THE DISCOVERY OF ARCHAEOZOIC ZIRCONS FROM MANTLE-DERIVED GRANITOIDS IN EAST TIANSHAN CALEDONIAN OROGENIC BELT AND ITS GEOLOGICAL SIGNIFICANCE

From south to north, the eastern part of Tianshan Mountains situated between the Tarim and Junggar basins can be divided into the Middle Proterozoic orogenic zone, the Caledonian orogenic zone and the Hercynian orogenic zone successively. Detailed studies show that the Caledonian orogenic zone is an accretionary one at continental margin which evolved from the Andean-type to the Pacific-type active continental margin in the northern fringe of the Tarim plate during the Caledonian cycle and was finally formed following the