¹Alan E. Rubin
¹Department of Earth, Planetary, and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA

Several aubrites (e.g., LAP 03719, Bishopville, Khor Temiki, ALH 83015) contain orthopyroxene grains that exhibit more-pronounced shock effects than associated olivine grains. The orthopyroxene grains in these samples have clinoenstatite lamellae on (100) and exhibit weak mosaic extinction, characteristic of shock stage S4; the olivine grains exhibit either sharp optical extinction, characteristic of shock stage S1 (as in LAP 03719), or undulose extinction (shock stage S2), as in Bishopville and ALH 83015. The Khor Temiki regolith breccia contains S1 and S2 olivine grains. Because literature data show that diffusion is much slower in orthopyroxene than in olivine, it seems likely that aubrites experienced postshock, impact-induced annealing. After differentiation, the aubrite parent asteroid suffered major collisions that caused extensive brecciation of near-surface materials and damaged orthopyroxene and olivine crystal lattices. As a result of these impact events, some aubrites were shocked and buried within warm ejecta blankets or beneath fallback debris under the crater floor. Entombed olivine crystal lattices healed (and became unstrained, reaching shock stage S1), but orthopyroxene lattices retained their S4-level shock-damaged features. Aubrites with S4 orthopyroxene and S2 olivine were probably very weakly shocked again after olivine was annealed to S1.

Reference
Rubin AE (2015) Shock and annealing in aubrites: Implications for parent-body history. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12464]
Published by arrangement with John Wiley&Sons

^1,2,3Katherine H. Joy, ⁴Channon Visscher, ⁵Michael E. Zolensky, ⁶Takashi Mikouchi, ⁷Kenji Hagiya, ⁸Kazumasa Ohsumi, ^1,2David A. Kring
¹Center for Lunar Science and Exploration, The Lunar and Planetary Institute—USRA, Houston, Texas, USA
² NASA Solar System Exploration Research Virtual Institute
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
⁴ Dordt College, Iowa, USA
⁵ARES, NASA Johnson Space Center, Houston, Texas, USA
⁶Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
⁷Graduate School of Science, University of Hyogo, Ako-gun, Hyogo, Japan
⁸Japan Synchrotron Radiation Research Institute (JASRI), Sayo-gun, Hyogo, Japan

Lunar regolith breccias are temporal archives of magmatic and impact bombardment processes on the Moon. Apollo 16 sample 60016 is an “ancient” feldspathic regolith breccia that was converted from a soil to a rock at ~3.8 Ga. The breccia contains a small (70 × 50 μm) rock fragment composed dominantly of an Fe-oxide phase with disseminated domains of troilite. Fragments of plagioclase (An95-97), pyroxene (En74-75, Fs21-22,Wo3-4), and olivine (Fo66-67) are distributed in and adjacent to the Fe-oxide. The silicate minerals have lunar compositions that are similar to anorthosites. Mineral chemistry, synchrotron X-ray absorption near edge spectroscopy (XANES) and X-ray diffraction (XRD) studies demonstrate that the oxide phase is magnetite with an estimated Fe3+/ΣFe ratio of ~0.45. The presence of magnetite in 60016 indicates that oxygen fugacity during formation was equilibrated at, or above, the Fe-magnetite or wüstite–magnetite oxygen buffer. This discovery provides direct evidence for oxidized conditions on the Moon. Thermodynamic modeling shows that magnetite could have been formed from oxidization-driven mineral replacement of Fe-metal or desulphurisation from Fe-sulfides (troilite) at low temperatures (<570 °C) in equilibrium with H₂O steam/liquid or CO₂ gas. Oxidizing conditions may have arisen from vapor transport during degassing of a magmatic source region, or from a hybrid endogenic–exogenic process when gases were released during an impacting asteroid or comet Impact.

Reference
Joy KH, Visscher C, Zolensky ME, Mikouchi T, Hagiya K, Ohsumi K, Kring DA (2015) Identification of magnetite in lunar regolith breccia 60016: Evidence for oxidized conditions at the lunar surface. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12462]

Published by arrangement with John Wiley&Sons

¹Klaus Keil et al. (>10)*
¹Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii at Mānoa, Honolulu, Hawaii, USA
*Find the extensive, full author and affiliation list on the publishers Website

The Vicência meteorite, a stone of 1.547 kg, fell on September 21, 2013, at the village Borracha, near the city of Vicência, Pernambuco, Brazil. It was recovered immediately after the fall, and our consortium study showed it to be an unshocked (S1) LL3.2 ordinary chondrite. The LL group classification is based on the bulk density (3.13 g cm⁻³); the chondrule mean apparent diameter (0.9 mm); the bulk oxygen isotopic composition (δ¹⁷O = 3.768 ± 0.042‰, δ¹⁸O = 5.359 ± 0.042‰, Δ¹⁷O = 0.981 ± 0.020‰); the content of metallic Fe,Ni (1.8 vol%); the Co content of kamacite (1.73 wt%); the bulk contents of the siderophile elements Ir and Co versus Au; and the ratios of metallic Fe⁰/total iron (0.105) versus total Fe/Mg (1.164), and of Ni/Mg (0.057) versus total Fe/Mg. The petrologic type 3.2 classification is indicated by the beautifully developed chondritic texture, the standard deviation (~0.09) versus mean Cr₂O₃ content (~0.14 wt%) of ferroan olivine, the TL sensitivity and the peak temperature and peak width at half maximum, the cathodoluminescence properties of chondrules, the content of trapped ¹³²Xe_tr (0.317 × 10⁻⁸cm³STP g⁻¹), and the Raman spectra for organic material in the matrix. The cosmic ray exposure age is ~72 Ma, which is at the upper end of the age distribution of LL group chondrites. The meteorite is unusual in that it contains relatively large, up to nearly 100 μm in size, secondary fayalite grains, defined as olivine with Fa_>75, large enough to allow in situ measurement of oxygen and Mn-Cr isotope systematics with SIMS. Its oxygen isotopes plot along a mass-dependent fractionation line with a slope of ~0.5 and Δ¹⁷O of 4.0 ± 0.3‰, and are similar to those of secondary fayalite and magnetite in the unequilibrated chondrites EET 90161, MET 96503, and Ngawi. These data suggest that secondary fayalite in Vicência was in equilibrium with a fluid with a Δ¹⁷O of ~4‰, consistent with the composition of the fluid in equilibrium with secondary magnetite and fayalite in other unequilibrated ordinary chondrites. Secondary fayalite and the chondrule olivine phenocrysts in Vicência are not in isotopic equilibrium, consistent with low-temperature formation of fayalite during aqueous alteration on the LL parent body. That alteration, as dated by the ⁵³Mn-⁵³Cr chronology age of secondary fayalite, took place Ma after formation of CV CAIs when anchored to the quenched angrite D’Orbigny.

Reference
Keil K et al. (2015) The Vicência meteorite fall: A new unshocked (S1) weakly metamorphosed (3.2) LL chondrite. Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12456]
Published by arrangement with John Wiley&Sons

^1,2Ulli Raschke, ¹Ralf Thomas Schmitt, ³Iain McDonald, ^1,4Wolf Uwe Reimold, ⁵Dieter Mader, ^5,6Christian Koeberl
¹Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Science, Berlin, Germany
² Freie Universität Berlin, Institut für Geologische Wissenschaften, Berlin, Germany
³School of Earth & Ocean Sciences, Cardiff University, Cardiff, UK
⁴Humboldt-Universität zu Berlin, Berlin, Germany
⁵Department of Lithospheric Research, Center for Earth Sciences, University of Vienna, Vienna, Austria
⁶Natural History Museum, Vienna, Austria

The complex impact structure El’gygytgyn (age 3.6 Ma, diameter 18 km) in northeastern Russia was formed in ~88 Ma old volcanic target rocks of the Ochotsk-Chukotsky Volcanic Belt (OCVB). In 2009, El’gygytgyn was the target of a drilling project of the International Continental Scientific Drilling Program (ICDP), and in summer 2011 it was investigated further by a Russian–German expedition. Drill core material and surface samples, including volcanic target rocks and impactites, have been investigated by various geochemical techniques in order to improve the record of trace element characteristics for these lithologies and to attempt to detect and constrain a possible meteoritic component. The bedrock units of the ICDP drill core reflect the felsic volcanics that are predominant in the crater vicinity. The overlying suevites comprise a mixture of all currently known target lithologies, dominated by felsic rocks but lacking a discernable meteoritic component based on platinum group element abundances. The reworked suevite, directly overlain by lake sediments, is not only comparatively enriched in shocked minerals and impact glass spherules, but also contains the highest concentrations of Os, Ir, Ru, and Rh compared to other El’gygytgyn impactites. This is—to a lesser extent—the result of admixture of a mafic component, but more likely the signature of a chondritic meteoritic component. However, the highly siderophile element contribution from target material akin to the mafic blocks of the ICDP drill core to the impactites remains poorly constrained.

Reference
Raschke U, Schmitt RT, McDonald I, Reimold WU, Mader D, Koeberl C (2015) Geochemical studies of impact breccias and country rocks from the El’gygytgyn impact structure, Russia. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12455]

Published by arrangement with John Wiley&Sons

¹E. P. Gurov, ¹S. B. Shekhunova, ¹V. V. Permyakov
¹Institute of Geological Sciences, National Academy of Sciences of Ukraine, Kiev, Ukraine

Electron microprobe analyses of accessory and opaque minerals from the impact melt rocks of the Boltysh structure, in the central part of the Ukrainian Shield, are presented in this report. Our study establishes a variety of minerals represented by native metals, alloys, oxides, sulfides, phosphates, and silicates, formed during several stages of cooling and solidification of the thick impact melt sheet. Baddeleyite was determined to be the earliest high-temperature mineral to occur in the impact melt rocks. Iron and titanium oxides crystallized earlier or simultaneously with the microliths of orthopyroxene and feldspars. High concentrations of TiO2, Al2O3, and Cr2O3 were identified in some hematite varieties. Cu- and Ni-bearing pyrrhotites occur in impact melt rocks with a glassy matrix. Native metals—copper, platinum, and silver—were likely formed due to the hydrothermal alteration of the upper unit of the impact melt sheet. Zircon is the only accessory mineral found in impact melt rocks that is preserved from the basement granites of the Boltysh structure.

Reference
Gurov EP, Shekhunova SB, Permyakov VV (2015) Accessory and opaque minerals in impact melt rocks of the Boltysh structure, Ukraine. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12457]

Published by arrangement with John Wiley&Sons

¹A. Ody,²F. Poulet, C. ¹Quantin, ²J.-P. Bibring, ³J.L. Bishop, ⁴M.D. Dyar
¹LGLTPE, université Lyon1, bat Geode, campus de la Doua
²rue Raphael Dubois, 69622 Villerbanne CEDEX. 2. IAS, Centre universitaire d’Orsay, bat 121, 91405 Orsay CEDEX
³SETI Institute, Carl Sagan Center, 189 Bernardo Ave., Mountain View, CA 94043, USA
⁴Department of Astronomy, Mount Holyoke College, South Hadley, MA 01075

The objective of this study is to identify and map spectral analogues of some key Martian meteorites (basaltic shergottites Los Angeles, Shergotty, QUE 94201, lherzolitic shergottite ALH A77005, Nakhla, Chassigny and the orthopyroxenite ALH 84001) in order to localize terrain candidates for their source regions. We develop a best fit procedure to reproduce the near-infrared (NIR) spectral properties of the Martian surface as seen by the hyperspectral imaging spectrometer OMEGA/MEx from the NIR spectra of the Martian meteorites. The fitting process is tested and validated, and Root Mean Square (RMS) global maps for each meteorite are obtained. It is found that basaltic shergottites have NIR spectral properties the most representative of the Martian surface with best spectral analogues found in early Hesperian volcanic provinces. Sites with spectral properties similar to those of ALH A77005 are scarce. They are mainly localized in olivine-bearing regions such as Nili Fossae and small Noachian/early Hesperian terrains. The only plausible source region candidate for Chassigny is the Nili Patera caldera dated to 1.6Ga. Widespread spectral analogues for the ALH 84001 meteorite are found northeast of Syrtis major and northwest of the Hellas basin. While this distribution is in agreement with the low-calcium-pyroxene-rich composition and old age (4.1 Ga) of this meteorite, the modal mineralogy of these candidates is not consistent with that of this meteorite. No convincing spectral analogue is found for the Amazonian-aged Nakhla meteorite suggesting that its olivine/high-calcium-pyroxene-rich composition could be representative of the Amazonian terrains buried under dust. Finally, some young rayed craters are proposed as possible candidate for source crater of the studied Martian meteorites.

References
Ody A, Poulet F, Quantin C, Bibring J-P, Bishop JL, Dyard MD (2015) Candidates source regions of Martian Meteorites as identified by OMEGA/MEx. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.019]

Copyright Elsevier

¹F. Tosi et al. (>10)*
¹INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133 Rome, Italy
We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Quadrangle Av-10 ‘Oppia’ is one of five quadrangles that cover the equatorial region of asteroid (4) Vesta. This quadrangle is notable for the broad, spectrally distinct ejecta that extend south of the Oppia crater. These ejecta exhibit the steepest (‘reddest’) visible spectral slope observed across the asteroid and have distinct color properties as seen in multispectral composite images. Compared to previous works that focused on the composition and nature of unusual (‘orange’) ejecta found on Vesta, here we take into account a broader area that includes several features of interest, with an emphasis on mineralogy as inferred from data obtained by Dawn’s Visible InfraRed mapping spectrometer (VIR). Our analysis shows that the older northern and northeastern part of Av-10 is dominated by howardite-like material, while the younger southwestern part, including Oppia and its ejecta blanket, has a markedly eucritic mineralogy. The association of the mineralogical information with the geologic and topographic contexts allows for the establishment of relationships between the age of the main formations observed in this quadrangle and their composition. A major point of interest in the Oppia quadrangle is the spectral signature of hydrous material seen at the local scale. This material can be mapped by using high-resolution VIR data, combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Hydrated mineral phases studied previously on Vesta generally correlate with low-albedo material delivered by carbonaceous asteroids. However, our analysis shows that the strongest OH signature in Av-10 is found in a unit west of Oppia, previously mapped as ‘light mantle material’ and showing moderate reflectance and a red visible slope. With the available data we cannot yet assess the presence of water in this material. However, we offer a possible explanation for its origin.

Reference
Tosi F et al. (2015) Mineralogical analysis of the Oppia quadrangle of asteroid (4) Vesta: Evidence for occurrence of moderate-reflectance hydrated Minerals. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.018]

Copyright Elsevier

¹M.C. De Sanctis et al. (>10*)
¹INAF, Istituto di Astrofisica e Planetologia Spaziali, Area di Ricerca di Tor Vergata, 00133 Roma, Italy
We currently do not have a copyright agreement with this publisher and cannot display the abstract here

The equatorial Marcia quadrangle region is characterized by the large, relatively young impact craters Marcia and Calpurnia and their surrounding dark ejecta field, a hill with a dark-rayed crater named Aricia Tholus, and an unusual diffuse material surrounding the impact crater Octavia. The spectral analysis indicates that while this region is relatively uniform in the pyroxene band centers, it instead shows large differences in pyroxene band depths and reflectance. A large variation of reflectance is seen in the quadrangle: bright and dark materials are present as diffuse material, and as concentrated spots and outcrops. Moreover, OH signature is pervasive in the quadrangle, with a few exceptions. The region, especially the Marcia ejecta field, is characterized by spectra showing the 2 μm band shifted at long wavelenghts. This is commonly associated with eucritic material, believed to have crystallized as lava on Vesta’s surface or within relatively shallow-level dikes and plutons, thus suggesting that this region is a remnant of the old Vestan basaltic crust. However, other characteristics of the spectra do not fully fit the eucritic composition, indicating an alternative explanation for the band center distribution, including the presence of carbonaceous chondritic material mixed with the native Vestan pyroxene.
The detailed mineralogical analysis of the Marcia quadrangle indicates that this quadrangle is the result of the mixture of the Vestan “endogenic” minerals with the “exogenic” carbonaceous chondrites. The stratigraphic units around Marcia clearly show the bright, uncontaminated material interlaced and mixed with the dark material that contains a strong OH signature. Only few small areas can be considered as representative of the old Vestan original material.

Reference
De Sanctis MC et al. (2015) Eucritic crust remnants and the effect of in-falling hydrous carbonaceous chondrites characterizing the composition of Vesta’s Marcia Region. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.014]

Copyright Elsevier

¹Hanley, J., ²V. F. Chevrier, ³R. S. Barrows, ²C. Swaffer, ²T. S. Altheide
¹Department of Space Studies, Southwest Research Institute, Boulder, Colorado, USA
²Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas, USA
³Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, Colorado, USA

The presence and distribution of oxychlorine salts (e.g. chlorates and perchlorates) on Mars has implications for the stability of water, most notably that they lower the freezing temperature. To date, elemental chlorine has been measured by all lander missions, with the perchlorate ion identified at both the Phoenix and Curiosity landing sites, but detection by near-infrared (NIR) and mid-infrared (MIR) remote sensing has been limited to deposits of anhydrous chlorides. Given that oxychlorine salts can form numerous hydrated phases, we have measured their NIR and MIR reflectance spectra from 1–25 µm for comparison to data collected from orbiting spectrometers. Anhydrous oxychlorine salts show almost no features in the NIR, except for small bands of residual adsorbed water. However, hydrated oxychlorine salts show numerous features due to water in the NIR, specifically at ~1.4 and ~1.9 µm. Increasing the hydration state increases the depth and width of the water bands. All oxychlorine salts exhibit an additional feature at ~2.2 µm due to a Cl-O combination or overtone feature, though it is less prominent in the hydrated perchlorate salts, likely overwhelmed by the ClO4-H2O feature at 2.14 µm. All oxychlorine salts show features in the MIR, due to the fundamental vibrations of Cl-O longward of ~8 µm. The NIR spectral features of hydrated oxychlorine salts are similar to other hydrated salts, especially hydrated sulfates, thus identification from orbit may be ambiguous; however, by utilizing the NIR and MIR laboratory data presented here for comparison, oxychlorine salts may be detectable by orbiting spectrometers.

Reference
Hanley J, Chevrier VF, Barrows RS, Swaffer C, Altheide TS (2015) Near- and mid-infrared reflectance spectra of hydrated oxychlorine salts with implications for Mars. Journal of Geophysical Research Planets, 120
Link to Article [doi:10.1002/2013JE004575]

Published by arrangement with John Wiley&Sons

¹F. Hörz,²P. D. Archer Jr., ³P. B. Niles, ⁴M. E. Zolensky, ^3,4M. Evans
¹LZ Technology Inc., Houston, Texas, USA
²Jacobs, NASA Johnson Space Center, Houston, Texas, USA
³ARES, NASA Johnson Space Center, Houston, Texas, USA
⁴Texas A&M University, College Station, Texas, USA

We have investigated the carbonates in the impact melts and in a monolithic clast of highly shocked Coconino sandstone of Meteor Crater, AZ to evaluate whether melting or devolatilization is the dominant response of carbonates during high-speed meteorite impact. Both melt- and clast-carbonates are calcites that have identical crystal habits and that contain anomalously high SiO2 and Al2O3. Also, both calcite occurrences lack any meteoritic contamination, such as Fe or Ni, which is otherwise abundantly observed in all other impact melts and their crystallization products at Meteor Crater. The carbon and oxygen isotope systematics for both calcite deposits suggest a low temperature environment (100 °C) for their precipitation from an aqueous solution, consistent with caliche. We furthermore subjected bulk melt beads to thermogravimetric analysis and monitored the evolving volatiles with a quadrupole mass spectrometer. CO₂ yields were <5 wt%, with typical values in the 2 wt% range; also total CO₂ loss is positively correlated with H₂O loss, an indication that most of these volatiles derive from the secondary calcite. Also, transparent glasses, considered the most pristine impact melts, yield 100 wt% element totals by EMPA, suggesting complete loss of CO₂. The target dolomite decomposed into MgO, CaO, and CO₂; the CO₂ escaped and the CaO and MgO combined with SiO₂ from coexisting quartz and FeO from the impactor to produce the dominant impact melt at Meteor Crater. Although confined to Meteor Crater, these findings are in stark contrast to Osinski et al. (2008) who proposed that melting of carbonates, rather than devolatilization, is the dominant process during hypervelocity impact into carbonate-bearing targets, including Meteor Crater.

Reference
Hörz F, Archer Jr. PD, Niles PB, Zolensky ME, Evans M (2015) Devolatilization or melting of carbonates at Meteor Crater, AZ? Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12453]

Published by arrangement with John Wiley&Sons