Degassing of deep-sourced CO 2 from Xianshuihe-Anninghe fault zones in the eastern Tibetan Plateau

large number of gases are releasing from the medium-high temperature geothermal fields distributed along the large-scale strike-slip fault zones in the southeastern margin of the Tibetan Plateau. In this study, 11 hot spring water and the associated bubbling gas samples were collected along the Xianshuihe-Anninghe fault zones (XSH-ANHFZ) and analyzed for chemical and isotopic compositions. The δ ^18O_H_2O and δD_H_2O values indicate that hot spring waters are predominantly meteoric origin recharged from different altitudes. Most water samples are significantly enriched in Na + and HCO 3 − due to the dissolution of regional evaporites, carbonates and Na-silicates. 3 He/ 4 He ratios of the gas samples are 0.025–2.73 times the atmospheric value. The 3 He/ 4 He ratios are high in the Kangding region where the dense faults are distributed, and gradually decrease with increasing distance from Kangding towards both sides along the Xianshuihe fault zones (XSHFZ). Hydrothermal fluids have dissolved inorganic carbon (DIC) concentrations from 2 to 42 mmol L −1 , δ 13 C DIC from −6.9‰ to 1.3‰, δ ^13C_CO_2 from −7.2‰ to −3.6‰ and Δ 14 C from −997‰ to −909‰. Combining regional geochemical and geological information, the CO 2 sources can be attributed to deep-sourced CO 2 from mantle and metamorphism of marine carbonate, and shallow-sourced CO 2 from the dissolution of marine carbonate and biogenic CO 2 . The mass balance model shows that 11±6