Geological characteristics and tectonic evolution of Alxa terranein the northern Qilian Mountain
Wu Xiaozhi1, Zhao Yumei2, Wang Guijun3, Zheng min1
1. Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083;
2. Research Institute of Exploration & Development of Xinjiang Oil Field Company, Karamay, Xinjiang 834000;
3. Research Institute of Experiment and Detection, Xinjiang Oil Field Company, Karamay, Xinjiang 834000
Alxa terrane is located among Tarim block, North China block and Qilian-Qinling orogen. Alxa terrane was independently developed during the Archean-Proterozoic. Its crystalline basement displays certain differences with those of the Tarim plate and the North China plate in the lithology. Influenced by the Caledonian event, the Alxa terrane and its adjacent plates are characterized by convergent in the south and divergent in the north. In the Early Middle Ordovician, the Alxa terrane collided with the North China plate, and they share a common evolutionary stage as a unified plate. During the Middle Hercynian period, the Early Permian paleo-Asian ocean to its north was closed and juvenile crust was developed, forming a trench-arc-basin system. In the Late Hercynian period, the Alxa terrane subdued toward the south, the Qilian ocean was closed, generating abundant juvenile crust, and Alxa terrane was amalgamated with the Tarim and North China plates. Neo-Tethys tectonics played a significant influence on Alxa terrane, as suggested by the left-lateral strike-slip at its southern margin and the right-lateral strike-slip at its northern margin. In addition, the Paleozoic structures were modified by the Cenozoic NE-trending structural deformations. The frequent tectonic activities in Alxa terrane led the relatively stable Yanshanian coal-bearing medium-small basins(including Alxa-Yin'e Basin group, Beishan Basin group, Hexi Corridor Basin group, East Qilian Basin group, West Qilian Basin group, Altun Basin group, Chaidamu Basin group)to begin to subside or uplift rapidly. Afterward, these basin groups experienced strong modifications, which resulted in either lack of source rock or tight reservoir. As a whole, these factors are not to the advantage of the generation, migration and accumulation of hydrocarbons, showing poor prospects for petroleum exploration.