Oxygen isotopic variations in the outer margins and Wark–Lovering rims of refractory inclusions

摘要: Abstract Oxygen isotopic variations across the outer margins and Wark–Lovering (WL) rims of a diverse suite six coarse-grained Types A B refractory inclusions from both oxidized reduced CV3 chondrites suggest that CAIs originated 16 O-rich protosolar gas reservoir were later exposed to relatively 17,18 reservoirs. The O-isotope profiles can be explained by changes in composition near protoSun or migration through heterogeneous nebula. Variability within inclusion interiors appears have been set prior WL rim growth. Modeling zoning as diffusion gradients between edges establishes range permissible time–temperature combinations for their exposure At mean temperatures 1400 K, models match isotope yield timescales ranging 5 × 10 3 3 × 10 5  years. Assuming with (protosolar) composition, differences among melilite imply existence number isotopically distinct Evidence at some subsequent exchange may relate beginning formation. In layers surrounding interiors, spinel is but subtly different CAIs. Melilite often O-poor, rare grains also exist. Pyroxene generally exhibits intermediate compositions zoning. Olivine accretionary rims, when present, heterogeneous. extreme heterogeneity individual particular, observed trends outward O-enrichments, contained chondrites, like themselves, formed Collectively, these results support numerical protoplanetary disk which transported several nebular reservoirs multiple times accretion onto parent body.