¹Violaine Sautter et al. (>10)*
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.01.014]
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005 Paris, France
*Find the extensive, full author and affiliation list on the publishers website
Copyright Elsevier

Several recent studies have revealed that Mars is not a simple basalt-covered planet, but has a more complex geological history. In Gale crater on Mars, the Curiosity rover discovered 59 igneous rocks. This paper focuses on their textures (acquired from the cameras such as MAHLI and MastCam) and their geochemical compositions that have been obtained using the ChemCam instrument. Light-toned crystals have been observed in most of the rocks. They correspond to feldspars ranging from andesines/oligoclases to anorthoclases and sanidines in the leucocratic vesiculated rocks. Darker crystals observed in all igneous rocks (except the leucocratic vesiculated ones) were analyzed by LIBS and mainly identified as Fe-rich pigeonites and Fe-augites. Iron oxides have been observed in all groups whereas F-bearing minerals have been detected only in few of them. From their textural analysis and their whole-rock compositions, all these 59 igneous rocks have been classified in five different groups; from primitive rocks i.e. dark aphanitic basalts/basanites, trachybasalts, tephrites and fine/coarse-grained gabbros/norites to more evolved materials i.e. porphyritic trachyandesites, leucocratic trachytes and quartz-diorites. The basalts and gabbros are found all along the traverse of the rover, whereas the felsic rocks are located before the Kimberley formation, i.e. close to the Peace Vallis alluvial fan deposits. This suggests that these alkali rocks have been transported by fluvial activity and could come from the Northern rim of the crater, and may correspond to deeper strata buried under basaltic regolith (Sautter et al., 2015). Some of the basaltic igneous rocks are surprisingly enriched in iron, presenting low Mg# similar to the nakhlite parental melt that cannot be produced by direct melting of the Dreibus and Wanke (1986) martian primitive mantle. The basaltic rocks at Gale are thus different from Gusev basalts. They could originate from different mantle reservoirs, or they could have undergone a more extensive fractional crystallization. Gale basaltic rocks could have been the parental magma of residual liquid extending into alkali field towards trachyte composition as magma fractionated under anhydrous condition on its way to the surface before sub adiabatic ascent.

¹My E.I. Riebe, ¹Henner Busemann, ¹Rainer Wieler, ¹Colin Maden
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.02.004]
¹ETH Zurich, Institute of Geochemistry and Petrology, Clausiusstrasse 25, 8092 Zurich, Switzerland
Copyright Elsevier

We analyzed all the noble gases in HF-soluble phases in the CI chondrite Ivuna by in-vacuum gas release using the “Closed System Step Etching” (CSSE) technique, which allows for direct noble gas measurements of acid-soluble phases. The main motivation was to investigate if there are primordial noble gases in HF-soluble phases in Ivuna, something that has not been done before in CI chondrites, as most primordial noble gases are known to reside in HF-resistant phases. The first steps under mild etching released He, Ne, and Ar with solar-like elemental and isotopic compositions, confirming that Ivuna contains implanted solar wind (SW) noble gases acquired in the parent body regolith. The SW component released in some etch steps was elementally unfractionated. This is unusual as trapped SW noble gases are elementally fractionated in most meteoritic material. In the intermediate etch steps under slightly harsher etching, cosmogenic noble gases were more prominent than SW noble gases. The HF-soluble portion of Ivuna contained primordial Ne and Xe, that was most visible in the last etch steps after all cosmogenic and most SW gases had been released. The primordial Ne and Xe in the HF-solubles have isotopic and elemental ratios readily explained as a mixture of the two most abundant primordial noble gas components in Ivuna bulk samples: HL and Q. Only small fractions of the total HL and Q in Ivuna were released during CSSE analysis; ∼3% of 20NeHL and ∼4% of 132XeQ. HL is known to reside in nanodiamond-rich separates and Q-gases are most likely carried by a carbonaceous phase known as phase Q. Q-gases were likely released from an HF-soluble portion of phase Q. However, nanodiamonds might not be the source of the HL-gases released upon etching, since nanodiamond-rich separates are very HF-resistant and the less tightly bound nanodiamond component P3 was not detected.

¹Steven W. Ruff, ²Victoria E. Hamilton
American Mineralogist 102, 235-251 Link to Article [https://doi.org/10.2138/am-2017-5618]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-6305, U.S.A.
²Southwest Research Institute, Boulder, Colorado 80302, U.S.A.
Copyright: The Mineralogical Society of America

Previous observations by the Spirit rover in Gusev crater revealed a suite of rocks dubbed Wishstone and Watchtower Class in which the parent lithology and daughter products of a distinctive style of aqueous alteration are evident. Results from Spirit’s Miniature Thermal Emission Spectrometer (Mini-TES; ~2000–340 cm−1) were compromised by dust contamination of one of the instrument’s mirrors, for which a correction has since been developed. Now we have documented nearly 200 examples of rocks encompassing the span of alteration from Wishstone Class, which spectrally resemble minimally altered plagioclase-phyric basalt, to the most altered Watchtower Class. Among them is a rock dubbed Bruce that may be a previously unrecognized alteration spectral end-member. We employed factor analysis/target transformation and linear least-squares modeling to investigate the spectral characteristics and mineralogy of these rocks. Our results amplify those of a prior preliminary analysis showing that alteration produced a material resembling basaltic glass that masks the spectral features of plagioclase. The association of this amorphous silicate component with a ferric iron nanophase oxide phase identified via Spirit’s Mössbauer spectrometer is now clearly shown by our data, further characterizing the distinctive mineralogic expression of the alteration. These components and the absence of any recognizable secondary silicates or opaline silica may be an expression of alteration in the extreme aridity and cold of the martian environment. Similar mineralogic characteristics of soil measured with the CheMin X-ray diffraction instrument on the Curiosity rover in Gale crater may be an indication that this alteration process is widespread on Mars.

¹Huapei Wang, ¹Benjamin P. Weiss, ²Xue-Ning Bai, ¹Brynna G. Downey, ³Jun Wang, ³Jiajun Wang, ¹Clément Suavet, ¹Roger R. Fu, ⁴Maria E. Zucolotto
Science 355, 623-627 Link to Article [DOI: 10.1126/science.aaf5043]
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
²Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
³National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, NY, USA.
⁴Museu Nacional, Rio de Janeiro, Brazil.
Reprinted with permission from AAAS

A key stage in planet formation is the evolution of a gaseous and magnetized solar nebula. However, the lifetime of the nebular magnetic field and nebula are poorly constrained. We present paleomagnetic analyses of volcanic angrites demonstrating that they formed in a near-zero magnetic field (<0.6 microtesla) at 4563.5 ± 0.1 million years ago, ~3.8 million years after solar system formation. This indicates that the solar nebula field, and likely the nebular gas, had dispersed by this time. This sets the time scale for formation of the gas giants and planet migration. Furthermore, it supports formation of chondrules after 4563.5 million years ago by non-nebular processes like planetesimal collisions. The core dynamo on the angrite parent body did not initiate until about 4 to 11 million years after solar system formation.

¹M.Lugano et al. (>10)*
Nature Astronomy 1, 27 Link to Article [doi:10.1038/s41550-016-0027]
Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, 1121 Budapest, Hungary
Monash Centre for Astrophysics (MoCA), Monash University, Clayton, Victoria 3800, Australia
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We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹P. Lindgren, ¹M.R. Lee, ²N.A. Starkey, ²I.A. Franchi
Geochmica et Cosmochmica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.048]
¹School of Geographical and Earth Sciences, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ
²Planetary and Space Sciences, The Open University, Milton Keynes, MK7 6AA
Copyright Elsevier

The oxygen isotopic compositions of calcite grains in four CM carbonaceous chondrites have been determined by NanoSIMS, and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration. Two types of calcite were identified in Murchison, Mighei, Cold Bokkeveld and LaPaz Icefield 031166 by differences in their petrographic properties and oxygen isotope values. Type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration. On average, the type 1 grains have a δ18O of ∼32–36 ‰ (VSMOW), and Δ17O of between ∼2 and -1 ‰. Most grains of type 2 calcite precipitated after type 1. They contain micropores and inclusions, and have replaced ferromagnesian silicate minerals. Type 2 calcite has an average δ18O of ∼21–24 ‰ (VSMOW) and a Δ17O of between ∼-1 and -3 ‰. Such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose δ18O and δ17O values had changed by reaction with parent body silicates, as predicted by the closed-system model for aqueous alteration. Temperatures are likely to have increased over the timespan of calcite precipitation, possibly owing to exothermic serpentinisation. The most highly altered CM chondrites commonly contain dolomite in addition to calcite. Dolomite grains in two previously studied CM chondrites have a narrow range in δ18O (∼25–29 ‰ VSMOW), with Δ17O ∼-1 to -3 ‰. These grains are likely to have precipitated between types 1 and 2 calcite, and in response to a transient heating event and/or a brief increase in fluid magnesium/calcium ratios. In spite of this evidence for localised excursions in temperature and/or solution chemistry, the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions. The CM carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or, more probably, a single C-type asteroid.

¹Peter Hoppe, ²Marco Pignatari, ¹János Kodolányi, ¹Elmar Gröner, ³Sachiko Amari
Geochmica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.051]
¹Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
²E. A. Milne Centre for Astrophysics, University of Hull, Hull, HU6 7RX, UK, & NuGrid Collaboration
³McDonnell Center for the Space Sciences and the Physics Department, Washington University, St. Louis, MO 63130, USA
Copyright Elsevier

We have conducted a NanoSIMS ion imaging survey of about 1800 presolar silicon carbide (SiC) grains from the Murchison meteorite. A total of 21 supernova (SN) X grains, two SN C grains, and two putative nova grains were identified. Six particularly interesting grains, two X and C grains each and the two putative nova grains were subsequently studied in greater detail, namely, for C-, N-, Mg-Al-, Si-, S-, and Ca-Ti-isotopic compositions and for the initial presence of radioactive 26Al (half life 716000 yr), 32Si (half life 153 yr), and 44Ti (half life 60 yr). Their isotope data along with those of three X grains from the literature were compared with model predictions for 15 M⊙ and 25 M⊙ Type II supernovae (SNe). The best fits were found for 25 M⊙ SN models that consider for the He shell the temperature and density of a 15 M⊙ SN and ingestion of H into the He shell before the explosion. In these models a C- and Si-rich zone forms at the bottom of the He burning zone (C/Si zone). The region above the C/Si zone is termed the O/nova zone and exhibits the isotopic fingerprints of explosive H burning. Satisfactory fits of measured C-, N-, and Si-isotopic compositions and of 26Al/27Al ratios require small-scale mixing of matter originating from a region extending over 0.2 M⊙ for X and C grains and over 0.4 M⊙ for one of the putative nova grains, involving matter from a thin Si-rich layer slightly below the C/Si zone, the C/Si zone, and the O/nova zone. Simultaneous fitting of 14N/15N and 26Al/27Al requires a C-N fractionation of a factor of 50 during SiC condensation. This leads to preferential incorporation of radioactive 14C (half life 5700 yr) over directly produced 14N and can account for the 14N/15N along with 26Al/27Al ratios as observed in the SiC grains. The good fit for one of the putative nova grains along with its high 26Al/27Al points towards a SN origin and supports previous suggestions that some grains classified as nova grains might be from SNe. Apparent problems with the small-scale mixing scheme considered here are C/O ratios that are mostly <1 if C-, N-, and Si-isotopic compositions and 26Al/27Al ratios are simultaneously matched, underproduction of 32Si, and overproduction of 44Ti. This confirms the limitations of one-dimensional hydrodynamical models for H ingestion and stresses the need to better study the convective-boundary mixing mechanisms at the bottom of the convective He shell in massive star progenitors. This is crucial to define the effective size of the C/Si zone formed by the SN shock. The comparison between the Si isotope data of the SN grains and the models gives a hint that the predicted 30Si is too high at the bottom of the He burning shell.

¹A. S. P. Rae, ¹G. S. Collins, ²R. A. F. Grieve, ^2,3G. R. Osinski and ¹J. V. Morgan
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12825]
¹Department of Earth Science and Engineering, Imperial College London, London SW7BP, UK
²Department of Earth Sciences/Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario N6A 5B7, Canada
³Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 5B7, CanadaPublished by arrangement with John Wiley & Sons

Zaicong Wang, Harry Becker
Earth and Planetary Science Letters 463, 56-68 Link to Article [http://dx.doi.org/10.1016/j.epsl.2017.01.023]
Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstrasse 74-100, 12249 Berlin, Germany
Copyright Elsevier

It is generally believed that the Martian mantle and core are rich in sulfur and that shergottites originated from sulfide-saturated magma. However, recent work suggests that the high FeO contents would require very high S concentrations in shergottite parent magmas at sulfide saturation. Here we combine new and published data on chalcophile elements in shergottites, nakhlites and ALH84001 to constrain the sulfide saturation state of the parent magmas and the chalcophile element concentrations in their mantle sources.

Regardless of the MgO content and the long-term depletion history of incompatible lithophile elements as indicated by initial ε¹⁴³Nd, different groups of shergottites display limited variations in ratios of Pt, Pd, Re, Cu, S, Se and Te. The emplacement of most shergottites within the crust and limited variations of ratios of chalcophile elements with substantial differences in volatility during eruption (e.g., Cu/S, Cu/Se and Pt/Re) indicate little degassing losses of S, Se, Te and Re from shergottites. Limited variations in ratios of elements with very different sulfide–silicate melt partition coefficients and negative correlations of chalcophile elements with MgO require a sulfide-undersaturated evolution of the parent magmas from mantle source to emplacement in the crust, consistent with the FeO-based argument. Sulfide petrography and the komatiite-like fractionation of platinum group elements (PGE) in shergottites also support this conclusion. The absence of accumulated sulfides in the ancient Martian cumulate ALH84001 results in very low contents of PGE, Re, Cu, Se and Te in this meteorite, hinting that sulfide-undersaturated magmas may have occurred throughout the Martian geological history. The negative correlation of Cu and MgO contents in shergottites suggests approximately Cu in the Martian mantle. The ratios of Cu, S, Se and Te indicate 360±120 μg/g (1s) S, 100±27 ng/g (1s) Se and 0.50±0.25 ng/g (1s) Te in the Martian mantle. At such low S concentrations, all S in Martian mantle sources may dissolve in basaltic melts that form at >5 % partial melting.

Assuming equilibrium metal–silicate partitioning, and provided that the compositional model of the Martian mantle based on SNC meteorites is correct, Martian mantle inventories of Cu, S and Se were mostly established by core formation and the Martian core should contain <5–10 wt.% S only (depending on the choice of metal–silicate partition coefficients). The low S content in the Martian interior is consistent with the low Zn content in the Martian mantle, which indicates about 5 wt.% S in the core. In contrast, the highly siderophile PGE, Re and Te were added to the mantle by late accreted material after the Martian core formed. The near chondritic PGE ratios and the very low ratio of volatile Te to refractory PGE reflect a strongly volatile element-depleted late veneer and imply that the delivery of Martian water, presumably from carbonaceous chondrite like materials, must have occurred before accretion of the late veneer, likely within 2–3 million years after formation of the solar system.

¹Joshua L. Bandfield
American Mineralogist Link to Article [DOI: 10.2138/am-2017-5955]
¹Space Science Institute, Boulder, Colorado 80301, U.S.A.
Copyright: The Mineralogical Society of America

The Mars Exploration Rover “Spirit” provided us with a serendipitous opportunity to traverse a section of the ancient martian crust, acquiring a trove of imaging, geochemical, and mineralogical measurements along the way. This small window looking out on the Noachian period (>3.7 Ga), dubbed the Columbia Hills, pokes out from the younger, volcanically resurfaced floor of Gusev Crater. It was our first detailed look at early Mars, a time when liquid water appears to have played a much more prominent role in shaping and modifying the planet than later in its history.

The abundance of rocks that appear to be snapshots from early in the history of Mars is a luxury compared to the rarity and inevitable metamorphic overprinting of Hadean and early Archean samples from Earth. However, few planetary surfaces of this age anywhere in the solar system escape the disruption caused by impacts. In this sense, it is difficult to identify the geologic context of any given sample or series of samples. Although what appears to be an outcrop of a draping volcaniclastic unit in the Columbia Hills may still be in place, it is also possible for it to have been highly …