地幔矿物中硫化物熔体包裹体的成因

中国东部新生代碱性玄武岩中产出的巨晶、辉石岩和橄榄岩等地幔捕虏体内硫化物熔体包裹体的矿物组成不尽相同，反映了它们成因上的差异巨晶中除有磁黄铁矿相的硫化物熔体包裹体外还有一些磁黄铁矿士黄铜矿上镍黄铁矿共生的硫化物熔体包裹体这反映它们是在成分接近于上地幔硫化物平均组成的硫化物液滴逐步冷却过程中形成，即首先在1000℃以上的高温晶出单硫化物固溶体（MSS），然后在大约850℃晶出黄铜矿（固溶体），最后在610-300℃下由MSS中溶离出镍黄铁矿辉石岩中硫化物熔体包裹体有磁黄铁矿和镍黄铁矿，而橄榄岩中主要为镍黄铁矿这表明地慢部分熔融造成残余的橄榄岩中硫化物包裹体富Ni，生成镍黄铁矿；而在部分熔融期间作为堆晶产出的辉石岩变得相对贫Ni，可以生成磁黄铁矿．另外，Ni在橄榄石和辉石矿物中分配系数的不同也许是另一个原因河北汉诺坝、福建明溪和闽清的二辉橄榄岩中出现的硫化物都是镍黄铁矿，也表明它们经历过地幔部分熔融.

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.