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2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 7
Presentation Time: 3:00 PM

SUBMERSIBLE OBSERVATIONS OF THE NANKAI ACCRETIONARY PRISM EXPOSED ALONG THE SHIONOMISAKI SUBMARINE CANYON


ANMA, Ryo, Graduate School of Life and Environmental Sciences, University of Tsukuba, Ten-nodai 1-1-1, Tsukuba, 305-8572, Japan, OGAWA, Yujiro, Earth Evolution Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8572, Japan, MOORE, Gregory, SOEST, University of Hawaii at Manoa, Honolulu, HI HI 96822, KAWAMURA, Kiichiro, Research Group 3, Fukada Geological Institute, 2-13-12 Honkomagome, Bunkyo, Tokyo, 113-0021, Japan, DILEK, Yildirim, Geology, Miami University, 116 Shideler Hall, Oxford, OH 45056, KAWAKAMI, Shunsuke, Geo Environment Consultant, Earth-Appraisal Co., Ltd, 2-4-6 Kanda-awaji, F&F Royal Building 4F, Chiyoda, Tokyo, 101-0063, Japan, SASAKI, Tomoyuki, Ocean Research Institute, University of Tokyo, Minamidai 1-15-1, Nakano, Tokyo, 164-8639, Japan, HIRANO, Satoshi, Marine Work Japan, Department of OD Science Technical Support, c/o JAMSTEC, Yokohama, 236-0001, Japan, HARA, Hidetoshi, Geological Survey of Japan, AIST, Higashi, Tsukuba, 305-8567, Japan and YOKOYAMA, Shunji, Department of Natural Environmental Science, Kochi University, 2-5-1 Akebono, Kochi, Kochi, 780-8520, Japan, anma@arsia.geo.tsukuba.ac.jp

The Shionomisaki submarine canyon cuts five EW-trending major ridges developed in the Plio-Pleistocene Nankai accretionary prism. We observed lithology and structures of the prism on the cross sections across the first (YK06-02 6K#938 by Ogawa), third (YK99-09 6K#522 by Anma) and fifth ridges from the accretion toe in the south. The fifth ridge corresponds to the extension of the Omine ridge where the out-of-sequence thrust (Nankai OOST zone) were detected through CDEX seismic profiles. We observed structures developed around the Nankai OOST zone along the eastern slope the Shionomisaki canyon using submersible Shinkai 6500 during JAMSTEC cruises YK00-08 and YK05-08 (6K#579 by Anma; 6K#889 by Anma; 6K#890 by Moore; 6K#891 by Ogawa). Each dive was designed to start from the canyon bottom, climbing up the canyon slope and end in EW-trending gully developed in the fifth ridge, to obtain a 3D images of the Nankai OOST ridge. Four dives verified that Shionomisaki Canyon exposes sandstone dominant thick turbidite sequences. In contrast to the landward dipping strata expected from the seismic studies, seaward dipping strata were predominant in gently folded, often steeply inclined turbidites. Only near the Nankai OOST zone, extensive activities of fluid seepages were observed demarcated by the presence of chemosynthetic biocommunities, such as Calyptogena and Vesicomyid clams and Vestimentiferan tube worms. Distributions of the chemosynthetic biocommunities were also observed in the north of the Nankai OOST ridge suggesting a development of antithetic fault system. The ridge itself was disrupted by numerous EW-trending gullies where Calyptogena colonies were widely distributed. These gullies must correspond to spray faults that were bifurcated from the main OOST fault. Detailed observations on collected specimens revealed developments of web and vein structures together with black seams. Needle tests indicated that the rocks in the middle part of the OOST ridge is more consolidated compared to those of the north and south.

Session No. 110

T149. Modern to Precambrian Subduction Systems: Convergent Margin Behavior and Evolution Over Geologic Time II
Monday, 23 October 2006: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 38, No. 7, p.275
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