Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6438863 | Geochimica et Cosmochimica Acta | 2014 | 18 Pages |
Abstract
The isotopic and microstructural data indicate that the Al-Mg-rich and Fe-Cr-rich grains experienced different condensation and processing histories. The single-crystal, stoichiometric, nearly pure Mg-Al spinels are generally consistent with equilibrium condensation predictions, which constrain their condensation temperatures between 1161 and 1221Â K, assuming total gas pressures of 1Â ÃÂ 10â6 and 1Â ÃÂ 10â3Â atm, respectively. Minor stacking disorder is observed in one of the Mg-Al spinels and is probably a result of slight perturbations to crystal growth during condensation in the circumstellar environment or of impact-induced sheer strain as a response to grain-grain collisions, which could have occurred in the circumstellar environment, the interstellar medium, or the solar nebula. The minor Ca in one of the Mg-Al spinels suggests back reaction with the circumstellar gas from which it formed. In comparison, the similarly oriented Fe-Cr-rich grains of the Orgueil assemblage and their homogeneous isotopic compositions are consistent with their condensation as a single circumstellar dust particle. However, the Fe-Cr-rich compositions (nearly chromite) are inconsistent with predictions for equilibrium condensation and suggest a complex cooling history that is not possible to precisely constrain.
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Authors
Thomas J. Zega, Larry R. Nittler, Frank Gyngard, Conel M.O'D. Alexander, Rhonda M. Stroud, Ernst K. Zinner,