Tectonic Controls on Gas Venting in the Back-arc Basin of the Mid-Okinawa Trough
Abstract
Gas venting in marine environment is an important geological process of transferring methane from marine sediments to ocean. Massive methane escaping from marine sediments could cause the de-oxygenation and the acidification of the ocean and possibly accelerate climatic warming if entered the atmosphere. However, the relationship between active faulting and the formation of gas venting is only partially understood, though they have been often associated. Here we use the multi-channel seismic (MCS) and the multi-beam echo-sounder (MBES) data acquired between 2013 and 2016 to identity what we interpret to be multiple gas venting in the Mid-Okinawa Trough which is an incipient back-arc basin in the Northwestern Pacific. The features associated with gas venting include a set of gas flares in the water column, high-backscattering patches and domes at the seabed and columnar acoustic anomalies below the domes. There are 129 flare-shaped acoustic anomalies (previously termed gas flares) at the water depths of 750-1192 m and they can reach as shallow as 394 m below the sea level. Their bases are often located within the areas of the seabed that have high-backscattering values. 34 of the gas flares are located above the domes and their surrounding areas. The seismic cross sections show that the columnar acoustic anomalies, which are interpreted as vertical migration conduits, are right below these domes. The spatial relationship between the features mentioned above supports of the presence of rising of free gases through the shallow sediments and in the water column. The MCS and MBES data together image the pattern of the NE-SW oriented normal faults in the study area and show that most of gas flares are located along the present faults reaching the seabed. The δ13CCH4 and δDCH4 values (-79.4‰ to -34.6‰ and -241.9‰ to -159.6‰, respectively) from pore water at four sites suggest that methane vented to the surface has the shallow biogenic and deep thermogenic source. Methane produced at different depths fed the gas venting by migrating along the fault planes. We propose that normal faulting driven by rifting provides additional migration pathways for the free gases and thus controls the distribution of most of the gas vents in the Mid-Okinawa Trough.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMOS43B1698L
- Keywords:
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- 3002 Continental shelf and slope processes;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3004 Gas and hydrate systems;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3050 Ocean observatories and experiments;
- MARINE GEOLOGY AND GEOPHYSICS