Yi Liu¹, Maoliang Zhang¹, Wei Liu², Xian-Gang Xie³, Sheng Xu¹

(¹Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; ²College of Resources and Environmental Engineering, Inner Mongolia University of Technology, Hohhot 010051, China; ³State Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China)

Abstract: Tectonic degassing along active fault zones in continental collisional orogens has attracted increasing attention due to its critical role as a major pathway for the release of deeply sourced CO₂ to Earth’s surface. Active faults are generally characterized by three forms of deep CO₂ emissions (i.e., dissolved inorganic carbon (DIC) in spring water, bubbling gases, and diffuse soil micro-seepage), but their fluxes were rarely estimated simultaneously in a single study area. Here, we focus on the Sangri-Cona rift (SCR) in the southern Tibetan Plateau, investigating the source and geochemical process of geothermal gases and carrying out the estimation of three forms of deep carbon fluxes. The ³He/⁴He values (0.03-0.07 Ra) of the bubbling gases in the SCR indicate a typical crustal source. The deeply sourced CO₂ fluxes from the spring water, bubbling gases, and diffuse soil CO₂ in the SCR are estimated to be 1586±26 t yr⁻¹, 801±54 t yr⁻¹, and 0.46±0.09 Mt yr⁻¹, suggesting that diffuse soil CO₂ emissions account for >99% of the total deep CO₂ output of the SCR. In the Himalayan block, deeply sourced CO₂ in the geothermal fluids mainly originates from metamorphic decarbonation of crustal carbonaceous rocks at different depths. Our results indicate that the SCR serves as an excellent example for the Himalayan orogenic CO₂ degassing associated with post-collisional lithospheric extension.

Keywords: He-C isotopes; Soil CO₂; Deep carbon; Sangri-Cona rift; Tibetan Plateau

Author Profile (first author):

Yi Liu, Female, PhD Candidate, mainly engaged in fluid geochemistry research. E-mail: yi_liu@tju.edu.cn