Oxygen-isotopic compositions of relict and host grains in chondrules in the Yamato 81020 CO3.0 chondrite

Takuya Kunihiro, Alan E. Rubin, Kevin D. McKeegan, John T. Wasson

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

We report the oxygen-isotope compositions of relict and host olivine grains in six high-FeO porphyritic olivine chondrules in one of the most primitive carbonaceous chondrites, CO3.0 Yamato 81020. Because the relict grains predate the host phenocrysts, microscale in situ analyses of O-isotope compositions can help assess the degree of heterogeneity among chondrule precursors and constrain the nebular processes that caused these isotopic differences. In five of six chondrules studied, the Δ17O (=δ17O - 0.52 · δ18O) compositions of host phenocrysts are higher than those in low-FeO relict grains; the one exception is for a chondrule with a moderately high-FeO relict. Both the fayalite compositions as well as the O-isotope data support the view that the low-FeO relict grains formed in a previous generation of low-FeO porphyritic chondrules that were subsequently fragmented. It appears that most low-FeO porphyritic chondrules formed earlier than most high-FeO porphyritic chondrules, although there were probably some low-FeO chondrules that formed during the period when most high-FeO chondrules were forming.

Original languageEnglish
Pages (from-to)3599-3606
Number of pages8
JournalGeochimica et Cosmochimica Acta
Volume68
Issue number17
DOIs
Publication statusPublished - Sep 1 2004
Externally publishedYes

ASJC Scopus subject areas

  • Geochemistry and Petrology

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