Three-dimensional Electrical Structure Research Articles

Three-Dimensional Electrical Structure and Metallogenic Background of the Southeastern Hubei Ore Concentration Area

The Southeastern Hubei Ore Concentration Area (SHOCA) is located in the west section of the Middle and Lower Yangtze River Metallogenic Belt in China, and it is a significant copper and iron mining region in China. Here, 117 pieces of magnetotelluric array data were used to obtain a three-dimensional resistivity model of the SHOCA and to investigate the relationship between the deep electrical features and the genesis of mineral deposits. The model shows that the Qinling-Dabie Orogenic Belt exhibits high-resistivity characteristics, representing Mesozoic granites and high-pressure to ultra-high-pressure metamorphic rocks. There are several low-resistivity anomalies in the upper crust of the SHOCA, which are connected to the widespread low-resistivity anomaly in the middle-lower crust. Near the Yangxin-Changzhou Fault, there is evidence of an electrical gradient zone. The Xiangfan-Guangji Fault, located at the south margin of the Qinling-Dabie Orogenic Belt, also exhibits distinct high- and low-resistivity boundaries at the upper crust. However, the Yangtze Fault and the Tancheng-Lujiang Fault manifest as resistivity gradient zones at the lithospheric scale. These faults are connected the low-resistivity anomaly in the middle to lower crust, possibly serving as upwelling channels of deep thermal fluids, exerting control over shallow diagenesis and mineralization processes. The low-resistivity anomaly in the middle to lower crust of the SHOCA is explained as partial melting resulting from the mixing of crustal and mantle materials. These low-resistivity anomalies play a role as source components in the mineralization system, where mineral-rich hydrothermal fluids migrate upward along intra-basin faults, exerting control over the distribution of shallow mineral deposits.

Three-dimensional electrical structure model of the Yangbajain geothermal field in Tibet: Evidence obtained from magnetotelluric data

Three-dimensional electrical structure model of the Yangbajain geothermal field in Tibet: Evidence obtained from magnetotelluric data

The formation mechanism of the Cona Woka rift in Eastern Himalaya and its influence on the Tethyan Himalayan polymetallic deposits revealed by magnetotelluric imaging

Located in the eastern Himalaya and surrounded by Yalaxiangbo dome, the Cona Woka rift may provide valuable information for the extensional mechanism of crust and distribution of the Tethyan Himalayan polymetallic deposits. Here, for the first time we obtain the three-dimensional electrical structure reaching a depth of approximately 45 km across the Cona Woka rift. Underneath the Cona Woka rift, the electrical model reveals the intersection between the deep electrically conductive body (effective conductivity value of 0.29 s/m, 10–45 km depth) and the shallow conductive layer (conductivity value of 0.3–1 s/m, <10 km depth). We propose that the tearing of Indian slab should have contributed to the partial melting of the crust. The upper and middle crust has a melt fraction of approximately 17–20 vol%, which may deform locally to form the Cona Woka rift. The Yalaxiangbo dome is also influenced by the local deformation of the crust. Moreover, the local deformation may drive the upward migration of the fluids along the rift zone to mix with the shallow meteoric water, especially in the intersection of the Cona Woka rift and the east-west trending faults, affecting the distribution of Tethyan Himalayan polymetallic deposits.

Three-dimensional electrical structure and seismogenic environment of the crust–mantle in the Lushan earthquake region, China

The Longmenshan (LMS) southern section is the front of the eastwards material migration from the Qinghai–Tibet Plateau. To understand whether the 2022 Ms6.1 Lushan earthquake was a strong aftershock of the 2013 Ms7.0 Lushan earthquake and why the aftershocks of the two earthquakes were concentrated relative to the 2008 Wenchuan earthquake, a three-dimensional electrical structural model of the Lushan earthquake region is established based on magnetotelluric (MT) array data. The model shows high-conductor layers (HCL) in the Songpan–Ganzi terrane (SGT) middle crust, Sichuan Basin (SCB) shallow surface, western Sichuan foreland depression (WSCFD) and LMS Moho. The analysis suggests that the HCL in the study area at a depth of 10 km is caused by saline fluids in the fracture zone or porous sedimentary rock voids, while the high-conductor body in the middle and lower crust and upper mantle is caused by partial melting of rocks. The Lushan earthquake area is subject to compressional deformation horizontally as the eastwards migration of Qinghai–Tibet Plateau material is blocked by the SCB and vertically by the upwards extension of high-conductor plastic material at depth. The aftershocks of the Lushan earthquake area are mainly confined within the Baoxing–Zhonglin–Daxing–Lushan high-conductor region, which has noticeable electrical structural differences compared to the overall high-resistivity structure of the LMS southern section; these differences explain why the aftershocks of the two earthquakes did not expand in the northeast and southwest directions of LMS. Because the 2022 and 2013 Lushan earthquakes both occurred in the same high-conductor region in the deep part of the Dachuan–ShuangShi fault to the Danyi blind fault, the 2022 Lushan earthquake was a strong aftershock of the 2013 Lushan earthquake in terms of electrical structural characteristics.

Three-dimensional electrical structure of the Huya fault and adjacent areas of the eastern margin of the Tibetan Plateau and its geological significance

In this study, we present new two- and three-dimensional resistivity models of the Huya fault region in the east margin of the Tibetan Plateau, imaged with magnetotelluric (MT) method. According to those models, a high-angle low-resistivity anomaly beneath the Huya fault is revealed, which is interpreted as a crustal thrust fault. The Minshan Uplift is imaged as a two-layered resistivity structure. The Bikou Block exhibits relatively uniform high-resistivity characteristics in our models, with its basement connected to a high-resistivity body beneath the Longmenshan fault belt. Thus, we infer that the Bikou Block belongs to the Yangtze Block. The Longmenshan fault belt exhibits strips of alternating high- and low-resistivity anomalies in the upper crust, with its middle and lower crust being highly resistive. The middle and lower crust of the western study region shows low resistivity, with its geometry changed greatly as it extends southeastward and upward. This is interpreted as an eastward channel of escaping material of the Tibetan Plateau. However, this channel is imaged to be blocked horizontally by the Bikou Block near the Huya fault, causing part of mid-to-lower crustal material to be upwelling, resulting in the Minshan Uplift. Another part of the low resistivity anomaly extended southeastward and was blocked by the lithospheric high-resistivity body beneath the Longmenshan fault belt, and then extended to the northeast and the southwest.

Three-dimensional electrical structure and deep dynamics of the Khondalite Belt and adjacent areas in the Western Block of the North China Craton

The Khondalite Belt is an important orogenic belt in the Western Block of the North China Craton that was formed by the collision of the Ordos and Yinshan blocks in the Paleoproterozoic. In the background to the Mesozoic multi-plate convergence, the Western Block lithosphere was activated along with magma and tectonic activity. Being an important collision zone, the Khondalite Belt is a key area where the modification and destruction of the Western Block can be studied. In this study, 440 sets of magnetotelluric array data were used to obtain a three-dimensional resistivity model of the study area. The resulting model revealed that the crust in the study area could be divided into three layers. The first layer exhibited an overall low-resistivity anomaly with some regional high-resistivity anomalies, while the second and third layers exhibited high- and low-resistivity anomalies, respectively. Furthermore, the model elucidated obvious boundaries between the Khondalite Belt and the Yinshan Block. The area controlled by the western and eastern Helanshan faults may be the western boundary of the Khondalite Belt. However, there was no obvious boundary to the south or east, as the bounding area exhibited low resistivity, possibly caused by a severely modified lithosphere. As a result of the characteristics of the magmatic rocks’ xenoliths, magnetic anomalies, and low S-wave velocities, low-resistivity anomalies developed in the lower crust and upper mantle, which were related to the partial melting. The scale of the partial melting did not cover the entire collision zone. Rather, it only covered the structural weak zone, especially the Jining area in the eastern Khondalite Belt. Therefore, the eastern section of the lithosphere was potentially modified by the Paleo-Pacific Plate subduction.

The three-dimensional electrical structure and metallogenic prospect of the Ning (Nanjing)-Wu (Wuhu) basin and the southern adjacent area in eastern China

The Ning (Nanjing city)-Wu (Wuhu City) volcanic basin, which is famous for its large-scale, high-grade ore deposits, is a typical iron ore district in the middle-lower reaches of the Yangtze River Metallogenic Belt (MLRYMB). The southern part of the basin is primarily covered by Quaternary strata. Few in depth studies have been conducted on this area. Due to the increasing demand for mineral resources and the controversy over regional tectonic models, some fundamental geological issues still need to be addressed. These questions include defining the characteristics of the geological structures and the mineralization prospects. Therefore, a three-dimensional (3D) magnetotelluric survey was conducted in this area to obtain a deep 3D electrical model. It was found that the Yangtze fault (CJF) and the main thrust fault (MTF) in the upper crust have the same deep (middle crust to upper mantle) setting and part of the thrust tectonics of the metallogenic belt. The southern boundary of the Ning-Wu Basin is located on a fault belt (boundary fault, BF) with a northeast-east (or east-west) strike influenced by the MTF in the southern part of the study area. Bounded by the BF and MTF, the southeastern part of the study area exhibits signs of uplift. With the recent discovery of a large porphyry copper deposit to the southeastern part of the study area, which is located in an uplift structure similar to the one south of the Ning-Wu Basin, this local uplift could have potential mineralization prospects based on a previous mineralization theory developed for this belt.