Long‐period magnetotelluric (MT) data from project SINOPROBE were acquired and modeled, using three‐dimensional (3D) MT inversion, to study the electrical structure of Ordos Block, a component of the North China Craton. For the first time, a high‐resolution 3D resistivity model of the lithosphere is defined for the region. Contrary to what would be expected for a stable cratonic block, a prominent lithospheric conductive complex is revealed extending from the upper mantle to the mid‐to‐lower crust beneath the northern part of Ordos. Correlating well with results of seismic studies, the evidence from our independent magnetotelluric data supports regional modification of the lithosphere under the north Ordos and lithosphere thinning beneath Hetao Graben. The abnormally conductive structure may result from upwelling of mantle material in mid‐to‐late Mesozoic beneath the northern margin of the Ordos block.

The ongoing India‐Asia collision since the Paleogene created the Tibetan Plateau, the most prominent elevated plateau on our planet. This convergence also contributed to the formation of two distinct types of active surface deformation of the plateau, namely, north–south trending normal fault systems and “conjugate” strike‐slip fault systems. The tectonics and geodynamic mechanism(s) behind this curious combination are still unclear, despite numerous theories proposed over past decades. Here we present a new three‐dimensional, lithospheric‐scale, electrical conductivity model with unprecedented resolution of the central part of Tibetan Plateau derived from the SINOPROBE magnetotelluric array data set and discuss its inferences related to this question. Our model reveals contrasting conductivity structures corresponding to the surface deformation patterns, namely, highly conductive lower crustal anomalies beneath the graben systems in the Lhasa and Qiangtang terranes and moderately resistive crustal features in the strike‐slip region near Bangong‐Nujiang Suture Zone. With the help of experimentally calibrated constraints between conductivity and melt fraction, the conductivity model and the inferred lateral viscosity distribution together suggest a weak lower crust beneath the graben regions, compared to a stronger crustal rheology associated with the strike‐slip zone. Here we expand the previously proposed “extensional extrusion” tectonic model in central Tibet to interpret our conductivity model and other geophysical/geodesic observations. The weak rheology under a N‐S directed primary stress may have caused the east–west extension of the graben regions, which further aides the eastward extrusion of the conjugate strike‐slip zone and eventually shapes the surface deformation of central Tibetan Plateau into its current, complex pattern.

A weak middle crust induced by fluid phases is generally considered to exist beneath the Himalayan‐Tibetan orogen; however, there remains controversy regarding the interpretation of high‐conductivity and low‐velocity regions imaged in various geophysical studies. To better understand middle crustal rheological behaviors and associated triggering mechanisms beneath southern Tibet, we present a geoelectrical model derived from a three‐dimensional magnetotelluric inversion in this study. An effective conductivity of 0.3 S/m at depths of 10–28 km indicates a high melt fraction of ∼35 vol% in the Lhasa terrane. In the Tethyan Himalayan orogen, an effective conductivity of <0.2 S/m corresponds to a melt fraction <15 vol%, which is lower than previous estimations. We obtain very low viscosities either from laboratory data (10¹⁰–10¹² Pa s) or empirical models (10¹⁶–10¹⁸ Pa s). A combination of radiogenic heat and strain heating may account for the weakened middle crust. We prefer a weak coupling between crustal east‐west extensions and mantle lithospheric deformations.

The Xainza‐Dinggye rift, an approximately north‐south trending Cenozoic fault zone across the Lhasa Terrane, is an ideal location to investigate extensional mechanisms in the upper crust and lithospheric deformation caused by the subducting Indian Plate beneath the central‐southern Tibetan Plateau. The 3‐D electrical resistivity structure was obtained by modeling magnetotelluric data from an array across the rift zone. Using the temperature distribution throughout the crust combined with the pressure and water content, we compute the pure melt conductivity. This enables estimation of the partial melt fraction of large‐area conductive zones imaged throughout the crust, and thus allows their rheology and strength to be evaluated. The heterogeneous distribution of high melt fraction areas in the crust has implications for the local continuous migration of fluids in the east‐west direction. The electrical structure also reveals a dipping resistive zone beneath the Tethys‐Himalaya terrane that represents the subducted Indian Plate. Significantly, its depth is observed to vary substantially from east (deeper) to west (shallower), which may indicate tearing of the plate. We suggest that the cause of extension and the formation of the crustal rift zone is related to tearing of the plate directly below this location, and the subsequent partial melting of the mid‐lower crust. Furthermore, the ascent of deep hydrothermal fluids, and heating of the shallow subsurface, likely led to the formation of the congruent Xainza‐Dinggye Thermal Belt. Additionally, the emplacement of numerous adjacent magmatic‐hydrothermal ore deposits is also likely related to partial melting and hydrothermal fluid migration in the crust.