Discovery and genesis of high-temperature geothermal energy adjacent to the South Tibetan Detachment System, central Himalaya

The 193 °C geothermal fluids have been newly discovered in Lolo at the depth of 350 m through drilling in May 2024, identifying the occurrence of high-temperature geothermal energy adjacent to the South Tibetan Detachment System. Studies on such geothermal field will provide new insights into the distribution of high-temperature geothermal systems in Xizang. Here, we present element geochemistry (major and trace elements) and multi-isotope (H, O, and Sr) compositions of thermal spring, geothermal well, river, and snow waters to reveal the formation of the Lolo high-temperature geothermal system. The major elemental results of water samples show that the Lolo geothermal waters belong to Na-HCO3 type, mainly affected by carbonate dissolution, silicate weathering, and cation exchange through water-rock interaction. The positive correlations of trace alkali metals (Li, Rb, and Cs) and metalloid (B) with Cl indicate that these elements were derived from the same source, mainly released from Himalayan leucogranites with minor slate and limestone via water-rock reaction. The interpretation is further supported by varied Sr isotopic values recorded in geothermal waters. Combination of major and trace elements, and H-O isotopic results reveals that the geothermal waters were sourced from meteoric precipitation from the eastern parts of the region at an elevation of ∼4733 m, which were conducted along the WE-trending fault (F5). The temperature of deep geothermal reservoir was calculated to be 204–205 °C by using quartz geothermometers, and the temperature of shallow reservoir has been calculated to be 100–130 °C based on chalcedony geothermometers and computed mineral saturation index by PHREEQC. The shallow thermal fluids were suggested to be formed by mixing of deep thermal fluids with cold groundwater near to the surface, evidenced by positive linear correlations between B and Cl. The deep-circulated meteoric waters have been heated by partial melting and the circulation depth is up to ∼5 km. These new findings help us understand the formation of Lolo geothermal field and also provide guides in high-temperature geothermal resources exploration adjacent to the South Tibetan Detachment System.