Marrocchi, Y.; Piralla, M.; Regnault, M.; Batanova, V.; Villeneuve, J.; Jacquet, E.
Earth and Planetary Science Letters, 2022, 593, 117683
Voir en ligne : https://doi.org/10.1016/j.epsl.2022.117683
Abstract :
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
(17O > -4) chondrules (type I-CR chondrules) appear to have formed late out of a CR reservoir already
populated by typically smaller, 16O-rich (17O < -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.