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<p>This study examines the geochemical characteristics of soil gas emissions along the Chihshang Fault (CSF) in eastern Taiwan, with a focus on carbon dioxide (CO<sub>2</sub>) flux, soil gas isotopes, and gas composition. Situated within the tectonically active boundary between the Eurasian Plate and the Philippine Sea Plate, the CSF forms part of the Longitudinal Valley Fault system and is characterized by complex fault structures and high seismic activity. Previous research suggested a potential for mantle-derived gas emissions in this area, motivating this comprehensive study aimed at quantifying CO<sub>2</sub> flux, identifying gas sources, and evaluating the role of the fault in facilitating gas migration. Soil gas surveys were conducted over a 3&#xa0;km<sup>2</sup> area, employing CO<sub>2</sub> flux measurements, radon analysis, helium isotopes, and carbon isotope analyses to discern gas sources. The detection of high CO<sub>2</sub> fluxes along the fault and its branches suggests that the CSF plays a significant role in promoting the upward migration of crustal gases. The study categorizes soil gas emissions into deep-sourced and shallow-sourced groups: deep-sourced gases are characterized by high CO<sub>2</sub> flux, crustal helium isotope ratios, and elevated radon levels, indicative of an origin within the deep crust. In contrast, shallow-sourced gases exhibit lower CO<sub>2</sub> flux and isotopic signatures consistent with biogenic sources, likely influenced by the lithology of the Lichi mélange. Findings indicate that CO<sub>2</sub> emissions from the CSF reach approximately 78 tons/day, with an estimated annual emission of 0.028 Mt. When extrapolated to encompass all active faults in Taiwan, these emissions constitute a relatively small fraction of the country’s total CO<sub>2</sub> output. The results highlight the role of the CSF and its western subsidiary faults as conduits for crustal gas migration, with limited mantle contributions. Under ongoing compressive tectonic stress, the CSF may continue to generate new subsidiary faults near the surface. Overall, this study offers valuable insights into gas emission patterns along active faults, enhancing the understanding of fault-related degassing in tectonically active regions. </p>

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Geochemical characteristics and origins of CO2 emissions within the tectonic collision boundary of the Chihshang fault, eastern Taiwan

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年5月12日

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  • Ching-Chou Fu,
  • Chung-Hsiang Mu,
  • Hao Kuo-Chen,
  • Pei-Ling Wang,
  • Li-Hung Lin,
  • Vivek Walia,
  • Kuo-Hang Chen,
  • Kuo-Wei Wu

摘要

This study examines the geochemical characteristics of soil gas emissions along the Chihshang Fault (CSF) in eastern Taiwan, with a focus on carbon dioxide (CO2) flux, soil gas isotopes, and gas composition. Situated within the tectonically active boundary between the Eurasian Plate and the Philippine Sea Plate, the CSF forms part of the Longitudinal Valley Fault system and is characterized by complex fault structures and high seismic activity. Previous research suggested a potential for mantle-derived gas emissions in this area, motivating this comprehensive study aimed at quantifying CO2 flux, identifying gas sources, and evaluating the role of the fault in facilitating gas migration. Soil gas surveys were conducted over a 3 km2 area, employing CO2 flux measurements, radon analysis, helium isotopes, and carbon isotope analyses to discern gas sources. The detection of high CO2 fluxes along the fault and its branches suggests that the CSF plays a significant role in promoting the upward migration of crustal gases. The study categorizes soil gas emissions into deep-sourced and shallow-sourced groups: deep-sourced gases are characterized by high CO2 flux, crustal helium isotope ratios, and elevated radon levels, indicative of an origin within the deep crust. In contrast, shallow-sourced gases exhibit lower CO2 flux and isotopic signatures consistent with biogenic sources, likely influenced by the lithology of the Lichi mélange. Findings indicate that CO2 emissions from the CSF reach approximately 78 tons/day, with an estimated annual emission of 0.028 Mt. When extrapolated to encompass all active faults in Taiwan, these emissions constitute a relatively small fraction of the country’s total CO2 output. The results highlight the role of the CSF and its western subsidiary faults as conduits for crustal gas migration, with limited mantle contributions. Under ongoing compressive tectonic stress, the CSF may continue to generate new subsidiary faults near the surface. Overall, this study offers valuable insights into gas emission patterns along active faults, enhancing the understanding of fault-related degassing in tectonically active regions.