Lithospheric electrical structure and geodynamic model of the red river fault zone and its adjacent areas in southwest China: Constraints from 3-D magnetotelluric imaging

Abstract

The Red River Fault (RRF) zone is situated on the southeastern boundary of the Tibetan Plateau. To further explore the geodynamic model of the region and the collision mechanism of the Eurasian continent, the electrical structure model of the lithosphere in the RRF was obtained through 3-D inversion of MT data. The preferred model indicated that fault zones were primarily distinguished by low resistivity anomalies, with some exhibiting high resistivity characteristics. It was hypothesized that the low resistivity anomalies may be attributed to the presence of saline fluids or metal sulfide within the fault zones, on the other hand, the high resistivity characteristics suggested inactivation due to fault cooling. Rapid changes in the electrical structure occurred on both sides of the fault zones, causing the upper and middle crust to be divided into distinct secondary tectonic units. Based on the effective viscosity calculation, we analyzed the crust-mantle rheology of the RRF area. We assumed that the RRF area was composed of three geodynamic models: the “crustal flow” model was distributed from the northern part of the Lancang River Fault (LCRF) zones to the southern part of the RRF zones. The “ductile continuum rheology” model was distributed from the north of the RRF to the western part of the Xiaojiang Fault (XJF) zones. The “mantle upwelling” model was distributed in the southeast part of the RRF.