Crustal Thinning Characteristics Beneath the Weihe Graben

The Weihe Graben lies on the northern margin of the Qinling Orogenic Belt, the collisional suture between the North China Craton and South China Block, and records Cenozoic extensional overprinting of its earlier tectonic evolution. We integrate deep seismic reflection profiles and tomographic datasets to characterize heterogeneous lithospheric modification and elucidate the geodynamics of post-orogenic crustal thinning and graben formation. A single Moho occurs beneath the Dabashan and southern Ordos Block, where crustal thickness exceeds 43 km, whereas a distinctive double-Moho structure occurs beneath the Weihe Graben. Its upper and lower interfaces reach depths of 36 and 51 km, respectively, defining a ~15 km–thick lenticular transitional layer. Low–velocity and low–resistivity anomalies in the upper mantle indicate Cenozoic asthenospheric upwelling beneath the region. Our results suggest that mantle upwelling promoted regional crustal thinning, while the Moho doublet mainly reflects eclogite relics and subsequent modification. Since the Eocene, the stress regime changed from compression to extension, associated with far–field Pacific Plate subduction and continuous counter-clockwise rotation of the Ordos Block. Block rotation promoted lithospheric tearing along its southeastern margin and destabilization of the crust–mantle boundary, facilitating mantle upwelling. Pre–existing Late Triassic–Middle Jurassic thrust faults were selectively reactivated, with northern boundary faults transformed into listric normal faults, ultimately forming the extensional Weihe Graben and accompanying differential uplift of the northern Qinling Block and graben margins.