CHEMICAL COMPOSITION OF PROTEROZOIC COSMIC DUSTS IN SOUTHERN JILIN PROVINCE, CHINA
Wang Zhihua; Liang Yilin; Xu Guangrong; Lin Wenwei;Chen Keqiao; Liang Xirong; Wang Anping (Changchun College of Technology, Changchun 130021)(Institute of Mineral Deposits, Chinese Academy of Geological Sciences, Beijing 100037)(Changchun University of
Three hundred and ninety-two magnetic spherules were discovered in Proterozoic quartzite in southern Jilin Province, China. These spherules are demonstrated as cosmic dusts of fusion type, based on their characteristics of occurrence, shape feature,general physical property, microstructure and chemical composition. The spherules were divided into 4 subtypes, including 4 sorts in two subtypes of them, and the spherules in southern Jilin could be refered as a series of cosmic dusts. They are: (1) metal spherules, including pure iron spherules and FCN (Fe-Cr-Ni alloy, natural stainless steel) spherules; (2) oxide spherules, including Si-Fe oxide spheruls (common iron cosmic dusts) and Cr-Fe oxide spherules; (3) glassy spherules and (4) the oxide-metal spherules. Both the Si-Fe oxide spherules and pure iron spherules are very similar to common magnetic iron cosmic dusts. FCN spherules are a sort of natural stainless steel,which contain ca 18% Cr and average 5.85% Ni. The Cr-Fe oxide spherules contain 10.43% to 26.70% Cr2O3. The parent body of this sort of cosmic dust series may be a differential stone-iron meteorite of FCN type. The inner part (i.e. the core) of the parent, which consists of a Fe-Cr-Ni alloy originally, has turned into pure iron spherules and natural stainless steel spherules by fusion differentiation. The outer part of the parent, which is a crust of Fe-Cr silicate composed of fayalite, ferrosilite and chromite etc., has turned into the common iron cosmic dust, Cr-Fe oxide spherules and glassy spherules by fusion differentiation. The oxide-metal spherules are generated from the boundary zone between the core and the crust of parent body. In a word,the chemical compositions of the cosmic dust series are charcterized by higher ischromiun and less magnesium.