HR: 15:25h
AN: T23D-07 [Abstracts]
TI: Stress and Strain in the Mantle Wedge
AU: * Kneller, E A
EM: ekneller@umich.edu
AF: Department of Geological Sciences University of Michigan, 425 E. University Avenue, Ann Arbor, Mi 48109
United States
AU: van Keken, P E
EM: keken@umich.edu
AF: Department of Geological Sciences University of Michigan, 425 E. University Avenue, Ann Arbor, Mi 48109
United States
AU: Karato, S
EM: shun-ichiro.karato@yale.edu
AF: Department of Geology and Geophysics Yale University, 210 Whitney Avenue, New Haven, CT 06520
United States
AU: Park, J
EM: jeffrey.park@yale.edu
AF: Department of Geology and Geophysics Yale University, 210 Whitney Avenue, New Haven, CT 06520
United States
AB:
In many subduction zones around the world the seismically fast vibration direction of split shear waves is parallel to the
trench. Possible explanations include 3-D trench-parallel flow and water-induced olivine fabrics. The type-B olivine fabric,
which may explain trench-parallel anisotropy, occurs above a critical stress under wet and low-temperature conditions. The
formation of fabric is also dependent on the accumulation of sufficient finite strain in the dislocation creep regime. We
investigate stress and finite-strain structures in the mantle wedge for high-resolution, time-dependent, finite element
models with a kinematic-dynamic setup and water-dependent composite rheology. We use experimentally determined diffusion and
dislocation creep parameters from Karato and Wu (1993) and Karato and Jung (2003). Our models show low stresses throughout
most of the mantle wedge under dry conditions and that stress is even lower under wet conditions ($<$ 1 MPa). Relatively high
stresses ($>$ 5 MPa) are confined mainly to boundary layers above the slab and below the overriding plate. These boundary
layers are the best candidates for the water-induced type-B fabric that may be responsible for trench-parallel shear wave
splitting in subduction zones.
DE: 8162 Rheology--mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting