¹James J. Papike, ²Steven B. Simon, ¹Paul V. Burger,¹ Aaron S. Bell, ¹Charles K. Shearer, ³James M. Karner
¹Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.
²Department of Geophysical Sciences, The University of Chicago, Chicago, Illinois 60637, U.S.A.
³Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, Ohio 44106, U.S.A.

Pyroxene is arguably the most powerful, single-phase geochemical and petrologic recorder of Solar System processes, from nebular condensation through planetary evolution, over a wide range of temperatures, pressures, and fO2. It is an important mineral phase in the crusts and mantles of evolved planets, in undifferentiated and differentiated asteroids, and in refractory inclusions—the earliest Solar System materials. Here, we review the valence state partitioning behavior of Cr (Cr2+, Cr3+), Ti (Ti3+, Ti4+), and V (V2+, V3+, V4+, V5+) among crystallographic sites in pyroxene over a range of fO2 from approximately fayalite-magnetite-quartz (FMQ) to ~7 log units below iron-wüstite (IW-7), and decipher how pyroxene can be used as a recorder of conditions of planetary and nebular environments and planetary parentage. The most important crystallographic site in pyroxene with respect to its influence on mineral/melt partitioning is M2; its Ca content has a huge effect on partitioning behavior, because the large Ca cation expands the structure. As a result, distribution coefficients (Ds) for Cr and V increase with increasing Ca content from orthopyroxene to pigeonite to augite. In addition, it is noted that V3+ is favored over V4+ in olivine and pyroxene. In pyroxene in refractory inclusions, Ti3+ is favored over Ti4+ and incorporation of Ti is facilitated by the high availability of Al for coupled substitution. The most important results from analysis of pyroxene in martian meteorites (e.g., QUE 94201) are the oxygen fugacity estimates of IW+0.2 and IW+0.9 derived from partitioning and valence data for Cr and V, respectively, obtained from experiments using appropriate temperatures and melt compositions. In angrites, changes in V valence state may translate to changes in fO2, from IW-0.7 during early pyroxene crystallization, to IW+0.5 during later episodes of pyroxene crystallization. In addition to fO2, the partitioning behavior of Cr, V, and Ti between pyroxene and melt is also dependent upon availability of other cations, especially Al, for charge-balancing coupled substitutions.

Reference
Papike JJ, Simon SB, Burger PV, Bell AS, Shearer CK, Karner JM (2016) Chromium, vanadium, and titanium valence systematics in Solar System pyroxene as a recorder of oxygen fugacity, planetary provenance, and processes
American Mineralogist 101, 907-918.
Link to Article [doi:10.2138/am-2016-5507]
Copyright: The Mineralogical Society of America

¹Joshua L. Bandfield, ²Elena S. Amador
¹Space Science Institute
²Earth and Space Sciences, University of Washington, Seattle

Thermal Emission Imaging System (THEMIS) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral datasets were used to identify high bulk SiO2 and hydrated compositions throughout the Nilosyrtis Mensae region. Four isolated locations were identified across the region showing short wavelength silicate absorptions within the 8–12 μm spectral region, indicating surfaces dominated by high Si phases. Much more extensive exposures of hydrated compositions are present throughout the region, indicated by a spectral absorption near 1.9 μm in CRISM data. Although limited in spatial coverage, detailed spectral observations indicate that the hydrated materials contain Fe/Mg-smectites and hydrated silica along with minor exposures of Mg-carbonates and an unidentified hydrated phase. The high SiO2 and hydrated materials are present in layered sediments near the base of topographic scarps at the hemispheric dichotomy boundary, typically near or within low albedo sand deposits. The source of the high SiO2 and hydrated materials appears to be from groundwater discharge from Nili Fossae and Syrtis Major to the south, where there is evidence for extensive aqueous alteration of the subsurface. Although discontinuous, the exposures of high SiO2 and hydrated materials span a wide area and are present in a similar geomorphological context to previously identified deposits in western Hellas Basin. These regional deposits may reflect aqueous conditions and alteration within the adjacent crust of the martian highlands.

Reference
Bandfield JL, Amador ES (2016) Extensive aqueous deposits at the base of the dichotomy boundary in Nilosyrtis Mensae, Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.04.002]
Copyright Elsevier

¹Christopher M. Wright, ^1,2Tho Do Duy, ¹Warrick Lawson
¹School of Physical, Environmental and Mathematical Sciences, UNSW Canberra, PO Box 7916, Canberra BC 2610, Australia
²Department of Physics, International University – Vietnam National University HCM, Block 6, Linh Trung, Thu Duc, Ho Chi Minh City, Viet Nam

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Reference
Wright CM, Duy TD, Lawson W (2016) Absorption at 11 μm in the interstellar medium and embedded sources: evidence for crystalline silicates. Monthly Notices of the Royal Astronomical Society 457, 1593-1625.
Link to Article [doi:10.1093/mnras/stw041]

^1,2F. C. Pignatale, ²Kurt Liffman, ²Sarah T. Maddison, ³Geoffrey Brooks
¹Université de Lyon, Lyon, F-69003, France; Université Lyon 1, Observatoire de Lyon, 9 avenue Charles André, Saint-Genis Laval, F-69230, France CNRS, UMR 5574, Centre de Recherche Astrophysique de Lyon; Ecole Normale Supérieure de Lyon, F-69007, France
²Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
³FSET, Swinburne University of Technology, Hawthorn, VIC 3122, Australia

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Reference
Pignatale FC, Liffman K, Maddison ST, Brooks G (2016) 2D condensation model for the inner Solar Nebula: an enstatite-rich environment. Monthly Notices of the Royal Astronomical Society 457, 1359-1370
Link to Article [doi:10.1093/mnras/stv3003]

¹Jangmi Han, ¹Adrian J. Brearley
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA

We have carried out a FIB/TEM study of refractory CAI-like objects in one AOA from the ALHA77307 CO3.0 chondrite. The CAI-like objects in the AOA consist of a zoned sequence with a spinel-rich core through an intergrowth layer of spinel and Al-Ti-rich diopside to a diopside rim. The spinel-rich core consists of polycrystalline aggregates of spinel and ±minor melilite showing equilibrated grain boundary textures. The intergrowth layer contains fine-grained diopside and spinel with minor anorthite with highly curved and embayed grain boundaries. The diopside rim consists of polycrystalline aggregates of diopside. The compositions of pyroxene change significantly outward from Al-Ti-rich diopside in contact with the spinel-rich core to Al-Ti-poor diopside next to the surrounding olivine of the AOA. Overall microstructural and chemical characteristics suggest that the spinel-rich core formed under equilibrium conditions whereas the intergrowth layer is the result of reactions that occurred under conditions that departed significantly from equilibrium. The remarkable changes in formation conditions of the CAI-like objects may have been achieved by transport and injection of refractory objects into a region of a partially-condensed, Ca,Ti-saturated gas which reacted with spinel and melilite to form Al-Ti-rich diopside.

Crystallographically-oriented TiO2 nanoparticles decorate the grain boundaries between spinel grains and between spinel and Al-Ti-rich diopside grains. During the disequilibrium back-reaction of spinel with a partially-condensed, Ca,Ti-saturated gas, metastable TiO2 nanoparticles may have condensed by an epitaxial nucleation mechanism and grown on the surface of spinel. These TiO2 nanoparticles are disordered intergrowths of the two TiO2 polymorphs, anatase and rutile. These nanoparticles are inferred to have nucleated as anatase that underwent partial transformation into rutile. The local presence of the TiO2 nanoparticles and intergrowth of anatase and rutile imply that the disequilibrium back-reaction of spinel with the gas occurred on a short timescale, i.e., minutes to hours at maximum.

Reference
Han J, Brearley AJ (2016) Microstructural constraints on complex thermal histories of refractory cai-like objects in an amoeboid olivine aggregate from the ALHA77307 CO3.0 chondrite. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.011]
Copyright Elsevier

¹F. Liu, ¹D. Yong, ¹M. Asplund, ²I. Ramírez, ³J. Meléndez, ^4,5B. Gustafsson, ^1,6L. M. Howes, ⁷I. U. Roederer, ²D. L. Lambert, ⁶T. Bensby
¹Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
²McDonald Observatory and Department of Astronomy, University of Texas at Austin, 2515 Speedway, Austin, TX 78712-1205, USA
³Departamento de Astronomia do IAG/USP, Universidade de Sao Paulo, Rua do Matao 1226, Sao Paulo 05508-900, SP, Brasil
⁴Institution for Physics and Astronomy, Uppsala University, Box 515, SE-75120 Uppsala, Sweden
⁵Nordita, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden
⁶Lund Observatory, Department of Astronomy and Theoretical physics, Lund University, Box 43, SE-22100 Lund, Sweden
⁷Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USA

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Reference
Liu F, Yong D, Asplund M, Ramírez I, Meléndez J, Gustafsson B, Howes LM, Roederer IU, Lambert DL, Bensby T (2016) The detailed chemical composition of the terrestrial planet host Kepler-10. Monthly Notices of the Royal Astronomical Society 456, 2636-2646
Link to Article [doi:10.1093/mnras/stv2821]

¹S. Ieva, ¹E. Dotto, ²D. Lazzaro, ³D. Perna, ⁴D. Fulvio, ³M. Fulchignoni
¹INAF–Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio Catone (Roma), Italy
²Observatorio Nacional, Rua General José Cristino, 77 – São Cristóvão, Rio de Janeiro – RJ-20921-400, Brazil
³LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, F-92195 Meudon, France
⁴Departamento de Fisíca, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marques de São Vicente 225, Rio de Janeiro 22451-900, Brazil

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Reference
Ieva S, Dotto E, Lazzaro D, Perna D, Fulvio D, Fulchignoni M (2016) Spectral characterization of V-type asteroids – II. A statistical analysis. Monthly Notices of the Royal Astronomical Society 455, 2871-2888.
Link to Article [doi: 10.1093/mnras/stv2510]

¹Schröder, C., ^2,5Köhler, I., ³Muller, F.L.L., ⁴Chumakov, A.I., ⁴Kupenko, I., ⁴Rüffer, R., ²Kappler, A.
¹Biological and Environmental Sciences, School of Natural Sciences, University of Stirling, Stirling FK9 4LA, Scotland, United Kingdom
²Geomicrobiology, Centre for Applied Geoscience, Eberhard Karls University of Tübingen, Sigwartstr. 10, Tübingen, Germany
³Department of Biological and Environmental Sciences, Qatar University, PO Box 2713, Doha, Qatar
⁴ESRF-The European Synchrotron, CS40220, Grenoble Cedex 9, France
⁵Institute of Geosciences, Friedrich Schiller University of Jena, Burgweg 11, Jena, Germany

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Reference
Schröder C, Köhler I, Muller FLL, Chumakov AI, Kupenko I, Rüffer R, Kappler A (2016)
The biogeochemical iron cycle and astrobiology. Hyperfine Interactions 237, 85
Link to Article [DOI: 10.1007/s10751-016-1289-2]

^1,2Oshtrakh, M.I., ¹Yakovlev, G.A., ¹Grokhovsky, V.I., ^1,2Semionkin, V.A.
¹Department of Physical Techniques and Devices for Quality Control, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation
²Department of Experimental Physics, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation

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Reference
Oshtrakh MI, Yakovlev GA, Grokhovsky VI, Semionkin VA (2016) Re-examination of Dronino iron meteorite and its weathering products using Mössbauer spectroscopy with a high velocity resolution. Hyperfine Interactions 237, 42
Link to Article [DOI: 10.1007/s10751-016-1214-8]

¹Maksimova, A.A., ²Klencsár, Z., ^1,3Oshtrakh, M.I., ¹Petrova, E.V., ¹Grokhovsky, V.I., ⁴Kuzmann, E., ⁴Homonnay, Z., ^1,3Semionkin, V.A.
¹Department of Physical Techniques and Devices for Quality Control, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation
²Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, Budapest, Hungary
³Department of Experimental Physics, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation
⁴Institute of Chemistry, Eötvös Loránd University, Budapest, Pázmány sétány1/A, Hungary

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Reference
Maksimova AA, Klencsár Z, Oshtrak, MI, Petrova EV, Grokhovsky VI, Kuzmann E, Homonnay Z, Semionkin VA (2016) Mössbauer parameters of ordinary chondrites influenced by the fit accuracy of the troilite component: an example of Chelyabinsk LL5 meteorite. Hyperfine Interactions 237, 33
Link to Article [DOI: 10.1007/s10751-016-1218-4]