The Crustal Structure of the Northern Margin of Qinghai-Tibet Plateau and Its Genetic Analysis

Qaidam basin-Qilian mountain is situated on the north margin of Qinghai-Tibet plateau. Like the main part of the plateau, there commonly exist a muti layer crustal structure and the low velocity layers. The crust thickness of the region is twice more than that of northern and southern China. It may be caused by the transverse compressive shortening and the upper mantle underplating .With the crust underplating getting strong, the thickness of the crust increase , and the lithospheric thickness tend to decrease. A tension condition in the upper crust and the deep melting or the mantle derived fluid replacement in the lower crust exist, which bring on the low velocity layers,terrestrial heat and shallow earthquake in the crust . It is also the reason showing hot crust and cold mantle in Qinghai-Tibet plateau region.