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 basins. These basins are situated adjacent to the Tibetan Plateau and have undergone contrasting evolutionary histories. Here we review results from three newly-obtained wide-angle seismic reflection/refraction profiles across these basins. 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 seismic velocity boundaries between the felsic upper, intermediate middle, and mafic lower crust display clear divisions. Conversely, the Qaidam Basin, which lies at an elevation of ~3,000 m above sea level, has a thicker crust that is more similar to the soft deforming crust of the Tibetan Plateau. This crust is more felsic and lacks a high velocity mafic lower crust. The crustal structure of the Junggar basin is similar to typical intracratonic basins of Eastern Europe. Average crustal thicknesses are 55 km for the Tarim, 60 km for the Qaidam, and 50 km for the Junggar and the average seismic 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 the highest average crustal velocity.