Geothermal-geological model of Xiong'an New Area: Evidence from geophysics

Geothermal resources are abundant in the Xiong'an New Area, including Niutuozhen geothermal field, Rongcheng geothermal field and Gaoyang geothermal field. The geothermal resources in this area were developed and utilized earlier, but there is still no unified view on its deep heat source mechanism. In order to study the deep heat source mechanism, deep reflection seismic and long-period magnetotelluric survey were carried out in Xiong'an New Area and its periphery. The deep reflection seismic data and magnetotelluric data of the same section were processed and jointly interpreted. The geological structure and electrical structure in the study area from the surface to the Moho surface were explored. The lower crustal structure has a good corresponding relationship between the deep reflection seismic profile and the magnetotelluric profile. The area of low resistivity corresponds to the existence of a series of reflection events on the deep reflection seismic profile, and the event axis can continue to the Moho surface. The areas of high resistivity correspond to the absence of obvious continuous reflection events on the deep reflection seismic profile. Especially above the Moho surface, there is an approximate "blank area" of seismic reflection. Combined with regional geothermal data, a deep geothermal geological model of the study area was constructed, and the deep geothermal mechanism in the new area was explained. This model is a "dual" heat generation model, and its heat source consists of two parts, the deep mantle heat source and the heat generated by the decay of radioactive elements in the crust. The decay heat of radioactive elements accounts for nearly 30% of the surface heat flow, and the mantle-derived heat flow accounts for about 70% of the surface heat flow. Below Niutuo Town and above the Moho, the lower crust was uplifted due to the upwelling of hot mantle material, and the undercut of mantle-derived magma formed a local thermal anomaly in the lower crust. This thermal anomaly has low-speed and high-conductivity geophysical characteristics. It is considered to be the deep heat source of the Niutuozhen geothermal field and the Rongcheng geothermal field. With regional faults as the heat channel, the terrestrial heat flow is conducted upward from depth and diffused to the top of the Niutuozhen and Rongcheng bulges, which is a source of carbonate reservoirs. The water layer is heated to form a geothermal reservoir; the overlying Neogene sedimentary stratum is a good thermal cap layer.