Crustal structure and deep geotherm of the Pearl River Delta in South China: Insights from gravity and thermal modeling

Abstract

Granite-basin geothermal systems show promise as renewable resources for heat and potential electricity production. Nevertheless, a deeper understanding of their structural relationships and heat accumulation patterns is crucial for enhancing the exploration and evaluation of their energy potential. The intricate granite-basin structure evident on the surface of the Pearl River Delta (PRD) in South China poses significant challenges and uncertainties for deep geothermal exploration. To offer a deeper understanding, we introduce a comprehensive three-dimensional (3-D) lithospheric-scale structural model of the PRD, leveraging gravity anomaly and other geophysical data. Subsequently, utilizing this model as a foundation, we successfully derived the three-dimensional steady-state conductive thermal field of the crust through numerical simulation techniques. Our findings reveal that the deep fault zones control the morphology of basins and intrusions. The model indicates that the granite has an average thickness of approximately 3.5 km, whereas the region proximate to Hong Kong and Macau exhibits the greatest thickness (∼12 km). In forward modeling, the presence of significant gravity anomalies that cause challenges in accurately fitting within the Sanshui Basin and littoral region are attributed to basaltic intrusions located within the lower crust. The measured data reveals that the granites in the PRD have a high radiogenic heat production rate (average > 5 μW/m³). The thermal simulation result shows that the subsurface high-temperature areas are predominantly concentrated within the Sanshui Basin, Xinhui Basin, and Yunkai Massif. Notably, the surface heat flow exhibits considerable fluctuations, ranging from 68 and 122 mW/m², with granitic intrusions contributing as much as 48%. This study reveals that mantle heat serves as the primary controlling factor in the thermal field. Moreover, over half of the regions examined possess the capability to generate high-temperature geothermal resources.