¹Alexei V. Fedkin, ^1,2Lawrence Grossman, ³Munir Humayun, ¹Steven B. Simon, ¹Andrew J. Campbell
¹Dept. of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637
²Also Enrico Fermi Institute, The University of Chicago
³National High Magnetic Field Laboratory and, Dept. of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, Florida 32310

The impact hypothesis for the origin of CB chondrites was tested by performing equilibrium condensation calculations in systems composed of vaporized mixtures of projectile and target materials. When one of the impacting bodies is composed of the metal from CR chondrites and the other is an H chondrite, good agreement can be found between calculated and observed compositions of unzoned metal grains in CB chondrites but the path of composition variation of the silicate condensate computed for the same conditions that reproduce the metal grain compositions does not pass through the measured compositions of barred olivine (BO) or cryptocrystalline (CC) chondrules in the CBs. The discrepancy between measured chondrule compositions and those of calculated silicates is not reduced when diogenite, eucrite or howardite compositions are substituted for H chondrite as the silicate-rich impacting body. If, however, a CR chondrite body is differentiated into core, a relatively CaO-, Al2O3-poor mantle and a CaO-, Al2O3-rich crust, and later accretes significant amounts of water, a collision between it and an identical body can produce the necessary chemical conditions for condensation of CB chondrules. If the resulting impact plume is spatially heterogeneous in its proportions of crust and mantle components, the composition paths calculated for silicate condensates at the same Ptot, Ni/H and Si/H ratios and water abundance that produce good matches to the unzoned metal grain compositions pass through the fields of BO and CC chondrules, especially if high-temperature condensates are fractionated in the case of the CCs. While equilibrium evaporation of an alloy containing solar proportions of siderophiles into a dense impact plume is an equally plausible hypothesis for explaining the compositions of the unzoned metal grains, equilibrium evaporation can explain CB chondrule compositions only if an implausibly large number of starting compositions is postulated. Kinetic models applied to co-condensing metal grains and silicate droplets in a region of the plume with very similar composition, but with high cooling rate and sharply declining Ptot during condensation, produce very good matches to the zoning profiles of Ir, Ni, Co and Cr concentrations and Fe and Ni isotopic compositions observed in the zoned metal grains in CB chondrites but produce very large positive δ56Fe in the cogenetic silicate, which are not found in the chondrules.

Reference
Fedkin AV, Grossman L, Humayun M, Simon SB, Campbell AJ (2015) Condensates from vapor made by impacts between metal-, silicate-rich bodies: Comparison with metal and chondrules in CB chondrites. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.05.022]

Copyright Elsevier

¹Zongcheng Ling,²Alian Wang
¹Shandong Provincial Key Laboratory of Optical Astronomy & Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China
²Department of Earth & Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, MO, United States

Miller Range (MIL) 03346 is a nakhlite meteorite that has been extensively studied due to its unique complex secondary mineral phases and their potential implications for the hydrologic history of Mars. We conducted a set of Raman spectroscopic and Raman imaging studies of MIL 03346,168, focusing on the secondary mineral phases and their spatial distributions, with a goal to better understand the possible processes by which they were generated on Mars. This study revealed three types of calcium sulfates, a solid solutions of (K, Na)-jarosite and two groups of hydrated species with low crystallinity (HSLC) in the veins and/or mesostasis areas of the meteorite. The most abundant Ca-sulfate is bassanite that suggests two possible paths for its direct precipitation from a Ca-S-H2O brine, either having low water activity or with incomplete development (producing bassanite with gypsum microcrystals) on Mars. The second most abundant Ca-sulfate is soluble γ-CaSO4 which raises a new question on the origins of this phase in the martian meteorite, since γ-CaSO4 readily hydrates in the laboratory but is apparently stable in Atacama Desert. The close spatial relationship of (K, Na)-jarosite solid solutions with rasvumite (KFe2S3), magnetite, HSLC, and fine-grained low crystallinity alkali feldspar in mesostasis suggests a potential in situ formation of mesostasis jarosite from these Fe-K,Na-S-O-H2O species.

Reference
Ling Z, Wang A (2015) Spatial distributions of secondary minerals in the Martian meteorite MIL 03346,168 determined by Raman spectroscopic Imaging. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004805]

Published by Arrangement with John Wiley&Sons

^1,2Steven M. Chemtob,¹Ryan D. Nickerson,³Richard V. Morris,⁴David G. Agresti,^1,2Jeffrey G. Catalano
¹Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri, USA
²McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri, USA
³EIS Directorate, NASA Johnson Space Center, Houston, Texas, USA
⁴Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama, USA

Widespread detections of phyllosilicates in Noachian terrains on Mars imply a history of near-surface fluid-rock interaction. Ferrous trioctahedral smectites are thermodynamically predicted products of basalt weathering on early Mars, but to date only Fe3+-bearing dioctahedral smectites have been identified from orbital observations. In general, the physicochemical properties of ferrous smectites are poorly studied because they are susceptible to air oxidation. In this study, eight Fe2+-bearing smectites were synthesized from Fe2+-Mg-Al-silicate gels at 200° C under anoxic conditions. Samples were characterized by inductively-coupled plasma optical emission spectrometry, powder X-ray diffraction, Fe K-edge X-ray absorption spectroscopy (XAS), Mössbauer spectroscopy, and visible/near-infrared (VNIR) reflectance spectroscopy. The range of redox states was Fe3+/ΣFe = 0 to 0.06±0.01 as determined by both XAS and, for short integration times, Mössbauer. The smectites have 060 distances (d(060)) between 1.53 and 1.56 Å, indicating a trioctahedral structure. d(060) and XAS-derived interatomic Fe-(Fe,Mg,Al) distance scaled with Fe content. Smectite VNIR spectra feature OH/H2O absorption bands at 1.4 and 1.9 µm, (Fe2+,Mg,Al)3-OH stretching bands near 1.4 µm, and Fe2+Fe2+Fe2+-OH, MgMgMg-OH, AlAl(Mg,Fe2+)-OH, and AlAl-OH combination bands at 2.36 µm, 2.32 µm 2.25 µm, and 2.20 µm, respectively. The spectra for ferrrous saponites are distinct from those for dioctahedral ferric smectites, permitting their differentiation from orbital observations. XRD patterns for synthetic high-Mg ferrosaponite and high-Mg ferrian saponite are both consistent with the Sheepbed saponite detected by the CheMin instrument at Gale Crater, Mars, suggesting that anoxic basalt alteration was a viable pathway for clay mineral formation on early Mars.

Reference
Chemtob SM, Nickerson RD, Morris RV, Agresti DG, Catalano JG (2015) Synthesis and structural characterization of ferrous trioctahedral smectites: Implications for clay mineral genesis and detectability on Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004763]

Published by arrangement with John Wiley&Sons

¹Toru Matsumoto, ²Akira Tsuchiyama, ²Akira Miyake, ³Takaaki Noguchi, ⁴Michihiko Nakamura, ⁵Kentaro Uesugi, ⁵Akihisa Takeuchi, ⁵Yoshio Suzuki, ⁶Tsukasa Nakano
¹Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
²Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto-shi, 606-8502, Japan
³Faculty of Arts and Science, Kyushu University, 2-1-1 Bunkyo. Motooka, Nishi-ku, Fukuoka 819-0395, Japan
⁴Department of Earth Science, Tohoku University, 6-3, AramakiAoba, Aoba-ku, Sendai-shi, Miyagi 980-8578, Japan
⁵Japan Synchrotron Radiation Research Institute/ SPring-8, Sayo, Hyogo 679-5198, Japan
⁶Geological Survey of Japan/National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8567, Japan

Surface morphologies of a regolith particle retrieved from asteroid 25143 Itokawa were observed using field-emission scanning electron microscopy (FE-SEM). The images were compared with the internal structures of the space-weathered rim of the same particle observed by transmission electron and scanning transmission electron microscopies (TEM/STEM) to investigate whether there is a direct link between the surface morphology and internal structure. FE-SEM observation showed that most of the particle surface is covered by convex spots less than 100 nm in size. TEM/STEM observation revealed that this particle has a space-weathered rim composed of partially amorphous structures with nano-Fe particles and vesicles. The vesicles swell the surface and form blisters that correspond to the spotted structures observed by FE-SEM. These observations indicate that a space-weathered rim with blisters can be observed by FE-SEM without using destructive methods. The observation of the space-weathered rim by FE-SEM also enabled us to obtain the distribution of the space-weathered rim on the particle surfaces. The existence of space-weathered rims on the opposing surfaces of the particle shows that most of the surfaces were directly exposed to the space environment by movement on the Itokawa surface. The depths of the blister locations and the chemical composition of the space-weathered rim indicate that the observed space-weathered rim with blisters was formed mainly by solar wind irradiation. The space-weathered rim analyzed in this study is thicker than those of Itokawa particles previously examined, indicating that the rim may has experienced longer solar wind exposure than those previously observed.

Reference
Matsumoto T, Tsuchiyama A, Miyake A, Noguchi T, Nakamura M, Uesugi K, Takeuchi A, Suzuki Y, Nakano T (2015)
Surface and internal structures of a space-weathered rim of an Itokawa regolith particle. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.001]

Copyright Elsevier

¹Driss Takir, ¹Joshua P. Emery, ¹Harry Y. McSween Jr.
¹Department of Earth and Planetary Sciences and Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996, United States

Proposed mineralogical linkages between CM/CI carbonaceous chondrites and outer Main Belt asteroids remain uncertain due to a dearth of diagnostic absorptions in visible and near-infrared (∼0.4 to 2.5 μm) spectra of the two sets of objects. Absorptions near 3 μm in both sets hold promise for illuminating the potential linkages. Spectral comparisons of meteorites and asteroids have been challenging because meteorite spectra have usually been acquired in ambient terrestrial environments, and hence were contaminated by atmospheric water. In this study, we compare near-infrared spectra of chondrites measured in the laboratory under asteroid-like conditions (Takir et al. 2013) and spectra of asteroids measured with the long-wavelength cross-dispersed (LXD: 1.9-4.2-μm) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility (IRTF) (Takir and Emery 2012). Using the 3-μm band shape, we find that spectral Group 2 CM and CI (Ivuna) chondrites are possible meteorite analogs for asteroids with the sharp 3-μm features, which are predominately located in the 2.5 < a < 3.3 AU region. Spectral Group 2 CM chondrites contain phyllosilicate phases intermediate between endmembers Fe-serpentine and Mg-serpentine, with a petrological subtype ranging from 2.2 to 2.1 (Takir et al. 2013). No meteorite match was found for asteroids showing a rounded 3-μm feature, which tend to be located farther from the Sun (3.0 < a < 4.0 AU), or for asteroids with distinctive spectra like 1 Ceres or 52 Europa. The study of the 3-μm band in meteorites and asteroids has implications for the understanding of phyllosilicate mineralogy and its distribution in the outer Main Belt region.

Reference
Takir D, EmeryJP, McSween Jr. HY (2015) Toward an Understanding of Phyllosilicate Mineralogy in the Outer Main Asteroid Belt. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.04.042]
Copyright Elsevier

¹Nazarov, M.A., ¹Shornikov, S.I., ¹Demidova, S.I.
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, Russian Federation

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Reference
Nazarov MA, Shornikov SI, Demidova SI (2015) Origin of native silicon and iron silicides in the Dhofar 280 lunar Meteorite. Petrology 23, 168-175
Link to Article [DOI: 10.1134/S0869591115020071]

¹Demidova, S.I., ¹Nazarov, M.A., ²Ntaflos, T., ³Brandstätter, F.
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, Russian Federation
²Department für Lithosphärenforschung, Universität Wien, Althanstrasse 14, Wien, Austria
³Naturhistorisches Museum, Burgring 7, Wien, Austria

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Reference
Demidova SI, Nazarov MA, Ntaflo T, Brandstätter F (2015) Possible serpentine relicts in lunar meteorites.
Petrology 23, 116-126
Link to Article [DOI: 10.1134/S0869591115020034]

¹Badyukov, D.D., ²Raitala, J., ²Kostama, P., ³Ignatiev, A.V. 
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, Russian Federation
²Department of Physics, University of Oulu, PO Box 3600, Oulu, Finland
³Far East Geological Institute, Far East Branch, Russian Academy of Sciences, pr. Stoletiya Vladivostoka 159, Vladivostok, Russian Federation

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Reference
Badyukov DD, Raitala J, Kostama P, Ignatiev AV (2015) Chelyabinsk meteorite: Shock metamorphism, black veins and impact melt dikes, and the Hugoniot. Petrology 23, 103-115
Link to Article [DOI: 10.1134/S0869591115020022]

¹Ivanova, M.A., ² Petaev, M.I. 
¹Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, 19 Kosygin St., Moscow, Russian Federation
²Harvard University Department of Earth and Planetary Sciences and Department of Solar, Stellar and Planetary Physics, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, United States

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Reference
Ivanova MA, Petaev MI (2015) Characteristics and origin of the components of the carbonaceous chondrite NWA 470. Petrology 23, 150-167.
Link to Article [DOI: 10.1134/S0869591115020058]

¹Pati, J.K., ^2,3Reimold, W.U, ²Greshake, A., ²Schmitt, R.T., ^4,5Koeberl, C., ¹Pati, P., ¹Prakash, K
¹Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad, India
²Museum für Naturkunde Berlin, Invalidenstrasse 43, Berlin, Germany
³Humboldt-Universität zu Berlin, Unter den Linden 6, Berlin, Germany
⁴Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, Austria
⁵Natural History Museum, Burgring 7, Vienna, Austria

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Reference
Pati JK, Reimold WU, Greshake A, Schmitt RT, Koeberl C, Pati P, Prakash K (2015) Pseudotachylitic breccia from the Dhala impact structure, north-central India: Texture, mineralogy and geochemical characterization. Tectonophysics 649 18-32
Link to Article [DOI: 10.1016/j.tecto.2015.01.021]