GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 170-1
Presentation Time: 9:00 AM-6:30 PM


WAN, Zhifeng1, WANG, Xianqing1, SHI, Qiuhua2, TIAN, Hongyu3 and XIA, Bin1, (1)School of Marine Sciences, Sun Yat-sen University, Guangzhou, 510006, China, (2)Center for Assessment and Development of Real Estate, Shenzhen, 518034, China, (3)Department of Geology & Geophysics, Texas A&M University, College Station, TX 77843,

Mud volcanoes are a common geological phenomenon in tectonically compressed areas on land and offshore. Mud volcano eruptions hold great significance for research on tectonic activity, sedimentary environment and oil & gas accumulation. Many mud volcanoes have developed in the southern margin of Junggar Basin, Northwest China. In this study, the geochemical characteristics of erupted natural gas and the formation mechanism of these mud volcanoes are analyzed. The major component of gas erupted from the mud volcanoes in the southern Junggar Basin is methane, with an average value of 92.81%. The methane carbon isotope ratios (δ13C1) are between -38.92‰ and -42.82‰, and ethane carbon isotope ratios (δ13C2 ) are -20.50‰ ~ -22.95‰. All these data have similar characteristics to other mud volcanoes around the world. Based on the C1 (methane) / (C2 (ethane) + C3 (propane)) and δ13C1, δ13C2 results, the released gas is a coal-type thermogenic gas. The gas is from a middle-low Jurassic coal-measure source.

Mud volcanoes in the study area are all located along the third anticline belt on the southern margin of the basin. The extensive, thick mudstone in the deep provides a wealth of material for the formation of mud volcanoes. Simultaneously, the overpressure serves as the driving force for the eruption of the mud volcanoes. The torsional-compressional stress field created by the collision between the Indian and Eurasian plates not only enhanced the abnormal formational pressure in the region, but also lead to the development of extensional faults in the core of the Dushanzi Anticline, which served as the conduits for the mud volcanoes. The continuous collision between the Indian and Eurasian plates and the regional torsional-compressional stress field may largely control the cyclical activity of the mud volcanoes and serve as their primary trigger mechanism.