Geochemical characteristics and formation mechanisms of the geothermal waters from the Mapamyumco, Tibet

Tibet is located at the Indian-Eurasia collision orogenic belt, where the tectonic activity is intense, resulting in abundant geothermal resources. In this study, the hot spring samples from the Mapamyumco geothermal field situated at the Ngari Prefecture of Tibet with strong geothermal activity were collected for hydrochemical analysis. Based on the hydrochemical characteristics of the geothermal water, the equilibrium state and temperature of the reservoir was evaluated; the hydrogeochemical processes of deep geothermal fluid was analyzed; and the heat source type of the geothermal system was identified. These results are contributed to clarify its genesis mechanism. This study shows that: the geothermal water in the area are mainly alkaline Cl-Na type or HCO₃-Cl-Na type and acidic SO₄-Na type water; the geothermal water has reached a complete equilibrium state with the thermal reservoir rocks at depth, and the thermal reservoir temperature is about 200℃ based on geochemical geothermometer calculation; surface geothermal manifestations, hydrochemical characteristics of geothermal water, and the reservoir temperatures reveal that Mapamyumco geothermal field is a magmatic geothermal system, and different types of geothermal water are formed by different hydrogeochemical processes during the upward transport of deep parent geothermal fluid along the fault.