¹Mangold et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.11.004]
¹Laboratoire de Planétologie et Géodynamique, CNRS, UMR 6112, Université de Nantes, Université d’Angers, Nantes, France
Copyright Elsevier

From Sol 750 to 1550, the Curiosity rover documented >100 m thick stack of fine-grained sedimentary rocks making up part of the Murray formation, at the base of Mt Sharp, Gale crater. Here, we use data collected by the ChemCam instrument to estimate the level of chemical weathering in these sedimentary rocks. Both the Chemical Index of Alteration (CIA) and the Weathering Index Scale (WIS) indicate a progressive increase in alteration up section, reaching values of CIA of 63 and WIS of 25%. The increase in CIA and WIS values is coupled with a decrease in calcium abundance, suggesting partial dissolution of Ca-bearing minerals (clinopyroxene and plagioclase). Mineralogy from the CheMin X-ray diffraction instrument indicates a decrease in mafic minerals compared with previously analyzed strata and a significant proportion of phyllosilicates consistent with this interpretation. These observations suggest that the sediments were predominantly altered in an open system, before or during their emplacement, contrasting with the rock-dominated conditions inferred in sedimentary deposits analyzed at Yellowknife Bay.

^1,2J. Licandro, ^1,2,3M. Popescu, ^1,2J. de León, ^1,2D. Morate, ^4,1,2O. Vaduvescu,⁵ M. De Prá, ⁶Victor Ali-Laoga
Astronomy & Astrophysics 618, A170 Link to Article [https://doi.org/10.1051/0004-6361/201832853]
¹Instituto de Astrofísica de Canarias (IAC), CVía Láctea sn, 38205 La Laguna, Spain
²Departamento de Astrofísica, Universidad de La Laguna, 38206, La Laguna, Tenerife, Spain
³Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
⁴Isaac Newton Group of Telescopes, Apto. 321, Santa Cruz de la Palma, Canary Islands, Spain
⁵Departamento de Astrofísica, Observatório Nacional, 20921-400, Rio de Janeiro Brazil
⁶Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany

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P. MANZARI¹, S. DE ANGELIS¹, M. C. DE SANCTIS¹, G. AGROSI², and G. TEMPESTA²
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13221]
¹Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, via Fosso del Cavaliere, 100–00133, Roma, Italy
²Dipartimento di Scienze della Terra e Geoambientali (DiSTeGeo), University of Bari, Via E. Orabona 4, 70125 Bari, Italy
Published by arrangement with John Wiley & Sons

Microimaging spectroscopy is going to be the new frontier for validating reflectance remote sensed data from missions to solar system bodies. In this field, microimaging spectroscopy of Martian meteorites can provide important and new contributions to interpret data that will be collected by next instruments onboard rover missions to Mars, such as for example Exomars‐2020/Ma_MISS spectrometer. In this paper, a slab from the Northwest Africa (NWA) 8657 shergottite was studied using the SPectral IMager (SPIM) microimaging spectrometer, in the visible‐infrared (VIS‐IR) range, with the aim to subsequently validate the spectral data by means of different independent techniques. The validation was thus carried out, for the first time, comparing SPIM spectral images, characterized by high spatial and spectral resolution, with mineralogical–petrological analyses, obtained by scanning electron microscopy (SEM). The suitability of the SPIM resolution to detect and map augite, pigeonite, maskelynite, and other minor phases as calcite, Ca‐phosphates, and troilite/pyrrhotite with no loss of information about mineral distribution on the slab surface, was ascertained. The good agreement found between spectral and mineralogical data suggests that spectral‐petrography of meteorites may be useful to support in situ investigations on Martian rocks carried out by MaMiss spectrometer during Exomars2020 mission. Moreover, micro spectral images could be also useful to characterize, in a nondestructive way, Martian meteorites and other rare minerals occurring in meteorites. The results obtained in this work represent not only a methodological contribution to the study of meteorites but furnish also elements to reconstruct the history of this sample. The finding of zoned pyroxene, symplectitic texture, amorphous phases as maskelynite, and Fe‐merrillite permits us to hypothesize four stages, i.e., (1) igneous formation of rimmed pyroxenes and other minerals, (2) retrograde metamorphism, (3) shock by impact, and (4) secondary minerals by terrestrial contamination.

^1,2G. Borisov, ¹A. A. Christou, ³F. Colas, ¹S. Bagnulo, ⁴A. Cellino, ⁵A. Dell’Oro
Astronomy & Astrophysics 618, A178 Link to Article [https://doi.org/10.1051/0004-6361/201732466]
¹Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Northern Ireland, UK
²Institute of Astronomy and NAO, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussée Blvd., 1784 Sofia, Bulgaria
³IMCCE, Observatoire de Paris, UPMC, CNRS UMR8028, 77 Av. Denfert-Rochereau, 75014 Paris, France
⁴INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese (TO), Italy
⁵INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy

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¹P.Vernazza et al. (>10)
Astronomy & Astrophysics 618, A154 Link to Article [https://doi.org/10.1051/0004-6361/201833477]
¹Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), Marseille, France

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Alexander N. Krot^a,b. Kazuhide Nagashima^a, Krisztián Fintor^c, ElemérPál-Molnár^c
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1021/j.gca.2018.11.002]
^aSchool of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, HI 96822, USA
^bGoethe University Frankfurt Altenhoeferallee 1, 60438 Frankfurt am Main, Germany
^c’Vulcano’ Petrology and Geochemistry Research Group, Department of Mineralogy Geochemistry and Petrology, Faculty of Science and Informatics, University of Szeged, Hungary
Copyright Elsevier

We report on the mineralogy, petrology, and in situ measured oxygen-isotope compositions of three Fluffy Type A Ca,Al-rich inclusions (FTA CAIs) and two amoeboid olivine aggregates (AOAs) from the CV3.1 carbonaceous chondrite Kaba. The FTA CAIs are aggregates of several inclusions composed of spinel, Al,Ti-diopside, and gehlenitic melilite replaced to various degrees by anorthite; they are surrounded by the Wark-Lovering rim layers made of spinel, anorthite, Al-diopside, and forsterite. One of FTA CAIs contains a relict ultrarefractory inclusion composed of Sc-rich Al,Ti-pyroxene, spinel, and Zr-rich oxides. The AOAs are aggregates of Ca- and/or Al-rich minerals (spinel, anorthite, and Al,Ti-diopside) surrounded by forsterite ± Fe,Ni-metal condensates; Fe,Ni-metal is almost entirely replaced by magnetite and Fe,Ni-sulfides. Neither the FTA CAIs nor the AOAs show evidence for being melted after aggregation, and contain very minor secondary alteration minerals resulted from fluid-rock interaction on the CV parent asteroid. These include magnetite, fayalite, hedenbergite, phyllosilicates, and Fe-bearing Ti-free Al-diopside; secondary anorthite of asteroidal origin is absent in Kaba CAIs and AOAs. There are large variations in Δ¹⁷O (deviation from the terrestrial fractionation line = δ¹⁷O – 0.52×δ¹⁸O) within the individual FTA CAIs and AOAs: anorthite and melilite are systematically ¹⁶O-depleted (Δ¹⁷O range from ∼ −14 to ∼ −2‰) relative to the uniformly ¹⁶O-rich forsterite and Al,Ti-diopside (Δ¹⁷O ∼ −25 to −20±2‰, 2σ). Scandium-rich Al,Ti-pyroxene has ¹⁶O-poor composition (Δ¹⁷O ∼ −4‰). Many anorthite and melilite analyses plot close to or along mass-dependent fractionation line with Δ¹⁷O of −1.5±1‰ (average ± 2SD) defined by the aqueously-formed magnetite and fayalite from Kaba, and, therefore, corresponding to Δ¹⁷O of an aqueous fluid that operated on the CV parent asteroid. We conclude that anorthite and probably melilite in the Kaba FTA CAIs and AOAs experienced postcrystallization oxygen-isotope exchange with this fluid. The similar process must have affected plagioclase/plagioclase mesostasis and probably melilite in refractory inclusions and chondrules from CV3 chondrites of higher petrologic types [e.g., Allende (CV_oxA3.6) and Efremovka (CV_red3.1–3.4)], which appear to have experienced higher temperature metasomatic alteration than Kaba and were subsequently metamorphosed.

We conclude that the carbonaceous chondrite anhydrous mineral (CCAM) line defined by oxygen-isotope compositions of whole-rock and mineral separates of Allende CAIs and having a slope of 0.94 is not the primary nebular line. Instead this line results from superposition of the nebular slope-1 line recorded by the primitive chondrule mineral (PCM) line, the mass-dependent fractionation line with slope of ∼0.5 defined by the secondary minerals, and the minerals which experienced oxygen-isotope exchange with an aqueous fluid.

C. C. Bedford^a, J. C. Bridges^b, S. P. Schwenzer^c, R. C. Wiens^d, E. B. Rampe^e, J. Frydenvang^f, P.J.Gasda^d
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1021/j.gca.2018.11.031]
^aSchool of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
^bLeicester Institute for Space and Earth Observation, University of Leicester, Leicester, LE1 7RH, UK
^cSchool of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
^dLos Alamos National Laboratory, Los Alamos, New Mexico, USA
^eNASA Johnson Space Centre, Houston, TX, USA
^fNatural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
Copyright Elsevier

The Mars Science Laboratory’s Chemistry and Camera (ChemCam) instrument suite on-board the Curiosity rover has analysed ∼1200 sedimentary targets during the mission up to sol 1482. These targets have included sedimentary rock, diagenetic features (e.g., fracture-associated alteration halos, mineral veins, nodules, and erosion resistant raised ridges), active aeolian fines, soils and float. We have isolated ChemCam geochemical trends relating to diagenetic features and alteration products from those of the sedimentary rock in order to identify the compositional characteristics of Gale crater’s sediment source regions. The effects of grain size variation on sedimentary unit geochemistry have been taken into account by grouping and analysing geological units according to grain size. With obvious diagenetic features removed from the database, and predominately isochemical aqueous alteration inferred for the Mt Sharp Group samples, we propose that source region composition is a stronger source of geochemical change between the Bradbury and Mt Sharp Groups than open-system alteration. Additionally, a lack of correlation between the Chemical Index of Alteration (CIA) values and SiO₂, MgO or FeO_T indicates that the slight increase in chemical weathering of the Mt Sharp Group sediments was insufficient to overprint sediment source compositional signatures. This has led to the identification of five unique igneous endmember compositions which we hypothesise to have contributed to Gale crater’s stratigraphic record. These endmembers are: (1) a subalkaline basalt, compositionally similar to the tholeiitic Adirondack Class basalts of Gusev crater, and dominant within the finer grained units up to the base of Mt Sharp; (2) a trachybasalt, mostly identified within conglomerate units from the Darwin waypoint to the base of Mt Sharp; (3) a potassium-rich volcanic source, determined from strong potassium enrichment and a high abundance of sanidine that is most dominant in the fluvial sandstones and conglomerates of the Kimberley formation; (4) a highly evolved, silica-rich igneous source that correlates with the presence of tridymite, and is recorded in the lacustrine mudstone of Mt Sharp’s Marias Pass locality; and, (5) a fractionated, relatively SiO₂-rich subalkaline basalt, seen to have influenced the composition of mudstone deposited in the lower part of the Mt Sharp Group. Endmembers (1), (2), (3), and (4) have previously been identified at specific waypoints along the rover’s traverse, but we show that their influence extends throughout Gale’s stratigraphic record. The occurrence of detected endmembers is also strongly correlated with stratigraphic position, which suggests changing sediment source regions with time. We conclude that Gale sediment provenances were much more varied than suggested by the largely homogenous, globally-distributed Martian basalt inferred from orbit, showing that complex magmatic assemblages exist within the ancient highland crust surrounding Gale.

¹N. Ysard, ¹A. P. Jones, ²K. Demyk, ¹T. Boutéraon, ¹M. Koehler
Astronomy & Astrophysics 617, A124 Link to Article [https://doi.org/10.1051/0004-6361/201833386]
¹Institut d’Astrophysique Spatiale, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bât. 121, 91405 Orsay cedex, France
e-mail: nathalie.ysard@ias.u-psud.fr
²Institut de Recherche en Astrophysique et Planétologie, CNRS, Université de Toulouse, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 4, France

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Scott HASSLER¹, Sandra BILLER², and Bruce M. SIMONSON³
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13223]
¹The Wilderness Society, One Kaiser Plaza, Oakland, California 94612, USA
²SNAP-Ed Program Manager, University of Wyoming Extension, 1000 E University Ave Dept. 3354, Laramie,Wyoming 82071, USA
³Geology Department, Oberlin College, Oberlin, Ohio 44074, USA
Published by arrangement with John Wiley & Sons

The ~2490 Ma DS4 impact layer in the Dales Gorge Member is the only bed in the Brockman Iron Formation (Hamersley Group, Western Australia) known to contain “splash form” impact spherules. At a newly discovered site in Munjina Gorge (MG), the internal stratigraphy of the DS4 impact layer differs from previously known occurrences; it ranges from 36 to 57 cm in total thickness and consists of two distinct subunits. The lower subunit contains abundant cobble‐ to boulder‐scale intraclasts and spherules supported by a finer matrix. We interpret this subunit as the product of poorly cohesive debris flows. The upper subunit is 11–15 cm of low‐density turbidites. The DS4 layer also consists of two newly recognized subunits at Yampire Gorge (YG). The lower subunit is rich in well‐sorted spherules, 0–22 cm thick, and comprises an unstratified bedform with an irregular or swaley upper surface. This is overlain by 2 dm‐scale, fine‐grained, irregularly laminated beds that we interpret as low density turbidites laterally equivalent to the upper subunit at MG. The bedform at YG could be the lateral equivalent of the debrite at MG, genetically related to the overlying turbidites, or a product of impact tsunami‐induced bottom return flow. Other DS4 layer sites that have debrites similar to the one at MG are geographically separated from one another by sites that both lack debrite facies and feature well‐sorted spherules like YG. These characteristics suggest the DS4 layer had a complex depositional history that generated multiple debrites.

S. B. Simon^a, A. N. Krot^b,f, K. Nagashima^b, L. Kööp^c,d, A. M. Davis^c,d,e
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1021/j.gca.2018.11.029]
^aInstitute of Meteoritics, University of New Mexico, Albuquerque, NM 87131
^bHawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822
^cDepartment of the Geophysical Sciences, The University of Chicago, 5734 S. Ellis Ave., Chicago, IL 60637
^dChicago Center for Cosmochemistry, The University of Chicago, 5734 S. Ellis Ave., Chicago, IL 60637
^eEnrico Fermi Institute, The University of Chicago, Chicago, IL 60637
^fGeoscience Institute / Mineralogy, Goethe University Frankfurt, Altenhoeferallee 1, 60438 Frankfurt am Main, Germany
Copyright Elsevier

We have found two refractory inclusions in the CO3.00 carbonaceous chondrite Dominion Range (DOM) 08006 that appear to be primary condensates from the early solar nebula. One, inclusion 56-1, contains the first four phases predicted to form by equilibrium gas-solid condensation: corundum; hibonite; grossite; and perovskite. The other, 31-2, contains nine predicted condensate phases: hibonite; grossite; perovskite; melilite; spinel; FeNi metal; diopside; forsterite; and enstatite. Except for melilite/spinel, the phases occur in the predicted sequence from core to rim of the inclusion, which has an irregular shape inconsistent with a molten stage. This inclusion preserves the most complete record of condensation in the early solar nebula that has yet been found. The physical evidence reported here supports equilibrium condensation calculations that predict the observed sequence as well as the assumptions upon which they are based, such as total pressure (∼10^–3 atm), bulk system composition (solar), and C-O-H proportions. All phases in both inclusions and the associated ferromagnesian silicates are ¹⁶O-rich, with Δ¹⁷O between –25 and –20‰, implying that this is the original composition of the vast majority of primary condensates and that ¹⁶O-poor compositions observed in many isotopically heterogeneous inclusions are largely due to subsequent isotopic exchange. While the nebula was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in Ca and Ti isotopic compositions indicate that some isotopic heterogeneity existed early and was preserved during condensation. Inclusion 31-2 did not incorporate live ²⁶Al and and has nucleosynthetic anomalies in the heavy Ca and Ti isotopes (i.e., δ⁴⁸Ca=4.3±1.9‰; δ⁵⁰Ti=8.8±2.0‰). In contrast, inclusion 56-1 has radiogenic ²⁶Mg excesses yielding a (²⁶Al/²⁷Al)₀ ratio of (1.0±0.1) × 10^–5and negative nucleosynthetic isotopic anomalies in Ca (δ⁴⁸Ca=–10.3±4.2‰) and Ti (δ⁵⁰Ti=–4.3±2.9‰). Thus, it represents a deviation from the mutual exclusivity relationship between ²⁶Al incorporation and large nucleosynthetic anomalies. The reservoirs in which these inclusions formed had similar O-isotopic and different Al-, Ca– and Ti-isotopic compositions, suggesting that while the CAI-forming region was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in Ca and Ti isotopic compositions indicate that some isotopic heterogeneity existed and was preserved during condensation.