Chondrules in the Qingzhen type-3 enstatite chondrite: Possible precursor components and comparison to ordinary chondrite chondrules

Abstract

The Qingzhen (EH3) fall appears to be the least equilibrated enstatite chondrite; mineral compositions vary widely from chondrule to chondrule, and in some cases, from grain to grain within individual chondrules. As in ordinary chondrite (OC) chondrules, most elements show appreciable ranges in concentration. Porphyritic olivine-pyroxene (POP) chondrules are richer than porphyritic pyroxene (PP) and radial pyroxene (RP) chondrules in refractory lithophiles and siderophiles. Unlike OC chondrules, Qingzhen's RP and PP chondrules have similar bulk compositions.Elements in each of the following sets intercorrelate significantly, probably because these elements were present in the same nebular components: 1.(1) Fe-Co-Ni-Ir-Au,2.(2) Ca-Eu-Se,3.(3) Al-Sc-Hf,4.(4) Na-REE,5.(5) Cl-Br. Several additional elements show no correlations. Set (1) elements were probably derived from a metal component, as in OC chondrules. Set (3) elements, which occur in higher concentrations in olivine-bearing (POP) chondrules, suggest the existence of a refractory lithophile-rich, olivine-rich component, similar to the one previously inferred for OC chondrules. Set (2) elements suggest a precursor component rich in oldhamite and set (4) elements suggest another refractory-bearing component. Components (2) and (4) were not precursors of OC chondrules.For some chondrules, interelement ratios of refractory lithophiles such as Ca, Al, Ti, Sc and REE are similar to CI ratios. This indicates that these elements were probably derived from silicates. We suggest that the earliest solid phases were refractory silicates that were sulfurized before chondrule formation. Some of these sulfurized components (e.g., one rich in oldhamite) were abundant in the region where the Qingzhen chondrules formed.