HR: 1340h
AN: OS23A-1043    [Abstracts]
TI: BSR 3D Architecture and Heat Flow Derivation on the Kumano Forearc Basin - Nankai Margin
AU: * GAILLOT, G
EM: ggaillot@jamstec.go.jp
AF: Yokohama Institute for Earth Sciences (YES) Japan Agency for Marin-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: KURAMATO, S
EM: s.kuramoto@jamstec.go.jp
AF: Center for Deep Earth Exploration (CDEX) Japan Agency for Marin-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: MOORE, G F
EM: gmoore@jamstec.go.jp
AF: Center for Deep Earth Exploration (CDEX) Japan Agency for Marin-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AB: 3D seismic reflection data acquired on the Kumano forearc basin to guide the NanTroSEIZE drilling project on the Nankai accretionary prism reveal a high amplitude bottom simulating reflector (BSR) interpreted as marking a phase transition between methane hydrate and free gas in the pore space of both accreted and forearc sediments. Detailed 3D mapping of the BSR shows lateral variations of the reflection pattern in terms of continuity and amplitude correlated to the properties of the cross-cut sediments suggesting the greater role taken by the permeable layers in the migration of free gas produced within the column until the Base of the Hydrate Stability Zone (BHSZ). The BSR is locally underlined by a lower bright reflection with the same polarity as the seafloor. Its context of appearance above possible deep fluid drains better suggest a gas-water contact reflection rather than a remnant BSR from a former position. We also determine the depth of the hydrate-gas phase boundary in order to estimate the geothermal gradient and hence the regional heat-flow in 3D. It offers information about active processes occurring in this area over the downgoing plate. In sub-surface, erosion-sedimentation and shallow faulting take an important part of the calculated BSR derived heat flow. However, we also evidenced the impact of deeper processes related with fluid migration and initiation of mud diapirism. The results suggest a model of the Kumano Basin with free gas produced by biodegradation within the shallow sedimentary column and then stacked under the BHSZ after migration along permeable layers. In addition, possible important amount of gas-charged fluids migrates from deeper depths within accreted sediments and along deep faults to reach the BHSZ with generation of a lower brilliant reflector at the base of the gas-charged fluids – pure water interface.
DE: 3004 Gas and hydrate systems
DE: 3015 Heat flow (benthic)
DE: 3025 Marine seismics (0935, 7294)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting