肇东和亳县陨石中的黑包体及其成因意义

肇东、毫县陨石中的黑包体在总体成分、形状、大小上与陨石球粒相似,但两者的内部结构以及矿物组合不同。黑包体中矿物呈密堆状,主要由细粒橄榄石以及其它硅酸盐微晶组成,不含火成玻璃等特点表明黑包体未经历过熔融,它们可能是形成球粒的毛坯。因此认为球粒的形成有三个阶段:星云凝聚形成尘粒—尘粒吸积形成黑包体—黑包体熔融形成球粒。

THE DARK INCLUSIONS IN ZHAODONG CHONDRITE AND BOXIAN CHONDRITE AND THEIR GENETIC SIGNIFICANCE

There are some dark inclusions in Zhaodong chondrite(L_4) and Boxian chondrite(LL_(3-4)). These dark inclusions are similar to chondrules in shape and size, but they differ from chondrules in mineral components and texture. Dark inclusions are composed of fine-grained olivines and other silicate mineral microcrystallines, but no glass. The silicate mineral microcrystallincs are of analogic lowcalcium pyroxene or plagioclase composition. Each dark inclusion possesses an accumulation and is of ten surrounded by a black ring composed of metal Fe-Ni, troilite and silicate mineral microcrystallines. Therefore, it is inferred that dark inclusions arc acccumulations of nebula condensates and are semifinished chondrules, but they did not melt. A model of chondrule-form is established: nebula condensated to form dust, dust accreted to form dark inclusions, dark inclusions were melted to form chondrules.