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.

The closure of the Paleo‐Asian Ocean along the Solonker Suture Zone (SSZ) during the Late Permian and Triassic represented the final stage in the formation of the Central Asian Orogenic Belt between the Siberian Craton and the North China Craton. In order to better understand the structure and formation of this ancient plate boundary, a high‐resolution magnetotelluric (MT) profile was collected in 2010–2012 with both broadband and long‐period MT data. Dimensionality analysis showed that a 2‐D analysis was valid. Both 2‐D isotropic and anisotropic resistivity models were derived from the joint inversion of MT and tipper data. The high‐resolution mapping achieved in this study is due to the closely spaced MT stations (2–3 km). The major south dipping conductive layer was detected beneath the SSZ and found to be electrically anisotropic with the highest conductivity in the down dip direction. This feature was interpreted as evidence for southward subduction forming the suture. Previous studies of electrical anisotropy in Paleoproterozoic orogens have reported electrical anisotropy with the maximum conductivity in the strike direction. The high conductivity has been interpreted as being due to graphite or sulfides concentrated in fold hinges. In contrast to these studies, the Solonker Suture conductor shows an enhanced conductivity in the dip direction. The difference between these situations could be explained if the Solonker Suture has the fold axes rotated by high strain into the strike direction. This would result in the highest conductivity being parallel to the dip direction.

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.

Northeast China was formed during the progressive closure of the Paleo‐Asian Ocean before the Early Mesozoic, and was then later affected by the westward subduction of the Paleo‐Pacific Plate and the west‐to‐east closure of the Mongolia‐Okhotsk Ocean. Huge volumes of granites were emplaced across this region during the Mesozoic, and widespread Cenozoic volcanism is still active in the Quaternary. To study past and present magmatic processes in this region, two parallel high‐resolution magnetotelluric profiles were collected to produce lithospheric resistivity models. Northwest of the Greater Xing'an Range, the lithosphere has a relatively low resistivity. The resistivity of the upper mantle low‐resistivity anomaly (C2) is consistent with the presence of a few percent of basaltic melt. This feature connects with a shallower low‐resistivity zone (C1) that extends into the crust. Its properties are consistent with 5–10% shoshonitic melt. The lithosphere in the southeast part is highly resistive. The upper mantle high‐resistivity zones (R1 and R2) are interpreted as regions of thickened lithosphere that may be undergoing delamination. The lower crust exhibits localized low‐resistivity zones (C3, C4, and C5), and they are interpreted as partial melt which may have originated in the ongoing upwelling. The overall pattern of magmatism appears to be driven by asthenosphere upwelling which might have been triggered by the Paleo‐Pacific Plate retreat, but the upper mantle low‐resistivity zone originates and rises from the northwest. Down‐welling in the southeast might be the combined effect of the subduction and retreat of the Paleo‐Pacific Plate and the instability of thickened lithosphere.