Abstract:

The northwestern China is a component of several global tectonic units in different geological periods, with the structural characteristics of NS zoning and EW districting. This area underwent crustal growth, oceancontinent transition, and oceanic basin open and close cycles in the Middle Neoproterozoic to the Paleozoic. The evolution process has obvious periodic characteristics, with superimposing and rebuilding since the Late Permian and with the far source effect of India and Eurasia plate collision in the Cenozoic. Most basins are based on the variable sized PreSinian crystalline basements; the basements of Tazhong, Tabei, and Tadong areas may be of the Proterozoic, whereas basement of Bachu region was Jinning period metamorphic rocks; The Junggar Basin based upon different sized independently developed preSinian basements displayed the tectonic pattern of archipelagic ocean during the Paleozoic. Many smallmedium size basins in the Hexi Corridor, the Qaidam Basin and adjacent areas were developed on small blocks or Paleozoic active continental margin arcs with crystallized Proterozoic basements, and different metamorphic events took place and formed bolded basement under the Dunhuang Basin. The northwestern China underwent a full plate open close cycle in the early Paleozoic, accompanied with diversified presentation in different regions. The ophiolites occurred more than three times in the northern Xinjiang region in the CambrianEarly Ordovician, the Silurian and the Devonian, respectively, which were identified as certain scale oceanic basins in the Paleozoic with different closing periods in disparate area. The South Tianshan ocean around Tarim Basin and oceanic basins developed around West Kunlun, Arkin, Qilian, East Kunlun, and Beishan underwent oceanic basin expansion from the Middle and Late Cambrian to the Early Ordovician, with the tectonic setting transition from the compressional system to the tensional system in the late period of the Early Ordovician. In the Late Silurian to the Early Devonian, the convergence and collision of plate and varying degrees of deformation and metamorphism occurred in northwestern China. Also, a complete plate breakup and close cycle was developed in the Late Paleozoic. The east and west sides of the Tianshan region and south Junggar underwent large scale postcollison extensional tectonic setting and formed the limited ocean basins at different periods with structural transformation between the early and the Late Carboniferous. The Early Carboniferous extension of southwest Tarim initiated the Late Paleozoic west Kunlun ocean and continental margin rift basin. The late Hercynian movement in the middle and Late Permian was a significant transformative movement in northwestern China. From the Late Permian to the Cenozoic, the multistage tectonic adjustment was developed and the tectonic framework was finalized in the northwestern China. On the background of intracontinental multiplate convergence, the western basins have undergone tectonic evolution of episodic multistage compression and extension; they are not simply the combination of the foreland basins as given by early researches. Compressional stress initiated by the remote effects of the rapid uplift of Qinghai Tibet Plateau made profound reform in the northwestern region. In the northwestern basins, the different development and combination models resulted from the different evolution phases and tectonic patterns. The petroleum geological conditions and the abundance of oil and gas are significantly different.

Key words: northwestern China, regional tectonic framework, tectonic evolution, basin basement, plate openclose cycle, superimposed basin