¹F. Zambona et al. (>10)*
¹INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
*Find the extensive, full author and affiliation list on the publishers website

The Av-13 (Tuccia) and Av-14 (Urbinia) quadrangles are located in the south-west region of Vesta. They are characterized by a large topographic variability, from the highest (Vestalia terra highlands) to the lowest (Rheasilvia basin). Many geological units in these quadrangle are not associated with mineralogical variability, as shown by the color-composite maps. Maps of mafic absorption band-center position reveal that the principal lithology is eucrite-rich howardite, but diogenite-rich howardite areas also are present, corresponding to particular features such as Antonia and Justina craters, which are also characterized by strong mafic absorptions. These quadrangles, especially Urbinia, are characterized by many bright ejecta, such as those of Tuccia crater, which are the highest reflectance materials on Vesta (Zambon et al., 2014). Dark areas are also present and correspond with regions with deeper OH-signature. The two quadrangle also contain many vertical ridge crests associated with the Rheasilvia impact. These ridges do not show mineralogical differences with respect to their surroundings, but have a distinctive appearance in color-ratio composite images.

Reference
Zambona F et al. (2015) Spectral Analysis of the Quadrangles Av-13 and Av-14 on Vesta. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.015]
Copyright Elsevier

¹A.J. King, ¹P.F. Schofield, ^2,3K.T. Howard, ¹S.S. Russell
¹Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
²Kingsborough Community College of the City University of New York, 2001 Oriental Boulevard, Brooklyn, New York, NY 11235, USA.
³Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA.

The CI chondrites are some of the most hydrated meteorites available to study, making them ideal samples with which to investigate aqueous processes in the early Solar System. Here, we have used position-sensitive-detector X-ray diffraction (PSD-XRD) to quantify the abundance of minerals in bulk samples of the CI chondrite falls Alais, Orgueil and Ivuna, and the Antarctic CI-like chondrites Y-82162 and Y-980115. We find that Alais, Orgueil and Ivuna are dominated by a mixed serpentine/saponite phyllosilicate (81 – 84 vol%), plus minor magnetite (6 – 10%), sulphides (4 – 7%) and carbonates (<3%). This reflects an extended period of aqueous alteration and the near-complete transformation of anhydrous phases into a secondary mineral assemblage. The similarity in total abundance of phyllosilicate suggests that the CI chondrites all experienced the same degree of aqueous alteration on the parent body. In contrast, Y-82162 contains a highly disordered serpentine/saponite phyllosilicate (68 vol%), sulphide (19%), olivine (11%) and magnetite (2%). This mineralogy is distinct from that of the CI chondrites, attesting to both a different starting mineralogy and alteration history. The structure and relatively low abundance of the phyllosilicate, and the high abundance of olivine, are consistent with previous observations that Y-82162 represents CI-like material that following aqueous alteration suffered thermal metamorphism at temperatures >500°C. Similarly, Y-980115 contains disordered serpentine/saponite (71 vol%), sulphide (19%), olivine (8%) and magnetite (2%), confirming that it too is a thermally metamorphosed CI-like chondrite. We suggest that the CI-like chondrites are derived from a different parent body than the CI chondrites, which underwent short-lived thermal metamorphism due to impacts and/or solar radiation.

Reference
King AJ, Schofield PF, Howard KT, Russell SS (2015) Modal mineralogy of CI and CI-like chondrites by X-ray diffraction. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.05.038]

Copyright Elsevier

The most popular papers on Cosmochemistry Papers in May were:

1-Liu N et al. (2015) Correlated Strontium and Barium Isotopic Compositions of Acid-cleaned Single Mainstream Silicon Carbides from Murchison. Astrophysical Journal 803,12 Link to Article [doi:10.1088/0004-637X/803/1/12]

2-Rubin AE (2015) Maskelynite in asteroidal, lunar and planetary basaltic meteorites: An indicator of shock pressure during impact ejection from their parent bodies. Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2015.05.010]

3-Tomeoka K, Ohnishi I (2015) Redistribution of chondrules in a carbonaceous chondrite parent body: A model. Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2015.05.012]

4-Hartmann WK (2014) The giant impact hypothesis: past, present (and future?). Philosophical Transactions of the Royal Society A 13,372, 2024 Link to Article [doi: 10.1098/rsta.2013.0249]

5-Dauphas N, Pourmand A (2015) Thulium anomalies and rare earth element patterns in meteorites and Earth: Nebular fractionation and the nugget effect. Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2015.03.037]

^1,2Xiaojia Zeng, ¹Xiongyao Li, ¹Shijie Wang, ¹Shijie Li, ³Nicole Spring, ¹Hong Tang, ¹Yang Li, ¹Junming Feng
¹Lunar and Planetary Science Research Center, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 55002, China
²University of Chinese Academy of Sciences, Beijing 10049, China
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK

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

Reference
Zeng X, Li X, Wang S, Li S, Spring N, Tang H, Li Y, Feng J (2015) JMSS-1: a new Martian soil simulant.
Earth, Planets and Space 67:72
Link to Article [doi:10.1186/s40623-015-0248-5]

¹E. Ammannito
¹University of California Los Angeles, Earth Planetary and Space Sciences, Los Angeles, CA-90095, USA
*Find the extensive, full author and affiliation list on the publishers website

We present and describe the maps of spectral parameters such as pyroxene band centers and depths, reflectance at 1.4 μm and 2.8μm band depth in the Rheasilvia quadrangle. We found a broad anti-correlation between pyroxene band centers and depths while the reflectance is not correlated with the pyroxene spectral parameters. In addition, we found that the Rheasilvia quadrangle is free of OH absorption signatures. We also derived lithological maps with improvements in the spatial resolution with respect to previous lithological maps of the same region. We confirm that the central mound is dominated by eucritic/howarditic pyroxene while diogenitic lithology has been found mainly in a region delineated by Tarpeia, Severina and Mariamne craters. We found small scale variations in the composition of pyroxene. These variations identify lithological units that extend for tens of km, although small units of less than 1 km have also been found. We consider this fact as an indication of a high level of compositional heterogeneity within the Vestan crust.

Reference
Ammannito E et al. (2015) Compositional variations in the Vestan Rheasilvia basin. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.017]

Copyright Elsevier

¹Lidia Pittarello, ²Fabrizio Nestola, ³Cecilia Viti, ⁴Alvaro Penteado Crósta, ^1,5Christian Koeberl
¹ Department of Lithospheric Research, University of Vienna, Vienna, Austria
² Department of Geosciences, University of Padova, Padova, Italy
³ Department of Physics, Earth and Environmental Sciences, University of Siena, Siena, Italy
⁴ Institute of Geosciences, Campinas SP, Brazil
⁵ Natural History Museum, Vienna, Austria

Shatter cones are one of the most widely recognized pieces of evidence for meteorite impact events on Earth, but the process responsible for their formation is still debated. Evidence of melting on shatter cone surfaces has been rarely reported in the literature from terrestrial impact craters but has been recently observed in impact experiments. Although several models for shatter cones formation have been proposed, so far, no one can explain all the observed features. Shatter cones’ from the Vista Alegre impact structure, Brazil, formed in fine-grained basalt of the Jurassic-Cretaceous Serra Geral Formation (Paraná large igneous province). A continuous quenched melt film, consisting of a crystalline phase, mica, and amorphous material, decorates the striated surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine-grained matrix, occur subparallel to the striated surface. Several techniques were applied to characterize the crystalline phase in the melt, including Raman spectroscopy and transmission electron microscopy. Results are not consistent with any known mineral, but they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of tensile fracturing at the tip of a fast propagating shock-induced rupture, which led to the formation of shatter cones at the tail of the shock front, likely during the early stage of the impact events.

References
Pittarello L, Nestola F, Viti C, Crósta AP, Koeberl C (2015) Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure, Brazil. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12466]

Published by arrangement with John Wiley&Sons

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