HR: 1340h
AN: T53B-1420    [Abstracts]
TI: Variations in fluid pressure and fluid source near the updip limit of the seismogenic zone: An example from the Shimanto accretionary complex, southwest Japan
AU: * Yamaguchi, A
EM: asuka@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo, Science Building 1-849 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Ujiie, K
EM: ujiiek@jamstec.go.jp
AF: Institute for Research on Earth Evolution, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Kimura, G
EM: gaku@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo, Science Building 1-849 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Kimura, G
EM: gaku@eps.s.u-tokyo.ac.jp
AF: Institute for Research on Earth Evolution, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AB: The ancient underplated-related fault (or subduction thrust) is well developed in the Shimanto accretionary complex, southwest Japan. To better understand how fluid affects the faulting near the updip limit of the seismogenic zone (i.e. 5-7 km depth, 130-200 ° C) in the subduction zone, we examined the fault-fill and network veins developed within the fault zone. The fault-fill veins are marked by implosion breccia, which occur along the dilational jogs. The network veins are developed in the damage zones. The characteristics of faulting-related fluid flow reconstructed by lines of structural, thermometric and isotopic evidence are as follows: (1) The fault-fill and network veins show crosscutting relationship, which were formed by repeated crack opening; (2) The orientation of network veins sub-perpendicular to the fault plane, suggest the thrust faulting under low shear stress probably associated with high fluid pressure; (3) Variations in homogenization temperatures of fluid inclusions likely reflect significant drop in fluid pressure during opening of extension fracture at the dilational jogs, which is consistent with decrease in calcite solubility due to fluid pressure (or CO2 pressure) reduction; (4) Carbon and oxygen isotopic compositions of vein calcite are obviously different between fault-fill and network veins, suggesting the temporal changes in fluid compositon; and (5) The calculated oxygen isotopic composition of vein-forming fluid is +5 to +9 permil (SMOW), possibly representing dehydration of hydrous mineral (e.g. clay minerals) due to metamorphic and/or diagenetic reaction at depths. These features clearly show variations in fluid pressure and fluid source during the faulting near the updip limit of the seismogenic zone, possibly representing the earthquake cycle in subduction plate boundary.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8021 Melanges
DE: 8045 Role of fluids
SC: Tectonophysics [T]
MN: Fall Meeting 2005