The condensation origin of zoned metal grains in Queen Alexandra Range 94411: Implications for the formation of the Bencubbin-like chondrites

Abstract

Thermodynamic analysis of the compositional profiles across large chemically-zoned Fe, Ni metal grains in the Bencubbin-like chondrite Queen Alexandra Range (QUE) 94411 suggests that these grains formed by non-equilibrium gas-solid condensation under variable oxidizing conditions, isolation degree, and Cr depletion factors. The oxidizing conditions must have resulted from the complete vaporization of nebular regions with enhanced dust/gas ratios (∼10-40 x solar). Because the origin of each of the metal grains studied requires different condensation parameters (dust/gas ratio, isolation degree, and Cr depletion factor), a high degree of heterogeneity in the formation region of the Bencubbin-like chondrite metal is required. To preserve compositional zoning of the metal grains and prevent their melting and sulfidization, the grains must have been removed from the hot condensation region into cold regions where the accretion of the Bencubbin-like asteroidal body took place.