Characteristics and Formation Mechanism of Geothermal Resources in Tectonically Active Regions: A Case Study of the Red River Fault in Western Yunnan Province, China

Geothermal Resource as a kind of renewable energy is widely distributed in tectonically active regions. Using hot springs along the Red River fault zone as an example, this study attempts to analyze the recharge source, recharge elevation, reservoir temperature, circulation depth, mixing of cold groundwater, and heat source through ions, stable hydrogen and oxygen isotopes, and data in previous studies to determine the characteristics and formation mechanism of geothermal resources in tectonically active regions. The findings show that whereas the non-thermal groundwater is abundant in \({\text{HCO}}_{3}^{ - }\)–Ca²⁺, the hot springs in the Red River Fault are predominantly of the \({\text{HCO}}_{3}^{ - }\)–Na⁺ type. The stable hydrogen and oxygen isotopes indicate that the geothermal water is derived from local meteoric precipitation, with a positive excursion in the oxygen isotope indicating that the geothermal water has undergone the strong water-rock interaction under high reservoir temperature. The recharge area is located in the mountainous regions on both sides of the Red River Fault, with recharge elevations ranging from 2252 and 3482 m. The reservoir temperature varies from 67.4 to 173.42°C calculated by the SiO₂ geothermometer, and the associated circulation depth is between 1601.18–5134.12 m. Furthermore, the data of previous studies suggest that the primary heat sources in the study area are mantle-derived heat, crust-derived heat, and radioactive heat, while the composition ratio of various heat sources is different from north to south because of the influence of structural development. The primary determinants of geothermal resources in tectonically active regions are the composition of the heat source and the scale and number of large faults, which in turn affect the temperature of geothermal resources.