|Title:||Calcium‐aluminum‐rich inclusions in enstatite chondrites (II): Oxygen isotopes|
|Authors:||T.J. Fagan, K.D. McKeegan, A.N. Krot, and K. Keil|
|Publication:||Meteorit. Planet. Sci., v. 36, p. 223‐230.|
In situ ion microprobe analyses of spinel in refractory calcium‐aluminium‐rich inclusions (CAIs) from type 3 EH chondrites yield 16O−rich compositions (δ18O and δ17O about −40‰). Spinel and feldspar in a CAI from an EL3 chondrite have significantly heavier isotopic compositions (δ18O and δ17O about −5‰). A regression through the data results in a line with slope 1.0 on a three−isotope plot, similar to isotopic results from unaltered minerals in CAIs from carbonaceous chondrites. The existance of CAIs with 16O−rich and 16O‐poor compositions in carbonaceous as well as enstatite chondrites indicates that CAIs formed ina at least two temporally or spatially distinct oxygen reservoirs. General similarities in oxygen isotopic compositions of CAIs from enstatite, carbonaceous, and ordinary chondrites indicate a common nebular mechanism or locale for the production of most CAIs.