湘黔桂地区晚前寒武纪层状硅质岩地球化学特征及成因

湘黔桂地区晚前寒武纪发育厚度较大的层状硅质岩层 ,岩石化学成分纯净 ,硅质矿物含量 95%以上。岩石贫微量元素 ,但富Ba、As、Sb、Ag、U元素 ;稀土元素总量低 ,Ce呈明显的负异常 ,轻稀土含量大于重稀土含量 ;δ30 Si值变化范围为 0 .0‰～ 0 .7‰ ,δ18O值变化范围为 2 0 .1‰～ 2 3 .6‰。硅质岩地球化学特征表明其成因为介于热水沉积与生物沉积之间的过渡类型。

ORIGIN AND GEOCHEMICAl CHARACTERISTICS OF LATE PRECAMBRIAN BEDDED SILICALITES IN HUNAN, GUIZHOU AND GUANGXI

Late Precambrian bedded silicalites are widely distributed in western Hunan, eastern Guizhou and northern Guangxi. Their thickness is from 20 to 150m. The silicalites are very simple in composition and the contents of siliceous minerals exceed 95%. These silicalites have the following characteristics: lower contents of total trace elements, higher contents of Ba, As, Sb, Ag and U; lower total REE, the contents of LREE are higher than those of HREE, comparative enrichment of HREE, remarkably negative Ce anomaly, slightly negative Eu anomaly; δ{}+{30}Si values range from 0.0‰ to 0.7‰, δ{}+{18}O values range from 20.1‰ to 23.6‰. The geochemical characteristics of silicalites show that the rocks are of the transition type between hydrothermal sediments and biogenic sediments.;