Composition and exhalation flux of gases from mud volcanoes in Taiwan

Abstract

Many mud volcanoes are distributed along the tectonic sutures in southern Taiwan and can be divided into five zones based on their relative positions in different tectonic domains. Most active mud volcanoes are exhaling methane-dominated gases. Nevertheless, some gases show unusual carbon dioxide-dominated and/or nitrogen-excess compositions. This implies that there are multiple sources for the gas compositions of mud volcanoes in Taiwan. For better understanding the total amount of exhalation gases and its flux, the gas flow and compositions were continuously measured in the interval of two minutes at Chung-lun (CL) bubbling mud pool for a few months. The major compositions of gases exhaling from this site were 75$90% of CO 2 and 5$12% of CH 4 . The amount of gases exhaling from the mud pool can be estimated to be about 1.4 ton/year for CH 4 and 28 ton/year for CO 2 , respectively. The preliminary results of exhaling gas flux from the major vents of representative active mud volcanoes, yielded an estimated total CH 4 output of the mud volcanoes in Taiwan of ca. 29 ton/year during quiescent period.

Distribution and Characters of Gas Hydrate Offshore of Southwestern Taiwan

“…Muddy fluids emitted from active mud diapirs form mud volcanoes on the seafloor Chiu et al 2006). Most of the diapiric ridges trend in NNE-SSW direction, parallel to the structural trend of the folds and thrust faults and mud volcanoes on land Taiwan (Yang et al 2004), and many diapiric ridges connect to anticlinal structures on land SW Taiwan (Huang 1995;Chuang 2006). …”

Extremely High Methane Concentration in Bottom Water and Cored Sediments from Offshore Southwestern Taiwan

“…This may explain the presence of submarine mud volcanoes in offshore southwestern Taiwan (e.g., Chou et al 2000;Chiu et al 2006), which have been considered to be related to on-land mud volcanoes (Yang et al 2003(Yang et al , 2004 by Yeh (2003). Moreover, these methane-rich fluids influence the composition of pore water and bottom seawater around these gas-expelling craters.…”

Methane Venting in Gas Hydrate Potential Area Offshore of SW Taiwan: Evidence of Gas Analysis of Water Column Samples

“…Numerous mud volcanoes and diapiric intrusion have been found along tectonic structures both on-shore and offshore of southwestern Taiwan (e.g., Chow et al 2000;Yang et al 2004;Chiu et al 2006). The gases vented from on-shore mud volcanoes are dominated by methane (Yang et al 2004) and exhibit mainly typical crustal helium isotopic ratios, i.e., lower 3 He/ 4 He ratio ( < 0.2 times of R A , R A is the air ratio; Yang et al 2003b). However, the composition and flux of gases released from the Chung-lun mud pool showed significant variation and are considered to be controlled by tectonic structures (Yang et al 2003b) and related to the changes of local stress and strain .…”

“…This collision has propagated progressively southward, thus the northern part of the arc has already been accreted onto the continental margin resulting in the formation of an accretionary prism in southwestern Taiwan (Teng 1990;Huang et al 1997;Liu et al 1997). Numerous mud volcanoes and diapiric intrusion have been found along tectonic structures both on-shore and offshore of southwestern Taiwan (e.g., Chow et al 2000;Yang et al 2004;Chiu et al 2006). The gases vented from on-shore mud volcanoes are dominated by methane (Yang et al 2004) and exhibit mainly typical crustal helium isotopic ratios, i.e., lower 3 He/ 4 He ratio ( < 0.2 times of R A , R A is the air ratio; Yang et al 2003b).…”