Study On The Tectonic Framework Of Qinghai

Qinghai is geographically located in northeastern Qinghai-Tibet Plateau and tectonically in the mid-western part of the Pan-Cathysian Block Group and the north part of eastern Tethys. It is laid between the Laurisia land and the Gondwanaland during the Phanerozoic and recorded the evolutional process of Palaeo-Asia Ocean and Palaeo-Tethyan Ocean. As a junction among Tarim, Alashan, Yangzi and Qiangtang blocks Qinghai region played an important role during the geological evolution of Sino-continent and relavant continental blocks.Geological records in Qinghai and its adjacent regions indicated that the plate tectonics region in Qinghai started from the Cambrian and the tectonic framework, essentially formed in the Triassic. The Qinghai crust was gradually collaged during the Paleozoic and mainly underwent Caledonian and Hercynian-Indosinian tectonic events. It can be divided into eight units, consisting of plates, continental blocks and sutures in different scale. These tectonic units varied with time during the tectonic evolution. So it is important to distinguish the differences in tectonic framework among various tectonic stages, and to determine main tectonic stage during the evolution history of Qinghai.According to plate tectonic theory and the principle of "compare the past with the present", this thesis compiles a great deal of data of regional geological mapping and sample analysis, and focus on the tectonic framework of Qinghai region.The conclusions are reached as follows:1. The tectonic facies and petrotectonic assemblages analyses are the efficient methods and key basis for the research on principal tectonic framework and classification of tectonic units. The size of disappeared oceanic basin, which could be estimated from the type of petro-assemblage in compressive basins and the scale of intrusions, serves as a macroscopical indicator to recognize the scale and type of tectonic belts. Eleven indicators, such as the features of fault zone, the type of ophiolites and so on, have been used for distinguishing the nature of tectonic conjunction zones. The idea of determining the major tectonic epoch is the key point to set up regional tectonic framework.2. Based on analysis of sedimentary and deformational features, this work set up the first tectonic facies system of Qinghai region, which is divided into 25 tectonic facies and ranked into 7 types. Remnant oceanic basin facies was newly set up. It provided valuable basin analysis result for establishment of the plate tectonic pattern and prediction of mineralization.3. Based on systematic study of Bayan Har basin, the thesis has brought forward an opinionthat the basin was a typical remnant oceanic basin, which was developed on a "soft" basement during later Permian to Triassic and occurs as main part of northern Tethys oceanic relics, together with the Jingyu lake-eastern Kunlun Suture Zone, western Jinwulan- Jinshajiang Suture Zone and Longmenshang fault zone.4. The petrotectonic assemblages of igneous rocks in Qinghai have been systemically studied and a space-time framework of igneous rocks has been set up.The intrusions have been divided into 11 petrotectonic assemblages, 20 tectonic magma epoch and 6 types of assemblage based on a great deal of isotopic dating of the petro-assemblages combined with regional geology and tectonic environments. The characters of the petrotectonic assemblages indicate that the Eastern Kunlun orogenic belt was mainly as a result of the subduction and closure of the Animaqing-Bayan Har-Jinshajiang oceanic basin, forming the largest magma belt in Qinghai. The Variscian-Indian orogeny was the main orogenic cycle and tectonic epoch in the region studied.5. The principal framework of Qinghai tectonics consists of two sutures, one ocean and two massifs. The southern Kunlun suture zone is considered as the main tectonic suture, and the Jinsha River belt as secondary suture. The Bayan Har remnant ocean basin as the main part of the Palaeo-Tethyan ocean relics, which divide the Qinghai into two parts: Xiyu massif, western part of the Pan-Cathysian Continental Blocks, in the north, and the Tanggula-Qiangtang massif in the south.