^1,2Shuying Yang, ^1,2Munir Humayun, ³Kevin Righter, ^1,4Gwendolyn Jefferson, ^1,5Dana Fields, ⁶Anthony J. Irving
¹National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA
²Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, Florida, USA
³National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas, USA
⁴Carter High School, Rialto, California, USA
⁵Rickards High School, Tallahassee, Florida, USA
⁶Department of Earth & Space Sciences, University of Washington, Seattle, Washington, USA

Elemental abundances for volatile siderophile and chalcophile elements for Mars inform us about processes of accretion and core formation. Such data are few for Martian meteorites, and are often lacking in the growing number of desert finds. In this study, we employed laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) to analyze polished slabs of 15 Martian meteorites for the abundances of about 70 elements. This technique has high sensitivity, excellent precision, and is generally accurate as determined by comparisons of elements for which literature abundances are known. However, in some meteorites, the analyzed surface is not representative of the bulk composition due to the over- or underrepresentation of a key host mineral, e.g., phosphate for rare earth elements (REE). For other meteorites, the range of variation in bulk rastered analyses of REE is within the range of variation reported among bulk REE analyses in the literature. An unexpected benefit has been the determination of the abundances of Ir and Os with a precision and accuracy comparable to the isotope dilution technique. Overall, the speed and small sample consumption afforded by this technique makes it an important tool widely applicable to small or rare meteorites for which a polished sample was prepared. The new volatile siderophile and chalcophile element abundances have been employed to determine Ge and Sb abundances, and revise Zn, As, and Bi abundances for the Martian mantle. The new estimates of Martian mantle composition support core formation at intermediate pressures (14 ± 3 GPa) in a magma ocean on Mars.

Reference
Yang S, Humayun M, Righter K, Jefferson G, Fields D, Irving AJ (2015) Siderophile and chalcophile element abundances in shergottites: Implications for Martian core Formation. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12384]

Published by Arrangement with John Wiley&Sons

¹Miriam Sharp, ²Kevin Righter,¹Richard J. Walker
¹Department of Geology, University of Maryland, College Park, Maryland, USA
²NASA Johnson Space Center, Houston, Texas, USA

This study uses experimentally determined plagioclase-melt D values to estimate the trace element concentrations of Sr, Hf, Ga, W, Mo, Ru, Pd, Au, Ni, and Co in a crystallizing lunar magma ocean at the point of plagioclase flotation. Similarly, experimentally determined metal-silicate partition experiments combined with a composition model for the Moon are used to constrain the concentrations of W, Mo, Ru, Pd, Au, Ni, and Co in the lunar magma ocean at the time of core formation. The metal-silicate derived lunar mantle estimates are generally consistent with previous estimates for the concentration of these elements in the lunar mantle. Plagioclase-melt derived concentrations for Sr, Ga, Ru, Pd, Au, Ni, and Co are also consistent with prior estimates. Estimates for Hf, W, and Mo, however, are higher. These elements may be concentrated in the residual liquid during fractional crystallization due to their incompatibility. Alternatively, the apparent enrichment could reflect the inappropriate use of bulk anorthosite data, rather than data for plagioclase separates.

Reference
Sharp M, Righter K, Walker RJ (2014) Estimation of trace element concentrations in the lunar magma ocean using mineral- and metal-silicate melt partition coefficients. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12396]

Published by arrangement with John Wiley&Sons

^1,2Elmar Buchner, ³Martin Schmieder
¹HNU – Neu-Ulm University, Wileystraße 1, D-89231 Neu-Ulm, Germany
²Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Azenbergstraße 18, 70174 Stuttgart, Germany
³Philamlife Village, Pueblo de Oro, Upper Carmen, Cagayan de Oro, 9000 Philippines

The ∼24 km Nördlinger Ries and the ∼3.8 km Steinheim Basin in southern Germany are thought to represent a ∼14.8 Ma old impact crater doublet. The complex craters of the Steinheim Basin with its crater fill deposits and the Nördlinger Ries and its voluminous impact ejecta blanket are still widely preserved. Although located in an environmental setting that presumably underwent the same erosional history as the Ries crater, field geologic studies suggest that no proximal or distal ejecta of the Steinheim impact event are presently preserved. Generally, the lack of the ejecta blanket around the crater could be explained either by intense erosion, the scarcity of outcrops, or it never formed. In contrast to the lack of ejecta, fluvial and lacustrine Middle Miocene sediments deposited prior to, synchronous with, and shortly after the impact are preserved in many places in the surroundings of to the Steinheim Basin.

On low-density asteroids or planets with highly porous target rocks (⩾ 30-40% effective porosity), impact structures can form without significant ejecta outside the craters due to the compaction of porosity and a concordant drastic reduction of the ejecta velocity. In the Steinheim area, the target rocks comprised loose, porous Miocene sands, Upper Jurassic limestones and Middle Jurassic porous sand- and claystones. The average porosity of the entire sedimentary target suite may have reached 20-30% or even higher values assuming the existence of open karst cavities in the Upper Jurassic carbonates. Compaction of the porous target rocks, resulting in the reduction of ejected material, in combination with erosion could explain the apparent lack of impact ejecta in the wider periphery of the Steinheim impact structure.

Reference
Buchner E, Schmieder M (2015) The Steinheim Basin impact crater (SW-Germany) – where are the ejecta? Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.12.026]

Copyright Elsevier

¹Uwe Fink
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Az, 85721

The Single scattering albedos (SSA’s) determined for 9P /Tempel 1 are interpreted in terms of the Hapke model of irregular particle scattering efficiencies. Absorption coefficients versus wavelength from 0.31 to 2.5 μm are obtained. It is shown that the colors and exceedingly low reported SSA’s in the UV region of the spectrum below 0.4 μm cannot be reproduced with the geometric Hapke scattering model for irregular particles. However, by increasing the reported SSA’s by a small amount, absorption coefficients for particle radii of 10-100 μm vs. wavelength from 0.31 to 2.5 μm can be fitted. Several reasons are given for slightly increasing the SSA’s, such as neglect of the effects of porosity, having a more complex phase function for the particles, uncertainties in the absolute calibration and the uncertainties associated with the complex treatment of surface roughness. The absorption coefficients determined show good agreement with potential surface constituents Mg rich olivine and pyroxene with some amount of darkening iron or organic component.

Reference
Fink U (2015) Considerations regarding the Colors and low Surface Albedo of Comets using The Hapke Methodology. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.12.018]

Copyright Elsevier

^1,4Chaitanya Giri, ¹Fred Goesmann, ²Andrew Steele, ^1,3Thomas Gautier, ¹Harald Steininger, ¹Harald Krüger, ⁴Uwe J. Meierhenrich
¹Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
²Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd, Washington DC 20015, USA
³NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁴Université Nice Sophia Antipolis, Institut de Chimie de Nice, UMR 7272 CNRS, F-06108 Nice, France

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Reference
Giri C, Fred Goesmanna, Steele A, Gautier T, Steininger H, Krüger H, Meierhenrich UJ (2014) Competence evaluation of COSAC flight spare model mass spectrometer: In preparation of arrival of Philae lander on comet 67P/Churyumov-Gerasimenko. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2014.12.017]

¹Liping Qin, ²Nicolas Dauphas, ³Mary F. Horan, ⁴Ingo Leya, ³Richard W. Carlson
¹CAS Key Laboratory of Crust-Mantle Materials and Environment, University of Science and Technology of China, Hefei, Anhui, 230026, China
²Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA
³Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
⁴Space Research and Planetology, University of Berne, Sidlerstrasse 5, 3012 Berne, Switzerland

An obstacle for establishing the chronology of iron meteorite formation using 182Hf-182W systematics (t1/2= 8.9 Myr) is to find proper neutron fluence monitors to correct for cosmic ray modification of W isotopic composition. Recent studies showed that siderophile elements such as Pt and Os could serve such a purpose. To test and calibrate these neutron dosimeters, the isotopic compositions of W and Os were measured in a slab of the IID iron meteorite Carbo. This slab has a well-characterized noble gas depth profile reflecting different degrees of shielding to cosmic rays. The results show that W and Os isotopic ratios correlate with distance from the pre-atmospheric center. Negative correlations, barely resolved within error, were found between ε190Os-ε189Os and ε186Os-ε189Os with slopes of -0.64± 0.45 and -1.8(+1.9/-2.1), respectively. These Os isotope correlations broadly agree with model predictions for capture of secondary neutrons produced by cosmic ray irradiation and results reported previously for other groups of iron meteorites. Correlations were also found between ε182W-ε189Os (slope = 1.02 ± 0.37) and ε182W-ε190Os (slope = -1.38 ± 0.58). Intercepts of these two correlations yield pre-exposure ε182W values of -3.32 ± 0.51 and -3.62 ± 0.23, respectively (weighted average ε182W=-3.57±0.21). This value relies on a large extrapolation leading to a large uncertainty but gives a metal-silicate segregation age of -0.5 ±2.4 Myr after formation of the solar system. Combining the iron meteorite measurements with simulations of cosmogenic effects in iron meteorites, equations are presented to calculate and correct for cosmogenic effects on 182W using Os isotopes.

Reference
Qin L, Dauphas N, Horan MF, Leya I, Carlson RW (2014) Correlated cosmogenic W and Os isotopic variations in Carbo and implications for Hf-W chronology. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2014.11.015]

Copyright Elsevier

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]

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