HR: 1330h
AN: T52B-0266    [PDF]
TI: Discontinuous accretion in the Tokai segment of Nankai Trough.
AU: Martin, V
EM: vmartin@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: Henry, P
EM: henry@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005 France
AU: * Lallemant, S J
EM: siegfried.lallemant@geol.u-cergy.fr
AF: Departement des Sciences de la Terre, Universite de Cergy-Pontoise, 2 avenue du Parc, 8 Le Campus, Bat I, Cergy-Pontoise, 95031 France
AU: Dessa, J
EM: dessa@obs.vlfr.fr
AF: Geosciences Azur, Obervatoire de Villefranche sur mer, La Darse BP 48, Villefranche-sur-Mer, 06235 France
AU: Noble, M
EM: noble@
AF: Centre de Geophysique, Ecole des Mines de Paris, 35 rue St Honore, Fontainebleau, 77305 France
AU: Operto, S
EM: operto@obs.vlfr.fr
AF: Geosciences Azur, Obervatoire de Villefranche sur mer, La Darse BP 48, Villefranche-sur-Mer, 06235 France
AB: The Eastern Nankai Margin was investigated within the framework of the KAIKO-SFJ project by 3D reflection imaging and dense OBS surveying, which yield complementary images of the margin above the seismogenic zone. The margin is divided in three units, the forearc basin, the active splay fault zone, and the active accretionary wedge. The forearc basin sediments are deposited over Eocene (Shimanto) accretionary wedge. The observed structure, age constrains from drilling, and seafloor sampling indicate accretion was not steady state and a scenario consistent with the plate tectonic context is proposed. The initial stage is the massive Eocene to Oligocene accretion of the Shimanto belt accretionary complex. Our interpretation of the seismic profiles is in good agreement with a rate of subduction in Nankai going through a relatively stagnant phase 14-9 Ma but then increasing again at 8-5 Ma. Accretion likely restarted during the Late Miocene, forming a wedge that now corresponds to the active splay fault zone. This wedge is overlain by forearc basin and slope deposits straddling the Pliocene-Miocene boundary contemporary with the middle forearc sequence. The small active accretionary complex is estimated to have started not later than 2 Ma and more probably less than 1 Ma. Finally, the small volume of material accreted between 15 and 2 Ma (barely the volume of the quaternary wedge) suggests that significant accreted volumes have been eroded.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8105 Continental margins and sedimentary basins
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2003 Fall Meeting