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The Yangbajain Geothermal Field in Tibet is located in the fault subsidence basin of the central Yadong-Gulu Rift Valley. The spatial distribution of the field is controlled by mountain-front fault zones on the northwestern and southeastern sides of the basin. Geothermal power has been generated in Yangbajain for more than 40 years. However, owing to the lack of three-dimensional (3D) geophysical exploration data, key geological issues related to the partial melt body of the Yangbajain Geothermal Field, such as its location, burial depth, and geometric form, as well as the ascending channel of the geothermal fluid, have for a long time been controversial. In this study, 3D inversion was performed using measured geo-electromagnetic total impedance tensor data from 47 survey points. The extracted horizontal sections at different depths and profiles, and at different lines, reflect the 3D electrical structure model of the geothermal field in the study area. Subsequently, three findings were obtained. First, the partial melt body, located below the China-Nepal Highway extending along the northeast direction, is the heat source of the Yangbajain Geothermal Field. The burial depth range of the molten body was determined to range between approximately 6.2 and 14 km. Moreover, the geothermal fluid ascended a horn-shaped circulation channel with an up-facing opening, located in the northern section of the sulfur ditch area. The study results revealed that deep rock fissures (>2 km) were not well developed and had poor permeability. In addition, no layered heat reservoirs with high water richness were observed in the northern part of the study area. However, the application of enhanced geothermal system (EGS) technology in the northern region would be essential to improving the power generation capacity of the Yangbajain Geothermal Field. In addition, the study found no deep high-temperature heat storage areas in the southern region of the study area. [ABSTRACT FROM AUTHOR]

Mantle tectonics, such as asthenospheric upwelling and lithospheric decoupling, usually controls subsequent fluid formation and migration from deep to shallow levels in the lower lithosphere and promotes rock failure and deformation. Based on the concept whereby the fluid migration location defines the structural inheritance, we aim to relate crustal processes to mantle tectonics using fluids revealed by a new magnetotelluric (MT) array across the Ailao Shan-Red River belt. As imaged via a 3D resistivity model, two lower-lithospheric conductive anomalies are determined as consistent with the Dian-Qiong (DQ) suture and Song Da (SD) belt and interpreted to contain interconnected melt. Because potassic magmatism was enabled by partial melting in the lower lithosphere, we could infer that the DQ and SD have reworked as the major fluid migration channels. Fluid migration is considered to drive lithospheric decoupling at a low-viscosity conductive layer, which is inferred feeding by aqueous and melt fluids originating from the two channels and diffusing at depths from 15 to 20 km. Constrained by the geochronology results, this weak layer could have provided convenience to induce the entirely upper crustal translation-rotation within the time interval between potassic magmatism and strike-slip of the Red River fault. This translation-rotation process is inherited from the underlying mantle processes and may further be remotely affected by the upper crustal movement of the Tibetan Plateau, conforming with the crustal rotation observed to the north of our study region. This work provides a compelling example of the tectonic control of the mantle on inherited responses in the crust. Plain Language Summary Crustal deformation is usually controlled by mantle tectonic processes, especially the southeastern Tibetan Plateau. Some models have proposed that lithospheric shearing and lower-crustal flow have controlled the crustal deformation in the Cenozoic. However, crustal rotation models show less possibility of a channel flow and relate the crustal deformation to the remote effect of India-Asia collision. Our study investigates above hypotheses by imaging the electrical resistivity of rocks beneath the major Red River Fault area in southeastern Tibet, using magnetotelluric data with high quality in a dense array. The lithosphere of the study area is interpreted to have been divided into two horizontal systems by a fluid diffusion layer at the bottom of upper crust. Resistivity low in the lower lithosphere is inferred due to partial melting of deep lithosphere and reworking of the paleo sutures in the Late Cenozoic, which have spread at the bottom of upper crust. Rather than the channel flow, this fluid migration process sensitively reflected in our model relates the mantle tectonics to crustal rotation by providing rheological conditions. We, hence, propose an inherited structure model featured by lithospheric decoupling and upper-crustal translation-rotation that may occur before the major strike-slip event. [Display omitted] • A new 3D model reveals electrical structures on the southeastern Tibetan Plateau. • The Red River fault is discontinuous at a depth of ∼20 km and may move away from the palaeo-suture. • Palaeo-suture was reconstructed into two activated zones and reworked as channels for fluid migration. • Fluid migration has driven the lithospheric decoupling and upper crustal inheritance. • The upper crust experienced a translation-rotation process before the internal strike-slip event. [ABSTRACT FROM AUTHOR]

The Yangyi geothermal field in southern Tibet has enormous potential for geothermal energy development. It is the high-temperature geothermal field at the highest elevation in the world, and the second largest high-temperature geothermal field in China. The total planned installed capacity of the geothermal power station is 32 MW. At present, no detailed three-dimensional (3D) geophysical survey has been carried out in the Yangyi geothermal field, and in-depth research is urgently needed. The main goal of our geophysical exploration is to study the geothermal structure of this region. In this study, the audio magnetotelluric (AMT) data of 85 stations were collected in the Yangyi geothermal field. The average distance between the stations was about 500 m, and the dimensions of the exploration area were 6 × 7 km. First, we analyzed the magnetotelluric data using the phase tensor method to qualitatively estimate the dimensionality of the subsurface resistivity structure. Then, by performing 3D inversion of 85 AMT data with relatively high quality, the 3D resistivity model from the surface to a depth of 2 km was determined, the high-temperature hydrothermal system under the Yangyi geothermal field was displayed for the first time. In addition, the main characteristics of the geothermal system were identified, and the genetic mechanism of the geothermal system was discussed based on the geological information and borehole data. • Yangyi is the magma-type high-temperature geothermal field at the highest elevation in the world. • Yangyi is the second largest high-temperature geothermal field in China. • For the first time, the three-dimensional resistivity structure of the Yangyi geothermal field was obtained. • The Yangyi high temperature hydrothermal system was imaged for the first time, and the main features of the geothermal system were identified. [ABSTRACT FROM AUTHOR]