¹T. Kevin Croat, ¹ Thomas J. Bernatowicz, ^1,2Tyrone L. Daulton
¹Laboratory for Space Sciences and Department of Physics, Washington University, Saint Louis, MO 63130, USA
E-mail: tkc@wustl.edu
²Institute of Materials Science and Engineering, Washington University, Saint Louis, MO 63130, USA

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Reference
Croat TK, Bernatowicz TJ, Daulton TL (2014) Graphitic Carbon: Presolar Graphitic Carbon Spherules: Rocks from Stars. ELEMENTS 10, 441-446.
Link to Article [doi:10.2113/gselements.10.6.441]

¹Melissa D. Lane, ²Janice L. Bishop, ³M. Darby Dyar, ⁴Takahiro Hiroi, ⁵Stanley A. Mertzman, ⁶David L. Bish, ^7,8Penelope L. King, ⁹A. Deanne Rogers
¹Planetary Science Institute, 1700 E. Fort Lowell Road, Suite 106, Tucson, Arizona 85719, U.S.A.
²SETI Institute/NASA-Ames Research Center, Mountain View, California 94043, U.S.A.
³Mount Holyoke College, South Hadley, Massachusetts 01075, U.S.A.
⁴Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, U.S.A.
⁵Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania 17603, U.S.A.
⁶Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, U.S.A.
⁷Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
⁸Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 3K7, Canada
⁹Department of Geosciences, State University of New York at Stony Brook, Stony Brook, New York 11790, U.S.A.

Sulfate minerals are important indicators for aqueous geochemical environments. The geology and mineralogy of Mars have been studied through the use of various remote-sensing techniques, including thermal (mid-infrared) emission and visible/near-infrared reflectance spectroscopies. Spectral analyses of spacecraft data (from orbital and landed missions) using these techniques have indicated the presence of sulfate minerals on Mars, including Fe-rich sulfates on the iron-rich planet. Each individual Fe-sulfate mineral can be used to constrain bulk chemistry and lends more information about the specific formational environment [e.g., Fe2+ sulfates are typically more water soluble than Fe3+ sulfates and their presence would imply a water-limited (and lower Eh) environment; Fe3+ sulfates form over a range of hydration levels and indicate further oxidation (biological or abiological) and increased acidification]. To enable better interpretation of past and future terrestrial or planetary data sets, with respect to the Fe-sulfates, we present a comprehensive collection of mid-infrared thermal emission (2000 to 220 cm−1; 5–45 μm) and visible/near-infrared (0.35–5 μm) spectra of 21 different ferrous- and ferric-iron sulfate minerals. Mid-infrared vibrational modes (for SO4, OH, H2O) are assigned to each thermal emissivity spectrum, and the electronic excitation and transfer bands and vibrational OH, H2O, and SO4 overtone and combination bands are assigned to the visible/near-infrared reflectance spectra. Presentation and characterization of these Fe-sulfate thermal emission and visible/near-infrared reflectance spectra will enable the specific chemical environments to be determined when individual Fe-sulfate minerals are identified.

Reference
Lane MD, Bishop JL, Dyar MD, Hiroi T, Mertzman SA, Bish DL, King PL, Rogers AD (2014) Mid-infrared emission spectroscopy and visible/near-infrared reflectance spectroscopy of Fe-sulfate Minerals. American Mineralogist 100, 66-82.
Link to Article [doi:10.2138/am-2015-4762]

Copyright: The Mineralogical Society of America

¹A. Deanne Rogers,²Victoria E. Hamilton
¹Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
²Department of Space Science, Southwest Research Institute, Boulder, CO, USA

We identified ten distinct classes of mineral assemblage on Mars through statistical analyses of mineral abundances derived from Mars Global Surveyor Thermal Emission Spectrometer (TES) data at a spatial resolution of eight pixels per degree. Two classes are new regions in Sinus Meridiani and northern Hellas basin. Except for crystalline hematite abundance, Sinus Meridiani exhibits compositional characteristics similar to Meridiani Planum; these two regions may share part of a common history. The northern margin of Hellas basin lacks olivine and high-Ca pyroxene compared to terrains just outside the Hellas outer ring; this may reflect a difference in crustal compositions and/or aqueous alteration. Hesperian highland volcanic terrains are largely mapped into one class. These terrains exhibit low-to-intermediate potassium and thorium concentrations (from Gamma Ray Spectrometer (GRS) data) compared to older highland terrains, indicating differences in the complexity of processes affecting mantle melts between these different-aged terrains. A previously reported, locally-observed trend towards decreasing proportions of low-calcium pyroxene relative to total pyroxene with time is also apparent over the larger scales of our study. Spatial trends in olivine and pyroxene abundance are consistent with those observed in near-infrared data sets. Generally, regions that are distinct in TES data also exhibit distinct elemental characteristics in GRS data, suggesting that surficial coatings are not the primarily control on TES mineralogical variations, but rather reflect regional differences in igneous and large-scale sedimentary/glacial processes. Distinct compositions measured over large, low-dust regions from multiple data sets indicate that global homogenization of unconsolidated surface materials has not occurred.

Reference
Rogers AD, Hamilton VE (2014) Compositional Provinces of Mars from Statistical Analyses of TES, GRS, OMEGA and CRISM Data. Journal of Geophysical Research (Planets) (in Press)
Link to Article [DOI: 10.1002/2014JE004690]

Published by arrangement with John Wiley&Sons

^1,2Devin L. Schrader, ^2,3,4,5Harold C. Connolly Jr., ²Dante S. Lauretta, ²Thomas J. Zega,
⁶Jemma Davidson,²Kenneth J. Domanik
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA
²Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
³Department Physical Sciences, Kingsborough Community College of the City University of New York, Brooklyn, New York, USA
⁴Department of Earth and Environmental Sciences, The Graduate Center of CUNY, New York, New York, USA
⁵Department Earth and Planetary Sciences, AMNH, Central Park West, New York, New York, USA
⁶Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, District of Columbia, USA

To better understand the formation conditions of ferromagnesian chondrules from the Renazzo-like carbonaceous (CR) chondrites, a systematic study of 210 chondrules from 15 CR chondrites was conducted. The texture and composition of silicate and opaque minerals from each observed FeO-rich (type II) chondrule, and a representative number of FeO-poor (type I) chondrules, were studied to build a substantial and self-consistent data set. The average abundances and standard deviations of Cr2O3 in FeO-rich olivine phenocrysts are consistent with previous work that the CR chondrites are among the least thermally altered samples from the early solar system. Type II chondrules from the CR chondrites formed under highly variable conditions (e.g., precursor composition, redox conditions, cooling rate), with each chondrule recording a distinct igneous history. The opaque minerals within type II chondrules are consistent with formation during chondrule melting and cooling, starting as S- and Ni-rich liquids at 988–1350 °C, then cooling to form monosulfide solid solution (mss) that crystallized around olivine/pyroxene phenocrysts. During cooling, Fe,Ni-metal crystallized from the S- and Ni-rich liquid, and upon further cooling mss decomposed into pentlandite and pyrrhotite, with pentlandite exsolving from mss at 400–600 °C. The composition, texture, and inferred formation temperature of pentlandite within chondrules studied here is inconsistent with formation via aqueous alteration. However, some opaque minerals (Fe,Ni-metal versus magnetite and panethite) present in type II chondrules are a proxy for the degree of whole-rock aqueous alteration. The texture and composition of sulfide-bearing opaque minerals in Graves Nunataks 06100 and Grosvenor Mountains 03116 suggest that they are the most thermally altered CR chondrites.

Reference
Schrader DL, Connolly Jr HC, Lauretta DS, Zega TJ, Davidson J, Domanik KJ (2014) The formation and alteration of the Renazzo-like carbonaceous chondrites III: Toward understanding the genesis of ferromagnesian chondrules. Meteoritics&Planetary Society (in Press)
Link to Article [DOI: 10.1111/maps.12402]

Published by Arrangement with John Wiley&Sons

¹Antonio S. Buono, ¹David Walker
¹Lamont Doherty Earth Observatory, Department of Earth and Environmental Sciences, Columbia University, Palisades, New York, USA

The Fe-FeS system maintains a eutectic temperature of 990 ± 10 °C to at least 8 GPa if starting materials and pressure media are rigorously dehydrated. Literature reports of pressure-induced freezing point depression of the eutectic for the Fe-FeS system are not confirmed. Modest addition of oxygen alone is confirmed to cause negligible freezing point depression at 6 GPa. Addition of H alone causes a progressive decrease in the eutectic temperature with P in the Fe-FeS-H system to below 965 °C at 6 GPa to below 950 °C at 8 GPa. It is our hypothesis that moisture contamination in unrigorously dried experiments may be an H source for freezing point depression. O released from H2O disproportionation reacts with Fe and is sequestered as ferropericlase along the sample capsules walls, leaving the H to escape the system and/or enter the Fe-FeS mixture. The observed occurrence of ferropericlase on undried MgO capsule margins is otherwise difficult to explain, because an alternate source for the oxygen in the ferropericlase layer is difficult to identify. This study questions the use of pressure-depressed Fe-S eutectic temperatures and suggests that the lower eutectic temperatures sometimes reported are achieved by moving into the ternary Fe-S-H system. These results adjust slightly the constraints on eutectic temperatures allowed for partly solidified cores on small planets. H substantially diminishes the temperature extent of the melting interval in Fe-S by reducing the melting points of the crystalline phases more than it depresses the eutectic.

Reference
Buono AS, Walker D (2014) H, not O or pressure, causes eutectic T depression in the Fe-FeS System to 8 GPa. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12372]

Published by arrangement with John Wiley&Sons

¹Sebastian Sturm,¹Thomas Kenkmann, ²Malte Willmes, ³Gisela Pösges, ⁴Harald Hiesinger
¹Institute of Earth and Environmental Sciences—Geology, Albert-Ludwigs-Universität Freiburg (ALU), Freiburg, Germany
²Research School of Earth Sciences, Australian National University (ANU), Acton, Canberra, Australia
³Rieskrater Museum, Nördlingen, Germany
⁴Institut für Planetologie, Westfälische Wilhelms-Universität Münster (WWU), Münster, Germany

The Ries crater is a well-preserved, complex impact crater that has been extensively used in the study of impact crater formation processes across the solar system. However, its geologic structure, especially the megablock zone, still poses questions regarding crater formation mechanics. The megablock zone, located between the inner crystalline ring and outer, morphologic crater rim, consists of allochthonous crystalline and sedimentary blocks, Bunte Breccia deposits, patches of suevite, and parautochthonous sedimentary blocks that slumped into the crater during crater modification. Our remote sensing detection method in combination with a shallow drilling campaign and geoelectric measurements at two selected megablocks proved successful in finding new megablock structures (>25 m mean diameter) within the upper approximately 1.5 m of the subsurface in the megablock zone. We analyzed 1777 megablocks of the megablock zone, 81 of which are new discoveries. In our statistical analysis, we also included 2318 ejecta blocks >25 m beyond the crater rim. Parautochthonous megablocks show an increase in total area and size toward the final crater rim. The sizes of allochthonous megablocks generally decrease with increasing radial range, but inside the megablock zone, the coverage with postimpact sediments obscures this trend. The size-frequency distribution of all megablocks obeys a power-law distribution with an exponent between approximately −1.7 and −2.3. We estimated a total volume of 95 km3 of Bunte Breccia and 47 km3 of megablocks. Ejecta volume calculations and a palinspastic restoration of the extension within the megablock zone indicate that the transient cavity diameter was probably 14–15 km.

Reference
Sturm S, Kenkmann T, Willmes M, Pösges G, Hiesinger H (2014) The distribution of megablocks in the Ries crater, Germany: Remote sensing, field investigation, and statistical analyses. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12408]
Published by arrangement with John Wiley&Sons

¹Sherry K. Fieber-Beyer, ¹Michael J. Gaffey, ²William F. Bottke, ¹Paul S. Hardersen
¹Department of Space Studies, University Stop 9008, University of North Dakota, 58202
²Southwest Research Institute and NASA Lunar Science Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA

The research is an integrated effort beginning with telescopic observations and extending through detailed mineralogical characterizations to provide constraints on the albedo, diameter, composition, and meteorite affinity of near-Earth object-potentially hazardous asteroid (NEO-PHA 2007 LE). Results of the analysis indicate a diameter of 0.56 kilometers (km) and an albedo of 0.08. 2007 LE exhibits a 1-μm absorption feature without a discernible Band II feature. Compositional analysis of 2007 LE reveal Fs17 and Fa19 values, which are consistent with the Fa and Fs values for the H-type ordinary chondrites (Fs14.5-18 and Fa16-20) and of asteroid (6) Hebe (Fs17 and Fa15). Spectroscopically, 2007 LE does not appear like the average H-chondrite spectra, exhibiting a reddened spectrum and subdued absorption feature. Further investigation of the meteorite classes yielded a black chondrite, Rose City, which is both similar in mineralogy and spectrally to PHA 2007 LE. Dynamical analysis could not directly link the fall of the Rose City meteorite to 2007 LE. As it stands, 2007 LE and Rose City have a compositional link, and both could come from the same parent body/possible family, one known source of the H chondrites is (6) Hebe.

Reference
Fieber-Beyer SL, Gaffey MJ, Bottke WF, Hardersen PS (2014) Potentially Hazardous Asteroid 2007 LE: Compositional Link to the Black Chondrite Rose City and Asteroid (6) Hebe. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.12.021]

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