^1,2Lu Pan, ^1,3Bethany L. Ehlmann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2017JE005461]
¹Division of Geological and Planetary Sciences, California Institute of TechnologyPasadena, CA, USA
²Laboratoire de Geologie de Lyon, Université Claude Bernard Lyon 1Villeurbanne, France
³Jet Propulsion Laboratory, California Institute of TechnologyPasadena, CA, USA
Published by Arrangement with John Wiley & Sons

Amazonian‐aged Lyot crater is the best‐preserved and deepest peak‐ring impact crater (diameter, D=220km) in the northern lowlands of Mars. Morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater. In this study, we analyze images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter (MRO) to investigate the mineralogical record in Lyot and its surroundings, which are presently enriched in ground ice, to understand the associated aqueous processes, their relative timing, and a possible role for ground ice in hydrous mineral formation. We find diverse hydrous minerals, including Fe/Mg phyllosilicates, chlorite, illite/muscovite and prehnite in Lyot crater walls, central peak, and ejecta, as well as in two craters to the west of Lyot. The exposure and distribution of the hydrous minerals suggests they are related to the impact process, either exposed by the excavation of hydrothermally altered rocks or formed through syn‐depositional hydrothermal alteration immediately after impacts. The Lyot impact induced channel formation to the north, but no mineralogical evidence of aqueous alteration associated with the channels is observed. The sinuous channels within Lyot, diverted by bedrock units with hydrous mineral detections, did not cause mineralization but likely represent the last stage of water activity in Lyot crater. The separate episodes of water activity indicate flow of liquid water on Mars’ surface during the Amazonian but limited to no aqueous alteration to generate hydrous minerals.

¹Arya Udry,²Esteban Gazel,³Harry Y. McSween Jr
Journal of Geophyisical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005602]
¹Department of Geoscience, University of Nevada, Las Vegas
²Department of Earth and Atmospheric Sciences, Cornell University
³Department of Earth and Planetary Sciences, University of Tennessee
Published by Arrangement with John Wiley & Sons

The recent discovery of some ancient evolved rocks in Gale crater by the Curiosity rover has prompted the hypothesis that continental crust formed in early martian history. Here we present petrological modeling that attempts to explain this lithological diversity by magma fractionation. Using the thermodynamical software MELTS, we model fractional crystallization of different martian starting compositions that might generate felsic igneous compositions like those analyzed at Gale crater using different variables, such as pressure, oxygen fugacities, and water content. We show that similar chemical and mineralogical compositions observed in Gale crater felsic rocks can readily be obtained through different degrees of fractional crystallization of basaltic compositions measured on the martian surface. The results suggest that Gale crater rocks may not represent true primary liquids as they possibly accumulated and/or fractionated feldspar. In terms of major element compositions and mineralogy, we found that the Gale crater felsic compositions are more similar to fractionated magmas produced in Earth’s intraplate volcanoes than to terrestrial felsic continental crust as represented by tonalite‐trondhjemite‐granodiorite (TTG) suites. We conclude that the felsic rocks in Gale crater do not represent continental crust, as it is defined on Earth.

^1,2A.Galiano et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.05.020]
¹IAPS-INAF, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
² Università degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica, 1, 00133 Rome, Italy
Copyright Elsevier

The dwarf planet Ceres is a heavily cratered rocky body, and complex craters with a central peak are widely observed on its surface. These types of craters form when a large body impacts the surface, generating extreme temperatures and pressures. During the impact event a large volume of rock is raised from the subsurface and a central uplift is formed. The material composing the central uplift is called crater central peak material (ccp) and the spectral analysis of such geologic areas can provide information about the composition of Ceres’ subsurface. Reflectance spectra of 32 ccps, acquired by the VIR spectrometer on board the NASA/Dawn spacecraft, were analysed and shows absorption bands located at about 2.7, 3.1, 3.4 and 4.0 µm which are also common on the Cerean surface. These absorptions are related, respectively, to Mg-phyllosilicates, NH4-phyllosilicates and Mg/Ca-carbonates.
The spectral parameters considered in this work are: spectral slopes estimated between 1.2 µm and 1.9 µm, band depths at 2.7-, 3.1-, 3.4- and 4.0-µm, and band centers near 4.0-µm. The ccps spectral parameters were analysed in conjunction with other Cerean parameters, such as the estimated depth of excavation of the material composing the central peak, in order to search for correlations and information about Ceres’ subsurface.
Central peak material located polewards show stronger 2.7- and 3.1-µm band depths with respect to those at the equatorial region, suggesting that subsurface deposits closer to poles are probably richer in Mg- and NH4-phyllosilicates. The 3.4-µm spectral feature is also deeper in ccps located at poleward latitudes, similar to the phyllosilicates. Conversely, the 4.0-µm band does not show this trend with latitude.
An increase in both 3.1- and 3.4-µm band depths with the estimated depth of excavation indicates that the spectral feature at 3.4-µm is the result of different contributions from carbonates and NH4-phyllosilicates, as expected. However, depending on their relative influence, the shape of the 3.4-µm spectral feature can vary.
Phyllosilicates and carbonates are the resulting products of aqueous alteration of chondritic material and, given the increasing abundance of such minerals (in particular ammoniated phyllosilicates) with depth of excavation, it is likely that our investigation involved subsurface layers nearby the boundary between the volatile-rich crust and the silicate-rich mantle.
Na-carbonate is found in the crater central peak material of Ernutet, Haulani and Ikapati, characterized by an estimated depth of excavation of about 6-9 km, where deposits of sodium carbonates could be locally present.

^1,2Hiroshi Naraoka,² Minako Hashiguchi
Rapid Communications in Mass Spectrometry 32, 959-964 Link to Article [https://doi.org/10.1002/rcm.8121]
¹Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
²Research Center for Planetary Trace Organic Compounds, Kyushu University, Fukuoka, Japan

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¹R. Terik Daly, ¹Peter H. Schultz, ²John C. Lassiter, ²Staci W. Loewy, ³Lucy M. Thompson, ³John G. Spray
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.06.002]
¹Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook St, Box 1846, Providence, RI 02912, USA
²Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 1 University Station C1100, Austin, TX 78712, USA
³Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
Copyright Elsevier

Osmium isotopes provide a powerful tool for identifying meteoritic signatures in impactites. We apply the osmium isotope method to impact melt and country rocks from the Clearwater East and Clearwater West craters located in Quebec, Canada. Impact melts from Clearwater East have 187Os/188Os ratios of 0.1281 to 0.1285. These values indicate a significant meteoritic component, which exceeds that of all terrestrial craters studied to date, except Morokweng. Such findings align with earlier results from chromium isotopes and platinum-group elements. In contrast, impact melts from Clearwater West have 187Os/188Os ratios between 6.604 and 59.12. These highly radiogenic ratios are indistinguishable from the 187Os/188Os ratios in country rocks. Hence, osmium isotopes provide no evidence for a meteoritic component in impact melts at Clearwater West. The Clearwater craters formed in almost identical targets. Therefore, target effects cannot readily explain the stark difference between the two Clearwater craters. If melt sheet heterogeneity is similar at the two craters, the probability that melts at Clearwater West host an undetected chondritic component is < 0.1%. Multiple scenarios may explain the non-detection of a meteoritic signature at West; the possibility of a differentiated achondrite impactor could be tested using chromium isotopes. At Clearwater East, a low impact speed (<10 km s-1) may best explain the unusually strong meteoritic signature. Although the signature (or its nondetection) at each crater may be related to asymmetric preservation of the impactor component, the results presented here provide further evidence that Clearwater East and Clearwater West were temporally separate impact events.

¹M.Dell’Aglio, ²M.López-Claros, ² J.J.Laserna,^1,3,4S.Longo, ^1,3A.De Giacomo
Spectrochimica Acta Part B: Atomic Spectroscopy 147, 87-92 Link to Article [https://doi.org/10.1016/j.sab.2018.05.024]
¹CNR-NANOTEC, Via Amendola 122/D, 70126 Bari, Italy
²Universidad de Málaga, Facultad de Ciencias, Departamento de Química Analítica, Campus de Teatinos s/n, 29071 Málaga, Spain
³Chemistry Department, University of Bari, Via Orabona 4, 70126 Bari, Italy
⁴INAF Osservatorio Astrofisico di Arcetri, Largo E Fermi 5, 50125 Firenze, Italy

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¹Edivaldo Dos Santos,²Rosa B. Scorzelli,³Maria E. Varela
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13121]
¹Instituto de Ciência e Tecnologia—ICT/UFVJM, Minas Gerais, Brazil
Centro Brasileiro de Pesquisas Físicas—CBPF, Rio de Janeiro, Brazil
²Instituto de Ciencias Astronómicas, de la Tierra y del
³Espacio—ICATE/CONICET, San Juan, Argentina
Published by arrangement with John Wiley & Sons

São João Nepomuceno (SJN) is an IVA iron meteorite, found in Minas Gerais state (Brazil) in 1960, that consists of Fe‐Ni metal matrix and coarse‐grained silicate inclusions. In spite of the extensive work performed on the IVA irons, there is still no consensus about their origin and thermal history. Their particular chemistry and range in metallographic cooling rates are difficult to explain using conventional models. Furthermore, metal–silicate mixing of the IVA group remains a complex issue. In this work, the 57Fe Mössbauer spectroscopy was applied for measuring the intracrystalline Fe‐Mg distribution in orthopyroxenes extracted from SJN. The Mössbauer data associated with Ganguly’s cooling rate numerical model were used to investigate the thermal history of SJN meteorite. The results are the background for discussions about the IVA formation models, aiming to improve the understanding of the origin of IVA iron meteorite group.

^1,2,3Alan E. Rubin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13128]
¹Department of Earth, Planetary and Space Sciences, University of CaliforniaLos Angeles, California, USA
²Institute of Geophysics and Planetary Physics, University of CaliforniaLos Angeles, California, USA
³Maine Mineral & Gem Museum, Bethel, Maine, USA
Published by arrangement with John Wiley

Iron‐meteorite groups that appear from published isotopic data to have been derived from melted carbonaceous‐chondrite‐like precursors (CC irons) (IIC, IID, IIF, IIIF, IVB) tend to have higher median refractory siderophile element (RSE) contents, higher median Ni contents, and higher median Ir/Ni and Ir/Au ratios than magmatic noncarbonaceous (NC) iron‐meteorite groups (IC, IIAB, IIIAB, IIIE, IVA). (Group IIG is also NC.) One potential source of RSEs in magmatic CC irons is the set of refractory metal nuggets from inherited CAIs. Magmatic CC‐iron groups tend to have longer cosmic‐ray exposure (CRE) ages than magmatic NC‐iron groups, indicating long residence times as small bodies in interplanetary space. The lower membership of CC‐iron groups is probably mainly due to the high oxidation state of their precursors. Such oxidation would have produced lesser amounts of free metal; parent body differentiation of such bodies would have produced smaller cores, resulting in fewer samples available to make CC‐iron meteorites in the first place. (Ungrouped magmatic irons, most of which can be considered groups with only one member, also tend to be carbonaceous.) It is possible that a subset of the chondrule‐poor dark inclusions in many carbonaceous chondrites represent unmelted materials related to the precursors of the CC irons. The Eagle Station pallasites (also CC‐related) are analogous to CC irons in being more oxidized, richer in Ni and RSEs, and fewer in number than main‐group pallasites (PMG). However, Eagle Station has a shorter CRE age than most PMG.

^1,2Philip R. Heck et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13129]
¹Department of Science and Education, Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, Chicago, Illinois, USA
²Chicago Center for Cosmochemistry and Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
Published by Arrangement with John Wiley & Sons

We present He and Ne isotopes of individual presolar graphite grains from a low‐density separate from Orgueil. Two grain mounts were analyzed with the same techniques but in a different sequence: The first one was measured with NanoSIMS followed by noble gas mass spectrometry, and the second one in reverse order. No grain contained 4He and only one grain on the second mount contained 3He. On the first mount, the grains had been extensively sputtered with NanoSIMS ion beams prior to noble gas analysis; we found only one grain out of 15 with presolar 22Ne above detection limit. In contrast, we found presolar 22Ne in six out of seven grains on the second mount that was not exposed to an ion beam prior to noble gas analysis. All 22 grains on the two mounts were imaged with scanning electron microscopy (SEM) and/or Auger microscopy. We present evidence that this contrasting observation is most likely due to e‐beam–induced heating of the generally smaller grains on the first mount during SEM and Auger imaging, and not primarily due to the NanoSIMS analysis. If thermal contact of the grains to the substrate is absent, such that heat can only be dissipated via radiation, then the smaller, sputter‐eroded grains are heated to higher temperatures such that noble gases can diffuse out. We discuss possible gas loss mechanisms and suggest solutions to reduce heating during e‐beam analyses by minimizing voltages, beam currents, and dwell times. We also found small amounts of 21Ne in five grains. Using isotope data we determined that the dominant sources of most grains are core‐collapse supernovae, congruent with earlier studies of low‐density presolar graphite from Murchison. Only two of the grains are most likely from AGB stars, and two others have an ambiguous origin.

¹Clément Ganino,^2,3Guy Libourel,⁴Akiko M. Nakamura,⁵Suzanne Jacomet,⁶Olivier Tottereau,²Patrick Michel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13131]
¹Université Côte d’Azur, OCA, CNRS, Géoazur, Sophia‐Antipolis, Valbonne, France
²Université Côte d’Azur, OCA, CNRS, Lagrange, Boulevard de l’Observatoire, Nice Cedex 4, France
³Hawai’i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai’i at MānoaHonolulu, Hawai’i, USA
⁴Graduate School of Science, Kobe University, Kobe, Japan
⁵MINES ParisTech, PSL—Research University, CEMEF—Centre de mise en forme des matériaux, CNRS, UMR 7635Sophia‐Antipolis, France
⁶CRHEA, CNRS UPR 10Sophia Antipolis, France
Published by Arrangement with John Wiley & Sons

Hypervelocity impacts are common in the solar system, in particular during its early phases when primitive bodies of contrasted composition collided. Whether these objects are chemically modified during the impact process, and by what kind of processes, e.g., chemical mixing or gas–liquid–solid fractionation, are still pending questions. To address these issues, a set of impact experiments involving a multielemental doped phonolitic projectile and a metallic target was performed in a 3–7 km s−1 range of impact speeds which are typical of those occurring in the asteroid belt. For each run, both texture and chemistry of the crater and the ejecta population have been characterized. The results show that the melted projectiles largely cover the craters at all speeds, and that melted phonolitic materials are injected into fractures in the crater in the metallic target. Ejecta are generally quenched droplets of silicate impact melt containing metal beads. Some of these beads are extracted from the target, but we propose that some of the Fe metal beads are the result of reduction of FeO. A thin FeO‐SiO2‐rich condensate layer is found at the edge of the crater, suggesting that a limited amount of vapor formed and condensed. LA‐ICP‐MS analyses suggest, however, that within analytical uncertainties, no volatility‐controlled chemical fractionation of trace elements occurred in the ejecta. The main chemical fractionation during impact at such velocities and energies are the result of projectile‐target mixing.