西藏阿里西部地区的放射虫硅质岩

<正>一、产出概况阿里西部地区的放射虫硅质岩相当发育,在北喜马拉雅区、冈底斯区和喀喇崑仑区均有出露.岩石多为棕红色、紫红色和灰绿色,少数为灰色.呈层状,似层状或透镜状,产于三叠纪、侏罗纪和白垩纪的地层中,其产出情况各地有所不同,分述如下;

THE RADIOLARIAN SILICALITES IN THE WESTERN AREA OF NGARI,TIBET

The radiolarian silicalites in the westrn area of Ngari, Tibet are well developed in the Mesozoic strata with various occurences. Some of them in-tercalately occur in the basic and intermediate-acidic volcanic rocks or in the carbonate rocks. Some of them directly overlie the bodies of the ultramafic rocks.Based on the difference in composition, the radiolarian silicalites in this area can be divided into five types. , (pure) Radiolarian silicalites. 2,Fer-riginous radiolarian silicalites. 3, Argillaceous radiolarian silicalites. 4, Tuffaceous radiolarian silicalites and 5, Calcic(Carbonatized) radiolarian silicalites. The origin of the radiolarian silicalites in the western area of Ngari has been discussed. The authors suggest that the silica in the radiolarian silicalites was presumabaly provided mainly by the volcanism, whereas the activities of radiolaria may promoted the precipitation of the silica. Not all the radiolarian silicalites in the western area of Ngari formed in deep sea environments, some of them may be the representatives of the shallow sea environments.Based on the difference in composition, the radiolarian silicalites in this area can be divided into five types. , (pure) Radiolarian silicalites. 2,Fer-riginous radiolarian silicalites. 3, Argillaceous radiolarian silicalites. 4, Tuffaceous radiolarian silicalites and 5, Calcic(Carbonatized) radiolarian silicalites. The origin of the radiolarian silicalites in the western area of Ngari has been discussed. The authors suggest that the silica in the radiolarian silicalites was presumabaly provided mainly by the volcanism, whereas the activities of radiolaria may promoted the precipitation of the silica. Not all the radiolarian silicalites in the western area of Ngari formed in deep sea environments, some of them may be the representatives of the shallow sea environments.