Letian Zhang

The growing demand for critical minerals, precious and base metals, industrial minerals, geothermal energy, and other subsurface resources is pushing geophysical exploration toward greater depths and increasingly complex geological settings

To investigate lithospheric destruction of the North China Craton (NCC), we obtained a three‐dimensional resistivity model using a magnetotelluric (MT) array covering the Western Block, the Trans‐North China Orogen, and the Eastern Block. Using the Nernst‐Einstein, Arrhenius equations and Hashin‐Shtrikman ( HS ) bounds, we quantitatively estimated temperature and melt fraction from the resistivity model. The model reveals two low‐resistivity anomaly systems separated by the resistive Taihang Uplift. The northern Western Block and its peripheral grabens display a large‐scale anomaly, whereas the southern Western Block remains resistive. The Eastern Block also shows an upper mantle low‐resistivity anomaly. The low‐resistivity anomaly in the Western Block is localized and multi‐causal: it results from partial melting, water, and carbon dioxide. In contrast, the anomaly in the Eastern Block is primarily controlled by Mesozoic westward subduction and retreat of the Paleo‐Pacific Plate, causing lithospheric thinning and partial melting, with the Tanlu Fault Zone and southern Taihang Uplift as melt conduits. The NCC destruction is multi‐stage: Mesozoic Paleo‐Pacific subduction modified the Eastern Block, while Cenozoic far‐field effects of Tibetan Plateau uplift induced anticlockwise rotation of the Western Block, triggering localized upwelling along pre‐existing faults and forming Cenozoic volcanoes and rift basins. MT data provide key electrical evidence for this heterogeneous, multi‐stage destruction process.

The Songpan-Ganzi and Eastern Kunlun region on the northern margin of the Tibetan Plateau is a key area for the evolution of the Paleo-Tethys tectonic domain and hosts abundant gold, lithium, and polymetallic mineral resources. To reveal the deep structure of this region and its metallogenic background, this study constructed a lithospheric electrical structure model based on magnetotelluric (MT) data along a profile traversing tectonic units such as the Qiangtang, Songpan-Ganzi, and Eastern Kunlun blocks. Data processing, dimensionality analysis, and two-dimensional inversion were performed. The results show that a large-scale, funnel-shaped conductor, originating from the upper mantle and penetrating the middle-lower crust, exists beneath the Songpan-Ganzi and Qiangtang terranes, indicating a major channel for deep-seated thermal material upwelling. Driven by Cenozoic tectonic reactivation, the thermal materials ascended along pre-existing lithospheric weak zones formed during the closure of the Paleo-Tethys Ocean. It spread extensively within the upper-middle crust of the Songpan-Ganzi terrane and migrated to the Eastern Kunlun orogenic belt via complex fault systems, ultimately forming low-resistivity bodies that closely coincide with the locations of major shallow ore-controlling faults. This electrical model suggests the presence of a “thermal material channel” system extending from the mantle to the shallow crust. The study suggests that the migration pathways of ore-forming fluids, represented by gold deposits in the Eastern Kunlun metallogenic belt, are highly correlated with the fault-magma channel system constituted by intra-crustal conductors. In contrast, the lithium-rich granitic magmatism associated with lithium mineralization within the Songpan-Ganzi terrane may be related to the deep thermal background reflected by the large-scale conductor in the upper mantle. From the perspective of electrical structure, this study suggests that mineralization in this region may be closely linked to deep crust–mantle processes. The reactivation of pre-existing tectonic-magmatic channels by Cenozoic thermal material is key to controlling the distribution pattern of dominant shallow mineral resources. The research results provide important geophysical constraints for a deeper understanding of the tectonic–magmatic–mineralization coupling mechanism on the northern margin of the Tibetan Plateau.

Mechanisms governing the stress‐induced surface deformation of the Tibetan Plateau and other continental collision zones remain vigorously debated in the geoscience community. Crustal rheological properties can offer valuable insights into the Earth's deformation patterns. Here, we present an electrical anisotropic study of the crust and upper mantle along a profile in the central‐southern Tibetan Plateau. Our resistivity models unveil a large‐scale conductive layer beneath the study region, with distinct electric anisotropic orientations within the middle and lower crust. The middle crust exhibits nearly north–south (N–S) directed anisotropy features, whereas the lower crust anisotropy axis is east–west (E–W) directed. From the conductivity model, we estimate the melt fraction and viscosity distribution using an experiment‐based empirical formulation. As demonstrated by the petrological experiments, the amphibole‐rich mid‐to‐lower crust could host the aligned fractures/microcracks and melt pockets, possibly facilitating the observed anisotropy. With an anisotropic conduction model, we also show that the distribution characteristics of these cracks and pockets may directly influence the effective conductivity. The two‐layered electrical anisotropy observed likely reflects distinct deformation types and rheological strengths: the N–S electrical anisotropy may originate from fluid‐filled fractures from the brittle deformation in the middle, while the E–W anisotropy may arise from the deformed conductive melt pockets in the ductile lower crust. These findings may provide a novel way to characterize the crustal deformation mechanisms using geo‐electrical anisotropy, in other tectonically active regions.

The Northeastern Hunan Province (NEH), situated within the Central Jiangnan Orogen, hosts abundant Au-polymetallic deposits. However, the coupling mechanism between the deep tectono-magmatism and Au-polymetallic mineralization remains poorly understood. In this study, a three-dimensional (3D) resistivity model derived from 59 magnetotelluric (MT) stations is presented to investigate the lithospheric architecture and its relationship to Au-polymetallic mineralization. The model reveals three prominent mid-to-lower crustal conductors (3–30 Ω·m) at 15–35 km depth beneath Au-polymetallic deposits along NE faults. These anomalies are interpreted as source zones and pathways for magmatic-hydrothermal fluids during the Late Mesozoic tectono-magmatism, likely formed by the enrichment of graphite films and sulfides along faults, which thus account for the observed conductive features. Moreover, the model reveals a thinning electrical lithosphere–asthenosphere boundary (eLAB) at ~80 km depth beneath the Southeastern NEH, attributed to lithospheric delamination triggered by the rollback of the Paleo-Pacific plate. This delamination facilitated the upwelling and lateral migration of asthenospheric materials, which promoted intense extension and crust–mantle interaction. Consequently, metallic elements were extensively extracted from the crust and concentrated into large-scale Au-polymetallic deposits in the NEH. Integrating with previous geochemical study, a deep-seated magmatic underplating and MASH model is proposed as key drivers of Au-polymetallic enrichment in the NEH, effectively linking deep tectono-magmatism with shallow mineralization. From a rheological perspective, three low-viscosity zones within the mid-to-lower crust likely acted as both vertical conduits and deep sources for metallogenic fluids, providing favorable pathways for their migration and accumulation.

Robust test of conductors and deep seismic reflection profile.

Robust test of conductors and deep seismic reflection profile.

Robust test of conductors and deep seismic reflection profile.

The Central Asian Orogenic Belt (CAOB) was originated from the subduction, closure, convergence, and post-collisional extension of the Paleo-Asian Ocean located between the North China Craton, Tarim Craton, and the Siberian Craton during the late Permian to early Triassic. The Magnetotelluric (MT) method can detect the deep structure and properties of the orogenic belt, and further reveal the crust and mantle deformation mechanism and deep dynamic process inside the orogenic belt. In this paper, we summarize recent developments in the MT studies of the CAOB, including 2 MT studies that we recently conducted for the Beishan and Bainaimiao segments of the CAOB, which briefly describe the complex electrical structure of the crust and upper mantle, and provide valuable information for understanding its deep processes and continental dynamic mechanisms. Finally, we summarize the general characteristics of the lithospheric electrical structure and formation mechanism of low-resistivity zones, based on which we look forward to future MT studies.

The Yangbajing geothermal field, located in the south part of the Tibetan plateau is the largest high-temperature geothermal system of the whole plateau. Numerous hydrological, geological, and geothermal studies have been conducted to gain insights into the heat source of the geothermal system. Geothermal studies show that heat flow in this area is extremely high. However, heat flow contributed by the crustal radiogenic heating together with mantle heating still can not explain the anomalously high heat flow (~116 mW/m2) here. In this study, we use the high-resolution 3D electrical resistivity models, generated from magnetotelluric data in the Yangbajing region of southern Tibet, that image zones of enhanced conductivity in the middle crust. Such features may relate to partial melts (or magma chambers) with a melt fraction of more than 19%. Here, with the help of other available data, primarily hydrothermal and geochemical data, we estimated the heat flow generated by the partial melts in this area. Furthermore, we performed a set of simulations to reproduce the thermal evolution of the magma chambers in this region. our results indicate that the magma chambers below the study region may provide sufficient heat flow to fill the relatively large heat flow gap (~20.25 mW/m2 ), apart from the mantle heat conduction and radiogenic heating for the geothermal system. In addition, the thermal evolution simulations show that the magma chambers beneath the Yangbajing geothermal system may remain relatively warm, after the long cooling procedure. Our results highlight the possible contribution of the magmatic heat generation to the Yangbajing geothermal system, and reveal that crust contributes a significant proportion of the total surface heat flow (~70.75 mW/m2) in the Yangbajing geothermal field, which is much higher when compared with the typical rift basins in China.