Fluid geochemical constraints on the geological genesis of carbonate geothermal systems: A case study of Quzhuomu in southern Tibet, China

The southern Tibet in China is characterized by the widespread distribution of high-temperature geothermal systems that possess significant potential for development and utilization. However, current studies in this area have been predominantly focused on geothermal systems with felsic rock reservoirs, while studies on geothermal systems with carbonate reservoirs are scarce. Thus, the large-scale exploitation of such geothermal resources remains limited. In this study, we selected the typical carbonate geothermal system of Quzhuomu in southern Tibet as the research object. Based on the hydrochemical and isotopic (δD, δ¹⁸O, δ¹³C, δ³⁴S, and δ¹¹B) characteristics of the geothermal water, we investigated the geochemical origin of Quzhuomu geothermal water, evaluated the reservoir temperature of the geothermal system, identified its heat source, and ultimately proposed a genetic mechanism for the geothermal system. The chemical components of the geothermal water showed that it primarily originated from the dissolution of marine carbonate rocks and tourmaline granite. Further, an improved mineral assemblage geothermometer showed that the reservoir temperature varied in the range 118–150 °C (mean, 128 °C). Comparative analysis between a typical magmatic geothermal system, the Gudui system, which is also located in the Sangri–Cuona rift zone, and the Quzhuomu system revealed that the strong surface geothermal manifestations and high reservoir temperature in Quzhuomu are closely related to a deep-seated magma chamber. However, the hydrochemical composition of the Quzhuomu geothermal water is not influenced by the magmatic fluids differentiated from the magma. These findings are of great significance with respect to the scientific and rational utilization of geothermal resources in the Quzhuomu geothermal field as they provide valuable insights for estimating the reservoir temperature of carbonate geothermal systems like the Quzhuomu system and investigating their genetic mechanisms.