Earth Science Frontiers ›› 2025, Vol. 32 ›› Issue (3): 334-349.DOI: 10.13745/j.esf.sf.2025.3.68

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Preliminary study on hydrothermal CO2 flux from active fault zones in southern Tibet: Constraints from travertine geochronology and geochemistry

CAO Chenxi1(), ZHANG Maoliang1,*(), WANG Lisheng2, WANG Xuefeng2, DUAN Wuhui2, XU Sheng1   

  1. 1. School of Earth System Science, Tianjin University, Tianjin 300072, China
    2. State Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences,Beijing 100029, China
  • Received:2025-02-07 Revised:2025-02-21 Online:2025-03-25 Published:2025-04-20

Abstract:

Active tectonics in southern Tibetan Plateau create favorable pathways for the formation and release of deeply-sourced CO2-rich fluids, making it a globally significant carbon source at present. However, in the case of southern Tibetan Plateau, estimating the deep carbon outgassing flux for tectonic degassing in the geological past remains challenging but is crucial for reconstructing the geological carbon cycle that operates in the India-Asia continental collision zone. Here, we report, for the first time to our knowledge, the hydrothermal CO2 fluxes during the Quaternary period for representative active faults in southern Tibetan Plateau based on an integrated dataset of U-Th ages, mineralogical, elemental, and C-O isotopic compositions of travertine deposits. The U-series dating results show that the travertines were formed during the Middle Pleistocene to Holocene periods (267.3-1.8 kyr B.P.), with the deposition rates ranging approximately from 0.02 to 1.49 mm·yr-1. These Quaternary travertines, primarily composed of calcite with rare samples exhibiting mixed calcite and aragonite in mineral assemblage, have an average CaCO3 content of 94.2 wt.%. Carbon and oxygen isotopic compositions (δ13CV-PDB=-3.1‰ to +8.6‰; δ18OV-SMOW=-0.5‰ to +15.0‰) suggest a thermogenic origin influenced by varying degrees of CO2 degassing, spring boiling, and evaporation, with deep metamorphic CO2 being the primary carbon source of the travertines. Based on the volume, porosity, CaCO3 content, and deposition ages of the travertines, the CO2 outgassing fluxes accompanied with travertine deposition are estimated to be in the magnitude of 104 to 106 mol·km-2·yr-1 for the study areas, comparable to some travertine deposits in tectonically active regions of the central and western Italy. Our results provide new insights into the deposition ages, genesis, and CO2 outgassing fluxes of Quaternary travertines in southern Tibetan Plateau and would contribute to our understanding of geological carbon cycle in the India-Asia continental collision zone.

Key words: travertine, U-Th dating, carbonate geochemistry, deep carbon release, southern Tibetan Plateau

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