Deep electrical structure and tectonic implications of the Yinchuan basin and surrounding areas

The Yinchuan Basin is located in the northern segment of the north-south tectonic belt formed by the collision between the Alxa and Ordos blocks. This region experiences intense extensional activity and was the site of the 1739 Pingluo M8.0 earthquake. To investigate the deep structure of the study area and its relationship with seismic activity, this study employed magnetotelluric sounding data covering the Yinchuan Basin and its surrounding areas to perform a three-dimensional inversion, obtaining a high-resolution electrical structure model of the upper mantle scale. Analysis indicates: the western margin of the Ordos Block exhibits a “low-high-low” layered resistivity distribution, while its northwestern margin retains a stable, high-resistivity crustal structure. The Helan Mountains possess a thick, high-resistivity “mountain root”. Beneath the Yinchuan-Hetao Basin, there exist extensive, ribbon-like low-resistivity bodies extending into the upper mantle, distributed in NE and NWW trends at depth. The resistivity model reveals significant lithospheric modification and thinning in the study area. We propose that the influence of the northeastward expansion of the Tibetan Plateau has reached the Yinchuan–Hetao Basin. Superimposed on the far-field stress effects of the Paleo-Pacific Plate subduction, this has led to extensive modification and partial melting of the mantle and lower crust beneath the western margin of the Ordos Block. One portion of the modified material continues to migrate northeastward, while another portion undergoes dehydration and ascends along the weakened rift basins. The interaction between fluid-rich, low-resistivity bodies and rigid, high-resistivity rocks generates stress accumulation, leading to crustal rupture. This is one of the reasons for the frequent seismicity in the study area. • We utilized MT data covering the Yinchuan Basin and its surrounding areas. • The western margin of the Ordos Block shows lithospheric thinning and modification. • Tectonic stress accumulation and deep fluids jointly control earthquake generation.