Crustal structure of the middle segment of the Qilian fold belt and the coupling mechanism of its associated basin and range system

Abstract

We present an analysis of the P-wave seismic velocity structure of the Qilian fold belt based on a 750-km-long seismic wide-angle reflection/refraction profile. The results show that the internal portion of the Alxa block has a crustal thickness of approximately 45–48km, with an average velocity of 6.19km/s. Although the Alxa crust is thick, it is lateral homogeneous and relatively stable. The Hexi Corridor, which is located on the southern margin of the Alxa block, has been affected by the collision and extrusion of the northern margin of the Tibetan Plateau. The Hexi Corridor has a crustal thickness of 48–59km with substantial thickening southward and an average seismic velocity of 6.10–6.13km/s, indicating strong crustal deformation. Located on the northeastern margin of the Tibetan Plateau, the Qinling fold belt (QFB), Gonghe basin and Elashan mountains all have a crustal thickness is 51–56km with a low average seismic velocity of 5.86–6.10km/s, indicating significant reconstruction via shortening that has resulted in thickening of the northeastern Tibetan plateau crust. The tectonic coupling between the Qilian fold belt and the neighboring blocks in the south and north form a crustal-scale depression. Combining the regional geology, gravity and GPS measurements, and strong earthquake focal mechanism solutions, we constrain the crustal deformation processes of the northeastern of Tibet Plateau.