THE ORIGIN OF SULFIDE-MELT INCLUSIONS IN MANTLE MINERALS

The fact that the sulfide-melt inclusions existing in megacryst, pyroxenite, andperidotite xenoliths hosted in the Cenozoic alkali-basalts in the eastern China are mineralogically not the same reflects their difference in the origin. In megacrysts, except for some sulfide-melt inclusions with only pyrrhotite phase, there are some sulfide inclusions with existing pyrrhotite±chalcopyrite±pentlandite minerals. This suggests that the sulfide inclusions preduced during gradually cooling of some sulfide-liquid drops with the mantle average of sulfides, including that monosulfide solid solution (i. e., MSS) firstly produced at high temperature above 1000℃, then chalcopyrite(solid solution) formed at about 850℃and, finally, pentlandite exsolved from MSS between 610-300℃. The sulfide inclusions are composed of pyrrhotite and pentlandite in the pyroxetites, but are basically composed of pentlandite in peridotites. It indicates that the partial melting of the mantle resulted in Ni enrichment in sulfide-melt inclusions for the residual peridotites, so that pentlandite prepuced in the inclusions, and resulted in poor Ni in the recrystallized pyroxenites, so that pyrrhotite formed. Also, another important factor is probably the different partition coefficient of Nibetween olivine and pyroxene. Occurrence of the pentlandite inclusions hosted in peridotites in Hannuoba, Hebei province and Mica and Minqing, Fujian province indicates that those peridotites underwent partial melting of the mantle.