FRACTIONATED SULFUR ISOTOPES IN SULFIDES OF THE KAIDUN METEORITE

The Kaidun meteorite contains carbonaceous chondrite (CM1) clasts that have been highly altered by reactions with hydrothermal fluids. Pyrrh otite in these clasts occurs as unusual needles wrapped by sheaths of phyllosilicate, and pentlandite forms veins that crosscut aggregates o f phyllosilicate and garnet but not pyrrhotite. The isotopic compositi ons of S(delta(34)S(CDT)) in individual sulfide grains, measured by io n microprobe, are fractionated compared to troilite in ordinary chondr ites. The S in Kaidun sulfides is isotopically light (as much as -4.2 parts per thousand for pyrrhotite and -5.7 parts per thousand for pent landite), unlike sulfides in other carbonaceous chondrites, which are enriched in S-34. The unusual S-isotopic composition of these textural ly unique sulfides supports the hypothesis that Kaidun CMI clasts were pervasively altered under extreme thermal conditions, possibly by flu ids that had lost isotopically heavy SO2.