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Oxygen and magnesium isotopic compositions of amoeboid olivine aggregates from the Semarkona LL3.0 chondriteItoh, S.; Russell, S. S.; Yurimoto, H. (The Meteoritical Society, 2007-01-01)Amoeboid olivine aggregates (AOAs) in the LL3.0 Semarkona chondrite have been studied by secondary ion mass spectrometry. The AOAs mainly consist of aggregates of olivine grains with interstitial Al-Ti-rich diopside and anorthite. Oxygen-isotopic compositions of all phases are consistently enriched in 16O, with delta-17,18O = ~-50 ppm. The initial 26Al/27Al ratios are calculated to be 5.6 +/- 0.9 (2-sigma) x 10^(-5). These values are equivalent to those of AOAs and fine-grained calciumaluminum- rich inclusions (FGIs) from pristine carbonaceous chondrites. This suggests that AOAs in ordinary chondrites formed in the same 16O-rich calcium-aluminum-rich inclusion (CAI)-forming region of the solar nebula as AOAs and FGIs in carbonaceous chondrites, and subsequently moved to the accretion region of the ordinary chondrite parent body in the solar nebula.