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