HR: 09:45h
AN: T11E-07 [Abstracts]
TI: Fluid seepage, Deformation, Tectonics and Accretionary Prism Formation in Two Different Settings of the
Nankai Accretionary Prism- Dive Results of YK05-08 Leg 2
AU: * Ogawa, Y F
EM: yogawa@arsia.geo.tsukuba.ac.jp
AF: Univ. Tsukuba, Tennodai 1-1-1, Tsukuba, Iba 305-8572
Japan
AU: Kawamura, K
EM: kichiro@fgi.or.jp
AF: Fukada Geological Inst., Hon-Komagome 2-13-12, Bunkyo, Tok 113-0021
Japan
AU: Anma, R
EM: anma@arsia.geo.tsukuba.ac.jp
AF: Univ. Tsukuba, Tennodai 1-1-1, Tsukuba, Iba 305-8572
Japan
AU: Yokoyama, S
EM: yokoshun@cc.kochi-u.ac.jp
AF: Kochi Univ., Akebonocho, Kochi, Koc 780-8520
Japan
AU: Kawakami, S
EM: ukulele-kawakami@aist.go.jp
AF: Geological Survey of Japan, Higashi, Tsukuba, Iba 305-8567
AU: Moore, G F
EM: gmoore@hawaii.edu
AF: Univ. Hawaii, SOEST, Manoa, Honolulu, HI 96822
United States
AU: Dilek, Y
EM: dileky@muohio.edu
AF: Miami Univ., 116 Shideler Hall, Oxford, OH 45056
United States
AU: , S Y
EM: yogawa@arsia.geo.tsukuba.ac.jp
AF: Univ. Tsukuba, Tennodai 1-1-1, Tsukuba, Iba 305-8572
Japan
AU: , S Y
EM: yogawa@arsia.geo.tsukuba.ac.jp
AF: c/o Earth Evolution, Univ. Tsukuba, Tennodai, Tsukuba, Iba 305-8572
Japan
AB:
Fluid seepages recognized by the presence of bacterial mats, chemosynthetic biocommunities, and carbonate deposits were
critically analyzed in relation to large to small scale deformation features in two different settings of the Nankai
accretionary prism by the manned submersible Shinkai 6500 during JAMSTEC cruise YK05-08 Leg 2. We present dive profiles in
the Shionomisaki and Tenryu submarine canyons that form a 3D transect extending from the outer-arc ridge formed by
out-of-sequence thrusts (OOST ridge) to the prism toe. Ten dives in addition to six previous dives (including three unmanned
ROV Kaiko dives) verified that Shionomisaki Canyon exposes typical accretionary prism features, including regular repetition
of offscraping and underplating structure, whereas Tenryu Canyon shows highly modified structures caused by the collisional
subduction of the Paleo-Zenisu ridge of the Izu island arc. The fluid seepages were observed in three different settings: (1)
just beneath large thrust faults which demarcate the sharp ridge foot; (2) the open fractured crests of the thrust-anticline
folds; and (3) the conspicuous circular expression on the OOST ridge top. The last case and previously known examples in the
forearc basin setting are both examples of large scale seepage that might be due to intermittent, sometimes explosive
methane seepage, whereas the first two cases are of constant flow rate of smaller magnitude. Such differences may be due to
differences in the tectonic setting between the two; the large flow rate example is due to open or strike-slip regime
tectonics where large amount of seepage occurs along the high permeability zones. In contrast, the small flow rate example is
seepage along a thrust, with rather constant (although intermittent during co-seismic stage) flow rate along thrust faults
which are of relatively lower permeability. In addition, we verified some carbonate veins in fractured or sheared rocks along
faults, and the various deformation styles in relation to the fluid seepages in various fashions.
UR: http://www.geo.tsukuba.ac.jp/press_HP/index.html
DE: 3021 Marine hydrogeology
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8010 Fractures and faults
DE: 8045 Role of fluids
SC: Tectonophysics [T]
MN: Fall Meeting 2005