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

作　　者：Sheng XU Lufeng GUAN Maoliang ZHANG Jun ZHONG Wei LIU Xian'gang XIE Congqiang LIU Naoto TAKAHATA Yuji SANO 

机构地区：[1]Institute of Surface-Earth System Science,School of Earth System Science,Tianjin University,Tianjin 300072,China [2]Atmosphere and Ocean Research Institute,The University of Tokyo,Kashiwa,Chiba 277-8564,Japan

出　　处：《Science China Earth Sciences》2022年第1期139-155,共17页中国科学（地球科学英文版）

基　　金：supported by China Seismic Experimental Site(CSES)(Grant No.2019CSES0104);the National Natural Science Foundation of China(Grant No.41930642)。

摘　　要：A 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^(18)_(H_(2)O) and δD_(H_(2)O) 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^(13)C_(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% of the DIC is sourced from the dissolution of shallow carbonate minerals,9±8% formed by pyrolysis of sedimentary organic matter,80±9% derived from deep metamorphic origin and mantle-derived CO_(2).Among them,the deep-sourced CO_(2)in Anninghe fault zones(ANHFZ)is merely metamorphic carbon,whereas ca.12% and ca.88% of the deep-sourced CO_(2)in the XSHFZ are derived from the mantle and metamorphic carbon,respectively.The average deep-sourced CO_(2)flux in the Kangding geothermal field is estimated to be 160 ta^(-1).If all the hot springs in various fault zon

关 键 词：Hot spring Fluid geochemistry Deep-sourced carbon Xianshuihe-Anninghe fault zones Tibetan Plateau 

分 类 号：P593[天文地球—地球化学] X16[天文地球—地质学]