HR: 0800h
AN: T21B-0536    [Abstracts]
TI: Numerical simulation for spontaneous generation of one-sided subduction with hysterisis-dependent rheology
AU: * Tagawa, M
EM: tagawa@geol.sci.hiroshima-u.ac.jp
AF: Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi Hiroshima, 739-8526 Japan
AU: Nakakuki, T
EM: nakakuki@geol.sci.hiroshima-u.ac.jp
AF: Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi Hiroshima, 739-8526 Japan
AU: Tajima, F
EM: fumiko@geol.sci.hiroshima-u.ac.jp
AF: Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi Hiroshima, 739-8526 Japan
AB: Two-dimensional numerical simulations are conducted to build a self-consistent subduction model using a newly developed code based on finite volume method. This code can perform simulation with non-uniform grid spacing to solve fine structure at the plate boundary efficiently. We utilize a thin lubricating layer as thin as an oceanic crust that depends on the hysterisis of the past fracture (Honda {\it et al}., 2000; Nakakuki and Hamada, 2003) with an extended Boussinesq fluid in a 2-D rectangular box. A pre-existing weak zone is given at the oceanic-continental plate boundary as an initial condition. Otherwise, no artificial forces are applied to the surface boundary and plates in the modeling. Results show that a subduction process of an oceanic plate was produced in an one-sided regime spontaneously, with a realistic narrow low viscosity zone formed at the plate boundary. We also examined the effects of tensional and compressional strengths of the subducting and/or overriding lithosphere accounting for some recent laboratory experiments. As the tensional strength is weaker than the compressional strength in the lithosphere, the ratio of tensional strength to compressional strength (1, 1/2, or 1/3) was tested systematically in the yielding condition. When a steep dip angle (45$^{\circ}$) of the initial weak zone (IWZ) was set, weak tensional strength in the subducting lithosphere promoted subduction initiation more effectively than in the cases with a shallow dip angle (18.4$^{\circ}$). Nonetheless, this strength did not affect the shape of subducting slab that directs downward. The initiation of subduction was constrained by the imposed IWZ at the plate boundary but the subduction was driven by negative buoyancy. Trench retreat took place when the thin overriding lithosphere had weak tensional strength. In this case, the shallow dipped subduction style was generated.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
DE: 8160 Rheology--general
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting