Origin of metal-troilite aggregates in six ordinary chondrites

Coarse metal-troilite aggregates several mms in sizes have been studied in six ordinary chondrites, Yamato (Y)-794006 (L4), Y-793211 (L6), Y-793213 (L6), Y-791629 (H4), Y-791686 (H5), and Y-791555 (H6). In each sample, textures of an aggregate and host meteorite show an evidence for the aggregate being solidified from metal-sulfide melt under a slow cooling condition. Metal and silicate texture in the host meteorite suggest a formation of the metal-sulfide melt by weak or moderate reheating by an impact process on the parent body. Bulk Fe-S compositions of the aggregates show variations in melting temperatures which correlate with petrologic grades of the host meteorites. These evidences suggest that the aggregates formed by impact melting on the "hot" parent bodies by weak or moderate reheating piled on the pre-impact temperatures during thermal metamorphism.