吉林陨石中橄榄石和辉石的化学成份特征兼谈平衡球粒陨石中的不平衡性

吉林陨石中的球粒分为正常快速冷却和过冷冷却球粒两种。前一类球粒中的橄榄石和辉石的化学成份相对稳定,代表了平衡球粒陨石的特征。后一类球粒中的橄榄石和辉石不仅在总的化学成份上有别于前者,而且矿物本身成份不稳定,反映了平衡球粒陨石中存在着不平衡性。

CHEMICAL COMPOSITIONAL CHARACTERISTICS OF OLIVENE AND PYROXENE IN JILIN METEORITE A DISCUSSION OF UNEQUILIBRIUM IN THE EQUILIBRATED CHONDRITES

Chondrules in the Jilin meteorite may be divided into two groups: normal rapid cooling(granular and porphyritic) chondrules and supercooling(grating and excentro-radial)chondrules. Chondrules of the first group are dominant in the Jilin meteorite. The chemical compositions of olivine and pyroxene in these chondrules are relatively stable and typical of equilibrated chondrites. Olivine and pyroxene in the second group contain more minor elements such as Na, Ca, Al, Cr, etc. The variation in chemical composition of these chondrules indicates a phenomenon of unequilibrium in the equilibrated chondrites.Granular and porphyritic textures observed in the first group are common in the earth's rocks, but grating and excentro-radial textures with the second group have never been observed in the earth's rocks, indicating different conditions for grating and excentro-radial-textured chondrules and earth's rocks of the same textured.The formation of various textures in different types of ehondrules depends on their cooling rates. But in chondrules of the same type the quantity of phenocrysts and the type of minerals depend on the chemical composition of the primary chondrules.Textural and comoositional studies of minerals in the chondrules have confirmed that chondrules must have been formed from molten drops of silicates rather than products of shocking.