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This Article Figures Only Full Text Full Text (PDF) All Versions of this Article: B26219.1v1 121/11-12/1629    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Kawamura, K. GeoRef GeoRef Citation

Structural architecture and active deformation of the Nankai Accretionary Prism, Japan: Submersible survey results from the Tenryu Submarine Canyon

Kiichiro Kawamura^1,, Yujiro Ogawa^2,, Ryo Anma², Shunji Yokoyama³, Shunsuke Kawakami^4,#, Yildirim Dilek⁵, Gregory F. Moore⁶, Satoshi Hirano^7,*, Asuka Yamaguchi⁸, Tomoyuki Sasaki⁸, YK05-08 Leg 2⁹ and YK06-02 Shipboard Scientific Parties¹⁰

¹ Fukada Geological Institute, 2-13-12 Honkomagome, Bunkyo, Tokyo 113-0021, Japan
² Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, Japan
³ Kochi University, 2-5-1 Akebonocho, Kochi 780-8520, Japan
⁴ Geological Survey of Japan, Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba 305-8567, Japan
⁵ Miami University, 116 Shideler Hall, Oxford, Ohio 45056, USA
⁶ School of Ocean and Earth Science and Technology (SOEST), University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
⁷ IFREE4, Japan Marine-Earth Science and Technology Center, 2-15, Natsushimacho, Yokosuka, 237-0061, Japan
⁸ University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
⁹ Kenichiro Hayashi (University of Tsukuba), Yuji Yagi (University of Tsukuba), Tomohiro Toki (Ryukyu University), Ryota Endo (Inpex Corporation), Teppei Ota (University of Tsukuba), and Satoru Sano (Nippon Marine Enterprises)
¹⁰ Akira Nakamura (University of Tsukuba), Hidetoshi Hara (Geological Survey of Japan), Hiroyuki Mizumoto (Agency for Fishery Research Center), Driss Elouai (Kyoto University), Yoko Michiguchi (University of Tsukuba), Hisatoshi Sato (University of Tsukuba), Ai Togami (University of Tsukuba), Satoru Muraoka (University of Tsukuba), Satoshi Okada (Nippon Marine Enterprises), and Hideki Mukoyoshi (Marine Works Japan) (onshore)

Correspondence: E-mail: kichiro{at}fgi.or.jp

Correspondence: E-mail: fyogawa45{at}yahoo.co.jp

Two research cruises that deployed submersible surveys were undertaken along the Tenryu Submarine Canyon to directly observe the structural architecture of the eastern Nankai Accretionary Prism off the coast of southern Japan. The surveys have demonstrated that the accreted sediments are strongly deformed turbidite sequences that occur in repeated thrust-anticline structures. From the leading edge of the prism near the trench toward the arc, the following deformation zones have been identified within the prism: Frontal Thrust zone, Prism Toe zone, Imbricate Thrust zone, and Tokai Thrust zone (or out-of-sequence thrust or OOST zone). The Frontal Thrust zone is characterized by debris deposits within the hanging wall that have an age of 0–0.43 Ma, as determined from radiolarian biostratigraphy. The Prism Toe zone is characterized by unconsolidated turbidite sequences that are 1.98–3.4 Ma; these sequences are cut by normal and thrust faults. The Imbricate Thrust zone includes consolidated muddy layers and unconsolidated sandy layers that contain numerous fracture cleavages. The OOST zone consists of highly deformed consolidated sediments, ranging in age from 0.18 to 1.03 Ma. From the Prism Toe zone to the Imbricate Thrust zone, the uniaxial compressive strength increases gradually from 0.5–3.0 to 1.0–6.0 MPa, while the anisotropy of magnetic susceptibility changes from oblate to prolate shapes, and porosity decreases from 40%–50% to 30%–50%. These data indicate that the eastern Nankai Accretionary Prism appears to have been deformed toward the Imbricate Thrust zone just south of the OOST. Stable isotope analyses of calcite veins and calcite cement of the sandstone samples from the Tokai Thrust zone have shown that fluid temperatures for calcite precipitation were 24–63 °C in the OOST zone. The occurrence of highly deformed and consolidated rocks within the Nankai Accretionary Prism likely resulted from tectonic transportation of deeply buried rocks along major out-of-sequence thrust faults, such as the Tokai OOST. We infer therefore that out-of-sequence thrust faults play a major role in transporting deeply buried, deformed rocks in accretionary prisms to the shallower depths and even to the seafloor during ongoing subduction.