Primordial Compositions of Refractory Inclusions [electronic resource].
- Washington, D.C. : United States. Dept. of Energy, 2008.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
- Physical Description:
- PDF-file: 57 pages; size: 2.5 Mbytes
- Additional Creators:
- Lawrence Berkeley National Laboratory
United States. Department of Energy
United States. Department of Energy. Office of Scientific and Technical Information
- Bulk chemical and oxygen, magnesium and silicon isotopic compositions were measured for each of 17 Types A and B refractory inclusions from CV3 chondrites. After bulk chemical compositions were corrected for non-representative sampling in the laboratory, the Mg and Si isotopic compositions of each inclusion were used to calculate its original chemical composition assuming that the heavy-isotope enrichments of these elements are due to Rayleigh fractionation that accompanied their evaporation from CMAS liquids. The resulting pre-evaporation chemical compositions are consistent with those predicted by equilibrium thermodynamic calculations for high-temperature nebular condensates but only if different inclusions condensed from nebular regions that ranged in total pressure from 10⁻⁶ to 10⁻¹ bar, regardless of whether they formed in a system of solar composition or in one enriched in OC dust relative to gas by a factor of ten relative to solar composition. This is similar to the range of total pressures predicted by dynamic models of the solar nebula for regions whose temperatures are in the range of silicate condensation temperatures. Alternatively, if departure from equilibrium condensation and/or non-representative sampling of condensates in the nebula occurred, the inferred range of total pressure could be smaller. Simple kinetic modeling of evaporation successfully reproduces observed chemical compositions of most inclusions from their inferred pre-evaporation compositions, suggesting that closed-system isotopic exchange processes did not have a significant effect on their isotopic compositions. Comparison of pre-evaporation compositions with observed ones indicates that 80% of the enrichment in refractory CaO + Al₂O₃ relative to more volatile MgO + SiO₂ is due to initial condensation and 20% due to subsequent evaporation for both Type A and Type B inclusions.
- Published through SciTech Connect.
Geochimica et Cosmochimica Acta, vol. 72, N/A, June 15, 2008, pp. 3001-3021 72 ISSN 0016-7037; GCACAK FT
Grossman, L; Ding, T; Galy, A; Hutcheon, I D; Williams, R W; Simon, S B; Rai, V K; Thiemens, M H; Fedkin, A V; Clayton, R N; Mayeda, T K.
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