Imaging the geothermal system using MT and CSEM data in the Xinzhou geothermal field, northern China

The Xinzhou geothermal field， situated within the Xinzhou Basin of northern China， represents a classic hydrothermal system with substantial development and utilization potential. To characterize the distribution of the geothermal system in this region， we deployed an integrated electromagnetic survey network comprising 98 Magnetotelluric (MT) stations and 226 Controlled-Source Electromagnetic (CSEM) stations. Through the application of three-dimensional MT inversion techniques and two-dimensional CSEM inversion methodologies， we constructed a comprehensive electrical conductivity model of the region， revealing the distinctive electrical characteristics of the deep subsurface structures. The crustal structure within the study area can be vertically subdivided into three primary stratigraphic units. The uppermost unit (C1)， composed of Quaternary and Neogene sedimentary sequences， presents as a low-resistivity layer with thickness varying from 20 to 360 meters. Within this layer， anomalous conductive zones associated with clay alteration zones have been identified. The intermediate unit， predominantly consisting of Archaean metamorphic rocks， manifests as a high-resistivity layer (R1)， which contains three distinct low-resistivity anomalies (C2-C4). These anomalous bodies， characterized by resistivity values below 40 Ω·m， are interpreted as geothermal reservoirs located at depths ranging from 0.5-3 km. The basal unit comprises an extensive low-resistivity layer (C5)， primarily situated at depths between 6-12 kilometers. This layer is interpreted as an indirect heat source for the geothermal field， with estimated temperatures ranging from 195°C to 420°C. The formation of this heat source is likely attributed to crust-mantle thermal conduction processes. Distinct thermal conduits exist between the heat source and the geothermal reservoirs， characterized by relatively low resistivity features that are closely associated with concealed fault systems in the region. These conduits facilitate heat transfer within the system. This comprehensive investigation not only delineates the spatial distribution of the Xinzhou geothermal system but also provides crucial technical support for the sustainable development and utilization of geothermal resources in the region.