The deep electrical structure of Motuo fault zone in Beibeng area

To elucidate the contact relationship between Indian and Eurasian plates along the Yarlung-Zangbo suture zone (IYS) and associated geodynamic processes, we acquired a high-resolution magnetotelluric (MT) profile extending 20 km across the Motuo fault zone near Beibeng Township, Motuo County, eastern Xizang. This NW-SE oriented transect employed 30 MT stations with approximately 300-m spacing, covering frequency bands of 10000–0.0001 Hz to resolve crustal structure down to 30 km depth. Key findings from the electrical resistivity model reveal: (1) At shallow crustal levels (<5 km depth), the Motuo fault system exhibits a negative flower structure characterized by downward-converging conductive shear zones, diagnostic of dominant strike-slip deformation. (2) Preservation of Indian slab subduction traces beneath the Lhasa Block along the IYS, with possible development of a pop-up structure in the Indian upper crust near the eastern Himalayan syntaxis. (3) The resistive Lhasa Terrane upper crust is ~20 km thick –33% thinner than the 30-km average in southern Xizang. This disparity implies either: (i) incomplete syn-collisional crustal shortening due to strain partitioning into strike-slip faults, or (ii) absence of crustal growth episodes that thickened the Lhasa Terrane. (4) A mid-crustal conductor at 15–30 km depth aligns with the suture zone. Its upward-flaring geometry indicates southward migration of melts from the Lhasa lower crust, which is facilitated by transpressional uplift along the IYS.These results demonstrate that the Motuo fault system operates as a crustal-scale transfer zone, where strike-slip kinematics preserve early collisional features while enabling melt migration through reactivated suture structures. The integrated model provides new constraints on strain accommodation mechanisms during continental indentation.