CONTROLLING EFFECTS OF MULTI-SCALE STRUCTURES ON BEDROCK GEOTHERMAL RESOURCES IN THE CENTRAL JIZHONG DEPRESSION USING COMPREHENSIVE GEOPHYSICAL AND GEOCHEMICAL METHODS

Geothermal resources are environmentally friendly, efficient, and abundant. The Jizhong Depression is known for its hydrothermal geothermal resources, making it a key area for study. Previous studies have indicated that faulted structures play a crucial role in controlling the bedrock geothermal reservoir. However, further investigations are required to understand the specific modes and levels of influence that multi-scale structures have on geothermal resources. Utilizing a comprehensive range of geophysical and geochemical methods, including gravity surveys, magnetic measurements, magnetotelluric surveys, seismic analysis, controlled source electromagnetic surveys, and soil radon-mercury gas measurements, we have successfully identified the bedrock thermal storage-controlled thermal faults in the central Jizhong Depression. Our research has revealed the significant influence of fault structures at various scales and depths, as well as regional tectonic processes, on the geothermal field. The structural genetic model of typical geothermal field was established.

Multi-scale structures in the Jizhong Depression control geothermal elements, including the heat source(HS) and water source(WS), migration channel(MC), thermal reservoir(TR) and cap layer(CL). The favorable area for geothermal resources is formed through the combined effects of multi-scale structures. The shallow crust-mantle depth in the central part of the depression facilitates the upward conduction of underground HS. The WS for geothermal resources primarily originate from atmospheric precipitation. The major fracture is a MC of underground hot water and promotes the accumulation of heat energy to the bedrock thermal reservoir. The TR in the study area is a Marine carbonate reservoir, with small structures like pores and fractures become favorable spaces for bedrock heat storage. The Cenozoic strata (CL) in the study area are predominantly sand-mud, providing good thermal insulation. In conclusion, the formation of the bedrock geothermal resources in the central part of the Jizhong Depression is influenced by the multi-scale structural controls on various geothermal resource elements, including HS, WS, MC, TR, and CL.

Keywords: Bedrock geothermal resources; Multi-scale structures; Geophysical methods; Geochemical methods