INSPIRATION FROM STUDY OF ANTARCTIC METEORITES I:PETROGRAPHIC AND COMPOSITIONAL EVIDENCES FOR EARLY CONTINUOUS CHEMICAL FRACTIONATION OF THE SOLAR NEBULA

Bulk concentrations of Ir, Os, Co and other siderophile elements of metal phase in chondrites increase significantly with degree of oxidation, which together with Co-content of kamacite and Fa-content of olivine, reveal a continuous variation of redox in chondrites. Intermediate groups of E/H, H/L, L/LL, and LL/C, lying between E and H, H and L, L and LL, LL and C, respectively, were proposed based on Co content in kamacite, Fa value of olivine, Fs value of low-Ca pyroxene, bulk concentrations of Ir, Os and Co of metal phase and other taxonomic parameters. The discovery of intermediate groups increases the number of chemical groups of chondrites from 9 to 13. Both variation of redox in chondrites and presence of the intermediate groups of chondrites suggest a continuous chemical fractionation in the primordial solar nebula.