Geochemical Characterization Of Soil Gas CO₂ Degassing In The Anninghe-Zemuhe Fault Zone

The Anninghe-Zemuhe fault zone is located on the southeastern edge of the Tibetan Plateau in China,at the intersection of the Chuandian block,Bayanhar block and South China block,and is one of the important active fracture zones along the eastern boundary of the Chuandian rhombic block,with high seismic hazard.In this study,soil gas CO₂ fluxes were investigated in 67 cross-fault profiles with a total of1483 measurement points on the Anninghe-Zemuhe fault zone by static accumulation chamber methods.In addition,soil gas samples were collected on eight profiles using the drainage method to determine carbon isotope values.Based on the measurements,this study provides the first estimate of soil gas fugitive emissions from the AnningheZemuhe fault zone in the southeastern Tibetan Plateau,China,and the results show that:（1）The source of soil gas CO₂ in the Anninghe-Zemuhe fault is derived from sedimentary organic matter,mantle fluid intrusion,and a small amount of atmospheric mixing.However,the crust-mantle fluid intrusion caused by tectonic activity is a critical factor that leads to the spatial distribution changes of CO₂ flux in the AnningheZemuhe fault.（2）The total CO₂ emissions from the Anninghe-Zemuhe fault are approximately1.2 Mt·a^-1,which is equivalent to 15% of the emissions from all volcanoes in China.Therefore,the CO₂ emissions from non-volcanic areas play a significant role in the global carbon cycle.（3）The CO₂ flux of the soil gas near the fault is positively correlated with the seismic activity in the Anninghe-Zemuhe fault.Among which,the earthquake activity is frequent in the southern part of the Zemuhe fault zone and the northern part of the Anninghe fault zone.Earthquake activity promotes the development of fractures in the fault zone and intensifies the water-rock interaction and the degree of rock fragmentation within the fault zone.This,in turn,facilitates the escape of soil gas CO₂ along the fault zone into the atmosphere.In addition,the present study has implications for the scientific aspects of CO₂ leakage from geological reservoir storage.