¹James M.T. Lewis, ¹Jonathan S. Watson, ²Jens Najorka, ¹Duy Luong, ¹Mark A. Sephton
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, United Kingdom.
²Impacts and Astromaterials Research Centre, Department of Mineralogy, Natural History Museum, London, United Kingdom.

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Reference
Lewis JMT, Watson JS, Najorka J, Luong D, Sephton MA (2015) Sulfate Minerals: A Problem for the Detection of Organic Compounds on Mars? Astrobiology 15(3): 247-258
Link to Article [doi:10.1089/ast.2014.1160]

¹Charles A. Poteet, ¹Douglas C. B. Whittet, ²Bruce T. Draine
¹New York Center for Astrobiology, Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180, USA
²Princeton University Observatory, Peyton Hall, Princeton, NJ 08544, USA

We investigate the composition of interstellar grains along the line of sight toward ζ Ophiuchi, a well-studied environment near the diffuse-dense cloud transition. A spectral decomposition analysis of the solid-state absorbers is performed using archival spectroscopic observations from the Spitzer Space Telescope and Infrared Space Observatory. We find strong evidence for the presence of sub-micron-sized amorphous silicate grains, principally comprised of olivine-like composition, with no convincing evidence of H2O ice mantles. However, tentative evidence for thick H2O ice mantles on large (a ≈ 2.8 μm) grains is presented. Solid-state abundances of elemental Mg, Si, Fe, and O are inferred from our analysis and compared to standard reference abundances. We find that nearly all of the Mg and Si atoms along the line of sight reside in amorphous silicate grains, while a substantial fraction of the elemental Fe resides in compounds other than silicates. Moreover, we find that the total abundance of elemental O is largely inconsistent with the adopted reference abundances, indicating that as much as ~156 ppm of interstellar O is missing along the line of sight. After taking into account additional limits on the abundance of elemental O in other O-bearing solids, we conclude that any missing reservoir of elemental O must reside on large grains that are nearly opaque to infrared radiation.

Reference
Poteet PA, Whittet DCB, Draine BT (2015) The Composition of Interstellar Grains toward ζ Ophiuchi: Constraining the Elemental Budget near the Diffuse-dense Cloud Transition. Astrophysical Journal 801, 110.
Link to Article [doi:10.1088/0004-637X/801/2/110]

¹Nicole G. Lunning,¹Harry Y. McSween Jr.,²Travis J. Tenner,³Noriko T. Kita,⁴Robert J. Bodnar
¹Department of Earth and Planetary Sciences and Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996, USA
²Department of Geosciences, University of Wisconsin, Madison, WI 53706, USA
³Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA

A number of meteorites contain evidence that rocky bodies formed and differentiated early in our solar system’s history, and similar bodies likely contributed material to form the planets. These differentiated rocky bodies are expected to have mantles dominated by Mg-rich olivine, but direct evidence for such mantles beyond our own planet has been elusive. Here, we identify olivine fragments (Mg# = 80–92) in howardite meteorites. These Mg-rich olivine fragments do not correspond to an established lithology in the howardite–eucrite–diogenite (HED) meteorites, which are thought to be from the asteroid 4 Vesta; their occurrence in howardite breccias, combined with diagnostic oxygen three-isotope signatures and minor element chemistry, indicates they are vestan. The major element chemistry of these Mg-rich olivines suggests that they formed as mantle residues, in crustal layered intrusions, or in Mg-rich basalts. The trace element chemistry of these Mg-rich olivines supports an origin as mantle samples, but other formation scenarios could be possible. Interpreted as mantle samples, the range of Mg-rich olivine compositions indicates that Vesta’s structure differs from that predicted by conventional models: Vesta has a chemically heterogeneous mantle that feeds serial magmatism. The range of olivine major element chemistries is consistent with models of an incompletely melted mantle such as in the model proposed by Wilson and Keil (2013) rather than a whole-mantle magma ocean for Vesta. Trace element chemistries of Mg-rich pyroxenes (Mg# = 85–92) provide support that some of these pyroxenes may represent initial fractional crystallization of mantle partial melts.

Reference
Lunning NG,McSween Jr. HY,Tenner TJ, Kita NT, Bodnar RJ (2015) Olivine and pyroxene from the mantle of asteroid 4 Vesta. Earth and Planetary Science Letters 418, 126–135
Link to Article [doi:10.1016/j.epsl.2015.02.043]

Copyright Elsevier

^1,2Haolan Tang, ¹Nicolas Dauphas
¹Origins Lab, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA
²Ion Probe Group, Department of earth and Space Sciences, University of California, Los Angeles, 595 Charles E. Young Drive East, Los Angeles, CA 90095, US

Iron-60 (t1/2 = 2.62 Myr) is a short-lived nuclide that can help constrain the astrophysical context of Solar System formation and date early Solar System events. A high abundance of 60Fe(60Fe/56Fe ≈ 4 × 10−7) was reported by in situ techniques in some chondrules from the LL3.00 Semarkona meteorite, which was taken as evidence that a supernova exploded in the vicinity of the birthplace of the Sun. However, our previous multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) measurements of a wide range of meteoritic materials, including chondrules, showed that 60Fe was present in the early Solar System at a much lower level (60Fe/56Fe ≈ 10−8). The reason for the discrepancy is unknown but only two Semarkona chondrules were measured by MC-ICPMS and these had Fe/Ni ratios below ~2× chondritic. Here, we show that the initial 60Fe/56Fe ratio in Semarkona chondrules with Fe/Ni ratios up to ~24× chondritic is (5.39 ± 3.27) × 10−9. We also establish the initial 60Fe/56Fe ratio at the time of crystallization of the Sahara 99555 angrite, a chronological anchor, to be (1.97 ± 0.77) × 10−9. These results demonstrate that the initial abundance of 60Fe at Solar System birth was low, corresponding to an initial 60Fe/56Fe ratio of (1.01 ± 0.27) × 10−8.

Reference
Tang H, Dauphas N (2015) Low 60Fe Abundance in Semarkona and Sahara 99555. Astrophysical Journal 802 22.
Link to Article [doi:10.1088/0004-637X/802/1/22]

¹Lonia R.Friedlander, ¹Timothy D. Glotch, ²David L. Bish, ³M. Darby Dyar, ⁴Thomas G.Sharp, ¹Elizabeth C. Sklute, ⁵Joseph R. Michalski

¹Geosciences Department, Stony Brook University, Stony Brook, NY, 11794-2100 USA
¹Department of Geological Sciences, Indiana University, 1001 East 10th Street, Bloomington,
IN, 47405-1405 USA
³Department of Astronomy, Mount Holyoke College, 50 College Street, South Hadley, MA, 01075 USA
⁴School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, AZ,85287-1404 USA
⁵Planetary Science Institute, 1700 E. Fort Lowell, Tucson, AZ, 85719 USA

Many phyllosilicate deposits remotely detected on Mars occur within bombarded terrains. Shock metamorphism from meteor impacts alters mineral structures, producing changed mineral spectra. Thus, impacts have likely affected the spectra of remotely sensed martian phyllosilicates. We present spectral analysis results for a natural nontronite sample (NAu-1) before and after laboratory-generated impacts over five peak pressures between 10 – 40 GPa. We conducted a suite of spectroscopic analyses to characterize the sample’s impact-induced structural and spectral changes. Nontronite becomes increasingly disordered with increasing peak impact pressure. Every infrared spectroscopic technique used showed evidence of structural changes at shock pressures above ~25 GPa. Reflectance spectroscopy in the visible near-infrared (VNIR) region is primarily sensitive to the vibrations of metal-OH and interlayer H2O groups in the nontronite octahedral sheet. Mid-infrared (MIR) spectroscopic techniques are sensitive to the vibrations of silicon and oxygen in the nontronite tetrahedral sheet. Because the tetrahedral and octahedral sheets of nontronite deform differently, impact-driven structural deformation may contribute to differences in phyllosilicate detection between remote sensing techniques sensitive to different parts of the nontronite structure. Observed spectroscopic changes also indicated that the sample’s octahedral and tetrahedral sheets were structurally deformed, but not completely dehydroxylated. This finding is an important distinction from previous studies of thermally altered phyllosilicates in which dehydroxylation follows dehydration in a step-wise progression preceding structural deformation. Impact-alteration may thus complicate mineral-specific identifications based on the location of OH-group bands in remotely detected spectra. This is a key implication for martian remote sensing arising from our results.

Reference
Friedlander R, Glotch TD, Bish DL, Dyar MD, Sharp TG, Sklute EC, Michalski JR (2015) Structural and spectroscopic changes to natural nontronite induced by experimental impacts between 10 and 40 GPa. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004638]

Published by arrangement with John Wiley&Sons

^1,2,3T.J. Peter,^2,3J.I. Simon,²J.H. Jones,⁴T. Usui,⁴R. Moriwaki,⁵R.C. Economos,⁵A.K. Schmitt,⁵K.D. McKeegan
¹Lunar and Planetary Institute, Houston, TX 77058, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
³Center for Isotope Cosmochemistry and Geochronology, NASA Johnson Space Center, Houston, TX 77058, USA
⁴Department of Earth & Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan
⁵Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA

The apparent lack of plate tectonics on all terrestrial planets other than Earth has been used to support the notion that for most planets, once a primitive crust forms, the crust and mantle evolve geochemically-independent through time. This view has had a particularly large impact on models for the evolution of Mars and its silicate interior. Recent data indicating a greater potential that there may have been exchange between the martian crust and mantle has led to a search for additional geochemical evidence to support the alternative hypothesis, that some mechanism of crustal recycling may have operated early in the history of Mars.
In order to study the most juvenile melts available to investigate martian mantle source(s) and melting processes, the trace element compositions of olivine-hosted melt inclusions for two incompatible-element-depleted olivine-phyric shergottites, Yamato 980459 (Y98) and Tissint, and the interstitial glass of Y98, have been measured by Secondary Ionization Mass Spectrometry (SIMS). Chondrite-normalized Rare Earth Element (REE) patterns for both Y98 and Tissint melt inclusions, and the Y98 interstitial glass, are characteristically light-REE depleted and parallel those of their host rock. For Y98, a clear flattening and upward inflection of La and Ce, relative to predictions based on middle and heavier REE, provides evidence for involvement of an enriched component early in their magmatic history; either inherited from a metasomatized mantle or crustal source, early on and prior to extensive host crystallization.
Comparing these melt inclusion and interstitial glass analyses to existing melt inclusion and whole-rock data sets for the shergottite meteorite suite, defines mixing relationships between depleted and enriched end members, analogous to mixing relationships between whole rock Sr and Nd isotopic measurements. When considered in light of their petrologic context, the origin of these trace element enriched and isotopically evolved signatures represents either (1) crustal assimilation during the final few km of melt ascent towards the martian surface, or (2) assimilation soon after melt segregation, through melt–rock interaction with a portion of the martian crust recycled back into the mantle.

Reference
Peters TJ, Simon JI, Jones JH, Usui T, Moriwaki R, Economos RC, Schmitt AK, McKeegan KD (2015) Tracking the source of the enriched martian meteorites in olivine-hosted melt inclusions of two depleted shergottites, Yamato 980459 and Tissint. Earth and Planetary Science Letters 418, 91–102.
Link to Article [doi:10.1016/j.epsl.2015.02.033]

Copyright Elsevier

¹Jennifer L. Claydon,¹Sarah A. Crowther,^1,2,3Vera A. Fernandes,¹Jamie D. Gilmour
¹School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
²Museum für Naturkunde- Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, 10115 Berlin, Germany
³UNINOVA, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Monte de Caparica, Portugal
⁴The Centre for Earth Evolution and Dynamics, Univ. of Oslo, PO Box 1048 Blindern 0316 Oslo, Norway

The meteorite Graves Nunataks 06128/06129 is the only known example of felsic asteroidal crust. Knowledge of its history can help shed light on the evolution processes of planetesimals. The noble gases can be used to constrain both the chronology of meteorites and the processes that result in movements of volatile elements on asteroidal bodies. We have examined the I-Xe and Ar-Ar systems of the plagioclase-rich achondrite, Graves Nunataks 06129 by high-resolution laser step-heating of irradiated samples. Iodine and 129Xe∗ are both present but are released at different temperatures and do not show a correlation, therefore the I-Xe system in GRA 06129 has no chronological significance. We propose that radiogenic 129Xe∗ was lost from primary phases and parentless 129Xe∗ was later introduced into the rock by interaction with a fluid sourced from a reservoir that evolved with a high I/Xe ratio. This could have been the same halogen-rich fluid that induced the conversion of merrillite and pyroxene into chlorapatite. Inherited 40Ar (i.e. not generated by in situ decay of 40K) is also present in one of three fragments studied here and may have been introduced at the same time as parentless 129Xe∗.

Reference
Claydon CK, Crowther SA, Fernandes VA, Gilmour JD (2015) Noble gases and halogens in Graves Nunataks 06129: the complex thermal history of a felsic asteroid crust. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.03.01]

Copyright Elsevier

Pavel P. Povinec¹, Jozef Masarik¹, Ivan Sýkora¹, Andrej Kováčik¹, Juraj Beňo¹, Matthias M. M. Meier^2,3, Rainer Wieler², Matthias Laubenstein⁴ and Vladimir Porubčan^5,6

¹Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
²Department of Earth Sciences, ETH Zürich, Zürich, Switzerland
³Centre de Recherches Pétrographiques et Géochimiques, CNRS Nancy, Vandœuvre les Nancy, France
⁴National Laboratory of Gran Sasso, INFN, I-67100, Assergi (AQ), Italy
⁵Department of Astronomy, Physics of the Earth and Meteorology, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
⁶Astronomical Institute, Slovak Academy of Sciences, Bratislava, Slovakia

Results of nondestructive gamma-ray analyses of cosmogenic radionuclides (7Be, 22Na, 26Al, 46Sc, 48V, 54Mn, 56Co, 57Co, 58Co, and 60Co) in 19 fragments of the Košice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic-ray particles in the space affecting radionuclides with different half-lives. Monte Carlo simulations of the production rates of 60Co and 26Al compared with experimental data indicate that the pre-atmospheric radius of the meteoroid was 50 ± 5 cm. In two Košice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble-gas cosmic-ray exposure age of the Košice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Košice is a regolith breccia. The agreement between the simulated and observed 26Al activities indicate that the meteoroid was mostly irradiated by a long-term average flux of galactic cosmic rays of 4.8 particles cm−2 s−1, whereas the short-lived radionuclide activities are more consistent with a flux of 7.0 protons cm−2 s−1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall.

Reference
Povinec PP, Masarik J, Sýkora I, Kováčik A, Beňo J, Meier MMM, Wieler R, Laubenstein M and Porubčan V (2015) Cosmogenic nuclides in the Košice meteorite: Experimental investigations and Monte Carlo simulations. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12380]

Published by arrangement with John Wiley & Sons

Xenia Ritter1,*, Alexander Deutsch2, Jasper Berndt1 andEric Robin3

¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster (WWU), Münster, Germany
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster (WWU), Münster, Germany
³CEA-Grenoble INAC/SP2M/LEMMA, Grenoble Cedex 9, France

We have investigated six impact glass spherules from the K-Pg event bed at Beloc, Haiti, using optical and electron microscopy, electron microprobe and in situ laser ablation–mass spectrometry (LA-ICP-MS; 37 trace elements, spot size 90–35 μm), in order to understand geochemical changes during alteration. The mm-sized glass spherules are partly or totally altered to smectite, but original textural features are preserved. The average trace-element composition of glass matches that one of the upper continental crust. Hints for a “meteoritic component” are lacking (Ni/Cr < 1.3; Pt below detection limit). Compared to this fresh glass, smectites are strongly depleted in trace elements, except for Li, Sc, V, Ni, Ga, Ge, and Ba. The chondrite-normalized REE distribution patterns are flat with subchondritic abundances, related to their very low degree of crystallinity. We observe a positive Eu and a strong negative Ce anomaly; the latter is explained by formation of an organic Ce4+-complex, soluble under reducing conditions. Zr/Hf of glasses and smectites is chondritic to superchondritic (35–40), whereas Nb/Ta in smectite is subchondritic (5–12) compared to Nb/Ta in the glass (~14–18). The low Nb/Ta is due to the low Nb concentrations in the smectite. Using in situ techniques with high spatial resolution, we have documented for the first time the significant changes in diagnostic elemental ratios during alteration of glass spherules. This has to be taken into account in the interpretation of geochemical data of not only impact materials but also volcanic glass, especially if bulk rock methods are used.

Reference
Ritter X, Deutsch A, Berndt J and Robin E (2015) Impact glass spherules in the Chicxulub K-Pg event bed at Beloc, Haiti: Alteration patterns. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12432]

Published by arrangement with John Wiley & Sons

Li Li^1,2, Zongyu Yue¹, Kaichang Di¹ and Man Peng¹

¹State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing, China
²University of Chinese Academy of Sciences, Beijing, China

The formation mechanism of layered ejecta craters on Mars has remained a topic of intense debate since their discovery. In this study, we perform a global morphological analysis of Martian layered ejecta craters using Thermal Emission Imaging System (THEMIS) images and Mars Orbiter Laser Altimeter (MOLA) data. The study focuses on the ejecta morphologies and well-defined distal rampart characteristics associated with 9945 layered ejecta craters with a diameter greater than 1.5 km distributed across the entire Martian surface. Data analysis based on the new database provides new information on the distribution and morphological details of the three major layered ejecta morphologies (single layer ejecta [SLE], double layer ejecta [DLE], and multiple layer ejecta [MLE]). Global analysis is applied to the latitudinal distribution of characteristic parameters, including the ejecta mobility, lobateness values, and onset diameter. Our survey of the distribution and characteristics of layered ejecta craters reveals that strong correlations exist between ejecta mobility and latitude, and there is a latitudinal dependence of onset diameter. Our study of Martian layered ejecta craters provides more detailed information and insights of a connection between the layered ejecta morphologies and the subsurface volatiles.

Reference
Li L, Yue Z, Di K and Peng N (2015) Observations of Martian layered ejecta craters and constraints on their formation mechanisms. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12438]

Published by arrangement with John Wiley & Sons