HR: 14:55h
AN: T42D-06    [PDF]
TI: HIGH TEMPERATURE DEFORMATION OF OMPHACITE IN ECLOGITE: IMPLICATIONS FOR SUBDUCTED LITHOSPHERE
AU: * Zhang, J
EM: jezhang@citrus.ucr.edu
AF: Inst. Geophys. Planet. Phys., University of California, Riverside, CA 92521 United States
AU: * Zhang, J
EM: jezhang@citrus.ucr.edu
AF: Dept. of Earth Sciences, University of California, Riverside, CA 92521 United States
AU: Green, H W
EM: hgreen@mail.ucr.edu
AF: Inst. Geophys. Planet. Phys., University of California, Riverside, CA 92521 United States
AU: Green, H W
EM: hgreen@mail.ucr.edu
AF: Dept. of Earth Sciences, University of California, Riverside, CA 92521 United States
AU: Jung, H
EM: hjung@citrus.ucr.edu
AF: Inst. Geophys. Planet. Phys., University of California, Riverside, CA 92521 United States
AB: Omphacite is a major component mineral in subducted oceanic crust at depth. It often develops strong lattice preferred orientation and dominates the flow properties and seismic anisotropy in eclogite. Investigation on the rheology of omphacite is important for a better understanding of geodynamic problems associated with eclogite in subduction zones. The high temperature deformation behavior of polycrystalline omphacite (Di$_{58}$Jd$_{42}$) is being studied at temperatures of 1300-1500 K, a confining pressure of 3 GPa, and strain rates of 10$^{-4}$/s to 10$^{-5}$/s. We obtained a power-law creep for the high temperature deformation of omphacite with n=3.1, Q=289 KJ/mol, and a preexponential factor of 10$^{-1.2}$MPa$^{-n}$s$^{-1}$. These results show that the creep strength of omphacite falls between its two end members of solid solution (diopside and jadeite), which supports the previous arguments that sodic pyroxene could be significantly weaker than other pyroxenes (enstatite and diopside). A steady increase of flow strength is also observed after adding garnet. Eclogite reconstituted from powders of 50% garnet (Pry$_{21}$Alm$_{18}$Gro$_{61}$), 40% omphacite (Di$_{58}$Jd$_{42}$), 10% quartz shows strength about 3 times that of polycrystalline omphacite. These data are consistent with observations of extensive deformation of omphacite in eclogite at low peak metamorphism temperatures during deep subduction and exhumation. These preliminary results also suggest that strain will concentrate into omphacite-rich domains within the subducting zones.
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
DE: 5120 Plasticity, diffusion, and creep
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Tectonophysics [T]
MN: 2003 Fall Meeting