Fractionated sulfur isotopes in sulfides of the Kaidun meteorite

Abstract— The Kaidun meteorite contains carbonaceous chondrite (CM1) clasts that have been highly altered by reactions with hydrothermal fluids. Pyrrhotite in these clasts occurs as unusual needles wrapped by sheaths of phyllosilicate, and pentlandite forms veins that crosscut aggregates of phyllosilicate and garnet but not pyrrhotite. The isotopic compositions of S (δ34SCDT) in individual sulfide grains, measured by ion micro‐probe, are fractionated compared to troilite in ordinary chondrites. The S in Kaidun sulfides is isotopically light (as much as −4.2% for pyrrhotite and −5.7%0 for pentlandite), unlike sulfides in other carbonaceous chondrites, which are enriched in 34S. The unusual S‐isotopic composition of these texturally unique sulfides supports the hypothesis that Kaidun CM1 clasts were pervasively altered under extreme thermal conditions, possibly by fluids that had lost isotopically heavy SO2.