Citation: | SHI Hongjie, LIU Mingliang, WEI Xing, CAO Yuanyuan, SHANG Jianbo. 2023. Geochemical characteristics and formation mechanisms of the geothermal waters from the Mapamyumco, Tibet. Sedimentary Geology and Tethyan Geology, 43(2): 311-321. doi: 10.19826/j.cnki.1009-3850.2023.04009 |
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.
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Brief tectonic map of the Qinghai-Tibet Plateau (a) (modified from Li, 2002 and Zhang et al., 2018); Geological map of Mapamyumco geothermal field (b) (modified from Wang et al., 2016) and Sampling point location diagram; d: Geological profile (d) (modified from Wang et al. (2016))
Piper diagram of Mapamyumco geothermal water
Na-K-Mg triangular diagram for Mapamyumco geothermal water (The geothermal water data of Yangbajing and Xinzhou were obtained from Guo et al. (2019) and Zhang et al. ( 2022), same as the following)
log(SiO2)-log(K2/Mg) diagram of Mapamyumco geothermal water
Activity plots of Mapamyumco geothermal water (a)K2O-Al2O3-SiO2-H2O; (b)Na2O-Al2O3-SiO2-H2O; (c)MgO-Al2O3-SiO2-H2O; (d)CaO-Al2O3-SiO2-H2O
Composition diagram of Mapamyumco geothermal water
Histograms of the average concentrations of microcomponent in Mapamyumco geothermal water
Si-Enthalpy diagram of Mapamyumco geothermal water (Surface cold water data from Wang et al. (2016))
Conceptual model of formation mechanism of Mapamyumco geothermal system (Some views on stratigraphic lithology and thickness are cited from Wang et al. (2016))