DEEP STRUCTURE AND TECTONIC EVOLUTION OF THE BASINS OF NORTHWESTERN CHINA

Northwest China contains a system of large sedimentary basins that include the Tarim, Qaidam, and Junggar. These basins are situated adjacent to the Tibetan Plateau and exhibit basements with contrasting evolutions. Here we present a review of three seismic wide angle reflection/refraction profiles and their tectonic implications. The profiles include (1) a 1,400 km transect extending from the northern margin of the Tarim Basin to the eastern margin of the Qaidam Basin crossing the Altyn Tagh Range, (2) a 300 km transect extending from the northern to the southern margins of the Qaidam Basin, and (3) a 600 km transect extending from the northwestern to the southwestern margins of the Junggar Basin. The crustal structure of the Tarim Basin is interpreted as a typical stable continental platform. The boundaries between the felsic upper, intermediate middle, and mafic lower crust display clear divisions. Conversely, the Qaidam Basin, which rests at an elevation of ~3,000 m above sea level, is more similar to the soft deforming crust of the Tibetan Plateau. The crust is more felsic and lacks a high velocity mafic lower crust. Crustal structure of the Junggar basement includes a mix of oceanic materials and older blocks. Average crustal thicknesses are 55 km for the Tarim, 60 km for the Qaidam, and 50 km for the Junggar and the velocities are 6.0 km/s, 5.8 km/s, and 6.3 km/s (respectively). Of the three basins described, the Junggar is the thinnest and has a higher velocity.