Isotopic evidence for two chondrule generations in CR chondrites and their relationships to other carbonaceous chondrites
Yves Marrocchi, Maxime Piralla, Maxence Regnault, Valentina Batanova, Johan Villeneuve, Emmanuel Jacquet
Earth and Planetary Science Letters
Volume 593, 1 September 2022
“Highlights
• CR chondrites are characterized by two distinct chondrule populations.
• Large CR chondrules derived from smaller ones through the recycling of CI-like dust.
• The CR reservoir was dominated by CI−like dust.
• Recycling processes are responsible for the singular compositions of CR chondrites.
• Our data support the homogeneous distribution of 26Al throughout the protoplanetary disk.”
“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 (Δ17O>-4‰) chondrules (type I-CR chondrules) appear to have formed late out of a CR reservoir already populated by typically smaller, 16O-rich (Δ17O<-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.”
