Lithospheric thermo-rheological structure of the Huangshadong geothermal field in Huizhou of Guangdong and its heat-sources implications

The thermo-rheological structure of the lithosphere is an effective method to reveal the thermal state within the lithosphere. Studies of the thermo-rheological structure of the lithosphere in geothermal anomaly areas can effectively constrain the contribution of heat sources. The southeastern China is an important distribution region for geothermal resources, with a large number of natural hot springs emerging on the land surface. Boreholes in this region have identified high geothermal gradients at depth. However, the mechanism of the heat sources is still controversial, and whether the hot dry rock resources exists is not clear. In this study, we take the Huangshadong geothermal field in Huizhou of Guangdong as the research target. We analyze the temperature distribution and rheological strength of the lithosphere, discuss the heat sources of the Huangshadong geothermal field, examine the thermal influence of shallow hydrothermal systems, and predict the prospects of dry hot rock resources. The results show that the heat flux under the influence of hydrothermal systems in the Huangshadong geothermal field is 130.3 mW/m², and the crustal heat flow is similar to the mantle heat flow, showing a warm-crust-warm-mantle lithospheric thermal structure. In addition, the structural heat flux reaches 30.5–60.3 mW/m². The rheological structure of the lithosphere shows that the middle crust has a ductile rheological layer, the upper crust and the lower crust are mainly controlled by brittle failure, and the lower crust and the lithosphere mantle show coupling in the rheological structure, which indicates a relatively stable crustal bottom boundary. The heat sources of the Huangshadong geothermal field is dominated by the tectonic heat source, and the mantle heat source and radiogenic heat production are the main heat source components. The main parts of tectonic heat source include the heat accumulation in regional deep faults and cyclic heat transfer in hydrothermal systems, both of which may carry heat to the surface through “relay” heat transfer. The proportion of heat accumulation of regional deep faults in the tectonic heat source is the key factor affecting the prospects of dry hot rock resources.