Isotopic evidence for two chondrule generations in CR chondrites and their relationships to other carbonaceous chondrites

1Yves Marrocchi,1Maxime Piralla,1Maxence Regnault,2Valentina Batanova,1Johan Villeneuve,3Emmanuel Jacquet
Earth and Planetary Science Letters 593, 117683 Link to Article []
1Université de Lorraine, CNRS, CRPG, UMR 7358, Vandœuvre-lès-Nancy 54500, France
2Université Grenoble Alpes, ISTerre, CNRS, UMR 5275, Grenoble 38000, France
3Institut 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
Copyright Elsevier

Among primitive meteorites, CR chondrites have peculiar isotopic compositions, the origin of which is uncertain and may have involved contributions from primordial molecular cloud material or the chondrites’ formation and agglomeration late during the evolution of the protoplanetary disk. Here, we report a comprehensive textural and isotopic characterization of type I CR chondrules and provide new insights on their formation conditions. We find that two chondrule populations characterized by different sizes and oxygen isotopic compositions co-exist in CR chondrites. The typically larger, 16O-poor (-4‰) chondrules (type I-CR chondrules) appear to have formed late out of a CR reservoir already populated by typically smaller, 16O-rich (-4‰) chondrules (type I-CO chondrules). Before formation of type I-CR chondrules, the CR reservoir was likely dominated by CI-like dust, in line with the proximity of CR with CI chondrites for many isotopic ratios. The CR reservoir thus may have largely belonged to the continuum shown by other carbonaceous chondrites, although some isotopic ratios maintain some originality and suggest isotopic variation of CI-like dust in the outer disk. Combined with literature data, our data (i) demonstrates that recycling processes are responsible for the singular compositions of CR chondrites and their chondrules for isotopic systems with drastically different geochemical behaviors (O, Cr, Te) and (ii) support the homogeneous distribution of 26Al throughout the protoplanetary disk.


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