^1,2Emmanuel Jacquet, ^3,4Jean-Alix Barrat, ^5,6Pierre Beck, ¹Florent Caste, ⁷Jérôme Gattacceca, ⁷Corinne Sonzogni,^1,8Matthieu Gounelle
¹Institut de Minéralogie de Physique des Matériaux et de Cosmochimie, CNRS & Muséum National d’Histoire Naturelle, UMR 7202, Paris, France
²Canadian Institute for Theoretical Astrophysics, Toronto, Ontario, Canada
³Laboratoire Domaines Océaniques, UMR 6538, Université Européenne de Bretagne, Bretagne, France
⁴CNRS UMR 6538 (Domaines Océaniques), U.B.O.-I.U.E.M., Plouzané Cedex, France
⁵1 Univ. Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Grenoble, France
⁶CNRS, IPAG, Grenoble, France
⁷CEREGE UM 34, CNRS/Université d’Aix-Marseille 3, Aix-en-Provence, France
⁸Institut Universitaire de France, Paris, France

Northwest Africa (NWA) 5958 is a carbonaceous chondrite found in Morocco in 2009. Preliminary chemical and isotopic data leading to its initial classification as C3.0 ungrouped have prompted us to conduct a multitechnique study of this meteorite and present a general description here. The petrography and chemistry of NWA 5958 is most similar to a CM chondrite, with a low degree of aqueous alteration, apparently under oxidizing conditions, and evidence of a second, limited alteration episode manifested by alteration fronts. The oxygen isotopic composition, with ∆’17O = −4.3‰, is more 16O-rich than all CM chondrites, indicating, along with other compositional arguments, a separate parent body of origin. We suggest that NWA 5958 be reclassified as an ungrouped carbonaceous chondrite related to the CM group.

Reference
Jacquet E, Barrat J-A, Beck P, Caste F, Gattacceca J, Sonzogni C, Gounelle M (2016) Northwest Africa 5958: A weakly altered CM-related ungrouped chondrite, not a CI3. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12628]
Published by arrangement with John Wiley & Sons

^1,2Melissa A. Morris, ³Stuart J. Weidenschilling,²Steven J. Desch
¹State University of New York at Cortland, Cortland, New York, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
³Planetary Science Institute, Tucson, Arizona, USA

Chondrules represent one of the best probes of the physical conditions and processes acting in the early solar nebula. Proposed chondrule formation models are assessed based on their ability to match the meteoritic evidence, especially experimental constraints on their thermal histories. The model most consistent with chondrule thermal histories is passage through shock waves in the solar nebula. Existing models of heating by shocks generally yield a good first-order approximation to inferred chondrule cooling rates. However, they predict prolonged heating in the preshock region, which would cause volatile loss and isotopic fractionation, which are not observed. These models have typically included particles of a single (large) size, i.e., chondrule precursors, or at most, large particles accompanied by micron-sized grains. The size distribution of solids present during chondrule formation controls the opacity of the affected region, and significantly affects the thermal histories of chondrules. Micron-sized grains evaporate too quickly to prevent excessive heating of chondrule precursors. However, isolated grains in chondrule-forming regions would rapidly coagulate into fractal aggregates. Preshock heating by infrared radiation from the shock front would cause these aggregates to melt and collapse into intermediate-sized (tens of microns) particles. We show that inclusion of such particles yields chondrule cooling rates consistent with petrologic and isotopic constraints.

Reference
Morris MA, Weidenschilling SJ, Desch SJ (2016) The effect of multiple particle sizes on cooling rates of chondrules produced in large-scale shocks in the solar nebula. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12631]
Published by arrangement with John Wiley & Sons

¹Justin Filiberto, ^2,3Juliane Gross,⁴Francis M. McCubbin
¹Department of Geology, Southern Illinois University, Carbondale, Illinois, USA
²Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
³Department of Earth and Planetary Sciences, The American Museum of Natural History, New York, New York, USA
⁴NASA Johnson Space Center, Houston, Texas, USA

Previous estimates of the volatile contents of Martian basalts, and hence their source regions, ranged from nearly volatile-free through estimates similar to those found in terrestrial subduction zones. Here, we use the bulk chemistry of Martian meteorites, along with Martian apatite and amphibole chemistry, to constrain the volatile contents of the Martian interior. Our estimates show that the volatile content of the source region for the Martian meteorites is similar to the terrestrial Mid-Ocean-Ridge Mantle source. Chlorine is enriched compared with the depleted terrestrial mantle but is similar to the terrestrial enriched source region; fluorine is similar to the terrestrial primitive mantle; and water is consistent with the terrestrial mantle. Our results show that Martian magmas were not volatile saturated; had water/chlorine and water/fluorine ratios ~0.4–18; and are most similar, in terms of volatiles, to terrestrial MORBs. Presumably, there are variations in volatile content in the Martian interior as suggested by apatite compositions, but more bulk chemical data, especially for fluorine and water, are required to investigate these variations. Finally, the Noachian Martian interior, as exemplified by surface basalts and NWA 7034, may have had higher volatile contents.

Reference
Filiberto J, Gross J, McCubbin FM (2016) Constraints on the water, chlorine, and fluorine content of the Martian mantle. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12624]
Published by arrangement with John Wiley & Sons

^1,2,3Hideaki Miyamoto, ^1,4Takafumi Niihara, ⁵Takeshi Kuritani, ¹Peng K. Hong, ¹James M. Dohm, ²Seiji Sugita
¹University Museum, University of Tokyo, Tokyo, 113-0033, Japan
²Department of Earth and Planetary Sciences, University of Tokyo, Tokyo, 113-0033, Japan
³Planetary Science Institute, Tucson, Arizona, USA
⁴Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
⁵Department of Natural History Sciences, Hokkaido University, Sapporo, Japan

Remote sensing observations by recent successful missions to small bodies have revealed the difficulty in classifying the materials which cover their surfaces into a conventional classification of meteorites. Although reflectance spectroscopy is a powerful tool for this purpose, it is influenced by many factors, such as space weathering, lighting conditions, and surface physical conditions (e.g., particle size and style of mixing). Thus, complementary information, such as elemental compositions, which can be obtained by X-ray fluorescence (XRF) and gamma-ray spectrometers (GRS), have been considered very important. However, classifying planetary materials solely based on elemental compositions has not been investigated extensively. In this study, we perform principal component and cluster analyses on 12 major and minor elements of the bulk compositions of 500 meteorites reported in the National Institute of Polar Research (NIPR), Japan database. Our unique approach, which includes using hierarchical cluster analysis, indicates that meteorites can be classified into about 10 groups purely by their bulk elemental compositions. We suggest that Si, Fe, Mg, Ca, and Na are the optimal set of elements, as this set has been used successfully to classify meteorites of the NIPR database with more than 94% accuracy. Principal components analysis indicates that elemental compositions of meteorites form eight clusters in the three-dimensional space of the components. The three major principal components (PC1, PC2, and PC3) are interpreted as (1) degree of differentiations of the source body (i.e., primitive versus differentiated), (2) degree of thermal effects, and (3) degree of chemical fractionation, respectively.

Reference
Miyamoto H, Niihara T, Kuritani T, Hong PK, Dohm JM, Sugita S (2016) Cluster analysis on the bulk elemental compositions of Antarctic stony meteorites. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12634]
Published by arrangement with John Wiley & Sons