Electrical structure of the eastern segment of the Qilian orogenic belt revealed by 3-D inversion of magnetotelluric data: New insights into the evolution of the northeastern margin of the Qinghai-Tibet Plateau

Crustal structure and geodynamics of the eastern Qilian orogenic belt, NE margin of the Qinghai-Tibet plateau, revealed by teleseismic receiver function

“…We believe that the continuous west-dipping negative seismic phase (104 °-104.5 °) below the Maxianshan fault zone in the CCP imaging results is the location of the ancient suture line between the Longzhong block and the Linxia block. This conclusion is consistent with the research results of magnetotelluric (MT) and deep seismic reflection profiles (Guo et al, 2016;Xin et al, 2021). There is a continuous negative seismic phase boundary with a length of ~250 km at a depth of 10 km between the Maxianshan fault and the Xiaoguanshan fault, which may be deep evidence of the local overall uplift of the Longzhong block and its extension to the Ordos block.…”

“…The Maxianshan fault is an important boundary fault that divides the Linxia block and the Longzhong block. The Linxia block has an obvious layered structure in the crust, a developed Conrad interface, and low-velocity anomalies in the middle and lower crust, which may contain saline fluid (Jin et al, 2012) and have the characteristics of a Japanese-type island arc (Guo et al, 2016;Xin et al, 2021). The layered structure of the upper crust in the Longzhong block is obvious, the layered structure of the middle and lower crust is weak and presents weak low-velocity characteristics, the Conrad interface is not developed, and it has the characteristics of ocean-island basaltic crust.…”

“…There is good correspondence between the Qinling and the lower part of Liupanshan structural belt. The results of magnetotelluric inversion show that there are structural differences in the electrical conductivity between the Linxia block and the Longzhong block (Xin et al, 2021), as shown by the blue line in Figure 6B. The Linxia block has high conductance, while the Longzhong block has low conductance.…”

“…The eastern section of the Qilian orogenic belt on the Qinghai-Tibet Plateau's northeastern margin is composed of the Linxia block and Longzhong block, with the Maxianshan fault as the dividing line between them (Guo et al, 2016;Xin et al, 2021). The eastern side of the study area crosses the Liupanshan tectonic belt and enters the southwest margin of the Ordos block, and its northern side is bounded by the Haiyuan fault and Xiangshan-Tianjingshan fault, which extends to the Alxa block.…”

“…The eastern part of the Longzhong block is connected to the southwest edge of the Ordos block by the Liupanshan fault zone. The electrical structures on both sides of the Maxianshan fault zone are significantly different, where a pillow-shaped basaltic rock belt is exposed (Pei et al, 2006;Song et al, 2006), forming the boundary between the Linxia block and the Longzhong block (Xin et al, 2021;Figures 1A, B). Since the Cenozoic loess strata in the Linxia block and the Longzhong block are heavily covered and the deep bedrock is rarely exposed, research on the suture line position and the structural boundary of the Linxia block and Longzhong block is scarce.…”