CH4and CO2Emissions From Mud Volcanoes on the Southern Margin of the Junggar Basin, NW China: Origin, Output, and Relation to Regional Tectonics

The concentrations, isotope ratios, and fluxes of CH4and CO2from mud volcanoes measured during a field survey on the southern margin of the Junggar Basin are reported. The origins and outputs of CH4and CO2from the four mud volcanoes are assessed, and the relationship between the characteristics of degassing and regional tectonics is discussed. The geochemical data indicate that thermogenic gases derived from the hydrocarbon reservoirs beneath anticlines could be the main source of the CH4emitted from the mud volcanoes and that hydrocarbon degradation by microbes and carbonate decomposition could be the primary contributors to CO2emissions from the soil in and around the mud volcanoes. Microseepage was the main mode of release for CH4and CO2from the mud volcanoes. The total CH4output from the mud volcanoes was 147.83 ton/year, comparable to that from mud volcanoes elsewhere. The total output of CO2from the mud volcanoes was 603.96 ton/year, which suggests that more attention should be paid to CO2from mud volcanoes. The CH4and CO2outputs from the mud volcanoes, and from the Xihu fold in the four anticlines, decreased from south to north. This observation is consistent with the intensity of regional tectonic activity, which weakens from south to north. The results suggest that regional compression is the major triggering mechanism for CH4and CO2emissions from the mud volcanoes. The geochemistry of the gases and fluxes of CH4and CO2from mud volcanoes in the southern margin of the Junggar Basin were investigatedMicroseepage is the main mode for CH4and CO2emissions from the mud volcanoes; methane output from the mud volcanoes is comparable to that from other mud volcanoes worldwide; the high output of CO2suggests that CO2production by mud volcanoes requires more attentionRegional compression might be the major triggering mechanism for CH4and CO2emissions from mud volcanoes