¹Yves Marrocchi,²Emmanuel Jacquet,²Julia Neukampf,²Johan Villeneuve,³Michael E. Zolensky
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13947]
¹Université de Lorraine, CNRS, CRPG, UMR 7358, Vandœuvre-lès-Nancy, 54500 France
²Institut 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
³X12 Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

The ungrouped carbonaceous chondrite (CC) Bells has long been considered petrographically similar to CM chondrites based on its matrix abundance and degree of aqueous alteration, but also shows significant isotopic affinities to CR chondrites. Its taxonomic status is thus important for clarifying the relationship of the CRHB (formerly “CR”) clan with other CCs. In this study, we measured the oxygen isotopic compositions of olivines in type I chondrules and isolated olivine grains in Bells. Bells olivines mostly have ∆17O > −4‰, similar to CR chondrites but unlike other CCs that are rich in refractory inclusions, in which chondrules are generally richer in 16O. Therefore, Bells is a CR chondrite (albeit an anomalous one), most similar to the rare, matrix-rich CRs like Al Rais. These chondrites (i) may not necessarily derive from the same primary parent body as mainstream CRs, (ii) bear witness to significant variations of the matrix/chondrule ratio within the CRHB clan, and (iii) may be a good analog for samples retrieved by the space mission OSIRIS-REx.

^1,2A. Stephant,¹C. Carli,²M. Anand,³A. Néri,⁴J. Davidson,^1,5G. Pratesi,⁵T. Cuppone,²R. C. Greenwood,²I. A. Franchi
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13944]
¹Istituto di Astrofisica e Planetologia Spaziali – INAF, Rome, 00133 Italy
²School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA UK
³Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, 95447 Germany
⁴Buseck Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287 USA
⁵Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Firenze, 50121 Italy
Published by arrangement with John Wiley & Sons

The Northwest Africa (NWA) 090 meteorite, initially classified as an acapulcoite, presents petrological, chemical, and isotopic characteristics comparable to a group of seven primitive winonaites: Dhofar 1222, NWA 725, NWA 1052, NWA 1054, NWA 1058, NWA 1463, and NWA 8614. Five of these samples were previously classified as acapulcoites or ungrouped achondrites before being reclassified as winonaites based on their oxygen isotopic compositions. These misclassifications are indicative of the particular compositional nature of these primitive achondrites. All contain relict chondrules and a lower closure temperature of metamorphism of 820 ± 20 °C compared to other typical winonaites, as well as mineral elemental compositions similar to those of acapulcoites. The oxygen isotopic signature of these samples, δ17O of 1.18 ± 0.17‰, δ18O of 3.18 ± 0.30‰, and Δ17O of −0.47 ± 0.02, is in fact resolvable from both acapulcoites and winonaites. We investigate the relationship between these eight primitive achondrites, typical winonaites, and acapulcoites, to redefine petrological, mineralogical, and geochemical criteria of primitive achondrite classification. Distinguishing between winonaites, acapulcoites, and this group of eight primitive achondrites can be unambiguously done using a combination of several mineralogical and chemical criteria. A combination of olivine fayalite content and FeO/MnO ratio, as well as plagioclase potassium content allow us to separate these three groups without the absolute necessity of oxygen isotope analyses. NWA 090 as well as the other seven primitive achondrites, although related to winonaites, are most likely derived from a parent body distinct from winonaites and acapulcoites–lodranites, and define a new group of primitive achondrites that can be referred to as tissemouminites.