Dawei Hong, Institute of Geology, Chinese Academy of Geological Sciences (China)
Tao Wang, Institute of Geology, Chinese Academy of Geological Sciences (China)
Ying Tong, Institute of Geology, Chinese Academy of Geological Sciences (China)
The Mesozoic granites are widespread in South China with total area of outcrop amounting to more than 135000 km2, which make up 80% of outcropping area of granites in South China. Among these granites, the Triassic granites occupy about 15%, the Jurassic ones about 46%, and the Cretaceous ones about 37%. Since the 1970s, the Mesozoic granites of South China were suggested to relate to subduction of a plaeo-Pacific plate beneath the Eurasian continent and the subduction zones must have retreated successively oceanwad in a southeasterly direction. However, such subduction models have encountered two puzzling problems: 1. the width of contemporaneous magmatic arcs (greater than 1000km) is far greater than normally observed in subduction zones (less than 500km); 2. Most of the granites and volcanic rocks from South China are felsic and approach minimum melt compositions, in contrast to the granodioritic to tonalitic compositions commonly observed in subduction zones.
The presently available geological data revealed that the collision between Indochina and South China blocks could be occurred in the late PermianĘCearly Triassic (258ĘC243 Ma), whereas the collision between Sibumasu and Indochina-South China, and between Indochina-South China and North China blocks could be started in the early Triassic and ended in the late Triassic (245 ĘC 220 Ma). However, the amalgamation between South China, Indochina and Sibumsu blocks had been completed in the middle Jurassic. If the extensive occurrence of the Jurassic granites of South China was resulted from westerly subduction of a paleo-Pacific plate, Indochina and Sibumasu blocks should also subject to the subduction, and occur the Jurassic granites. But the correlation of the Mesozoic granites between above mentioned three blocks indicates that there were only the Permian ĘC Triassic and Cretaceous granites and no the Jurassic granites in Indochina and Sibumasu blocks.
All these facts probably reveal that the subduction of a paleo- Pacific plate could be started until to the Cretaceous (about 135 Ma). The extensive Cretaceous metaluminous granites from Japan through South China to Indochina and Sibumasu, showing a nature of arc-magmtic rocks association in different degree, could be resulted from the subdction, whereas the Triassic-Jurassic strongly peraluminuous and weakly peraluminous granites in South China could not be related to the subduction, whereas derived from decompressional partial melting of Paleoproterozoic metamorphic pelite during the thinning and extension of the crust after the closure of the Paleo - Tethys ocean and successive collision and amalgamation between South China, North China, Indochina and Sibumasu blocks. They are typical intraplate magmatic products.