1038/s41550-018-0656-0]
¹Southwest Research Institute, Boulder, CO, USA

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^1,2Haruna Sugahara,¹Yoshinori Takano,³Yuzuru Karouji,⁴Kazuya Kumagai,³Toru Yada,¹Naohiko Ohkouchi,³ Masanao Abe and Hayabusa2 project team
Earth, Planets and Space 70, 194 Link to Article [https://doi.org/10.1186/s40623-018-0965-7]
¹Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsushima, Yokosuka 237-0061, Japan
²Institut de Chimie de Nice, Université Côte d’Azur, CNRS, UMR 7272, 28 Avenue Valrose, 06108 Nice, France
³Japan Aerospace Exploration Agency (JAXA), Yohinodai, Sagamihara 252-5210, Japan
⁴Marine Works Japan Ltd., Oppamahigashi, Yokosuka 237-0063, Japan

We currently do not have a copyright agreement with this publisher and cannot display the abstract here