Cold Seeps and Their Tectonic Implications in the IODP NanTroSEIZE Drilling Area
Abstract
The seismogenic zone drilling "NanTroSEIZE" will start from fall 2007 in the central Nankai Trough, where the seismic rupture zone of the 1944 earthquake extends to the splay fault area and the penetration depth to the target is acceptable for riser drilling technology. The eastern and western parts of the Nankai Trough have been well investigated by the KAIKO projects since 1984, dense seismic surveys and DSDP/ODP drillings. In contrast, the numbers of surveys in the central Nankai are limited before 2000. Series of dive cruises using submersibles since 2001, conducted as site surveys for drilling proposals, revealed the cold seep distributions, fluid chemistry, thermal structure and geological structures. The prism toe is characterized by exposure of semi-consolidated mudstone and no evidence of cold seep activity, although large chemosynthetic biological communities accompany most toe regions at other accretionary prisms. The rocks collected from the toe have low porosities and middle Miocene ages, which correspond to the drilling sample off Shikoku at the depth of 500 meters below the seafloor. It is inferred that the prism toe is suffered from erosion after large-scale frontal accretion. The densest chemosynthetic biological communities are observed along the scarp base of the splay fault. This site is characterized by high heat flow, low salinity pore fluids and high total intensity of natural gamma ray, suggesting up-dip migration of fluids through the fault plane, probably from the deep prism. Recent dives deployed four seep-meters for one year's monitoring and discovered the whitish-yellow colored chimney with living tubeworms. Collected samples had very strong hydrogen sulfide smell. Preliminary onshore study indicates that chimney consists of barite and shows high uranium series radionuclide content. Existence of chimney at the base of the unstable scarp suggests its recent rapid growth probably due to episodic fluid expulsion.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.T11G..07A
- Keywords:
-
- 3022 Marine sediments: processes and transport;
- 3036 Ocean drilling;
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- 3060 Subduction zone processes (1031;
- 3613;
- 8170;
- 8413);
- 3080 Submergence instruments: ROV;
- AUV;
- submersibles