^1,2Honglei LIN, ¹Xia ZHANG
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.01.019]
¹State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Science, Beijing 100101,China
¹University of Chinese Academy of Sciences, Beijing 100049, China
Copyright Elsevier

The hydrous minerals on Mars preserve records of potential past aqueous activity. Quantitative information regarding mineralogical composition would enable a better understanding of the formation processes of these hydrous minerals, and provide unique insights into ancient habitable environments and the geological evolution of Mars. The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has the advantage of both a high spatial and spectral resolution, which makes it suitable for the quantitative analysis of minerals on Mars. However, few studies have attempted to quantitatively retrieve the mineralogical composition of hydrous minerals on Mars using visible-infrared (VISIR) hyperspectral data due to their distribution characteristics (relatively low concentrations, located primarily in Noachian terrain, and unclear or unknown background minerals) and limitations of the spectral unmixing algorithms. In this study, we developed a modified sparse unmixing (MSU) method, combining the Hapke model with sparse unmixing. The MSU method considers the nonlinear mixed effects of minerals and avoids the difficulty of determining the spectra and number of endmembers from the image. The proposed method was tested successfully using laboratory mixture spectra and an Airborne Visible Infrared Imaging Spectrometer (AVIRIS) image of the Cuprite site (Nevada, USA). Then it was applied to CRISM hyperspectral images over Gale crater. Areas of hydrous mineral distribution were first identified by spectral features of water and hydroxyl absorption. The MSU method was performed on these areas, and the abundances were retrieved. The results indicated that the hydrous minerals consisted mostly of hydrous silicates, with abundances of up to 35%, as well as hydrous sulfates, with abundances ≤10%. Several main subclasses of hydrous minerals (e.g., Fe/Mg phyllosilicate, prehnite, and kieserite) were retrieved. Among these, Fe/Mg- phyllosilicate was the most abundant, with abundances ranging up to almost 30%, followed by prehnite and kieserite, with abundances lower than 15%. Our results are consistent with related research and in situ analyses of data from the rover Curiosity; thus, our method has the potential to be widely used for quantitative mineralogical mapping at the global scale of the surface of Mars.

¹Thomas J. Lapen, ¹Minako Righter, ^1,2Rasmus Andreasen, ³Anthony J. Irving, ^4,5Aaron M. Satkoski, ^4,5Brian L. Beard, ⁶Kunihiko Nishiizumi, ⁷A. J. Timothy Jull,^8,9Marc W. Caffee
Science Advances 3, e1600922 Link to Article [DOI: 10.1126/sciadv.1600922]
¹Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204–5007, USA.
²Department of Geoscience, Aarhus University, Aarhus, Denmark.
³Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195–1310, USA.
⁴Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706–1692, USA.
⁵NASA Astrobiology Institute, University of Wisconsin–Madison, Madison, WI 53706, USA.
⁶Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA, USA.
⁷Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA.
⁸Department of Physics, Purdue University, West Lafayette, IN 47907–2036, USA.
⁹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907–2051, USA

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¹A. Lindskog, ^2,3M. M. Costa, ^2,4C.M.Ø. Rasmussen, ^2,3J. N. Connelly, ¹M. E. Eriksson
Nature Communications 8, 14066 Link to Article [doi:10.1038/ncomms14066]
¹Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden
²Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen K, Denmark
³Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen K, Denmark
⁴Center for Macroecology, Evolution and Climate, University of Copenhagen, Denmark

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^1,2S.R. Sutton, ^3,4C.A. Goodrich, ²S. Wirick
Geochimica et Cosmochmica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.036]
¹Dept. of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA
²Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA
³Planetary Science Institute, 1700 E. Ft. Lowell, Tucson, AZ 85719, USA
⁴Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston TX 77058
Copyright Elsevier

Titanium, Cr, and V valences were determined by applying micro-X-ray Absorption Near Edge Structure (micro-XANES) spectroscopy methods to individual grains of olivine and pyroxene in the ungrouped achondrite NWA 7325 and ureilite Y-791538, as well as to plagioclase in NWA 7325. The advantages of applying multiple, multivalent-element-based oxybarometers to individual grains are (1) the ability to cover the entire oxygen fugacity (fO2) range encountered in nature, and (2) the increased reliability from consistent results for semi-independent fO2 proxies. fO2 values were inferred from each mineral valence determination after correcting with available laboratory-experiment-derived, valence-specific partition coefficients to obtain melt valences and then calibrating with the fO2 values of the relevant equal species proportions points suggested for igneous (primarily basaltic) systems.

The resulting olivine and pyroxene valences are highly reduced and similar in the two meteorites with substantial fractions of Cr2+, Ti3+ and V2+. The exception is Cr in NWA 7325 pyroxene which is much more oxidized than the Cr in its olivine. Chromium and Ti in plagioclase in NWA 7325 is relatively oxidized (V valence not determined). The anomalously oxidized Cr in NWA 7325 pyroxene may be due to a secondary reheating event that oxidized Cr in the pyroxene without similarly oxidizing Ti and V. Such a separation of the redox couples may be an effect of re-equilibration kinetics, where the valence of Cr would be more rapidly modified. These valences yielded similar mean fO2s for the two meteorites; IW-3.1 ± 0.2 for NWA 7325 and IW-2.8 ± 0.2 for Y-791538, consistent with an origin of NWA 7325 in either Mercury or an asteroid that experienced redox conditions similar to those on the ureilite parent body.

¹Shiyong Liao, ²Weibiao Hsu
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.037]
¹Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Nanjing, China
²Space Science Institute, Macau University of Science and Technology, Macau
Copyright Elsevier

Studies of petrology, mineralogy and geochronology of eucrites are keys to reconstruct the thermal and impact history of 4 Vesta, the proposed parent body for HED meteorites. Here we report the petrography, mineralogy and geochemistry of NWA 8009, a newly found eucritic impact-melt breccia, and present SIMS U-Pb ages of zircon and phosphates. NWA 8009 consists of coarse- and fine-grained lithic and mineral clasts set in fine-grained recrystallized matrix. It was derived from a protolith of non-cumulate eucrite. Evidence for intense shock metamorphism observed in NWA 8009 includes mosaicism, deformed exsolution lamellae and partial melting of pyroxene, melting and incipient flow of plagioclase, planar fractures and granular textures of zircon. These shock effects indicate NWA 8009 was subjected to an impact metamorphism with peak pressure of ∼50–60 Gpa and post-shock temperature of ∼1160–1200 °C. NWA 8009 is among the most intensely shocked HEDs reported yet. After the impact, the sample was buried near the surface in target rocks and experienced rapid cooling (∼23°C/h) and annealing, resulting in recrystallization of the matrix and devitrification of plagioclase and silica glasses. U-Pb isotopic system of apatite within plagioclase groundmass of lithic clasts is completely reset and constrains the timing of impact at 4143 ± 61 Ma, providing a new robust impact age on Vesta. Combined with the presence of synchronous impact resetting events, especially those recorded by Lu-Hf, Sm-Nd, and Pb-Pb isotopic systems, we identified a period of high impacts flux at ca. 4.1–4.2 Ga on Vesta. This impact flux occurred coincident with the uptick at ca. 4.1–4.2 Ga in impact age spectra of the moon, probably reflects widespread intense bombardment throughout the inner solar system at ca. 4.1–4.2 Ga. Based on evidence from zircon chemical zoning, petrographic occurrences, as well as the distinctive Zr/Hf ratios, we suggested that zircons in NWA 8009 have had a metamorphic, instead of magmatic origin. They mainly crystallized from melts produced by partial melting of mesostasis area due to reheating event during early global thermal metamorphism, rather than by Zr release from Zr-rich minerals. The U-Pb isotopic system in zircons was not disturbed by subsequent impacts, the weighted-mean 207Pb/206Pb age of 4560 ± 8 Ma represents the timing of zircon growth during thermal metamorphism. Zircons from NWA 8009 and other eucrites may share a common origin during metamorphic growth events, and constraining the global thermal metamorphism on Vesta at ca. 4.55 Ga. The main heat sources responsible for global metamorphism in basaltic crust of Vesta might be heating from the hot interior, especially heat flow related to magmatism, rather than impact.

^1,2Bryné A. Hadnott, ^2,3Bethany L. Ehlmann, ¹Bradley L. Jolliff
American Mineralogist 102, 284-301 Link to Article [https://doi.org/10.2138/am-2017-5608]
¹Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri 63105, U.S.A.
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, U.S.A.
⁴Department of Earth and Atmospheric Sciences, Room 414 Spaces Sciences Building, Cornell University, 122 Garden Avenue, Ithaca, New York 14853, U.S.A.
Copyright: The Mineralogical Society of America

The discovery of Fe, Mg, and Al phyllosilicates on Mars using visible and short-wave infrared (VSWIR) spectroscopy from orbit indicates aqueous alteration of basaltic rocks. Analyses at Gusev Crater by the Spirit rover and Gale Crater by the Curiosity rover have discovered alkaline basaltic rocks. In this work, multiple methods—VSWIR spectroscopy, X-ray diffraction (XRD), and chemical analyses—were used to study a suite of alkaline basalts from San Carlos, Arizona, which have been altered by water in an oxidative, semi-arid environment. As an analog for the weathering of alkaline basaltic rocks on Mars, a suite of rocks visually identified to have different degrees of alteration were characterized to understand the spectral, mineralogical, and chemical trends in alteration as sensed by multiple techniques. Samples with strong 1.9 μm H2O-related absorptions in VSWIR commonly exhibited absorption bands at 1.4, 2.2, and/or 2.3 μm, indicating the presence of clay minerals or silica as well as features at 0.5–0.9 μm indicative of ferric iron oxides. Primary mineralogy for all samples, as determined by point analyses with the microprobe and XRD, consisted of olivine, plagioclase, nepheline, augite, and titanomagnetite. Compositional imaging and spot analyses with the microprobe revealed distinct alteration textures and phases, suggesting weathering pathways involving the oxidation of iron in olivine and primary Fe2+ oxides to form Fe3+ oxides as well as the formation of aluminum phyllosilicates and magnesium phyllosilicates from feldspars and olivines, respectively, while pyroxene remained relatively unaltered. Bivariate plots of major oxides both from bulk-chemical analysis and microprobe measurements also revealed trends in alkali and silica depletion and calcium enrichment, but there was little chemical fractionation in most of the major oxides. The strength of the 1.9 μm H2O absorption, loss on ignition, and depletion in silica and sodium, correlated with increasing alteration. The data sets provide an analog for understanding possible weathering pathways in martian alkaline basalts and thresholds for the detection of aqueous alteration in multiple data sets.

¹Aaron J. Lussier, ²Sergei Rouvimov, ^1,3Peter C. Burns, ¹Antonio Simonetti
American Mineralogist 102, 445-460 Link to Article [https://doi.org/10.2138/am-2017-5739]
¹Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A.
²Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana, 46556, U.S.A.
³Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A.
Copyright: The Mineralogical Society of America

The Half Dome Granodiorite, Yosemite National Park, California, is recognized in the field by euhedral, fresh-looking, black hornblende phenocrysts up to 2 cm in length. This variety of granodiorite typifies intermediate-age hornblende-phyric units of Cretaceous nested plutonic suites in the Sierra Nevada batholith. Although only inclusions of feldspar are evident in hand samples, the phenocrysts are riddled with up to 50% inclusions of every major mineral found in the host granodiorite plus metamorphic minerals formed during cooling. Amphibole compositions within single phenocrysts vary from actinolite with less than 1 wt% Al2O3 to magnesiohornblende with over 8 wt%. Elemental zoning within the amphibole is highly irregular on the micrometer scale, showing patches and polygonal zones with dramatically different compositions separated by sharp to gradual transitions. The chemical compositions of entire phenocrysts are equivalent to hornblende plus a small proportion of biotite, suggesting that the non-biotite inclusions are the result of metamorphism of the phenocrysts. Backscattered electron imaging shows evidence of brecciation that may have been the result of volume changes as hornblende was converted to actinolite. Pressure calculations using the Al-in-hornblende barometer show unreasonably wide variations on the micrometer scale that cannot have been produced by temperature or pressure variations during crystallization. These hornblende phenocrysts would thus be unsuitable for geobarometry, and caution must be used to avoid similarly zoned phenocrysts in the application of the Al-in-hornblende geobarometer.

¹T. J. Barrett, ²D. W. Mittlefehldt, ¹R. C. Greenwood, ¹B. L. A. Charlier, ¹S. J. Hammond, ^2,3D. K. Ross, ¹M. Anand, ¹I. A. Franchi, ¹F. A. J. Abernethy, ¹M. M. Grady
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12818]
¹School of Physical Sciences, The Open University, Milton Keynes, UK
²Astromaterials Research Office, NASA Johnson Space Center, Houston, Texas, USA
³UTEP and Jacobs Technology, Houston, Texas, USA
⁴Department of Earth Sciences, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

The Emmaville eucrite is a relatively poorly studied basaltic achondrite with an anomalous oxygen isotope signature. In this study, we report comprehensive mineralogical, petrographic, and geochemical data from Emmaville in order to understand its petrogenesis and relationship with the basaltic eucrites. Emmaville is an unusually fine-grained, hornfelsic-textured metabasalt with pervasive impact melt veins and mineral compositions similar to those of typical basaltic eucrites. The major and trace element bulk composition of Emmaville is also typical of a basaltic eucrite. Three separated individual lithologies were also analyzed for O isotopes; a dark gray fraction (E1), a shocked lithology (E2), and a lighter gray portion (E3). Fractions E1 and E2 shared similar O isotope compositions to the bulk sample (E-B), whereas the lighter gray portion (E3) is slightly elevated in Δ17O and significantly elevated in δ18O compared to bulk. No evidence for any exogenous material is observed in the thin sections, coupled with the striking compositional similarity to typical basaltic eucrites, appears to preclude a simple impact-mixing hypothesis. The O-isotopes of Emmaville are similar to those of Bunburra Rockhole, A-881394, and EET 92023, and thus distinct from the majority of the HEDs, despite having similarities in petrology, mineral, and bulk compositions. It would, therefore, seem plausible that all four of these samples are derived from a single HED-like parent body that is isotopically distinct from that of the HEDs (Vesta) but similar in composition.

^1,2M. Ebert, ^2,3L. Hecht, ^2,3C. Hamann, ²R. Luther
Meteoritics & Planetary Sciences (in Press) Link to Article [DOI: 10.1111/maps.12809]
¹Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg (ALU), Freiburg, Germany
²Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Museum für Naturkunde (MfN), Berlin, Germany
³Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
Published by arrangement with John Wiley & Sons

This study introduces an experimental approach using direct laser irradiation to simulate the virtually instantaneous melting of target rocks during meteorite impacts. We aim at investigating the melting and mixing processes of projectile (iron meteorite; steel) and target material (sandstone) under idealized conditions. The laser experiments (LE) were able to produce features very similar to those of impactites from meteorite craters and cratering experiments, i.e., formation of lechatelierite, partial to complete melting of sandstone, and injection of projectile droplets into target melts. The target and projectile melts have experienced significant chemical modifications during interaction of these coexisting melts. Emulsion textures, observed within projectile-contaminated target melts, indicate phase separation of silicate melts with different chemical compositions during quenching. Reaction times of 0.6 to 1.4 s could be derived for element partitioning and phase-separation processes by measuring time-depended temperature profiles with a bolometric detector. Our LE allow (i) separate melting at high temperatures to constrain primary melt heterogeneities before mixing of projectile and target, (ii) quantification of element partitioning processes between coexisting projectile and target melts, (iii) determination of cooling rates, and (iv) estimation of reaction times. Moreover, we used a thermodynamic approach to calculate the entropy gain during laser melting. The entropy changes for laser-melting of sandstone and iron meteorite correspond to shock pressures and particle velocities produced during the impact of an iron projectile striking a quartz target at a minimum impact velocity of ~6 km s−1, inducing peak shock pressures of ~100 GPa in the target.

^1,2A. Yamaguchi, ³N. Shirai, ³C. Okamoto, ³M. Ebihara
Meteoritics & Planetary Science (in Press) link to Article [DOI: 10.1111/maps.12821]
¹National Institute of Polar Research, Tachikawa, Tokyo, Japan
²Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, Japan
¹Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo, Japan
Published by arrangement with John Wiley & Sons

We report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low-Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.