¹Zack Gainsforth et al. (>10)*
¹Space Sciences Laboratory, University of California at Berkeley, Berkeley, California, USA
*Find the extensive, full author and affiliation list on the publishers website

Using chemical and petrologic evidence and modeling, we deduce that two chondrule-like particles named Iris and Callie, from Stardust cometary track C2052,12,74, formed in an environment very similar to that seen for type II chondrules in meteorites. Iris was heated near liquidus, equilibrated, and cooled at ≤100 °C h-1 and within ≈2 log units of the IW buffer with a high partial pressure of Na such as would be present with dust enrichments of ≈103. There was no detectable metamorphic, nebular, or aqueous alteration. In previous work, Ogliore et al. (2012) reported that Iris formed late, >3 Myr after CAIs, assuming 26Al was homogenously distributed, and was rich in heavy oxygen. Iris may be similar to assemblages found only in interplanetary dust particles and Stardust cometary samples called Kool particles. Callie is chemically and isotopically very similar, but not identical to Iris.

Reference
Gainsforth Z et al. (2015) Constraints on the formation environment of two chondrule-like igneous particles from comet 81P/Wild 2. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12445]

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^1,2Masaaki Miyahara, ^1,3Eiji Ohtani, ⁴Ahmed El Goresy, ⁵Yangting Lin, ⁵Lu Feng, ⁵Jian-Chao Zhang, ⁶Philippe Gillet, ⁷Toshiro Nagase, ¹Jun Muto, ⁸Masahiko Nishijima
¹Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
²Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
³V. S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Science, 630090 Novosibirsk, Russia
⁴Bayerisches Geoinstitut, Universität Bayreuth, D-95440, Bayreuth, Germany
⁵Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China
⁶Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL) Station 1, 1015 Lausanne, Switzerland
⁷Center for Academic Resources and Archives, Tohoku University, Sendai 980-8578, Japan
⁸Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

The Almahata Sitta MS-170 ureilite (a piece of a breccia originating from the asteroid, 2008 TC3) consists mainly of olivine, with many diamond and graphite grains existing between the olivine grains. The occurrences of the diamonds are unique; i.e., i) some diamonds exhibit sub-euhedral habits and ii) some diamonds have large grain-size (up to about 40 μm). Several diamonds are segmented into many fragments by fractures. Individual fragments have similar crystallographic orientation, which implies that the adjacent diamond segments were originally a single crystal. Large diamond assemblages occur besides such individual diamond grains. In one of the largest assemblages (almost about 100 m in size) has also the same crystallographic orientation. They can be regarded as the pieces of a previously unique single diamond, which provides evidence for large single-crystals diamond in meteorites. Almahata Sitta MS-170 is a meteorite fragment from the 2008 TC3 asteroid that underwent less shock than other ureilitic meteorites. It is unlikely that such large diamonds were formed from graphite through a shock-induced phase transformation during planetesimal collision, despite this idea being now widely accepted as the diamond formation mechanism of ureilites. Fine-scale heterogeneous distribution of impurities (hydrogen, nitrogen, and oxygen) exists in single crystal diamonds, indicative of sluggish growth. This distribution is reminiscent of sector zoning growth. Its grain size, the shock features of MS-170, and the C- and N- isotopic composition signatures allow us to revive classical and but not widely accepted models for diamond formation in ureilites; i.e., a diamond formed from partially melted magma or a C–O–H fluid in the deep interior of the ureilite parent-body or, alternatively, through a chemical vapor deposition (CVD) process in the solar nebula. Considering present mineralogical and isotopic features, the former scenario is more favorable.

Reference
Miyahara M, Ohtani E, El Goresy A, Lin Y, Feng L, Zhang J-C, Gillet P, Nagase T, Muto J, Nishijima M (2015)
Unique large diamonds in a ureilite from Almahata Sitta 2008 TC3 Asteroid. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.04.035]

Copyright Elsevier

¹Ryan C. Ogliore, ¹Kazuhide Nagashima, ¹Gary R. Huss, ²Andrew J. Westphal, ²Zack Gainsforth, ²Anna L. Butterworth
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
²Space Sciences Laboratory, University of California at Berkeley, Berkeley, CA 94720, USA

Individual particles from comet 81P/Wild 2 collected by NASA’s Stardust mission vary in size from small sub-μm fragments found in the walls of the aerogel tracks, to large fragments up to tens of μm in size found towards the termini of tracks. The comet, in an orbit beyond Neptune since its formation, retains an intact a record of early-Solar-System processes that was compromised in asteroidal samples by heating and aqueous alteration. We measured the O isotopic composition of seven Stardust fragments larger than ∼2 μm extracted from five different Stardust aerogel tracks, and 63 particles smaller than ∼2 μ m from the wall of a Stardust track. The larger particles show a relatively narrow range of O isotopic compositions that is consistent with 16O16O-poor phases commonly seen in meteorites. Many of the larger Stardust fragments studied so far have chondrule-like mineralogy which is consistent with formation in the inner Solar System. The fine-grained material shows a very broad range of O isotopic compositions (-70-70‰< Δ17OΔ17O<+60<+60‰) suggesting that Wild 2 fines are either primitive outer-nebula dust or a very diverse sampling of inner Solar System compositional reservoirs that accreted along with a large number of inner-Solar-System rocks to form comet Wild 2.

Reference
Ogliore RC, Nagashima K, Huss GR, Westphal AJ, Gainsforth Z, Butterworth AL (2015) Oxygen Isotopic Composition of coarse- and fine-grained material from Comet 81P/Wild 2. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.04.028]

Copyright Elsevier

^1,2Alex Ruzicka, ¹Richard Hugo, ^1,2Melinda Hutson
¹Portland State University, Department of Geology, 1721 SW Broadway, Portland, OR, U.S.A
²Cascadia Meteorite Laboratory, Portland State University, 1721 SW Broadway, Portland, OR, U.S.A

We show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post-deformation cooling setting of the meteorites, and to discriminate between collisions affecting cold and warm parent bodies. The L6 chondrites Park (shock stage S1), Bruderheim (S4), Leedey (S4), and Morrow County (S5) were affected by variable shock deformation followed by relatively rapid cooling, and probably cooled as fragments liberated by impact in near-surface settings. In contrast, Kernouvé (H6 S1), Portales Valley (H6/7 S1), and MIL 99301 (LL6 S1) appear to have cooled slowly after shock, probably by deep burial in warm materials. In these chondrites, post-deformation annealing lowered apparent optical strain levels in olivine. Additionally, Kernouvé, Morrow County, Park, MIL 99301, and possibly Portales Valley, show evidence for having been deformed at an elevated temperature (⩾800-1000 °C). The high temperatures for Morrow County can be explained by dynamic heating during intense shock, but Kernouvé, Park, and MIL 99301 were probably shocked while the H, L and LL parent bodies were warm, during early, endogenically-driven thermal metamorphism. Thus, whereas the S4 and S5 chondrites experienced purely shock-induced heating and cooling, all the S1 chondrites examined show evidence for static heating consistent with either syn-metamorphic shock (Kernouvé, MIL 99301, Park), post-deformation burial in warm materials (Kernouvé, MIL 99301, Portales Valley), or both. The results show the pitfalls in relying on optical shock classification alone to infer an absence of shock and to construct cooling stratigraphy models for parent bodies. Moreover, they provide support for the idea that “secondary” metamorphic and “tertiary” shock processes overlapped in time shortly after the accretion of chondritic planetesimals, and that impacts into warm asteroidal bodies were common.

Reference
Ruzicka A, Hugo R, Hutson M (2015) Deformation and thermal histories of ordinary chondrites: Evidence for post-deformation annealing and syn-metamorphic shock. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.04.030]

Copyright Elsevier

^1,2Tomáš Magna, ³James M.D. Day, ^1,4Klaus Mezger, ^5,6Manuela A. Fehr, ⁷Ralf Dohmen, ⁸Hasnaa Chennaoui Aoudjehane, ⁹Carl B. Agee
¹Institut für Mineralogie, Universität Münster, Corrensstr. 24, D-48149 Münster, Germany
²Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic
³Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0244, USA
⁴Institut für Geologie, Universität Bern, Baltzerstr. 1+3, CH-3012 Bern, Switzerland
⁵CEPSAR, Department of Environment, Earth & Ecosystems, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
⁶Institut für Geochemie und Petrologie, ETH Zürich, Clausiusstr. 25, CH-8092 Zürich, Switzerland
⁷Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstr. 150, D-44780 Bochum, Germany
⁸Faculty of Sciences, Hassan II University, BP 5366 Maârif, Casablanca, Morocco
⁹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA

Lithium abundances and isotope compositions are reported for a suite of martian meteorites that span the range of petrological and geochemical types recognized to date for Mars. Samples include twenty-one bulk-rock enriched, intermediate and depleted shergottites, six nakhlites, two chassignites, the orthopyroxenite Allan Hills (ALH) 84001 and the polymict breccia Northwest Africa (NWA) 7034. Shergottites unaffected by terrestrial weathering exhibit a range in δ7Li from 2.1 to 6.2‰, similar to that reported for pristine terrestrial peridotites and unaltered mid-ocean ridge and ocean island basalts. Two chassignites have δ7Li values (4.0‰) intermediate to the shergottite range, and combined, these meteorites provide the most robust current constraints on δ7Li of the martian mantle. The polymict breccia NWA 7034 has the lowest δ7Li (−0.2‰) of all terrestrially unaltered martian meteorites measured to date and may represent an isotopically light surface end-member.
The new data for NWA 7034 imply that martian crustal surface materials had both a lighter Li isotope composition and elevated Li abundance compared with their associated mantle. These findings are supported by Li data for olivine-phyric shergotitte NWA 1068, a black glass phase isolated from the Tissint meteorite fall, and some nakhlites, which all show evidence for assimilation of a low-δ7Li crustal component. The range in δ7Li for nakhlites (1.8 to 5.2‰), and co-variations with chlorine abundance, suggests crustal contamination by Cl-rich brines. The differences in Li isotope composition and abundance between the martian mantle and estimated crust are not as large as the fractionations observed for terrestrial continental crust and mantle, suggesting a difference in the styles of alteration and weathering between water-dominated processes on Earth versus possibly Cl–S-rich brines on Mars. Using high-MgO shergottites (>14 wt.% MgO) it is possible to estimate the δ7Li of Bulk Silicate Mars (BSM) to be 4.2 ± 0.9‰ (2σ). This value is at the higher end of estimates for the Bulk Silicate Earth (BSE; 3.5 ± 1.0‰, 2σ), but overlaps within uncertainty.

Reference
Magna T, Day JMD, Mezger K, Fehr MA, Dohmen R, Aoudjehane CH, Agee CB (2015) Lithium isotope constraints on crust–mantle interactions and surface processes on Mars. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.04.029]

Copyright Elsevier

^1,2Lev J. Spivak-Birndorf et al. (>10*)
¹Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
²Department of Geological Sciences, Indiana University, Bloomington, Indiana, USA
*Find the extensive, full author and affiliation list on the publishers website

Bunburra Rockhole is a unique basaltic achondrite that has many mineralogical and petrographic characteristics in common with the noncumulate eucrites, but differs in its oxygen isotope composition. Here, we report a study of the mineralogy, petrology, geochemistry, and chronology of Bunburra Rockhole to better understand the petrogenesis of this meteorite and compare it to the eucrites. The geochemistry of bulk samples and of pyroxene, plagioclase, and Ca-phosphate in Bunburra Rockhole is similar to that of typical noncumulate eucrites. Chronological data for Bunburra Rockhole indicate early formation, followed by slow cooling and perhaps multiple subsequent heating events, which is also similar to some noncumulate eucrites. The 26Al-26Mg extinct radionuclide chronometer was reset in Bunburra Rockhole after the complete decay of 26Al, but a slight excess in the radiogenic 26Mg in a bulk sample allows the determination of a model 26Al-26Mg age that suggests formation of the parent melt for this meteorite from its source magma within the first ~3 Ma of the beginning of the solar system. The 207Pb-206Pb absolute chronometer is also disturbed in Bunburra Rockhole minerals, but a whole-rock isochron provides a re-equilibration age of ~4.1 Ga, most likely caused by impact heating. The mineralogy, geochemistry, and chronology of Bunburra Rockhole demonstrate the similarities of this achondrite to the eucrites, and suggest that it formed from a parent melt with a composition similar to that for noncumulate eucrites and subsequently experienced a thermal history and evolution comparable to that of eucritic basalts. This implies the formation of multiple differentiated parent bodies in the early solar system that had nearly identical bulk elemental compositions and petrogenetic histories, but different oxygen isotope compositions inherited from the solar nebula.

Reference
Spivak-Birndorf LJ et al. (2015) Geochemistry and chronology of the Bunburra Rockhole ungrouped achondrite. Meteoritics and Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12443]

Published by arrangement with John Wiley & Sons

¹Lidia Pittarello, ²Gang Ji, ³Akira Yamaguchi, ²Dominique Schryvers, ⁴Vinciane Debaille,¹Philippe Claeys
¹Analytical, Environmental and Geo-Chemistry (AMGC), Earth System Science, Vrije Universiteit Brussel, Brussels, Belgium
²Electron Microscopy for Materials Science (EMAT), University of Antwerp, Antwerp, Belgium
³National Institute of Polar Research, Tachikawa, Tokyo, Japan
⁴Laboratoire G-Time (Géochimie: Tracage isotopique, minéralogique et élémentaire), Université Libre de Bruxelles, Brussels, Belgium

The study of shock metamorphism of olivine might help to constrain impact events in the history of meteorites. Although shock features in olivine are well known, so far, there are processes that are not yet completely understood. In shock veins, olivine clasts with a complex structure, with a ringwoodite rim and a dense network of lamellae of unidentified nature in the core, have been reported in the literature. A highly shocked (S5-6), L6 meteorite, Asuka 09584, which was recently collected in Antarctica by a Belgian–Japanese joint expedition, contains this type of shocked olivine clasts and has been, therefore, selected for detailed investigations of these features by transmission electron microscopy (TEM). Petrographic, geochemical, and crystallographic studies showed that the rim of these shocked clasts consists of an aggregate of nanocrystals of ringwoodite, with lower Mg/Fe ratio than the unshocked olivine. The clast’s core consists of an aggregate of iso-oriented grains of olivine and wadsleyite, with higher Mg/Fe ratio than the unshocked olivine. This aggregate is crosscut by veinlets of nanocrystals of olivine, with extremely low Mg/Fe ratio. The formation of the ringwoodite rim is likely due to solid-state, diffusion-controlled, transformation from olivine under high-temperature conditions. The aggregate of iso-oriented olivine and wadsleyite crystals is interpreted to have formed also by a solid-state process, likely by coherent intracrystalline nucleation. Following the compression, shock release is believed to have caused opening of cracks and fractures in olivine and formation of olivine melt, which has lately crystallized under postshock equilibrium pressure conditions as olivine.

Reference
Pittarello L, Ji G, Yamaguchi A, Schryvers D, Debaille V, Claeys P (2015) From olivine to ringwoodite: a TEM study of a complex process. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12441]

Published by arrangement with John Wiley & Sons

¹Tóth, J. et al. (>10*)
¹Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
We currently do not have a copyright agreement with this publisher and cannot display the abstract here

We provide the circumstances and details of the fireball observation, search expeditions, recovery, strewn field, and physical characteristics of the Košice meteorite that fell in Slovakia on February 28, 2010. The meteorite was only the 15th case of an observed bolide with a recovered mass and subsequent orbit determination. Despite multiple eyewitness reports of the bolide, only three videos from security cameras in Hungary were used for the strewn field determination and orbit computation. Multiple expeditions of professionals and individual searchers found 218 fragments with total weight of 11.3 kg. The strewn field with the size of 5 × 3 km is characterized with respect to the space distribution of the fragments, their mass and size-frequency distribution. This work describes a catalog of 78 fragments, mass, size, volume, fusion crust, names of discoverers, geographic location, and time of discovery, which represents the most complex study of a fresh meteorite fall. From the analytical results, we classified the Košice meteorite as an ordinary H5 chondrite.

Reference
Tóth J et al. (2015) The Košice meteorite fall: Recovery and strewn field. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12447]

Published by arrangement with John Wiley & Sons

¹Rahat Khan, ¹Naoki Shirai, ¹Mitsuru Ebihara
¹Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan

Rare earth elements (REEs), Th, U and P were determined in 15 Rumuruti (R)-type chondrites and the Allende CV chondrite. Repeated analyses of Allende for REEs, Th and U by ICP-MS and P by ICP-AES, and comparisons of these data with literature values ensure high reproducibility (precision) and reliability (accuracy) of acquired data. CI-normalized REE abundances in R chondrites are slightly enriched in heavy REEs with a small, positive Ce anomaly, in contrast to Allende. CI-normalized Pr/Tm and Nd/Yb ratios show a positive correlation, suggesting the heterogeneous mixing of two components (CI-like and refractory-rich materials) during the accretion of the R chondrite parent body. A Ce anomaly, however, was likely homogeneously present in the nebula. A mean Th/U ratio of R chondrites is View the MathML source3.81±0.13(1σ), which is 5.1% higher than the CI ratio. Probably, the Th–U fractionation was inherited from the nebula from which the R chondrite parent body formed. Besides the Th–U fractionation, REEs and Th–U are heterogeneously fractionated in R chondrites, for which parent body processing is assumed to be the cause. A mean P content of R chondrites (1254 μg/g) is higher than for any ordinary chondrite and is close to the EL mean. There appears to be a negative correlation between P and REEs contents in R chondrites. It is probable that REEs were diluted by extraneously supplied, REEs-depleted and P-containing materials (schreibersite or metal). This process must have occurred heterogeneously during accretion so that the heterogeneity of P-containing materials was preserved in the R chondrite parent body and individual R chondrites.

Reference
Khan R, Shirai N, Ebihara M (2015) Chemical characteristic of R chondrites in the light of P, REEs, Th and U abundances. Earth and Planetary Science Letters 422, 18–27
Link to Article [doi:10.1016/j.epsl.2015.04.008]

Copyright Elsevier

¹A.V. Andronikov, , ¹I.E. Andronikova, ¹D.H. Hill
¹Lunar and Planetary Laboratory, University of Arizona, 1415 North 6th Ave, Tucson, AZ, 85705, USA

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Reference
Andronikov AV, Andronikova IE, Hill DH (2015) Impact history of the Chelyabinsk meteorite: Electron microprobe and LA-ICP-MS study of sulfides and metals. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2015.03.028]