¹Emmanuel Jacquet
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13896]
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum national d’Histoire naturelle, Sorbonne Université, CNRS, CP52, 57 rue Cuvier, 75005 Paris, France
Published by arrangement with John Wiley & Sons

The current meteorite taxonomy, a result of two centuries of meteorite research and tradition, entangles textural and genetic terms in a less than consistent fashion, with some taxa (like “shergottites”) representing varied lithologies from a single putative parent body while others (like “pallasites”) subsume texturally similar objects of multifarious solar system origins. The familiar concept of “group” as representative of one primary parent body is also difficult to define empirically. It is proposed that the classification becomes explicitly binominal throughout the meteorite spectrum, with classes referring to petrographically defined primary rock types, whereas groups retain a genetic meaning, but no longer tied to any assumption on the number of represented parent bodies. The classification of a meteorite would thus involve both a class and a group, in a two-dimensional fashion analogous to the way Van Schmus and Wood decoupled primary and secondary properties in chondrites. Since groups would not substantially differ, at first, from those in current use de facto, the taxonomic treatment of “normal” meteorites, whose class would bring no new information, would hardly change. Yet classes combined with high- or low-level groups would provide a standardized grid to characterize petrographically and/or isotopically unusual or anomalous meteorites—which make up the majority of represented meteorite parent bodies—for example, in relation to the carbonaceous/noncarbonaceous dichotomy. In the longer term, the mergers of genetically related groups, a more systematic treatment of lithology mixtures, and the chondrite/achondrite transition can further simplify the nomenclature.

¹Sergey E. Kichanov,^1,2Bekhzodjon A. Abdurakhimov,¹Ivan Yu Zel,¹Andrei K. Kirillov,¹Denis P. Kozlenko,³Irina K. Lapina,³Yulii L. Mentsin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13903]
¹FLNP, Joint Institute for Nuclear Research, 141980 Dubna, Russia
²Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan, 100214 Tashkent, Uzbekistan
³Museum of the History of Astronomy, Sternberg Astronomical Institute, Lomonosov Moscow State University, 119992 Moscow, Russia
Published by arrangement with John Wiley & Sons

We present the results of neutron methods, specifically neutron diffraction and neutron tomography, in studying the structural organization of a Kunya-Urgench chondrite fragment. The major phases of the meteorite fragment and variation of the phase content across the studied volume were revealed using neutron diffraction. The 3-D model of the spatial distribution of metal and silicate phases inside the meteorite volume was obtained using neutron tomography. The distributions of volumes, average sizes, and shape-related parameters of kamacite and silicate phases were analyzed. Shape preferred orientations of the kamacite particles were observed and the origins of shape fabric of these particles were discussed.

^1,2Brendt C. Hyde,¹Desmond E. Moser,²Kimberly T. Tait,³James R. Darling,⁴Qing-Zhu Yin,⁴Matthew E. Sanborn,^1,2Neil R. Banerjee,^1,2Arshad Ali,¹Iffat Jabeen,³Hugo Moreira
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13897]
¹Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7 Canada
²Department of Natural History, Royal Ontario Museum, Toronto, Ontario, M5S 2C6 Canada
³School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, PO13QL UK
⁴Department of Earth and Planetary Sciences, University of California Davis, One Shields Avenue, Davis, California, 95616 USA
Published by arrangement with John Wiley & Sons

Detailed textural and geochemical analyses of the carbonaceous achondrites Northwest Africa (NWA) 7680 and NWA 6962 support a rapid progression of thermal events, by similar processes, on the same parent body. The achondrites have olivine compositions of Fa44.8 and Fa47.4 for NWA 7680 and NWA 6962, respectively. Replicate oxygen isotope analyses of grains and bulk powders from NWA 7680 yielded average Δ17O values of −1.04 ± 0.03‰ and −1.00 ± 0.05‰, respectively, which is identical to that reported for NWA 6962. The whole rock ɛ54Cr compositions are also equivalent for NWA 7680 and NWA 6962 (1.36 ± 0.05 and 1.30 ± 0.05, respectively). Both meteorites are plagioclase-rich, and NWA 7680 is also Fe-metal-rich, suggesting they both formed via differentiation processes that resulted in the pooling of partial melt products. Major element geochemical trends show that both rocks could be formed through the melting of chondritic material on a CR chondrite-like parent body. This is consistent with oxygen isotope and chromium isotope compositions. Intrusion of a late-stage melt is evident in both meteorites and the crystallization products include silica-rich, alkali-deficient nepheline. The late-stage liquid has partially melted and mixed with primary plagioclase in NWA 6962. In contrast, the late-stage liquid was often restricted to grain boundaries in NWA 7680, leaving some of the primary plagioclase crystals intact. In situ dating of NWA 7680 phosphate minerals (merrillite and fluorapatite) reveals that it has not experienced long duration thermal metamorphism, or impact-related Pb loss and age resetting since 4578 ± 17 Ma (207Pb/206Pb age ± 2σ, within error of solar system age). Phosphates associated with the late-stage melt in NWA 6962 yield a 207Pb/206Pb age of 4556.6 ± 8.0 Ma (2σ) within 2σ of the NWA 7680 age. These early dates indicate that the observed chromium isotope signatures in these meteorites were not introduced by a later high-temperature event, such as late impact accretion processes. These data are consistent with a rapid separation of inner and outer solar system chemical reservoirs, planetesimal melting, differentiation, and cooling, all within several million years of calcium-aluminum-rich inclusion formation.