HR: 08:15h
AN: T31A-02    [Abstracts]
TI: Subduction Zone Plate Boundary Coupling, and Subduction Angle Changes
AU: * Sacks, I S
EM: sacks@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, United States
AU: Suyehiro, K
EM: suyehiro@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima-cho, Yokosuka, Japan
AB: Data from the ocean floor drilling programs, volcano flux, volcanic front migration, mountain building and gravity residual anomalies, allow modeling of the varying geometry and the forces involved in subduction zones. The Pacific plate subduction beneath North-East Japan has been relatively constant in direction and fairly steady in rate over more than 20 my. However, the tectonics and volcanism have changed markedly. The westward migration of the volcanic front over the last 20 my, and the change in tectonic stress from tension to compression at about 14 ma is well documented. We postulate that subduction geometry changed from "Marianas-type" with steep dip and weak coupling to its present 30 degree dip and strong coupling. Once the present geometry is approached, the apex of the mantle wedge is cooled sufficiently by conduction to the cold subducting slab and overlying plate, that its viscosity increases, flow avoids the corner, leading to further conductive cooling. Convection modeling (Kincaid and Sacks, 1997) suggests that the growth of a stiff, cold region trenchward of the volcanic front takes of order 3 million years. The depth range over which strong interplate coupling occurs would therefore increase. Finite element deformation and faulting modeling constrained by observed gravity residual anomalies, topography and heat flow (Huang et al, 1998) show mountain building and erosion strongly affected by this coupling force. The overlying plate is warped, and mountains (Kitakami range) build, and erosion increases. The cores retrieved from holes drilled into the sea floor during leg 186 of the ODP and legs 56 and 57 of the DSDP off the east coast of Japan show a spatially consistent increase in sedimentation rate at about 7 ma. The timing is consistent with the modeling and the migration of the volcanic front.
DE: 4863 Sedimentation (1861)
DE: 8122 Dynamics: gravity and tectonics
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly