The distribution characteristics of the Beidashan fault structure on the southern margin of the Alxa Block

The expansion in the northeastern direction of the Qinghai-Tibet Plateau has had a significant impact on the topography and geomorphology of the Alxa Block. Among the numerous faults on the southern margin of the Alxa Block, the Beidashan Fault is the fault with the strongest tectonic activity. However, at present, there are few studies on the tectonic distribution characteristics of the Beidashan Fault and its coupling relationship with the surrounding basins. In this paper, by using the measured gravity and magnetotelluric sounding data and through the inversion of gravity and magnetotelluric sounding data, the structural distribution characteristics of the Beidashan Fault and its coupling relationship with the Yabulai Basin and the Chaoshui Basin are studied. The research finds that the Beidashan Fault on the southern margin of the Alxa Block is a normal fault in the shape of a “V”, located at the leading edge of the Beidashan. The Beidashan separates the Yablai Basin from the Chaoshui Basin and provides material sources for the two basins during the evolution process. The low-resistance anomaly area of Beidashan gradually decreases with the increase of depth and converges into a small area in the eastern section. Moreover, the vertical section shows that the low-resistance anomaly beneath Beidashan is divided into two layers at about 8 kilometers, forming an hourglass shape. It might be a volcanic channel that transported the deep, low-resistance material to the upper part. At the same time, both layers of materials have the phenomenon of expanding and moving northward, indicating that the compression of the Beidashan Mountain by the Qinghai-Tibet Plateau causes it to thrust northward, resulting in the Beidashan Fault having both thrust and strike-slip properties.