兰坪中新生代盆地沉积岩源区构造背景和物源属性研究——砂岩地球化学证据

Tectonic Setting and Provenance of Source Rock for Sedimentary Rocks in Lanping Mesozoic-Cenozoic Basin:evidences from geochemistry of sandstones

沉积盆地中砂岩的地球化学成分主要受物源区控制。因此 ,通过分析砂岩的化学成分可以揭示盆地沉积岩的源区构造背景和物源属性。对兰坪盆地中新生界砂岩的常量成分、稀土和微量元素进行的分析 ,揭示盆地沉积岩的源区构造背景属被动大陆边缘和大陆岛弧 ,结合岩相古地理资料认为在中生代以前 ,盆地东侧可能主要处于被动大陆边缘环境 ,而西侧则可能以大陆岛弧环境为主 ,这与区域地质资料相吻合。沉积物源岩的原始物质应来自上地壳 ,以长英质岩石为主 ,并有少量安山质岩石和古老沉积物的混入 ,故兰坪中新生代盆地属典型的大陆型盆地。从而为正确认识古特提斯洋的演化和盆山转换过程提供了强有力的地球化学证据。

The geochemical compositions of sandstones in sedimentary basin are controlled by the tectonic setting of source rock, and it is, therefore, possible to discriminate the tectonic setting of source rock area and provenance of source rock by studying the geochemical compositions of sandstones. The major compositions, rare earth elements and trace elements of Mesozoic Cenozoic sandstones in Lanping Basin are studied in this paper, and which reveals that the tectonic settings of source rock area for Mesozoic Cenozoic sedimentary rocks in in Lanping Basin, belong to passive continental margin and continental island arc. Combined with the data of sedimentary facies and palaeogeography, it is referred that the east area of basin is mainly located at tectonic setting of passive continental margin before Mesozoic , whereas the west area of basin may be at continental island arc. This is compatible with the results of regional geological studied data. The primary materials of sedimentary rocks should come from the upper continental crust, and are mainly composed of felsic rocks, mixed with few andesitic rocks and old sediment components. Therefore , Lanping Mesozoic Cenozoic Basin is the typical continental type basin. This provides strong geochemical evidences for correctly understanding the evolution of the old Tethys and the basin range transition.