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

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

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

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

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.

¹Hans-Peter Gail, ^2,3Mario Trieloff
Astronomy & Astrophysics 615, A147 Link to Article [https://doi.org/10.1051/0004-6361/201732456]
¹Zentrum für Astronomie, Institut für Theoretische Astrophysik, Heidelberg University, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
e-mail: gail@uni-heidelberg.de
²Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany
e-mail: Mario.Trieloff@geow.uni-heidelberg.de
³Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany

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

Peter Fawdon^a, Sanjeev Gupta^b, Joel M. Davis^c, Nicholas H. Warner^d, Jacob B. Adler^e, Matthew R. Balme^a, James F. Bell III^e, Peter M. Grindrod^c, Elliot Sefton-Nash^f
Earth and Planetary Science Letters 503, 88-94 Link to Article [https://doi.org/10.1016/j.epsl.2018.07.040]
^aSchool of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
^bDepartment of Earth Sciences and Engineering, Imperial College London, London, SW7 2AZ, UK
^cDepartment of Earth Sciences, Natural History Museum, Cromwell Road, Kensington, London, SW7 5BD, UK
^dDepartment of Geological Sciences, Integrated Science Center, State University of New York at Geneseo, One College Circle, Geneseo, NY 14454, USA
^eSchool of Earth and Space Exploration, Arizona State University, ISTB4 Room 795, 781 Terrace Mall, Tempe, AZ 85287, USA
^fEuropean Space Research and Technology Centre, Keplerlaan 1, 2201 AZ Noordwijk, Netherlands
Copyright Elsevier

One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars’ dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km²). This has an extensive catchment (<span id="MathJax-Element-1-Frame" class="MathJax_SVG" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.399999618530273px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml=""
4.6×105 km2) incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (∼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend ∼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia – an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perhaps even an ocean that filled the northern plains of Mars.

Ming CHEN^1,2, Jinfu SHU³, Xiande XIE^2,4, and Dayong TAN^2,4
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13222]
¹State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640Guangzhou, China
²Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640Guangzhou, China
³Center for High Pressure Science and Technology Advanced Research, 201203 Shanghai, China
⁴Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, China
Published by arrangement with John Wiley & Sons

Maohokite, a post‐spinel polymorph of MgFe₂O₄, was found in shocked gneiss from the Xiuyan crater in China. Maohokite in shocked gneiss coexists with diamond, reidite, TiO₂‐II, as well as diaplectic glasses of quartz and feldspar. Maohokite occurs as nano‐sized crystallites. The empirical formula is (Mg_0.62Fe_0.35Mn_0.03)²⁺Fe³⁺₂O₄. In situ synchrotron X‐ray microdiffraction established maohokite to be orthorhombic with the CaFe₂O₄‐type structure. The cell parameters are a = 8.907 (1) Å, b = 9.937(8) Å, c = 2.981(1) Å; V = 263.8 (3) ų; space group Pnma. The calculated density of maohokite is 5.33 g cm⁻³. Maohokite was formed from subsolidus decomposition of ankerite Ca(Fe²⁺,Mg)(CO₃)₂ via a self‐oxidation‐reduction reaction at impact pressure and temperature of 25–45 GPa and 800–900 °C. The formation of maohokite provides a unique example for decomposition of Fe‐Mg carbonate under shock‐induced high pressure and high temperature. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2017‐047). The mineral was named maohokite after Hokwang Mao, a staff scientist at the Geophysical Laboratory, Carnegie Institution of Washington, for his great contribution to high pressure research.

M. D. SUTTLE^1,2,3, M. J. GENGE^1,2, L. FOLCO³, M. VAN GINNEKEN^4,5, Q. LIN1,S. S. RUSSELL², and J. NAJORKA²
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13220]
¹Department of Earth Science and Engineering, Imperial College London, South Kensington, London SW7 2AZ, UK
²Department of Earth Science, The Natural History Museum, Cromwell Rd, London SW7 5BD, UK
³Dipartimento di Scienze della Terra, Universita di Pisa, 56126 Pisa, Italy
⁴Analytical, Environmental and Geo-Chemistry (AMGC), Vrije Universiteit Brussel, Av. F.D. Roosevelt 50,1050 Brussels, Belgium
⁵Laboratoire G-Time, Universite Libre de Bruxelles, Franklin Rooseveltlaan 50, 1050 Brussels, Belgium
Published by arrangement with John Wiley & Sons

The early stages of atmospheric entry are investigated in four large (250–950 μm) unmelted micrometeorites (three fine‐grained and one composite), derived from the Transantarctic Mountain micrometeorite collection. These particles have abundant, interconnected, secondary pore spaces which form branching channels and show evidence of enhanced heating along their channel walls. Additionally, a micrometeorite with a double‐walled igneous rim is described, suggesting that some particles undergo volume expansion during entry. This study provides new textural data which links together entry heating processes known to operate inside micrometeoroids, thereby generating a more comprehensive model of their petrographic evolution. Initially, flash heated micrometeorites develop a melt layer on their exterior; this igneous rim migrates inwards. Meanwhile, the particle core is heated by the decomposition of low‐temperature phases and by volatile gas release. Where the igneous rim acts as a seal, gas pressures rise, resulting in the formation of interconnected voids and higher particle porosities. Eventually, the igneous rim is breached and gas exchange with the atmosphere occurs. This mechanism replaces inefficient conductive rim‐to‐core thermal gradients with more efficient particle‐wide heating, driven by convective gas flow. Interconnected voids also increase the likelihood of particle fragmentation during entry and, may therefore explain the rarity of large fine‐grained micrometeorites among collections.