Sulfide-melt inclusions in mantle xenoliths from the Changbaishan district, Jilin province, China

摘要

Mantle xenoliths are common in the Cenozoic basalts of the Changbaishan District, Jilin Province, China. Sulfide assemblages in mantle minerals can be divided into three types: isolated sulfide grains, sulfide-melt inclusions and filling sulfides in fractures. Sulfide-melt inclusions occur as single-phase sulfides, sulfide-silicate melt, and CO_2-sulfide-silicate melt inclusions. Isolated sulfide grains are mainly composed of pyrrhotite, but cubanite was found occasionally. Sulfide-melt inclusions are mainly composed of pentlandite and MSS, with small amounts of chalcopyrite and talnakhite. The calculated distribution coefficient K_(D3) for lherzolite are similar to that of mean experimental value. The bulk sulfides in lherzolite were in equilibrium with the enclosing minerals, indicating immiscible sulfide melts captured in partial melting of upper mantle. Sulfide in fractures has higher Ni/Fe and ( Fe + Ni)/S than those of sulfide melt inclusions. They might represent later metasomatizing fluids in the mantle. Ni/Fe and ( Fe + Ni)/S increase from isolated grains, sulfide inclusions to sulfides in fractures. These changes were not only affected by temperature and pressure, but by geochemistry of Ni, Fe and Cu, and sulfur fugacity as well.