Oxygen isotopic composition of the solar nebula gas inferred from high-precision isotope imaging of melilite crystals in an Allende CAI

摘要: – High-precision isotope imaging analyses of reversely zoned melilite crystals in the gehlenitic mantle Type A CAI ON01 Allende carbonaceous chondrite reveal that there are four types oxygen isotopic distributions within single crystals: (1) uniform depletion 16O (δ18O ≈ −10‰), (2) enrichment (δ18O ≈ −40‰), (3) variations composition from 16O-poor core to 16O-rich rim (δ18O ≈ −10‰ −30‰, −20‰ −45‰, and −10‰ −35‰) with decreasing akermanite content, (4) (δ18O ≥ −10‰) along crystal rim. Hibonite, spinel, perovskite grains (δ18O ≈ −45‰), adjoin melilites. Gas-solid or gas-melt exchange nebula is inconsistent both distinct compositions among minerals reverse zoning melilite. Fluid-rock interaction on parent body resulted limited areas near holes, cracks, secondary phases, such as anorthite grossular. We conclude melilites mostly preserve primary either 16O-enriched 16O-depleted gas which they were condensed. The correlation between content may indicate isotopes solar changed during growth. suggest radial excursions inner edge protoplanetary disk simultaneously variation melilite, due mixing coronal gas. Gas condensates aggregated form gehlenite ON01.