On the Continental Tectonics and Dynamics of China
Institute of Geology, Chinese Academy of Geological Sciences; Key laboratory of Continental Dynamics, Ministry of Minerals and Resources, Beijing, 100037
Abstract:The Chinese continent, which is strongly constrained by the Tethyan, Paleo Asian and Pacific tectonic systems, is characterized by a complex tectonic framework and a particular lithospheric structure. Based on the theory of continental tectonics and dynamics, here we provide a comprehensive overview of recent research results with a particular attention to four important scientific problems on the Chinese (East Asian) continent. ①Tectonics of the mantle beneath the Chinese continental lithospheric plate. Seismic tomographic profiling reveals that the western Pacific slab is subducted westward to depths of 400~600km beneath the East Asian continent, and the subducted slab becomes subhorizontal and listric shaped in the mantle transitional zone. The Indian slab is subducted northward to a depth of ~800km far north under the Banggonghu Nujiang sutute zong between the the Lhasa and Qiangtang terrains. Double subductions are asymmetrical beneath the western syntaxis of the Himalayan belt. In the eastern syntaxis, however, the Indian slab is subducted eastward to depths of 300~500km beneath the Burma Sanjiang terrain. ②Reactivation of the Chinese continent's metamorphic basements. Most blocks of the Chinese continent have not been reactived by significant tectonic, metamorphic or igneous events since the Phanerozoic. The north Indian and Arabian blocks (northern edge of Gondwana) were shaped by pan African orogenic belts at 530 470 Ma. This tectonic field occurred mainly in the higher Himalaya, Lhasa terrain and Sanjiang terrain. The Cenozoic metamorphic reactivation appeared ubiquitously and uniquely in the Himalaya, Namche Barwa, Lhasa terrain and Burma Sanjiang terrain with the youngest metamorphic ages of 2~1 Ma. ③The tectonic backgrounds and processes for the formation and exhumation of HP UHP metamorphic belts in China. The eclogite bearing HP UHP metamorphic belts in China formed in either oceanic or continental deep subduction zones. Most of the oceanic HP UHP belts in the Tibetan plateau are related to the collisions of multiple small oceanic basins among multiple micro continental blocks. Two mechanisms of the continental deep subduction are plausible: subduction drived by interblock shear collision and subduction of wedge shaped, teared lithospheric slabs. ④Three categories of mechanisms for the extrusion of deep materials within the Chinese continental orogenic belts: constrictional extrusion; lateral extrusion; and transcompressional extrusion.