11:30 AM - 11:45 AM
[PPS07-16] Extreme 16O-rich CAIs in Isheyevo chondrite
Keywords:Oxygen isotope, Isheyevo chondrite, CAI, SIMS
Thirteenthick sections of Isheyevo chondrite were newly prepared. X-ray elemental maps were obtaind for whole sections by FE-SEM-EDS. Al-rich inclusions on the sections were picked up as many as possible for isotope analysis in order to prevent biased sample selection. Oxygen isotope analysis for the inclusions were performed by SIMS.
Oxygen isotopic compositions of 263 CAIs were measured and 4 extreme 16O-rich CAIs were found. Two CAIs are composed of grossite core rimmed by spinel, melilite and Ti-rich diopside layer and others lack diopside and/or melilite. While the heterogeneous composition of grossite (Δ17O = -36 to -32‰) would be affected by altered feature of grossite, the spinel grains have uniform 16O-rich compsition (Δ17O = -37‰). If we draw a line in 3 oxygen isotope diagram with the extreme 16O-rich spinel and spinel in chondules near the CAI, the slope is in good agreement with a slope of olivine in a006 chondrule and porphiritic olivine chondrule infer that the oxygen isotopic composition of the spinel grains maintain the signature of an16O-rich end member of the Solar System.
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