HR: 1340h
AN: T53B-1421    [Abstracts]
TI: A Hydrous Seismogenic Fault Rock Indicating A Coupled Lubrication Mechanism
AU: * Okamoto, S
EM: shinya@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, Science Building#1,7-3-1Hongo, 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, Science Building#1,7-3-1Hongo, Bunkyo-Ku, Tokyo, 113-0033 Japan
AU: Kimura, G
EM: gaku@eps.s.u-tokyo.ac.jp
AF: The Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15Natsushima, Yokosuka, Kanagawa, 237-0061 Japan
AU: Takizawa, S
EM: takizawa@arsia.geo.tsukuba.ac.jp
AF: Institute of Life and Environmental Sciences, University of Tukuba, 1-1-1Tennodai, Tsukuba, Ibaraki, 305-8577 Japan
AU: Yamaguchi, H
EM: harukay@jamstec.go.jp
AF: The Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15Natsushima, Yokosuka, Kanagawa, 237-0061 Japan
AB: In the seismogenic subduction zone, the predominant mechanisms have been considered to be fluid induced weakening mechanisms without frictional melting because the subduction zone is fundamentally quite hydrous under low temperature conditions. However, recently geological evidence of frictional melting has been increasingly reported from several ancient accretionary prisms uplifted from seismogenic depths of subduction zones (Ikesawa et al., 2003; Austrheim and Andersen, 2004; Rowe et al., 2004; Kitamura et al., 2005) but relationship between conflicting mechanisms; e.g. thermal pressurization of fluid and frictional melting is still unclear. We found a new exposure of pseudotachylyte from a fossilized out-of-sequence thrust (OOST) , Nobeoka thrust in the accretionary complex, Kyushu, southwest Japan. Hanging-wall and foot-wall are experienced heating up to maximum temperature of about 320/deg and about 250/deg, respectively. Hanging-wall rocks of the thrust are composed of shales and sandstones deformed plastically. Foot-wall rocks are composed of shale matrix m‚lange with sandstone and basaltic blocks deformed in a brittle fashion (Kondo et al, 2005). The psudotachylyte was found from one of the subsidiary faults in the hanging wall at about 10 m above the fault core of the Nobeoka thrust. The fault is about 1mm in width, and planer rupture surface. The fault maintains only one-time slip event because several slip surfaces and overlapped slip textures are not identified. The fault shows three deformation stages: The first is plastic deformation of phyllitic host rocks; the second is asymmetric cracking formed especially in the foot-wall of the fault. The cracks are filled by implosion breccia hosted by fine carbonate minerals; the third is frictional melting producing pseudotachylyte. Implosion breccia with cracking suggests that thermal pressurization of fluid and hydro-fracturing proceeded frictional melting.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005