HR: 1330h
AN: T52C-0300    [PDF]
TI: M\'{e}lange as a Plate Boundary Rock and its Seismogenic Roof Thrust - An Example From the Shimanto Belt, Japan
AU: * Kitamura, Y
EM: yujin@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Sato, K
EM: sato@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Ikesawa, E
EM: a-say@@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Kimura, G
EM: gaku@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Kimura, G
EM: gaku@eps.s.u-tokyo.ac.jp
AF: Institute for Frontier Research on Earth Evolution Japan Marine Science and Technology Center, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Kondo, H
EM: h-kondo@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Ujiie, K
EM: ujiiek@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution Japan Marine Science and Technology Center, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Onishi, C T
EM: ctonishi@lbl.gov
AF: Lawrence Berkeley National Laboratory, One Cyclotron Road MS:90-1116, Berkeley, CA 94720 United States
AU: Kawabata, K
EM: kuniyo@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Hashimoto, Y
EM: kuniyo@solid.eps.s.u-tokyo.ac.jp
AF: Department of Natural Environment Science, Kochi University, 2-5-1 Akebono-cho, Kochi, 780-8520 Japan
AU: Mukoyoshi, H
EM: mukoyoshi@jamstec.go.jp
AF: Department of Natural Environment Science, Kochi University, 2-5-1 Akebono-cho, Kochi, 780-8520 Japan
AU: Masago, H
EM: masago@solid.eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AB: A tectonic m\'{e}lange of the ancient accretionary prism of the Shimanto Belt, Japan is investigated to understand a plate boundary process, especially of seismogenic zone in subduction zone. We analyzed deformation fabric, magnetic fabrics, deformation mechanisms and their thermal condition by using vitrinite reflectance. The investigated Mugi m\'{e}lange is located in western Shikoku. In the Mugi m\'{e}lange, systematic fabrics such as Y-P-R fabric formed by micro shear and pressure solution mechanisms are penetrated throughout the m‚lange pile. Magnetic ellipsoids obtained from the anisotropy of magnetic susceptibility (AMS) are highly oblate. Maximum and minimum axes of the ellipsoids are in accordance with shear orientation of m\'{e}lange and mean pole of foliation, respectively. These facts suggest that the Mugi m\'{e}lange was formed as a result of underthrusting of trench filling sediments. Vitrinite reflectance ranges from 2.52% to 3.08%, which correlates to the maximum paleo-temperature of ca. 240 §C to 260 §C. Pseudotachylite of the most reliable seismogenic rock was found from the upper boundary roof fault of the Mugi m\'{e}lange. The fault is composed of about 1 m thick cataclastic zone injected by many veins. The overlying Hiwasa formation is sandstone-dominated and folded coherent piles. The finding of the pseudotachylite in this study area is another example from the ancient accretionary complex after the first one from the Okitsu m\'{e}lange in western Shikoku Island. The setting of the pseudotachylite from the boundary fault between tectonic m\'{e}lange and overlying folded coherent pile is quite similar to that of the first one. There is no thermal gap between the m‚lange and coherent piles but temperature obtained from vitrinite reflectance gradually rises in descending from the coherent piles to the m\'{e}lange beyond the boundary fault. Such setting suggests that paleo-isotherm was parallel to the orientation of the boundary fault. The isotherm in the seismogenic zone is estimated almost in parallel to the plate boundary decollement, therefore the setting of the cataclastic boundary fault including pseudotachylite appears to be a major plate boundary thrust. Consistency of the sense of shear from the Mugi m\'{e}lange and the seismogenic roof fault suggests that a slip along the plate boundary fault was partitioned in space and time: interseismic slip in the m‚lange and seismic slip along the roof fault.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8105 Continental margins and sedimentary basins
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting