Abstract
The Gudui-Riruo geothermal system, located in the southern Tibet, exhibits higher temperatures compared with other geothermal systems at similar depths in China. However, the origin and circulation mechanisms of the geothermal water in the Gudui-Riruo geothermal field remain unclear. Therefore, this study offers a detailed comparative analysis of hydrochemical and hydrogen-oxygen isotopic characteristics of geothermal waters from five geothermal manifestation zones within the Gudui-Riruo geothermal system, aiming to improve the understanding of their genesis and circulation mechanisms. Hydrochemical characteristics indicate that the geothermal waters are notable variations in different manifestation zones in the study area. Na-Cl-type geothermal waters are present in the Buxionglanggu (BXLG), Shagalangga (SGLG), and Babudemi (BBDM) zones, whereas Na·Ca-Cl·HCO(3) type waters are distributed in the Chaka (CK) and Riruo (RR) zones. The geothermal waters originate from a common deep parent geothermal fluid with the Cl concentration and enthalpy of 645 mg/L and 1757 J/g °C, respectively. Hydrogen and oxygen isotopic characteristics reveal that the primary source of the Gudui-Riruo geothermal waters is high-altitude atmospheric precipitation, with about 14% to 18% attributed to mixing with magmatic water. Based on the geological background of the southern Tibetan Plateau and the hydrochemical and isotopic characteristics of the geothermal waters in the study area, a genesis circulation model for the Gudui-Riruo geothermal system is established. Infiltrating meteoric water mixes with residual magmatic fluid to create the parent geothermal fluid, which then ascends along fractures and experiences various cooling processes, resulting in hot springs that exhibit varying hydrochemical characteristics. Based on hydrochemical analysis, five cooling processes have been identified for geothermal waters ascending from the reservoir to the surface: conductive cooling, adiabatic cooling, mixing with cold groundwater, and combinations of these processes.