Genetic mechanisms of hot dry rock geothermal resources in central Inner Mongolia

Central Inner Mongolia, located at the junction of plates, has undergone multi-phase tectono-magmatic activities and boasts abundant shallow hydrothermal resources. However, there is a lack of in-depth research on deep hot dry rock (HDR) geothermal resources in this region. Based on the regional geological and tectonic settings, magnetotelluric sounding results, and geothermal anomaly manifestations, this study systematically explored the genetic mechanisms and geodynamic process of HDR geothermal resources in central Inner Mongolia and determined the genetic modes of HDRs. The results show that the major heat sources of deep HDR geothermal resources in the region include deep local melts and residual high-temperature magma pockets, with heat flow channels encompassing suture zones between plates, regional deep-seated fault zones and their intersections, secondary faults, and weak layers such as ductile shear zones with plastic rheological properties in the crust. The HDR reservoirs in central Inner Mongolia primarily comprise Cenozoic mafic intrusive rocks, namely diabase and gabbro. Additionally, granites heated by high-temperature magmas and intrusive bodies are potential HDR reservoirs in the study area. The regional cap rocks of HDRs include the Cretaceous, Neogene and Quaternary sedimentary strata. The continental collision and amalgamation between the Siberian plate and the North China Craton led to the formation of collision zones that are prone to be destroyed. The subduction of the Paleo-Pacific Plate to the North China plate in the west since the Late Mesozoic Cenozoic resulted in the melting of the lithosphere bottom, the extension and thinning of the lithosphere, and the upwelling of thermal materials in the mantle asthenosphere. These, together with the accompanied intense activity of Cenozoic faults and fault depressions, jointly led to the strong magmatic and volcanic activity during the Late Mesozoic and Cenozoic. There are three heat accumulation modes in central Inner Mongolia: (1) The high-temperature HDR systems of Cenozoic diabase and gabbro reservoirs are dominant HDR reservoir in the region. (2) The moderately-high-temperature HDR systems of granite reservoirs prior to the Cenozoic are potential HDR reservoirs. (3) The hydrothermal systems of shallow clastic-rock, granite, or metamorphic rock reservoirs are dominant shallow hydrothermal reservoirs. Since shallow high-temperature hydrothermal systems are consanguineous and paragenetic with deep HDR geothermal systems in central Inner Mongolia, delineating shallow high-temperature anomalous areas will provide indicators for the discovery of deep HDRs.