Cold seeps and their tectonic implications in the IODP NanTroSEIZE drilling area

Author(s): Ashi, J.; Toki, T.; Kuramoto, S.; Kinoshita, M.
Kumano Dive Scientific Party
Author Affiliation(s): Primary:
University of Tokyo, Ocean Research Institute, Tokyo, Japan
Other:
University of the Ryukyus, Japan
Japan Agency fro Marine-Earth Science and Technology, Japan
Volume Title: AGU 2006 fall meeting
Source: Eos, Transactions, American Geophysical Union, 87( Fall Meeting Suppl.); American Geophysical Union 2006 fall meeting, San Francisco, CA, Dec. 11-15, 2006. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0096-3941 CODEN: EOSTAJ
Note: In English. Accessed on Oct. 16, 2007
Summary: The seismogenic zone drilling gNanTroSEIZE h 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 fs 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.
Year of Publication: 2006
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 16 Structural Geology; Accretionary wedges; Chemosynthetic taxa; Cold seeps; Communities; Drilling; Ecosystems; Faults; Fluid phase; Integrated Ocean Drilling Program; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Ocean floors; Pacific Ocean; Sampling; Scarps; Seismic zoning; Splay faults; Tectonics; West Pacific
Record ID: 2009096186
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.

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