长白山地区幔源捕虏体的硫化物相及其演化

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

长白山地区新生代玄武岩的一些层位广布地幔岩捕虏体，在其橄榄石、辉石等矿物内 发现有较多的硫化物相，按产出特征可鉴别出３种类型，即早期硫化物颗粒、硫化物包裹体和 裂隙中硫化物。硫化物包裹体可以单相硫化物、硫化物－硅酸盐熔体、ＣＯ２－硫化物－硅酸盐熔 体形式存在。早期硫化物颗粒以磁黄铁矿为主，并发现有方黄铜矿；硫化物包裹体以镍黄铁矿 为主，并有黄铜矿、硫铜铁矿出现；裂隙中硫化物均为镍黄铁矿，并具有比硫化物包裹体高的 Ｎｉ／Ｆｅ和（Ｆｅ＋Ｎｉ）／Ｓ值。地幔岩中存在自早期硫化物颗粒、硫化物包裹体至裂隙硫化物，Ｎｉ／Ｆｅ和 （Ｆｅ＋Ｎｉ）／Ｓ比值逐渐增加的规律。这种演化不仅受温度和压力制约，而且受Ｎｉ，Ｆｅ，Ｃｕ的地球化学 特性和硫逸度的控制。

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 C02-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 pentlan-dite 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.