HR: 14:55h
AN: T42C-06    [PDF]
TI: Heat flow distribution and thermal regime across the Nankai accretionary complex
AU: * Kinoshita, M
EM: masa@jamstec.go.jp
AF: Japan Marine Science and Technology Center, 2-15Natsushima, Yokosuka, 237-0061 Japan
AU: Goto, S
AF: Aso Volcanological Laboratory, Kyoto University, Aso, Kumamoto, 869-2200 Japan
AU: Hamamoto, H
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo, 113-0032 Japan
AU: Yamano, M
EM: yamano@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo, 113-0032 Japan
AB: The seismogenic feature along subducting plate boundaries is largely controlled by the thermal structure, as well as material difference and hydrological parameters. By April, 2003, the NanTroSEIZE (Nankai Trough Seismigenic Zone Experiment) working group submitted a CDP (Complex Drilling Project) proposal to IODP, consisting of an_h umbrella_h proposal and two proposals. The foremost goal of this CDP proposal is to understand the state and behaviour of seismigenic fault zone. The Nankai accretionary complex is one of the well-known field of accretionary-dominant tectonics; many heat flow data exist, either measured using probes or estimated from gas hydrate BSR depths. Heat flow profile across the Nankai forearc region was obtained off Muroto, and was shown that; 1) heat flow is almost twice as high On the trough axis as that predicted from the age of Shikoku Basin, 2) heat flow gradually decreases landward on the forearc slope, and 3) there are local high heat flow anomalies near the toe of accretionary complex, probably related to the cold seep activities. Gradual decrease in heat flow can be explained be a conductive cooling of the overlying accertionary prism, and a thermal regime of the subducting plate plays a significant role on the overall thermal structure of the accretionary prism. The forearc structure off Kumano;, where we submitted the drilling proposal, is basically similar to that off Muroto. Recent intensive heat flow measurements revealed a heat flow profile off Kumano. On the trough floor heat flow mostly uniform around 100 mW/m2. This is basically consistent with theoretical estimates, if corrected for a sedimentation effect. Heat flow on the forearc slope decreases gradually landward, which can be explained similarly to Muroto. The conductive regime beneath the slope would be supported by the fact that heat flow obtained by the probes is consistent with those estimated from BSR. In the Kumano Basin heat flow is 60-80 mW/m2, with some anomalies on the mud volcanoes. We found, however, that there is significant variation in the bottom water temperatures down to 3000 m water depth. This raises a serious problem when we measure and interpret heat flow in the shallow part of forearc slope, where we expect active faulting causing a surface offset and associated cold seep activities.
DE: 3015 Heat flow (benthic) and hydrothermal processes
DE: 7209 Earthquake dynamics and mechanics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting