HR: 1340h
AN: T13B-0463    [Abstracts]
TI: Structural Architecture of the Nankai Accretionary Prism along the Tenryu Submarine Canyon as Revealed in Submersible Studies
AU: * Kawamura, K
EM: kichiro@fgi.or.jp
AF: Fukada Geological Institute, 2-13-12 Honkomagome Bunkyo, Tokyo, 113-0021 Japan
AU: Ogawa, Y
EM: yogawa@arsia.geo.tsukuba.ac.jp
AF: University of Tsukuba, 1-1-1 Tennodai Tsukuba, Ibaraki, 305-8572 Japan
AU: Anma, R
EM: anma@arsia.geo.tsukuba.ac.jp
AF: University of Tsukuba, 1-1-1 Tennodai Tsukuba, Ibaraki, 305-8572 Japan
AU: Dilek, Y
EM: dileky@muohio.edu
AF: Miami University, 116 Shideler Hall, Oxford, OH 45056 United States
AU: Yokoyama, S
EM: yokoshun@cc.kochi-u.ac.jp
AF: Kochi University, 2-5-1 Akebono Kochi-shi, Kochi, 780-8520 Japan
AU: Kawakami, S
EM: ukulele@aist.go.jp
AF: Geological Survey of Japan, 1-1-1 Higashi Tsukuba, Ibaraki, 305-8567 Japan
AB: Previous geologic structures of the Nankai accretionary prism have consisted mainly of seismic data analysis of 3D macrostructures and structural analysis of 1D vertical microstructures in drilled core samples. In this study, we have examined the structural architecture of the prism using the manned submersible _gShinkai 6500_h and the unmanned submersible _gKaiko_h operated by JAMSTEC. The accretionary prism strata exposed in the NNE-running Tenryu Canyon are deeply incised, providing excellent exposures in 3D along the canyon walls, locally up to 1000 meters in height. We collected structural data and rock samples successively from the shallower fore-arc basin deposits down to 1000 m deeper into the prism proper during the course of our studies. A total of eleven dive surveys were performed during four consecutive cruises, R/V Kairei-Kaiko (KR97-05 and 97-06) and R/V Yokosuka-Shinkai 6500 cruises (K03-03 and YK05-08). The unmanned Kaiko dived three times at the mouth of the Tenryu Canyon, and the manned Shinkai dived eight times at the sidewalls of the canyon. The strata in the Nankai prism are composed mainly of gently folded turbiditic beds, approximately several cm to several 10s of cm in thickness. Muddy layers in these turbidites commonly display vein structures and fracture cleavages, oriented approximately N-S and E-W near the large thrust faults. We observed five ENE-WSW-running large thrust faults associated with fault propagation folds (anticlines), collectively forming asymmetric topographic ridges. Observed thrust faults are mostly gently dipping (low-angle), although high-angle thrust faults with high asymmetric ridges also occur as an artifact of late-stage deformation caused by the subduction-collision of the Paleo-Zenisu ridge of the Izu Island Arc. The structural architecture of the Nankai accretionary prism along the Tenryu Canyon is a result of the combined effects of tectonic accretionary processes, including offscraping and underplating, and an arc-arc collision.
UR: http://www.geocities.jp/mochitukitaikai/
DE: 3022 Marine sediments: processes and transport
DE: 3030 Micropaleontology (0459, 4944)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 5112 Microstructure
SC: Tectonophysics [T]
MN: Fall Meeting 2005