| Abstract |
In recent years, high-temperature geothermal resources with temperatures above 150 °C have been successively discovered at the depths of <4000 m in the Matouying and Tianzhen areas of Tangshan City and Datong City, North China. Nevertheless, the heat source, genesis, and geodynamic processes of these high-temperature geothermal formations have not been clearly understood. In this paper, we analyze the deep geological background, crust-mantle structure, deep-large fractures, magmatic activity, as well as motion, upwelling and geodynamic mechanism of asthenosphere in the study area. Combining with the research of geophysics and geochemistry, to elaborate the problem that the effects of internal and external forces on shaping of the Earth's shallow geothermal field and thermal anomaly. The results show that: 1) under the interaction of far-field effect of the collision of Indo-European plate and the subduction and retreat of the western Pacific Ocean, deep geological processes, e.g. lithospheric demolition, sinking and thermal erosion of asthenosphere, occurred in the east-central part of the North China Craton. As a consequence, the destruction, lithospheric thinning, lithospheric induced extension, oblique tensional slip, extrusion and deformation, basin fracture and uplift occurred. These geological activities creates a favorable geological background for the upwelling of mantle-derived thermal materials; 2) the tectonic environment, caused by the relative movement between the blocks, and deep-large slip fractures cutting through the lithosphere constitute the main channels for the upward invasion of mantle-derived thermal materials; 3) the high-conductivity and low-velocity bodies, geochemical evidence and the location of high-temperature geothermal resources have formed a good correspondence. Hence, it is believed that the upward invasion of mantle-derived thermal material caused the shallow thermal anomalies. The lithospheric tectonic weak zones such as block combination zone and deep-large slip fractures constitute the upward invasion channels of mantle-derived thermal material. The concave-convex tectonic pattern and the flow field of groundwater dominate the distribution of heat in the shallow part of the earth's crust. The suitable tectonic parts of Fenwei rift valley, Zhangjiakou-Bohai fracture zone are favorable target areas for finding high-temperature geothermal resources in 2,000-4,000 m depth. |