CLASSIFICATION AND SOURCE MATERIALS OF CONTINENTAL CRUST TRASFORMATION SERIES GRANTOIDS IN SOUTH CHINA
Liu Changshi, Zhu Jinchu, Shen Weizhou and Xu Shijing (Department of Earth Sciences, Nanjing University)
According to the tectonic settings, tbe continental crust transformation series grantoids of South China may be divided into three types. (1) Synorogenic migmatitic and magmatic granitoid type, (2) anorogenic continental crust anatexis type, and (3) syncollision type. The first type of granitoid is usually closely related to orogenic movements in different periods (from the Xuefengian to Yanshanian periods). The rocks are usually strongly peraluminous, with ANKC values ranging from 1.209 to 1.223, and rich in potasium relative to sodium, with Na/K values ranging from 0.88 to 0.90. The second type is usually related in time and space to intracontinental deep fault zones. Differing from the first type, the granitoids are weekly peraluminous, with an average ANKC value of 1.106, and relatively rich in sodium, with an average Na/K ratio of 1.05. The third type granitoids are similar in chemical composition to those of the first type or S-type.Taking the Daroshan granite as the endmember of the upper crust of South China (I_(Sr) (0)=0.7283; I_(Nd) (0)=0.511827; Sr=140 ppm; Nd=28ppm) and the depleted mantle as the other endmember (I_(Sr)(0)=0.70264; I_(Nd) (0)=0.513151; Sr=470 ppm; Nd=14 ppm), based on the analytic results of Sr and Nd isotopic compositions and results of calculation of binary mixing simulation, the source matcrials for the first type granitoids consist of 78.6—89.7% upper crust (UC) materials and 21.4—10.3% depleted mantle (DM) materials; the source materials for the second type grantoids, 63.7% UC and 36.3% DM materials: those for the third type granitoid, 100% UC materials. This suggests that the continental crust transformation series granitoids in South China were essentially derived from the upper crust materials.