Relationship of the Crustal Structure, Rheology, and Tectonic Dynamics Beneath the Lhasa‐Gangdese Terrane (Southern Tibet) Based on a 3‐D Electrical Model

Abstract

The tectonic dynamics of the Lhasa-Gangdese terrane, southern Tibet, are still unclear and open questions persist regarding the structure, physical properties, and rheology of the lithosphere. A three-dimensional electrical resistivity model was generated beneath the Lhasa terrane, 79°−94°E and 28°–33°N, an area of ∼1,500 by ∼600 km, using data from 537 magnetotelluric measurements. To overcome computational challenges, we present an approach in which multiple high-resolution models from overlapping subregions are combined by means of an error-weighted averaging scheme to construct a continuous electrical resistivity model. Based on the electrical structure, the rheology of the mid-lower crust was investigated by constraining the melt fraction, in order to explore controls on dynamic mechanisms from a whole-system perspective. The models shed light on the vertical and lateral migration of crustal materials, magma transportation, and continental deformation in the Lhasa terrane. The model shows resistive features in the south that may represent the Indian plate, and conductive features above this that may represent the migration of materials beneath the Lhasa terrane, both of which vary substantially along the Indus-Yarlung Zangbo suture. In the mid-lower crust, conductive features (with a likely corresponding decrease of the effective viscosity) may be related to underplating, magma reservoirs, mineralization sources, and vertical motion of buoyant materials. A weakened mid-lower crust has consequences for surface deformation and may have contributed to the formation of (north-south) rift zones. Furthermore, the inhomogeneous distribution of weakened areas in the mid-lower crust has implications for the local lateral migration of materials.