Abstract
The southeast coastal areas in China have distributed lots of granite outcrops of different periods. Previous research has shown that granite geothermal reservoirs are also distributed under sedimentary basins in these areas, such as in Zhangzhou basin. Therefore, granites with fractures buried in deep can be used as a potential deep geothermal reservoir in these areas. In order to study geological conditions of the deep granite reservoir and discuss the genesis of the deep granite geothermal system, rock geochemistry and zircon U-Pb chronology from outcrop and parts of the drilling cores of granitic rocks have been analyzed, combined with the anatomy of the deep seismic data and electromagnetic detection data in selected area. Based on the results of geochemistry and zircon U-Pb chronology, most granites in this area are of Yanshanian periods. Based on the seismic data, the thickness of the overlying strata on granite in Huangshadong area of Huizhou City is up to 1.5 km. According to the regional geological survey, multi-stage joints are developed in the granite, and most of hot springs rise from intersection of fracture with different directions to the surface. The heat source in the study area mainly comes from the mantle carried up by the deep NNE-trending faults. There are a large number of thermal springs at the intersection of the surface and the NW-trending fault, and the NW-trending fault provides the drainage conditions for the upwelling of underground thermal springs. There is a huge amount of deep granite geothermal resources in the southeast coastal area. The analysis of deep granite geological conditions and genetic models can provide guidance for the evaluation of deep granite geothermal resources and the further optimization of favorable zones in these areas.
Highlights
Geothermal resources, as a renewable and clean energy, have been widely used globally in recent years, and the utilization has been increasing year by year (Bertani, 2012; Bertani, 2016; Lund and Boyd, 2016)
Most of the deep geothermal reservoir are granite (Brown et al, 2012), and Metamorphic rocks (Li et al, 2019) beneath the sedimentary basins and numerous studies have shown that the granite radioactive heat production has significant contribution to the heat source, such as Australia Cooper basin geothermal field caused by granites with intrusion age less than 0.5 Ma (Goldstein et al, 2008), Rose-manowes geothermal field in England due to Early Permian granite heat generation (Richards et al, 1992), the Soultz geothermal field in France due to Late Paleozoic granite heat generation (Genter et al, 1995)
Granites in South China are widely distributed, with an outcropping area of 20,000 km2, accounting for about 1/5 of the area, and it is considered to be formed in three phases, i.e., Caledonian, Indosinian and Yanshanian period (Zhou et al, 2006) (Figure 1)
Summary
Geothermal resources, as a renewable and clean energy, have been widely used globally in recent years, and the utilization has been increasing year by year (Bertani, 2012; Bertani, 2016; Lund and Boyd, 2016). In the southeast coastal area of China, ground or near surface geothermal manifestations are widely distributed, such as hot springs and other surface heat They are mainly located in the fractures within igneous rock, such granites. Granites in South China are widely distributed, with an outcropping area of 20,000 km, accounting for about 1/5 of the area, and it is considered to be formed in three phases, i.e., Caledonian, Indosinian and Yanshanian period (Zhou et al, 2006) (Figure 1). Radioactive elements from those granites such as U, Th, K, are important radioactive elements to generate heat by atom decaying. The region is rich in geothermal resources, covering medium-low temperature, medium-high temperature and high-temperature geothermal resources
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