Abstract:

High-temperature geothermal reservoirs with temperature above 150 ℃ have been successively discovered in China—mainly in southern Tibet, Yunnan and Sichuan in the Mediterranean-Himalayan geothermal belt, and Taiwan in the Pacific Rim geothermal belt. In recent years breakthroughs in high-temperature geothermal prospecting have also been made in cental and eastern North China. For example, in 2019 in Hebei, granite dry hot rock mass with a temperature of 151 ℃ was drilled at a depth of 4000 m in Matouying. In 2020, a geothermal fluid of 167 ℃ in high temperature gneiss fissure reservoir was drilled at 1586 m depth in Tianzhen County, Shanxi Province. And in 2023 in Shandong, a high-temperature Ordovician limestone karst reservoir with a temperature of 167.5 ℃ was drilled at 4283 m depth in Zhuanxi area, Dongying City. It is therefore an urgent task to systematically study the formation of high-temperature geothermal reservoirs in this region as well as related exploration technologies. Taking the above three high-temperature geothermal fields as examples, this paper analyzes the dynamic process underlying the effect of regional crust-mantle structure, deep geological processes—such as crust-mantle upwelling and Moho uplift-on the shallow high-temperature thermal anomalies in the Earth’s crust. Combined with geophysical and geochemical studies and exploration results, this paper explains how deep geodynamic processes shape the Earth’s shallow geothermal field and constrain high-temperature thermal anomalies, and discusses technologies to identify deep heat sources, upwelling channels and thermal energy gathering structures. The paper also explores the formation mechanism of high-temperature geothermal reservoirs in typical locations and its significance for high-temperature geothermal exploration in central and eastern North China. Briefly, (1) under the far field effect of the India-Eurasia plate collision and subduction retreat of the Western Pacific plate, the destruction of the North China Craton (NCC) leads to deep geodynamic processes—such as lithospheric thinning, asthenospheric upwelling and thermal erosion, extensional rift basin and deep strike-slip fault development—which are the main driving forces behind the upwelling of mantle-derived molten material to the shallow crust. (2) There is a good corresponding relationship between a high conductivity-low velocity-low resistivity body, geochemical evidence and high-temperature geothermal resource distribution. Therefore, it is believed that the upward infiltration of molten materials causes shallow thermal anomalies, and the molten/semi-molten magma sac in the crust provides a stable heat source to form high-temperature geothermal reservoirs. The weak lithospheric structures-such as plate margin zones and deep strike-slip faults—cut into the lithosphere, constituting the main channels for the upward infiltration of the molten material. (3) The concave-convex tectonic pattern and groundwater flow field mainly control the heat distribution in the shallow crust. Under the “thermal refraction” effect driven by the difference in thermal conductivity of shallow rocks, heat flow accumulates from the sag to the uplift, forming high-temperature thermal anomalies in ancient buried hills.

Key words: deep dynamic processes, mantle-derived heat, upwelling channel, heat accumulation, high temperature reservoir, central and eastern North China Block