TY - JOUR
T1 - Oxygen-isotopic compositions of relict and host grains in chondrules in the Yamato 81020 CO3.0 chondrite
AU - Kunihiro, Takuya
AU - Rubin, Alan E.
AU - McKeegan, Kevin D.
AU - Wasson, John T.
N1 - Funding Information:
We thank Frank Kyte for help with the electron microprobe and Haibo Zou for help with the ion microprobe. We also thank Tim Fagan, Mariana Cosarinsky, and Rhian Jones for constructive reviews. This research was supported mainly by NSF grant EAR-0074076 (J. T. Wasson). K.D.M. receives support from NASA Grant NAG5-9789. The UCLA ion probe was made possible by a gift from the W. M. Keck Foundation and is mainly supported by a grant from the NSF Instrumentation and Facilities Program.
PY - 2004/9/1
Y1 - 2004/9/1
N2 - 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.
AB - 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.
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U2 - 10.1016/j.gca.2004.02.011
DO - 10.1016/j.gca.2004.02.011
M3 - Article
AN - SCOPUS:4844219801
VL - 68
SP - 3599
EP - 3606
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
IS - 17
ER -