Moho depth of the Qilian orogen revealed by wide-angle reflection/refraction profiles

Abstract

The Qilian Orogenic Belt is located on the northeastern edge of the Qinghai-Tibet Plateau, 1500 km far from the front of the Himalayan collision zone to the south, manifesting as an orogenic belt with a NW orientation between the Alxa Block to the north and the Qaidam Block to the south (approximately 1000 km long from east to west and 200～400 km wide from north to south). It is truncated by the NE-trending Altyn left-lateral strike-slip fault to the west and surrounded by the northeastern Tibetan Plateau, Qilian Mountain, and Hexi Corridor to the north. To the southeast, it is connected to the west Qinling orogenic belt, and the eastern margin is adjacent to the Ordos Block. It has played an important role in the collisional process between the Indian and Asian continental plates, and the mountain-building of the Qinghai-Tibet Plateau since the Cenozoic. Exploration of the deep structure of the crust is key to study the uplift and northward expansion processes of the Qinghai-Tibet Plateau and understand the intracontinental deformation caused by the collision between India and Eurasia plates. In this study we integreted the wide-angle reflection/refraction profiles conducted in this area since the 1980s and summarizes the outcome of the Moho depth. The results show that the Moho becomes shallower from west to east as a whole, and the deepest Moho in the west section, which may be induced by the continental two-way subduction and underplating. In the central section, the low-velocity anomalies with high conductivity are well developed, which may present the decollement in the crust, and the crustal deformation was mainly accommodated by the overthrusting in the upper crust. whereas the crustal deformation is released by the large-sccale-lateral strike-slip faults.

Keywords

• qilian orogen
• northeastern margin of qinghai-tibet plateau
• moho depth
• wide-angle reflection/refraction profile