¹Jean-Alix Barrat,²Albert Jambon,^3,4Akira Yamaguchi,⁵Addi Bischoff,⁶Marie-Laure Rouget,¹Céline Liorzou
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.08.042]
¹Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer, CNRS UMR 6538, Place Nicolas Copernic, 29280 Plouzané, France
²Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France
³National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
⁴Department of Polar Science, School of Multidisciplinary Science, Graduate University for Advanced Sciences, Tachikawa, Tokyo 190-8518, Japan
⁵Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
⁶Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer, CNRS UMS 3113, Place Nicolas Copernic, 29280 Plouzané Cedex, France
Copyright Elsevier

Ureilites are among the most common achondrites and are widely believed to sample the mantle of a single, now-disrupted, C-rich body. We analyzed 17 ureilite samples, mostly Antarctic finds, and determined their incompatible trace element abundances. In order to remove or reduce the terrestrial contamination, which is marked among Antarctic ureilites by light-REE enrichment, we leached the powdered samples with nitric acid. The residues display consistent abundances, which strongly resemble those of the pristine rocks. All the analyzed samples display light-REE depletions, negative Eu anomalies, low (Sr/Eu∗)n, and (Zr/Eu∗)n ratios which are correlated. Two groups of ureilites (groups A and B) are defined. Compared to group A, group B ureilites, which are the less numerous, tend to be richer in heavy REEs, more light-REE depleted, and display among the deepest Eu anomalies. In addition, olivine cores in group B ureilites tend to be more forsteritic (Mg# = 81.9-95.2) than in group A ureilites (Mg# = 74.7-86.1). Incompatible trace element systematics supports the view that ureilites are mantle restites. REE modelling suggests that their precursors were rather REE-rich (ca. 1.8-2 x CI) and contained a phosphate phase, possibly merrillite. The REE abundances in ureilites can be explained if at least two distinct types of magmas were removed successively from their precursors: aluminous and alkali-rich melts as exemplified by the Almahata Sitta trachyandesite (ALM-A), and Al and alkali-poor melts produced after the exhaustion of plagioclase from the source. Partial melting was near fractional (group B ureilites, which are probably among the least residual samples) to dynamic with melt porosities that did not exceed a couple of percent (group A ureilites). The ureilite parent body (UPB) was almost certainly covered by a crust formed chiefly from the extrusion products of the aluminous and alkali-rich magmas. It is currently uncertain whether the Al and alkali-poor melts produced during the second phase of melting reached the surface of the body. The fact that initial silicate melting of ureilitic precursors would have produced relatively low density liquids capable of forming an external crust to the UPB casts doubt on models that invoke chondritic outer layers to achondritic asteroids.

¹Kevin Righter, ²Steve R. Sutton, ³Lisa Danielson, ³Kellye Pando, ²Matt Newville
American Mineralogist 101Link to Article [DOI: 10.2138/am-2016-5638]
¹NASA-JSC, 2101 NASA Parkway, Houston, Texas 77058, U.S.A.
²GSECARS University of Chicago, 9700 South Cass Avenue, Building 434A, Argonne, Illinois 60439, U.S.A.
³ESCG, Jacobs Engineering, Houston, Texas 77058, U.S.A.
Copyright: Mineralogical Society of America

Many igneous rocks contain mineral assemblages that are not appropriate for application of common mineral equilibria or oxybarometers to estimate oxygen fugacity. Spinel-structured oxides, common minerals in many igneous rocks, typically contain sufficient V for XANES measurements, allowing use of the correlation between oxygen fugacity and V K pre-edge peak intensity. Here we report V pre-edge peak intensities for a wide range of spinels from source rocks ranging from terrestrial basalt to achondrites to oxidized chondrites. The XANES measurements are used to calculate oxygen fugacity from experimentally produced spinels of known Embedded Image . We obtain values, in order of increasing Embedded Image , from IW-3 for lodranites and acapulcoites, to diogenites, brachinites (near IW), ALH 84001, terrestrial basalt, hornblende-bearing R chondrite LAP 04840 (IW+1.6), and finally ranging up to IW+3.1 for CK chondrites (where the Embedded Image of a sample relative to the Embedded Image of the IW buffer at specific T). To place the significance of these new measurements into context we then review the range of oxygen fugacities recorded in major achondrite groups, chondritic and primitive materials, and planetary materials. This range extends from IW-8 to IW+2. Several chondrite groups associated with aqueous alteration exhibit values that are slightly higher than this range, suggesting that water and oxidation may be linked. The range in planetary materials is even wider than that defined by meteorite groups. Earth and Mars exhibit values higher than IW+2, due to a critical role played by pressure. Pressure allows dissolution of volatiles into magmas, which can later cause oxidation or reduction during fractionation, cooling, and degassing. Fluid mobility, either in the sub-arc mantle and crust, or in regions of metasomatism, can generate values >IW+2, again suggesting an important link between water and oxidation. At the very least, Earth exhibits a higher range of oxidation than other planets and astromaterials due to the presence of an O-rich atmosphere, liquid water, and hydrated interior. New analytical techniques and sample suites will revolutionize our understanding of oxygen fugacity variation in the inner solar system, and the origin of our solar system in general.

¹Neyda M. Abreu
Geochmica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.08.031]
¹Earth Science Program, The Pennsylvania State University – Du Bois Campus, Du Bois, PA 15801, USA
Copyright Elsevier

A number of different classification schemes have been proposed for the CR chondrites; this study aims at reconciling these different classification schemes. Mineralogy-based classification has proved particularly challenging for weakly to moderately altered CRs because incipient mineral replacement and elemental mobilization arising from aqueous alteration only affected the most susceptible primary phases, which are generally located in the matrix. Secondary matrix phases are extremely fine-grained (generally sub-micron) and heterogeneously mixed with primary nebular materials. Compositional and isotopic classification parameters are fraught with confounding factors, such as terrestrial weathering, impact processes, and variable abundance of clasts from different regions of the CR parent body or from altogether different planetary bodies. Here, detailed TEM observations from eighteen FIB sections retrieved from the matrices of nine Antarctic CR chondrites (EET 96259, GRA 95229, GRO 95577, GRO 03116, LAP 02342, LAP 04516, LAP 04720, MIL 07525, and MIL 090001) are presented, representing a range of petrologic types. Amorphous Fe-Mg silicates are found to be the dominant phase in all but the most altered CR chondrite matrices, which still retain significant amounts of these amorphous materials. Amorphous Fe-Mg silicates are mixed with phyllosilicates at the nanometer scale. The ratio of amorphous Fe-Mg silicates to phyllosilicates decreases as: (1) the size of phyllosilicates, (2) abundance of magnetite, and (3) replacement of Fe-Ni sulfides increase. Carbonates are only abundant in the most altered CR chondrite, GRO 95577. Nanophase Fe-Ni metal and tochilinite are present small abundances in most CR matrices. Based on the presence, abundance and size of phyllosilicates with respect to amorphous Fe-Mg silicates, the sub-micron features of CR chondrites have been linked to existing classification sequences, and possible reasons for inconsistencies among classification schemes are discussed.

¹Pizzarello, S.
Israel Journal of Chemistry (in Press)  Link to Article [DOI: 10.1002/ijch.201600039]
¹Arizona State University School of Molecular Sciences Tempe AZ 85018-1604 USA

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^1,2J. Kempl, ¹P.Z. Vroon, ¹B. van der Wagt, ³E. Zinngrebe, ⁴D.J. Frost, ¹W. van Westrenen
Netherlands Journal of Geosciences 95, 113-129  Link to Article [DOI: http://dx.doi.org/10.1017/njg.2015.34]
¹Faculty of Earth and Life Sciences, Vrije Universiteit University Amsterdam, De Boelelaan 1085, 1081HV Amsterdam, the Netherlands
²Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, the Netherlands
³Ceramics Research Center, Tata Steel IJmuiden, Building Code 3J-22, P.O. Box 1000, 1970 CA IJmuiden, the Netherlands
⁴Bayerisches Geoinstitut, University of Bayreuth, D-95440 Bayreuth, Germany

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^1,2,3Valiev, R.R., ⁴Berezhnoy, A.A., ^1,5Minaev, B.F., ⁶Chernov, V.E., ¹Cherepanov, V.N.
Russian Physics Journal, Augus1 2016, 1-8 Link to Article [DOI: 10.1007/s11182-016-0803-y]
¹National Research Tomsk State University, Tomsk, Russian Federation
²National Research Tomsk Polytechnic University, Tomsk, Federation
³V. D. Kuznetsov Siberian Physical-Technical Institute at Tomsk State University, Tomsk, Russian Federation
⁴P. K. Sternberg Astronomical Institute at Moscow State University, Moscow, Russian Federation
⁵Bogdan Khmel’nitskii National University, Cherkassy, Ukraine
⁶Voronezh State University, Voronezh, Russian Federation

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¹Nicola Ferralis,²Emily D. Matys,³Andrew H. Knoll,²Christian Hallmann,²Roger E. Summons
Carbon 108, 440-449 Link to Article [http://dx.doi.org/10.1016/j.carbon.2016.07.039]
¹Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²Department of Earth Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA

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¹Mark S. Bentley et al. (>10)*
Nature 537, 73-75 Link to Article [doi:10.1038/nature19091]
¹Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
*Find the extensive, full author and affiliation list on the publishers website

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¹Leitzke, F.P., ¹Fonseca, R.O.C., ¹Michely, L.T., ²Sprung, P., ²Münker, C., ^1,3Heuser, A., ¹Blanchard, H.
Chemical Geology 440, 219-238 Link to Article [10.1016/j.chemgeo.2016.07.011]
¹Steinmann-Institut für Geologie, Mineralogie un Paläontologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
²Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany
³GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Wischhofstraße 1-3, Kielz, Germany

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¹P. Boehnke, ¹T. Mark Harrison, ²M.T. Heizler, ¹P.H. Warren
Earth and Planetary Science Letters (in Press) Link to Article [http://dx.doi.org/10.1016/j.epsl.2016.07.014]
¹Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095, United States
¹New Mexico Bureau of Geology and Mineral Resources, Socorro, NM 87801, United States
Copyright Elsevier

Results of whole-rock 40Ar/39Ar step-heating analyses of extra-terrestrial materials have been used to constrain the timing of impacts in the inner solar system, solidification of the lunar magma ocean, and development of planetary magnetic fields. Despite the importance of understanding these events, the samples we have in hand are non-ideal due to mixed provenance, isotopic disturbances from potentially multiple heating episodes, and laboratory artifacts such as nuclear recoil. Although models to quantitatively assess multi-domain, diffusive 40Ar⁎ loss have long been applied to terrestrial samples, their use on extra-terrestrial materials has been limited. Here we introduce a multi-activation energy, multi-diffusion domain model and apply it to 40Ar/39Ar temperature-cycling, step-heating data for meteoritic and lunar samples. We show that age spectra of extra-terrestrial materials, the Jilin chondrite (K-4) and Apollo 16 lunar breccia (67514,43)(67514,43), yielding seemingly non-ideal behavior commonly interpreted as either laboratory artifacts or localized shock heating of pyroxene, are meaningful and can be understood in context of the presence of multi-diffusion domains containing multiple activation energies. Internally consistent results from both the meteoritic and lunar samples reveal high-temperature/short duration thermal episodes we interpret as due to moderate shock heating.