Sulfide Phases and Their Evolution in Mantle Xenoliths from Changbaishan Mountain District in China

Mantle xenoliths occur widely in some strata of Cenozoic basalts in Changbaishan mountains, Jilin province. Sulfide phases are usually found in olivine and pyroxene of lherzolite, which can be identified into three typies:early sulfide grains, sulfide-melt inclusions and sulfides in fractures. Sulfide-melt inclusions occur as single-phase sulfide, sulfide-silicate melt, or CO₂-sulfide-silicate melt inclusions. Early sulfide grains are mainly composed of pyrrhotite, but cubanite was found occasionally. Sulfide-melt inclusions are mainly composed of pentlandite, with small amounts of chalcopyrite and talnakhite. Sulfides in fractures are pentlandite without exception, which have higher Ni/Fe and (Fe+Ni)/S (molar ratio) than those of sulfide inclusions. Ni/Fe and (Fe+Ni)/S are gradually increased from early grains, sulfide inclusions to sulfides in fractures. These changes were not only controlled by temperatures and pressures, but by geochemistry of Ni, Fe and Cu, and sulfur fugacity as well.